Effect of Preoxidation on the Corrosion of Some Alloys in Coal Chars and Sulfur Vapor. Final Report

摘要

Preoxidation of several chromia-former and of several alumina-former alloys at temperatures ranging from 1800 to 2300 exp 0 F in either water-saturated argon or in air was performed prior to corrosion in coal char or in sulfur vapor. Chromia films offered no protection to sulfidation in both char and sulfur vapor environments. The chromia films were adherent but permitted rapid inward penetration of sulfur and outward penetration of cations to form extensive sulfides. Alumina films offered protection for much longer times than chromia films but localized cracking and/or spalling of the alumina permitted rapid attack at the exposed areas. The addition of yttrium as either a metallic element or as an oxide dispersion improved the mechanical stability of the films and prolonged the period of protectiveness. A binary alloy, Fe-13Al, sulfidized more raidly after preoxidation than before preoxidation. Alumina films would provide an excellent protective barrier if thick, crack-free films could be grown at reasonable temperatures. The low growth rates at very high temperatures and the susceptibility of alumina films to crack and spall during thermal cycling suggest that preoxidation will not offer adequate corrosion resistance for alloys exposed to char in goal gasifiers. (ERA citation 05:035872)