Effect of coating thickness and surface treatment of titanium on the properties of IrO2-Ta2O5 anodes

The effect of coating thickness and the effect of surface treatment of the titanium base metal on the surface morphology and electrochemical properties of IrO2-TaO5 anodes were investigated. It was observed that for an iridium content of 0.45-1.2 mg cm(-2) the service life is proportional to the iridium content in the coating. During etching of titanium in 5% HF at 25 degrees C a surface with macroroughness is formed, while during etching in HCl at 30, 50 and 80 degrees C a microrough surface with visible pitting is formed. The morphology of the IrO2-Ta2O5 active layer (0.32-0.39 mgIrcm(-2)) depends strongly on the pretreatment of the titanium base metal. After etching of titanium in HF, the resulting IrO2-Ta2O5 layer is adherent to the macrorough surface of the titanium base metal. After etching of titanium in HCl the resulting surface of the IrO2-Ta2O5 layer is microrough with partly filled pitting holes. The service life of IrO2-Ta2O5 coating with different roughness does not differ and has a value of 1500+/-400 h (0.5 M H2SO4, 25 degrees C and j=2 A cm(-2)).