| 摘要 |
Ductile palladium coatings for electrical contacts are made by electro-deposition using a plating bath containing Pd(NH3)4. Br2 termed tetra-amino palladous bromide. Preferably the plating bath contains 15 to 30 g. of the Pd. compound per litre of solution containing ammonia, and is applied at about 1.5 A. Dm2. A diaphragm cell may be used with ammonium salts as anolyte and at pH 8 to 9. Without a diaphragm pH is 9 to 9.5, and ductility is slightly higher e.g. providing elongations up to 15 per cent, but the electrolyte deteriorates rapidly. The parts may be plated in a barrel. Base metals treated are copper, brass, beryllium-copper, nickel, or nickel silver, preferably after degreasing and etching with H3PO4, and a copper flash coat. Pd coatings up to 5m or higher are referred to. It is stated that the process is limited to the bromide compound, other halides and other salts are unsuitable, and details are quoted.ALSO:Tetra-aminopalladous bromide Pd(NH3)4-Br2 is made by dissolving palladium sponge in excess of conc. HBr with addition of small amounts of bromine to aid solution, and evaporating the solution to dryness, which also reduces any tetravalent palladium to the divalent state. The dry palladous bromide is taken up in the minimum amount of dilute HBr, and ammonia added with warming until the precipitate first formed is re-dissolved. The solution is used for palladium electro-plating (see Division C7). |
