Characteristics of electrodeposition of Ni and Ni-P alloys from methanesulfonate electrolytes

Abstract

The characteristics of electrodeposition of Ni-P alloys from a methanesulfonate electrolyte have been investigated. Ni-P alloys electrodeposited from an electrolyte containing 0.03–0.12moldm−3 of sodium hypophosphite, produce uniform, smooth, and well adherent to the substrate deposits. Phosphorus content of the alloy increases with an increase in the sodium hypophosphite concentration in the electrolyte and a decrease in the electrodeposition current density. Nickel-phosphorus alloys have a refined surface structure with small grains closely adjacent to each other. Ni-P alloys obtained from the methanesulfonate electrolyte at pH 3, have gloss levels of up to 20%. The coatings exhibit higher internal stresses and hardness, which increase with an increased concentration of sodium hypophosphite in the electrolyte. A decrease in the electrolyte pH increases the phosphorus content of the deposits and enhances the properties studied. The phosphorus content of the coatings obtained from a methanesulfonate electrolyte is lower than in the coatings deposited from a sulfate electrolyte under the same conditions. However, the deposits produced from the methanesulfonate electrolyte are characterized by higher values of gloss, hardness and internal stresses. This is due to the fact that along with phosphorus incorporated into the coating, the deposit structure is distorted by nickel hydroxide incorporated to the deposit during the electrolysis. The methanesulfonate electrolyte has lower buffering properties and, correspondingly, a higher amount of nickel hydroxide dispersion is formed in the near-electrode layer. The experimental data indicate that, in spite of lower phosphorus content, Ni-P alloys deposited from a methanesulfonate electrolyte have better physical-mechanical properties than those deposited from a sulfate electrolyte.