Voltamperometry of 1,4-dihydropyridine derivatives

Thirty-nine -substituted 1,4-dihydropyridine derivatives were subjected to electrochemical oxidation on a rotating platinum microelectrode in acetonitrile, and the E_p (E_1/2) values were measured. A satisfactory linear correlation between the E_p and Taft. ^* constants of the substituents in the position was observed. A linear correlation of the E_p values with the ⁰, - and ^– constants also exists.See [1] for communication I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1525–1529, November. 1975.     

Macroparticle reflection from a biased substrate in a vacuum arcdeposition system

The reflection of macroparticles, generated by a vacuum arc, from a substrate biased negatively with respect to the surrounding plasma is considered. Charging of macroparticle in the near-substrate sheath and its influence on the macroparticle motion were taken into account. It was found that macroparticles can be either reflected or attracted to the substrate depending strongly on the ion current density. The possibility of macroparticle reflection increases with negative bias voltage and saturates at about a few hundred volts     

Application of vacuum arc cathode spot model to graphite cathode

A model of near-electrode processes is applied here to describe the behavior of cathode spots on graphite cathode in vacuum arc. The physical model is based on a kinetic treatment of cathode evaporation, electron emission from the cathode, and plasma production. The model consists of physical assumptions and a system of equations that are formulated in the paper. Spot parameters, such as cathode erosion rate, cathode potential drop, cathode surface temperature, current density, electric field, and plasma density, temperature, and velocity in the near-electrode region are calculated numerically. The calculation includes the dependence of spot parameters on spot current and spot lifetime. The variation of spot parameters as a function of spot lifetime are very strong at lifetimes shorter than 10 μs. The calculations indicate that Joule heating in the cathode body is significant, and may exceed cathode heating by the ion heat flux. Calculated spot parameters are compared with the corresponding experimental data for relatively low arc currents (<100 A) and their agreement is discussed     

W-C Synthesis in a Pulsed Arc Submerged in Liquid

Pulsed arc production of tungsten carbide (W-C) powders in deionized water and analytical (99.8%) ethanol was studied. The arc was ignited between two submerged electrodes: one of 99.99% graphite (C) and the other of 99.5% W. The pulse energy and duration were in the ranges of 7.7–192 mJ and 25–65 μs, respectively. The WC_1−x production rate was maximized by configuring the C electrode as the anode and the W electrode as the cathode. The rate was greater in ethanol than in water. The rate of producing ∼10 nm particles in ethanol was two orders of magnitude greater when using W anode -C cathode configuration, than with the opposite polarity.     

Esters of 1,4-dihydropyridine-3- and -3,5-carbothiolic acids

Methods for the preparation of esters of 1,4-dihydropyridine-3- and -3,5-carbothiolic acids were developed, and their structure and reactivity were studied. A comparative analysis was made of the spectroscopic characteristics of sulfur-containing esters of the 1,4-dihydropyridine series and their oxygen analogs. More strongly expressed electron-acceptor properties of the COSAlk groupings as compared with alkoxycarbonyl substituents were observed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 219–228, February, 1982.     

Electrical discharge in the Teflon cavity of a coaxial pulsedplasma thruster

In this work, we analyze the physical processes of a pulsed discharge in a dielectric (Teflon) cavity. This type of discharge is generated in a coaxial pulsed plasma thruster (PPT) having a central Teflon cavity to produce a high-pressure cloud of ablation products during the discharge pulse. The primary intended role of this model is to provide upstream boundary conditions for particle simulation codes used to study the exhaust plume. The main features of the electrical discharge in the dielectric cavity include Joule heating of the plasma, heat transfer to the dielectric, decomposition of the dielectric followed by partial ionization, and acceleration of the plasma up to the sound speed at the cavity exit. We consider a diffuse type of discharge assuming that all plasma parameters are uniform in the cavity. The system of equations is based on the plasma energy balance, thermal conductivity, dielectric ablation, and mass balance. It is found that most of the energy of the plasma column is carried off by particle convection to the dielectric and by radiation. It is found that during the pulse, the electron density peaks at about 10²⁴ m^-3 and decreases to 10²¹ m^-3 toward the end of the pulse, whereas the electron temperature peaks at about 2.2 eV and decays to 1.5 eV. Teflon surface temperature peaks at about 650 K. Predicted plasma temperature and ablated mass are found to be in agreement with available experimental data     

Vacuum arc cathode spot grouping and motion in magnetic fields

Two of the important vacuum arc phenomena observed when the arc runs in a transverse magnetic field are cathode spot grouping and the cathode spot retrograde motion, i.e., in the anti-Amperian direction. This paper summarizes the main experimental observations and proposes a physical model for spot grouping and spot retrograde motion. The proposed spot motion model take in account the previous theoretical model of the cathode thermal regime and the plasma flow near the cathode surface that is based on two conditions: i) the heat loss in the cathode bulk is relatively small to the heat influx, and ii) the plasma flow in the Knudsen layer is impeded. In the present model, the current per group spot is calculated by assuming that the plasma kinetic pressure is comparable to the self-magnetic pressure in the acceleration region of cathode plasma jet. The model includes equations for the current per spot group, spot velocity dependence on the magnetic field and on the arc current in vacuum, as well as in gas filled arc gap. The calculated currents per spot group and spot velocity increase linearly with the magnetic field and arc current, and this dependencies well agree with previous observations. The cathode spot retrograde motion in short electrode gaps and at atmospheric pressure arcs, and the reversal motion in strong magnetic fields (>1 T) observed by Robson and Engel are discussed. The details of the retrograde motion observed in the last decades including the spot velocity dependence on the electrode gap, roughness, temperature, and material could be understood in the frame of the proposed model.