In recent decades, the monolithic refractory is attracted due to the no requirement to any treatment for shaping and sintering. Tendency to use Alumina – magnesia spinel phase has increased due to favorable properties such as improved mechanical properties and slag corrosion resistance. Recently by attention to the effect of fine grain size materials on the properties of refractory castables and by employment of nano technology in material engineering, widespread researches has begun about using nano particles for refractory castables. In this study, production of alumina monolithic refractory containing in situ nano spinel was considered. In situ nano spinel formation at higher temperatures, helps to counterbalance the volume expansion. Different parameters such as the kind and amount of raw materials and aggregates, suitable binder at different firing temperatures were considered and bulk density (BD), apparent porosity (AP), strength was measured and XRD and SEM consideration were performed. Results showed that by using suitable amounts of alumina with magnesia, at 110 °C and firing at 1300°C, in situ nano spinel is formed in the castable. Therefore, in this research to acquire the suitable binders replacement for calcium alumina cement, different combinations of Sulphate binders, phosphate binders and silicate binder were considered. Result of the Brazilian strength test showed hexameta phosphate binder with calcium sulfate binder and white cement making a strong bond beside hydraulic and ceramic bonds. Studies by SEM and XRD showed use of refractory clay and lime, glass phase and mullite is produced. Mullite together with in situ nano spinel increase the strength and other properties of castable. Aggregates of Iranian sieved bauxite, has developed good properties. Key words : Monolithic Refractory Castable, In Situ nano spinel, Binder, Bauxite, Calcium Aluminate cement, Alumina-Magnesia
