MIL-A-8625

Type I Chromic Acid
Chromic anodize is the thinnest and softest anodic film, and is used primarily in military and aerospace applications that require strong corrosion resistance and adhesive bond ability. Chromic acid produced films are more dense, very thin (.2 to .5 mils), and darker in color. This process is utilized for corrosion protection rather than decorative purposes. Use of the chromic acid process may be advantageous where there is a possibility of solution entrapment in holes or cavities in pieces to be coated. Entrapment of sulfuric acid, as may occur in the case of the conventional sulfuric process, may adversely affect the service of the part.