Synthetic Process of Enviromentally-Friendly Coating on Magnesium by Chemical Conversion Treatment

Titanium dioxide (TiO2) coatings were prepared by chemical conversion treatment of magnesium in (NH4)2[TiO(C2O4)2] with H2O2, then, anatase type TiO2 coatings were prepared by sintering. To identify the coating structure, coating analysis was carried out using an infrared absorption spectrum analyzer. Based on the infrared absorption results, a component of the coating was found in the hydrolysis product of peroxo-titanium compound. Furthermore, the coating analysis was carried out using X-ray diffractometry (XRD), and non-sintered coating was amorphous; however, the coating sintered at more than 573 K was anatase-type titanium dioxide. In the forming process of the conversion treatment in (NH4)2[TiO(C2O4)2] with H2O2, first, the magnesium was dissolved to H+ in the bath and then, hydrogen ions on the magnesium surface were consumed to generated hydrogen gas. Thus, the pH of the interface became alkali. The hydrolysis of the peroxo-titanium compound was deposited on the magnesium because pH increased on the surface. From the XPS results and the TG-DTA results, a component of the coating is a hydrolyzation product of a peroxo-titanium compound and Mg(OH)2. Because Mg(OH)2 is generates in pH more than 11, it is considered that the pH on the magnesium surface is more than 11. The coating sintered at 573 K had the highest photocatalytic activity. The photocatalytic activity of the coating sintered at 623 K was lower than the coating heated at 573 K, which is attributed to growth of TiO2 particle. This forming process of the coating is low cost because of the useless electrolytic decomposition process and increasing the speed of the treatment. It is possible to treat complicated form of the substrate metal, so this method can be expected to use in various fields. Therefore this method is expected to practical use for environmental purification.