Preparation of W–Cu nano-composite powder using a freeze-drying technique

W–Cu composite materials have been widely used in heat sink apparatus and as electronic packaging materials. The preparation of the materials, especially the synthesis of W–Cu nanopowder, is a subject much more researches on. This paper focuses on the synthesis of W–Cu composite nanopowder using the freeze-drying technique, an environment-friendly and advanced technique for powder manufacturing. The process involved mixing ammonium metatungstate with CuSO4·5H2O as preliminary liquid solution and the use of liquid nitrogen as a cryogenic media; W–5Cu, W–10Cu and W–20Cu composite nanopowders were obtained after vacuum drying and following thermal decomposition reduction. X-ray diffraction, infrared spectroscopy and field emission scanning electron microscopy were used to characterize these nanopowders. The results showed that the freeze-drying precursor was the amorphous matter containing tungstate, sulfate, crystal water and ammonia. Copper appeared at 200 °C, tungsten and β-tungsten could not be obtained until 500 °C, and pure tungsten was found above 700 °C, which meant that the whole reduction process was completed. Crystallized W–Cu composite nanopowder, with particle sizes of 10–20 nm, was produced via a two-stage reduction: 400 °C for 2 h and then 700 °C for 2 h.