Microstructural development and mechanical performance of mullite-alumina and hibonite-alumina ceramics with controlled addition of a glass phase

Robust mechanical properties of refractory ceramics are critical to their performance in industrial applications. To investigate the effects of glass on the sinterability and mechanical properties of refractory ceramics, a controlled amount of glassy phase (10 wt%) was added to mullite (Al6Si2O13)-alumina (Al2O3) and hibonite (CaAl12O19)-alumina composites. Two liquid compositions within the Al2O3-SiO2-CaO system were chosen to produce a glass at 1600 degrees C that exists in equilibrium with a mullite-alumina composite and a hibonite-alumina composite. We performed a comparative study of the mechanical properties (hardness, flexural strength, and creep resistance) of mullite-alumina and hibonite-alumina composites with and without glassy phases. The observed microstructures clearly affected the mechanical properties. The strong interface created between the three phases in each subsystem and the reduced amount of residual porosity in the composites with an added glassy phase may explain the increase in strength, hardness, and creep resistance of the composites. However, better mechanical properties and finer grain sizes of mullite make the mullite-alumina (-glass) system a better candidate for refractory applications that require improved mechanical properties.