Formation Process of Electrodeposited Hard Gold-Alumina Composite Coatings

Abstract

Effects of codeposition conditions and surface chemical and electrochemical behavior in the electrodeposition of hard gold(gold-nickel)-alumina composite have been examined in order to clarify the codeposition mechanism. The alumina particles were scarcely codeposited in the absence of nickel ions in solution, but were codeposited in the presence of nickel ions owing to the adsorption of nickel ions onto the particles. Addition of caesium ions increased the amount of adsorbed nickel ions onto alumina particles and increased the codeposited alumina content: the codeposition of alumina particles from the acid gold-nickel electrolyte depends on the positive surface charge caused by the adsorption of nickel ions onto the particles. The positively charged alumina particle would be held by the electrostatic force of attraction on the negatively charged cathode electrode, and would be bound on cathode electrode by nickel atom produced by thereduction of adsorbed nickel ions and the electrodeposition of metal ions in solution. The codeposition process of alumina particle can be divided into the following three steps:
(1) Adsorption pro cess of nickel ions onto alumina particles;
(2) Holding process of alumina particle onto the cathode elec trode;
(3) Bonding process by the reduction of nickel ions onto alumina and the electrodeposition of metal ions in solution.
In the electrodep osition of hard gold-alumina composite, the codeposited alumina content was strikingly affected by the process (1).