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Non-hydrolytic sol-gel synthesis of Al<inf>2</inf>W<inf>3</inf>O<inf>12</inf> nanopowders

Abstract:

Al2W3O12, a low positive thermal expansion phase, has been studied for applications demanding high thermal shock resistance. However, nanopowders used for the preparation of bulk components generally present high agglomeration and low specific surface areas. Non-hydrolytic sol-gel (NHSG) method could be useful for the preparation of nanopowders from A2M3O12 family with high surface area, such as Al2W3O12. Al2W3O12 was synthesized by NHSG in two steps: amorphous powder synthesis with solvent evaporation under an inert atmosphere (2–4 days) and crystallization by calcination (20 min). There was no need for cryogenic temperatures during synthesis. Almost completely monophasic Al2W3O12 nanopowder with a specific surface area, as high as 26 m2 g−1, was prepared from the 0.1 M solutions. This area was ~170% higher than the values reported by other soft chemistry routes. Lower specific surface areas were identified for the Al2W3O12 powders prepared from 0.005 M solutions. This occurred since those samples were kept in dispersion for a longer time and the reduction of surface area could be explained by the Ostwald ripening. The crystalline and orthorhombic Al2W3O12 phase was synthesized for the first time using NHSG route, to the best of the authors’ knowledge. The results confirmed the high efficiency of the proposed modified NHSG method once it decreased the agglomeration of Al2W3O12 nanopowders to levels as low as 100 nm. The excess of organic material acts to prevent the agglomeration during the calcination with the advantage of being a less laborious method than previously reported NHSG routes. [Figure not available: see fulltext.]