Preparation of Mullite Nanocomposites Powders by The Hydrothermal Crystallization Method from Coal Gangue

Mullite nanocomposites powders have been successfully synthesized from pretreated coal gangue via hydrothermal crystallization process. The mullite nanocomposites powders are investigated and charactered by laser particle size analysis, X-ray diffraction analysis, transmission electron microscopy analysis, selected area electron diffraction analysis and energy-dispersive X-ray analysis. Moreover, the reaction mechanism of this process is speculated according to MAS-NMR results. It is indicated that mullite nanocomposites powders can be prepared at 80-90 degrees C for 3 h with NaOH concentration of 2-4 mol/L and US ratio (liquid/solid ratio in mass) of 10 mL/g by using calcined coal gangue as precursor. The agglomerate powder size of D-50 is about 3.83-4.71 mu m. Furthermore, some imperfective puncheon-shaped crystals exist among a large number of whole puncheon-shaped crystals which are about 30-70 nm in length and about 10-20 nm in diameter. MAS-NMR analysis indicates that the nano-size mullite grows around the central atom-Al, Si of [AlSi]O-4 tetrahedral and the growth unit Al[OH](4)(-) exists in this process definitely.