Cyanide-plating baths acid electrolytes

Copper Copper is mostly plated from acid, fluoroborate, or cyanide baths (see Table 4). Among these, the cyanide electrolyte reveals the best throwing power but needs intensive convection. 

Sulfite electrolytes for colored gold alloys are also in use for decorative deposition thanks to their excellent distribntion and leveling properties and also for their superior ductility compared to gold alloy deposits from acid cyanide electrolytes giving similar shades and colors [90], Alloy plating from snlflte electrolytes comprises binary and ternary compositions, such as Au-Cu, Au-Pd, and An-Cn-Pd—already reported by Rapson [3] and later incorporated into proprietary processes [91-93], The later is an alloy finish widely used in the electroplating of spectacle frames. Example formnlations of nentral and alkaline sulflte baths for the electrodeposition of gold alloy deposits are reported in Table 11.8. 

Most of the kinetic studies conducted in gold electrodeposition were concerned with the electrolytes most widely used for gold plating, i.e., acid or neutral Au-cyanide baths and the Au-sulfite bath. In the following account, the main results emerging from these studies are presented. 

Acid Au(III) cyanide baths were introduced for industrial applications in the late 1970s see Wilkinson for a short account of its development [22], and have seen an increasing use since then. The main limits of Au(III) cyanide baths are the corrosiveness, the low rate of deposition, and the comparatively inadequate wear resistance when used as a contact finish, compared to hard gold from acid Au(I)-cyanide electrolytes. The acid Au(III) bath are especially recommended for deposition onto difficult to plate materials (because of passivity) such as stainless steel and chromium. They are currently also formulated for decorative plating (rack and brush) in a range of color shades and for deposition of thick, ductile coatings. 

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