Anodizing with chromium

{
  "id": "MLC-T-ENV-001756",
  "term": "Anodizing with chromium",
  "field": "Environment",
  "term_source": "Anodizing with Chromium",
  "definition": "1. Producing a protective oxide film on aluminum, magnesium, or other light metal, usually by passing an electric current through an electrolyte bath in which the metal is immersed. Anodizing may be followed by a sealant operation. Chromic acid anodic coatings have a relatively thick boundary layer and are more protective than are sulfuric acid coatings. For these reasons, chromic acid is sometimes used when the part cannot be rinsed completely. These oxide coatings provide corrosion protection, decorative surfaces, a base for painting and other coating processes, and special electrical and mechanical properties. Wastewaters generated during anodizing include spent anodizing solutions, sealants, and rinse waters. Because of the anodic nature of the process, anodizing solutions become contaminated with the base metal being processed. These solutions eventually reach an intolerable concentration of dissolved metal and require treatment or disposal. Rinse water following anodizing, coloring, and sealing typically is discharged to a treatment system.\n\n2. Electrolytic process by which an oxide layer is produced on the surface of a base metal for functional purposes (e.g., corrosion resistance or electrical insulation) using a chromic acid solution. In chromium anodizing, the part to be anodized acts as the anode in the electrical circuit, and the chromic acid solution, with a concentration typically ranging from 50 to 100 grams per liter (g/L), serves as the electrolyte.",
  "subject": "Commercial processes",
  "references": [
    "40 CFR 438 Appendix C (CFR 2013)",
    "40 CFR 63.341 (CFR 2018)"
  ],
  "url": "https://mlchart.com/terminology/environment/anodizing-with-chromium/"
}