Induced electromagnetic pressure during microwave sintering of ZnO in magnetic field

This paper presents a unique technological approach for producing a tailored and controlled microstructure in pure zinc oxide using two different sintering methods. A microstructural comparative study between conventional and 2.45 GHz microwave sintered pure ZnO ceramics has been established. Data on the sintering behavior and grain growth as a function of the nature of the heating cycle are collected. The use of two step sintering cycles showed that high density can be achieved with almost complete suppression of grain growth. Compared to conventional sintering, microwave heated samples revealed a denser structure, as two step heated samples presented highest final densities for shorter sintering times. As a semiconductor, the material showed greater heating behavior in H-field which is traduced by higher energy absorption (higher ramp) at the beginning of the heating cycle. H-field sintered pellets showed higher densities and grain size uniformity than the ones sintered in E-field for identical heating cycles. This is likely due to an electromagnetic pressure induced by the combined effect of current loops submitted to a MW–H field.