Analytical Electron Microscope Analysis of the Formation of BaO · 6Al ₂ O ₃

Abstract

The formation process of barium hexaaluminate (BaO 6Al 2 O 3 ) from BaCO 3 /γ‐Al 2 O 3 powders or hydrolyzed alkoxides was studied by analytical electron microscopy. Barium hexaaluminate is produced by a two‐step solid‐state reaction from BaCO 3 and Al 2 O 3 via formation of BaO·Al 2 O 3 . Marked grain growth and inclusion of nonequilibrium phase were inevitable in this powder mixture process. However, in an alkoxide‐derived precursor, homogeneous mixing of components is attained and hence the formation of BaO·6Al 2 O 3 proceeds readily. Powders obtained by this latter route consisted of fine planar particles with a uniform size and retained a large surface area (20.2 m 2 /g) even after heating at 1300°C. Electron diffraction results implied that suppression of crystal growth along the c axis is the reason for the large surface area of BaO·6Al 2 O 3 .