Effect of barium to aluminium ratio on phases leading to barium aluminates

Abstract

In our earlier studies, pure barium mono-aluminate and beta(1) beta(2)-barium hexa-aluminate were prepared by keeping Ba/Al ratio as 1:2 and 1: 12, respectively. In the present work, effect of varying Ba/Al ratio from 1:4 to 1:10 on the formation of barium aluminates has been studied. The samples obtained during hydrothermal precipitation contained mixtures of BaCO3 and gamma-AlOOH. The MCD (mean crystallite diameter) values along (1 1 1) plane corresponding to BaCO3 phase for these precursors were in the range of 70-99 nm whereas the MCD values along (0 2 0) plane corresponding to gamma-AlOOH were in the range of 10-12 nm. The precursors, when calcined at 400 degrees C did not show any crystalline phases of alumina and most of the peaks corresponded to barium carbonate with diminished peaks of gamma-AlOOH when compared to the precursor. At 800 degrees C, some peaks for (Al2O3)(O) under bar were observed along with major phase of BaCO3. At 1200 degrees C, irrespective of the Ba/Al ratio, formation of major phase of BaA1(2)O(4) along with minor phases of alpha-Al2O3 and Ba-beta(11)-Al2O3 were observed. At 1400 degrees C also BaAl2O4 remained the major phase at all Ba/Al ratios with crystalline phase of alpha-Al2O3. Typical peaks corresponding to Ba-beta(11)-Al2O3, alummate became more prominent when the Ba/Al ratio was >= 1:6. No other intermediate phases such as tri-barium mono-aluminate, barium tetra aluminate or non-stoichiometric barium aluminates were formed. (c) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.