| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 101 === The electrolytic MgO coating on Mg alloy has been carried out in 0.1 M Mg(NO3)2 aqueous solution to improve its corrosion resistance. By X-ray diffraction (XRD), and scanning electron microscopy (SEM),the as-deposited film was Mg(OH)2 formed by the electrolysis, (Mg2+‧2H2O → Mg(OH)2 + H2) , and finally condensed into MgO at 370 ℃. It was also found that the crystal orientation and morphology of Mg(OH)2 was linked to the applied voltage. The more negative the applied voltage and the more the OH- concentration was, finally resulting in the more (001) preferred orientation and various related surface appearances. Therefore, the controllable fabrication of highly dense and uniform Mg(OH)2 film could be carried out by tuning deposition potential. An optimum process conducted at -2.0 V(Ag/AgCl) for 2400s and annealed at 400 ℃ was suggested to derive a more uniform and densified MgO protective film, revealing corrosion current density reduced from 114 down to 5.82 μA/cm2 and a passivation region from -1.72 to -1.57 V(Ag/AgCl) in 3.5 wt% NaCl aqueous solution, comparable with micro-arc oxidation.
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