On-line concentration measurement for anti-solvent crystallization of β-artemether using UV–vis fiber spectroscopy

Concentration monitoring is essential for quality control of crystallizations. This work establishes the technical feasibility of Ultraviolet (UV) fiber spectroscopy for on-line concentration measurement of anti-solvent crystallization of β-artemether, where ethanol was selected as solvent and water was used as anti-solvent. The orthogonal signal correction (OSC) algorithm was selected to preprocess the UV spectra, and the results showed that the wavelength shift of UV maximum absorbance of β-artemether in ethanol+water solvent mixtures can be effectively eliminated by OSC algorithm. Then models for prediction of β-artemether concentration based on Lambert–Beer law were developed, and the models were verified by comparison between the training set and the validation set, as well as its directly application to the anti-solvent crystallization process of β-artemether. The results show that the model is suitable for on-line concentration measurement of anti-solvent crystallization of β-artemether, with reasonable accuracy and precision.     

Influence of Bi2O3 content on the crystallization behavior of TeO2–Bi2O3–ZnO glass system

Glass ceramic materials with composition 75TeO₂–xBi₂O₃–(25-x)ZnO (x = 13, 12, 11) possessing transparency in the near- and mid-infrared (MIR) regions were studied in this paper. It was found that as the Bi₂O₃ content increased in the glass composition, the observed crystallization tendency is enhanced, and high crystal concentrations were obtained for the glasses with high Bi₂O₃ content while maintaining transparency in the MIR region. Crystal size in the glass ceramic was reduced by adjusting the heat treatment conditions; the smallest average size obtained in this study is 700 nm. Bi_0.864Te_0.136O_1.568 was identified using X-ray Diffraction (XRD) and found to be the only crystal phase developed in the glass ceramics when the treatment temperature was fixed at 335 °C. The morphology of the crystals was studied using Scanning Electron Microscopy (SEM), and crystals were found to be polyhedral structures with uniform sizes and a narrow size distribution for a fixed heat treatment regime. Infrared absorption spectra of the resulting glass ceramics were studied. The glass ceramic retained transparency in the infrared region when the crystals inside were smaller than 1 μm, with an absorption coefficient less than 0.5/cm in the infrared region from 1.25 to 2.5 μm. The mechanical properties were also improved after crystallization; the Vickers Hardness value of the glass ceramic increased by 10% relative to the base glass.     

Determination of metastable zone width for combined anti-solvent/cooling crystallization

The metastable zone width (MSZW), induction time and primary nucleation kinetics have been measured and estimated for simultaneous anti-solvent and cooling crystallization of paracetamol in iso-propanol/water solution. ATR-FTIR spectroscopy and laser back-scattering are used to measure the solute concentration and primary nucleation event, respectively. Response surface analysis was applied to find the contribution of the crystallization mechanism on the MSZW and obtain a statistical model for quick estimation of the MSZW. Two theoretical approaches for the estimation of nucleation rate kinetic parameters from experimental data are presented. The methods are obtained by modifying the classical Nyvlt's correlation for simultaneous cooling/anti-solvent crystallizations. The nucleation order n for primary nucleation was deduced from the slope of a linear plot of log(MSZW) vs. log(cooling and anti-solvent rates). The induction time was also estimated by changing the classical methods for combined cooling and anti-solvent crystallization.     

Influence of solvent and crystallization method on the crystal habit of metronidazole

In the present study, metronidazole was crystallized in several solvents, according to both the “cooling crystallization” and the “crystallization by non‐solvent addition”. Particle properties, such as crystal habit, elongation ratio, and mean particle size, were determined by SEM analysis. Structural changes and development of polymorphic forms were excluded by both Differential Scanning Calorimetry (DSC) and X‐Ray Powder Diffractometry (XRPD). Crystal habit (and thus elongation ratio) was typically influenced by both the solvent polarity index and the crystallization method: solvents with higher polarity index tended to promote acicular or stick‐shaped crystals with a high elongation ratio, while isodimensional crystals were promoted by decreasing the polarity index, as was particle aggregation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation, characterization and non-linear optical properties of pristine m-nitroaniline (m-NA) and its recycled polystyrene (Re-PS) coated single crystals

Meta-nitroaniline (m-NA) is one of the organic single crystals extensively studied due to its high non-linear effect. m-NA is also known to exhibit comparable or even better non-linear optical (NLO) properties than known inorganic materials. In this paper, we report development of m-NA single crystals by solution growth technique using different solvent systems. The size of the single crystal varies depending on solvent. The highest average crystal size acquired was 10 mm×5 mm×5 mm using methyl ethyl ketone and acetone as solvent. These single crystals were characterized using various physico-chemical techniques such as XRD and scanning electron microscopy (SEM). The developed crystals were subsequently coated with recycled polystyrene (Re-PS) (1, 2, 5 and 10 wt% concentrations) to study the effect of polymer coating on the second harmonic generation (SHG) properties of the single crystals. The purpose of polymer coating on m-NA single crystal is to improve surface morphology of crystal (i.e. it makes surface smooth) and to enhance power handling capacity for pulse laser of a crystal which, in turn, improves the SHG intensity. The optimum percentage of coating was determined for the m-NA single crystals obtained from different solvent systems. Furthermore, the polymer coating also plays key role in preventing the degradation of the m-NA crystal (well-known as highly sublime material) and ultimately increasing the shelf life of the crystal for its device application.     

微波辅助水热合成条件对直接合成纳米HZSM-5晶体性质的影响

利用微波辅助水热合成法直接制备了纳米HZSM-5晶体.采用XRD、FT-IR、SEM、BET和NH3-TPD等手段对合成样品进行了分析表征,研究了晶化温度和时间对合成产物晶体性质的影响.结果表明,晶化温度和时间对微波辅助水热直接合成产物微观形貌、晶粒尺寸和分散度影响明显.较低的晶化温度和较短的晶化时间均难以形成形貌规则的HZSM-5晶体.随着晶化温度的升高,合成样品逐渐变为球形晶粒、晶粒尺寸逐渐增大、分散度逐渐提高,继续提高晶化温度达180 ℃时,晶粒长大使比表面积稍有降低;随着晶化时间的延长,样品的微孔和介孔增多,比表面积和孔容逐渐增大,继续延长晶化时间,晶体内微孔可能的收缩和晶粒的长大使得样品孔容和比表面积减小.160 ℃和1.5 h条件下制备的HZSM-5分子筛晶体形貌呈球形,晶粒尺寸约为60 nm,分散程度较好;其比表面积、孔容和平均孔径分别为398.45 m2·g-1、0.63 cm3·g-1和6.27 nm;晶体表面具有弱酸特征.     

Effect of phosphonate additive on crystallization of gypsum in phosphoric and sulfuric acid medium

Understanding the mechanisms of growth and inhibition during crystallization of calcium sulfate is of primary importance for many industrial applications. For instance, inhibition of the crystallization process may be required to prevent scale formation in pipes, boilers, heat exchangers, reactors, reverse osmosis membrane surfaces, cooling water systems, secondary oil recovery utilizing water flooding techniques and desalination evaporators, etc. On the other hand, control growth and morphology of gypsum crystals is desired in achieving higher filtration rate and higher productivity of phosphoric acid from phosphate rocks. In this regard, this basic study is carried out to understand effect of Aminotris (methylenephosphonic acid (ATMP) on calcium sulfate dihydrate (gypsum) crystallization. The time elapsed between the achievement of supersaturation and the appearance of a solid phase (termed as induction time) is measured under different supersaturation ratios ranging from 1.018 to 1.979. The data are used to calculate the surface energy, critical nucleus size, and crystal growth rates of gypsum under different conditions. The results show that, the induction time decreases exponentially with increasing the supersaturation ratio. In addition, the surface energy decreases with ATMP compared to the baseline (without ATMP). Interestingly, with addition of the ATMP, the crystals mean and median diameters are found to decrease. The inhibition efficiency ranges from 16% to 59% depending on supersaturation ratio.     

Growth aspects of barium oxalate monohydrate single crystals in gel medium

Single crystals of barium oxalate monohydrate (BaC₂O₄.H₂O, BOM) were grown in pure form by controlled diffusion of Ba²⁺ using the gel technique at different temperatures. Starting from aqueous Ba²⁺ chloride (BaCl₂) and acetic acid (C₂H₂O₄) in gel, this method offers a low‐cost and an easiest alternative to other preparation methods for the production of barium oxalate bulky single crystals. The optimal conditions for the growth of BOM crystals in silica gel were found by investigating different growth parameters such as gel pH, gel aging and crystallization temperature. Irrespective of all such crystallization environments, growth rate of the crystals were initially less and then exhibited supersaturation effect leading to non‐linearity. Gel aging and temperature has profound effect on nucleation density that resulted less number of crystals of maximum size in the gel matrix. Perfect single crystals were grown on gels of higher pH. The macropore morphology and porosity was controlled by changing age of the gel. It has been found that temperature has a fabulous effect in controlling the nucleation density by altering the supersaturation conditions for the formation of critical nuclei. The entire growth kinetics informed that the grown crystals were derived by the one dimensional diffusion controlled process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The combined effects of supersaturation and Ba2+ on the batch cooling crystallization of potassium dihydrogen phosphate

The combined effects of supersaturation and Ba²⁺ on potassium dihydrogen phosphate (KDP) were investigated in batch cooling suspension crystallization. Growth size, morphology, and impurity Ba²⁺ adsorbed in the KDP crystals were measured with changing Ba²⁺ concentration and supersaturation. Significant changes in shapes and volume of the grown crystals have been observed. The results further confirmed that the size and shape of crystals were greatly determined by supersaturation. Ba²⁺ ions significantly modified the growth habit of KDP crystals. The concentration of Ba²⁺ ions adsorbed in the crystals increases with the increasing Ba²⁺ ions in the solutions and supersaturation. The foggy phenomena caused by the addition of Ba to the KDP solution were also described. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

GaN single crystals of different habit grown from solution at near atmospheric pressure

Near atmospheric pressure solution growth is one of the many developing methods for growing bulk GaN from solution. Apart from other approaches, this method holds certain advantages, such as relatively low growth pressure and temperature, and the ability to grow high quality GaN crystals with different orientations by varying the solvent composition. GaN whiskers of millimeter scale size with exceptional mechanical and optical properties were grown from solution. Crystals of near isotropic shape were also grown from solution by manipulating additives in the basic solvent.     

Effect of CuCl2 on hydrothermal crystallization of calcium sulfate whiskers prepared from FGD gypsum

Using purified flue‐gas desulfurization (FGD) gypsum as raw material, effects of CuCl₂ on crystal morphology, phase structure, aspect ratio and crystallization of hydrothermal products prepared via hydrothermal crystallization in H₂SO₄‐H₂O solutions were investigated. The results show that dosage of CuCl₂ has a significant effect on the morphology, aspect ratio and crystallization of calcium sulfate whiskers (CSWs), but no effect on their phase transformation . At a dosage of 15 g CuCl₂/kg FGD gypsum, the produced calcium sulfate whiskers had diameters ranging from 1 to 3 μm with average aspect ratio greater than 200 . Transmission electron diffraction patterns and highly magnified surface morphology of CSWs were found different from those of self‐assembly crystals. Compared to self‐assembly crystals, the produced CSWs showed a single crystal structure and their surface was very smooth.     

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.     

Rapid sonocrystallization in the salting-out process

Power ultrasound is applied as a mechanical aid to blend and cavitate the medium during the process of salting-out crystallization. Immediately following the addition of the total precipitant needed to the solution, the ultrasound is turned on. The sonoprocess including nucleation and crystal growth is completed in seconds. The experimental results indicate that the variation of ultrasonic energy, duration or mixture volume can be used to yield advantageous control of the mean size and size distribution of resulting crystals. The crystals insonated have perfect shape and show little agglomeration. Since crystallization in such highly supersaturated solutions is uncontrollable by conventional methods, the insonation plays an irreplaceable role in the process. Based on our experiment, it should be feasible and valuable to scale up this sonoprocess for industrial application.     

Behavior of LiOH·H2O crystals obtained by evaporation and by drowning out

In the present work, the behavior of crystals derived from two different crystallization methods applied in a concentrated aqueous lithium salt solution was studied. The LiOH·H₂O crystals obtained by a simple evaporation (Crystal I) differed in terms of morphology and solubility from those precipitated from lithium hydroxide solutions by addition of ethanol as a co‐solvent (Crystal II). Solubility of Crystal II at different temperatures (15 to 35°C) and mass ratios of ethanol to water (0 to 0.1) was determined. Polymorphic like behavior of these crystals was evidenced from X‐ray diffraction patterns. Measurement of density, refractive index, absolute viscosity and electrical conductivity of saturated solutions are reported. A thermodynamic analysis in terms of the Chen model for the calculation of activity coefficients, indicate that the polymorphic system in water and in water + ethanol (ethanol/water ratio 0.1) is enantiotropic. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Drug recrystallization using supercritical anti-solvent (SAS) process with impinging jets: Effect of process parameters

The aim of this study is to improve mixing in supercritical anti-solvent process (SAS) with impinging jets in order to form finer particles of sulfathiazole, a poorly water-soluble drug. The influence of several process parameters upon the powder characteristics is studied. Parameters are jets' velocity (0.25 m s^?1 to 25.92 m s^?1), molar ratio solvent/CO₂ (2.5% to 20%), temperature (313 K to 343 K), pressure (10 MPa to 20 MPa) and sulfathiazole concentration in the organic solution (0.5% to 1.8%). Two solvents are used: acetone and methanol. Smaller particles with a more homogeneous morphology are obtained from acetone solutions. For the smallest jets' velocity, corresponding to a non-atomized jet, the stable polymorphic form is obtained, pure or in mixture. At this velocity, pressure is the most influential parameter controlling the polymorphic nature of the powder formed. The pure stable polymorph is formed at 20 MPa. Concerning the particle size, the most influential parameters are temperature and sulfathiazole concentration.The use of impinging jets with different process parameters allows the crystallization of four polymorphs among the five known, and particle sizes are varied. This work demonstrates the studied device ability of the polymorph and the size control. A comparison with the classical SAS process shows that particle size, size distribution and morphology of particles crystallized with impinging jets are different from the ones obtained with classical SAS introduction device in similar operating conditions. Mean particle sizes are significantly smaller and size distributions are narrower with impinging jets device.     

Isoprenoid-chained lipid β-XylOC16+4—A novel molecule for in meso membrane protein crystallization

Here we report a successful use of a recently developed isoprenoid-chained lipid family for in meso crystallization of membrane proteins. The isoprenoid-chained lipid 1-O-(3,7,11,15-tetramethylhexadecyl)-β–d-xyloside (β-XylOC₁₆₊₄) used as a host lipid for in meso crystallization provided high quality bacteriorhodopsin (bR) crystals (P6₃ space group) diffracting to high resolution and characterized by low twinning ratio. β-XylOC₁₆₊₄ has an isoprenoid chain with methyl branches at each 4th position and a xylose group in the water-soluble part. These peculiarities make the lipid clearly distinguishable in the bR crystalline lattice and provides a unique opportunity to study the role of the host lipid in the in meso crystallization. We conclude that β-XylOC₁₆₊₄ may have a general application for in meso crystallization for a wide range of membrane proteins. The cubic phase of β-XylOC₁₆₊₄ is present over a wide range of temperatures and is stable at low temperature (down to about 8 °C). This opens up the possibility of using temperature as a tool for the optimization of in meso crystallization with additional advantages for the crystallization of membrane proteins at lower temperatures where the proteins of interest may be more stable.     

Modeling the distribution of Ga and Sb impurities in Ge‒Si single crystals grown by double feeding of the melt: Growth conditions for homogeneous single crystals

Mathematical modeling of the distribution of Ga and Sb impurities in homogeneous (with respect to the content of the main components) single crystals of Ge–Si alloys, grown by double feeding of the melt, has been performed in the Pfann approximation. It is shown that the axial gradient of impurity concentration in Ge–Si crystals can be controlled in wide limits by changing the ratio of crystallization rate and the rates of feeding of the melt by silicon and germanium rods. The conditions for growing alloy single crystals, homogeneous both with respect to the content of the main components and to the impurity concentration distribution, have been determined.     

Lactose particle engineering: Influence of ultrasound and anti-solvent on crystal habit and particle size

This study focuses on ultrasound-assisted anti-solvent crystallization of lactose, expanding on previous studies and presenting, for the first time, the results of large scale implementation of sonocrystallization for lactose. The results further clarify the interplay between solution chemistry – namely the role of β-lactose – and crystallization, representing a step forward in the fine tuning of lactose properties for pharmaceutical manufacturing applications. Batches manufactured at laboratory and pilot scales were extensively characterised, including an approach for the quantification of β-lactose in α-lactose based on powder X-ray diffraction (PXRD), which is described here.     

Synthesis of zeolite ZSM‐5: Effect of emulsifiers

Zeolite ZSM‐5 has been synthesized in presence of various emulsifiers. Influence of types and proportions of cationic, anionic and non‐ionic emulsifier has been studied. Cationic emulsifier, cetyl trimethyl ammonium bromide resulted in an amorphous phase, whereas anionic emuisifier, sodium lauryl sulphate afforded crystalline phase, identified as magadiite. Non‐ionic emulsifiers, 1,2,3‐benzotriazole and sorbital mono‐stearate led to the formation of pure crystalline ZSM‐5 phase. Emulsifier concentration was found to affect the process of crystallization, and the crystal size and morphology of ZSM‐5. Emulsifier necessitated higher crystallization temperature and/or longer hydrothermal period. ZSM‐5 crystallization was observed to proceed through magadiite phase formation. In case of benzotriazole, unusual stacked square platelet type morphology and with sorbital monostearate, very small crystals were observed.     

Growth and characterization of 4‐Aminopyridinium‐4‐nitro phenolate single crystals

Organic optical material 4‐Aminopyridinium‐4‐nitro phenolate (4AP4NP) has been synthesized, and single crystals of size 20 x 14 x 6 mm³ have been grown from acetone solvent at room temperature by solvent evaporation technique. The grown crystals have been characterized by X‐ray diffraction to determine the cell parameters, and by FT‐IR technique to confirm the formation of the expected compound. The crystal belongs to monoclinic crystal system with space group P2₁/a.The structural perfection of the grown crystals has been analyzed by high‐resolution X‐ray diffraction (HRXRD) rocking curve measurements. The thermal stability of the compound has been determined by TG‐DTA curves. The transmittance of 4AP4NP has been used to determine the refractive index n; the extinction coefficient K and both the real ε_r and imaginary ε_i components of the dielectric constant as functions of photon energy. The optical band gap of 4AP4NP is 2.4 eV. The dielectric and mechanical behavior of the specimen was also studied. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)