Formation and transformation of Mg(OH)2 in anodic coating using FTIR mapping

FTIR microscopic mapping was used to investigate the surface distribution of Mg(OH)2 on anodic coatings. The results indicated Mg(OH)2 was formed accompanying with micro-arc sparking and the amount of Mg(OH)2 was related to the intensity of sparking, which depends on the applied voltage. The distribution and amount of Mg(OH)2 varied with immersion time in 3.5 wt.% NaCl solution. The transformation process of anodic coatings was researched by FTIR microscopic mapping and smart map. The Cl− could be absorbed on the surface of anodic coatings where Mg(OH)2 is present and promote Mg(OH)2 to transform into the soluble magnesium salt MgCl2.