Effect of Al(OH)3 sol concentration on characteristics of microarc oxidation coatings of titanium alloy

The effect of Al(OH)3 sol on the growth characteristics, microstructure, phase structure and electrochromic properties of the coating fabricated on titanium alloy substrates were investigated by means of changing the Al(OH)3 sol concentration. The results show that the rate of growth of coating thickness gradually increased from slow to fast with the increasing concentration of Al(OH)3 sol and the roughness and size of micropore on the coating surface gradually increased, while its pore density was reduced. The coating was composed of anatase TiO2 when the volume fraction C≤10%. The rutile TiO2 began to emerge at C>10%, and its relative content gradually increased with the increase of the Al(OH)3 sol concentration. When C=40%, the obtained coating was composed of rutile TiO2. The cyclic voltammetry tests in pH 2.0 HCl solution showed that the color of the sample fabricated at C≤20% did not change significantly, with the increase of the Al(OH)3 sol concentration, the color change of the sample became clear. When C=40%, the obtained sample showed good stability and reversibility between blue coloration and bleaching cycles in pH 2.0 HCl solution.