The influence of crystallization conditions on the growth of polycrystalline particles of L-glutamic acid, an aromatic amine derivative and calcium carbonate

摘要

The effect of initial supersaturation and temperature on the particle morphology of L-glutamic acid, an aromatic amine derivative and calcium carbonate was compared in batch experiments by reaction crystallization in water at temperatures of 5-90 deg C. It was found that both the aromatic amine and L-glutamic acid give rise to polycrystalline particles at higher initial supersaturation ratios. On the other hand, monocrystals were obtained at low values of the initial supersaturation, plate-like crystals in the aromatic amine system and needle-like particles of the beta-polymorph in the L-glutamic acid system. For the aragonite polymorph of calcium carbonate it has been observed that higher initial supersaturation ratios give rise to polycrystalline particles. This agrees well with the findings for the aromatic amine and L-glutamic acid which illustrates the role of the supersaturation in the switching from monocrystalline to polycrystalline growth. Moreover lower temperatures were found to favour polycrystalline growth of aragonite. Also for the calcite polymorph of calcium carbonate the switching from monocrystalline to polycrystalline growth was observed as the temperature was decreased. However, in this case the onset of polycrystalline growth might also be the effect of a higher level of supersaturation. Unlike aragonite and calcite, the normal enlargement mode of vaterite is polycrystalline growth. In the study of the vaterite polymorph the feed rate of Ca~(2+) was varied in seeded semi-batch experiments to study changes in the particle morphology. It was found that the crystal subunits are larger at an initial supersaturation ratio of S_(0)velence1.4 than at a higher value of S_(0)velence3 as a consequence of the higher degree of growth front nucleation at larger supersaturation.