Effect of B4C on the properties and microstructure of Al2O3 -SiC-C based trough castable refractories

The effect of B4C addition (0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%) on properties and microstructure of Al2O3-SiC-C (ASC) based trough castables was studied in this paper. The results showed that the bulk density of samples after firing at 1450 °C decreased when the addition of B4C was over 1 wt%. The cold modulus of rupture of samples improved significantly with the addition of B4C when the treating temperature was over 1100 °C. Among them, sample with 1.5 wt% of B4C had the best anti-slag performance and thermal shock resistance. The SiC fibers were formed in the non-oxidized zone of ASC castables with addition of B4C after firing at 1450 °C in air condition. The obtained fibers rooted in the walls of inner micropores of samples with the diameter of 50-200 nm, and the lengths of 10-50 µm. The experiment revealed the nucleation of SiC started at about 1000 °C, and then the growth of SiC fibers happened at higher temperature in a favorable condition. A stepped twin structure perpendicular to the growth direction of fibers could be observed. Finally, the growth mechanism was interpreted by thermodynamic calculations.