Effect of matrix component on the microstructures and properties of spinel-corundum (periclase)-calcium aluminate refractory

In this study, MgAl2O4 (MA)-CaAl2O4 (CA)-CaAl4O7 (CA2) multiphase materials were synthesized and used as refractory aggregates, combined with different matrices to prepare two types of refractories. The first is spinel-aluminate-corundum (SCCA) refractory, whose matrix is composed of reaction-formed spinel and corundum; the second is spinel-aluminate-periclase (SPCA) refractory, whose matrix is composed of reaction-formed spinel and periclase. The effect of the matrix composition on the microstructure and properties of the fired products at 1700 °C was investigated. The results indicate that the aggregates in two type of refractories exhibit different porosities owing to the migration of low-valence Ca2+ ions during sintering. In SCCA materials, Ca2+ in the multiphase aggregate migrated to the matrix, particularly at the interface of the aggregate and matrix, resulting in further facilitation of aggregate lightweighting and matrix densification. Although this phenomenon reduces the compressive strength of the materials, it enhances the thermal shock resistance and decreases the thermal conductivity owing to the formation of plate CA6 and C2M2A14 phases, as well as the presence of small pores and cracks. Static crucible slag resistance tests showed that the SCCA samples had good slag resistance owing to the following: (1) A dense CA6 layer was formed between the aggregates and the matrix in the samples. (2) The pore size in the matrix of the SCCA samples was smaller than that in the SPCA samples. (3) A dense slag layer composed of high-melting-point phases (MA, CA2, and Ca2Al2SiO7) was formed on the corroded sample surface. (4) The formation reaction of aluminates can consume Ca in the slag, absorb Si and Fe, and increase slag viscosity. These factors collectively prevent further penetration of slag liquid into the SCCA refractories.