Preparation and properties of MgAl2O4 spinel ceramics by double-doped CeO2 and La2O3

Magnesium aluminate spinel (MgAl 2 O 4 ) ceramics are high-performance and carbon-free materials widely used in both military and civilian fields. However, it is usually challenging to densify during the solid-state sintering process. The excellent properties of some rare earth oxides have been proved to promote the densification of MgAl 2 O 4 spinel ceramics. But the mechanism of promoting sintering is not clear. In the present work, MgAl 2 O 4 spinel ceramics have been successfully fabricated by co-doping CeO 2 and La 2 O 3 via a single-stage solid-state reaction sintering . The effects of addition amounts of CeO 2 and La 2 O 3 on phase compositions, microstructures, sintering characteristics, cold compressive strength , and thermal shock resistance of as-prepared MgAl 2 O 4 spinel ceramics were systematically investigated. The results show that by co-doping CeO 2 and La 2 O 3 can increase the defect concentration due to the lattice distortion. This could promote the movement of Al 3+ and Mg 2+ at high temperature, which is beneficial to the formation of more secondary MgAl 2 O 4 spinel. t-ZrO 2 with more Ce 4+ filling between spinel grains could prevent the growth of grains and promote the densification, besides the new-formed LaAlO 3 that was mainly distributed along the grain boundary of the MgAl 2 O 4 phase, both of which were favorable for the formation of dense microstructure of MgAl 2 O 4 spinel materials. At the same time, the formation of more secondary MgAl 2 O 4 spinel and sintering densification also improve the mechanical properties of spinel ceramics. La 3+ will segregate to the spinel grain boundary, preventing grain boundary movement and absorbing the main crack's fracture energy. With 3 wt% CeO 2 and 3 wt% La 2 O 3 co-doping, the bulk density of the sample increased from 3.02 g∙cm −3 to 3.55 g∙cm −3 ; the apparent porosity decreased from 12.21% to 9.97%; the cold compressive strength increased from 172.88 MPa to 189.54 MPa; and the residual strength retention ratio after thermal shock increased from 84.92% to 89.15%.