GB1110412A - Improvements in or relating to chromium plating - Google Patents

Abstract

A decorative chromium plate is formed on a metal by first forming on the surface a thin coating of a hydrogen-acceptor composition, i.e. compositions which react with hydrogen and which raise the hydrogen overvoltage at the metal as cathode, and then electro-plating chromium on to the metal thus coated in such a manner that substantially none of the coating remains in the final product. Typical hydrogen acceptor compositions are natural and synthetic rubbers; styrene, acrylate, acrylonitrile and butadiene monomers and polymers; acetylenic compounds; ethylenically unsaturated non-aromatic compounds; non-aromatic compounds with groupings -N=N- and >C=O sulphur; carbon disulphide; organic sulphur-containing compounds; antimony oxide; arsenic oxide; arsenous acid; 2-nitrobenzene arsonic acid; p-(phenylselenyl) aniline; hippuric acid; ethylene dicyclohexanol; and perthiocyanic acid. The organic compounds may form continous films of 10 to 2000A thickness while the sulphur coating may be discontinuous. The coatings may be formed by dipping, spraying, swabbing electro-phoretic deposition or electrolytic action and may be dried before the electroplating step. The organic composition coatings may also include protective colloids such as gelatine, gums, cellulose ethers alginates and pectins and may be subjected to cathodic treatment, e.g. in dilute sulphuric acid before chromium plating which typically is effected from a chromic acid bath containing sulphate and silicofluoride at 42 to 43 DEG C. to give a micro-cracked deposit at a thickness greater than 0.25 micron.