Metal Finishing Guide Book


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Page 358 of 903

Ammonium chloride, 30 g/L Hydrochloric acid to pH 0.1-0.5 Temperature, 40-50��C Current density, 0.1-1.0 A/dm2 Anodes, pure palladium Deposits from the acid chloride system are dull to semibright. Current efficiency is 97 to 100%. The plating solution itself is notably sensitive to contamination by copper, which can displace palladium from solution. Work to be plated in this solution should thus be struck with palladium or with gold. PALLADIUM-NICKEL PLATING Palladium readily forms alloys with other metals and has been plated in numerous alloy formulations. Of these, the most important commercially has been palladium-nickel, which can be deposited as a homogeneous alloy over a composition range from approximately 30% to over 90% palladium by weight. Current practice favors an alloy composition from approximately 75 to 85% wt. palladium. A formulation suitable for alloys in this range is as follows: Palladium as Pd(NH3)4Cl2, 18-28 g/L (palladium metal, 8-12 g/L), Ammonium chloride, 60 g/L Nickel chloride concentrate, 45-70 ml/L (nickel metal 8-12 g/L) Ammonium hydroxide to pH 7.5-9.0 Temperature, 30-45��C Current density, 0.1-2.5 A/dm2 Anodes, platinized Palladium-nickel alloy electrodeposits are notably less sensitive to hydrogeninduced cracking than are pure palladium deposits. They are, however, somewhat more susceptible than pure palladium to stress cracking upon deformation. As with pure palladium plating systems, various proprietary additives are available for brightening and stress control. 351

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