Application of Gas Plasma Treatment for Testing of Structural Ceramic Composite Materials of the Discharge Chambers of Electrojet Engines

The effectiveness of stationary plasma thrusters was proved by many years of experience of their on board operation on various spacecraft especially on geostationary orbits. One of the main factors that affects the duration of the SPT operation time is the lifetime of the edges of the discharge chamber walls. One of the factors affecting the discharge chamber lifetime is the erosion of the edges of the insulators. Ceramic wear is cause by the destruction of the high-energy ion flow that takes place in thruster plasma.Theoretical study of the processes of discharge chamber insulators sputtering still does not allow mathematically determining the rate of development of the ceramic edges erosion processes with the necessary accuracy that is required for the SPT lifetime forecast. That is why all the researches require a full-scale testing of the thruster on a long time trial basis with subsequent measurements of the insulators value of erosion.In this paper, several methods for measuring the degree of insulators wear are considered. The analysis of the method for measuring the thickness of the ends of discharge chamber insulators was carried out, followed by the determination of radial erosion. It has been shown that this method is the most suitable for non-separable constructions of SPT due to the high accuracy of the measurements and its simplicity.A method for noncontact profilometry of the edges of thruster discharge chamber insulators was proposed. The use of a non-contact method allows measurements to be carried out, excluding the possibility of any deformations to the surface of insulators. Measurements were provided with the help of modern metallographic microscope. Advantages and disadvantages of the methodology are shown. The analysis of the factors that influences the error during measurements of the ceramic profile is carried out.A method is proposed for contact profilometry of the edges of thruster discharge chamber insulators. Advantages and disadvantages of the methodology are shown. The results of measurements of the profile of the two thrusters with the construction differences are provided.

Polylactic acid (PLA) has been widely used in the field of medical devices. However, few studies have been conducted on the extrusion molding of PLA micro tubes for the preparation of biodegradable vascular stents. In this paper, the extrusion die for PLA single-cavity micro tubes was designed and manufactured by micro-extrusion theory. Taking the outer diameter, wall thickness, wall thickness uniformity and ovality of micro tubes as the evaluation index, the influence of the main extrusion process parameters on the evaluation index was studied. The experimental results show that the outer diameter and wall thickness are significantly affected by screw speed, pulling speed and gas flow rate; extrusion process parameters have little influence on wall thickness uniformity and ovality within a certain range, which mainly depends on the processing accuracy and assembly accuracy of the extrusion die. However, excessively high screw speed and low gas flow rate have significant effects on ovality. Finally, according to the influence of extrusion process parameters on the evaluation index, a series of micro tubes that meet the design requirements are extruded and carved into vascular stent structures.

Studies have shown that the structure of dolphin skin controls fluid media dynamically. Gaining inspiration from this phenomenon, a kind of bionic structural heterogeneous composite material was designed. The bionic structural heterogeneous composite material is composed of two materials: a rigid metal base layer with bionic structures and an elastic polymer surface layer with the corresponding mirror structures. The fluid control mechanism of the bionic structural heterogeneous composite material was investigated using a fluid–solid interaction method in ANSYS Workbench. The results indicated that the bionic structural heterogeneous composite material’s fluid control mechanism is its elastic deformation, which is caused by the coupling action between the elastic surface material and the bionic structure. This deformation can decrease the velocity gradient of the fluid boundary layer through changing the fluid–solid actual contact surface and reduce the frictional force. The bionic structural heterogeneous composite material can also absorb some energy through elastic deformation and avoid energy loss. The bionic structural heterogeneous composite material was applied to the impeller of a centrifugal pump in a contrast experiment, increasing the pump efficiency by 5% without changing the hydraulic model of the impeller. The development of this bionic structural heterogeneous composite material will be straightforward from an engineering point of view, and it will have valuable practical applications.

A double-chamber gas-liquid phase DBD reactor (GLDR), consisting of a gas-phase discharge chamber and a gas-liquid discharge chamber in series, was designed to enhance the degradation of benzene and the emission of NOx. The performance of the GLDR on discharge characteristics, reactive species production and benzene degradation was compared to that of the single-chamber gas phase DBD reactor (GPDR). The effects of discharge gap, applied voltage, initial benzene concentration, gas flow rate and solution conductivity on the degradation and energy yield of benzene in the GLDR were investigated. The GLDR presents a higher discharge power, higher benzene degradation and higher energy yield than that of the GPDR. NO2 emission was remarkably inhibited in the GLDR, possibly due to the dissolution of NO2 in water. The benzene degradation efficiency increased with the applied voltage, but decreased with the initial concentration, gas flow rate, and gas discharge gap, while the solution conductivity presented less influence on benzene degradation. The benzene degradation efficiency and the energy yield reached 61.11% and 1.45 g kWh–1 at 4 mm total gas discharge gap, 15 kV applied voltage, 200 ppm benzene concentration, 0.2 L min−1 gas flow rate and 721 μS cm−1 water conductivity. The intermediates and byproducts during benzene degradation were detected by FT-IR, GC-MS and LC-MS primarily, and phenols, COx, and other aromatic substitutes, O3, NOx, etc, were determined as the main intermediates. According to these detected byproducts, a possible benzene degradation mechanism was proposed.

In brittle composites, spontaneous microcracking might occur due to the presence of residual stresses. As microcracking has a significant influence on the properties of composite ceramic materials, it is important to understand the mechanism of microcrack formation in order to introduce a controlled amount of microcracking. However, there are fairly few materials where toughening by microcracking has been rigorously verified. Fully validated examples of microcracking toughening are restricted to the composite materials such as zirconia toughened alumina (ZTA) [1], SiC/TiB2 [2] and some of the liquid-phase sintered SiC ceramics [3]. The appropriate addition of additives plays an important role in improving physical and mechanical properties of ceramic composites [4, 5]. Various additives such as the rare earth, the oxide of alkaline metals, metallic elements and carbon, and so on, have got wide applications in both structural and functional ceramics. Specifically, the addition of carbon is beneficial for sintering and improvement of the properties of SiC/TiB2/TiC ceramic composite [6]. Moreover, it was reported by Sigl et al. [7] that the fracture toughness of B4C/TiB2 ceramic was notably increased because of the addition of a certain amount of free carbon. On the other hand, Al2O3/TiC composite is one of the popularly used structural ceramic materials. Since the 1970s, a great deal of research work has been done focusing on the microstructure, mechanical property and engineering performance of Al2O3/TiC composite [5, 8–10]. Sintering aids like MgO, TiO2, Y2O3, TiH2, Ni and Mo, etc. has been adopted in the fabrication of Al2O3/TiC composite for high density and properties [10–14]. In the present study, a certain amount of free carbon is purposely incorporated into Al2O3/TiC ceramic composite. Attempts have been made to investigate its influence on the microstructure and fracture toughness of the material. High purity Al2O3 and TiC powders were used as the starting materials with average sizes of 0.5 and 0.8 μm, respectively. Al2O3 was blended with TiC (30 vol.%) and doped with different amounts of phenolic resins to yield samples with varying amounts of free carbon additives in the as-sintered bodies. The mixtures were subsequently homogenized with alcohol media in a ball

A new kind of structural and functional integration ceramic matrix composite material was prepared from high‐performance alumina (Al 2 O 3 ) fibers and absorbing silicon carbonitride (SiCN) ceramics via a combination of polymer infiltration pyrolysis (PIP) and chemical vapor infiltration (CVI) methods. The Al 2 O 3 fiber annealed at its cracked temperature had enhanced permittivity, because the sizing agent on the Al 2 O 3 fiber surface was cracked into pyrolysis carbon. For PIP + CVI Al 2 O 3 f /SiCN composites, PIP SiCN matrix with low conductivity was used as the matching phase, while CVI SiCN matrix with medium permittivity and dielectric loss was regarded as the reinforcing phase distributed in porous PIP SiCN matrix and inter‐bundles of Al 2 O 3 fiber to improve their mechanical and microwave absorption properties. The fracture toughness and flexural strength of Al 2 O 3 f /SiCN composite were determined to be 9.4 ± 0.5 MPa m 1/2 and 279 ± 28 MPa, respectively. Based on the design principles for impedance matching, the Al 2 O 3 f /SiCN composites before and after oxidation were used as loss and impedance layers, respectively. It was found that the optimized composite had the lowest reflection coefficient (RC) of −70 dB and the effective absorption bandwidth covering the whole X‐band. In conclusion, Al 2 O 3 f /SiCN composite can serve as a high‐temperature structural material with excellent microwave absorption properties for aerospace applications.

The application efficiency of composite plastic materials in structures of modern civil and military airplanes are investigated. Detaled analisys of Antonov branch airplanes is presented on general diagrams. The 25–27% diaposon of the mass reduction that was achieved due to composite materials application is determined.

A 2-cm electron cyclotron resonance ion source has the advantages of long life and high specific impulse, which can meet the requirements for space gravitational waves detection. In the experiment on finding the lower limit of thrust, it is found that when the ion source operates under the extreme condition of 0.5-W microwave power and 0.1-sccm gas flow rate, increasing the voltages of grid system excessively may cause flameout. The plasma discharge level is controlled by the gas supply, microwave, and power supply system, and their small disturbances will make experimental results different, thus the flameout of the ion source appears randomly and transiently. Besides, it is difficult to observe the flameout phenomenon experimentally, because the probe diagnosis has big interference to low-density plasma, and the optical diagnosis is blocked by the grid system. Therefore, the integrative simulation with the full particle-in-cell method is used to simulate the operating process of the ion source, whose calculation range includes the discharge chamber, grid system, and plume. Through simulating the processes of plasma discharge and ion beam extraction continuously in space and time, the flameout phenomenon can be reproduced artificially after increasing the voltages of grid system. The simulation results show that the ambipolar diffusion between the antenna and discharge chamber is the fundamental reason for the flameout of the ion source. In the circuit, the antenna does not touch the discharge chamber but for bulk plasma, which makes its surface gradually accumulate charges until it reaches the floating potential. Because the increase of the voltage of antenna lags behind that of grid system, a strong electric field will appear between the antenna and chamber. Then, electrons and ions respectively move toward the chamber and antenna, the ambipolar diffusion helps the antenna reach the floating potential rapidly. When the plasma density inside the chamber is low, the ambipolar diffusion will cause flameout. In order to avoid the flameout of the ion source in such an extreme situation, an improvement measure that the voltage of antenna equals the voltage of chamber is proposed, which is verified by the integrative simulation. The study on the flameout phenomenon will provide a theoretical basis for the design and application of the ion source, which can help the ion source operate safely to meet the requirements for space gravitational wave detection.

This paper provides a large number of computational results describing the discharge chamber operation for a number of thruster operating conditions of NEXT. In all, 15 thrust levels for NEXT have been simulated with a large number of results produced; however, only a representative sample of these results is included in this paper. These results are generated with a detailed PIC-MCC computer model of the discharge chamber developed at Wright State University in the period from 2004 to 2007. In the past this computer code has been shown to produce reasonable results for the NSTAR ion engine. With the Wright State discharge chamber code a large number of spatially resolved results can be obtained in a relatively inexpensive manner. The spatially resolved results include particle number density distributions, particle energy distributions, and particle current distributions. These distributions can be obtained for each of the particle types included in the analysis: neutrals, first ions, second ions, primary electrons, and secondary electrons. In addition, global operating parameters can also be obtained from this computer code. Global current results from the PIC-MCC computer model are within 57.4% of experimentally determined values and computational trends match those obtained from experiments.

Plasma-activated water (PAW) represents a promising green antibacterial agent for biomedical and agricultural applications. In this study, a novel AC multi-needle-to-water discharge device was developed to investigate the effects of gas flow on the generation and chemical composition of PAW. It is shown that the concentrations of and N(III) ( and ) in the PAW both increased with an extension of the plasma-processing time and a reduction of the gas-flow rate. The absorption of gas-phase products carried by the gas flow from the discharge chamber was found to be beneficial for the generation of both and N(III) in the PAW at a gas flow rate of 20–60 L h−1, yet their concentrations were still lower than those without any feeding gas. As opposed to or N(III), the concentration in the plasma-activated phosphate buffer solution (PAPBS) increased under stronger gas flows and was almost unaffected by absorption in PAPBS. The pH value of PAW increased at higher gas flow rates. A comparison of the N(III) in PAW and PAPBS reflects the effects of the reactions of and in the two different working liquids. To quantify the effects of gas flow on the discharge characteristics, gas temperatures were calculated from the optical emission spectra and were proven to be flow-independent near the discharge channel. Fourier transform infrared (FTIR) measurements of the gaseous products during the discharge, and further analysis of possible reaction pathways indicated that by controlling the gas flow in the multi-needle-to-water discharge system, the concentration of long-lived species in PAW could be tuned, which might favor the generation of These findings contribute to a better understanding of effective electric discharge-related mechanisms for enhancing the biochemical and chemical activities of PAW.

At present, the modern society utilizes composite materials in various branches of the national economy. The properties of such materials depend on their composition and structure, and may considerably differ from the properties of source materials. In turn, texture and structure of crystals, their packing order, size and level of sophistication affect the structure of materials. This is particularly demonstrated by hydration curing materials on the basis of gypsum and magnesia binding materials, as well as portland cement. Structuring control is one of the key problems of composite materials. Gypsum binding materials with various modification composition are suggested as a model system to study the influence of texture and structure of materials on their properties. One of them is the construction gypsum – an anhydrite binder and a multiphase gypsum binder (MGB). Scanning electron microscopy (SEM) was chosen as the main method of study. It is found that gypsum crystals that are formed during hydration and curing of gypsum binders with various modification composition have different texture and structure. It prevents from getting the optimal packing of a material. It is justified and confirmed that the MGB consisting of several modifications of calcium sulfate allow choosing the best material composition due to the combination of crystals having different size and form. Besides, MGB contains significant amounts of insoluble anhydrite that reduces the water-gypsum ratio of a binder and compacts its structure. Considerable attention is paid to microfillers, which significantly affect the texture and structure of materials based on gypsum binders. Iron ore concentrate of the Lebedinsky GOK generally consisting of magnetite, as well as impalpable flour cullet waste of sodium and potassium glass were used as microfillers in the given study. Ultra- and nanodispersed powders at their introduction to gypsum and anhydrite compositions change the size and morphology of crystal newgrowths and ensure the formation of ordered, denser and uniform fine-crystalline structures of composite materials, which leads to the reduction of structure imperfection, porosity and increase in contact areas of crystalline hydrates increasing physical and mechanical performance of gypsum materials. Efficient composite construction materials are obtained on the basis of MGB and microfillers.

We evaluate the anti-cancer capacity of plasma-treated PBS (pPBS), by measuring the concentrations of NO2− and H2O2 in pPBS, treated with a plasma jet, for different values of gas flow rate, gap and plasma treatment time, as well as the effect of pPBS on cancer cell cytotoxicity, for three different glioblastoma cancer cell lines, at exactly the same plasma treatment conditions. Our experiments reveal that pPBS is cytotoxic for all conditions investigated. A small variation in gap between plasma jet and liquid surface (10 mm vs 15 mm) significantly affects the chemical composition of pPBS and its anti-cancer capacity, attributed to the occurrence of discharges onto the liquid. By correlating the effect of gap, gas flow rate and plasma treatment time on the chemical composition and anti-cancer capacity of pPBS, we may conclude that H2O2 is a more important species for the anti-cancer capacity of pPBS than NO2−. We also used a 0D model, developed for plasma-liquid interactions, to elucidate the most important mechanisms for the generation of H2O2 and NO2−. Finally, we found that pPBS might be more suitable for practical applications in a clinical setting than (commonly used) plasma-activated media (PAM), because of its higher stability.

A 2D fully kinetic particle-in-cell plus Monte Carlo collision (PIC/MCC) model was developed to study the physical characteristics of the ion thruster discharge chamber <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> . The PIC method is used to track the four major particles in the discharge chamber, including primary electrons, secondary electrons, ions and neutral atoms. The MCC method is used to describe the collisions between particles, the elastic, excitation and ionization collisions for electrons, and the elastic and charge exchange collisions for ions are considered. The motion of charged particles is affected by dynamic electric field and external magnetic field, in which the electric field is obtained by solving Poisson equation with DADI (Dynamic Alternating Direction Implicit Iteration) method <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Such a full kinetic model is challenging because it requires a huge number of grids and computation time. Therefore, a self-similar scaling scheme proposed by Taccogna is used to simplify the discharge chamber model <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . This scaling scheme reduces the size of discharge chamber while keeping the main physical parameters (Knudsen number, specific impulse, and electron magnetization process) unchanged. It shortens the computation time and is helpful for analyzing the actual physical characteristics of the discharge chamber. In this work, a 20-cm diameter axisymmetric cylindrical model with three rings of magnets is established to test the discharge chamber. The steady-state results such as the electric potential distributions and particle number density distributions are obtained, and the neutral atom density variation and its effects on plasma distribution are discussed.

This study presents an experimental and numerical investigation on a surface sliding discharge in a supersonic airflow in the presence of an oblique shock wave. In experiments, flow Mach numbers were 1.20–1.68 in the shock tube combined with the discharge chamber. A single high-voltage 25 kV pulse sustains the plasma; the discharge current has a duration of ~500 ns. A surface sliding discharge is developed as a localized channel in a zone of interaction of an oblique shock wave with a boundary layer on the upper wall of the discharge chamber. The discharge channel acts as a linear source of heat and is at the origin of the induced shock wave. The flow field in the discharge chamber is spatio-temporally surveyed using high-speed shadowgraphy imaging with a frequency of up to 525,000 frames per second. The experiments show that the perturbed flow restored the initial structure after more than 100 μs. Numerical simulation with local energy input into the supersonic flow in a flat channel is carried out on the base of unsteady two-dimensional Navier–Stokes equations. It is determined that the dynamics of an induced shock wave are dependent on the energy input regime and on the flow parameters. The thermal energy release in the discharge channel of 0.22–0.29 J was estimated from a comparison of experimental data and numerical simulations.

Sintering polycrystalline silicon carbide composite ceramics with ultra-high hardness under high pressure