Mullite-Corundum Composites from Bauxite: Effect of Chemical Composition

In situ mullite-corundum composites have been prepared from low grade Indian bauxite containing high percentage of impurities (SiO2, Fe2O3, TiO2, CaO) and silica sol to study the effect of different mullite proportions on the refractory properties. Formation of different phases has been identified by X-ray diffractometry and the microstructure has been studied by field emission scanning electron microscopy. XRD analysis shows the presence of mainly mullite and corundum peaks. The bulk density increases and apparent porosity decreases with decreasing amount of mullite phase proportion in the mullite-corundum sintered aggregate. Refractoriness under load of mullite-corundum composites increases with increasing corundum amount up to a certain level and then decreases marginally. The unit cell parameter and cell volume calculated from X-ray diffraction data for mullite also follows the similar trend

Anomalous densification behavior of Al2O3-Cr2O3 system

Densification behavior of (Al1-xCrx)(2)O-3 (where, x = 0, 0.1, 0.3, 0.5) compacts in the temperature range 1000-1700 degrees C under reducing condition were studied. Up to 1300 degrees C, densification behavior followed the normal trend, i.e., bulk density increases with increase in Cr2O3 content. Anomaly in the densification behavior was observed from 1400 degrees C onwards. Al2O3 samples showed high densification; but the addition of 10 mol%Cr2O3 resulted in a sharp decrease in densification; while further Cr2O3 addition showed a steady rise in densification. XRD studies revealed the solid solution formation starts at 1400 degrees C. A broad endothermic peak at around 1400 degrees C in DTA thermogram corresponds to the formation of solid solution which actually absorbs extra heat energy resulting less dense Al2O3-Cr2O3 compacts. The average grain size of sintered Al2O3-Cr2O3 samples increases with increase in Cr2O3 content. (C) 2015 Elsevier Inc. All rights reserved