The Relationship Between Strength And Microstructure Of Corundum Based Refractory Castables Under Intermediate Temperature

The addition of microsilica in aluminate calcium cement bonded refractory castables can not only improve the particle size distribution, rheological property and bulk density, but also achieve relatively higher strength at intermediate temperature. However, the reason why aluminate calcium cement bonded castables with microsilica addition possess such a high strength under intermediate temperature isn’t very clear. There are no reports which have investigated the improved strength from the analysis of microstructure. Moreover, there isn’t systematic research about the relationship between strength and microstructure under intermediate temperature in aluminate calcium cement bonded castables with and without microsilica. In addition, strength under intermediate temperature was found to be used to evaluate the tendency to structural spalling of refractory castables. Therefore, this project will examine the influence of microsilica addition, heat treatment temperature on strength at intermediate temperature, aiming at establishing the relationship among microsilica addition, heat treatment, strength at intermediate temperature and microstructure. The main purpose of this work is to confirm whether or not the high strength of the castables fired at intermediate temperature (1000℃and lower) is attributed to sintering in the castable matrix by high magnification SEM observation.The effect of different addition of microsilica on strength at intermediate temperature is approached in this project. The castable samples and matrix samples were prepared by using fused corundum, alumina micro powder, microsilica and aluminate calcium cement as raw materials and investigated the microstructure and mechanical strength. The strength results and the microstructural observation of the castables confirm the high strength of the castables fired at intermediate temperatures (1000℃and lower) is due to sintering in the castable matrix. The addition of microsilica has substantial effect on the strength of refractory castables at intermediate temperature. Strength of samples without microsilica addition don’t change much after firing at600～1000℃, while strength of those containing more than3%microsilica increases dramatically with the increasing microsilica content. The changing strength of castables both with and without microsilica addition is consistent with degree of sintering of matrix after firing at600-1000℃. Particles in the microstructure of the samples without microsilica addition have no contact with neighbor particles. The structure turns much looser, porosity increased and no sintering behavior is observed. As a result, strength decreases gradually during the temperature region of600℃～1000℃. However, particles of microsilica in the samples are of smooth spherical shapes and there isn’t neck formation at600℃. But neck growth and compact structure were identified after heat treatment at800℃. Furthermore, both the number and the size of necks increase significantly and obvious sintering occurs at1000℃, which is the cause for considerably enhanced strength of the samples with more than3%microsilica addition after firing at600℃,800℃and1000℃.The research shows that the strength of the samples with and without microsilica is in accordence with the sintering degree of matrix after firing at600℃～1000℃. After heat treatment at intermediate temperature, the matrix without containing microsilica has relatively looser microstructure and no formation of necks. However, the matrix with microsilica addition possesses relatively compact microstructure. Furturemore, there are abundent neck formations which is the characteristic of sintering phenomenon. The samples with microsilica have higher strength under intermediate temperature becasue of the occurence of sintering.The research of the influence of the addition of microsilica and heat treatment temperature on the strength and microstructure of aluminate calcium cement bonded castables at intermediate temperature could not only be used to further understand of the relationship between strength and microstructure at intermediate temperature, and find effective way to improve the strength at intermediate temperature, but also provide practically useful direction for improving the application properties of castables.