The results of investigation of a low-pressure glow discharge with a hollow cathode and a large-volume hollow anode in argon and nitrogen are presented. The data on plasma density and electron ...temperature are obtained. A model is proposed, which describes the mechanisms of plasma sustainment in a hollow anode. The model includes the non-uniformity of plasma density distribution in the anode cavity. The estimations of the plasma parameters are made. The model is in a good agreement with the experimental data.
Gaseous CePO2 has been identified by Knudsen effusion mass spectrometry during vaporization of CeO2 and magnesium diphosphate from tungsten double, two‐temperature effusion cell. Structure and ...molecular parameters of gaseous cerium phosphate under study were determined using quantum chemical calculations. On the basis of equilibrium constants measured for gas‐phase reaction, standard formation enthalpy of CePO2 was determined to be −508 ± 41 kJ ⋅ mol−1 at the temperature 298 K.
Arc discharges operation in “elion” mode Lopatin, I V; Akhmadeev, Yu H; Kovalsky, S S ...
Journal of physics. Conference series,
11/2021, Letnik:
2064, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
This paper presents the results of a study of an electron-ion-plasma alitization system using two arc plasma generators: a gas plasma generator based on a non-self-sustained arc discharge ...with a thermionic cathode “PINK” and a gas-metal plasma generator based on an arc discharge with a cathode spot. The system for discharges supplying and biasing of the samples assumes two sub-modes of operation: the ion cleaning sub-mode (ion sub-mode) and the sub-mode of samples electron heating (electron sub-mode), thus realizing the “elion” mode of the system operation. During the experiments, both the dependences of the average values of currents and voltages of discharges burning and probe measurements of the instantaneous plasma parameters values in both system operating sub-modes were investigated. It is shown, that the electron sub-mode of system operation is characterized by an increased burning voltage, which is caused by the formation of a positive anode drop of more than 10 V in the plasmas. Such a potential distribution in the discharges ensures effective heating of the samples by the discharges plasmas electron component.
It is suggested a combined method of silumin surface treatment, including deposition of a metal film and the subsequent irradiation by an intensive pulsed electron beam in the mode of surface layer ...melting. The formation of the multilayered multiphase surface volume having submicro- and nanocrystalline structure is revealed. It is shown that the sizes of crystallites of the modified layer rise at increase of the distance from the treated surface.
Finely dispersed powders of neodymium and gadolinium hafnates (Nd2Hf2O7 and Gd2Hf2O7) with pyrochlore structure were synthesized. Variations in particle size and morphology during thermal treatment ...under different conditions (1273–1673 K, 2–4 h) were studied for these compounds. The vaporization behavior of Nd2Hf2O7 and Gd2Hf2O7 was examined in the temperature range 2100–2750 K. In addition, the thermodynamic properties of Nd2Hf2O7 and Gd2Hf2O7 in the above‐mentioned temperature interval were determined by using high‐temperature mass spectrometry.
Finely dispersed powders of Nd2Hf2O7 and Gd2Hf2O7 were synthesized, their temperature agglomeration processes at different conditions were examined, and special features of the vaporization process in the temperature range 2100–2750 K were investigated by high‐temperature mass spectrometry. Some thermodynamic properties were also determined.
The parameters of the plasma of a non-self-sustaining glow discharge generated inside a metal hollow cathode 300 mm long and 25 mm in inner diameter are investigated. A feature of this system is the ...additional injection of electrons from the auxiliary discharge plasma formed by the plasma source with a combined PINK heated and hollow cathode. The dependences and combustion modes of the non-self-sustaining glow discharge are presented and described at a pressure in the range (0.06–1.4) Pa and a combustion voltage of (70–300) V. Studies of the plasma parameters using double Langmuir probes have shown that this discharge system provides generation of the nitrogen plasma inside the hollow cathode with inhomogeneity from ±12 to ±63%.
Abstract
The results of experiments on low-energy implantation of AISI 321 stainless steel by nitrogen ions are presented. The treatment was carried out by a pulsed beam of nitrogen ions obtained ...using a ballistic ion focusing system. The surface modification occurs with the formation of a two-layer structure, which is typical for ion-plasma nitriding processes of stainless steels. The thickness of the modified layer can reach 27 μm after 1 hour of ion-plasma treatment. The influence of subsequent modification of the ion-doped layer by the action on the surface of the pulsed high-current electron beam of microsecond duration is studied. The work presents the results of the studying the regularities of changes in the depth distribution of dopants, microstructure and phase composition of the modified and matrix layers by optical metallography, diffraction analysis and transmission electron microscopy.
Abstract
This work represents the investigations for decreasing acceleration gap breakdown probability of plasma source of electrons SOLO, with grid stabilization of the boundaries of the arc cathode ...plasma. We increased the distance to the treated target, bent the transportation channel of the electron beam, created additional plasma in the anode space, and increased the beam front. The effect of the above measures on the breakdown probability when the target is exposed of a low-energy electron beam with a power density of up to 0.5 MW/cm
2
with a diameter of 2.5 cm was investigated separately. Beam deflection is most effective at relatively long pulse durations of 150 μs and accelerating voltage of 20 kV, rather than a lower one. It was possible to double the maximum power for the same beam transport length applied to a low-melting target. Preionization in the anode proved to be effective for relatively short beams of 15 μs duration.
Rationale
CeO2–WO3 and CeO2–MoO3 catalysts have shown excellent performance in the selective reduction of NOx by ammonia (NH3‐selective catalytic reduction) over a wide temperature range. Strong ...interaction between CeO2 and WO3 or MoO3 might be the dominant reason for the high activity of these mixed oxides. Studies of ceria‐containing gaseous salts involve considerable experimental difficulties, since the transition of such salts to vapor requires high temperatures. To predict the possibility of the existence of gaseous associates formed by cerium and molybdenum (tungsten) oxides it is important to know their thermodynamic characteristics. Until the present investigation, gaseous cerium oxyacid salts were unknown.
Methods
Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species and the equilibrium constants of gas‐phase reactions, as well as the formation and atomization enthalpies of gaseous cerium molybdates and tungstates. CeO2 was evaporated from molybdenum and tungsten effusion cells containing gold metal as a pressure standard. A theoretical study of gaseous cerium molybdates and tungstates was performed by several quantum chemical methods.
Results
In the temperature range 2050–2400 K, CeO, CeO2, XO2, XO3, CeWO3, CeXO4, CeXO5 (X = Mo, W) and CeMo2O7 were found to be the main vapor species over the CeO2–Mo(W) systems. On the basis of the equilibrium constants of the gaseous reactions, the standard formation enthalpies of gaseous CeWO3, CeXO4, CeXO5 (X = Mo, W) and CeMo2O7 at 298 K were determined. Energetically favorable structures of gaseous cerium salts were found and vibrational frequencies were evaluated in the harmonic approximation.
Conclusions
The thermal stability of gaseous cerium oxyacid salts was confirmed by high‐temperature mass spectrometry. Reaction enthalpies of the gaseous cerium molybdates and tungstates from gaseous cerium, molybdenum and tungsten oxides were evaluated theoretically and the obtained values are in reasonable agreement with the experimental ones.
This paper presents an auxiliary source of anode plasma developed for the electron source with a plasma cathode based on a low-pressure arc discharge. The plasma source consists of three cells: the ...main ion-plasma system with closed electron drift and two auxiliary ones. The latter include a hollow cathode and a reflective discharge cell. The construction allows to generate and transport a submillisecond low-energy beam up to 25 keV with a diameter of 40 mm in axial magnetic field up to 80 mT. In the main mode of the auxiliary discharge, the anode plasma is created at a current of up to 15 A and with discharge voltage about 300 V. Using the source of auxiliary anode plasma allows you to expand the range of operating pressures of the electron source down to 3.6×10−3 Pa of argon and get rid of high-frequency beam current oscillations when operating at low pressure (up to 1.2×10−2 Pa).
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