Abstract:The service life of Ti based IrO2+Ta2O5coating 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%IrO2+30%Ta2O5(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 IrO2deposits while on the close-packed planes for the IrO2and Ta2O5mixed ones in electrolysis. This dissolution characteristic can interpret a low service life for the coating anodes with a low IrO2content since the close-packed planes orientations are dominant in these flesh samples. Two mechanisms for the degradation of Ti/(IrO2+Ta2O5) anodes were also proposed.

Key words: oxide anodes; iridium oxide; tantalum oxide; degradation