In broad terms, the interaction between a material and its environment that results in a degradation of the physical, mechanical, or even esthetic properties of that material. More specifically, corrosion is usually associated with the oxidation and/or dissolution of a metal, oxide, or semiconductor. For example, immersing a piece of iron in a moderately acidic solution is a typical example of corrosion; the vigorous reaction is the electrochemical oxidation of iron from the zero valence state to divalent ferrous ions (Fe⁺²) dissolved in the water. Corrosion encompasses principles from diverse fields such as electrochemistry, metallurgy, physics, chemistry, and biology.