Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Trivalent Chromium Throwing power Covering power Mixed Good Good Sulfate Good Good Current interruptions Completely tolerant Completely tolerant Rectifier ripple Deposit structure Micro-discontinuous High current density Ease or rinsing Filtering Conditioning/ dummying Passivity of unplated surfaces Waste treatment Relative safety Misting Odor Removal of impurities Chromium contamination Completely tolerant Completely tolerant Amorphous Yes as plated No burning Easy Amorphous Some Some misplate Easy Occasional Very seldom Needs post-treatment Easy ≈ 1/10 the sludge, no PFOS Similar to nickel Almost eliminated Almost eliminated Easy Hexavalent chromium destroyed Daily with carbon Needs post-treatment Easy ≈ 1/10 the sludge, no PFOS Similar to nickel Almost eliminated Almost eliminated Easy Occasional treatment for hexavalent chromium Table II. Trivalent and Hexavalent Chromium Comparison not be used with trivalent processes. Trivalent chromium processes do not require scrubbers and, if the room is ade- quately 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. 183 Hexavalent Chromium Poor Poor Intolerant Intolerant Crystalline Need particle nickel Burning Moderate (viscous) Never Routinely on start up Routinely on start up Natural "chromating" gives mild protection Moderate Similar to cyanide Heavy, need to be controlled Strong and dangerous Hard Treatment for trivalent chromium

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