Effective Synthesis of Nanocrystalline Tungsten Carbide Powders by Mechanical and Thermal Activation of Precursors

Production of nanostructured WC powders is regarded with difficulties related to excessive crystalline grain growth and/or agglomeration of particles at the temperatures needed for completing the synthesis. In this work, WC powders have been obtained by a two-step process: mechanical activation of precursors followed by thermal activation of the mixes. Different combinations of tungsten powders (W or WO3) and carbon sources for carburization (solid graphite or carbon black powders) have been considered.Thermogravimetry experiments carried out in different atmospheres (Ar, Ar-50%H2) allow describing the reactions taking place between solid precursors and gaseous phases. The evolution of the synthesis is evaluated by XRD, and the characteristics of the WC powder produced are described based on microscopic examination by SEM. The results show how very fine WC powders can be obtained from mixes W+C heated at 1100 ⁰C in inert atmospheres, where carburizing efficiency of both carbon sources is very similar. When WO3 is used as tungsten source, both reduction and carburization processes are needed for complete transformation into WC. In this latter case, thermal activation in H2 atmosphere promotes reduction of oxides at lower temperatures and should preferably be combined with the use of carbon black sources, which present the highest reactivity under these conditions