U.S. patent application number 11/987979 was filed with the patent office on 2008-05-22 for electrode support substrate for solid oxide type fuel cell, and process for producing the same.
Invention is credited to Kazuo Hata, Teruhisa Nagashima, Masatoshi Shimomura.
Application Number | 20080118786 11/987979 |
Document ID | / |
Family ID | 29552342 |
Filed Date | 2008-05-22 |
United States Patent
Application |
20080118786 |
Kind Code |
A1 |
Shimomura; Masatoshi ; et
al. |
May 22, 2008 |
Electrode support substrate for solid oxide type fuel cell, and
process for producing the same
Abstract
Disclosed is an electrode support substrate for a fuel cell
which is even, gives a small fluctuation in gas permeability, and
is capable of carrying out printing of an anodic electrode with
high adhesiveness, and which comprises a ceramic sheet having a
porosity of 20 to 50%, a thickness of 0.2 to 3 mm and a surface
area of 50 cm.sup.2 or more wherein the variation coefficient of
measured values of the gas permeable amounts of areas measured by
the method according to JIS K 6400 ranges from 5 to 20% and further
the surface roughness measured with a laser optical manner
three-dimensional shape measuring device may be 1.0 to 40 .mu.m as
the maximum roughness depth (Rmax) thereof.
Inventors: |
Shimomura; Masatoshi;
(Himeji-shi, JP) ; Nagashima; Teruhisa;
(Himeji-shi, JP) ; Hata; Kazuo; (Suita-shi,
JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
29552342 |
Appl. No.: |
11/987979 |
Filed: |
December 6, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10515227 |
Feb 1, 2005 |
7351492 |
|
|
PCT/JP03/06318 |
May 21, 2003 |
|
|
|
11987979 |
Dec 6, 2007 |
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Current U.S.
Class: |
429/495 ;
429/532 |
Current CPC
Class: |
H01M 2008/1293 20130101;
H01M 4/9033 20130101; H01M 4/8652 20130101; H01M 4/8605 20130101;
H01M 4/9066 20130101; Y02P 70/50 20151101; Y02E 60/50 20130101;
H01M 8/1226 20130101 |
Class at
Publication: |
429/012 |
International
Class: |
H01M 8/02 20060101
H01M008/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 22, 2002 |
JP |
2002-147601(PAT.) |
May 22, 2002 |
JP |
2002-147602(PAT.) |
Claims
1. A electrode support substrate for solid oxide type fuel cell
characterized in comprising a ceramic sheet having a porosity of 20
to 50%, a thickness of 0.2 to 3 mm and a surface area of 50
cm.sup.2 or more, and the variation coefficient of measured values
of the gas permeable amounts of any area of 4 cm.sup.2 selected
optionally from the whole of the surface area of the substrate, the
values being measured by the method according to JIS K 6400, is
from 5 to 20%.
2. The electrode support substrate according to claim 1, wherein a
surface roughness thereof measured with a laser optical manner
three-dimensional shape measuring device is 1.0 to 40 .mu.m as the
maximum roughness depth (Rmax: German Standard "DIN 4768").
3. The electrode support substrate according to claim 1, wherein
height of burrs thereof measured with a laser optical manner
three-dimensional shape measuring device is 1/2 or less of the
thickness of the sheet.
4. The electrode support substrate according to claim 1, wherein
largest height(s) of undulations and/or projections measured with a
laser optical manner three-dimensional shape measuring device
is/are 1/3 or less of a thickness of the sheet.
5-9. (canceled)
10. The electrode support substrate according to claim 2, wherein
height of burrs thereof measured with a laser optical manner
three-dimensional shape measuring device is 1/2 or less of the
thickness of the sheet.
11. The electrode support substrate according to claim 2, wherein
largest height(s) of undulations and/or projections measured with a
laser optical manner three-dimensional shape measuring device
is/are 1/3 or less of a thickness of the sheet.
12. The electrode support substrate according to claim 3, wherein
largest height(s) of undulations and/or projections measured with a
laser optical manner three-dimensional shape measuring device
is/are 1/3 or less of a thickness of the sheet.
13. The electrode support substrate according to claim 4, wherein
largest height(s) of undulations and/or projections measured with a
laser optical manner three-dimensional shape measuring device
is/are 1/3 or less of a thickness of the sheet.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electrode support
substrate for a solid oxide type fuel cell. In particular, the
present invention relates to an electrode support substrate for a
fuel cell, which is even in the size and the distribution situation
of pores all over the surface of the substrate, which is even and
good in the permeability/diffusibility of gas and which makes it
possible that when an electrode or an electrolyte is formed on a
single face of the electrode support substrate by screen printing
or the like, the printed electrode or electrolyte is made excellent
in evenness and adhesion, and to a useful process for producing the
same.
[0002] In this specification, an electrode support substrate
includes an electrode-forming substrate having, on a single face
thereof, a formed anodic electrode layer or a solid electrolyte
film. The substrate has a function as an anodic electrode in itself
and is a support substrate for constituting a cell by forming a
solid electrolyte layer and a cathodic electrode layer successively
on the support substrate itself. In the present invention, these
are referred to as electrode support substrates.
BACKGROUND ART
[0003] In recent years, attention has been paid to fuel cells as
clean energy sources. The use purposes thereof are mainly power
generation for home use, power generation for business, power
generation for automobiles, and others, and researches for
improving the cells and making the cells practicable have been
rapidly advanced.
[0004] A typical structure of solid oxide type fuel cells is
basically a stack obtained by stacking a large number of cells
wherein an anodic electrode is formed on one face side of a planar
solid electrolyte self-supporting film and a cathodic electrode is
formed on the other face side. In order to make the power
generation performance of the fuel cells high, it is effective to
make the solid electrolyte self-supporting film dense and thin.
This is based on the following reason. The solid electrolyte
self-supporting film needs to have denseness for blocking the
mixing of a fuel gas which is a power generation source with air
surely, and an excellent ionic conductivity capable of suppressing
electric conductance loss as much as possible. For this purpose,
the film is required to be as thin and dense as possible. Moreover,
a large stacking-load is imposed on the solid electrolyte
self-supporting film since a fuel cell has a structure wherein a
cell having an anodic electrode, a solid electrolyte
self-supporting film and a cathodic electrode and a separator for
separating and circulating a fuel gas and air are alternately
stacked many times. Additionally, the operation temperature thereof
is about 700 to 1000.degree. C.; thus, the fuel cells receive
considerable thermal stress. Accordingly, the fuel cells are
required to have high-level strength and thermal stress
resistance.
[0005] From the viewpoint of such required properties, a ceramic
sheet made mainly of zirconia is mainly used as the material of the
solid electrolyte self-supporting film for a solid oxide type fuel
cell. A cell, wherein anodic and cathodic electrodes are formed on
both faces of the sheet by screen printing or the like, is
used.
[0006] The present inventors have been advancing research on such
planar solid electrolyte self-supporting films for solid oxide type
fuel cells for some time, and the research has been advanced so as
to aim to make the thickness as small as possible for the purpose
of decreasing ionic conductance loss while keeping physical
properties and shape properties resisting stacking-load or thermal
stress (preventing cracks based on local stress by decreasing
undulations, projections, burrs and others) and, further, so as to
aim to make the surface roughness appropriate for the purpose of
heightening evenness and adhesion of the printed electrode.
Previously, the present inventors suggested techniques disclosed in
JP-A 2000-281438, JP-A 2001-89252, JP-A 2001-10866 and others.
[0007] These techniques made it possible that the solid electrolyte
self-supporting film is largely thin and dense, and further the
strength which resists stacking-load generated when cells are
stacked, the thermal stress resistance, together with the adhesion
and evenness of printed electrodes, are largely improved by
improving the shape property, that is, decreasing undulations,
projections, burrs and others.
[0008] Subsequently, the present inventors have been advancing
research in order to improve the performance of fuel cells. This
time, research has been made to aim to modify the property of
electrode support substrates for support film type cells instead of
the modification of the property of ceramic sheets used as solid
electrolyte self-supporting films. This is based on the following
reason. Ceramic solid electrolyte self-supporting films are more
easily cracked by stacking-load as the films are made thinner;
therefore, there is naturally generated a limitation in making the
films thin and there is generated a limitation in decreasing in the
ionic conductance loss.
[0009] In order to obtain cells having structure strength suitable
for practical use in the case that thin solid electrolyte films are
used therein, electrode support substrates are jointed, as
supporting members for the cells, in between the cells or their
electrodes are caused to have a sufficient thickness. The
substrates have electrical conductivity for electric conduction.
Furthermore, the substrates are made of porous ceramic material
through which a fuel gas that becomes a power generation source,
air, or exhaust gas (carbon dioxide, water vapor and others)
generated by burning these gases can permeate and diffuse, which is
different from the above-mentioned solid electrolyte
self-supporting films.
[0010] In recent years, the following method has also been
investigated. A method of forming an anodic electrode on a porous
electrode support substrate by screen printing, forming a solid
electrolyte film thereon by coating or the like, and further
forming a cathodic electrode thereon by screen printing or the like
to produce a cell, thereby making the solid electrolyte film still
thinner so as to decrease electric conductance loss still more.
[0011] The most important theme when such a method is realized is
that a cell has even and excellent gas permeability/diffusibility
throughout its electrode support substrate. This is because this
support substrate must be a porous substrate having pores
sufficient for allowing a fuel gas and others to permeate and
diffuse through the substrate. Further, the substrate is desired to
have an even distribution state of the pores in such a manner that
the gas can permeate and diffuse evenly through the whole of the
substrate.
[0012] Another property desired for the electrode support substrate
is that a superior printing adaptability is given to the surface
thereof so that an electrode wherein the number of defects is as
small as possible can be printed. As described above, the electrode
support substrate is required to have an appropriate electrical
conductivity. Further, the substrate must be a porous substrate
having pores sufficient for allowing a fuel gas and others to
permeate and diffuse through the substrate. Thus, numerous openings
are present in the surface thereof. Therefore, in order to make
superior electrode-printing possible in spite of the presence of
such openings, it is indispensable to clarify surface properties
peculiar to the porous electrode support substrate since the
surface properties prescribed about the above-mentioned dense solid
electrolyte film cannot be applied, as they are, to the porous
electrode support substrate.
[0013] Still another property desired for the electrode support
substrate is that the shape property of the support substrate
itself is improved so that burrs, projections, undulations and
others, which become stress-concentrated spots when they receive
stacking-load or thermal shock, are made as small as possible. This
is based on the following reason. As described above, the electrode
support substrate is required to have an appropriate electrical
conductivity. Further, the substrate must be a porous substrate
having pores sufficient for allowing a fuel gas and others to
permeate and diffuse through the substrate; thus, numerous openings
are present in the surface thereof. Therefore, in order to restrain
the support substrate, even admitting that the substrate is such a
porous sheet, from being cracked or damaged by local stress
concentration caused when it receives stacking-load, it is
necessary to restrain the generation of burrs, which are formed at
its internal and external circumferential edges at the time of
punching, and projections or undulations, which may be formed
inside the substrate, as much as possible. Furthermore, the
electrode support substrate which is intended in the present
invention must be a porous body through which a gas can permeate
and diffuse. Therefore, the shape property effective for the
printability of a dense sheet, such as a solid electrolyte film,
and effective for the prevention of stress concentration thereon
cannot be applied, as it is, to the electrode support
substrate.
[0014] The present invention has been made, paying attention to a
situation as described above. An object thereof is to provide an
electrode support substrate to which electrode or a solid
electrolyte film may be applied by screen printing. The substrate
has the following characteristics. The entire surface of the
substrate is stable against a fuel gas and others; the substrate
has superior gas permeability/diffusibility. The substrate is able
to form a printed electrode and a solid electrolyte film that are
even and closely adhesive. The substrate has such a shape property
that even if a plurality of the substrates are laminated into a
cell stack and each of the substrates receives a large
stacking-load, the substrate is not easily cracked or damaged by
local stress concentration.
DISCLOSURE OF THE INVENTION
[0015] The subject matter of the electrode support substrate of the
present invention for a fuel cell, which has solved the
above-mentioned problems, is that the substrate comprises a ceramic
sheet having a porosity of 20 to 50%, a thickness of 0.2 to 3 mm
and a surface area of 50 cm.sup.2 or more, and the variation
coefficient of measured values of the gas permeable amounts of any
area of 4 cm.sup.2 selected optionally from the whole of the
surface area of substrate, the values being measured by the method
according to JIS K 6400, is from 5 to 20%.
[0016] The electrode support substrate of the present invention for
a fuel cell preferably satisfies the following as a requirement for
obtaining superior adhesion and evenness when an anodic electrode
and so on are printed and formed on the surface of substrate, as
well as the above-mentioned requirement: the surface roughness
measured with a laser optical manner three-dimensional shape
measuring device is 1.0 to 40 .mu.m as the maximum roughness depth
(Rmax: German Standard "DIN 4768") thereof.
[0017] Furthermore, the electrode support substrate of the present
invention for a solid oxide type fuel cell is used in a
multi-layered and laminated state, as described above; therefore,
in order to suppress cracking or breaking based on stacking-load as
much as possible when the substrate is used, it is desired that
height of burrs measured with the laser optical manner
three-dimensional shape measuring device is 1/2 or less of the
thickness of the sheet. Further, it is desired that largest
height(s) of undulations and/or projections measured with the same
laser optical manner three-dimensional shape measuring device
is/are 1/3 or less of the thickness of the sheet.
[0018] The producing process of the present invention is placed as
a producing process making it possible to obtain surely an
electrode support substrate for a fuel cell, in particular, an
electrode support substrate for a fuel cell which satisfies the
above-mentioned properties. Above process has a feature in: using,
as a slurry for producing a green sheet which becomes a ceramic
precursor, a slurry which comprises an conductive component powder,
an skeleton component powder, a pore-forming agent powder, and a
binder, defoamed under reduced pressure after milling to adjust the
viscosity thereof to 40 to 100 poise (25.degree. C.), and kept at
room temperature while rotating stirring fans therein at a rotating
speed of 5 to 30 rpm for 20 to 50 hours; fashioning the slurry into
a sheet by a doctor blade method to obtain a green sheet; cutting
the green sheet into a given shape; and then firing the green sheet
having the given shape.
[0019] When the producing process is carried out, it is desired to
use, as the slurry for producing the green sheet, a slurry wherein
its particle size distribution has a peak in each of ranges of 0.2
to 2 .mu.m and 3 to 50 .mu.m and the content ratio by mass of fine
particles in the range of 0.2 to 2 .mu.m to coarse particles in the
range of 3 to 50 .mu.m is in a range of 20/80 to 90/10. Further, it
is preferred to use a slurry containing 5 to 30 parts by mass of
the binder and 2 to 40 parts by mass of the pore-forming agent
powder with respect to 100 parts by mass of the total of the
conductive component powder and the skeleton component powder.
[0020] In order to obtain the electrode support substrate
satisfying the above-mentioned preferred height of burr and
preferred height of undulation and/or projection, which is intended
in the present invention, it is desired that when the green sheet
is punched into a shape used as product, a punching blade having a
waver-form blade edge is used. It is more preferred to use the
punching blade which the angle (.alpha..sub.1), (.alpha..sub.2),
(.theta..sub.1) and (.theta..sub.2) thereof satisfy the following
relationship: .alpha..sub.1=30 to 120.degree.,
20.degree..ltoreq..alpha..sub.2=.theta..sub.1+.theta..sub.2.ltoreq.70.deg-
ree., and .theta..sub.1.ltoreq..theta..sub.2, the angle
(.alpha..sub.1) meaning of angle being viewed from the side face of
the wave-form blade, the angle (.alpha..sub.2) meaning of blade
edge angle of the cross section of the blade, the angle
(.theta..sub.1) meaning of angle made between the surface thereof
on the side of the sheet becoming a product and a center line (x)
passing through the blade edge, the angle (.theta..sub.2) meaning
of angle made between the surface thereof on the side of the rest
of the sheet and the center line (x) passing through the blade
edge. According to this, height of undulations and/or projections
and/or burrs can be favorably suppressed into as low a value as
possible.
BRIEF DESCRIPTION OF THE INVENTION
[0021] FIG. 1 is a frequency graph illustrating a preferred
particle size distribution of a slurry, for producing a green body,
which is preferably used upon producing an electrode support
substrate for a fuel cell according to the present invention;
[0022] FIG. 2 is an explanatory sectional view illustrating the
shape of a burr formed on an electrode substrate, which is measured
with a laser optical manner three-dimensional shape measuring
device;
[0023] FIG. 3 is an explanatory enlarged view illustrating a
projection which may be generated in the surface of an electrode
substrate, which is measured with a laser optical manner
three-dimensional shape measuring device; and
[0024] FIG. 4 is an explanatory view illustrating an undulation
which may be generated in the whole of an electrode substrate,
which is measured with a laser optical manner three-dimensional
shape measuring device.
[0025] FIG. 5 is a view showing an example of the particle size
distribution of a slurry which is preferably used upon producing a
green body which becomes a precursor of an electrode substrate
according to the present invention;
[0026] FIG. 6 is an explanatory side view illustrating the blade
edge shape of a preferred punching blade used to punch a green
sheet upon producing an electrode substrate for a fuel cell
according to the present invention;
[0027] FIG. 7 is an explanatory sectional view illustrating the
blade edge shape of a preferred punching blade used to punch a
green sheet upon producing an electrode substrate for a fuel cell
according to the present invention;
[0028] FIG. 8 is an explanatory sectional view illustrating a
preferred example expect FIG. 7 of a punching blade used in the
present invention;
[0029] FIG. 9 is an explanatory schematic sectional view showing
the structure of a punching machine adopted preferably in the
present invention and a punching work example;
[0030] FIG. 10 is an explanatory schematic sectional view showing
the structure of the punching machine adopted preferably in the
present invention and the punching work example;
[0031] FIG. 11 is an explanatory schematic sectional view showing
the structure of the punching machine adopted preferably in the
present invention and the punching-work example; and
[0032] FIG. 12 is an explanatory view showing an outline of a gas
permeation resistance measuring device used in examples of the
present invention.
1: blade edge portion, h: height of blade, p: pitch of blade edge,
t: thickness of blade, and .alpha..sub.1, .alpha..sub.2,
.theta..sub.1 and .theta..sub.2: angle of blade edge
BEST MODE FOR CARRYING OUT THE INVENTION
[0033] The present inventors have been advancing research for
providing an electrode support substrate which can surely obtain a
printed electrode that is particularly dense, even and closely
adhesive while gas permeability/diffusibility necessary for a
practical electrode support substrate is kept under the
above-mentioned themes to be solved.
[0034] As a result, it has been found out that a ceramic sheet
having a porosity of 20 to 50%, a thickness of 0.2 to 3 mm and a
surface area of 50 cm.sup.2 or more, as a ceramic constituting a
substrate. The substrate satisfies the following: the variation
coefficient of measured values of the gas permeable amounts of any
areas of 4 cm.sup.2 selected optionally from the whole of the
surface area, the values being measured by the method according to
JIS K 6400, is from 5 to 20% is substantially even in the state of
pore distribution throughout the substrate for supporting an
electrode, and can exhibit stable and superior gas
permeability/diffusibility.
[0035] The electrode support substrate of the present invention is
essentially a porous substrate having electrical conductivity,
superior thermal shock resistance and mechanical strength and
further having sufficient gas permeability/diffusibility, as
described above. The specific structure of the electrode support
substrate which can satisfy these requirements will be described in
detail hereinafter.
[0036] The electrode support substrate comprises, as main
constituting materials, a conductive component for giving
electrical conductivity, and a ceramic material which becomes a
skeleton component of a substrate. The conductive component is a
component essential for giving electrical conductivity to the
substrate. Examples of the component which becomes a component of
an anodic electrode support substrate include metals oxides which
are changed to conductive metals under reducing atmosphere when the
fuel cell operates, such as iron oxide, nickel oxide and cobalt
oxide; metal oxides which exhibit electrical conductivity in
reducing atmosphere, such as ceria, yttria-doped ceria,
samaria-doped ceria, prasea-doped ceria, and gadolia-doped ceria;
and noble metals which exhibit electrical conductivity, such as
platinum, palladium, and ruthenium. These may be used alone, or may
be used in combination of two or more which are appropriately
selected therefrom if necessary. Of these conductive components,
nickel oxide has the highest wide-usability, considering cost or
electrical conductive characteristics.
[0037] The skeleton component is a component important for keeping
strength necessary for an electrode support substrate, in
particular, strength which resists thermal shock and stacking-load
and further important for relieving difference in thermal expansion
from the solid electrolyte. In the case that the solid electrolyte
is zirconia, a single material or a composite material from
zirconia, alumina, magnesia, titania, aluminum nitride, mullite and
others are used. Of these, stabilized zirconia has the highest
wide-usability. Preferred examples of the stabilized zirconia
include solid solutions obtained by dissolving, into zirconia, one
or more oxides selected from the following as a stabilizer or
stabilizers: oxides of alkaline earth metals, such as MgO, CaO, SrO
and BaO; oxides of rear earth elements, such as Y.sub.2O.sub.3,
La.sub.2O.sub.3, CeO.sub.2, Pr.sub.2O.sub.3, Nd.sub.2O.sub.3,
Sm.sub.2O.sub.3, Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Tb.sub.2O.sub.3,
Dy.sub.2O.sub.3, Er.sub.2O.sub.3, Tm.sub.2O.sub.3, and
Yb.sub.2O.sub.3; and Sc.sub.2O.sub.3, Bi.sub.2O.sub.3, and
In.sub.2O.sub.3. Additional preferred examples include dispersion
strengthened zirconia wherein a dispersing strengthening agent such
as alumina, titania, Ta.sub.2O.sub.5 or Nb.sub.2O.sub.5 is added to
the above-mentioned solid solutions.
[0038] There can also be used a ceria based or bismuth based
ceramic wherein one or more of the following are added to CeO.sub.2
or Bi.sub.2O.sub.3: CaO, SrO, BaO, Y.sub.2O.sub.3, La.sub.2O.sub.3,
Ce.sub.2O.sub.3, Pr.sub.2O.sub.3, Nb.sub.2O.sub.3, Sm.sub.2O.sub.3,
Eu.sub.2O.sub.3, Gd.sub.2O.sub.3, Tb.sub.2O.sub.3, Dr.sub.2O.sub.3,
Ho.sub.2O.sub.3, Er.sub.2O.sub.3, Yb.sub.2O.sub.3, PbO, WO.sub.3,
MoO.sub.3, V.sub.2O.sub.5, Ta.sub.2O.sub.5 and Nb.sub.2O.sub.5; or
a gallate based ceramic such as LaGaO.sub.3.
[0039] Of these, particularly preferable are zirconia stabilized
with 2.5 to 12% by mole of yttria, or zirconia stabilized with 3 to
15% by mole of scandia.
[0040] The content blend between the conductive component and the
skeleton component is important for giving appropriate electrical
conductivity and strength property to the resultant electrode
support substrate. When the amount of the conductive component
becomes relatively large, the electrical conductivity of the
substrate is improved but the strength property lowers since the
amount of the skeleton component becomes relatively small.
Conversely, when the amount of the conductive component becomes
relatively small, the strength property becomes high because of an
increase in the amount of the skeleton component. Thus, the blend
ratio between the two should be appropriately decided under the
consideration of the balance between the above-mentioned matters.
The ratio is changed on the basis of the kind of the conductive
component, and others, but it is preferable in the present
invention, which mainly aims at an anodic electrode support
substrate, that the ratio of the skeleton component amount to the
conductive component amount is in the range of 60-20 to 40-80% by
mass, more generally 50-30 to 50-70% by mass.
[0041] The electrode support substrate of the present invention
comprises a conductive component and a skeleton component, as
described above. The mechanical strength and thermal stress
resistance thereof are kept by the skeleton component, and
electrical conductivity is given to the substrate by the conductive
component. The electrode support substrate, which is made of them,
needs to have pores through which a fuel gas or a burning exhaust
gas permeates or diffuses, as described above. In order to pass
these gases smoothly under low pressure loss, it is indispensable
that the substrate has a porosity of 20% or more as a whole under
oxidizing atmosphere. If the porosity is less than 20%, the gases
permeate or diffuse insufficiently so that the efficiency of power
generation falls. The porosity is more preferably 25% or more, even
more preferably 30% or more.
[0042] However, if the porosity is too large, the strength property
and thermal stress resistance of the substrate lower so that the
following tendencies are generated: when the substrate is
integrated into a stack, the substrate is easily cracked or
deteriorated by staking-load, thermal shock or the like; or the
distribution state of the conductive component becomes thin so that
the substrate has an insufficient electrical conductivity.
Therefore, it is advisable that the porosity is restrained into 50%
or less at highest, preferably 45% or less, more preferably 40% or
less.
[0043] It is indispensable that the thickness of the electrode
support substrate of the present invention is in the range of 0.2
to 3 mm. If the thickness is less than 0.2 mm, the substrate is too
thin so that the substrate does not easily keep strength for a
practical electrode support substrate. On the other hand, if the
substrate is made excessively thick to make the thickness into more
than 3 mm, the strength is improved but when a large number of the
electrode support substrates are laminated to be made practicable
as a cell stack, the whole of the laminated structure becomes
thick. The structure is not easily suitable for a desire that the
structure is made compact as a power generator. When the electrode
support substrate is made practicable as a substrate for a fuel
cell, the thickness thereof is more preferably 0.3 mm or more and 2
mm or less.
[0044] The size of the electrode support substrate according to the
present invention, which depends on the use purpose or scale
thereof, is important for ensuring electric power generation at a
level satisfactory for practical use. For this purpose, the
substrate should ensure a necessary and minimum surface area. It is
desired that the substrate ensures a sheet area (surface area on a
single side thereof) of 50 cm.sup.2 or more, more preferably 100
cm.sup.2 or more.
[0045] It is essential that the electrode support substrate
satisfies the following: under the conditions that the
above-mentioned porosity, thickness and surface area are satisfied,
the above-mentioned variation coefficient of the measured values of
the gas permeable amounts of any plural areas of 4 cm.sup.2
selected optionally from the whole of the surface area of the
substrate ranges from 5 to 20%, and the substrate exhibits
substantially even gas permeability/diffusibility as a whole.
[0046] In order to pass a fuel gas or a reaction-produced gas
rapidly into the electrode support substrate, it is naturally
preferred that the whole of the substrate has even gas
permeability/diffusibility as a whole. For this purpose, it is
desired that the distribution state of pores throughout the
substrate is even.
[0047] However, only by measuring the porosity of the whole, it is
impossible to specify whether the pores are pores continuing to the
inside of the substrate or pores which are closed inside the
substrate. Thus, the porosity may be insufficient as information on
permeability.
[0048] Permeability is an important factor as a physical property
of any electrode support substrate. The permeability thereof has
been repeatedly investigated, so as to find out: when the gas
permeable amounts of any specified areas in the entire surface area
of a substrate fluctuate, a fuel gas is unevenly distributed in the
entire surface of the substrate to generate locally regions where
electric power generation is large and regions where electric power
generation is small, so that a temperature distribution is
generated to cause the generation of a crack in the substrate; and
the specification of the fluctuation causes the electrode support
substrate to exhibit excellent property for a practical electrode
support substrate.
[0049] The size of any electrode support substrate for a solid
oxide type fuel cell is expected to be from about 50 to 1000
cm.sup.2, more generally about 100 to 500 cm.sup.2 for practical
use. Therefore, a standard for checking the evenness of the
distribution state of pores throughout the substrate has been
defined as 4 cm.sup.2, which is 1/10 or less of the minimum area 50
cm.sup.2 of the substrate, considering the minimum area. In the
case that the area to be measured is made smaller, the distribution
state of the pores throughout the substrate can be observed. Thus,
this case is preferred. However, even if an area having each side
of 1.5 cm length (area: 2.25 cm.sup.2) was measured, a significant
different between the measurement results and the measurement
results about 4 cm.sup.2 was not recognized. In the measurement of
the gas permeability distribution, it is preferable that at least
five spots are selected optionally from the entire surface of a
supplied substrate and then the gas permeable amounts thereof are
measured. In the present invention, the variation coefficient of
measured values of the gas permeable amounts obtained by this
method is specified as 5 to 20%.
[0050] Any one of the gas permeable amounts is a value measured
according to gas permeable amount measuring method of JIS K 6400
(1997) about soft urethane foam testing methods. Specifically, a
stationary flow differential pressure measuring method is adopted
which comprises cutting a substrate into a piece 3 cm square (area:
9 cm.sup.2) with a diamond cutter, reducing the pressure on a
single surface side (low pressure side) of this test piece,
introducing air onto the other surface side thereof, and measuring
the gas permeable amount by an increase in the pressure on the low
pressure side. Both ends of the test piece are used by 0.5 cm,
respectively, to hold the test piece, thereby yielding an effective
gas permeable area of 4 cm.sup.2. As the resultant gas permeable
amount data of the supplied substrate, the variation coefficient is
used which is obtained by obtaining the standard deviation for
representing the fluctuation or scattering of measured values of
the gas permeable amount relatively, and then dividing it by the
average thereof.
[0051] In the present invention, the variation coefficient is
specified as 5 to 20%, more preferably 5 to 15%, even more
preferably 5 to 13%. For reference, if the variation coefficient
exceeds 20%, the substrate is cracked or broken in almost all
cases. It appears that this is based on the following reason: when
a fuel gas permeates through the inside of the substrate, the gas
cannot pass evenly to be unevenly distributed so that the fuel gas
reaching the vicinity of the electrolyte becomes uneven dependently
on spots; consequently, regions where electric power generation is
large and regions where this is small can be locally generated so
that a temperature distribution is generated.
[0052] If the gas permeable amount in the substrate is completely
constant over the entire surface thereof, the variation coefficient
is 0%. However, the variation coefficient obtained by the
above-mentioned method is 5% at lowest; therefore, this is decided
as the lower limit for practical use.
[0053] In the present invention, it is desired that the
distribution state of the pores throughout the substrate is even
and further it is preferable that the size of the pores is 3 .mu.m
or more and 20 .mu.m or less as the average diameter thereof. If
the average diameter of the pores is less than 3 .mu.m, the gas
permeability/diffusibility are insufficient so that the same
problems as in the case that the porosity is insufficient may be
caused. Conversely, if the average diameter is too large, the
strength tends to deteriorate and the electrical conductivity tends
to be insufficient in the same manner as in the case that the
porosity is excessive. Therefore, it is preferable to suppress the
diameter into 20 .mu.m or less.
[0054] The porosity of the substrate, the variation coefficient of
measured values of the gas permeable amounts, and the preferable
average diameter of the pores can be adjusted by the kind and the
blend amount of a pore-forming agent used when the substrate is
produced, the particle size construction of starting material
powder, the temperature at the time of firing a green sheet which
will become a substrate precursor, and others. Specific methods
thereof will be described later.
[0055] As described, an anodic electrode or an electrolyte layer is
formed on a single surface of the electrode support substrate of
the present invention by screen printing or the like. In order to
make the electrode or electrolyte printing even and sure with close
adhesion, it is necessary to control the surface thereof into an
appropriate surface roughness. The present inventors have made it
evident by experiments that the maximum roughness depth (Rmax:
German Standard "DIN 4768") thereof is set to 1.0 .mu.m or more and
40 .mu.m or less. Furthermore, in the electrode support substrate
of the invention, which is porous in order to ensure the gas
permeability/diffusibility thereof, whether the surface property is
good or bad cannot be precisely estimated according to the surface
roughness obtained by using a contact type surface roughness meter
which is generally adopted for dense sheets. Thus, it is desired
that the surface is made to satisfy the above-mentioned Rmax on the
basis of the surface roughness measured with a laser optical manner
three-dimensional shape measuring device.
[0056] If the Rmax is less than 1.0 .mu.m, the surface is too
smooth so that the electrode printing tends to be insufficient in
close adhesion. Thus, it is feared that the printed electrode layer
is peeled from the substrate by thermal shock receiving when the
fuel cell is handled or operated. Additionally, the gas
permeability/diffusibility tend to turn insufficient. On the other
hand, if the Rmax exceeds 40 .mu.m, the thickness of the electrode
layer becomes uneven when the electrode is printed, or a part of
the electrode-constituting material is embedded in concave portions
in the surface. Thus irregularities are formed in the electrode
layer surface to result in an increase in electric conductance
loss. Furthermore, a crack may be generated in the electrode layer
when the electrode-constituting material is fired or the resultant
cell is used as a fuel cell. In order to decrease the electric
conductance loss as much as possible and heighten the close
adhesion of the printed electrode layer, the Rmax is more
preferably 0.2 .mu.m or more and 30 .mu.m or less, even more
preferably 20 .mu.m or less.
[0057] The reason why the laser optical manner three-dimensional
shape measuring device, which is of a non-contact type, is used in
the present invention to evaluate the surface roughness is based on
the following. In the case of the electrode support substrate of
the invention, which is porous and has a surface on which
innumerable pores are opened, the surface roughness is not smoothly
and easy measured with any surface roughness meter of a contact
type, such as a stylus type, since the stylus is caught by the
pores; moreover, the surface roughness cannot be precisely measured
in the contact manner since the pores opened in the surface are
relatively deep.
[0058] At any rate, in the present invention, the variation
coefficient of measured values of the gas permeable amounts, which
is obtained by the above-mentioned method, is from 5 to 20%, and
further the maximum roughness depth (Rmax) is preferably made into
an appropriate range. Thereby make it possible to print an
electrode on surface of substrate, substrate is porous and have
even in thickness, which has even gas permeability/diffusibility in
the entire surface thereof not to cause any uneven gas flow or any
extreme temperature distribution when the electrode is operated,
and which has a highly close adhesion. In order to ensure such
evenness of the gas permeability/diffusibility and an appropriate
surface roughness, it is necessary to control properly the particle
size construction of starting material powder used to produce a
green sheet which will become a precursor of the ceramic which
constitutes the electrode support substrate, conditions for
producing or firing the green sheet, and others. These will be
described later.
[0059] Since a large number of the electrode support substrates of
the invention are laminated in the upper and lower directions so as
to be integrated into a stack as described above, the stack is
subjected to a large stacking-load and further receives thermal
shock or thermal stress based on heat generated when the stack is
operated. Therefore, even if a slight number of burrs or
projections are present on the lamination faces, stress is
concentrated on the portions thereof so that cracking or breaking
may be caused. When such cracking or breaking is generated in the
substrates, the cracking spreads to the anodic electrodes and
others formed on the surfaces so that the electrical conductivity
thereof is blocked. If the cracking or breaking spreads to the
solid electrolyte film, the effect of shielding the fuel gas and
others is lost so that the stack comes not to act as a fuel cell.
If the burrs, projections or undulations on the substrate
surface(s) become large, the anodic layers and the solid
electrolyte layer(s) formed on the surfaces become uneven and
further the adhesion of the layers to the substrates becomes poor.
It is therefore desired that the burrs generated to the
circumferential edges of the substrates are made as small as
possible and further the projections or undulations on the
substrate surfaces are preferably made as small as possible,
thereby restraining local stress concentration generated in the
lamination state into as small a value as possible.
[0060] The present inventors has made it evident by experiments
that: a substrate sheet wherein height of burrs in the
circumferential edge thereof, measured with a laser optical manner
three-dimensional shape measuring device, is 1/2 or less of the
thickness of the sheet, the height of the largest projection
measured with the same laser optical manner three-dimensional
shape, measuring device, is preferably 1/3 or less of the sheet
thickness, and the height of the largest undulation, measured with
the same laser optical manner three-dimensional shape measuring
device, is 1/3 or less of the sheet thickness. The substrate sheet
exhibit stable and have superior resistance against stacking-load,
thermal shock resistance, and thermal stress resistance. Further
the substrate sheet can have superior performance about printing
adaptability when an electrode is formed or a solid electrolyte
film is formed thereon.
[0061] If the height of the burrs in the substrate circumferential
edge exceeds 1/2 of the sheet thickness, at the time of using this
substrate as one element and integrating the substrate into a
stack, stress based on integrating force or stacking-load is
concentrated onto the large burr. Consequently, before the stack is
operated as a fuel cell, the substrate is broken or cracked
together with the electrode layers or solid electrolyte films
thereon. Alternatively, the stress-concentrated portions are
cracked or broken by receiving thermal hysteresis when the stack is
operated even if cracks and others are not generated at the time of
the integration. Thus, the power generation performance of the fuel
cell is remarkably decreased. However, it has been made evident
that: a substrate wherein the burr height is 1/2 or less of the
sheet thickness, more preferably 1/3 or less thereof, even more
preferably 1/4 or less thereof is hardly cracked or broken even if
the substrate receives stacking-load or thermal stress at a
practical level; and this substrate can use as substrate for a fuel
cell which can maintain a given power-generating performance for a
long term.
[0062] The burr height in the present invention means the
difference between the highest portion and the lowest portion in a
section in a perpendicular line direction from the external
circumferential (or internal circumferential) edge of a cut face of
a substrate, and can be obtained with a laser optical manner
three-dimensional shape measuring device, which is of a non-contact
type, as illustrated, for example, in FIG. 1.
[0063] At any rate, when the burr height obtained by the
above-mentioned method is restrained into 1/2 or less of the sheet
thickness in the present invention, local stress concentration
based on load or thermal shock in the laminated state is suppressed
into a minimum so that the generation of cracking or breaking can
be suppressed into a minimum. In order to obtain such a surface
roughness, it is important to contrive a blade shape when a green
sheet which becomes a ceramic precursor constituting the electrode
substrate is subjected to punching work. This will be described
later.
[0064] In the present invention, it is desired to make the height
of the largest projection or the largest undulation on the
substrate surface, besides the burr height, as small as possible.
The standard thereof is as follows: in order to restrain stress
concentration when stacking-load is received and restrain cracking
or breaking similarly and further make even an electrode layer or a
solid electrolyte film formed on the electrode surface, the largest
projection height, measured with the same laser optical manner
three-dimensional shape measuring device, is desirably set to 1/3
or less of the sheet thickness, more preferably 1/4 or less
thereof, even more preferably 1/5 or less thereof and the largest
undulation height is desirably set to 1/3 or less of the sheet
thickness, more preferably 1/4 or less thereof, even more
preferably 1/5 or less.
[0065] The projections mean convex portions which are basically
independently generated on the surface of the electrode sheet and
have a diameter of about 2 to 15 mm (more generally 5 to 10 mm),
for example, as illustrated in FIG. 2, and the undulations mean
distortion which is easily generated on the electrode sheet, in
particular, a circumferential edge portion thereof and which is
continuous into a wave form, for example, as illustrated in FIG. 3.
These can be obtained by radiating a laser ray onto the surface of
the sheet and analyzing the light reflected thereon
three-dimensionally.
[0066] The shape of the ceramic sheet which constitutes the
electrode support substrate of the present invention may be any
shape, such as a circle, ellipse, rectangle, or rectangle having a
roundish corner, and may be a shape wherein such a sheet has
therein one or more holes which have a shape of a similar circle,
ellipse, rectangle or rectangle having a roundish corner, or some
other shape. The area of the sheet is not particularly limited, and
is generally 50 cm.sup.2 or more, more preferably 100 cm.sup.2 or
more, even more preferably 200 cm.sup.2 or more under the
consideration of practical use. When the holes are present in the
sheet, this area means the total area including the area of the
holes.
[0067] The following describes a process for producing an electrode
support substrate according to the present invention.
[0068] About the electrode support substrate of the present
invention, a powder made of a metal or metal oxide which becomes
the above-mentioned conductive component, a metal oxide powder
which becomes the skeleton component, and a pore-forming agent
powder blended for making pores are homogeneously mixed with an
organic or inorganic binder, a dispersing medium (solvent), an
optional dispersing agent, an optional plasticizer and others in
the same method as described above, so as to prepare a paste. The
resultant paste is applied onto a flat and smooth sheet (such as a
polyester sheet) by any method such as a doctor blade method, a
calendar roll method or an extruding method, so as to have an
appropriate thickness. The resultant is dried to volatilize and
remove the dispersing medium (solvent), thereby yielding a green
sheet.
[0069] The pore-forming agent used herein may be an agent of any
kind if the agent is burned up under the above-mentioned firing
conditions. The following is used: a natural organic powder such as
wheal powder, corn starch, sweet potato powder, potato powder or
tapioca powder, a crosslinked fine particle aggregate made of
(meth)acrylic resin or the like, a thermally-decomposing or
sublimating resin powder of melamine cyanurate, or a carbonous
powder such as carbon black or activated carbon Of these,
preferable are corn starch, the acrylic crosslinked fine particle
aggregate, carbon black and so on since they can carry and contain
a large amount of the conductive component as described later.
[0070] The shape of these pore-forming agent powders is desirably a
spherical shape or a rugby ball shape in order to cause a large
amount of the conductive component to be carried and contained
therein and promote an even distribution of the conductive
component into the ceramic substrate obtained by firing.
Preferably, the powder or fine particle aggregate itself has pores
or capillaries so as to cause the conductive component to be
contained in the powder or the fine particle aggregate.
[0071] A preferable particle size of the powder or the crosslinked
fine particle aggregate which become the pore-forming agent is 0.5
to 100 .mu.m, more preferably 3 to 50 .mu.m as the average particle
size thereof measured with a laser diffraction type particle size
distribution meter (trade name: "SALD-1100", manufactured by
Shimadzu Corp.), and is 0.1 to 10 .mu.m, more preferably 1 to 5
.mu.m as the 10% by volume diameter thereof.
[0072] Particularly preferable is a fine particle aggregate of 0.5
to 100 .mu.m average particle size, wherein crosslinked polymer
fine particles of 0.01 to 30 .mu.m average particle size aggregate
with each other, the fine particle aggregate being obtained by
emulsion-polymerizing a (meth)acrylic monomer, as disclosed in, for
example, JP-A 2000-53720.
[0073] In the present invention, the pore-forming agent may be
mixed with each of the above-mentioned starting powders to prepare
slurries for forming the green sheet. It is however effective to
mix or compound the pore-forming agent and the above-mentioned
conductive component and subsequently mix the resultant with the
other staring materials. That is, the following method can be
adopted:
[0074] (1) a method of blending the conductive component powder or
a precursor compound thereof with the pore-forming agent at a given
ratio, and wet-mixing or dry-mixing the blended components, thereby
sticking the conductive powder or the precursor compound evenly
onto the surface of the pore-forming powder,
[0075] (2) a method of sticking the conductive component powder or
a precursor compound evenly onto the surface of the pore-forming
agent by a spray method or the like, and
[0076] (3) a method of incorporating the conductive component
powder or a precursor compound thereof into pores or gaps in a fine
particle aggregate for forming pores.
[0077] More specifically, it is possible to modify a method as
disclosed in JP-A 07-22032 (1995) and adopt a method of mixing the
pore-forming agent powder with a precursor compound which can
generate an conductive component by thermal decomposition, and
volatilizing the solvent while dry-pulverizing the mixture in a
mill or the like, or volatilizing the solvent while wet-pulverizing
the mixture, or some other method.
[0078] It is preferable to adopt a method as disclosed in JP-A
2000-53720 or JP-A 2001-81263 or some other method. It is
emulsion-polymerized a (meth)acrylic polymerizable monomer mixture
to produce a fine particle aggregate of 0.5 to 100 .mu.m average
particle size wherein crosslinked polymer fine particles of 0.01 to
30 .mu.m average particle size adhere to each other. The fine
particle aggregate mix with a precursor compound which can generate
an conductive component by thermal decomposition, causing these to
enter gaps in the fine particle aggregate, and then drying the
resultant to volatilize and remove the solvent.
[0079] When the pore-forming agent into which the conductive
component is incorporated is used in this way, the following
advantageous effects can be obtained: the pore-forming agent is
burned up when the green sheet is fired, so that pores are made in
the portions thereof when the conductive component is also present
in the portions, the pores are present near the conductive
component after the firing; and even if the conductive component is
oxidized to undergo volume expansion at the time of making the
substrate practicable as an electrode support substrate for a fuel
cell, the above-mentioned pore portions absorb strain generated by
the volume expansion so that the generation of breaking or
cracking, which may easily be caused in the electrode support
substrate, is prevented. As a result, in particular, the thermal
shock resistance and the thermal stress resistance of the electrode
support substrate can be made high.
[0080] The pore-forming agent is an important component, which is
burned up at the time of the heating and firing as described above
so as to give gas permeability/diffusibility to the electrode
support substrate. In order to ensure a porosity of 20% or more and
50% or less, which is desired for the porous body in the present
invention, it is desired that the blend amount of the pore-forming
agent is set to 2 parts or more and 40 parts or less, more
preferably 5 parts or more and 30 parts or less by mass for 100
parts by mass of the total of the conductive component powder and
the skeleton component powder. If the blend amount of the
pore-forming agent is insufficient, pores made by thermal
decomposition when the green sheet is heated and fired tend to be
short so that an electrode support substrate having satisfactory
gas permeability/diffusibility is not easily obtained. Conversely,
if the blend amount of the pore-forming agent is too large, the
number of the pores made at the time of the heating and firing
becomes excessively large so that the sintered product becomes
sufficient in strength and further a flat substrate is not easily
obtained In this case, it is possible to advance the sintering and
lower the porosity by making the sintering temperature high or
extending the sintering time. However, this is not economical since
a long time is required for the sintering and further energy
consumption also increases to a large extent.
[0081] The kind of the binder used in the production of the green
sheet is not particularly limited, and a binder selected
appropriately from organic binders which have been known hitherto
can be used. Examples of the organic binders include ethylene type
copolymer, styrene type copolymer, acrylate or methacrylate type
copolymer, vinyl acetate type copolymer, maleic acid type
copolymer, vinyl butyral type resin, vinyl alcohol type resin,
waxes, and ethyl celluloses.
[0082] Of these, the following examples are given from the
viewpoints of the formability into a green sheet, punchability,
strength, thermal decomposability when they are fired, and others:
polymers obtained by polymerizing or copolymerizing at least one of
alkyl acrylates having an alkyl group having 10 or less carbon
atoms, such as methyl acrylate, ethyl acrylate, propyl acrylate,
butyl acrylate, isobutyl acrylate, cyclohexyl acrylate, and
2-ethylhexyl acrylate; alkyl methacrylates having an alkyl group
having 20 or less carbon atoms, such as methyl methacrylate, ethyl
methacrylate, butyl methacrylate, isobutyl methacrylate, octyl
methacrylate, 2-ethylhexyl methacrylate, decyl methacrylate,
dodecyl methacrylate, lauryl methacrylate, and cyclohexyl
methacrylate; acrylates or methacrylates having a hydroxyalkyl
group, such as hydroxyethyl acrylate, hydroxypropyl acrylate,
hydroxy methacrylate, and hydroxypropyl methacrylate; aminoalkyl
acrylates or aminoalkyl methacrylates, such as dimethylaminoethyl
acrylate, and dimethylaminoethyl methacrylate; carboxyl-containing
monomers, such as acrylic acid, methacrylic acid, maleic acid, and
monoisopropyl maleate. These may be used alone. Alternatively, if
necessary, these may be used in an appropriate combination of two
or more thereof.
[0083] Of these, particularly preferable are acrylate or
methacrylate type copolymers having a number-average molecular
weight of 5,000 to 200,000, more preferably 10,000 to 100,000. Of
these, the following is recommendable as preferred one: copolymer
comprising, as a monomer component, isobutyl methacrylate and/or
2-ethylhexyl methacrylate in an amount of 60% or more by mass.
[0084] About the use ratio between the starting powders (the total
of the conductive component, the skeleton component, and the
pore-forming agent) and the binder, the amount of the latter is 5
parts or more and 30 parts or less, more preferably 10 parts or
more and 20 parts or less by mass for 100 parts by mass of the
former. If the used amount of the binder is short, the strength or
the flexibility of the green sheet becomes insufficient.
Conversely, if the amount is too large, the viscosity of the slurry
is not easily adjusted and further the binder component is actively
decomposed or released into a large amount when the green sheet is
fired. Thus, the surface property of the green sheet does not
become even with ease.
[0085] As the dispersing medium used in the production of the green
sheet, the following is appropriately selected and used: an
alcohols such as methanol, ethanol, 2-propanol, 1-butanol,
1-hexanol or 1-hexanol; a ketone such as acetone or 2-butanone; an
aliphatic hydrocarbons such as pentane, hexane, or heptane; an
aromatic hydrocarbons such as benzene, toluene, xylene, or
ethylbenzene; an acetates such as methyl acetate, ethyl acetate, or
butyl acetate; or the like. These dispersing medium may be used
alone. Alternatively, if necessary, these may be used in an
appropriate combination of two or more thereof. The most ordinary
ones of these dispersing medium are 2-propanol, toluene, ethyl
acetate and so on.
[0086] In the preparation of the slurry for producing the green
sheet, the pore-forming agent powder into which the above-mentioned
conductive component powder or a precursor compound thereof is
incorporated, the skeleton powder, and an conductive component
powder which may be optionally replenished are homogeneously mixed
with the binder, the dispersing medium, an optional dispersing
agent for promoting the dissociation or dispersion of the starting
powders, an optional plasticizer and others, so as to prepare the
slurry in a homogeneous dispersion state.
[0087] As the dispersing agent used therein, the following is used:
a polymer electrolyte such as polyacrylic acid or polyacrylic
ammonium; an organic acid such as citric acid or tartaric acid; a
copolymer made from isobutylene and styrene or maleic anhydride, or
an ammonium salt or amine salt thereof, a copolymer made from
butadiene and maleic anhydride. The plasticizer has an effect of
making the flexibility of the green sheet high, and specific
examples thereof include phthalates such as dibutyl phthalate and
dioctyl phthalate; and glycols such as propylene glycol and glycol
esters.
[0088] The starting powder which becomes the skeleton of the
electrode support substrate according to the invention is
preferably one wherein the average particle size is 0.1 .mu.m or
more and 3 .mu.m or less and the particle size of the 90% volume
thereof is 6 .mu.m or less; more preferably one wherein the average
particle size is 0.1 .mu.m or more and 1.5 .mu.m or less and the
particle size of the 90% volume is 3 .mu.m or less; and even more
preferably one wherein the average particle size is 0.2 .mu.m or
more and 1 .mu.m or less and the particle size of the 90% volume is
2 .mu.m or less. The powder used as the starting material of the
conductive component is preferably one wherein the average particle
size is 0.6 .mu.m or more and 15 .mu.m or less and the particle
size of the 90% volume is 30 .mu.m or less; more preferably one
wherein the average particle size is 0.6 .mu.m or more and 3 .mu.m
or less and the particle size of the 90% volume is 20 .mu.m or
less; and even more preferably one wherein the average particle
size is 0.6 .mu.m or more and 1.5 .mu.m or less and the particle
size of the 90% volume is 10 .mu.m or less. In particular, in the
case that nickel oxide powder is used as the constituent material
of the conductive component, it is preferable to use a powder
wherein the particle size of the 90% volume is 6 .mu.m or less,
more preferably 3 .mu.m or less and the amount of contained coarse
particles is made as small as possible.
[0089] In the case that a powder wherein the average particle size
exceeds 3 .mu.m and the particle size of the 90% volume exceeds 6
.mu.m is used as the starting powder which constitutes the skeleton
component and further a powder wherein the average particle size
exceeds 15 .mu.m and the particle size of the 90% volume exceeds 30
.mu.m is used as the starting powder which becomes the constituent
material of the conductive component, desired thermal shock
resistance and mechanical strength are not easily obtained since
the green sheet is pre-fired to be made porous and further gaps
between the particles become pores. On the other hand, in the case
that a powder wherein the average particle size is less than 0.1
.mu.m is used as the constituent material of the skeleton component
and further a powder wherein the average particle size is less than
0.6 .mu.m is used as the constituent material of the conductive
component, pores in the sintered body becomes too small even if the
pore-forming agent is used together. As a result, the gas
permeability/diffusibility thereof is liable to become
insufficient.
[0090] However, in order to obtain surely an electrode support
substrate satisfying an appropriate surface roughness, that is, the
requirement that the maximum roughness depth (Rmax) is 1.0 .mu.m or
more, and 40 .mu.m or less as the surface roughness measured with a
laser optical manner three-dimensional shape measuring device while
the variation coefficient of measured values of the gas permeable
amounts is kept into the range of 5 to 20%, which is the most
important in the invention, it is desired to adopt a process of
[0091] using a slurry for producing of green sheet becoming a
ceramic precursor, including an conductive component powder, an
skeleton component powder, a pore-forming agent powder and a
binder, defoamed under reduced pressure after milling to adjust the
viscosity thereof to 40 to 100 poise (25.degree. C.), and kept at
room temperature while rotating stirring fans therein at a rotating
speed of 5 to 30 rpm for 20 to 50 hours;
[0092] fashioning the slurry into a sheet by a doctor blade method
to obtain a green sheet;
[0093] cutting the green sheet into a given shape; and then firing
the green sheet having the given shape
[0094] This is based on the following reason. When this process is
adopted, air bubbles present in the slurry adjusted into the given
viscosity are effectively removed so that air bubbles remaining in
the slurry, in particular, fine air bubbles having a level of 1
.mu.m can be reduced as much as possible. Further the pore-forming
agent powder, which is thermally decomposed at the time of the
firing so as to make pores in the substrate, can be more evenly
dispersed into the slurry. Thereby it makes the distribution of air
permeability in the substrate plane slight. Moreover, the effect of
ripening the slurry is also obtained with ease so that the slurry
can be made more stable.
[0095] It is advisable to adjust the viscosity of the slurry into
40 to 100 poise (25.degree. C.). If the viscosity is less than 40
poise, the fluidity of the slurry is too high so that a substrate
having a thickness of 1 mm or more, in particular 2 mm or more, is
not easily formed. Conversely, if the viscosity exceeds 100 poise,
the viscosity is too high so that air bubbles remaining in the
slurry, in particular, fine air bubbles having a level of 1 .mu.m
are not easily reduced. From such a viewpoint, the slurry viscosity
is more preferably from 50 to 80 poise (25.degree. C.).
[0096] If the rotating speed of the stirring fans is below 5 rpm,
air bubbles present in the slurry is insufficiently removed and
further it is difficult to disperse the pore-forming agent powder
evenly into the slurry. Consequently, it is indispensable to extend
the above-mentioned keeping time to 50 hours or more. Thus, this
case is not practicable.
[0097] On the other hand, if the rotating speed is over 30 rpm, air
is easily incorporated into the slurry while the slurry is stirred.
Inversely, air bubbles are easily generated.
[0098] From such a viewpoint, a more preferred rotating speed is
from 5 to 20 rpm. The shape of the stirring fans is not
particularly limited. Preferable are stirring fans each having an
anchor shape, which causes air mixture to be reduced.
[0099] If the time for keeping the rotation of the stirring fans is
less than 20 hours, air bubbles present in the slurry is
insufficiently removed and further it is difficult to disperse the
pore-forming agent powder evenly into the slurry. Conversely, if
the time is made excessively long so as to be over 50 hours, a long
time is required for the process. Thus, this case is unsuitable for
practical use.
[0100] In order to make a scattering in the permeability between
lots of the green sheets small in the above-mentioned process, it
is advisable to use, as the slurry for producing the green sheets
which become ceramic precursors, a slurry obtained by: adding, to
the viscosity-adjusted slurry which comprises the conductive
component powder, the skeleton component powder, the pore-forming
agent powder, and the binder and obtained by defoaming the
components under reduced pressure after milling the components to
set the viscosity thereof into the range of 40 to 100 poises
(25.degree. C.) and then keeping the resultant at room temperature
while rotating the stirring fans in the slurry at a rotating speed
of 5 to 30 rpm for 20 to 50 hours, a slurry which is subjected to
the same milling, has the same composition and has a viscosity not
adjusted; defoaming the resultant mixture slurry under reduced
pressure to adjust the viscosity into the range of 40 to 100 poise
(25.degree. C.); and then keeping the resultant at room temperature
while rotating the stirring fans in the slurry at a rotating speed
of 5 to 30 rpm for 20 to 50 hours.
[0101] In order to make a scattering in the green sheet lots
smaller in this case, it is preferable to add 95 to 105 parts by
mass of the total of the conductive component powder and the
skeleton component powder in the slurry the viscosity of which is
not adjusted to 100 parts by mass of the total of the conductive
component powder and the skeleton component powder in the
viscosity-adjusted slurry.
[0102] An instrument used for the defoaming under reduced pressure
is preferably a concentrating and stirring defoaming machine having
a refrigerator and a collecting tank for collecting solvent and
having an internal volume of 10 liters or more, preferably 30
liters or more, more preferably 50 liters or more. According to a
separable flask having an internal volume of less than 10 liters
and having a cock for reducing pressure, or some other flask, which
is used in ordinary laboratories, a substrate having a sufficient
quality intended in the present invention is not easily obtained,
probably, because of scale effect.
[0103] For satisfying the above-mentioned properties, important is
the size distribution of particles in the slurry state used in the
production of a green sheet which becomes a ceramic precursor which
becomes an electrode support substrate, and it is important to use
a slurry having one peak in each of the ranges of 0.2 to 2 .mu.m
and of 3 to 50 .mu.m in the particle size distribution of the
starting slurry for producing the green sheet.
[0104] In other words, the surface roughness of a support substrate
is affected, to some extent, by the above-mentioned particle size
construction of the used starting materials. If coarse materials
are used, the surface roughness of the resultant sintered body
becomes relatively coarse. If fine materials are used, the surface
roughness thereof becomes relatively dense. If a material having
the above-mentioned preferable particle size construction is used
as each of the conductive component material powder and the
skeleton component material powder which constitute the electrode
support substrate, this substrate can easily have the
above-mentioned proper porosity and a maximum roughness depth
(Rmax) in the preferred range.
[0105] However, the present inventors have repeatedly made research
so as to find out following. A more important matter for obtaining
a sintered body satisfying, in particular, the above-mentioned
variation coefficient of measured values of the gas permeable
amounts and Rmax defined in the present invention is the particle
size distribution of solid components contained in the slurry for
obtaining a ceramic molded body which becomes a sintering material
rather than the above-mentioned particle size construction of the
starting powders themselves. Moreover, when a slurry having one
peak in each of the ranges of 0.2 to 2 .mu.m and of 3 to 50 .mu.m
in the particle size distribution thereof is used to produce a
green sheet and then the sheet is fired, a sintered body (electrode
support substrate) having a porosity of 20 to 50% and a Rmax of 1.0
to 40 .mu.m can be more surely obtained.
[0106] When the slurry is prepared, there is adopted a method of
treating the above-mentioned starting material blended suspension
including the starting powders in a ball mill or the like to knead
and pulverize the powders. Dependently on conditions for the
kneading (examples of which include the kind of a dispersing agent,
and the added amount thereof), a part of the starting powders
aggregates secondarily in this slurry-preparing step and a part
thereof is crushed. Therefore, the particle size construction of
the starting powders is not kept as it is in the particle size
construction of solid components in the slurry. Thus, when the
electrode support substrate of the present invention is produced,
it is important to adjust the particle size distribution of the
slurry-state solid components used to produce a green sheet which
is not fired, as a factor which produces the largest effect on the
porosity and the surface roughness of the electrode support
substrate, to satisfy the above-mentioned requirements.
[0107] The particle size distributions of the solid components in
the starting powders and in slurry are values measured by the
following methods. The particle size distribution of the starting
powders is a measured value after using a laser diffraction manner
particle size distribution meter "SALD-1100", manufactured by
Shimadzu Corp., using, as a dispersing medium, an aqueous solution
wherein 0.2% by mass of sodium metaphosphoric acid is added as a
dispersing agent to distilled water, adding 0.01 to 1% by mass of
each of the starting powders to about 100 cm.sup.3 of the
dispersing medium, and treating the resultant with ultrasonic waves
for 3 to 10 minutes to disperse the powders. The particle size
distribution of the solid components in each slurry is a measured
value after using a solvent having the same composition as the
solvent in the slurry, as a dispersing medium, adding the slurry to
100 cm.sup.3 of the dispersing medium into a concentration of 0.1
to 1% by mass, and treating the resultant with ultrasonic waves for
3 to 10 minutes in the same way to disperse the solid components.
It is obtained as a particle size distribution frequency graph as
illustrated, for example, in FIG. 4.
[0108] When the slurry having one peak in each of the ranges of 0.2
to 2 .mu.m and of 3 to 50 .mu.m in the particle size distribution
thereof in the slurry state as described above is used to form a
green sheet, the formed green sheet is a green body wherein
relatively fine particles having of 0.2 to 2 .mu.m size are filled
into gaps between relatively coarse particles of 3 to 50 .mu.m
size. When this is fired, a sintered body having the preferred
surface roughness can be obtained.
[0109] In order to ensure the above-mentioned preferable surface
roughness, the content ratio by mass of the fine particles of 0.2
to 2 .mu.m size to the coarse particles of 3 to 50 .mu.m size, in
the slurry state thereof, is more preferably from 20/80 to 90/10,
even more preferably from 40/60 to 80/20. The average particle size
of the whole is preferably from 0.2 to 5 .mu.m, more preferably
from 0.3 to 3 .mu.m.
[0110] Means for adjusting the particle size distribution in the
slurry state into the preferable range is not particularly limited,
and examples of ordinary methods thereof are as following
methods:
[0111] (i) a method of pre-firing a part of powders which are
starting materials at 900 to 1400.degree. C. for 1 to 20 hours to
make the particle size thereof large, and then mixing the part with
the powders that are not fired,
[0112] (ii) a method of separating the addition of starting powders
into two stages when the starting powders and others are mixed in a
ball mill, and adding a part thereof after a given time passes,
thereby suppressing the degree of the pulverization, and
[0113] (iii) a method of kneading starting powders and others in
two kinds of ball mills having balls different in diameter to
prepare two slurries of different particle sizes, and then mixing
the two slurries.
[0114] The above-mentioned methods may be adopted alone.
Alternatively, if necessary, two or more out of the methods can be
appropriately combined to be carried out.
[0115] For the electrode support substrate of the present
invention, the following method is adopted: a method of laying and
spreading a slurry obtained as described above, which is comprised
a ceramic starting powder, a binder, and a dispersing medium, into
an appropriate thickness onto a supporting plate or a carrier sheet
by a doctor blade method, a calendering method, an extrusion method
or some other method so as to be molded into a sheet form, drying
this, volatilizing the dispersing medium to yield a green sheet,
adjusting the sheet into pieces of an appropriate size by cutting,
punching or the like. The resulting sheet of an appropriate size
put one of the pieces on a porous setter on a shelf board or put
one of the pieces between setters as disclosed in Re-Publication
Patent WO 99/59936, and heat and fire the piece in this state, at
about 1100 to 1500.degree. C., preferably about 1200 to
1450.degree. C., most preferably about 1250 to 1500.degree. C. in
the case of an anodic electrode support substrate, under the
atmosphere of air for about 1 to 5 hours.
[0116] As the porous setter, there is preferably used a setter, for
producing a porous ceramic sheet, which is made of a sheet-form
ceramic body comprising 40 to 90% by mass of a (Ni) unit having a
high gas permeability so as to emit smoothly gas which is generated
in a large amount from the binder or the pore-forming agent when
the green sheet is fired.
[0117] In the case that the electrode support substrate of the
present invention is made practicable for a fuel cell, it is
advisable to set the thickness of the sheet to 0.3 mm or more, more
preferably 0.5 mm or more and set to 3 mm or less, more preferably
1 mm or less in order to suppress electric conductance loss as much
as possible while satisfying required strength.
[0118] Incidentally, the burr height, which is very important for
preventing cracking or breaking when the electrode support
substrate receives stacking-load or the like in the present
invention, is remarkably changed by the edge shape of a punching
blade used when the green sheet is punched into a given size. It
has been found out that when a punching blade wherein the shape of
its edge is wave-form is used, the height of burrs formed on the
punched-line of the green sheet can be suppressed into a remarkably
smaller value than in the case of using an ordinary straight
punching blade. The reasons for this would be as follows.
[0119] In the case that a straight punching blade is used, the
whole of the blade edge contacts the green sheet in a linear form
when the green sheet is cut with the blade. Simultaneously, tensile
stress is linearly generated in the punching direction so that the
cut face of the green sheet comes to be curled in the punching
direction. Consequently, large burrs are easily formed. On the
other hand, in the case that a wave-form punching blade is used,
some parts of the blade edge (that is, the highest points of the
wave form) contact the green sheet in the form of points.
Therefore, the tensile stress in the punching direction is relieved
so that the degree of the curl becomes small. Thus, the burr height
would be remarkably lowered.
[0120] For example, FIG. 5 is an explanatory view for illustrating
a punching blade 1 used preferably in the present invention. A
blade edge portion 1a is made into the form of the teeth of a saw.
As described above, in order to suppress the curl as much as
possible at the time of punching the green sheet to make the burr
height small, it is desired to form the blade edge portion 1a as
sharp as possible to make the blade edge portion which firstly
contacts the green sheet surface as small as possible. Further, it
set the angle .alpha..sub.1 of the blade edge (which means the
angle of the wave-form blade edge portion when the blade is viewed
from the side thereof) into the range of about 30 to 120 degrees,
more preferably about 45 to 90 degrees, set the height h of the
blade into the range of about 0.5 to 2 mm, more preferably about
0.5 to 1 mm, and set the pitch p into the range of about 0.2 to 7
mm, more preferably about 0.2 to 4 mm.
[0121] A preferred sectional structure of the punching blade 1 is
as illustrated in FIG. 6. The angle .alpha..sub.2 of the blade edge
(which means the tip angle of any section in the thickness
direction of the blade) is preferably from 20 to 70 degrees, more
preferably from 20 to 50 degrees, and the thickness t of the edge
is preferably from 0.3 to 1 mm, more preferably from 0.4 to 0.7
mm.
[0122] For example, as illustrated in FIG. 7, the structure of the
blade edge is preferably made as follows: for a green sheet G to be
punched, the standing-up angle .theta..sub.1 on its Gx side
(ordinarily, its internal circumferential side) which will be a
punched product is made acuter than the standing-up angle
.theta..sub.2 on its cut-off side G.sub.Y side (ordinarily, its
external circumferential side). The angle .theta..sub.1 is
preferably from 10 to 25 degrees, more preferably from 10 to 20
degrees, and the angle .theta..sub.2 is preferably from 10 to 35
degrees, more preferably from 10 to 30 degrees. By use of the
punching blade 1 having a blade edge structure satisfying such
angles, burrs formed on the external circumferential edge on the
punched-product side can be made even smaller.
[0123] In the illustrated example, the blade edge portion having a
recurring structure of the same pitch and the same shape is shown.
However, the shape of the blade edge portion and the recurring
units thereof are not limited to the illustrated example. Of
course, it is allowable to modify the shape, the size or the like
appropriately and carry out punching as far as the blade structure
is a structure suitable for suppressing burrs.
[0124] At the time of the punching, it is preferable to drop down
the punching blade 1 as perpendicularly as possible to a surface of
the green sheet. In this case, it is desirable to sandwich and fix
the green sheet between soft and elastic supporting plates not to
be out of position.
[0125] For example, FIGS. 8 to 11 are explanatory schematic
sectional views illustrating the structure of a punching member A
used in the present invention, and a punching method using this. A
punching blade 1 is fixed to a blade holder 2 with a hard member 3
and further a projecting plate 4 made of a soft rubber or the like
is fitted to the front end portion side of the hard member 3. The
blade 1 is set not to penetrate through the projecting plate 4, so
as not to project from the front end face thereof as far as the
projecting plate 4 is not deformed by compression (see FIG. 8). In
the illustrated example, illustrated is a structure wherein an
elastic plate 6 is laminated also on the upper face of the hard
plate 5 in a sheet supporting member B arranged oppositely to the
punching member A in order to ensure the fixation of a green sheet
even more when the sheet is punched. However, the elastic plate 6
is not necessarily essential. The green sheet G which is an object
to be punched is arranged on the supporting member B and then a
punching work is performed.
[0126] When the green sheet G is punched, the punching member A is
caused to approach the surface of the green sheet G put on the
sheet supporting member B in the direction substantially
perpendicular to the surface, from the state illustrated in FIG. 8.
The punching blade 1 fitted into in the punching member A is set
not to project from the front face of the projecting plate 4 as
described above. Therefore, when the punching member A is caused to
approach the green sheet G as described above, the upper face of
the sheet G firstly contacts the projecting plate 4 so that the
green sheet G is sandwiched from the upper and lower sides between
the projecting plate 4 and the elastic plate 6 (see FIG. 9).
[0127] Thereafter, the punching member A is further dropped down.
As a result, the projecting plate 4 which is made of the elastic
material is compressed and deformed so that the punching blade 1
comes to project out toward the green sheet G. Simultaneously, the
green sheet G is urged from both sides thereof by elastic force
resulting from the elastic deformation of the projecting plate 4
and elastic force, based on the plastic plate 6, from the lower
face side of the sheet. Thus, the sheet G is supported and fixed,
and in this state the blade 1 advances to punch the sheet (see FIG.
10).
[0128] After the punching blade 1 penetrates through the green
sheet G so that the sheet is punched, the punching member A is
backed up to move the blade 1 backwards from the green sheet G
punched portion. In this step, similarly, the sandwich and fixation
state is maintained by elastic forces of the projecting plate 4 and
the elastic plate 6 until the punching blade 1 is withdrawn from
the green sheet G, and the state is cancelled after the punching
blade 1 is withdrawn (see FIG. 11. in the figure, y represents the
punched portion).
[0129] In other words, a fall in the punching dimensional accuracy,
based on positional slippage, is prevented and additionally the
generation of burrs is restrained as much as possible since the
punching and withdrawing which follow the forward and backward
movement of the punching blade 1 are performed in the state that
the green sheet G is elastically sandwiched and fixed.
[0130] Thus, when the present invention is carried out, a blade
having a waver-form blade edge portion is used as a device for
punching a green sheet, whereby the height of burrs formed in the
punched-out portion can be made as low as possible. As a result,
when the resultant substrate receives stacking-load or the like,
stress concentration on the burrs thereof can be suppressed as much
as possible and the generation of cracking or breaking can be
suppressed into a minimum. In particular, the green sheet which
becomes a precursor of the electrode support substrate according to
the present invention comprises a large amount of a pore-forming
agent in order to ensure given porosity, and the green sheet is
softer than any green sheet used in the production of a dense
sintered body. Therefore, burrs generated when the green sheet is
punched into a given size easily become large. However, a punching
blade and a punching method as described above are adopted, whereby
the burrs can be controlled as slightly as possible.
[0131] Clacking or breaking caused when the sheet substrate
receives stacking-load or the like may also be caused on the basis
of large projections, undulations and so on that are present on the
substrate surface besides the burrs. Therefore, in order to make
the cracking resistance or breaking resistance thereof even higher,
the projections or undulations should be made as small as possible
as well as the burr height is decreased. About a standard thereof,
each of the largest projection height and the largest undulation
height is 1/3 or less of the thickness of the sheet, more
preferably 1/4 or less thereof, even more preferably 1/5 or less
thereof, as described above. The reason why the burr height, the
largest projection height and the largest undulation height are
defined as the ratio thereof to the sheet thickness as described
above is that these values tend to be relatively larger as the
sheet thickness is larger.
[0132] It appears that the largest cause that the projections are
generated when the porous electrode support substrate according to
the present invention is produced is as follows. In the case that a
granular alien substance is present on the shelf board or setter
used when the green sheet is fired, the alien substance is caught
in the green sheet, which is put thereon, so that the sheet is
hindered from being evenly shrunk in a flat state.
[0133] It also appears that the largest cause that the undulations
are generated is as follows. When the binder or pore-forming agent
in the green sheet is burned up so that the sheet is sintered, the
content thereof is too large or when the green sheets are put on
each other and fired, the burning does not evenly advance with
ease. Thus, a scattering in the decomposed amount or burned amount
thereof per unit time is generated so that the amount of generated
decomposition gas becomes uneven. The shrinkage amount (about 10 to
30% of the length) of the green sheet generated when the sheet is
fired is larger in the circumferential edge portion than in the
central portion of the sheet. Therefore, the undulations are easily
generated in the circumferential edge portion.
[0134] Thus, means for suppressing the projections into a minimum
may be a method of performing removal and cleaning sufficiently so
that adhering particles, fallen particles and others may not be
present on the shelf board or setter used in the firing. A specific
and effective example of means for suppressing the undulations in a
minimum may be a method of suppressing the use of the binder or the
pore-forming agent into a minimum and further firing the green
sheets in the state that a porous setter is put as a spacer in
between the green sheets and a spacer for a weight is put onto the
topmost portion, in particular when the green sheet are laminated
and fired, so as to emit decomposition gas evenly from the binder
or the like.
[0135] When the electrode support substrate of the present
invention is used as a member for a solid electrolyte type fuel
cell, an anodic electrode and a thin electrolyte film are formed on
a single surface of the substrate. The method for forming the
electrode or the thin electrolyte film is not particularly limited.
The following can be appropriately used: a gas phase method, such
as plasma spraying such as VSP, flame spraying, PVD (physical vapor
deposition), magnetron sputtering, or electron beam PVD; or a wet
method such as screen printing, sol-gel process, or slurry coating.
The thickness of the anodic electrode is usually from 3 to 300
.mu.m, preferably from 5 to 100 .mu.m, and the thickness of the
electrolyte layer is usually from 3 to 100 .mu.m, preferably from 5
to 30 .mu.m.
EXAMPLES
[0136] The following describes the present invention more
specifically, giving working examples and comparative examples.
However, the present invention is not basically limited by the
following working examples, and may be carried out with appropriate
modification within a scope suitable for the subject matters which
have been described above and will be described below. All of them
are included in the technical scope of the present invention.
Example 1
Formation of Setters
[0137] The following were mixed to produce a mixed powder as a
starting material: 40% by mass of 8% by mole yttrium oxide
stabilized zirconia powder (hereinafter referred to as the "8YSZ")
wherein the average particle size thereof was 0.5 .mu.m and the
particle size of the 90% volume thereof was 1.2 .mu.m; and 60% by
mass of nickel oxide powder obtained by decomposing nickel
carbonate powder thermally wherein the average particle size was
4.5 .mu.m and the particle size of the 90% volume was 8 .mu.m.
[0138] To 100 parts by mass of this mixed powder were added 12
parts by mass of an acrylic binder made of a copolymer obtained by
use of 79.5% by mass of isobutyl methacrylate, 20% by mass of
2-ethylhexyl methacrylate and 0.5% by mass of methacrylic acid as
monomer units, 40 parts by mass of toluene and ethyl acetate (ratio
by mass: 2/1) as solvents, and 2 parts by mass of dibutyl phthalate
as a plasticizer. The mixture was kneaded in a ball mill and then
defoamed, and the viscosity thereof was adjusted, thereby yielding
a slurry of 40 poise viscosity.
[0139] This slurry was fashioned into a sheet form by a doctor
blade method, thereby forming green sheets, for setters, having a
thickness of about 0.5 mm. This was cut into a given size.
Subsequently, the resultants were put on a shelf board made of
alumina and having a thickness of 20 mm, and fired at 1400.degree.
C. for 5 hours to yield porous setters 17 cm square and about 0.4
mm thick, the porosity thereof being 15%.
[0140] (Formation of Electrode Support Substrate)
[0141] (1) Formation of Green Sheet For Electrode Support
Substrate
[0142] Commercially available 3% by mole yttria-stabilized zirconia
powder (trade name "HSY-3.0", manufactured by Daichi Kigenso Kagaku
Kogyo Co., Ltd., particle size construction: particle size of the
50% by volume=0.4 .mu.m; and particle size of the 90% by volume=1.4
.mu.m) (hereinafter referred to as the "3YSZ") was pre-fired at
1200.degree. C. under the atmospheric of air for 3 hours. The
following were put into a ball mill wherein alumina balls of 15 mm
diameter were put: 20 parts by mass of the pre-fired powder
(particle size construction: particle size of the 50% by volume=14
.mu.m; and particle size of the 90% by volume=29 .mu.m), 20 parts
by mass of the above-mentioned zirconia powder not pre-fired, 60
parts by mass of nickel oxide powder (manufactured by Kishida
Chemical Co., Ltd., particle size construction: particle size of
the 50% by volume=0.6 .mu.m; and particle size of the 90% by
volume=2.7 .mu.m), 10 parts by mass of corn starch (manufactured by
Kanto Chemical Co., Inc.), 15 parts by mass of a methacrylic acid
based copolymer (molecular weight: 30,000, glass transition
temperature: -8.degree. C.) as a binder, 2 parts by mass of dibutyl
phthalate as a plasticizer, and 50 parts by mass of a mixed solvent
of toluene and isopropyl alcohol (ratio by mass: 3/2) as a
dispersing medium. The mixture was kneaded at about 60 rpm for 20
hours to prepare a slurry.
[0143] The particle size distribution of the resultant slurry was
measured with a laser diffraction manner particle size distribution
meter (trade name "SALD-1100", manufactured by Shimadzu Corp.), and
the resultant frequency graph of the particle size distribution was
observed. As a result, two peaks were observed in a section of 0.2
to 0.3 .mu.m and a section of 4 to 5 .mu.m, and the content ratio
of fine particles in the range of 0.2 to 2 .mu.m and coarse
particles in the range of 3 to 50 .mu.m was 82/18.
[0144] This slurry was put into a pressure-reducing defoaming
machine, concentrated and defoamed to adjust the viscosity into 50
poise (25.degree. C.). Anchor-shaped stirring fans immersed in the
slurry were rotated at a rotating speed of 10 rpm for 24 hours, and
finally the slurry was passed through a 200-mesh filter. The
resultant was applied onto a polyethylene terephthalate (PET) film
by a doctor blade method. At this time, a gap based on a blade was
adjusted to form a green sheet having a thickness of about 0.59
mm.
[0145] (2) Punching and Firing of Green Sheet for Electrode Support
Substrate
[0146] The green sheet obtained as described above was punched into
a piece 15 cm square by the method as illustrated in FIGS. 8 to 11
using a punching blade (manufactured by Nakayama Shiki Zairyo Co.,
Ltd.) having a wave-form blade edge (in the form of the teeth of a
saw as illustrated in FIGS. 5 to 7) and having blade edge angles
.alpha..sub.1 and .alpha..sub.2 of 60.degree. and 45.degree.,
respectively, blade edge angles .theta..sub.1 and .theta..sub.2 of
15.degree. and 30.degree., respectively, a blade width t of 0.7 mm,
a blade height h of 1 mm, and a pitch p of 1.1 mm.
[0147] The upper and lower faces of the punched substrate green
sheet were sandwiched between the setters produced as described
above so as not to force out the circumferential edge of the green
sheet therefrom. Then the resultant was put onto a shelf board
(trade name: "Dialight DC-M", manufactured by Tokai Konetsu Kogyo
Co., Ltd.) having a thickness of 20 mm and fired at 1300.degree. C.
for 3 hours to yield an electrode support substrate about 12.5 cm
square and about 0.5 mm thick.
Example 2
[0148] In the item "(1) Formation of green sheet for electrode
support substrate" in Example 1, a slurry having no adjusted
viscosity, obtained by treatment with a ball mill in the same way
as in Example 1, and a slurry having a viscosity adjusted to 50
poise with the pressure-reducing defoaming machine were prepared.
The slurry having no adjusted viscosity was added to the slurry
having the adjusted viscosity. At this time, the addition was
performed to make the total mass of the 3YSZ powder and the nickel
oxide powder in the slurry having the adjusted viscosity equal to
the total mass of the 3YSZ powder and the nickel oxide powder in
the slurry having no adjusted viscosity.
[0149] Next, the viscosity of the mixed slurry was adjusted to 50
poise (25.degree. C.) by pressure-reducing defoaming in the same
way. The slurry was kept at room temperature while stirring fans in
the slurry were rotated at a rotating speed of 12 rpm for 20 hours.
The resultant green-sheet-producing slurry was used and fashioned
into a sheet form. Thus, a green sheet having a thickness of about
0.59 mm was yielded.
[0150] Subsequently, in the same way as in Example 1, punching and
firing were performed to yield an electrode support substrate about
12.5 cm square and about 0.5 mm thick.
Example 3
[0151] In the item "(1) Formation of green sheet for electrode
support substrate" in Example 1, the viscosity of the slurry was
adjusted to 60 poise by pressure-reducing defoaming. The slurry was
kept at room temperature while the stirring fans were rotated at a
rotating speed of 18 rpm for 30 hours. Subsequently, a gap based on
the doctor blade was adjusted to form a green sheet having a
thickness of 0.35 mm. In the very same way as in Example 1 except
the above, an electrode support substrate about 12.5 cm square and
about 0.3 mm thick was yielded.
Example 4
[0152] In the item "(1) Formation of green sheet for electrode
support substrate" in Example 1, 10 parts by mass of corn starch
(manufactured by Kanto Chemical Co., Inc.), 15 parts by mass of a
binder made of methacrylic copolymer and 2 parts by mass of dibutyl
phthalate as a plasticizer, the latter two of which were the same
as in Example 1, were used for 15 parts by mass of pre-fired powder
(particle size concentration: diameter of the 50% volume=20 .mu.m;
and diameter of the 90% volume=41 .mu.m) obtained by pre-firing
8YSZ powder (particle size concentration: diameter of the 50%
volume=0.5 .mu.m; and diameter of the 90% volume=1.2 .mu.m) at
1200.degree. C. under the atmosphere of air for 3 hours, and 15
parts by mass of the above-mentioned powder not pre-fired, and 70
parts by mass of nickel oxide (manufactured by Seido Chemical
Industry Co., Ltd., particle size concentration: diameter of the
50% volume=0.8 .mu.m; and diameter of the 90% volume=2.1 .mu.m). In
the same way as in Example 1 except the above, a green sheet for a
substrate was formed, and subsequently punching and firing were
performed in the same way to yield an electrode support substrate
about 12.5 cm square and about 0.5 mm thick.
Example 5
[0153] In the item "(1) Formation of green sheet for electrode
support substrate" in Example 1, 10 parts by mass of corn starch
(manufactured by Kanto Chemical Co., Inc.), 15 parts by mass of a
binder made of methacrylic copolymer and 2 parts by mass of dibutyl
phthalate as a plasticizer, the latter two of which were the same
as in Example 1, were used for 20 parts by mass of pre-fired powder
obtained by pre-firing commercially available 3YSZ powder (ditto)
at 1200.degree. C. under the atmosphere of air for 3 hours, 10
parts by mass of the above-mentioned powder not pre-fired, and 70
parts by mass of nickel oxide (manufactured by Kishida Chemical
Co., Ltd.). In the same way as in Example 1 except the above, a
green sheet for a substrate was formed, and subsequently punching
and firing were performed in the same way to yield an electrode
support substrate about 12.5 cm square and about 0.5 mm thick.
Example 6
[0154] In the item "(1) Formation of green sheet for electrode
support substrate" in Example 1, 20 parts by mass of corn starch
(manufactured by Kanto Chemical Co., Inc.), 15 parts by mass of a
binder made of methacrylic copolymer and 2 parts by mass of dibutyl
phthalate as a plasticizer, the latter two of which were the same
as in Example 1, were used for 15 parts by mass of pre-fired powder
obtained by pre-firing commercially available 3YSZ powder (ditto)
at 1200.degree. C. under the atmosphere of air for 3 hours, and 15
parts by mass of the above-mentioned powder not pre-fired, and 70
parts by mass of nickel oxide (manufactured by Seido Chemical
Industry Co., Ltd.). In the same way as in Example 1 except the
above, a green sheet for a substrate was formed, and subsequently
punching and firing were performed in the same way to yield an
electrode support substrate about 12.5 cm square and about 0.5 mm
thick.
Comparative Example 1
[0155] In Example 1, the viscosity was adjusted to 50 poise
(25.degree. C.), and immediately after this the slurry was passed
through a 200-mesh filter without keeping the slurry at room
temperature while stirring the slurry. Subsequently, the slurry was
applied onto a PET film by a doctor blade method so as to form a
green sheet about 0.59 mm thick similarly. Furthermore, in the same
way as in Example 1, an electrode support substrate about 12.5 cm
square and about 0.5 mm thick was produced.
Comparative Example 2
[0156] In Example 1, the viscosity was adjusted to 120 poise
(25.degree. C.), and subsequently stirring fans were immersed into
the slurry. The stirring fans in the slurry were rotated at a
rotating speed of 10 rpm for 10 hours. Thereafter, the slurry was
passed through a 200-mesh filter and then the slurry was applied
onto a PET film by a doctor blade method so as to form a green
sheet about 0.59 mm thick similarly. Furthermore, in the same way
as in Example 1, an electrode support substrate about 12.5 cm
square and about 0.5 mm thick was produced.
Comparative Example 3
[0157] In the item "(1) Formation of green sheet for electrode
support substrate" in Example 1, the same materials were used
except that the 1200.degree. C. pre-fired powder made of the
commercially available 3YSZ powder (ditto) was not used and 40
parts by mass of the 3YSZ powder (ditto) were used. The materials
were put into a ball mill in which zirconia balls of 5 mm diameter
were charged, and kneaded at about 50 rpm for 3 hours to prepare a
slurry. In the same way as in the item 1) of Example 1 except the
above, a green sheet of about 0.59 mm thickness was formed.
Furthermore, in the same way as in Example 1, an electrode support
substrate about 12.5 cm square and about 0.5 mm thick was
formed.
Comparative Example 4
[0158] In the item "(1) Formation of green sheet for electrode
support substrate" in Example 1, the same materials were used
except that the 3YSZ powder (ditto) was not used and the following
were used: 40 parts by mass of 3YSZ powder pre-fired at
1200.degree. C. for 3 hours and 60 parts by mass of powder obtained
by pre-firing nickel oxide powder (manufactured by Kishida Chemical
Co., Ltd.) at 1100.degree. C. in the atmosphere of air for 3 hours
(particle size concentration: diameter of the 50% volume=17 .mu.m;
and diameter of the 90% volume=30 .mu.m). The materials were put
into a ball mill in which alumina balls of 20 mm diameter were
charged, and kneaded at about 40 rpm for 10 hours to prepare a
slurry. In the same way as in the item 1) of Example 1 except the
above, a green sheet of about 0.59 mm thickness was formed.
Furthermore, in the same way as in Example 1, an electrode support
substrate about 12.5 cm square and about 0.5 mm thick was
formed.
Comparative Example 5
[0159] In Comparative Example 1, the conditions for ripening the
slurry was changed as follows: 2 rpm.times.2 hours. In the item
"(2) Punching of Green Sheet for Substrate", a single edge blade
(manufactured by Nakayama Shiki Zairyo Co., Ltd.) having a straight
blade edge having a thickness t of 0.7 mm and an blade edge angle
.alpha..sub.2 of 45.degree. was used to punch the sheet into a
piece 15 cm square. In the very same way except the above, punching
and firing were performed to form an electrode support
substrate.
Comparative Example 6
[0160] In the item "(1) Formation of green sheet for electrode
support substrate" in Comparative Example 1, 25 parts by mass of
the binder made of the methacrylic acid based copolymer were used
and further the conditions for ripening the slurry was changed as
follows: 2 rpm.times.54 hours. Additionally, in the item 2) Firing
of Green Sheet for Substrate therein, the
electrode-substrate-forming green sheet was fired without putting
any setter thereon and further the following was used as the setter
for underlay: a setter wherein about ten adhering particles having
a diameter of about 0.5 to 2 mm were observed per 100 cm.sup.2. In
the same way as the above-mentioned example except the above, an
electrode support substrate was formed.
Performance Tests
[0161] Each of the electrode support substrates obtained in
Examples 1 to 6 and Comparative Examples 1 to 6 was used to make
the following performance evaluating tests. The results are shown
in Tables 1 to 6.
[0162] (1) Gas Permeable Test
[0163] The electrode support substrate about 12.5 cm square and
about 0.5 mm thick, which was obtained as described above, was cut
into 16 pieces 3 cm square with a diamond cutter fitted to a
ceramic grinder (manufactured by Marutoh Co., Ltd.). These were
used as permeability testing pieces.
[0164] Any one of the testing pieces was set to a permeability
testing machine (trade name: "KES-F8-AP1", manufactured by Kato
Tech Co., Ltd.), to which an assistant member for holding a sample
was fitted. This testing machine is a machine which has a mechanism
wherein a constant flow rate of air is sent to the test piece by
piston movement of a plunger and a cylinder to emit the air into
the atmosphere or absorb air therefrom, and which is capable of
measuring the pressure loss based on the sample with a differential
pressure semiconductor gauge within 10 seconds per cycle and
showing the gas permeation resistance (the reciprocal number of the
gas permeability) of the sample directly with a digital panel
meter. The size of the sample piece was 3 cm square, and both ends
thereof were necessary by 0.5 mm for holding the sample piece.
Therefore, the effective area thereof was 2 cm square (area: 4
cm.sup.2). The outline of the machine is illustrated in FIG. 12 (in
this figure, S represents the sample; 11, a compressor; 12, a flow
rate meter; and 13, a differential pressure meter).
[0165] About each of the 16 sample pieces, the gas permeability
thereof was measured. The average value and the standard deviation
were obtained, and further the variation coefficient was
obtained.
[0166] (2) Measurement of Porosity
[0167] The porosities of the electrode support substrate obtained
as described above were measured with an automatic porosimeter
(trade name: "Autopore III9240", manufactured by Shimadzu
Corp.).
[0168] (3) Surface Roughness
[0169] A laser optical manner non-contact three-dimensional shape
measuring device (trade name: "Micro-focus Expert UBM-14 model",
manufactured by UBM Co.) was used to measure the maximum roughness
depths (Rmax) of the front and rear faces (the side contacting the
PET surface when the green sheet was formed is referred as the
front side) of each of the electrode support substrates at a pitch
of 0.1 mm.
[0170] Simultaneously, burrs on the circumferential edge of each of
the electrode support substrates, and projections and undulations
on the surface were measured.
[0171] (4) Load Test
[0172] Each of the sample substrates was arranged on an alumina
underlying-plate in the state that the substrate was sandwiched
between two alumina plates (trade name: "SSA-S1", manufactured by
Nikkato Co., Ltd.), the surfaces of which were smooth and had kept
parallelism, and then a load of 0.2 kg/cm.sup.2 was applied onto
the entire surface of the substrate. In this state, the temperature
of the substrate was raised from room temperature to 1000.degree.
C. over 10 hours, and kept at 1000.degree. C. for 1 hour, and then
dropped to room temperature. This operation was repeated ten times
to obtain the generation frequency of cracking or breaking. It was
judged with the naked eye whether or the cracking or breaking was
generated.
[0173] (5) Observation of Cell Printed Interface
[0174] The states of the interfaces between each of the electrode
support substrates and an anodic electrode and between each of the
electrode support substrates and an electrolyte layer were observed
from an SEM photograph thereof.
[0175] (Formation of Cell)
[0176] (a) Preparation of Paste
[0177] To 100 parts by mass of 10% by mole scandia- and 1% by mole
ceria-stabilized zirconia powder (manufactured by Daichi Kigenso
Kagaku Kogyo Co., Ltd.) were added 350 parts by mass of turpentine
oil and 2 parts by mass of ethylcellulose as a binder. Then, the
mixture was kneaded in a planetary mill for 2 hours to yield a
slurry. The slurry was used as an electrolyte paste.
[0178] To 50 parts by mass of 3YSZ powder (ditto) and 50 parts by
mass of nickel oxide (manufactured by Kishida Chemical Co., Ltd.)
were added 350 parts by mass of turpentine oil and 2 parts by mass
of ethylcellulose as a binder. Then, the mixture was kneaded in a
planetary mill for 2 hours to yield a slurry. The slurry was used
as an anode paste.
[0179] To 100 parts by mass of La.sub.0.8Sr.sub.0.2MnO.sub.3 powder
(manufactured by Seimi Chemical Co., Ltd.) were added 350 parts by
mass of turpentine oil and 2 parts by mass of ethylcellulose as a
binder. Then, the mixture was kneaded in a planetary mill for 2
hours to yield a slurry. The slurry was used as a cathode
paste.
[0180] (b) Formation of Cell
[0181] Next, the anode paste was printed onto one surface of the
above-mentioned electrode support substrate by screen printing. The
resultant was dried at 100.degree. C. for 1 hour and fired at
1350.degree. C. for 2 hours to form an anode layer on the electrode
support substrate, thereby forming an anode-layer-attached
electrode support substrate (AS-A).
[0182] The electrolyte paste was printed on the anode layer of the
anode-layer-attached electrode support substrate (AS-A) by screen
printing. The resultant was dried at 100.degree. C. for 1 hour and
fired at 1350.degree. C. for 2 hours to form a half cell wherein
the anode layer and an electrolyte layer were formed on the
electrode support substrate (AS-A-E).
[0183] Finally, the cathode paste was applied onto the electrolyte
layer of this half cell by screen printing. The resultant was dried
at 100.degree. C. for 1 hour and fired at 1300.degree. C. for 2
hours to form a cell wherein the anode layer, the electrolyte layer
and a cathode layer were formed on the electrode support substrate
(AS-A-E-C). The electrode area of the cell was about 121
cm.sup.2.
[0184] (c) An electrolyte layer, an anode layer, and a cathode
layer were formed on the electrode support substrate about 12.5 cm
square and about 0.5 mm thick, obtained in each of the Examples and
the Comparative Examples, by screen printing in accordance with the
method described in the item (Formation of cell), so as to produce
an anode-layer-attached electrode support substrate (AS-A) and a
half cell (AS-A-E). The surface of each thereof was observed with
the naked eye. Further the state of the printed interface was
observed from an SEM photograph thereof. In this way, the state of
the interface between the electrode support substrate and the anode
layer, the state of the interface between the anode layer and the
electrolyte layer, and the state of the electrolyte layer were
examined.
[0185] (6) Power Generation Test
[0186] Furthermore, in a single cell power generation test device
using the cell (AS-A-E-C) produced in accordance with the method
described in the item (Formation of cell), humidified hydrogen and
air were used as a fuel and an oxidizer, respectively, to make a
power generation test at a power generation temperature of
800.degree. C. for 24 hours. The highest power density at the
initial of the test and the highest power density after 24 hours
from the start of the test were obtained so as to calculate the
decreasing rate of the highest power.
[0187] The results are shown in Tables 1 to 6 TABLE-US-00001 TABLE
1 Example 1 Example 2 Example 3 NiO/3YSZ + pre-sintered NiO/3YSZ +
pre-sintered NiO/3YSZ + pre-sintered 3YSZ/starch 3YSZ/starch
3YSZ/starch Composition 60/20 + 20/10 60/20 + 20/10 60/20 + 20/10
Peak sections in slurry 0.2 to 0.3 .mu.m and 4 to 5 .mu.m 0.2 to
0.3 .mu.m and 4 to 5 .mu.m 0.2 to 0.3 .mu.m and 4 to 5 .mu.m
particle size distribution Content ratio of fine 82/18 82/18 82/18
particles to coarse particles Slurry viscosity (poise) 50 50 60
Conditions for keeping 10 rpm .times. 24 hours 12 rpm .times. 20
hours 18 rpm .times. 30 hours slurry at room temperature Green
sheet thickness (mm) 0.59 0.59 0.35 Punching die Wave form Wave
form Wave form Support substrate thickness 0.5 0.5 0.3 (mm)
Porosity (%) 25 23 27 Burr height/substrate 0.30 0.27 0.34
thickness Undulation 0.13 0.11 0.17 height/substrate thickness
Projection height/substrate 0.15 0.12 0.17 thickness
[0188] TABLE-US-00002 TABLE 2 Example 4 Example 5 Example 6
NiO/SYSZ + pre-sintered NiO/SYSZ + pre-sintered NiO/3YSZ +
pre-sintered 8YSZ/starch 3YSZ/starch 3YSZ/starch Composition 70/15
+ 15/10 70/20 + 10/10 70/15 + 15/20 Peak sections in slurry 0.2 to
0.3 .mu.m and 5 to 6 .mu.m 0.2 to 0.3 .mu.m and 4 to 5 .mu.m 0.2 to
0.3 .mu.m and 4 to 5 .mu.m particle size distribution Content ratio
of fine 86/14 82/18 Dec-88 particles to coarse particles Slurry
viscosity (poise) 50 70 50 Conditions for keeping 10 rpm .times. 24
hours 10 rpm .times. 24 hours 10 rpm .times. 24 hours slurry at
room temperature Green sheet thickness (mm) 0.59 0.59 0.59 Punching
die Wave form Wave form Wave form Support substrate thickness 0.5
0.5 0.5 (mm) Porosity (%) 28 28 32 Burr height/substrate 0.41 0.32
0.36 thickness Undulation 0.11 0.15 0.13 height/substrate thickness
Projection height/substrate 0.12 0.17 0.14 thickness
[0189] TABLE-US-00003 TABLE 3 Comparative Example 1 Comparative
Example 2 NiO/3YSZ + pre-sintered NiO/3YSZ + pre-sintered
Comparative Example 3 3YSZ/starch 3YSZ/starch NiO/3YSZ/starch
Composition 60/20 + 20/10 60/20 + 20/10 60/40/10 Peak sections in
slurry 0.2 to 0.3 .mu.m and 4 to 5 .mu.m 0.2 to 0.3 .mu.m and 4 to
5 .mu.m Only 0.2 to 0.3 .mu.m particle size distribution Content
ratio of fine 82/18 82/18 -- particles to coarse particles Slurry
viscosity (poise) 50 120 40 Conditions for keeping Nothing 10 rpm
.times. 10 hours 50 rpm .times. 3 hours slurry at room temperature
Green sheet thickness (mm) 0.59 0.59 0.59 Punching die Wave form
Wave form Wave form Support substrate thickness 0.5 0.5 0.5 (mm)
Porosity (%) 25 29 28 Burr height/substrate 0.33 0.37 0.39
thickness Undulation 0.14 0.19 0.21 height/substrate thickness
Projection height/substrate 0.15 0.26 0.12 thickness
[0190] TABLE-US-00004 TABLE 4 Comparative Example 4 Pre-sintered
Comparative Example 5 Comparative Example 6 NiO/pre-sintered
NiO/3YSZ + pre-sintered NiO/3YSZ + pre-sintered 3YSZ/starch
3YSZ/starch 3YSZ/starch Composition 60/40/10 60/20 + 20/10 60/20 +
20/10 Peak sections in slurry Only 7 to 8 .mu.m 0.2 to 0.3 .mu.m
and 4 to 5 .mu.m 0.2 to 0.3 .mu.m and 4 to 5 .mu.m particle size
distribution Content ratio of fine -- 82/18 82/18 particles to
coarse particles Slurry viscosity (poise) 80 50 50 Conditions for
keeping 40 rpm .times. 10 hours 2 rpm .times. 2 hours 2 rpm .times.
54 hours slurry at room temperature Green sheet thickness (mm) 0.59
0.59 0.59 Punching die Wave form Linear Wave form Support substrate
thickness 0.5 0.5 0.5 (mm) Porosity (%) 37 26 26 Burr
height/substrate 0.24 0.68 0.42 thickness Undulation 0.14 0.31 0.35
height/substrate thickness Projection height/substrate 0.19 0.28
0.38 thickness
[0191] TABLE-US-00005 TABLE 5 Example 1 Example 2 Example 3 Example
4 Example 5 Example 6 Crack generation 0 0 0 0 5 0 frequency (%/in
20 sheets) Surface roughness (.mu.m) Front face Rmax 4.15 2.89 3.74
18.13 5.57 3.11 Rear face Rmax 3.97 3.13 3.61 22.09 3.96 3.83 Gas
permeability test (mL/min kPa) Gas permeability 33 28 62 41 30 30
maximum value Gas permeability 19 18 45 23 19 19 minimum value
Average value 23 23 54 32 15 24 Standard deviation 2.1 1.7 8.3 3.7
1.9 2.5 Variation coefficient 9 7 15 12 13 10 Anode formation
Interface between Close adhesion Close adhesion Close adhesion
Close adhesion Close adhesion Close adhesion substrate and anode
Electrolyte formation Interface between Close adhesion Close
adhesion Close adhesion Close adhesion Close adhesion Close
adhesion anode and electrolyte State of electrolyte Substantially
Substantially Substantially Substantially Substantially
Substantially thickness even even even even even even Power
generation performance Highest-power 8 6 7 11 14 9 decreasing rate
(%) Crack after the test Not generated Not generated Not generated
Not generated Not generated Not generated
[0192] TABLE-US-00006 TABLE 6 Comparative Comparative Comparative
Comparative Comparative Comparative Example 1 Example 2 Example 3
Example 4 Example 5 Example 6 Crack generation 0 5 10 45 26 36
frequency (%/in 20 sheets) Surface roughness (.mu.m) Front face
Rmax 4.36 3.84 4.75 47.3 3.42 3.86 Rear face Rmax 4.19 4.33 4.96
45.8 3.06 4.11 Gas permeability test (mL/min kPa) Gas permeability
35 30 33 43 35 33 maximum value Gas permeability 12 9 15 17 14 13
minimum value Average value 20 21 21 24 23 19 Standard deviation
6.6 5.5 5.9 5.5 7.1 4.2 Variation coefficient 33 26 28 23 31 22
Anode formation Interface between Close adhesion Close adhesion
Exfoliation Partial Close adhesion Partial substrate and anode
exfoliation exfoliation Electrolyte formation Interface between
Close adhesion Close adhesion Close adhesion Partial Close adhesion
Close adhesion anode and electrolyte exfoliation State of
electrolyte Substantially Substantially Substantially Uneven
Substantially Substantially thickness even even even even even
Power generation performance Highest-power 35 23 28 31 18 20
decreasing rate (%) Crack after the test Generated Generated
Generated Generated Generated Generated
INDUSTRIAL APPLICABILITY
[0193] The present invention is constructed as described above, and
comprises a ceramic sheet having appropriate porosity, thickness
and surface area. In particular, the variation coefficient of
measured values of the gas permeable amounts thereof is set into a
given range and further the surface roughness measured with a laser
optical manner three-dimensional shape measuring device is
controlled, as the maximum roughness depth thereof, into a specific
range, thereby making it possible to provide an electrode support
substrate wherein a dense, even and highly-adhesive printed
electrode can be formed while even and superior gas
permeability/diffusibility can be ensured, the substrate having
performances eminent for a solid oxide type fuel cell.
[0194] Furthermore, the height of burrs, and the height(s) of
undulations and/or projections, which are measured with the same
laser optical manner three-dimensional shape measuring device, are
specified, thereby making it possible to provide an electrode
support substrate for giving a high-performance fuel cell capable
of suppressing cracking or braking based on local stress
concentration when stacking-load is applied to the cell and capable
of resisting thermal shock, thermal stress and others.
* * * * *