Barium oxide as a modifier to stabilize the γ-Al₂O₃ structure

Abstract

This research concentrated on the structural stability of γ-alumina (γ-Al 2 O 3 ) was investigated by a combination of differential thermal analysis, X-ray diffractometry and surface-area measurements. The γ -to-θ and then α phase transitions were observed as an exothermic peak at 1000°C-1400°C in the DTA curves. The role of barium oxide as a modifi er to stabilize γ-Al 2 O 3 structure has been investigated. XRD measurements show that after calcination at 1000°C for 2 h, a signifi cant fraction of the pure γ-Al 2 O 3 (BaO-free) transformed to θ-Al 2 O 3 while that the transition phase in alumina samples modifi ed by BaO have been reduced signifi cantly. Barium oxide, eliminate pentacoordinated aluminum ions through coordinative saturation and alter these ions into octahedral cations and effectively suppressed the γ -to-α phase transition in Al 2 O 3 , which concluded as improving the thermal stability and porous properties of the experimental samples.

La-Doped Alumina, Lanthanum Aluminate, Lanthanum Hexaaluminate, and Related Compounds: A Review Covering Synthesis, Structure, and Practical Importance

“…In the past, many studies have aimed at improving the thermal stability of aluminas by using new preparation methods or through the addition of dopants. ,,− Such additives exert an influence on the kinetics of sintering and phase transformation . Ca 2+ , Sr 2+ , Ba 2+ , Sn 4+ , Y 3+ , Zr 4+ , La 3+ , Er 3+ , Th 4+ , and other rare earth (RE) ions inhibit the transformation of t-aluminas into the α-phase; Mg 2+ , Ga 3+ , and In 3+ have the opposite effect. − , ,, , − , , − The cation size seems to have a major influence on the effectiveness of dopants. , Figure shows the specific surface areas at 1200 °C for an alumina powder doped with various elements. The corresponding surface area of the undoped alumina was 8–12 m 2 /g, while those of the modified aluminas are ≥40 m 2 /g …”