Hydrothermal preparation and characterization of boehmites

Boehmites (Al2O3 . xH(2)O, 1 < x < 1.5) have been prepared hydrothermally from Al(NO3)(3) . 9H(2)O and urea. Effect of temperature on preparation was studied in the range of 160 degrees-220 degrees C. No precipitation of boehmite was observed until the attainment of similar to 160 degrees C at which temperature a partly amorphous gel started precipitating. With the increase in temperature, transformation of the amorphous precipitate into crystalline boehmites took place as indicated by the X-ray diffraction (XRD) patterns. From the weight loss studies of the samples prepared at different temperatures and for different reaction time intervals, the value of x was estimated to vary between 1.3 and 1.5. The Fourier transform infrared (FTIR) spectra of samples obtained at 180 degrees, 200 degrees or 220 degrees C showed 25-40 cm(-1) upward shift in the -OH stretching and bending vibrations assigned to boehmites. gamma-Alumina obtained by subsequent calcination of boehmite at 725 degrees C was also characterized by XRD. (C) 2000 Elsevier Science B.V. All rights reserved.