Corrosion-resistant and protective properties of amorphous nickel-phosphorous coatings

The effect of deposition mode, cathode current density, support, time, and temperature of thermal treatment on corrosion resistance and protective properties of amorphous Ni-P coatings deposited from an original acid electrolyte was investigated. The constant concentration of Nickel was maintained by using nonpassivated Nickel anodes dissolved at high current densities of 80 A/m2. The studies show that the phosphorus content in coatings is reduced from 9.5% to 6% with pulse galvanization of the cathode current density increased from 2 A/dm2 to 6 A/dm2. The change in corrosion potential to a negative direction is due to partial sublimation of phosphorus from the coating and its diffusion to the support. The increase in temperature from 200°C to 400°C increases corrosion content density and shifts corrosion potential to a negative direction.