If increasing the oxidizing power of the environment causes the corrosion rate to slow,  the material has become __________

The material has become passivated.

Passivation refers to the process through which a material, typically a metal, becomes less reactive and less prone to corrosion due to the formation of a protective oxide layer on its surface. In environments with high oxidizing power, metals can form stable oxide layers that hinder the further corrosion of the underlying material. This protective layer can significantly reduce the corrosion rate by blocking the pathways for corrosive agents, such as moisture and ions, to reach the metal surface. The effectiveness of passivation is influenced by factors like the type of metal, the environmental conditions, and the nature of the oxide layer formed. As a result, passivation is a desirable trait in materials used in corrosive environments, enhancing their durability and lifespan.