Growth and thermal behavior of mixed crystals of calcium cadmium tartrate in silica gels

In this study, calcium cadmium tartrate single crystals were grown in silica gel at ambient temperature. Effects of various parameters like gel pH, gel aging, gel density, and concentration of reactants on the growth of these crystals were studied. Crystals having different morphologies and habits were obtained. Transparent, diamond-like pyramidal-shaped crystals of calcium cadmium tartrate were obtained. Some of the crystals obtained were faint yellowish, with some milky white crystals being attched to them due to fast growth rate; faces are well developed and polished. The grown crystals were characterized by thermoanalytic techniques (TG, DTA, and DTG), and powder X-ray diffraction (XRD). The crystal system is confirmed to be orthorhombic having lattice parameters a = 7.9411 Å, b = 7.0396 Å, and c = 6.7271 Å as determined by powder XRD analysis. TG, DTA, and DTG analyses show a remarkable thermal stability. The results of these observations are described and discussed.     

Imaging of crystal morphology and molecular simulations of surface energies in pentacene thin films

We have investigated the crystal growth of the organic semiconductor pentacene by complementing molecular simulations of surface energies with experimental images of pentacene films. Pentacene thin films having variations in thickness and grain size were produced by vacuum sublimation. Large (approximately 20 microm) faceted crystals grew on top of the underlying polycrystalline thin film. The films were characterized using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Single crystals most commonly grew in a truncated diamond shape with the largest crystal face, (001), growing parallel to the substrate. Crystal morphologies and surface energies were calculated using force field-based molecular simulations. The (001) surface was found to have the lowest energy, at 76 mJ/m(2), which was consistent with experimental observations of crystal face size. It was demonstrated that the morphology of the large faceted crystals approached the equilibrium growth shape of pentacene. From contact angle measurements, the critical surface tension of textured pentacene thin films in air was determined to be 34 mJ/m(2).     

Stereospecific morphogenesis of aspartic acid helical crystals through molecular recognition

Helical morphologies were generated from aspartic acid (Asp) crystals in agar gel matrix. The morphogenesis stereospecifically proceeded in the helical crystal growth: D- and L-Asp provided left- and right-handed structures, respectively. The backbone of the helical morphology was twisted twins of tilted unit crystals, as was the case with inorganic helical crystals. The molecular recognition between the Asp crystals and agar matrix molecules resulted in the stereospecific morphogenesis. The chirality in Asp and agar molecules, the enantiomorph of unit crystals, and the resultant macroscopic helix were exquisitely associated with each other.     

Effect of the Microstructural Morphology on UO2 Powders

Several UO₂ powders with different morphologies were synthetized and characterized. Three different morphologies were synthesized thanks to sol gel process (big heap of about 200μm wide consisting of sintered crystallites) on the one hand, and to oxalic precipitations (one square platelet morphology and one hexagonal stick morphology) on the other hand. Significant differences in dissolution kinetics were observed. Therefore, the morphology of the powders was found to be a key parameter that has to be considered in studies of UO₂ dissolution kinetics. The second part of the study consists in dissolving in nitric acid in in the same operating conditions three UO₂ powders having different crystallites sizes. It was shown that dissolution kinetics is dependent on the morphology but also on the powder stoichiometry.     

Single-chain single crystals

Single-chain single crystals of isotactic polystyrene and poly(ethylene oxide) were studied by using transmission electron microscopy, high resolution electron microscopy, electron diffraction. Single-chain single crystals were prepared by spreading a dilute solution of polymers on a water surface and collecting the resulting single-chain particles on copper grids, followed by isothermal crystallization. A statistical analysis of the sizes of single-chain crystals was found to match with the known molecular weight distribution of original sample, indicating the particles to be composed of single chain. Observation of the morphology and electron diffraction gave evidence of the single crystal nature. Regular-shaped single-chain crystals were obtained after isothermal crystallization for a longer time. By close observation, several types of morphologies were found for single-chain crystals of isotactic polystyrene and poly(ethylene oxide); in addition to the conventional morphologies observed for multi-chain crystals, new morphologies were observed in both cases. The morphologies of poly(ethylene oxide) were explained according to the crystal structure and twin modes. Tent-like single-chain crystals were often observed. Because of the small size of the crystals, they can avoid collapse on the substrate. The crystalline c-axis of single-chain crystals were found to orient preferably in the direction normal to the substrate. The investigation of electron diffraction and high resolution electron microscopy revealed that the structure of the single-chain crystals of isotactic polystyrene is the same as for multi-chain crystals. A reasonable explanation is given for the unusual resistance to electron irradiation and the missing of lower-index reflections. Regular periodic stripes were found on the top surface of single-chain crystal of isotactic polystyrene with an average periodic length in accordance with (220) spacing. In addition, a statistical thermodynamics theory was developed for single-chain crystal. It is found that the equilibrium dimensions are related to molecular weight and annealing temperature, while the equilibrium melting temperature depends on molecular weight.     

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。     

An organic hydrogel as a matrix for the growth of calcite crystals

The growth of calcite in an aqueous gel of was studied and the appearance of the crystals was found to change over time. Crystals removed from the gel at progressively longer times showed severely affected surfaces resulting from dissolution. If crystals were removed from the gel after 3.5 hours, at which point there were no etch pits, and then placed in either buffer or pure water, etch pits, similar to those observed on crystals that are left in the gel, were observed. Control calcite crystals exposed to similar conditions (water or buffer) show no significant dissolution after equivalent times. A probable cause of the altered dissolution is the non-specific occlusion of gelator aggregates at sites of imperfection. The gel appears to provide a microenvironment in which the molecules that form the matrix also participate in the crystallization. This system allows the study of the unique properties of a gel for influencing the nucleation and growth of inorganic crystals, some of which may be important for better understanding biomineralization.     

FTIR and thermal studies of gel-grown,lead–cadmium-mixed levo tartrate crystals

Metal tartrate compounds find various applications. Lead tartrate is added in gasoline to prevent knocking in motors, and cadmium tartrate crystals possess piezoelectric nature. In the present study, lead–cadmium-mixed levo tartrate crystals were grown using silica hydro gel as growth medium. Long and dendrite-type white crystals were obtained. The crystals were characterized by EDAX, powder XRD, FTIR spectroscopy, TG, DTA, and DSC. The composition of the crystals was determined by EDAX. The FTIR spectra revealed the presence of water molecules, O–H, C–H, C–O, C–C, and C=O functional groups. TG curves suggested that the crystals were thermally unstable and decomposed into oxide through three stages. DTA curves showed endothermic and exothermic reactions.     

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.     

Carbon Nanotubes Modified Graphite Electrodes for Monitoring of Biointeraction Between 6‐Thioguanine and DNA

In this present study, single‐walled carbon nanotubes (SWCNT) modified disposable pencil graphite electrodes (SWCNT‐PGEs) were developed for the electrochemical monitoring of anticancer drug, and its interaction with double stranded DNA (dsDNA). Under this aim, SWCNT‐PGEs were applied for the first time in the literature to analyse of 6‐Thioguanine (6‐TG), and also to investigate its interaction with DNA by voltammetric and impedimetric methods. The surface morphologies of PGE and SWCNT‐PGE were explored using scanning electron microscopy (SEM) and electrochemical characterization of unmodified/modified electrodes was performed by cyclic voltammetry (CV). Experimental parameters; such as, the concentration of 6‐TG and its interaction time with dsDNA were optimized by using differential pulse voltammetry (DPV). Additionally, the interaction of 6‐TG with dsDNA was studied in case of different interaction times by electrochemical impedance spectroscopy (EIS) in contrast to voltammetric results. The detection limit of 6‐TG was found to be 0.25 μM by SWCNT‐PGE.     

Non-isothermal decomposition of Indian limestone of marine origin

Single crystals of pure and neodymium doped calcium hydrogen phosphate were grown in sodium meta silicate gels, by the single diffusion gel method. Platelet and needle shaped crystals were obtained. The grown crystals were characterized by different techniques. The thermal behaviour of the crystals was studied using the thermo analytical techniques, which included TG, DTA, DTG and DSC. These studies reveal that the decomposition of the material occurs in one or more stages. The enthalpy value is also calculated.     

Effects of Hydroxypropylmethylcellulose macromolecules used as organic template on the crystallization of CaCO<Subscript>3</Subscript>

Hydroxypropylmethylcellulose (HPMC) was used as an organic template to synthesize calcium carbonate. Crystals were synthesized in HPMC solution and HPMC hydrogel, respectively. For the mineralization system of HPMC solution, the effects of adding HPMC and rotating the reaction system on the crystal polymorph and morphology of CaCO₃ were investigated by X-ray diffractometer (XRD) and scanning electron microscope (SEM). The results showed that the presence of HPMC induced the formation of aragonite. And its content became higher when the concentration of solution increased or when rotating the system with the presence of HPMC. Moreover, it can be seen from SEM that bundle-like CaCO₃ appeared and became more with the increase of concentration. The structure and shape of the crystal had close relationship with the condition of mineralization. On the other hand, for the first time, CaCO₃ was synthesized in HPMC gel, SEM results indicated that a special structure, a long bar with some slight slots at intervals on the surface, of the crystals which may be caused by the network structure of the gel was found. Thermogravimetry (TG) results showed that CaCO₃ crystal products contained some HPMC. Further research on how the gel network modulates the growth of crystals is left to be done in the future.     

Simultaneous IR/TG study of calcium carbonate in two aged cement pastes

Two aged cement pastes (7 years) were studied for H₂O and CO₂ evolution, the combined amounts of which were measured by TG and identified by thermo-IR analysis. This indicated the presence of three forms of carbonates, which decomposed at different temperatures. The displacement with time of the evaporation of sorbed water to higher temperatures (500–700°C, TG, MS) shows the possibility of its incorporation into carbonate hydrates and/or hydroxy hydrates, postulated previously. The decomposition of all the hydration products needed a thermal energy increasing with ageing (increased temperature measured by TG). The carbonation process proceeded for 7 years in the weaker paste, whereas it terminated before 5 years in the stronger one. The CSH water content did not change with ageing, whereas that of portlandite was lowered, which though did not account for the increase in carbonate content (TG). Possibly some Ca²⁺ from the CSH gel was involved in this process. In the stronger paste the growth with time of organic matter was found (IR, TG/DTG).     

柠檬酸溶胶凝胶法制备LiCoO_2电极材料及其表征

目前研究较多的锂离子电池正极材料主要有LiCoO2、LiNiO2和LiMn2O4犤1犦,虽然LiCoO2的成本相对较高,但LiCoO2具有最为优良的电化学性能,如高且平稳的充放电平台、高比容量以及良好的循环性能犤2犦,是目前应用最广泛的商品化电极材料。LiCoO2材料主要采用高温固相法犤3～5犦制备,该方法工艺简单,容易实现大规模生产,但缺点是需要较高的焙烧温度和较长的焙烧时间,且反应原料混合均匀程度有限,易导致非化学计量、非均相以及不规则的颗粒形貌等,因此材料的比容量、循环寿命等电化学性能以及反应的可控性还不甚理想。研究表明犤6犦电极材…     

Shaping Microcrystals of Metal–Organic Frameworks by Reaction–Diffusion

When components of a metal–organic framework (MOF) and a crystal growth modulator diffuse through a gel medium, they can form arrays of regularly-spaced precipitation bands containing MOF crystals of different morphologies. With time, slow variations in the local concentrations of the growth modulator cause the crystals to change their shapes, ultimately resulting in unusual concave microcrystallites not available via solution-based methods. The reaction–diffusion and periodic precipitation phenomena 1) extend to various types of MOFs and also MOPs (metal–organic polyhedra), and 2) can be multiplexed to realize within one gel multiple growth conditions, in effect leading to various crystalline phases or polycrystalline formations.     

Shaping Microcrystals of Metal–Organic Frameworks by Reaction–Diffusion

When components of a metal–organic framework (MOF) and a crystal growth modulator diffuse through a gel medium, they can form arrays of regularly‐spaced precipitation bands containing MOF crystals of different morphologies. With time, slow variations in the local concentrations of the growth modulator cause the crystals to change their shapes, ultimately resulting in unusual concave microcrystallites not available via solution‐based methods. The reaction–diffusion and periodic precipitation phenomena 1) extend to various types of MOFs and also MOPs (metal–organic polyhedra), and 2) can be multiplexed to realize within one gel multiple growth conditions, in effect leading to various crystalline phases or polycrystalline formations.     

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.     

Antimony(III)-doped PbWO4 crystals with enhanced photoluminescence via a shape-controlled sonochemical route

Sb(III)-doped lead tungstate single crystals with controlled shapes and enhanced green emission have been synthesized via a facile, Pluronic P123 (EO(20)PO(70)EO(20))-assisted, sonochemical method. The surfactant Pluronic P123 was found to play a crucial role in the morphology control of the final products. The growth process was investigated by carefully following time-dependent experiments, and the oriented attachment process accompanying Ostwald ripening was proposed for the possible formation mechanism. The optical properties, such as the Raman spectra and PL spectra, of doped PbWO(4) were studied. Room-temperature photoluminescence of doped PbWO(4) samples with different morphologies at desired Sb doping concentrations showed greatly enhanced luminescence intensity compared to the undoped PbWO(4).     

Study of Recrystallization Kinetics of AgBr Microcrystals in Water–Gelatin Gel

Recrystallization kinetics (Ostwald ripening) of silver bromide microcrystals in gelatin gel was studied. The study was made on model mixtures containing small silver bromide particles (about 60 nm) and larger microcrystals of different sizes (100–400 nm) and habits (cubic and octahedral). Variations in the average size of large crystals in the system were controlled by spectral turbidimetry. The growth rate of the large crystals was found to be directly proportional to the total solubility of a substance constituting the dispersed phase, as well as to difference in sizes of large and small particles. The kinetics of large crystal growth was also shown significantly to depend on the average distance between particles of the system. The theoretical model describing mass transfer during the Ostwald ripening in the closed disperse system was proposed, providing that interacting particles are immovable.     

FTIR and thermal studies on gel grown neodymium tartrate crystals

The growth of neodymium tartrate crystals was achieved in silica gel by single diffusion method. Optimum conditions were established for the growth of good quality crystals. Fourier transform infrared (FT-IR) spectroscopic study indicates the presence of water molecules and tartrate ligands and suggests that tartrate ions are doubly ionised. The thermal behaviour of the material was studied using thermogravimetry (TG), differential thermal analysis (DTA), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). Thermogravimetric analysis support the suggested chemical formula of the grown crystal to be Nd₂(C₄H₄O₆)₃·7H₂O, and the presence of seven water molecules as water of hydration. It is shown that the material is thermally stable up 45 °C beyond which it decomposes through many stages till the formation of neodymium oxide (Nd₂O₃) at 995 °C. The decomposition pattern is reported to be typical of a hydrated metal tartrate.