抄録
Electrodeposition of Fe-Ni alloys was conducted galvanostatically in sulfate baths of pH 1-3 at 40ºC to investigate their codeposition mechanism. The results obtained are described as follows :
(1) The electrodeposition behavior of Fe-Ni alloy showed a typical feature of anomalous codepostion, in which electrochemically less noble Fe deposits preferentially under most plating conditions. This anomalous codepostion was caused by the suppression of Ni deposition due to codeposition of Fe.
(2) The anomalous codeposition was evidently dependent on the pH buffer capacity of the baths, which can be explained in terms of the preferential adsorption of FeOH on the deposition sites due to different dissociation constants between FeOH+ and NiOH+ in the multi-step reduction process of hydrated iron-group metal ions.
(3) The degree of the preferential deposition of less noble Fe was decreased under the plating conditions to decrease the adsorption of FeOH on the cathode.
(4) The pH titration curves were measured in an Fe2+ single bath using NaOH solution. The Fe2+ -single bath showed pH buffering action around pH 6.3, which corresponds to FeOH+ formation in the titration curve calculated from the dissociation constant of FeOH+.
