ニッケル-クエン酸めっき浴におけるニッケル-クエン酸の錯平衡

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Ni (II)-Citrate complexing equilibrium and the correlation with electrolysis in nickel-citrate plating baths were studied. From absorption spectra, pH buffer capacity, and calculated simulation studies, it has been revealed that various complexes, NiHCit0, NiCit-, NiCit24-, Ni (H-1Cit)2- etc., were formed in nickel citrate solutions, and the concentration distributions of these complexes were varied by the changes in the compositions and/or pH of the solutions. Above pH 4, the formation of 1:1 complex (NiCit-) was recognized. In the pH range of 5 to 8, the proportion of NiCit- decreased and that of NiCit24-, which has lower molar absorptivity, increased with an increase in the Cit/Ni ratio in the solution. Above pH8, nickel-tetraionized citrate complex Ni (H-1Cit)2-, which has large molar absorptivity, was formed, and the pH value of formation of this complex became higher with an increase in the Cit/Ni ratio in the solution.Electrolysis studies have revealed that, in neutral or alkali solutions, nickel-citrate equilibrium affected nickel deposition from nickel citrate solutions, and NiCit24- and Ni (H-1Cit)2- were more electrochemically innert than NiCit-. In acidic solutions, the addition of citrate accelerated the evolution of hydrogen, and decreased the current efficiency of nickel deposition.
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