Structural analysis on spinel (MgAl2O4) for application in spinel-bonded castables

An intimate mixture of common hydrated magnesium salt and cheaper boehmite sol had been used as a cost-effective precursor of reactive nanometric spinel (1:1) powder. It was gelled at controlled pH, temperature and time, and calcined at significantly lower temperature after soft mechanochemical treatment. X-ray diffraction (XRD), infrared spectra, differential thermal analysis (with thermogravimetry), proton-nuclear magnetic resonance (NMR) and transmission electron microscope studies were carried out to investigate the incipient formation of low crystalline nanosized domains in the still-hydrated spinel. Spinel nanoparticles are protected by a thin chemisorbed layer of (OH) groups held around the active surface of the aggregates. Selected properties of conventional Al2O3–spinel and Al2O3MgO castables were compared with the same formulated by the chemical-route spinel fines. Cold and hot strengths of the refractory castable containing commercial spinel with excess alumina powder were the best, while the same bonded by reactive magnesia and coprecipitated spinel fines were not satisfactory. Performance of sol–gel spinel is comparable to the preformed spinel with 78% alumina.