Corrosion is the adverse change in the properties of a material caused by its reaction with its environment. The direct reaction of the metal with another substance is termed chemical corrosion. This is almost always a case of oxidation. It can be seen as sealing in high temperature applications. Stresses resulting from the reaction of the material with aqueous media or with other metals are termed electrochemical corrosion. In refractory applications the main corrosions are from sulphur and sulphur compounds, chlorine and chlorine compounds and alkalis alkaline earths.