The effect of calcium magnesium aluminate (hereinafter referred to as CMA) on the microstructural distribution of the main impurity SiO2 in magnesia was investigated in this research. The XRD, SEM, and EDS analyses were used in this work. It can be seen from the result that SiO2 in low-grade sintered magnesia diffused into CMA area at high temperature and the distribution of SiO2 in sintered magnesia was significantly reduced. The main mineral phase of sintered magnesia was periclase and monticellite, and impurities in sintered magnesia mainly existed in the form of monticellite, which was completely decomposed into liquid phase and periclase above 1400 degrees C, SiO2 in the liquid phase in the sintered magnesia migrated into the liquid phase that formed in the CMA. Furthermore, the adsorption energy of CaO on SiO2 is stronger than that of MgO on SiO2, so the SiO2 in sintered magnesia diffused into CMA due to its relatively higher CaO content compared with the sintered magnesia. The SiO2 content in fused magnesia was lower than that of sintered magnesia and the dicalcium silicate (C2S) content in fused magnesia was higher than that of sintered magnesia, so the influence of CMA on microstructural distribution of SiO2 in fused magnesia was obviously different than that with low grade sintered magnesia.

This paper aims to improve the density and thermal shock resistance of Y2O3 ceramics for the preparation of ultra-pure high-temperature alloy crucible materials. The doping effect of MgF(2 )content on the densification behavior, physical properties, and thermal shock resistance of Y2O3 ceramics was systematically investigated in this paper. The results suggested that the presence of MgF2 greatly promoted the growth of Y(2)O(3 )grains and the transformation of the pore structure by liquid-phase sintering. And the mechanical properties of the MgF2-doped Y2O3 ceramics were significantly improved. Besides, the marked improvement in the thermal shock resistance of MgF2-doped Y2O3 ceramics was attributed to the synergistic action resulting from the growth of grain size and the enhancement of the crack deflection effect. In particular, the relative density of Y(2)O(3 )ceramics doped with 1.5 wt% MgF2 reached 96.4% and the residual flexural strength ratio after thermal shock achieved 45.0%, showing an excellent application prospect.

Y 2 O 3 materials have been widely applicated in high temperature industry owing to its high temperature stability. However, the poor sintering behavior and thermal shock resistance limited its application. The existing studies were focused on its sintering properties, yet the increase in densification of Y 2 O 3 materials could weaken its thermal shock resistance. Y 2 O 3 materials with smaller closed pores were fabricated by the decomposition of Al(OH) 3 and the effect of Al(OH) 3 on the microstructure, mechanical properties and thermal properties of Y 2 O 3 materials were investigated in this paper. We concluded that the migration of grain boundaries was accelerated due to the ionic radii difference and the diffusion coefficient between Y 3+ and Al 3+ , and the diffusion coefficient of Y 3+ was relatively weak while the diffusion of Al 3+ was mainly dominated. The Al 2 O 3 produced by decomposition of Al(OH) 3 was active, which promoted the sintering of Y 2 O 3 materials. Meanwhile, the porosity and pore structure of Y 2 O 3 materials were affected by the decomposition of Al(OH) 3 , and the appropriate pores improved the thermal shock resistance by absorbing thermal stresses. Furthermore, it indicated that adding Al(OH) 3 into Y 2 O 3 materials had a powerful influence in balancing its sintering properties and thermal shock resistance. The sample with 3 wt% Al(OH) 3 exhibited the better performance in this study, with the relative density of 93.2% and the thermal shock stability factor parameter R st of 1.74 W m 1/2 .

Y2O3 materials have become a popular candidate for preparing refractory crucibles for ultra-pure high-temperature alloy melting in recent years. However, its difficulty in sintering and poor thermal shock resistance limited its industrial application. The effect of CaF2 on the densification microstructure, mechanical properties, and thermal shock resistance of Y2O3 materials was investigated in this paper. The main purpose of this study was to optimize the amount of CaF2 added in the preparation of Y2O3 materials to improve its thermal shock resistance and get better mechanical properties. The mechanism of the densification process of CaF2-doped Y2O3 materials was analyzed by phase analysis and microstructure. The results showed that successive doping of large Ca2+ ions caused more lattice distortion in the Y2O3 materials, and the diffusion rate of Y3+ was increased, thus enhanced grain boundary diffusion and promoted sintering densification in the Y2O3 materials. Meanwhile, the addition of CaF2 also significantly reduced the apparent porosity and enhanced the mechanical properties of the materials. The improvement of these properties was attributed to the increased relative density of CaF2-doped Y2O3 materials and the high sintering activity of CaF2. In addition, crack deflections effectively improved the thermal shock resistance of the materials. The residual flexural strength ratio of Y2O3 materials doped with 1 wt % CaF2 was increased by 21.2% after thermal shock test compared with undoped specimens.