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

Juan An,Hongdan Wang,Kai Liu,Xiaoli Yuan,Gang Xie,Wentang Xia,Hao An

doi:10.3390/met12030413

Abstract

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.

Highlights

Copper powder is one of the most important basic raw materials in the powder metallurgy industry, which can be prepared by electrolysis, atomization, as well as chemical reduction [1–3]
The copper powder produced by the atomization is mostly spherical and irregular, while that obtained by chemical reduction is spherical, flaky, and irregular
Thermogravimetric analysis (TGA) is a common and essential method to measure the reaction rate, which is widely used to investigate the reduction of metallic oxide by hydrogen [10–13]

Summary

Introduction

Copper powder is one of the most important basic raw materials in the powder metallurgy industry, which can be prepared by electrolysis, atomization, as well as chemical reduction [1–3]. The electrochemical process is more complex, it is currently the only effective way to produce dendritic copper powder. Copper oxides nucleate on the surface of the dendrite, which causes the dendrite arms to become brawnier, with smaller gaps between the dendrite arms These changes have significant impacts on the apparent density of copper powder, which is a key indicator for the quality of metallic powders. A partially oxidized commercial copper powder, produced by electrolysis, was reduced by hydrogen in this paper, in which the kinetics control of the reduction process, the surface morphology of the cauliflower-like copper powder, and the apparent density were investigated

Materials and Methods

Reduction Rate and the Kinetics Study

Conclusions