U.S. patent application number 12/406690 was filed with the patent office on 2010-02-11 for reusable vacuum pumping apparatus with nanostructure material.
This patent application is currently assigned to Raytheon Company. Invention is credited to Timothy J. Imholt.
Application Number | 20100034669 12/406690 |
Document ID | / |
Family ID | 41653119 |
Filed Date | 2010-02-11 |
United States Patent
Application |
20100034669 |
Kind Code |
A1 |
Imholt; Timothy J. |
February 11, 2010 |
Reusable Vacuum Pumping Apparatus with Nanostructure Material
Abstract
According to one embodiment, a vacuum system comprises a vacuum
chamber, a construct of nanotubes, and a heat source. The vacuum
chamber contains one or more gases. The construct of nanotubes is
located proximate to the vacuum chamber and is operable to absorb
or adsorb gases from the vacuum chamber. The hear source is located
proximate to the construct of nanotubes and is operable to heat the
construct of nanotubes such that the construct of nanotubes desorbs
the gases from the vacuum chamber.
Inventors: |
Imholt; Timothy J.;
(Richardson, TX) |
Correspondence
Address: |
BAKER BOTTS LLP
2001 ROSS AVENUE, 6TH FLOOR
DALLAS
TX
75201-2980
US
|
Assignee: |
Raytheon Company
Waltham
MA
|
Family ID: |
41653119 |
Appl. No.: |
12/406690 |
Filed: |
March 18, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61188195 |
Aug 7, 2008 |
|
|
|
Current U.S.
Class: |
417/51 |
Current CPC
Class: |
B82Y 30/00 20130101;
C01B 3/0021 20130101; Y02E 60/32 20130101; Y02E 60/325
20130101 |
Class at
Publication: |
417/51 |
International
Class: |
F04B 37/02 20060101
F04B037/02 |
Claims
1. A vacuum system comprising: a vacuum chamber containing one or
more gasses; a construct of nanotubes located proximate to the
vacuum chamber, the construct of nanotubes operable to absorb or
adsorb gases from the vacuum chamber; and a heat source located
proximate to the construct of nanotubes, the heat source operable
to heat the construct of nanotubes such that the construct of
nanotubes desorbs the gases from the vacuum chamber.
2. The vacuum system of claim 1, wherein the vacuum chamber
contains Hydrogen.
3. The vacuum system of claim 1, wherein the nanotubes are carbon
single-walled nanotubes.
4. The vacuum system of claim 1, wherein the nanotubes are carbon
multi-walled nanotubes.
5. The vacuum system of claim 1, further comprising: a vacuum pipe
containing the construct of nanotubes; and a vacuum valve
connecting the vacuum pipe to the vacuum chamber.
6. The vacuum system of claim 5, further comprising an atmosphere
valve connecting the vacuum pipe to the outside atmosphere.
7. The vacuum system of claim 6, wherein the atmosphere valve is a
one-way valve operable to block gases from the outside atmosphere
from reentering the vacuum pipe.
8. The vacuum system of claim 1, wherein the heat source is a
microwave energy generator, the microwave energy generator operable
to produce a microwave field.
9. The vacuum system of claim 8, further comprising a device for
directing the microwave field from the microwave energy generator
toward and through the construct of nanotubes.
10. The vacuum system of claim 8, wherein the microwave energy
generator generates a frequency between 0.1 GHz and 100 GHz.
11. The vacuum system of claim 8, wherein the microwave energy
generator comprises at least one of a dual cavity klystron with
planar triodes, a reflex klystron, a backward wave oscillator, or a
magnetron.
12. A method of removing gases from a chamber, comprising:
providing a vacuum chamber containing one or more gases; placing a
construct of nanotubes located proximate to the vacuum chamber such
that the construct of nanotubes can absorb or adsorb gases from the
vacuum chamber; and heating the construct of nanotubes such that
the construct of nanotubes desorbs the gases from the vacuum
chamber.
13. The method of claim 12, wherein the gases from the vacuum
chamber includes Hydrogen.
14. The method of claim 12, wherein the nanotubes are carbon
single-walled nanotubes.
15. The method of claim 12, wherein the nanotubes are carbon
multi-walled nanotubes.
16. The method of claim 12, further comprising: pumping gases out
of the vacuum chamber with a vacuum pump.
17. The method of claim 12, wherein heating the construct of
nanotubes such that the construct of nanotubes desorbs the vacuum
chamber comprises: sealing the construct of nanotubes from the
vacuum chamber; heating the construct of nanotubes such that the
construct of nanotubes desorbs the gases from the vacuum chamber;
and releasing the desorbed gases into the outside atmosphere.
18. The method of claim 12, wherein heating the construct of
nanotubes such that the construct of nanotubes desorbs the vacuum
chamber further comprises: generating a microwave field.
19. The method of claim 18, further comprising providing a device
for directing the microwave field from toward and through the
construct of nanotubes.
20. The method of claim 18, wherein the microwave field has a
frequency between 0.1 GHz and 100 GHz.
21. The method of claim 18, wherein generating a microwave field
further comprises: generating a microwave field with at least one
of a dual cavity klystron with planar triodes, a reflex klystron, a
backward wave oscillator, or a magnetron.
Description
TECHNICAL FIELD OF THE DISCLOSURE
[0001] This disclosure generally relates to vacuum systems, and
more particularly, to a reusable vacuum pumping apparatus with
nanostructure material and a method of using the same.
BACKGROUND OF THE DISCLOSURE
[0002] Vacuum pumps are devices that remove gas molecules from a
sealed volume in order to leave behind a partial vacuum. Vacuum
systems are used in many types of scientific research, as well as
in many fields of manufacturing and industry. Vacuum systems are
especially critical in fields such as electronics manufacturing and
experimental sciences, where trace gases left in the sealed volume
may disrupt manufacture and research.
SUMMARY OF THE DISCLOSURE
[0003] This disclosure generally relates to vacuum systems, and
more particularly, to a reusable vacuum pumping apparatus with
nanostructure material and a method of using the same.
[0004] According to one embodiment, a vacuum system comprises a
vacuum chamber, a construct of nanotubes, and a heat source. The
vacuum chamber contains one or more gases. The construct of
nanotubes is located proximate to the vacuum chamber and is
operable to absorb or adsorb gases from the vacuum chamber. The
hear source is located proximate to the construct of nanotubes and
is operable to heat the construct of nanotubes such that the
construct of nanotubes desorbs the gases from the vacuum
chamber.
[0005] Certain embodiments of the disclosure may provide numerous
technical advantages. For example, a technical advantage of one
embodiment may include the capability to achieve lower pressures in
a vacuum chamber by adsorbing trace gases in the system. Other
technical advantages of other embodiments may include the
capability to achieve low vacuum pressures faster than alternative
vacuum systems. Yet other technical advantages of some embodiments
may include the capability to recycle nanostructure materials and
provide a long-lasting vacuum system.
[0006] Although specific advantages have been enumerated above,
various embodiments may include all, some, or none of the
enumerated advantages. Additionally, other technical advantages may
become readily apparent to one of ordinary skill in the art after
review of the following figures and description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] For a more complete understanding of embodiments of the
disclosure and its advantages, reference is now made to the
following detailed description, taken in conjunction with the
accompanying drawings, in which:
[0008] FIGS. 1 and 2 show vacuum systems according to several
embodiments;
[0009] FIG. 3 show the results of an experiment testing the
adsorptive power of nanotubes in a vacuum system;
[0010] FIGS. 4A and 4B show two techniques for generating microwave
fields according to some embodiments; and
[0011] FIG. 5 show the results of an experiment testing the
recyclability of nanotubes in a vacuum system.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0012] It should be understood at the outset that, although example
implementations of embodiments of the invention are illustrated
below, the present invention may be implemented using any number of
techniques, whether currently known or not. The present invention
should in no way be limited to the example implementations,
drawings, and techniques illustrated below. Additionally, the
drawings are not necessarily drawn to scale.
Vacuum Systems
[0013] FIG. 1 shows a vacuum system 100 according to several
embodiments. Vacuum system 100 features a vacuum chamber 110 and a
vacuum pump 120.
[0014] Embodiments of the vacuum chamber 110 may include any sealed
enclosure operable to maintain a vacuum at a pressure lower than
the outside atmospheric pressure. Two concepts help characterize
the strength of a vacuum in the vacuum chamber 110. First, the
"mean free path" of a molecule or atom of gas is defined as the
average distance it can travel before colliding with another atom
or molecule. A lower vacuum pressure will result in a higher mean
free path for each molecule or atom remaining in the vacuum chamber
110. Second, "particle flux" is the rate at which particles hit the
surface of a vacuum vessel. The particle flux rate depends on the
gas's number density and molecular weight. Number density is how
many particles of gas are contained in the vacuum chamber 110, and
molecular weight is the mass of one molecule of a substance
relative to the unified atomic mass unit. A lower vacuum pressure
will result in a lower particle flux rate inside the vacuum chamber
110.
[0015] Embodiments of the vacuum pump 120 may include any device
operable to remove gas molecules from the vacuum chamber 110 and
create a partial vacuum. In general, certain embodiments of the
vacuum pump 120 may be broadly categorized into two categories:
gas-transfer pumps (such as turbomolecular and diffusion pumps) and
gas-capture pumps (such as cryo and ion pumps).
[0016] The vacuum pump 120 may be rated based on various
performance measures. For example, "pumping speed" refers to the
volume flow rate of the pump at its inlet. Pumping speed measures
how many liters of gas a vacuum pump can permanently remove from a
vacuum chamber every second. Pumping speed may identify whether a
vacuum pump can achieve a specified vacuum pressure in a specified
amount of time.
[0017] The vacuum system 100 may include more than one type of the
vacuum pump 120. For example, not all vacuum pumps will work at
atmospheric pressures. Some embodiments of the vacuum system 100
may include a rough pump designed to reduce the pressure in vacuum
chamber 110 from atmospheric pressure to some lower pressure, at
which point another type of the vacuum pump 120 can then obtain
even lower pressures. One example of a rough pump is a coarse vane
pump. A course vane pump may reduce vacuum chamber pressure from
atmospheric pressure to approximately 10.sup.-3 to 10.sup.-4
torr.
[0018] Once the rough pump has lowered the vacuum chamber 110
pressure to an appropriate level, the vacuum system 100 may employ
a gas-transfer pump, such as a turbomolecular pump, which may lower
the vacuum chamber pressure from 10.sup.-4 to 10.sup.-10 torr. A
turbomolecular pump, for example, may include a stack of rotors,
each rotor containing many angled blades that rotate at a very high
speed. When a gaseous atom or molecule hits the blades, the blade
momentum and pressure differences force the atom or molecule in the
direction of the exhaust.
[0019] However, pumps such as turbomolecular pumps are limited by
their rotational speeds and may not be able to pump all types of
gases. For example, hydrogen at approximately 25 degrees Centigrade
moves at approximately 1700 meters per second. A turbomolecular
pump with a 6 inch diameter rotating at 36,000 revolutions per
minute can only achieve speeds of approximately 280 meters per
second, thus allowing the hydrogen and other gases to flow back
into the vacuum chamber. Hydrogen is not the only problematic gas,
but it can be one of the most difficult for turbomolecular pumps to
pump.
[0020] However, some applications require extremely low vacuum
pressures. Most pumping schemes have a tendency to leave some types
of residual trace gases, such as Hydrogen, Helium, Nitrogen, water
vapor (a primary source of Hydrogen), and several others. This
residual gas may cause the pressure in the vacuum chamber to be
higher than some applications requiring vacuum conditions will
allow. There are two normal choices when faced with this situation:
spend an enormous amount of money on pumps--most of which will only
partially deal with the problem--or simply allow the problem to
exist.
[0021] Accordingly, teachings of certain embodiments recognize the
use of nanotubes as an adsorbant in a vacuum chamber. Teachings of
certain embodiments recognize that nanotubes may adsorb particles
from the vacuum chamber, thus lowering the gas's number density,
particle flux, and vacuum chamber pressure. Additionally, teachings
of certain embodiments recognize that nanotubes have the capability
to adsorb many residual gases, such as Hydrogen, Helium, Nitrogen,
water vapor, and several others. Furthermore, teachings of certain
embodiments recognize that nanotubes may allow lower vacuum chamber
pressures than alternative pumping systems.
[0022] FIG. 2 shows a vacuum system 200 according to several
embodiments. Vacuum system 200 features a vacuum chamber 210, a
valve 215 connecting vacuum chamber 210 to a vacuum pipe 220, a
valve 225 connecting vacuum pipe 220 to the outside atmosphere, a
construct of nanotubes 230, and a heat source 240. Some embodiments
of vacuum system 200 may also include additional vacuum pumps such
as the vacuum pumps 110, not illustrated in FIG. 2.
[0023] Embodiments of the vacuum chamber 210 and the vacuum pipe
220 may include any sealed enclosure operable to maintain a
pressure lower than the outside atmospheric pressure. Embodiments
of the valves 215 and 225 may include any device operable to
regulate the flow of fluid by opening, closing, or partially
obstructing various passageways. For example, the valve 215 may
open to allow gases to flow from the vacuum chamber 210 to the
vacuum pipe 220, and the valve 225 may open to allow gases to flow
from vacuum pipe 220 to the outside atmosphere. In some
embodiments, the valves 215 and 225 may be one-way valves, only
allowing gas flow from the vacuum chamber 210 to the vacuum pipe
220 and from the vacuum pipe 220 to the outside atmosphere.
[0024] Some embodiments of the vacuum system 200 may also include a
waveguide 245 in embodiments where the heat source 240 is a
microwave heat source. Microwave waveguide 245 may represent any
device or structure operable to guide microwave waves toward and
through the nanotubes 230. For example, in some embodiments, the
microwave waveguide 245 may include a hallow metallic conductor.
Some embodiments may include a rectangular or circular waveguide.
Other embodiments may include waveguides of other shapes and sizes.
Yet other embodiments may incorporate the functionality of the
waveguide 245 into other vacuum system 200 components, such as the
vacuum pipe 220.
Nanostructure Materials
[0025] Nanotubes 230 may include any nanometer-scale tube-like
structures, such as carbon nanotubes. Conceptually, a nanotube is a
very small cylinder, typically capped at each end by a hemisphere
of atoms, such as carbon atoms. There are two categories of
nanotubes: multi-walled nanotubes (MWNT) and single-walled
nanotubes (SWNT). MWNTs may be thought of as a number of layers of
concentric pipes or tubes. MWNTs also include double-walled
nanotubes and triple-walled nanotubes, which may exhibit different
properties from SWNTs and other MWNTs.
[0026] SWNTs are nanotubes with only a single shell of atoms. The
structure of a SWNT can be conceptualized by wrapping a
one-atom-thick layer of atoms into a seamless cylinder. In this
manner, SWNTs can be thought of as little pipes or tubes with
diameters typically ranging from, but not limited to, approximately
0.6 to 5.0 nanometers. The lengths of SWNTs can range from a few
hundred nanometers to several centimeters in length.
[0027] Although SWNTs share some physical similarities with MWNTs,
they exhibit important properties not shared by MWNT variants, such
as unique spectroscopical and electrical characteristics. The
difference between SWNTs and MWNTs originates at the formation or
synthesis level. For example, MWNT synthesis does not require a
catalytic material, whereas SWNT synthesis requires a metallic
catalyst of some sort to give the nanotubes a nucleation point. In
addition, MWNTs form individually, although MWNTs may resemble a
tiny plate of spaghetti under electron microscopy. On the other
hand, SWNTs rarely form individually, but instead form as entwined
nanotubes resembling ropes. These ropes tend to have some number of
SWNTs forming strands, which may also resemble a tiny plate of
spaghetti under electron microscopy.
[0028] These differences in formation or synthesis may cause MWNTs
and SWNTs to exhibit unqiue qualities. For example, SWNTs form with
unique electrical properties, with some being very good conductors
and others being very good semiconductors. In addition, SWNTS also
exhibit higher potential for reversible gas storage.
[0029] SWNTs can also achieve a high purity level. Purity in a
nanotube refers to how much catalyst material and carbonaceous
material has been removed from the sample. In general, nanotubes
may form in very impure ways, such as forming with large amounts of
unformed carbon or including leftover pieces of catalyst material
clinging to the nanotubes. However, once purified, SWNTs may
provide a very large surface area as compared to other structures
as well as a very high affinity to adsorb hydrogen and other
gases.
[0030] Several techniques are available to purify nanotubes. For
example, some embodiments may include nanotubes 230 purified by the
following purification technique. The first step is performing acid
reflux in 3 Molar HNO.sub.3 for ten to twenty hours. The next step
is pouring the mixture through filter paper. A membrane of
approximately 0.20 .mu.m will suffice. Then, the remainder of the
material on the filter is rinsed with deionized water until the pH
of the filtrate approaches neutral. Finally, the nanotubes 230 are
then dried overnight in atmospheric conditions and then oxidized at
some raised temperature. However, there are other techniques
available, such as techniques involving electromagnetic waves. Some
embodiments of nanotubes 230 may employ purification techniques
other than the technique described above.
[0031] Both SWNTs and MWNTs exhibit the ability to adsorb gases
such as Hydrogen, Nitrogen, and water vapor. The adsorptive nature
of both SWNTs and MWNTs depend on various factors, such as degree
of crystallinity, tube diameter, tube wall structure, bundling
behavior, and Van der Waals forces.
[0032] FIG. 3 shows the results of an experiment testing the
adsorptive power of nanotubes in a vacuum system. In this
experiment, a purified 20 milligram SWNT sample with an average
diameter of approximately 1.5 nanometers was placed in a 24 liter
vacuum system. The SWNT adsorbed enough hydrogen to reduce the
hydrogen background pressure by a full order of magnitude. This in
turn caused the overall chamber pressure to be reduced. This
experiment, along with similar testing, confirms that nanotubes
make good adsorbents for various gases. More importantly, however,
this research represents the first time that nanotubes have
demonstrated the ability to improve the quality of background gases
in a high vacuum or ultra high vacuum system.
Heat Sources
[0033] Once the nanotubes 230 adsorb the trace gases, the nanotubes
may still require a technique for releasing the trace gases outside
of the vacuum chamber. Accordingly, teachings of certain
embodiments recognize the use of a heat source 240 for desorbing
the nanotubes. For example, in one embodiment, the heat source 240
may heat nanotubes 230 to 800 degrees Centigrade above the ambient
temperatures to remove adsorbed Hydrogen. Other embodiments of the
heat source 240 may include different types of heat sources that
provide various levels of heat to desorb different types of
gases.
[0034] The heat source 240 may include any device operable to heat
the nanotubes 230 and desorb the trace gases. In some embodiments,
regular resistive heating can achieve this desorption, although
this may take several minutes. Some applications may require a
faster method of achieving desorption. Thus, in some embodiments,
the heat source 240 may include a microwave field generator.
Teachings of certain embodiments recognize the use of microwave
fields to create a reusable device that will efficiently and
inexpensively remove these trace gases from the vacuum system.
These teachings recognize that desorption may be achieved in mere
milliseconds. Additionally, teachings of certain embodiments
recognize that microwave fields may provide rapid and complete
desorption as compared to some other desorption techniques.
[0035] One example of a microwave heat source 240 is described in
U.S. Patent Application Publication No. 2004/0180244 A1, entitled
PROCESS AND APPARATUS FOR MICROWAVE DESORPTION OF ELEMENTS OR
SPECIES FROM CARBON NANOTUBES, filed Sep. 16, 2004. U.S. Patent
Application Publication No. 2004/0180244 is hereby incorporated by
reference.
[0036] In general, microwave radiation includes a range of
frequencies in the electromagnetic ("EM") spectrum. Microwave
frequencies comprise one of the widest regions of the EM spectrum,
typically ranging from 300 mega-Hertz to 300 giga-Hertz (GHz). Due
to this range of wavelengths, the microwave region may be further
subdivided into decimeter, centimeter, and millimeter waves.
[0037] A variety of applications use electromagnetic waves in the
microwave region. For example, a microwave oven emits a microwave
field that excites water molecules in foods and beverages.
Scientists can also use microwave fields to accelerate many
chemical reactions to the point that they take mere minutes rather
than days or weeks.
[0038] In the microwave oven example, microwave radiation creates
heat by driving water molecules into an excited state. However,
microwaves, which exist at the lower end of the EM spectrum, do not
have sufficient quantum energy to cause atoms to go from a ground
state to an excited state. In fact, microwave fields several orders
of magnitude away from being able to accomplish this directly. But
microwave radiation can drive many different atomic species into an
excited state by coupling to transitions in the hyperfine structure
of a dynamical state. Of course, this is merely one method of
microwave interaction, and exact interactions of microwave fields
and matter will vary.
[0039] Many different methods are available for producing low
powered and lower frequency magnetic fields, only a few of which
are described in this disclosure. For example, one such method is
generating low frequency EM signals via the transfer of electrical
energy from a steady electric field into an alternating field. In
this example, a signal with the desired frequency is present due to
thermal noise. The desired frequency is then selectively amplified
to the desired power level by feedback with the phase relation that
is appropriate to the application. This technique works reasonably
well for frequencies up to approximately 1 GHz.
[0040] A different technique may be necessary for frequencies of 1
GHz to 10 GHz because the finite transit times of electrons will
have a degrading effect on such things as the oscillator circuit.
FIG. 4A shows one alternative technique for generating microwave
fields in this frequency range according to some embodiments. FIG.
4A features a dual-cavity klystron 400 with planar triodes.
Electron transit time has no effect on these devices due to their
geometry. These devices consist of small distances between the
triodes and a high accelerating voltage. These triodes are used in
conjunction with a tunable dual-resonant cavity. These devices can
typically be tuned to the 1 to 10 GHz portion of the microwave
spectrum, and the maximum power output from such a device is in the
range of 10 Watts.
[0041] The dual-cavity klystron 400 may include a pair of resonant
cavities in tandem through which an electron beam may be passed. A
radio frequency ("RF") field in the first of the two cavities will
bunch the electrons into groups. These groups then pass into the
second cavity and induce an RF field. In other words, the first of
the two cavities slightly accelerates some electrons, while others
slow down. The acceleration and deceleration is determined by which
portion of the RF cycle the electrons are in. After several
millimeters of transit, the faster electrons will catch the slower
ones and the maximum allowable "bunching" will occur. The second of
the two resonant cavities is situated at this exact position.
Further along the beam line, the accelerated electrons have passed
the slower ones, and the electrons are again debunched.
[0042] If in some portion of the RF cycle, energy from the second
resonant cavity is fed back to the first resonator in the correct
phase, dual-cavity klystron 400 will become an oscillator. The
frequency of oscillation is determined by the resonant frequencies
of the cavities, which may be adjusted by changing their physical
size. The accelerator voltage may cause a small change in the
oscillation frequency.
[0043] The dual-cavity klystron 400 has an upper limit of frequency
it can reach. FIG. 4B shows a technique for generating microwave
fields with higher frequencies according to some embodiments. FIG.
4B features a reflex klystron 401 with only a single cavity, unlike
the dual-cavity klystron 400, which features two cavities. A reflex
klystron is capable of emitting higher frequencies than a
dual-cavity klystron. A reflex klystron is typically not capable of
emitting signals with power levels higher than 1 Watt, which makes
it very useful for applications requiring continuous, low-power,
very clean signals. However, due to the removal of the second
cavity found in the dual-cavity klystron 400, the reflex klystron
401 includes a reflector electrode with a negative charge to
reflect the electron beam. After the beam is reflected, it
re-enters the cavity and delivers more energy than originally
received by the cavity, provided the cavity distance is properly
tuned and the "repeller" voltage is properly set.
[0044] Some embodiments may also include a backward wave oscillator
("BWO") as a microwave signal source. In a BWO, the electron beam
is compressed with the application of a static magnetic field along
the longitudinal axis. These sources are very useful as sweep
signal generators due to their ability to be tuned over a fairly
wide range of frequencies. This sweeping is not done by mechanical
means, but rather by varying the electron beam voltage.
[0045] For some applications, a much higher power level may be
required from a microwave source. These applications typically
employ a magnetron. In a magnetron source, a static magnetic field
is applied perpendicularly to the electron beam, forcing the
electrons into a nearly circular path. This path extends the amount
of interaction time and allows a much higher power level to be
achieved.
[0046] The majority of moderate to high power commercial microwave
applications will use a magnetron source. Occasionally, a
scientific application will require a cleaner signal than a
magnetron can produce while also requiring higher powers than can
be achieved with typical clean sources. In these instances, the two
typical options are either massive klystron sources or high-power
amplifiers. However, both of these methods are often
cost-prohibitive.
[0047] The interaction of the nanotubes with microwaves is complex,
with possibly several mechanisms at work. However, although
embodiments are not bound by any particular mechanism, one known
interaction may be derived from previous long chain molecule
research. The valence electrons in long chain, or any nonlinear
molecules, do not move in a cylindrically symmetric field. For this
reason, no component of their orbital angular momentum can be found
to be constant. The electron orbital momentum W must be considered
as a portion of the rotational momentum of the entire molecule (if
one assumes that the interaction is for only one molecule at a
time).
[0048] The interaction of the electron spin L and orbit S of the
type ALS.sup.1 is only possible when there is a slight uncoupling
of L from the rotation of the molecule, where A is the largest
rotational constant of an asymmetric rotor, L is the electronic
angular momentum of an entire atom or molecule, and S is the
electron spin angular momentum. This must occur as a second or
higher order perturbation. Thus:
W = X + Y , where ##EQU00001## X = A [ aE + .beta. ( a NK ) 2 K 2 +
.gamma. ] N ( N + 1 ) C and ##EQU00001.2## Y = A 2 2 [ a ' E +
.beta. ' ( a NK ) 2 K 2 N ( N + 1 ) + .gamma. ' ] 3 / 4 C ( C + 1 )
- S ( S + 1 ) N ( N + 1 ) ( 2 N - 1 ) ( 2 N + 3 ) ;
##EQU00001.3##
and where .alpha., .beta., .gamma., .alpha.', .beta.', and
.gamma.', are constants dependent on the structure of the molecule;
E is the energy of molecular rotation without electron spin
effects; .alpha..sub.NK is the wave function in terms of symmetric
top waves; J is the total angular momentum, excluding nuclear spin;
N is the total orbital angular momentum, including rotation of the
molecule; and C=J(J+1)-S(S+1)-N(N+1).
[0049] The first term, X, is a type of dipole interaction. The
second term, Y, is a quasi-quadruple interaction with the same
dependence on angular momentum. The second term must be zero when S
is less than 1 (i.e., for singlet and doublet states). These
interactions may allow an extensive analysis of the fine structure
spectra of SWNTs to be conducted in a way similar to that performed
on other nonlinear molecules. Another mechanism can be found in
that both MWNT and SWNT are conductors themselves, and therefore,
do not require the presence of any traditional metallic material to
have a metallic type of interaction.
Recyclable Nature of Various Embodiments
[0050] Experiments regarding several embodiments establish that
nanotubes can be used to improve the quality of the background
gases in a high vacuum or ultra high vacuum system. These
experiments also suggest that nanotubes can be recycled for this
same purpose.
[0051] FIG. 5 shows the results of an experiment testing the
recyclability of nanotubes in a vacuum system. Following the
experiment from FIG. 3, the same 24 liter vacuum system was brought
back to atmospheric pressure, and then a new vacuum was generated
inside the vacuum system. Next, the same purified 20 mg SWNT sample
with an average diameter of approximately 1.5 nanometers from the
FIG. 3 experiment were desorbed of adsorbed material and then
placed back in the vacuum system. Referring to FIG. 5, it appears
that the recycled nanotubes exhibited some initial outgassing of
Hydrogen in the first hour to two hours, followed by a drastic
reduction in pressure from all gas species.
[0052] Further experiments established that, if the microwave
source is calibrated to keep the nanotubes below 2100 degrees
centigrade during desorption, the nanotubes will remain undamaged.
This type of reaction can be used for a long period of time with
little or no oxidation or other damage to the nanotube structures,
thereby allowing for a very long lasting pump.
[0053] The present disclosure refers to the adsorption of gases in
a nanostructure material. Embodiments of the present disclosure are
not limited to adsorption processes, but instead may include
absorption or other processes. The present disclosure also refers
to the desorption of gases out of a nanostructure material;
however, embodiments may include other phenomenas resulting in the
release of gases out of a nanostructure material.
[0054] Although the present disclosure has been described with
several embodiments, a myriad of changes, variations, alterations,
transformations, and modifications may be suggested to one skilled
in the art, and it is intended that the present disclosure
encompass such changes, variations, alterations, transformation,
and modifications as they fall within the scope of the appended
claims.
[0055] To aid the Patent Office, and any readers of any patent
issued on this application in interpreting the claims appended
hereto, applicants wish to note that they do not intend any of the
appended claims to invoke 6 of 35 U.S.C. .sctn.112 as it exists on
the date of filing hereof unless the words "means for" or "step
for" are explicitly used in the particular claim.
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