Patent GB-1202525-A (GB)
Title: Improvements in and relating to the electrodeposition of metals
Inventor: AIKEN JOHN KEMPTON
IPC: C25D3/02
Filed: 1966-09-28
Abstract: 1,202,525. Electro-plating baths containing dipyridinium compounds. NATIONAL RESEARCH DEVELOPMENT CORP. Sept. 19, 1967 [Sept. 28, 1966], No.43446/66. Heading C7B. In electro-depositing metals such as copper, silver, gold, zinc, cadmium, chromium, iron or nickel from an aqueous bath containing an ionizable compound of the metal to be deposited, the bath also includes a brightener compound of the general formula where n is 2 or 3; R1 and R2 which may be the same or different, are hydrogen or alkyl groups; R3 and R4 which may be the same or different, are alkyl, haloalkyl alkoxyalkyl, acylalkyl or carbalkoxyalkyl groups or amidoalkyl groups in which the nitrogen atom may be substituted by alkyl groups or may form part of an optionally substituted heterocyclic ring; and X is an anion such as a halide, sulphate or methosulphate radical, said compound having a redox potential in the range of from -0À25 to -0À55 volt. Typically the brightener compound concentration in the bath is from 0À001 to 0À1 g/l. Other compatible known additives such as stress-relievers, levelling agents, and brighteners including metal cations, polymers and dyes may be included in the bath. In examples, bright copper is deposited from acid sulphate baths containing 1:1<1>-ethylene-2:2<1>- dipyridinium dibromide, the bright plating range being extended by the addition of the dyestuff safranine O and the same effect being obtained when the corresponding 5:51-dimethyl substituted dipyridinium dibromide is used; stressed bright nickel is obtained from a Watts bath of p5 at 40‹C. containing the same unsubstituted pyridinium dibromide as used for copper, a brilliant less stressed nickel deposit being obtained with the coaddition of saccharin, while a brilliant deposit is obtained from an air-agitated bath containing as cobrightners #-toluene sulphonamide and 1:1<1>- dimethyl-4:4<1>-dipyridinium dicholoride or similar dipyridinium chlorides containing in the 1:1<1> positions propyl, chloroethyl, ethoxyethyl,carbethoxy-methyl or -propyl, or diethyl-acetamides groups, a similar 4:4<1>-dipyridinium chloride containing the substituents 1-methyl-1<1>-methoxymethyl, or 1:1<1> -di-(2<11> :6<11> -dimethylmorpholino)- acetamido-4:4<1>-dipyridinium disulphate; bright gold plate is obtained from a solution of potassium gold cyanide in aqueous potassium citrate solution brought to pH4 with citric acid at a temperature of 105‹ F. (40‹ C.) to which has been added as brightener the same morpholino-acetamido dipyridinium sulphate used for nickel or from the same gold cyanide-citrate bath at a temperature of 115‹ F. (45‹ C.) to which has been added as brightener 1:1<1>-dimethyl-4:4<1>-dipyridinium dichloride or dimethosulphate or the corresponding 1:1<1>-dipropyl di-iodide or 1:1<1>-ethylene-2:2<1>- dipyridinium dibromide; bright zinc, which after a subsequent nitric acid dip has a brilliant bluish, tinge is deposited from an alkaline sodium based cyanide bath to which is added the 2:2<1>-dipyridinium dibromide brightener used for copper and gold above together with oxidized polyvinyl alcohol and potassium nickel cyanide; semi-bright silver is obtained, instead of the usual matt deposit, from a strongly alkaline (pH 12À5) potassium based cyanide bath containing carbonate to which has been added the same 2-21 - dipyridinium dibromide; and the matt deposit of cadmium obtained from a cyanide bath, when subjected to a subsequent nitric acid dip has a greater brilliance when 1:1<1> -dimethyl-4:4<1> -dipyridinium dichloride is added to the plating bath.