Abstract
Disproportionation reaction (2Cu+-Cu0+Cu2+) of acidic cuprous sulfate solution was studied to obtain fine copper powder suitable for conductive paste. Cuprous sulfate solution was made by mutual reaction (Cuo+Cu2+-2Cu+) in a high temperature autoclave, e.g. 220°C, with copper wire and acidic cupric sulfate solution. In order to obtain fine copper powder, the solution was transferred into another vessel and cooled.
Cooling rate of cuprous solution had a large effect on the diameter and shape of the powder obtained. In batch operation, submicron particles with rough surface were obtained when cuprous solution was rapidly quenched, while some larger particles were obtained with relatively slow cooling rate. In continuous operation, copper particles of 2-3μm in diameter were obtained which were surrounded with well-developed crystal planes and showed an excellent oxidation resistance.
