Effect of Incremental Addition of ZrO2 on the Densification, Phase Formation, Microstructure, and Strength Development of Pre-reacted Magnesium Aluminate Spinel

Commercially available magnesium aluminate spinel powder (AR-78) was taken as the starting raw material and then the effect of incremental addition of zirconia (ZrO2), in the concentration range of 1-8 wt.% (in steps of 1 wt.%) on the property development of magnesium aluminate spinel, sintered in the temperature range of 1550-1650 °ree celsius, was investigated. The study showed that the combined effect of ZrO2 addition and increased sintering temperature aided in the densification of spinel with maximum density shown by the 6 wt.% ZrO2 containing batches. All ZrO2 containing batches revealed the presence of spinel as major phase; unreacted monoclinic zirconia, and aluminum zirconium oxide or Al(0.5)2Zr(0.48)O(1.7)4 with a tetragonal structure as minor phases. Owing to the similar crystal structure of the secondary phase-Al0.52Zr0.48O1.74 with that of the parent spinel, the densification of spinel was improved. Further, the ZrO2 phases served as grain-growth inhibitors by serving as pinning agents along the spinel grain boundaries and helped in restrict the growth of spinel grains. This resulted in a controlled grain structure and led to improvement in strength values (cold crushing strength and flexural strength) in comparison with additive-free spinel batch. Improvement in thermal shock behavior in terms of strength retainment capacity was also observed with the addition of ZrO2.

Automated summary

This study investigates the effect of incremental addition of zirconia (ZrO2) on the property development of magnesium aluminate spinel. The results show that adding ZrO2 aids in the densification of spinel and improves its grain structure and strength. ZrO2 also acts as a grain-growth inhibitor, restricting the growth of spinel grains and enhancing thermal shock behavior.