X-Ray topographic characterization of α-Fe2O3 single crystals obtained by chemical transport with TeCl4

The method of Lang is used to study the defect structure of „as-grown”︁ hematite crystals obtained by chemical transport with TeCl₄. The presence of twin boundaries, dislocations and crystallites built in the platelet matrices is established. Considerable differences in density and distribution of the crystal disturbances are observed with samples grown under the same experimental conditions. In some cases the real structure is found to be nearly perfect.     

Comments and reconciliation of the Ni–Bi‐system thermodynamic reassessments

The binary Ni‐Bi alloys as well as multicomponent materials comprising systems like Ni‐Bi‐Sn, Ni‐Bi‐Sb etc. are recently considered as prospective for design of lead‐free solders. For that reason various authors focused their attention to the Ni‐Bi system thermodynamics. The studies identified five phases in the above system. Two of them (i.e., (Ni) and liquid), were treated as disordered substitutional solutions. The phase NiBi₃ is stoichiometric and a standard two‐sublattice model was repeatedly applied to describe its Gibbs free energy, while for the nonstoichiometric NiBi phase, a three‐sublattice model was retained. The pure bismuth phase ((Bi)) is stoichiometric as well. The results are discussed and compared to literature thermochemical and topological data. In liquid state, strong repulsions between nickel and bismuth atoms are anticipated in the nickel rich‐side, but no data about a liquid phase miscibility gap is available yet. Therefore, the stability of the liquid phase has to be reassured, in spite of positive deviations from ideal behaviour. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enthalpies of formation of Ni-Sn compounds

Enthalpies of formation (Δ_fH) of nickel-tin compounds have been measured by direct reaction calorimetry: (approximate value); .Standard states are solid Ni and liquid Sn at the respective working temperatures: 728, 1288, 1389, 1332, 943 and 846 K.The enthalpy of formation of the Ni₃Sn high-temperature form is measured for the first time, while that of Ni₃Sn₂_LT must be considered as approximate because the corresponding calorimetric reaction was incomplete.The chemical and phase compositions of the specimens have been verified by electron probe microanalyses and by high- and room-temperature X-ray diffraction analyses. Unidentified thermal effects have been observed in the Ni₃Sn₂ phases region.     

Phase equilibria in the GeSe2-SnTe system

Journal of Thermal Analysis and Calorimetry - The phase diagram of the system GeSe2-SnTe is studied by means of X-ray diffraction, differential thermal and measurements of the microhardness and the...     

Hydrolysis of 4-imino-imidazolidin-2-ones in acid and the mechanism of cyclization of hydantoic acid amides

The hydrolysis of iminohydantoins generates the same tetrahedral intermediate as that obtained in the cyclization of hydantoic acid amides to hydantoins. The ratio of the products of imine hydrolysis under kinetic control is determined by the relative height of the barriers of the breakdown of to amide or to hydantoin. Thus the partitioning of products unequivocally proves which is the rate determining step in the cyclization reaction-formation or breakdown of . UV and 1H NMR monitoring of the acid catalyzed hydrolysis of four 5-substituted 4-imino-1-methyl-3-(4-nitrophenyl)imidazolidin-2-ones found hydantoins as the only products. The kinetics of hydrolysis of imines were measured in 0.001-1 M HCl. Contrary to the remaining imines, 1,5-dimethyl-4-imino-3-(4-nitrophenyl)imidazolidin-2-one is readily oxidized as stock solution in THF containing peroxides to 1,5-dimethyl-5-hydroxy-4-imino-3-(4-nitrophenyl)imidazolidin-2-one . In all cases, hydrolysis was found to be zero order with respect to [H+]. As imines are fully protonated under the acidity studied, this is evidence of a transition state of a single positive charge. Comparison of imine hydrolysis rates with previous data on rates of cyclization of the corresponding amides of hydantoic acids allowed conditions (acid concentration, substitution pattern-gem-dimethyl effect) to be found that guaranteed kinetic control of the products obtained. Thus it was unequivocally proven that formation of the tetrahedral intermediate is rate determining in the cyclization of hydantoic acid amides. The small steric effects upon methyl substitution at 5-C and a solvent kinetic isotope effect kH/kD of 1.72 favour a mechanism for imine hydrolysis whereby the rate is limited by water attack on the protonated imine concerted with proton transfer from attacking water to a second water molecule.     

A note on the stability of local zeta functions

We show the existence of an interval of stability under small perturbations of local zeta functions corresponding to non-trivial local solutions of an elliptic equation with Lipschitz coefficients.

RÉSUMÉ. Nous démontrons l'existence d'un intervalle de stabilité pour la fonction zêta associée à une équation uniformément elliptique du second ordre à coefficients lipschitziens.

     

Influence of the discharge gas on the emission and thermal characteristics of laser-induced microplasmas

Summary An investigation has been made of the influence of argon, oxygen, and argon/oxygen blends in various ratios as the protective gas medium, on the intensities of the spectral lines, the amount of substance evaporated, and the excitation temperatures in the evaporation of an aluminium sample with the aid of laser irradiation and subsidiary excitation of the microplasma obtained. Maximum intensifying effect was observed when a pure argon medium was used. The gas medium does not influence the amount of substance evaporated from the sample. Within the experimental error of the twoline method used, the excitation temperatures do not appear to be influenced by the type of gas blend. An auxiliary voltage device was added to the laser equipment, which allows evaporation of the substance in an atmosphere of inert gas and in minute absolute amounts, with high energy in the discharge gap. This new approach improves the limits of detection.

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Zusammenfassung Der Einfluß der Schutzgasatmosphäre aus Argon, Sauerstoff oder Argon/Sauerstoff-Mischung in verschiedenen prozentualen Verhältnissen auf die Intensitäten der Spektrallinien, die Menge der verdampften Substanz und die Anregungstemperaturen wurde bei der Verdampfung einer Aluminiumprobe mit Hilfe von Laserstrahlung und mit Nebenanregung des Mikroplasmas untersucht. Ein maximaler Verstärkungseffekt wurde in reinem Argon beobachtet. Das Gasmedium übt keinen Einfluß auf die Menge der verdampften Probensubstanz aus. Im Rahmen der Fehler und der Genauigkeit der angewandten Zweilinienmethode wurden die Anregungstemperaturen von der Art der Gasmischung nicht beeinflußt. Die Laserausrüstung war mit einer Vorrichtung für Hilfsspannung ausgestattet, welche die Verdampfung und Anregung der Probensubstanz in einer Inertgasatmosphäre und in minimalen absoluten Mengen unter Hochenergiebildung in der Entladungsstrecke ermöglichte. Damit konnten die Nachweisgrenzen der Mikroelemente erweitert werden.

     

A Reference Direction Algorithm for Solving Multiple Objective Integer Linear Programming Problems

In this paper, we propose a reference direction approach and an interactive algorithm to solve the general multiple objective integer linear programming problem. At each iteration, only one mixed integer linear programming problem is solved to find an (weak) efficient solution. Each intermediate solution is integer. The decision maker has to provide only the reference point at each iteration. No special software is required to implement the proposed algorithm. The algorithm is illustrated with an example.     

Combined photoacoustic differential scanning calorimeter cell: Application to phase transitions

A variable temperature PhotoAcoustic (PA) cell built on a conventional Differential Scanning Calorimeter (DSC) is described. It can operate between 300 and 800 K and allows to perform PA and DSC measurements simultaneously. The frequency and temperature characteristics of the cell are examined using standard samples. The utilities of this combined PA-DSC cell for studying different types of phase transitions, such as solid-liquid, structural and glass transitions, are demonstrated.     

Chemical sensors with chalcogenide glassy membranes

The present review is emphasized on the recent achievements in the application of chalcogenide glasses (ChG) as membrane materials in chemical sensors, microsensors and multisensor systems. The questions concerning material synthesis, sensor designs and the concepts for the potential-generating mechanisms have briefly discussed. Most of the chalcogenide glass-forming systems and compositions investigated as membrane active materials have been summarized, and their analytical characteristics have been considered. The efficiency of chalcogenide-based chemical sensors in the real system analyses, as well as the advantages and disadvantages in their analytical performance have been evaluated and compared with the corresponding polycrystalline analogous.