Thermodynamics of cementite layer formation

The formation of cementite layers upon carburization of iron is described by a thermodynamic approach assuming the establishment of an equilibrium within the carburizing gas atmosphere and between the solid and the gas. Based on that, the suppression of soot formation by adding ammonia to the gas, which has recently been reported in the literature as a kinetically determined surprising phenomenon, can be explained sufficiently well and, hence, proves to be a thermodynamically predictable effect.