The influence of mass transfer on the mechanism of electropolishing of nickel in aqueous sulphuric acid

✍ Scribed by I.L. Alanis; D.J. Schiffrin

• Publisher: Elsevier Science
• Year: 1982
• Tongue: English
• Weight: 799 KB
• Volume: 27
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(82)80205-3

✦ Synopsis

The effect of mass transfer on the elcctropolishing of nickel in sulphuric acid solutions has been studied using a rotating disc electrode technique. Two well d&ted regions for different rotation rate-s have been observed having (a) pure diffusion control, and (b) mixed kinetic and diffusion control. The presence of a solid layer of a hydrated nickel salt covering a contaminated oxide layer is proposed. The rate of chemical attack of the underlying layer apes to depend on the SO4 'ion concentration for H2S04 concentrations greater than 8 M. When the rate of mass transfer is increased, changes in the morphology of the surface are observed, polishing gives way to levelling, and finally either to metallographic etching or corrosion. The disappearance of electropolishing is observed in general when the rate of mass transfer is sufficient to eliminate from the surface the solid layer of hydrated nickel sulphate, and the results indicate a coupling between diffusional rates in the solution and ionic transport through the oxide or contaminated oxide phases.