Degradation characteristics of Ti/( IrO_2 + Ta_2O_5) coating anodes in H_2SO_4 solution

摘要

The service life of Ti based IrO_2 + Ta_2O_5 coating anodes over the whole composition range and prepared at different temperatures was atudied by the accelerated electrolysis tests. The results show that as a result of incompleted decomposition, coatinngs obtained at low temperature are not stable. At the preparing temperature up to 450deg.C, the stabili- ty of the resulting deposits increase dramatically, and is independent on temperature. However, of 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 ai 450deg.C. Resulting from the maximum sol- ubility between the iridium and tantalum oxides, coatings with 70/100 IrO_2 + 30/100 Ta_2O_5 (mole fraction) exhibited the maxi- mum 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 charac- teristic can interpret a low service life for the coating anodes with a low IrO_2 content since the close-packed planes orienta- tions are dominant in these flesh samples. Two mechanisms for the degradation of Ti/(IrO_2 + Ta_2O_5) anodes were also proposed.