Calcium phosphate materials are widely investigated for the study of biomineralization processes and for the development of new biomaterials. It has been proposed that the crystallization of hydroxyapatite in aqueous media occurs in steps and not directly by ion-by-ion accretion. Prenucleation nanoclusters aggregate to form amorphous spheres and further crystallize into hydroxyapatite. However, conventional analytical techniques cannot visualize phase transformations over time continuously, and the nonclassical crystallization of hydroxyapatite is still under debate. In situ liquid-phase transmission electron microscopy (TEM) is a novel technique that allows us to follow reactions occurring during TEM in real time and thus to visualize the formation of calcium phosphate crystals from the formation of the first mineral nucleus to the final crystallized phase. In this work, in situ TEM was performed, and videos showed the exact moment of hydroxyapatite nucleation and crystallization. During the experiment, different amorphous calcium phosphate nanoparticles were identified prior to the formation of the plate/needle-like hydroxyapatite particles. Crystallization was achieved only after particle elongation. A combined kinetic model that considered the thermodynamic nonideality of the electrolyte solution was applied. Sensitivity analyses were performed to interpret the thermodynamic environment of the liquid cell and the possible species formed over time.

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In this work, the modeling and control of batch crystallization for racemic compound forming systems is addressed in a systematic fashion. Specifically, a batch crystallization process is considered for which the initial solution has been preenriched in the desired enantiomer to enable crystallization of only the preferred enantiomer. A method for determining desired operating conditions (composition of the initial pre-enriched solution and temperature to which the mixture must be cooled for maximum yield) for the batch crystallizer based on a ternary diagram for the enantiomer mixture in a solvent is described. Subsequently, it is shown that the information obtained from the ternary diagram, such as the maximum yield attainable from the process due to thermodynamics, can be used to formulate constraints for an optimization-based control method to achieve desired product characteristics such as a desired yield. The proposed method is demonstrated for the batch crystallization of mandelic acid in a crystallizer with a fines trap that is seeded with crystals of the desired enantiomer. The process is controlled with an optimization-based controller to minimize the ratio of the mass of crystals obtained from nuclei to the mass obtained from seeds while maintaining the desired enantioseparation.

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An experimental methodology for inferring brine dissolution rate in monoethylene glycol (MEG) solutions at different temperatures using a webcam combined with a mathematical model is presented. The measurement system is designed to track the RGB (red, green, and blue) colour variations during the dissolution process. A dynamic model augmented with the population balance equation is applied to describe the dissolution process. Moreover, the dissolution rate is consistently related to the temperature and MEG concentration through the driving force based on the Gibbs energy and chemical affinity. The applied low-cost measurement apparatus proved to be a useful resource for tracking the dissolution dynamics in a wide range of undersaturation.

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