Preparation Of MgO-Al₂O₃-Cr₂O₃ Composite Sol And Its Application In Refractory Castables

In the refractory industry,aluminate cement-bonded castables have the advantages of high early strength and good rheological properties,and are the most widely used binders in castables.The performance declines,limiting the application range of the castable.At the same time,the study found that compared with aluminate cement,sol-bonded castables have obvious advantages in baking performance,thermal shock resistance,slag resistance,high temperature strength,etc.Low mold strength,poor rheological properties,and less industrial applications.The research of sol-combined castables by scientific researchers mainly focuses on silica sol,and there is less research on aluminum sol,magnesium sol,and chromium sol.In this context,a magnesium-aluminum-chromium composite sol was prepared by the sol-gel method for the purpose of preparing a high-performance sol binder,and the prepared sol and its gel powder were added to corundum castables.Its effect on castable properties.In addition,according to the problem of poor fluidity of the sol-bonded castable found in the study,the effect of dispersant on the performance of the sol-bonded castable was explored.The specific research contents and conclusions are as follows:（1）Using magnesium nitrate,aluminum nitrate and chromium nitrate as raw materials and citric acid as complexing agent,a series of magnesium-aluminum-chromium composite sols with different chromium contents were synthesized through a simple water bath heating process.The sols were characterized and the results showed that A composite sol with stable properties was prepared;in addition,the influence of the introduction of chromium on the formation of nano-Mg Al₂O₄ crystals after heat treatment of the sol was studied by different material analysis methods.At the same time,the introduction of chromium will lead to abnormal growth of the spinel,and the chromium will dissolve into the crystal structure of the spinel,so that the grain size varies from a uniform 20nm to 20-50nm.（2）The magnesium-aluminum-chromium composite sol was added to the CMA72 low-cement castable to study the effect of the sol on the properties of the castable.The results show that the addition of sol helps to maintain the volume stability of the castable,the setting speed of the castable becomes faster,and the curing time becomes shorter,but the addition of sol and the reduction of water lead to the poor fluidity of the castable.Part of the pores cannot be discharged,resulting in an increase in apparent porosity and a decrease in bulk density,which is not conducive to improving the strength and slag resistance of the castable;in addition,the research results obtained after adding the magnesium-aluminum-chromium gel powder to the castable are similar to those of the sol.,it can increase the volume stability of the castable,but it still has the disadvantages of poor fluidity and low strength.（3）In view of the poor fluidity of the castable after adding the sol,the rheological properties of the sol combined castable can be improved by adding a dispersant to the castable.In the experiment,FS10,FD35,SD80 and SD83 were added to the castable as dispersants,and their effects on the properties of the sol-bonded castable were studied respectively.The fluidity test results showed that FS10 and FD35 dispersants not only did not improve the fluidity of castables,but made them worse,while SD80 and SD83 dispersants could improve the fluidity of castables.0.1%and 0.2%respectively;the demolding strength test results show that SD80 reduces the demolding strength of the castable to a certain extent,SD83reduces the flexural strength of the castable,but the addition of SD83 at 0.15%increases the castable’s strength.compressive strength;in addition,SD80damages the volume stability of the castable,but the damage is not large,SD83has no effect on the volume stability of the castable,both of them can reduce the apparent porosity of the castable and increase the volume density.