SPHERICAL GAMMA ALUMINA NANO-POWDERS PRODUCED FROM ALUMINIUM SALTS BOEHMITE SOL BY SPAY-PYROLYSIS PROCESSES

摘要

The hot-wall aerosol synthesis, or spray pyrolysis (SP), offers the significant advantages over other material processing techniques as gas-to-particle conversion, liquid or solid-state processing followed by milling in industrial applications. Within this aerosol procedure, the evaporation, precipitation, drying and decomposition of the precursors occur in the droplet reactors in a single step. The resulting particles, or secondary particles, arise from the growth and agglomeration of primary nanoclusters generated within droplet reactors.1,2 Therefore, it is expected that the properties of droplets and precursors exert the remarkable influences on the final size and distribution and microstructures of the resulting products. Alumina nanopowders have important applications in manufacturing fine ceramics, heterogeneous catalysis, fillers in metal-matrix composites and so on. Generally, alumina products have preferentially been required with small particle size and narrow size distribution, large surface area, spherical morphology and absence of agglomerates, in order to improve properties of alumina-based materials. The ultrasonic spray-pyrolysis (USP) technique has been considered as a versatile SP process applied in fabricating inorganic powders with spherical morphology and controlled microstructures. However, in the USP process, the co-generated hollow and/or foaming porous structures, even collapsing, are usually formed due to surface precipitation and/or poor thermoplastics of solutes within aerosol process of atomized droplets,2'3 which broaden the particle size distribution and worsening the properties of the final products. In the present work, SP synthesis of spherical alumina is comparatively investigated using aluminium salt and beohmite sol as the starting materials, respectively. The morphology and structures, crystallinity and thermal behaviours are also examined. The formation process of alumina products derived from different precursors are also explored.