Formation of porous anodic films on Ti–Si alloys in hot phosphate-glycerol electrolyte

Porous anodic films, with pore size of ∼10 nm, have been developed by anodizing of magnetron sputtered Ti–25 at.% Si alloy at constant formation voltages in glycerol electrolyte containing dibasic potassium phosphate at 433 K. The films, of amorphous structure, contain titanium and silicon species, as units of TiO2 and SiO2, throughout the film thicknesses, with negligible amounts of phosphorus species. The silicon is enriched in the film relative to the composition of the alloy, the level of enrichment suggesting that anion migration is increased in comparison with amorphous film growth at ambient temperature. In contrast to the behaviour of the alloy, essentially barrier films were formed on commercially pure titanium in the glycerol electrolyte, when a main anodic reaction was generation of oxygen, which was probably promoted by the development of anatase.