Initial stage sintering of binderless tungsten carbide powder under microwave radiation

This work represents an investigation concerning neck growth kinetics during microwave sintering of free-packed spherical shaped binderless tungsten carbide particles. Application of classical sphere-to-sphere approach showed possibility to identify main diffusion mechanisms operating during initial stage of microwave sintering of tungsten carbide powder. An anomalous neck growth in the initial period during microwave sintering was also revealed, which was then followed by neck growth obeying mechanisms of volume and surface diffusion. Numerical simulation of neck growth process revealed anomalous values for diffusion coefficients - 7.16 × 10^-13 and 3.41 × 10 ^-8 m² s^-1 for 950 and 1200 °C respectively. The value of activation energy of neck growth process has been calculated as 69.18 kJ mol^-1. That value is significantly lower then any data on activation energy of diffusion processes in W-C system, and may be explained by overheating in the neck zone, or even formation of liquid phase in the neck area.