Introduction

Abstract

Solid and liquid metals in contact with the reactive gases of the earth atmosphere are examples for unstable chemical systems. The equilibrium state is attained only after the whole volume of metal has been transformed to an oxide. Fortunately, kinetics retards this process in everyday live to rates low enough to avoid substantial problems in the use of metallic objects. Depending on pressure and temperature the elements hydrogen, oxygen, carbon, nitrogen, sulfur, and others can either be dissolved in the bulk of metal phases or compounds are formed on the surface, for example, oxides. The processes of gas absorption as well as the reverse ones of gas desorption or compound decomposition are complex heterogeneous reactions composed of transport processes in the gas phase and in condensed phases and of surface and interface partial reactions.