Preparation Of Spinel Precursor Sol And Their Effects On Properties Of Alumina Castables

Castables,as principal monolithic refractories,are widely used in high temperature industries,and the optimization and development of their properties are closely related to their composition.Aggregate,powder,binder and additives are the key factors affecting properties and performance of refractory castables.The particle size distribution of the castables especially micropowder additions affect the properties and sintering performance of the castables.Different types and contents of binders not only affect the bonding properties of refractory castables,but also the physical and chemical properties and service performance.The commonly binders used have advantages and disadvantages.Castables bonded by alumina cement show insufficient medium temperature strength,and the presence of Ca O in alumina cement causes low melting point liquid phase formed at high temperature.The castable bonded with hydrated alumina has insufficient strength at room temperature and is prone to explosion during heating and drying.The strength of castables bonded by silica sol binder at room temperature is insufficient,and Si O₂ has a negative impact on the slag resistance of the material.In addition to a single type of sol,binary or multi-system sols have been developed in recent years to improve further the performance of castables.In this paper,the preparation and properties of magnesium-aluminum bicomponent sol were studied by taking magnesium-aluminum sol as spinel precursor sol.Firstly,the stability of single component aluminum sol was investigated.It is found that with the addition of different dispersants,the viscosity and Zeta potential of aluminum sol will be affected by the type and content of additives.However,on the whole scale,the less effect of micro-addition is observed,because of the particle size of nano-alumina,the large specific surface area and surface energy,and it is easy to agglomerate,resulting in less effect of the addition of dispersant.There is no significant effect on the fluidity of the sol.Secondly,magnesium aluminate spinel precursor sol was prepared by adjusting the p H value in the mixed solution with aluminum nitrate as alumina precursor and magnesium nitrate as magnesia precursor.The density of the sol is 1.20 g/cm³,and the appearance is transparent,uniform and stable.It is converted into a soft and transparent gel above 50°C.When the p H of the sol between 3-4 and the calcination temperature at 1000°C,the solid content can reach about 7.5%.The thermal behavior of the sol was studied by TGA analysis,and single-phase Mg Al₂O₄ was formed at 600°C.It was also investigated and analyzed that properties and the microstructure of magnesia-alumina precursor sol bonded corundum castables by different particle size distribution and sol addition.It was found that the particle size of the castable had a significant effect on the properties of the castable,and castables with the closest packing mode showed high strength,high density and good slag corrosion resistance.Different sol additions result in different spinel content in the castables.The expansion caused by the formation of spinel provides a choice for the microstructure design.With the increase of the amount of spinel precursor sol,the micro-crack effect generated by spinel formation is greater than the beneficial effect brought by the low-temperature combination of sol,which has a tendency to increase first and then decrease for various properties.Finally,the effects of spinel precursor sol,silica sol,alumina sol and alumina cement on the properties of corundum castables were studied comparatively.It is found that in terms of various properties,the spinel precursor sol-bonded material has better properties and performance,which is conducive to the application under ultra-high temperature conditions.The alumina sol has the worst performance due to the large amount of water required for preparation of specimens.