Preparation And Properties Of Magnesium Aluminate Spinel Refractories Used In Oxygen-Fuel Glass Melting Furnace

With the advantages of saving fuel,decreasing environmental pollution and improving glass quality,oxygen-fuel combustion technology has been an important development direction in glass melting industry.While with the development of this technology,the temperature,the contents of alkali steam,water vapor and other erosive substances in the melting part of the furnace have been greatly increased.In addition,the gravity of crown refractories and the stress from adjacent bricks will lead to a big creep strain of refractories.Therefore,higher requirements for corrosion resistance and high-temperature creep properties of refractories for crown in glass melting furnaces are put forward.Compared with silicon,mullite and alumina refractories which have been widely used in this technical field at present,magnesia aluminum spinel?MgAl₂O₄?materials have many advantages,such as high strength,low thermal expansion coefficient,low thermal conductivity and strong corrosion resistance.Therefore,MgAl₂O₄ shows wide application prospects for crown refractories.However,MgAl₂O₄ spinel materials still have some problems to be solved urgently,such as they are hard to be sintered,the mechanical properties need to be enhanced further,and the creep rate under load at high temperature is still relative big,etc.Therefore,it is of great significance and practical value to improve the sinterability as well as high-temperature creep resistance and vapor attack resistance of MgAl₂O₄ spinel refractories.Based on above,the sintering properties,high-temperature creep resistance and corrosion resistance of MgAl₂O₄ spinel materials were improved by activating lattice through ionic solid solution and forming functional phase with excellent mechanical properties at the grain boundaries of spinel in this work.By introducing ZnO and utilizing Zn²⁺ions to replace Mg²⁺ions in MgAl₂O₄ for activating lattice,the sintering of MgAl₂O₄ spinel can be promoted.By introducing Y₂O₃ and utilizing it to react with alumina-rich spinel to form a low creep phase?yttrium aluminum garnet,YAG?,the grain boundary structure can be adjusted to improve the high-emperature creep resistance of the materials.By introducing La₂O₃ and utilizing it to react with alumina-rich spinel to form a lamellar phase?Lanthanum magnesium hexaaluminate,LMA?with high toughness,the high-temperature creep resistance and toughness of the materials can be improved.On this basis,the influence mechanism of doping ions existent states on the sinteringability,high-temperature creep resistance,and vapor attack resistance of MgAl₂O₄ spinel refractories were discussed.The results obtained in this work can provide a theoretical basis for the application of spinel refractories in glass kiln crown.The following conclusions have been drawn:1.ZnO,Y₂O₃,and La₂O₃ can effectively promote the sintering of MgAl₂O₄spinel,but the sintering mechanisms were different.Zn²⁺ions can partially replace Mg²⁺ions in MgAl₂O₄ spinel to form solid solution,the ion diffusion and mass transfer rate were accelerated with the lattice being activated,and the sintering activation energy was decreased.After Y₂O₃ introduced,some of the Y³⁺ions entered the MgAl₂O₄ lattice to form solid solution,and the residual Y³⁺ions reacted with alumina-rich spinel to form the second phase?YAG?.They distributed uniformly on the spinel grain boundary,which promoted the sintering activity of the spinel materials.Appropriate amount of added La₂O₃ reacted with alumina-rich spinel to form a lamellar second phase?LMA?,which promoted the sintering and densification of spinel.2.After adding appropriate amount of ZnO,Y₂O₃ and La₂O₃,the mechanical properties of MgAl₂O₄ spinel refractories can be increased by solution strengthening,in-situ forming YAG and LMA second phase,respectively.Compared with MgAl₂O₄refractory without additives,when the amount of ZnO added was 1.2 wt%,the cold modulus of rupture?CMOR?,crushing strength?CCS?,and modulus of elasticity?ME?values increased from 18.7 MPa,57.0 MPa,and 71.8 GPa to 23.2 MPa,79.8 MPa,and 90.5 GPa,respectivly.When the addition amount of Y₂O₃ and La₂O₃ were 2 wt%and 0.4 wt%,respectively,the CMOR,CCS,and ME values were further increased.3.ZnO can improve the fracture energy and creep activation energy of MgAl₂O₄spinel refractories through solution strengthening.When the addition amount of ZnO is 1.2 wt%,the fracture energy increased from 122.2 kJ/mol to 378.6 kJ/mol,the compression creep rate decreased from 0.38%to 0.14%,and the creep activation energy increased from 799 kJ/mol to 960 kJ/mol.The in-situ formation of low-creep second phase YAG further improved the fracture energy and creep activation energy of MgAl₂O₄ refractories through ceramic combination.When the amount of Y₂O₃added was 2 wt%,the fracture energy at 1400?increased to 405.1 kJ/mol,the creep rate at high temperature decreased to 0.08%,and the activation energy increases to1088 kJ/mol.The in-situ formation of lamellar high toughness LMA further improved the fracture energy and creep activation energy of MgAl₂O₄ spinel refractories through grain boundary control.The creep rate at high temperature was close to 0.4.Although adding ZnO can increase the densification of spinel,it had little effect on the alkali vapor erosion resistance of spinel refractories due to the little changed pore distribution and average pore size.With the addition of Y₂O₃ and La₂O₃,a dense layer of YAG and LMA formed on the grain boundaries of spinel grains,respectively.This not only decreased the apparent porosity,but also decreased the average pore size and improved the alkali vapor attack resistance effectively.The present spinel refractories were stable in high temperature water vapor environment and little chemical reaction took place.The formation of ZnO solid solution had little effect on water vapor attack resistance.When Y₂O₃ and La₂O₃ were added,CaO from the spinel as well as small amount of CaAl₁₂O₁₈8 generated by CaO reacting with Al₂O₃ aggregated at the spinel grain boundary.This resulted in a slight decrease in the water vapor attack resistance of the spinel refractories.