The influence of HCl on the oxidation of iron at elevated temperatures

A study has been made of the effects of 0.1 to 1.0% HCl on the oxidation of iron in argon - 20% O 2 at 600°C and 700°C. The overall weight-change kinetics included contributions from weight increases due to growth of oxide and chloride scale by solid-state diffusion and to deposition of oxide following vaporization of FeCl 2 and subsequent reaction with oxygen, and weight losses due to complete removal of FeCl 2 vapour to the environment. The weight gains in HCl-containing gases were less than that in the HCl-free gas at 600 °C, but greater than that in the HCI-free gas at 700 °C. The kinetics could be described by a modified Tedmon equation; it was found that much of the scale growth resulted from the chloride-to-oxide reaction following vaporization of FeCl 2 from local sites on the metal surface while the contributions from solid-state diffusion were relatively small.