Water-soluble terpolymer-mediated calcium carbonate crystal modification

The structure of the polymeric substrate plays an important role in the nucleation of calcium carbonate crystals. In this study a synthetic water-soluble poly(acrylamide-co-2-acrylamido-2-methyl-1-propane sodium sufonate-co-n-vinyl pyrrolidone) was found to be a substrate favoring the nucleation of polymorphs of calcium carbonate crystals under specific experimental conditions. Morphological characterization of the polymorphs was done using atomic force microscopy, scanning electron microscopy, energy dispersive spectroscopy, FTIR analysis, and X-ray diffraction. If calcium carbonate is precipitated in the presence of terpolymer, a remarkable increase in nucleation density (number of crystals per unit area) was observed. Stacked crystals of rhombohedral morphology that formed may be due to the presence of sodium sulfonate groups on the terpolymer. However, in the presence of poly-L-aspartic acid, almost all crystals are hollow and have needlelike or plate like morphology was formed. This change in calcium carbonate morphology can be explained by the variation of the polymer conformation, if poly- L-aspartic acid is present.     

Studies on the dehydration and decomposition of calcium and dicalcium magnesium aconttate hydrates

The thermal decomposition of calcium and dicalcium magnesium aconitate hydrates were studied by TG/DTG, DTA, EGA, SEM and other physico-chemical techniques. The decomposition proceeds in four stages: dehydration; oxidation of the carboxylic acid portion of the salt; complete fragmentation of the hydrocarbon portion; and finally, decarboxylation of the metal carbonate to the oxide. The crystal morphologies of the hydrate and anhydrous salts of each compound are very similar. Tricalcium aconitate consists of well-developed twinned crystals and stellate clusters intergrown with flat platy crystals. On the other hand, dicalcium magnesium aconitate crystals are monoclinic with well-developed pinacoidal faces. The activation energy,E _d (43±2 kJ mol^?1 water), calculated from Borchardt and Daniels' method, for the dehydration process of calcium aconitate trihydrate is of the same order of magnitude as some simple metal salt hydrates. The rate constant, k_d increased from 0.04/min at 238°C to greater than 0.86/min at 295°C. It is concluded that the dehydration process is due to cation bound water.     

Synthesis of V2O5 micro-architectures via in situ generation of single-crystalline nanoparticles

Rose-like crystalline particles of ammonium vanadium sulfate hydroxide (NH₄V₃(OH)₆(SO₄)₂) were synthesized by a solvothermal route using dimethyl sulfoxide (DMSO)–water as the solvent. Following a thermal decomposition process, rose-like V₂O₅ micro-architectures were fabricated via the in situ generated single-crystalline nanoparticles. When used as the cathode material in lithium-ion batteries, the rose-like V₂O₅ micro-architecture exhibited high initial discharge capacity. Sphere-like precursor was also prepared via selecting suitable carboxylic acid. This facile synthesis method would be used to prepare various vanadium oxides with different morphologies as well as other compounds.     

柠檬酸钠与碳酸钙晶型和形貌的控制

晶体的晶型和形貌是碳酸钙制备中的关键问题之一。 采用尿素水解均匀沉淀法来控制碳酸钙的晶型和形貌。 利用XRD和SEM等技术手段对CaCO₃晶体的结构和形貌进行了表征。 结果表明,高温条件下(90 ℃)水溶液中得到均匀的针状结构的文石晶体。 添加适量柠檬酸钠后,则得到的是特殊形貌的方解石晶体。 在乙醇/水混合溶剂中,柠檬酸钠对CaCO₃晶体的形貌也有重要影响,通过改变乙醇体积分数,得到了中空绒毛球状的球霰石。     

Synthesis of ZnO crystals with unique morphologies by a low-temperature solvothermal process and their photocatalytic deNO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> properties

A series of unique morphologies of ZnO were synthesized by a simple mild solvothermal process using equimolar of Zn(NO₃)₂/Zn(AC)₂–hexamethylenetetramine (HMT) acting as precursors and ethylene glycol (EG) and triethylamine (TEA) as the dispersant and surfactant additive, respectively. When the as-prepared particles were further treated in 0.02 M HMT solution for such a long time as 72 h, screw-like and rose-like crystals with three-dimensional and developed structure could be formed. The deNO _x photocatalytic activity was characterized and the analysis results showed that the modified ZnO crystals possessed a three-dimensionally developed structure and had higher deNO _x photocatalytic activity compared to that of the as-prepared untreated ZnO.     

Facile fabrication of hierarchical ZnO nanowire aggregates using rose-like peroxide precursor as the inorganic template

The complex rose-like inorganic templates assembled by the ZnO/ZnO₂ hybrid nanosheets have been constructed with hydrogen peroxide as an additive to control the structure of a precursor. The surface morphologies of the inorganic templates can be controlled by varying the reaction time and the amount of hydrogen peroxide. The process of the precursor growth takes a dissolution-growth route under hydrothermal conditions. The chemical composition of the precursor is determined by X-ray diffraction (XRD) and Raman analyses, indicating the existence of peroxide in the precursor. Combined with transmission electron microscopy (TEM) data, the ZnO/ZnO₂ hybrid precursor is proposed to act as an inorganic template for the growth of secondary crystal structures. The dandelion-like ZnO crystal is fabricated by using rose-like peroxide precursor as the inorganic template. The structural evolution of hierarchical ZnO crystal is studied by monitoring the influence of the reaction time.     

Role of Polyelectrolytes in Crystallogenesis of Calcium Carbonate

The effects anionic polyelectrolytes, having various molecular weights and repeating unit structures, on the crystallization of calcium carbonate in supersaturated solutions are studied. The induction times of the crystals grown in the presence of the polymers were optically evaluated; X-ray diffraction and Scanning Electronic Microscopy (SEM) analyses were performed to determine, respectively, their crystalline structures and morphologies. The polyelectrolyte is found to lengthen the induction time and to reduce the size of CaCO₃ nanocrystallites, to an extent depending on the interaction efficiency between the polymer anionic repeating units and the calcium ions. Further, depending on their sizes and their crystalline structures (calcite, vaterite) the nanocrystallites aggregate and yield final calcium carbonate particles having various sizes and morphologies. The data indicate that nanocrystals having vaterite structure, as determined by X-ray analysis, give spherical CaCO₃ final particles, while nanocrystals having calcite structure lead to either acicular or flower shapes of CaCO₃ final particles.     

自组装单层诱导生长不同形貌碳酸钙晶体

本文将实验结果和软件模拟图像相结合,从结晶学角度探讨了通过L-半胱氨酸自组装单层诱导得到的不同形貌方解石晶体的成因. 阐明了晶体的SEM照片与XRD谱峰的对应关系.     

乙醇/水混合溶剂体系中碳酸钙晶体晶型和取向的控制

采用(NH4)2CO3分解法,制备得到了晶型和形貌可控的CaCO3晶体。研究结果表明,乙醇/水混合溶剂、陈化时间和L-半胱氨酸自组装单层模板对CaCO3晶体的晶型、取向和形貌都具有重要影响。无单层模板情况下,溶液中主要得到了球霰石,球霰石的形貌随陈化时间从花朵外形变为树叶形。同样的醇/水体系中,在自组装单层上却得到了取向为(104)晶面的方解石。这与水溶液中同一自组装单层上主要获得(001)结晶面的方解石有明显不同。方解石的形貌也随陈化时间变化而改变。陈化时间为3h时,得到具有孔洞结构的方解石;陈化时间为12 h时,得到表面光滑的菱面体方解石。     

Influence of the primary structure of enzymes on the formation of CaCO2 polymorphs: a comparison of plant (Canavalia ensiformis) and bacterial (Bacillus pasteurii) ureases

The influence of the primary structures of plant (Canavalia ensiformis) and bacterial (Bacillus pasteurii) ureases on the precipitation of calcium carbonate polymorphs in solutions of calcium salts and urea at room temperature was investigated. Despite a similar catalytic function in the decomposition of urea, these ureases exerted different influences on the crystal phase formation and on the development of unusual morphologies of calcium carbonate polymorphs. Spherical and uniform vaterite particles were precipitated rather than calcite in the presence of Bacillus urease, while the presence of Canavalia urease resulted in the precipitation of calcite only. Vaterite particles were shown to be built up of nanosized crystallites, proving the importance of nanoscale aggregation processes on the formation of colloidal carbonates. Reduction of the concentration of Bacillus urease in the reacting solution results in the formation of calcite crystals with a more complex surface morphology than the ones obtained by Canavalia urease. These differences may be explained by dissimilarities in the amino acid sequences of the two examined ureases and their different roles in nucleation and physicochemical interactions with the surface of the growing crystals, during the precipitation processes. This study exemplifies the diversity of proteins produced by different organisms for the same function, and the drastic effects of subtle differences in their primary structures on crystal phase formation and growth morphology of calcium carbonate precipitates, which occur as inorganic components in a large number of biogenic structures.     

乙醇/水混合溶剂体系中碳酸钙晶体晶型和取向的控制

采用（NH₄）₂CO₃分解法,制备得到了晶型和形貌可控的CaCO₃晶体。研究结果表明,乙醇/水混合溶剂、陈化时间和L-半胱氨酸自组装单层模板对CaCO₃晶体的晶型、取向和形貌都具有重要影响。无单层模板情况下,溶液中主要得到了球霰石,球霰石的形貌随陈化时间从花朵外形变为树叶形。同样的醇/水体系中,在自组装单层上却得到了取向为（104）晶面的方解石。这与水溶液中同一自组装单层上主要获得（001）结晶面的方解石有明显不同。方解石的形貌也随陈化时间变化而改变。陈化时间为3h时,得到具有孔洞结构的方解石;陈化时间为12h时,得到表面光滑的菱面体方解石。     

Effects of PAA additive and temperature on morphology of calcium carbonate particles

Calcium carbonate particles with various shapes were prepared by the reaction of sodium carbonate with calcium chloride in the absence and presence of a polyacrylic acid (PAA) at 25°C and 80°C, respectively. The as-prepared products were characterized with scanning electron microscopy and X-ray diffraction. The effects of pH, temperatures, aging time and concentration of PAA and CaCO₃ on the crystal form and morphologies of the as-prepared CaCO₃ were investigated. The results show that pH, temperatures, concentration of PAA and CaCO₃ are important parameters for the control of morphologies of CaCO₃. Various crystal morphologies of calcite, such as, plates, rhombohedras, rectangles, ellipsoids, cubes, etc. can be obtained depending on the experimental conditions. Especially, the monodispersed cubic calcite particles can be produced by PAA addition at 80°C. Moreover, higher temperature is beneficial to the formation of monodispersed cubic or rectangular calcite particles. This research may provide new insight into the control of morphologies of calcium carbonate and the biomimetic synthesis of novel inorganic materials.     

The effect of PVP-<Emphasis Type="Italic">b</Emphasis>-PMAA block copolymer on morphologies control of calcium carbonate

A novel double-hydrophilic block copolymer (DHBC) poly(vinyl pyrrolidone)–block–poly(methacrylic acid) (PVP-b-PMAA) was synthesized via reversible addition–fragmentation chain transfer polymerization. The structure of the resulting copolymer was characterized by ¹H nuclear magnetic resonance, and the molecular weight of the block copolymer was determined by gel permeation chromatography. The study of morphological control of calcium carbonate (CaCO₃) has been performed in the presence of the PVP-b-PMAA block copolymer. Various morphologies of CaCO₃ particles such as rhombohedral, multilayered, and aggregated with cavities can be produced by varying the copolymer concentrations. The all-obtained CaCO₃ particles were calcite, which was confirmed by either X-ray diffraction or Fourier transform infrared spectra. Such calcium carbonate/polymer hybrids with complex morphologies may find valuable applications in biomimic mineralization.     

Synthesis of barium and strontium carbonate crystals with unusual morphologies using an organic additive

In this paper, strontium carbonate (SrCO₃) and barium carbonate (BaCO₃) crystals were synthesized in the presence of an organic additive-hexamethylenetetramine (HMT) using two CO₂ sources. Scanning electron microscopy and X-ray powder diffractometry were used to characterize the products. The results showed that the morphologies of orthorhombic strontianite SrCO₃ transformed from branch-like to flower-like, and to capsicum-like at last, while the morphologies of BaCO₃ change from fiber-like to branchlike, and to rod-like finally with an increase of the molar ratio HMT/Sr²⁺ and HMT/Ba²⁺ from 0.2 to 10 using ammonium carbonate as CO₂ source. When using diethyl carbonate instead of ammonium carbonate as CO₂ source, SrCO₃ flowers aggregated by rods and BaCO₃ shuttles were formed. The possible formation mechanisms of SrCO₃ and BaCO₃ crystals obtained in different conditions were also discussed.     

Morphological control of calcium oxalate particles in the presence of poly-(styrene-alt-maleic acid)

Calcium oxalate (CaOx) particles exhibiting different shapes and phase structures were fabricated by a simple precipitation reaction of sodium oxalate with calcium chloride in the absence and presence of poly-(styrene-alt-maleic acid) (PSMA) as a crystal modifier at room temperature. The as-obtained products were characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effects of reaction conditions including pH, [Ca²⁺]/[C₂O₄²⁻] ratio and concentration of PSMA and CaC₂O₄ on the crystal forms and morphologies of the as-obtained calcium oxalate were investigated. The results show that various crystal morphologies of calcium oxalate, such as parallelograms, plates, spheres, bipyramids etc. can be obtained depending on the experimental conditions. Higher polymer concentration favors formation of the metastable calcium oxalate dihydrate (COD) crystals. Lower pH is beneficial to the formation of plate-like CaOx crystals. Especially, the monodispersed parallelogram-like CaOx crystals can be produced by PSMA as an additive at pH 2. PSMA may act as a good inhibitor for urolithiasis since it induces the formation of COD and reduces the particle size of CaOx. This research may provide new insight into the morphological control of CaOx particles and the prevention of urolithiasis.     

Calcium Carbonate Scale Formation in Pipes: Effect of Flow Rates,Temperature, and Malic Acid as Additives on the Mass and Morphology of the Scale

It is well recognized that calcium carbonates (CaCO₃) is one of the main components of scale that is commonly encountered in chemical and related industries. The calcium carbonate scale often grows extensively on equipment and parts, causing major operational difficulties. This paper presents experiments on calcium carbonate scale formation and control in a piping system where the scale-forming solution flowed in a laminar manner: 30, 40, and 50 mL/min, respectively. Other parameters evaluated were: solution temperature (25, 30 and 40 °C), and concentrations of malic acid (C₄H₆O₅) added as impurities (3.00 and 5.00 ppm). The scale-forming solution was made by mixing equimolar solutions of CaCl2 and Na2CO3, respectively. The scale formation process was monitored by measuring the conductivity of the solution coming out of the piping system. It was found that in all experiments, conductivity decreased abruptly after a certain induction period, during which time the conductivity remained steady. The induction period varied from 17 min to 34 min, which means that the scale starts forming 17 min to 34 min after the mixing of the solution. Higher flow rates resulted in more calcium carbonate scale mass, which indicate that the fluid flow enhances the scale formation. Similarly, increasing the temperature of the solution (25, 30, and 40 °C) resulted in the increase of the scale mass. Overall, higher malic acid concentrations resulted in longer induction time and less scale mass. Depending on the temperature and the malic acid concentration tested, the reduction in scale mass could be ≥ 200%. This drastic reduction in scale mass suggests that malic acid could be an effective anti-scalant for calcium carbonate scale. SEM imaging and its associated EDS analysis confirmed that the scale formed corresponds to that of calcite (CaCO3). The X-ray diffraction analysis of the scale showed that the scale consisted of crystalline matter which corresponds to the powder diffraction data for calcium carbonate. The addition of malic acid in trace amounts (0.00 to 5.00 ppm) was able to alter the morphology of the scale crystals, indicating the preference adsorption of malic acid on specific crystal surface.     

Shape evolution of SrCO3 particles in the presence of poly-(styrene-alt-maleic acid)

In this paper, strontium carbonate particles with different morphologies were prepared by a simple precipitation reaction of sodium carbonate with strontium nitrate in the absence and presence of poly-(styrene-alt-maleic acid) (PSMA). The as-prepared products were characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effects of the concentration of PSMA on the morphologies and phase structures of strontium carbonate particles were investigated and discussed. The results showed that SrCO₃ particles with various shapes, such as bundles, dumbbells, irregular aggregates and spheres could be obtained by varying the concentration of PSMA. A schematic illustration was proposed to account for the shape evolution of the as-prepared SrCO₃ particles.     

Regulation of Microstructure of Calcium Carbonate Crystals by Egg White Protein

Crystal growth of calcium carbonate in biological simulation was investigated via egg white protein with different volume fractions,during which calcium carbonate was synthesized by calcium chloride an...     

Influence of Calcium Sources on Microbially Induced Calcium Carbonate Precipitation by Bacillus sp. CR2

Stimulation of microbially induced calcium carbonate precipitation (MICCP) is likely to be influenced by calcium sources. In order to study such influences, we performed MICCP using Bacillus sp. CR2 in nutrient broth containing urea, supplemented with different calcium sources (calcium chloride, calcium oxide, calcium acetate and calcium nitrate). The experiment lasted 7 days, during which bacterial growth, urease activity, calcite production and pH were measured. Our results showed that calcium chloride is the better calcium source for MICCP process, since it provides higher urease activity and more calcite production. The influences of calcium sources on MICCP were further studied using Fourier transform-infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. These analyses confirmed that the precipitate formed was CaCO₃ and composed of predominantly calcite crystals with a little amount of aragonite and vaterite crystals. The maximum yield of calcite precipitation was achievable with calcium chloride followed by calcium nitrate as a calcium source. The results of present study may be applicable to media preparation during efficient MICCP process.     

Controlled synthesis of calcium carbonate in a mixed aqueous solution of PSMA and CTAB

A mixed system of poly (styrene-alt-maleic acid) (PSMA) and cetyltrimethylammonium bromide (CTAB) was used as a very effective crystal growth modifier to direct the controlled synthesis of CaCO₃ crystals with various morphologies and polymorphs. The as-prepared products were characterized with scanning electron microscopy and X-ray diffraction. It was found that the concentrations and relative ratios of PSMA and CTAB in the mixed aqueous solution were turned out to be important parameters for the morphology and polymorph of CaCO₃ crystals. Various morphologies of CaCO₃ crystals, such as hollow microsphere, peanut and so on, were produced depending on the concentrations and relative ratios of PSMA and CTAB. Moreover, the formation mechanisms of CaCO₃ crystals with different morphologies were discussed.