Effect of SiC–graphite–Al-metal addition on low- and ultra-low cement bauxite castables

Abstract

Eight batches of low- and ultra-low cement castables were prepared from calcined Chinese bauxite and high alumina cement (HAC). The effect of alumina-cement replacement by SiC, graphite and aluminum metal on the sinterability and properties of these castables was investigated. Physical properties such as bulk density and apparent porosity of hydrated and sintered castables were studied. The sintered castables were also characterized for their solid phase compositions and microstructure using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. In the castables containing SiC, new phases such as mullite (3Al2O3·2SiO2), SiC, and quartz (SiO2) were formed at the expense of calcium aluminate phases (i.e. CA and CA2; the main cement phases). Generally, the bulk density of the control castable sample was the highest among all prepared samples, while the batches containing graphite showed the lowest bulk density. The presence of Al-metal reduced the oxidation of SiC and consequently increased the densification of the castables compared with castables containing graphite only. Cold crushing strength (CCS) of the hydrated specimens i.e. green castables, decreased as the additives contents increased at the expense of HAC which is responsible for the bonding at room temperature. The highest CCS value of the sintered castable was obtained for the sample containing 6wt.% SiC, 3wt.% CA and 0.5wt.% Al-metal.