Influence Of Accelerators Addition On Workability And Strength Of Colloidal Silica Bonded Corundum-based Castables

In contrast to hydration-bonded castables, castables bonded with colloidal silicapossess good baking property, good sinterability, high volume stability and highstrength at medium and low temperature. However, the demolding strength ofcastables bonded with colloidal silica is low, which restrict its wide application.In this paper, corundum castables are prepared using tabular corundum, sinteredalumina as main raw materials and colloidal silica as binder. The effects ofdispersants on the fluidity of corundum castables bonded with colloidal silica andaccelerator on the strength of green body have been studied. The strength of greenbody of corundum castables bonded with colloidal silica is enhanced via addingaccelerator A, B, and C during the experiment.For adding different kinds of dispersants (sodium tripolyphosphate, sodiumhexametaphosphate, FS10, and FDN300), castables with sodium hexametaphosphatesodium addition have the highest fluidity. The optimal addition is0.08wt.%, which isdetermined by Zeta analysis.The demolding strength of samples tends to increase with the addition of theaccelerators (A, B, and C). The accelerator A addition has the best coagulating effect,while the coagulating effect of accelerator C addition is not obvious. When additionof accelerator A is5awt.%, the demolding strength of castable reaches1.7MPa,which meets the requirements of construction. However, the fluidity of castable willdecrease with the addition of coagulants.The cold modulus of rupture and cold crushing strength of corundum castablesbonded with colloidal silica are considerably improved after drying at110C, andcontinue to increase during calcination at800C and1100C. By contrast, thestrength of castable bonded with low-content cement (3wt.%) increases after dryingat110C, but decreases dramatically after firing at800C and1100C. Themicrostructure analysis of samples show that the hydration products in castablebonded with low-content cement are decomposed after heat treatment at mediumtemperature, which increases pores in castable and forms the loose structure. That results in the decrease of strength at medium temperature. For castable bonded withcolloidal silica, slightly sintering occurs during heat treatment. By XRD analysis, itcan be seen that there is only corundum phase in castable bonded with colloidal silica,which improves the properties of castable in high temperature.