Electrodeposition of Ni-Sn alloy from ethylene glycol electrolyte. Part 2. Reactions in the bulk electrolyte

Previously, the authors developed a stable citrate ethylene glycol (EG) electrolyte providing the electrodeposition of Ni-Sn alloy at quite high rate, current efficiency and nickel content in the alloy. In this study a complexation in the solution containing nickel and tin(II) chlorides, and citric acid was studied. IR spectroscopy data have shown the availability of Ni(EG)(2)Cl-2 and Sn(EG)Cl-2 complex compounds in the EG solution. At the addition of citric acid complexation of Ni(II) and Sn(II) with dihydrocitrate ions occurs. Binding of Sn(II) ions into complex compounds like Sn(EG)(H(2)Cit)(2) promotes regulation of Ni(II) and Sn(II) reduction rates, and ensures the increased nickel quota in the alloy and the stability of electrolyte against Sn(II) to Sn(IV) oxidation. The rate of coating deposition strongly depends on the electrical conductivity of the EG solution and rises with an increase in the temperature and concentration of metal halide crystalline hydrates.