POLARIZATION CHARACTERISTICS OF METAL-OXIDE ANODES BASED ON RUTHENIUM, IRIDIUM, AND TITANIUM-OXIDES - A COMPARISON WITH TRADITIONAL DSA IN THE CONDITIONS PERTAINING TO SODIUM-CHLORATE PRODUCTION

Galvanostatic polarization curves are measured during electrolysis of chloride-chlorate solutions on anodes coated with RuO2-TiO2 (DSA) and IrO2-RuO2-TiO2 (DSA-I). The curves show that, on DSA-I, the increase i n the curve slope related to the transition into the supercritical pot ential region is significantly less-defined as compared to that on DSA . The distinction is interpreted using the assumption that such a tran sition results from appearance of conditions favorable to transformati on of RuO2 into RuO4 practically over the whole working surface of the anode coating, while IrO2 is stable almost throughout the potential a nd pH range typical for the process. With the chromate concentration i ncreasing above 2 g/l, the DSA-I transition to the supercritical regio n becomes more distinct. This may be related to the blocking of active centers of the IrO2 component.