Affiliation:
1. School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510641, P. R. China
Abstract
Film-forming effects of cathodic deposition on pure Mg substrate at constant DC in aqueous solutions of magnesium nitrate (Mg(NO3)[Formula: see text]6H2O), magnesium chloride (MgCl[Formula: see text]6H2O) and magnesium sulfate (MgSO[Formula: see text]7H2O) respectively were investigated systematically. Typical processes were studied by potentiodynamic cathodic polarization and galvanostatic polarization and typical samples were analyzed by SEM and XRD. The results indicate that the depositing efficiency is not only the highest but stablest, and deposited coatings show the best uniformity with Mg(NO3)[Formula: see text]6H2O solution employed as depositing medium and applied current density [Formula: see text][Formula: see text]mA cm[Formula: see text]. Cathodic deposition leads to regular mass loss of Mg substrate. The cathodic polarization curve of pure Mg in magnesium nitrate solution shows more obvious pseudo-passivation, several Tafel regions with different slopes appearing before diffusion-limited current density region, and oxygen consumption is the major cathodic reduction reaction under specified current density. However, hydrogen evolution reaction is dominant in both Mg chloride and Mg sulfate solutions. The deposition coatings are all composed of continuous and uniform mesh-like “basic layer” adjacent to substrate and discrete distributed snowball-like particles on the microscopic scale. The phase compositions are all crystal Mg(OH)2, and the coatings deposited in Mg chloride solution have (011) preferred orientation.
Publisher
World Scientific Pub Co Pte Lt
Subject
Materials Chemistry,Surfaces, Coatings and Films,Surfaces and Interfaces,Condensed Matter Physics