Lead/platinum bi-electrodes

The action of platinum microelectrodes has been extensively studied Trials carried out by Peplow have shown that lead/ platinum bi-electrodes can be used in high velocity seawater at current densities up to 2 000 Am and that blister formation with corrosion under the blisters is decreased by the presence of platinum microelectrodes. The current density range in which the anode is normally operated is 200-750 Am with the maximum working current density quoted as 1 000 Am The consumption rate of theje anodes ranged from 0-0014 kg A y at 500Am , but increased to 0-003 kg... 

In seawater, lead anodes with 1 or 2% silver may be used for cathodic protection of ships " at current densities of up to 120Am Lead with 6Vo antimony and 1 Vo silver has also been recommended. It is thought that silver might provide small stable nucleation sites for PbOj formation " in a manner similar to the Pb/Pt bi-electrode " (see Section 11.3), which is serviceable at 250 A m . A lead. Wo Ag, 0.5% Bi or 0.5% Te alloy with a platinum micro-electrode will perform well at 500 A m. ... 

The formation of PbOj is favoured in solutions containing passivating anions such as SO4 and in chloride solutions of intermediate concentrations very high and very low concentrations of chloride inhibit the formation of Pb02- The platinum/lead bi-electrode performs best in seawater, and is not recommended for use in waters of high resistivity. 

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