Effect of electrolysis conditions on the deposition of silver-bismuth alloys

The electrochemical deposition and dissolution of silver, bismuth and silver-bismuth alloy from a cyanide-tartrate electrolyte were studied by means of cyclic voltammetry. The influence of the electrolyte composition on the electrochemical reactions is discussed. The deposition potentials of the two metals could be maintained close to each other by means of appropriate complex forming agents, leading to their codeposition. Silver deposition is the predominant reaction in the electrolyte studied and the bismuth content in the coating increases with increased current density. The dissolution potentials of the two metals are quite distinct; they differ by more than 0.5 V. In the presence of a free complex forming agent, both the deposition and the dissolution potentials of silver can be shifted in the negative direction. Depending on the type and amount of the complex forming agent, they can become more negative than the deposition and dissolution potentials of bismuth. Predominant deposition of bismuth is realized in this case and the codeposition of silver is enhanced at higher current densities. By varying the amount of the complex forming agent, silver-bismuth coatings of any desired composition can be obtained.