Advanced Al2O3–SiC–SiO2–C refractories with B2O3 addition

Abstract

This study investigates the effect of B2O3 addition (0.4 wt%, 0.8 wt%, 1.2 wt%, and 1.6 wt%) on the properties and microstructure of Al2O3–SiC–SiO2–C (ASSC) refractories. The results indicate that B2O3 plays an important role in accelerating mullite formation at low temperature. The substitution with Si by B in mullite crystal resulted in the formation of short and strong B–O bonds after firing at 1450 °C, causing the formation of boron-doped mullite with a smaller cell volume and leading to a decrease in the overall expansion of ASSC refractories. The addition of B2O3 to the ASSC refractories accelerated the growth of mullite along the direction parallel to the c axis, resulting in the improvement of mullite morphology (needle-like). The presence of in situ boron-doped mullite allowed the performance improvement of this class of refractory materials. The mechanical properties of the specimens improved significantly at various thermal-treatment temperatures. Moreover, the addition of B2O3 was beneficial for increasing the bulk density of the specimens, owing to the formation of a boron-rich liquid phase, which could accelerate sintering and densification. The optimal amount of B2O3 added in the specimens was <1.2 wt%, as above this value, an excessive liquid phase was formed, which degraded the high temperature performance.