Preparation of w–cu nano-composite powders with high copper content using a chemical co-deposition technique

Abstract

A novel chemical co-precipitation was used to produce W-70%Cu nanocomposite powders with coating structure. The precursors consistingofCuC2O4·xH2O and WO3·2H2O were first synthesizedusing copper nitrate, ammoniummetatungstate(AMT) and oxalicacid as the raw materials at 80 °C for 1.5 h when the concentrations of the reactants were 0.8 mol/L and the hydrogen ion concentration was 1.2 mol/L. The precursors were calcined to produce the powders with different phase componentsandmicrostructureatvarious temperatures.The CuWO4 and CuO nano-powders were obtained at 300 °C, which is colder than the traditional reaction temperature (1000 °C) of CuO + WO3 = CuWO4. However, the cubic Cu2Oand Cu2WO4 could beformed when the calcining temperature was 600 °C. The hydrogen reduction results show that the calcined powder is reduced to obtain W-Cu composite powder at 750 °C and 800 °C. In reduction process, volatile WO2(OH)2 through chemical vapor transport(CVT) continuously spreads to the copper surface and is reduced to form W and the coated particle is eventually formed. This particle is Cu particle coated by W phase and the interface between W and Cu phases is semi-coherent. It is found that the average particle size of the reduced powder is 30–50 nm observed by TEM images.