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.     

Factors affecting the phase and morphology of CaCO3 prepared by a bubbling method

Precipitated calcium carbonate (PCC) was prepared by bubbling a CO₂/N₂ mixed gas into a CaCl₂ solution. The influence of preparation conditions on the phase and morphology of PCC was discussed with the help of XRD and SEM measurements. The results showed that the initial CaCl₂ concentration, flow rate and temperature play an important role on the morphology of PCC. At low initial CaCl₂ concentration or high flow rate, spherical vaterite was preferably formed. Otherwise, the rhombic calcite was ready to form. Temperature is a determining factor on the formation of aragonite. Needle-like aragonite was precipitated at 60 °C. The results also indicated that both the bubbling time and stirring rate have a minor effect on the phase and morphology of PCC.     

Influence of sodium dodecyl sulfate and cetyl trimethylammonium bromide upon calcium carbonate precipitation on bacterial cellulose

Calcium carbonate was deposed on bacterial cellulose (BC) never-dried membranes in the presence of different concentrations of sodium dodecyl sulfate (SDS) and cetyl trimethylammonium bromide (CTAB) by a precipitation reaction between aqueous solutions of calcium chloride (CaCl₂) and sodium carbonate (Na₂CO₃) containing, or not, surfactant in their composition. Different shapes of crystals were obtained from rhombohedral ones to flowerlike, depending on surfactant type and concentration. From the two surfactants tested, SDS has a greater influence on calcium carbonate morphology than CTAB. The only polymorph obtained in all studied cases was calcite. The composite films BC-calcite were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and color measurements. The obtained BC-calcium carbonate composites could be used in paper manufacturing.     

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.     

碳酸钙晶型的肉豆蔻酸调控研究

采用硝酸钙和碳酸钠的复分解反应制备碳酸钙,通过加入肉豆蔻酸对碳酸钙的晶体结构和表面性质进行调控,采用SEM、XRD、FT-IR、TG和XPS等方法研究了添加肉豆蔻酸对碳酸钙晶体结构的影响。结果表明,加入肉豆蔻酸之后,碳酸钙的晶体结构由球霰石变成方解石,形貌由球形变成了不规则的长方体形;碳酸钙的表面全部被活化,由亲水性变成疏水性,表面疏水后,碳酸钙的团聚程度明显降低;肉豆蔻酸的羧基阴离子和钙离子发生了化学结合反应,增强了碳酸钙结构的稳定性。总之,肉豆蔻酸的加入为碳酸钙的晶型调控与表面改性提供了一条简单的思路。     

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.     

Synthesis of nanosized calcium carbonate (aragonite) via a polyacrylamide inducing process

A carbonation route for the synthesis of nanosized calcium carbonate (aragonite) was studied. In the process, polyacrylamide was used as an organic substrate to induce the nucleation and growth of calcium carbonate. The calcium carbonate particles were produced by means of carbonation of the mixture of calcium hydroxide and polyacrylamide by bubbling CO₂/N₂ gas mixture_. The operating parameters such as the concentration of organic substrate and temperature were varied to study their influences on the polymorph and crystal sizes of calcium carbonate particles. The morphology of the calcium carbonate particles was characterized with transmission electron micrograph (TEM). The synthesized calcium carbonate particles in the presence of organic substrate are the mixture of aragonite with needle shape and calcite with cubic shape. Fourier transform infrared spectroscopy (FTIR) analysis reveals the presence of aragonite and calcite. The polymorphs and their crystal sizes were characterized with X-ray diffraction (XRD). The calcium carbonate nucleated in the organic substrate exhibited different endothermic peak in differential thermal gravity (DTG) results compared to one coexisting with the organic substrate.     

二水硫酸钙间接矿化二氧化碳CTAB对碳酸钙晶型的影响

提升产品附加值对改善二氧化碳矿化过程的经济性具有重要意义。在二水硫酸钙与碳酸铵溶液进行间接矿化反应过程中,采用十六烷基三甲基溴化铵（CTAB）为晶型调节剂,可以获得球霰石晶型的碳酸钙。系统研究了反应时间、反应温度、CTAB加入量对碳酸钙晶型和形貌的影响,通过X射线衍射（XRD）、扫描电镜（SEM）和红外光谱（FT-IR）对碳酸钙的晶型、形貌进行了表征。结果表明：反应过程为先形成亚稳定相的球霰石,再向热力学最稳定的方解石相转化;添加CTAB能够明显地增强球霰石的稳定性;较低温度有利于球霰石的形成;在反应温度为30 ℃、二水硫酸钙和碳酸铵加入量均为0.1 mol/L、CTAB加入量为0.54 mmol/L条件下,碳酸钙中球霰石占比高达80%以上;CTAB在球霰石表面上的吸附降低了其表面能,从而抑制了球霰石向方解石的转化。     

Synthesis of single phase aragonite precipitated calcium carbonate in Ca(OH)2-Na2CO3-NaOH reaction system

The formation behavior of precipitated calcium carbonate polymorphs was investigated in three different supersaturation levels. Because the most easily adjustable and influential variable determining supersaturation is the ion concentration of the major reactants — Ca²⁺ and CO3 ₃ ²⁻ — the supersaturation can be adjusted by changing the ion concentration of these two ions. At high supersaturation, free energy is necessary for a decrease in nucleation, promoting the formation of a sphere-shaped vaterite, while aragonite and calcite were seen to co-exist at medium supersaturation. At low supersaturation, aragonite was mainly formed by mixing with some calcite. Hence, we considered that lower supersaturation was necessary to obtain a single phase aragonite. Furthermore, we found that the solubility of Ca(OH)₂ was decreased with the addition of NaOH by a common ion effect. Thus, it is possible to perform an experiment at a lower Ca²⁺ concentration. The aragonite was synthesized by adding the Na₂CO₃ solution to the Ca(OH)₂ slurry containing several concentrations of NaOH solution at 75°C and under the addition rate of Na₂CO₃ at 3 ml/min. The formation yield of calcite decreased when the NaOH concentration was increased. In conclusion, in the case of the reaction of the 2.5 M NaOH solution over 210 minutes, single-phase aragonite with an aspect ratio of 20 was obtained.     

Casein phosphopeptides–vaterite calcium carbonate enhance cytocompatibility and osteoinductivity of poly(l‐lactic acid)

Although calcium carbonate has been proved to be effective in neutralizing the acid degradation products of poly(l ‐lactic acid) (PLLA), it has no osteoinductivity. In this study, casein phosphopeptides (CPPs)‐containing CaCO₃ vaterite were synthesized by fast precipitation in an aqueous solution of CaCl₂, Na₂CO₃, and 2 mg/ml of CPPs. CaCO₃–PLLA composite membranes (P‐vaterite–CPP) were prepared (CaCO₃/PLLA =1:2) and exhibited uniform structure and increased hydrophilicity. These composite membranes enhanced hydroxyapatite formation after incubated in simulated body fluid at 37°C for 7 days. The P‐vaterite–CPP membranes promoted human bone marrow stromal cells (hBMSCs) proliferation 4 and 7 days after seeding. Scanning electron microscope images of hBMSCs on the composite membranes exhibited a polygonal and unevenly spreading morphology. Immunofluorescent staining of cytoskeleton and focal adhesion showed that hBMSCs had more stress fibers and were more spreading, indicating a good cell adhesion on the CPPs‐containing composite membranes. Osteogenesis related genes (alkaline phosphatase, collagen type, osteocalcin, and osteopontin) expressions were significantly higher on the CPPs‐containing membranes than those on the CPPs‐free membranes (P < 0.05). It can be concluded that the addition of CPPs induces vaterite formation and thus improve cytocompatibility and osteoinductivity of PLLA. POLYM. COMPOS., 36:1213–1223, 2015. © 2014 Society of Plastics Engineers     

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.     

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.     

Crystallization of Nano‐Calcium Carbonate: The Influence of Process Parameters

Precipitated calcium carbonate was synthesized by carbonation of calcium hydroxide in the presence and absence of ultrasound (conventional stirring) at atmospheric as well as at elevated pressures and different initial concentrations of Ca(OH)₂. Spherical morphology of the formed calcite was favored at high Ca(OH)₂ concentrations and low CO₂ pressures. The presence of ultrasound did not show any influence on the reaction rate in case of efficient mixing. A small increase of the reaction rate was observed at lower CO₂ pressures. Elevated pressures in combination with ultrasound did not lead to notable changes of reaction rate or particle morphology.     

“Metakaolin‐Slag‐Clinker Blends.” The Role of Na+ or K+ as Alkaline Activators of Theses Ternary Blends

This article reports on research into the use of solid alkalis (Na₂CO₃ and K₂CO₃) as activators to obtain hybrid cement (cement whose hydration generates a mix of C–A–S–H and (N,C)–A–S–H gels) from a blend of 20% clínker + 40% blast furnace slag + 40% metakaolin. More specifically, the study aimed to determine the effect of activator dosage (5 and 8 wt%) and type of alkaline cation (Na⁺ or K⁺) on the 2‐ and 28‐d mechanical strength of the end materials. The findings showed that the highest mechanical strength values were obtained with 5% Na₂CO₃. According to the XRD, NMR, and SEM/EDX analyses conducted on the reaction products, the alkalinity and solubilized chemical species generated by adding 5% Na₂CO₃ to the system yielded a mix of (N,C)–A–S–H and C–A–S–H cementitious gels as the main reaction products. The secondary reaction products included metastable (3CaO·Al₂O₃·CaCO₃·11H₂O‐type) carboaluminates that evolved into the calcite or vaterite forms of calcium carbonate. When K₂CO₃ was used (instead of Na₂CO₃), a (3CaO·Al₂O₃·0.5Ca(OH)₂·0.5CaCO₃·11H₂O‐type) hemicarboaluminate also formed. The study also revealed that Na⁺ favors coagulation/precipitation more effectively than K⁺, generating gels with a wider range of Qⁿ species.     

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。     

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.     

Studies on impurity ion and radiofrequency electric field effects on calcium carbonate deposition

The influences of impurity ions (Mg²⁺, Zn²⁺, Fe²⁺, Fe³⁺, and Al³⁺ ) and radiofrequency (44 MHz) electric field (RF) on calcium carbonate deposition in glass capillaries were studied. Calcium carbonate was precipitated from 0.1 M CaCl₂ and Na₂CO₃ solutions (100+ 100 ml) just before the inlet to the capillary. It was found that except for Al ³⁺ ions at 0.001 M concentration, the rest of the ions studied decreased CaC0₃ deposition. A minor influence of the RF field on the deposition was found in some of the systems tested, but it was in the range of the standard deviation of the results. An increase in deposition was observed in systems without impurity ions when equimolar volumes (500 + 500 ml) of 0.0025 M solutions of CaCl₂ and Na₂CO₃ were used for the experiment.     

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.     

NaOH–烟道气法卤水净化中成垢离子的沉降行为

卤水中的成垢离子(Ca2+, Mg2+和CO32–等)在真空蒸发浓缩过程中易形成低热力学活性和强吸附性的碳酸钙和硫酸钙垢层,降低换热管传热效率。NaOH–烟道气法卤水净化可利用电厂废气–烟道气以及氯碱厂低浓度的废碱,在节能环保方面具有绝对的优势和广阔的前景。为研究NaOH–烟道气法卤水净化过程中成垢离子的沉降行为规律,采用CO2替代烟道气开展卤水净化实验研究。采用Factsage热力学软件、XRD和SEM–EDS等分析手段探究了不同CO2通入时间和pH值对Ca2+, Mg2+和CO32–沉降行为的影响及所得沉淀物的矿物学特征。结果表明,当控制pH=11.5,CO2通入时间60 min时,可将卤水中的Ca2+浓度降低至6.0~8.0 mg/L,延长沉降时间至80 min,Mg2+浓度可降低至0.65 mg/L。此外,该pH值条件下沉淀反应的平衡常数最大,钙、镁的净化效果较其他pH条件下更佳。控制过程pH=9.5时,所得沉淀物为球霰石(Vaterite)型碳酸钙晶体;当pH升至10,碳酸钙的晶型由球霰石转化为霰石型(Aragonite)晶体,其形貌由规则的球形转变为椭圆形;当pH=11和11.5时,沉淀物为钙和镁的共晶体,碳酸钙的晶型由球霰石转换为热力学更加稳定的方解石型(Calcite)晶体。     

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.