Thermodynamic Roles of Metallic Elements in Carburization and Metal Dusting

Abstract

This paper addresses the thermodynamic aspects of metallic elements (typically Fe, Ni, and Cr) in carburization and metal-dusting processes in CH₄–H₂, CO–CO₂, and CO–H₂O–H₂ carburizing gas mixtures, and their possible contributions to understanding of carburization and metal-dusting phenomena. Carburization requires $a_C \left( {gas} \right) > a_C \left( {M_Z C/M} \right) \cdot a_C \left( {M_Z C/M} \right)$ is solely temperature-dependent, while a_C (gas) is dependent not only on temperature but also on gas chemistry and total pressure. In general, metallic elements tend to be carburized at higher temperatures in CH₄–H₂, but at lower temperatures in CO–CO₂ and CO–H₂O–H₂ carburizing gas mixtures. For metal dusting to occur, $a_C \left( {M_Z C/M} \right)$(gas)> 1 (first-type) and $a_C \left( {gas} \right) > a_C \left( {M_Z C/M} \right)$; 1 (second-type) should be satisfied. Possible regimes for first- and second-type metal dusting are discussed for pure Fe and Ni, and the range for first-type metal dusting of Ni is considerably broader than that for Fe.