We investigated the feasibility of long-term, continuous electroplating using an Fe-W alloy bath. When an Fe-soluble anode was used for Fe-W alloy plating, the W content of plating films decreased concomitantly with the plating time. Furthermore, precipitation, which is expected to be iron hydroxide, was observed in the bath after 10 hr operation of the plating. These results were ascribed to the increase in the Fe（II）concentration, which was the result of dissolution of the Fe anode. When a Pt insoluble anode was used instead, oxidation of Fe（II）ions and organic complexing agents occurred at the anode. Cracks and delamination were also observed in plating films. Furthermore, after precipitation was observed in the bath after 48 hr, the bath was abandoned. Oxidation of Fe（II）to Fe（III）occurred even when the bath was kept in air. Immersion of an Fe plate in the bath was effective to suppress the generation of Fe（III）ions. Stress measurements revealed that a bath with high Fe（III）concentration generated tensile stress in the plating films, which can be expected to cause cracks and delamination. To alleviate the stress, we investigated a system using an ion-exchange membrane and multiple anodes. This system provides long-term, continuous, and stable electroplating of Fe-W alloy.
Three-dimensional （3D） impedance spectroscopy was applied to the evaluation of film growth rate of a chromate film formed on a steel and a galvanized steel. Impedance spectra were plotted on a 3D diagram with real, imaginary, and time axes. Scratched electrodes of three types were used for 3D impedance measurements to investigate the film growth rate of the chromate film （1） with a scratch reaching to the substrate steel of the chromated steel （C/FeFe）, （2） with a scratch reaching to the substrate steel of the chromated galvanized steel （C/Zn/FeFe）, and （3）with a scratch reaching to the zinc layer of the chromated galvanized steel（ C/Zn/FeZn）. Subscripts of C/FeFe, C/Zn/FeFe and C/Zn/FeZn denote the layer to which the scratch reached. The 3D impedance of the C/FeFe and C/Zn/FeFe demonstrated that the impedance was decreased drastically at the initial stage, and that it increased remarkably with time. The 3D impedance of C/Zn/FeZn indicated that the impedance was decreased gradually at the initial stage, and that it increased slightly with time. The instantaneous impedance at an arbitrary time was determined from the cross-section of the 3D impedance plot. The film resistance Rdf of each electrode was estimated by curve fitting of the instantaneous impedance using the equivalent circuit. Results indicate that the increasing rate of Rdf until the steady-state condition is in the order of C/Zn/FeZn < C/Zn/FeFe < C/FeFe.
Results show that bright tin-iron alloy deposits were obtained by polyoxyethyleneglycol （average molecular weight 4000） to gluconic acid baths containing 0.05 mol/dm3 SnSO4, 0.1 mol/dm3 FeSO4･7H2O, 0.15 mol/dm3 potassium gluconate, 0.05 mol/dm3 NTA, 0.5 mol/dm3 urea, and 0.45 mol/dm3 NH4Cl. The optimum operating conditions were pH 3, bath temperature 45°C, and current density 7-12 A/dm2. Tin-iron alloy films were superior in corrosion resistance to bright nickel plating films because of the formation of tin-iron intermetallic compounds.