Characterization of mullite in silicoaluminous fly ash by XRD, TEM, and Si-29 MAS NMR

Mullite contained in a silicoaluminous fly ash (originating from power plan t of La Mere, near Metz in the east of France) issue from bituminous coal c ombustion has been studied by X-ray diffraction, nuclear magnetic resonance of Si-29 spinning at magic angle, and transmission electron microscopy lin ked with energy-dispersive spectroscopy. By using results from X-ray diffra ction [1] and nuclear magnetic resonance spectroscopy [2], an average value of 0.35 for x, the oxygen holes rate in mullite Al4+2xSi2-2xO10-x, could b e determined. Thus, Al2O3 content is only slightly higher than those corres ponding to the classical formula (Al2O3)(3).(SiO2)(2). It is shown also tha t the composition is heterogeneous and depends on the crystallites; Ti and Fe are impurities substituting for Al in the structure. The average chemica l formula of the mullite determined here is Al4.61Fe0.05Ti0.02O9.65. (C) 20 00 Elsevier Science Ltd. All rights reserved.