U.S. patent application number 10/184804 was filed with the patent office on 2003-03-20 for production method for ceramic porous material.
This patent application is currently assigned to Toshiba Ceramics Co., Ltd.. Invention is credited to Kawai, Kazuhide, Matsuyama, Takashi, Shimai, Shunzo, Uemoto, Hideo.
Application Number | 20030052428 10/184804 |
Document ID | / |
Family ID | 19038329 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030052428 |
Kind Code |
A1 |
Uemoto, Hideo ; et
al. |
March 20, 2003 |
Production method for ceramic porous material
Abstract
To provide a method for producing a ceramic porous material
which has a high strength, though it has a high porosity, and which
is excellent in permeability without dust generation. In a ceramic
porous material having a three-dimensional mesh-like skeleton
structure with a large number of substantially spherical adjacent
cells communicating with each other via communication holes, the
crystal particle size at the rim of each communication hole in the
skeleton structure is provided substantially equal to the crystal
particle size in the other parts.
Inventors: |
Uemoto, Hideo; (Hadano-shi,
JP) ; Kawai, Kazuhide; (Nishio-shi, JP) ;
Shimai, Shunzo; (Tougane-shi, JP) ; Matsuyama,
Takashi; (Sagamihara-shi, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
Toshiba Ceramics Co., Ltd.
Tokyo
JP
|
Family ID: |
19038329 |
Appl. No.: |
10/184804 |
Filed: |
July 1, 2002 |
Current U.S.
Class: |
264/43 ;
264/44 |
Current CPC
Class: |
C04B 38/10 20130101;
C04B 38/10 20130101; C04B 38/0045 20130101; C04B 35/00 20130101;
C04B 38/0058 20130101 |
Class at
Publication: |
264/43 ;
264/44 |
International
Class: |
B29C 065/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 2, 2001 |
JP |
2001-201350 |
Claims
What is claimed is:
1. A production method for a ceramic porous material comprising the
steps of preparing a bubble-like slurry by mixing and whipping a
ceramic powder, a liquid medium, a dispersing agent if necessary, a
foaming agent and a gellation main agent, adding and mixing a
gellation sub agent to the bubble-like slurry, pouring into a mold
for obtaining a gellation product, drying the gellation product for
having a compact having a three dimensional mesh-like skeleton
structure with a large number of substantially spherical adjacent
cells communicating with each other via communication holes, and
sintering or fireing the compact directly, or temporarily baking
(calcinating) the same before sintering or fireing for obtaining a
sintered or fired product and then baking the same for obtaining a
baked product, wherein the rim of each communication hole in the
compact, the temporarily baked product or the sintered or fired
product is eliminated mechanically.
2. A production method for a ceramic porous material comprising the
steps of preparing a bubble-like slurry by mixing and whipping a
ceramic powder, a liquid medium, a dispersing agent (if necessary),
a forming agent and a gellation main agent, adding and mixing a
gellation sub agent to the bubble-like slurry, pouring into a mold
for obtaining a gellation product, drying the gellation product for
having a compact having a three dimensional mesh-like skeleton
structure with a large number of substantially spherical adjacent
cells communicating with each other via communication holes, and
sintering or fireing the compact directly, or temporarily baking
(calcinating) the same before sintering or fireing for obtaining a
sintered or fired product, wherein the rim of each communication
hole in the compact, the temporarily baked product or the sintered
or fired product is eliminated chemically.
3. A production method for a ceramic porous material comprising the
steps of preparing a bubble-like slurry by mixing and whipping a
ceramic powder, a liquid medium, a dispersing agent if necessary, a
forming agent and a gellation main agent, adding and mixing a
gellation subagent to the bubble-like slurry, pouring into a mold
for obtaining a gellation product, drying the gellation product for
having a compact having a three dimensional mesh-like skeleton
structure with a large number of substantially spherical adjacent
cells communicating with each other via communication holes, and
sintering or fireing the compact directly, or temporarily baking
(clcinating) the same before sintering or fireing for obtaining a
sintered or fired product, wherein the evaporation-condensation
mechanism with respect to the crystal particles at the rim of each
communication hole is promoted during the sintering or fireing
operation of the compact or the temporarily baked product, or the
re-sintering or re-fireing operation of the sintered or fired
product.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a ceramic porous material
having a bubble-like appearance to be used as a filter, a bubbler,
a gas supplying member, a semiconductor producing device member, an
artificial bone, a cell culturing supporter, an artificial organ, a
catalyst supporter, or the like, and a production method
therefor.
[0003] 2. Description of the Related Art
[0004] Conventionally, as a ceramic porous material of this kind,
one having a three-dimensional mesh-like skeleton structure with a
large number of substantially spherical adjacent cells (pores)
communicating with each other via communication holes has been
known (see the official gazette of the Japanese Patent Laid Open
Application (JP-A) No. 4-202071 (Patent No. 2,506,502).
[0005] The ceramic porous material is produced by preparing a
slurry by dispersing or dissolving in a solvent a ceramic powder
and an organic substance to be hardened by the cross-linking
polymerization, adding a cross-linking agent to the slurry, molding
and hardening (gellation molding) in an agitated and bubbled state,
drying the compact and baking (fireing, sintering).
[0006] However, according to the conventional ceramic porous
material, problems are involved in that the mechanical strength is
low, dusts (particles) are generated, and the transmissivity is
poor.
[0007] In order to find the cause of the problems, the periphery of
the communication holes in the skeleton structure was observed with
a scanning type electron microscope so that an abnormal form of
crystal particles forming the rim of the communication holes was
observed.
[0008] That is, at the rim of the communication holes, single
particles of a cockscomb shape and a cactus shape were observed.
Moreover, the fact that minute holes of the size equivalent to the
crystal particle size, communicating the adjacent pores were found
at the rim part of the communication holes and the growth of the
crystal particles are restrained at the rim of the communication
holes was found.
[0009] It can easily be assumed that the above-mentioned crystal
particle growth abnormal part became the breakage starting point
when the external force was applied to the ceramic porous material
so as to cause stress concentration, and furthermore, the cockscomb
shaped and cactus shaped parts were peeled off so as to generate
dusts.
[0010] Accordingly, it is considered that the abnormal form of the
crystal particle growth forming the rim of the communication holes
is generated in the production process of the ceramic porous
material.
[0011] That is, the cells of the slurry stage are formed by the
liquid medium containing the ceramic powder, and in most cases by
the aqueous slurry. The slurry before hardening is moved by the
surface tension and parts between the adjacent cells are partially
thinned and broken so as to form the communication holes. The
communication hole rims linking the cells accordingly formed are of
a sharp shape because they are broken after thinning and the
viscosity of the slurry at the time of breaking is high and the
flowability after film breakage to rounding the rims is low. Or in
the case of forming the communication holes by breaking the thin
film at the time of expansion and shrinkage of the air in the cells
due to the temperature change after drying, or the like, the small
pieces of the dried substances generated by the breakage can be
adhered on the wall surface of the cells.
[0012] The average particle sizes of the crystal particles at the
rim of the communication holes of the alumina ceramic porous
material of the 80% porosity (baked at 1,600.degree. C. for 2 hours
in the air), at a position 2 .mu.m away from the rim, and at a
position 4 .mu.m away from the rim were 0.80 .mu.m, 1.67 .mu.m, and
1.81 .mu.m, respectively, and it was 8.52 .mu.m at a position 100
.mu.m away from the rim. The average particle sizes of the crystal
particles at the rim of the communication holes of the hydroxyl
apatite porous material of the 75% porosity (baked at 1,200.degree.
C. for 2 hours in the air), at a position 0.5 .mu.m away from the
rim, at a position 1 .mu.m away from the rim, and at a position 1.5
.mu.m away from the rimwere 0.42 .mu.m, 0.5 .mu.m, and 0.55 .mu.m,
and 0.62 .mu.m, respectively. Moreover, the average particle sizes
of the crystal particles at the rim of the communication holes of
the silicon carbide porous material of the 75% porosity (baked at
2300.degree. C. for 2 hours in the reduced pressure argon gas
atmosphere), at a position 2 .mu.m away from the rim, and at a
position 4 .mu.m away from the rim were 0.49 .mu.m, 4.38 .mu.m, and
4.38 .mu.m, respectively.
SUMMARY OF THE INVENTION
[0013] Accordingly, an object of the present invention is to
provide a production method for a ceramic porous material having a
high strength for its high porosity and the excellent
transmissivity without the risk of generation of dusts.
[0014] A first aspect of the production method for a ceramic porous
material is a production method for a ceramic porous material
comprising the steps of preparing a bubble-like slurry by mixing
and whipping a ceramic powder, a liquid medium, a dispersing agent,
forming agent if necessary and a gellation main agent, adding and
mixing a gellation sub agent to the bubble-like slurry, pouring
into a mold for obtaining a gellation product, drying the gellation
product for having a compact having a three dimensional mesh-like
skeleton structure with a large number of substantially spherical
adjacent cells communicating with each other via communication
holes, and sintering or fireing the compact directly, or
temporarily baking (calcinating) the same before sintering or
fireing for obtaining a sintered or fired product, wherein the rim
of each communication hole in the compact, the temporarily baked
product or the sintered or fired product is eliminated
mechanically.
[0015] A second aspect of a production method for a ceramic porous
material is a production method for a ceramic porous material
comprising the steps of preparing a bubble-like slurry by mixing
and whipping a ceramic powder, a liquid medium, a dispersing agent
if necessary, a forming agent and a gellation main agent, adding
and mixing a gellation subagent to the bubble-like slurry, pouring
into a mold for obtaining a gellation product, drying the gellation
product for having a compact having a three dimensional mesh-like
skeleton structure with a large number of substantially spherical
adjacent cells communicating with each other via communication
holes, and sintering or fireing the compact directly, or
temporarily baking (calcinating) the same before sintering or
fireing for obtaining a sintered or fired product, wherein the rim
of each communication hole in the compact, the temporarily baked
product or the sintered or fired product is eliminated
chemically.
[0016] Moreover, a third aspect of a production method for a
ceramic porous material is a production method for a ceramic porous
material comprising the steps of preparing a bubble-like slurry by
mixing and whipping a ceramic powder, a liquid medium, a dispersing
agent if necessary, a forming agent and a gellation main agent,
adding and mixing a gellation sub agent to the bubble-like slurry,
pouring into a mold for obtaining a gellation product, drying the
gellation product for having a compact having a three dimensional
mesh-like skeleton structure with a large number of substantially
spherical adjacent cells communicating with each other via
communication holes, and sinterd or fired the compact directly, or
temporarily baking calcinating the same before sintering or fireing
for obtaining a sintered or fired product, wherein the
evaporation-condensation mechanism with respect to the crystal
particles at the rim of each communication hole is promoted during
the sintering or fireing operation of the compact or the
temporarily baked product, or the re-sintering or re-fireing
operation of the sintered or fired product. In addition, in the
above-mentioned three methods, the dispersing agent is used when a
large-sized product is manufactured, and otherwise it is
omissible.
[0017] According to the above-mentioned ceramic porous material,
the crystal particle size in the entire skeleton structure can be
even.
[0018] It is preferable that the skeleton structure itself includes
only the closed cells or it has substantially no cells.
[0019] As the ceramic for forming the skeleton structure, alumina,
alumina-silica, calcium phosphate based substance, silicon carbide,
zirconia, or the like can be used.
[0020] In contrast, according to the first aspect of the production
method for a ceramic porous material, the abnormal part at the rim
of each communication hole can be eliminated so that the hole size
of the communication holes is made larger.
[0021] The mechanical elimination of the rim of each communication
hole can be executed by permeating a liquid such as water or a gel
such as an agar with a hard fine particle such as a diamond powder
and a silicon carbide powder dispersed through the compact, the
temporarily baked product, or the sintered or fired product.
[0022] Although the elimination of the rim of each communication
hole can be executed also to the sintered or fired product, it is
more efficient to execute the same to the temporarily baked product
with a low strength, and in the case of executing the same to the
compact, a liquid medium not to dissolve the compact is used.
[0023] The permeating operation of the liquid or the gel with the
hard fine particle dispersed through the compact, the temporarily
baked product or the sintered or fired product can be executed
either from one direction or from multiple directions.
[0024] It is necessary that the hard fine particle, or the like
does not remain in the temporarily baked product or the sintered or
fired product after elimination of the rim of each communication
hole. Therefore, it is preferable that the hard fine particle has a
particle size larger than the cell diameter in the skeleton
structure (gap between the primary particles) because the hard fine
particle is in a state stuck between the primary particles in the
skeleton structure in the case they have the substantially same
size.
[0025] According to the second aspect of the production method for
a ceramic porous material, similar to the case of the first aspect,
the abnormal part at the rim of each communication hole can be
eliminated so that the hole size of the communication holes is made
larger.
[0026] The chemical elimination of the rim of each communication
hole can be executed by soaking the temporarily baked product or
the sintered or fired product in phosphoric acid or sulfuric acid,
or the like, or dissolution at a high temperature by a sodium
borate fused salt.
[0027] This is because the abnormal part unstable in terms of shape
has a larger dissolution speed than that of the other parts.
[0028] It is also possible to promote the dissolution speed by
heating and pressuring the phosphoric acid(pressuring the
phosphoric acid is dangerous) or the sulfuric acid at the time of
the soaking operation.
[0029] Moreover, according to the third aspect of the production
method for a ceramic porous material, the crystal particle size at
the rim of each communication hole can be equivalent to the crystal
particle size of the other parts.
[0030] The evaporation is carried out selectively quickly at a part
with a high potential, that is, in the abnormal part, and the
condensation is carried out selectively at a part with a low
potential, that is, in the recessed part.
[0031] The sintering, fireing, re-sintering, or re-fireing or
re-baking operation is carried out at a high temperature of
1,800.degree. C. or higher in a hydrogen gas atmosphere or in a
vacuum atmosphere, or in an atmosphere containing a halogen of a
chlorine. According to the atmospheres, the
evaporation-condensation mechanism promotion temperature is lowered
by production of a volatile compound.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is an electron microscope photograph showing the
crystal structure of an alumina ceramic porous material baked at
1,200.degree. C. for 2 hours in the air without the mechanical
process or the like; and
[0033] FIG. 2 is an electron microscope photograph showing the
crystal structure of the alumina ceramic porous material of FIG. 1
after re-fireing at 1,840.degree. C. for 10 hours in a hydrogen
atmosphere.
DETAILED DESCRIPTION OF THE INVENTION
[0034] Hereinafter, embodiments of the present invention will be
explained with reference to specific examples and comparative
examples.
EXAMPLES 1 to 5, Comparative Example 1
[0035] First, a bubble-like slurry was prepared by mixing and
agitating 100 parts by weight of a low soda alumina having a 1
.mu.m average particle size as the ceramic powder, 20 parts by
weight of ion exchange water as the liquid medium, 1 part by weight
of an ammonium polyacrylate as the dispersing agent, 0.5 part by
weight of a triethanol amine lauryl sulfate as the foaming agent,
and 4 parts by weight of an epoxy resin as the gellation main agent
by an agitator while introducing the air.
[0036] Next, while agitating the bubble-like slurry, 1 part by
weight of an iminobispropyl amine as the gellation sub agent was
added thereto. After pouring the same in a mold and passage of 30
minutes, the gellation proceeded sufficiently so as to obtain a
gellation product.
[0037] Then, the gellation product was taken out from the mold and
dried at 60.degree. C. for whole day and night so as to obtain a
compact (dried product).
[0038] The obtained compact has a three-dimensional mesh-like
skeleton structure with a large number of substantially spherical
adjacent cells communicating with each other via communication
holes.
[0039] Next, the compact was heated (temporarily baked) at
1,200.degree. C. for 2 hours in the air so as to obtain a
temporarily baked product. It was processed with a diamond grinding
stone so as to obtain 6 pieces of columnar temporarily baked
product with a 50 mm diameter and a 100 mm length.
[0040] In contrast, a cube-like test piece of a 2 mm side size was
cut out from a part of the temporarily baked product and observed
with an electron microscope. It was found that the alumina crystal
particles of the part except the rim of the communication holes in
the skeleton structure were grown up to about 1.5 .mu.m, while
those of the part of the rim of the communication holes in the
skeleton structure were grown up to about 1.0 .mu.m.
[0041] Moreover, the cell distribution was measured with a mercury
pressure penetrated porosimeter so as to find peaks at 0.3 .mu.m
and 50 to 100 .mu.m. As a result, it is learned that the gap
between the alumina primary particles is 0.3 .mu.m and the cell
diameter is 50 to 100 .mu.m, and the minimum size of the
communication hole is about 20 .mu.m.
[0042] Next, 50 parts by weight of a silicon carbide powder having
a 5 .mu.m average particle size, 50 parts by weight of ion exchange
water and 0.1 part by weight of an ammonium polyacrylate as the
dispersing agent were mixed so as to prepare a slurry. The slurry
was sent with pressure at 30 cm/second flow rate by a pump
comprising a circulation system for permeating 5 pieces of the
columnar temporarily baked product therewith from the longitudinal
direction for 10 minutes, 1 hour, 2 hours, 5 hours and 10 hours
(examples 1 to 5). In contrast, the remaining one piece was
provided as the temporarily baked product without permeation with
the slurry (comparative example 1).
[0043] The 5 pieces of the temporarily baked product with the
slurry permeation were washed sufficiently with ion exchange water
for eliminating the silicon carbide powder. After drying at
120.degree. C. for 1 hour, including the temporarily baked product
without the slurry permeation, they were fired at 1,600.degree. C.
for 2 hours in the air so as to obtain the fired products and
obtain 6 pieces of alumina ceramic porous materials.
[0044] The average cell size of each of the obtained alumina
ceramic porous materials was 150 .mu.m. Moreover, the porosity, the
existence or absence of the abnormal part, the condensation
strength, the pressure loss and the time to the particle number
zero count were as shown in the table 1.
[0045] As to the existence or absence of the abnormal part, a
cube-like test piece of a 2 mm side size was cut out form each
alumina ceramic porous material and taking a scanning type electron
microscope photograph thereof for observing the rim of the
communication holes communicating the cells at a high magnification
ratio of about 5,000 times. Thereby, whether or not the crystal
particle growth was restrained compared with the other parts of the
skeleton structure was observed, and furthermore, the existence or
absence of the abnormality such as the cactus-like shape was
observed.
[0046] As to the condensation strength, a short columnar-like
shaped test piece of a 10 mm diameter and a 10 mm height was cut
out from each alumina ceramic porous material with a diamond tool,
and after a drying operation, the condensation strength was
measured.
[0047] Moreover, as to the time to the particle number zero count,
after washing the above-mentioned test pieces sufficiently with ion
exchange water, time until elimination of dust generation was
measured with a particle counter while applying the shock.
1 TABLE 1 time to existence the or particle absence Condensa-
number of the tion pressure zero porosity abnormal strength loss
count (%) part (MPa) (KPa) (minute) example 60.2 exist 350 0.9 5 1
example 61 absent 420 0.6 0.5 2 example 62 absent 400 0.45 0.4 3
example 65 absent 400 0.3 0.3 4 example 70 absent 380 0.2 0.2 5
Compara- 60 exist 300 0.1 60 tive example 1
[0048] As it is shown in the table 1, in the case the abnormal part
at the rim of communication holes is eliminated by applying the
mechanical process, the porosity and the mechanical strength are
made higher as well as the transmission resistance is made
dramatically smaller according to the enlargement of the
communication hole diameter accompanying the elimination of the
abnormal part, and the particle generation was substantially
eliminated.
EXAMPLES 6 TO 10
[0049] First, with reference to the examples 1 to 5, 5 compact
pieces were produced with different porosities in the substantially
same manner therewith. The compacts were temporarily baked so as to
obtain columnar-shaped compacts. After the elimination process by
permeation with the silicon carbide slurry, they were made to have
the same porosity.
[0050] Next, in the same manner as in the examples 1 to 5, the
temporarily baked products were fired for providing the fired
products so as to obtain 5 pieces of alumina ceramic porous
materials of a 60% porosity.
[0051] The porosity of the obtained alumina ceramic porous
materials, the existence or absence of the abnormal part, the
pressure loss and the time to the particle number zero count were
measured in the same manner as in the examples 1 to 5. Results are
shown in the table 2 together with those of the comparative example
1.
2 TABLE 2 time to existence the or particle absence Condensa-
number of the tion pressure zero porosity abnormal strength loss
count (%) part (MPa) (KPa) (minute) example 60 exist 350 0.9 5 6
example 60 absent 550 0.8 2 7 example 60 absent 600 0.7 1 8 example
60 absent 800 0.6 0.5 9 example 60 absent 1000 0.5 0.2 10 Compara-
60 exist 300 1 60 tive example 1
[0052] As it is shown in the table 2, in the case the abnormal part
with a small crystal particles at the rim of the communication
holes is eliminated by applying the mechanical process so as to
have the crystal particle size at the rim of the communication
holes substantially equivalent to the crystal particle size in the
other parts of the skeletons structure, the mechanical strength of
the alumina ceramic porous materials of the same cell size and the
porosity can dramatically be improved.
[0053] The air transmission amount and the pressure loss of the
alumina ceramic porous material were measured so as to confirm the
pressure loss inversely proportional to the square value of the
average value of the communication hole size.
EXAMPLES 11 TO 15, COMPARATIVE EXAMPLE 2
[0054] First, a bubble-like slurry was prepared by mixing and
agitating 100 parts by weight of a silicon carbide powder having a
0.5 .mu.m average particle size as the ceramic powder, 40 parts by
weight of ion exchange water as the liquid medium, 1.0 parts by
weight of a triethanol amine lauryl sulfate as the foaming agent, 2
parts by weight of a carbon black having a 260 m.sup.2/g specific
surface area and 0.5 part by weight of a boron carbide having a 1.6
.mu.m average particle size as the sintering auxiliary agent, and 6
parts by weight of a polyethylene imine as the gellation main agent
by an agitator while introducing the air.
[0055] Next, while agitating the bubble-like slurry, 2 parts by
weight of an epoxy resin as the gellation sub agent was added
thereto. After pouring the same in a mold and passage of 30
minutes, the gellation proceeded sufficiently so as to obtain a
gellation product.
[0056] Then, the gellation product was taken out from the mold and
dried at 60.degree. C. for whole day and night so as to obtain a
compact (dried product).
[0057] The obtained compact has a three-dimensional mesh-like
skeleton structure with a large number of substantially spherical
adjacent cells communicating with each other via communication
holes.
[0058] Next, the compact was heated (temporarily baked) at
1,800.degree. C. for 1 hour in an argon gas atmosphere so as to
obtain a temporarily baked product. It was processed with a diamond
grinding stone so as to obtain 6 pieces of columnar temporarily
baked product with a 50 mm diameter and a 100 mm length.
[0059] In contrast, a rectangular parallelopiped-like test piece of
a 5 mm longitudinal size, a 5 mm lateral size and a 10 mm length
was cut out from a part of the temporarily baked product and the
cell distribution was measured with a mercury pressure penetrated
porosimeter so as to find peaks at 0.02 .mu.m, 0,2 .mu.m, and 10
.mu.m.
[0060] Next, as in the examples 1 to 5, 50 parts by weight of a
silicon carbide powder having a 5 .mu.m average particle size, 50
parts by weight of ion exchange water and 0.1 part by weight of an
ammonium polyacrylate as the dispersing agent were mixed so as to
prepare a slurry. The slurry was sent with pressure at 30 cm/second
flow rate by a pump comprising a circulation system for permeating
5 pieces of the columnar temporarily baked product therewith from
the longitudinal direction for 10 minutes, 1 hour, 2 hours, 5 hours
and 10 hours (examples 11 to 15). In contrast, the remaining one
piece was provided as the temporarily baked product without
permeation with the slurry (comparative example 2).
[0061] As in the examples 1 to 5, the 5 pieces of the temporarily
baked product with the slurry permeation were washed sufficiently
with ion exchange water for eliminating the silicon carbide powder.
After drying at 120.degree. C. for 1 hour, including the
temporarily baked product without the slurry permeation, they were
sintered at 2, 200.degree. C. for 1 hours in an argon gas
atmosphere so as to obtain the baked products and obtain 6 pieces
of silicon carbide ceramic porous materials.
[0062] The average cell size of each of the obtained silicon
carbide ceramic porous materials was 100 .mu.m. Moreover, the
porosity, the existence or absence of the abnormal part, the
condensation strength, the pressure loss and the time to the
particle number zero count were measured as in the examples 1 to 5.
Results are shown in the table 3.
3 TABLE 3 time to existence the or particle absence Condensa-
number of the tion pressure zero porosity abnormal strength loss
count (%) part (MPa) (KPa) (minute) example 55.2 exist 520 1.1 5 11
example 56 absent 800 0.8 0.3 12 example 57 absent 900 0.65 0.2 13
example 60 absent 1000 0.4 0.1 14 example 64 absent 950 0.3 0.1 15
Compara- 55 exist 500 1.2 75 tive example 2
[0063] As it is shown in the table 3, in the case the abnormal part
at the rim of communication holes is eliminated by applying the
mechanical process, the porosity and the mechanical strength are
made higher as well as the transmission resistance is made
dramatically smaller according to the enlargement of the
communication hole diameter accompanying the elimination of the
abnormal part, and the particle generation was substantially
eliminated.
EXAMPLE 16
[0064] First, the alumina ceramic porous material of the
comparative example 1 was processed into a rectangular
parallelepiped-like shape of a 1 cm square and a 10 cm length. A
slurry with a sodium borate powder dispersed by 30% in an acetone
was poured thereon for introducing the sodium borate slurry into
the cells of the alumina ceramic porous material.
[0065] Next, after dying the acetone, it was introduced into a
furnace kept at 1,000.degree. C. for fusing the sodium borate.
After maintaining the same in the furnace for 10 minutes, it was
taken out from the furnace and cooled down in the air. Then, it was
boiled in a diluted hydrochloric acid for 2 hours for dissolving
and eliminating the sodium borate so as to obtain an alumina
ceramic porous material.
[0066] The porosity, the existence or absence of the abnormal part,
the condensation strength, the pressure loss and the time to the
particle number zero count were measured as in the examples 1 to 5.
Results are shown in the table 4 together with those of the
comparative example 1.
4 TABLE 4 time to existence the or particle absence Condensa-
number of the tion pressure zero porosity abnormal strength loss
count (%) part (MPa) (KPa) (minute) example 75 absent 500 0.1 0.1
16 Compara- 60 exist 300 1 60 tive example 1
[0067] As it is shown in the table 4, by eliminating the abnormal
part by applying the chemical process, the porosity and the
mechanical strength are made higher as well as the particle
generation is eliminated, and the transmission resistance is made
smaller.
EXAMPLES 17, 18
[0068] The temporarily baked product of the comparative example 1
and the fired product of the comparative example 1 were fired or
re-fired at 1,900.degree. C. in a hydrogen gas atmosphere for 5
hours for providing a baked product or a re-baked product so as to
obtain an alumina ceramic porous material, respectively.
[0069] The crystal particles of both of the obtained ceramic porous
materials had grain growth to about 20 .mu.m. Moreover, the
porosity, the existence or absence of the abnormal part, the
condensation strength, the pressure loss and the time to the
particle number zero count were measured as in the examples 1 to 5.
Results are shown in the table 5 together with those of the
comparative example 1.
5 TABLE 5 time to existence the or particle absence Condensa-
number of the tion pressure zero porosity abnormal strength loss
count (%) part (MPa) (KPa) (minute) example 60 absent 400 0.1 0.1
17 example 60 absent 400 0.1 0.1 18 Compara- 60 exist 300 1 60 tive
example 1
[0070] As it is shown in the table 5, by denaturing the abnormal
part by processing the temporarily baked product or the fired
product in a high temperature hydrogen gas so as to have the
crystal particle size in the entire skeleton structure evenly, a
high porosity and a high mechanical strength can be provided as
well as the particle generation was eliminated, and the
transmission resistance is made smaller.
[0071] The particle structure of the alumina ceramic porous
material baked at 1,600.degree. C. for 2 hours in the air without
the mechanical process is as shown in FIG. 1. Moreover, the crystal
structure of the above-mentioned alumina ceramic porous material
after re-fireing at 1,840.degree. C. for 10 hours in a hydrogen
atmosphere is as shown in FIG. 2.
[0072] As it is shown in the FIG. 2, by the process in the high
temperature hydrogen gas, the entire crystal particle size is made
substantially equivalent.
[0073] As heretofore explained, according to a ceramic porous
material and a production method therefore of the present
invention, since the entire crystal particle size of the skeleton
structure can be even, to provide a ceramic porous material which
has a high strength, though it has a high porosity, and which is
excellent in permeability without dust generation.
* * * * *