| Al2O3-MgO refractory has been widely used as working linings of steel ladles and functional elements,owing to its excellent high temperature mechanical property,thermal shock resistance and slag corrosion resistance.However,its further applications were limited by the higher production costs and the higher heat storage loss due to the higher bulk density of the alumina containing refractories,which is not adapt to the requirements of high efficiency,low energy consumption and low emissions of iron and steel industry.Therefore,to solve these problems,the cheap CaCO3 with lower theoretical density was introduced as CaO resource into this refractory by replacing partial alumina raw material,which would be favorable to promote the lightweight of this refractory.In addition,this refractory could effectively purify the molten steel and promote the production of clean steel for the introduction of CaO is easily to react with P,S and other impurity elements of molten steel.However,both the main phases MA and CA6 in the new type refractory show poorly sintering ability,with the general sintering temperature to obtain the high density and excellently high temperature mechanical properties is higher than 1700?,thus restricting its further development.Therefore,the thesis embarked on enhancing sintering to solve existing question for the recent Al2O3-MgO-CaO refractories,the effect and mechanism of additives(La2O3,MnO,Y2O3)on the densification,microstructure,mechanical properties and slag corrosion resistance were investigated.Based on the important results,the following conclusions have been drawn:(1)The formation and growth of CA6 and MA grains were mainly controlled by the diffusion of Ca2+and Mg2+ions in the sintering process of MA-CA2-CA6 refractory composite,thus improving the sintering activity of CA6 and MA phases by enhancing the diffusion and mass transfer of Ca2+ and Mg2+ ions is benefit to promote the densification of this refractory composite.(2)The introduction of additives could significantly promote sintering densification process of the MA-CA2-CA6 refractory composite.Among them,the substitutional solid solution of La3+,Mn2+ and Y3+could significantly improve the sintering activity and promote the grain growth.Meanwhile,the transformation of grains morphology from platelet structure to equiaxed morphology could effectively exhaust pores and promote the densification process,the apparent porosity dramatically decreasing from 18.3%to 4.8%,4.4%and 4.1%when adding the mass fraction of 0.4%La2O3,4%MnO and 2%Y2O3 respectively after heating at 1600?.Therefore,the introduction of the above additives could effectively promote sintering densification process of this refractory composite.(3)The introduction of the additives has an important impact on micro structure of the MA-CA2-CA6 refractory composite,and the grain morphology of CA6 and MA has obviously shown positive correlation.Forming the solid solution of La3+ and Y3+ in the CA6 mirror surface layer by substituting Ca2+ of CA6 grains lowered the surface energy anisotropy,consequently,the abnormal grain growth rate of CA6 along the basal plane was decreased,the grain size and grain uniformity were greatly improved,and the shift of CA6 grains morphology would contribute to promote the development of MA grains as well.Forming the solid solution of Mn2+ and Y3+in MA grains by substituting Mg2+of MA grains could significantly promote the growth of MA grains and eliminate the porosity of this refractory,the shift of MA grains restricted the growth space of CA6 grains,resulting in the aspect ratio of CA6 grains significantly reduced.(4)The introduction of additives could significantly enhance the mechanical properties of the MA-CA2-CA6 refractory composite.By introducing the mass fraction of 0.4%La2O3,4%MnO and 2%Y2O3,the compressive strength was increased from 317MPa to 487,562 and 576MPa,the flexural strength was increased from 186MPa to 276,297 and 313MPa,and the fracture toughness was increased from 2.3MPa m1/2 to 3.3,3.5 and 3.6MPa m1/2,respectively.The great enhancement in the strength was mainly owing to the significant decrease in porosity and pore sizes.In addition,the reinforcement in grain-grain bonding increased the resistance to crack initiation and increased the resistance to crack propagation,contributing to optimize the fracture toughness.(5)The corrosion behavior of LF slag on the MA-CA2-CA6 refractory composite with the La2O3,MnO and Y2O3 added was close to the Al2O3-MgO refractory with similar relative density.On the one hand,the introduction of the additives was easily to form dense reaction layer of CA2 phases between slag and uncorroded region,which increased the slag penetration resistance.On the other hand,the presence of La2O3,MnO and Y2O3 with high melting points inside the slag increased the viscosity and decreased the penetration ability of the slag,contributing to further maintain the mechanical integrity of the refractory.Meanwhile,the existence of MnO,Y2O3 also could effectively promote the precipitation of MA phases with the slag corrosion resistance and high temperature resistance from the saturated slag,contributing to further effectively prevented the slag penetration and corrosion.(6)Replacing part of the bauxite aggregate by using of the MA-CA2-CA6 refractory aggregate could significantly enhance the corrosion resistance of the Al2O3-MgO-C bricks.During the process of the erosion,the dissolution of the CA2 and CA6 of the MA-CA2-CA6 refractory aggregate accelerated the precipitation of MA,promoted the formation of MA dense areas,and improved the slag corrosion resistance.On the other hand,in the reaction layer,the CA6 of the MA-CA2-CA6 refractory aggregate reacted with the liquid slag resulting in forming more dense CA2 phases,which was favorable to promote the slag penetration resistance and the slag corrosion resistance.In addition,in the original brick layers,the CA2 of the MA-CA2-CA6 refractory aggregate reacted with Al2O3 to form more toughening CA6 phases,thus the role of bridging was effectively promoted,which would significantly enhance the mechanical properties and the thermal shock resistance of Al2O3-MgO-C bricks. |
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