Magnetically-Induced Flow during Electropolishing. Issue 13 (27th September 2018)

• Record Type: Journal Article
• Authors: Monzon, Lorena M. A.; Nair, Vishnu; Reilly, Barry; Coey, J. M. D.
• Is Part Of: Journal of the Electrochemical Society. Volume 165:Issue 13(2018)
• Page Start: E679
• Page End: E684
• Publication Date: 2018-09-27
• Subjects: bubble surface charge -- Joule heating -- magnetoelectrochemistry; Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/2.0581813jes
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : Electropolishing (EP) of stainless steels in the presence of a uniform magnetic field is known to improve the surface finish. The current in electrochemical systems is usually enhanced because of magnetohydrodynamic convection, but in electropolishing it is actually reduced. Gas released during electrolysis leads to heating that normally enhances the dissolution current, but a magnetic field tends to limit the heating by sweeping gas bubbles away from the anode surface. Thus, the mass loss that is directly linked to dissolution rate is larger for anodes processed without a field. Moreover, magnetically-induced vortex flow around the anode exerts an additional polishing effect on the surface. Electrogenerated bubbles of hydrogen and oxygen spin in circular paths around the magnetic field lines. From these trajectories, we deduce the sign and estimate the magnitude of the bubble charge; hydrogen bubbles produced at the cathode are positively charged whereas oxygen bubbles produced at the anode are negative. Their surface charge density is approximately 0.1 C m −2 .