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1.
    
Magnesium hydroxide (Mg(OH)2) is an important chemical raw material and product. Since narrow crystal size distribution of Mg(OH)2 determines its excellent physical and chemical properties, gaining insight into the reactive crystallization kinetics of Mg(OH)2 to obtain narrow particle size distribution is essential. The reactive crystallization kinetics of Mg(OH)2 for the Mg(NO3)2‐NaOH system is systematically investigated during batch crystallization. The effects of supersaturation and temperature on the reactive crystallization kinetics of Mg(OH)2 are studied. Ion concentration over crystallization time at different temperatures is measured by the conductivity method so that the induction period is well defined. Several kinetic parameters during the nucleation and growth process are determined by using the experimental data of ion concentration over crystallization time at different temperatures. Results show that the induction period decreases with increase of temperature and initial reagent concentration. The specific surface Gibbs energy decreases with the increase of temperature. Crystallization rate increases with increase of temperature and initial reagent concentration, and the nucleation and crystal growth rates can be described as the first order reaction model.  相似文献   

2.
    
Polymorphic control and crystal nucleation of α and β polymorphs of dl -methionine, an essential amino-acid, is attained from saturated aqueous solution through swift cooling crystallization process by generating wide range of supersaturation (0.02 < σ < 2.19) in the temperature range of 323–274 K. The type of nucleation is very much supersaturation dependent: while lower supersaturation range (0.02 < σ < 0.08) prefers the stable β form, higher supersaturation range (1.20 < σ < 2.19) yields metastable α form. In situ optical microscopy and X-ray diffraction analyses confirm the morphological and structural distinction of the grown polymorphs.  相似文献   

3.
晶体的结晶路径分为经典结晶路径和非经典结晶路径。经典结晶路径往往涉及一些简单的化学结构,晶体的成核、生长是通过单体的依次添加实现的,经过长期研究,目前研究人员已对其有了较为深刻的理解并形成了一套相对完善的理论体系;但对于非经典的结晶路径,由于涉及复杂中间态粒子的形成和多步结晶过程,尚未获得全面、统一的理论支持。在药物结晶领域,有机分子构象自由度的引入增加了体系的复杂性,分子间弱的相互作用使得固态药物分子存在多晶型现象。由于药物的理化性质及生物利用度与其晶型息息相关,同时,药物结晶过程中出现的一些复杂中间态粒子往往会改变最终得到的药物晶型,因此迫切需要加强对药物晶体成核和生长路径的研究,以期发展能实现对药物晶体成核和生长过程主动控制的方法。本文简要综述了目前药物在溶液或熔体中结晶的经典与非经典结晶路径,包括奥斯特瓦尔德阶段定律、独立成核、交叉成核。从溶液化学的角度看,分子在浓溶液中会通过自组装形成结构合成子,成核与溶液中的生长单元、结构合成子密切相关。从分子水平上探索溶液中有关分子运动的信息、分析各体系下晶核与结构合成子之间的关系是区分两种结晶路径的关键所在,非经典结晶在药物结晶领域是机遇也是挑战。  相似文献   

4.
    
In crystal structure prediction simulations based on lattice energy minimization, usually hundreds of structures within a reasonable range of lattice energy and density are found, whereas in practice, it is very rare to find more than a few polymorphs of the same compound. In the work presented here, this discrepancy is investigated from a structural and energetic point of view. 56 crystal structures of 26 polymorphic mono‐ and disubstituted aromatic compounds, extracted from the Cambridge Structural Database, have been analysed with respect to inter‐polymorphic structural similarity. For comparison, potential crystal packing arrangements of the substances have been predicted with molecular mechanics simulations using a generic force field. The predicted structures are analysed with respect to structural features and similarity, and with respect to the number of structures and their lattice energy. It is found that the real polymorphs studied in this work tend to be structurally quite dissimilar with regard to hydrogen bonding and spatial packing of structural motifs, while many of the predicted structures of a given compound are very similar to each other. The results suggest that structure and lattice energy alone cannot explain why so few polymorphs are found in practice compared to the very large numbers predicted in simulations. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

5.
    
The Influence of antisolvent water on the polymorphic nucleation of N‐benzyl‐2‐methyl‐4‐nitroaniline (BNA) during its crystallization from methanol solution is revealed. The solubility of BNA in methanol‐water solvent mixtures is determined by gravimetric method and the variation in the level of supersaturation generated with respect to antisolvent concentration is assessed at different volume combinations of saturated methanol BNA solution and water. The supersaturation dependent polymorphic nucleation of orthorhombic and monoclinic forms and their growth morphologies such as platy‐like orthorhombic and needle‐like monoclinic are examined through in‐situ optical microscopy. Single crystals of the grown polymorphs are successfully separated and their structural, thermal, spectroscopic and optical transmittance properties are confirmed through PXRD, DSC, FTIR and UV‐Vis‐near IR analyses respectively.  相似文献   

6.
    
A design for an air cooler (`air saw') with a series of movable teeth (`modular crystallization comb') installed in a laboratory chamber furnace is presented. The setup allows easy regulation of a series of different temperature gradients, shapes of crystallization fronts and rates, in crucible columns, with the purpose of obtaining crystals. This method can also be applied in crucible or tube furnaces.  相似文献   

7.
通过直接水热合成法在吡咯烷和四甲基氢氧化铵双模板剂体系下制备出具有层状薄片组成的球形镁碱沸石,并且考察了四甲基氢氧化铵加入量对镁碱沸石的结晶度、晶化曲线、晶体形貌、比表面和孔结构的影响,采用X射线衍射(XRD)、扫描电镜(SEM)、氮气吸附脱附等手段对合成样品进行分析表征.结果表明:随着四甲基氢氧化铵加入量的增加,其晶化过程逐渐延长,但最终得到的镁碱沸石相对结晶度无明显变化;四甲基氢氧化铵的加入可以显著改变镁碱沸石的晶体形貌、比表面和孔结构.  相似文献   

8.
铌酸锂晶体历史悠久,物理效应最为齐全,被用于制备声学滤波器、谐振器、延迟线、电光调制器、电光调Q开关、相位调制器等器件,在电子技术、光通信技术、激光技术等领域得到了广泛应用,并且在第五代无线通信技术、微纳光子学、集成光子学及量子光学等近期快速发展的领域中展示了重要的应用前景。本文简要综述了铌酸锂晶体的基本性质、晶体制备以及应用情况,对铌酸锂晶体未来的应用发展进行了简要分析。  相似文献   

9.
    
In this study, effects of diluting either protein or crystallization agents in the droplets on the success rate of protein crystallization was investigated. Diluting the crystallization agent was found to increase the success rate of protein crystallization. Theoretical analysis showed that, concentration ranges of both protein and crystallization agent that can be scanned during the vapor diffusion process are wider with diluting the crystallization agent than that without dilution, resulting in more opportunities for the crystallization solution to be in the nucleation zone. On the other hand, diluting protein could lead to controversial results depending on the location of the initial concentration relative to that of the nucleation zone in the phase diagram. The method of diluting the crystallization agent is therefore proposed as an alternative modification to the conventional vapor diffusion method for obtaining more crystallization conditions in protein crystallization screening. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

10.
    
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)  相似文献   

11.
对过饱和溶液在施加一定的流体压力差使之循环流动,实验结果测算草酸、草酸钠、硼酸和磷酸氢二钠等在不同温度下饱和溶液降温结晶时流动电位随时间的变化规律.实验结果表明流动电位大小与结晶物质的种类、温度和浓度有关,同时易受外界因素的干扰,实验数据的严格重现较难.但多次实验结果都显示:过饱和溶液在某一温度下形成晶核过程中其流动电位均发生显著变化;当饱和溶液起始结晶温度较高时,其流动电位突变点温度也更高.  相似文献   

12.
近化学计量比铌酸锂晶体中机械孪晶的消除   总被引:1,自引:1,他引:0  
在用掺钾的助熔剂提拉法生长近化学计量比LiNbO3晶体时,长出的晶体尾部很容易出现孪晶裂纹现象,这种孪晶被认为是机械孪晶.这种孪晶的起因是由于晶体生长的收尾和从熔体中提起晶体阶段,在晶体底部产生直径的缩进,在缩进产生的台阶处出现应力集中,从而造成孪晶的成核.通过采用适当的收尾过程,以避免直径台阶的出现,可以很好地消除这种孪晶及其引起的裂纹.  相似文献   

13.
    
Single‐crystals of the layered copper hydroxide acetate Cu2(OH)3(CH3COO)·H2O were synthesized by heating copper acetate solution at 60 °C. The standard synthesis of the title compound based on slow titration of copper acetate solution with NaOH yielded materials with worse morphology and an additional phase present. The obtained products were characterized with powder X‐ray diffraction, high temperature powder X‐ray diffraction, scanning electron microscopy and infrared spectroscopy. The crystal structure was determined from single‐crystal X‐ray diffraction data, collected both at 120 K and at 293 K. The title compound crystallizes in the monoclinic botallackite‐type layered structure, space group P 21, with the lattice parameters a = 5.5776(3) Å, b = 6.0733(2) Å, c = 18.5134(8) Å, β = 91.802(4)° and a = 5.5875(4)Å, b = 6.0987(4) Å, c = 18.6801(10)Å, β = 91.934(5)° for 120 K and for 293 K, respectively. Acetate groups and water molecules are interlayered between corrugated sheets of edge‐sharing CuO6 octahedra exhibiting strong distortion resulted from the Jahn‐Teller effect. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
研究了LiF为助熔剂体系下的δ-LiZnPO4的结晶特性,通过自发结晶得到了尺寸为1~3 mm的透明块状δ-LiZnPO4和Li4Zn(PO4)2共晶体,通过PXRD衍射分析和元素分析确定了共晶体的相组成,并对从共晶体中分离出的δ-LiZnPO4晶体结构进行了分析.结果表明:δ-LiZnPO4晶体具有非中心对称结构,属于正交晶系,空间群为Pna21,晶格常数a=1.00085 nm,b=0.49390 nm,c=0.66545 nm,Z=4;δ-LiZnPO4是由PO4、ZnO4和LiO4四面体构筑成的具有类似ABW型分子筛结构的化合物.采用水热法制备了尺寸约为10 μm的纯相透明的δ-LiZnPO4晶体.粉末倍频测试表明,δ-LiZnPO4晶体倍频效应约为KDP的1.7倍,紫外截止边约为218 nm,是一种有潜在应用价值的紫外非线性光学晶体.  相似文献   

15.
制备了双晶体匹配的钽酸锂电光调Q开关。首先理论分析了两匹配晶体通光方向尺寸偏差、轴向角偏差等对自然双折射补偿的影响,估算了消光比为100∶1时各加工参数应满足的指标要求。在此基础上,以平晶为基准面来保证晶向精度、同盘抛光来保证晶体尺寸,制备了满足条件的钽酸锂双晶匹配调Q开关。用锥光干涉的方法检测了匹配后晶体的光学均匀性,并在激光系统中测试了其调Q性能。结果表明匹配较好的LT调Q开关能够满足实际光学应用的需求。  相似文献   

16.
The laser crystals of chromium doped yttrium oxyorthosilicate (YSO) were grown from the melt by Czochralski technique. The crystals of YSO, yttrium pyrosilicate and stillwellite-like lanthanum borosilicate were obtained from high temperature solutions. Lithium and potassium di- and trimolybdates were used as fluxes in the growth experiments on silicate crystals. In the case of borosilicate crystals, the choice of fluxes was based on the potassium trimolybdate with an excess of potassium fluoride. The composition of grown crystals was studied by electron microprobe analysis, and structural characteristics were determined for all the single crystals.  相似文献   

17.
    
Protein crystallization is a delicate process that is always sensitive to environmental factors. When the environmental factors are not well controlled or not controlled at all, identical crystallization droplets from the same mother liquid may yield different crystallization results. One environmental factor, the weather conditions during crystallization solution preparation, is not usually considered as a parameter for protein crystallization. In this paper, it is shown that the weather parameters during preparation of the crystallization experiment, including the ambient temperature, humidity, pressure and particulate matter in the air, can all affect the reproducibility of lysozyme crystallization. An identical lysozyme crystallization experiment was repeated for an entire year, and the weather conditions when each crystallization experiment was set up were recorded along with the crystallization results. Among the parameters recorded, the humidity during the experiment setup showed the strongest effect on lysozyme crystallization. On the basis of these results, it is suggested that the weather conditions during crystallization solution preparation should be considered as a potential factor that can influence protein crystallization.  相似文献   

18.
铌酸锂晶体的生长研究   总被引:3,自引:1,他引:2  
近年来,铌酸锂晶体由于其自身所具有的多种优异性能和巨大的应用前景而受到了人们的广泛关注,但生长出满足不同市场要求的高质量铌酸锂单晶体比较困难.本文从晶体生长技术的角度综述了铌酸锂单晶体不同的生长方法以及各自的特点,并分析了在生长铌酸锂晶体时出现的一些问题.  相似文献   

19.
    
Pure perovskite Pb0.92La0.08(Zr0.68Ti0.32)0.98O3 (PLZT (8/68/32)) crystal powders with good dispersibility are prepared by using gel-hydrothermal method. The effects of mineralizer concentration, hydrothermal treatment time, and excess lead content on powder crystallization and morphology are examined and analyzed. The suitable mineralizer concentration and hydrothermal treatment time are found to be helpful to promote the PLZT crystal powders growth and improve the particle surface morphology. Noticeably, the introduction of excessive Pb can well compensate for the lack of A-site ions in the solution, thereby promoting the formation of rhombohedral PLZT crystal powders. The following optimized hydrothermal conditions are established: the temperature ≈230 °C, the mineralizer concentration ≈2 m , the hydrothermal treatment time ≈24 h, and the amount of excess Pb ≈ 80%. The obtained PLZT crystal powders with clean and complete cube morphology, uniform particle size, and excellent dispersibility would be used as the crystal seeds applying in the seed-induced growth of PLZT ceramics.  相似文献   

20.
    
A design for a modular device (`crystallization shelf') installed in a laboratory furnace is presented. The setup allows regulation and simultaneous crystallization tests of several substances at different temperature gradients, shapes of crystallization fronts and rate intervals, with the purpose of obtaining crystals.  相似文献   

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