MICROSTRUCTURAL PROPERTIES OF BOEHMITE FORMED UNDER HYDROTHERMAL CONDITIONS

The microstructural properties of boehmite formed in an alkaline mediu m under hydrothermal conditions were investigated using X-ray diffract ion (XRD), Fourier transform IR (FT-IR) spectroscopy, transmission ele ctron microscopy (TEM) and microelectrophoresis. The bayerite formed a t the beginning of the precipitation process converted to boehmite by the dissolution/ reprecipitation mechanism. Boehmite crystallites were in the nanosize range and of anisotropic shape, as determined by XRD. A tendency toward an increase in the crystallite size with prolonged duration of autoclaving was evident both at 160 and 120 degrees C. The boehmite particles produced by autoclaving at 160 degrees C for 10 h looked like thin microfoils, i.e. different from the boehmite morpholo gy usually obtained (rods, fibrils and very small plates). The factors that influence the pH(iep) of boehmite particles are discussed. The F T-IR spectra of bayerite and boehmite are interpreted. (C) 1998 Elsevi er Science S.A. All rights reserved.