Effect Of Particle Size Of Calcium Aluminate Cementon The Properties Of Corundum-Based Castables

Calcium aluminate cement(CAC)is an important binder,providing effective demolding strength via hydration process,for refractory castables.It is known that the particle size of cement is an important factor which has an effect on the hydration of calcium aluminate cement,so it will have an impact on the properties of castables.In this paper,the effect of calcium aluminate cement on the mechanical strength,volumetric stability and thermal shock resistance of corundum-based castables were investigated.In order to establish the relationship between the properties of castables with different addition and particle size of cements and the phase change and microstructure of calcium dialuminate(CA2)and calcium hexaluminate(CA6),the phase change and microstructure of CA2 and CA6,which are the main phases in CAC bonded corundum-based castables after firing at high temperatures,were also investigated.In order to study the effect of particle size of calcium aluminate cement on the properties of corundum-based castables,the calcium aluminate cement was ground for different times(0h,1h and 2h).The influence of particle size of cement on the properties of castables was explored by measuring the permanent linear change,cold modulus of rupture,cold-crushing strength and thermal shock resistance of corundum-based castables after firing at 1100 and 1450°C,respectively.In order to establish the relation between the properties of castables with different particle size of cements and the phase change and microstructure of CA2 and CA6,the matrix samples were prepared similarly as castable samples.The results indicated that the particle size of the cement is considerably reduced with the increasing grinding time(the median particle sizes(d50)of the cement were 16.98 ?m,3.26 ?m and 3 ?m for the cement after grinding for 0h,1h and 2h,respectively).The mechanical strength,volumetric stability and thermal shock resistance of corundum castables were increased with the reduced particle size of cement.The results of XRD presented that the peaks heights of Al2O3 and CA2 after firing at 1100°C and the peaks of Al2O3 and CA6 after firing at 1450°C were almost not noticeable different with the increasing time of cement grinding.The results of SEM showed that the matrix with finer cement particles could form finer CA2 grains after firing at 1100°C.Such newly-formed finer CA2 grains were distributed more evenly and could fill the voids among the grains to reduce the pores.After firing at 1450°C,the platelet CA6 was formed.The platelet CA6 particlescould form interlock structures to improve strength of castables.With the particle size of cement reduced,the interlock structure is more stable.Thus,it is the reason why the diminishing particle size of calcium aluminate cement could improve the volumetric stability,mechanical strength and thermal shock stability of castables.In order to investigate the influence of the addition of calcium aluminate cement on the properties of corundum-based castables,different amounts of calcium aluminate cement(1%,2%,3%,5% and 7%)were added to castables obtaining castables with different addition of cement.The effect of contents of cement on the properties of castables was studied by measuring the permanent linear change,cold modulus of rupture,cold-crushing strength and thermal shock resistance of corundum-based castables after firing at 1100 and 1450°C,respectively.In order to establish the relation between the properties of castables with different addition of cements and the phase change and microstructure of CA2 and CA6,the matrix samples were prepared similarly as castable samples.The results indicated that the cold and high strength of corundum-based castable samples were improved with cement addition increased.The results of XRD indicated that the peak heights of CA6 after firing at 1450°C were improved with the increasing cement addition.Due to a massive amount of CA6,so the permanent linear change of castables was increased with the increasing cement addition after firing at 1450°C.The results of SEM demonstrated that the contents of CA2 grains of matrix samples were increased with the improved cement addition after firing at 1100°C.These CA2 grains filled the voids among the grains and distributed densely,leading to the improved strength of corundum-based castables after firing at 1100°C.When the heating temperature reached 1450°C,the increased contents of interlocked CA6 grains of matrix samples with the increasing cement addition could increase the connection between particles and form stable interlock structure.Thus,the mechanical strength of castables after firing at 1450°C was improved with the increasing addition of cement.