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

In recent years, the research results show that sol bonded castables have obviousadvantages over low cement or hydratable alumina bonded castables in dryingperformance, low and intermediate temperature strength, sintering properties andvolume stability. However, the current studies focus more on silica sol bondedcastables. With regard to other sol bonded castables such as colloidal alumina bondedcastables, there are few systematic and sound researches. Aimed at improving thegreen strength of colloidal alumina bonded corundum-based castable, the workmainly studies the effect of different dispersants on the flowability of castables andhow accelerators affect the green strength of castables.The castable samples and matrix samples were prepared by using differentparticle size tabular corundum, alumina micropowder, colloidal alumina, B and A asraw materials. After fired at different temperatures, the samples were investigatedusing a variety of testing techniques such as mechanics performance testing, TG-DTA,XRD and SEM. Firstly, the experiment investigated the effect of sodiumhexametaphosphate, FS10, sodium tripolyphosphate, citric acid and FDN-3000on theflowability of castables. The experimental results show that sodiumhexametaphosphate is the most effective dispersant and the optimum additive amountis0.2%.With the optimum amount of sodium hexametaphosphate, adding accelerators toimprove the green strength of castables, it found that the flowability of colloidalalumina bonded castables obviously decreased. In terms of the effect of acceleratorson improving the green strength, A and B behave relatively well. Through theinteraction of accelerators and colloidal alumina or the hydration and hardening of Aand B, they can almost double the green flexural strength, reaching target strength of1MPa or above.In addition, in the TG-DTA experiment, it was found that the dehydrating rate ofcolloidal alumina bonded castables was significantly higher than that of low cementbonded castables during removal stage of free water at around50℃. The easier removal of free water in colloidal alumina bonded castables at around50℃may bedue to that the permeability of colloidal alumina bonded castables without hydrationphases after natural curing24hours is higer than that of low cement bonded castablesin which the hydration phases block the pores.In this work, the flexural and compressive strength of low cement bondedcastables with different treatment (natural curing,110℃,800℃,1100℃,1450℃)were higher than that of colloidal alumina bonded corundum-based castables;Accelerators A and B can improve the green strength of colloidal alumina bondedcastables, but doesn’t work to the intermediate and high temperature strength. Asshowed in the XRD patterns, the main phase of low cement bonded castables (800℃,1100℃,1450℃) was corundum,and CA6appeared in the samples fired at1450℃;Also, the main crystal phase of colloidal alumina bonded castables was corundum. Itwas found that the spinel phase existed in the colloidal alumina bonded castablescontaining0.3%of A after fired at1450℃.At the same time, the microstructuregraphs of castable samples also verified the appearrance of CA6and spinel.The research about the effect of dispersants and accelerators on the flowabilityand green strength of castables can help to solve the de-moulding green strengthproblems, and can also lay foundation for furtherly studying colloidal aluminabonded corundum-based castables.