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Biomaterials, like hydroxyapatite (HAp), are the subject of many scientific investigations. Their specific application, however, is determined by the form and some characteristic features of the resulting material. Synthesis methods and optimization procedures leading to a product of predetermined characteristics are therefore of great interest. To broaden the existing knowledge, sonoprecipitation was investigated as a potential method for the production of nanosized HAp particles. The research was carried out in a static mixer (STM) immersed in the ultrasonic bath. The influence of operating conditions, e.g., ultrasonic power PUS (εUS), ultrasonic frequency (fUS), and unit mixing power (εmix), was investigated in terms of nucleation intensity, product quality, and characteristics (particle size distribution (PSD), mean size, shape, etc.). As a result, the optimal conditions for the HAp nanoparticles synthesis (mean size: d~150 nm; length: L1~250 nm; width: L2~80 nm) in the form of needles/whiskers/rods—similar to the shape of the HAp present in natural human bones, free from agglomerates, with negligible signs of particle destruction—were determined. The formation of HAp of smaller sizes (d ≤ 100 nm) and more compact shapes (L1~155 nm, L2~90 nm), useful in bone regeneration processes, was also discussed. [ABSTRACT FROM AUTHOR]

The use of materials requires adjusting their features to current applications/needs. In crystallization, the production methods leading directly to the product with pre-determined characteristics are being sought. The research focuses on the abilities of "shaping" the solid product (CSD, shape, form, etc.) and is based on experimental work carried out in the ultrasound (US)-assisted Koflo static mixer (STM). As the model reaction calcium fluoride precipitation has been used as a "common denominator" that complements the previous authors' studies, providing comprehensive knowledge and a more general look at the mentioned problem. It has been shown that it is possible to obtain crystals with the desired characteristics; however, one should be aware of the used reactors' limitations. The conscious selection of operating conditions, as well as US parameters (if they are used), is also essential. It has been revealed that the introduction of US to the STM only affects the turbulence intensity, but it doesn't change the mixing profile. The kinetics of crystallization remain unchanged, but crystals are subjected to greater attrition. In the stirred tank reactors, one might significantly improve the homogeneity of the unit mixing distribution by the selection of the relative input power εrel and, thus, affect the kinetics of crystallization. [ABSTRACT FROM AUTHOR]

• Precipitation process enhancement. • Equilibrium states analysis in the reaction system. • Agglomeration intensity control. • Development of the particle morphology and the size distribution by means of the reactor construction. • Universal description of the turbulence intensity in different reactors' types by the use of the modified Reynolds number. On the basis of the CaF 2 precipitation, the influence of a reactor construction on the obtained solid product characteristics and the reaction efficiency has been analyzed. For experiments a tank reactor with a mechanical stirrer and two in-line reactors Kenics and Koflo static mixers were used. For the description of flow conditions, the definition of the equivalent Reynolds number Re eqv , based, among others, on the local unit dissipation energy ε , has been introduced. According to the provided study, it was found, that in the tank reactor with stirrer the obtained solid product was present in the agglomerated form, where the size of each particular grain did not exceed 2.5 μm. The shape of the obtained particles was close to the sphere with the volume shape factor k v = 0.812. The precipitation of CaF 2 in static mixers resulted in obtaining plate-shaped single crystals (k v = 0.347–0.943), where the agglomeration phenomenon was negligible, and where the mean particle size was in the range of 10–275 μm depending on fluid dynamic conditions. If it is about the reaction efficiency, the conversion rate in both types of reactors was at a very high level (η > 98%), however, the tank reactor showed a higher efficiency. To conclude, tank reactors are applicable when a very high conversion rate is desirable, when the agglomerated entity is acceptable and when the residence time should be selected in an individual way. If larger crystals with a negligible contribution of agglomerates are of order, static reactors become irreplaceable. [ABSTRACT FROM AUTHOR]