Influence of calcium binding proteins on the precipitation of calcium carbonate: A kinetic and morphologic study

In our experiments, the thermodynamic effect of calcium binding proteins (CBP) on the growth of calcium carbonate (CaCO₃) was studied in vitro. The CaCO₃ crystals obtained in systems with and without CBP were characterized by scanning electron microscope (SEM), Fourier Transform Infrared spectrograph (FT‐IR) and powder X‐ray diffractometer (XRD). The kinetic process was studied by monitoring the conductivity and pH value, which revealed the obvious inducement effect of CBP on the CaCO₃ crystals growth, and the possible formation mechanism of CaCO₃ in CBP solution was discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

PSSS‐controlled synthesis of CaCO3 superstructures

Complex CaCO₃ superstructure can be easily synthesized by using poly (sodium 4‐styrenesulfonate) (PSSS) as a structure directing agent to direct the controlled precipitation of calcium carbonate from aqueous solution. The products were characterized by scanning electron microscopy (SEM), and powder X‐ray diffraction (XRD) analysis. The results revealed that the morphology of the products changed significantly with the increasing of the concentration of PSSS in solution, from rhombohedral particles to plate‐packed aggregates to spheres with smooth surface, to sponge‐like spheres and finally to complex spherical superstructure consisted of plate‐like sub‐units. We hypothesize that the observed sequential changes in morphology of CaCO₃ particles with added PSSS concentration may be due to the influence of PSSS on nucleation, growth and aggregation of CaCO₃ crystals. The formation mechanisms of CaCO₃ crystals with different morphologies were discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of hierarchical calcium carbonate crystals templated by biomolecules of lotus root

In this paper, crystal growth of calcium carbonate (CaCO₃) in the presence of biomolecules of lotus root was investigated. Scanning electron microscopy, Fourier transform infrared spectroscopy and X‐ray powder diffractometry were used to characterize the products. The results indicate that calcite spherical particles were constructed from small rhombohedral subunits. Similar CaCO₃ crystals were also gained when crystal growth of CaCO₃ in aqueous solution containing extracts of lotus root was performed, suggesting that the soluble biomolecules of lotus root play a crucial role in directing the formation of hierarchical calcite spherical particles. The possible formation mechanism of the CaCO₃ crystals by using lotus root is also discussed, which can be interpreted by particle‐aggregation based non‐classical crystallization laws. The biomolecules of lotus root might induce and control the nucleation and growth of calcium carbonate crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of polyacrylamide on the crystallization of calcium carbonate: Synthesis of aragonite single-crystal nanorods and hollow vatarite hexagons

CaCO₃ nanorods were synthesized via a facile solution route by polymer-controlled crystallization in the presence of polyacrylamide (PAM). The morphology, size and crystal structure were characterized by means of scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The results suggest that the as-synthesized product was CaCO₃ (aragonite) nanorods with diameter ca. 50 nm and length ca. 1 μm. Selected area electron diffraction (SAED) pattern shows the single-crystal nature of CaCO₃ nanorods. The reaction time, temperature, pH and reactant concentration were systemically investigated. With the increase in the reaction time, hollow vaterite hexagonal disks can be obtained.     

Synthesis of strontium carbonate rods and hierarchical branches in the presence of two organic additives

In this paper, strontium carbonate (SrCO₃) crystals have been synthesized in the presence of two organic additives, including sodium citrate and hexamethylenetetramine (HMT). Scanning electron microscopy, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, X‐ray powder diffractometry and selected area electron diffraction (SAED) were used to characterize the products. The results indicate that SrCO₃rods with the ratio of length to diameter about 20 are obtained in the aqueous solution containing sodium citrate. While polycrystalline SrCO₃ hierarchical branches with about 10 μm length are produced by using HMT.The possible formation mechanism of the SrCO₃crystals obtained in above two systems is discussed, which can be interpreted by particle‐aggregation based non‐classical crystallization laws. Sodium citrate and HMT may direct the formation of SrCO₃ rod‐like or branch‐like structures by adsorbing onto certain facets of SrCO₃ crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

PMA‐b‐PAA‐controlled synthesis of one‐dimensional CaCO3 superstructures

Crystallization of calcium carbonate (CaCO₃) crystals by a gas‐liquid diffusion method has been carried out in aqueous solution using a double‐hydrophilic block copolymer (DHBC) poly(maleic anhydride)‐b‐poly(acrylic acid) (PMA‐b‐PAA). The as‐prepared products were characterized with X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), selected area electron diffraction (SAED), high‐resolution transmission electron microscopy (HRTEM) and infrared spectroscopic analysis (FT‐IR). Uniform one‐dimensional calcite micro/nanostructures with different morphologies are fabricated through an assembled process. The influence of PMA‐b‐PAA copolymer concentration on the morphology of calcite nano/microwires is investigated, which plays an important role in the morphological control of building blocks composed of one‐dimensional calcite crystals. The possible formation mechanism of one‐dimensional CaCO₃ crystals was discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Precipitation of nesquehonite from homogeneous supersaturated solutions

The homogeneous (unseeded) precipitation of nesquehonite (MgCO₃·3H₂O) was studied over the temperature range of 10‐40 °C. Precipitation was triggered by the supersaturation created by mixing MgCl₂ solution (0.5‐1.5 M) with Na₂CO₃ solution in the same concentration range. The Meissner's method was adopted in the calculation of supersaturations during the MgCl₂‐Na₂CO₃ reaction to monitor the precipitation. Solids were identified using X‐ray diffraction (XRD) analysis and scanning electron microscope (SEM) images. In the temperature range of 10‐40 °C, MgCO₃·3H₂O with needle‐like or gel‐like morphology was precipitated. It was seen that the length, width and surface smoothness of the particles changed with reaction temperature and supersaturation. The supersaturation (S) was in the range of 1.09‐58.68 during titration of Na₂CO₃ solution. The dimension of the crystals increased with longer addition time (or lower initial concentration of reactant) at the same temperature. Slower addition via titration of 2 h followed by 2 h of equilibration at 40 °C proved successful in producing well developed needle‐like MgCO₃·3H₂O crystals of 30‐50 μm long and 3‐6 μm wide. MgCO₃·3H₂O obtained were calcined to produce highly pure magnesium oxide (MgO) at 800 °C. The morphology of MgO was similar to that of their corresponding precursors. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Facile preparation of diversified patterns of calcium carbonate in the presence of DTAB

Nano- and micro-sized calcium carbonate (CaCO₃) with various morphologies including multi-petal-flower-shaped, multi-step-cube-shaped, coral-shaped, dendrite-shaped and multi-antenna-shaped was successfully prepared using dodecyltrimethylammonium bromide (DTAB) micellar vevulsant. The effects of temperature, pH and the concentration of DTAB micellar solution on the morphology and crystalline form of CaCO₃ were systematically investigated. The prepared CaCO₃ was characterized by Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The concentration of DTAB micelle, pH and reaction temperature are found to play crucial roles in the morphology, size and crystalline form of the final products. On the base of the characterizations, a possible self-assembled mechanism was proposed. The novel multi-petal-flower-shaped and multi-antenna-shaped CaCO₃ may have some unique properties and potential applications in the future.     

Evolution of hierarchical‐structured CaCO3 in binary mixed solvent

Calcium carbonate with hierarchical structure was synthesized in water/organic compound binary soluvent by a chemical solution process within CaCl₂/NaCO₃ reaction system. Acetone, isopropanol, glycol, tetrahydrofuran were selected as the organic compound. Evolution of the hierarchical structure of CaCO₃ was investigated. The as‐prepared products were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). CaCO₃ aggregations with spicate hierarchical structure were obtained with a high volume fraction of the organic solvent. Aspect ratio of the hierarchical structure increases to the highest when the volume fraction was 50%. Solvent with low dielectric constant was conducive to the oriented aggregation of the CaCO₃ grains.     

Investigation of the Conditions for the Production of Calcium Magnesium Acetate (CMA) Road Deicer in an Extractive Crystallization Process

Calcium magnesium acetate (CMA) is considered as the best road deicer to replace the environmentally unacceptable NaCl and CaCl₂. However, the high cost of CMA prohibits its widespread use. The present study is dealing with the investigation of a crystallization method for the production of deicing CMA crystals of desired physical properties and the elucidation of the conditions under which such a product can be formed. Extractive crystallization is promising for the low cost production of CMA crystals considering that acetic acid is produced by a biochemical method and removed from the fermentation broth in situ by organic extractant systems. In this method, this organic phase, which contains the acetate ions is contacted with an aqueous phase which is the source of calcium and magnesium ions. The extractive crystallization process resulted in the production of well‐formed, large, and non‐spherical crystals of calcium acetate (CA), magnesium acetate (MA), and calcium magnesium acetate double salt (CMADS). The crystal size was affected by the concentration of acetic acid in both the organic and aqueous phases, whereas the crystal type and hydration level were determined primarily by the acetic acid concentration in the aqueous phase. The molar ratio of the precursor salts (CaCO₃/MgCO₃) in the reaction mixture was found to be the major factor for determining the habit and Ca/Mg content of crystals. Crystallization of CMADS was favored at high concentrations of acetic acid in the aqueous phase and at higher temperatures as shown from supplementary evaporation‐to‐dryness experiments.     

Controllable mineralization of calcium carbonate on regenerated cellulose fibers

Gel–forming fibers (GF fibers) can serve as nucleation sites to prepare calcium carbonate (CaCO₃) because they can adsorb large amounts of Ca²⁺ due to their porous structure. In this paper, mineralization behavior of CaCO₃ on GF fibers in ethanol–water mixed solvents without any additives has been investigated. The results showed that some crystals covered the fibers, while others were embedded in fibers. Twin–sphere based vaterite, zonary and rodlike calcite with large aspect ratio could be prepared successfully. The effect of ethanol content inside GF fibers, concentration of Ca²⁺ and CO₃^2‐, mineralization time, miscibility between alcohol and water, and temperature were studied. Lastly, a possible mineralization mode was suggested. This work could provide a new method to prepare inorganic/polymer hybrid materials. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphological lattice complexes

Binary and pseudobinary compounds AB like NaCl and CaCO₃, with the center of charge at carbon position, are characterized by self‐coordination numbers of nearest, second and third neighbors T ₁ T ₂ T ₃ of A and B positions. The maximum Madelung factor of compounds with identical T _i values of A and B atoms is obtained for a maximum of B positions at the border of the A–A Dirichlet domain. The A and B positions form a packing with different T _i values, if all B positions are on the border of the Dirichlet domain. This packing like the primitive cubic packing of Na and Cl atoms with T _i values 6 12 8 or the rhombohedrally distorted packing 6 8 6 of CaCO₃ as morphological lattice complexes can be related to cubic NaCl crystals or the cleaved rhombohedron of calcite. A different habit of crystals is expected for sphere, rod or layered packings. Many well‐defined nanoparticles can be obtained from microemulsions at variation of temperature, water content or water partial pressure. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solubility data of trisodium citrate hydrates in aqueous solution and crystal‐solution interfacial energy of the pentahydrate

In this paper, the solubility of trisodium citrate dihydrate and trisodium citrate pentahydrate in water was experimentally determined. From solubility data, it was found that the relationship between trisodium citrate dihydrate and trisodium citrate pentahydrate is enantiotropic with a transition temperature at 315.4±1.0 K. Different hydrates can be isolated safely by controlling the crystallization temperature. The induction periods of trisodium citrate pentahydrate in aqueous solution were measured at different temperatures. The crystal–solution interfacial energy was calculated by using classical nucleation (CL) theory, mononuclear (MN) and polynuclear (PL) mechanisms through the relationship between induction period and supersaturation. It was found that the interfacial energy values calculated by using the CL theory and the MN model are nearly the same while interfacial energy calculated by PN model are about 40% higher. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of big single crystals of a new magnetic superconducting double perovskite Ba2PrRu1–xCuxO6

Single crystals of Ba₂PrRu_1–xCu_xO₆ with x = 0 to 0.2, have been grown from high temperature solutions of a mixture of PbO‐PbF₂ in the temperature range 1100–1200 °C. Thin crystals with mostly a hexagonal and triangular plate like habit measuring up to 1–2 mm across and 0.1–0.2 mm thick were obtained. The size, quality and morphology of the crystals were improved by varying the solution volume as well as additives like B₂O₃. Large crystals measuring up to 3 mm across and 0.3 to 0.5 mm thick were obtained with 5–7 wt% solute concentration and 0.51 wt% of B₂O₃. The ZFC curves exhibit a spin glass like behavior with x = 0 and a superconducting transition at 8 to 11 K depending on x = 0.05 to 0.1. The transition was also influenced by the growth temperature and post growth annealing. Powder x‐ray diffraction, EDS and Raman spectroscopic measurements confirm the presence of Cu in the crystals. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A controllable ionic liquid‐assisted hydrothermal route to prepare CoCO3 crystals and their conversion to porous Co3O4

In this work, we have synthesized CoCO₃ microaggregation, microcubes and nanoplates by an ionic liquid‐assisted hydrothermal method. The morphologies of the CoCO₃ crystals depend on the concentration of the ionic liquid and the reaction temperature. Moreover, the as‐prepared CoCO₃ crystals can serve as a useful precursor to obtain porous Co₃O₄ particles with similar morphology by means of calcinations. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of SiO32‐ impurity on growth habit of potassium dihydrogen phosphate crystal

By altering the concentration of silicate (SiO₃^2‐) impurity in the solution, a series of potassium dihydrogen phosphate (KDP) crystals was obtained by the conventional temperature cooling and the rapid growth methods, respectively. It was observed that the presence of SiO₃^2‐ made KDP crystals tapering in conventional cooling method, while more SiO₃^2‐ induced inclusions at prismatic sectors in the rapid growth method. Laser‐polarization‐interference results showed that SiO₃^2‐ extended the dead zone and reduced the growth rate of (100) face of KDP crystals. The negative influence of SiO₃^2‐on the growth was considered absolutely similar to the effect of cations. It was also suggested that the stability of solution doped with SiO₃^2‐ was improved without seed crystals, while it was destructed with seed crystals. The inhibition mechanism was analyzed in terms of SiO₃^2‐ absorption on (100) face. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of stirring speed on the crystallization of calcium carbonate

Control over crystal morphology of calcium carbonate (CaCO₃) was investigated by simply changing the stirring speeds in the process of CaCO₃ formation. Scanning electron microscopy (SEM) and powder X‐ray diffraction (XRD) measurements explore the morphology evolution of CaCO₃ at varying stirring speeds. As the stirring speeds increase, rhombohedral calcite, spherical vaterite, and monoclinic crystal with coexistence of calcite phase and vaterite phase were formed, suggesting a facile control over calcium carbonate crystallization in constructing crystals with desired morphology. Moreover, almost pure vaterite spherical particles of narrow particle size distribution were formed at optimum stirring speed. Finally, also elucidated in this work is the mechanism investigation into the construction of various crystal forms via this simple route. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase‐controlled crystallization of amorphous calcium carbonate in ethanol‐water binary solvents

The evolution of amorphous calcium carbonate (ACC) into crystals in ethanol/water binary solvents under ambient temperature was investigated, and it was found to depend on the volume ratio of ethanol to water (R). Calcite remained dominant when the amount of water was high (R = 1/3). A slight change in the amount of ethanol (R = 3/1) could lead to a dramatic change in the polymorph from calcite to aragonite. However, when poly (allylamine hydrochloride) (PAH) was added at R = 3/1, almost pure vaterite could be obtained, which has a specific morphological variation (from hollow microspheres to cloud‐like). This study provides an alternative polymorphic route for the CaCO₃ mineral by using the evolution of ACC in different solvent environments, which provides some useful clues for understanding the importance of kinetic control of the morphologies and polymorphs of a wide range of inorganic materials. In addition, this simple mild phase‐controlled synthetic method could be scaled up as a green chemistry route for the industrial production of different polymorphs of CaCO₃.     

Effects in B–doped KDP crystals irradiated with neutrons of large spectra energy

The results obtained for the r₆₃ electro‐optic coefficient of B‐doped and undoped KDP (KH₂PO₄) crystals irradiated with neutrons (including thermalized neutrons) produced by scattering of 30 Mev cyclotron protons on a target of Ta²⁰¹, are presented and compared to those obtained for non‐irradiated doped and undoped crystals. The B‐doped (H₃BO₃, Na₂B₄O₇ and Li₂B₄O₇) crystals were obtained by the conventional growth method by temperature decrease with 1 wt % dopant concentration in solution. The thermal neutron flux was around ϕ = 1. 10¹⁰ n/cm² s. Pulses of ∼15 μs long, in damped oscillatory mode (V= 8 kV, τ=1.95 μs) were used for the electro‐optic measurements. A Pockels cell, a photomultiplier, a He‐Ne laser (λ=632.8 nm, 5 mW, linearly polarized) and a Tk 720 A oscilloscope complete the experimental setup. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrothermal synthesis of nano‐crystalline BaMoO4 under mild conditions using simple additive

Large‐scale high‐quality BaMoO₄ nanocrystals have been synthesized in aqueous solutions under mild conditions with citrate as a simple additive. The crystals have bone‐like, spindle‐like and wheatear‐like morphologies assembled from nanoparticles, nanofibers and have been characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques. The results showed that experimental parameters had great influences on the shape evolution of products. The adjustment of these parameters such as room temperature stirring time, reaction temperature and reaction time of hydrothermal reaction, can lead to obvious morphology changes of products, and the growth mechanism has been proposed. Room‐temperature photoluminescence indicated that the as‐prepared BaMoO₄ nanocrystals had a strong blue emission peak at 481.5 nm. This facile route could be employed to synthesize more promising nanomaterials with interesting self‐assembly structures. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)