Preparation And Investigation Of Closed-cell Porous Al₂O₃-based Refractory Aggregate

At present,high-purity and high-density are properties of traditional refractory industry in China,high-purity has brought many excellent propertites to us,althought the high-density can improve the slag resistance and the high temperature strength of refractory to a certain extent,the consumption of the bauxite resource is greatly increased and it shows poor slag resistance and thermal-insulating property.In recent years,many researchers have done a great deal of work on the porous refractory aggregates,but the pores prepared by them were open pores,and it gone against the improvement of slag resistance of the refractory aggregetes.If the pores in the material are closed pores,the above problems can be solved completely.Therefore in this paper,the alumina-based refractory aggregate was selected as research object,and it aimed to prepare closed-cell porous refractory aggregate,in order to achieve the double purpose of reducing resource consumption and saving energy.In this paper,sub-micron Al2O3 powder was used as raw material,MgO powder as addictive,nano SiC powder as high temperature forming agent,the closed-cell porous alumina-based refractory aggregate was fabricated by using ball-milling process and gel-casting method.The effects of different amounts of SiC and MgO powder on sintering behaviors,porosity,phase composition,microstructure,pore distribution of refractory aggregate have been investigated,the properties of slag resistance,thermal shock resistance and flexural strength were also studied.Finally the closed-cell formation mechanism of alumina-based refractory aggregate was discussed.The main conclusions are as follows:(1)In this experiment condition,the closed porosity of the refractory aggregates which are prepared by two methods reached approximately to 15.9%and 13.06%respectively.(2)The alumina-based refractory aggregates' phase composition is identical,their compositions are mainly Al2O3 and MgAl2O4 with little amount of mullite.(3)Compared with the alumina-based refractory aggregate fabricated by ball-milling method,the pore size and distribution of the refractory aggregate prepared by gel-casting method are more uniform,and the body strength is better.(4)The experiment of slag resistance shows that the molten slag can not penetrate into the alumina-based refractory aggregate with closed-cell structure easily;the closed-cell alumina refractory aggregate has better thermal shock reisitance,and it cycles to 3 times;moreover,the closed-cell alumina-based refractory aggregate obviously has a higher flexural strength compared with porous alumina-based refractory aggregate.(5)The closed-cell formation mechanism of the refractory aggregate is the oxidation of SiC and generate gases,meanwhile,remaining SiC reacts with matrix materials and releases gases too.The gases generated by above reactions "push" the boundaries between grains and slip to form the cell under high temperature superplasticity effect of alumina refractory aggregate.Moreover,the generated SiO2 at high temperature can promote the sintering of matrix material and densify it further.Finally,the gases are sealed in materials to form closed pore.