Study On The Application Performance Of Al-Si-Al₂O₃ Refractories

Metal-oxide composite is a novel material system integrating preparation and application,which has a very good application prospect.During high temperature service,the metals in the system react to form non-oxide reinforcements in situ,improving the comprehensive performance of the materials.In this work,the application performance of a resin bonded Al-Si-Al2O3 composite was studied.The evolution mechanism of phase compositions,and microstructure of the Al-Si-Al2O3 system at high temperature were investigated.The controllable synthesis of non-oxide reinforcements in the composite,including(Al2OC)1-x(AlN)x solid solution,15R/21RSiAlON,AlN-SiC solid solution,and AlON,were investigated.The high temperature performance and industrial application feasibility of Al-Si-Al2O3 composite were evaluated.The controllable synthesis of(Al2OC)1-x(AlN)x solid solution in Al-Si-Al2O3 composite at 1300? in nitrogen atmosphere was investigated.The results show that,by holding in nitrogen at 580? for 8 h,an AIN coating film is formed on Al particle,which temporarily fixes the Al(1)to prevent it from blocking the pores prematurely.With temperature increases to about 1100?,the AlN film ruptures,and highly active Al(1)is released.Al(1)preferentially reacts with trace O2 in the atmosphere to form volatile Al2O(g),which has a high reactivity,and further reacts with AlN(s)and C(s)from phenolic resin,forming whisker-like(Al2OC)1-x(AlN)x solid solution.The gas-solid reaction has advantages in kinetics,and the presynthesis of the isomorphic AlN nucleus greatly reduces the potential energy required for(Al2OC)1-x(AlN)x solid solution formation.Therefore,the(Al2OC)1x(AlN)x reinforcement was successfully synthesized in the composite at 1300?.The phase composition and structure evolution of Al-Si-Al2O3 composites in nitrogen at temperatures from 1500? to 1700? were further studied.The results show that Al and Si preferentially react with trace O2 in nitrogen and form Al2O(g)and SiO(g),which diffuse outward from the interior,and react with N2 at the peripheral to deposit,forming a flake 15R/21R-SiAlON dense layer.This process consumes oxygen,the Po2 inside the sample is greatly reduced,and the reactions of the system changes.At 1500? and 1600?,Al(1)in the interior further reacts with N2 to form AlN on the preformed AlN nucleus,which also reduce the potential energy required for the formation of isomorphic AlN-SiC solid solution.So,Si(1)and C(s)diffuse into AlN(s)in atomic form,forming granular AlN-SiC solid solution reinforcement.At 1700?,active ?-Al2O3 powders further participate in the reaction,and octahedron ?-AlON is formed by the reaction of Al(1),N2(g)and?-Al2O3.And granular and whisker ?-SiC are formed in-situ by reaction of Si(1)and SiO(g)with C(s)from resin.The cold crush strength of the samples is in the range of 180?444 MPa.The oxidation resistance of Al-Si-Al2O3 composites at 1100? and 1550?were studied respectively.After holding for 3 h in air,a dense oxide film(<2 mm)is formed on the surface of the samples,while Al and Si in the interior are transformed into whisker-like(Al2OC)1-x(AlN)x solid solution(at 1100?)and granular AlN-SiC solid solution(at 1550?)non-oxide reinforcements.In structure,the metal phases on the surface of the material are oxidized to form a dense oxide film,which hinders the inward penetration of O2.In terms of reaction mechanism,under high temperature and low PO2,the internal metals undergo active oxidation reaction to generate gaseous protoxides,which are filled in the material to hinder the penetration of O2.Therefore,the composites show excellent oxidation resistance.The creep test of Al-Si-Al2O3 composite was carried out at 1300? and 0.2 MPa in air for 50 hours.During creep,A1 and Si react to form non-oxide reinforcements,and all the phase composition,structure and occurrence of liquid phase of the composite are optimized.The samples directly get a steady-state creep with a low rate,and the deformation is only 0.12%after 50 hours test.Initially,Al(s)?Al(1),making the process liquid phase sintering,forming a uniform micro pore structure,which improves the ability of material to resist stress.Then,whisker like(Al2OC)1-x(AlN)x solid solution and granular ?-SiC are formed in situ by reactions of Al(1)and Si(s)at 1300?,forming a tough network structure,which greatly improves the bonding strength of the material.In addition,the liquid phases cannot wet the non-oxide phases,and shrinks in the network structure gap during creep,which effectively improves the creep resistance of the material.An Al-Si-Al2O3 sliding gate and Al-Si-MgAl2O4-Al2O3 brick for RH refining furnace were prepared and tested in practical induction,and the postmortem products were analyzed.The results show that the phase composition and structure of the postmortem brick show a gradient distribution of "corrosion layer-reaction layer-original brick layer".In the reaction layer,non-oxide reinforcements including Al4O4C,21 R-SiAlON,and AlON are formed in situ to form a dense layer,which improves the corrosion resistance and thermal shock resistance of the material.The internal metals are retained in the structure due to the lower temperature.The state of the gradient structure of metal-oxide composite is dynamic during service,that is,its phase composition and microstructure migrate sequentially and dynamically with the change of residual thickness(or temperature)of products.Metal-oxide composite is a kind of self-repairing material.