CA6 reinforcing role in high-alumina refractory castables containing CAC or CaCO3 as binders

Reference Presenter Authors
14-003 Ana Paula da Luz da Luz, A.(Universidade Federal de São Carlos); Consoni, L.B.(Universidade Federal de São Carlos); Guimarães Gabriel, A.H.(Universidade Federal de São Carlos); Aneziris, C.G.(TU Bergakademie Freiberg); Pandolfelli, V.C.(Universidade Federal de São Carlos); In situ self-reinforced oxide ceramic systems have been receiving more attention in recent years, due to the growing awareness that elongated phases can act as bridging site in the wake of a crack. Consequently, improved mechanical behavior might be achieved, as observed in alumina or zirconia-based compositions containing hexaluminate phases. Preliminary studies indicated that the morphology of CA6 can be readily changed (from equiaxed to platelet) by adding specific additives and/or modifying the processing conditions of the designed compositions. Therefore, considering the availability of novel alumina sources and the interaction of these oxides with calcium aluminate cement or CaCO3 to generate in situ elongated CA6 crystals in high-alumina refractory compositions, this work addresses the evaluation of the sintering/densification process of high-alumina CAC or CaCO3-bonded refractory castables. The morphology and distribution of the CA6 grains formed were characterized via SEM/EDS, in order to provide additional information for the discussion of the attained performance of the designed compositions. The thermo-mechanical properties of the prepared samples were analyzed via traditional tests (cold and hot mechanical strength, thermal shock resistance, etc.) and using in situ techniques (i.e., hot elastic modulus and assisted sintering measurements). According to the obtained results, the compositions containing 2.1 wt.% or 3.2 wt.% of CaCO3 as binder showed faster densification than the CAC-containing ones (the samples’ stiffness increase took place between 400-750°C), which was associated with sintering-coarsening-coalescence process of calcium carbonate particles. Elongated CA6 grains could be identified in all designed castable compositions after firing 1400°C for 5h. Furthermore, the most effective sintering of the CaCO3-containing refractories resulted in materials with enhanced thermo-mechanical performance in the 600-1600°C temperature range.
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