Degradation characteristics of Ti/(IrO2+Ta2O5) coating anodes in H2SO4 solution

The service life of Ti based IrO 2+Ta 2O 5 coating anodes over the whole composition range and prepared at different temperatures was studied by the accelerated electrolysis tests. The results show that as a result of incompleted decomposition, coatings obtained at low temperature are not stable. At the preparing temperature up to 450 ℃,the stability of the resulting deposits increase dramatically, and is independent on temperature. However, at higher temperature, oxidation of Ti base occurred leading to a decrease in the adhesion of coatings which resulted in decreasing of the service life of anodes. The maximum durability was obtained for the anodes prepared at 450 ℃.Resulting from the maximum solubility between the iridium and tantalum oxides, coatings with 70%IrO 2+30%Ta 2O 5 (mole fraction) exhibited the maximum stability. A preferential dissolution of Ir on the non close packed planes of the rutile oxides was observed for the pure IrO 2 deposits while on the close packed planes for the IrO 2 and Ta 2O 5 mixed ones in electrolysis. This dissolution characteristic can interpret a low service life for the coating anodes with a low IrO 2 content since the close packed planes orientations are dominant in these flesh samples. Two mechanisms for the degradation of Ti/(IrO 2+Ta 2O 5) anodes were also proposed.