Effect of H3PO3 concentration on the electrodeposition of nanocrystalline Ni–P deposited in an emulsified supercritical CO2 bath

The electrodeposition of Ni–P alloy in an emulsified supercritical carbon dioxide (sc-CO2) bath was investigated to explore the effect of H3PO3 concentration (ranging from 0 to 1.6 M) on the material characteristics of the deposits. The experimental results showed that the P content in the deposit increased with increasing H3PO3 concentration in the emulsified sc-CO2 bath, while the weight gain of the Ni–P film decreased. At the same concentration of H3PO3, the significant decreases in weight gain and P content of the Ni–P films deposited in the emulsified sc-CO2 bath were found, as compared with that plated in the conventional aqueous electrolyte at ambient pressure. X-ray photoelectron analyses revealed that the carbon-containing Ni–P deposit could be obtained in the bath with the presence of sc-CO2 fluid. Transmission electron microscopy was employed for microstructure analysis. The average grain size of the Ni–P films deposited in the conventional aqueous electrolyte at ambient pressure or in the emulsified sc-CO2 bath varied, depending on the H3PO3 concentration and P content. The Ni–P films deposited from the emulsified sc-CO2 bath had a higher hardness as compared with that formed in conventional electrolyte. The hardness of Ni–P alloy deposited in the emulsified sc-CO2 bath was enhanced by the additional solid solution strengthening mechanism.