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.     

Polymorph and morphology of CaCO3 in relation to precipitation conditions in a bubbling system

Simulating the typical carbonation step in a mineral CO2 sequestration,precipitated calcium carbonate (PCC) was prepared by bubbling CO2 gas into a rich Ca solution.These carbonation reactions were conducted at three pH ranges,namely 10.0-9.0,9.0-8.0,and 8.0-7.0,in which temperature and CO2 flow rate are additional experimental variables.The PCC obtained in experiments was examined by Fourier transform infrared spectroscopy (FrIR) and X-ray diffraction (XRD).It was found that supersaturation determined by pH value and flow rate of CO2 has significant influence on polymorph of PCC.Vaterite was preferably formed at high supersaturation,while dissolution of metastable vaterite and crystallization of calcite occurred at low supersaturation.High temperature is a critical factor for the formation of aragonite.At 70 ℃,vaterite,calcite and aragonite were observed to coexist in PCC because transformation from vaterite to aragonite via calcite occurred at this temperature.Scanning electron microscopy (SEM) technology was performed on prepared PCC,and various morphologies consistent with polymorphs were observed.     

反应-萃取-结晶过程制备碳酸钙的晶型转变与结晶机理

氨碱法制碱过程中产生的大量蒸氨废液制约了纯碱工业的发展。本文对反应-萃取-结晶耦合工艺产物碳酸钙的晶型转变和结晶机理进行了研究。结果表明,在此耦合过程中,二氧化碳优先被有机相吸收,然后传递到水相进行反应,首先生成的是碳酸氢钙,之后迅速分解为无定形碳酸钙。温度对碳酸钙晶型影响显著,温度较高时,无定形碳酸钙优先转变为针状文石;温度较低时,无定形碳酸钙优先转变为球状球霰石。随后文石和球霰石均会通过溶解-重结晶作用逐渐转变为稳定的菱形方解石。常温下,反应过程中同时进行着新的球霰石的生成和球霰石转变为方解石两个过程,参与反应的二氧化碳浓度越高,晶体中球霰石的含量越高。     

Crystallization kinetics of organogels prepared by rice bran wax and vegetable oils

Rice bran wax (RBX) obtained during rice bran oil purification can form organogels in edible oils. The kinetics of crystallization and the viscous properties of RBX organogels were studied using differential scanning calorimetry (DSC), viscosity changes with varying temperature, hardness measurements by penetrometry, and synchrotron radiation X-ray diffraction (SR-XRD). The organogels were prepared by RBX in concentrations of 1%, 3%, 6%, and 10% on a weight basis in salad oil, olive oil, and camellia oil. The liquid oil type had no significant effect on the melting and crystallization temperatures of the RBX. However, the viscosity and the texture of the organogels differed with liquid oil type, temperature, and RBX concentration. Changes in the viscosity of the RBX organogels were monitored during cooling from 80°C to 20°C. Drastic viscosity changes occurred in accordance with the onset of crystallization in DSC thermographs obtained at a rate of 5°C/min. RBX in the olive oil and camellia oil mixtures had higher viscosity than RBX in the salad oil mixture, which correlates with the hardness obtained in texture measurements at 20°C. SR-XRD was used to clarify the crystal structures of the building blocks of the RBX organogels in salad oil. It was found that the RBX formed crystals with a long spacing of 7.3 ± 1 nm and short spacings of 0.41 ± 1 nm and 0.37 ± 1 nm. The intensity of the long-spacing pattern was remarkably weaker than that of the short-spacing patterns, which demonstrated strong anisotropy in the crystal growth of RBX crystal particles.     

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.     

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.     

Synthetic Aragonite (CaCO3) as a Potential Additive in Calcium Phosphate Cements: Evaluation in Tris‐Free SBF at 37°C

Conventional SBF (simulated/synthetic body fluid) solutions are buffered at pH 7.4°C and 37°C using 50 mM Tris [(HOCH₂)₃CNH₂]. Tris is not present in human blood or metabolism and its high concentration makes it the third major component of SBF solutions. All three crystalline polymorphs of calcium carbonate (calcite, aragonite and vaterite) have never been tested simultaneously in an SBF solution. This study presents the SBF‐testing of the particles of these polymorphs at 37°C in Na‐L‐lactate (22 mM)‐buffered Lac‐SBF solution. While the calcite rhombohedra remained completely inert in the solution, vaterite spherulites and aragonite needles accrued apatitic CaP (calcium phosphate) deposits on their surfaces. Mg‐doped (1050 ppm) synthetic aragonite particles did not transform into calcite for 96 h in the Lac‐SBF solution while increasing their BET surface area by about 560% via the apatitic CaP deposits. Given the well‐established use of calcite powders in CaP cement formulations, synthetic aragonite particles may be a potential replacement for calcite due to their rapid response to blood plasma‐like solutions in between 24 and 48 h at 37°C.     

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.     

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.     

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.     

Setting behavior and bioactivity assessment of calcium carbonate cements

Calcium carbonate cements have emerged in the last few years as an attractive candidate for biomedical applications. They can be easily prepared by mixing water with two metastable calcium carbonate phases––amorphous calcium carbonate (ACC) and vaterite––which (re)crystallize into calcite during setting reaction. The transformation kinetics (and therefore the final surface cement composition) strongly depends on the initial mixture design and is controlled by the dissolution of ACC, whereas calcite nucleation typically controls their recrystallization in fluid batch experiments. Novel compositions are presented in this paper by incorporating organic molecules as a proxy to test their capability to carry on other biomolecules like proteins or antibiotics. The hardened samples are microporous and show excellent bioactivity rates, although their mechanical properties still remain poor. However, this would not be a handicap for in-vivo applications such as bone filling, especially in low mechanical stress locations.     

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.     

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.     

Effects of sodium dodecyl benzenesulfonic acid (SDBS) on the morphology and the crystal phase of CaCO<Subscript>3</Subscript>

The effects of anionic surfactant on the morphology and crystallization of calcium carbonate precipitated from CaCl₂ and Na₂CO₃ were investigated. Although reaction temperature did not have an effect on the morphology of calcium carbonate, it did have an effect on the cluster size. The cluster size became bigger with high reaction temperature. With the addition of sodium dodecyl benzenesulfonic acid (SDBS), the morphology of precipitated calcium carbonate changed from cubic to porous spheres with over 98% of the crystal phase transformed from calcite to vaterite. The analysis of precipitates formed by the reaction of CaCl₂ solution (from limestone (CaO 50% content)) and Na₂CO₃ found that the morphology of precipitated calcium carbonate changed from cubic to spherical, and the crystal phase changed from calcite to over 94% vaterite with the addition of sodium dodecyl benzenesulfonic acid. These vaterite structures were solid spheres rather than hollow ones.     

A protected annealing strategy to enhanced light emission and photostability of YAG:Ce nanoparticle-based films

A significant obstacle in the development of YAG:Ce nanoparticles as light converters in white LEDs and as biological labels is associated with the difficulty of finding preparative conditions that allow simultaneous control of structure, particle size and size distribution, while maintaining the optical properties of bulk samples. Preparation conditions frequently involve high-temperature treatments of precursors (up to 1400 °C), which result in increased particle size and aggregation, and lead to oxidation of Ce(iii) to Ce(iv). We report here a process that we term protected annealing, that allows the thermal treatment of preformed precursor particles at temperatures up to 1000 °C while preserving their small size and state of dispersion. In a first step, pristine nanoparticles are prepared by a glycothermal reaction, leading to a mixture of YAG and boehmite crystalline phases. The preformed nanoparticles are then dispersed in a porous silica. Annealing of the composite material at 1000 °C is followed by dissolution of the amorphous silica by hydrofluoric acid to recover the annealed particles as a colloidal dispersion. This simple process allows completion of YAG crystallization while preserving their small size. The redox state of Ce ions can be controlled through the annealing atmosphere. The obtained particles of YAG:Ce (60 ± 10 nm in size) can be dispersed as nearly transparent aqueous suspensions, with a luminescence quantum yield of 60%. Transparent YAG:Ce nanoparticle-based films of micron thickness can be deposited on glass substrates using aerosol spraying. Films formed from particles prepared by the protected annealing strategy display significantly improved photostability over particles that have not been subject to such annealing.     

硅酸盐水泥混凝土的碳化分析

介绍了硅酸盐水泥混凝土的碳化反应和碳化过程,分析了Ca(OH)_2与水化硅酸钙(C-S-H)的碳化作用.Ca(OH)_2发生碳化反应的同时,C-S-H也会发生碳化反应;Ca(OH)_2的碳化产物是方解石,而C-S-H碳化后会转变成无定形硅胶,可能形成稳定性差、结晶度差的球霰石、文石,其分解温度低于方解石的分解温度;C/S低、结晶度差的C-S-H凝胶易于碳化;水泥浆体孔隙溶液中的碱含量越高,碳化速度越快,深度越大.     

电石渣制备碳酸钙微粉的晶型转变

为了提高电石渣的附加值,在未使用晶型诱导剂的情况下,研究盐酸的用量、提取温度和二氧化碳的流量对电石渣合成碳酸钙形貌的影响。用XRD、FT-IR 表征了合成的产物,用扫描电子显微镜（SEM）观察研究了产物粒子的形状,结果表明,盐酸的用量和提取温度均会对碳酸钙的晶型和形状有影响。随着盐酸用量的增大,碳酸钙由不规则的方解石型转变为部分规则的球状结构,当浸取剂完全是盐酸的时候,碳酸钙的晶型从方解石型完全转变为球霰石型结构,颗粒粒径为4~5 μm。另外,当提取温度从18 ℃升高到30 ℃以上后,碳酸钙由方解石和球霰石两种晶体结构并存的状态转变为单一的球霰石型结构。     

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.     

Phase-controllable synthesis of nanosized nickel phosphides and comparison of photocatalytic degradation ability

In this paper, we employed a facile hydrothermal route to successfully synthesize nanosized nickel phosphide particles with controlled phases via selecting different surfactants at different temperatures and times. The phases of the as-obtained products were determined by X-ray powder diffraction (XRD) patterns and Rietveld refinement of XRD data. The morphologies of the products were characterized by (high resolution) transmission electron microscopy (HR/TEM) and field emission scanning electron microscopy (FESEM). Experiments indicated that pure Ni2P phase could be prepared when nontoxic red phosphorus and nickel dichloride were used as starting materials in the presence of polyvinylpyrrolidone (PVP, 30 K), sodium dodecylbenzene sulfonate (SDBS), cetyltrimethylammonium bromide (CTAB) or polyethylene glycol 10000 (PEG-10000) at 160 °C for 10 h. When acrylamide (AM) was selected as the surfactant, however, pure Ni12P5 phase could be prepared by prolonging the reaction time to 20 h at 160 °C, or enhancing the reaction temperature to 180 °C for 10 h. Furthermore, the experiments indicated that the pure Ni2P phase possessed a stronger photocatalytic degradation ability than the pure Ni12P5 phase.     

Controllable synthesis of calcium carbonate polymorphs at different temperatures

Calcium carbonate with various structures and morphologies were prepared by double injection of the CaCl₂ and NH₄HCO₃ solutions with molar ratio of 1:1 at 30-80 °C. The lamellar vaterite particles, the mixture composed of vaterite, aragonite and calcite, and the aragonite whiskers were formed at 30-40 °C, 50-70 °C and 80 °C, respectively. Thermodynamic calculation showed that the value of [CO₃²⁻]/[Ca²⁺] decreased with the increase of temperature, which may be one of the reasons for the formation of the lamellar vaterite at 30-40 °C and the aragonite whiskers at 80 °C.