The use of gold in autocatalytic plating processes

Abstract

Certain electroless gold plating procedures are autocatalytic in nature, while gold can also be used as an activator or initiator in the autocatalytic plating of plastics and of other non-conducting materials by metals such as nickel and copper. This paper describes the scientific basis of autocatalytic plating, and reviews electroless gold plating procedures. The effectiveness of gold as an activator in the autocatalytic plating of plastics is also briefly surveyed.The literature relating to so-called "electroless" plating is confusing, not only because it tends to be largely of an empirical nature, but also because the term "electroless" has often been used to describe processes which are different in character. True "electroless" or autocatalytic plating should not be confused either with electrochemical displacement deposition, or with homogeneous chemical reduction processes, such as silvering. In the former, deposition is accompanied by dissolution of the basis metal, which must therefore be less noble than the metal being plated. It does not, therefore, occur on gold. Moreover, deposition ceases immediately access of plating metal ions to the basis metal is not possible. Only thin platings can therefore be expected by this procedure. In the latter, deposition occurs indiscriminately over all objects in contact with the solution. After initial deposition has occurred, however, autocatalytic deposition may constitute the main plating process.

Spectrophotometric and Electrochemical Study of Gold‐Iodide in Aqueous Borate Medium

“…The only reported value, 4 X l0' M2, is about ten times larger. 26 The method of measurement is not identified.…”

A comprehensive review of various non-cyanide electroplating baths for the production of silver and gold coatings

“…Electroplating baths prepared from Au 2+ are rare. Baths designed from Au + and Au 3+ are abundantly available for gold electroplating [32][33][34]. Gold in Au + form is not stable in aqueous solutions and quickly disproportionates to form metallic gold [13,35,36].…”

“…When compared to cyanide salts of gold, thiosulphates reported a lower stability constant; the stability constant of the [Au(SO 3 ) 2 ] 3− complex is equal to 10 26 , and that of cyanide complex is 10 56 [161]. Despite having higher stability than sulphite complexes, the thiosulphate-based gold electroplating baths were significantly less explored [162]. The primary issue with not using thiosulphate baths was their inherent instability concerning disproportionation.…”

Chrysotype: Photography in nanoparticle gold

“…An increase in effective photographic 'speed' of this process is observed when the ligand-to-gold ratio in the sensitizer is low, giving a more labile gold(I) complex, which suggests that the gold nanoparticles may be capable of growing by 'physical development', akin to the process of selective gold deposition from 'electroless' autocatalytic plating baths (37). If a sufficiently stable latent image in gold at the smallest particle size can be formed, and subsequently grown from these 'nuclei', it is possible that a 'projectionspeed' material could be devised, to avoid the need for contact-printing.…”