U.S. patent application number 12/286328 was filed with the patent office on 2009-02-12 for method and apparatus for measuring gas sorption and desorption properties of materials.
Invention is credited to Karl J. Gross.
Application Number | 20090041629 12/286328 |
Document ID | / |
Family ID | 39776488 |
Filed Date | 2009-02-12 |
United States Patent
Application |
20090041629 |
Kind Code |
A1 |
Gross; Karl J. |
February 12, 2009 |
Method and apparatus for measuring gas sorption and desorption
properties of materials
Abstract
The invention relates to a method and an apparatus (herein
referred to as a "gas sorption/desorption analyzer") for measuring
the gas sorption properties of substances (for example hydrogen
sorption by metal alloys). Measurements include: Pressure
Composition Temperature isotherm (PCT), Kinetic, Cycle-life, and
density. Measurements are made by sorption of aliquots of gas to or
from a sample of the substance. The amount of gas in each aliquot
is determined from the gas pressure and temperature in calibrated
reservoir volumes. The apparatus comprises components rated for
operation up to 200 atm, a plurality of sensors covering a broad
pressure range, and minimized volumes to enable accurate
measurements of small samples. Aliquot pressures are controlled
using a feed-back controlled pressure regulator that can also be
used for constant pressure sorption measurements. The gas
temperature is regulated using a temperature controlled enclosure.
The apparatus also comprises a plurality of safety and failsafe
mechanisms.
Inventors: |
Gross; Karl J.; (Fremont,
CA) |
Correspondence
Address: |
DUANE MORRIS LLP - San Diego
101 WEST BROADWAY, SUITE 900
SAN DIEGO
CA
92101-8285
US
|
Family ID: |
39776488 |
Appl. No.: |
12/286328 |
Filed: |
September 3, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10440069 |
May 17, 2003 |
7429358 |
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12286328 |
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60381945 |
May 20, 2002 |
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Current U.S.
Class: |
422/69 |
Current CPC
Class: |
G01N 2015/0873 20130101;
Y10T 436/11 20150115; G01N 7/02 20130101; Y10T 436/22 20150115;
Y10T 436/25875 20150115; G01N 25/00 20130101; Y10T 436/20
20150115 |
Class at
Publication: |
422/69 |
International
Class: |
G01N 30/00 20060101
G01N030/00 |
Claims
1-48. (canceled)
49. A gas sorption and desorption measurement apparatus comprising:
a sample container; a gas storage reservoir configured to hold a
gas; a first gas transmission line configured to couple with the
gas storage reservoir to a gas supply source, the gas transmission
line having a first gas valve; a gas discharge line coupled to the
gas storage reservoir, the gas discharge line having a second gas
valve; a second gas transmission line coupling the gas storage
reservoir to a gas supply source to the sample container, the gas
transmission line having a third gas valve; an inlet gas pressure
regulator, coupled to the gas storage reservoir, configured to
deliver the gas to the gas storage reservoir; and a computer
configured to open or close the first, second and third valves to
intermittently supply and discharge the gas from the gas storage
reservoir to the sample container.
50. The apparatus of claim 49 wherein the inlet gas pressure
regulator delivers the gas at a predetermined pressure.
51. The apparatus of claim 50 wherein the computer is further
configured to control the inlet gas pressure regulator.
52. The apparatus of claim 51 wherein the inlet gas pressure
regulator is PID regulated.
53. The apparatus of claim 52 wherein the predetermined pressure is
a constant differential gas pressure above a measured gas pressure
within the sample container.
54. The apparatus of claim 53 wherein at least one of the valves is
actuated electrically or pneumatically.
55. The apparatus of claim 54 wherein the sample container further
comprises a pressure failsafe mechanism configured to discharge a
pressurized gas below a burst pressure of the sample container.
56. The apparatus of claim 55 wherein at least one of the valves
close in the event of electrical power loss or of pneumatic control
gas pressure.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/381,945, filed May 20, 2002
GROSS, "METHOD AND APPARATUS FOR MEASURING GAS SORPTION AND
DESORPTION PROPERTIES OF MATERIALS"
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to an apparatus (herein
referred to as a "gas sorption/desorption analyzer") adapted to
measure the adsorption and absorption (collectively referred to as
"sorption") and desorption properties of a materials capable of gas
sorption, and more particularly to an apparatus for measuring the
hydrogen adsorbing, absorbing or desorbing properties of hydrogen
absorbing alloys, hydrogen adsorbing carbons, and oxygen absorbing
substances. The apparatus is unique in the following respects: 1)
it can perform these measurement in a precise manner at high gas
pressures (0 to 200 atm), 2) it performs these measurement by
applying precise aliquots of gas at specific pressures using an
automated pressure regulator, 3) it incorporates many unique
features which enhance the precision, utility, and safety of the
measurement. These features are described below in the summary of
the invention.
[0004] Note: all pressures in atm are absolute pressures (atma).
PID means Proportional Integral Differential.
[0005] 2. Description of Prior Art
[0006] In recent years, much attention has been directed to
hydrogen absorbing alloys for the negative electrodes of alkali
batteries and for gaseous hydrogen storage. More recently, there
has been an increased interest in complex hydrides and carbon
materials for gaseous hydrogen storage. Typical examples of
hydrogen absorbing alloys are LaNi.sub.5, MmNi.sub.2 Co.sub.3
(wherein Mm is a misch metal). In the case of LaNi.sub.5, when
hydrogen is absorbed it can form a solid solution alloy
LaNi.sub.5H.sub.x, as well as a metal-hydride LaNi.sub.5H.sub.6, at
near ambient temperatures and pressures. An example of a complex
hydride that may be used for gaseous hydrogen storage is
NaAlH.sub.4 doped with titanium by reaction with TiCl.sub.3. This
material can release and re-absorb more than 3 weight percent
hydrogen through solid-state processes of decomposing and reforming
NaAlH.sub.4. Hydrogen gas can also be absorbed onto and desorbed
from graphite and other carbon materials low temperatures (less
than -100.degree.C.). Potential applications for these materials
are rechargeable alkali batteries, hydrogen storage for use with
fuel cells, gas chromatographs, etc. Many of the hydrogen
sorption/desorption properties of these materials can be modified
and, ultimately, tailored to suit the desired application. For
example, the pressure and temperature at which hydrogen sorption
and desorption takes place in many hydrogen absorbing alloys can be
changed by through minor changes in the alloy composition.
Therefore, it is very important to measure the hydrogen
absorption/desorption properties of all of these types of
materials.
[0007] One aspect of the hydrogen sorption (or desorption)
properties of a material is the thermodynamics of hydride formation
(or decomposition). This is determined by measuring a
pressure-composition isotherm (PCT) diagram. FIG. 1A shows an
idealized version of such a PCT measurements. This diagram
represents the relationship between the pressure (ordinate) and the
amount of hydrogen absorption (abscissa) at three different sample
temperatures. By performing such measurements at several different
temperatures the enthalpy of hydride formation can be determined.
This is done by plotting the natural logarithm of the plateau
pressure (flat portion of the PCT diagram) versus inverse
temperature resulting in a van't Hoff diagram. The enthalpy of
hydride formation is taken from the slope of this plot. FIG. 1B
shows an idealized version of such a van't Hoff diagram.
[0008] Another aspect of the hydrogen sorption (or desorption)
properties of a material is the kinetics of hydride formation (or
decomposition). This is simply the rate of hydrogen sorption or
desorption from the material. This is generally determined by
measuring the change in hydrogen pressure versus time in a fixed
volume containing the sample. If the volume of the vessel and the
volume and mass sample are known the amount of hydrogen sorption or
desorption by the sample can be quantified. FIG. 2 shows an example
of such a kinetics measurement for La.sub.2Mg.sub.17. By performing
such measurements at several different temperatures the activation
energy of hydride formation can be determined. This is done by
plotting the natural logarithm of the rate (usually the initial
linear portion of the kinetics measurement) versus inverse
temperature resulting in an Arrhenius diagram. The activation
energy of hydride formation is taken from the slope of this plot.
FIG. 3 shows an example of such a van't Hoff diagram for
La.sub.2Mg.sub.17.
[0009] A third and very important aspect of the hydrogen sorption
(or desorption) properties of a material is the cycle life. That
is, how the hydrogen capacity and kinetics hold up with repetitive
hydrogen sorption and desorption cycles. In practice, this consist
of making a series of kinetics measurements and quantifying the
changes in capacity and kinetics as a function of the number of
cycles.
[0010] The most common way to measure these hydrogen sorption
properties of a material is to measure the drop in pressure in a
calibrated volume as hydrogen is adsorbed or absorbed by a test
sample of the material. Likewise, desorption properties are
determined by measuring the increase in pressure in a calibrated
volume as hydrogen is desorbed from the test sample into the
volume. The quantity of hydrogen absorbed (adsorbed) or desorbed in
each measurement is found from the equation of state of gaseous
hydrogen. The equation of state is well approximated by the ideal
gas law at pressures below about 10 atm. Above this pressure,
non-ideal gas laws or tables of experimentally determined values
may be used. In any case, it is necessary to know three parameters
to determine the quantity of hydrogen absorbed (adsorbed) or
desorbed. These are, the pressure, temperature and volume of the
gas. By holding the volume and temperature constant, the quantity
of hydrogen is determined simply by measuring the pressure. Knowing
the mass of the sample it is then possible to determine the mass
concentration of hydrogen that has been absorbed (adsorbed) or
desorbed by the sample. If the composition of the sample is well
known, then the stoichiometry of hydrogen in the sample may also be
determined from the measured concentration.
[0011] In a PCT measurement, the sample is dosed with small
"aliquots" of hydrogen from a small volume or desorbed into a small
volume such that only a small fraction of hydrogen is absorbed
(adsorbed) or desorbed at one time. A sorption PCT diagram is
measured by increasing the pressure in each aliquot of hydrogen
applied to the sample in a step-wise fashion. Similarly, a
desorption PCT diagram is measured by decreasing the pressure in a
step-wise fashion, in the small volume into which the sample is
desorbed. The conventional apparatus for performing such
measurements is referred to as a Sieverts' device. Such a device is
shown in the schematic illustration of FIG. 4.
[0012] While this simple device has been used extensively over the
years to make hydrogen sorption and desorption measurements, there
are a number of technical issues which plague the accuracy and ease
with which these measurements can be made. The following is a list
and description of the most important problems effecting the prior
art. The present invention overcomes each of these problems through
the use of unique, effective, and simple, hardware or software
solutions.
[0013] Problem 1: Automation. Most measurements require data
collection over long periods of time and may involve large numbers
of repetitive operations (such as delivering aliquots in a PCT
measurement, or switching between sorption and desorption in
cycle-life measurements). This stresses the importance of using
automation in such measurements. The present invention comprises an
automated gas sorption/desorption analyzer that employs computer
controlled operations and data collection.
[0014] Problem 2: Uniform PCT Gas Aliquots. Providing an evenly
spaced distribution of sorption/desorption measurement points along
PCT curve is of critical importance because without a detailed and
even distribution of measurements the low pressure region of the
PCT plot will not be well resolved. The result is that the solid
solution portion of the hydrogen behavior may not be observed at
all. In the worst case, which has been known to occur, changes in
the equilibrium plateau pressure identified with hydride phase
transitions could be missed entirely.
[0015] The classic Sieverts apparatus uses a fixed applied pressure
equal to the highest pressure of the measurement for sorption and
usually vacuum for desorption. This creates the undesirable
situation of requiring very large aliquots of gas for the initial
portion of sorption measurements and the reverse for desorption.
The best approach to resolve this problem is to be able to vary the
applied pressure at will. One method which addresses this problem
is described in U.S. Pat. No. 5,591,87. In that method three
automated valves work in conjunction to step the applied pressure
up or down to the desired aliquot pressure. The method consists of
alternately filling (or emptying) a first volume with hydrogen by
opening a primary valve, closing the primary valve and then opening
a secondary valve to the reservoir volume. In this manner the
pressure is stepped up or down to the desired pressure prior to
application of the aliquot to the sample. The disadvantage of this
method is that every point measured on a PCT curve requires a
tedious process of multiple valve operations in order to reach the
desired pressure. This process takes time, increases the noise
level of the measured response produced by such devices, and
greatly increases wear on the automated valves. In addition, during
the time that it takes for this process to be completed hydrogen
interaction with the material of interest may continue to proceed
within the sample volume. This will contributes to a certain amount
of error in the measurements of hydrogen capacity.
[0016] Another method uses a needle valve to increase or decrease
the supply pressure. The problem with this method is that the
supply pressure increases or decreases without feed-back control.
Because of this, the supply pressure will not be adjusted with
respect to changing conditions during gas sorption or desorption to
or from the sample. For example, during a hydrogen absorption PCT
measurement of a metal hydride the equilibrium pressure will rise
until the plateau pressure is reached. The supply pressure, on the
other hand, will continue to rise. The increasing difference
between the equilibrium pressure and the supply pressure will cause
the data points to spread out as the measurement continues.
Important phase change information towards the end of the plateau
may be missed. The increasing applied pressure differential may
also lead to non-equilibrium conditions as the measurement
progresses. In addition, needle valves demonstrate non-linear
behavior such that the supply pressure will increase (or decrease)
more slowly as the pressure differential across the needle valve
decreases. This non-linearity often causes sorption PCT
measurements to slow down at high pressures to the point where the
measured change in ad/absorbed gas is less than the systematic
error. For desorption PCT's with plateau pressures near or below
one atmosphere the pressure differential across the needle valve is
reduced to the point that there is very little flow and the
measurement essentially stalls when the plateau is reached.
[0017] These problems are easily overcome in the present invention
by using an automated pressure regulator to supply the working gas
either at a predetermined pressure or at a specified pressure
difference above or below the measured equilibrium pressure. In an
alternative embodiment the working gas can be supplied (or removed)
at a controlled flow rate using a gas flow controller.
[0018] Problem 3: Constant Gas Temperature. Variations in the air
temperature in the room in which a volumetric instrument such as
that shown in FIG. 4 can produce significant errors in calculating
the quantities of hydrogen sorption or desorption from a material.
Even if the surrounding air temperature is measured and introduced
into the equation of state, the lag time between changes in the
temperature of the surrounding air and the temperature of the
hydrogen gas in the Sieverts apparatus can be significant enough
that the data can not be sufficiently corrected. The problem of
variations in the temperature of hydrogen gas in a Sieverts'
apparatus can be resolved in two ways. The first is to position a
temperature measuring device such as a thermocouple inside of the
gas reservoir volume to get an accurate measurement of the gas
temperature. This value can then be used in the equation of state
to compensate for temporal changes in the temperature of the gas.
The problem with this method is that if the apparatus employs
several separated volumes and interconnecting tubing the gas
temperature in the system may not be equilibrated to the
temperature measured in one part of the apparatus. The second
solution is to maintain the main body of the apparatus at a fixed
temperature. This can be accomplished by submerging the main body
of the apparatus in a controlled temperature bath (usually using a
water bath). The inherent difficulty with this is that there are
commonly many electrical devices such as pressure transducers that
are connected to the apparatus which are not compatible with water.
Another approach is to have the main body of the apparatus in
thermal contact with a temperature controlled thermal ballast. This
is typically a large metal plate which is heated and maintained at
a fixed temperature slightly above room temperature by an
electrical heater and a feedback control system. The difficulty
with this concept is to obtain good enough heat transfer throughout
the apparatus that the gas temperature is truly constant through
out the system.
[0019] The best approach and one aspect of the present invention is
to regulate the gas temperature by placing the main gas handling
portion of the apparatus (gas sorption/desorption analyzer) in an
enclosure and regulating the air temperature within the enclosure
to a fixed value slightly above room temperature
[0020] Problem 4: Gas Temperature When Sample is Heated. To
calculate the quantity of gas adsorbed, absorbed (hereafter
"ad/absorbed"), or desorbed in a volumetric measurement, it is also
necessary to know the temperature of the gas. This is not a problem
if the gas temperature is uniform throughout the gas handling
system, as provided in the present invention by using a controlled
temperature enclosure. However, if the sample is heated, or the
temperature is different for the gas handling portion of the
apparatus outside of the enclosure, then the exact temperature of
the gas is not known. This may cause significant errors in
quantifying gas sorption.
[0021] The present invention overcomes this problem through two
methods. The first is to measure the temperature of the gas within
the enclosed part of the gas handling system as well as the
temperature of the gas in the sample container. The operator is
then given the option to use a weighted average of the gas
temperature in calculating the quantity of gas (weighted by
relative volume of gas at each temperature). A second, and even
more effective manner, to overcome this problem is to reduce the
volume of the heated gas to a minimum. This is accomplished in the
present invention by using small diameter external gas lines and
spacers in the sample container to reduce the volume of gas that at
a different temperature than the main body of gas in the enclosed
and temperature regulated gas handling system.
[0022] Problem 5: Non-ideal Gas Behavior at Elevated Pressures. At
pressures above about 20 atm molecular interactions in gases begin
to have an effect on the relationship between pressure,
temperature, volume of a given quantity of gas. These effects cause
a deviation from the "ideal gas" behavior. The properties of the
gas are no longer adequately described by the linear Ideal Gas Law.
This deviation can cause errors in using pressure measurements of a
volumetric device to determining the amount of gas that is
ad/absorbed or desorbed by a sample. At pressures above 100 atm,
this error may be significant (on the order of 5% or more).
[0023] These errors can be successfully overcome by utilizing one
of the several non-ideal equations of state developed for gases at
high pressure. The present invention includes data analysis
software employing automatically calculation of non-ideal gas
behavior to correctly determine the hydrogen capacity from changes
in pressure.
[0024] Problem 6: Small sample quantities. Small samples (<1
gram) and/or samples that ad/absorb only small quantities of gas
(50 milliliters) are difficult to investigate using typical
volumetric devices that often have calibrated volumes and piping
with volumes on the order of 50 milliliters or more. For example, a
0.5 gram sample of a LaNi.sub5.-type alloy subjected to a 2 atm
aliquot of hydrogen gas from a 50 milliliter calibrated reservoir
volume will be completely hydrided in one step. Under such
conditions it would not be possible to measure an equilibrium PCT
plateau curve.
[0025] The present invention utilizes small gas vessels, spacers,
and small internal diameter gas lines (c.a. 1 mm diameter) to
reduce the minimum working volumes to about 15 milliliters. This
enables the measurement of gas sorption properties of small (<1
gram) samples and samples with limited gas sorption. For larger
samples and for desorption, the present invention includes
additional calibrated volumes to increase the working volume of the
gas sorption/desorption analyzer. These volumes may be accessed by
opening valves connecting them to the gas handling system.
[0026] Problem 7: Flexibility in Measuring Different Sample Types
and Sizes. The calibrated reservoir volume may be too large or too
small for the aliquot that is desired. The most obvious example is
that a very small volume (15-50 milliliters) is needed for making
absorption kinetics measurements using high pressures (100 atm) and
a large volume is needed for a desorption kinetics measurement (1
liter at <2 atm). In addition, different types of measurements
(PCT, kinetics, and cycle-life) as well as, different types or
quantities of samples (1 gram vs. 100 grams) may all have different
requirements for the quantity of gas to be supplied or desorbed in
an aliquot. Simple Sievert's devices often provide only one or two
different calibrated volumes, or required the volumes to be changed
manually. The problem with a manual change is that air will be
introduced into the system, requiring an additional out-gassing.
Also, such hardware changes significantly increase the possibility
of system leaks, lost hardware, and possible mistakes or changes in
the calibration of the actual volumes being used. There is a great
advantage to being able to change to a reservoir of a different
volume, even during a measurement.
[0027] As mentioned above, the present invention includes at least
3 additional calibrated volumes permanently attached to the gas
handling system that are accessed when needed by opening automated
valves that connect these volumes to the gas handling system.
[0028] Problem 8: Gas Sorption and Desorption Properties May Vary
Over a Broad Time Range. It is common that gas sorption or
desorption rates will vary by over 2 orders of magnitude during a
single measurement. For example, a hydride may absorb hydrogen at
10 wt. %/minute in the first few minutes of a kinetics measurement
and continue to absorb hydrogen but at a much lower rate of 0.1 wt.
%/minute after several hours. Ideally, one would like to record
such data frequently during the rapid part of the measurement and
less frequently when changes are occurring slowly. The problem with
current data-collection schemes is that data is taken at a fixed
time interval. To be able to collect all the pertinent information
data must be collected at the shortest required time interval (e.g.
2 seconds). Unfortunately, doing this for a measurement that often
lasts hours or days creates enormous data files. And a large
portion of the data collected after the most active part of the
measurement will be of little value since dozens or hundreds of
data point could be equally as well represented by a single data
point. Sometimes it is possible to change this interval during a
measurement, but this requires operator to be input new values and
therefore, they must schedule their time accordingly.
[0029] The present invention overcomes this problem by taking
advantage of the fact that for typical experiments, gas sorption
and desorption rates decrease as a function of time. The present
invention includes different algorithms to decrease the frequency
with which data is recorded as a function of time. These algorithms
are described in a later section.
[0030] Problem 9: Constant Pressure Measurements. It is often very
useful to be able to make gas sorption or desorption measurement
while maintaining a constant active gas pressure over the sample.
This is important for kinetic comparison or mechanism studies
because kinetics are often strongly influenced by changes in the
applied pressure. This is also important in simulating real
conditions encountered in applications, such as filling up a
hydride bed under a constant hydrogen pressure. Currently,
volumetric systems measure gas sorption (of desorption) properties
of materials by measuring the pressure drop (or rise) in a
calibrated volume which contains the sample material. The need to
measure a moderate change in pressure to obtain accurate data means
that the sample is subjected to a non-constant pressure during the
measurement which may have a significant effect on the results.
[0031] The present invention overcomes this problem by employing a
computer controlled pressure regulator for gas sorption and a
computer controlled back-pressure regulator for desorption
measurements. These devices are used to maintain a constant gas
pressure over the sample during measurements. The quantity of gas
ad/absorbed in a sorption measurement is determined by measuring
the drop in pressure in a small (100 milliliter) calibrated volume
which supplies the gas to the sample through the pressure
regulator. In desorption measurements, the quantity of gas desorbed
is determined by measuring the pressure increase in a large (1
liter) calibrated volume to which the gas flows from the sample
through the back-pressure regulator.
[0032] Problem 10: Changes in Sample Density. Hydrides undergo
lattice expansion during hydrogen absorption and lattice
contraction during desorption causing minor changes in the
calibrated system volumes. These changes are typically not
accounted for in the prior art. In addition, it is of interest to
be able to measure these expansions and contractions.
[0033] The present invention overcomes this problem by performing
semi-automatic measurements of the volume (and therefore packing
density) of the sample using an inert gas such as He to measure the
empty volume of the sample container with and without the sample
present. Changes in the sample volume may be made during sorption
or desorption experiments by performing a volume measurement with
the inert gas at selected intervals during the experiment.
[0034] Problem 11: Large Dynamic Pressure Range. The measured
pressure often extends over a larger dynamic range than most
pressure transducers can measure with good accuracy. In typical
devices of the prior art, only one pressure transducer is employed,
limiting the range over which experimental measurements can be
performed.
[0035] The present invention overcomes this problem by utilizing at
least two pressure transducers, one covering a low pressure range
(e.g. 0-20 atm) and another for higher pressures (e.g. 20-200 atm).
Computer controlled automation (PCT, kinetics and cycle-life) is
used to determine at any point in an experiment whether the
pressure is in the range that should be measured using either a low
range transducer or a high range transducer. In the case of the
present preferred embodiment of the invention two transducers are
used. The pressure is first measured with the high-range
transducer. If the high-range transducer indicates a low enough
value (below a selected set point), an automated valve is opened to
allow the pressure to be measured with the low-range transducer.
The automated valve is used to protect the low-range pressure
sensor from damage by over-pressurization. In this case the change
in the calibration volume is adjusted to account for the additional
volume of the low-range transducer, valve and connections.
[0036] Problem 12: Elevated Pressure and Temperature Operation.
Many materials require temperatures and pressures substantially
above ambient conditions (ca. 400.degree.C. and 200 atm.) The prior
art has focused on measurements of hydrogen absorption in classic
interstitial metal hydrides for hydrogen gas storage and battery
applications. In most cases, these materials have equilibrium
hydride formation plateaus that are measured either near ambient
conditions or at elevated temperatures (e.g. MgH.sub.2 at
300.degree.C.) and pressures of 30 atm or less. It is desirable
(particularly in light of new reversible hydride development e.g.
Ti doped NaAlH.sub.4) to be able to make measurements at higher
pressures and temperatures. The currently available systems either
do not go to pressures above about 30 atm, are not accurate at
temperatures above 300.degree.C., or are not automated.
[0037] The present invention overcomes this problem by using
high-pressure components, lines, fittings, and a sample container
which are rated for hydrogen service up to 200 atm. The present
invention also includes a sample container which is rated for
service at up to 400.degree.C. at 200 atm of hydrogen. Errors
caused by variations in the gas temperature when operating at this
high sample temperature are minimized by reducing the empty volume
of the external gas handling system and sample container, as well
as offering the option to use a weighted average temperature for
concentration calculations. The present invention also includes
automated pneumatic valves, and the use of valves in series to
minimize the leak rates across the valves when performing
high-pressure measurements. Automated valves also have a great
advantage with respect to durability and life-time of an apparatus.
This is because they are operated in a repeatable and consistent
manner which significantly reduces damage to the internal
components. Manual valve are subjected to the inconsistent behavior
of the operator. In particular, when used with high-pressure the
experimenter has a tendency to over-tighten such valve, which will
damage the valve seat and cause the valve to leak. Manual systems
have been known to operate for only a few experiments before the
valves leak to the point that the data is seriously compromised.
Automated pneumatic-valves, on the other hand, can be set to
operate over thousands of cycles using an air pressure that is
appropriate and constant.
[0038] Problem 13: Air Exposure. Typical prior-art apparatus have
been designed such that the sample cannot be place in the sample
container or that the sample container cannot be connected to the
apparatus without exposing the sample to air. This is a very big
problem for samples that become inactive because of the formation
of surface oxides or other coatings and is a serious problem for
samples which are highly reactive with air such as Na--Al--H
compounds.
[0039] The present invention overcomes this problem by using a
sample container that is small enough to fit through an entry
chamber of a glove box so that it can be loaded with samples in an
inert atmosphere such as argon gas. In the present invention, the
sample container is comprised of the body of the container with two
open ends. This has two advantages, the first is that samples can
be easily loaded and more importantly easily removed from the
sample container. The other advantage is that different types of
end-pieces can be attached to each end. In the preferred embodiment
one end-piece has a valve between the body of the sample container
and a connector for attaching the sample container to the external
gas-handling system of the gas sorption/desorption analyzer. This
allows the sample to be sealed under an inert atmosphere while the
sample container is removed from the glove box attached to the gas
sorption/desorption analyzer and all lines of the gas
sorption/desorption analyzer are pumped free of air. In this manner
the sample is loaded, transferred and ready for measurements
without ever being exposed to air. In the preferred embodiment, the
other end of the sample container is sealed with a fitting that
contains a tube closed at one end and sealed to the fitting.
[0040] This tube is known as a thermocouple "well". It runs up
inside of the sample container to make precise measurements of the
actual sample temperature. In an alternative embodiment, this
end-piece could be replace with another valve and connector
end-piece. This allows other devices to be attached in an air-less
manner to the sample valve. Such devices could be a turbo-molecular
pump, gas or liquid vessel containing a reactive or calibration gas
or liquid, a residual gas analyzer, etc.
[0041] Problem 14: Safety. Measurements made using high-pressure
hydrogen at high temperature and in many cases with highly reactive
materials presents many safety issues and challenges that are not
properly addressed in much of the prior art.
[0042] The present invention comprises several innovative hardware
and control logic mechanisms to improve safety. Examples include
failsafe mechanisms, such as a pop-top, which will minimize that
would otherwise be caused by a build-up of hydrogen and ignition
within the gas sorption/desorption analyzer enclosure. Other
examples include logical mechanisms, such as temperature limits for
the enclosure heating system and sample-container heater which are
built into the control software. These mechanisms will be discussed
in detail below.
SUMMARY OF THE INVENTION
[0043] The following is a summary of the novel aspects of the
invention: [0044] 1. The use of gas handling components that
function at high and low gas pressures (0 to 200 atm) to allow the
measurement of gas sorption properties of materials over a broad
range pressures and in particular at high pressures. [0045] 2. The
use of two different pressure transducers to cover a broad range of
pressures with increased accuracy. One transducer covers a
low-pressure range with precision (e.g. 0 to 7 atm) and the other a
high-pressure range with, precision (e.g. 0 to 200 atm). An
automated valve and control software protect the low-pressure
transducer from the damaging effects of high pressure by first
reading the high-pressure transducer and only then opening the
valve to the low-pressure transducer if the pressure is below a
safe limit (e.g. 7 atm). [0046] 3. The apparatus control and
measurement software automatically compensates for the non-ideal
behavior of gases at high pressures (>10 atm) to correctly
determine the amount of gas sorbed or desorbed from a sample.
[0047] 4. Gas is automatically applied to or removed from a sample
in aliquots from one of several calibrated volumes. The amount of
gas in the aliquot is precisely controlled by adjusting the
pressure in the calibrated volume using an automated PID controlled
pressure regulator. The automated pressure regulator is a unique
addition to this type of apparatus and in particular the use of an
automated regulator that functions at high pressures. [0048] 5.
Precise low-pressure aliquots are obtained by accurately setting a
high pressure in a small calibrated volume and then releasing this
gas to a larger calibrated volume. The final low pressure is
accurately obtained by setting the initial high-pressure to an
exact predetermined value based on the ratio of the small and large
volumes. [0049] 6. The automated pressure regulator combined with a
calibrated volume on the inlet of the automated pressure regulator
allows the unique possibility to make quantitative gas sorption
measurements with the sample exposed to a constant pressure. A
back-pressure regulator attached to the sample holder can provide
the same possibility for desorption measurements. [0050] 7. In
order to make precise volumetric measurements of gas
sorption/desorption from a sample, it is necessary to know the
pressure, volume and temperature of the working gas. The pressure
is measured, the volume is fixed and likewise, in this apparatus
the temperature of the gas is fixed. This is done by active heating
of all (or nearly all) of the gas handling portions of the
apparatus inside an insulated enclosure. The temperature is
maintained at a constant value by using a PID feedback control of
the electrical heating element and circulating air in the enclosure
using an electric fan. [0051] 8. The use of fully automated valves
(generally pneumatic valves) provides a powerful benefit of
dramatically increasing the ease and productivity of measurements.
For, example PCT, kinetics, and especially cycle-life measurements
can be performed without the operator being present. One
particularly unique automated process is to use the automated
valves and calibrated volumes to calibrate the gas volume of sample
holder with and without a sample in it. Ordinarily this is a very
tedious manual process. The volume with the sample must be measured
to perform precise gas sorption/desorption measurements. The
difference between the volumes with and without the sample can be
used to determine the density and packing-density of the material.
In addition, this automated process can be used to measure density
changes (volume expansion) of substances in situ, during the
sorption or desorption processes. [0052] 9. The apparatus is novel
in providing several different combinations of calibration volumes
of different size (generally 3 to 1500 ccm). This allows small
aliquots for PCT measurements and large aliquots for kinetics and
cycle-life measurements. Thus a broad range of gas quantities can
be measured. The very small volumes enable PCT measurements on
small samples (<1 gram). In addition, using the large volumes
which are also rated for high-pressure use, PCT measurements can be
performed on very large samples (>10 kg). [0053] 10. The
apparatus as described herein provides 16 novel safety features to
enhance the safe operation of the invention when using
high-pressure, flammable, reactive, or toxic gases.
[0054] The present invention relates to an apparatus (gas
sorption/desorption analyzer) for measuring gas adsorption,
absorption, and/or desorption properties of a sample or substance
having a property to absorb a gas. The gas sorption/desorption
analyzer comprises a sample container for containing the sample or
substance, gas storage consisting of one or more calibrated volumes
connected to the sample container, a gas supply source for
supplying the gas to the gas storage, a vent line and a vacuum line
to discharge gas from the gas storage, pressure transducers to
measure the gas pressure over an extended range, an automated
pressure regulator to charge or discharge the gas storage to a
predetermined pressure, automated pressure regulators to maintain
constant gas pressure over the sample during sorption or
desorption, automated valves for controlling the flow of gas within
the gas sorption/desorption analyzer, an air supply system to
provide air to control the automated valves and pressure
regulators, a calibration gas system to provide an inert gas for
volume calibrations and density measurements, an automated sample
container valve to automate experimental preparations, a heated
enclosure to maintain a constant gas temperature in the gas
storage, an automated heater for heating a sample in the sample
container, an electrical data-acquisition and control system, a
safety systems comprised of, a safety shield, a failsafe top panel,
a sample heater open shield cut-off, a system of open panel power
cut-offs, over-temperature cut-offs on the enclosure heater and
sample heater, failsafe hydrogen leak mechanisms, gas-handling
system and sample-container pressure relief mechanisms, and methods
or means to compensate for non-ideal gas conditions, to correct or
avoid errors due to variations in gas temperature, to small sample
sizes, to low concentrations, to prevent sample air exposure, to
measure changes in sample densities, to reduce the amount of data
collected, and to provide uniform gas aliquots.
[0055] The primary object of the invention is to provide an
automated means of measuring gas adsorption, absorption and
desorption in materials. Other objects of the invention include the
following: [0056] 1. to provide a method of controlling pressure
during gas sorption or desorption measurements; [0057] 2. to
provide a method of maintaining a constant gas pressure around a
sample during gas sorption or desorption measurements; [0058] 3. to
provide better apparatus for measuring gas sorption and desorption
properties of materials by maintaining a constant gas temperature;
[0059] 4. to provide a measuring apparatus that works with
high-pressure gases and control software that corrects for the
non-ideal behavior of gasses at high pressure; [0060] 5. to provide
an apparatus for measuring gas sorption or desorption of materials
that aids the operator by performing volume calibrations through a
semi-automated process; [0061] 6. to provide an apparatus that
performs sample density measurements in addition to gas sorption
and desorption measurements; [0062] 7. to provide an apparatus that
measures gas sorption and desorption over a wider dynamic range of
pressures than those currently available; [0063] 8. to provide an
apparatus that measures gas sorption and desorption properties of
materials over a wider range of gas concentrations than can be done
using existing technology; [0064] 9. to provide a sample container
that provides better data, allows airless sample transfers and is
easier to use; [0065] 10. to provide improved safety features in an
apparatus that measures gas sorption and desorption properties of
materials.
[0066] Other objects and advantages of the present invention will
become apparent from the following descriptions, taken in
connection with the accompanying drawings, wherein, by way of
illustration and example, an embodiment of the present invention is
disclosed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0067] The drawings constitute a part of this specification and
include exemplary embodiments to the invention, which may be
embodied in various forms. It is to be understood that in some
instances various aspects of the invention may be shown exaggerated
or enlarged to facilitate an understanding of the invention.
[0068] FIG. 1a) is an example of a typical PCT plot; and 1b) an
example of a van't Hoff diagram;
[0069] FIG. 2) is an example Kinetics measurement of hydrogen
absorption by the alloy La.sub.2Mg.sub.17;
[0070] FIG. 3) is an example Arrhenius plot of the log 10 rate of
hydrogen absorption versus inverse temperature measured for the
alloy La.sub.2Mg.sub.17;
[0071] FIG. 4) is a schematic diagram of a conventional Sieverts
type volumetric measuring device;
[0072] FIG. 5a-d) are illustration showing different embodiments of
the invention;
[0073] FIG. 6) is a schematic diagram showing an interior view of a
portion of the apparatus (gas sorption/desorption analyzer)
embodying the invention as viewed from the back-side;
[0074] FIG. 7) is a schematic diagram showing an interior view and
exterior cross-section of a portion of the apparatus (gas
sorption/desorption analyzer) embodying the invention as viewed
from the left-side;
[0075] FIG. 8) is a cross-sectional diagram of a sample container
embodying a portion of the invention;
[0076] FIG. 9) is an illustration of an external gas handling
portion of the invention;
[0077] FIG. 10) is an illustration of a heating jacket embodying a
portion of the invention for heating a sample in a sample
container;
[0078] FIG. 11) is a schematic diagram of a data acquisition,
control and safety system embodying a portion of the invention as
viewed from the back-side;
[0079] FIG. 12) is an illustration of a sample container safety
shield attached to the apparatus (gas sorption/desorption analyzer)
embodying a portion of the invention;
[0080] FIG. 13a) is an illustration of a failsafe top panel of the
apparatus (gas sorption/desorption analyzer) embodying a portion of
the invention, shown in the open position;
[0081] FIG. 13b) is an illustration of a failsafe top panel of the
apparatus (gas sorption/desorption analyzer) embodying a portion of
the invention, shown in the closed position;
[0082] FIG. 14) is a schematic diagram of an alternative embodiment
of the invention comprising the apparatus (gas sorption/desorption
analyzer) of the invention and an automated sample container
valve;
[0083] FIG. 15) is a diagram showing the open or closed states of
valves involved in gas sorption measurements, a) Step 1 illustrates
filling of a calibrated reservoir volume, b) Step 2 illustrates gas
sorption to an equilibrium state;
[0084] FIG. 16) is a schematic representation showing the opening
or closing of valves and pressure changes with time during gas
sorption measurements;
[0085] FIG. 17) is a diagram showing the open or closed states of
valves involved in gas desorption measurements, a) Step 1
illustrates filling of a calibrated reservoir volume, b) Step 2
illustrates gas desorption to an equilibrium state;
[0086] FIG. 18) is a schematic representation showing the opening
or closing of valves and pressure changes with time during gas
desorption measurements;
[0087] FIG. 19) is a flow chart for measuring gas sorption or
desorption kinetic properties of a sample using the apparatus (gas
sorption/desorption analyzer) of the invention;
[0088] FIG. 20) is a flow chart for measuring gas sorption or
desorption PCT properties of a sample using the apparatus (gas
sorption/desorption analyzer) of the invention;
[0089] FIG. 21) is a flow chart for measuring gas sorption or
desorption cycle-life properties of a sample using the apparatus
(gas sorption/desorption analyzer) of the invention;
[0090] FIG. 22) is a plot of the number of moles in a gas versus
pressure calculated for hydrogen gas using the ideal gas law, the
Beattie-Bridgeman equation of state, and the Van der Wall's
equation of state;
[0091] FIG. 23) is PCT plot of hydrogen absorption in LaNi.sub.5
using a fixed calibrated reservoir pressure of about 12 atm;
[0092] FIG. 24) is PCT plot of hydrogen absorption in LaNi.sub.5
using a calibrated reservoir pressure that increases slowly with
each aliquot up to a pressure of about 12 atm;
TABLE-US-00001 [0093] 501 gas sorption/desorption analyzer 502
enclosure 503 panels 504 frame 505 feet 506 computer 507
communication link 508 main power switch 509 a-f temperature
measurement inputs 510 sample heater power supply plug 511 vent for
an electronics compartment 512 vent for a gas handling compartment
601 air connector 602 air supply line 603 air controller 604 a-j
air control solenoids 605 variable air control line 606 gas
pressure regulator 607 calibration gas connector 608 calibration
gas supply line 609 calibration gas check valve 610 calibration gas
line 611 calibration gas pressure relief valve 612a-j automated
valve 613 gas connector 614 gas supply line 615 gas supply line 616
gas vessel 617 supply gas input pressure transducer 618 gas supply
line 619 supply gas output pressure transducer 620 gas line 621
discharge line 622 discharge pressure relief valve 623 vacuum line
624 vacuum connector 625 vent line 626 vent connector 627 gas line
628 gas line 629 gas vessel 630 gas line 631 gas vessel 632 gas
line 633 high pressure transducer 634 gas line 635 gas connector
636 gas line 637 low pressure transducer 638 low pressure
transducer failsafe pressure relief valve 639 enclosure heating
element 640 enclosure air circulating fan 701 furnace 702
jack-stand 703 furnace power cord 704 furnace power plug 705 sample
thermocouple 706 sample container thermocouple 707 furnace
thermocouple 720 back-pressure regulator 721 back-pressure
regulator input gas line 722 gas connector 723 back-pressure
regulator output gas line 724 gas connector 725 back-pressure
regulator input pressure transducer 726 back-pressure regulator
output pressure transducer 727 pressure Transducers power and
signal wires 728 back-pressure regulator pneumatic PlD controller
729 back-pressure regulator air line 801 sample container 802 valve
top female nut 803 valve copper gasket 804 valve top gland 805
sample container valve 806 valve bottom gland 807 valve bottom
female nut 808 sample container copper gasket 809 sample container
top male nut 810 sample container top gland 811 sample container
body piece 812 sample container conductive jacket 813 sample
container spacer 814 sample 815 thermocouple well 816 sample
container bottom gland 817 sample container bottom male nut 818
sample container bottom female nut 819 sample container bottom plug
820 sample thermocouple 820 sample thermocouple 901 external gas
handling portion 902 external gas line 903 external female
connector 904 external bulkhead connector 905 supporting arm 906
mounting bracket 907 angle bracket 908 extension bracket 909
connector bracket 1001 heating jacket 1002 heat resistant fabric
1003 insulation 1004 resistive hearing element 1005 fastener 1006
power cord 1007 power plug 1101 electrical system 1102 Gas
sorption/desorption analyzer power plug 1103 Enclosure power safety
switch 1104 110 V AC power in 1105 110 V AC fuse 1106 110 V AC
power out 1107 110 V AC to 24 V DC transformer 1108 24 V DC power
lines 1109 Sample heater control relay 1110 Data acquisition,
control and safety system 1111 Communications control hub 1112
Analog input device 1113 Digital output device 1114 Pressure
regulator analog output device 1115 Back-pressure regulator analog
output device 1116 Enclosure heating element 110 V AC analog output
device 1117 Thermocouple input device 1118 Enclosure heating
element 110 V AC line 1119 Sample heater 110 V AC line 1120 Sample
heater relay control line 1121 Sample heater safety shield switch
1122 Pressure transducer output lines 1123 Enclosure thermocouple
1124 air solenoids control lines 1125 Pneumatic valves air control
lines 1126 Enclosure heater safety switch 1127 Power safety relay
1201 Sample container safety shield 1202 see-through safety shield
1203 Vent hole 1204 Safety shield hinge 1205 Safety shield latch
hook 1206 Safety shield latch pin 1207 Safety shield handle 1301
Failsafe top panel 1302 gas handling compartment top panel 1303 top
panel hinge 1304 top panel weak fastener 1401 Automated sample
container valve system 1402 Automated sample container valve 1403
Valve top connector 1404 Valve bottom connector 1405 Automated
sample container valve air connector 1406 Automated sample
container valve air line 1407 Automated sample container valve
connector
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0094] The present invention relates to an apparatus (gas
sorption/desorption analyzer) for measuring gas sorption (herein
understood to mean either adsorption or absorption) and/or
desorption properties of a substance having a property to absorb a
gas. In the preferred embodiment, the substance is any hydrogen
absorbing material consisting of an element, compound, alloy or
combination thereof. The working gas described herein is hydrogen,
but it is to be understood that the invention is not limited to
hydrogen alone. For example, in another embodiment the invention is
useful for a substance which forms a nitride by absorbing nitrogen
or an oxide by absorbing oxygen or adsorbs gases such as oxygen,
carbon dioxide, hydrocarbons, etc. The apparatus can be used for
any gas which reacts or is absorbed, adsorbed or desorbed by a
sample or substance which may be either solid or liquid. In the
following disclosure, the substance to be measured for gas sorption
and/or desorption properties is referred to as the "sample" and the
working gas (in this case hydrogen) is referred to as the "gas".
Other gases employed in the process of making measurements, but not
used as the working gas, are referred to as "air" and "calibration
gas".
[0095] While the invention has been described in connection with a
preferred embodiment, it is not intended to limit the scope of the
invention to the particular form set forth, but on the contrary, it
is intended to cover such alternatives, modifications, and
equivalents as may be included within the spirit and scope of the
invention as defined by the appended claims.
Apparatus
Main Body of the Device
[0096] FIG. 5a is a perspective view of the exterior of a basic gas
sorption/desorption analyzer embodying the present invention. FIG.
5b is a photograph of one embodiment of the invention. FIG. 5c and
FIG. 5d are alternate embodiments of the same.
[0097] The gas sorption/desorption analyzer 501 is comprised of an
enclosure, housing, body, box, or cabinet 502 that contains all of
the internal gas handling lines, volumes, valves, sensors and
control devices and an external gas handling portion 901 of the gas
sorption/desorption analyzer 501. The internal parts are described
below and shown in the schematic diagrams of FIGS. 6, 7 and 8. The
gas sorption/desorption analyzer 501 has a set of feet or fixtures
505 used as a means to stand upright or may be fixed to a wall or
frame. A computer or logical control device 506 controls the gas
sorption/desorption analyzer 501. It is connected to the gas
sorption/desorption analyzer 501 by a communication link 507 for
example using an Ethernet line. A sample container, container, or
vessel 801 is connected to the internal workings of the gas
sorption/desorption analyzer 501 by the external gas handling
portion 901. A sample container valve 805 isolates a sample 814 in
the sample container 801 from the external gas handling portion
901. A thermocouple, thermistor or temperature measuring device 820
is inserted into a thermocouple well 815 that extends up through
the center of the sample 814 that is inside of the sample container
801. A main power switch 508 is located on the exterior of the
enclosure 502. Thermocouple or temperature measurement inputs 705,
706, 707 and sample heater (not shown) power supply plug or output
510 are located on the exterior of the enclosure 502. Vents or
ventilation ports are located at the top of the enclosure 502.
These include a vent for an electronics compartment 511 and a vent
for a gas handling compartment 512.
[0098] FIG. 6 shows a schematic diagram of the interior parts and
plumbing of the gas sorption/desorption analyzer 501 view from the
back of the gas sorption/desorption analyzer.
Air Supply System
[0099] Indicated at 601 in FIG. 6 is a connector for attaching a
source of pressurized air to the gas sorption/desorption analyzer
501. The air connector 601 is preferably a quick coupling but may
be any connector rated for air service at least 20 atm. An air
supply line 602 is connected from the air connector 601 to an air
controller 603. According to the embodiment the air controller 603
is a PID (Proportional, Integral, and Derivative)
electric-pneumatic controller. The air supply line 602 is also
connected to a series of air controlled solenoids 604a-k. The
output of the air controller 603 is connected via an variable air
control line 605 to a gas pressure regulator 606. According to the
embodiment the gas pressure regulator 606 is a pneumatically
controlled pressure regulator capable of regulating hydrogen gas to
a fixed pressure above 1 atm and below 200 atm.
Calibration Gas Supply System
[0100] Indicated at 607 in FIG. 6 is a connector for attaching a
source of pressurized calibration gas to the gas
sorption/desorption analyzer. The calibration gas connector 607 is
preferably a metal gasket sealed coupling but may be any connector
rated for gas service of at least 200 atm. In the preferred
embodiment helium gas is used as the calibration gas, but the
invention is not limited to this case. Other gases such as nitrogen
or argon may also be used. A calibration gas supply line 608 is
connected from the calibration gas connector 607 to a calibration
gas check valve 609. The check valve 609 closes if the gas pressure
on the outlet (right side) of the check valve is greater than the
gas pressure on the inlet (left side) of the check valve. This
helps to prevent gases other than the calibration gas from
back-flowing to the source of the calibration gas. This is an
important feature as it prevents contamination of the calibration
gas with other gases.
[0101] A calibration gas line 610 is connected from the calibration
gas check valve 609 to a calibration gas pressure relief valve 611.
The calibration gas pressure relief valve 611 vents any gas that is
in excess of the valve's set pressure which is usually 2 atm to 10
atm above the pressure of the supply pressure of the calibration
gas. The calibration gas pressure relief valve 611 operates to
prevent gases at higher pressures than the calibration gas from
leaking through the calibration gas check valve 609 over time and
causing damage to calibration gas lines, regulators or
contamination of the calibration gas with other gases. The
calibration gas line 610 is further connected from the calibration
gas pressure relief valve 611 to an automated valve 612a. When the
automated valve 612a is opened in response to an operating signal,
the calibration gas is allowed to flow from the calibration gas
source into the gas lines, vessels and components beyond 612a. The
calibration gas is thus used to calibrate the volume of empty
spaces in the gas lines, vessels, components and spaces surrounding
the sample 814 to be measured.
Working Gas Supply System
[0102] In the preferred embodiment hydrogen gas is used as a
working gas, but the invention is not limited to this case. Other
working gases such as but not restricted to nitrogen, oxygen,
ammonia, carbon dioxide, carbon monoxide, or hydrocarbons may also
be used. Indicated at 613 in FIG. 6 is a connector for attaching an
external source of the working gas to the gas sorption/desorption
analyzer 501. The gas connector 613 is preferably a metal gasket
sealed coupling but may be any connector rated for gas service of
at least 200 atm. A gas line 614 is connected from the gas
connector 613 to an automated valve 612b. A gas supply line 615 is
connected from the automated valve 612b to a gas vessel or
container 616. In the preferred embodiment, the gas vessel 616
comprises a 150 milliliter 316L stainless steel cylinder rated to
operate at gas pressures of at least 200 atm. The gas supply line
615 is further connected to a supply gas pressure transducer 617
which is shown in FIG. 6 in a location on top of the gas vessel
616. In the preferred embodiment, the supply gas input pressure
transducer 617 comprises strain-gauge or capacitance pressure
measuring device with a range of 0 to 207 atm, but the invention is
not limited to this type of pressure measuring device or this
pressure range. The gas supply line 615 is further connected to an
input on the gas pressure regulator 606. The inside region of the
gas vessel 616, gas line 615, supply gas input pressure transducer
617, the automated valves 612b, and the gas pressure regulator 606,
serves as a working gas storage, the volume of which is expressed
by VS. The volume of VS is determined using common methods of
volume calibration, for example by venting working gas at a known
pressure from VS into an evacuated calibrated standard volume and
measuring the resulting equilibrium pressure. When the automated
valve 612b is opened in response to an operating signal, the
working gas is allowed to flow from the external source of working
gas into VS. Then the automated valve 612b is closed in response to
an operating signal. The pressure of the working gas in VS is
measured using pressure transducer 617. Thus VS is employed as a
calibrated volume source of working gas that provides quantified
allotments of working gas into the rest of the gas handling system.
This restricted working gas supply volume serves several measuring
and safety related purposes that are outlined in the process
descriptions that follow.
[0103] A gas supply line 618 indicated in FIG. 6 is connected from
an output on the gas pressure regulator 606 to a supply gas output
pressure transducer 619. The supply gas output pressure transducer
619 measures the pressure of the working gas supplied to the rest
of the gas handling system by the pressure regulator 606. In the
preferred embodiment, the supply gas output pressure transducer 619
comprises strain-gauge or capacitance pressure measuring device
with a range of 0 to 207 atm, but the invention is not limited to
this type of pressure measuring device or this pressure range. The
gas supply line 618 is further connected to an automated valve
612c. When the automated valve 612c is opened in response to an
operating signal, the working gas is allowed to flow from the gas
pressure regulator 606 into the rest of the gas handling
system.
Working Gas, Calibration Gas, Residual Air Discharge System
[0104] A gas line 620 shown in FIG. 6 is connected from the
automated valve 612c to the automated valve 612a. Together these
two automated valves supply either working gas or calibration gas
into the rest of the gas handling system. The gas line 620 is
further connected to automated valves 612d and 612e. When the
automated valve 612e is opened in response to an operating signal,
working gas, calibration gas or residual air is allowed to flow to
or from the rest of the gas handling system. When the automated
valve 612d is opened in response to an operating signal, working
gas, calibration gas or residual air is allowed to flow from the
rest of the gas handling system to a discharge line 621. The
discharge line 621 is connected from the automated valve 612d to a
discharge pressure relief valve 622. The discharge pressure relief
valve 622 is set to open and discharge working gas, calibration gas
or residual air when the pressure in the discharge line 621 is
greater than the pressure on the exhaust side of the discharge
pressure relief valve 622 (usually 1 atm). The discharge line 621
is further connected to an automated valve 612f. When the automated
valve 612f is opened in response to an operating signal, working
gas, calibration gas or residual air is allowed to flow from the
discharge line 621 to a vacuum line. The discharge line 621 is
further connected to an exhaust port on the gas pressure regulator
606. The exhaust port on the gas pressure regulator 606 allows
working gas to be discharge from the gas supply line 618 if the
pressure in the gas supply line 618 is greater than the pressure
setting of the gas pressure regulator 606. This allows the gas
pressure regulator 606 to regulate the output pressure to a desired
pressure regardless of whether the initial pressure in the gas
supply line 618 is above or below the desired pressure. For
example, if the desired pressure setting of the gas pressure
regulator 606 is changed from 100 atm to 50 atm, the regulator
adjusts the pressure in the gas supply line 618 from 100 atm to 50
atm by exhausting the excess working gas in the gas supply line 618
through the regulator exhaust port to the discharge line 621 and in
this case out of the discharge pressure relief valve 622.
Vacuum System
[0105] A vacuum line 623 shown in FIG. 6 is connected from the
automated valve 612f to a vacuum connector 624. In the preferred
embodiment, the vacuum connector 624 is preferably a rubber gasket
sealed vacuum coupling but may be any connector rated for vacuum
service of at least 10 millitorr. An external vacuum line is
connected from the vacuum connector 624 to an external vacuum pump
(not shown). The discharge pressure relief valve 622 operates to
prevent working gas, calibration gas or residual air at pressures
greater than 1 atm from being discharged through the vacuum line
623, thereby avoiding needlessly overworking the external vacuum
pump.
Vent System
[0106] A vent line 625 indicated in FIG. 6 is connects a vent
connector 626 to the discharge pressure relief valve 622 and also
to a calibration gas pressure relief valve 611. In the preferred
embodiment the vent connector 626 is a hose-barb connector, but may
be any connector rated for vacuum service or pressures of at least
2 atm. An external vent line is connected from the vent connector
626. The external vent line is generally connected to some kind of
laboratory ventilation system. Such systems generally run just
slightly sub-atmospheric.
Aliquot System
[0107] Indicated at 627 in FIG. 6 is a gas line connecting
automated valves 612e, 612g, 612h and 612i. When the automated
valve 612e is opened in response to an operating signal, gas,
calibration gas or residual air is allowed to flow to or from the
portion of gas handling system that provides a means to deliver
aliquots of gas to or from the sample 814. The inside region of the
gas line 627 and the automated valves 612e, 612g, 612h and 612i,
serves as a gas storage, the volume of which is expressed by
VR1.
[0108] A gas line 628 connects the automated valve 612g to a gas
vessel 629. In the preferred embodiment, the gas vessel 629
comprises a 150 milliliter 316L stainless steel cylinder rated to
operate at gas pressures of at least 200 atm. The inside region of
the gas line 628, the gas vessel 629, and the automated valve 612g,
serves as a gas storage, the volume of which is expressed by
VR2.
[0109] A gas line 630 connects the automated valve 612i to gas
vessels 631a and 631b. In FIG. 6 the gas vessel 631a is located on
top of 631b. In the preferred embodiment, the gas vessels 631a and
631b are comprised of 500 milliliter 316L stainless steel cylinders
rated to operate at gas pressures of at least 200 atm. The inside
region of the gas line 630, the gas vessels 631a and 631b, and the
automated valve 612i, serves as a gas storage, the volume of which
is expressed by VR3.
[0110] Indicated at 632 in FIG. 6 is a gas line connecting
automated valves 612h, 612j, 612k and a high pressure transducer
633. The inside region of the gas line 632, the automated valves
612h, 612j, 612k, and the high pressure transducer 633, serves as a
gas storage, the volume of which is expressed by VR0.
[0111] A gas line 634 connects the automated valve 612k to a gas
connector 635. The gas connector 635, in turn connects the gas line
634 to the external gas handling portion 901 of FIG. 5, which in
turn is connected to the sample container 801. The inside region of
the automated valve 612k, the gas line 635, the gas connector 635,
the external gas handling portion 901, and the sample container
801, serves as a gas volume surrounding the sample 814, the volume
of which is expressed by VC.
[0112] The high pressure transducer 633 provides a means to measure
the pressure of the gas in a given aliquot. When the automated
valve 612k is open the high pressure transducer 633, also provides
a means to measure the gas pressure surrounding the sample 814
either in equilibrium or during sorption or desorption. In the
preferred embodiment, the high pressure transducer 633 comprises
strain-gauge or capacitance pressure measuring device with a range
of 0 to 207 atm, but the invention is not limited to this type of
pressure measuring device or this pressure range.
[0113] Indicated at 636 in FIG. 6 is a gas line connecting the
automated valve 612j to a low pressure transducer 637 and a low
pressure transducer failsafe pressure relief valve 638. The low
pressure transducer 637 provides a means to make more accurate
measurements at pressures below 7 atm, than by using the high
pressure transducer 633. The low pressure transducer 637 provides a
means to measure the pressure of the gas in a given aliquot when
the automated valve 612j is open. When the automated valve 612k is
also open, the low pressure transducer 637, also provides a means
to measure the gas pressure surrounding the sample 814 either in
equilibrium or during sorption or desorption. In the preferred
embodiment, the low pressure transducer 637 comprises strain-gauge
or capacitance pressure measuring device with a range of 0 to 7
atm, but the invention is not limited to this type of pressure
measuring device or this pressure range. The logical control system
provides that the automated valve 612j can not open if the
indicated pressure read on the high pressure transducer 633 is
greater than 1 to 7 atm depending on the chosen setting. As a
failsafe mechanism, should the gas line 636 be exposed to gas
pressures greater than 7 atm the low pressure transducer failsafe
pressure relief valve 638 will open and vent the gas to the vent
line 625 to which it is connected. The transducer failsafe pressure
relief valve 638 will close as soon as the gas pressure drops below
7 atm. This failsafe mechanism provides a means to protect the low
pressure transducer 637 from pressures above 7 atm which might
damage the transducer.
[0114] The volumes of gas storage volumes VC, VR0, VR1, VR2, and
VR3 are determined using common methods of volume calibration, for
example by venting gas at a known pressure from the gas storage
volumes VC, VR0, VR1, VR2, or VR3 into an evacuated calibrated
standard volume and then measuring the resulting equilibrium
pressure using either the low-pressure transducer 637 or the
high-pressure transducer 633. The gas storage volumes VR1, VR2, and
VR3 can be employed separately or in different combinations
together with the gas storage volume VR0 to provide quantified
aliquots of gas to or from the sample 814.
[0115] The automated valves 612a-j are each two-position valves
having an open position and a closed position. According to the
preferred embodiment, the valves are pneumatic valves. When the
pneumatic valve is opened in response to an operating signal, air
flows there-into, holding the valve in the open position. The
automated valves 612a-i are each normally closed valves and
according to the preferred embodiment, the automated valve 612j is
a normally open valve.
[0116] Piping constituting the lines and the vessels, etc.
connected to the line are made preferably of stainless steel, and
in particular 3161 stainless steel for the prevention of corrosion
or other degradation. The various gaskets, lines, fittings and
valves provide a leak-free means to seal the gas portion inside of
the gas sorption/desorption analyzer 501 from the exterior
atmosphere.
Enclosure
[0117] The enclosure 502 provides a means of insulating the gas
handling parts of the gas sorption/desorption analyzer 501 from
changes in the ambient air temperature. The enclosure 502 is
comprised of panels, a skin, or cover 503 and a frame, or support
504. The panels 503 are insulated by means of covering the interior
surface with an insulating material such as spun glass or plastic
foam. The enclosure 502 also protects the internal components from
outside activities and acts as a safety barrier in the event of
rupture of any of the internal components.
Enclosure Heater
[0118] The temperature of the enclosure 502 is maintained at a
chosen level using an enclosure heating element 639 and an
enclosure air re-circulating fan 640 as shown in FIG. 6. The
enclosure air re-circulating fan 640 operates continuously,
circulating air past the heating element 639, to maintain a
constant temperature of and all of the components within the
enclosure 502. The enclosure temperature is maintained at a
constant level by adjusting power to the enclosure heating element
639 using PID control feed-back from a thermocouple located inside
of the enclosure 502.
[0119] FIG. 7 is a schematic diagram of the interior and part of
the exterior of the gas sorption/desorption analyzer 501 view from
the side of the gas sorption/desorption analyzer.
Sample Heater
[0120] Indicated at 701 in FIG. 7 is a furnace used as a means of
heating the sample container 801 and thus the sample 814. However,
the means of heating the sample 814 is not limited to the types of
heating described herein. In the preferred embodiment the furnace
is replaced by a flexible heating jacket 1001 for heating the
sample container for gas sorption and desorption of the sample 814
(shown in FIG. 8 and FIG. 10). The sample container 801 heating
jacket 1001 shown in FIG. 10 comprises a resistive heating element
1004 that produces heat when passing a current. This is covered on
the exterior by insulation 1003 to reduce heat loss and provide
some protection for the operator from direct contact with the
heating element 1004. The heating element 1004 and insulation 1003
are covered with a heat resistant fabric 1002. The heating jacket
1001 may be loosely fit around the sample container 801. The
heating jacket 1001 is fixed in place by a fastener 1005 (generally
of hook and loop type) that fixes one overlapping side of the
jacket to the other side. Current to the heating element 1004 is
supplied through a power cord 1006. At the end of the power cord
1006 is a power plug 1007. The power plug 1007 is preferably of a
type that can not be plugged into a standard electrical wall socket
to prevent accidental, uncontrolled heating of the heating jacket
1001.
Back-Pressure Regulator
[0121] A back-pressure regulator 720 shown in FIG. 7 is connected
to the sample container 801 via a back-pressure regulator input gas
line 721. The connection to the sample container 801 is made using
a gas connector 722. The output on the back-pressure regulator 720
is connected to the external gas handling portion 901 via a
back-pressure regulator output gas line 723 and a gas connector
724. The gas connectors 722 and 724 are preferably a metal gasket
sealed couplings but may be any connector rated for gas service of
at least 200 atm. The back-pressure regulator 720 serves to
maintain a constant gas pressure in the sample container 801 during
constant pressure desorption measurements. As gas is desorbed from
the sample 814 it flows out of the sample container through the
back-pressure regulator 720 and into the calibrated volumes of the
gas sorption/desorption analyzer 501. The amount of gas desorbed
can be determined by measuring the pressure increase in the chosen
calibrated volume with either the high pressure transducer 633 (or
the low pressure transducer 637 if the pressure is below 7 atm).
PID control of the back-pressure regulator 720 is achieved using
feed-back from a back-pressure regulator input pressure transducer
725 mounted on the sample container side of the back-pressure
regulator 720. The back-pressure regulator input pressure
transducer 725 sends an signal via pressure transducers power and
signal wires 727 to a back-pressure regulator pneumatic PID
controller 728. The back-pressure regulator pneumatic PID
controller 728 adjusts the output air pressure that is sent via a
back-pressure regulator air line 729 to the back-pressure regulator
720. In this manner the back-pressure regulator 720 adjusts the
flow of gas out of the sample container 801 such that a constant
pressure that is chosen is maintained in the sample container 801.
A back-pressure regulator output pressure transducer 726 mounted on
the output side of the back-pressure regulator 720 sends an signal
via pressure transducers power and signal wires 727 to the computer
506 to record the output pressure.
[0122] For most other types of measurements the back-pressure
regulator 720 is not needed. Therefore the back-pressure regulator
720 is removed and the sample container 801 is connected directly
to the gas sorption/desorption analyzer 501 by connecting a valve
top female nut 802 on the sample container 801 to an external
bulkhead connector 904 on the external gas handling portion 901 of
the gas sorption/desorption analyzer 501.
Sample Container
[0123] The sample container 801 shown in FIG. 8 uses a valve top
female nut 802, a valve copper gasket 803, and a valve top gland
804, to connect the sample container 801 to the gas
sorption/desorption analyzer 501 at either the external bulkhead
connector 904 or the back-pressure regulator connector 722
depending on whether a measurement requires the back-pressure
regulator 720 or not. The sample container valve 805 to which the
valve top gland 804 is connected, serves several purposes. First,
it isolates the sample 814 from the external environment, most
particularly air, if the sample 814 has been loaded into the sample
container 801 in a special environment, for example in an argon
glove box. Second, the sample container valve 805 isolates the
sample 814 from the gas inside of the gas sorption/desorption
analyzer 501 when the sample container 801 is connected to the gas
sorption/desorption analyzer 501. This is necessary for purging the
gas sorption/desorption analyzer 501 of residual air, or can be
used if the sample 814 is under a gas pressure that will be
released into the gas lines of the gas sorption/desorption analyzer
501. The sample container valve 805 is connected via a valve bottom
gland 806, to a sample container top gland 810 using a valve bottom
female nut 807, and sample container copper gasket 808 and a sample
container top male nut 809. In the preferred embodiment, the
gaskets 803 and 808 are comprised of copper, but may also be made
of steel or other materials. The sample container top gland 810 is
welded into a sample container body piece 811 comprised of steel.
In the preferred embodiment, the sample container body piece 811 is
comprised of but not limited to 316L stainless steel with a wall
thickness great enough to withstand hydrogen pressures of more than
200 atm when heated up to 400.degree.C. without sustaining
significant material degradation. The sample container body piece
811, is encased by a sample container conductive jacket 812. In the
preferred embodiment, sample container conductive jacket 812 is
comprised of but not limited to aluminum or copper for good heat
conduction. The sample container conductive jacket 812 is fit
tightly to the sample container body piece 811 to provide a means
of good thermal conductivity and equalize the temperature
distribution within the sample container body piece 811. The empty
space inside of the sample container body piece 811 that remains
after the sample container 801 has been loaded with a sample 814,
is taken up by sample container spacers 813. This reduces the empty
volume of the sample container 801 which improves the accuracy of
the measurements. A thermocouple well 815 runs up the center of the
sample container body piece 811. A sample container bottom gland
816 is welded into the bottom portion of the sample container body
piece 811. The bottom portion of the sample container body piece
811 is sealed with a sample container bottom plug 819 using a
sample container bottom male nut 817, a sample container bottom
female nut 818, and a sample container copper gasket 808. The
thermocouple well 815 is welded into the sample container bottom
plug 819 providing access into the center of the sample container
body piece 811 while allowing the inside portion of the sample
container 801 to be sealed from the exterior atmosphere. A sample
thermocouple 820 is inserted into the thermocouple well 815 which
runs up into and is partially surrounded by the sample 814. This
enables more accurate measurements of the temperature of the sample
814 than using external thermocouples.
External Gas Handling Portion
[0124] The external gas handling portion 901 shown in FIG. 9
comprises an external gas line 902 that connects the gas connector
635 via an external female connector 903, to an external bulkhead
connector 904 to which either the sample container 801 or
back-pressure regulator 720 may be connected. The external gas
handling portion 901 is supported by a supporting arm 905 that is
comprised of a mounting bracket 906 to which is attached an angle
bracket 907 and a extension bracket 908. The external bulkhead
connector 904 is mounted to the supporting arm 905 using a
connector bracket 909.
Alternative Sample Heater
[0125] With regard to FIG. 7 a means of heating the sample
container 801 will be referred to as a furnace. The furnace 701 is
sitting on a jack-stand 702. The jack-stand 702 provides a means to
adjust the position of the furnace 701 with respect to the sample
container 801 so as to optimize the heating of the sample 814. The
furnace 701 is powered by a furnace power cord 703. At the end of
the furnace power cord 703 there is a furnace power plug 704. The
furnace power plug 704 is plugged into the sample heater power
supply plug 510. The power to the furnace 701 is controlled by a
furnace relay 1106 which opens and closes the electrical power
circuit to the furnace 701. The furnace relay is controlled by the
computer 506 via the data acquisition and control system 1101. The
temperature of the sample 814 is measured using a thermocouple
placed inside of the thermocouple well 810 which extends up into
the sample 814. The thermocouple can be jacketed probe type 820 as
shown in FIG. 5 and FIG. 8 or simply a bimetal wire type
thermocouple 705 as shown in FIG. 7. PID control of the furnace 701
can be regulated using feed-back from the thermocouple 705 in the
thermocouple well 810, or a thermocouple 706 attached to the sample
container 801, or a thermocouple 707 located within the furnace
701.
Data Acquisition and Gas Sorption/Desorption Analyzer Control
[0126] The heart of the gas sorption/desorption analyzer 501 is a
an electrical system 1101 shown in FIG. 11. The entire electrical
system is powered at 110V AC from a standard wall outlet into which
is plugged a gas sorption/desorption analyzer power plug 1102.
While the preferred embodiment specifies 110 V AC 60 hertz
operation other voltages and frequencies may also be used such as
220 V AC and 50 hertz. The gas sorption/desorption analyzer power
plug 1102 is connected via an enclosure power safety switch 1103 to
a 110 V AC power in 1104 line and via a 110 V AC fuse 1105 to a 110
V AC power out 1106 line. The enclosure power safety switches 1103
shut off power to the gas sorption/desorption analyzer 501 by
opening the 24 V DC circuit of the power safety relay 1127 if any
of the enclosure panels 503 are removed. The enclosure power safety
switch 1103 may represent a multitude of enclosure power safety
switches, each on a different panel 503. A 110 V AC to 24 V DC
transformer 1107 converts the 110 V AC input voltage to 24 V DC to
run the data acquisition and control system 1110 as well as the
enclosure air circulating fan 640 via 24 V DC power lines 1108. The
110 V AC power in 1104 line also goes to a sample heater control
relay 1109. The data acquisition and control system 1110 is
comprised of a communications control hub 1111, a analog input
device 1112, a digital output device 1113, a pressure regulator
analog output device 1114, a back-pressure regulator analog output
device 1115, an enclosure heating element 110 V AC analog output
device 1116, and a thermocouple input device 1117. The
communications control hub 1111 relays information to and from
these devices to and from the computer 506 via the communication
link 507. The enclosure heating element 639 receives power via an
enclosure heating element 110 V AC line 1118 from the enclosure
heating element 110 V AC analog output device 1116. The enclosure
heater safety switch 641 shuts off power to the enclosure heating
element 639 if the temperature in the enclosure 502 rises above a
certain level. The sample heater control relay 1109 supplies power
via a sample heater 110 V AC line 1119 to the sample heater 1001 or
701. The sample heater control relay 1109 is turned on or off via a
sample heater relay control line 1120 by a signal from the computer
506 to the digital output device 1109. There is a sample heater
safety shield switch 1121 on the sample heater relay control line
1120 to shut off power to the sample heater 1001 or 701 if a sample
container safety shield 1201 has been opened. Pressure measurements
from the pressure transducers 617, 619, 633, 637, 725, and 726 are
transmitted via pressure transducer output lines 1122 to the analog
input device 1112 and from there to the computer 506. Pressure
measurements from the pressure transducers 619 is also transmitted
directly to the air controller 603 to provide feed-back to the gas
pressure regulator 606. An enclosure thermocouple 1123 is used to
measure the temperature inside of the enclosure. This and
measurements from the sample thermocouples 705 or 820, sample
container thermocouple 706, and furnace thermocouple 707 are
transmitted via the thermocouple input device 1117 to the computer
506. The air control solenoids 604a-j are opened or closed by
electrical power supplied via air solenoids control lines 1124 from
the digital output device 1113 on command from the computer 506.
The automated valves 612a-j are like-wise controlled via pneumatic
valves air control lines 1125 by air delivered from the air supply
line 602 that passes through the air control solenoids 604a-j that
have been opened.
Sample container Safety Shield
[0127] One safety aspect of the gas sorption/desorption analyzer
501 is the use of sample container safety shield 1201 shown in FIG.
12. The sample container safety shield 1201 is comprised of a
see-through safety shield 1202 made of a see-through material such
as plastic and a material able to substantially protect against
flying objects in case of failure of the sample container 801,
external gas handling portion 901, or components of or affixed to
the back-pressure regulator 720. The see-through safety shield 1202
has a vent hole 1203 at the top to prevent the build-up of hydrogen
gas and to allow heat from the furnace 701 to escape. The sample
container safety shield 1201 is attached to the gas
sorption/desorption analyzer 501 by means of a fastener such as a
set of safety shield hinges 1204. These allow the sample container
safety shield 1201 to be moved (swung) out of the way when setting
the sample container 801, furnace 701, and jack-stand 702 up to
make a measurement. During a measurement the sample container
safety shield 1201 is held in a protective position (closed) by one
or more latches. In the preferred embodiment, the latches are
comprised of a set of safety shield latch hooks 1205 and safety
shield latch pins 1206 which fasten the opening side of the sample
container safety shield 1201 to the gas sorption/desorption
analyzer 501. The sample container safety shield 1201 may be swung
open and closed using a safety shield handle 1207 attached to the
see-through safety shield 1202. The sample heater safety shield
switch 1121 is attached to the front of the gas sorption/desorption
analyzer 501 in such a way that it is in a closed circuit condition
only when the sample container safety shield 1201 is latched shut.
The sample heater safety shield switch 1121 is on the circuit which
controls the furnace 701 (or heating jacket 1001). This safety
feature prevents the furnace 701 (or heating jacket 1001) from
operating if the sample container safety shield 1201 is not latched
shut.
Failsafe Top Panel
[0128] Another safety aspect of the gas sorption/desorption
analyzer 501 is a failsafe top panel 1301 shown in FIGS. 13A and
13B. The failsafe top panel 1301 is comprised of a gas handling
compartment top panel 1302 that is attached to the gas
sorption/desorption analyzer 501 by means of a fastener such as a
set of safety shield hinges 1204. The other side of the gas
handling compartment top panel 1302 is weakly attached to the gas
sorption/desorption analyzer 501 by means of a top panel weak
fastener 1304. In the preferred embodiment this fastener is
comprised of two pieces of material one with hooks and the other
with loops. These are attached to the gas handling compartment top
panel 1302 and the frame 504 of the gas sorption/desorption
analyzer 501. The vent for a gas handling compartment 512 is
mounted into gas handling compartment top panel 1302. In the event
that there is a rapid build up of pressure inside of the gas
sorption/desorption analyzer 501, either by a release of
pressurized gas or as a result of combustion, the gas handling
compartment top panel 1302 will pop open and swing out of the way
to release the pressure in a safe manner.
Automated Sample Container Valve System
[0129] In an alternative embodiment shown in FIG. 14 the sample
container valve 805 is replaced by an automated sample container
valve system 1401. The automated sample container valve system 1401
is comprised of an automated sample container valve 1402 that is
connected to the external gas handling portion 905 of the gas
sorption/desorption analyzer 501 by a valve top connector 1403. The
sample container valve 1402 is connected to the sample container
801 via a valve bottom connector 1404. The automated sample
container valve system 1401 and sample container 801 may be removed
as a unit to be loaded with a sample in an airless glove box and
then re-connected to the external gas handling portion 905 of the
gas sorption/desorption analyzer 501 to make a measurement. The
automated sample container valve 1402 is a normally closed valve so
that sample transfers can be performed without exposing the sample
814 to air. In the preferred version of this alternative
embodiment, the automated sample container valve 1402 is a
pneumatic valve. Supply air to control the valve comes from an
additional air control solenoid 604k that is controlled via the
data acquisition, control and safety system 1101 by the computer
506. Air to control the automated sample container valve 1402
passes from the additional air control solenoid 604k through an
automated sample container valve connector 1407 on the outside of
the gas sorption/desorption analyzer 501, through an automated
sample container valve air line 1406 to an automated sample
container valve air connector 1405 on the automated sample
container valve 1402. The automated sample container valve air
connector 1405 is disconnected when the automated sample container
valve system 1401 and sample container 801 are removed for
loading.
Methods
[0130] The following is illustrative of the operation of the
invention for measuring gas sorption properties of materials.
[0131] Sorption Concentration Measurement: The process of
volumetrically measuring the concentration (or quantity, or
capacity) of a gas adsorbed or absorbed by a sample is shown in the
schematic diagrams of FIG. 15 and FIG. 16. As FIG. 15 illustrates,
the measurement of one point (j FIG. 16) on a PCT plot proceeded in
two steps. The valves E1 and E2 in FIG. 15 and FIG. 16 represent
valve 4 and valve 5 respectively in the simple volumetric apparatus
shown schematically in FIG. 4. In the schematic diagram of the
preferred embodiment of the present invention FIG. 6, valves E1 (of
FIG. 15 and FIG. 16) is representative of the automated valve 612h
(or 612e if 612h and none, one, or both of 612g and 612i are open)
and E2 is representative of the automated valve 612k. The method of
sorption concentration proceeds as follows: First, valve E2 is
closed. Following this, valve E1 is opened and the calibrated
reservoir volume V.sub.R is filled with gas by opening valve 1
(valve 612c in FIG. 6). In the second step valve E1 is closed and
the aliquot pressure P.sub.Rj in the calibrated reservoir volume
V.sub.R is recorded using pressure transducer 633 or 637 if the
pressure is below the maximum reading pressure of 637 and valve
612j is open. Following this, valve E2 is opened and the pressure
in the sample container (and gas lines) V.sub.C and the reservoir
volume V.sub.R due to sorption is recorded and continues to be
recorded at specified time intervals. Again, the pressure is
measured using pressure transducer 633 or 637 if the pressure is
below the maximum reading pressure of 637 and valve 612j is open.
This pressure change measurement provides a means to evaluate the
amount of gas sorption from the aliquot of gas. The quantity of gas
ad/absorbed at each step N.sub.j is given by:
N j = 1 RT j ( P Rj V R + P j - 1 V C - P j ( V R + V C ) ) EQ . 1
##EQU00001##
where V.sub.R is the reservoir volume (V.sub.0, V.sub.1, V.sub.2,
and/or V.sub.3 in FIG. 6), V.sub.C is the sample container volume,
P.sub.Rj is the pressure measured in the reservoir volume V.sub.R
at step j, P.sub.j is the pressure measured in the combined volumes
V.sub.R and V.sub.C at step j (at any time, and multiple times
while valve E2 open), R is the universal gas constant, and T is the
average gas temperature. When the change in pressure finally slows
to a specified limit, this pressure reading P.sub.j is taken as the
equilibrium pressure P.sub.Ej and the calculated quantity of gas
ad/absorbed N.sub.j corresponding to the equilibrium pressure is
taken as the equilibrium concentration N.sub.Ej ad/absorbed in that
aliquot. For PCT measurements the process is repeated.
[0132] Two important considerations in making these measurements
are: 1) that the length of time allowed between each aliquot should
be sufficiently long so that the system has reached true
equilibrium and, 2) that valve E2 is closed only for a short period
of time to fill the reservoir, so that P.sub.j-1 correctly
represents the initial state of the sample at the beginning of each
new aliquot of gas. This is demonstrated in FIG. 16.
[0133] Desorption Concentration Measurement: The process of
volumetrically measuring the concentration (or quantity, or
capacity) of a gas desorbed by a sample is similar to the sorption
process described above. This is shown in the schematic diagrams of
FIG. 17 and FIG. 18. As FIG. 17 illustrates, the measurement of one
point (j in FIG. 18) on a PCT plot proceeded in two steps. The
valves E1 and E2 in FIG. 17 and FIG. 18 represent valve 4 and valve
5 respectively in the simple volumetric apparatus shown
schematically in FIG. 4. In the schematic diagram of the preferred
embodiment of the present invention FIG. 6, valves E1 (of FIG. 15
and FIG. 16) is representative of the automated valve 612h (or 612e
if 612h and none, one, or both of 612g and 612i are open) and E2 is
representative of the automated valve 612k. The method of sorption
concentration proceeds as follows: First, valve E2 is closed. Then
valve E1 is opened and the calibrated reservoir volume V.sub.R is
discharged of gas. This is done, either by opening valve 2 (valve
612d in FIG. 6) and discharging to the vent and vacuum connections
624 and 626, or by discharging to a preset pressure through the gas
pressure regulator 606. In the second step valve E1 is closed and
the aliquot pressure P.sub.Rj in the calibrated reservoir volume
V.sub.R is recorded using pressure transducer 633 or 637 if the
pressure is below the maximum reading pressure of 637 and valve
612j is open. Then E2 is opened and the pressure in the sample
container (and gas lines) V.sub.C and the reservoir volume V.sub.R
due to desorption is recorded and continues to be recorded at
specified time intervals. Again, the pressure is measured using
pressure transducer 633 or 637 if the pressure is below the maximum
reading pressure of 637 and valve 612j is open. This pressure
change measurement provides a means to evaluate the amount of gas
desorption from the sample. The quantity of gas desorbed at each
step N.sub.j is again given by EQ. 1. When the change in pressure
finally slows to a specified limit, this pressure reading P.sub.j
is taken as the equilibrium pressure P.sub.Ej and the calculated
quantity of gas desorbed N.sub.j corresponding to the equilibrium
pressure is taken as the equilibrium concentration N.sub.Ej
desorbed in that aliquot. For PCT measurements the process is
repeated.
[0134] Kinetics Measurement: The process making both sorption and
desorption kinetics measurements is identical to the two processes
respectively described above. For sorption, an aliquot represents
exposing the sample to a quantity of gas at a pressure high enough
for sorption by the sample to occur at the given sample
temperature. For desorption, an aliquot represents exposing the
sample to a large volume filled with gas at a pressure low enough
for desorption by the sample to occur at the given sample
temperature. In general, kinetics measurements are performed using
only one cycle (i.e. j=1 consisting of Steps 1 and 2). The
measurement is usually made with a large enough aliquot to
completely ad/absorb or desorb the sample. However, smaller and
multiple aliquots in a kinetics measurement may be performed. After
proceeding as described in Step 1 above, E2 is opened and the
pressure in the sample container (and gas lines) V.sub.C and the
reservoir volume V.sub.R is recorded and continues to be recorded
at specified time intervals. The quantity of gas ad/absorb or
desorb N.sub.j at each time interval is given by EQ. 1. The results
of the kinetics measurement are plotted as the quantity of gas
ad/absorb or desorb N.sub.j at each time interval (left axis)
versus the corresponding total amount of time passed for each
measured value of N.sub.j. An example of such a measurement is
given in FIG. 2. FIG. 19 shows a flow chart of the preferred
process for measuring gas sorption or desorption kinetic properties
of a sample using the gas sorption/desorption analyzer of the
invention.
[0135] PCT Measurement: The process for making both sorption and
desorption PCT measurements is identical to the kinetics
measurements described above. In this case, however, small volumes
and small pressure differentials are used to provide only small
aliquots. Thus, the sample ad/absorbs or desorbs a small quantity
of gas. The process as described for the kinetics measurements is
repeated for many cycles (i.e. j>1, with each cycle consisting
of Steps 1 and 2 as described above). The applied aliquot pressure
is increased with each cycle for sorption PCT measurements and
decreased with each cycle for desorption PCT measurements. At the
end of each cycle the equilibrium pressure P.sub.j and total
equilibrium concentration N.sub.Ej are recorded. A PCT curve is
constructed by plotting P.sub.j versus the corresponding value of
the total equilibrium concentration N.sub.Ej. A typical PCT diagram
constructed in this manner is shown in FIG. 20 shows a flow chart
of the preferred process for measuring gas sorption or desorption
PCT properties of a sample using the gas sorption/desorption
analyzer of the invention.
[0136] In addition to the PCT data that is collected during such a
measurement, the change in time of the gas pressure (and therefore
concentration) with each aliquot is essentially a localized
kinetics measurement. In the preferred embodiment of the present
invention, this data can also be collected during PCT measurements
to provide measurements of sorption and desorption kinetics at each
measuring point along a PCT curve.
[0137] Cycle-Life Measurement: The process making cycle-life
measurements is simply a series of cycles consisting of a sorption
measurement followed by a desorption measurement (or vise versa).
Each kinetic measurement is made in an identical manner to the
kinetics measurement process described above. For sorption, an
aliquot represents exposing the sample to a quantity of gas at a
pressure high enough for sorption by the sample to occur at the
given sample temperature. For desorption, an aliquot represents
exposing the sample to a large volume filled with gas at a pressure
low enough for desorption by the sample to occur at the given
sample temperature. The measurement is usually made with a large
enough aliquot to completely ad/absorb or desorb the sample.
However, smaller and/or multiple aliquots in a kinetics measurement
may be performed. The cycle-life measurement can be set up to cycle
indefinitely, or for a fixed number of cycles, or until a certain
criteria has been met. Examples of such criteria are: 1) the
reversible sorption or desorption capacity has dropped below a
specified value, or 2) the sorption or desorption rate has dropped
below a specified value, or any other criteria that changes with
continued cycling. The duration of the sorption and desorption
steps of each cycle may be set for a fixed amount of time or be
continuous until a certain criteria has been met. Examples of such
criteria are: 1) the reversible sorption or desorption capacity has
reached a specified value, or 2) the sorption or desorption rate
has dropped below a specified value, or any other criteria that
changes with time. In the preferred embodiment of the present
invention the experiment parameters chosen for the sorption part of
the cycle can be different than the experiment parameters chosen
for the desorption part of the cycle. Such parameters include: the
criteria controlling the duration of sorption and desorption, the
applied pressures, the sample temperature, the data collection
interval, whether or not weighted averages are used for the gas
temperature, whether or not constant applied sample pressures are
used, and the size of the calibrated reservoir volume used. These
parameters can also be changed during the cycle-life measurement by
the operator or as a function of the number of cycles completed.
FIG. 21 shows a flow chart of the preferred process for measuring
gas sorption or desorption cycle-life properties of a sample using
the gas sorption/desorption analyzer of the invention.
[0138] Automation: Computer software algorithms are designed to
simulate the manual operations that an experimenter would perform
on an identical system with manual valves. Among other things the
advantage of automation is that the experimenter need not be
present during the duration or even at intervals during the
experiment. Many gas sorption and desorption experiments are of a
slow nature, requiring hours, even days or months to run to
completion. It is not practical for the experimenter to be present
to make manual manipulations in such cases. In the present
invention automation is achieved using the pneumatic valves 612a-j
which are operated using pressurized air switched on and off by the
electric solenoid valves 604a-j that are controlled by the computer
506. Hardware PID controllers 603 and 728 are used to automatically
achieve desired gas pressures. Software PID controllers are used to
automatically achieve desired sample and reservoir temperatures.
The operator inputs the desired pressure and/or temperature into
the computer 506. The computer software algorithms send these
values through the communication link 507 to the data acquisition,
control, and safety system module 1110 via the communication
control hub which sends a signal to the pressure controllers 603 or
728 to regulate the pressures of the regulators 606 or 720
respectively and/or to the digital output device 1113 that delivers
power to either the enclosure heating element or the sample heater
701 (or 1001). Data collection is also automated using analog to
digital conversion of readings from the pressure transducers 633,
637, 617, 619, 725, 726 and the thermocouples 705, 706, 707, 820,
1121, 1122. Data collection is also automated using analog to
digital conversion of the pressure transducer and thermocouple
readings. Data is collected at logical intervals determined by the
type of measurement and the current dynamics of the process being
measured. For example, during kinetics measurements, data is
collected at time intervals of dt=.delta.t(e (1+ki)), or
alternatively dt=.delta.t(1+e (ki)), or alternatively dt=1+(t*k) 3,
where .delta.t is the starting time interval, k is a constant which
determines the rate at which dt changes with i, an i is the
interval. This enables data to be collected rapidly at the
beginning of a kinetics measurement and then at increasing larger
intervals as time goes on and the rates drop off. This dramatically
reduces the quantity of data collected while retaining all of the
pertinent information. One significant advantage of using automated
pneumatic valves is that the pneumatic force applied to the valves
is generally constant and well regulated. It is known that this
greatly improves the operating life time of such valves compared to
manual operations. Thus, an automated apparatus of this type is
expected to function for a significantly longer period of time
before requiring maintenance than a manual system.
[0139] Pressure Regulation: In the present invention the problem of
making finely spaced measurements of gas sorption and desorption
along the PCT curve has been solved by utilizing a pneumatically
controlled pressure regulator combined with a pneumatic PID
feed-back controller. These components is shown in FIG. 6. They
consists of a hardware PID air controller 603 and gas pressure
regulator 606 that regulates the pressure of the gas supplied to
the system from an internal gas vessel 616 which is filled with a
gas from an external supply. The hardware PID controller receives a
signal from a computer interface (in the form of an applied voltage
from the pressure regulator analog output device 1114) which
indicates the desired gas pressure. The controller then regulates
the air pressure supplied to the pneumatic gas pressure regulator
until the desired gas pressure is achieved. PID feedback comes from
a supply gas output pressure transducer 619 positioned downstream
of the gas pressure regulator that is connected directly to the
hardware PID air controller 603 as well as the analog input device
1112. In the case of PCT measurements, the pressure of each aliquot
is regulated to a desired value slightly above the plateau pressure
for sorption and slightly below the plateau for desorption. In the
preferred embodiment of the present invention, the actual value of
the desired pressure can be selected using any number of criteria.
For example, the applied pressure can simply be increased (or
decreased) linearly over the duration of the measurement. The most
common method, however, is to adjust the applied pressure to a
fixed value above (or below for desorption) the last measured
equilibrium pressure. In this manner the quantity of gas absorbed
or desorbed from each aliquot is nearly the same. Thus, the data
points will be distributed fairly evenly along the PCT curve. The
advantages of this method can be seen by comparing FIG. 23 with
FIG. 24. The PCT measurement shown in FIG. 23 was made on the
absorption of hydrogen by the intermetallic compound LaNi.sub.5.
The applied aliquots were fixed at a pressure of 12.5 atm. This
caused the broad distribution of data points for the lower pressure
portion of the measurement. FIG. 24, on the other hand, was made
for hydrogen absorption by the same sample on the same device,
however, the applied pressure was increased slowly from vacuum to
12.5 atm over the duration of the measurement. This gave smaller
aliquots of gas, and therefore, a more even distribution of data
points on the PCT curve. This is important to be able to discern
details in the PCT measurement such as phase transitions that might
other-wise be overlooked. The same process can be applied to
desorption measurements as sorption measurements. In the desorption
case the gas pressure regulator 606 is used to decrease the aliquot
pressures with each new aliquot by discharging gas through the
discharge line 621 until the desired supply pressure is
achieved.
[0140] Constant Pressure Measurements: In many cases, it is
important to be able to test gas sorption and desorption in a
material under conditions that most closely resemble those found in
the application for which the materials are being developed. For
instance, hydrogen storage materials used to supply hydrogen to a
fuel cell would need to do so at pressures at or above 1 atm.
Likewise, the procedure for charging such materials with gaseous
hydrogen would generally be performed at a constant overpressure,
for example, by loading directly from a pressure regulator on a gas
cylinder. In the laboratory, volumetric sorption measurements are
often performed by measuring the pressure drop as gas is absorbed
from a small known volume. Similarly, desorption experiments are
performed by measuring the increasing gas pressure while desorbing
into a small known volume that had been evacuated. Both
measurements involve changes in pressure of the gas surrounding the
sample. These pressure changes may effect the sorption or
desorption behavior of the material to some degree. To best
simulate real conditions, sorption and desorption measurements on
test samples should be performed using constant pressures. The
preferred embodiment of the present invention implements constant
pressure sorption and desorption measurements by placing gas
pressure regulator (606 and 720 respectively) between the sample
814 and the calibrated reservoir volume. The sorption or desorption
properties of the material are still determined by measuring the
change in pressure in a calibrated volume. However, the pressure of
the gas surrounding the sample is held constant using a pressure
regulator. Constant pressure sorption experiments utilize the same
internal PID controlled gas pressure regulator 606 used for
regulating the supply pressure of aliquots in PCT measurements
described above. This pressure regulator maintains a constant
pressure greater than the equilibrium plateau pressure over the
sample. The difference is that these experiments use a calibrated
reservoir volume (vessel 616, gas supply line 615, and fittings)
that is upstream of the pressure regulator. The pressure drop in
this volume is then used to calculate the quantity of gas taken up
by the sample. Constant pressure desorption measurements utilize an
external back-pressure regulator 720, shown in FIG. 7, to maintain
a constant pressure of the desorbed gas surrounding the sample 814.
This pressure regulator maintains a constant pressure which is
below the equilibrium plateau pressure of the sample. It is
attached between the sample container 801 and the external gas
handling portion 901. The gas released from the sample flows
through the back-flow regulator 720 into a large evacuated
calibrated reservoir volume (either vessels 629 or 631 or both, and
gas lines 632, 627 and fittings). The desired back-pressure is
controlled using a hardware back-pressure regulator pneumatic PID
controller 728 that regulates the pressure of the gas supplied from
the desorbing sample to the evacuated reservoir volume. The
hardware back-pressure regulator pneumatic PID controller 728
receives a signal from a computer interface (in the form of an
applied voltage from the pressure regulator analog output device
1114) which indicates the desired gas pressure. The controller then
regulates the air pressure supplied to the pneumatic gas
back-pressure regulator 720 until the desired gas back-pressure is
achieved. PID feedback comes from a back-pressure regulator input
pressure transducer 725 positioned on the sample side of the gas
back-pressure regulator 720. The pressure increase in the
calibrated reservoir volume is measured to calculate the quantity
of gas released by the sample. For complete sorption and desorption
measurements the calibrated volumes must be large enough, and the
pressures high (or low) enough, and/or the samples small enough
that the pressure in the calibrated volume does not reach the
plateau pressure of the sample. If this occurs sorption or
desorption may stop without being complete. In the preferred
embodiment of this invention, PID controlled pressure regulators
are used for both constant pressure sorption and desorption
measurements.
[0141] Regulated Gas Temperature: Changes in temperature of the gas
due to changes in the ambient air temperature will cause errors in
the measurements that are difficult to compensate for simply by
making corrections to the data. A distinguishing feature of this
invention over the prior art is that the main portion of the gas is
maintained at a constant temperature at using an insulated
enclosure 502, an enclosure heating element 639 and a air
re-circulating fan 640. In a volumetric measurement, it is critical
that the temperature of the gas is know for an accurate
determination of the quantity of gas sorption or desorption by a
sample. It is possible to measure the gas temperature at a point,
however, that might not be representative of the average gas
temperature throughout the gas sorption/desorption analyzer. The
best method is to maintain the gas at a fixed temperature within
most of the gas sorption/desorption analyzer and to minimize the
gas volume that may be at another temperature. In the present
invention, the gas is maintained at a constant temperature slightly
above room temperature by placing the main portion of the gas
sorption/desorption analyzer within an insulated enclosure 502
which is heated. In the preferred embodiment of the present
invention, the heating is provided by an electric resistive
enclosure heating element 639, however, other types of heating may
also be used. The temperature is regulated using a software PID
controller that supplies power to the enclosure heating element 639
through the enclosure heating element 110 V AC analog output device
1116. Feedback for the software PID controller comes from an
enclosure thermocouple 1123 place inside of the enclosure. The
internal temperature distribution is made uniform by using an
internal circulating air fan 640.
[0142] Software PID Controls: In the preferred embodiment, this
invention utilizes software PID controllers running on the computer
506 and interfacing with the gas sorption/desorption analyzer 501
through the communication link 507, data acquisition, control and
safety system 1110, and communications control hub 1111, combined
with an analog input device 1112 and a digital output device 1113
and analog output devices 1114, 1115, and 1116 to control the
pressure regulators 606 and 720, enclosure heater 639, and the
sample heaters 701 or 1001. This reduces the complexity of the
system hardware. The first software PID control is used to regulate
the temperature of the air inside the enclosure using an electric
resistive heater and internal fan to circulate the air as described
above. The second PID control regulates the temperature of the
sample 814 by controlling the sample heater control relay 1109
through the digital output device 1113. PID feedback comes from one
of several thermocouple (705, 706, 707 or 820) place inside of or
in close proximity to the sample container.
[0143] Non-Ideal Gas Compensation: The preferred embodiment of the
present invention includes data analysis software employing
automatically calculation of non-ideal gas behavior to correctly
determine the quantity of gas from changes in pressure. The
preferred embodiment uses a zero-point solving routine to solve the
"Beattie-Bridgeman" equation of state to determine the quantity of
gas sorption or desorption based on changes of pressure in a known
volume. Similarly, other equations of state (for example Van der
Waals equation of state) for non-ideal gas behavior can also be
used. FIG. 22 shows a plot of these two methods for calculating the
quantity of gas from pressure, volume and temperature compared with
the ideal gas law. The plot shows the number of moles in of
hydrogen gas in a one liter volume at 20.degrees.C. versus pressure
calculated using the ideal gas law, the Beattie-Bridgeman equation
of state, and the Van der Wall's equation of state.
[0144] Semi-Automated Volume Calibrations: To be able to accurately
calculate the quantity of gas taken-up by or released from a
sample, it is generally necessary that the entire gas volume be
known. The various control volumes of the gas sorption/desorption
analyzer can be calibrated once for every measurement. However, the
gas volume of in sample container will change if different sample
containers are used and will also be dependent on the volume of the
sample itself. For this reason, the volume of the sample container
801 including the sample 814 should be measured every time it is
changed. The volume of the sample container (and sample) can be
determined after it is attached to the gas sorption/desorption
analyzer 501 by evacuating or supplying a given pressure to the
sample container 801, closing the sample container valve 805,
measuring the pressure of a gas (this should be equivalent to the
pressure in the sample container). Then a calibrated volume on the
gas sorption/desorption analyzer is either evacuated or filled to a
pressure which is different from that in the sample container and
this pressure is measured. The sample container valve 805 is then
opened and when the pressure has come to equilibrium between the
sample container and the calibrated volume, the volume of the
sample container can be determined from the resulting change in
pressure. Usually this procedure is repeated several times to get
an accurate measurement of the sample container plus sample volume.
The calibration gas that is used for these measurements should be
inert and the measurement done at temperatures for which there will
be no significant sorption or desorption of the calibration or
other gasses by or from the sample. In the preferred embodiment of
this invention the calibration gas is helium. To aid in this
calibration process, the present invention includes a
semi-automated routine for performing such a sample volume
calibration measurement. The routine opens the appropriate valves
or instructs the operator to do so, supplies and measures the
helium pressures, and calculates the volume of the combined sample
container and sample. Helium gas is supplied to the gas
sorption/desorption analyzer through the calibration gas connector
607 and calibration gas supply line 608. The helium is introduced
into the gas handling system by opening the automated valve
612a.
[0145] Sample Density Measurements: The same type of volume
calibration measurements as described above can be used to
determine the density of the sample. To do this, the sample
container 801 is first attached to the gas sorption/desorption
analyzer without a sample. Its empty volume is calibrated as
described above. Next the same sample container 801 is filled with
a sample 814 of a known mass and then attached to the gas
sorption/desorption analyzer. The volume calibration is performed
once again as described above. The difference in the volume of the
sample container 801 with and without the sample 814 is the solid
volume of the sample. The mass of the sample divided by this volume
gives the density of the sample. The semi-automated volume
calibration procedure of this invention (described above) provides
an aid to simplify this process.
[0146] In Situ Sample Density Measurements: In addition, there is a
unique advantage to performing the type of density measurement
procedure described above. By performing such measurements directly
on the gas sorption/desorption analyzer 501 that is used for making
gas sorption and desorption property measurements the density of
the sample (or volume expansion/contraction) can be measured in
different states of gas loading. This is done by placing the sample
under conditions with respect to temperature and hydrogen partial
pressures that it will not desorb the active gas. In the preferred
embodiment of this invention, the sample container 801 and solid
sample 814 volume are measured before any gas sorption or
desorption measurements (as described above). Then active gas
loading or unloading is performed. When the desired active gas
content of the sample is achieved, the sample container valve 805
is closed and the temperature of the sample is lowered to the point
at which active gas will desorb only very slowly when exposed to an
atmosphere containing only an inert gas. The sample container 805
and solid sample 814 volume are measured again using an inert gas
as described above. Thus, any changes the solid volume (and
therefore changes in density) of the sample associated with active
gas loading can be measured. In the case where there is no change
in the crystal structure, the active gas induced change in density
may be a good indirect measurement of lattice expansion or
contraction associated with a change in active gas concentration in
the sample.
[0147] Extended Dynamic Pressure Range: The preferred embodiment of
the present invention includes high- and low-range pressure
transducers, sensors, or gauges to be able to cover a large dynamic
range of pressures. Strain gauge pressure transducers are available
that are very accurate (generally 0.2% of full scale). However,
because the accuracy has a constant value over the entire range of
pressures the error at low pressures is quite substantial.
Capacitance manometers, on the other hand, have proportional errors
which decrease as the pressure decreases. Unfortunately, these
devices are often less accurate (generally 1% of reading) than the
strain gauge type at higher pressures. The present invention
overcomes this problem by using two or more pressure transducers to
cover a broad range of pressures accurately. In the preferred
embodiment, this invention includes two pressure transducers (shown
in FIG. 6), one covering the range 0 to 200 at, (high-pressure
transducer 633) and a second covering the range 0 to 7 atm
(low-pressure transducer 637). The correct transducer is
automatically chosen depending on the range pressure of the
pressure being measured. This is accomplished by first reading the
pressure with the high-pressure transducer 633 to determine the
range that the pressure falls into and then selecting the
appropriate transducer to make the final pressure measurement.
[0148] Multiple Calibrated Reservoir Volumes: The present invention
is an gas sorption/desorption analyzer that includes several
calibrated volumes. These volumes allow the control reservoir
volume to be changed from small to large volumes depending on: a)
the type of measurement to be made, b) the quantity of sample to be
measured, and c) the quantity of gas that will be ad/absorbed by
the sample. For example, a kinetics measurement in which a sample
is completely ad/absorbs or desorbs a gas in one step, requires a
larger reservoir volume than a PCT measurement in which sorption or
desorption takes place in a series of small aliquots from or to a
much smaller reservoir volume. Another example, is that sorption of
a gas at high pressure (ca. 100 atm) requires a small volume (to
accurately measure pressure changes). Whereas, desorption at low
pressures (ca. 1 atm) requires a large volume to be able to
maintain a pressure below the equilibrium plateau pressure. In the
preferred embodiment, the reservoir volumes can be switched as
required between approximately 0.01 to 1 liter. An additional
advantage in the preferred embodiment of the invention, is
automated valves on each of several pre-calibrated volumes allows
the reservoir volume to be changed at any time even during an
experiment, either manually or through automated computer
algorithms for making a given experiment. In the preferred
embodiment of the invention, these calibrated reservoir volumes
(shown in FIG. 6) includes either vessels 629 or 631 or both, and
gas lines 632, 627, valves 612h,j,k,i,g,e, fittings, and pressure
transducers 633 and or 637. Other calibrated volumes include the
gas vessel 616 and many of the other gas lines, fittings, valves,
and pressure transducers.
[0149] Reduced Operating Volumes: Small working volumes is an
important feature of the present invention. The quantity of gas in
an aliquot depends on the pressure, temperature and volume of the
gas. Small quantities of a sample, low gas concentrations in a
sample, or high working pressures require measurements to be made
with small aliquots of gas. Therefore, small reservoir volumes must
be used to measure such small quantities of gas or even large
quantities at high pressure (ca. 100 atm). The present invention
employs small internal diameter tubing, short distance, and spacers
to fill empty spaces in the sample container to reduce the actual
working volumes in the gas sorption/desorption analyzer. The entire
working volume of the system can be reduce to on the order of 15
milliliters. This includes the total added volumes of the external
gas handling system 901, the sample container 801 using spacers
811, the gas lines 632, 634, 638, the pressure transducers 633 and
637, and the automated valves 612 h,j,k. In addition, the
implementation of small gas volumes in the sample container 801
also reduces the problem of uncertainty in the gas temperature when
the sample 814 is at a temperature significantly different than the
bulk of the gas in the gas sorption/desorption analyzer. By
reducing the free gas space in and close to the sample container,
the average temperature of the gas in the system is approximately
equal to that of the temperature of the reservoir. In this manner
the gas temperature being chosen as the enclosure temperature is a
good approximation for calculating the quantity of gas in the
system, even at elevated sample temperatures.
[0150] Mobility: The external gas handling portion 901 and feet 505
are designed to be removed for easy transport of the gas
sorption/desorption analyzer 501.
[0151] System Power Failsafe Mechanism: In the preferred
embodiment, this invention employs a failsafe mechanism to shut off
power to the gas sorption/desorption analyzer if enclosure is
opened. This is accomplished using low voltage power safety relay
1127 and electrical pressure switches 1103 (such as push-button
enclosure power safety switches) in contact with the enclosure's
panels 503. These switches form a series safety circuit as shown in
FIG. 11. The main power supply is controlled by the power safety
relay 1127. If the safety circuit is broken by removing a panel
from the gas sorption/desorption analyzer, the relay will open,
shutting off power to the system.
[0152] Enclosure Heating Failsafe Mechanism 1: In the preferred
embodiment, this invention employs a failsafe mechanism that shuts
off power if enclosure temperature goes above a preset temperature
limit (for example 50.degree.C.). The control software checks the
enclosure temperature on a regular basis and will shut off power to
the system by opening the safety relay on the main power supply to
the gas sorption/desorption analyzer if the enclosure temperature
rises above the maximum set point. This is not shown in FIG. 11,
but it is comprised of adding a relay device to the data
acquisition, control, and safety system 1110. This relay would be
wired in series with the power safety relay 1127 and controlled by
the computer 506. When a signal is sent from the computer to this
relay the circuit would be broken and the power safety relay 1127
would open shutting off power to the gas sorption/desorption
analyzer 501.
[0153] Enclosure Heating Failsafe Mechanism 2: In the preferred
embodiment, this invention employs a failsafe mechanism to prevent
over-heating of the enclosure. This is done by selecting an
electrical resistive heater enclosure heating element 639, that
will only deliver enough heat to raise the enclosure temperature to
a reasonable temperature (for example 50.degree.C.).
[0154] Gas Leak Failsafe Mechanism 1: In the preferred embodiment,
this invention employs a failsafe mechanism to prevent buildup of
hydrogen or other flammable gasses and the possibility of an
explosion if there is a gas leak within the enclosure 502. The
enclosure 502 is designed not to be air-tight. There are vents 511
with dust filters at the bottom and top of the enclosure. In the
event that there is a gas leak within the enclosure, the vents
prevent the gas concentrations from building up to dangerous levels
by allowing the gas to escape through the top or bottom vent by
natural buoyancy and thermal convection. In another embodiment of
the invention, outside air is slowly forced through the enclosure
by a ventilation fan mounted on either the bottom inlet vent or the
top outlet vent.
[0155] Gas Leak Failsafe Mechanism 2: In the preferred embodiment,
this invention employs a failsafe mechanism to prevent serious
damage from an explosion in the case in which there is a
significant flammable gas leak within the enclosure 502. If the
leak is so large as to achieve explosive concentrations and an
ignition does occur, the damage will be minimized by allowing the
force to be released through opening of the failsafe top panel 1301
of the enclosure 502. This is accomplished by using a failsafe top
panel 1302 which is not rigidly affixed to the enclosure, but
rather is on top panel hinges 1303 or some other means of
attachment as shown in FIG. 13B. In the case of ignition the top
will pop open and move safely out of the way as shown in FIG.
13A.
[0156] Gas Leak Failsafe Mechanism 3: In the preferred embodiment,
this invention employs a failsafe mechanism that limits the amount
of gas used by the gas sorption/desorption analyzer during an
experiment. This is achieved by taking the gas from external source
(bottle) and filling small internal gas vessel 616 shown in FIG. 6
that is used to supply gas to the gas sorption/desorption analyzer
during experimental measurements. An automated valve 612b between
the external gas supply and the small internal gas vessel 616
limits the amount of gas used by the gas sorption/desorption
analyzer. The automated valve 612b (preferably pneumatic) is a
normally closed valve. This valve is opened only at the beginning
of an experiment or when the pressure in the internal gas vessel
616 has dropped to a point such that it needs to be refilled. The
automated valve 612b is controlled through a computer interface by
the software which is used to control the gas sorption/desorption
analyzer. A signal generated by the software is sent to an
electrical air control solenoid (one of 604a-j) valve that supplies
air pressure to open or close the automated valve 612b, filling the
internal gas vessel 616 with more gas.
[0157] Gas Leak Failsafe Mechanism 4: In the preferred embodiment,
this invention employs a failsafe mechanism whereby all automated
valves 612a-j except 612k are normally closed valves. Thus, in the
event that the electrical power or air supply is cut off, all of
these normally closed valves will shut. This limits the amount of
gas that could potentially leak from the gas sorption/desorption
analyzer to the gas in the small volume between the closed valves
where the leak occurred.
[0158] Sample Container Pressure Failsafe Mechanism: In the
preferred embodiment, this invention employs a failsafe mechanism
for gas over-pressurization of the sample container 801 (FIG. 8).
This is provided by using a pressure relief valve or a sample
container valve 805 which releases gas at a pressure above the
normal operating limit of the gas sorption/desorption analyzer
(typically 200 atm) but at a pressure (less than 300 atm) that is
below the burst pressure of the sample container 801. For example,
a failure could occur if the sample container valve 805 was closed
and a fully gas loaded sample 814 was heated to a very high
temperature. The equilibrium pressure of the gas released could be
at elevated pressures high enough to rupture the sample container
801. However, the failsafe mechanism described herein would employ
a sample container valve 805 or pressure relief device that would
release the gas at pressures lower than the pressure that would
rupture the sample container. The preferred sample container valve
805 is typically a diaphragm valve. To provide a pressure failsafe
mechanism, this valve should be positioned with the valve seat
towards the sample 814 and the valve stem and diaphragm upstream of
the sample. At elevated pressures the force of the gas pushing
against the stem will cause the valve to unseat releasing the gas
from the sample container 801. If the pressure continues to build
on both sides of the valve, the diaphragm will rupture and leak. In
this case, it is much safer for the diaphragm to rupture than for
the sample container to rupture. As an additional measure of
safety, a pressure relief device (valve or burst disk) can also be
connected on the sample side of the sample container. This device
would have its release pressure set above the normal maximum
operating pressure of the gas sorption/desorption analyzer but
below the rupture pressure of the sample container 801 or other
components of the gas sorption/desorption analyzer.
[0159] Gas Pressure Failsafe Mechanism: In the preferred
embodiment, this invention employs a failsafe mechanism that shuts
off the power supply to the gas handling and heating circuits of
the electrical system 1101 if the pressure measured by the high
pressure transducer 633 indicates that the system pressure is
higher than a specified safety limit. The pressure within the
calibrated reservoir volume is monitored on a regular basis during
most experiments using the high pressure transducer 633. This
failsafe mode provides a signal from the controlling software to
shut off the power supply to the gas handling and heating circuits
if the measured pressure in the reservoir is higher than an upper
safety limit set in the software (generally 200 atm).
[0160] Power Supply Failsafe Mechanism: In the preferred
embodiment, this invention employs a failsafe mechanism that shuts
off gas supply if power or air supply is cut off. The pneumatic
automated valve 612b that is employed for filling the small
internal supply gas vessel 616 from an external gas source
(described above) is a normally closed valve. In the event that
either electrical power or the air supply to the gas
sorption/desorption analyzer 501 is cut off, this pneumatic valve
will close. If there is a leak in the gas sorption/desorption
analyzer, it will be limited to the amount of gas in the gas
sorption/desorption analyzer when the power or air is cut off.
[0161] Low Pressure Transducer Failsafe Mechanism: In the preferred
embodiment, this invention employs a failsafe mechanism to protect
the low pressure transducer 637 from exposure to gas at pressures
above the maximum rated pressure of the transducer. In general, the
lower range pressure transducers can not be exposed to pressures
significantly higher than the upper measuring limit of the
transducer without sustaining damage (generally 1.5 times the
maximum reading). To protect the low pressure transducer(s), a
automated valve 612j is placed between the low pressure transducer
637 and the rest of the system. The automated valve 612j may be
controlled (either by software and/or electrical or pneumatic
hardware) such that it remains closed if the pressure on the other
side of the valve is above the maximum readable pressure of the
transducer. In addition, a low pressure transducer failsafe
pressure relief valve 638 or burst disc may be placed on the
transducer side of the automated valve 612j. This relief valve or
burst disc protects the low pressure transducer 637 (which tend to
be expensive) by venting or rupturing if the transducer is
inadvertently exposed to a pressure greater than the limit of the
transducer. In the preferred embodiment of this invention all
pressure relief valves or burst discs located inside of the
enclosure 502 are connected to a vent line 625 that directs any
released gas via the vent connector 626 to an external ventilation
system.
[0162] One-way Flow Failsafe Mechanism: In the preferred
embodiment, this invention employs a set of failsafe one-way check
valve mechanisms (e.g. calibration gas check valve 609) to protect
certain parts of the gas sorption/desorption analyzer from
over-pressurization. These check valves are set to close if the
applied pressure exceeds a specified value. This helps to protect
any components downstream of the check valve. For example, one such
check valve is located on the calibration gas supply line 608 to
protect the line from inadvertent over-pressurization or
contaminated by high-pressure gas in the system. Another check
valve could also be located on the low-pressure transducer gas line
636 between the automated valve 612j and the low pressure
transducer failsafe pressure relief valve 638. This provides
additional protection to prevent exposing the low pressure
transducer 637 to gas at pressures above the maximum rated pressure
for the transducer.
[0163] Safety Shield: In the preferred embodiment, this invention
employs a safety mechanism that consists of a sample container
safety shield 1201 surrounding the sample container 801 as shown in
FIG. 12. The purpose of this shield is to protect the operator or
other persons in the event that the sample container 801, gas lines
or other fixtures fail in a catastrophic manner. The see-through
safety shield 1202 would be composed preferably of a material that
is transparent and strong such as Lexan. The shield is designed to
stop objects flying in most directions away from the area of the
sample container 801. The shield is mounted on safety shield hinges
1204 so that it may be opened to change the sample or perform other
operations within its space. During experiments, the shield is
latched in the closed position using a safety shield latch hook
1205 and pin 1206 such as shown in FIG. 12.
[0164] Safety Shield Failsafe Mechanism: In the preferred
embodiment, this invention employs a failsafe mechanism to shut off
power to the sample heater furnace 701 or heating jacket 1001 if
the sample container safety shield 1201 described above is opened.
This is achieved using a low voltage sample container safety shield
switch 1121 (such as a push-button switch) that is pushed into the
closed position by the see-through safety shield 1202 when the
shield is closed properly. This switch forms a safety circuit as
shown in FIG. 11 connected to the sample heater control relay 1109
which controls the furnace 701 or heating jacket 1001. If the
safety circuit is broken by opening the see-through safety shield
1202, the sample heater control relay 1109 will open, shutting off
power to the furnace 701 or heating jacket 1001.
[0165] Sample Heater Failsafe Mechanism: In the preferred
embodiment, this invention employs a failsafe mechanism to shut off
power to the sample heater furnace 701 or heating jacket 1001, if
the temperature of the sample container 801 goes above
450.degree.C. This is achieved by monitoring an thermocouple (705,
706, or 707) other than the thermocouple that is being used to
control the temperature of furnace 701 or heating jacket 1001. If
this other thermocouple (705, 706, or 707) registers (when
monitored by the computer 506) a temperature greater than
450.degree.C. it shuts off the power to the furnace 701 or heating
jacket 1001 by opening the sample heater control relay 1109. In an
alternative embodiment the entire system power can be shut off
using the power safety relay 1127 if after some time the computer
still registers a temperature greater than 450.degree.C. in the
furnace 701 or heating jacket 1001.
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