Study On Mixed Metal Oxide Anodes For Cathodic Protection

Studies on the anode material with mixed metal oxides of IrO2 and Ta2O5 coated titanium, the impressed current anode component of large current output and the simulation test in the field were carried out to meet the need of corrosion prevention by cathodic protection for large marine vessels. The following results have been achieved in this work:The microstructure and the electrochemical characterization in the neutral solutions of IrO2 and Ta2O5 coated titanium anode were analyzed systematically. The effect of composition of the oxide coating and the pretreatment of the titanium substrate on the morphologies and fine structures of the anodes was studied. The relationship between the microstructure and the electrochemical surface characteristics of the oxide anodes was explained. It was found that the morphology of the oxide anode presents the outline characteristics of the etched titanium substrate. The Ir content affects the microstructure of the oxide anode significantly. The surface of the oxide anode is controlled by Ir(III)/Ir(IV) redox transition. The anodes with 50~70% Ir content show the highest electrochemical activity and the largest electrochemical active surface area, which is attributed mainly to the contribution from the inner surface revealed with the analysis of the voltammetric charges.The anode with 70% Ir also presents the highest stability and utilization efficiency of the active element due to the fact that the synergistic interaction of the oxide mixture will enhance the stability, and the oxide coating with 70% Ir has not only good electrocatalytic effect but also the largest electrochemical active surface area, which lowers the real current density significantly.The deactivation of IrO2 and Ta2O5 coated titanium anode was monitored electrochemically. The failure mechanism of the oxide anode was elucidated based on the results of analyses with CV, EIS, SEM and EDX. The possible measures to further improve the properties of the oxide anodes were also suggested.The electrochemical properties of mixed metal oxide anode were evaluated in sea water. The oxide anode has higher electrochemical activity and lower consumption rate than platinized anode and lead silver alloy when it is energized in seawater, indicating that the oxide anode belongs to anode material of high performance.An anode component with large current output was designed and manufactured with the oxides coated titanium as the anode body, and the glass fiber reinforced epoxy resin as the anode holder. The simulation test in seawater showed that the anode component can discharge a current output of over 100 A, having excellent performance in resistance to the negative potential, the action of seawater and the attack of evolved chlorine.The effect of the thickness of epoxy putty coating as dielectric shield of anode on the resistance to cathodic disbonding was determined. The cathodic potential distribution around the anode component of large current output was measured. The applicability of the calculating formula of the anode shield dimension in the standards was discussed. The results can provide technical support reliably for the reasonable design of the anode shield coating.