GB1366355A - Chromium plating - Google Patents

Abstract

1366355 Composite electro-plating M & T CHEMICALS Inc 18 Aug 1971 [21 Aug 1970] 38793/71 Heading C7B A Cr composite coating is prepared on an article made of basis material provided with a Cu plate 5-50 microns thick by depositing thereon an inner layer of Co e.g. 0À25-12À5 microns thick, a middle layer containing Ni (e.g. Ni-Co alloy) 1-12À5 microns thick, and an outer layer of bright decorative Cr e.g. at least 0À02 micron thick. The basis material may be Fe alloy e.g. steel, brass, bronze, Zn, Zn alloy e.g. die casting, Ni, Ni alloy or plastic, e.g. ABS, polypropylene, polyethylene, polystyrene or polyacrylate. The initial Cu plate may be electro-deposited from a cyanide, pyrophosphate, acid sulphate or fluoroborate bath; Rochelle salt, phenol sulphonic acid, a heterocyclic urea, polyether and polysulphide are specified as additives. The Co layer may be formed by decomposition of cobalt carbonyl, or electro-deposition from a sulphamate, chloride, sulphate, mixed chloride-sulphate, fluoborate or pyrophosphate bath; many additives are specified, e.g. boric or citric acid, saccharin, sodium allyl or benzene sulphonate, sodium di-n-hexyl succinate, bis-#-hydroxyethyl ether of 2-butyne-1, 4-diol, sodium beta-styrene sulphonate, dibenzene sulphonimide, sodium-3-chloro-2-butene-1- sulphonate, 2 methyl-3-butyn-2-ol, N-1, 2-dichloropropenyl pyridinium chloride, N-allyl quinaldinium bromide, 2, 4, 6-trimethyl N- propargyl pyridinium bromide, sodium lauryl or other sulphate, sodium di-n-hexyl or benzene sulphosuccinate, and bis-omega sulphopropyl. The Ni layer may be electro-deposited from a Watts, sulphamate, sulphate, fluoborate or high chloride bath containing primary and secondary brighteners, e.g. 2-butyne-1, 4-diol or quaternized pyridine derivatives and saccharin, sodium benzene and allyl sulphonates. Prior to Ni electro-deposition, a stratum of particles, e.g. of plastics, talc, kaolin, MoS 2 , WS 2 , graphite, wax, barytes or other pigments, silica, alumina, Al, activated C, silicates, carbonates, carbides or colloidal S, may be affixed to the Co layer, at least some of the particles intercepting the Ni latex surface. The same NiSO 4 - CoSO 4 -NiCl 2 - H 3 BO 3 bath may be used for plating the Co and Ni- Co alloys layers by adjusting the current and additive system. The Cr plating may be effected from a bath containing CrO 3 , SO 4 , F, SiF 6 , Sr ions and fume suppressant to obtain a microcracked and porous structure.