What is formed on the surface of metals when they are oxidized?

When metals are oxidized, they react with oxygen in the environment, leading to the formation of an oxide layer on their surface. This layer is comprised of metal oxides that can protect the underlying metal from further corrosion or degradation. The oxide layer is often more stable than the base metal itself, providing a barrier that limits the metal's exposure to moisture and other corrosive elements.

In cases such as aluminum and titanium, this oxide layer is particularly effective at passivating the metal, enhancing its resistance to further oxidation and corrosion. However, in some situations, this layer may not be sufficiently protective, leading to potential vulnerability.

Other options do not accurately describe the result of oxidation. For instance, a brinell layer pertains to a hardness testing method rather than oxidation. A pitting layer refers to localized corrosion, while a corrosion layer would be a more general term and doesn't specifically represent the product of oxidation processes catalyzed by oxygen. Therefore, the correct identification of the oxide layer highlights a fundamental concept in metallurgy and materials science related to the behavior of metals in various environmental conditions.