Study on Reduction of Partially Oxidized Cauliflower-like Copper Powder by Hydrogen

The copper powder produced by electrolysis has a dendritic structure, which gives it excellent green strength as a raw material for producing powder metallurgical components. Yet its large specific surface makes it susceptible to oxidation. Although the oxidation tends to occur only on the surface, it still needs to be reduced. The partially oxidized cauliflower-like copper powder was reduced by hydrogen in this paper. Internal diffusion was found as the rate controlling step for the hydrogen reduction reaction, in which the apparent activation energy was determined to be 14.18 kJ/mol using the Arrhenius-based expression for the diffusion coefficient. Controlling copper powder particles were still compact after reduction, and the tips of dendrite arms became round and smooth. The apparent density decreased after reduction, but excess temperature led to sintering, and as a result, increased apparent density of metallic powder. Therefore, lower reduction temperature and appropriately long reduction times yielded better apparent density. These research results can provide reference for metallic powder plants.