Far-infrared spectroscopy of alumina phases

Far-infrared spectroscopy (FIR) has been used to distinguish alumina phases boehmite, diaspore, gibbsite and bayerite. The pellets of samples were prepared by mixing alumina phases with polyethylene at a ratio of 1:50, and the spectra were recorded between 50 and 400 cm −1. The spectrum of boehmite resembles that of diaspore in the 300–400 cm −1 region. Boehmite has two characteristic FIR bands at 366 and 323 cm −1, while diaspore has five at 354, 331, 250, 199 and 158 cm −1. The spectrum of gibbsite resembles that of bayerite in the 230–300 cm −1 region. Gibbsite shows three characteristic FIR bands at 371, 279 and 246 cm −1, whereas bayerite shows six at 383, 345, 326, 296, 252 and 62 cm −1. The overlapping bands were resolved, and the spectra were manipulated appropriately using band analysis techniques. The FIR spectra are in harmony with the FT-Raman spectra. Far-infrared spectroscopy allows the study and differentiation of the stretching of AlO 4 units to characterize these four alumina phases. Far-IR spectroscopy complements the mid-IR and near-IR for distinguishing alumina phases in bauxites.