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The modelling of the habit modifying effect of water on crystalline substances is still problematic, since the approaches for morphology prediction are investigated for organic molecules rather than for inorganic molecules. Therefore, selected well known 3-, 4- and 5-site water models have been implemented as the solvent in a molecular modelling method. By means of the surface docking method, the investigations on crystalline benzoic acid aimed to model the effect of water as a solvent. The modelling comprised additional geometry constraints of water as a flexible and a rigid molecule. By proof of experimental results, one 3-site water model was favoured for the application in morphology predictions. Future modelling work will be simplified, since it can focus on one single model of water. Furthermore, corresponding to the desired level of supersaturation, the best model can be taken from a modelling toolbox. [ABSTRACT FROM AUTHOR]

The influence of Fe3+as an example of an impurity on the crystallization of ammonium sulfate as an example of an inorganic compound is discussed based on theory and experiments. The metastable zone width was increased up to 4.5 times by 100 ppm of impurity but the effect seems to level out at higher Fe3+concentrations. Fe3+also proves to be a very effective growth and dissolution rate suppressor. The achieved data were analyzed and described by the use of the model of Kubota–Mullin. A growth stoppage could be observed at 86.5 ppm. The effect on the dissolution rate is less pronounced. This growth suppressive behavior was not consistent for all of the individual faces of ammonium sulfate. As a consequence a change in the crystal morphology could be observed. With increasing Fe3+concentrations the crystal habit changes from cubic to a needle like shape. [ABSTRACT FROM AUTHOR]