Metal Finishing Guide Book

2013

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Trivalent Chromium Mixed Throwing power Covering power Sulfate Hexavalent Chromium Good Good Poor Good Good Poor Current interruptions Completely tolerant Completely tolerant Intolerant Rectifier ripple Completely tolerant Completely tolerant Intolerant Deposit structure Amorphous Amorphous Crystalline Micro-discontinuous Yes as plated Some Need particle nickel High current density No burning Some misplate Burning Easy Easy Moderate (viscous) Occasional Daily with carbon Never Ease or rinsing Filtering Conditioning/ dummying Very seldom Routinely on start up Routinely on start up Passivity of unplated surfaces Needs post-treatment Needs post-treatment Natural "chromating" gives mild protection Waste treatment Easy ≈ 1/10 the sludge, no PFOS Easy ≈ 1/10 the sludge, no PFOS Moderate Relative safety Similar to nickel Similar to nickel Similar to cyanide Misting Almost eliminated Almost eliminated Heavy, need to be controlled Odor Almost eliminated Almost eliminated Strong and dangerous Easy Easy Hard Hexavalent chromium destroyed Occasional treatment for hexavalent chromium Treatment for trivalent chromium Removal of impurities Chromium contamination Table II. Trivalent and Hexavalent Chromium Comparison Trivalent chromium processes do not require scrubbers and, if the room is adequately ventilated, tank ventilation might not be required. In many regions, the same practices used for nickel baths apply to trivalent chromium. This is due to the almost complete elimination of misting and odor. Trivalent chromium processes have a non-PFOS mist suppressor, a low chromium concentration, and a greatly reduced toxicity and oxidizing properties as compared to hexavalent chromium. Trivalent chromium solution drains and rinses easily, thus greatly reducing the amount of chromium drag-out. If any solution does dry on the part, it is less hazardous since the chromium is in the trivalent state. It also does not stain the part. 256

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