Partial fluorination of γ-alumina by gaseous fluorine

Abstract

Pluorination of γ-alumina samples with 100 and 300 mbar of undiluted gaseous fluorine at room temperature, results in the incorporation of 3.0% (sample a) and 6.7% in weight (sample b) of fluorine, respectively. The fluorinated samples were studied by XRD and FT-IR. The X-ray diffractograms show no significant changes for sample a and the Formation of a second phase of aluminum hydroxyfluoride for sample b. Infrared spectra of the hydroxyl region show important modifications of the OH hands: for sample a, the removal of the OH groups of basic character can be observed, as well as the near disappearance of the hydrogen bond interaction among other OH groups; on the other hand, sample b presents a new strong and sharp band related to the OH groups of the aluminum hydroxyfluoride phase. The deconvolution analysis of the Al-O vibration region, for sample b, allows the identification of new bands associated with the aluminum hydroxyfluoride phase. The splting of the former Al-O bands of the γ-alumina is attributed to the loss of symmetry of the polyhedral AlO 4 and AlO 6 croups due to the O/F substitution.