Metal Finishing Guide Book

2012-2013

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ammonium bifluoride, 75-90OF (24-32OC). or Chromic acid containing solution consisting of: 44-48 oz/gal chromic acid, 34 oz/gal sodium nitrate, 1.5 oz/gal sodium chloride, 0.1 oz/gal sodium sulfate, 65-90OF (18-32OC). Nickel and Cobalt Alloys 1. Alkaline soak clean. 2. Cathodically condition in a highly conductive electrocleaner blended for steel. 3. Acid dip in a solution consisting of 50% v/v of 70% hydrofluoric acid and 7% v/v of 42OB�� nitric acid at 75-90OF (24-32OC). Silver and Silver Alloys 1. Alkaline soak clean. 2. Acid dip in either of the following solutions: A. 66% v/v of 42OB�� nitric acid at 75-160OF (24-71OC). B. 88% v/v of 66OB�� sulfuric acid, 75-90OF (24-32OC). C. 22% v/v of 42OB�� nitric acid at 75-90OF (24-32OC). Titanium 1. Alkaline soak clean. 2. Acid treatment in solution consisting of 40% v/v of 42OB�� nitric acid and 2-3% v/v of 75% hydrofluoric acid, at 120-135OF (52-57OC). Zinc and Zinc Alloys Comprehensive information describing zinc alloys, castings, and suggested acid baths is described in the chapter titled ���Surface Preparation of Various Metal Alloys Before Plating and Other Finishing Applications.��� Activation of Bright Nickel Electroplate There are two effective acid solutions for activating passive nickel deposits and to salvage reject parts. Their application is recommended for sulfur bearing electrolytic nickel deposits. The immersion dip consists of 5 to 10% v/v sulfuric acid and 2 to 4 oz/gal of potassium iodide at 75 to 90OF (24-32OC), 1 to 5 minutes or as required. A cathodic activation of nickel consists of 5 to 11% v/v sulfuric acid, 1 to 3 oz/gal fluoride, 2 to 4 oz/gal chloride at 5 to 7 V for 1 to 2 minutes (as required) at 20 to 40 A/ft2 and 75 to 120OF (24-49OC). 88

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