L-精氨酸掺杂下ZTS溶液的稳定性研究

研究了L-精氨酸掺杂下硫脲硫酸锌(ZTS)溶液中的成核过程,测量了在不同掺杂浓度下ZTS溶液的亚稳区和诱导期.结果表明:随掺杂浓度的增加,溶液的亚稳区变宽,诱导期增大;根据经典成核理论计算了晶体的成核热、动力学参数,分析了溶液稳定性与掺杂浓度的关系,即随着L-精氨酸掺杂浓度的增加,溶液的稳定性得到明显提高.利用化学腐蚀法对ZTS晶体(100)面进行了腐蚀,并用光学显微镜对腐蚀面进行观察,得到了清晰的位错蚀坑.当L-精氨酸掺杂浓度为1.5mol;时,ZTS晶体(100)面位错蚀坑密度最小,适合高光学质量晶体的生长.     

EDTA和KCl双掺杂下KDP溶液的稳定性研究

研究了EDTA与KCl不同掺杂浓度和不同过饱和比下KDP溶液的成核过程,测定了不同条件下KDP过饱和溶液的诱导期;根据经典成核理论计算了成核热、动力学参数,并分析了溶液稳定性随掺杂浓度的变化情况。利用化学腐蚀法对KDP晶体(100)面进行了腐蚀,得到了清晰的位错蚀坑,并使用光学显微镜观察了(100)面位错蚀坑的分布特点。结果表明,当过饱和度为4%、掺杂浓度为0.01 mol%EDTA和1 mol%KCl时,不仅KDP过饱和溶液的稳定性比较高,而且位错蚀坑的分布比较均匀、密度小,适合高质量的KDP晶体生长。     

不同EDTA添加剂浓度下ZTS溶液诱导期及其成核特性研究

测定了25℃下,添加不同浓度的EDTA后,不同过饱和比下ZTS溶液的诱导期,研究了掺杂浓度及过饱和比对ZTS溶液成核的影响.研究显示,当溶液处于较高过饱和比时(S＞1.13),均匀成核占主导;而在较低过饱和比时(S＜ 1.11),则以非均匀成核为主.利用经典成核理论对实验所得数据进行分析,计算得到了界面张力、临界核形成功、临界核半径等成核特性,发现了溶液过饱和比及掺杂浓度对成核速度的影响,解释了添加EDTA能提高溶液稳定性的原因.利用界面张力的值计算得到了表面熵因子.     

F-及SiF2-6对α型半水硫酸钙结晶成核及形貌的影响

本文模拟了半水法湿法磷酸生产过程中α型半水硫酸钙(α-HH)的结晶过程。在30%P₂O₅,反应温度95 ℃,过饱和度S=1.64~2.10条件下,通过浊度仪监测溶液中浊度变化,测定了不同F^-及SiF^2-₆浓度下α-HH结晶诱导时间,采用经典成核理论公式计算了α-HH的临界晶核半径及成核速率,并通过扫描电子显微镜(SEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)表征分析了F^-及SiF^2-₆对α-HH结晶过程的影响。结果表明:随着F^-、SiF^2-₆浓度的升高,α-HH晶体的结晶诱导时间延长,表面能和临界晶核半径都增大,然而成核速率减小。当过饱和度S=1.64时,加入0.06 mol·L^-1 F^-,α-HH结晶诱导时间延长了465 s,成核速率减小到0.403×10²⁹ 晶核数·cm^-3·s^-1,然而,加入0.06 mol·L^-1 SiF^2-₆,α-HH结晶诱导时间延长了710 s,成核速率减小到0.339×10²⁹晶核数·cm^-3·s^-1。SiF^2-₆对α-HH晶体抑制成核作用大于F^-。F^-、SiF^2-₆阻碍了α-HH晶体沿C轴方向生长,使得晶体长径比减小,晶体形貌向短柱状变化。F^-、SiF^2-₆影响了α-HH晶体(200)、(310)、(400)晶面衍射峰强度和结晶度。控制半水法湿法磷酸中F^-及SiF^2-₆浓度水平,可以得到短柱状的α-HH晶体,有利于过滤洗涤。     

不同pH值下磷酸二氢铵(ADP)溶液成核过程研究

利用全程摄像的方法测定了不同情况下ADP过饱和溶液的诱导期,研究了不同pH值、不同温度的ADP过饱和溶液的成核过程,讨论了pH值、温度和过饱和度S等因素对诱导期的影响.结果表明:改变pH值后,在同一过饱和度下,溶液的稳定性在不同温度间差异较小,更利于晶体在较高的温度下稳定快速的生长;改变pH值后,溶液在整个过饱和度范围内更趋向于均匀成核.根据经典均匀成核理论,针对ADP溶液均匀成核的状况计算出了不同pH值和温度下的固-液界面张力、临界成核功等成核参数,并从上述参数的相互比较中得到了改变pH值后溶液稳定性变强的微观原因.最后通过对表面熵因子的计算,确定了ADP晶体的微观生长机制为连续生长模式.     

晶格动力学性质对钛酸锶介电行为的影响

在105 K钛酸锶(SrTiO3)发生立方-四方的反铁畸变,对量子效应的吉布斯自由能取极小值,可得到一系列方程,原则上可以确定任意系统相变时的介电性质.研究了晶格动力学性质,特别是软模的行为,对理解介电性非常重要.介电常数完全由低频的光学声子模决定,从晶格动力学的性质出发,分析了低温时的居里-外斯定律行为.     

Li3N-hBN体系合成cBN单晶“V”形区的相变热力学

利用静态高温高压触媒法合成优质cBN单晶,合成温度和压强范围形成一“V”形区域.从Gibbs自由能(△G)角度分析了采用Li3N为触媒合成cBN单晶时,不同物相在“V”形区及其扩大区域(1600～2200 K、4.8 ～6.0 GPa)内向cBN相变的可能性.分别计算了高温高压下hBN+ Li3 N-→Li3 BN2 、hBN→cBN和Li3BN2→cBN+ Li3N三个反应的△G.结果表明:在“V”形区及其扩大区域内,前二个反应的△G均为负值,分别为-35～-10 kJ/mol和-25 ～-19k J/mol;而第三个反应的△G有正有负,其正值范围形成了一个温度、压强的“V”形区域.该“V”形区基本覆盖了以前文献中提到的“V”形区.这说明在合成优质cBN单晶的温度压强范围内,Li3 BN2稳定存在,不能分解出cBN.Li3N触媒体系内的cBN可能源自hBN的直接相变,而非Li3BN2的分解.但分析表明Li3BN2促进了hBN→cBN的相变.     

成核层温度对非掺杂GaN外延薄膜结晶质量的影响

利用金属有机化学气相沉积系统(MOCVD),在蓝宝石的(0001)面采用不同的成核层生长温度,通过两步法获得不同质量的GaN外延薄膜.利用HALL测试仪,高分辨X射线衍射仪(HRXRD),原子力显微镜(AFM)和光致发光光谱仪(PL)对GaN薄膜的表面形貌,位错密度,光学性能等进行表征,研究不同的成核温度对GaN外延薄膜晶体质量的影响.结果表明,在成核层生长温度为650℃时,所得到的GaN外延薄膜表面粗糙度和位错密度均达到最低,并且同时具有最高的带边发光峰强度,最高的载流子迁移率以及最低的载流子浓度.过低或过高的成核温度都会导致GaN外延层的晶体质量和光电性能变差.     

对甲苯磺酸(PTSA)对DAST晶体生长、表征的影响

向4-(4-二甲基氨基苯乙烯基)甲基吡啶对甲苯磺酸盐(DAST)甲醇溶液中加入对甲苯磺酸(PTSA),从中生长出DAST晶体.测试了纯生长溶液和加入PTSA后溶液的亚稳区,发现PTSA能够明显增加DAST生长溶液的亚稳区的宽度.通过粉末XRD和FTIR分别测试了PTSA掺杂和未掺杂溶液中生长的DAST晶体的晶体结构和官能团,测试结果表明PTSA并不会改变其晶体结构.溶液的稳定性有助于生长出大尺寸DAST晶体.     

KDP晶体快速生长溶液的稳定性研究

本文研究了搅拌,过滤,过热和添加剂对KDP晶体快速生长溶液的稳定性的影响并分析了其影响机理.结果表明,利用0.2μm的滤膜对溶液过滤,在饱和点以上20℃时对溶液过热20h,或在溶液中添加某些特定的添加剂均可有效提高KDP晶体快速生长溶液的稳定性.通过对生长溶液进行综合的前处理,利用“点籽晶”快速生长技术实现了KDP晶体的快速生长,生长速度达20 mm/d,生长尺寸达5 cm量级.     

Crystallization and Characterization of Orthorhombic β‐MgSO4 · 7H2O

In solution, the growth rate and the crystal habit are influenced by a number of factors such as supersaturation, temperature, pH of the solution, cooling rate, agitation, viscosity, initial state of the seed crystal and the presence of impurities. The crystallization of orthorhombic β‐MgSO₄ · 7H₂O, from low temperature aqueous solution by slow cooling process was studied. The metastable zone width, the induction periods (τ) for different supersaturations and the effect of pH on the growth rate of the crystals were investigated. The increase of pH yielded bigger crystals. The structural, optical, thermal and mechanical properties of β‐MgSO₄ · 7H₂O have been studied using FT‐IR, X‐ray diffraction, TGA‐DTG and micro hardness analyses.     

Metastable zone width for secondary nucleation and secondary nucleation inside the metastable zone

This study presents an evaluation of a new method, called zero growth activation free energy, used to determine the metastable zone width for the secondary nucleation case. It predicts the metastable zone width with a maximum error of 5‐10%. Estimation of the metastable zone width for different isothermal crystallization conditions can be modeled according to a chosen reference set of growth experiments carried out in the volume diffusion regime at different initial supersaturations, using seed crystals of a certain characteristic size. Moreover, the activation free energy of the secondary nucleation was estimated. The role of the enthalpy of immersion in the formation of secondary nucleation events inside the metastable zone was pointed out, as well as its effect in causing extra‐fast growth rate. Furthermore, sucrose crystal surface free energy was estimated. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of nucleation kinetics of lovastatin in acetone solution

The metastable zone widths of lovastatin in acetone solution were determined at different temperatures, cooling rates and initial concentrations by polythermal method. It decreases with the increase of temperature and initial concentration, increases with the increase of cooling rate. The induction periods of lovastatin in acetone solution were also investigated as a function of supersaturation ratios. The crystal‐liquid interfacial tension, thus the fundermental nucleation parameters including Gibbs free energy change for the formation of critical nucleus, radius of critical nucleus and number of molecules in the critical nucleus have been gotten based on the classical homogeneous nucleation theory. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison Study of Mixing Effect on Batch Cooling Crystallization of 3‐Nitro‐1,2,4‐triazol‐5‐one (NTO) Using Mechanical Stirrer and Ultrasound Irradiation

The insensitive explosive 3‐Nitro‐1,2,4‐triazol‐5‐one (NTO) has been recrystallized from water in an effort to prepare crystals with smaller size and narrower distribution in a batch cooling crystallizer. Two mixing devices, i.e., a mechanically stirred system with and without ultrasound in aqueous media were employed to compare the mixing effect on the crystallization. Under ultrasound irradiation, the metastable zone width was significantly reduced by more than 2 fold and the crystal size was shifted from 140∼160 μm to 50∼70 μm with a narrower CSD compared to the mechanically stirred system. However in the mechanical stirrer, the mixing effect on NTO crystallization was negligible if the impeller speed was sufficient to suspend all crystals in the crystallizer. It was found that the crystal growth was not influenced by mixing. We suggest that the NTO crystals were formed by primary heterogeneous nucleation that is common in batch cooling system. Finally, the population balance model (PBM), with the empirical nucleation and growth kinetic expressions, was solved numerically to predict the crystal size and the CSD with batch time, and the results were in good agreement with the experimental data.     

Effect of Urea on Metastable Zone Width,Induction Time and Nucleation Parameters of Ammonium Dihydrogen Orthophosphate

Enhancement of the metastable zone width in ammonium dihydrogen ortho phosphate (ADP) was achieved by the addition of the organic compound Urea to ADP solution. The metastable zone width studies were carried out for various temperature cooling rates and the nucleation parameters are studied. The induction period was studied and the critical nucleation parameters calculated based on classical theory for homogeneous nucleation are discussed. The critical nucleation parameters increase with the increase in concentration of doping.     

On the interpretation of metastable zone width in anti‐solvent crystallization

Considering nonlinear dependence of solute concentration on anti‐solvent–solvent composition a modified Nývlt‐like equation based on traditional power‐law relation between nucleation rate and developing supersaturation and a new equation based on the classical theory of three‐dimension nucleation are proposed to explain the dependence of anti‐solvent addition rate on metastable zone width defined as excessive anti‐solvent composition in anti‐solvent crystallization. The experimental data on the metastable zone width in anti‐solvent crystallization of benzoic acid are analyzed and discussed from the standpoint of these equations. It is found that the new approach based on the classical nucleation theory provides better insight into the processes involved in anti‐solvent crystallization. Analysis of the experimental results on anti‐solvent crystallization of benzoic acid [D. O'Grady, M. Barret, E. Casey, and B. Glennon, Trans. IChemE A 85 , 945, (2007)] revealed that: (1) the value of metastable zone width for a solvent–anti‐solvent system is determined by the solute–solvent and solute–anti‐solvent interactions, (2) the dependence of the metastable zone width on stirring is associated with the enthalpy of mixing, and (3) the new approach predicts a threshold anti‐solvent addition rate associated with the setting up of an equilibrium between solvent and anti‐solvent and a maximum anti‐solvent addition rate connected with the induction period t_ind for the onset of crystallization. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal and molecular structure of 3-chloro-3,6-dinitro-2,2-dimethyl-4-chromanone, C11H9N2O6Cl

3-Chloro-3,6-dinitro-2,2-dimethyl-4-chromanone is the first 3-chloro-3-nitro-4-chromanone to be synthesized by nitrating its corresponding 4-chromanone at the 3 position and then chlorinating the nitration product. Its structure was determined by IR, NMR, MS and x-ray crystallography. It crystallizes as a pair of enantiomers with 2 molecules in the primitive triclinic space group P (#2) with a = 9.476(2), b = 10.906(3), c = 6.578(5) Å, and = 101.08(3), = 90.13(3), = 73.23(1)°, V = 637.7500 ų, and Z = 2. The nitro group at the 6 position conjugates with the benzene ring. The pyranone ring has a half-chair conformation; the chloro group occupies the pseudoequatorial position, and the nitro group occupies the pseudoaxial position. The 2 and 3 positions are essentially antiperiplanar, minimizing steric interaction.     

X-ray crystal structure of 2,5-dioxo-4-imidazolidineethanesulfonamide, C5H9N3O4S

The crystal structure of 2,5-dioxo-4-imidazolidineethanesulfonamide or homocysteine sulfonamide hydantoin, C₅H₉N₃O₄S (1) was obtained by single-crystal X-ray diffraction. Crystallization of 1 occurs in the centrosymmetric monoclinic space group C2/c (No. 15) with a = 15.653(2), b = 9.6489(10), c = 11.066(2) Å, = 94.64(2), and Z = 8. Molecules are in an extended structure with a C–C–C–S torsion angle of –174.2(1). The imidazolidinedione ring is planar and the sulfonamide group has a distorted tetrahedral geometry. A three-dimensional network of intermolecular hydrogen bonding occurs within the crystal lattice involving both imidazolidinedione and sulfonamide functional groups.