| 摘要 |
In electroplating an object with successive deposits of bright nickel and chromium, an intermediate metal layer of an average thickness of not substantially more than 2 m consisting of nickel, silver, or a metal or alloy which occupies a position between these metals in the electrochemical series, is electrodeposited from a bath containing also a solid non- or less-conducting material in suspension in the bath. The solid non- or less-conducting material preferably comprises particles of diameter not greater than 5m . The intermediate layer may be produced from a bright nickel sulphate-chloride bath to which is added colloidal silica, SiC, or BaSO4, AgCl or NiS formed by addition of Ba Cl2, Ag2CO3, or H2S respectively, or from a cyanide silver bath to which is added alumina or Ag2S formed by addition of K2S. The solid particles may be kept in suspension by stirring or if organic wetting agents are not present by air agitation. Reference is also made to the use of hydroxides of Fe, In, Al and Th but PbCrO4, PbS and HgS are mentioned as less suitable. Examples of bright nickel baths referred to are sulphate or sulphate-chloride baths buffered with boric acid and containing saccharin and butin-diol together with sodium lauryl sulphate, or formic acid and formaldehyde with cobalt as a metal brightener. If a bright nickel bath is used for the intermediate layer, adhesion to the original bright nickel layer may be improved either by first immersing the bright nickel plated object in an aqueous sulphuric acid solution of KI or by adding fluoride or fluoborate to the intermediate layer bath. |
