The impact of alumina bubble particle size on the microstructure and physical properties of mullite castables

Mullite castables are widely used in hot metal pretreatment processing equipment. In this work, the effects of alumina bubble particle size on the microstructure and physical properties of mullite castables were studied. Grey relational analysis is a useful method for analyzing patterns in multivariate cases. In this paper, the grey relational analysis was used to estimate the relationship between the properties of samples and the structure of alumina bubbles. Using grey analysis, the specific surface area of alumina bubbles was determined to have the greatest influence on the properties of apparent porosity, cold mechanical properties and thermal shock resistance. The hollow radius of alumina bubbles has the greatest relationship to bulk density, hot modulus of rupture, flow values and coefficient of thermal expansion of samples. Finally, the mullite castables with a high modulus of rupture and thermal shock resistance was obtained by adding alumina bubbles with a particle size between 0.5 and 1 mm. The high modulus of rupture was shown to be caused by the alumina bubble spherical shape, hollow structure and the appropriate bonding at the alumina bubble/matrix interface.