What metals commonly form a passive film?

The formation of a passive film is a crucial aspect of corrosion resistance in metals. Stainless steel and titanium are commonly known for their ability to form a strong passive film, which is an oxide layer that protects the underlying metal from further oxidation and corrosion in various environments.

Stainless steel contains a significant proportion of chromium, which reacts with oxygen to form a thin, stable oxide layer on the surface. This passive film adheres well and prevents additional corrosion by acting as a barrier against aggressive environmental factors.

Titanium, similarly, has a remarkable ability to form a robust passive oxide layer when exposed to oxygen. This oxide layer not only protects the metal from corrosion but also enhances its biocompatibility, making titanium a popular choice in medical implants and other applications where both strength and resistance to corrosion are essential.

Other metals may form passive films, but the ones mentioned tend to have more notable and widely recognized passive film properties, particularly in aggressive environments. This is why the choice highlighting stainless steel and titanium is correct in the context of metals that form a passive film.