Preparation of low-cost mullite ceramics from natural bauxite and industrial waste fly ash

Low-cost mullite ceramics were prepared from the mixtures of natural bauxite and industrial waste fly ash. The fired samples, including fly ash, bauxite and their mixture based on the composition of 3:2 mullite, were characterized respectively by XRD (X-ray diffraction). The results indicate that the secondary mullitization occurred by the solid-state reaction of cristobalite and corundum below 1300 degrees C, followed by the dissolution of corundum into transitory glassy phase at higher temperatures. The dilatometric results reveal that the formation of secondary mullite resulted in a slight expansion in spite of the shrinkage induced by sintering. In addition, the samples were fired at elevated temperatures and then characterized in terms of relative density, porosity, micro-structure and fracture strength. At 1600 degrees C, the relative density and fracture strength are 93.94% and 186.19 MPa, respectively. Only a small amount of nearly spherical closed pores were observed in the sintered body. (c) 2007 Elsevier B.V. All rights reserved.