Titanium is the leading material for artificial knee and hip joints because it's strong, wear-resistant and nontoxic, but an unexpected discovery by Rice University physicists shows that the gold standard for artificial joints can be improved with the addition of some actual gold.
Passivation (chemistry)
Titanium, aluminum, chromium, nickel and many other metals passivates rapidly in the presence of oxygen and water.
Thank you. I enjoyed https://en.wikipedia.org/wiki/Passivation_(chemistry). I don’t see the opposite nature though as being to incongruous as the material that passivates does so such that it never really is utilized without its coating while the non passivating just never gets the coating. In both cases, in the state they are utilized, they are very unreactive.
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.