Ageing of spherulites of an industrial relevant aromatic amine derivative

Polycrystalline spherulites of an aromatic amine derivative have been precipitated in a batch process by pH‐shift with hydrochloric acid from stirred aqueous solutions. The time dependent behaviour of the spherulites has been studied during crystallization in the temperature range from 5 °C to 60 °C. Cake resistance values have been obtained from batch filtration tests performed at 2 bar pressure difference at different stages of the crystallization process. The FBRM mean chord length of the crystals decreases with time as a result of crystal ageing into plate‐like crystals. The rate of the ageing process increases with temperature. XRD‐studies show no significant differences in the crystal structure during the ageing process, and the mechanism of the transformation was not established. The filterability of aromatic amine crystals deteriorates as the crystallization progresses. The decrease in the filterability is attributed to the appearance of small plate‐like crystals and a change in the interaction between the crystal surface and the solution, during the ageing of the particles. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of citric acid on calcium sulfate dihydrate crystallization in aqueous media

The crystallization of Calcium sulfate dihydrate produced by the reaction between pure Ca(OH)₂ suspension and H₂SO₄ solution was investigated at different pH values, temperatures and citric acid concentrations. Crystal size distributions, filtration rates and zeta potentials of gypsum were determined as a function of citric acid concentrations at pH 3.5 and 65°C. The influence of citric acid on the morphology of gypsum was also investigated and discussed. The average particle size of gypsum was reached to maximum in the presence of approximately 2500 ppm citric acid concentration, where the minimum cake resistance and maximum filtration rate were obtained. In the presence of citric acid, various crystal morphologies such as tabular, plate‐like, double‐taper leaf‐like and flower‐like, etc., were obtained. The change of morphology is related to the preferential adsorption of citric acid on different crystallographic faces. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Centrifugal separation of primary silicon crystal in solvent refining of silicon using Al‐30% Si alloy

This study describes the formation of a primary silicon network during separation of an Al‐30% Si melt and the process conditions to make bigger primary silicon crystals. As the crucible rotates in the centrifugal separation, the unfrozen aluminum‐rich phase and small silicon particles are pushed outside through the openings in the silicon network. As a result, primary silicon crystals are separated in the form of a foam after centrifugation. The recovery of the silicon ranged from 13 to 18% depending on the location in the crucible. The size of the primary silicon achieved by changing the cooling rate and quenching temperature during solidification is also measured using a quenching furnace. Primary silicon particles exhibit a coarse, plate‐like morphology, although small star‐like silicon particles are also found in the aluminum‐rich matrix. The fraction of plate silicon decreases, while the fraction of small globular silicon increases with an increasing cooling rate. The thickness of the primary silicon plate also decreases with an increasing cooling rate in the samples quenched at various temperatures during solidification.     

Growth and Kinetic Studies of Spherulitic Gadolinium Tartrate Crystals from Silica Gel

Spherulitic growth of gadolinium tartrate dihydrate crystals by controlled diffusion in silica gel is reported. The influence of growth parameters e.g., reactant concentration, gel pH and gel ageing, on the size, quality and nucleation density of the spherulites has been studied. It is observed that under varying experimental conditions involving change in reactant concentrations, gel pH and gel ageing, the material crystallizes in the form of spherulites. The results of growth kinetics are discussed. Scanning electron microscopy confirms spherulites to be aggregates of single crystallites, with each micro-sized crystal exhibiting a cuboid morphology. Surface structures exhibited by the micro-sized crystals indicate their growth by two-dimensional nucleation mechanism.     

Shape diversity in particles obtained by low temperature pyrolysis of ferrocene

Synthesis experiments, made in a hermetically closed steel container through pyrolytical decomposition of various mixtures like ferrocene and xylene; ferrocene and water; ferrocene, xylene and water in different ratios have resulted in emergence of different in shape particles. The necessary for the realization of each experiment temperature increases linearly with 20 K/min up to the needed temperature and decreases mostly with no delay with a cooling rate of 30 K/min down to room temperature. The obtained particles are shaped as spheres, entirely or partially finished octahedrons or resemble stars. The spheres are perfect in shape and consist of pure incompletely graphitisized carbon. The octahedron and star‐like shaped particles, synthesized in the presence of ferrocene as precursor, have magnetite nuclei and carbon coating. Particle morphology has been examined by Scanning (SEM) and Transmission Electron Microscopy (TEM) and their chemical composition and crystal structure by the means of X‐ray diffraction (XRD), Mössbauer spectroscopy and Electron Probe X‐ray Micro Analysis and Energy Dispersive X‐ray Spectrometry (EDS). Based on the results obtained it has been concluded that the synthesized particle morphology depends on the simultaneous proceeding magnetite crystal growing and crystal coating with partially graphitisized carbon deposit. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Estimation of shear-banding resistance in metallic glass containing nano-crystalline particles

Bulk metallic glasses (BMGs) have a variety of excellent properties compared with the majority of conventional crystalline alloys. However, they exhibit limited global plasticity at room temperature because of shear banding. Several methods have been proposed to improve the limited ductility of BMG; one method is the homogeneous distribution of crystalline particles. However, our understanding of the interaction between the crystalline particles and shear bands (SB) is not sufficient. Here, we performed molecular dynamics (MD) simulations of mode II deformation of a notched BMG plate and BMG plates containing one nano-crystalline particle ahead of the notch bottom. To compare the effect of crystalline particle size on the resistance to SB propagation, we used the J-integral. By comparing J-R curves and the deformation behavior of the BMG plates with and without nano-crystalline particles, we found that the resistance to shear banding is efficiently improved by introducing crystalline particles with sufficient size, compared to the SB width.     

溶胶-凝胶法制备La2CuO4纳米晶生长动力学研究

以硝酸镧和硝酸铜为起始原料,柠檬酸为络合剂,乙二醇为交联剂,采用溶胶-凝胶法制备了La2CuO4纳米晶.通过XRD和FESEM对La2CuO4粉体进行了测试和表征,研究了不同柠檬酸配比对La2CuO4相组成、显微结构以及晶体生长活化能的影响.结果表明:当柠檬酸与金属阳离子总和(La3++Cu2+)的物质的量比为1∶1,600℃煅烧保温2h后,可获得单一正交晶型的La2CuO4,颗粒形貌为球状结构,平均尺寸为65 nm;在制备过程中提高柠檬酸的加入量,能够降低La2CuO4晶体的生长活化能,当物质的量比由0.5∶1增加至1∶1时,生长活化能由67.3 kJ/mol降低到50.5 kJ/mol.     

Preparation of low-density xerogels from mixtures of TEOS with substituted alkoxysilanes. II. Viscosity study of the sol–gel transition

Mixtures of TEOS with substituted methoxysilanes generate low-density xerogels due to a nucleation mechanism involving the substituted alkoxysilane. The sol–gel transition of these mixtures was followed by rheological characterisation. The transition from sol to gel takes place in a few minutes at ambient temperature. For the series exhibiting nucleation by the additive, the gel time goes through a slight minimum when the ratio of additive/main reagent increases. The elastic modulus increases with increasing ratio of additive/main reagent as the particle size decreases because of the nucleation mechanism by the additive. Samples with smaller particles exhibit the highest modulus for equal silica concentrations.     

Synthesis of Submicron Silicalite‐1 Crystals from Clear Solutions

Discrete and monodisperse submicron crystals of silicalite‐1 with a mean size of 0.3 μ m were synthesized from clear crystallization solutions. The effects of silica content, alkalinity of batch and the nature of silica source on the product yield, crystal morphology and particle size distribution were investigated. The crystal shape was sphere‐like or hexagonal twinned disks when silicic acid was the silica source. Change of silica source to sodium silicate solution leads to the formation of rounded‐edged‐hexahedron crystals. Silica content of batch does not influence crystal morphology. Alkalinity of clear crystallization solution has a strong effect both on the particle size distribution and yield of product. Increase of alkalinity caused bimodal particle size distribution and decrease of yield.     

Crystallization of micro particles of sulindac using rapid expansion of supercritical solution

In pharmaceutical industry, many drugs exhibit poor solubility in biological fluid. Solubility of drugs affects on the rate of dissolution and bioavailability in biological fluids. The bioavailability of drugs can be enhanced by decreasing the drug particle size. In this study, sulindac was micronized via rapid expansion of supercritical solution (RESS) where CO2 was used as a solvent. The experiments were conducted to investigate the effect of the extraction pressure and temperature (140–230 bar and 40–60 °C), collection distance (1–10 cm), effective nozzle diameter (450–1700 μm) and nozzle length (2–15 mm) on the size and morphology of the sulindac particles. The size and morphology of the precipitated particles were monitored by scanning electron microscopy (SEM). The particle size of intact sulindac particles was about 33.03 μm, while the average particle size of the micronized sulindac particles was between 0.76 and 8.02 μm based on different experimental conditions. Additionally, the different morphology of the micronized particles was observed like needle, rectangular, quasi spherical and irregular form while the morphology of the intact particles of sulindac was rectangular and irregular.     

Synthesis,structural and optical properties of well dispersed anatase TiO2 nanoparticles by non‐hydrothermal method

The formation of nanocrystalline TiO₂ particles has been investigated via a surfactant‐free synthetic non‐hydrothermal method. Titanium isopropoxide and toluene were used as the starting materials. At a low temperature of 250 °C for 6 h, the reaction mixture turned in to a white precipitate (TiO₂) as a result of the thermal decomposition of metal alkoxide. The obtained product was found to crystallize purely in the anatase phase with well defined morphology. The powder XRD study confirms that the average size of the particle is close to ∼15 nm. The TEM analysis indicates the sizes of the primary and secondary particles in the range between 8‐10 nm and 15‐20 nm respectively. The quantum size confinement of the crystallites is evident from the blue shift of the absorption edge in the UV‐Visible absorption spectrum. The luminescence property of the TiO₂ nanoparticles studied by the emission spectrum confirms the presence of defect levels caused by the oxygen vacancies. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Size and morphology controlled synthesis of barium sulfate

In this work submicron barium sulfate (BaSO₄) particles were synthesized successfully by chemical precipitation technique. We focused on the effects of pH and additives on the size and morphology of BaSO₄ crystals. Polyacrylic acid, polyvinyl sulfonic acid and ethylenediaminetetraacetic acid were used as crystal growth modifiers. BaSO₄ crystals were characterized using scanning electron microscopy, X‐ray diffraction, and Fourier transform infrared resonance techniques. The results show that the submicron BaSO₄ particles have been synthesized successfully and the particle size of the barium sulfate was effectively controlled under the experimental conditions. Experimental studies revealed that the additive concentration and pH had great effect on the morphology and size of barium sulfate.     

Light Scattering and Contrast in Thermally Addressed Liquid Crystal Displays

The effects of structural order on the light scattering characteristics of liquid crystal display cells containing smetic p-n-octyl-p′-cyanobiphenyl have been investigated. The scattering characteristics of different structures in the cell due to surface treatments are qualitatively analyzed for their effects on the contrast ratio when used in the thermally addressed liquid crystal display (TALC). Of the four structures investigated, i.e., homeotropic, fan-like, uniaxial rods and spherulites, the spherulitic structure has been found to exhibit the scattering profile best suited for high contrast because of the near-zero scattering near the incident beam. Based on the light scattering theory for spherulites, optimization of structural parameters such as size and order of spherulites, and device design such as collecting angle of projection lens for maximum display contrast has been predicted. Methods to improve contrast have also been discussed.     

Microwave irradiation solvothermal technique: an optimized protocol for size‐control synthesis of Ru nanoparticles

Ruthenium (III) chloride salt and Poly (N‐vinyl‐2‐pyrrolidone) (PVP as a capping agent) was dissolved in ethylene glycol, which played a dual role for synthesis, as solvent and also as reducing agent. Microwave (MW) irradiation was applied to the solvent which provided controllable thermal activation for synthesis of ruthenium nanoparticles and also restricted the agglomeration of particles in presence of excess amount of solvent, which was recovered by distillation after completion of reaction. Synthesized particle was found to be in the range of 2–20 nm with narrow size distribution and average particle size was around 14 nm. Particle size and size distribution were studied by varying different parameters e.g. reaction temperature, time, PVP/RuCl₃ molar ratio and irradiation power and was characterized by Transmission electron microscopy (TEM). Mathematical model has been developed using matlab software to obtain the particle size as a function of microwave power.     

A novel thermolysis method of colloidal protein precursors to prepare hydroxyapatite nanocrystals

A novel thermolysis method of colloidal protein precursors is introduced to prepare hydroxyapatite (HAP) nanocrystals. The colloidal protein precursors are sonochemically synthesized from saturated Ca(OH)₂ aqueous solution, Ca(H₂PO₄)₂ aqueous solution and bovine serum albumin (BSA) molecules. The colloidal protein precursors are amorphous and composed of 15‐90 nm near spherical calcium phosphate nanoparticles and BSA molecules. The particle size analysis shows the volume particle size distribution is from 9.0 nm to 222.6 nm and the volume‐averaged particle size is 45.8 nm. During the calcination procedure BSA molecules are burningly removed and the HAP nanocrystals can be obtained at 500 °C. The effects of BSA concentration on the properties of samples are discussed. Results show that BSA combustion can promote the transformation of crystalline HAP from amorphous material. Moreover, the increase of BSA concentration reduces the crystalline sizes of HAP crystals and the crystallinity of product. With BSA concentration of 5 g/L, the obtained HAP nanocrystals are mainly 25∼100 nm similar spherical nanoparticles besides some 40∼70 nm×75∼150 nm short rod‐like crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A study of the growth process of Co3O4 microcrystals synthesized via a hydrothermal method

Pure Co₃O₄ microcrystals were prepared by a hydrothermal method from Co(NO₃)₂·6H₂O and urea solution, and the effect of thermal treatment time on the growth of Co₃O₄ microcrystals was studied by X‐ray diffraction (XRD), scanning electron microscopy (SEM), Raman and UV‐Vis absorption spectra. The results show that with the thermal treatment time increases from 2 h to 12 h, the shape of as‐prepared Co₃O₄ microcrystals changes from the hedgehog sphere‐like to the as‐cubic one that were stacked by lots of lamella, and finally cubes, and then longer time treatment will only lead to the size growth and agglomeration of particles. In conclusion, the cubic Co₃O₄ microcrystals of uniform size (∼6 μm) are synthesized via a 12‐h thermal treatment. Moreover, the synthesis mechanism has been studied.     

Application of a conproportionation reaction to a synthesis of shape-controlled gold nanoparticles

Synthesis of gold nanoparticles with multiple shapes by a modified seeding growth method is reported. The optical extinction spectra of a mixture of the seed and growth solutions indicate that the seed particle size decreases during stirring the mixture by a conproportionation reaction of Au metal with Au(III) ions. This conproportionation reaction is used to investigate the effects of variation in seed particle size on the resultant gold nanoparticle shape. When single crystalline and multiply twinned particles are used as the seed particles, they grow into gold nanorods and nanobipyramids, respectively. By letting the seed particles experience the conproportionation reaction before the particle growth to decrease the size, the surface of resultant nanoparticles roughens. Increasing the conproportionation reaction time up to 5 min, multi-branched gold nanoparticles with many lattice defects grow from both of the seed particles. This indicates that the conproportionation reaction is useful to generate lattice defects during the particle growth, which lead to the formation of gold nanoparticles with complex shapes.     

Nucleation kinetics of the formation of low dimensional calcium sulfate dihydrate crystals in isopropyl alcohol medium

Calcium sulfate dihydrate, constituted as uniform crystals of low dimensions, is a potential biomaterial for clinical applications like bone graft substitution and drug delivery. In this work, isopropyl alcohol has been used as a solvent to obtain low dimensional calcium sulfate dihydrate crystals from calcium nitrate ‐ sulfuric acid system. Reactants in 0.5 molar concentration at ambient conditions generated uniform rod‐shaped crystals of length 3–5 µm. Analysis using X‐ray Diffractometry and Fourier Transform Infrared Spectrometry showed the material to be well crystallized, phase‐pure calcium sulfate dihydrate. The nucleation kinetics has been studied by observing the induction time of phase formation in solutions of millimolar concentrations through turbidimetry at 300 K. The data have been analysed using classical nucleation theory to deduce parameters like interfacial tension (or surface free energy), nucleation rate and critical radius. The surface free energy obtained (5.6 mJ/m²) is comparatively lower than that reported for aqueous precipitation, which could be attributed to the presence of isopropyl alcohol. On escalating the supersaturation ratio, the nucleation rate drastically increased and the critical radius decreased exponentially. Particles formed at supersaturation 1.39 showed a monomodal distribution centered at 8.2 nm in Dynamic Light Scattering analysis. Comparable particle sizes were obtained in Transmission Electron Microscopy.     

Crystallization of silicalite‐1 from clear synthesis solutions: Effect of template concentration on crystallization rate and crystal size

Synthesis of silicalite‐1 powders and membranes from initially clear solutions with different tetrapropylammonium hydroxide or bromide concentrations was studied. While tetrapropylammonium bromide acts only as template, tetrapropylammonium hydroxide provides both the template and hydroxyl ions to the synthesis medium. The effects of template and hydroxyl ion concentration on the product yield, crystallization rate and crystal size were investigated. Pure and highly crystalline silicalite‐1 was obtained with all compositions. The nucleation time decreases from 100 h to 20 h and the crystal size decreases from 3.5 μm to 0.35 μm as the template amount x is increased from 5 to 30 moles at a batch composition of 80SiO₂.xTPAOH.1500H₂O at 95 °C. Yield of silicalite‐1 passes through a maximum at intermediate TPA concentration. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of Li2CO3 by gas‐liquid reactive crystallization of LiOH and CO2

A spinning disk reactor (SDR) was used in this research to prepare Li₂CO₃ by gas‐liquid reactive crystallization of LiOH and CO₂. It was found that the end pH value of the above reaction should be controlled within the range of 9.0‐9.5 to obtain a high yield of Li₂CO₃. The effects of operational parameters (including the temperature, the concentration of LiOH solution, the rotation rate of the spinning disk, the circulation rate of LiOH slurry, the flow rate of CO₂ and the ultrasound field) on the particle size and the yielding rate were investigated by an orthogonal experiment. The results show the significant factors influencing the particle size are the ultrasound field, the temperature and the flow rate of CO₂. As for the yielding rate, the temperature, the concentration of LiOH solution and the flow rate of CO₂ exert obvious impacts, while the effects of ultrasound field and the rotation rate of the spinning disk are limited. The SEM images show the Li₂CO₃products are flower‐like particles, which are composed of plate‐like primary crystals. The size analysis shows the volume mean particle size of the Li₂CO₃products ranges 37‐90 μm depending on the various experimental conditions. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)