GB1506496A - Gold plating baths - Google Patents

Abstract

1506496 Electo-plating gold OXY METAL INDUSTRIES CORP 18 April 1975 [19 April 1974] 16105/75 Heading C7B An aqueous Au electro-plating bath contains Au in the form of a complex, e.g. as ammonium, amine or alkali metal (Na or K) Au cyanide or sulphite, adjusted to a pH suitable for plating (at least 3.5 for cyanide or 5À5 to 10À5 for sulphite), and an amido-polyphosphate compound (ammonium or alkali metal) in sufficient quantity e.g. 1 to 100 g/l to produce a brighter deposit. Preferably the bath also contains at least 1 g/l of a polyphosphate compound, e.g. ammonium or alkali metal (Na or K) pyrophosphate, tripolyphosphate or tetrametapolyphosphate. At least 0À01 g/l of Co and/or Ni ion may be included in a cyanide complex bath to improve hardness. Other brighteners, such as hydrazine or piperazine derivatives, and As, Sb or Se ions, may be added. Alloying metals may also be present. The amidopolyphosphate compound may be made by reacting anhydrous ammonia with P 2 O 5 at 150‹C. Plating may be effected on brass panels or plastic rendered conductive by electroless plating. Examples of baths specified are Na 3 [Au(SO 3 ) 2 ], Na 2 SO 3 , NH 4 amidopolyphosphate, (optionally Na 4 P 2 O 7 , Na 5 P 3 O 10 or Na 4 P 4 O 12 ) and NaOH to pH 9(or 8À5); and KAu (CN) 2 , K 2 HPO 4 (or K 4 P 4 O 7 ), NH 4 amido-polyphosphate, (optionally CoSO 4 or NiSO 4 ), and H 3 PO 4 to pH 7 (or 4).