Effect Of Matrix Compositions On The Properties Of Alumina-spinel Castable

Alumina-spinel castables have become the major refractory material for steel ladle linings and venting system due to the high corrosion resistance to basic slag and the excellent resistance to structural spalling,which can effectively improve the service life of steel ladle and the quality of steel.However,the workability and the thermal shock resistance of alumina-spinel castables still need to be further improved.In addition,the silica fume plays an important role in the alumina-spinel system.Owing to the numerous types and the instable quality of comercial silica fume,it is necessary to refine the application of silica fume accroding to the actual conditions.Hence,this work has firstly investigated the rheological properties of the slurries of matrix compositions,i.e.four silica fume?92# ? 940 U ? 951 U ? 971U?,?-Al₂O₃ micropowder,ZrO₂ micropowder and the composite powders.Then the effects of the types and addition amount of silica fume,the addition amount and particle size of zirconia on the castables conventional physical performance,thermal-mechanical properties and slag resistance,etc.,have also been studied.The results indicated that:1)As the fraction of fine particles charactered by small middle particle size in the silica fume increased,the viscosity of slurry without dispersants was higher,and the slurries made from more coarse particles exhibited shear-thickening behavior.Compared to the dispersants of inorganic electrolytes SHMP and STPP,FS20 showed the better dispersing effect upon the various slurries,which was closely related to the generation of double effects,i.e.electrostatic repulsion effect and a strong space steric hindrance.Additionally,the complexation of metal ion Zr4+ with SHMP was helpful to obtain the better stability of ZrO₂ slurry.2)For the different kinds of silica fume,the high carbon content was responsible for the poor flowability of alumina-spinel castables and the high impurity content of alkali metal was responsible for the improvement of conventional physical performance.With the increasing amount of silica fume,the samples showed better sintering properties.When adding 4wt% silica fume,the castables flowability decreased significantly.Additionally,introduction of more silica fume was harmful for the corrosion resistance to slag but could improve the penetration resistance to slag simultaneously.3)The addition of ZrO₂ micropowder into alumina-spinel castable could promote the sintering process.However,the phase transformation of zirconia would take place during the heat treatment process,which leaded to a volume expansion and the deterioration of sintering properties.Therefore,the addition of ZrO₂ micropowder should be appropriate.The samples with 4wt% ZrO₂ micropowder showed the high hot strength and the excellent slag resistance.Besides,the thermal shock resistance could be improved significantly when adding 6wt% ZrO₂ micropowder.4)The effects of different sized ZrO₂ particles on the properties of alumina-spinel castables should mainly be resulted from the microstructure modifications.Fine ZrO₂ particles could effectively improve the hot modulus of rupture.Particularly,with the addition of ZrO₂ in median particle size of 2.5?m,the HMOR of samples could reach the maximum value of 3.27�0.49 MPa.However,as for the enhancement of thermal shock resistance,the coarse ZrO₂ particles seemed more effective.It was attributed to the fact that the coarse ones could lead to the generation of large matrix cracks,decreasing the stored elastic energy in the castables.