Abstract
A novel preparation method is proposed for Ba-β-Al203-type systems to be used in high-temperature catalytic combustion, consisting of precipitation in aqueous medium. Differential thermal analysis-thermogravimetry, X-ray diffraction, Fourier transform-infrared, TEM and surface area data are presented for Ba-Al-O samples with Al/Ba atomic ratios in the range 14-9 calcined at different temperatures up to 1670 K. The final materials consist of a barium-poor Ba-β1Al2O3 phase together with 1% α-Al2O3 in the case of Al/Ba = 14 and of a barium-rich Ba-β11-Al2O3 phase together with 2% BaAl2O4 in the case of Al/Ba = 9. A mono-phasic sample with a Ba-β-Al2O3 structure is obtained in the case of Al/Ba = 12; this phase is constituted by the simultaneous presence of both β1 and β11 structure types. Two routes operate above 1370 K in the formation of the Ba-β-Al2O3 phases involving solid-state reactions between γ-Al2O3 and BaAl2O4, and γ-Al2O3 and dispersed barium compounds. Based on the analogies between the structures of γ-Al2O3 and of the Ba-β-Al2O3 phases it is suggested that the formation of the latter occurs via diffusion of barium ions within oxygen close-packed planes of the γ-Al2O3-type spinel structure.
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