Large Eddy Simulation of a Free-Burning Arc Discharge in Argon with a Turbulent Cross Flow and External Field

In most of the numerical approaches proposed for modeling high-intensity plasma-arcs, the effects of turbulence on the arc structure are often excluded because of the intricate physics originating from the interaction of turbulent scales, high-temperature gas dynamics, magnetohydrodynamics (MHD) and chemical kinetics. The goal of this study is threefold: to develop a generic turbulent MHD model to simulate free-burning arc discharges, to validate the code with available experimental data, and to investigate the effect of an external field and turbulent cross flow on the free-burning arc configuration. The governing equations are solved in conservative form using a hybrid scheme that combines a high-order monotonic upwind scheme with a second-order central scheme. The fluid and MHD turbulence are resolved using a large eddy simulation (LES) approach with a recently developed sub-grid closure model. An implicit scheme is used to compute the magnetic diffusion term appearing in the magnetic induction equation to alleviate the severe time-step constraint. The comparison of the model prediction with experimental data for Argon arcs at different current intensities shows generally good agreement. When an external field is applied, the overall shape of the free-burning arc drastically changes. The straightening of the arc indicates the potential for stabilization of a free-burning arc by magnetic forces. Even though the turbulence is significantly attenuated as a result of the thermal expansion near the cathode, it adds an unsteady characteristic to the arc and, in general, has a negative impact on the stabilization of the electrical discharge.     

[B(O–C6H4–CN)4]– based Silver and Copper Coordination Polymers

A series of new coordination polymers bearing the [B(O–C₆H₄–CN)₄]^– anion was synthesized. Two new, one dimensional coordination frameworks of the type M[B(O–C₆H₄–CN)₄] (M = Ag, Cu) were obtained by salt metathesis. The reactivity towards organic Lewis‐bases was studied. The reaction with bidentate ligands yielded two dimensional networks with the general formula [M(L)][B(O–C₆H₄–CN)₄] {L = 2,2′‐bipyridine, 4,4′‐bipyridine, 1,2‐bis(pyridyl)ethane, 1,4‐diazabicyclo[2.2.2]octane}. The synthesis, properties and single crystal structure are reported.     

Synthesis and Characterization of Benzonitrile-Substituted Silyl Ethers

The silyl ethers (siloxanes) Me_{4? x}Si(OC₆H₅CN)_x (x = 1–4) (1–4), O(Si(OC₆H₄CN) (Me)₂)₂ (5), and Me₃Si–O–C₆F₄CN (6) have been synthesized by the reaction of the respective p-hydroxybenzonitriles and chlorosilanes in the presence of N,N,N′,N′-tetramethylethylenediamine (TMEDA) as hydrogen chloride acceptor. All compounds have been fully characterized by CHN-analysis, melting point, IR, Raman, mass spectroscopy, and ¹H, ¹³C, ²⁹Si NMR spectroscopy. Furthermore, the crystal structures of these compounds—with the exception of Me₂Si(OC₆H₅CN)₂, which is a liquid—were determined by X-ray diffractometry.     

Synthesis and Structure of Ionic Liquids Containing the ­[Al(OC6H4CN)4]– Anion

The synthesis, structure, and physical properties of ionic liquids (IL) bearing the novel [Al(O–C₆H₄–CN)₄]^– ion as counterion to the commonly used [NR₄]⁺, [PR₄]⁺ and imidazolium ions are reported. Both the influence of the alkyl chain length as well as the functionalization with cyano groups is studied. These ILs are easily obtained by reaction of Ag[Al(O–C₆H₄–CN)₄] with the corresponding ammonium, phosphonium, and imidazolium halides. The stability towards electrophilic cations was investigated. All prepared salts have a window for the liquid phase of ca. 200 °C and are thermally stable up to 450 °C. The solid‐state structures reveal only weak cation ··· anion and anion ··· anion interactions in accord with the observed low melting points (glass transition points).     

Synthesis of Heteroanellated Pyranosides Starting from Methyl 4,6‐O‐benzylidene‐2,3‐dideoxy‐α‐d‐erythro‐hexopyranosid‐2‐ylidenemalononitrile

The hexopyranosid‐2‐ylidenemalononitrile 1 reacted with phenyl isothiocyanate in the presence of triethylamine to furnish (2R,4aR,6S,10bS)‐8‐amino‐4a,6,10,10b‐tetrahydro‐6‐methoxy‐2‐phenyl‐10‐phenylimino‐4H‐thiopyrano[3′,4′:4,5]pyrano[3,2‐d][1,3]dioxine‐7‐carbonitrile (2). Starting from 1, cyclization with sulphur and diethylamine yielded (2R,4aR,6S,9bR)‐8‐amino‐4,4a,6,9b‐tetrahydro‐6‐methoxy‐2‐phenylthieno[2′,3′:4,5]pyrano[3,2‐d][1,3]dioxine‐7‐carbonitrile (3), which could be transformed into the corresponding aminomethylenamino derivative 4 by treatment with triethyl orthoformate and ammonia. Intramolecular cyclization of 4 to yield (2R,4aR,6S,11bR)‐4,4a,6,11b‐tetrahydro‐6‐methoxy‐2‐phenyl[1,3]dioxino[4″,5″:5′,6′]pyrano[3′,4′:4,5]thieno [2,3‐d]pyrimidin‐7‐amine (5) was achieved by using NaH as base. (2R,4aR,6S,9bS)‐8‐Amino‐4a,6,9,9b‐tetrahydro‐6‐methoxy‐9‐(4‐methylphenyl‐sulfonyl)‐2‐phenyl‐4H‐[1,3]dioxino[4′,5′:5,6]pyrano[4,3‐b]pyrrole‐7‐carbonitrile (6) was prepared by treatment of compound 1 with tosylazide and triethylamine.