Plasmas & Ions最新文献

The paper presents construction of a very simple and effective microdroplet filtering system. It describes the spatial angular distribution of different fractions of microdroplets generated by the cathode spots of the vacuum-arc evaporator equipped with the microdroplet filter and without it. The system was applied for TiN coating deposition. The influence of the filtering system on the TiN deposition process parameters is shown. Some properties of the TiN coatings (morphology, roughness, hardness and Young's modulus of elasticity, chemical composition and their adhesion to the steel substrate), deposited with the use of this filtering system, are pointed out.

This paper describes the role of hydrogen in titanium nitriding using an N₂–H₂ gas mixture plasma, which is empirically known to enhance the rate of nitriding. The nitrided titanium specimen was characterized by SIMS, ERD, XRD, SEM, and hardness measurements. Optical emission spectroscopy was conducted for plasma diagnostics of the N₂–H₂ plasma with various partial pressures of H₂ gas. The rate of nitriding was most enhanced when a 60 vol.%N₂–40 vol.%H₂ gas mixture plasma was applied. The hydrogen content of the titanium nitride layer was in the order of 10 wt.ppm and increased with increasing partial pressure of H₂ gas in the working gas. In N₂–H₂ plasma, NH, N₂, N and H radicals were detected as reactive species. The amount of NH radicals was greatest when 30–40 vol.%H₂ gas was added to plasma, while the amount of H radical increased monotonously with the ratio of H₂ gas. Based on the experimental results, we propose that H radicals pick up hydrogen from NH radicals to produce active nitrogen and thus enhance the rate of nitriding.

In many liquid alloys of the alkali metals with members of the post-transition sp elements intermediate-range ordering occurs. It is supposed that in such alloys, which have an ionic character, the anions form clusters (polyanions). These clusters are remnants of the so-called Zintl ions, found in many of the corresponding solid alloys. Tetrahedral (Pb₄)⁴⁻ is an example. Liquid alloys belonging to the alkali–Ga, –Tl, –Sn, –Pb, –Sb, –Bi and –Te systems are discussed. Experimental evidence for the survival of Zintl ions is provided by measurements of the electronic, thermodynamic and structural properties. Special attention is paid to the analysis of neutron diffraction data. The impact of recently developed ab initio methods for simultaneous calculation of the atomic distribution and the electronic structure is demonstrated. Analogies with the solid counterparts play an important role. The conclusion is that there are many indications for the survival of Zintl ions in the liquid state but that they do not remain unimpaired on melting and heating.

Direct current arc plasma that is used as an excitation source in analytical spectroscopy in different industrial areas has been discussed on the basis of plasma physics. A study was made into the voltage–current characteristics of a DC argon arc during the consumption of various amounts of potassium, as EIE, in the current range from 3 to 10 A. Records of voltage drops across a direct current (DC) arc carry direct evidence of the changes that take place in the plasma seeded with Easily Ionizable Elements (EIE). Voltage–current behavior, as well as some spectral characteristics of such plasma were combined, and used to assess plasma parameter changes. The goal was to correlate the recorded voltage with plasma parameters. There is a critical concentration of KCl in the sprayed solution that causes the highest voltage jump and, consequently, the fastest temperature drop and electron number density growth.

The chemical and electrochemical properties of americium chlorides have been studied in the fused LiCl–KCl eutectic at 743 K using a tungsten working electrode and a pO²⁻ indicator electrode. The standard potential of Am (III)/Am (II) and Am (II)/Am redox couples were determined using cyclic voltammetry. Titration of Am (III) chlorocomplex by O²⁻ demonstrated the existence of the soluble americium species AmO⁺ and the precipitation of AmOCl and Am₂O₃. The electrochemical behaviour of AmO⁺ was then studied by cyclic voltammetry. All these data allowed us to draw the potential–pO²⁻ diagram which summarises the properties of americium species in the melt.

The niobium–oxygen interaction in chloride–fluoride melts has been studied by methods of linear sweep voltammetry, X-ray diffraction, IR-spectroscopy and optic crystallography. The chemical reactions and their products in NaCl–KCl–K₂NbF₇; NaCl–KCl–K₃NbOF₆ and NaCl–KCl–K₃NbO₂F₄ melts have been studied. Moreover, a comparative study of the Na₂O and Nb₂O₅ dissolution in NaCl–KCl–K₂NbF₇ melt in the molar ratio range O/Nb from 0 to 2.5 was carried out. The crucial role of the relative excess K₂NbF₇ fluorine in reactions of ligand substitution in the coordination shell of niobium is shown. When the fluorine concentration in the melt is limited by its content in complex niobium fluoride, only mono oxohalide complexes are identified in the liquid phase. The addition of “free” fluoride ions results in the formation of a wide range of oxohalide complexes up to niobates depending on the O/Nb ratio.

The structure of melts and the role in them of 3d-metal coordination polyhedra as oxygenated metal complexes for the catalytic oxidation of saturated hydrocarbons has been elucidated using electronic absorption spectroscopy (EAS), ESR and mass-spectroscopy. The direct partial oxidation of methane to methanol and formaldehyde in sodium metaphosphate melts containing 3d-metal ions has been studied. It has been shown for the oxidation of isopropyl alcohol that the catalytic activity of these melts increases when there are two 3d-metal coordination centers in them.

Ultrasonic velocity and attenuation of 29 MHz waves in molten (K,Li)NO₃, (K,Na)NO₃, (K,Rb)NO₃, (Cs,Li)NO₃, (Cs,Na)NO₃, (Cs,K)NO₃, (Cs,Rb)NO₃, and (Rb,Ag)NO₃ are measured as a function of composition and temperature. An improved pulse transmission device is used together with a new measuring cell allowing a temperature accuracy of better than 1 K over the cell-vertical. The temperature dependence of the velocity is linear up to 675 K, the absorption is governed by the activation energy. The velocity and absorption (referred to the square of frequency) values are given in plots and analytical expressions. A reasonable general dependence on composition cannot be given. The isentropic compressibility is listed. The bulk viscosity of the eight investigated systems exceeding the shear viscosity by more than one order of magnitude is given together with an analytical expression for the ratio bulk/shear viscosity based on the Eyring theory.

Ionic and atomic absorption spectrometries were used to study magnesium ionization in cathodic sputtering glow discharge (CSGD) plasma with aluminum–magnesium alloys as cathodes. A method, based on Doppler broadening-dependent absorption width, of ionization degree resolution by relative absorbance is proposed. The experimental results reveal that there are plentiful magnesium ions in the plasma under the conventional discharge conditions of the atomizer. The matrix element aluminum shows preferential ionization and restricts that of magnesium. Also magnesium ionization degree increases with the discharge power but decreases with the distance from the cathode.

A comprehensive review of the physico-chemical properties of room-temperature molten salts composed of binary solutions of metal halides with either alkylpyridinium halides or di-alkylimidazolium halides is given. A special emphasis is given to the applications of these materials. The most important applications so far are in high-energy batteries and in electrodeposition of selected metals, which is only possible in these media.