Improvement of Thermal Characteristics of Refractory Castable by Addition of Gel-Route Spinel Nanoparticles

Selected physical and thermal properties of conventional spinel-alumina castables were compared with those of castables produced using spinel fines prepared from a prepared gel. Limited numbers of hydroxyl groups created around the spinel precursor helped to improve thermal shock resistance. Micrographic examination confirmed that retained nanodimensional spinels firmly connected the hibonite and corundum grains in the castable, developing multiple interfaces after densification. Castable-containing spinel with excess alumina powder was found to have the best combination of bulk density, apparent porosity, and hot modulus of rupture. The reactive magnesia fine used to prepare in situ spinel-bonded castable was not found to give satisfactory results, owing to progressive disintegration of brucite-type compounds and abnormally grown spinels. Thermal characteristics of castables were assessed by differential thermal analysis (DTA), measurement of porosity, and percent linear change (PLC). Transmission electron microscopy (TEM), selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDS) analysis of the gel-derived spinel and castable confirmed their differences, particularly with commercial spinel having comparable chemistry but lacking nanocrystalline structure.