亜鉛電解採取におけるPb-Ag-Ca系アノードの酸化物層の成長と電解挙動

The growth of the anodic oxide layer and electrolytic behavior of the Pb-0.5%Ag-xCa ( x = 0.4, 0.6 and 0.9mass%) anodes were studied in sulfuric acid solution for the as-cast specimen and the rolled-annealed materials. After 20 days of anodic polarization, the Pb-Ag-Ca ternary alloy anodes were compared with the Pb-1.0%Ag alloy anode conventionally employed in the practical operation of zinc electrowinning.The bath voltage was at similar level or decreased for the ternary alloy anodes compared with the Pb-1%Ag anode without calcium, and systematically reduced with an increasing Ca content.A trend is observed that the coverage of the anode surface mainly with dense layer of beta-PbO2 makes the generation of anode slime less in comparison with the anodes having oxide layer consisting largely of alpha-PbO2. Furthermore, it is noticed that the rolled-annealed alloys were associated by increased generation of anode slime at any calcium content and that the anode oxide layer on these alloys showed strong peaks coming from alpha-PbO2 in their XRD spectra.The observation of the cross section of the anode oxide layer indicated the thick oxide layer on the ternary alloy anodes with reduced generation of anode slime and development of cracks inside the oxide layer.The CaPb3 phase of less resistance against chemical attack was found to be distributed along the boundary of the lead-based alloy grains at 0.4 and 0.6% Ca content and, however, many CaPb3 grains of large size appeared also inside the grains in the 0.9% Ca ternary alloy.The Pb-0.5%Ag-0.4 to 0.6% Ca alloy seems to be most favorable for the reduced bath voltage and the minimized degradation of the anode material. The microstructure control by rolling and annealing the alloys is expected to affect the anode characteristics of the alloys.