SURFACE-REACTIONS AT 300-750-K IN THE IRON OXYGEN WATER-SYSTEM STUDIED BY SIMS

Secondary ion mass spectroscopy, SIMS, has been applied to the surface study of the iron-oxygen-water system in the 300-750 K temperature range in order to gain insight into the initial stages of wet oxidation of iron. During sputtering with Ar+ ions the emission of OH-containing ions was strongly dependent on temperature. In situ X-ray photoelectron spectrometry experiments were conducted in order to support this observation. In experiments where the metal was exposed simultaneously to (H2O)-O-18 and O-16(2), the source of O in the reaction product could be determined by analysis of the ions emitted at different temperatures. This analysis showed that a coupled reaction, 2Fe + H2O + 1/2O2 --> 2FeOH, is operating at room temperature. At higher temperatures iron reacts preferentially with water as can be seen from the abundance of O-18 in the emitted ions.