Study of the corrosion and electrochemical properties of anodic coatings in conditions of chlorine electrolysis

Summary

Traditionally for water purification and disinfection various oxidizing agents have been used, usually chlorine-containing products including low-concentration sodium hypochlorite obtained by electrolysis of aqueous solution of table salt at the point of consumption. The greatest influence on the electrolysis efficiency (current active chlorine yield), electrical and electrochemical performances, effectiveness of the process and operational practices, design of devices and their durability is exerted by the anode material; the main requirement to it being the chemical resistance in the mode of anodic polarization in the chemically active environment. Ruthenium-titanium oxide anodes have become widely used in practice owing to their high-wearing properties. A decrease in the rate of continuous decrease in the thickness of the active layer and the loss of ruthenium oxide can be achieved by using a three-component coating of the anode with the addition of a platinum group metal – iridium. Three-component coatings of anodes containing iridium (iridium-ruthenium-titanium oxide anodes), with a mass percentage of iridium to ruthenium of 80:20 provide for 8-fold increasing the corrosion resistance of the anodes (service life). As the iridium oxide concentration increases, the anode coatings consume less energy for generating sodium hypochlorite owing to the lower voltage across the electrolyzer. The corrosion resistance of anodes with different ruthenium and iridium oxide fills as well as their characteristics, i. e. chlorine yield in terms of current efficiency, electrolyzer voltage, dynamics of active chlorine concentration increase were determined.

Key words

low-concentrated sodium hypochlorite , oxide coatings , iridium , ruthenium , corrosion resistance of anodes , current chlorine yield , electrolysis of 3% solution of table salt