Microstructural Development in Milli Wave Sintered Silicon Nitride Based Ceramics

摘要

It is evident that a clear understanding of the effect of milliwave heating on ceramics will contribute to expand the scientific and technological applications of this heating method for sintering of these materials. In the present work, silicon nitride based ceramics, with Y_2O_3 and Al_2O_3 as additives, were sintered to almost full density by heating for two hours at 1800℃ in a nitrogen atmosphere (0.1 MPa) using a milliwave applicator fed by a 28 GHz Gyrotron source. The changes in microstructure and phase transformation that accompany the temperature increase up to 1800℃ were investigated by scanning electron microscopy and by X-ray diffraction and compared to equivalent specimens sintered by conventional resistance heating. Results show that milliwave heating enhances the densification and accelerates the α-β transformation in silicon nitride ceramics.