Effect of pressure on the electrodeposition of nanocrystalline Ni-C in supercritical CO₂ fluid

Electrodeposition of Ni in a Watt's bath at different applied pressure, and in the presence of CO₂ fluid was investigated. The reduction of carbon and its alloying into the Ni deposit was focused. The current efficiency of electrodeposition and the carbon content in the Ni deposit were found to vary with the applied pressure. The crystal structure of the resulting Ni-C film was characterized by performing X-ray diffraction. The composition of the deposit was analyzed using X-ray photoelectron spectroscopy. Transmission electron microscopy was employed for microstructure analysis. The results showed that nanocrystalline Ni-C deposit could be obtained. The grain size of the Ni-C film varied from 14 to 43 nm, depending on the deposition pressure and carbon content. A significant increase in microhardness from 450 to 720 Hv could be obtained for the Ni film electrodeposited from a bath of 15 MPa supercritical CO₂ fluid. In 1 M HCl solution, a higher open circuit potential and a lower anodic current density were found when the carbon content in the Ni deposit was increased.