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Batch fabrication of submicrometric silver particles and scaleup of the chemical precipitation method for the industrial production of silver powders for automotive applications


The fabrication of industrial batches of non-aggregated dry silver particles, with submicrometric dimensions, is a formidable challenge. Silver powders are used in the preparation of conducting inks and pastes, which are used in the fabrication of electrical conductors and contacts applied in the automotive industry, also in the electronics and photovoltaic energy industries. Compact electrical conductors, which have the necessary physical and chemical resistance for automotive applications, are formed by sintering silver particles with complex internal structure. Each individual particle is formed by several aggregated crystallites/primary particles of a few tens of nanometers, resulting in submicrometric final particles with quasi spherical shape. These particles must be compact and dense, as a result of the amorphous Ag0 atoms attachment inside the spaces between the aggregated primary particles. Silver particles with this internal structure, sintered at low temperatures (600°C to 800°C), form electrical conductors that meets the required conductivity in the application. During the sintering process of a conducting silver paste, the crystallization of amorphous domains of well packed particles on glass occurs along with the spatial reorientation of the crystallites aggregated inside individual particles, forming a compact conductor with large crystalline domains. Metaura was created to develop a fabrication technology of silver powders in industrial scale, that meet the demands of the automotive sector as a priority. The Method of Chemical Precipitation in aqueous solution of Ag+ ions using ascorbic acid as a mild reducing agent is well described in the literature and was adapted by Metaura for the obtention of silver powders with the structural characteristics described above. Dispersing agents Arabic gum (GA), polyvinylpyrrolidone (PVP) and condensed naphthalene formaldehyde sulfonate (NSC) will be used to control the primary particles diffusion in solution and, as a consequence, will be a control factor on it´s rate of aggregation in the final particles formation. The scientific investigation of this method, by understanding the influence of the synthetic parameters on the particles structural characteristics will provide repeatable synthesis of silver particles batches in high concentrations, suitable for industrial production. The separation and purification of the particles obtained in each batch, and the particle drying process, represents an additional technological challenge for this project. The separation of particles from the reaction environment by sedimentation under gravity is time demanding and the processing of particles demands three separations of the solids from the dispersion, causing the pos-synthesis processing the longer task for the obtention of the final silver powders. With the overcoming of these challenges, we will have developed a world-class technology for the fabrication of silver powders, that fulfil the demands of our potential clients and will pave the way for the exploration of new markets. (AU)

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