Etching Mechanism of a Rotating Steel Disk Electrode in 3.7-4.1mol dm^-3 Ferric Chloride Etchant

Abstract

The effect of rotation rate upon potential and etch rate of a steel was examined utilizing a rotating steel disk electrode. Being based upon these experiments, etching mechanism was discussed.
The principal ingredient of etchants was FeCl₃. The concentration of FeCl₃, FeCl₂ and free HCl were 3.7 to 4.1mol dm^-3, 0.17±0.02mol dm^-3 and 0.15±0.02mol dm^-3, respectively. The temperature of the etchants was maintained at 70°C and rotation rate of the steel disk was set at 400∼4900rpm. The etch rate was obtained from the weight loss.
The etch rate and square root of rotation rate are in proportionate relations at any concentrations of FeCl₃. The anodic reaction is controlled by surface reaction process, while the catholic reaction proceeds under mass transfer control.