Characterization of Products Obtained during Formation of Barium Monoaluminate through Hydrothermal Precipitation–Calcination Route

Nanosized (10–30 nm particle size) hexagonal barium monoaluminate,
having a high surface area of 30 m2/g, was
synthesized by calcination of hydrothermally prepared precursors.
The precursors were obtained by hydrolytic precipitation,
using a mixed solution of barium and aluminum nitrates
in the presence of aqueous urea at 180°C. Based on the results
of XRD, FTIR, SEM/EDS, TEM, and TG-DTA studies, the
most probable sequence of reactions leading to the formation
of barium monoaluminate was (i) conversion of aqueous
barium and aluminum nitrates in the presence of urea by
hydrothermal precipitation to crystalline orthorhombic barium
carbonate and boehmite, (ii) formation of an interim form
consisting of amorphous fibrillar aluminum oxide(s) interlaced
with crystalline barium carbonate in the calcination temperature
range of 500°–800°C, (iii) initiation of formation of
barium monoaluminate at 1000°C, and (iv) formation of a near
monophase nanosized barium monoaluminate at 1200°C.