Neutron activation analysis of heavy rare earths

A method of nondestructive activation analysis of heavy rare earth elements (Sm−Lu) is described. Intensities of γ-ray peaks are compared to that of an internal reference after irradiations by both thermal and fission spectrum neutrons. Results are obtained from computer comparisons of peak areas. Work was performed at the Ames Laboratory of the U.S. Atomic Energy Commission. Contribution No. 2895.     

Voltammetric trace determination of ubiquinones at mercury electrodes

Summary Voltammetric methods were developed for the determination of ubiquinones on the basis of their adsorption and redox behaviour at mercury electrodes. Linear calibration plots were obtained in the concentration range between 10^–4 mol/l and 2.3·10^–5 mol/l from differential pulse voltammetric measurements under experimental conditions avoiding significant adsorption of the analyte. A remarkable decrease of the detection limit down to 10^–7 mol/l was achieved with the help of adsorptive accumulation of ubiquinone molecules at the mercury electrode followed by differential pulse detection. The resulting non-linear calibration plot was explained with a model, which takes into account both adsorption and diffusion of the analyte.     

Templateless assembly of molecularly aligned conductive polymer nanowires: a new approach for oriented nanostructures

Although oriented carbon nanotubes, oriented nanowires of metals, semiconductors and oxides have attracted wide attention, there have been few reports on oriented polymer nanostructures such as nanowires. In this paper we report the assembly of large arrays of oriented nanowires containing molecularly aligned conducting polymers (polyaniline) without using a porous membrane template to support the polymer. The uniform oriented nanowires were prepared through controlled nucleation and growth during a stepwise electrochemical deposition process in which a large number of nuclei were first deposited on the substrate using a large current density. After the initial nucleation, the current density was reduced stepwise in order to grow the oriented nanowires from the nucleation sites created in the first step. The usefulness of these new polymer structures is demonstrated with a chemical sensor device for H(2)O(2), the detection of which is widely investigated for biosensors. Finally, we demonstrated that controlled nucleation and growth is a general approach and has potential for growing oriented nanostructures of other materials.     

Thermoanalytical investigations on the decomposition of double salts

The melting and decomposition behaviour of carnallite was investigated in the closed system under dynamic heating conditions and in the open system under dynamic and quasi-isothermal and quasi-isobaric conditions in the temperature range between 20 and 300°. DTA heating and cooling cycles in the closed system illustrate the incongruent melting of carnallite and the occurrence of different magnesium chloride hydrate phases. The thermal decomposition under quasi-isothermal and quasi-isobaric conditions begins at a pressure of at least 100 kPa from the melt and under reduced pressure from the solid. In any case KCl · MgCl₂ · 2 H₂O is formed which is decomposed to a basic product KMgCl_2.84–2.90(OH_0.10–0.16.

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Zusammenfassung Die Schmelz- und Zersetzungseigenschaften des Carnallits wurden im geschlossenen System unter dynamischen Heizbedingungen und im offenen System under dynamischen und quasi-isothermen und quasi-isobaren Bedingungen im Temperaturbereich von 20 bis 300°C untersucht. DTA Heiz- und Kühlzyklen im geschlossenen System verdeutlichen das inkongruente Schmelzen des Carnallits und das Auftreten verschiedener Magnesiumchlorid-Hydratphasen. Die thermische Zersetzung beginnt unter quasi-isothermen und quasi-isobaren Bedingungen bei einem Druck von mindestens 100 kPa aus der Schmelze und unter verminderten Druck aus der festen Phase. Die Zersetung verläuft stets über KCl · MgCl₂ · 2 H₂O zu einem basischen Produkt KMgCl_2.84–2.90(OH)_0.10–0.16.

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— -, - V 20–300°. . - - 100 , — . KCl · l₂ · 2 ₂, Kgl_2.84–2.90()_0.10–0.16.

     

Über Chalkogenolate. 82 [1]. N-Hydroxycarbamate und Ester der N-Hydroxycarbamidsäure und -carbimidsäure

On Chalcogenolates. 82. N-Hydroxy Carbamates and Esters of N-Hydroxy Carbamic Acid and Carbamic Acid The reaction between hydroxylammonium chloride, CO₂, and the corresponding hydroxide leads to N-hydroxy carbamates Esters of N-hydroxy carbamic acid have been prepared by reaction of N-hydroxy carbamates with alkyl bromide. – At room temperature the ethyl ester decomposes and forms the ester of N-hydroxy carbimic acid HO? N?C(OC₂H₅)₂. The prepared compounds have been characterized by different methods.     

N‐Heterocyclic Silylenes in Boron Chemistry: Facile Formation of Silylboranes and Silaborinines

Reaction of a N‐heterocyclic silylene (NHSi) with PhBX₂ (X=Cl, Br) readily afforded six‐membered silaborinines through an insertion/ring expansion sequence. Increasing the sterics of the borane from phenyl to duryl enabled the selective generation and isolation of the highly colored silylborane intermediates. Theoretical studies on the mechanism and energetics of the silaborinine formation were fully consistent with the experimental observations.     

Modeling and numerical approximations for bubbles in liquid metal

In simulations of liquid metals, various model approximations, each of which justified by experimental results lead to a simplified two-phase flow problem. This paper discusses numerical justifications for these approaches and provides quantitative results for a single rising bubble as a benchmark. Representing a bubble as a rigid object is shown to be valid for low Eötvös numbers in contaminated systems. Qualitative differences can be observed for larger Eötvös numbers. Further simulations are undertaken with different ratios of inner and outer viscosity. The benchmark problem considered may also be interesting for more general applications.     

Frequency doubling of Nd:YAG- and GaAs-lasers by KNbO3: Ta crystals

Abstract

For KNb_1-xTa_xO₃ crystals the influence of the Ta-concentration on the phase-matching properties for optical second harmonic generation (SHG) was measured. For non-critical phase matched SHG of the Nd:YAG-laser (1064nm) the coefficient d₃₁ of the tensor of the nonlinear susceptibility was applied, while for the GaAs-laser (905 nm) the coefficient d₃₂ was used. For both laser wavelengths the phase-matching temperature decreases with increasing Ta-concentration. Non-critical phase-matching at room temperature can be reached with the GaAs-laser for a Ta-concentration of ≈9%. The corresponding value for the Nd:YAG-laser is ≈14%.     

Evidence for Non-Innocence of a β-Diketonate Ligand

β-Diketonates, such as acetylacetonate, are amongst the most common bidentate ligands towards elements across the entire periodic table and are considered wholly redox-inactive in their complexes. Herein we show that complexation of 1,1,1,5,5,5-hexafluoroacetylacetonate (hfac⁻) to Cr^II spontaneously affords Cr^III and a reduced β-diketonate radical ligand scaffold, as evidenced by crystallographic analysis, magnetic measurements, optical spectroscopy, reactivity studies, and DFT calculations. The possibility of harnessing β-diketonates as electron reservoirs opens up possibilities for new metal–ligand concerted reactivity in the ubiquitous β-diketonate coordination chemistry.     

Freezing and Hydrate Formation in Aqueous Sodium Perchlorate Solutions

The determination of the phase diagram of the binary system sodium perchlorate – water is reported. Beside the eutectic point, two polymorph crystal structures of sodium perchlorate dihydrate were determined. The two crystal structures are discussed, compared to each other and to other known sodiumhalide dihydrate crystal structures. The two polymorphs of the perchlorate dihydrate represent the two variants of connected octahedra in the layer structure found for sodium halide dihydrates.