U.S. patent application number 14/369528 was filed with the patent office on 2015-01-15 for porous sintered body and process for producing porous sintered body.
This patent application is currently assigned to TAISEI KOGYO CO., LTD.. The applicant listed for this patent is TAISEI KOGYO CO., LTD.. Invention is credited to Yasuhiro Kanoko, Shigeo Tanaka.
Application Number | 20150017464 14/369528 |
Document ID | / |
Family ID | 48697624 |
Filed Date | 2015-01-15 |
United States Patent
Application |
20150017464 |
Kind Code |
A1 |
Tanaka; Shigeo ; et
al. |
January 15, 2015 |
POROUS SINTERED BODY AND PROCESS FOR PRODUCING POROUS SINTERED
BODY
Abstract
[Object] The present invention provides a porous sintered body
which has a uniform porosity, a high level of freedom in forming,
allowing to be formed into varieties of shapes and various levels
of porosity, and to be formed to an extremely high level of
porosity. [Means for Solution] There is provided a porous sintered
body 1 which is obtained by sintering a powder 4, and includes
hollow cores 5 following a vanished shape of an interlaced or
otherwise structured fibriform vanisher material 2; sintered walls
6 obtained by sintering the powder held around the cores and
extending longitudinally of the cores; and voids 7 between the
sintered walls.
Inventors: |
Tanaka; Shigeo;
(Neyagawa-shi, JP) ; Kanoko; Yasuhiro;
(Neyagawa-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TAISEI KOGYO CO., LTD. |
Neyagawa-shi, Osaka |
|
JP |
|
|
Assignee: |
TAISEI KOGYO CO., LTD.
Neyagawa-shi, Osaka
JP
|
Family ID: |
48697624 |
Appl. No.: |
14/369528 |
Filed: |
December 28, 2012 |
PCT Filed: |
December 28, 2012 |
PCT NO: |
PCT/JP2012/084188 |
371 Date: |
September 23, 2014 |
Current U.S.
Class: |
428/566 ;
419/2 |
Current CPC
Class: |
B22F 3/1112 20130101;
B22F 7/002 20130101; C04B 38/0038 20130101; H01M 4/0471 20130101;
B22F 3/1121 20130101; C04B 2235/6028 20130101; Y02E 60/50 20130101;
C22C 1/08 20130101; B22F 5/10 20130101; C04B 2237/32 20130101; B22F
5/006 20130101; B22F 2999/00 20130101; Y02E 60/10 20130101; C04B
2111/00853 20130101; Y10T 428/12153 20150115; B22F 1/0014 20130101;
B22F 3/1137 20130101; B22F 2998/10 20130101; H01M 4/8621 20130101;
B32B 18/00 20130101; B22F 3/1021 20130101; C04B 2237/62 20130101;
B22F 2999/00 20130101; B22F 3/1137 20130101; B22F 3/114 20130101;
B22F 2998/10 20130101; B22F 1/0014 20130101; B22F 1/0074 20130101;
B22F 3/1137 20130101; B22F 7/002 20130101; C04B 38/0038 20130101;
C04B 35/00 20130101; C04B 38/0058 20130101 |
Class at
Publication: |
428/566 ;
419/2 |
International
Class: |
B22F 3/11 20060101
B22F003/11 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2011 |
JP |
2011-288558 |
Claims
1. A porous sintered body obtained by sintering a powder,
comprising: hollow cores following a vanished shape of an
interlaced or otherwise structured fibriform vanisher material;
sintered walls extending longitudinally of the cores and obtained
by sintering the powder held around the cores; and voids between
the sintered walls.
2. The porous sintered body according to claim 1, wherein the
sintered walls include absent regions which provide communication
between the cores and the voids.
3. The porous sintered body according to claim 1, wherein the
sintered wall is obtained through necking sintering of the powder
which is laminated in one through three layers on outer
circumferential regions of the fibriform vanisher material.
4. The porous sintered body according to claim 1, wherein the
powder has an average particle size of 1/5 through 1/50 of a
diameter of the fibriform vanisher material.
5. The porous sintered body according to claim 1, wherein the
powder includes: a first powder which has a higher sintering
initiation temperature; and a second powder which has a lower
sintering initiation temperature.
6. The porous sintered body according to claim 5, wherein the first
powder has a higher sintering initiation temperature than a
vanishing completion temperature of the fibriform vanisher
material, whereas the second powder has a lower sintering
initiation temperature than the vanishing completion temperature of
the fibriform vanisher material.
7. The porous sintered body according to claim 5, wherein the
second powder is sintered to bridge particles of the first
powder.
8. The porous sintered body according to claim 5, wherein particles
of the first powder are not sintered with each other.
9. The porous sintered body according to claim 5, wherein the
second powder has an average particle size not greater than 1/10 of
an average particle size of the first powder.
10. The porous sintered body according to claim 1, wherein the
porous sintered body is sheet-like and has a thickness of 5 .mu.m
through 30 .mu.m.
11. The porous sintered body according to claim 1, wherein the
sintered wall has an outer circumference provided with a plated
layer.
12. The porous sintered body according to claim 1, wherein the
sintered wall has an outer circumference provided with a sintered
microparticulate layer.
13. The porous sintered body according to claim 1, obtained by
integrally sintering a plurality of porous bodies each provided by
an interlaced or otherwise structured fibriform vanisher material
having its outer circumferential regions holding a sinterable
powder.
14. A method of making a porous sintered body, comprising: a
fibriform vanisher material formation step of interlacing or
otherwise structuring a fibriform vanisher material into a porous
body of a desired shape; a sintering powder application step of
applying a sinterable powder on outer circumferential surfaces of
the fibriform vanisher material; a fibriform vanisher material
vanishing step of vanishing the fibriform vanisher material; and a
sintering step of sintering the powder thereby obtaining a porous
sintered body which includes: hollow cores resulting from vanishing
the fibriform vanisher material; and sintered walls resulting from
sintering the powder.
15. The method of making a porous sintered body according to claim
14, wherein in the sintering step, the sinterable powder is
sintered and absent regions are formed in the sintered wall,
providing communication between the hollow cores and its
outside.
16. The method of making a porous sintered body according to claim
14, wherein the sintering powder is applied in one through three
layers on the outer circumferential surfaces of the fibriform
vanisher material in the sintering powder application step.
17. The method of making a porous sintered body according to claim
14, wherein mutually adjacent powder particles are necking-sintered
in the sintering step.
18. The method of making a porous sintered body according to claim
14, wherein the fibriform vanisher material formation step
includes: a slurry adjusting step of adjusting a slurry by mixing
the fibriform vanisher material, the sinterable powder and a
dispersion liquid in which these components can stay in a mixed
state in a dispered manner; and a paper-making step of forming a
sheet-body out of the slurry by means of wet papermaking method;
whereas the sintering powder application step includes: a
dehydrating-drying step of dehydrating and/or drying the sheet-like
formed-body which contains the slurry, thereby allowing the powder
to be held on an outer circumference of the interlaced fibriform
vanisher material.
19. The method of making a porous sintered body according to claim
14, wherein the sintering powder application step includes: a
slurry adjusting step of adjusting a slurry by mixing the
sinterable powder with a dispersion liquid in which these
components can stay in a mixed state in a dispered manner; an
impregnation step of impregnating the prous body, which has been
formed into a desired shape in the fibriform vanisher material
formation step, with the slurry in which the sinterable powder is
dispersed; and a dehydrating-drying step of dehydrating and/or
drying the formed body which contains the slurry thereby allowing
the powder held on an outer circumference of the interlaced
fibriform vanisher material.
20. The method of making a porous sintered body according to claim
14, wherein the powder includes a first powder and a second powder
each having a different sintering temperature from each other, the
sintering step including: a first sintering step of sintering the
second powder to bridge particles of the first powder before the
first powder begins sintering.
21. The method of making a porous sintered body according to claim
20, wherein the first sintering step is started before the
fibriform vanisher material vanishes.
22. The method of making a porous sintered body according to claim
20, further comprising a second sintering step of sintering
particles of the first powder with each other after the fibriform
vanisher material has varnished.
23. The method of making a porous sintered body according to claim
14, wherein the fibriform vanisher material formation step
includes: a lamination step of laminating a plurality of fibriform
vanisher material of desired shapes; and/or a fibriform vanisher
material modification step of working on the fibriform vanisher
material.
24. The method of making a porous sintered body according to claim
14, wherein the sintering powder application step includes a
plurality of steps for application of different sintering powders.
Description
TECHNICAL FIELD
[0001] The present invention relates to porous sintered bodies.
Specifically, the invention relates to highly porous sintered
bodies having a high level of freedom in body formation.
BACKGROUND ART
[0002] Highly porous metal sheets are used widely, as electrode
base materials for nickel-hydrogen batteries and lithium batteries
and electrode base materials for fuel cells for example, and many
other fields as well, such as biomaterials, catalyzer base
materials, and so on.
[0003] Conventionally, the porous metal sheet is obtained by first,
e.g., compressing a metal fiber into a sheet form, and then
sintering the sheet. However, according to this method, it is
difficult to achieve a uniform metal fiber density, and therefore
has been difficult to obtain a porous metal sheet which has a
uniform porosity.
[0004] In order to solve this problem, there is proposed a method
for making a uniformly porous metal sheet which includes a process
of uniformly dispersing a fibriform raw material or a powdery raw
material within a dispersing chamber of a packing apparatus, and
then allowing the dispersed raw material to fall on a substrate
placed beneath.
LITERATURE ON CONVENTIONAL ART
Patent Literature
[0005] Patent Document 1: JP-A 2007-262571
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0006] The method described above is capable of forming a porous
metal sheet of a uniform porosity. However, it is difficult to
obtain thin porous sheets having a thickness of a few micrometers
through a few tens of micrometers because the method employs a raw
material which has a diameter of 10 .mu.m through 100 .mu.m. On the
other hand, it is also difficult with the above-described fibriform
metal, to forma shape which has a greater thickness such as a few
millimeters through a few tens of millimeters while maintaining the
uniform porosity. In other words, there is a limitation to the form
of formed bodies. In still other words, level of freedom in forming
a porous sintered body is low.
[0007] Also, the fibriform metal or the powdery metal, which serves
as a building block of the porous body, is utilized as it is, i.e.,
as of the size. In other words, the thickness and porosity of the
formed body are dependent upon the shape and dimensions of these
members. For this reason, it is difficult to make a wide range of
metal porous bodies of a variety of shapes and porosities.
[0008] Another problem is that powdery metal in dispersion liquid
tends to precipitate quickly, to concentrate in a lower layer. This
means that although it is possible to make porous sintered bodies
having a uniform density of the powdery metal in surface
directions, it is difficult to make one which has a uniform
composition in the thickness direction.
[0009] When a metal porous body is utilized as a catalyzer, it is
the surface of the fibriform metal or of the powdery metal that
provides functions as the catalyzer. In order to increase the
surface area, it is necessary that the fibriform metal has a small
diameter, or the powdery metal has a small particle diameter,
which, however, poses a problem of poor form retention during
formation and sintering. Because of this, if a fibriform metal or a
powdery metal of a small dimension is used directly to form a
porous body preparation, it is impossible to obtain a metal porous
body of a desired form or porosity.
[0010] An object of the present invention is to solve the
above-described problems and to provide a porous sintered body
which has a uniform porosity, a high level of freedom in body
formation which allows formation into varieties of shapes and
various levels of porosity, and formation into forms of even an
extremely high level of porosity.
Means for Solving the Problems
[0011] An arrangement described in claim 1 of the present
application discloses a porous sintered body obtained by sintering
a powder. The porous sintered body includes hollow cores following
a vanished shape of an interlaced or otherwise structured fibriform
vanisher material; sintered walls extending longitudinally of the
cores and obtained by sintering the powder held around the cores;
and voids between the sintered walls.
[0012] The present invention relates to porous sintered bodies
which are made by first applying a sinterable powder on a surface
of an interlaced or otherwise structured fibriform vanisher
material, then vanishing the fibriform vanisher material while
sintering the powder which is held on the fiber surface.
[0013] The porous sintered body according to the present invention
includes hollow cores resulting from vanishment of the fibriform
vanisher material; and sintered walls formed by sintering the
powder around the cores. The sintered wall is formed longitudinally
of the cores. Specifically, the sintered wall constitutes a porous
sintered body which follows an outer shape of the fibriform
vanisher material and has a shape resulting from the interlacing.
Therefore, the body not only has a shape along the longitudinal
axis of the fibriform vanisher material but also has voids on both
inner and outer sides of the sintered wall which are obtained by
sintering the powder. Hence, it is possible to obtain a porous
sintered body which has a greater porosity than that of the porous
body which is formed by interlacing or otherwise structuring the
fibriform vanisher material. Further, since the inside and the
outside of the sintered wall provide surfaces, it is possible to
make a porous sintered body which has a very large surface
area.
[0014] Also, according to the present invention, it is possible to
make the sintered wall thinner, by using the powder which has a
smaller particle size. In other words, it is now possible to
achieve remarkable increase in the porosity or in the surface
area.
[0015] As disclosed in claim 2, it is possible to make the sintered
walls provide communication between the cores and the voids via
absent parts. Since the absent part provides communication between
the core and the void, it becomes possible to use not only an
outside surface of the sintered wall but also an inside surface
thereof, providing an advantage, when used as a catalyzer for
example, that a remarkable increase can be achieved in the area
available as a reaction surface. The absent part can be adjusted
easily by adjusting the amount of lamination of the powder and
sintering temperature of the powder. Preferably, for example,
adjustment is made so that the absent part accounts for 50 through
20%.
[0016] As disclosed in claim 3, the sintered wall can be obtained
through necking sintering of the powder which is laminated in one
through three layers on outer circumferential regions of the
fibriform vanisher material. The above-described arrangement makes
it possible to remarkably reduce the thickness of the sintered
wall. The ratio of the absent part can also be adjusted easily by
adjusting the sintering temperature.
[0017] Also, by sintering the powder in a necking fashion,
corrugations are formed on the sintered wall following the powder
pattern. This makes it possible to further increase the surface
area in the porous body. Also, since the powder's shape is
retained, it becomes possible to decrease the amount of shrinkage
at the time of sintering, making it possible to obtain a porous
sintered body of increased accuracy in the form and dimensions.
Further, by performing necking sintering by way of diffused
junction, it becomes possible to sinter the powder at significantly
lower temperatures than temperatures required for fusion sintering.
As a result, it is now possible to bond powder particles with each
other and fix the particles on the outer circumferential surfaces
of the fibriform vanisher material before the fibriform vanisher
material vanishes, and after the fibriform vanisher material has
varnished, to keep the shape of the walls longitudinally of the
fibriform vanisher material until fusion sintering takes place.
[0018] There is no specific limitation to the material or the shape
of the fibriform vanisher material as far as the vanisher material
vanishes by the time the powder has been sintered. Examples of the
material include not only natural fibers from Mitsumata
(Edgeworthia chrysantha), Kozo (Broussonetia kazinoki.times.B.
papyrifera), etc. but also artificial fibers such as rayon.
[0019] By selecting appropriate dimensions and a shape for the
fibriform vanisher material, and a mode of structuring, i.e.,
interlacing or other, it is possible to obtain porous bodies of
predetermined dimensions and shapes. Since the powder is sintered
while being held on the outer circumferential surface of the
fibriform vanisher material, it is possible not only to obtain
porous sintered bodies of various shapes but also to have a uniform
porosity in different regions of the porous sintered body. For
example, it is possible to make a series of porous sintered bodies,
from a very thin sheet-like porous sintered body to a thick,
three-dimensional porous sintered body, of a uniform porosity and
predetermined shapes.
[0020] There is no specific limitation to material from which the
powder is made. Also, two or more materials may be mixed to produce
the powder. Further, the powder may be made of a mixture of a
sintering powder and a non-sintering powder.
[0021] There is no specific limitation to the particle size of the
powder; it is necessary, however, that the powder particle size
allows the powder to be held around the fibriform vanisher material
at sinterable densities. Specifically, it is preferable as
disclosed in Claim f4, that the powder has an average particle size
which is 1/5 through 1/50 of a diameter of the fibriform vanisher
material.
[0022] If the powder has a particle diameter which is greater than
1/5 of the diameter of the fibriform vanisher material, it becomes
difficult to hold the powder around the fibriform vanisher
material. On the other hand, if the powder has a particle diameter
which is smaller than 1/50 of the diameter of the fibriform
vanisher material, it is impossible to retain the form or achieve
strength during and/or after sintering.
[0023] As disclosed in claim 5, the powder may include: a first
powder which has a higher sintering initiation temperature; and a
second powder which has a lower sintering initiation temperature.
By using powders having different sintering initiation
temperatures, it becomes possible to ensure form retention during
the sintering.
[0024] The first powder and the second powder may be provided by
different metal powders. Also, in cases where the powders are
provided by the same material, the sintering initiation temperature
for one can be lowered by choosing a different particle size from
the other. For example, as disclosed in claim 9, the second powder
may have an average particle size not greater than 1/10 of an
average particle size of the first powder. This increases surface
activity and decreases the sintering initiation temperature. It is
not necessary that the sintering initiation temperature is the
melting temperature of the powder; rather, any temperature is
acceptable as far as the first powder can retain desired form at
that specific temperature. For example, under enhanced surface
activity, sticking force develops due to diffusion at areas of
contact between the first powder and the second powder, which
ensures form retention that the shape along the longitudinal axis
of the fibriform vanisher material is maintained even if the powder
is not melted yet.
[0025] Further, as disclosed in claim 6, there may be an
arrangement that the first powder has a higher sintering initiation
temperature than a vanishing completion temperature of the
fibriform vanisher material, whereas the second powder has a lower
sintering initiation temperature than the vanishing completion
temperature of the fibriform vanisher material.
[0026] If a high sintering temperature is required to sinter the
powder, there can be a case where the fibriform vanisher material
has vanished completely before the powder begins being sintered. In
such a case as this, it can become impossible to keep the powder at
the position along an outer circumference of the fibriform vanisher
material during sintering. Sintering under such a state can cause
unacceptably large deformation in the sintered wall, leading to
inability to obtain a porous sintered body of a predetermined
porosity or predetermined shape.
[0027] By using the second powder which has a lower sintering
initiation temperature than a vanishing completion temperature of
the fibriform vanisher material or which has a specific surface
characteristic for generating a cohesive force for bonding the
powder particles to each other, it becomes possible to hold the
first powder, via the second powder, on the outer circumferential
regions of the fibriform vanisher material after the fibriform
vanisher material has vanished. Then, by sintering particles of the
first powder with each other thereafter, the sintering powder is
sintered while the powder particles are held along the outer
circumferential surface of the fibriform vanisher material. The
second powder can be applied on the outer circumference of the
fibriform vanisher material simultaneously with the first powder.
Alternatively, the first powder may be first applied to the outer
circumference of the fibriform vanisher material, followed by
application of the second powder onto the first powder. Still
further, there may be an arrangement where the second powder is
contained in the fibriform vanisher material so that it appears as
the fibriform vanisher material vanishes. There is no specific
limitation to material from which the second powder is made. For
example, a metal powder may be used. There can also be an
arrangement where the second powder is provided by a residue
component, carbide, etc. which occur when the fibriform vanisher
material or solvent in slurry vanishes in the fibriform vanisher
material vanishing step or the sintering step. There may be
arrangements where the second powder is designed to stay after the
first powder is sintered, or there may be arrangements where the
second powder is designed to vanish.
[0028] claim 7 discloses an arrangement where the second powder is
sintered to bridge particles of the first powder. It becomes
possible to sinter the second powder to particles of the first
powder in a bridging manner by using the second powder which has a
lower sintering initiation temperature than that of the first
powder and by mixing the two powders at an appropriate ratio. This
arrangement provides an advantage in cases where the first powder
has a high sintering initiation temperature, that the second powder
keeps positional relationship among particles of the first powder
during the sintering, making it possible to obtain porous sintered
bodies having a uniform porosity.
[0029] Sometimes, a porous sintered body must be made from a powder
which is hard to sinter, or does not sinter. For example, when
sintering a functional ceramic which has a very high sintering
temperature, there can be cases where the sintering temperature is
so high that it is impossible to mix any other materials such as
metal. According to the present invention, as disclosed in claim 8,
it is possible to produce a structure in which the second powder is
sintered to bridge the first powder but particles of the first
powder are not sintered with each other. In addition, it is now
possible to perform sintering while keeping surfaces of the first
powder exposed. In other words, it is now possible to perform
sintering without inhibiting catalyzer functions, for example, of
the first powder.
[0030] There is no specific limitation to the shape or dimensions
of the porous sintered body according to the present invention. It
is possible to obtain porous sintered bodies of a variety of shapes
and dimensions as far as the fibriform vanisher material employed
allows formation by interlacing or other means of structuring the
material into the shape. For example, wet papermaking method may be
employed as disclosed in claim 10, to obtain sheet-like porous
bodies having a thickness ranging from 5 .mu.m through 30
.mu.m.
[0031] On the other hand, water stream or air stream may be
utilized to accumulate and interlace the fibriform vanisher
material, to make fiber bodies having complicated shapes or
three-dimensional shapes. Then, causing surfaces of the fiber to
hold a sintered body, porous sintered bodies of desired shapes are
obtained.
[0032] claim 11 discloses an arrangement in which the sintered wall
has its outer circumference provided with a plated layer. By
necking-sintering the powder, it is possible to form corrugations
which follow the shape of the sintered powder on the sintered wall.
Since the plated layer is formed on the corrugations in a laminated
fashion, the plated layer is also formed with corrugations,
resulting in remarkable increase in the surface area of the plated
layer. In cases where this arrangement is utilized to provide a
plated layer of platinum serving as a catalyzer layer for example,
remarkably high catalyzer effect is obtained. Also, when the
catalyzer is made of a precious metal, the invention makes it
possible to reduce cost of manufacture compared to conventional
catalyzer filters, since the invention is capable of reducing the
amount of the precious metal without decreasing catalyzer
performance. There is no specific limitation to the method for
forming the plated layer, so varieties of conventional methods can
be employed. There is no specific limitation, either, to material
for the plated layer or the thickness of the plated layer.
[0033] claim 12 discloses an arrangement in which the sintered wall
has its outer circumference provided with a sintered
microparticulate layer. Preferably, the micro particles are
provided by nanoparticles. For example, a fine metal powder having
a size of 20 nm through 900 nm can be used. Nanoparticles have much
lower sintering temperature than temperatures for sintering the
sintered wall. Thus, it becomes possible to form the sintered
microparticulate layer without altering the shape of the sintered
wall.
[0034] The micro particles for making the sintered microparticulate
layer can be applied by first forming a porous sintered body, then
impregnating a slurry which contains the micro particles, and
finally removing solvent components. There is no specific
limitation to material from which the sintered microparticulate
layer is made. For example, catalyzer metals such as platinum and
rhodium may be used. There is no specific limitation, either, to
the thickness of the sintered microparticulate layer. For example,
it is possible to form a micro particle layer which has a thickness
of 20 nm through 900 nm or greater.
[0035] The sintered microparticulate layer may be made by fusion
sintering, or may be made by necking sintering by way of diffusion
junction. If necking sintering is utilized, the shape of micro
particles is partially retained, which further increases the
surface area of the porous sintered body. It is also possible to
form the sintered microparticulate layer as a porous layer.
[0036] claim 13 discloses the porous sintered body which is
obtained by integrally sintering a plurality of porous bodies each
provided by an interlaced or otherwise structured fibriform
vanisher material having its outer circumferential region holding a
sinterable powder.
[0037] The porous sintered body according to the present invention
is made by first forming, and then sintering a porous body of an
interlaced fibriform vanisher material having its outer
circumferential surface holding a sintering powder. This
arrangement makes it possible to obtain porous sintered bodies of a
uniform porosity in a variety of three-dimensional shapes. Also, it
is possible to alter the porous body in many ways before sintering.
For example, holes may be drilled, and bending operations may be
performed. Also, modifications may be made after a plurality of
porous bodies are assembled to each other.
[0038] claim 14 discloses a method of making a porous sintered
body. The method includes: a fibriform vanisher material formation
step of interlacing or otherwise structuring a fibriform vanisher
material into a porous body of a desired shape; a sintering powder
application step of applying a sinterable powder on outer
circumferential surfaces of the fibriform vanisher material; a
fibriform vanisher material vanishing step of vanishing the
fibriform vanisher material; and a sintering step of sintering the
powder thereby obtaining a porous sintered body which includes:
hollow cores resulting from vanishing the fibriform vanisher
material; and sintered walls resulting from sintering the
powder.
[0039] As disclosed in claim 15, the sinterable powder is sintered,
and absent regions are formed in the sintered wall, providing
communication between the hollow cores and outside, in the
sintering step.
[0040] For example, by adjusting the lamination thickness of the
sinterable powder, the sintering temperature or the sintering time,
it is possible to make the sintered wall shrink by a predetermined
amount, thereby obtaining the absent part of a desired shape or
size. The absent part provides communication between the cores and
the voids, thereby increasing further the surface area available
for catalyzer reaction for example.
[0041] As disclosed in claim 16, preferably, the sintering powder
is applied in one through three layers on the outer circumferential
surfaces of the fibriform vanisher material in the sintering powder
application step. By applying the sintering powder in one through
three layers on the outer circumferential surfaces of the fibriform
vanisher material, porous sintered bodies having high levels of
porosity are obtained. The arrangement also allows to form desired
absent parts.
[0042] It is preferable, as disclosed in claim 17, that mutually
adjacent powder particles are necking-sintered in the sintering
step. This results in formation of corrugations on surfaces of the
sintered wall, whereby there is a remarkable increase in internal
surface area of the obtained porous sintered bodies. The necking
sintering is performed easily by selecting sintering temperatures
and time.
[0043] There is no specific limitation to the formation step. For
example, when a sheet-like formed-body is to be made, it can be
achieved by employing a papermaking technique such as wet
papermaking method, or a technique for making non-woven cloth.
There is no specific limitation to the powder application step,
either. For example, the step can be accomplished by soaking a
formed body which is made of the fibriform vanisher material into a
slurry in which a sintering powder is dispersed.
[0044] claim 18 discloses a method in which the formation step
includes: a slurry adjusting step of adjusting a slurry by mixing
the fibriform vanisher material, the sinterable powder and a
dispersion liquid in which these components can stay in a mixed
state in a dispersed manner; and a paper-making step of forming a
sheet-like body out of the slurry by means of wet papermaking
method; whereas the powder application step includes a
dehydrating-drying step of dehydrating and/or drying the sheet-like
formed body which contains the slurry thereby allowing the powder
to be held on an outer circumference of the interlaced fibriform
vanisher material.
[0045] Also, in claim 19, the sintering powder application step
includes: a slurry adjusting step of adjusting a slurry by mixing
the sinterable powder with a dispersion liquid in which these
components can stay in a mixed state in a dispersed manner; an
impregnation step of impregnating the porous body, which has been
formed into a desired shape in the fibriform vanisher material
formation step, with the slurry in which the sinterable powder is
dispersed; and a dehydrating-drying step of dehydrating and/or
drying the formed body which contains the slurry thereby allowing
the powder held on an outer circumference of the interlaced
fibriform vanisher material.
[0046] claim 20 discloses an arrangement that the powder includes a
first powder and a second powder each having a different sintering
temperature from each other; and with this, the sintering step
includes: a first sintering step of sintering the second powder to
bridge particles of the first powder before the first powder begins
sintering.
[0047] claim 21 discloses an arrangement that the first sintering
step is started before the fibriform vanisher material vanishes.
Starting the first sintering step before the fibriform vanisher
material vanishes ensures that the first powder is retained along
the outer circumferential surfaces of the fibriform vanisher
material. Thus, sintered walls are formed along the outer
circumferential surfaces of the fibriform vanisher material. It
should be noted here that the second powder need not be melted in
the first sintering step; rather it is enough as far as particles
are bonded to exert a desired level of shape retention. For
example, it is enough if particle surfaces are activated by heating
so that the second powder exerts a necessary level of adhesion to
surfaces of the first powder thereby takes hold on the first
powder. Also, it is preferable that the first powder has a particle
size suitable for being held along the outer circumferential
surface of the fibriform vanisher material, whereas the second
powder has a particle size suitable for finding ways to enter gaps
between particles of the first powder held along the outer
circumferential surface of the fibriform vanisher material. The
arrangement allows the second powder to be sintered to bridge
particles of the first powder.
[0048] The second powder can be applied onto the outer
circumference of the fibriform vanisher material together with the
first powder during the sintering powder application step. As
another option, a separate sintering powder application step may be
employed only for applying the second powder. As still another
arrangement, the fibriform vanisher material may contain the second
powder.
[0049] As disclosed in claim 22, the method may further include a
second sintering step of sintering particles of the first powder
with each other after the fibriform vanisher material has
varnished. Also, depending on necessity, the sintering step may be
stopped while the first powder is not yet sintered but particles of
the first powder which are not yet sintered to each other have
already been bridge-sintered via the second powder, to obtain a
specific type of porous sintered bodies.
[0050] claim 23 discloses an arrangement that the fibriform
vanisher material formation step includes: a lamination step of
laminating a plurality of fibriform vanisher material of desired
shapes; and/or a fibriform vanisher material modification step of
working on the fibriform vanisher material.
[0051] A formed body which has gone through the dehydrating-drying
step has a sinterable powder on outer circumferential surfaces of
its interlaced fibriform vanisher material. Thus, a plurality of
the formed bodies may then be combined and sintered together.
Through this, formed bodies of desired shapes can be easily made.
As a different process, a plurality of porous bodies, each formed
by interlacing or otherwise structuring a fibriform vanisher
material, may be combined first, then followed by a step of
applying a sintering powder. Further, the formed body may be
modified with such operations as drilling holes, bending, etc.
[0052] claim 24 discloses a method wherein the sintering powder
application step includes a plurality of steps for application of
different sintering powders. For example, when applying powders of
significantly different specific weights from each other, a
plurality of steps as described above may be performed in order to
distribute the powders uniformly all over the outer circumferential
surfaces of the fibriform vanisher material.
Advantages of the Invention
[0053] The invention makes it possible to obtain porous sintered
bodies which have a uniform porosity and desired shapes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] FIG. 1 is an electron micrograph of a porous sintered body
according to the present invention.
[0055] FIG. 2 is diagrammatic illustration of a sheet-like
formed-body formed from a fibriform vanisher material.
[0056] FIG. 3 is an enlarged illustration of a primary portion,
rendering how the fibriform vanisher material is interlaced.
[0057] FIG. 4 is an illustration, rendering an outer
circumferential region of the fibriform vanisher material in FIG. 3
holding a powder.
[0058] FIG. 5 is an illustration, rendering a section of the
fibriform vanisher material having its outer circumferential region
holding the powder.
[0059] FIG. 6 is an enlarged illustration of a primary portion,
rendering an axial section of the fibriform vanisher material in
FIG. 5.
[0060] FIG. 7 is an enlarged illustration of a primary portion,
rendering a section showing a sintered state of the powder shown in
FIG. 6.
[0061] FIG. 8 is an illustration of a second embodiment, rendering
an outer circumferential region of a fibriform vanisher material
holding a powder.
[0062] FIG. 9 is an enlarged illustration of a primary portion,
rendering a section showing a sintered state of the powder shown in
FIG. 8.
[0063] FIG. 10 is an illustration of a third embodiment, rendering
an outer circumferential region of a fibriform vanisher material
holding powders.
[0064] FIG. 11 is an enlarged illustration of a primary portion,
rendering a section to show how a first of the powders which are
shown in FIG. 10 is sintered.
[0065] FIG. 12 is an enlarged illustration of a primary portion,
rendering a section showing a second of the powders which are shown
in FIG. 10 is sintered.
[0066] FIG. 13 is an illustration showing a sectional view of a
fourth embodiment of the present invention.
[0067] FIG. 14 is an illustration showing a sectional view of a
fifth embodiment of the present invention.
[0068] FIG. 15 shows an embodiment of a porous sintered body which
includes a plated layer. FIG. 15(a) is an electron micrograph
showing a surface provided with a plated layer versus a surface not
provided with a plated layer; FIG. 15(b) is an electron micrograph
showing a section of a portion provided with a plated layer; and
FIG. 15(c) is an EDX element analysis photography of the section in
FIG. 15(b).
[0069] FIG. 16 shows an embodiment of a porous sintered body which
includes a microparticulate coating layer. FIG. 16(a) is an
electron micrograph of a surface provided with a sintered
microparticulate layer of Ni nanoparticles; FIG. 16(b) is an
electron micrograph of a surface provided with a sintered
microparticulate layer of Pt nanoparticles; and FIG. 16(c) is an
electron micrograph of a surface not provided with a
microparticulate coating layer.
MODE FOR CARRYING OUT THE INVENTION
[0070] Hereinafter, embodiments according to the present invention
will be described specifically, based on the drawings.
[0071] FIG. 1 is an electron micrograph showing an example of
porous sintered body according to the present invention. The
embodiment is an application of the present invention to a porous
sintered body made from a stainless steel powder.
[0072] A porous sintered body 1 is made of a sintered wall 6 along
an outer circumferential surface of an interlaced fibriform
vanisher material. As shown in FIG. 2, the porous sintered body 1
according to the present embodiment is made by interlacing a
fibriform vanisher material 2 into a predetermined form, i.e., into
a porous body 3, then having the vanishing material's outer
circumferential region hold a powder and then sintering the powder.
In the present embodiment, the fibriform vanisher material 2 is
like a short-fiber and this material is interlaced to form the
porous body 3. However, a continuous fiber may be interlaced or
otherwise structured into a sheet-like porous body.
[0073] FIG. 3 is an enlarged illustration, rendering a state of the
interlaced fibriform vanisher material 2. Also, FIG. 4 is an
illustration, rendering a state in which a powder 4 is held on the
outer circumferential surface of the fibriform vanisher material 2.
In the present embodiment, the outer circumferential surface of the
fibriform vanisher material 2 is coated with one through three
laminated layers of the powder 4. For the sake of easier
understanding, FIG. 4 illustrates only one layer of a powder of
ball-shaped particles of a uniform diameter.
[0074] In reality, the powder 4 is held in a laminated manner in
one through three layers. In addition, it is not necessary that
there is a uniform lamination of the powder on all regions; rather,
it is enough if there is a laminated coating of one through three
layers. Also, it is acceptable even if part or a significant part
is not covered by the powder.
[0075] FIG. 5 is an illustration, rendering a section of the
fibriform vanisher material which holds the powder. As shown in
this figure, the powder 4 is held along the outer circumferential
surface of the fibriform vanisher material 2. Although FIG. 5
illustrates the fibriform vanisher material 2 and the powder 4 as
having circular sections, this is not limiting. There is no
limitation, either, on the relative sizes of the fibriform vanisher
material 2 and the powder 4. Any size is acceptable as far as a
plurality of powder particles can be held along an outer
circumferential surface of the fibriform vanisher material.
[0076] FIG. 6 shows an axial section of the fibriform vanisher
material 2. As shown in this figure, the powder 4 is held along the
outer circumferential surface of the fibriform vanisher material 2
while there are certain regions 2a which do not hold the
powder.
[0077] As the porous body 3a, which is loaded with powder held by
the outer circumferential surface of the fibriform vanisher
material 2, is heated, the fibriform vanisher material 2 vanishes
and mutually adjacent particles of the powder 4 are sintered to
each other.
[0078] In the present embodiment, settings are made for heating
temperature and time so that there will be necking sintering first
occurring between mutually adjacent powder particles as shown in
FIG. 7. The mutually adjacent particles of the powder 4 then become
bonded to each other at their places of mutual contact, and then,
the sintering is brought to an end while each powder particle still
retains part of its outer form. The necking sintering is capable of
causing powder particles to be sparsely bonded with each other at
temperatures lower than temperatures at which the powder particles
are molten-sintered. Therefore, even after the fibriform vanisher
material has varnished at temperatures lower than a melting
temperature of the powder, it is possible to keep the powder in a
shape that follows the outer circumferential surface of the
fibriform vanisher material 2 while continuing with the
sintering.
[0079] FIG. 7 shows a porous sintered body 1, which includes hollow
cores 5 having a shape of the interlaced fibriform vanisher
material 2 which has been vanished; sintered wall regions 6 formed
by sintering the powder 4 around the cores 5; and voids 7 between
the sintered wall regions 6.
[0080] In the present embodiment, the sintered wall regions 6 have
their surfaces provided with corrugations 8 from the shape of
particles of the powder 4 as a result of necking sintering
performed to the powder 4. Also, the regions 2a in FIG. 5, where
there was no powder 4 present on the outer circumferential region
of the fibriform vanisher material 2, are turned into absent
regions 9. The sintered wall regions 6 as a whole is cylindrical,
following the outer circumferential surface of the fibriform
vanisher material 2, with the absent regions 9 scattering all over,
having a structure that hollow cores 5 and void 7 communicate with
each other via absent regions 9.
[0081] The void 7 substantially follows the shape of the porous
body 3 which is formed from the fibriform vanisher material 2 since
the porous sintered body 1 is provided by the sintered wall regions
6 made by sintering one through three layers of the powder 4 held
on an outer circumferential surface of the fibriform vanisher
material 2. Further, since the sintered wall regions 6 is provided
by a combination of the cores 5 and the void 7 which communicate
with each other via the absent regions 9, voids are formed on both
inside and outside of the sintered wall regions 6. Therefore, it is
possible to obtain a porous sintered body 1 which has a greater
porosity than that of a porous body 3 which is formed by
interlacing the fibriform vanisher material 2. Also, since both of
the inside and the outside of the sintered wall regions 6 provide
working surfaces, it is possible to make a porous sintered body 1
which has a very large surface area inside.
[0082] Also, through the necking sintering of the powder,
corrugations 8 are formed on surfaces of the sintered wall regions
6. This further increases the surface area in the porous body.
Further, since the powder's shape is retained, it becomes possible
to decrease the amount of shrinkage at the time of sintering,
making it possible to obtain a porous sintered body 1 of increased
accuracy in the form and dimensions.
[0083] In the present embodiment, Kozo (Broussonetia
kazinoki.times.B. papyrifera) fiber of an approximate diameter of
20 .mu.m and an average fiber length of 5 mm was used to form a
sheet-like porous body which had a thickness of approximately 20
.mu.m, with a wet papermaking method. There is no specific
limitation to the material or the shape of the fibriform vanisher
material as far as the vanisher material vanishes by the time the
powder 4 has been sintered. Examples include not only natural
fibers from Mitsumata (Edgeworthia chrysantha), Kozo (Broussonetia
kazinoki.times.B. papyrifera), etc. but also artificial fibers such
as polyester, polyethylene, rayon and acrylic; and pulp as well.
There is no specific limitation to the diameter or the length of
the fiber, as far as it is possible to interlace the fiber into a
porous body of a desired shape. For example, the formed body may be
formed of an endless fiber produced from electrospinning, etc.
Also, even in cases where the fibriform vanisher material 2
vanishes before the powder 4 starts melting and begins sintering,
the powder is in the state of diffused junction and therefore it is
possible to proceed with the sintering of the powder 4 while
keeping the shape of the sintered wall regions 6.
[0084] There is no specific limitation, either, to the forming
process of forming the porous body 3a from the fibriform vanisher
material 2. For example, wet papermaking method can be employed to
form sheet-like porous bodies. Also, needle punching and other
non-woven fabric making methods may be used to provide porous
bodies. Further, porous bodies may be provided in a
three-dimensional manner by using air streams, for example, when
interlacing fibers. By selecting appropriate dimensions and a shape
for the fibriform vanisher material, and a mode of interlacing, it
is possible to obtain porous bodies of predetermined dimensions and
shapes. It is also possible to use cloth-like porous bodies made by
weaving or other methods.
[0085] In the present embodiment, the porous body 3a is formed from
the fibriform vanisher material 2, and the powder 4 is held on the
outer circumferential surface of the fibriform vanisher material 2
while it is sintered. Therefore, it is possible not only to obtain
porous sintered bodies 1 of various shapes but also to achieve a
uniform porosity in all regions of the porous sintered body 1. For
example, it is possible to make a series of porous sintered bodies,
from a very thin sheet-like porous sintered body to a thick,
three-dimensional porous sintered body, of a uniform porosity and
predetermined shapes.
[0086] There is no specific limitation, either, on materials from
which the powder 4 is made. Examples of the materials include
metals such as nickel and copper, and ceramic powders as well.
Also, two or more powder materials may be mixed to produce the
powder. Further, the powder may be made of a mixture of a sintering
powder and a non-sintering powder. In the present embodiment, the
powder particles are bonded to each other by necking sintering, so
it is possible to sinter while retaining all surface
characteristics of each powder. This means that by using a mixed
powder which contains a powder having catalyzer capabilities, it is
possible to obtain a porous sintered body which has high catalyzer
capabilities.
[0087] Also, in this first embodiment, the powder 4 is provided by
stainless steel powder of particles having an average diameter
(average particle size) of 3 .mu.m; however, there is no specific
limitation to this, either. It is preferable, however, that the
particle is of a size which can be arranged and held in a
sinterable manner around the fibriform vanisher material 2. For
example, the powder 4 should have an average particle size of 1/5
through 1/50 of the diameter of fibriform vanisher material 2. If
the powder 4 has a particle diameter which is greater than 1/5 of
the diameter of the fibriform vanisher material 2, it becomes
difficult to hold the powder around the fibriform vanisher material
2. On the other hand, if the powder 4 has a particle diameter which
is smaller than 1/50 of the diameter of the fibriform vanisher
material 2, it becomes impossible to retain the form or achieve
strength during and/or after sintering.
[0088] There is no specific limitation, either, to the sintering
powder application step of having the outer circumferential region
of the fibriform vanisher material 2 hold the powder 4. By soaking
the porous body 3a, which is formed by interlacing afibriform
vanisher material, into, e.g., aslurry which contains a powder to
be sintered, it is possible to have the outer circumferential
region of the fibriform vanisher material 2 hold the powder. For
example, a metal powder is dispersed at a predetermined
concentration in an aqueous solution of a binder such as
carboxymethyl cellulose. Then, the porous body 3a formed of the
fibriform vanisher material 2 is soaked into the solution, and
thereafter, dehydrated or naturally dried. With this method it is
possible to obtain a porous body which holds the metal powder on
its outer circumferential region of the fibriform vanisher material
2. By adjusting the metal powder concentration, soaking time, etc.
in the sintering powder application step, it is possible to adjust
the amount of the metal powder applied.
[0089] Also, if wet papermaking method is used to forma sheet-like
porous body, the powder 4 may be added to a slurry which contains
the fibriform vanisher material 2, whereby it becomes possible to
interlace the fibriform vanisher material and to make the powder
held by the outer circumferential region of the fibriform vanisher
material 2, simultaneously.
[0090] The fibriform vanisher material according to the present
embodiment is made from Kozo (Broussonetia kazinoki.times.B.
papyrifera), and is vanishable when heated to a temperature of
approximately 500 degrees Celsius in the vanishing material
vanishing step. The powder 4, on the other hand, is brought to
necking sintering when heated to an approximate temperature of 800
degrees Celsius in the sintering step. The vanity-formation
sintering step and the sintering step may be performed as a
continuous process or as separate processes. It should be noted
here that the temperature for the vanishing material vanishing step
and for the sintering step are selected according to the materials
to be used.
[0091] FIG. 8 and FIG. 9 shows a second embodiment according to the
present invention. Whereas in the porous sintered body according to
the first embodiment, the powder 4 is applied on most of the outer
circumferential region of the fibriform vanisher material 2 and
then sintering follows, it is possible, as shown in FIG. 8, to form
a porous sintered body by applying a powder 24 onto part of an
outer circumferential region of a fibriform vanisher material
22.
[0092] Specifically, even if the powder 24 is applied only partly
on the fibriform vanisher material 22 as shown in FIG. 8, it is
possible to form a porous sintered body 200 as far as powder
particles are sufficiently adjacent to each other for necking
sintering. Also, in this case, mutually adjacent particles of the
powder 24 agglutinate with each other in the process in which the
fibriform vanisher material 22 vanishes, and for this reason, it is
possible to form a porous sintered body, as shown in FIG. 9, which
has a high ratio of absent regions.
[0093] FIG. 10 and FIG. 12 show a third embodiment of the present
invention. A porous sintered body 300 according to the third
embodiment is made by applying and sintering two kinds of powders
on an outer circumferential region of a fibriform vanisher material
32. Description will not be made for the fibriform vanisher
material 32, the sintering powder application step, etc. because
they are the same as those in the first embodiment.
[0094] As shown in FIG. 10, during the sintering powder application
step, the outer circumferential region of the fibriform vanisher
material 32 holds a powder 34 which contains a first powder 34a of
a larger particle size (average diameter), and a second powder 34b
of a smaller particle size than the first powder. FIG. 10 is an
illustration corresponding to FIG. 5, rendering how the applied
powder particles distribute.
[0095] Preferably, the particle size of the first powder 34a and
that of the second powder 34b are in a relationship that a particle
of the second powder 34b can sit between particles of the first
powder 34a. For example, it is preferable that the second powder
34b has an average particle diameter which is not greater than 1/10
of an average particle diameter of the first powder 34a. Also, the
first powder 34a and the second powder 34b are mixed with each
other at a ratio no higher than a ratio at which all sitting
positions provided by the first powder 34a will be occupied. When a
powder which contains the first powder 34a and the second powder
34b is held on an outer circumferential region of the fibriform
vanisher material 32, the state as shown in FIG. 10 is
achieved.
[0096] The first powder 34a has a higher sintering initiation
temperature than a vanishing completion temperature of the
fibriform vanisher material 32, whereas the second powder 34b has a
lower sintering initiation temperature than a vanishing completion
temperature of the fibriform vanisher material 32. For example, the
first powder 34a may be provided by a stainless steel powder, with
the second powder 34b made of silver.
[0097] From the state shown in FIG. 10, temperature is increased:
Then, the fibriform vanisher material 32 begins vanishing first,
i.e., a vanishing material vanishing step takes place. While the
vanishing material vanishing step is still going on, as shown in
FIG. 11, the second powder 34b begins being sintered, i.e., a first
sintering step takes place in which bridging is provided between
particles of the first powder 34a. The fibriform vanisher material
32 is still partially in existence in this process, so the bridging
by the second powder 34b between the particles of the first powder
34a is achieved while the particles of the first powder 34a are
remaining at their positions.
[0098] Thereafter, sintering temperature is increased and a second
sintering step takes place in which particles of the first powder
34a are sintered with each other, and as a result, a porous
sintered body 300 is obtained which has a section as shown in FIG.
12.
[0099] If a high sintering temperature is required to sinter the
powder, there can be a case where the fibriform vanisher material
32 has vanished completely before the powder begins being sintered.
In such a case as this, it will become impossible to sinter while
keeping the powder at the position along an outer circumference of
the fibriform vanisher material 32. Sintering under such a state
can cause unacceptably large deformation in the sintered wall,
leading to inability to obtain a porous sintered body of a
predetermined porosity or predetermined shape.
[0100] By using the second powder 34b which has a lower sintering
initiation temperature than a vanishing completion temperature of
the fibriform vanisher material 32, it becomes possible to fix the
first powder 34a via the second powder 34b while the particles are
held on the outer circumferential region of the fibriform vanisher
material 32, after the fibriform vanisher material 32 has vanished.
Then, by sintering particles of the first powder with each other
34a thereafter, it becomes possible to sinter the sintering powder
while the powder particles are held along the outer circumferential
surface of the fibriform vanisher material. Hence, this makes it
possible to make a porous sintered bodies which has a high level of
forming accuracy.
[0101] In this case, use of the second powder 34b which has a small
particle size and has a high surface activity makes it possible
that the second powder 34b begins to be bonded by way of diffused
junction at a lower temperature than the vanishing completion
temperature of the fibriform vanisher material 32. This makes it
possible to sinter the first powder 34a while retaining the shape
of the sintered wall.
[0102] In the present embodiment, the first powder 34a and the
second powder 34b are provided by powders of different metals.
However, it is possible to use powders which are made of the same
material. In this case, it is preferable that the second powder 34b
has a particle size not greater than 1/10 of a particle size of the
first powder 34a. Powder's surface activity increases as the
particle size decreases, which makes it possible to start sintering
at a lower temperature.
[0103] Also, in the present embodiment, the second sintering step
is performed to sinter the first powder 34a; however, it is
acceptable to stop without sintering the second powder. In this
case, a resulting porous sintered body has a structure that
particles of the first powder 34a are bridged by the second powder
34b.
[0104] For example, when sintering a functional ceramic which has a
very high sintering temperature, there can be cases where the
sintering temperature is so high that it is impossible to mix any
other materials such as metal. The present embodiment makes it
possible to produce a structure in which the second powder 34b is
sintered to bridge the first powder 34a but particles of the first
powder are not sintered with each other. In other words, it is now
possible to perform sintering while keeping most of surfaces of the
first powder 34a exposed, i.e., it is now possible to perform
sintering without inhibiting catalyzer functions, for example, of
the first powder 34a.
[0105] The second powder 34b can be applied onto the outer
circumference of the fibriform vanisher material 32 together with
the first powder during the sintering powder application step. As
another option, a separate sintering powder application step may be
employed only for applying the second powder 34b. As still another
arrangement, the fibriform vanisher material may contain the second
powder.
[0106] There is no specific limitation to material from which the
second powder is made. There can be an arrangement where the second
powder is provided by a residue component, carbide, etc. which
occur when the fibriform vanisher material or solvent in slurry
vanishes in the fibriform vanisher material vanishing step or the
sintering step. There may be arrangements where the second powder
is designed to stay after the first powder is sintered, or there
may be arrangements where the second powder is designed to
vanish.
[0107] FIG. 13 shows a fourth embodiment of the present invention.
In the fourth embodiment, a plurality of sheet-like porous bodies
43a, 43b made from a fibriform vanisher material which holds a
powder are laminated and sintered integrally with each other.
[0108] In the present embodiment, powder is held on outer
circumferential surfaces of the fibriform vanisher material which
provides each of the porous bodies 43a, 43b. Therefore, by
laminating and then sintering these bodies, it is possible to
obtain an integrated porous sintered body. This arrangement makes
it possible to obtain porous sintered bodies of a variety of
three-dimensional shapes having a uniform porosity.
[0109] Further, as shown in FIG. 14, there may be an arrangement
where a plurality of porous bodies 53a, 53b made from different
powders and/or interlaced in different pattern are combined. This
makes it possible to obtain a porous sintered body which has
different internal composition.
[0110] FIG. 15 shows a fifth embodiment of the present invention.
In this embodiment, the porous sintered body described thus far has
an outer circumferential surface provided with a Cu-plated layer.
There is no specific limitation to the method for forming the
plated layer or to the thickness of the plated layer. For example,
conventional electroplating method is usable to form a plated layer
which has a thickness of up to 1 .mu.m.
[0111] FIG. 15 (a) shows two electron micrograph: On the right hand
side there is shown a surface without a plated layer, while on the
left hand side shown a surface provided with a Cu-plated layer.
FIG. 15(b) is an electron micrograph of a section of a porous
sintered body formed with the plated layer. FIG. 15(c) is an EDX
element analysis photography of the section shown in FIG. 15(b).
FIG. 15(c) maps a Cu-plated layer of a substantially uniform
thickness around an Fe component which is a primary component of
the porous sintered body.
[0112] In the present embodiment, the sintered wall has
corrugations; so the plated layer also has corrugations formed on
its surface; and therefore the plated layer has a very large
surface area. Hence, in cases where the plated layer is provided by
a catalyzer layer made of platinum for example, significantly high
performance can be expected as a catalyzer. Also, when the
catalyzer is made of a precious metal, the invention makes it
possible to reduce cost of manufacture, by reducing the amount of
precious metal without decreasing performance.
[0113] FIG. 16 shows a sixth embodiment of the present invention.
In this embodiment, the porous sintered body has its outer
circumferential surface provided with a sintered microparticulate
layer. The sintered microparticulate layer can be formed as follows
for example: First, a sintered metal porous body is soaked into a
slurry which contains micro particles, and then solvent is removed
by drying for example. Through these steps the micro particles are
applied on a surface of the porous body. Thereafter, heating is
performed to sintering temperatures of the micro particles, to fix
the micro particles on the outer circumferential surface of the
porous sintered body.
[0114] FIG. 16 (c) shows a surface of a porous sintered body which
is not provided with a sintered microparticulate layer. On the
other hand, FIG. 16(a) shows a surface of a sintered
microparticulate layer formed on a surface of the porous sintered
body. The layer has a thickness of 900 nm, and is made of Ni micro
particles having an average particle size of 300 nm. FIG. 16(b)
shows a surface of a sintered microparticulate layer formed on a
surface of the porous sintered body. The layer has a thickness of
100 nm, and is made of Ni micro particles having an average
particle size of 30 nm.
[0115] In the sixth embodiment, sintering is performed so that the
micro particles will retain their shape at least partially on the
sintered microparticulate layer. As a result, the surfaces of each
sintered microparticulate layer is corrugated, following the shape
of the micro particles. This makes it possible to further increase
the surface area of the porous sintered body. Hence, by making a
sintered microparticulate layer which works as a catalyzer, the
invention increases catalyzer effect.
[0116] Preferably, the micro particles are provided by metal
nanoparticles. For example, nanoparticles having an average
particle size of 20 nm through 900 nm can be applied to a thickness
of 20 nm through 900 nm or to a greater thickness. Metal
nanoparticles is highly surface-active, making it possible to
sinter at lower temperatures than temperatures for sintering the
porous sintered body. This makes it possible to provide the
sintered microparticulate layer while retaining the shape of the
sintered wall. For example, the above-described Ni microparticulate
sintered layer can be sintered at 600 degrees Celsius. Also, a Pt
microparticulate sintered layer can be sintered at 100 degrees
Celsius.
[0117] The present invention is not limited to the scope covered by
the embodiments described thus far. For example, while the
embodiments use sheet-like porous bodies, the invention is not
limited by this. Types of the fibriform vanisher material and/or
the powder described do not limit the present invention, either.
Further, in cases where a plurality of powders are used to form a
porous sintered body, these powders may be applied to the fibriform
vanisher material in a single sintering powder application step, or
in a plurality of sintering powder application steps.
INDUSTRIAL APPLICABILITY
[0118] The present invention is capable of providing a porous
sintered body which has a uniform porosity, a high level of freedom
in forming, allowing to be formed into varieties of shapes and
various levels of porosity, and to be formed to an extremely high
level of porosity.
LEGEND
[0119] 1 Porous sintered body [0120] 4 Powder [0121] 2 Fibriform
vanisher material [0122] 5 Core [0123] 6 Sintered wall [0124] 7
Void
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