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 hypophosphite concentration must be higher than a certain threshold to induce the autocatalytic process. The impedance behaviour exemplifies the kinetic evolution: a large capacitive loop with a high-frequency inflection when only chemical displacement occurs and two well-defined capacitive features when the autocatalytic process is achieved. Mutual interactions 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 increases. A pH increase accelerates the plating process though it inhibits the cathodic discharge and reduces the copper content.