IR transparent hot pressed Mg-α/β-Sialon:Ba2+ ceramics

Abstract

IR transparent Mg-α/β-Sialon:Ba2+ ceramics were fabricated by the hot press sintering method. The influence of BaCO3 addition to Si3N4–MgO–AlN system on transparency, microstructures and mechanical properties were investigated. Reactions between the mixed powders were analyzed from differential thermogravimetric (DTG) curve and formation of Celsian (BaAl2Si2O8) was observed at 1175°C. The α-Sialon phase in sintered bodies was increased with BaCO3 addition due to the excess liquid phase that allows Mg2+ diffusion in α-Si3N4 lattice to give higher α-Sialon phase as revealed from XRD patterns. To minimize the light scattering by mismatch of refractive indices between the Sialon phase and glassy phase, barium ion was introduced to match the refractive index of glassy phase to Sialon phase. The study of electron spin resonance (ESR) spectra shows that unpaired electrons affect the IR transmittance in Sialon ceramics. Weak ESR spectrum was shown for the IR transparent BaCO3 added Sialon ceramics. The highest light transmission was observed around 78% in IR region (2500nm), and had better transparency than previously reported Sialon ceramics. The fabricated Sialon ceramics had high hardness of 21.4GPa and fracture toughness of 5.4MPam1/2.