Thermochemical diagrams: Some applications to the study of high temperature corrosion

Abstract

Diagrams of the electrode potential as a function of the temperature enable the influence of temperature and pressure on the stability and metastability of all substances which may exist in a given chemical or electrochemical system to be represented. Such diagrams show not only the equilibrium conditions of the reactions in which the substances may take part but also, for non-equilibrium conditions, the affinities of the reaction and, sometimes, kinetic information (catalytic action, exchange currents and velocities of reaction). Some examples of these diagrams are given for the following ten systems: OC, OFe, OH, OS, OSi, OHFe, OCSi, OCFe, OSFe and OSAl. Examples are also given of the applications of these diagrams in the study of (a) the corrosion and protection of iron in the presence of high temperature water, (b) the production of liquid silicon, the carbo-reduction of solid silica, (c) the corrosion of iron and aluminium in the presence of gaseous atmospheres containing oxygen and sulphur derivatives and (d) the production and stability of protective coatings in energy systems.