MORPHOLOGY AND STRUCTURE OF OXIDE-FILMS FORMED ON MAGNESIUM BY EXPOSURE TO AIR AND WATER

Oxide films formed naturally on pure Mg are investigated by the use of ultramicrotomed cross sections and transmission electron microscopy. The film formed in air immediately after scratching the metal surface is initially thin, dense, amorphous, and relatively dehydrated. Contin uing exposure to humid air or exposure to water leads to the formation of a thicker hydrated film adjacent to the metal. The film formed in water contains an additional toy! layer characterized by a plateletlik e morphology. The structure of these layers and their significance in corrosion protection are discussed. The changes occurring in these str uctures as a result of exposure to the electron beam are reported.