PARTIAL FLUORINATION OF GAMMA-ALUMINA BY GASEOUS FLUORINE

Fluorination of gamma-alumina samples with 100 and 300 mbar of undilut ed gaseous fluorine at room temperature, results in the incorporation of 3.0% (sample a) and 6.7% in weight (sample b) of fluorine, respecti vely. The fluorinated samples were studied by XRD and FT-IR. The X-ray diffractograms show no significant changes for sample a and the forma tion of a second phase of aluminum hydroxyfluoride for sample b. Infra red spectra of the hydroxyl region show important modifications of the OH bands: for sample a, the removal of the OH groups of basic charact er can be observed, as well as the near disappearance of the hydrogen bond interaction among other OH groups; on the other hand, sample b pr esents a new strong and sharp band related to the OH groups of the alu minum hydroxyfluoride phase. The deconvolution analysis of the Al-O vi bration region, for sample b, allows the identification of new bands a ssociated with the aluminum hydroxyfluoride phase. The splitting of th e former Al-O bands of the gamma-alumina is attributed to the loss of symmetry of the polyhedral AlO4 and AlO6 groups due to the O/F substit ution. (C) 1998 Elsevier Science S.A. All rights reserved.