An O18 study of the interaction between carbon monoxide and dry thermal SiO2 at 1100 °C

Abstract

The mechanisms of oxygen exchange between thermal silicon oxide films and carbon monoxide have been studied using O18 as an isotopic tracer. SiO2 layers of natural isotopic composition, obtained by thermal oxidation of silicon, were exposed at 1100 °C to C13O18 gas at pressures ranging from 50 to 350 mbars. O18 concentration depth profiles were determined using the nuclear narrow resonance profiling technique with the narrow resonance near 151 keV in the reaction O18(p,α)N15. The results show that oxygen exchange takes place via two distinct processes and a mechanism for each process is proposed in the present work. The diffusion coefficient of CO molecules in the silica and the oxygen exchange frequency between CO and the silica are also determined.