Degradation characteristics of
Ti/(IrO2+Ta2O5) coating anodes in H2SO4solution①
Ti/(IrO2+Ta2O5) coating anodes in H2SO4solution①
(Beijing Corrosion and Protection Center,
Open Laboratory of Corrosion, Erosion and Surface Technology,
University of Science and Technology Beijing, Beijing 100083, P.R.China)
Open Laboratory of Corrosion, Erosion and Surface Technology,
University of Science and Technology Beijing, Beijing 100083, P.R.China)
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