Dynamic synthesis of ultradispersed crystalline phases of the C-N system

The results are given of the research on dynamic synthesis of crystalline covalent carbon nitride C₃N₄ in a hyperdynamic pulse stream of carbon electrical discharge plasma emanating into a space with a nitrogen atmosphere. The plasma source is a high-current pulse coaxial magnetoplasma accelerator with a graphite accelerator channel. The possibility to synthesize ultradispersed covalent carbon nitride has been shown.     

Production of ultradispersed crystalline silicon carbide by plasmodynamic synthesis

The direct plasmodynamic synthesis of β-SiC ultradispersed cubic silicon carbide under the action of supersonic pulse flow of carbon-silicon electric-discharge plasma onto a copper barrier in the argon atmosphere has been realized. A powdered product with a high β-SiC content has been obtained, whose single crystals have a mean size of about 100 nm and natural crystallographic habit close to the ideal one.     

Direct dynamic synthesis of nanodispersed titanium nitride in a high-speed pulse electroerosion plasma jet

A possibility has been shown to produce nanodispersed TiN in a high-speed sputter-ion plasma jet generated by a coaxial magnetoplasma accelerator. The process is implemented in a short-time (～10^?3 s) operating cycle of the accelerator with titanium electrodes. The basic consumable is prepared by electroerosion from the surface of accelerating channel. Depending on the specific supplied energy dissipated in the channel powder particles can have both a spherical and an irregular form and sizes from 10 to 300 nm.     

Synthesis of a new cubic phase in the B-C-N system

Phase formation in the B-C-N system has been studied at pressures from 6 to 15 GPa and temperatures from 1000 to 1600°C using mixtures of carbon nitride (C₃N₄) nanospheres and boron. A new ternary phase with the structure of cubic boron nitride in which some of the nitrogen and boron atoms are replaced by carbon has been obtained at p ? 8 GPa and t ? 1500°C. According to the Rietveld refinement results, its composition is BC_0.47N_0.85.     

New data on the composition of the crystalline phases in the Cu-Te-O system

With the help of X-ray microanalysis and X-ray analysis new data about the composition of the crystal phase in the Cu-Te-O system have been obtained. The data from the X-ray microanalysis were treated by the method of the number of the oxygen atoms, and the chemical formulae of the crystal phases were evaluated. The following phases were established: the real composition of the stoichiometric composition 2TeO₂ · CuO corresponds to the crystalline phase 5TeO₂ · 2CuO with variable composition in the limits from 7TeO₂ · 3CuO to 11TeO₂ 4CuO with X-ray data presented as 2TeO₂ · CuO phase. The composition TeO₂ · CuO corresponds to a crystalline phase from TeO₂ · CuO to 6TeO₂ · 5CuO. From a melt of TeO₂ · CuO composition overcooled and crystallized is formed 5CuO · 2TeO₂. At a given composition 3CuO · TeO₂ or 3CuO · TeO₃ corresponds to the crystalline phase 5CuO · 2TeO₃ with two polymorphic modifications — cubic and tetragonal. The X-ray data obtained in the present investigation and those in literature are accepted to correspond to two polymorphic forms.     

On the possibility of supersonic pulsed gas jet blocking by transverse discharge

It is established that activation of a pulsed supersonic gas jet by transverse arc discharge can provide the effective blocking (delay) of the neutral gas flow. The delay time is determined by the duration of discharge operation. After the quenching of discharge, a delayed pulse of neutral gas species is formed, the intensity of which increases with the discharge power and can exceed the intensity of pulses observed in the absence of discharge. In addition, an intense pulse of working gas ions is formed that propagates at a velocity exceeding that of the gas flow.     

Mechanochemical synthesis of crystalline compounds in the Bi-V-O system

The phase composition of crystalline mechanochemical synthesis products in the Bi₂O₃-V₂O₅ system is determined by x-ray diffraction. The phases identified are sillenite, clinobisvanite, a fluorite phase, the high-temperature form of the Aurivillius phase -Bi₂VO_5.5-x , and new, metastable tetragonal fluorite-like solid solutions. The same compounds are obtained at other Bi : V ratios using Bi₂O₄ and VO₂ as starting reagents. Structural analysis of the synthesized compounds reveals high vacancy concentrations and substitutional disordering. The room-temperature ESR spectra of the samples show V⁴⁺ signals at g 2 and 4. The phase transitions characteristic of clinobisvanite and -Bi₂VO_{5.5 -x} are not detected by thermal analysis, in line with the structural data. Mechanical activation of high-purity -Bi₂O₃ converts it into the form; in the presence of impurities, the resulting phases have fluorite or slightly distorted fluorite-like structure.Translated from Neorganicheskie Materialy, Vol. 41, No. 2, 2005, pp. 201–209.Original Russian Text Copyright © 2005 by Zyryanov.     

Thermographic studies of a dynamic synthesis product in the C-N system

The results have been considered of the research into an ultradispersed product synthesized in a hyperspeed flow of a carbon electric-discharge plasma in the nitrogen atmosphere using electron scanning and transmission microscopies, thermography, and IR- Fourier spectroscopy. The aim of the studies has been to remove the impurity carbon phases from the product and to estimate the thermostability of covalent carbon nitride.     

On the possibility of electron-beam processing of dielectrics using a forevacuum plasma electron source

An insulated target was irradiated by an electron beam generated by a forevacuum plasma electron source operating in the pressure range of 5–15 Pa. Measurements of the target potential showed that plasma formed in the region of electron beam transport ensured the almost complete neutralization of charge accumulated on the target. This effect results in the possibility of direct electron-beam processing of nonconducting materials, including the melting and welding of ceramics.     

Direct dynamic synthesis of nanodispersed phases of titanium oxides upon sputtering of electrodischarge titanium plasma into an air atmosphere

Experimental investigations of the possibility of directly synthesizing nanodispersed crystalline phases of titanium dioxides with rutile and anatase structures in a hypervelocity jet of electroerosion plasma generated by a coaxial magnetoplasma accelerator with titanium electrodes are presented. A powder product containing nanosized polymorphic phases of titanium dioxide with a spherical shape of particles has been manufactured.     

Preparation of ultradispersed magnesium nitride by the electric-arc low-temperature plasma technique

The conditions are investigated for the preparation of ultradispersed magnesium nitride (UDMN) from elemental magnesium and nitrogen by the electric-arc low-temperature plasma (LTP) technique. Thermodynamic calculations are carried out with the objective of finding the values of the equilibrium constant for the synthesis reaction of magnesium nitride from its elements in the temperature range 298–1800 K as a function of the aggregation state of the components. By means of a cold wall (CW) plasma-chemical reactor (PCR), ultradispersed product (UDP) is synthesized with a specific surface of 33 m²g^–1 containing up to 56% of Mg₃N₂; the use of a warm wall (WW) PCR allows the preparation of UDP with a Mg₃N₂ content of up to 73% and a specific surface reaching 184 m²g^–1. The dominant role of the radial temperature gradient in the PCR in the synthesis of UDMN with maximal degree of nitride formation and maximal specific surface values is experimentally demonstrated. The UDMN exhibits a high chemical activity; heat-treatment at 900 K in an inert atmosphere decreases substantially its chemical affinity to water vapour and oxygen in the air.     

Ionic-liquid-assisted synthesis of YF3 with different crystalline phases and morphologies

YF₃ with different crystalline phases and morphologies have been prepared via a facile hydrothermal route assisted by imidazolium ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate (C₄mimBF₄) or 1-butyl-3-methylimidazolium hexafluorophosphate (C₄mimPF₆). The microstructures and morphologies of YF₃ particles were characterized by X-ray powder diffraction, X-ray photoelectron spectra (XPS), transmission electron microscopy (TEM), high resolution electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM). Cubic and orthorhombic YF₃ were selectively synthesized by adjusting the molar ratio of the reagents and using C₄mimBF₄ as the fluoride source, while only orthorhombic YF₃ was obtained using C₄mimPF₆, indicating that the crystalline phases and morphologies of the products were significantly influenced by fluoride source and reaction media.     

On the possibility of Bose-Einstein condensation in a solid

We treat the question of the existence of Bose-Einstein condensation (BEC) in Bose lattice systems. Simple examples are constructed that do display BEC while having a lattice symmetry. It is suggested, however, that these systems are not crystals in the ordinary sense. When a more conventional definition of a lattice is employed, we generalize the proof of Matsuda and Tsuneto that BEC does not exist in a Bose lattice, for a wider class of wave functions including two-body correlations. A solid with a finite vacancy concentration can display BEC, which is related to the BEC in the vacancy gas. We clarify the relation between BEC of vacancies and particles.     

Studying impurities in the plasma jet of a closed-electron-drift thruster

A new approach to the real-time diagnostics of the erosion of walls in the discharge chamber of a plasma accelerator (thruster) with closed electron drift (CED) is described. The proposed method is based on the measurement of intensities of (i) the spectral lines of atoms sputtered from the discharge chamber walls and (ii) the reference lines of the neutral working gas component. The rate of erosion of the dielectric walls in a discharge chamber of a CED thruster has been measured for the discharge voltage increased from 300 to 700 V. An experimental relationship is established that takes into account changes in the velocities and charge states of the sputtered species and allows the proposed method to be used for various discharge voltages.     

Propagation characteristics of the dynamic state in a capillary discharge jet

A study is made of the so-called dynamic state of a metastable substance, characterized by the onset of a nonequilibrium energy interaction (interchange), involving various waves, in the excited material. The intensity of the optical emission is used to analyze the dynamic state; an investigation is made of the propagation of its leading and trailing edges. Various propagation characteristics and natural solitary-wave forms are identified; their similarity to ionization waves allows making some assumptions about the essential nature of this process. The observed effects are important for establishing the physical conditions for the formation of the substance of ball lightning and are also interesting for the physics of flames, electrical breakdown, and electrode spots. Pis’ma Zh. Tekh. Fiz. 23, 54–59 (October 12, 1997)     

Plasmachemical synthesis of carbide compounds in metal-containing plasma jet from vacuum arc discharge

Features of the synthesis of metal carbides in metal-containing plasma jet from vacuum arc discharge have been studied. Factors determining the quality of coatings obtained using this plasmachemical method are revealed.     

On the possibility of preparing decoherence-free states in a cavity

The effect of decoherence in a quantum system can be viewed as a consequence of the interaction with the environment. As has been pointed out first by Dicke, in a system of N two-level atoms where each of the atoms is individually dipole coupled to the environment, there are collective subradiant states that have no dipole coupling to photon modes, and therefore they are expected to decay more slowly. We have recently proposed a scheme which is intended to create such states in a detuned cavity. We shall examine here the conditions under which our scheme can be used and compare them with the experimental possibilities. The analysis shows that our proposal can be implemented with present-day techniques achieved in atom—cavity interaction experiments.