Formation of aluminum oxide scales in sulfur-containing high temperature environments

A model alloy consisting of Fe-18 wt pct Cr-6 wt pct Al was used to study the formation of α-aluminum oxide under various oxygen (1 to 10⁻²⁰ atm) and sulfur (10⁻¹³ to 10⁻⁶ atm) partial pressures at 900 °C. Acoustic emission results indicate that at constanti,e2051-01 (10⁻²⁰ atm) the oxide scale became much more resistant to isothermal cracking with increasing sulfur potentials. In addition, adherence of the oxide scale to the alloy was also enhanced and the oxidation rates increased with increasing sulfur potentials. Using inert palladium markers, the diffusion processes in the growing aluminum oxide scale were studied. In environments where oxygen was the only oxidant present, the results indicated that inward oxygen diffusion is the predominant scale growth mechanism. In contrast, oxides grown in sulfur containing environments revealed a drastic change of the marker position, indicating that the oxide growth occurred predominantly by outward aluminum ion diffusion. Oxide scale morphologies are shown using scanning and transmission electron microscopy. formerly a Graduate Student of Chemical Engineering and Materials Science Department of The University of Minnesota