HIGH-TEMPERATURE CORROSION.

Abstract

Materials considered for application in the high-temperature gaseous environments that are present in various coal-gasification processes must possess good structural integrity at elevated temperatures and inherent resistance to the corrosive atmospheres. A thermodynamic approach has been developed to characterize the gas environment in different pilot plant coal-gasification processes. The analysis is used to examine the thermodynamic stability of iron- and nickel-base alloys in these process environments. The results show that the sulfur and oxygen potentials in all processes are in a region where chromium oxide will be thermodynamically stable. In the absence of a continuous oxide layer, sulfidation of the alloys is expected which can lead to severe corrosion rates, particularly when liquid nickel sulfides are formed. It is concluded that a protective Cr//2O//3 layer is essential for an effective application of these alloys in coal conversion processes.