Comparative Study on the Composition–Microstructure–Property Relationships of MgO-Based Ceramics Modified by TiO2 and Y2O3

Magnesia (MgO) ceramics are widely used in refractory and high-temperature structural applications, but their performance is often limited by incomplete densification, residual pores, and insufficient thermal-shock resistance. In this study, MgO-based ceramics modified with reactive TiO 2 and relatively stable Y 2 O 3 additives were prepared from Mg(OH) 2 precursor by vacuum hot-pressing at 1600 °C, and the effects of additive type and content (0–4 wt%) on phase evolution, microstructure, densification, compressive strength, and thermal-shock performance were comparatively investigated. XRD results showed that TiO 2 was predominantly converted into Mg 2 TiO 4 under the present sintering conditions, whereas Y 2 O 3 remained mainly as a secondary phase without detectable Mg–Y–O reaction products. The TiO 2 -doped ceramics achieved the highest bulk density of 2.998 g·cm -3 and the lowest apparent porosity of 1.50% at 2 wt% TiO 2 , and also exhibited the best thermal-shock performance, surviving 12 heating–quenching cycles before the first visible crack. The highest room-temperature compressive strength of the TiO 2 -doped ceramics was obtained at 3 wt% TiO 2 , reaching approximately 89.2 MPa. In contrast, Y 2 O 3 improved densification and compressive strength at moderate contents, but excessive Y 2 O 3 addition at 3–4 wt% caused microstructural heterogeneity because of local second-phase segregation. The improved performance of the TiO 2 -doped ceramics was mainly attributed to the in-situ formation of uniformly distributed intergranular Mg 2 TiO 4 , which promoted grain-boundary regulation, pore elimination, and crack-path tortuosity. These results demonstrated that reactive TiO 2 was more effective than relatively stable Y 2 O 3 in simultaneously improving densification and thermal-shock resistance under the present processing conditions, providing a comparative basis for additive selection in MgO-based refractory ceramics.