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

Abstract

Nanosized (10 -30 nm particle size) hexagonal barium monoaluminate, having a high surface area of ϳ30 m 2 /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 ϳ500°-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.

X-ray diffraction studies on aluminum-substituted barium hexaferrite

“…No crystalline phase of any metastable aluminum oxides were found in these samples. In a previous study on barium mono-aluminate, similar amorphous forms of Al-oxide/hydroxides were observed [11] after calcination at 800 jC. In all the XRD patterns, main peak of maximum intensity for BaCO 3 was observed for 2h varying between 23.55j and 23.96j, while the other major peak at 24.22j was not observed even when the main peak had 100% relative intensity.…”

Study of the microstructure and mechanical properties of halloysite–kaolinite/BaCO3ceramic composites

“…In addition, the combination of SiO 2 and Al 2 O 3 with CaO, MgO, Cr 2 O 3 and/or BaO is commonly employed to impart specific properties related to phase formation, sintering temperature, porosity, resistance to chemical attack or thermal shock, wettability, etc. (Allahevrdi et al, 1998;Mishra et al, 2002). During sintering, kaolinite is transformed into meta-kaolin with a highly disordered structure due to dehydroxylation and subsequent reorganization (Bundy, 1993;Chandrasekhar & Ramaswamy, 2002).…”