Effect Of Al/Si Powder Coated Modified Alumina Aggregates On The Properties And Microstructure Of Al₂O₃-C Refractory

The sliding plate is the functional refractory material for steelmaking,playing the role of regulating and controlling the flow of molten steel.Due to the harshness service environment,comprehensive high temperature properties such as high temperature strength,thermal shock resistance,corrosion resistance,oxidation resistance,were faced strict requirements.At present,the material of the sliding plate is usually Al₂O₃-C and the main reasons for the failure during use are wear of the sliding surface,bore enlarging,cracking,oxidation,erosion,etc.,of which the failure caused by the wear of the surface and bore enlarging accounts for more than 60%.However,it’s low bonding strength between the aggregates and matrix that the dominating reason for wear of the sliding surface and bore enlarging.Based on this,this subject prepared Al powder,Si powder and Al/Si composite powder coated modified tabular alumina aggregates to study the effect of modified alumina aggregates on the properties,composition and microstructure of Al₂O₃-C materials.The mixture of ethylene glycol and resin powder was used as the binding agent for coating modification,and the ratio of ethylene glycol and resin powder was designed to be70:30,65:35 and 60:40 respectively.The optimal ratio of ethylene glycol and resin powder was determined to be 60:40 by the mixing and wearing experiment.And then,Al powder,Si powder and Al/Si composite powder coated modified tabular alumina aggregates were fabricated with this binding agent.In the microstructure of Al₂O₃-C material with addition of modified tabular alumina aggregates,a ring of coated powder around the aggregates was observed,indicating that the bonding strength between the coated powder and the aggregates is relatively high,which can meet the requirements of mixing and molding preparation.Al₂O₃-C materials were prepared by coating modified tabular alumina aggregates with0%,2%,4%,and 6%Al powder in sequence,and the effect on the properties of the material at high temperature was studied.The results shown that the hot modulus of rupture（HMOR）of the material was as follows 24.4 MPa,28.8 MPa,30.5 MPa and 27.1 MPa,the ratio of residual strength after thermal shock was 63.1%,65.5%,75.1%,and 67.0%,respectively.After the introduction of modified aggregates,the high temperature properties of the material were improved,and the performance of the specimens with 4%Al powder modified alumina aggregates was fairly good.The phase composition and microstructure shown that the Al powder coated on the surface of the aggregates generated fibrous,needle-like Al₄C₃and AlN in-situ at high temperature,making the aggregates a"hammer-like structure",bridging the aggregates and the matrix,strengthening the combination of aggregates and matrix,thereby improving the HMOR of the material.Fibrous Al₄C₃and AlN with low expansion and high thermal conductivity had effect of toughening,which could absorb the thermal expansion of alumina,relieve the thermal stress and improve the thermal shock resistance of the material.Al₂O₃-C materials were prepared by coating modified tabular alumina aggregates with0%,1%,2%,and 4%Si powder,respectively,and studied its effect on the properties of the material at high temperature.The result shows that the HMOR of specimens was 8.4 MPa,9.2 MPa,11.0 MPa,8.7 MPa,respectively.The HMOR of specimen S2 was increased by31.0%after 2%Si powder was added to coat modified tabular alumina aggregates,and the thermal shock resistance of the material was fairly good.The phase composition and microstructure illustrated that at high temperature,the Si powder coated on the surface of the modified tabular alumina aggregates formed SiC fibers in-situ,producing a denser non-oxide network on the surface of the aggregates,further making a"hammer-like structure"with the aggregates.What’s more,binding force of the matrix to the aggregates was improved,enhancing the HMOR of the material.The total amount of mixed coating powder was 4%.Al₂O₃-C materials were prepared by coating modified tabular alumina aggregates with Al powder:Si powder equals to 4:0,3:1,and 2:2 respectively,and the effect of modified aggregates on properties at high temperature was further studied.The results shown that the HMOR of each specimen was35.4 MPa,35.3 MPa and 31.2 MPa,respectively,and the ratio of residual strength was as follows 83.3%,91.9%and 81.5%.It could be concluded that the effect of composite powder modified aggregates was better than that of single powder modified aggregates,and when Al:Si powder was 3:1,the comprehensive performances of the material was the best.The phase composition and microstructure shown that at high temperatures,the Al/Si composite powder coated on the surface of the tabular alumina aggregates formed in-situ needle-like,fibrous AlN,Al₄C₃,SiC and other non-oxides.Al was conducive to reduce the melting point of Si,promoting the formation of SiC,playing a role of synergistic strengthening and toughening,and finally,improving the HMOR and thermal shock resistance of the material.