Titanium Anodes with Active Coatings Based on Iridium Oxides: A Sublayer between the Active Coating and Titanium

An optimum composition and a technique for applying a protecting sublayer on titanium are substantiated experimentally. The sublayer prevents the oxidation of titanium during the production and application of highly porous metal oxide anodes. The formation of such a sublayer involves several stages: (a) coating chemically polished and etched in 5-% hydrofluoric acid titanium with hexachloroiridic acid, (b) drying hexachloroiridic acid, (c) a two-step treatment of anodes in argon with a low concentration of oxygen at 350°C, and (d) a brief annealing of the anodes in air at 400°C. The application of such a sublayer makes sense especially in the case of an anode with a thin highly porous active coating. The remarkable protecting properties of the sublayer are due to the formation of a dense coating on titanium. The coating consists of metallic iridium, titanium, and an amount of oxides of these metals. The titanium substrate itself undergoes minimum oxidation.