Effect of micro-spinel powders addition on the microstructure and properties of alumina refractory castables

The microstructural evolution and comprehensive properties of alumina refractory bonded with calcium aluminate cement and silica sol have been studied. Results have been correlated with the microstructural and phase evolutions using X-ray diffraction and scanning electron microscopy, as function of the pre-formed spinel powders. Matrix samples were obtained for phase and microstructural characterization in details, and the results were compared with those corresponding to the refractory castables. The room temperature and high temperature properties, including permanent of linear change, mechanical properties, hot modulus of rupture (HMOR) and slag resistance were measured. The castables exhibited a microstructural optimization and properties enhancement due to the addition of pre-formed spinel. A lot of secondary spinel and CA₆ (CaO·6Al₂O₃) with small size were produced in the castables, and the contents of micro pores were greatly increased. As a result, the permanent of linear change of castables was decreased by 61%, while cold modulus of rupture (CMOR) and HMOR were increased more than 45% and 100%, respectively. The penetration indexes in the static slag resistance were decreased from 28.8% to 12.2%.