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.     

Rheological behaviour of lamellar eutectic Al?Al2?Cu elaborated by induction heating

This paper presents solutions to the experimental problems encountered in the elaboration of lamellar Al Al₂Cu or fibrous Al Al₃Ni eutectic samples using the Bridgman technique. The objective is to prepare samples for use in mechanical tests. The investigation of the elaborated structures of Al Al₂Cu (orientation, grain selection, shape of the solid-liquid (S.L.) interface, interlamellar spacing λ…) can then be used to confirm the predicted behavior. Creep tests under constant applied stress σ (from 2 to 5 · 10⁷ N/m²) at temperatures from 300 to 450 °C show:

• – that a stationary state exists (with constant strain rate )
• – the influence of an imperfect orientation
• – the existence of a Bailey-Norton creep law = kσⁿ. This law leads to the possiblity of finding a constitutive equation for high temperatures tests.

     

Incorporation concentration dependence of phosphorus in the deposition of silicon epitaxial layers from silane-phosphine-hydrogen mixtures

The empirical incorporation characteristic N with the phosphine input pressure (P) as the controlling variable and the phosphorus incorporation concentration ((14 < lg N<18)) as the controlled variable is theoretically explained by comparing the thermodynamic equilibrium pressures of the various phosphorous hydrides and the various molecular species of the phosphorus vapour in the Si P H system in their respective incorporation equilibria with regard to the phosphorus incorporation concentration. In the lower incorporation concentration range (lgN > 18) there is an almost total agreement of the values of the phosphine equilibrium pressure (PPH_j; j = 2; 3) and the phosphine input pressure. In the upper concentration range (lg N > 18) there is a close approximation of the equilibrium partial pressure of the dimeric phosphorous vapour (PP₂) to the phosphine input pressure. There is no marked effect of the conduction electron density in silicon at the deposition temperatures considered on the incorporation characteristic.     

Lattice Thermal Expansion in CuGaT2 and CuInTe2 Compounds over the Temperature Range 80 to 650 K from X-ray Diffracion Data

The lattice parameters a and c as well as the thermal expansion coefficients α⟂ and α∥ in the two principal direction for CuGaTe2 and CuInTe 2 chalcopyrite-type compounds have been determined as a function of temperature in the range from 80 to 650 K by the X-ray diffraction method. It is found for both the compounds the coefficient of expansion along the α axis (α⟂) is larger than that along the c axis (α∥) over the whole investigated tem-perature range. When comparing the results for a series of the CuB^IIIC compounds (B Ga, In; C S, Se, Te) it is shown that the thermal expansion anisotropy increases strongly when the Ga atom replaces the In atom while it changes a little when the Te atom replaces the Se atom or the S atom.     

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].     

Phase lead determined growth of 〈100〉 — textured germanium crystallites in eutectic Ag?Ge alloys

Al Si type eutectics (Al Si, Ag Si, Ag Ge, Zn Ge) form 〈100〉 — textured eutectic dendrites of the semiconductor phase when a certain growth rate R and liquid temperature gradient G are held. The spacings of these eutectic dendrites λ follow the relationship: λ = (r_λ ≈︁ 0.2; g ≈︁ 0.5). The exponents of this relationship can be explained by the model of phase lead determined growth. This model is based on the consideration of the analogy to dendrite growth. The Al Si type eutectics have geometrically similar morphologies for determined G^x/R-relations (x = 1.25 in the case of Ag Ge) and the relation λ²R = const. is valid. In this paper the Ag Ge eutectic will be discussed in close detail.     

Reactivity of CCl4 plasma against SiO2 surfaces

SiO₂ is etched considerably by a CCl₄ plasma at surface power densities of about 0.3 W cm⁻². This etching process is investigated by the SiCl₄ formation with aid of mass spectroscopy where final products of the etching process and the extracted ions were studied in dependence on time in a closed plasma volume. The primary step of the etching process is the activation of SiO₂ by the plasma involving breaking of siloxan bridges. The overall mechanism of the SiO₂ etching by the CCl₄ plasma is proposed in form of The rate limiting constants are k₀ and k₃. The SiCl₄ formation is decreased or inhibited by an admixture of Cl₂, H₂, O₂ or CO to the CCl₄ plasma. CCl₄-Plasmen führen zu einem Ätzangriff an SiO₂-Oberflächen. Dieser Ätzprozeß ist bei Leistungsdichten an der zu ätzenden Oberfläche von > 0,3 W cm⁻² deutlich über eine SiCl₄-Bildung nachweisbar. Der Primärschritt ist eine Aktivierung der SiO₂-Oberfläche durch das Plasma, die zu Bindungsbrüchen der Siloxanbrücken führt.     

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.     

Strukturelle Umklapp-Vorgänge in metastabilen β1-Kupfer-Zink-Mischkristallen bei tiefen und höheren Temperaturen (I). Gitterdynamische Skizze1)

The quantity of the shear-modulus G′ = (c₁₁ – c₁₂)/2 is a measure for the probability of structural Umklapp-processes to occur in metastable β₁-Cu-Zn-solid solutions. Such processes take place, if G′ = G′(T, x) would fall below a critical limit, G′_crit, e.g. by lowering of temperature T or/and Zn-concentration x, because the Fermi-contribution to G′will sink in the 1^st and with him additional the Coulomb-contribution in te 2^nd case. Both ones are the authoritative stabilizing factors for β₁ and therefore specific fo its lattice-dynamical behaviour, especially in the longwavy range of thermoacoustic lattice-vibrations, by which the cooperative Umklapp-motion will escape. Umklapping can also be initiated by favourably oriented dislocations, is G′ would approach to G′_crit in their neighbourhood: G′_critG′(xM8), with xM8  Umklapp-concentration. This is possible by variation of x during isothermal reactions, in the course of whicht he β₁-matrix will heterogenize itself into Zn-poorer and -richer districts β and β (pre-diffusion by means of quenchy vacancies). Both kinds of districts, among which the latter ones will enhance their degree of stability, are joint together coherently. They build up a so called β /β -parquet. The parquet-bricks can reach a critical size, which is necessary that sufficient large atom-collectives can simultaneously be caused to an Umklapp-motion and to occupate new equilibrium positions by thermo-acoustic shear-waves (comparison with a sin-wave beeing changed to a zigzag-line). Only at higher temperatures the bricks come up to the critical size. Umklapping comes about only in the β -bricks, which turn by it to a transition lattice (β₂) with a structure similary to that of the lowtemperature-martensite β′′. After that β₂ changes to α-phase. The way β ⇒ α is marked by the following steps: prediffusion, Umklapping + dislocation, leading to β₂, and a further dislocation dissoziation, leading the atoms to the equilibrium positions in the α-lattice. The so stepped mechanism acts an nucleationmechanism of the α-phase. After the nucleation the α-nuclei grow at the cost of too much formed β (postdiffusion). By isothermal reactions at too low temperatures a mini-herterogenized state of the β₁-matrix will be caused comparable with coldhardening states of other alloys (Guinier-Preston-zones). A β₁-matrix in such a state is unable to isothermal Umklapping, so that α-crystals can be formed – provided that the mini-heterogenities are resolved by increasing of the reaction temperature.     

Density and mobility of anti-frenkel defects in SrF2 crystals

By fitting the theoretically calculated temperature-dependent conductivity σ to the measured dependencies log σT ÷ 1/T the following parameters have been determined: free formation enthalpy of anti-Frenkel defects g_AF = 2.05 eV – 6.35 kT; mobilities of F⁻ion vacancies F and interstitials F: v_νT = 600 exp (-0.70 eV/kT) cm² K/Vs, v_iT = 1.1 · 10⁴ exp (-0.93 eV/kT) cm² K/Vs. — The free association enthalpies of complexes consisting of single foreign ions (Sc³⁺, Y³⁺, La³⁺, Sm³⁺, Li⁺, K⁺, Na⁺, O⁻) and the charge-compensating defect were obtained. The vibration frequency of F⁻ ions in the neighbourhood of F and F is changed by a factor of 2.6 and 0.6, respectively.     

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.     

Untersuchung der Korngrenzendiffusion von Zn-65 in α-Aluminium-Zink-Legierungen

The diffusion of Zn-65 in large angle grain boundaries in Al and in 8-Al Zn alloys was investigated. p_K = γδD_K rises exponentially up to a Zn content of 7 at-%, then at a lower rate with concentration. Above 40 at-% Zn p_K is almost independent of concentration. At the solidus temperature, D_K is of the order of 10⁻⁵ cm²/sec. A simple vacancy model for the diffusion in large angle grain boundaries is being discussed. From the model, the following parameters for the grain boundary self diffusion in Al and Cu that have not been investigated so far can be estimated: The activation energies for the electromigration in thin polycrystalline Al films and for the superplasticity at the eutectoid composition are compatible with the results of this investigation. The kinetics of the discontinuous precipitation and the eutectoid transformation in Al Zn alloys is governed by the phase boundary diffusion.     

Thermal expansion anisotropy and individual bond expansion coefficients in ternary chalcopyrite compounds

The individual bond expansion coefficients of the A^IIB^IVC and A^IB^IIIC₂^VI chalcopyrite compounds are calculated from the principal linear thermal expansion coefficients of the lattice parameters using the regular B C tetrahedron model and a model with a temperature independent free parameter of the lattice. It is shown that the bond expansion coefficients derived from the latter model are in better agreement with the trends found for the interatomic forces in the chalcopyrite compounds and observed for the thermal expansion coefficients in the binary AC, A^IIC and BC compounds.     

The Precipitation of Barium Chromate with Slow Development of Supersaturation. Kinetics of the Crystal Growth

Slow barium chromate precipitation was studied in well-stirred solutions — final concentration 0.002 mole 1⁻¹ — at 20°C at mixing rates varying from 0.2 to 2 · 10⁶ mole 1⁻¹ sec⁻¹; the kinetics of the crystal growth process were studied by chemical analysis and by optical microscopy. The crystal growth started after induction periods; regular growth then took place on the nuclei formed during these periods. For the main growth, up to about seventy percent precipitation time, growth rates at any time depended on the (residual excess solute concentrations in solution)². Immediately after the induction periods, crystal lengths varied with growth time according to the relation, for the main growth, crystal lengths varied with growth time according to a more complex relation, where k_l is the rate constant for surface growth, R_c is the rate of development of metal salt concentration and K is a constant that depends on the number of precipitate crystals. After some growth time τ = τ^*, when l_τ = l_τ*, all fresh solute added to the solution was utilised immediately and was deposited onto the growing crystals; then, for the final thirty percent precipitation, crystal lengths varied with growth time according to the relation, .     

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 Precipitation of Strontium and Lead Sulphates from Aqueous Solution. Kinetics of the Crystal Growth

The precipitation of strontium and lead sulphates from well-stirred supersaturated aqueous solutions, of initial solute concentrations C₀ = 0.001 to 0.020 M and C₀ = 0.0002 to 0.003 M respectively, was studied at 20° and 40°C by chemical analysis and optical microscopy. Nucleation occurred during induction periods and continuous regular growth then took place onto the nuclei formed during these periods. Crystallisation was complete after 4 to 48 hr. The crystal growth was rate-controlled by the rate of deposition of metal salt ions onto the growing crystal surfaces. This rate (dC/dt), at any growth time, then depended on both the overall surface area (A_t) and on the residual excess solute concentration (ΔC_t) in solution according to the relation while the growth rate (dα/dt), expressed in terms of degree of crystallisation, was . The rate constants (k_α) for the crystal growth of strontium and lead sulphates at 20°C were 22 and 4200 sec⁻¹ M⁻² respectively — that is, greatest for the salt with least cation hydration –; these constants increased 4 to 6 times for 20°C temperature rise. The rate-determining process for the metal salt deposition was probably the ion dehydration.     

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.     

Transmission electron microscopy investigation of B27 martensitic phase in polycrystalline YCu intermetallic compound

Polycrystalline YCu specimens with a CsCl‐type B2 structure made by induction melting were investigated by transmission electron microscopy (TEM). TEM studies show that an orthorhombic YCu B27 martensite with FeB‐type structure having lattice parameters a = 0.71 nm, b = 0.45 nm and c = 0.54 nm forms during deformation at ambient temperature. (101) twins are observed in the YCu B27 phase. The orientation relationship of B27 with B2 matrix is (001)[1 0]_B27 ‖ (112)[1 0]_B2. Effects of B27 phase formation on the ductility of YCu alloy are discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The precipitation of barium chromate from aqueous solution (with rapid mixing): Kinetics of the crystal growth

The kinetics of precipitation of barium chromate from well-stirred aqueous solutions of initial solute concentrations C₀ = 0.0001 to 0.0010 M (supersaturations 8 to 80) was studied at 25 °C by conductivity measurements and chemical analysis. Nucleation occurred during induction periods and regular crystal growth then took place onto the crystallites formed during the induction periods. The crystal growth was rate-controlled, in this range, by the rate of deposition of metal salt ions onto the growing crystal surfaces. This rate, at any time, then depended on both the overall surface area (A_t) and on the residual excess solute concentration (ΔC_t) in solution according to the relation, the growth rate expressed in terms of degree of crystallisation was then The rate constant (K_α) for the crystallisation of barium chromate at 25 °C was 1.5 10⁶ sec⁻¹ M⁻².     

The influence of the direct quench and indirect quench to Ta > Th on the decomposition behaviour of an Al-2 at.% Zn-1 at.% Mg alloy

The decomposition behaviour of an Al-2.0 at.% Zn-1.0 at.% Mg alloy after direct quench (DQ) and indirect quench (IQ:T = 23 °C, t) to the ageing temperature T = 160 °C (above the temperature of the rapid homogeneous nucleation, T_h) was investigated by means of TEM and isothermal resistivity measurements. The precipitation density of the η-particles yields a maximum value at pre-ageing times about 10 min at T = 23 °C. To clear up the reason for that phenomenon a loop-formation and clustering model was introduced.