Abstract
Boehmites (Al 2O 3· xH 2O, 1< x<1.5) have been prepared hydrothermally from Al(NO 3) 3·9H 2O and urea. Effect of temperature on preparation was studied in the range of 160°–220°C. No precipitation of boehmite was observed until the attainment of ∼160°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°, 200° or 220°C showed 25–40 cm −1 upward shift in the –OH stretching and bending vibrations assigned to boehmites. γ-Alumina obtained by subsequent calcination of boehmite at 725°C was also characterized by XRD.
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