Role of Minor Elements In the Oxidation of Metals★

An analysis is made of the role of impurities in the oxidation of metals. The various impurities are considered in terms of their effects on the physical and chemical structure of the oxide, oxide-metal interface and metal. Eight types of effects are discussed and where experimental data are available these data are used to illustrate the nature of the effect. The eight types of effects are: (1) formation of new oxide of impurity atoms in outer layer, (2) formation of mixed oxides or spinels, (3) formation of impurity atom oxide in inner layer, (4) change in conductivity of oxide film, (5) change in physical properties and adhesive properties of oxide and oxide-alloy interface, (6) formation of inclusions and other defects in the metal, (7) concentration of impurities at the grain boundaries of the metal and (8) surface oxide-impurity atom reaction with volatile reaction product. 3.7.2