Fe-W合金めっきにおけるFe(III)の影響とイオン交換膜-複数陽極システムを用いた連続めっき

Abstract

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.