Synthesis of metastable phases in the magnesium spinel-alumina system

We report here the use of liquid-feed flame spray pyrolysis to produce 14 nanopowders along the Al2O3-MgAl2O4 tie-line by combusting varied ratios of aerosolized ethanol solutions of alumatrane [Al(OCH2CH2)(3)N] and magnesium acetylacetonate [Mg(C5H7O2)(2)]. The resulting nanopowders were characterized by X-ray fluorescence, N-2 adsorption (Brunauer-Emmett-Teller), scanning electron microscopy, X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The powders typically consist of single-crystal particles of < 30 nm diameter and specific surface areas of 30-80 m(2)/g. Complementary XRD and FTIR studies show a gradual change in the powder patterns and spectra from delta-Al2O3 to MgAl2O4, Intermediate compositions exhibit phases that fall well outside of the established phase diagram and provide insight into the structure of transition aluminas. These materials have been shown to exhibit novel photonic behavior and have potential value as a new catalyst or support.