Metal Finishing Guide Book

2013

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Table III. High-Efficiency Copper Cyanide Bath Potassium Copper cyanide Total potassium cyanide Sodium 60.0 g/L (8.0 oz/gal) 75.0 g/L (10.0 oz/gal) 102.0 g/L (13.6 oz/gal) — Total sodium cyanide — 97.5 g/L (13.0 oz/gal) Potassium carbonate 15.0 g/L (2.0 oz/gal) — — 15.0 (2.0 oz/gal) Sodium carbonate Potassium hydroxide 15.0 g/L (2.0 oz/gal) — — 15.0 g/L (2.0 oz/gal) Rochelle salt 45.0 g/L (6.0 oz/gal) 45.0 g/L (6.0 oz/gal) Free potassium cyanide by analysis 15.0 g/L (2.0 oz/gal) — — 15.0 g/L (2.0 oz/gal) Sodium hydroxide Free sodium cyanide by analysis 60-71°C (140-160°F) Temperature Current density up to 80 A/ft2 Cathode efficiency 90-99% Recommended agitation Mechanical, solution or air nificant copper thickness is required. The copper cyanide can be as high as 120.0 g/L (16.0 oz/gal) for applications such as wire plating. Although the brightness and grain refinement of the deposit can be improved by the use of periodic reverse current or current interruption, the best results are obtained by using suitable additives. Barrel Plating The strike bath, high-efficiency bath, or both in combination, can be used for barrel plating. Typical compositions for barrel plating are shown in Table IV. Bath Preparation Dissolve potassium or sodium cyanide in cold water. In a separate container, mix copper cyanide with water to form a thin slurry and slowly add to the potassium or sodium cyanide solution while mixing. The dissolving reaction is exothermic and the solution should not be allowed to overheat, as this may decompose some of the free cyanide. Add the rest of the required materials after dissolving the copper cyanide. Carbon treatment of the bath before use is recommended. All salts should be sulfur free to prevent dull, red deposits in low current density plating areas. Table IV. Copper Cyanide Baths for Barrel Plating Potassium Copper cyanide Total potassium cyanide Sodium 45.0-60.0 g/L (6.0-8.0 oz/gal) 45.0-60.0 g/L (6.0-8.0 oz/gal) 80.3-109.5 g/L (10.7-14.0 oz/gal) — Total sodium cyanide — 64.5-88.5 g/L (8.6-11.8 oz/gal) Potassium carbonate 15.0 g/L (2.0 oz/gal) — — 15.0 g/L (2.0 oz/gal) Sodium carbonate Potassium hydroxide Sodium hydroxide Rochelle salt 7.5-22.5 g/L (1.0-3.0 oz/gal) — — 7.5-22.5 g/L (1.0-3.0 oz/gal) 45.0 g/L (6.0 oz/gal) 45.0 g/L (6.0 oz/gal) Free potassium cyanide by analysis 15.0-22.5 g/L (2.0-3.0 oz/gal) — Free sodium cyanide by analysis — 15.0-22.5 g/L (2.0-3.0 oz/gal) Temperature 272 60-71°C (140-160°F)

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