THE CRYSTAL-STRUCTURE OF BA-BETA-ALUMINA MATERIALS FOR HIGH-TEMPERATURE CATALYTIC COMBUSTION

Structure refinement through Rietveld analysis has been performed on a series of Ba-Al-O samples with Al/Ba ratios in the range 9-14. This material is considered for its potential use in catalytic combustion. The results show that different beta-Al2O3-type structures are obtained upon calcination at 1670 K depending on the Al/Ba ratio. A beta(II)-Al2O3 phase forms for the lowest Al/Ba ratio and a beta(1)-Al2O3 forms for the highest one. Small amounts of additional phases are present in the samples with the border compositions. For an in-between composition (Al/Ba = 12) a monophasic sample is obtained with crystal structure and calculated cell parameters intermediate between those of beta(I) and beta(II). The sample with the intermediate composition exhibits the highest surface area. A strict relationship between surface area and aspect ratio of the crystallites has been observed. This indicates that the sintering resistance of these materials derives from the suppression of crystal growth along the crystallographic axis c. Experimental data also indicate that sintering resistance is closely related to Ba content. (C) 1995 Academic Press, Inc.