ON THE MECHANISM OF ELECTROLESS NI-P PLATING

The electroless deposition mechanism of nickel, in a chloride-based solution, using hypophosphite ion as reducing agent was examined using potentiodynamic method and open-circuit potential measurements. The results indicate that the mixed potential theory is unable to describe this system. This is due to the nature of the involved mechanism. It is assumed that the process is initialized by adsorption of hypophosphite ions, followed by the homolysis of primary reductant species, resulting in the formation of atomic and ionic radicals which promote nickel and hypophosphorous acid reduction to originate the Ni-P deposit. The initial deposition stages of Ni-P were observed, revealing that the substrate induction, which leads to an increase in the catalytic activity, is not related to a galvanic displacement process, but rather to the establishment of the electrochemical conditions which allow the adsorption/breakdown of the hypophosphite ions. The experimental results are in good agreement with the proposed mechanism.