U.S. patent application number 11/966262 was filed with the patent office on 2008-05-08 for method for manufacturing fuel cell metallic separator.
This patent application is currently assigned to HONDA MOTOR CO., LTD.. Invention is credited to Koji Kotani, Teruyuki Ohtani, Makoto Tsuji, Masao Utsunomiya.
Application Number | 20080108282 11/966262 |
Document ID | / |
Family ID | 27482720 |
Filed Date | 2008-05-08 |
United States Patent
Application |
20080108282 |
Kind Code |
A1 |
Ohtani; Teruyuki ; et
al. |
May 8, 2008 |
METHOD FOR MANUFACTURING FUEL CELL METALLIC SEPARATOR
Abstract
A metallic separator according to a first embodiment is formed
by obtaining a blank by rolling a metallic material having
conductive inclusions, and removing a surface of the blank by 2% or
more of the thickness of the blank. A metallic separator according
to a second embodiment is formed by pressing a metallic plate so as
to have a cross section including ridges and grooves alternatively,
and removing parts of the ridged portions so as to make flattened
surfaces. A metallic separator having conductive inclusions in its
metal texture according to a third embodiment is formed by blasting
a liquid containing two or more kinds of abrasives having different
particle diameters to a blank after it has been rolled. A metallic
separator having conductive inclusion in its metal texture
according to a fourth embodiment is formed by blasting a
passivation treatment liquid mixed with abrasives to the
separator.
Inventors: |
Ohtani; Teruyuki; (Saitama,
JP) ; Tsuji; Makoto; (Saitama, JP) ;
Utsunomiya; Masao; (Saitama, JP) ; Kotani; Koji;
(Saitama, JP) |
Correspondence
Address: |
ARENT FOX LLP
1050 CONNECTICUT AVENUE, N.W.
SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
HONDA MOTOR CO., LTD.
Tokyo
JP
|
Family ID: |
27482720 |
Appl. No.: |
11/966262 |
Filed: |
December 28, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10309320 |
Dec 4, 2002 |
7325432 |
|
|
11966262 |
Dec 28, 2007 |
|
|
|
Current U.S.
Class: |
451/38 |
Current CPC
Class: |
Y02P 70/50 20151101;
Y02E 60/50 20130101; H01M 8/026 20130101; Y10T 29/49108 20150115;
H01M 8/0254 20130101; H01M 8/0206 20130101; H01M 8/0228
20130101 |
Class at
Publication: |
451/038 |
International
Class: |
B24C 1/00 20060101
B24C001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 2001 |
JP |
2001-371331 |
Feb 1, 2002 |
JP |
2002-025476 |
Mar 15, 2002 |
JP |
2002-072794 |
Mar 15, 2002 |
JP |
2002-072804 |
Claims
1. A method for manufacturing a fuel cell metallic separator having
conductive inclusions in its metallic texture, comprising: blasting
a liquid containing two or more kinds of abrasives each kind having
different particle diameters from each other to a blank that has
been rolled.
2. A method for manufacturing fuel cell metallic separator as set
forth in claim 1, further comprising: applying a passivation
treatment to a surface of the blank.
3. A method for manufacturing a fuel cell metallic separator having
conductive inclusions in its metal texture, the method comprising:
blasting a passivation treatment liquid mixed with abrasives to the
separator.
4. A method for manufacturing fuel cell metallic separator as set
forth in claim 3, wherein the passivation treatment liquid includes
nitride acid.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a Divisional Application, which claims the benefit
of pending U.S. patent application Ser. No. 10/309,320, filed Dec.
4, 2002. The disclosure of the prior application is hereby
incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a metallic separator which
is installed in a proton-exchange membrane fuel cell and a method
for manufacturing the same metallic separator.
[0004] 2. Description of the Related Art
[0005] In a proton-exchange membrane fuel cell, a laminated body in
which separators are laminated on both sides of a flat plate-like
membrane electrode assembly (MEA) is made to be one unit, and a
plurality of units are stacked together to form a fuel cell stack.
The membrane electrode assembly is of a three-layer construction in
which an electrolytic membrane comprising an ion-exchanging resin
is held between a pair of gas diffusion electrodes which constitute
a positive pole (cathode) and a negative pole (anode). The gas
diffusion electrode is such that a gas diffusion layer is formed on
the outside of an electrode catalyst layer which contacts the
electrolytic membrane. In addition, the separator is laminated in
such a manner as to be brought into contact with the gas diffusion
electrode of the membrane electrode assembly, whereby a gas flow
path through which gas is allowed to flow and a coolant flow path
are formed between the separator so laminated and the gas diffusion
electrode. According to the fuel cell, for example, when hydrogen
gas which is fuel is allowed to flow through a gas flow path which
faces the gas diffusion electrode on the negative pole side,
whereas oxide gas such as oxygen or air is allowed to flow trough a
gas flow path which faces the gas diffusion electrode on the
positive pole side, an electrochemical reaction occurs and current
is generated.
[0006] The separators need to have a function to supply electrons
generated through a catalytic reaction of hydrogen gas on the
negative pole side to an outside circuit, as well as a function to
supply electrons from the outside circuit to the positive pole
side. To this end, conductive materials, such as graphite and
metallic materials, are used for the separators. In particular, the
metallic materials are considered to be advantageous in that they
have superior mechanical strength and that they can be formed into
a thin plate which can eventually provide a separator light in
weight and small in size. As the metallic separator, there is a
separator which is manufactured by rolling stainless steel
containing conductive inclusions which are deposited and/or
dispersed therein into a thin plate, and forming by pressing the
thin plate so as to have a cross section constituted by alternate
ridges and grooves so that the grooves formed on front and back
surfaces of the thin plate are used for the gas flow paths and
coolant flow paths. The conductive inclusions are such as to
contribute to the improvement in power generating performance by
forming a conductive path.
[0007] With the metallic separators so constructed, the ridges
surfaces are brought into contact with gas diffusion electrodes of
the membrane electrode assembly in a state in which the separators
are assembled to the membrane electrode assembly. The ridged
portions are formed into a trapezoid having sides which are
slightly inclined so that the separator can easily be removed from
the die after pressing. In addition, corners which are transitional
portions from the surface of the ridged portion to the sides are
inevitably formed into a round shape (R-shape) by bending. These
constitute restrictions on the enlargement of actual contact areas
to the membrane electrode assembly at the surfaces of the ridged
portions. A reduction in contact area of the separator to the
membrane electrode assembly leads to an increase in contact
resistance and prevents the improvement of power generating
performance. Therefore, the enlargement of the contact area is
desired. In addition, some of separator, the surfaces of the ridged
portions are each close to the round shape as a whole and hence
their flattened surfaces become limited. As this occurs, it is
difficult to ensure that a desired surface pressure is obtained at
the surfaces the ridged portions which are in contact with the
membrane electrode assembly, this also leading to an increase in
contact resistance.
[0008] Further, when stainless steel in which conductive inclusions
are deposited and/or dispersed is rolled into a thin plate, there
may be caused a case where an abnormal layer is produced on the
surface of the thin plate in which conductive inclusions which are
broken extremely finely by rolling are caused to aggregate. In case
a fuel cell is constituted by separators in which the abnormal
layers exist on the surfaces thereof and is then put in operation,
the conductive inclusions existing in the abnormal layers drop,
which leads to deterioration in power generating performance.
[0009] Moreover, in the manufacture of separators as has been
described above, since there exists a surface rolling-affected
layer on a stainless steel plate, the steps are required of
grinding to remove the surface rolling-affected layer so as to
allow good conductive inclusions that have not been affected by
rolling to be exposed on the surface of a base metal and,
furthermore, allowing the exposed conductive inclusions to protrude
so as to reduce the contact resistance. However, there has existed
a problem that a naturally oxidized film is formed on the surface
of the base metal between the step of grinding and removing the
surface rolling-affected layer and the step of allowing the
conductive inclusions to protrude. Once a naturally oxidized film
is formed on the surface of the base metal, even if the step of
allowing the conductive inclusions to protrude is implemented
thereafter, the effect on the improvement in conductivity by the
step of allowing the conductive inclusion to protrude cannot be
obtained sufficiently due to the existence of the naturally
oxidized film. Owing to this, in order to obtain sufficient
conductivity, a complicated step must be implemented further,
leading to another problem that the production costs are
increased.
[0010] Further, after the process of grinding to remove the surface
rolling-affected layers so that the conductive inclusions are
allowed to protrude in the vicinity of the surfaces of the
stainless steel plate to thereby reduce the contact resistance, a
process is conducted of applying to newly produced surfaces of the
stainless steel plate a treatment for providing corrosion
resistance thereto. In related art, the passivation treatment has
been used for providing the corrosion resistance to the newly
produced surfaces. However, there has been existing a problem that
a naturally oxidized film is formed on the newly produced surface
during the passivation treatment. The naturally oxidized film is
inferior to a film in a passive state in corrosion resistance, and
therefore, a further provision of corrosion resistance has been
required. However, even if the passivation treatment is implemented
after a naturally oxidized film has been formed, the naturally
oxidized film interrupts the passivation of the newly produced
surface, and therefore, the corrosion resistance improvement effect
by the passivation treatment cannot be attained sufficiently. Due
to this, in order to obtain a sufficient corrosion resistance, a
further complicated step has to be implemented, this leading to
another problem that the production costs are increased.
SUMMARY OF THE INVENTION
[0011] A first object of the present invention is to provide a fuel
cell metallic separator formed by pressing so as to have a cross
section constituted by alternate ridges and grooves wherein contact
areas of surfaces of ridged portions to a membrane electrode are
enlarged to secure a desired surface pressure, whereby the contact
resistance is reduced to thereby improve the power generating
performance and a method for manufacturing the same separator.
[0012] A second object of the present invention is to provide a
fuel cell metallic separator manufactured by rolling a metallic
material having conductive inclusions, wherein the fuel cell
metallic separator is not affected by abnormal layers of conductive
inclusions produced on the surfaces thereof by rolling, whereby its
power generating performance is attempted to be improved, as a
result, and a method for manufacturing the same separator.
[0013] A third object of the present invention is to provide a
method for manufacturing a fuel cell metallic separator in which
grinding a surface rolling-affected layer on a base metal and
allowing conductive inclusions to protrude can be implemented in a
single step.
[0014] A fourth object of the present invention is to provide a
method for manufacturing a fuel cell metallic separator in which a
passivation treatment can be applied to newly produced surfaces
obtained by grinding on a base metal at the same time as the
grinding to remove surface rolling-affected layers.
[0015] In order to accomplish the first object above, the following
means are adopted. According to a first aspect of the present
invention, there is provided a fuel cell metallic separator
comprising:
[0016] a metallic plate having alternatively ridges and grooves in
a cross section which are formed by pressing, each of the ridge
portions having a flattened surface which is brought into contact
with a membrane electrode assembly, the flattened surface being
formed by removing a part of the ridged portion after pressing.
[0017] In the fuel cell metallic separator, it is preferable that a
removed amount of the surface of the ridged portion is 3 .mu.m or
larger.
[0018] Further, according to a second aspect of the present
invention, there is also provided a method for manufacturing a fuel
cell metallic separator comprising:
[0019] forming a metallic plate having alternatively ridges and
grooves in a cross section, by pressing, and; removing a part of
each of the ridged portions so that each of the ridge portions has
a flattened surface. In this method, it is preferable that a
removed amount of the surface of the ridged portion is equal to or
larger than 3 .mu.m. As a method for removing the surface of the
ridged portion, there are an electrochemical method such as
electrolytic etching, a chemical method such as etching and a
physical method such as cutting or sandblasting.
[0020] Further, the inventor came to know that the thickness of the
abnormal layer produced on the surfaces of the separator by rolling
is something like in the order of 2% of the total thickness, and
therefore the present invention was eventually completed based on
this knowledge. Namely, in order to accomplish the second object
above, according to a third aspect of the present invention, there
is provided a fuel cell metallic separator formed by rolling a
metallic material having conductive inclusions and removing a
surface of the metallic material after rolling by an amount
corresponding to 2% or more of a thickness of the metallic material
after rolling so that the conductive inclusions are allowed to
protrude from the surface of the metallic material after
rolling.
[0021] According to the fuel cell metallic separator of the third
aspect of the present invention, since the surfaces of the
separator are removed by 2% or more of the thickness of the
metallic material after the material has been rolled, abnormal
layers produced on the surfaces of the metallic material by rolling
are removed. Therefore, the surfaces of the metallic material are
made good and the conductive inclusions are allowed to protrude
therefrom. Due to this, when the metallic separators so
manufactured are incorporated in a fuel cell, the contact
resistance relative to a membrane electrode assembly is reduced to
thereby improve its power generating performance.
[0022] Further, according to a forth aspect of the present
invention, there is also provided a method for manufacturing fuel
cell metallic separator comprising:
[0023] obtaining a blank by rolling a metallic material having
conductive inclusions, and;
[0024] removing a surface of the blank by an amount corresponding
to 2% or more of a thickness of the blank so that the conductive
inclusions are allowed to protrude from the surface of the blank.
As a method for removing the surfaces, there are an electrochemical
method such as electrolytic etching, a chemical method such as
etching and a physical method such as cutting or sandblasting.
[0025] In addition, in a case where the blank is formed into a
final separator shape by pressing the blank in such a manner as to
form alternate ridges and grooves on the blank, the surface
removing step may be implemented either before or after the blank
is pressed. For the separator so pressed, since surfaces of ridged
portions constitute contact portions to the membrane electrode
assembly, the present invention may be limited such that the
surface removing process according to the present invention is
applied only to the surfaces of the ridged portions. Furthermore,
in order to improve the corrosion resistance, a passivation
treatment may finally be applied to the surfaces of the
separator.
[0026] In order to accomplish the third object above, according to
a fifth aspect of the present invention, there is provided a method
for manufacturing a fuel cell metallic separator having conductive
inclusions in its metallic texture, comprising:
blasting a liquid containing two or more kinds of abrasives having
different particle diameters to a blank that has been rolled.
[0027] There exists, in its metal texture of a blank for a metallic
separator, conductive inclusions having a hardness higher than that
of a base metal. Therefore, normally, a method for manufacturing a
fuel cell metallic separator requires steps of grinding the surface
of the base metal for removing the conductive inclusions as well as
the parent phase and grinding only the surface of the base metal so
as to allow the conductive inclusions to protrude. A wet-blasting
method is used as one of common means used in these steps. In
general, this is a method for blasting a liquid containing a single
kind of abrasives from a slit-like injection port to a body to be
ground. In the step of grinding to remove the surface of the base
metal, abrasives having a large particle diameter are used which
can produce kinetic energy which is large enough in magnitude to
grind conductive inclusions as well as the parent phase. In
contrast, in the step of allowing the conductive inclusions to
protrude, abrasives having a small particle diameter are used which
can produce kinetic energy which is small but large enough in
magnitude to grind only the surface of the base metal.
[0028] On the contrary to this, the method for manufacturing a fuel
cell metallic separator according to the present invention uses a
specific wet blasting method for blasting a liquid containing two
or more kinds of abrasives having different particle diameters to a
separator. Consequently, according to the present invention, not
only the parent phase but also the conductive inclusions are ground
to be removed by the abrasives having a large particle diameter,
and at the same time as this occurs, only the surface of the base
metal is ground by the abrasives having a small particle diameter.
Therefore, allowing the conductive inclusions to protrude as well
as grinding and removing the surface of the base metal can be
implemented in a single step, whereby the formation of a naturally
oxidized film on the surface of the base metal can be prevented and
a superior conductivity improving effect can be obtained. In
addition, according to the present invention, since the related-art
complicated steps are no more required, there can be provided an
advantage that the production costs can be reduced to a lower
level. Furthermore, in the fuel cell using the separators, a
superior power generating voltage can be exhibited.
[0029] In addition, the step of blasting the liquid containing two
or more kinds of abrasives having different particle diameters may
be carried out after the separator blank has been pressed or before
the pressing is completed. Furthermore, in the manufacturing method
according to the present invention, a passivation treatment is
preferably applied to the surface of the separator blank, and this
passivation treatment applying step may be implemented in any step
after the wet-blasting step has been completed. In addition, any
passivation treatment liquid may be used provided that the liquid
can form a passive-state film on the surface of the base metal of
the separator.
[0030] Further, in order to accomplish the fourth object above,
according to the sixth aspect of the present invention, there is
provided a method for manufacturing a fuel cell metallic separator
having conductive inclusions in its metal texture, the method
comprising: blasting a passivation treatment liquid mixed with
abrasives to the separator.
[0031] As a common method for grinding a fuel cell metallic
separator using a wet-blasting process, there is a method in which
a separator body to be ground is ground by blasting water mixed
with abrasives to the separator body from a slit-like injection
port. On the other hand, in the method for manufacturing a fuel
cell metallic separator according to the present invention, a
unique wet-blasting process is used in which a passivation
treatment liquid mixed with abrasives is blasted to the separator.
According to this method, the surface rolling-affected layers of
the separator be ground can be removed by blasting the abrasives to
the separator surfaces so that the conductive inclusions can be
exposed. Further, at the same time as this grinding process takes
place, a passivation treatment can be applied to newly produced
surfaces of the separator which results from the grinding by
blasting the passivation treatment liquid.
[0032] There is no limitation on the passivation treatment liquid
that is used in the method for manufacturing a fuel cell metallic
separator according to the present invention provided that a film
in a passive state can be formed on the surface of the base metal
of the separator. In the present invention, however, the
passivation treatment liquid is preferably nitride acid. In
addition, the process of blasting the passivation treatment liquid
mixed with the abrasives of the present invention may be
implemented after the separator blank has been pressed or before
the pressing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1 is a diagram showing the concept of a separator
according to the present invention;
[0034] FIG. 2 is an image of a separator that represents separators
manufactured in examples of the present invention;
[0035] FIG. 3 is a sectional view of a current collecting portion
(a portion where alternate ridges and grooves are formed) of the
separators manufactured in the examples;
[0036] FIG. 4 is a graph showing the results of contact resistances
measured in the examples;
[0037] FIG. 5 is an image of a separator that is to be manufactured
in examples of the present invention;
[0038] FIG. 6 is an image of the surface of the separators of the
examples of the present invention;
[0039] FIG. 7 is an image of the surface of separators of
Comparison Examples which correspond to those of the invention;
[0040] FIG. 8 is a graph showing measured contact resistances of
the examples of the present invention;
[0041] FIG. 9 is a graph showing measured corrosion current
densities of the examples of the present invention;
[0042] FIG. 10 is a diagram showing a relationship between power
generating current density and power generating voltage in a fuel
cell using separators according to the present invention and a
comparison example; and
[0043] FIG. 11 is a diagram showing the relationship between power
generating voltage and power generating time in a fuel cell using
the separators of the example of the present invention or the
comparison example.
DETAILED DESCRIPTION OF THE INVENTION
[0044] FIG. 1 illustrates the concept of a separator according to a
first embodiment of the present invention, in which a surface 11 of
a ridged portion 10 is removed and a flattened surface 12 is newly
formed. In FIG. 1, a shaded portion denotes a portion that is
removed, and a range indicated by "a" or the surface 12 constitutes
a contact surface which is brought into contact with a membrane
electrode assembly. Incidentally, "b" denotes a contact area to the
membrane electrode assembly in a state in which the surface 11 is
not removed or of the related-art ridged portion 10.
[0045] As is clear in FIG. 1, the contact surface is enlarged by
removing the surface of the ridge portion, and due to this, a
desired surface pressure relative to the membrane electrode
assembly is ensured, and the contact resistance is reduced to
thereby improve the power generating performance. In a state in
which the surface of the ridge portion is removed, in case the
round shape of the corner portions generated by pressing is
removed, the contact area is enlarged further, which is preferable.
Stainless steel is preferably used for the separator according to
the present invention. Since stainless steel in which nonmetal
conductive inclusions which constitute a conductive path are
dispersed into the metallic texture exhibits good conductivity, it
is especially preferable as a material for fuel cell separators.
With such stainless steel being applied to the present invention,
the conductive inclusions are allowed to protrude from the surface
when the surface of the ridge portion is removed, whereby the
improvement in function as the separator can be attempted. In case
an amount of the surface that is removed after pressing lowers
below 3 .mu.m, the effect of reducing the contact resistance
relative to the membrane electrode assembly cannot be obtained
largely, and therefore, the removal amount is preferably equal to
or larger than 3 .mu.m.
EXAMPLES
[0046] Next, examples of the present invention will be
described.
A. Manufacture of Separator
Examples 1 to 10
[0047] An austenite stainless steel plate having a thickness of 0.2
mm was pressed to obtain a required number of square separator
blanks of 92 mm wide and 92 mm long. FIG. 2 shows these separator
blanks each have a current collecting portion having a cross
section formed to have alternate ridges and grooves at the center
thereof and a flat edge portion around the periphery of the current
collecting portion. FIG. 3 illustrates part of the cross section
and dimensions of the current collecting portion of the separator
blank. Next, masking was applied to interior surfaces of the
grooves on both sides of the separator blank, and only surfaces of
ridged portions on the sides of the separator blank were removed by
electrolytic etching to thereby flatten the surfaces. As shown in
Table 1, amounts (thicknesses) of the surfaces that were removed
were 1 .mu.m, 2 .mu.m, 3 .mu.m, 4 .mu.m, 5 .mu.m, 6 .mu.m, 7 .mu.m,
10 .mu.m, 20 .mu.m and 50 .mu.m, whereby 10 kinds of separators
which differ in removed amount were manufactured and they are
represented by Examples 1 to 10, respectively. Note that an
adhesive tape produced by Fleon Industries Co., Ltd. under the
trade name of F-7034 (0.8 mm thick) was used as a masking material.
In addition, a phosphoric acid electrolytic etching liquid produced
by Jusco Co., Ltd. under the trade name of 6C016 was used. Then
electrolytic etching was carried out in the following conditions;
temperature was 50 degrees centigrade and current density was 0.125
A/cm.sup.2.
Comparison Example
[0048] The separator blank in which the surfaces of the ridged
portions are not removed was made a separator of comparison
example. TABLE-US-00001 TABLE 1 Contact Removed Amounts Resistance
(.mu.m) to MEA (m.OMEGA./cm.sup.2) Comparison 0 68 Example Example
1 1 30 Example 2 2 27 Example 3 3 16 Example 4 4 17 Example 5 5 16
Example 6 6 15 Example 7 7 15 Example 8 10 14 Example 9 20 14
Example 10 50 14
B. Measuring Contact Resistances
[0049] Next, fuel cell units were manufactured using the separators
of Examples 1 to 10 and the comparison example, respectively, in
which the separators of each example were laminated on sides of a
membrane electrode assembly as an unit, and the units for each
example were activated to generate power to measure contact
resistances of the separators of those examples relative to the
membrane electrode assemblies. The results of the measurement were
also shown in Table 1, and the relationship between the removed
amount of the surface of the ridged portion and contact resistance
are graphed in FIG. 4.
[0050] As is clear from FIG. 4, it was verified that the contact
resistances of the separators of Examples 1 to 10 are far lower
than that of the separator of the comparison example and that
flattening the surface of the ridged portion by removing part
thereof contributed to the improvement of the power generating
performance. In particular, the contact resistance reduced
remarkably with the removed amount of the surface of the ridged
portion being 3 .mu.m. Then, it was confirmed that same reduction
effect was expected by a further increase in removed amount.
[0051] Next, the metallic separator according to a second
embodiment of the present invention will be explained. An austenite
stainless steel plate having conductive inclusions is raised as a
material for the separator according to the second embodiment of
the present invention. Specifically speaking, an austenite
stainless steel plate is used which contains respective components
shown in Table 2 and in the remaining portion thereof. Fe, B and
unavoidable impurities and in which Cr, Mo and B satisfy the
following expression (1). B is deposited on the surface as a boride
of M.sub.2B or MB type and a boride of M.sub.23(C, B).sub.6 type,
and these borides are conductive inclusions which form a conductive
path on the surface of the separator. Cr(wt %)+3.times.Mo(wt
%)-2.5.times.B(wt %).gtoreq.=7 (1) TABLE-US-00002 TABLE 2 C Si Mn P
S Al .ltoreq.0.15 0.01.about.1.5 0.01.about.2.5 .ltoreq.0.035
.ltoreq.0.01 0.001.about.0.2 N Cu Ni Cr Mo .ltoreq.0.3 0.about.3
7.about.50 17.about.30 0.about.7 (percent by weight)
Examples
[0052] Next, examples of the present invention will be
described.
A. Manufacture of Blank
[0053] A thin plate having a thickness of 0.2 mm was obtained by
cold rolling a stainless steel containing respective components
shown in Table 3, as well as Fe and unavoidable impurities in the
remaining portion thereof with an annealing process being suitably
carried out during pressing. Next, a required number of square
blanks of 100 mm wide and 100 mm long were obtained by cutting them
out of the thin plate so obtained. TABLE-US-00003 TABLE 3 C Si Mn P
S Cu Ni Cr 0.073 0.28 0.13 0.015 0.001 0.11 10.1 20.9 Mo Nb Ti Al N
B 2.03 -- -- 0.08 0.030 0.60 (percent by weight)
B. Surface Removing Process and Pressing
Example 11
[0054] The following wet-blasting process was applied to both
surfaces of the blank to thereby remove the surfaces by 4 .mu.m.
Alumina particles (produced by Fuji Seisakusho Co., Ltd. under
trade name of Fujirandom WA#300) having a particle diameter of 0.3
mm was mixed into water as grinding particles, and this grinding
particles mixed water was blasted to the surfaces at a blasting
pressure of 1 kg/cm.sup.2 for 20 seconds. Next, this blank was
pressed into a predetermined separator shape to thereby obtain a
separator of Example 11.
Example 12
[0055] After the blank was pressed into a predetermined separator
shape, the same wet-blasting process as that carried out for
Example 11 was applied to both surfaces of the blank to thereby
obtain a separator of Example 12 in which the surfaces were removed
by 4 .mu.m.
Example 13
[0056] The following chemical etching (nitro-hydrofluoric acid
etching) process was applied to the surfaces of the blank to
thereby remove the surfaces by 5 .mu.m. An etching liquid
containing 20% of nitride acid and 8% of hydrofluoric acid was held
at 30 degrees centigrade and was jet stirred, and the blank was
submerged in this etching bath for 30 minutes. Next, the blank was
then pressed into a predetermined separator shape to thereby obtain
a separator of Example 13.
Example 14
[0057] After the blank was pressed into a predetermined separator
shape, the same chemical etching as that carried out for Example 13
was applied to both surfaces of the blank so as to remove the
surfaces by 5 .mu.m to thereby obtain a separator of Example
14.
Example 15
[0058] The following sand blasting process was applied to both
surfaces of the blank so as to remove the surfaces by 10 .mu.m. The
alumina particles used for Example 11 were also used as grinding
particles, and the alumina particles in a dried state were blasted
at a blasting pressure of 2 kg/cm.sup.2 for 10 seconds. Next, the
blank so sand-blasted was then pressed into a predetermined
separator shape to thereby obtain a separator of Example 15.
Example 16
[0059] After the blank was pressed into a predetermined separator
shape, the same sand blasting process as that carried out for
Example 15 was applied to both surface of the blank so as to remove
the surfaces by 10 .mu.m to thereby obtain a separator of Example
16.
Comparison Example 11
[0060] The blank was only pressed into a predetermined separator
shape and no surface removing process was carried out, the blank
being made to be a separator of Comparison Example 11.
Comparison Example 12
[0061] A separator of Comparison Example 12 was obtained in the
similar manner as Example 11 except that both surfaces were removed
by 1.5 .mu.m in amount.
Comparison Example 13
[0062] A separator of Comparison Example 13 was obtained in the
similar manner as Example 12 except that both surfaces were removed
by 1.5 .mu.m in amount.
Comparison Example 14
[0063] A separator of Comparison Example 14 was obtained in the
similar manner as Example 11 except that both surfaces were removed
by 2.5 .mu.m in amount.
Comparison Example 15
[0064] A separator of Comparison Example 15 was obtained in the
similar manner as Example 12 except that both surfaces were removed
by 2.5 .mu.m in amount.
[0065] Note that FIG. 5 shows a pressed separator which is
something like those obtained in the examples of the present
invention and the comparison examples, and this separator has at
the center thereof a current collecting portion which is pressed so
as to have a cross section constituted by alternate ridges and
grooves and a flat edge portion around the periphery of the current
collecting portion.
C. Observation of Surfaces
[0066] The surfaces of the separators of Example 11 and Comparison
Example 11 were observed by a microscope. FIG. 6 is an image of the
surface of the separator of Example 11. FIG. 7 is an image of the
surface of the separator of Comparison Example 11. It is observed
that unbroken good conductive inclusions having a particle diameter
of in the order of 5 .mu.m were allowed to protrude from the
surface of the separator of Example 11. On the other hand, it is
observed that finely broken conductive inclusions aggregated on the
surface of the separator of Comparison Example 11.
D. Measurement of Power Generating Voltage
[0067] Using the respective separators of Examples 11 to 16 and
Comparison Example 11 to 15, respectively, fuel cell units were
manufactured in which the separators were laminated to both sides
of a membrane electrode assembly (MEA), and the fuel cell units so
manufactured were then activated to generate power to measure power
generating voltages when a current of 0.5 A/cm2 was generated at
such timings at an initial point in time (0 hour) and points in
time; 10 hours has elapsed, 100 hours has elapsed, 2000 hours has
elapsed and 3000 hours has elapsed, respectively. The results were
shown in Tables 4A and 4B together with manufacture processes
(order of surface removing process and pressing) and surface
removed amounts. TABLE-US-00004 TABLE 4A Surface Removed
Manufacture Processes Amounts (.mu.m) Example 11 wet-blasting ->
pressing 4 Example 12 pressing -> wet-blasting 4 Example 13
nitro-hydrofluoric acid 5 etching -> pressing Example 14
pressing -> 5 nitro-hydrofluoric acid etching Example 15 sand
blasting -> pressing 10 Example 16 pressing -> sand blasting
10 Comparison pressing only 0 Example 11 Comparison wet-blasting
-> pressing 1.5 Example 12 Comparison pressing ->
wet-blasting 1.5 Example 13 Comparison wet-blasting -> pressing
2.5 Example 14 Comparison pressing -> wet-blasting 2.5 Example
15
[0068] TABLE-US-00005 TABLE 4B Power Generating Voltage (V) when a
current of 0.5 A/cm.sup.2 is generated 0 10 100 1000 2000 3000 hour
hours hours hours hours hours Example 11 0.7 0.7 0.7 0.7 0.7 0.7
Example 12 0.7 0.7 0.7 0.7 0.7 0.7 Example 13 0.7 0.7 0.7 0.7 0.7
0.7 Example 14 0.7 0.7 0.7 0.7 0.7 0.7 Example 15 0.7 0.7 0.7 0.7
0.7 0.7 Example 16 0.7 0.7 0.7 0.7 0.7 0.7 Comparison 0.7 0.65 0.63
0.55 0.43 0.24 Example 11 Comparison 0.7 0.69 0.66 0.63 0.59 0.55
Example 12 Comparison 0.7 0.68 0.66 0.64 0.59 0.55 Example 13
Comparison 0.7 0.69 0.68 0.66 0.65 0.63 Example 14 Comparison 0.7
0.68 0.66 0.65 0.64 0.61 Example 15
[0069] As is clear from Table 2, with the separators of the
examples of the present invention, a power generating voltage at
the initial point in time was still maintained even at the point in
time when 3000 hours had elapsed, whereas with the separators of
Comparison Examples, it is observed that the initial power
generating voltage was reduced with time, this verifying the
effectiveness of the present invention.
E. Effect of Passivation Treatment
[0070] Next, the verification was made with respect to the
superiority resulting when a passivation treatment was finally
applied to the surfaces of the separator.
Example 17
[0071] An electrolytic etching process was applied to the surfaces
of the blank so as to remove the surfaces by 4 .mu.m. A phosphoric
acid electrolytic etching liquid (produced by Jusco Co., Ltd. under
the trade name of 6C016) was held at 50 degrees centigrade, a
current having a current density of 0.125 A/cm.sup.2 was conducted
through the etching liquid, and the blank was submerged in the
etching bath for 10 minutes. Next, the blank was then pressed into
a predetermined separator shape. Finally, the pressed separator was
submerged for 10 minutes in a liquid bath containing 50 percent by
weight of nitride acid for passivation treatment of the surfaces to
thereby obtain a separator of Example 17.
Comparison Example 16
[0072] The same passivation treatment as done for Example 17 was
applied to the separator of Comparison Example 11 to thereby obtain
a separator of Example 16.
[0073] The separators of Example 17, Comparison Example 11 and
Comparison Example 16 were brought into contact with membrane
electrode assembly, respectively to measure contact resistances of
the respective separators. The results of the measurements were
shown in FIG. 8. In addition, corrosion current densities of the
separators of Example 17, Comparison Example 11 and Comparison
Example 16 were measured. The results of the measurements were
shown in FIG. 9. As is clear from the results, the separator of
Example 17, to the surfaces of which the passivation treatment was
applied, showed the lowest values for both contact resistance and
corrosion current density. Consequently, it can be expected that a
separator to the surfaces of which a passivation treatment is
applied exhibits a higher power generating performance.
[0074] Next, the metallic separator according to a third embodiment
of the present invention will be explained. An austenite stainless
steel plate having conductive inclusions is raised as a material
for the separator according to the third embodiment of the present
invention, as is the case with that of the second embodiment of the
present invention. That is, an austenite stainless steel plate is
used which contains respective components shown in Table 2 above
and in the remaining portion thereof. Fe, B and unavoidable
impurities and in which Cr, Mo and B satisfy the above-mentioned
expression (1), B is deposited on the surface as a boride of
M.sub.2B or MB type and a boride of M.sub.23(C, B).sub.6 type, and
these borides are conductive inclusions which form a conductive
path on the surface of the separator.
Example
[0075] Next, the effectiveness of the present invention will be
described in detail using an example of the present invention.
A. Manufacture of Separator
Example
[0076] An austenite stainless steel plate containing respective
components shown in Table 5 and in the remaining portion thereof.
Fe and unavoidable impurities was cut into a square shape which is
100 mm wide and 100 mm long to thereby obtain a blank for a
separator. Next, tap water mixed with 33.3 percent by weight of two
kinds of alumina particles whose particle diameters are 60 .mu.m
and 180 .mu.m, respectively, at a weight ratio of 1 to 1 as
grinding particles and held at a temperature of 30 degrees
centigrade was sprayed to both sides of the blank from a spray
nozzle at a spraying pressure of 1 kg/cm.sup.2 for 30 seconds,
whereby grinding the parent phase and allowing conductive
inclusions to protrude were implemented using the wet-blasting
method. Next, the blank was rinsed and after it dried out, the
blank was pressed with a press load of 50 tons and a separator
according to the example was obtained. TABLE-US-00006 TABLE 5 C Si
Mn P S Al N Cu 0.073 0.28 0.13 0.015 0.001 0.08 0.03 0.11 Ni Cr Mo
B 10.1 20.9 2.03 0.60 (percent by weight)
Comparison Example
[0077] Next, tap water mixed with 33.3 percent by weight of alumina
particles whose particle diameters is 180 .mu.m as grinding
particles and held at a temperature of 30 degrees centigrade was
sprayed to both sides of a separator blank which was similar to one
used for the example from a spray nozzle at a spraying pressure of
1 kg/cm.sup.2 for 30 seconds, whereby grinding by the wet-blasting
method was implemented. Next, the blank was rinsed and after it
dried out, the blank was pressed with a press load of 50 tons and a
separator according to the example was obtained. Next, tap water
mixed with 33.3 percent by weight of alumina particles whose
particle diameters is 60 .mu.m as grinding particles and held at a
temperature of 30 degrees centigrade was sprayed to the sides of
the separator blank from the spray nozzle at the spraying pressure
of 1 kg/cm.sup.2 for 30 seconds, whereby allowing conductive
inclusions to protrude was implemented using the wet-blasting
method. Thereafter, the blank was rinsed and after it dried out,
the blank was pressed with a press load of 50 tons and a separator
according to the comparison example was obtained.
B. Deterioration with Age of Power Generating Voltage
[0078] Manufactured using the separators of the example of the
present invention and the comparison example which were obtained as
has been described above were fuel cell units in each of which the
separators were laminated on sides of a membrane electrode assemble
(MEA), and the units were activated so as to generate power and
deteriorations in power generating voltage as the power generating
current density increases were measured. The results of the
measurement are shown in FIG. 10.
[0079] As is clear from FIG. 10, with the fuel cell unit using the
separators of the example of the present invention which was
manufactured by implementing the steps of grinding a surface
rolling-affected layer and allowing conductive inclusions to
protrude at the same time, the deterioration in power generating
voltage as the power generating current density increases was
extremely low when compared with the fuel cell unit using the
separators of the comparison example which was manufactured by
implementing the steps of grinding a surface rolling-affected layer
and allowing conductive inclusions to protrude sequentially.
[0080] Next, the metallic separator according to a fourth
embodiment of the present invention will be explained. An austenite
stainless steel plate having conductive inclusions is raised as a
material for the separator according to the third embodiment of the
present invention, as is the case with that of the second
embodiment of the present invention. That is, an austenite
stainless steel plate is used which contains respective components
shown in Table 2 and in the remaining portion thereof. Fe, B and
unavoidable impurities and in which Cr, Mo and B satisfy the
above-mentioned expression (1), B is deposited on the surface as a
boride of M.sub.2B or MB type and a boride of M.sub.23(C, B).sub.6
type, and these borides are conductive inclusions which form a
conductive path on the surface of the separator.
Example
[0081] Next, the effectiveness of the present invention will be
described in detail using an example of the present invention.
A. Manufacture of Separator
Example
[0082] An austenite stainless steel plate containing respective
components shown in Table 6, as well as Fe and unavoidable
impurities in the remaining portion thereof and having a thickness
of 0.2 mm was cut into a square separator of 100 mm wide and 100 mm
long to thereby obtain a separator blank. Next, 5 percent by weight
of nitride acid mixed with 33.3 percent by weight of alumina
particles having a particle diameter of 60 .mu.m as grinding
particles and held at 50 degrees centigrade was blasted to both
surfaces of the blank at a blasting pressure of 1 kg/cm.sup.2 for
30 seconds so that grinding and passivation treatment using the
wet-blasting process were thus carried out. Next, after it was
rinsed and dried, the blank was pressed with a press load of 50
tons to thereby obtain a separator of an example of the present
invention. TABLE-US-00007 TABLE 6 C Si Mn P S Al N Cu 0.073 0.28
0.13 0.015 0.001 0.08 0.03 0.11 Ni Cr Mo B 10.1 20.9 2.03 0.60
(percent by weight)
Comparison Example
[0083] Tap water mixed with 33.3 percent by weight of alumina
particles having a particle diameter of 60 .mu.m as grinding
particles and held at 30 degrees centigrade was blasted to both
surfaces of the same blank as used for the above example at a
blasting pressure of 1 kg/cm.sup.2 for 30 seconds and grinding
using the wet-blasting process was thus carried out. Next, the
blank was submerged in 5 percent by weight of nitride acid which
was held at 50 degrees centigrade for 3 minutes and a passivation
treatment was thus carried out. Next, after it was rinsed and
dried, the blank was pressed with a press load of 50 tons to
thereby obtain a separator of a comparison example.
B. Deterioration with Time of Power Generating Voltage
[0084] Fuel cell units were manufactured using the separators of
the example of the present invention and the comparison example,
respectively, which were obtained as has been described above in
which the separators are laminated on both sides of a membrane
electrode assembly (MEA), and the units were activated to generate
power, whereby a deterioration in power generating voltage as power
generating time elapses when a current of 0.5 A/cm.sup.2 was
measured for each example. The results of the measurements were
shown in FIG. 11.
[0085] As is clear from FIG. 11, with the fuel cell unit using the
separators of the example of the present invention in which no
naturally oxidized film but a film in a passive state was formed on
the surfaces of the separator and which is superior in corrosion
resistance, there was extremely little deterioration in power
generating voltage even if power was generated over a long period
of time. In contrast, with the fuel cell unit using the separator
of the comparison example in which a film in a passive state was
formed on the surfaces of the separator via a naturally oxidized
film, it was found that the power generating voltage was reduced as
the power generating time elapsed.
[0086] Thus, as has been described heretofore, according to the
present invention, in the fuel cell metallic separator formed by
pressing so as to have a cross section constituted by alternate
ridges and grooves, the contact area at the surface of the ridged
portion is enlarged by removing the surface of the ridged portion
that is brought into contact with the membrane electrode assembly
after pressing so as to make the flattened surface. Therefore, the
desired surface pressure can be ensured, whereby the contact
resistance relative to the membrane electrode assembly is reduced,
and as a result, there can be provided an advantage that the power
generating performance is improved.
[0087] As has been described heretofore, according to the present
invention, the abnormal layers produced on the surfaces of the
metallic material when it is rolled are removed by removing the
surfaces of the metallic material by 2% or more of the thickness of
the metallic material after the material has been rolled, and the
resulting surfaces become good and the conductive inclusions are
allowed to protrude therefrom. Thus, there can be provided an
advantage that the contact resistance relative to the entirety of
the membrane electrode assembly is reduced, whereby the improvement
in power generating performance can be attempted.
[0088] As has been described above, according to the present
invention, since grinding the surface rolling-affected layer of a
base metal and allowing conductive inclusions to protrude can be
implemented simultaneously by using the unique wet-blasting method
in which the liquid containing two or more kinds of abrasives
having different particle diameters is blasted to a blank after the
blank has been rolled, the formation of a naturally oxidized film
on the surface of the base metal can be prevented to thereby obtain
a superior conductivity improvement effect, and a fuel cell using
the separators so manufactured can exhibit a superior power
generating voltage.
[0089] As has been described heretofore, according to the present
invention, by using the unique wet-blasting process in which the
passivation treatment liquid mixed with abrasives is blasted to the
separator, the surface rolling-affected layers of the separator can
be ground to be removed to thereby allow conductive inclusions to
be exposed by the abrasives so blasted, and at the same time as
this occurs, the passivation treatment can be applied to newly
produced surfaces of the separator which result from the grinding
through blasting the passivation treatment liquid to the
separator.
* * * * *