Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2007-07-24
2007-07-24
Zimmerman, John J. (Department: 1775)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C148S230000, C148S318000, C428S472100
Reexamination Certificate
active
11071830
ABSTRACT:
A nitridation treated stainless steel article (such as a bipolar plate for a proton exchange membrane fuel cell) having lower interfacial contact electrical resistance and better corrosion resistance than an untreated stainless steel article is disclosed. The treated stainless steel article has a surface layer including nitrogen-modified chromium-base oxide and precipitates of chromium nitride formed during nitridation wherein oxygen is present in the surface layer at a greater concentration than nitrogen. The surface layer may further include precipitates of titanium nitride and/or aluminum oxide. The surface layer in the treated article is chemically heterogeneous surface rather than a uniform or semi-uniform surface layer exclusively rich in chromium, titanium or aluminum. The precipitates of titanium nitride and/or aluminum oxide are formed by the nitriding treatment wherein titanium and/or aluminum in the stainless steel are segregated to the surface layer in forms that exhibit a low contact resistance and good corrosion resistance.
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Brady Michael P.
Turner John A.
Wang Heli
Quarles & Brady LLP
UT-Battelle LLC
Zimmerman John J.
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