GB1209936A - Nickel plating bath and process for non-electrolytic nickel plating - Google Patents

Abstract

1,209,936. Regeneration of electroless Ni plating baths: Ni base alloy. ELECTROCHEMICAL ENG. G.m.b.H. Nov.13, 1967 [Nov.14, 1966], No.51501/67. Headings C7A and C7F] Aqueous Ni plating solutions containing Ni, hypophosphite and surface active ions and NH4OH to give a pH of at least 7 are regenerated by adding a solution of a sparingly water soluble Ni compounds in aqueous ammonia with a strength of more than 20% at a rate corresponding to the consumption of Ni ions. The surface active ions comprise fluoride, bromide, iodide, borate, phosphate and/or polyphosphate ions and the plating solution may contain 5-100g/l lactic acid, 0À001-1g/l fluorinated melting agent, 1-30 ppm Pb<2+> as chromate and the hypophosphite content may be 10-150 g/ 1. The Ni salt may be the oxide, hydroxide or fluoride, the solution temperature being above 40‹ C; preferably 60‹ -95‹ C. The phosphite concentration formed in the solution by reduction is monitored and controlled by a photometer which controls the circulation of the solution through iron oxide or hydroxide and insoluble material is removed during plating by centrifugation. The regenerating solution also contains hypophosphite and its addition to the bath is monitored and controlled by circulating a sample of the bath through a colorimeter or absorption spectrometers. The substrates specified are Fe, Mg, Be, Cu alloy steels, Ti, Al-Zn-Mg alloy, semi-conductors, Si and plastics first heated with PdCl2 . The coating process is preferably carried out in apparatus made of the following alloy: 10-33%Cr, 50-75% Ni, 10-18Mo, Balance Fe. Metallic surfaces in contact with the solution may be passivated with an impulse current of 2x10<4> to 10<-1> amps /sq. cm from a thyristor controlled pulse generator.