Stainless steel sheet for a separator for a solid polymer fuel cell and a solid polymer fuel cell employing the separator

1. A stainless steel member for a separator for a solid polymer fuel cell, the stainless steel base metal comprising:

a stainless steel base metal;

a passive film; and

smut;

wherein the passive film, which is a film of an electrically insulating oxide. and the smut are provided on a surface of the stainless steel base metal;

wherein the smut is a substance, originating from the stainless steel base metal, which has precipitated on or adhered to the surface of the stainless steel member as a result of pickling of the stainless steel base metal;

wherein the smut includes electrically conductive precipitates;

wherein a thickness of the smut is larger than a thickness of the passive film and the electrically conductive precipitates penetrate the passive film; and

wherein the passive film partially covers the smut on a surface of the stainless steel base material.

2. A stainless steel member as set forth in claim 1 wherein the electrically conductive precipitates are a polycrystalline substance containing O, S, Fe, Cr, and C as constituent elements.

3. A stainless steel member as set forth in claim 1 wherein an electrically conductive layer comprising a nonmetallic electrically conductive substance is provided on the surface of the passive film, and the electrically conductive layer is electrically connected to the stainless steel base metal through the electrically conductive precipitates.

4. A stainless steel member as set forth in claim 3 wherein the nonmetallic electrically conductive substance includes graphite-based carbon.

5. A stainless steel member as set forth in claim 4 wherein the graphite-based carbon provided on the surface of the passive film has an interplane spacing d002 of at most 3.390 Angstroms.

6. A stainless steel member as set forth in claim 5 wherein when peak strengths of diffraction lines of atomic planes obtained by wide angle x-ray diffraction measurement of crystals of the graphite-based carbon provided on the surface of the passive film are compared, a ratio of the peak strength of the diffraction line of a (110) atomic plane to the peak strength of the diffraction line of a (004) atomic plane is less than 0.1.

7. A stainless steel member as set forth in claim 4 wherein the electrically conductive layer is formed by rubbing a member containing graphite-based carbon against a surface comprising the surface of the passive film and the surface of the electrically conductive precipitates.

8. A stainless steel member as set forth in claim 7 wherein the average surface roughness Ra of the surface comprising the surface of the passive film and the surface of the electrically conductive precipitates is at least 0.10 micrometers.

9. A stainless steel member as set forth in claim 4 wherein the electrically conductive precipitates and the electrically conductive layer are formed at the same time by performing electrolysis treatment of a stainless steel substrate comprising the stainless steel base metal and the passive film in an acidic solution containing sulfuric acid ions while rubbing a member including graphite-based carbon which functions as a counter electrode in the electrolysis treatment on the member being treated.

10. A stainless steel member as set forth in claim 9 wherein the average surface roughness Ra of the surface of the stainless steel substrate is at least 0.10micrometers.

11. A solid polymer fuel cell having a separator obtained from a stainless steel member as set forth in claim 1 .