Probing the microwave interaction mechanisms and reaction pathways in the energy-efficient, ultra-rapid synthesis of tungsten carbide

Tungsten carbide, WC, can be prepared by microwave (MW) synthesis in the solid state from its component elements in air on timescales that are orders of magnitude faster than those achieved by conventional heating methods. In a multimode cavity (MMC) MW reactor, the synthesis can be performed in less than 30 min; in a single mode cavity (SMC) reactor the reaction time is reduced to <1 min. Combinations of optical pyrometry, powder X-ray and neutron diffraction, thermal imaging and dielectric measurements demonstrate how these syntheses are self-terminating, initiated at elevated temperature and proceed via the intermediate formation of the sub-carbide W₂C. The result is phase-pure, dense, crystalline and stoichiometric WC (hexagonal P6m2, a = 2.90567(3) Å, c = 2.83641(3) Å, Z = 1).