Micro-sized powders by hydrochemical synthesis

The objectives have been the development of hydrochemical technology for the synthesis of micro-size nanostructured powders with design composition and properties for microFAST sintering process and then the demonstration of soft agglomerated nanostructured powders obtained by combined hydrothermal and spray drying technology A versatile hydrochemical process combined with spray drying in preparation of different types of nanopowders with controlled chemical, structural and morphological composition. These methods proved particularly promising in terms of controlling the grain size, degree of agglomeration and purity of powders that can be sintered without significantly changing the phase composition by micro-FAST process, such as: Ceria-doped zirconia-based powders for SWATCH watch parts and doped lead zirconate titanate (Nd,La-PZT) piezoceramics. The process is based on a hydrothermal process in autoclaves at temperatures below 2500C and pressures below 100 atm. starting from pure soluble metallic salts in the presence of a hydrolysis agent to control the pH process. The filtered and washed precipitate obtained is re-dispersed in the presence of a small amount of organic binder and granulated by spray-drying at temperatures below 2000C through a calibrated nozzle. No further thermal treatment is required for crystallization. The process is designed to minimize the wastes by a simple recycling loop of the by-products. The performances of the powders obtained are assessed by certified methods: ICP-OES chemical analysis (main elements, doping elements, purity); XRD (crystallinity); ASTM B 213-03 (flowability); ASTM B923-02, D7481-09 and B527 (density), particle sizes (sieve analysis). All powders are delivered with safety data sheets. A versatile hydrochemical process combined with spray drying was developed for preparation of different types of nanopowders with controlled chemical, structural and morphological composition. These methods allow controlling the grain size, degree of agglomeration and purity of powders that can be sintered close to theoretical density without significantly phase composition modifications by micro-FAST process, such as: Ceria-doped zirconia-based powders for SWATCH watch parts and doped lead zirconate titanate (Nd,La-PZT) piezoceramics.