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 m aterial is considered for its potential use in catalytic combustion. T he results show that different beta-Al2O3-type structures are obtained upon calcination at 1670 K depending on the Al/Ba ratio. A beta(II)-A l2O3 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 compositi on (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 th e highest surface area. A strict relationship between surface area and aspect ratio of the crystallites has been observed. This indicates th at the sintering resistance of these materials derives from the suppre ssion of crystal growth along the crystallographic axis c. Experimenta l data also indicate that sintering resistance is closely related to B a content. (C) 1995 Academic Press, Inc.