Preparation and performance optimization of MgAl2O4 spinel materials by single-step reaction sintering

To investigate the sintering mechanism of magnesium aluminate (MgAl2O4) spinel material. In this study, MgAl2O4 spinel materials were synthesized by single-step reaction sintering method using light calcined magnesia, white corundum as raw materials, and YSZ (yttrium oxide stabilized zirconia) as additive. The effects of w (MgO + Al2O3) content (20-80 wt%), molding pressure (100 MPa and 200 MPa), and YSZ additive (0-3 wt%) on the phase compositions, microstructures, sintering properties, mechanical properties, and thermal shock resistance were investigated. The results show that increasing the content of w (MgO + Al2O3) from 20 wt% to 80 wt% and molding pressure from 100 MPa to 200 MPa are a benefit to the formation of second MgAl2O4 spinel. Simultaneously this will lead to the increased apparent porosity due to the formation of point defects in MgO crystals during sintering. YSZ addition induced double vacancy defects in the MgAl2O4, which also facilitated the formation of the second MgAl2O4 spinel. Besides, YSZ additives plays a pinning role, preventing the migration of grain boundaries. The positive effect of adding 1 wt% of YSZ is intuitively manifested in increasing the sintering and mechanical properties. The material with superior comprehensive performance can be obtained by adding 1 wt% YSZ additive, 80 wt% of w (MgO + Al2O3), and forming under molding pressure of 200 MPa, followed by sintering at 1600 degrees C for 2 h. The final material exhibits the diameter shrinkage ratio of 3.32%, volume shrinkage ratio of 7.31%, apparent porosity of 14.21%, bulk density of 3.02 g cm-3, cold compressive strength of 176.88 MPa, and residual strength retention ratio of 84.92% after one thermal shock.