U.S. patent application number 16/048245 was filed with the patent office on 2018-11-22 for alumina body having nano-sized open-cell pores that are stable at high temperatures.
This patent application is currently assigned to Surperior Technical Ceramics Corporation. The applicant listed for this patent is Superior Technical Ceramics Corporation. Invention is credited to Tariq Quadir.
Application Number | 20180334411 16/048245 |
Document ID | / |
Family ID | 63491289 |
Filed Date | 2018-11-22 |
United States Patent
Application |
20180334411 |
Kind Code |
A1 |
Quadir; Tariq |
November 22, 2018 |
ALUMINA BODY HAVING NANO-SIZED OPEN-CELL PORES THAT ARE STABLE AT
HIGH TEMPERATURES
Abstract
An alumina body having nano-sized open-cell pores, the alumina
body is formed from .alpha.-Al.sub.2O.sub.3 and Al(OH).sub.3. The
alumina body has porosity of greater than 36-percent by volume and
a mean pore flow diameter less than 25-nm. The alumina body retains
porosity of over 20-volume percent for temperatures up to
1510.degree. C. for 1-hour. The nano-sized open-cell porous body
can be scaled to any 3-dimensional structure.
Inventors: |
Quadir; Tariq; (Colchester,
VT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Superior Technical Ceramics Corporation |
St. Albans |
VT |
US |
|
|
Assignee: |
Surperior Technical Ceramics
Corporation
St. Albans
VT
|
Family ID: |
63491289 |
Appl. No.: |
16/048245 |
Filed: |
July 28, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15409619 |
Jan 19, 2017 |
10077213 |
|
|
16048245 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 2325/22 20130101;
C04B 2235/5445 20130101; C04B 38/0058 20130101; C04B 2235/6567
20130101; B01D 71/025 20130101; C01P 2004/51 20130101; C04B 35/111
20130101; C01P 2002/88 20130101; C04B 35/62695 20130101; B01D
61/145 20130101; C04B 2235/3218 20130101; C01P 2004/62 20130101;
C04B 35/6261 20130101; C04B 38/067 20130101; C01P 2004/61 20130101;
C01P 2006/16 20130101; C04B 35/18 20130101; C04B 2235/5436
20130101; B01D 61/027 20130101; C01F 7/025 20130101; C04B 38/0041
20130101; C04B 2235/3217 20130101; C04B 35/6264 20130101; B01D
2325/02 20130101; C04B 38/0054 20130101; B01D 67/0041 20130101;
C04B 2111/00793 20130101; B01D 69/02 20130101; C04B 38/067
20130101; C04B 35/10 20130101; C04B 38/0054 20130101; C04B 38/0058
20130101; C04B 38/0074 20130101 |
International
Class: |
C04B 38/00 20060101
C04B038/00; C01F 7/02 20060101 C01F007/02; B01D 71/02 20060101
B01D071/02; B01D 67/00 20060101 B01D067/00 |
Claims
1. A ceramic body, comprising: .alpha.-Al.sub.2O.sub.3 having a
porosity of greater than 36 percent by volume and a mean open pore
flow diameter less than 25 nanometers.
2. A ceramic body as recited in claim 1, wherein said porosity
stays above 20 percent by volume at an annealing temperature of
1510.degree. C. for 1 hour.
Description
RELATED APPLICATIONS
[0001] This application is a division of U.S. patent application
Ser. No. 15/409,619, filed on Jan. 19, 2017, which claims the
benefit of priority of U.S. Provisional Patent Application No.
62/289,149, filed Jan. 29, 2016, which is herein incorporated by
reference.
FIELD
[0002] The present invention generally relates to an alumina body
having nano-sized open-cell pores. More specifically, the alumina
body has open pores with mean pore flow diameters less than 25-nm
and that retain porosities of at least 20-percent by volume for
temperatures of up to 1510.degree. C.
BACKGROUND
[0003] Open-cell porous bodies can be used as filters in a variety
of applications. Very fine porosity is desired for chemical
processing, pharmaceutical processing, refining waste water,
purifying foods and energy production to name a few. The filters
employed in these processes are used to purify, concentrate,
sterilize and separate materials. The listed applications require
filters with pores sizes in the ultrafiltration (100 nm to 10 nm)
and nanofiltration (10 nm to 1 nm) ranges. Some applications
require the filters survive thermal excursions in excess of
1500.degree. C., such as in high temperature gas mixing. Typically
filters having pores in the low end of ultrafiltration and into the
nanofiltration range have required the use of thin membrane (e.g.
polymers) of nano-sized pores supported on a substrate (e.g. metal,
polymer, ceramic) having larger pores. In general filters in the
nanofiltration range are complex to manufacture, do not sustain
significant amounts of open porosity during high thermal excursions
and are difficult to reproduce in 3-dimensional structures.
[0004] U.S. Pat. No. 6,565,825 to Ohji, which is herein
incorporated by reference, has shown that alumina powders can be
sintered to form porous alumina structures. However, sintering
temperatures in excess of 1250.degree. C. reduce porosities to
36-volume percent or below. Ohji further shows that combining
alumina hydroxide Al(OH).sub.3 with the alumina powder, and then
subsequently sintering, can transform the Al(OH).sub.3 through
.gamma..fwdarw..theta..fwdarw..alpha. phases to provide materials
that maintain porosities of 36-volume percent up to 1250.degree.
C.
[0005] The present invention aims to eliminate the need for a
membrane supported by a substrate and provide nano-sized open-cell
porosity that can be scaled to any 3-dimensional structure. The
present invention also aims to improve the thermal stability of
highly porous materials to beyond 1500.degree. C.
SUMMARY
[0006] The present disclosure is directed to a ceramic body, the
ceramic body comprising .alpha.-Al.sub.2O.sub.3 having a porosity
greater than 36-percent by volume, a mean pore flow diameter less
than 25-nanometers, and a porosity that stays above 20-percent by
volume at an annealing temperature of 1510.degree. C. for
1-hour.
[0007] Another aspect of the present patent application is directed
to a method of fabricating a ceramic body, comprising the steps of
providing crystalline .alpha.-Al.sub.2O.sub.3 particles having D50
of 0.4-0.6 microns and Gibbsite phase Al(OH).sub.3 particles of D50
of 5-6 microns. The method then involves combining, milling and
granulating the particles. The method further involves forming a
green compact and sintering the green compact in a temperature
range of 1316.degree. C. to 1510.degree. C.
BRIEF DESCRIPTION OF DRAWINGS
[0008] For the purposes of illustrating the invention, the drawings
show aspects of one or more embodiments of the invention. However,
it should be understood that the present invention is not limited
to the precise arrangements and instrumentalities shown in the
drawings, wherein:
[0009] FIG. 1 is a schematic, sectional view of one exemplary
embodiment of the ceramic body according to the present
invention;
[0010] FIG. 2 is a schematic diagram illustrating open pore sizes
achievable by the current invention with exemplary filtration
ranges and attributes;
[0011] FIG. 3 is DSC-TGA plot for the alumina trihydrate used in
the present invention;
[0012] FIG. 4 is a plot of volume percent porosity versus sintering
temperature for the ceramic bodies of the present invention;
[0013] FIG. 5 is a plot of mean pore diameter versus sintering
temperature for the ceramic bodies of the present invention;
[0014] FIG. 6 is a plot of porosity versus time for a ceramic body
of the present invention at 1510.degree. C.; and
[0015] FIG. 7 is a schematic diagram for thermodynamic phases and
stable transitions of alumina.
DETAILED DESCRIPTION
[0016] FIG. 1 shows ceramic body 20. Ceramic body 20 is a
3-dimensional ceramic body or a thin layer polished from such a
body. Ceramic body 20 comprises .alpha.-Al.sub.2O.sub.3 having
nano-sized pores 22. It is critical to have a volume porosity
greater than 36-percent so that the alumina body has a significant
number of open pores that allow fluids to flow there through. The
mean pore flow diameter within porous body 20 should be less than
25-nanometers. It is critical to have this mean flow pore diameters
less than 25-nanometers in order to perform the processes as listed
in FIG. 2.
[0017] Raw materials used in the preparation of the examples
(samples A-E) described below are crystalline alpha-alumina
(.alpha.-Al.sub.2O.sub.3) and alumina trihydrate (Al(OH).sub.3) in
the ratio of 40-percent hydrated alumina to 60-percent
alpha-alumina by weight. The hydrated alumina had a synthetic
Gibbsite phase structure as verified by the DSC-TGA curves in FIG.
3. It was found that the 40-percent hydrated alumina to 60-percent
alpha-alumina ratio was ideal for achieving good porosity though
other compositions where .alpha.-Al.sub.2O.sub.3 particles in the
range of 50-90 percent could be used. The .alpha.-Al.sub.2O.sub.3
crystalline particles used in the preparation of the examples
described below are Pechiney powders, specifically Pechiney P172
SB03 having a D50 particle size of 0.4-0.6 microns. Hydrated
alumina particles used in the preparation of the examples below
were J.M. Huber Corporation powders, specifically HYDRAL.RTM. 710
with D50 particle size of 5.0-6.0 microns. One or more organic
binders in combination with water, a dispersant, and a lubricating
agent were mixed with all particles to form a slurry. The organic
binders act as a binding agent that holds the mixture of particles
together. During sintering the organic binders burn off leaving the
shape of the body intact. Some examples of organic binders that may
be used to form green compact include polyvinyl alcohol (PVA) and
polyethylene glycol (PEG). Other binders may include, but are not
limited to, acrylic binders, gums and waxes.
[0018] Table 1 lists the formulation used to produce the porous
alumina samples analyzed.
TABLE-US-00001 TABLE 1 Exemplary Formulation for Al.sub.2O.sub.3
(weight percent) Material Weight (kg) Manufacturer Alpha Phase
Alumina Al.sub.2O.sub.3 90.0 Pechiney Hydrated Alumina Al(OH).sub.3
60.0 J. M. Huber Corp. Dispersant 1.5 Organic Binder I 8.8 Organic
Binder II 4.2 Lubricating Agent 2.5 Water 55.5
[0019] General preparation of the new porous alumina formulation is
as follows. Water is placed in a tank and mixed under a high shear
mixer. The pH level is adjusted to between 8.8 and 9.5. The
dispersant is then added to the mixture. After the solution is
adequately mixed the solution is poured into a ball mill and a
measured amount of hydrated alumina HYDRAL.RTM. 710 is added. After
the hydrated alumina is adequately mixed the alpha alumina is added
and the slurry is subsequently milled for 2-hours. Organic binder
I, organic binder II, and the lubricating agent are then added and
milled for an additional 1-hour. The resulting slurry is spray
dried into granulated powder and then pressed into a green compact
of a given shape. The green compact is then heated to temps of
300.degree. C. to 600.degree. C. as part of a binder burnout cycle.
The compact is then further heated to a sintering temperature of
1316.degree. C. to 1510.degree. C. with a 1-hour soak time. The
sintering temperature helps determine the porous properties of the
material, with higher temperatures trending toward less porosity
and larger maximum pore sizes. The firing ranges of the porous
alumina samples are listed in TABLE 2. TABLE 2 additionally lists
process parameters along with mechanical and porous properties.
TABLE-US-00002 TABLE 2 Formulations and Properties of
Al.sub.2O.sub.3 Porous Substrates Sample Sample Sample Sample
Sample A B C D E Sintered Temp 1316 1343 1399 1454 1510 (.degree.
C.) Time (hours) 1 1 1 1 1 Percent Porosity 46.4 42.9 37.1 28.3
22.3 Mean Flow 0.0208 0.0219 0.0200 Pore Diameter (microns) Bubble
Point 0.0752 0.0837 0.0606 Pore Diameter (microns) Std. Dev. of
0.0177 0.0143 0.0137 Avg. Pore Diameter (microns) Diameter at
0.0137 0.0137 0.0169 Max Pore Size Dist. (microns) Bulk Density
2.126 2.24 2.496 2.849 3.091 (g/cc)
[0020] TABLE 2 compares various properties of the differently
sintered samples. All samples A-E were made from the formulation in
TABLE 1, but kiln temperatures were altered to vary the mechanical
and porous properties. Firing temperatures ranged from 1316.degree.
C. to 1510.degree. C. Percent porosity by volume ranged from
46.4-percent (1316.degree. C.) to 22.3-percent (1510.degree. C.).
Samples sintered at temperatures roughly 1400.degree. C. or lower
had porosities greater than 36-percent by volume. Mean flow pore
diameter remained steady in a range of 0.0200-0.0219 microns, FIG.
5, while the bubble point, or largest pore size, ranged from
0.0606-0.0752 microns. The diameter at max pore size distribution,
which indicates the mode of the pore sizes, ranged from
0.0137-0.0169 microns, and the standard deviation of the pore sizes
ranged from 0.0137-microns to 0.0177-microns. All pore size
distribution and permeability data was taken using capillary flow
porometry. Specifically, the machine used was a model CFP-1500AEM
Capillary Flow Porometer produced by Porous Materials, Inc. It
should be noted that the pore size distribution and permeability
data in TABLE 2 is specific to this machine and to the testing
parameters applied during the tests. It should be noted that due to
limitations of this machine, open-cell pore sizes are measurable
down to only 13-nm. This does not preclude the existence of pores
less than 13-nm, but these pores are not measurable with the
equipment being used.
[0021] A plot of percent porosity versus sintering temperature,
FIG. 4, shows that the percent porosity decreases with increasing
temperature, but stays above 36-percent by volume for temperatures
of 1316.degree. C. to 1400.degree. C. The percent porosity also
stays above 20-percent by volume for temperatures under
1510.degree. C. FIG. 6 shows that at 1510.degree. C. increased
annealing time beyond 1-hour decreases percent porosity to about
16-percent by volume after 3-hours.
[0022] The present data shows that ceramic body 20 composed of
porous .alpha.-Al.sub.2O.sub.3 has porosities of 36-volume percent
or greater after annealing for 1-hour at temperatures up to
1400.degree. C. This is 150.degree. C. greater than prior art
materials utilizing Al(OH).sub.3. This unexpected result is
believed to be a result of a combination of larger initial particle
sizes and the synthetic Gibbsite structure of the Al(OH).sub.3
particles. Different thermodynamic phase transitions, FIG. 7, are
believed to be contributing to the higher percent porosity and
higher thermal stability of the pores. Ceramic body 20 can
therefore have a final porosity greater than 20-percent by volume
when annealed at a temperature over 1350.degree. C. for 1-hour. The
new structure provides a new, higher temperature resistant porous
alumina body that can be used for nanofiltration and that can be
shaped into any 3-dimensional structure.
[0023] While several embodiments of the invention, together with
modifications thereof, have been described in detail herein and
illustrated by the accompanying examples, it will be evident that
various compositions and further modifications are possible without
departing from the scope of the invention. The scope of the claims
should not be limited by the preferred embodiments set forth in the
examples, but should be given the broadest interpretation
consistent with the description as a whole.
* * * * *