Spherulitic Growth of Calcium Carbonate

Abstract

The onset of crystal nucleation was studied for seeded semibatch experiments in aqueous solutions in which either the feed rate, the seed size, or seed amount was varied. The results of these experiments show that the nucleation behavior of polycrystalline vaterite features striking similarities with monocrystalline particles in general. Investigations of the nucleation rate of vaterite during spontaneous precipitation experiments have revealed that it would take orders of magnitude higher supersaturation values to obtain the particle numbers required for a proposed nanoaggregation process. The subunit "size" of polycrystalline vaterite is markedly different from particle to particle in seeded semibatch experiments in which nucleation occurred. Differences in the subunit "size" of particles formed under the same process conditions can hardly be explained by aggregation of precursor particles, as nanoaggregation would lead to a uniform distribution of nanoparticles among all particles. Crystal growth, on the other hand, can explain this phenomenon as it may depend on the underlying crystal surface and on the spherulite size. This points at spherulitic growth as the underlying particle enlargement mechanism. The same could be shown for spherulites of calcite for which the particle growth mechanism has been found to be dependent on the crystal surface structure. The current study suggests furthermore the performance of further studies concerning other substances forming polycrystalline particles to establish the correct particle enlargement mechanism.

Synthesis of calcium carbonate particles with carboxylic-terminated hyperbranched poly(amidoamine) and their surface modification

“…Vaterite particles are usually obtained as a spherical shaped poly crystal, which is constructed of 25-35 nm nano-crystallites. 21,22 The 8.8 ± 0.8 nm nanoparticles observed on the surface of the red-colored particles might be assigned to the gold nanoparticle precursors. The composition of the red-colored precursor particles was further probed by an EDX analysis.…”

Crystallization of CaCO3in Water–Alcohol Mixtures: Spherulitic Growth, Polymorph Stabilization, and Morphology Change

“…Andreassen 27 reported cauliflower vaterite in experiments with no alcohol, but carried out at a higher temperature (50°C) where the resulting vaterite formed wider pellets on the cauliflower aggregates. Simpler vaterite cauliflowers with thin and unbranched pellets were grown on vaterite seed by Beck and Andreassen 28 while Zhang et al 43 used solutions containing p-aminobenzene sulfonic acid anhydrous and L-lysine complexes. The cauliflower morphology is typical for vaterite, but there are several hypotheses for the mechanisms responsible for its formation.…”

Composition inversion to form calcium carbonate mixtures

“…This finding is rather astonishing because it is known that, under identical precipitation conditions via the solution reaction, vaterite is obtained only at higher reaction temperatures and much shorter reaction times: 30 versus 10°C and 15 minutes versus 48 hours for vaterite and calcite, respectively. [44][45][46] In addition, the increase in pH due to evolution of ammonia gas from ammonium carbonate may affect the ratio of vaterite to calcite formed. 47 Knowing that vaterite is not the thermodynamically most stable polymorph, we remeasured the reaction product and noticed that after about one year the transition from vaterite to calcite, the most stable calcium carbonate polymorph, took place almost to completeness (cf.…”

“…Replacing sodium carbonate with lithium carbonate and increasing the temperature to 45°C and the duration to 64 hours lead to calcite platelets. 45 The SEM micrographs of AC-1 show three morphologically different objects: plates, rods and quite small spheres with a diameter of about 100 nm (cf. Fig.…”