The kinetics of crystal growth of succinonitrile and cyclohexanol from the melt

The crystal growth kinetics of two organic substances with low melting entropies — succinonitrile and cyclohexanol — was studied in the wide range of supercoolings. The values of kinetic coefficients which connect growth velocity and interface supercooling are equal to 0.17 – 0.72 m/(s · K) for succinonitrile and (1.6 – 2.0) · 10⁻⁴ m/(s · K) for cyclohexanol. Viscosity of these substances was measured to compare the experimental data with theoretical dependences for continuous growth. It has been found that experimental kinetics of substances under study differs significantly from the expression of Wilson-Frenkel type.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.     

Stearic acid polymorphs in correlation with crystallization conditions and solvents

Stearic acid has been crystallized from various organic solvents at different crystallization conditions. — The crystal structure modifications, A, B or C of the fatty acid are correlated to the solvent properties and depend on the interplay between the effect of the crystallization conditions and the solvent/solute interactions.     

Preparation of New Inorganic—Organic Layered Compounds,Hydroxy Double Salts,and Preferential Intercalation of Organic Carboxylic Acids into Them

Abstract

New inorganic—organic layered compounds were prepared by ion-exchange reactions of zinc-nitrate and copper-nitrate HDSs with organic carboxylic acids whose interlayer spacings increased depending on the sizes of carboxylic acids. The amounts of ion-exchanged 2-naphthoic acid and 2,6-naphthalene dicarboxylic acid were larger than those of 1-naphthoic acid and 2, 7-naphthalene dicarboxylic acid, respectively, indicating the molecule recognition ability of the HDSs.     

纳米金刚石的结构、光学性能和热稳定性研究

纳米金刚石兼具纳米材料和金刚石的双重特性,呈现出与微米金刚石、块体金刚石截然不同的特点。本文以不同尺寸金刚石样品为研究对象,采用扫描电镜、X射线衍射、光谱学、热重分析技术对其结构、光学性能和热稳定性进行研究。结果显示样品尺寸分别为300 μm、30 μm和100 nm,大尺寸样品结晶质量较好,富含孤氮杂质,为Ⅰb型金刚石。纳米金刚石样品结晶较差,含有少量石墨残留,并含有H₂O、N—H和C—H键,说明其表面存在诸多有机活性基团。大尺寸金刚石样品存在中性和带负电荷的氮空位缺陷,产生较强荧光,而纳米金刚石由于存在诸多的有机基团和表面缺陷,形成非辐射中心,导致荧光猝灭。大尺寸样品在300~525 nm具有较强吸收,而纳米金刚石样品在紫外-可见-近红外整个区域均呈现出较强吸收,透过率显著较低。随着颗粒尺寸的减小,金刚石的起始氧化温度逐渐下降,氧化速率降低,因此大颗粒尺寸金刚石样品具有更好的热稳定性。     

Methods of chemical and phase composition analysis of gallstones

This review presents the instrumental methods used for chemical and phase composition investigation of gallstones. A great body of data has been collected in the literature on the presence of elements and their concentrations, obtained by fluorescence microscopy, X-ray fluorescence spectroscopy, neutron activation analysis, proton (particle) induced X-ray emission, atomic absorption spectroscopy, high-resolution gamma-ray spectrometry, electron paramagnetic resonance. Structural methods—powder X-ray diffraction, infrared spectroscopy, Raman spectroscopy—provide information about organic and inorganic phases in gallstones. Stone morphology was studied at the macrolevel with optical microscopy. Results obtained by analytical scanning and transmission electron microscopy with X-ray energy dispersive spectrometry are discussed. The chemical composition and structure of gallstones determine the strategy of removing stone from the body and treatment of patients: surgery or dissolution in the body. Therefore one chapter of the review describes the potential of dissolution methods. Early diagnosis and appropriate treatment of the disease depend on the development of clinical methods for in vivo investigation, which gave grounds to present the main characteristics and potential of ultrasonography (ultrasound scanning), magnetic resonance imaging, and X-ray computed tomography.     

Some new electrically conducting complexes of nickel chelates

Some new complexes of organo-metallic nickel chelates with organic donors and acceptors and with halogens are found to have electrical resistivities lying in the semiconducting range. The results are discussed here briefly in terms of intermolecular interactions and molecular packing in the solid state. Ni₃O₂(OH)₄ — a mixed valence nickel compound was found to have metallic conductivity in the form of single crystals.     

The influence of inhibitors on the growth of barium sulfate crystals in suspension: Scale prevention (II)

The inhibiting influence of four organic bisphosphonates with different substituents on the growth rate of barium sulfate crystals, suspended in a supersaturated solution, has been investigated. The growth process has been studied conductometrically. Plots of both the relative supersaturation versus time and the mean linear rate versus the growth affinity have been given. — The results have been interpreted using a hypothesis, stating that growth inhibition occurs due to simultaneous coordination of the cations and hydrogen bonding of the anions at the active growth spots on the crystal surface.     

Stereochemistry of silicon in oxygen-containing compounds

Specific stereochemical features of silicon in oxygen-containing compounds, including hybrid silicates with all oxygen atoms of SiO_n groups (_n = 4, 5, or 6) entering into the composition of organic anions or molecules, are described by characteristics of Voronoi—Dirichlet polyhedra. It is found that in rutile-like stishovite and post-stishovite phases with the structures similar to those of СаСl₂, α-PbO₂, or pyrite FeS₂, the volume of Voronoi—Dirichlet polyhedra of silicon and oxygen atoms decreases linearly with pressure increasing to 268 GPa. Based on these results, the possibility of formation of new post-stishovite phases is shown, namely, the fluorite-like structure (transition predicted at ~400 GPa) and a body-centered cubic lattice with statistical arrangement of silicon and oxygen atoms (~900 GPa).     

Twinning due to Transformation from a more Favourable Energetic Transition Structure to a Higher Symmetrical Arrangement: Five-radiated Intergrowth Crystals of Metals (III)

Parts I and II investigated twins that form when a more favourable energetic transition structure initially occurs which then, at a certain growth stage (presumably in the nm-range), transform into a more symmetric structural arrangement. These transition structures, which could explain the transformation between the twin individuals, were found using lattice energy calculations on organic substances such as pentaerythrite, 1,2,4,5-tetrabromobenzene, 3,5-dimethylbenzoic acid, and maleic acid. The formation of a more favourable energetic but symmetrically lower transition structure is more likely. when lattice pseudosymmetries are present. Experimentally proving these transition structures is extremely difficult because of their low volume. It has nevertheless been possible to detect such a transition structure — around which crystal growth begins — in many metallic vapour-deposit layers. Crystal growth begins around a core and then continues as a three-dimensional periodically ordered cubic face-centered structure, at which point twins form. In Part III, the attempt is made to confirm these processes with energy calculations.     

Synthesis and Crystal Structure of NdCaGaO4

The crystal structure of the NdCaGaO₄ compound was investigated by means of X-ray structure analysis (powder diffractometer HZG-4, CuK_α): structure type LaCuO₄, space group Cmca, a = 5.3700(2) Å, b = 12.1058(3) Å, c = 5.3937(2) Å, Z = 4, R_I = 0.126. The shortest interatomic distances are: Nd(Ca)—O — 2.240(14) Å; Ga—O — 1.913(2) Å, O—O — 2.6852(2) Å, Nd(Ca)—Nd(Ca) — 3.442(3) Å, Nd(Ca)—Ga — 3.154(4) Å, Ga—Ga — 3.8056(2) Å. Atoms have the following coordination numbers: Nd(Ca) — 8; Ga — 6; O1 — 14(6); O2 — 9(5).     

Conformational Analysis of Thermotropic Liquid Crystalline Polyesters

PCILO conformational calculations have been carried out on several model compounds of thermotropic liquid crystalline polyesters [—OC—φ—φ—φ—CO—Os—R—O—] where R = (—CH₂—)₂; (—CHCH₃—)₂; (—CHCH₃—CH₂—). Several conformations corresponding to the trans and gauche states of the C-C single bonds are preferred, the TGT form being of lower energy than the TTT form. The replacement of—CH₂—group by—CH(CH₃) group results in a decrease of the number of the energy minima, an increase in the energy of the molecule in all the preferred conformations, compared to that of the TGT form, a sharpening of the potential energy wells and an increase in the energy barriers. The presence of a methyl group also shifts the aliphatic chain away from the ideal trans and gauche positions.     

Interfacial stability and grain diameter of the metal phase of directionally solidified Al-Si-type eutectics

The morphology of the solid-liquid interface and the metal phase grain diameter of Al—Si-type eutectics (Al—Si, Ag—Si, Ag—Ge, Zn—Ge) were investigated in the range of a growth rate R = 0.2 … 20 mm/h and of a temperature gradient at the solid-liquid interface G = 2 … 25 K/mm. Three types of interfacial morphologies depending on the G/R ratios were found out. The G/R ratio of the transition from a planar to a nonplanar solid-liquid interface corresponds to the critical G/R|_c ratio, which can be calculated by the criterion of the constitutional undercooling. The grain diameter of the metal phase depends on growth parameters as follows: d_K ∼ R^—rG^—g with r = 0.33 … 0.43 and g = −0.37 … 0.03.     

A Polymorph Crystal Structure of Hexaphenyl Observed in Thin Films

Highly oriented thin films of hexaphenyl — which are used in organic opto‐electronic applications — are characterised in terms of their crystal structures. Two different crystal structures of hexaphenyl (C₃₆H₂₆) are observed when the films are prepared by physical vapour deposition at various substrate temperatures. If the substrate is kept at room temperature, hexaphenyl crystallises within a structure which is already known from single crystal investigations. However, when the thin films are grown at a substrate temperature of 160°C a new crystalline phase appears. This structure was characterised by X‐ray and transmission electron diffraction. Due to the strong preferred orientation of the crystallites within the thin films, the lattice constants as well as main features of the new crystal structure could be determined. The lattice is indexed as monoclinic with: a = 7.98Å, b = 5.54Å, c = 27.64Å and β = 99.8°. The new crystal structure has high similarity to the already known crystal structure: Both structures are built by layers of hexaphenyl molecules, within one layer the aromatic planes of the hexaphenyl molecules are packed in a herringbone pattern. The characteristic feature of the new structure is that the long axes of the hexaphenyl molecules are arranged absolutely perpendicular to the layers, whereas, within the already known structure the long axes show an tilt angle of 17° to the layer normal direction.     

Microharness and dislocation mobility in ionic crystals

The correlation between microhardness and dislocation mobility was investigated for the series of ionic crystals in the wide temperature interval (77 – 400 K). It was shown that the dislocation mobility was not the main parameter responsible for the microharness change in the series of KCl—NaCl—NaF—LiF—MgO crystals or in temperature lowering from 293 to 77 K. A marked activation of the dislocation mobility can play a significant role in the range T > 293 K only. In the low temperature region the microhardness change may be connected with the parameters caracterising the dislocation multiplicatio and interaction.     

Growth of USb2 single crystals and their structural perfection

USb₂ single crystals were grown by three methods; I — Chemical vapour transport with iodine as transporting reagent, II — Crystallization from U Sb liquid solution, III — Crystallization from U Sb Sn liquid solution. The morphology of growth and results of X-ray topography examination of crystal surface are given.     

Synthesis and characterization of ZSM-8-type zeolite crystals

Procedure for hydrothermal synthesis of ZSM-8-type zeolite crystals, using TEA—OH as a template, in the system having molar composition 16.2 (Na₂O) — Al₂O₃ — 117 (SiO₂) — 4.8 (TEA)₂O — 3887 H₂O at 170 °C is described. Results of characterization of these crystals by XRD, IR, EDAX, SEM, TGA, and adsorption studies are described and discussed. X-ray diffraction studies establish that the crystals are ZSM-8-type with structure similar to that of ZSM-5-type crystals. Crystals have prismatic bipyramidal morphology with average size 18–25 microns. Degased calcined samples adsorb xylenes in the order p > m > 0. Pore length per unit cell, estimated from n-hexane adsorption studies, is 46 Å.     

Crystal structure,thermal analysis and IR spectroscopy investigations of N,N‐dimethyl‐1,3‐propanediammonium monohydrogenmonophosphate trihydrate

A new organic monohydrogenmonophosphate (C₅H₁₆N₂)HPO₄.3H₂O (abbreviate as MPAP) is prepared by reacting H3PO4 with N, N‐dimethyl‐1,3‐propanediamine. This compound crystallizes in the orthorhombic crystal system, space group Pca2₁. Unit cell parameters are a % 8.1445(1) Å, b % 11.7734(2) Å, c % 12.9021(2) Å, with, Z % 4 and ρ_m % 1.31 g cm⁻³. The structure was solved, using the direct methods and refined against F² to a reliability R factor of 0.0257. Three types of hydrogen bonds participate to the structural cohesion: O(P)—H…O, O(W)—H…O and N—H…O. The first one connects HPO₄ groups in infinite chains. This organization of the phosphoric groups creates voids in which are located the water molecules which are themselves connected by the second type of hydrogen bonds to the adjacent phosphoric groups that lead to a typical layer organization of a polyanion [HPO₄.(H₂O)₃ ]²ⁿ⁻_n. The third hydrogen bond type is responsible for the cohesion between the two‐dimensional polyanions. Thus, a framework in a threedimensional way is then created. The thermal decomposition of MPAP shows a large endothermic effect corresponding to the elimination of the water molecules and a set of endotherms which are probably due to the evolution of ammonia from the structure and the decomposition. The title compound was also characterized by IR spectroscopy, the interpretation of the spectra is based on theoretical analyses and literature data. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Density and Ultrasonic Velocity Measurements in Hexyloxybenzylidene Phenylazoaniline

The temperature variation of density and ultrasonic velocity of the liquid crystal hexyloxybenzylidene phenylazoaniline are reported. The density across the smectic A—smectic B transition is more predominant than the other transitions. The density variation with temperature and the calculated thermal expansion coefficients suggest that the transitions isotropic liquid—nematic, nematic—smectic A and smectic A—smectic B are of first order. Anomalous behaviour of ultrasonic velocity is observed across the isotropic liquid—nematic transition and prominent dips in velocity are observed at the nematic—smectic A and smectic A—smectic B transitions. The adiabatic compressibility (β _ad ) Rao number (R _a ) and molar compressibility (B) are estimated using the experimental density and ultrasonic velocity.     

ECLC 93 — European Conference on Liquid Crystals Science and Technology, 7–12 March 1993, Flims,Switzerland

Abstract

February 11th dawned clear and bitterly cold. The Pennines were white with Christmas card icing. The sky was blue. The sun was shining. God was clearly in his heaven and Blondie were back at number one, as representatives of the UK liquid crystal scene gathered at the University of Hull for a ceremony to mark the naming of the new organic chemistry laboratories after George W. Gray. The ceremony involved the unveiling of a plaque by the Vice Chancellor (Professor D. N. Dilks), followed by an afternoon of three lectures. The first, a tour of reminiscence by George Gray, outlined his early scientific life—how he narrowly escaped a career in the oil industry in the Middle East, and the events leading up to the synthesis of pentylcyanobiphenyl. The point he made about his gratitude to the University for giving him space and freedom to develop his liquid crystals work was well taken. The second talk, by Steven Ley of Cambridge University, described the synthesis of okadic acid. This was an impressive example of the power of modern organic synthetic chemistry. The third talk from John Goodby outlined some of the more recent liquid crystals interests at Hull, including smectic-C materials, and then concentrated on a new and promising class of mesogens: the liposaccharides.