Mechanochemical synthesis of low-fluorine doped aluminum hydroxide fluorides

Different aluminum hydroxide fluorides with varying Al/F molar ratios from 1:1.5 up to 1:0.05 were successfully synthesized by mechanochemical reactions. The characterization of the products by XRD, Al-27 and F-19 MAS NMR, thermal analysis, nitrogen adsorption and zeta potential techniques allows a detailed understanding of the structure and surface properties of the products. Using gamma-Al(OH)(3) and beta-AlF3 center dot 3H(2)O as OH- and F-sources, respectively, strongly disordered products were obtained with an Al: F molar ratio higher than 1:0.25. The fluorination degree has affected the amount of 4- and 5-fold co-ordinated Al sites, not present in the reactants. An evolution of the sub-coordinated Al-species has been detected also as a consequence of annealing processes. Obviously, these species affect the phase transition to alumina, by decreasing the transition temperature of the formation of alpha-Al2O3. Synthesis conditions (milling time, fluorination degree) play a crucial role for the product composition. (C) 2016 Elsevier Inc. All rights reserved.