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1.
Effect of monovalent salts on morphology of calcium carbonate crystallized in Couette‐Taylor reactor
Monovalent ionic additives, Na+, K+ and NHequation/tex2gif-stack-1.gif impact on the morphology and agglomeration of CaCO3 crystals. As increasing the additive concentration, the regular shaped crystals such as rhombohedron and spindle are changed to irregular one due to the inclusion of Na+ and K+ into the crystal structure. The inclusion of Na+ and K+ is detected using ICP‐AES. The partition of coefficients of Na+ and K+ are estimated as 9.74 × 10–4, 9.73×10–4, respectively and the amount of inclusion in the crystals is about 2×103 ppm. However, the inclusion of ions does not modify a crystal structure of calcite. Since NH4+ is large in radius, it is not included in crystal but shifts the spindle shape of crystal to the rhombohedral one. It is interesting to find that such modification of crystal morphology begins to appear at high additive concentration (0.05 M). In addition, the crystal agglomeration is promoted because the electric repulsive charge is reduced as increasing the additive concentration. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
2.
Xiaohui Zhang Fengwen Yan Cunyue Guo Fengbo Li Guochang Chen Zhijun Huang Guoqing Yuan 《Crystal Research and Technology》2011,46(7):664-668
Crystalline calcium carbonate with randomly dispersed porous structure was prepared through co‐ crystallization with calcium peroxide and the following template elimination by a post heating treatment and washing with water. The artificial CaCO3 possess abundant macro‐mesopores structures and high surface area. This approach may open a new general route for the preparation of crystals with high porosity and structure specialty. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
Fangzhi Huang Yuhua Shen Anjian Xie Xiuzhen Zhang Yan Cai Wenting Wu 《Crystal Research and Technology》2009,44(8):818-822
Controlled synthesis of amorphous calcium carbonate (ACC) films was realized by using the multiple templates, which are composed of a self‐assembled film (SAF, insoluble Poly (ε‐caprolactone) film) and a soluble modifier (poly allylamine), as modifiers. The formation of self‐assembled film was analyzed by monitoring the morphologies using atomic force microscopy. Even more noteworthy, using anhydrous ethanol as media, the ACC‐to‐vaterite‐to‐calcite transformation was also investigated, and the obtained products were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction. The results demonstrated that organic solvent has profound influence on transformation of amorphous calcium carbonate thin films. In the air of anhydrous ethanol, the controlled synthesis of calcium carbonate films with different morphologies, such as planar films with a few sporadic particles, symmetric rhombohedral crystals, novel crystals with symmetrical terraced convexity formation of calcite, was obtained by the fine‐tuning of induction time. It provides a new and simple method to prepare polymorphic CaCO3 crystal films from the ACC films by controlling the crystallization process (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
4.
Feng‐Wen Yan Shu‐Feng Zhang Cun‐Yue Guo Xiao‐Hui Zhang Guo‐Chang Chen Fang Yan Guo‐Qing Yuan 《Crystal Research and Technology》2009,44(7):725-728
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) 相似文献
5.
The influence of static magnetic field of strength 0.75 T on the nucleation of calcium carbonate crystals has been investigated. Particle size analysis shows that magnetic field can cause marked difference in distribution. One of the major impacts of magnetic exposure is the increase in number of the critical nuclei formed. Also, magnetic field promotes the formation of parallelepipedic calcite crystals and the dissolution of the smaller crystals by Ostwald ripening mechanism. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
Wenjun Xiao Jie Liu Qin Chen Ying Wu Lizong Dai Tinghua Wu 《Crystal Research and Technology》2011,46(10):1071-1078
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 CO32‐, 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) 相似文献
7.
An‐Jian Xie Chun‐Yan Zhang Yu‐Hua Shen Ling‐Guang Qiu Pei‐Pei Xiao Zhao‐Yang Hu 《Crystal Research and Technology》2006,41(10):967-971
Calcium Carbonate has been precipitated from aqueous solutions containing different concentrations and different molecular weight of Polyethylene Glycol (PEG). The precipitations were analyzed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR) and X‐ray diffraction (XRD). The results demonstrated that PEG has profound influence on the nucleation and crystal growth of CaCO3, under condition of low PEG6000 (refer to PEG MW=6000) concentration, it favored the formation of calcite, while high PEG6000 concentration promoted vaterite formation. Additionally, low molecular weight PEG can stabilize vaterite phase. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
Long Chen Fengkai Hu Quan Zhou Jinyu Sun Hui Zhang 《Crystal Research and Technology》2009,44(12):1289-1292
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) 相似文献
9.
B. Njegi Dakula J. Kontrec M. Ukrainczyk S. Sviben D. Kralj 《Crystal Research and Technology》2014,49(4):244-256
This paper reports on the precipitation of CaCO3 polymorphs, having various crystal morphologies under different conditions. In particular, systems that were subject to ultrasonic irradiation were compared to the corresponding reference systems in the absence of such a treatment. The application of ultrasonic irradiation predominantly resulted in a change of particle size distribution and polymorphic composition of the precipitate, in comparison to the reference systems. Thus, it was found that the supersaturation and temperature influenced the size distribution, in both the reference and sonicated systems. A mixture of calcite, vaterite and aragonite was obtained in all reference systems, at 25 °C. At this temperature, the sonication caused the vaterite content to increase, while aragonite was not detected. In reference and sonicated systems at 80 °C, only aragonite precipitated. The results also indicate that the principle parameter responsible for the morphology of vaterite was the initial supersaturation: at higher supersaturation spherical vaterite particles precipitated, while at lower supersaturation hexagonal platelets were obtained. The morphological investigations also indicated different mechanisms of vaterite formation in the systems in which precipitation was initiated at higher supersaturation: spherulitic growth of vaterite was observed in sonicated systems, while the aggregation of primary particles was predominant in the reference systems. At lower supersaturation, the effect of c(Ca2+)/c(CO32−) on the morphology of hexagonal platelets of vaterite was observed as well. By varying the c(Ca2+)/c(CO32−), significant changes of the polymorphic composition were observed only in the sonicated systems, at 25 °C. 相似文献
10.
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. 相似文献
11.
Calcium carbonate crystallization process, especially the prenucleation stage, has increasingly been the subject of several works. In the present work, a simple method based on electrical conductivity modeling applied to the FCP (Fast Controlled Precipitation) method data is used to highlight the role of CaCO3o ion pairs on calcium carbonate prenucleation stage. A good agreement was obtained between the resistivity vs pH curves estimated by the McCleskey model equation and obtained experimentally in a FCP test. Results showed that the nucleation process begins with the formation of CaCO3o ion pairs as pre‐nuclei as soon as the calcite‐equilibrium pH is reached. Additionally CaCO3o content increases with pH to form aggregates, which depend on the saturation state of the solution. Basing on our thermodynamic data, these aggregates do not form amorphous calcium carbonate ACC as an intermediate phase. They lead to the formation of stable calcium carbonate nuclei which will further evolve to crystallize. Furthermore we demonstrate that in addition to their inhibitory effect on the Ca2+ and CO32− association to form ion pairs, the two scale inhibitors sodium triphosphate (STP) and sodium polyacrylate (RPI) reduce ion pairs aggregation rate. 相似文献
12.
Y.R. Somarathna M.M.M.G.P.G. Mantilaka D.G.G.P. Karunaratne R.M.G. Rajapakse H.M.T.G.A. Pitawala K.G. Upul Wijayantha 《Crystal Research and Technology》2016,51(3):207-214
This research paper describes the synthesis of nano‐ and micro‐structures of high purity precipitated calcium carbonate (PCC) on poly(ethylene glycol)(PEG) templates for broad‐range industrial applications, using readily available and cheap impure dolomitic marbles. In the method, calcium components of impure dolomitic marbles are extracted as calcium sucrate which is then bubbled with carbon dioxide gas using a carbonation column in the presence of PEG. The effects of concentration of PEG, pH of calcium sucrate solution and temperature on the final yield, morphology and polymorphism of PCC have been studied. Vaterite and calcite are the crystalline forms of calcium carbonate found in final PCC products. The vaterite is observed as hollow spheres with particle diameter of 1.5‐2 μm which is formed by aggregation of vaterite nanoparticles with particle size of 20 nm on PEG templates. Optimum conditions for the highest PCC yield of 79.94% are 0.4 mol dm−3 of PEG, pH of 6.5 and temperature of 80 °C. The purity of PCC products is about 99%. Therefore, the synthesized PCC products are of required purity and quality for industrial applications. 相似文献
13.
AbstractThe effect of Mg2+ on the crystallization of precipitated calcium carbonate (PCC) via a bubbling carbonation method and the mechanism of eliminating its influence by glucose were investigated. The polymorph and morphology of crystals were characterized by field emission-scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. These results demonstrated that Mg2+ and Mg/Ca molar ratio played significant roles on the morphology of PCC. When the Mg/Ca molar ratio was below 0.5, only spindle-like calcite formed. The rod-like aragonite started to form when the ratio was 0.6. As the ratio increased, the amount of aragonite increased and the length of rod-like aragonite became longer. Notably, the effect of Mg2+ could be eliminated efficiently when the 1.5?wt% glucose was added into the carbonation system, in which system, the PCC crystals were all spindle-like calcite. Furthermore, the mechanism of the glucose to eliminate the influence of Mg2+ on PCC crystallization was proposed. 相似文献
14.
Crystallization habit of calcium carbonate in presence of sodium dodecyl sulfate and/or polypyrrolidone 总被引:7,自引:0,他引:7
The synthesis of calcium carbonate (CaCO3) crystals from aqueous solutions containing sodium dodecyl sulfate (SDS), poly(N-vinyl-1-pyrrolidone) (PVP) or SDS/PVP complexes has been performed through a slow titration method. It was found that aragonite and calcite coexisted in the prepared crystals. The formation of aragonite in the precipitation systems without magnesium ions indicates that at ambient temperature ca. 26.0°C, initially formed amorphous CaCO3 could also transfer into aragonite in the sedimentary phase, which indicates the controlling factor of organic additives in the nucleation and growth process of CaCO3 crystals. The appearance of hexagonal crystals in the suspensible phase confirmed the hexagonal crystallization cell of vaterite, and revealed the colloidal-dispersion function of the SDS/PVP complex in the crystallization process of CaCO3. 相似文献
15.
S. Ouhenia D. Chateigner M.A. Belkhir E. Guilmeau C. Krauss 《Journal of Crystal Growth》2008,310(11):2832-2841
Calcium carbonate precipitates are prepared from a solution of CaCl2 and K2CO3 in the presence of polyacrilic acid. The effect of polyacrilic acid incorporation in the [25–80 °C] temperature range on crystal morphologies and CaCO3 precipitated polymorph concentrations are investigated using scanning electron microscopy and X-ray diffraction quantitative microstructural and phase analysis. Large changes in morphology and phase proportions are observed in the presence of polyacrylic acid, which strongly depend on the solution temperature. While crystallization of vaterite is favoured in the presence of polyacrilic acid up to 50 °C, it is largely destabilized at higher temperatures. Our process also enables the elaboration of particles in the range 10–20 nm. 相似文献
16.
The quality of crystalline products, defined by e.g. purity or crystal size distribution (CSD), is primarily dominated by crystallization conditions but influenced by further downstream processes like solid‐liquid separation and drying also. Through uncontrolled agglomeration within the crystallization process chain the purity or CSD can be negatively affected. Therefore, in context of process optimization, missing knowledge of the impacts on the final product can lead to product batches out of specification. To increase the understanding of agglomeration and to provide insight into the relevance of holistic process optimization the agglomeration behavior of L‐alanine crystals is exemplarily quantified over the crystalline process chain. For the quantification the agglomeration degree (Ag) and the agglomeration degree distribution (AgD) are determined. The results show that the product quality achieved after crystallization is significantly affected by agglomeration during drying. Especially if washing after solid‐liquid separation is omitted, a broadening of the CSD is observed. Moreover, the evaluation by the AgD indicates that the final product can be ‐ despite similar characteristics of the CSD ‐ highly different. Consequently, it can be concluded that the characterization of the product quality by the CSD alone is insufficient and the quantification of agglomeration is essential for process optimization. 相似文献
17.
E. Ramachandran P. Raji K. Ramachandran S. Natarajan 《Crystal Research and Technology》2006,41(1):64-67
The study of the thermal properties of condensed matter is very essential both for crystallizing and thermal energy induced fracturing of solid materials. Photoacoustic spectroscopy (PAS) is a recently developed, nondestructive testing (NDT) tool, used for analyzing the surface properties of materials. This method is used here to determine the thermal diffusivity and thermal conductivity of the gel grown single crystals of calcium carbonate (CC), which is the major constituent of pancreatic calculi. Characterization of CC was made using single crystal X‐ray diffraction and density determination. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
18.
H. El‐Shall J.‐H. Jeon E. A. Abdel‐Aal S. Khan L. Gower Y. Rabinovich 《Crystal Research and Technology》2004,39(7):577-585
Kidney stones consist of various organic and inorganic compounds. Calcium oxalate monohydrate (COM) is the main inorganic constituent of kidney stones. However, the mechanisms for the formation of calcium oxalate kidney stones are not well understood. In this regard, there are several hypotheses including nucleation, crystal growth and/or aggregation of formed COM crystals. The effect of some urinary species such as oxalate, calcium, citrate, and protein on nucleation and crystallization characteristics of COM is determined by measuring the weight of formed crystals and their size distributions under different chemical conditions, which simulate the urinary environment. Statistical experimental designs are used to determine the interaction effects among various factors. The data clearly show that oxalate and calcium promote nucleation and crystallization of COM. This is attributed to formation of a thermodynamically stable calcium oxalate monohydrate resulting from supersaturation. Citrate, however, inhibits nucleation and further crystal growth. These results are explained on the basis of the high affinity of citrate to combine with calcium to form soluble calcium citrate complexes. Thus, citrate competes with oxalate ion for binding to calcium cations. These conditions decrease the amount of free calcium ions available to form calcium oxalate crystals. In case of protein (mucin), however, the results suggest that no significant effect could be measured of mucin on nucleation and crystal growth. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
M. Fernandes F. A. Almeida Paz J. F. Mano V. de Zea Bermudez 《Crystal Research and Technology》2014,49(6):418-430
The influence of myristyl alcohol (CH3(CH2)13OH), cetyl alcohol (CH3(CH2)15OH) and behenyl alcohol (CH3(CH2)21OH) on the structure, morphology, size and surface properties of calcium carbonate (CaCO3) has been investigated. Changes in the nature of the washing solvent, in the CnOH/Ca2+ and CO32−/Ca2+ molar ratios and in temperature have been also evaluated. The sole polymorph produced was rhombohedral calcite. At room temperature, while microspheres composed of submicrocubes were produced at a high molar ratio CO32−/Ca2+ and low CH3(CH2)15OH concentration, a stoichiometric molar ratio CO32−/Ca2+ and high CH3(CH2)15OH concentration induced the formation of microcubes and microboxes. In the presence of this alkanol (12 % molar) a significant enhancement of the water contact angle (ca. 40 °) resulted in a sample obtained with a stoichiometric CO32−/Ca2+ ratio. These results emphasize the key role played by the three non‐ionic surfactants in the formation of materials with variable crystal shape and wettability and thus technological interest for a range of applications. 相似文献
20.
Sara J. Homeijer Matthew J. Olszta Richard A. Barrett Laurie B. Gower 《Journal of Crystal Growth》2008,310(11):2938-2945
Fibrous barium carbonate (BaCO3/witherite) crystals 50–100 nm in diameter and several microns in length were grown on calcium carbonate (CaCO3) seeds at temperatures as low as 4 °C. The BaCO3 fibers were deposited onto calcite rhombs or CaCO3 films using the polymer-induced liquid-precursor (PILP) process, which was induced with the sodium salt of polyacrylic acid (PAA). The structure and morphology of the resultant fibers were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and polarized light microscopy (PLM). Fibers were successfully grown on calcite seeds of various morphologies, with a range of barium concentrations, and PAA molecular weight and concentration. Two categories of fibers were grown: straight and twisted. Both types of fibers displayed single-crystalline SAED diffraction patterns, but after examining high-resolution TEM lattice images, it was revealed that the fibers were in fact made up of nanocrystalline domains. We postulate that these nanocrystalline domains are well aligned due to a singular nucleation event (i.e., each fiber propagates from a single nucleation event on the seed crystal) with the nanocrystalline domains resulting from stresses caused by dehydration during crystallization of the highly hydrated precursor phase. These BaCO3 fibers grown on calcite substrates further illustrate the robustness and non-specificity of the PILP process. 相似文献