this post was submitted on 11 Sep 2023
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Chemistry
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I think I get what you say : if I take your words, you could say 2 metals are "opposite in nature" in the sense that they would form a galvanic couple that would (that may) in certain conditions, inhibit the passivation.
This can happen to alloys (as well) as follows. Start with a piece of stainless steel that passivates well. Now, heat it at about 500 degrees Celsius. Doing this, you produce chromium carbide precipitates around which the alloy is depleted in chromium and though enriched in iron. The result is that, after this treatment, you would notice the metal now corrodes and rust dots appear on the surface.