| Al2O3-MgO refractory has been widely used as working linings of steel ladles,owing to its excellent high temperature mechanical property,thermal shock resistance and slag corrosion resistance.However,its further applications are limited by the higher heat storage loss due to the higher bulk density,which is not adapt to the requirements of energy-saving and emission-reduction.On the other hand,the cost of this refractory has been increased continuously in recent years,due to the supply shortage of the raw materials of corundum and/or bauxite.Therefore,decreasing the amount of higher theoretical density raw material of alumina in Al2O3-MgO refractory and promoting the lightweight of this refractory will be of great importance.Based on this aspect,CaCO3 was introduced as CaO resource into this refractory by replacing partial alumina raw material in the present study considering the abundance of limestone resources,to fabricate Al2O3-MgO-CaO refractory by solid state reaction sintering,and the basic academic questions during the preparation of this new refractory were investigated in detail.The following research results have been drawn:(1)The internal reaction and sintering densification behavior of the Al2O3-MgO-CaO refractory were investigated.After CaO was introduced into the Al2O3-MgO refractory,calcium hexaluminate(CA6)and calcium dialuminate(CA2)were formed.The plate structure of CA6 grains was not favorable for the densification.However,the CA2 grains showed good sintering ability.CaO content had a great influence on the phase composition and sintering ability of this new refractory.For the refractory with addition of 8wt%CaO,the presence of CA2 as stable phase after heating at 1600? not only improved the densification,but also decreased the bulk density of the refractory,which effectively promoted the lightweight of Al2O3-MgO refractory.(2)The effect of prefiring technology on the sintering densification was investigated.The prefiring temperature had an important influence on the sintering and densification.After prefiring at 1200?,the density of the raw materials was significantly increased and the high sintering activity was maintained,and the relative density after heating at 1600? was higher compared to that with prefiring treatment at higher temperatures for all the investigated refractories.Therefore,1200? is considered as the optimal prefiring temperature with relatively low energy consumption.For the refractory with 4wt%CaO content,a high porosity of 31.6%was obtained after heating at 1600? with prefiring treatment at 1200?.For the refractory with 8wt%CaO content,the porosity was decreased to 22.1%due to the good sintering ability of CA2.(3)Based on the above research,the effect of additives(ZrO2,TiO2)on the sintering densification and microstructure of the MA-CA2-CA6 refractory composite was investigated.The addition of ZrO2 and TiO2 could significantly improve the sintering activity of this refractory composite and promote the grain growth along the thickness direction of CA6.Besides,the surface energy anisotropy of CA6 grains was decreased due to the incorporation of Zr02 and TiO2 into its structure,which decreased the abnormal grain growth rate of CA6 along the basal plane.For the composites with higher content of ZrO2 and TiO2,this growth rate was further decreased due to the pinning effect of t-ZrO2 and Al2TiO5 particles at the CA6 grain boundaries,resulting in a more equiaxed morphology and consequently greatly improving the densification,with the apparent porosity dramatically decreasing from 22.1%to 5.3%and 3.7%when adding 6wt%ZrO2 and TiO2 respectively after heating at 1600?with prefiring treatment at 1200?.(4)The mechanism of additives(ZrO2,TiO2)on promoting the mechanical properties of the MA-CA2-CA6 refractory composite was proposed.By introducing 6wt%ZrO2 and Ti02,the compressive strength was increased from 307 MPa to 584 and 636 MPa,and the flexural strength was increased from 173 MPa to 255 and 276 MPa,and the fracture toughness was increased from 2.2 MPa ml/2 to 3.9 and 3.8 MPa m1/2,respectively.The great enhancement in the strength was mainly owing to the significant decrease in porosity and pore sizes as well as the improvement in uniformity of grain size due to the change of the CA6 grain morphology.In addition,the reinforcement in grain-grain bonding increased the resistance to crack initiation and the presence of t-ZrO2 and Al2TiO5 increased the resistance to crack propagation,both contributing to optimize the fracture toughness.(5)The corrosion behavior of LF slag on the MA-CA2-CA6 refractory composite at 1600? was firstly studied,and the mechanism of additives(ZrO2,TiO2)on promoting the slag corrosion resistance was proposed.The main corrosion process was consisted of the dissolution of refractory phases,especially for CA6 and the precipitation of MA and CA2 from the saturated slag,forming two reaction layers between slag and uncorroded region.The amount of the dissolved phases and the corrosion thickness of this refractory composite were high due to the high slag penetration caused by high porosity.The MA-CA2-CA6 refractory composites with addition of ZrO2 and TiO2 achieved lower corrosion thickness which was close to that for Al2O3-MgO refractory with similar relative density.On the one hand,this was due to the improvement in sintering densification by addition of ZrO2 and TiO2,which increased the slag penetration resistance and thus decreased the dissolution of refractory phases.On the other hand,the presence of ZrO2 and precipitation of CaZrO3,CaTiO3 with high melting points inside the slag increased the viscosity and decreased the penetration ability of the slag.The above research results can provide theoretical basis and technical support for the application of Al2O3-MgO-CaO refractory with high density and high properties.It also has important significance for promoting the lightweight of the refractory and energy saving of the iron and steel industry. |
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