GB1093701A - An improved process for protecting surfaces against chemical plating - Google Patents

Abstract

Metallic surfaces are protected against chemical plating, particularly an 18/8 Cr-Ni steel vessel containing a chemical nickel plating bath for coating iron plates immersed therein with Ni-B or Ni-P, by connecting the surfaces into an electric circuit containing a plating bath electrolyte, at least one counter-electrode and D. C. voltage source, applying to the surfaces an electric potential corresponding on the current density/potential curve to the rest potential or to the protection potential region lying between the mottling potential and the transpassivity, and adjusting the current density to not more than 104A/cm2. Preferably, with the surfaces to be protected connected as the anode and the counter-electrode as the cathode, the potential is regulated potentiostatically by at least one standard electrode immersed in the plating bath. In a nickel plating bath, standard and counter-electrodes can be used made of nickel or a Ni-B or Ni-P alloy corresponding to composition of the alloy chemically deposited from the bath; the electrode may be made from a molten Ni alloy or one applied by chemical plating on other material such as Cu, brass, Fe, SiC, graphite, glass, resin or porcelain. The plating bath may contain sodium borohydride or hypophosphite, or a borazane or borazole: e.g. (a) 30 g/l NiCl2, 10 g/l Na citrate and 10 g/l NiCl2, 40 g/l NaOH, 60 g/l ethylene diamine, 30 g/l NaF and 0.6 g/l Na borohydride. For plating other metals such as Co, Fe or Cu, or a B- or P- containing alloy of one of these metals, a standard electrode made of the corresponding metal or alloy is used.