Effect of La2O3 Addition on the Thermal, Microstructure and Mechanical Properties of Mullite–Zirconia Composites

Mullite–zirconia composites were prepared using lanthanum oxide (La2O3) additive at three different molar ratios via reaction sintering (RS) of alumina, kaolinite and zircon. Starting materials were planetary milled, shaped into pellets and bars and sintered at a temperature range of 1450–1550 0C with 5 h soaking at peak temperature. Mullite- zirconia composites were characterized in this study by thermal expansion coef􀀘cient, physical, microstructural, and mechanical properties. The X-ray diffraction (XRD) method was employed for determining the crystalline phase composition of these composites. Samples with 8 mol% La2O3 exhibited a 􀀚exural strength of ~197 MPa and elastic modulus of 143 GPa. Signi􀀘cant improvements in thermal expansion coef􀀘cient were observed in samples with 5 mol % La2O3. Composite microstructures were examined via scanning electron microscopy (SEM). ZrO2 takes part in both the intergranular as well as intragranular positions. However, intragranular zirconia particles are much smaller compared to intergranular zirconia particles.