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

摘要

In our earlier studies, pure barium mono-aluminate and β{sub}1 β{sub}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 BaCO{sub}3 and γ-AlOOH The MCD (mean crystallite diameter) values along (111) plane corresponding to BaCO{sub}3 phase for these precursors were in the range of 70-99 nm whereas the MCD values along (020) plane corresponding to γ-AlOOH were in the range of 10-12 nm. The precursors, when calcined at 400℃ did not show any crystalline phases of alumina and most of the peaks corresponded to barium carbonate with diminished peaks of γ-AlOOH when compared to the precursor. At 800℃, some peaks for (Al{sub}2O{sub}3)O were observed along with major phase of BaCO{sub}3. At 1200℃, irrespective of the Ba/Al ratio, formation of major phase of BaAl{sub}2O{sub}4 along with minor phases of α-Al{sub}2O{sub}3 and Ba-β{sub}11-Al{sub}2O{sub}3 were observed. At 1400℃ also BaAl{sub}2O{sub}4 remained the major phase at all Ba/Al ratios with crystalline phase of α-Al{sub}2O{sub}3. Typical peaks corresponding to Ba-β{sub}11-Al{sub}2O{sub}3 aluminate 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.