LONG SERVICE LIFE IRO2/TA2O5 ELECTRODES FOR ELECTROFLOTATION

Ti/IrO2-Ta2O5 electrodes prepared by thermal decomposition of the respective chlorides were successfully employed as oxygen evolving electrodes for electroflotation of waste water contaminated with dispersed peptides and oils. Service lives and rates of dissolution of the Ti/IrO2-Ta2O5 electrodes were measured by means of accelerated life tests, e.g. electrolysis in 0.5 M H2SO4 at 25-degrees-C and j = 2 A cm-2. The steady-state rate of dissolution of the IrO2 active layer was reached after 600-700 h (0.095 mug Irh-1 cm-2) which is 200-300 times lower than the initial dissolution rate. The steady-state rate of dissolution of iridium was found to be proportional to the applied current density (in the range 0.5-3 A cm-2). The oxygen overpotential increased slightly during electrolysis (59-82 mV for j = 0.1 A cm-2) and the increase was higher for the lower content of iridium in an active surface layer. The service life of Ti/IrO2 (65 mol%)-Ta2O5 (35 mol%) in industrial conditions of electrochemical devices was estimated to be greater than five years.