An IR spectroscopic characterization of α-FeOOH (goethite)

Several preparations of α-FeOOH, all cnaracterized by low surface area and good pigmentary properties, have been studied by IR spectrosoopy. Light scattering properties were found to vary severely from preparation to preparation, following the crystal dimensions, so that the specimens of lowest surface area ( ~ 10 m2g−1) are very difficult to work on with the conventional absorption-trasrnission technique at high wavenumbers. Several bands due to surface species and/or to species that are sensitive to the state of the surface, are discussed in detail. These include free hydroxil species, whose number, spectral position, ana relative intensity in respect of bulk modes do not coincide with previous findings reported in the literature for hign surface area preparations. Three steps, i.e. discrete temperature intervals, are distinguished within the vacuum thermal treatment bringing about the goethite-haematite phase transition.