Influence Of Additives On Green Strength And Flowability Of Silica Sol Bonded Corundum-Based Castables

The sol bonded castables have obvious advantages over low cement or hydratable alumina bonded castables in drying performance and sintering properties. However, the castables with high-performance above was not widely used because of its low green strength.The castable samples were prepared by using brown fused alumina with different particle sizes, alumina micro-powder, silicon carbide, high temperature ball pitch, colloidal silica as raw materials. The work aimed at improving the green strength and the flowability of Al2O3-SiC-C castables bonded with the colloidal silica. Studied the effect of silica fume on the strength, volume density and apparent porosity of Al2O3-SiC-C castables and how additive affect the flowability and the green strength of castables.Firstly, the experiment investigated the effect of silica fume on the green strength of Al2O3-SiC-C castables bonded with the colloidal silica. The experimental results show that the optimum amount of silica fume is 1 wt.% and the green strength of castables is 1.08 MPa in this condition.With the optimum amount of silica fume, the experiment investigated the effect of sodium hexametaphosphate, sodium tripolyphosphate, citric acid, FS10 and FDN3000 on the flowability of Al2O3-SiC-C castables bonded with the colloidal silica. The results show that sodium hexametaphosphate is the most effective dispersant and the optimum additive amount is 0.1wt.%.The green strength of castables with the addition of coagulant, sintered magnesia and CA70 cement, is much higher than that of the castables without the addition of coagulant at 20 for 24 h for curing. The green strength of samples with the addition ℃of sintered magnesia is higher than the samples with the addition of CA70 cement when the coagulant had the same amount. The samples get the highest strength and the lowest flowability when the amount of sintered magnesia reaches at 0.3wt.%, however the fluidity of samples decrease with the increasing the amount of coagulants. The samples with the addition of sintered magnesia get the lowest flowability.The Mg2+ or Ca2+ of coagulants could withdraw hydrogen ions out of the Si-OH groups increasing the siloxane bond formation(–Si–O–Si–), and the ions could acting as a bridge by reacting with two particles on the surface of silica particles increasing the bond formation(–Si–O–Mg–O–Si–). Contrast the effect of the coagulants on the green strength of castables with three different dispersants to be found that the sample with sodium hexametaphosphate get the highest green strength.