Microsegregation in liquid Pb-based eutectics

Temperature dependence of electrical conductivity, σ(T), thermoelectric power, S(T), and viscosity, η(T), of Pb-based eutectic systems was studied. Anomalous changes of thermophysical properties in liquid binary Pb_26.1Sn_73.9, Pb₄₄Bi₅₆, Pb₈₃Mg₁₇ and ternary Bi₄₆Pb₂₉Sn₂₅ eutectics occurred well above the liquidus. The temperature range of anomalies reached hundreds of degrees. The obtained results are interpreted assuming that microsegregation areas exist in the eutectic systems.     

In Situ Generated Gold Nanoparticles on Active Carbon as Reusable Highly Efficient Catalysts for a C −C Stille Coupling

Gold nanoparticle catalysts are important in many industrial production processes. Nevertheless, for traditional C ?C cross‐coupling reactions they have been rarely used and Pd catalysts usually give a superior performance. Herein we report that in situ formed gold metal nanoparticles are highly active catalysts for the cross coupling of allylstannanes and activated alkylbromides to form C ?C bonds. Turnover numbers up to 29 000 could be achieved in the presence of active carbon as solid support, which allowed for convenient catalyst recovery and reuse. The present study is a rare case where a gold metal catalyst is superior to Pd catalysts in a cross‐coupling reaction of an organic halide and an organometallic reagent.     

Nonclassical SNAPFL analogue as a Cy5 resonance energy transfer partner

We have synthesized a new SNAPFL analogue (1) that exhibits a large Stokes shift (78 nm) (abs. 542 nm, em. 620 nm) and a good quantum yield. Because of the large overlap between the emission spectrum of 1 and the absorption spectrum of Cy5, 1 functions well as a fluorescence donor to Cy5 and has been used in FRET-based experiments using estrogen receptor site-specifically labeled with Cy5 and a receptor ligand conjugated to SNAPFL.     

The cycloacylation — 1,3‐Acylrearrangement sequence as tool for highly substituted pyrrolones

The cyclization reactions between bis‐imidoylchlorides 1 and ketones, which possess different CH‐acidity, were investigated. Diphenylacetone 2 reacts under mild conditions via C,O‐cyclization of the preformed enolate to yield the iminofurane derivative 3 . Upon treatment with trifluoroacetic acid, the latter can be rearranged quantitatively into the pyrrolone 5 . In contrast, 1,3‐acetonedicarboxylate 9 and cyclohexanone 12 immediately lead to highly substituted pyrrolones 11 and 14 . Obviously, the primarily formed cyclization products undergo a very fast 1,3‐acyl rearrangement (Dimroth‐/Mumm‐Rearrangement). The structures of the maleiimide 11 and the indolone 14 were determined by single crystal X‐ray structure analysis. Due to its amino/imino substructure, compound 3 is an efficient ligand for metal complexation reactions, exemplified by the synthesis of two different Zn‐complexes 7 and 8 .     

PM IRRAS investigation of thin silica films deposited on gold. Part 1. Theory and proof of concept

Polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) was successfully used for the first time to characterize an optically transparent thin oxide film. SiO2 layers of 7 nm thickness were synthesized by plasma enhanced chemical vapor deposition (PECVD) on 200 nm thick gold covered glass slides. Despite the fact that silica is transparent and absorptive to IR radiation when deposited in the form of thin films on a gold surface, it preserves the high metallic reflectivity for the IR light. At grazing angles of incidence of the IR beam, the enhancement of the normal component of the electric field at the interface is comparable to that of Au alone. In addition, the analysis of the structure of a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid monolayer deposited using the Langmuir-Blodgett technique is demonstrated.     

Dilithium Hexaboride,Li2B6

Li₂B₆ is formed from the elements as transparent red microcrystalline compound (Li : B = 1 : 3; Mo crucible in closed Nb ampoule; 1723 K; 4 h). Single crystals are grown from a lithium silicide melt with large Li excess at 1923 K. Li₂B₆ is a semiconductor with electron as well as Li⁺ ionic conductivity which dominates above 600 K. Microcrystalline samples react with H₂O liberating gases and forming a brownish amorphous product, but larger crystals are not very sensitive. – Li₂B₆ crystallizes tetragonally in a new tP16 structure type which is a variant of the CaB₆ structure (a = 5.975 Å, c = 4.189 Å; Z = 2; space group P4/mbm). The [B₆^2–] net of the polymeric octahedro-anion is slightly distorted to give space for the insertion of a (3²434) net of the Li⁺ cations in the cavities (d(B–B)_endo = 1.766 Å; d(B–B)_exo = 1.720 Å; d(Li–B) = 2.363 Å; d(Li–Li) = 3.094 Å). The incomplete occupancy of the Li position (80%) and the electron density at a further position (20%) indicate the mobility of the Li⁺ cations.     

Instability of the melt flow in VGF growth with a traveling magnetic field

The linear instability of a thermally stratified melt flow in the VGF configuration driven by a traveling magnetic field (TMF) is considered numerically and experimentally. The dependency of the instability threshold on the governing parameters is found for several cuts through the parameter space covering a wide range of possible applications. In a first approximation the linear instability occurs when the dimensionless TMF forcing parameter reaches the magnitude of the Grashof number. This is particularly true in a medium-sized crucible where the first instability is axisymmetric and sub-critical. As the Grashof number increases the flow develops self-similar boundary layers and the instability becomes three-dimensional. The instability originates in the bottom boundary layer where the convection tends to suppress the imposed temperature gradient in the central part of the melt zone. It is shown that the TMF may serve as a tool to control the phase interface shape without causing flow instationarity when the crucible diameter exceeds a certain value. This value is estimated to be around 6 cm for GaAs. The flow stays stable if the TMF is used for a reversal of the meridional flow with the aim to remove a possible dopant concentration peak on the axis.     

Über 2,4-Difluorzimtsäure

Zusammenfassung Aus 2,4-Difluortoluol wurden nach üblichen Methoden 2,4-Difluorbenzaldehyd und 2,4-Difluorzimtsäure hergestellt.     

The Influence of Activating Co and Ni Additions on the Mechanisms of Reaction and Diffusion Interaction During Sintering of PV-N55Т45 TiNi-Based Powders

Russian Physics Journal - An investigation of the influence of reaction- and diffusion-induced interactions in the system of PV-N55Т45 TiNi-based powders and activating Co and Ni additions...