| A kinetic study on the electrodeposition of Ni-Cr-P alloys onto a steel has been performed using a rotating disk geometry. Activation energies of nickel and phosphorus in the temperature range between 8℃ and 45 C were 12.1㎉/mole and 9.6㎉/mole, respectively, and that of chromium between 8℃ and 25℃ was 5.4㎉/mole. The rates of electrodeposition of nickel and phosphorus seems to be controlled partly by electrochemical reaction and partly by mass transport, namely mixed controlled. However, the rate of chromium deposition seem to be controlled by mass transport. As the stirring speed increased, the concentration of nickel in the deposit decreased, but that of chromium increased and phosphorus was not affected. On the other hand, as the temperature was increased, the concentration of nickel in the deposit increased, that of chromium decreased and phosphorus did not vary. A model was proposed to evaluate composition of nickel, chromium and phosphorus in the Ni-Cr-P alloys. The model included the influence of diffusion, forced convection and equilibrium concentration considering the activity coefficient of chemical species in the electrolytic solutions of Ni-Cr-P system. The composition in the coating layer predicted by the model agreed well with the measured composition at various experimental conditions, such as disc rotating speed, applied potential and temperature. |
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