Synthesis of Nano-structured Aragonite in Ultrasonic Field

Well known inorganic products such as aragonite, a polymorph of calcium carbonate, became lately more important due to the development of nanotechnology. Sub-micron sized aragonite may contribute to the development of composite materials with applications in sensor building or bio-materials. Aragonite precipitation was studied experimentally by controlled double jet precipitation using calcium nitrate tetra hydrate and potassium carbonate solutions of various concentrations. The influence of working conditions, meaning reaction medium, additives and ultrasonic field, on the final solid product morphology and particle size distribution was investigated. The reaction medium was either bi-distilled water or a mixture of bi-distilled water and alcohols. Ultrasonic field was applied in several experimental runs. Solid phase composition was identified by FT-IR spectroscopy and by powder X-ray diffraction. Particle size distribution was measured using a laser beam particle size analyzer and a microscopic technique. TEM was performed using a JEOL 200CX electron microscope to obtain a relevant image of the solid structure. A mathematical model in terms of population balance equation was derived. The kinetic parameters characterizing the overlapping mechanisms: nucleation, growth and agglomeration were estimated to get a theoretical insight of the process. The mathematical model derived proved to correctly represent the mechanisms involved in the precipitation of arago-nite. The evaluation of kinetic parameters will allow developing mathematical models to design precipitation processes with predefined particle size distributions.