Effects Of Optimizing Micro/nano Matrix Microstructure On The Properties Of Corundum- Based Refractory Castables

Corundum-based refractory castables have high refractoriness,good volume stability and resistance to corrosion.So they are widely used in metallurgy,building materials,petrochemical and other industries.At present,low cement,ultra-low cement and lately cement-free castables have become mainstream.Therefore,it will bring problems such as low strength,poor construction performance and small application range.The addition of micro-nano powders to the matrix can effectively solve the above problems.To begin with,the rheological behavior of corundum-based castables matrix slurry have been studied.Five kinds of dispersant types and amounts of polyethylene glycol-based polymers FS10,FS20,FS60,sodium tripolyphosphate?TSP?and sodium hexametaphosphate?SHP?were selected as variables.It is found that the TSP and SHP are classified as inorganic electrolytes,but FS10,FS20 and FS60 are polymer nonionic dispersants.Due to the electrolytes and polymer dispersants have different dispersion principles,so it should not rely solely on the change of the?-potential of the surface of the slurry as a criterion for evaluating the dispersion effect of the dispersant on the sample.The amount of dispersant added to the matrix slurry has an optimum value.For this experimental system,the viscosity of the matrix slurry is relatively small and the dispersion is better at the same shear rate when the dispersant is FS10 which the addition amount is 0.18%.Based on the type and content of the selected dispersant,the mechanical properties and microstructure evolution of corundum-based castables with different nano-alumina contents were investigated.The results show that the hot modulus of rupture of the sample with 2%nano-alumina is 13.4 MPa,which is 21.5%higher than the sample without nano-alumina.The thermal shock resistance of the samples was studied from several aspects.Compared with the sample without nano-alumina,the elastic modulus retention rate of the sample with nano-alumina increased from 49.6%to 59.6%after eight thermal shock cycles.In addition,an optimum nano-alumina amount is 2 wt%,insufficient or excess nano-alumina powder can not play a dense microstructure on the sample and enhance the effect of high temperature performance.Based on the rheological behavior of corundum-based castable matrix slurry and the effect of introducing nano-alumina on the microstructure and properties of corundum castables,it was found that the viscosity of slurry and water addition are increased due to the addition of excessive?-Al₂O₃ micropowder during the casting process.Therefore,?-A1₂O₃ micropowder was used as the variable and the matrix premixing method was improved.The aggregate was poured into a stirring pot to prepare a corundum refractory castable after the matrix was premixed for 3 hours.As a result,it was found that only pure calcium aluminate cement was used as the binder,the strength of the sample was too poor after firing at 110°C,and the properties of the samples after heat treatment at1 100°C and 1 500°C were also unsatisfactory.With the increase of the content of?-A1₂O₃ micropowder,the water addition and apparent porosity of the material are slightly reduced first and then significantly improved and the bulk density and strength of the material increase first and then decrease.The samples with 2%?-Al₂O₃ micropowder have relatively high cold modulus of rupture,cold crushing strength and hot modulus of rupture.The cold modulus of rupture of samples increased from 3.26 MPa to 10.16 MPa after firing at 110°C.In order to further improve the strength,thermal shock resistance and slag resistance of corundum-based castables,it is considered to introduce nano-alumina into the corundum-based castables based on the optimization of?-Al₂O₃ micropowder.It is found that the sintering driving force of sample with nano-alumina is 1.15×10³ and1.125×10³ times that of the sample without nano-alumina after heat treatment at 1 100°C and 1 500°C,respectively.This sintering driving force increases the grain boundary migration speed and significantly enhances the sintering effect of the sample with nano-alumina.The addition of nano-alumina has little effect on the apparent porosity of the samples.Compared with the sample without nano-alumina,the pore size of the sample with nano-alumina is significantly reduced after heat treatment at different temperatures.Among them,the pore size of the sample with 2%nano-alumina reduced to 55 nm after heat treatment at 1 100°C.Furthermore,the sample without nano-alumina has the highest erosion of 5.84 mm²/min,so its slag resistance was poor.The erosion of the sample with 2%nano-alumina is 2.75 mm²/min,and its slag resistance is relatively excellent.The introduction of nano-alumina facilitates the evolution of the pore size of the sample from micron to sub-micron or even nano-scale,which contributes to the substantial enhancement of the slag resistance of the sample.