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

In our earlier studies, pure barium mono-aluminate and β1 β2-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 γ-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 γ-AlOOH were in the range of 10–12 nm. The precursors, when calcined at 400 °C 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 °C, some peaks for (Al2O3)O were observed along with major phase of BaCO3. At 1200 °C, irrespective of the Ba/Al ratio, formation of major phase of BaAl2O4 along with minor phases of α-Al2O3 and Ba-β11-Al2O3 were observed. At 1400 °C also BaAl2O4 remained the major phase at all Ba/Al ratios with crystalline phase of α-Al2O3. Typical peaks corresponding to Ba-β11-Al2O3 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.