A CALCULATION METHOD FOR ANALYSIS OF SIMS SPECTRA FROM OXIDATION OF METALS IN (H2O)-O-16/(H2O)-O-18/O-16(2) GAS-MIXTURES

A calculation method for the secondary ion mass spectrometry (SIMS) analysis of the reaction of a pure metal with gas mixtures of water and oxygen is introduced. Equation systems are to be solved, each expressed as: Y = A x X, where Y is an amplitude column measured from the SIMS spectrum, A is a matrix constructed from the relative abundances of isotopes of the metal and X is an unknown amplitude column of the relevant species Me(a)OH(b)+/-(a = 1, 2; b = 0, 1, 2 and 3). The applicability of the calculation method his been tested in SIMS analysis of ex situ-grown iron oxides with different and known O-18 contents. In in situ oxidation, measurement of the ratio of (H2O)-O-16/(H2O)-O-18 in the metal-water-oxygen reaction allows fractions of O in the species Me(a)OH(b)+ that originate from water to be calculated. Data from such calculations have been used to study the initial stage of the reaction of Fe and Cr in (H2O)-O-16/(H2O)-O-18/O-16(2) gas mixtures. The results are interpreted in terms of coupled/uncoupled reaction type, reactivity of metal to water relative to oxygen in the mixed gas and degree of dissociation of water.