Hydrothermal preparation and characterization of boehmites

BoehmitesAl2O3PxH2O, 1-x-1.5.have been prepared hydrothermally from AlNO3.3P9H2O and urea. Effect of temperature on preparation was studied in the range of 1608–2208C. No precipitation of boehmite was observed until the attainment of ;1608C 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 infraredFTIR.spectra of samples obtained at 1808, 2008 or 2208C showed 25–40 cmy1 upward shift in the –OH stretching and bending vibrations assigned to boehmites. g-Alumina obtained by subsequent calcination of boehmite at 7258C was also characterized by XRD