Synthesis and thermal decomposition of nitrate-free boehmite nanocrystals by supercritical hydrothermal conditions

Single-phase boehmite nanocrystals that are free of nitrate contamination could be prepared at supercritical hydrothermal conditions at 400 degreesC and 35 MPa for 30 min. XRD analysis showed that the single phase boehmite was formed in the absence of alkali species. Two well-defined and strong absorption bands observed at 3300 and 3092 cm(-1) in the present infrared spectra showed that the boehmite by supercritical hydrothermal conditions was highly crystallized. Furthermore, IR. spectra confirmed that the boehmite samples were free of NO3--related impurities in contrast to boehmite produced by hydrothermal conditions as reported by Music et al. [Mater. Lett., 40 (1999) 269] and Mishra et al. [Mater. Lett., 42 (2000) 38]. At a temperature of 725 degreesC, the present boehmite powders were decomposed into 10 nm gamma-Al2O3. Further heating of the samples to 1250 degreesC led to the formation of single-phase alpha-Al2O3. (C) 2002 Elsevier Science B.V. All rights reserved.