Hydrothermal synthesis and characterization of a new boron-aluminium oxochloride

A new boron-aluminium oxochloride denoted as BAC(8) was synthesized hydrothermally in the system H3BO3-AlCl3-CaO-H2O, and the compound was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), inductive coupled plasma analysis (ICP), infrared spectroscopy (IR), magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and thermal analysis. The effects of pH, temperature, cations and anions on the crystallization of BAC(8) are discussed. Chemical analysis shows that BAC(8) has an empirical molar composition of 1.0B(2)O(3):1.0Al(2)O(3):0.2HCl:2.6H(2)O. The basic building units for BAC(8) are triangular BO3 and tetrahedral BO4 with a BO3/BO4 ratio of 11.5, as well as octahedrally coordinated Al. Thermal analysis indicates that BAC(8) is stable up to 420 degrees C, and at higher temperature HCl and H2O evolve from the sample. Calcination at above 700 degrees C causes BAC(8) to transform via an amorphous phase to the known crystalline material Al4B2O9. Copyright (C) 1996 Elsevier Science Ltd