Papers by Keyword: Aragonite

Abstract: Abstract. In this study, the CaCO₃ powder has been successfully synthesized by mixing CaCl₂ from natural limestone and Na₂CO₃ in the same molar ratio. The mixing process of solutions was carried out by employing the molar contents of 0.125, 0.25, 0.375 and 0.5M at varying temperatures of 30, 40, 60 and 80ᴼC. The produced CaCO3 microparticles were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The highest content of aragonite phase with morphology rod-like of the samples is around 29 wt%, resulting from the process using solution of 0.125 M at 80 ᴼC. While at 30 ᴼC and 40 ᴼC produced 100 wt% calcite phase.

Abstract: The formation of the molluscan shell nacre is regulated to a large extent by a matrix of extracellular macromolecules that are secreted by the shell forming tissue, the mantle. This so called “calcifying matrix” is a complex mixture of proteins and glycoproteins that is assembled and occluded within the mineral phase during the calcification process. While the importance of the calcifying matrix to shell formation has long been appreciated, the molecular basis that dictates nacre formation remains largely uncharacterized.Recent expressed sequence tag (EST) investigations of the freshwater mussels (Elliptio complanata and Villosa leinosa) provide an opportunity to further characterize the proteins in the bivalve shell by a proteomic approach. In this study, we have identified a total of 15 proteins from their nacre insoluble matrices. Few of these proteins, such as Pif, MSI60, Nacrein-like, Shematrin, Kunitz-like containing, Papilin-like, LamG containing, Chitin-binding containing, M-rich and Q-rich proteins, appear to be analogs, if not true homologs, of proteins previously described from the pearl oyster or the edible mussel nacre matrices. This work constitutes a comprehensive EST-based nacre proteomic study of non-pteriomorphid bivalves that concretely gives us the opportunity to describe the molecular basis of deeply conserved nacre biomineralization toolkit within nacreous shell bearing bivalves.

Abstract: Bivalve shell microstructures are important traits that can be used for evolutionary and phylogenetic studies. Here we examine the crossed lamellar layers forming the shells of the arcoids, Arca noae, Glycymeris glycymeris and Glycymeris nummaria in order to better understand the crystallography of this complex biomaterial. Textural aspects and crystallography of the outer crossed lamellar layer of these species have been clarified using high-resolution electron microscopy and X-ray diffraction (XRD) techniques. These shells are made of aragonite crystals in a crossed lamellar arrangement with a high preferred crystal orientation (texture). The distribution of maxima in the pole figures implies that there is not a single crystallographic pattern within the measured area, but a continuous variation between two classes of distinct patterns. In the first of these, there is a set of four crystal orientations (referred to as upper set). These four crystal orientations are distributed in two pairs (which are coplanar), with the crystals of each pair being twinned on {110}. The pairs are tilted with respect to each other by approximately 20-40º around an axis perpendicular to the {110} common twinning plane. In the second pattern (referred to as lower set), the crystal orientations of each pair are rotated around a <–110> direction until the a-axes of the diametrically opposing crystal orientations of two different twinned pairs become parallel. As a result of this rotation, in the lower set the crystal orientations no longer form pairs twinned on {110}.These crystallographic relationships are unknown in inorganic aragonite. Our results are similar to those reported for the neogastropod Conus marmoreus. Thus, the common crossed lamellar crystallography in the arcoid bivalves and in C. marmoreus is a striking example of convergence in the development of crossed lamellar microstructures.

Abstract: CaCO₃ polymorphs are intensively studied due to their importance in the nature and the widespread use in the industry as well. This work is dealing with the crystallization of aragonite from vaterite dispersion during the refluxation at 100°C. The characterization of CaCO₃ polymorphs during vaterite transformation was performed with Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD). The influence of the different refluxing times on the aragonite crystallization was discussed. The purest aragonite, 70.7(2) wt.%, was synthetized in the sample refluxed for 60 minutes. Prolonged refluxation strongly affected aragonite crystals with gradual transformation into calcite.

Abstract: The scale-inhibition effect of electromagnetic field was tested on circulating cooling water of power plant, and then the scale sample was analyzed by SEM and XRD. The results showed that, under optimum scale-inhibition conditions, aragonite content increased and calcite content decreased, and scale-inhibition rate was up to 78.2%; under the poorest conditions, both aragonite and calcite crystals existed, and the scale-inhibition rate was-201.0%; after treating with electromagnetic field, size of both calcite and aragonite particles decreased, making them more easily flown away and thus showing better overall scale-inhibition effect; when energy provided by the electromagnetic field was more than the decrease in free energy of the system, extra energy turns the calcite CaCO₃ into other forms of metastable crystalline phases, then content of different crystalline phases is changed in favor of scale inhibition.

Abstract: Hierarchical structure of biomaterials comprised of three dimensional organic matrix and inorganic minerals exhibit unique morphologies and outstanding properties. Herein, modified bacterial cellulose (BC) nanofibres/CaCO₃ composites are prepared using the ammonium carbonate diffusion method at room temperature. The copper coinage shaped aragonite has been synthesized in the 3D matrix and investigated by X-ray powder diffraction, Fourier transform infrared spectrometry, and scanning electron microscopy. It can be concluded that the carboxyl modified BC nanofibres can control the mineralization in vivo by physical confinement within the organic structure to allow the growth of non-equilibrium morphology and chemical interaction to influence polymorph selection and oriented nucleation. The system which was to mimic the biomineralization in vivo can help to produce bio-mimetic materials similarly in living creatures.

Abstract: In this paper, a kind leaf of fresh plant  bamboo, was used as template to control the growth of calcium carbonate at room temperature. The products were characterized by SEM, XRD and FTIR. The nucleation and growth of aragonite crystals were induced by making use of the bamboo leaves containing a lot of biomacromolecules in the presence of Mg2+. Different morphologies and structures of the products were obtained by adjusting the concentration ratio of Mg2+ to Ca2+. The results show that crystal morphologies of CaCO3 produced on the bamboo leaves and glass in the presence of Mg2+ were changed. The products with self-assembly and self-similarity superstructures were gained in bamboo leaves/Mg2+ system. This study may supply a new method for the synthesis of inorganic materials with superstructures.

Abstract: Drainage inlets at the Namsan #3 traffic tunnel in Seoul, South Korea were found to be clogged with calcium carbonate scale deposits. Officials were concerned the clogged drains would further stress the already deteriorating traffic tunnel and wanted to see if there were any practical and economical solutions in removing or preventing scale deposits. A tunnel drainage simulator was constructed to determine the feasibility of using magnets to inhibit scale precipitation and deposition. Test results from the simulation show 6.0 and 4.4 g of deposited calcium carbonate in pipes inclined at 2° and 5° respectively, while magnetically treated water resulted in 10.8 and 4.3 g of deposited calcium carbonate in pipes inclined at 2° and 5° respectively. Calcium carbonate scale samples from the tunnel drainage test underwent x-ray diffraction analysis and showed the magnetically treated water to precipitate more aragonite. The solubility product and crystalline structures of calcite and aragonite are able to help explain tunnel drainage test results and suggest water flow velocity to be a potentially important factor in calcium scale inhibition if magnets are used.

Abstract: Morphology and crystal phase of calcium carbonate, which formed with the presence of Mg²⁺, were characterized by SEM and XRD. The effect of Mg²⁺ on crystallization and crystal phase of calcium carbonate was studied. The results showed that the crystal phase of calcium carbonate were mainly calcite and aragonite and the content of aragonite was higher after adding Mg²⁺ to the blank solution. With the increase of Mg²⁺ concentration, the content of aragonite increased. The calcium carbonate crystals grain became more fine and the content of aragonite was higher by synergistic treatment between Mg²⁺ and magnetic field. There was a strong inhibitory effect on calcite when the concentration of Mg²⁺ was more than 0.50mmol.L-1. The calcite could be transformed into aragonite in the presence of Mg²⁺ in solution.

Abstract: CaO samples prepared from calcining the powdered waste shells at 1300°C for 4 h were tested the efficiency of humidity adsorption. The samples were characterized via X-ray diffraction (XRD) and Fourier transform infrared analysis (FT–IR) to identify the characteristic of CaO after humidity adsorption test. The results indicate that duck eggshells are highest capable of humidity adsorption while hydration rate of chicken eggshells is rather equal to that of cockle shells, and lowest hydration rate was found with sample prepared from Mussel shells. Therefore, we can conclude that the waste shells are suitable to be use as humidity adsorbent for commercial in the future