Sintering behavior, microstructures and mechanical properties of porous CaO-Al2O3-SiO2-Si3N4 glass-ceramics

Novel porous CaO-Al2O3-SiO2-Si3N4 glass-ceramics with in-situ grown rod-like β-Si3N4 crystals were fabricated by sintering under a nitrogen atmosphere. Sintering behavior, microstructures and mechanical properties of various compositions in the CaO-Al2O3-SiO2-Si3N4 system were investigated, using differential scanning calorimeter (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM) methods, followed by physical and chemical property measurements. Depending on our experiments, the coexistence of CaO-Al2O3-SiO2 glass and α-Si3N4 can lower the phase transition temperature of α-Si3N4 and promote the in-situ formation and growth of β-Si3N4 grains during sintering process. The in-situ grown rod-like β-Si3N4 grains in the glass-ceramics are useful to the improvement of physical and chemical properties by addition of α-Si3N4 to the system. This was attributed to that the in-situ grown β-Si3N4 grains formed a spatial inter-locking microstructure. The physical and chemical properties of the porous glass-ceramics are mainly determined by the β-Si3N4 content, the porosity and the residual glassy phase. The porous CaO-Al2O3-SiO2-Si3N4 glass-ceramics with high porosity, high mechanical strength and low dielectric constant were obtained, indicating it is potential high-temperature industrial applications.