The mechanochemical route of vaterite synthesis using sodium hexametaphosphate as an inorganic additive

Vaterite is a metastable phase of CaCO₃ and was prepared mechanochemically for the first time with the assistance of sodium hexametaphosphate (SHMP). First, CaCO₃ was prepared without SHMP and was characterized using X-ray diffraction (XRD) to study the effect of milling times and speeds on the polymorphs of product. The results indicate that the reaction is complete at 60 minutes producing only calcite. Additionally, amorphous CaCO₃ (ACC) was obtained at a milling speed of 300 rpm, while calcite was obtained at 600 and 1000 rpm. Then, the effect of SHMP concentration on the fraction of vaterite was investigated, and the vaterite fraction increased with increasing SHMP amount. Subsequently, the effect of milling speed in the presence of 0.8 g of SHMP was studied, and the vaterite fraction increased with decreasing milling speed. Finally, gentler manual milling was employed, and the effect of the amount of added SHMP on vaterite formation was evaluated. The results confirmed that vaterite increased with increasing amounts of SHMP, and that vaterite formed more readily via manual milling than via mechanical milling. Observations with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that calcite and vaterite particles formed by mechanical milling were irregular agglomerates composed of primary nanoparticles while calcite particles formed by manual milling were irregular microparticles. Moreover, vaterite readily aggregated into spherical particles as the amount of SHMP increased. To investigate the reaction process and mechanism, the ethanol-washed product was characterized using XRD, SEM/EDS and TEM/SAED. The results demonstrate that ACC and calcite were concomitant during the milling process, and ACC transformed into vaterite during subsequent water washing.     

Biomineralization of calcium carbonate by adding aspartic acid and lysozyme

Calcium carbonate is one of the most abundant materials present in nature. Crystal structures of CaCO₃ become three polymorphic modifications, namely calcite, aragonite and vaterite. Polymorphic modifications are mediated by adding aspartic acid (Asp) and lysozyme. Lysozyme, which is a major component of egg white proteins, has influenced the calcification of avian eggshells. The influence of Asp and lysozyme on the crystallization of CaCO₃ was investigated by adding these additives and calcium chloride solution into sodium carbonate solution in a crystallization vessel. CaCO₃ crystals were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared spectrometry (FT-IR). XRD was used to select the intensities and crystal structure of specific calcium carbonate. SEM was employed for the analysis of the morphology of the precipitation and particle size. Two kinds of crystals were identified by FT-IR spectrum. Hexagonal crystals of vaterite were affected by the Asp in the crystallization solution. However, rhombohedral crystals of calcite by lysozyme were formed without any sign of vaterite.     

CaCO<Subscript>3</Subscript> crystallization with feeding of aspartic acid

Aspartic acid (Asp) was employed as the organic template in inducing the nucleation and growth of calcium carbonate. Crystallization experiments were carried out by the addition of Asp into the solution of sodium carbonate and calcium chloride. The effects of reaction time, dropping velocity of Asp and Na₂CO₃ solution were tested. The CaCO₃ crystals were analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and Fourier transform infrared spectrometry (FT-IR). Two kinds of crystals were identified by FT-IR spectrum. In the presence of Asp, formation of vaterite is induced in crystallization solution. Also, under the initial condition of an excess amount of Asp, vaterite morphology is the major one. Various morphologies of CaCO₃ are made by changing dropping velocity of added Asp and Na₂CO₃.     

Calcium carbonate inhibition by a phosphonate-terminated poly(maleic-co-sulfonate) polymeric inhibitor

The precipitation of calcium carbonate scale on heat transfer surfaces widely occurs in numerous industrial processes. For the control of calcium carbonate scale and in response to environmental guidelines, the new low phosphonic copolymer was prepared through reaction of maleic anhydride with sodium p-styrene sulfonate in water with redox system of hypophosphorous and hydrogen peroxide as initiator. The anti-scale property of the low phosphonic copolymer towards CaCO₃ in the artificial cooling water was studied through static scale inhibition tests, and the effect on formation of CaCO₃ was investigated with combination of scanning electronic microscopy (SEM), X-ray powder diffraction (XRD) analysis and Fourier transform infrared spectrometer, respectively. The results showed that the low phosphonic copolymer was excellent calcium carbonate scale inhibitor in artificial cooling water. The crystallization of CaCO₃ in the absence of inhibitor was rhombohedral calcite crystal, whereas a mixture of calcite with vaterite crystals was found in the presence of the low phosphonic copolymer. For actions of carboxyl and phosphonic acid groups, the calcite was inhibited and the metastable vaterite was stabilized in the presence of the low phosphonic copolymer during the CaCO₃ formation process.     

Synthesis of vaterite CaCO3 as submicron and nanosized particles using inorganic precursors and sucrose in aqueous medium

It is reported the synthesis of CaCO₃ vaterite as stable nanoparticles and submicron-sized by a simple and relatively rapid procedure. XRD, SEM and FTIR techniques have been used to characterize the precipitated products. The synthesis is based on chemical precipitation of inorganic salt precursors, calcium nitrate tetrahydrate and sodium bicarbonate, and using the disaccharide sucrose as an additive in aqueous medium. The role of the disaccharide sucrose is to control the vaterite precipitation after nucleation and growth. It has been found that an increase in sugar concentration promotes the crystal precipitation of vaterite with spherulitic morphology, as revealed by SEM, and changed the surface of the precipitated particles. There is a significant difference between CaCO₃ precipitation in the absence and presence of sucrose. Addition of 0% of sucrose leads to 83% of calcite as identified by XRD methods. In contrast, addition of 67% of sucrose in aqueous medium produces 100% vaterite. The present results may be useful to provide a quick, simple, inexpensive and novel method for the controlled synthesis of new advanced biomaterials based on vaterite particles without hazardous chemicals and inert atmosphere, with great possibilities for industrial scale production.     

The synthesis of vaterite and physical properties of PP/CaCO3 composites

Vaterite was synthesized in the emulsion state at 50 ‡C. The mixing method was found to have a significant effect on the shape of vaterite. In order to investigate the effect of CaCO₃ morphology on mechanical property and thermal property of polypropylene, cubic forms of calcite and needle forms of aragonite were also prepared in the emulsion states. When vaterite was used as a filler in the PP/CaCO₃ composites, the crystallization temperature and crystallinity were higher than those with other forms. In addition, the size of spherullite of polypropylene was the finest when vaterite was used. Therefore, the vaterite is considered as a proper nucleating agent for polypropylene.     

Mineralization of Calcium Carbonate Induced by Egg Substrate and an Electric Field

Egg substrates, including eggshell, egg membranes, and egg white, exert a significant influence on CaCO₃ biomineralization. CaCO₃ crystallization at different temperatures, concentrations, and with various egg substrates was systematically investigated via rapidly mixing solution method. The crystals were determined by scanning electron microscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction. As the CaCl₂ concentration increased, the CaCO₃ crystal form gradually changed from calcite to vaterite. Under rising temperature, the single‐hole vaterite and besom‐like aragonite were formed on the raw and boiled egg white substrate, respectively. The effects of electric field on CaCO₃ crystallization were also explored. The findings may offer a novel approach to CaCO₃ synthesis.     

Curcumin and quercetin as templates in the in vitro biomineralization of CaCO3: A comparative study on phase modulation

Biomineralization of calcium-based biominerals is influenced by organic molecules containing oxygen donor atoms. In this work, we were able to synthesize and stabilize the least stable crystalline phase of CaCO₃, vaterite, using the biologically useful organic molecule curcumin as the template. The vaterite phase formed was stable in solution at least for 18 h. A comparative study with chemically similar molecule quercetin, a flavonoid, was performed. Though quercetin as a template could not stabilize the vaterite phase, an interesting observation was made in terms of the morphology of the calcite particles obtained. A dumbbell-shaped morphology, different from the usual rhombohedral morphology of the calcite crystals was obtained under ambient conditions. The maturation of the CaCO₃ crystals in solution with time was studied to observe the changes in terms of phase and morphology of the particles. Additionally, extended studies were performed to investigate the influence of the change in parameters such as; template concentration, the sequence of addition, temperature and ionic strength on the phase, morphology and size of the particles in the presence of both the templates.     

Biomimetic synthesis of calcium carbonate films on bioinspired polydopamine matrices

We combine the active surface of polydopamine (PDA) with the biomimetic mineralization of CaCO₃ to obtain the macroscopically continuous CaCO₃ films under mild conditions. In this approach, the organic matrices were adhesive PDA coatings, which were dip-coated on silicon wafers by the self-polymerization of dopamine in an alkaline aqueous solution (pH 8.5). The inorganic layers were CaCO₃ films, which were formed in a CaCl₂ solution in the presence of poly(acrylic acid) (PAA) via a CO₂ diffusion method. During the biomimetic mineralization, amorphous calcium carbonate (ACC) was formed on PDA matrices with the help of PAA, which, subsequently, was transformed into a flat continuous calcite film on the PDA matrices. As the mineralization time increased, a new layer of CaCO₃ crystals was formed over the calcite and, as a result, led to continuous CaCO₃ films with rough surfaces. The thicknesses of CaCO₃ films can be controlled by tuning the mineralization time. Our approach may provide a simple, yet efficient way for the preparation of macroscopically continuous organic–inorganic composite CaCO₃ films under mild conditions. Moreover, superhydrophobic surfaces can be successfully achieved via a hydrophobic modification of the rough CaCO₃ films, which make them suitable candidates for a variety of superhydrophobic applications, such as self-cleaning surfaces or anticorrosion, antiadhesive coatings.     

换热面上碳酸钙的结垢行为及垢形

研究了循环冷却水及池式沸腾系统中换热面上碳酸钙的结垢行为 ,对垢形进行了分析 .考察了分子自组装膜 (SAM)低能表面循环冷却水系统中碳酸钙结垢诱导期及过诱导期特性 ,研究了污垢的脱除现象 .结果表明 ,在诱导期内进行脱除可减少污垢的发生 ,在诱导期后进行脱除会增加污垢的发生 .扫描电镜 (SEM )表明 ,在阻垢剂存在下 ,循环冷却水系统中形成的碳酸钙垢形发生了变化 .利用扫描电镜与原子力显微镜 (AFM)对池式沸腾系统中生成的碳酸钙形貌进行了研究 ,发现在阻垢剂存在下以方解石为主的垢形变成了以文石和球霰石为主的垢型 ,同时碳酸钙表面的台阶发生了聚并现象 .垢形分维分析表明 ,在阻垢剂存在下两种系统中生成的碳酸钙垢形的分维值都增大了 .     

Transformation of CaCO3 to single crystalline micro/nanowires

Single crystalline CaCO₃ micro-nanowires were grown from the solution using poly-vinyl alcohol (PVA) to direct crystal growth and SiO₂ nanoparticles acting as seeds for the growth of amorphous CaCO₃. The aragonite and calcite micro/nanowire, diameter ranging from 70 to 700 nm, were transformed mostly from rhombohedral calcite and vaterite. The micro/nanowires or spicules grown on glass substrate had lengths ranging from 10 to 50 μm and the growth direction showed no orientational relationship to substrate. Without the use of either SiO₂ or PVA, there was no formation of either the amorphous CaCO₃ or the micro/nanowires or spicules.     

Preferential mineralization of CaCO3 layers on polymer surfaces from CaCl2 and water‐soluble carbonate salt solutions supersaturated by poly(acrylic acid)

CaCO₃ was mineralized from solutions supersaturated only by poly(acrylic acid) (PAA), without bubbling any CO₂ gas in the solution. For example, a layer of CaCO₃ was built up on the surface of a chitosan membrane from a supersaturated aqueous solution containing CaCl₂, Na₂CO₃, and PAA. In this newly developed method, the PAA alone suppresses the precipitation of CaCO₃ from the bulk solution, and therefore, increases the supersaturated concentration. This concentration is estimated to be the same order as that attained in the method in which both CO₂ gas and PAA were used. At the same time, PAA supplies nucleation fields by forming a polymer complex with chitosan. The crystal system obtained was different from those obtained when using CO₂ gas. Self‐organization of aragonite crystallites led to the formation of uniform, concentric, or branching patterns in the surface‐domain structure. These patterns had morphologies similar to those discovered by other researchers, typically in the crystallization of ascorbic acid. Thicker layers of CaCO₃ could be formed on chitosan membranes, the surfaces of which had been converted to a polyelectrolyte complex (PEC) by exposure to PAA solution before the onset of mineralization. Under certain conditions, the CaCO₃ layer had a small spherical curvature, similar to a half‐lens, and generated Newton's ring pattern from the interference fringes of visible light. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3627–3634, 2004     

Growing Innovative Calcium Carbonate Morphologies by Utilizing the Colloidal Gas Aphron System as a Surfactant-Based Template Method

Many studies have been conducted to study the various polymorphs and morphologies of calcium carbonate crystals in nature and living organisms. In this experimental work, a novel method has been employed to crystallize calcium carbonate by using colloidal gas aphron dispersion. The polymorph and morphology of prepared particles were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectrometry techniques. SEM and XRD analyses demonstrated that the morphology of synthesized CaCO₃ can be changed from spherical (vaterite phase) to novel rod and plate-like shapes (mixture of vaterite and calcite phases) with changes in the surfactant concentration. The quantitative examination results of different calcium carbonate polymorph orientations showed that the precursor concentrations had no significant effect on the orientation of calcite phase, but rather they affected the orientation development of vaterite phase at a higher surfactant concentration.     

Effects of magnetic field on calcium carbonate precipitation: Ionic and particle mechanisms

There are two most widely reported mechanisms to study the effect of magnetic fields on calcium carbonate (CaCO₃) precipitate, namely ionic and particle mechanisms. The effects are most debatable because they are contrary to each other. This study explored the effects of both mechanisms in CaCO₃ deposit and total CaCO₃ precipitation using ionic and particle methods. The ionic method showed reductions in CaCO₃ deposit and total precipitation rate of CaCO₃, whereas the particle method showed the opposite results. The particle number decreased and the average particle diameter of CaCO₃ deposit increased in the ionic method. Meanwhile in the particle method, the particle number increased, average particle diameter decreased and particle aggregation of CaCO₃ was observed. XRD measurement on all deposits showed that the crystal deposit was mostly of calcite and the traces of vaterite. However, the amount of the crystal in the particle method was observed to be less than that in the ionic method, indicating that CaCO₃ deposit was more amorphous. Particle mechanism decreased the Ca²⁺ ion concentration in solution during magnetization, and ionic mechanism reduced scale (CaCO₃) formation after magnetization and separation processes. This method could be applied for decreasing water hardness and prevent the formation of scaling.     

Comparison of calcite and vaterite as precursors for CO3Ap artificial bone fabrication through a dissolution–precipitation reaction

Carbonate apatite (CO₃Ap) artificial bone is fabricated in an aqueous solution using calcium carbonate as a precursor. CO₃Ap has attracted attention because it demonstrates high osteoconductivity and can replace a damaged bone based on the bone remodeling process. This study aims to compare vaterite and calcite, which are metastable and stable polymorphs of calcium carbonate, respectively, as precursors. When the vaterite granules, which have higher solubility and consist of smaller crystals than calcite, prepared from calcium oxide granules were immersed in disodium hydrogen phosphate solution, the compositional transformation to CO₃Ap was quicker than that of calcite. Based on the investigations on rabbit femurs, it was observed that the remodeling of CO₃Ap to a new bone was faster when vaterite was used as a precursor compared to when calcite was used as a precursor. It is concluded that vaterite can be a better precursor than calcite for CO₃Ap artificial bone fabrication.     

Effect of polyethylene glycol on phase and morphology of calcium carbonate

Calcium carbonate (CaCO₃) with different phases and morphologies were prepared and characterized by scanning electron microscopy (SEM), powder X‐ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The effect of polyethylene glycol (PEG) with different molecular weight and concentrations on the phase and morphology of CaCO₃ was studied. The results showed that aragonite was the only phase in the solution without PEG, while calcite phase could be obtained by the use of PEG as the additive. The possible crystallization mechanism for the formation of CaCO₃ polymorphs in the presence of different PEG was also discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis of hybrid linear-dendritic block copolymers with carboxylic functional groups for the biomimetic mineralization of calcium carbonate

A series of carboxylic acid functionalized hybrid linear-dendritic block copolymers (LDBCs) derived from methoxy poly(ethylene glycol) (MPEG) and variant generation dendrons from 2,2-bis(hydroxymethyl) propionic acid were synthesized and employed as CaCO₃ crystallization growth modifiers. Mainly spherical vaterite particles of gradually reduced sizes were produced with the increase of the polymer additive concentration and/or the dendron segment generation number, while the incorporated polymer organic components in the particles increased for the promoted binding efficiency and ever enhanced adsorption ability. A higher mineralization temperature resulted in significantly larger particle size and partly calcite formation. Under the same molar concentration of carboxylic acid, the same size level particles were obtained which manifested the crucial role of the functional group, meanwhile, the slight decrease of the spherical vaterite diameters with increasing generation number and especially the formation of particular pine-cone shaped calcite crystals also revealed the significant effect of the architectural structure of variant generations and some special characters of the hybrid LDBC structures.     

The crystallization behavior of calcium carbonate in ethanol/water solution containing mixed nonionic/anionic surfactants

Crystallization of CaCO₃ was performed in an ethanol/water solution containing Pluronic F127 (EO₉₇PO₆₈EO₉₇) and sodium dodecyl sulfate (SDS). The effects of the ethanol/water volume ratio, concentration of surfactants, and aging temperature (30-90 °C) on the morphology and polymorphs of CaCO₃ were investigated using scanning electron microscopy (SEM) and powder X-ray diffraction (XRD). The presence of both F127 and SDS in solution favored the vaterite phase of CaCO₃. A binary calcite-vaterite mixture and a ternary calcite-vaterite-aragonite mixture were produced at low (< 60 °C) and high temperatures, respectively. Spherical, plate-like, flower-like, and rod-like crystals were obtained at different ethanol/water volume ratios. Controllable synthesis of nearly pure flower-like vaterite and rod-like aragonite can be realized by adjusting the ethanol/water volume ratio. The formation mechanism of flower-like CaCO₃ crystals is discussed.     

Nonenzymatic Transformation of Amorphous CaCO3 into Calcium Phosphate Mineral after Exposure to Sodium Phosphate in Vitro: Implications for in Vivo Hydroxyapatite Bone Formation

Studies indicate that mammalian bone formation is initiated at calcium carbonate bioseeds, a process that is driven enzymatically by carbonic anhydrase (CA). We show that amorphous calcium carbonate (ACC) and bicarbonate (HCO₃^?) cause induction of expression of the CA in human osteogenic SaOS‐2 cells. The mineral deposits formed on the surface of the cells are rich in C, Ca and P. FTIR analysis revealed that ACC, vaterite, and aragonite, after exposure to phosphate, undergo transformation into calcium phosphate. This exchange was not seen for calcite. The changes to ACC, vaterite, and aragonite depended on the concentration of phosphate. The rate of incorporation of phosphate into ACC, vaterite, and aragonite, is significantly accelerated in the presence of a peptide rich in aspartic acid and glutamic acid. We propose that the initial CaCO₃ bioseed formation is driven by CA, and that the subsequent conversion to calcium phosphate/calcium hydroxyapatite (exchange of carbonate by phosphate) is a non‐enzymatic exchange process.     

Synthesis of calcium carbonate–chitosan composites via biomimetic processing

The crystal growth of calcium carbonate on a chitosan substrate was achieved using a supersaturated calcium carbonate solution, at different concentrations of polyacrylic acid (PAA) as an additive. Several techniques have been employed to characterize the systems. The pH of the solution as the one of indices was used to monitor the crystallization. In the absence of polyacrylic acid, the pH of the solution changed from 6.00 to 8.50 during the crystallization; meanwhile, sporadic nucleation and crystallization was observed via optical microscopy. By introducing polyacrylic acid to the systems, positively charged protonated nitrogen and negatively charged carboxylate ions were produced by reaction between the amino group in chitosan and the carboxyl group in polyacrylic acid, which were detected by ATR-IR and XPS techniques. These charges induced calcium carbonate nucleation of calcite and vaterite crystals on the chitosan-film surface. The average size of the vaterite phase was about 15 nm, determined by XRD. The pH of the solution changed from 5.80 to 9.25 during the crystallization; moreover, the crystals showed spherical morphology, which consisted of a large number of small particles with a diameter of about 0.2 μm. © 1995 John Wiley & Sons, Inc.