Investigation On The Properties Of Al₂O₃-SiO₂ Castables For Aluminum-melting Furnace

China's automobile industry has been developed rapidly in recent years,and also will become one of the main industries in the next few decades.In order to reduce the weight,improve quality,and decrease energy cost of the automobile,high performance Aluminum Alloy has been used a lot in the car.Thus,refractory lining of the melting furnaces for aluminum alloy is demanded to be higher properties and quality.However,there is very little research of refractory report about materials for aluminum melting furnace in China at present.In this work,based on M85 and M75 calcined bauxite,M60 and M45 kyanite based mullite as the main raw materials,the influence of different Al₂O₃ content in the raw materials on the properties of the castable used in aluminum melting furnace was investigated.Based on the tests,the influence of K₂CO₃,BaSO₄,H₃BO₃ additives and aluminum sol binder on the properties of castable was researched.Through testing the cold and hot properties of the specimens,and analyzing the phase compositions and microstructures by XRD,SEM and EDS,the experimental results are obtained as follows:The research on effects of Al₂O₃ content in the raw material on the properties of the castables for aluminum melting furnace shows: the specimens display a some degree sinter from the judgment of their porosity after firing at 1200?;M75 specimens are difficult to sintered,which leaded to the strength of the minimum;M45 and M85 specimens have the highest CMOR?18.2MPa?and CCS?103.4MPa?respectively.With an increase of Al₂O₃ content,thermal conductivity increase.The thermal conductivity of M85 specimens are the largest,and that of M60 specimens are the smallest.HMOR of the specimens at 850? are higher than that of the CMOR 3-6MPa,and the M45 specimens show the highest?22MPa?HMOR.Which shows that micropowder promotes the specimens sintering at 850?.Corrosion behavior of the castables is closely related to Al₂O₃ content and apparent porosity of the specimens,the higher the Al₂O₃ content is and the lower the porosity is,the better the penetration and the corrosion resistance of the specimen is.Aluminum alloy liquid reacts with SiO₂ to form Al₂O₃ and Si at 850?,and accompanying with volume shrinkage,which will lead to cracking of the refractory lining.In reaction layer of the specimens,particle boundary is fuzzy,and the erosion areas appear more dense,which will be able to result in structural spalling under intermittent working condition.At the same time,Zn vapors remove from aluminum alloy liquid and enrich in boundary of transition layer,which leads to composition change of the aluminum alloy and influences the quality of aluminumWhen K₂CO₃ is added,the fluidity of the specimens were the best when sodium citrate and FS20 are used as water reducer.K₂CO₃ can react with Al and O₂ to produce KAlO₂ and CO₂ under high temperature,which will reduce the corrosion resistance of the material.While using aluminum sol as binder,the corrosion resistance of the specimens increase with the small addition?2%?of aluminum sol.However,with the increase of the aluminum sol content,the castables show a poor liquidity,which leads to higher porosity and poorer corrosion resistance.With the increase of BaSO₄ content,the porosity of the specimens increase,while the bulk density,the strength and the thermal conductivity of the specimens decrease.BaSO₄ reacts with Al₂O₃ and SiO₂ in the refractory at 900? to produce barium feldspar?BaAl2Si2O8?and barium rich liquid phase,and because of this,the content of SiO₂ and mullite of the castables decrease,the corrosion resistance of the material improve obviously.The erosion rate decrease from 5.1% to 3.75% as the BaSO₄ content increase from 0 to 1%,and when the BaSO₄ content is more than 2%,the crucible specimens are completely free from corrosion.But,when the BaSO₄ content is more than 2%,the liquid phase increase,which leads to the CMOR and HMOR of the specimens decreasing.As a whole,the best addition amount of BaSO₄ is 2%.With the increasing of the amount of H₃BO₃,the color of the specimens gradually change to yellow after firing at 1200?.The color changes to a muddy color when the H₃BO₃ content is 0.2%,and the surface shows about 0.5mm cracks,which leaded to a high porosity and a low strength of the specimens.The corrosion resistance of the specimens increase with the addition of H₃BO₃,the crucible specimens are completely free from corrosion while the content of H₃BO₃ are 0.1% and 0.2%.The SEM pictures show that the corundum of the specimens fired at 1200? are granular,and the pores between the particles are filled with glass phase.When the H₃BO₃ content is low?0.05%?,the corrosion resistance of the material is poor,and when the cotent of H₃BO₃ is high?0.2%?,the cracks will occur after fired,which would affect the strength of the specimens.As a whole,the best amount of H₃BO₃ is 0.1%,the optimum treatment temperature is 900?.