ピロリン酸浴からのCu-Zn合金めっきにおけるヒスチジンの作用機構

抄録

Measurements of current density-potential (I-E) curves and AC impedance during electrodeposition of Cu-Zn alloys showed that Zn was codeposited only under conditions of diffusion-limited Cu deposition in the case of baths without histidine. This was confirmed by the characteristics of the I-E curves and by the characteristic Warburg impedance behavior. In the case of the baths containing histidine, on the other hand, Zn was codeposited under conditions where Cu deposition was not diffusion-controlled. I-E curves and double layer capacitances suggest that the adsorbed histidine suppressed Cu deposition and markedly increased the surface concentration of Cu⁺ adions. The adsorbed histidine suppressed Cu deposition even at negative potentials sufficient for Zn codeposition in the alloy baths Therefore, the rate of Cu deposition in the alloy baths was so small that it did not exceed the diffusion limited current of Cu²⁺ ion at negative potentials sufficient for Zn codeposition and this resulted in the smooth Cu-Zn alloy deposits. Data from AC impedance measurements suggest that an adsorbed intermediate plays an important role in alloy deposition processes from the baths containing histidine.