Preparation and properties of alumina-baria nano-composites
Barium doped alumina was prepared by calcination of gels obtained from metal chloride solutions by homogeneous precipitation with urea. The gels were either air-dried, oven-dried, microwave-dried or autoclave treated. The materials were analysed by small angle X-ray scattering (SAXS), X-ray diffraction (XRD), differential thermal analysis/thermogravimetry (DTA/TG) and transmission electron microscopy (TEM). The phase composition of the calcined products depended on the gel drying procedure. Barium aluminates formed directly at low temperatures in the microwave treated gel because of the uniform distribution of barium in the dried gel. After calcination at 1200 C the aluminates were uniformly distributed as nanoscale particles within an alpha Al(2)O(3) matrix. In contrast, autoclave treated samples initially consisted of boehmite crystals coated with barium carbonate which reacted on calcination to form a surface layer of BaAl(2)O(4). The autoclaved material withstood 1 h at 1400 C in air without transformation to alpha Al(2)O(3). This increased thermal stability of transition alumina, theta Al(2)O(3) is attributed to the presence of the BaAl(2)O(4) surface layer. The final transformation of alpha Al(2)O(3) was associated with the transformation of a surface layer of BaAl(2)O(4) to nanoscale particles of BaAl(9.2)O(14.8).
Bibliographic Reference: Article: Journal of Material Science
Record Number: 199711369 / Last updated on: 1997-10-23
Original language: en
Available languages: en