Metal Finishing Guide Book


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EXPERIMENTAL Reagents and apparatus: All the materials were reagents grade and were used without further purification. Distilled water was used in the preparation of all solutions. Solutions were stored in glass and polyethylene bottles. Used deionized water (�� ��� 1-2 microSiemens) Phosphorus standard solution (1 ml = 1.0 mg P) Transfer 2.292 g of anhydrous Na2HP04, previously dried to constant weight at 105��C, to a 500-ml volumetric flask. Dissolve in about 100 ml of water, dilute to volume and mix. Ammonium molybdate solution (acidic): ��� Part A: Add 50 ml NH4AOH (conc.) to 300 ml water. Add 80g of ammonium molybdate [(NH4)6Mo7O24 x 4H2O] (M.w. = 1235.9) and heat to dissolve. Cool and mix. ��� Part B: Add 400 ml HNO3 conc. (d = 1.41 g/ml) to 300 ml water. Finally, add part A dropwise into part B with permanent mixing. PROCEDURE Weigh accurately to the nearest 0.001g a sample of a 1.0��� 2.0 g of a deposit and transfer the sample to a 250 ml Erlenmeyer flask. Add about 100 ml of 1:1 nitric acid and boil gently to complete dissolution of the sample and to expel brown fumes of nitrogen oxides. Cool, transfer the solution to a 250 ml volumetric flask, fill to the mark and mix. (Solution A) 3Ni3P + 41HNO3 = 3H3PO4 + 9Ni(NO3)3 + 14NO +16H2O Ni3P + 13HNO3 = H3PO3 + 3Ni(NO3)3 + 4NO + 5H2O Transfer 20 ml aliquote sample to a 200-ml beaker, add 100 ml of water and 5 ml of 4% KMn04. Boil for a few minutes and then destroy the excess of KMn04 and MnO2 with drop by drop addition of 30% NaNO2. Boil for a few minutes to expel nitrogen oxides. 5H3PO3 + 2KMnO4 +6HNO3 = 5H3PO4 + 2Mn(NO3)2 +2KNO3 + 3H2O 4KMnO4 +2H2O +4HNO3 = 4MnO(OH)2 +4KNO3 +3O2 MnO(OH)2 + KNO2 +2HNO3 = Mn(NO3)2 + KNO3 + 2H2O Cool and neutralize with 25% NH40H to pH 7-8 (by pH-meter). Add 1-2 drops of (1:1) HN03 to dissolve the precipitate. Add 10g of NH4N03. Heat to 45�����50��C (with water bath), add 50 ml of acidic ammonium molybdate solution drop wise and 2 drops of 25% NH4OH. Mix the solution with precipitate for 12 minutes and let it stand for 2-3 hours. 271

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