Morphology Of CaCO3 Crystals Research Articles

Crystallization of CaCO3 Mesocrystals and Complex Aggregates in a Mixed Solvent Media Using Polystyrene Sulfonate as a Crystal Growth Modifier

Crystallization behavior of calcium carbonate (CaCO3) in water/ethanol mixed solutions under ambient conditions using polystyrene sulfonate (PSS) as a crystal growth modifier has been systematically investigated. The results have demonstrated that a switch from thermodynamic control to kinetic control in the crystallization process of CaCO3 can be easily realized by adding ethanol, which can have a significant influence on the polymorphs and morphologies of CaCO3 crystals. Calcite mesocrystals and vaterite complex aggregates with increasingly developed shapes can be obtained with an increase of the ethanol content in the solution. The polymorph change of CaCO3 crystals from pure calcite to a calcite dominated mixture and finally to a vaterite dominated mixture has also been nicely captured. Both CaCO3 crystals with different evolving phases and the polymorph change of CaCO3 from calcite to vaterite can be attributed to the balance between thermodynamic control and kinetic control in this special crystallization media. This work sheds light on the possibility of adding ethanol to control the kinetic/thermodynamic balance and thus to possibly control the morphologies and polymorphs of a wide range of inorganic materials.

Preparation of calcium carbonate crystals in the presence of trisodium citrate

AbstractThe dumbbell‐like calcium carbonate (CaCO3) crystals were synthesized in the presence of trisodium citrate. Different morphologies were obtained by changing the reaction temperature and the trisodium citrate concentration. The obtained samples were characterized by means of X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the morphology of CaCO3 crystals was markedly affected by the reaction temperature and citrate anion concentration. The possible growth mechanism of CaCO3 crystals was proposed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Crystal growth of CaCO3 induced by monomethylitaconate grafted polymethylsiloxane

We report the preparation of a new monomethylitaconate grafted polymethylsiloxane (CO2H-PMS) copolymer and its effect as template for crystal growth of CaCO3. The in vitro crystallization of CaCO3 was carried out using the gas diffusion method at different pH values at room temperature for 24 h. The CO2H-PMS was prepared using polydimethylsiloxane-co-methylhydrogensiloxane (PDMS-co-PHMS), obtained through cationic ring opening polymerization, from cyclic monomers and monomethyltaconate (MMI) via hydrosilylation reactions with platinum complex as catalyst. FTIR results are in an agreement with the proposed template structure and confirmed that the hydrosilylation was complete. Experimental results from pH values and SEM analysis showed that the carboxylate groups of CO2H-PMS alter the nucleation, growth and morphology of CaCO3 crystals. SEM revealed single-truncated (ca. 5 μm) modified at pH 7–9, aggregated-modified (ca. 20 μm) at pH 10–11, and donut-shaped crystals at pH 12. These morphologies reflect the electrostatic interaction of carboxylic moieties with Ca2+ modulated by CO2H-PMS adsorbed onto the CaCO3 particles. EDS confirmed the presence of Si atoms on the crystals surface. XRD analysis showed the existence of only two polymorphs: calcite and vaterite revealing a selective control of CaCO3 polymorphisms. In summary, the use of grafted polymethylsiloxane template offer a good alternative for polymer controlled crystallization and a convenient approach for understanding the biomineralization process useful for the design of novel materials.

Purification and characterization of a matrix shell protein from the shell of scallop Patinopecten yessoensis

A new protein named MSP-SC (matrix shell protein from scallop) with a molecular weight of 14 kDa was isolated from the shell of a scallop, Patinopecten yessoensis, using gel filtration column chromatography, ion exchange column chromatography, and reverse phase C4 column chromatography. A comparison of the known protein sequences with the N-terminal sequence of MSP-SC showed that the protein sequence of MSP-SC was novel. Immunohistochemistry using a polyclonal antibody against MSP-SC showed that MSP-SC is expressed in the mantle pallial cell layer but not in the muscle tissue, and showed a punctate distribution along the horizontal calcified layer in the shell. The isolated MSP-SC inhibited the formation of calcium carbonate (CaCO3) crystals in a dose-dependent manner. The CaCO3 crystals grown in the presence of a lower concentration of MSP-SC were much larger and aggregated when compared with those formed in the absence of MSP-SC. In addition, the crystal had a radial and not cubical morphology. These results suggest that MSP-SC regulates the formation and the morphology of CaCO3 crystals in the shell. Moreover, its ability to aggregate CaCO3 crystals and its localization along the horizontal calcified layer in the shell suggest that MSP-SC may serve to connect the CaCO3 layers in the scallop shell.

Oriented crystallization of CaCo3under compressed monolayers. Part 2.—Morphology, structure and growth of immature crystals

Transmission electron microscopy and electron diffraction have been used to determine the structure, orientation and morphology of CaCO3 crystals at the early stages of growth under compressed Langmuir monolayers of stearic acid [CH3(CH2)16CO2H] and octadecylamine [CH3(CH2)17NH+3]. At [Ca]≈ 9 mmol dm–3, elongated plate-like calcite single crystals of narrow particle size distribution were nucleated under fully compressed stearate monolayers. The crystals were elongated along the c axis and oriented with a {1text-decoration:overline10} face parallel to the monolayer/solution interface. Subsequent development of the crystals resulted in rhombohedral outgrowth into the bulk solution. Calcite crystals nucleated under partially compressed monolayers showed the same crystal chemical properties but had a more uniform size population. Nucleation under octadecylamine monolayers resulted in disc-shaped vaterite single crystals of narrow particle size distribution. Two types of disc were observed: (a) circular/hexagonal crystals oriented with their c axis perpendicular to the monolayer, and (b) oval-shaped crystals oriented with their a axis perpendicular to the monolayer. Changes in monolayer surface pressure did not influence these properties. The preferred orientation of calcite can be rationalized in terms of geometric and stereochemical matching between the carboxylate headgroups and the ions in the {1text-decoration:overline10} crystal face. There is no geometric match for vaterite but a stereochemical relationship exists on stearate monolayers with respect to the (00.1) face. For octadecylamine monolayers, bidentate binding of HCO–3 may be important in determining the preferential orientation of nuclei formed at the organic surface.