The effect of such variables as etchant concentration, bath temperature, current density and current sweep rate on the cubic pit propagation and porous etch structure formation is discussed by means of electron microscopy and galvanovoltammetry. Maximum values of electrostatic capacitance were obtained under conditions for the formation of a deep porous etched layer. The formation of such a layer was found to be due to the formation and breakdown of a thin anodic film covering the inner surface of the cubic pits during etching. As indicated by the shape of cyclic polarization curves, the breakdown of the anodic film was facilitated by increases in the concentration and temperature of the etching solution, and suppressed by increases in the current sweep rate. This is explained by the rate at which Cl- ions are supplied to the bottoms of cubic etch pits.
