结晶生长的化学键合理论

针对一般晶体的生长过程,在测定相应溶液(熔体)组成结构的基础上,我们引入了晶体生长过渡相区的概念,并采用键价模型来衡量生长过程中发生变化的化学键的键强度。过饱和溶液(熔体)中的生长单元经过生长过渡相区时,依据彼此之间弱的化学键合作用来微调其内部强的化学键,并以单个生长单元或者生长单元的简单连接体的形式键合进入晶格。在整个结晶生长过程中,生长单元之间弱的键合作用对整个结晶过程(生长速度、晶相的形成)起着决定性作用;同时,中等强度的化学键在生长过渡相区中的变化情况对晶体的最终形貌具有重要影响。     

溶液中结晶生长的动力学模拟:化学键合方法

基于化学键合的角度对晶体生长过程的理解,提出了一个由动力学因素控制的形貌预测模型.该模型同时考虑了晶体内部结构和环境生长因素对晶体最终形貌的影响.对磷酸二氢钾 (KDP) 和磷酸二氢铵 (ADP) 晶体在不同动力学条件下的生长形貌进行了理论模拟,所预测的结果与实验观测结果基本一致.同时比较了相同过饱和度条件下KDP和ADP晶体的生长形貌,认为晶体局部成键性质不同是导致两者形貌差异的根本原因.本文通过对动力学因素控制的生长形貌的分析,为实际晶体生长过程中的形貌调控研究及应用提供理论依据.     

三水碳酸镁合成与形貌演变过程研究

设计正交实验,以MgCl2·6H2O和NH4HCO3为原料,采用低温水热法合成三水碳酸镁晶须.通过改变实验条件,实现了对三水碳酸镁晶须形貌的调控.利用X射线衍射(XRD)、扫描电子显微镜(SEM)对产物结构和形貌进行了表征.结果表明:反应温度40～ 50℃、n(Mg2+)∶n(HCO3-)=1∶2.2、pH =8.8 ～9.0、搅拌速度130 r/min、陈化时间3h、反应时间70 min,制备出的MgCO3·3H2O晶须呈一维针状,沉降性能好,长径比可达29.60.最优实验条件同样适用于卤水资源体系.     

流动电位法对降温结晶过程的研究

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.     

定位锌结晶釉的析晶动力学分析

本文以ZnO作为定位结晶剂在1100℃下制备了ZnSiO3结晶釉,测试了其在不同析晶保温时间下釉面晶花大小,并根据结晶动力学理论,对结晶釉中ZnSiO3晶花的生长规律和结晶机理进行了分析探讨.结果表明:当析晶保温时间超过30 min,晶花的形成速率随时间增加而显著提高,并在45 min到60 min范围内达到最大值;当析晶保温时间超过90 min,晶花形成速率随时间增加而快速下降,并在析晶保温时间超过150 min后,晶花基本上不再生长,形成速率达到稳定值.采用ZnO作定位晶种的釉面结晶稳定性好,釉面晶花大小与析晶保温时间符合S型生长曲线关系,可用Logistic函数拟合,本研究为实现锌结晶釉的可控生长提供了参考.     

高长径比三水碳酸镁晶须的合成研究

本文以MgCl2·6H2O和NH4HCO3作为反应物料,采用低温液相合成法制备出三水碳酸镁晶须.考查了Mg2+初始浓度、NH4HCO3溶液的滴加速度、搅拌速度及表面活性剂种类等因素对三水碳酸镁晶须的长度及长径比的影响.研究结果表明:在Mg2+初始浓度为0.5 mol/L、NH4HCO3的滴加速度5 mL/min、搅拌速度为120 r/min、选用KH2PO4作表面活性剂的试验条件下,可以合成出长度325 μm、直径8.25 μm,长径比高达32的三水碳酸镁晶须产品.     

L-天门冬氨酸对三水碳酸镁晶体合成的影响研究

依据仿生合成的原理,选择无水MgCl2和无水Na2CO3作为反应原料,通过L-天门冬氨酸和五种无机表面活性剂分别对晶体生长进行调控,应用XRD、SEM对晶体的物相组成以及形貌结构进行表征.试验结果表明当表面活性剂为L-天门冬氨酸时,晶体生长效果最佳.又通过以L-天门冬氨酸添加量和体系pH值为参数变量进行研究,结果表明L-天门冬氨酸质量分数为0.15;,体系pH为9.5为最佳条件,有毫米级束状三水碳酸镁晶体的生成,并对L-天门冬氨酸在仿生合成三水碳酸镁过程中的作用机理进行了初步探讨.     

药物结晶中的经典与非经典结晶路径

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。     

Investigation of the Conditions for the Production of Calcium Magnesium Acetate (CMA) Road Deicer in an Extractive Crystallization Process

Calcium magnesium acetate (CMA) is considered as the best road deicer to replace the environmentally unacceptable NaCl and CaCl₂. However, the high cost of CMA prohibits its widespread use. The present study is dealing with the investigation of a crystallization method for the production of deicing CMA crystals of desired physical properties and the elucidation of the conditions under which such a product can be formed. Extractive crystallization is promising for the low cost production of CMA crystals considering that acetic acid is produced by a biochemical method and removed from the fermentation broth in situ by organic extractant systems. In this method, this organic phase, which contains the acetate ions is contacted with an aqueous phase which is the source of calcium and magnesium ions. The extractive crystallization process resulted in the production of well‐formed, large, and non‐spherical crystals of calcium acetate (CA), magnesium acetate (MA), and calcium magnesium acetate double salt (CMADS). The crystal size was affected by the concentration of acetic acid in both the organic and aqueous phases, whereas the crystal type and hydration level were determined primarily by the acetic acid concentration in the aqueous phase. The molar ratio of the precursor salts (CaCO₃/MgCO₃) in the reaction mixture was found to be the major factor for determining the habit and Ca/Mg content of crystals. Crystallization of CMADS was favored at high concentrations of acetic acid in the aqueous phase and at higher temperatures as shown from supplementary evaporation‐to‐dryness experiments.     

软模板调控碳酸锶结晶特性的研究

本文在实验室的条件下,通过用均相沉淀法和共沉淀法,采用多聚磷酸钠、酒石酸钠、EDTA/氯化锌、EDTA、氯化镁作为晶形控制剂分别合成了长为2～4μm,直径为200nm左右的柱状、长为1～3μm,直径为80nm左右的线状、长为1～2μm,直径为50nm左右的线状、粒径为200nm左右的球状以及粒径为2～3μm的不规则状等碳酸锶晶体.并且对利用多种软模板调控碳酸锶晶体的生长机理进行了初步的分析,得出了软模板导致晶体结晶的大小和形貌变化的多样性机理.     

Crystallization of mefenamic acid and polymorphs

The crystallization of Mefenamic Acid, (MA), which has a prevalent usage in drug formulation, was investigated. MA is a high‐dose, anti‐inflammatory, analgesic agent used for pain in menstrual disorders. Some negative properties of MA are a high hydrophobicity and propensity to stick to surfaces, which cause great problems during granulation and tabletting. To facilitate tabletability, enhance dissolution rates, and develop a stable and reproducible dosage form, investigation of the physicochemical properties of mefenamic acid is necessary. Pharmaceutical drugs are commonly crystalline materials and are therefore subject to polymorphism. Polymorphism, the ability of a substance to exist in more than one crystalline form, is a significant phenomenon in the field of chemical engineering sciences, including pharmaceutical development. Establishing the polymorphic behaviour of a drug molecule early in development minimizes the number of unsuitable candidates developed and reduces the risk of encountering issues later which may have a major financial and time impact. Mefenamic acid crystals were recrystallized from five different solvents of N, N‐dimethylformamide (DMF), acetone, N, N‐dimethylacetamide (DMA), Dimethylsulfoxide (DMS) and Ethyl Acetate (EA). In order to characterize the Mefenamic Acid crystal structure and the polymorphic forms of the crystals obtained by recrystallization, the scanning electron microscopy (SEM), Raman diffractometry and X‐ray pattern were used. From the industrial crystallization point of view, the crystal size distribution (CSD), the crystal shape, the polymorphic form and the crystallization steps are important factors that affect the quality and bioavailability of a drug. For the determination of crystal size distribution of MA, The Focused Beam Reflectance Measurement (FBRM) technique was practiced and CSD profiles were obtained. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Addition to the theory of LPE growth: Crystallization mechanisms

Different possible mechanisms of crystal growth for the used in the practice LPE techniques are considered in the present paper. The time dependences of the super saturation for the cases of normal growth mechanism and screw dislocations growth mechanism are presented. The values of the stationary super saturation, of the stationary growth rate and of the time constant for the transient growth process are obtained. The effect of the initial super saturation on the growth rate is considered. Relation between the stationary value of the super saturation, the time constant of the transient process, the cooling rate and the liquidus surface slope has been ascertained. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallization and structural studies of n‐benzyloxycarbonyl‐L‐tyrosine‐L‐glycine‐ethyl ester (Z‐Tyr‐Gly‐OEt)

It is axiomatic that efficient crystal production reflects upon the quality of structure. An empirical relation for mass proportions of two solvents in crystallization of Z‐Tyr‐Gly‐OEt shows a linear relationship. The dipeptide crystallizes in orthorhombic space group P2₁2₁2_1, with cell parameters a = 5.0680(1) Å, b = 13.8650(1) Å and c = 28.2630(1) Å, Z = 4, D_calc= 1.339Mg/m³, μ=0.820mm^‐1, F₀₀₀=848, CuKα = 1.5418 Å. The structure was solved by direct methods and final R1 and wR2 are 0.444 and 0.1276, respectively. The structure analysis reveals the trans conformation of the peptide unit with ω = ‐178.2(5)°, implying only a slight deviation from planarity. The torsion angles at glycine [ϕ, ψ = ‐84.4(7)°, 179.9(5)°] are characteristic of left‐handed poly glycine II helices. A number of N‐H…O, O‐H…O and C‐H…O hydrogen bondings play a role in stabilizing the molecules within unit cell. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)