A novel process of electroless Ni–P plating by nonisothermal method

A novel process called nonisothermal method was developed by this work for the electroless Ni–P plating using operating temperature as high as 180 °C and even higher. Results obtained from measuring the open circuit potential (OCP) and the peak current of cyclic voltammetry (CV) indicated that a temperature depended thermal boundary layer with thickness of about 4–10 mm do exist by encompassing the heating substrate in our system. Based on the phenomena of the electrochemistry thermodynamics, the kinetic contour of a nonisothermal deposition (NITD) system could be described since the temperature profile of the thermal layer that governs the deposition reaction and the distance of the heat source with respect to the peak current of CV could be well correlated. The existence of the thermal boundary layer implied that the deposition reactions took place mainly within the thermal boundary layer itself rather than the bulk solution. By this method, the electroless Ni–P plating system even in the absence of the stabilizer can still be stably operated and it could even show two-fold deposition rate in comparison with the conventional method. Deposits performed by the NITD method having the phosphorous content at a level of 10–13% could exhibit a great enhancement on the physicochemical property and the microhardness from 500 up to 612 Hv0.1 as well.