A method to improve emission homogeneity of pressed palladium–barium cathodes applied in magnetrons with self-heating initiation is proposed. The initial palladium powder is annealed at 950°C for 60 min and then calcined in vacuum under pressure of residual gases P ≤ 1 × 10–4 Pa. It is demonstrated that cathodes produced by pressing and subsequent sintering of a powdered mixture of palladium and intermetallic compound Pd5Ba in vacuum are characterized by a high distribution homogeneity of components. Within testing of magnetrons produced with such cathodes, the yield of good items is increased by a factor of 1.5.
In this paper the calculations for coefficients of weakening of both photon and neutron beams when the ones pass through the iron-magnet-serpentinit cement concrete (IMSCC) have been presented. IMSCC is using for biological protection of nuclear reactors. At the energies of photons in the range from 0.2 to 11 MeV the main contribution to weakening of beam gives Compton's effect. But at the photon energies more than 11 MeV the main contribution to weakening of beam gives effect of electron-positron couples formation. At an assessment of influence of fast neutrons, it has been shown that, despite the low density of hydrogen in the studied composite, a contribution of hydrogen to coefficient of weakening of a neutron stream was very important. It is connected with both a high concentration of hydrogen and the fact that at neutron irradiation the higher kinetic energy is transferred to light atomic nuclei than heavy ones.
Compounds of compositions С+4О7 and А+2 О7 that are not yet obtained (A and B are cations of different elements; C is Si or Ge) with a melilite-type crystal structure are predicted and their crystal lattice parameters are evaluated. Predicting is based only on data on the properties of elements and simple oxides. The mean accuracy of predicting is at least 85%. The calculations are performed using scikit-learn system programs and an information analytical system based on machine learning approaches.
Alumina ceramics with corundum structure (α-Аl2О3) manufactured by powder technology method was irradiated by pulsed ion beams and high-temperature plasma in Plasma Focus device and by free running mode laser radiation. Irradiation in the PF-5M device was carried out with nitrogen and air working gases with power flux density for the plasma flow q ≈ 107 W/cm2 and pulse duration τp ≈ 100 ns, and for ion flow q ≈ 108 W/cm2, τi ≈ 20 ns. Exposure with pulsed laser radiation was carried out in air with q ≈ (3 – 5)105 W/cm2 and τ ≈ 0.7 ms. The features of erosion (weight loss) and the damage of the surface layer of ceramics for these modes of exposure were investigated. It has been shown that the joint use of Plasma Focus and pulsed laser exposure is promising for simulation of extreme processes of damage and erosion of materials in thermonuclear fusion reactor (such as ELMs effects in the reactor Iter or at the first wall of the chambers with inertial plasma confinement) in order to study and predict their behavior under these conditions.
A database (DB) on the bandgap of inorganic substances available via the Internet (http://bg.imetdb.ru) was developed for the information service of specialists in the sphere of inorganic chemistry and materials science. The DB is integrated with other information systems on the properties of inorganic substances and materials, which provides the search of a wide range of parameters of a specific sub stance. The possibility of the use of the information from the developed DB for the search of relations between the bandgap width and other parameters of thermoelectric materials and for predicting the bandgap of chal copyrites is considered.
Diffusion-thermal phase transformations in modified titanium hydride containing a multi-barrier system of hydrogen traps are considered. Modification of titanium hydride was carried out by the method of layer-by-layer electrochemical precipitation of metallic titanium and copper from organic and inorganic solutions of their salts. The creation of a multilayer coating (Ti–Cu) on the surface of the titanium hydride by the electrochemical precipitation method increases the thermal stability of the metal hydride system by 229.7°C. By using the methods of X-ray-phase, X-ray structural, and electron-probe microanalysis, it has been shown that the phase composition of the modified titanium hydride in a temperature range 100–700°C is constant. The most significant changes in the crystal lattice in the modified titanium hydride occur at a temperature of 500 °C owing to hydrogenation of the modified titanium shell and blocking of the microcracks of the surface with a copper coating; the period of the unit cell and the volume of the hydride-phase crystal change. The highest concentration of hydrogen in the surface layer (up to 87.9%) occurs in the temperature range of 300–500°C, which ensures the maximum defect density in the crystal lattice. At 700°C, one can observe a decrease in the dislocation density and a decrease in the crystal cell parameters associated with the annealing mode of titanium hydride and hydrogen thermal diffusion into the volume of material. The metallic titanium precipitated on the titanium hydride surface is an effective structural trap of hydrogen diffusing into the surface layers during thermal heating; the creation of an additional protective copper sheath prevents thermal diffusion of hydrogen into the environment.
The paper presents experimental data on the effects of the flow of atomic oxygen (AO) for highly filled composites of high impact polystyrene (HIPS) and superfine silicon-organic filler. The coefficients of erosion after exposure to AО, by scanning electron microscopy of the composites was studied relief after irradiation. Also in the paper, the physical and mathematical modeling of erosion processes on the basis of the data.
Features of formation and migration of radiation-induced defects in carbon nanotubes (CNT) and nanostructured materials are examined. The main methods and software tools used for the simulating nanomaterial structure and space factors are described. The results of mathematical simulation are presented.
The degradation of a bilateral pressed tungsten surface layer by pulsed laser irradiation in the freerunning mode (power density q = 105–5 × 106 W/cm2, pulse duration τ = 0.7 ms) and the Q-switched mode (q = 109–1010 W/cm2, τ = 80 ns) as well as under plasma beam irradiation in a plasma focus (PF) device (q = 108–1012 W/cm2, τ = 10–100 ns) has been investigated. The features of the degradation, erosion, and structural changes in the tungsten surface layer under different irradiation conditions have been determined. It has been shown that the use of PF devices in combination with laser equipment is promising for the simulation of the extreme radiation–thermal effects in materials that are typical of thermonuclear fusion devices with magnetic and inertial plasma confinement.
The work presents the technological regime of manufacturing of the high-filled composites on the base of a fluoroplastic matrix, and results about the modification of polymer composites obtained under γ-irradiation action. Paramagnetic centers on atoms of silicon Х• and peroxide CFO2 • macroradicals form by the action of γ- irradiation in the structure of polymer composite. The relations radicals X•/SFO2• are defined by the EPR method. The optimal degree of filling of fluoroplastic matrix modified bismuth oxide is chosen. At accumulated dose of 5 MGy the strength of composite did not change.
In the paper we demonstrate that the thermal doping of SiO2 film by phosphorus, causing formation of thin film of phospho-silicate glass on its surface, allows to rise charge stability of gate dielectric of MIS structure. We have ascertained that a presence of the film of phospho-silicate glass has given a possibility to significantly lower local injection currents flowing within defects because of electron capturing by traps located in the film of phospho-silicate glass what results in the rising of energy barrier. As a result, amount of the structures that comes to a state of breakdown at low values of charge injected into the dielectric under high fields noticeably reduces. We show that heating processes of injected electrons lowers in the films of phospho-silicate glass and this results in increasing of charge stability of the gate dielectric under high-field injection.
The damage and structural state of the surface layer of Al–Li–Mg samples composed of Al–5% Mg–2% Li (wt %) under pulsed action of power streams of high-temperature deuterium plasma and highenergy deuterium ions in the Plasma Focus (PF) device have been investigated. The radiation power density was q ~ 106 W/cm2; the pulse duration was 50–100 ns. Pulsed thermal heating and rapid cooling is established to lead to the melting and solidification of a thin surface layer of the alloy for several tens of nanoseconds. At the same time, in the superheated surface layer of the alloy, microcavities of a spherical shape are formed which is associated with intense evaporation of lithium into micropores within the heated layer. Thermal stresses caused by abrupt heating, melting, and cooling of a thin surface layer of metal result in formation of microcracks in the near-surface zone of the samples. The evaporation by the power electron beam of the elements of the anode material of the PF device (copper and tungsten) and their subsequent deposition onto the irradiated surface of the investigated samples in the form of droplets of submicron size are noted. It is shown that the thermal and radiationstimulated processes generated in the alloy under the action of pulsed energy fluxes in the implemented irradiation regime lead to the redistribution of elements in the surface layer of the aluminum solution, contributing to an increase in magnesium content and the formation of magnesium oxide on the surface.
The charge state change of MOS structures with multilayer dielectric films SiO2–PSG under highfield injection modification at different temperatures is studied in this article. The effect of temperature on the thermal stability of the negative charge component used to adjust the threshold voltage of MOS transistors is investigated. It is found that the performance of the highfield injection modification of MOS structures in the mode of constant current at elevated temperatures increases not only the density of the trapped negative charge but also its thermally stable component.
Abstract—Charging of polymeric samples with grounded metal layer is studied by two main schemes of experiment. In the first scheme, a polymer film is irradiated with the low-energy electrons with energy of 20–40 keV under conditions of absence of grounded metal objects nearby. It is demonstrated that development of breakdown in the double electrical layer on the open surface of the polymer is impossible. In the second scheme, when a grounded metallic mask is placed on the surface of the polymer film in the irradiation zone, discharges are easily initiated and represent spark creeping discharges. A possible mechanism of their initiation is proposed.
Dielectric films and siliconinsulator interfaces in metalinsulatorsemiconductor (MIS) structures are modified using injectionthermal treatment, which involves highfield injection of a specified charge into the gate dielectric and subsequent annealing of the structure. The effect of the injectionthermal treatment modes on the MIS structure modification is investigated. The injectionthermal treatment is shown to reduce imperfection of the dielectric films and, thus, enhance reliability of the MIS devices. It is established that the MIS structure modification processes occurring at the injectionthermal treatment are largely identical to those occurring at the radiation thermal treatment; therefore, for certain MIS devices, the radiation thermal treatment can be replaced by the injectionthermal one.
The article presents the possibility of obtaining polymer composite materials based on thermoplastic polyimide and tungsten oxide (WO3) modified with a hydrophobic silicone fluid. Data on surface microscopy, Vickers microhardness, density, and thermal stability of composites with different tungsten oxide contents are presented. As a result of modifying tungsten oxide, its surface becomes hydrophobic, and the contact angle increases from 31° to 101°. The microstructure of the surface of composites has a fine-grained structure without microcracks and chips. The lowest density material has no filler. With increasing filler content, the density increases. When the content of the filler is 80 wt %, the density is 4.35 g/cm3. The optimum content of tungsten oxide filler is 60 wt % as measured by the surface microhardness. The work shows that the introduction of the proposed filler significantly increases the heat resistance of polyimide. Pure polyimide is stable up to 425°С, and at a temperature of 680°С, its full thermal decomposition takes place. With increasing content of modified tungsten oxide in the composite, the rate of mass loss decreases. In the composite containing 60 wt % filler at 680°C, the mass loss is 38%.
New chalcospinels of the most common compositions were predicted: AIBIIICIVX4 (X = S or Se) and AIIBIIICIIIS4 (A, B, and C are various chemical elements). They are promising for the search for new materials for magneto-optical memory elements, sensors, and anodes in sodium-ion batteries. The parameter “a” values of their crystal lattice are estimated. When predicting, only the values of the properties of chemical elements were used. The calculations were carried out using machine learning programs that are part of the information-analytical system developed by the authors (various ensembles of algorithms of the binary decision trees, the linear machine, the search for logical regularities of classes, the support vector machine, Fisher linear discriminant, the k-nearest neighbors, the learning a multilayer perceptron, and a neural network) for predicting chalcospinels not yet obtained, as well as an extensive family of regression methods, presented in the scikit-learn package for the Python language, and multilevel machine learning methods that were proposed by the authors for estimation of the lattice parameter value of new chalcospinels. The prediction accuracy of new chalcospinels according to the results of the cross-validation is not lower than 80%, and the prediction accuracy of the parameter of their crystal lattice (according to the results of calculating the mean absolute error when cross-validation in the leave-one-out mode) is ±0.1 Å. The effectiveness of using multilevel machine learning methods to predict the physical properties of substances is shown.
It is shown that a constructional radiation-shielding composite material with high resistance to radiation-thermal loads can be obtained. The material was produced using a Portland cement mix, boroncontaining chrysotile, magnetite filler, plasticizing additives, and metal fraction by the vibro-packing method. The content of chemically bound water was at least 1.5 wt %. Exposure to high doses of gamma radiation led to formation of monocalcium ferrite CaFe2O4 with high physical and X-ray density in the cement– magnetite–serpentinite composite. Its formation resulted in radiation hardening and increased the mechanical strength of the composite up to the dose of 10 MGy. When a protective composite was exposed to γ radiation with the absorbed dose of 20 MGy, the mechanical strength of the composite was reduced by only 4– 5% compared to that of the unirradiated sample.