Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2002-02-28
2004-03-02
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S672000, C428S925000, C428S935000, C428S938000, C205S222000, C427S337000, C427S360000, C427S367000
Reexamination Certificate
active
06699593
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a corrosion-resistant metallic material or member, a metallic separator for fuel cells which comprises the metallic member, and a process for producing them. More particularly, the invention relates to a highly corrosion-resistant material or member improved in corrosion resistance, adhesion, contact electrical resistance, electrical conductivity, airtightness, etc. and suitable for use as a metallic separator for polymer electrolyte fuel cells (PEFC), and to a process for producing the same.
DESCRIPTION OF THE RELATED ART
In applications where corrosion resistance is required, highly corrosion-resistant materials such as, e.g., stainless steel, nickel-based alloys, titanium, and titanium alloys have hitherto been used as they are, or materials obtained by plating steel, stainless steel, or the like with copper, nickel, chromium, or the like have been used. In applications where higher corrosion resistance is required, materials obtained by plating stainless steel or another base with a noble metal such as, e.g., gold or platinum have generally been used.
In producing plated products, plating is conducted after the base has been formed into the shape of the final product, because forming after plating may result in peeling of the deposit. There has hence been a problem that a film is less apt to be deposited by plating at corners such as groove edges and the plated product thus obtained has poor corrosion resistance in these parts.
Deposit films formed by plating have a porous structure and hence have poor adhesion to the base. In addition, since deposit films have pinholes, they have reduced corrosion resistance when they are thin. Although increasing the deposit thickness is necessary for heightening corrosion resistance, this poses a problem of increased cost in the case of noble-metal plating.
A metallic separator for polymer electrolyte fuel cells (PEFC) functions not only to electrically connect an electrode of a unit cell to an electrode of an adjacent unit cell but also to separate the reaction gas. The separator should therefore have high electrical conductivity and high gastightness, i.e., high impermeability to the reaction gas. Furthermore, the separator should have high corrosion resistance in the reactions in which hydrogen/oxygen is oxidized/reduced.
A metallic separator which has been known as a separator for polymer electrolyte fuel cells (PEFC) is one produced by a process comprising cutting a carbon plate such as a graphite plate to form therein many grooves arranged in corrugations for passing a fuel gas or oxidizing gas therethrough. This process, however, has a problem that the costs of the carbon plate material and the cutting are high, so that the separator produced by the process is too costly to be used practically.
Another metallic separator for polymer electrolyte fuel cells (PEFC) is disclosed in JP-A-10-228914. This separator is produced by pressing a stainless-steel plate to form therein many grooves arranged in corrugations for passing a fuel gas or oxidizing gas therethrough and then directly plating the edges of the protruding tips with gold in a thickness of from 0.01 to 0.02 &mgr;m.
JP-A-2000-21418 discloses a metallic separator produced by pressing an SUS 316 plate to form therein many grooves arranged in corrugations for passing a fuel gas or oxidizing gas therethrough and then subjecting the surface thereof to nickel strike, nickel plating, and gold plating.
The separators for fuel cells which have been proposed further include one produced by forming a metal plate into a given shape, depositing a thin metal layer on at least one side thereof, and then filling up the pinholes in the thin metal layer by roller pressing, anodization, or resin coating (see JP-A-2001-68129).
However, those techniques of the related art have problems that the corrosion-resistant metallic member produced still has insufficient corrosion resistance, that in some of the techniques, there are limitations on the materials of metals usable as the base, and that the production of the corrosion-resistant metallic member is laborious.
Furthermore, the technique of the related art in which a metal film is deposited by plating on a surface having grooves formed therein beforehand has a drawback that there are cases where voids remain between the deposit film and the stainless steel and where the deposit film has too small a thickness at the edges (corners) of the groove tops. In addition, there have been problems that since the deposit film has a porous structure, it has poor adhesion to the stainless steel, and that the stainless steel corrodes through the pinholes and pores of the deposit film.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a highly corrosion-resistant inexpensive material which has no limitations on the materials of metals usable as the base, is improved in corrosion resistance, adhesion, contact electrical resistance, and other properties, and is usable as, e.g., a metallic separator for polymer electrolyte fuel cells (PEFC). Another object of the invention is to provide a process for producing the material.
Still another object of the invention is to provide a corrosion-resistant metallic member having high corrosion resistance and low electrical resistance and suitable for mass production. Further objects of the invention are to provide a metallic separator for fuel cells which comprises the metallic member, and to provide a process for producing the separator.
In order to eliminate the problems described above, attention was directed to the coating of a surface of a metallic base made of any desired material with a thin noble-metal layer having a dense structure and retaining high adhesion strength.
Intensive investigations were made in order to develop a corrosion-resistant material or corrosion-resistant member which is improved in corrosion resistance and contact electric resistance and is inexpensive, a metallic separator for polymer electrolyte fuel cells (PEFC) which comprises the corrosion-resistant material or member, and a process for producing the same. As a result, it has been found that when a base coated with a film of a noble metal deposited by plating or another technique is rolled together with the coating film, then not only almost the same adhesion strength as in clad metals is obtained but also the porous structure of the coating film is densified and pinholes are filled up, whereby corrosion resistance is improved. It was also found that since adhesion strength is enhanced, the coating film does not peel off even when passages for passing a fuel gas or oxidizing gas are formed thereafter by plastic working. The following have been further found. Since corrosion resistance is improved, the thickness of the coating film can be reduced, leading to a cost reduction. Because of the surface coating layer made of a noble metal, the corrosion-resistant member has reduced contact electrical resistance. Furthermore, a preferred process for producing the corrosion-resistant member was found to comprise depositing a thin noble-metal layer on the desired part of the surface of a metallic base, compression-working the thin noble-metal layer, and then subjecting the coated base to an anticorrosive treatment with a liquid phase containing a peroxide or ozone or with an active gas atmosphere.
The present invention was accomplished based on these findings.
The invention provides a corrosion-resistant metallic member which comprises a metallic base and a thin noble-metal layer deposited on at least part of the metallic base and which has undergone compression working to reduce the total thickness of the base and the thin layer by 1% or more (preferably 5% or more).
The highly corrosion-resistant material (member) of the invention is preferably one which comprises a metallic material, e.g., an elemental metal selected from the group consisting of iron, nickel, titanium, copper, and aluminum or an alloy comprising at least one metal selected from said group, and dep
Kaneta Yasushi
Shinkawa Masaki
Suzuki Yoshihisa
Takagi Shinobu
Yoshida Hiroaki
Bacon & Thomas PLLC
Daido Tokushuko Kabushiki Kaisha
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