| Alumina-magnesia refractory castables are widely used as lining material of ladle in steelmaking processes because of their excellent slag corrosion resistance and thermal shock resistance.However,with the progress and development of steelmaking technology,higher requirements are put forward for the performance of alumina-magnesia castables.Generally,calcium aluminate cement is used as binder of alumina-magnesia castables.However,too much Ca O introduced by calcium aluminate cement will have a negative impact on the slag corrosion resistance of the material.Therefore,in recent years,low cement castables(LCCs)and no cement castables(NCCs)are the main trend to be applied.For LCCs,the conventional cement(Secar71)with sintered calcium aluminate is still used,thus the Ca O content in the materials is still high;however,for NCCs with no cement,the strength after demoulding is generally low,which can not meet the requirements of workability.In order to solve the above mentioned problems,firstly,a new type of fused calcium aluminate cement(Hi Per Cem)is proposed as the binder of alumina magnesia castables to reduce the amount of cement and the content of Ca O.The content of calcium aluminate hydrated phase(CA)playing a major role in the early strength of the materials is more than 90%and much higher than that of Secar71(60-70%CA).Secondly,the powder composed of different kinds of alumina and magnesia sources by co-grinding process is used as no cement binder for alumina-magnesia castables,which can improve the early strength of the materials,meet the requirements of workability,and improve the slag corrosion resistance of the castable.Based on the above research work,the following results are obtained.1)The introduction of Hi Per Cem into alumina-magnesia castables can not only meet the requirements of early strength,but also improve the properties of the material.Compared with the conventional calcium aluminate cement Secar71 and CMA72,the new cement Hi Per Cem bonding alumina-magnesia castables showed better workability.Additionally,with less Ca O introduction,the material can obtain better slag corrosion resistance without sacrificing its demoulding strength and drying strength.With the increase of Hi Per Cem content,the permanent linear change and apparent porosity increased gradually,the erosion index decreased and the penetration one increased gradually.Overall,the appropriate addition amount of Hi Per Cem cement is 2wt%.2)The composite powder prepared by co-grinding hydrated alumina,micro-alumina and different Mg O sources(fused magnesia,Mg(OH)2 and hydrotalcite)as binder of alumina-magnesia castables can meet the requirements of early strength and improve the slag corrosion resistance of the material.Hydrated alumina,micro-alumina and different Mg O sources(fused magnesia,Mg(OH)2 and hydrotalcite)were co-grinded to prepare binder for corundum based alumina-magnesia castables.In contrast to the hydrated alumina bonded alumina-magnesia castables,the binder obtained by co-grinding of hydrated alumina,fused magnesia and micro-alumina can improve the flowability and early strength of the castables,reduce the apparent porosity and volume expansion after firing,and obtain better slag resistance.Besides,the results showed that the binder composed of hydrated alumina,micro-alumina and Mg(OH)2 or hydrotalcite got a decrease in early strength of the material,but its volume expansion is better controlled,and its slag resistance is better than that of hydrated alumina.Compared with the commercial alumina-magnesia castables binder,alumina-silicate gel powder and alumina-magnesia-silicate gel powder,there is no SiO2 component in the binder system,which has obvious advantages in slag corrosion resistance. |
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