A PROCESSABLE MULLITE PRECURSOR PREPARED BY REACTING SILICA AND ALUMINUM HYDROXIDE WITH TRIETHANOLAMINE IN ETHYLENE-GLYCOL - STRUCTURAL EVOLUTION ON PYROLYSIS

A simple, processable precursor to mullite can be synthesized in quant ities of 100 g in a few hours by direct reaction of silica, aluminum h ydroxide, and triethanolamine in ethylene glycol, To delineate a proce ssing window whereby precursor shapes can be transformed into mullite, the chemical and phase microstructural evolution of this precursor on pyrolysis to selected temperatures in air is followed by thermal grav imetric analysis, differential thermal analysis, diffuse reflectance i nfrared Fourier transform spectroscopy, solid-state Al-27 and Si-29 nu clear magnetic resonance, X-ray diffractometry, and Brunauer-Emmett-Te ller analytical methods, The precursor behaves as a single-phase, atom ically mixed material that initially transforms to a porous, amorphous aluminosilicate when heated to temperatures as high as 950 degrees C, Above 950 degrees C, the precursor first transforms to tetragonal mul lite, based on comparison with the literature, and, on continued heati ng above 1200 degrees C, to orthorhombic mullite with coincident loss of porosity.