Destruction of coating material during spark anodizing of titanium

An investigation has been carried out, using a sequential anodizing procedure, of the loss of coating species to the electrolyte during spark anodizing of titanium. Anodic coatings were formed galvanostatically in alkaline silicate electrolyte and then further thickened by re-anodizing in alkaline phosphate electrolyte. In addition to examination of coating compositions and morphologies following different times of anodizing in each electrolyte, solution analyses for silicon and titanium were carried out subsequent to anodizing in the phosphate electrolyte. Significant amounts of both elements were detected, indicative of destruction of the coating at sites of dielectric breakdown in the phosphate electrolyte. The lost coating material is replaced by formation of phosphorus-rich material at the breakdown sites, as evident from elemental mapping of coatings.