Investigation of the Interaction of Quartz with Hydrogen under Supply of Mechanical Energy (II) Investigation by IR Spectroscopy

Infrared investigations demonstrate a chemical interaction of quartz in hydrogen atmosphere during mechanical activation: By means of the SiH stretching band the number of formed SiH-groups is estimated as a function of the period of activation. of activation. This number is more than one order of magnitude less than the total number of adsorbed molecules.     

New thermotropic cubic mesophases

1,2-Bis-[4-n-alkyloxybenzoyl]-hydrazines with the general formula possess smectic C phases and at lower temperatures additional optically isotropic phases. According to X-ray investigations these isotropic phases show cubic symmetry. The lattice units consist of aggregations with micellar dimensions. The substances were characterized by microscopic, dilatometric and calorimetric investigations. The new cubic mesophases do not exhibit complete miscibility with the “smectic D” phases.     

OD interpretation of the crystal structure of lithium tellurite,Li2TeO3

The OD groupoid family of the structure of lithium tellurite, Li₂TeO₃, is characterized by the symbol: . The OD groupoid of the structure is deduced from the observed arrangement of points in reciprocal space, the symmetry of the intensity distribution and the systematic absences. The structure is built of OD layers of one kind. Any OD layer is idendical to a Li₂TeO₃ double sheet. The assumption of Folger that the structure is an OD structure has been found to be justified.     

Thermotropic Liquid Crystalline Compounds with Lateral Long Chain Substituents (VII). X-Ray Studies in 1,4-Bis-(4-n-oetyloxybenzyoloxy)-2-n-alkylbenzenes

X-ray studies in substances with the general formula in the nematic states were performed. The results prove the existence of cybotactic groups despite the fact that the branched substances do not show smectogenic properties. We propose a model for the packing of the molecules, which explains the influence of the lengths of the lateral branches on the structure of the cybotactic groups.     

OD Interpretation of Pyroxenes

The structures of pyroxenes are interpreted as OD structures consisting of layers. The symmetry relations of the idealized structures of “high pyroxenes”, consisting of only one kind of silicate sheets are described by the OD groupoid family: In this case the tetrahedral layers (OD layers) are identical with silicate sheets and the octahedral layers (OD layers) are identical with the chemical octahedral sheets, apart from the fact, that the O atoms are considered to belong partly to one and partly to the other idealized layer. In the idealized pyroxene structures, which are called in this paper “low pyroxenes”, every second silicate sheet is of lower symmetry. A silicate sheet of higher symmetry is considered as an OD layer, called tetrahedral layer. An OD layer of the other kind, called compound layer, consists of one silicate sheet of lower symmetry with an octahedral sheet attached to it on either side. With this definition of the two kinds of layers, the OD groupoid family has the following symbol: Polymorphism, disorder, twinning and parallel intergrowth are explained on this basis.     

EDA Complexes in Liquid Crystalline Mixed Phases of Novel Compounds with Lateral Dicyanoethenyl Substituents

We synthesized each four members of the new series All compounds are nematic. The dicyanoethenyl derivatives possess strong elecgtron acceptor properties. This is demonstrated by EDA complex formation in two binary systems in which induced smectic phases are lacking.     

On the characterization of individual defects in silicon by EBIC

EBIC recombination-contrast of defects is mainly caused by impurity atmospheres surrounding them. The contrasts for geometrically similar defects in samples having different diffusion lengths L > 100 μm are in proportion to the defect strengths .     

The polymorphism of some liquid crystalline 4′-n-alkyloxy-3′-nitro-biphenylcarboxylic acids

The substances of the homologous series with n = 6, 12, 14, 15, 16, 18 were investigated by calorimetry and microscopy. In the lower members exist nematic, smectic A and smectic C phases, in the homologs with n = 16 and 18 appear phases of the type smectic D with cubic structure. The kinetics of these phase transitions, in which smectic D is participating shows a strong dependence upon the experimental conditions. Supercooling, as well as, overheating effects were found. In the supercooled state we could detect for the first time smectic phases, which are metastable with respect to another liquid crystalline phase (S_D).     

Chiral SmC* liquid crystals obtained by mixing of SmC and cholesteric phase

The binary mixtures of the substance providing cholesteric phase exhibit a chiral SmC* phase for certain concentration and temperature range. This phase was verified to be ferroelectric. The temperature dependences of the spontaneous polarization and the coercive field were determined for three concentrations. The pitch of the helical structure is approximately indirectly proportional to the molar concentration of the cholesteric substance and varies from 3 μm to about 25 μm in the concentration range from 20 mol% to 5 mol% of the cholesteric substance. For the lower concentrations the sample is unwound in planar samples due to the surface anchoring. Two possible unwound planar configurations can be switched by electric field.     

Thermotropic liquid crystalline compounds with lateral long-chain substituents (IV). Physical properties of 1,4-bis-[4-n-octyloxybenzoyloxy]-2-n-alkylbenzenes

In 15 Substances of general formula transition temperatures, transition enthalpies and entropies, densities and phase transition volumina, order parameters of a dissolved dye and optical refractive indices were measured. Additional miscibility and X-ray investigations were performed. The results are discussed on the basis of molecular statistical theories of the nematic state and point to a conformation of the long lateral chains which is nearly parallel to the molecular long axes. The results further show the dominating importance of the steric repulsive forces in stabilizing the nematic state.     

Influence of lateral branches on the properties of liquid-crystalline 1,4-Bis-[4-n-hexylbenzoyloxy]-2-subst.-benzenes (I).: measurement of density,viscosity and optical anisotropy

8 compounds of the substance class of the 1,4-bis-[4-n-hexylbenzoyloxy]-2-subset.-benzenes and additionally 1,4-bis-[4-n-hexyleyclohexanoyloxy]-2-ethylbenzene were sythesized and density, viscosity and optical refractive indices were measured in the nematic and isotropic state. The lateral branching causes decrease of the melting and clearing temperatures, diminishing of the optical anisotropy and order parameter, but increase of the viscosity.     

Thermotropic liquid crystalline compounds with lateral long-chain substituents (II).: Synthesis and liquid crystalline properties of 1,4-Bis [4-substituted-benzoyloxy]-2-n-alkylbenzenes

We synthesized 102 new 1,4-bis-[4-subst.-benzoyloxy]-2-n-alkylbenzenes of the general formula with R = alkyl, alkyloxy, alkanoyloxy, alkyloxycarbonyloxy and n = 0 to 16. Surprisingly all of the new compounds are liquid crystalline nematic. Thus it is proved that lateral long chain substituents are compatible with liquid crystalline properties.     

The OD Structure of Dinitrosylcobalt Chloride, [Co(NO)2Cl]2

The OD groupoid family of the structure of dinitrosylcobalt chloride, [Co(NO)₂Cl]₂, is characterized by the symbol: The OD groupoid family of the structure is deduced from the observed arrangement of points in reciprocal space, the symmetry of the intensity distribution and the systematic absences. The structure is built of OD layers of one kind. The determination of the structure of the ordered orthorhombic form (MDO₂) has been determined from Weissenberg data obtained by JAGNER and VANNERBERG refined with OD full-matrix least-squares methods, based on a total of 150 reflections and anisotropic temperature coefficients. An R value of 0.13 has been obtained. The assumption of JAGNER that the structure is composed of dimers has been found to be justified.     

Thermotropic liquid crystalline compounds with lateral long-chain substituents (III). Molar volumina,viscosities, optical refractive indices and order parameters of 1,4-Bis-[4-n-octyloxybenzoyloxy]-2-n-alkylbenzenes

In the substance class of the general formula densities, thermal expansion coefficients, viscosities, optical refractive indices and the order parameters of a dissolved dye were measured in the isotropic and nematic states. The results are discussed briefly.     

The precipitation of sparingly-soluble metal ‘oxinates’ induction periods and nucleation rates

The precipitation of barium, strontium, calcium, magnesium, zinc, cadmium, lead, cobalt, nickel and copper 8-quinolinolates (‘oxinates’) was studied in buffer solutions (pHs from 10 to 4.5) at 22 °C: the metal cation and overall ‘oxinate’ with ‘oxine’ concentrations were varied from 0.0005 to 0.010 M (and saturation rations varied from 3 to 3.000). The induction periods, before the main growth surge, were measured at different metal oxinate concentrations (C) and saturation ratios S = (C)/S · P_r^1/3. Nucleation rates were determined from combined measurements of induction periods and final crystal numbers. Nucleation rates varied with saturation ratios according to the relation \documentclass{article}\pagestyle{empty}\begin{document}$ R_n = k_1 \cdot S^8 {\rm\ nuclei cm}^{ - {\rm 3}} {\rm sec}^{ - {\rm 1}} $\end{document} Induction periods decreased with increasing concentration and supersaturation; over the range t > 3.000 to < 1 sec, . Where t and t were factors that depended on nucleation rates and metal salt solubility. t values decreased and t values increased with decreasing solubility. Precipitation occurred through homogeneous nucleation. Low nucleation rates and prolonged induction periods in solutions of medium to high supersaturation were related to slow rate-determining stages in nucleus formation and to complex formation between metal cation and oxinate anion.     

The structure of N-Pyrid-2-yl-iminotriphenylphosphorane,C23H19N2P

M_r = 353.9, monoclinic, P 2₁/c, a = 11.371(4), b = 11.391(5), c = 14.699(11) Å, β = = 97.78(2)⁰, Z = 4, V = 1888.6(6) ų, D_x = 1.28 Mgm⁻³, final R = 0.052 for 2360 independent reflections excluding those with |F₀| < 5 σ(F₀). Intensities were measured with an automatic diffractometer. The PN C- part of the molecule is nearly coplanar with the pyridinring (torsion angle 6.4°). The P atom and the N(2) atom of the pyridinring overlap with their van der Waals spheres and have nearly the position with the maximum of steric hindrance. This conformation of the molecule is the consequence of a conjugation between the Ph₃P=N-group and the N-standing pyridine ring as well as of an attraction between the P atom and the N(2) atom.     

The Precipitation of Sparingly-Soluble Alkaline-Earth Metal and Lead Salts with Slow Development of Supersaturation (Slow Anion and Hydroxyl Ion Addition): Kinetics of Nucleation and Induction Periods

Barium and lead sulphate and chromate precipitations were studied at 20° to 95°C at precipitation rates varying from 10⁻³ to 10⁻⁷ ion l⁻¹ sec⁻¹: the supersaturation was developed by slow direct addition of anion to metal nitrate solution and by neutralisation of equivalent metal salt in excess acid solution. Slow heterogeneous nucleation occurred onto particles dispersed within the aqueous solution. The nucleation rate at any time was Where k_n is the rate constant for heterogeneous nucleation, N_∞ is the maximum number of potential nuclei, n_t is the number of nuclei after time t, I. P_t is the ionic product (C_mt)(C_mt) and 2π is the number of metal salt ions in the critical nucleus, generally eight. Crystal growth started after induction periods (t̄) at times just after the times for maximum rate of formation of nuclei. The induction periods (t̄) for precipitations from solutions of initial cation concentration ^cM₀ varied with precipitation rate (R) according to the relation, where γ = π/(π + 1) and k₁ (the unit reciprocal induction period) = . Nucleation rate constants for different precipitations were estimated from the k₁ values and are tabulated. For slow precipitations by direct anion addition, the rate constants were lower for precipitation from solution of the salt of greater solubility. The rate constants for slow precipitation of metal chromates from acid solution were far lower than those for slow precipitation by direct chromate addition. Rate constants decreased somewhat with rise in precipitation temperature.     

Absorption and ionic conductivity of oxygen-containing SrF2 crystals

An absorption band at 3644 cm⁻¹ is caused by isolated OH⁻ ions. O⁻ ions cause an absorption band at 213 nm the oscillator strength of which is 0.020. Charge-compensation of O⁻ ions is effected by F⁻ ion vacancies (F). As for CaF₂ crystals there occur monomers and dimers of [O⁻ – F] complexes. The mass action constants of association of F with oxygen centres are K_AD = ⅓ exp (4.28 – 0.82 eV/kT) for [O⁻ – F], K_AT = 4 exp (17.4 – 1.25 eV/kT) for [2 O⁻ – F] and K_AQ = exp (4.2 – 0.89 eV/kT) for [2 O⁻ – 2 F].     

The precipitation of alkaline-earth metal and transition metal ‘oxinate’ powders from aqueous solution. Crystal numbers and final sizes

The precipitation of barium strontium, calcium, magnesium, zinc, cadmium and lead, manganese, cobalt, nickel and copper 8-quinolinolates (‘oxinates’) was studied from equivalent solutions, at pHs from 4.5 to 10, by optical microscopy: the metal cation and overall ‘oxinate’ with ‘oxine’ concentrations were varied from 0.0002 to 0.020 M (while the mean metal oxinate concentrations varied from 10⁻⁷ to 0.001 M). Crystal growth started after induction periods; the precipitations were heterogeneously nucleated at low supersaturations and homogeneously nucleated at medium to high supersaturations. The final precipitate crystal numbers depended on the number of nuclei formed during the induction periods. Crystal numbers at medium to high supersaturations increased with increasing initial metal oxinate concentration according to the relation, The final crystal lengths in this supersaturation range then decreased (from maximum values) with increasing initial mean metal oxinate concentration according to the relation, For precipitation from solutions of any concentration at any pH, smaller crystals were generally obtained in the precipitates from solutions of the metal oxinate of lower solubility.     

Effect of the seed crystallographic orientation on AlN bulk crystal growth by PVT method

The growth of AlN crystals by PVT method was investigated using TaC crucible in the temperature range of 2250‐2350 °C. AlN boules with 30 mm in diameter were successfully grown on the crucible lid by self‐seeded growth. The AlN boules consist of the spontaneously nucleated AlN single crystal grains with the {1010} natural crystalline face. The fast growth rate of more than 1 mm/h was achieved. AlN crystals grown on (11 0)‐, (10 0)‐, and (0001)‐face AlN seeds were investigated. Different experimental phenomena have been observed under particular condition. The crystal grown on (11 0)‐face seed has different natural crystalline face from the seed. For the crystal grown on (10 0) or (0001) seed, the crystal natural crystalline face is same as the crystallographic orientation of the seed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)