CRYOSOL SYNTHESIS OF NANOCRYSTALLINE ALUMINA

In the present research we employed the newly developed cryosol techni que for the preparation of nanocrystalline Al(OH)(3). The technique yi elds sols of aluminum hydroxide stable under a wide range of pH values and concentrations. Freeze-drying of the sols results in the formatio n of aluminum hydroxide powders with extremely low density and small p article size. Thermal behavior and phase evolution of the cryosol-deri ved aluminum hydroxide has been studied. According to X-ray diffractio n data, annealing of cryosol-derived aluminum hydroxide results in amo rphous alumina stable up to 800 degrees C. However DTA, electron diffr action, and Al-27 NMR studies indicate that the samples amorphous to X -ray diffraction are composed of crystalline nanoparticles. The therma l stability of nanocrystals is supposed to be due to the high uniformi ty of the particles size distribution, the latter resulting from the s ynthetic method employed.