Effect of carbide on Al2O3/B4C burnable poison sintered in Ar

Highlights: ► C element improves the densification of B4C/Al2O3 ceramics. ► C eliminates oxide behavior of B4C/Al2O3. ► The B2O3 and Al18B4O33 is produced at 1500 °C. - Abstract: Al2O3–14 wt%B4C composites with 0–1 wt% C addition were sintered in Ar at 1550–1650 °C. The influence of the C additive on the B loss, densification behavior, and microstructure of the Al2O3–B4C composites were investigated. The results show that there are B2O3, H3BO3 and Al18B4O33 exist between Al2O3 and B4C interface, which result in B loss because of B2O3's high vapor tension at above 1500 °C. The presence of Al18B4O33 grains formed by chemical reaction of Al2O3 with surface oxides on B4C inhibit the densification of pellets by reducing the specific free surface energy of the Al2O3. However, the added C eliminates those oxides to reduce B loss because of its higher activity than B4C, and it also coarsens Al2O3 grain although the density of pellets is decreased by gas products.