Contact precipitation of silver on copper powder

Abstract

The processing characteristics of articles made from copper powder can be improved by alloying the copper powder with additions of silver (up to 0.2%). The simplest and most economical method is deposition of silver onto copper powder particles by contact exchange. We have studied the effect of different types of electrolytes (nitrate, pyrophosphate, sulfosalicylate, sulfite, ferricyanide, cyanide thiocyanate, and thiocyanate) on the kinetic characteristics of the electrode processes. We have done structural studies of copper powder alloyed with silver. We have determined the bulk (as-poured) density of the powders after cementation, and also the density, shrinkage, electrical resistance, and hardness of specimens prepared by the traditional procedure from the alloyed powders. In most of the studied systems, the cementation process occurs with diffusion control of the cathode reaction. However, this does not lead to visible formation of growths and dendrites of silver on the surface of the copper particles. According to x-ray phase analysis results, during cementation a solid solution of copper in silver is formed on the surface of the particles. After sintering the green compacts, the alloy is homogenized with formation of a solid solution of silver in copper. The nature of the electrolyte markedly affects the properties of the Cu−Ag material. In some cases, the hardness and electrical conductance of the specimens increase simultaneously. Technological and economic considerations lead to choosing cyanide thiocyanate electrolyte as the best for alloying copper powder with silver.