The effects of pre-sintering temperature and La2O3 addition on sinterability and corrosion resistance of stoichiometric magnesium aluminate spinel

In this study, effects of pre-sintering temperature and subsequent La2O3 addition on the densification of magnesium aluminate spinel (MgAl2O4) were investigated. Further, the role of La2O3 was evaluated in terms of sintering/mechanical properties and corrosion resistance. Results reveal that two-step sintering achieves higher relative density than one-step pressureless sintering (from 70.21% to 83.86%) because it avoids volume expansion effect of MgAl2O4, but high pre-sintering temperature leads to a decrease in the activity of the raw material (for post-sintering). Subsequent experimental data show that the introduction of La2O3 endows the sample with greater relative density (from 91.24% to 95.65%), which is attributed to the formation of LaAlO3 and defect activation effect caused by stoichiometric mismatch. Besides, corrosion resistance of MgAl2O4 gets improved due to the formation of 2CaO·4La2O3·6SiO2, CaO·2Al2O3, and CaO·6Al2O3.