ELECTROCHEMICAL INVESTIGATION OF THE AUTOCATALYTIC DEPOSITION OF NI-CU-P ALLOYS

Autocatalytic deposition of Ni-Cu-P alloys (55-65 wt % Ni, 25-35 wt % Cu, 7-10 wt % P) has been carried out. It is shown that the hypophosph ite concentration must be higher than a certain threshold to induce th e autocatalytic process. The impedance behaviour exemplifies the kinet ic evolution: a large capacitive loop with a high-frequency inflection when only chemical displacement occurs and two well-defined capacitiv e features when the autocatalytic process is achieved. Mutual interact ions occur between partial oxidation and reduction reactions which are both depolarized as compared to the separate reactions. In addition, phosphorus incorporation is always reduced when the copper content inc reases. A pH increase accelerates the plating process though it inhibi ts the cathodic discharge and reduces the copper content.