engleski

Chemical and microstructural properties of Al-oxide phases obtained from AlCl3 solutions in alkaline medium

Chemical and microstructural properties of Al-oxide phases obtained from AlCl3 solutions at pH~11 were investigated using X-ray powder diffraction (XRPD), Fourier transform infrared spectroscopy, microelectrophoresis and transmission electron microscopy. The bayerite and a small amount of gibbsite formed at the beginning of the precipitation process at 160 oC transformed to boehmite by the dissolution/reprecipitation mechanism. The rate of this process was significantly decreased at 90 oC. At 50 oC, an opposite kind of phase transition was observed between 25 min and 1 day of aging, when bayerite was found as a single phase. It was also found that formation of gibbsite was dependent on the type of Al(III)-salt used. The boehmite crystallites had an anisotropic shape, with sizes in the nanometer range. Formation of boehmite was preferred in all precipitation systems containing 0.02 M sodium citrate, and the crystallinity of boehmite depended on the experimental conditions. Specifically adsorbed citrates significantly decreased pHiep values of Al-oxide particles. Boehmite particles were in the form of tiny plates, while bayerite particles showed somatoid morphology.

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