Abstract
Recently, the color of gold alloy plating tends to be preferred red and pink, and the thick deposit with greater wear resistance is required. But the said properties depend upon bath component, operating condition and metallographic properties of deposited alloy. Bath component varies, depending, for instance, upon the decrease of metal ion concentration, increase of free cyanide concentration, etc. It is, therefore, impossible to keep the composition of deposited alloy constant regardless of the proper starting operating conditions.
The author studied the bath component and operating condition which affect the composition, color, hardness, and other properties of the deposited alloy, and investigated proper conditions of practical operation.
The bath component and operating condition are as follows:
Gold as potassium gold cyanide 1g/l Free cyanide as potassium cyanide 4-8g/l
Copper as cuprous cyanide 12-20g/l Disodium phosphate 30g/l
Nickel as potassium nickel cyanide 30-50g/l Current density 2-6A/dm2
Temperature 25°C Without agitation
The results are as follows: (1) Increase in free cyanide concentration tends to increase gold content in deposited alloy, while increase in current density tends to decrease the alloy gold content. (2) The deposited copper contend varies with current density, inversely with free cyanide concentration, and is not affected by cuprous ion concentration in plating solution. (3) Nickel content in alloy tends to be constant roughly, the range being 2 to 8%, under various conditions, such as nickel ion and free cyanide concentration and current density. (4) The hardness of deposited alloy in the said bath reaches 200 Vickars. (5) The thickness of the deposit per unit time is not affected by current density, while it decreases with an increase of free cyanide concentration.
