Conditions Of Low-temperature Plasma Research Articles

Composition and Magnetic Properties of Composites Based on Ultrafine NiFe2O4 Particles Produced under Conditions of Low-Temperature Underwater Plasma

Composition and Magnetic Properties of Composites Based on Ultrafine NiFe2O4 Particles Produced under Conditions of Low-Temperature Underwater Plasma

Ignition and combustion stabilization of multicomponent supersonic chemically active flows in low-temperature plasma conditions

An electrodeless freely localized microwave discharge, a surface microwave discharge, a non-equilibrium non-stationary transverse-longitudinal pulsating discharge were used for ignition and combustion stabilization. The induction periods for various discharges and the possibilities of their application for supersonic combustion stabilization inside the direct-flow aerodynamic channels are experimentally determined. A comparison of experimental results with the data of mathematical modeling is presented.

Electrostatic enhancement factor for the coagulation of silicon nanoparticles in low-temperature plasmas

The coagulation enhancement factor due to electrostatic (Coulomb and polarization-induced) interaction between silicon nanoparticles was numerically computed for different nanoparticle sizes and charges in typical low-temperature argon-silane plasma conditions. We used a rigorous formulation, based on a multipole moment coefficients, to describe the complete electrostatic interaction between dielectric particles. The resulting interaction potential is non-singular at the contact point, which allows to adapt the orbital-motion limited theory to calculate the enhancement factor. It is shown that, due to induced polarization, coagulation is enhanced in neutral-charged particles encounters up to several orders of magnitude. Moreover, the short-range force between like-charged nanoparticles can become attractive as a direct consequence of the dielectric nature of the nanoparticles. The multipolar coefficient potential is compared to an approximate analytic form which can be readily used to simplify the calculations. The results presented here provide a better understanding of the electrostatic interaction in coagulation and can be used in dust growth simulations in low-temperature plasmas where coagulation is a significant process.

Plasma coatings containing high-baring phases

Results of comparative researches of the initial and processed in a plasma flow oxidic microcomposites, consisting of TiO2, SiO2, Al2O3, ZrO2, and plasma coverings from them – the materials which are characterized by amorphous and crystal structure and strengthened by ultradispersed phases of the stishovit, are presented. It is shown the influence of a type, structure and a way of processing of material (initial powder of different dispersion; the powder obtained in a plasma flow at the different modes and with the normal and accelerated cooling; a plasma layered composite) on the content of silicon oxides, aluminum and titanium, on the type of polymorphic transformations (anatase is found both in powders, and in coverings; the accelerated cooling of spheroids leads to growth of its contents in microcomposites) and also on feature of forming in ceramic materials of a high-bar phase – the stishovit (stishovit it is found only in coverings). It is established that increase in power of the plasma generator leads to increase in extent of amorphicity of plasma-layered composites. In the structure of layered composites three groups of the inclusions, combined by the composition, are revealed: two groups of aluminosilicates and inclusions on the basis of zirconium dioxide. Inclusions of the third group are characterized by two types of structures: homogeneous, consisting of zircon, and plated (with a kernel of dioxide of zirconium and a cover from zircon). The developed layered composites are characterized by high wear resistance, corrosion resistance and antifriction properties. In the conditions of low-temperature plasma at atmospheric pressure the stishovit-containing materials are obtained for the first time.

Influence of low-temperature plasma treatment on properties of ramie fibers

In this study, ramie fibers were treated under various low-temperature plasma conditions such as different output powers (100, 150, 200, 250, and 300 W) and irradiation times (1, 1.5, 2, 2.5, and 3 min). The effects on fiber surface morphology, contact angle, friction and tensile properties were investigated. The results showed that properties of ramie fibers changed significantly after low-temperature plasma treatment. Compared with the untreated fibers, surface free energy increased 117.0 and 122.9%, friction coefficient improved 10.7 and 13.4% after 1 min-300 W and 3 min-100 W treatment. However, with the higher output power and the prolonged treatment time, low-temperature plasma treatment may cause damage to the tensile property of ramie fiber. Scanning electron microscopy showed that pectin and impurities covering of fibers were removed after low-temperature plasma treatment and alkali treatment, and the surface of ramie fiber was etched by low-temperature plasma treatment. Based on the analysis of experimental results, three groups (1 min-100 W, 2 min-150 W, and 3 min-200 W) were chosen as the following treatment process and compared with alkali treatment. It was found that properties of ramie fibers had more significant change after low-temperature plasma treatment.

Electron presheaths: the outsized influence of positive boundaries on plasmas

Electron sheaths form near the surface of objects biased more positive than the plasma potential, such as a Langmuir probe collecting electron saturation current. Generally, the formation of electron sheaths requires that the electron-collecting area be sufficiently smaller ( times) than the ion-collecting area. They are commonly thought to be local phenomena that collect the random thermal electron current, but do not otherwise perturb a plasma. Here, using experiments on an electrode embedded in a wall in a helium discharge, particle-in-cell simulations, and theory it is shown that under low temperature plasma conditions () electron sheaths are far from local. Instead, a long presheath region (27 mm, approximately an electron’s mean free path) extends into the plasma where electrons are accelerated via a pressure gradient to a flow speed exceeding the electron thermal speed at the sheath edge. This fast flow is found to excite instabilities, causing strong fluctuations near the sheath edge.

Heterogeneous recombination of oxygen atoms on an aluminum foil surface under low-temperature plasma conditions

According to direct kinetic measurements under conditions of a positive column of a low-pressure glow discharge, the probabilities of recombination of oxygen atoms (γ) on an aluminum foil surface have been determined and the effective activation energies of the recombination process have been calculated. It has been found that the γ value depends on the gas pressure in the system at a discharge current above 30 mA. The fluxes of the main active components of oxygen plasma onto the plasma-bounding surface have been calculated. It has been shown that an increase in the heterogeneous recombination probability is attributed to an increase in the flux of metastable oxygen molecules О2(b1∑g+ onto the surface.

Calculation of the Melting Process of a Quartz Particle Under Low-Temperature Plasma Conditions

The melting process of a quartz particle under low-temperature plasma conditions has been considered. The melting stages of the quartz particle in an experimental electroplasma plant have been modelled mathematically, and the value of the limiting melting radius of particles has been established.

Theory of the electron sheath and presheath

Electron sheaths are commonly found near Langmuir probes collecting the electron saturation current. The common assumption is that the probe collects the random flux of electrons incident on the sheath, which tacitly implies that there is no electron presheath and that the flux collected is due to a velocity space truncation of the electron velocity distribution function (EVDF). This work provides a dedicated theory of electron sheaths, which suggests that they are not so simple. Motivated by EVDFs observed in particle-in-cell (PIC) simulations, a 1D model for the electron sheath and presheath is developed. In the model, under low temperature plasma conditions (Te≫Ti), an electron pressure gradient accelerates electrons in the presheath to a flow velocity that exceeds the electron thermal speed at the sheath edge. This pressure gradient generates large flow velocities compared to what would be generated by ballistic motion in response to the electric field. It is found that in many situations, under common plasma conditions, the electron presheath extends much further into the plasma than an analogous ion presheath. PIC simulations reveal that the ion density in the electron presheath is determined by a flow around the electron sheath and that this flow is due to 2D aspects of the sheath geometry. Simulations also indicate the presence of ion acoustic instabilities excited by the differential flow between electrons and ions in the presheath, which result in sheath edge fluctuations. The 1D model and time averaged PIC simulations are compared and it is shown that the model provides a good description of the electron sheath and presheath.

Superelastic collisions under low temperature plasma and afterglow conditions: A golden rule to estimate their quantitative effects

A simple equation describing the formation of plateaux induced by superelastic collisions in the electron energy distribution function (EEDF) of low temperature and afterglow plasmas is derived. The EEDFs predicted from this equation are in good agreement with those obtained from the numerical solution of the full Boltzmann equation in the presence of excited states.

Interaction of a tin-based capillary porous structure with ITER/DEMO relevant plasma conditions

Sn filled capillary porous structures were exposed to high flux low temperature plasma conditions at the Pilot-PSI linear device. Enhanced erosion above that expected classically was investigated via spectroscopic observation of Sn0 emission from the plasma in front of the target surface while the surface temperature was monitored by both thermography and pyrometry. An anomalous erosion flux was observed as temperature increases, with onset for this occurrence varying strongly between different ion species. The results appear incompatible with existing ‘adatom’ models for the anomalous erosion flux. Further targets were exposed in turn to increasing heat fluxes and the heat removed determined from cooling water calorimetry, which was then compared to a solid Mo reference target. At high powers the total energy of the cooling water is reduced, indicating a shielding of the surface from the plasma heat flux by the vapour cloud in front.

Trend of Nitriding on Chromium-Molybdenum Steel via Low Temperature Screen Plasma Technology

Low temperature screen plasma technology, a high plasma density, through using a low energy supply, shows excellent effects on a low alloy chromium-molybdenum steel for plastic molds because it does not show a compound layer and a high surface hardness without a deterioration in matrix hardness. For interest about hardening depth, both the screen plasma nitriding and plasma nitro-carburizing processes were tested including nitrogen, hydrogen and a methane mixed gas environmental at 653 K, 713 K. The optical emission spectroscopy (OES) has been analyzed during screen plasma nitriding (SPN) and a nitro-carburizing process (SPNC) was proceeded at 713 K and the same pressure. I find it difficult to dissociate nitrogen molecules perfectly with neutral nitrogen atoms via the DC-plasma nitriding process. Therefore, the SPN and SPNC process have shown a high density of plasma species even though low temperature plasma conditions have a high peak intensity of Hβ and Hγ in the results of the analysis by OES. The hardness value was measured with the micro-Vickers hardness tester after the SPN, SPNC process and the chemical composition of nitriding layers were traced by GDOES. The screen nitriding layer via the screen plasma technology has shown excellent properties with a thickness depth of about 850 ~ 900 HV without the deterioration of matrix hardness value.

Особенности электролиза воды в условиях неравновесной низкотемпературной плазмы

Особенности электролиза воды в условиях неравновесной низкотемпературной плазмы

External combustion of high-speed multicomponent hydrocarbon-air flow under conditions of low-temperature plasma

The stabilization of external combustion (at the plate surface) of high-speed multicomponent (air, alcohol, and propane) flows is realized experimentally. It is shown that heat fluxes during alcohol combustion rise by a factor of about 7 and during propane combustion by a factor of 15, in comparison with the heat flux from a discharge in a high-speed air flow. The electron concentration measured at a distance of 10 cm down-stream from the electrode ends is approximately 109 cm−3 in the case of the discharge in an air flow, whereas during alcohol combustion it attains 2 × 1011 cm−3 and during propane combustion it is 3 × 1011 cm−3. The flame temperature in the area of the discharge existence varies from 2000 up to 2500 K and outside the discharge at the distance of z = 20 cm from electrodes is 1800 K, gradually decreasing downstream. It is shown that the combined discharge in the subsonic flow allows for complete combustion of liquid and gaseous hydrocarbons. The completeness of combustion in supersonic flows attains 95%, depending on the flow velocity.

Specific Features of Generation of Low-Temperature Plasma in High-Frequency Plasma Electrosurgical Apparatuses

Specific features of generation of low-temperature plasma in high-frequency plasma discharge electrosurgical apparatuses are discussed for electrolyte solution surrounding a metal electrode. Ignition and stable burning conditions of low-temperature plasma in electrolyte medium at atmospheric pressure are considered. Necessary conditions of plasmochemical electrosurgical action in medicine are discussed. High-frequency electrosurgical apparatuses Plasmatom are presented. The apparatuses operate in low-temperature plasma mode.

Influence of surface microwave discharge on ignition of high-speed propane-air flows

Ignition of supersonic propane-air flow under conditions of low-temperature plasma of surface microwave discharge is experimentally studied. We show that both rich and poor mixtures ignite, and the combustion intensity is maximal for the stoichiometric mixture. The dependence of the supersonic propaneair flow ignition time on the reduced electric field, E/n, under conditions of nonequilibrium gas-discharge plasma is experimentally obtained. The induction period is shown to decrease from 1 ms to 5 μs with the increase in E/n from 40 to 200 Td. The propagation velocity of the combustion front boundary (depending on the equivalent mixture ratio and the input microwave power) is maximal for the stoichiometric mixture and reaches 160 m/s at E/n = 150 Td. Under these conditions, the combustion temperature is about 3000 K.

Surface modification of polyester and polyamide fabrics by low frequency plasma polymerization of acrylic acid

AbstractIn this study, the surface characteristics of polyester and polyamide fabrics were changed by plasma polymerization technique utilizing acrylic acid as precursor. This monomer was used to produce hydrophilic materials with extended absorbency. The hydrophilicity, total wrinkle recovery angle (WRA°) and breaking strength of the fabrics were determined prior and after plasma polymerization treatment. The modification of surfaces was carried out at low pressure (<100 Pa) and low temperature (<50°C) plasma conditions. The effects of exposure time and discharge power parameters were optimized by comparing properties of the fabrics before and after plasma polymerization treatments. It was shown that two sides of polyester fabric samples were treated equally and homogeneously in plasma reactor. For polyester fabrics, the minimum wetting time, 0.5 s, was observed at two plasma processing parameters of 10 W–45 min and 10 W–20 min, where untreated fabric has a wetting time of 6 s. For polyester fabrics, the maximum value was obtained at 60 W–5 min with the wrinkle recovery angle of 306° where the untreated fabric has 290°. The optimum plasma conditions for polyamide fabrics were determined as 30 W–45 min where 2 s wetting time was observed. Wrinkle recovery angle of untreated polyamide fabric was 264°. In this study, after plasma polymerization of acrylic acid, wrinkle recovery angle values were increased by 13%. No significant change was observed in breaking strength of both fabrics after plasma treatment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2318–2322, 2007

Influence of low-temperature plasma conditions on wicking properties of PA/PU knitted fabric

Plasma surface treatment has been extensively applied in the textile industry for the modification of polymer materials. In this study low-temperature plasma (LTP) is used for surface treatment of polyamide/polyurethane (PA/PU) knitted fabric. The envisaged plasma effect is an increase in the surface energy of the treated textile, leading toward improved hydrophilic properties. The knitted fabric was treated by LTP using three non polymerizing gases: oxygen, air, and carbon dioxide. After plasma treatment, wettability of samples was tested through their wicking properties measuring capillary rise after water bath contact. The PA/PU knitted fabric samples treated with different plasma gases exhibited different hydrophilic performances. The influence of plasma variables (discharge power, time, pressure) was investigated. Although the chemical characteristics of elastan (PU) and nylon (PA) threads are different, the study has demonstrated that plasma treatment can in the same time alter the surface-wetting behavior of both the components of the knitted fabric. It was also shown how these treatments can be regulated to produce the desired level of hydrophilicity dependently on the request application. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Modeling of the Temperature Distribution in Arc Discharge Plasma Reactor

AbstractFor pollution control the non-thermal plasma seems to be the most convenient source of energetic electrons and chemically active species. In the electrical discharges the non-thermal plasma condition at atmospheric pressure can be obtained with fast gas flow through the discharge chamber volume, like in DC glow discharge or AC gliding arc discharge. The electrons temperature and its volumetric distribution is one of the fundamental parameters that should be study if we want to obtain the non-equilibrium low temperature plasma conditions in given geometry of the plasma reactor. These conditions depend on the kind of plasma gas and its velocity, geometry of the gliding arc reactor and on parameters of the power supply system. Paper presents a simplified mathematical model of the two -electrode gliding arc reactor to determine electron temperature and its distribution. Results of calculations are useful for selection of the power supply systems parameters and their design as to ensure the non-equilibrium state of gliding arc discharge plasma. Further calculations aim at three-and multielectrode reactors and three-dimension temperature distribution.

Modification of food contacting surfaces by plasma polymerisation technique. Part I: Determination of hydrophilicity, hydrophobicity and surface free energy by contact angle method

In this study, the surface characteristics of three major materials which are widely used in food industry, glass, polyethylene (PE) and stainless steel (SS 316), were studied. The hydrophilicity, hydrophobicity and surface free energy (SFE) of those surfaces were determined by contact angle measurements prior and after plasma polymerisation treatment. The modification of the surfaces was carried out at low pressure and low temperature plasma conditions by using different monomers with functional properties. Phenol and 1,1,1,3,3,3-hexaflouroisopropylacrylate (HFIPA) were used to produce hydrophobic materials with low surface energy, and hydroxyethylmethacrylate (HEMA), ethylenediamine (EDA), polyethyleneglycolethylethermethacrylate (PEGEEMA) and polyethyleneglycolmethacrylate (PEGMA) were used to produce hydrophilic materials with higher surface energy. The effects of monomer flow rate, exposure time and discharge power parameters were optimized by comparing surface characteristics before and after plasma polymerisation treatments. Contact angle measurements were performed by using the captive bubble technique, and the geometric mean equation was used to calculate the surface free energy values. Air and n-octane bubbles with different polarity were used to determine the changes on the surface energy including the dispersive and polar components. Polyethylene was the most hydrophobic material among the materials used in this study related to its air contact angle and γ sw values. γ sw value was found 38.91 mJ/m 2 for polyethylene. Glass was determined as the most hydrophilic material ( γ sw: 1.11 mJ/m 2) among the used surfaces, and its surface energy ( γ sv) was 58.95 mJ/m 2. The contact angle and SFE values were affected by monomer flow rate, exposure time and power parameters used for all modification processes. The equilibrium between etching and deposition processes can be controlled by these plasma parameters. Therefore, we tried to optimize plasma parameters according to the results from contact angle and surface energy data.