Glow Plasma Research Articles

Enhanced Interfacial Adhesion of Nylon 66 to Epoxy Resin EPON 825 by Non-thermal Atmospheric Pressure Dielectric Barrier Discharge Plasmas

Poly(hexamethylene adipamide), nylon 66, is a popular plastic that requires high surface wettability and strong adhesive bonds for many applications. However, pristine nylon is difficult to bond due to its hydrophobic nature and poor surface wettability. The objective of this work was to modify the physio-chemical surface properties of nylon 66 via a novel atmospheric plasma surface treatment approach using oxygen (O2) or water vapor (H2O) plasma glow. The surface hydrophilicity of the plasma-treated nylon surface was substantially enhanced immediately after either helium (He)/H2O or He/O2 plasma surface treatment. The average water contact angle was reduced from 65 degrees to ~30 degrees after He/H2O plasma and ~40 degrees after He/O2 plasma treatments. The improved hydrophilicity was also evidenced by the increased intensities of the surface oxygen and hydroxyl bonds in the X-ray photoelectron spectra. The interfacial adhesion strength of nylon surfaces before and after plasma treatment was further evaluated by uniaxial tensile tests of nylon single-joint lap shears bonded with three adhesives, i.e., thermoset epoxy resins EPON 825/ JEFFAMINE D-230 and EPON825/JEFFAMINE D-2000, and the thermoelastic polyurethane adhesive Sikaflex 252. The most significant improvements in bond strengths due to plasma treatment were found for lap shears bonded with the EPON 825/JEFFAMINE D-230 epoxy resin; their shear strengths with maximum loads were more than doubled—from 299–451 to 693–1594 N—after plasma treatment and were further enhanced by a factor of four to 895–1857 N after a subsequent silane treatment. In contrast, the bond strength of lap shears bonded with EPON 825/JEFFAMINE D-2000 and Sikaflex was not significantly improved because of the different a, re-affirming the importance of adhesive bulk properties This work presents the preliminary success of effective surface functionalization leading to enhanced interfacial adhesive bonds for nylon 66 via the development of scalable atmospheric plasma surface treatments.

Decontamination and Germination of Buckwheat Grains upon Treatment with Oxygen Plasma Glow and Afterglow.

Buckwheat is an alternative crop known for its many beneficial effects on our health. Fungi are an important cause of plant diseases and food spoilage, often posing a threat to humans and animals. This study reports the effects of low-pressure cold plasma treatment on decontamination and germination of common (CB) and Tartary buckwheat (TB) grains. Both plasma glow and afterglow were applied. The glow treatment was more effective in decontamination: initial contamination was reduced to less than 30% in CB and 10% in TB. Fungal diversity was also affected as only a few genera persisted after the glow treatment; however, it also significantly reduced or even ceased the germination capacity of both buckwheat species. Detailed plasma characterisation by optical spectroscopy revealed extensive etching of outer layers as well as cotyledons. Afterglow treatment resulted in a lower reduction of initial fungal contamination (up to 30% in CB and up to 50% in TB) and had less impact on fungal diversity but did not drastically affect germination: 60–75% of grains still germinated even after few minutes of treatment. The vacuum conditions alone did not affect the fungal population or the germination despite an extensive release of water.

The Impact of Dry Yeast Rehydrated in Different Plasma Treated Waters (PTWs) on Fermentation Process and Quality of Beer.

Yeast plays a key role in the production of alcoholic beverages. Effective fermentation requires appropriate conditions to ensure the production of high-quality beer. The paper discusses the effect of dry brewing yeast (Saccharomyces cerevisiae and Saccharomyces pastorianus) after rehydration with water exposed to low-temperature, low-pressure glow plasma (PTW) in the atmosphere of air (PTWAir) and nitrogen (PTWN) in the course of the fermentation process, the formation of volatile compounds and other quality parameters of the finished beer. The obtained results show that the lager yeast strain initiated the process of fermentation faster after rehydration in the presence of PTWAir compared to all of the other treatments. It was observed that PTWAir significantly changed the composition of volatile compounds in the finished beer, especially by increasing the number of terpenes, which are compounds that positively shape the aroma of beer. In the case of PTWN samples, lower alcohol content, real extract, apparent extract and amount of biomass were observed in all analyzed strains.

Data driven discovery of a model equation for anode-glow oscillations in a low pressure plasma discharge

A plasma glow discharge tube, a versatile device widely employed in several scientific and industrial applications, is also a useful tool for many basic plasma studies in the laboratory. Anode glow oscillations are well-known phenomena in such devices that arise from an instability of the plasma glow around a small positively charged electrode. Depending upon the gas pressure, the applied DC voltage, and the distance between the electrodes, these oscillations can display a rich dynamical behavior. Over a certain parametric regime, these nonlinear oscillations exhibit a stable limit cycle behavior that has been modeled in the past by a Van der Pol like equation. While such a model equation provides a qualitative description of the observations, it lacks quantitative agreement and does not have any predictive capability. We employ the sparse identification of nonlinear dynamics (SINDy) method to obtain a model equation directly from a time series of the experimental data. Our model captures well the main features of the experimental data in a quantitative manner. It also shows a significant deviation from the Van der Pol model due to additional contributions that are akin to nonlinear damping in a Rayleigh oscillator. Such a hybrid Van der Pol–Rayleigh oscillator model could provide a useful paradigm for future explorations of the nonlinear dynamics of this system.

194 nm microplasma lamps driven by excitation transfer: optical sources for the 199Hg ion atomic clock and photochemistry

A series of miniature, microcavity plasma lamps emitting predominantly at 194 nm has been successfully developed and tested as the optical pump for the microwave 199Hg-ion atomic clock (40.507 GHz), replacing low pressure, RF-powered Ar/Hg discharges. Intense fluorescence on the 6p 2P1/2 → 6s 2S1/2 transition of the singly-charged 202Hg ion at 194.23 nm has been generated in arrays of cylindrical microplasmas through electron-impact excitation of He, followed by three-body formation of He2(a 3 ) and Penning ionization of Hg. Emission spectroscopy and kinetic modeling of He/Hg vapor plasmas demonstrate that the population of the Hg+(62P1/2) radiating state (16.82 eV), produced by direct or two-step electron impact processes, is 1% of that generated by excitation transfer to Hg by H. Flat, fused silica lamps having emitting areas as small as 4 mm2 and containing several mg of 202Hg and 50–800 Torr of He have been fabricated and serve as optical drivers for the Hg+ atomic clock cycle. Based on small arrays of 500 μm–1 mm diameter microcavities, these lamps produce peak and average intensities at 194 nm greater than those associated with the Hg resonance transition at ∼ 254 nm, despite the factor of 3 difference between the energies of the 6p 3P1 and 6p 2P1/2 states of neutral Hg and Hg+, respectively. These lamps are unique in the sense that the desired radiating species is an excited ion and the background He gas pressure can reach 1 atm, both of which contribute to a dense glow plasma placing severe demands on E/N, power conditioning, and materials selection. Nevertheless, with proper attention given to design, vacuum processing, and preparation of the lamps, lifetimes above 1500 h have been realized to date. When these lamps drive Jet Propulsion Laboratory Hg+ clocks, the stability floor has been measured to be −14. The implications of this lamp for gas-phase and solid-state photochemistry are also discussed.

Self-catalytic Fenton-like reactions stimulated synergistic Cu-EDTA decomplexation and Cu recovery by glow plasma electrolysis

• Multiprocess stimulated Cu-EDTA decomplexation by plasma electrolysis was realized. • Cu-EDTA decomplexation was mainly triggered by •OH. • Sequence breakages of functional groups in Cu-EDTA were confirmed by 2D-COS. • Self-catalytic Fenton-like reactions were induced by Cu-based byproducts and H 2 O 2 . • Released Cu 2+ was simultaneously reduced to Cu + /Cu 0 by •H and e aq - on cathode. Heavy metal–organic complexes have potential threats to organisms in water environment and human health, and it is a big challenge to remove them by traditional chemical precipitation. In this study, a glow discharge plasma (GDP) system coupling oxidation and reduction processes was established to decompose heavy metal–organic complex, taking Cu-ethylenediaminetetraacetic acid (Cu-EDTA) as a model. Approximately 87% of Cu-EDTA decomplexation and 64% of Cu recovery were achieved after 90 min of GDP treatment. Cu-EDTA decomplexation was mainly triggered by oxidation by •OH in the GDP system, leading to successive breakage of Cu–O > C-O > C-N > OH > C = O based on two-dimensional correlation spectroscopy analysis. Self-catalytic Fenton-like reactions were induced by Cu-based byproducts and H 2 O 2 , further promoting Cu-EDTA decomplexation. The released Cu 2+ was simultaneously reduced to Cu + /Cu 0 by •H and e aq - on the cathode surface. The technique exhibited great performance for Cu-EDTA decomplexation in water environment, as well as for other heavy metal complexes. This study disclosed the underlying mechanisms of synchronous Cu-EDTA decomplexation and Cu recovery in the GDP system, providing a prospective technique for heavy metal complex control.

Fabrication of porous micro/nano structured Cr coating with superhydrophobic and ultrahigh adhesion properties by plasma reverse sputtering process

In this study, a superhydrophobic Cr porous surface with better abrasive resistance was prepared on Ti6Al4V substrates by double glow plasma surface alloying and the plasma reverse sputtering process. These results showed that the Cr coating with rough and porous micro-nano structures was formed on the surface of Ti6Al4V alloy, which could be attributed to the Kirkendall effect during the process of the plasma reverse sputtering. The role of the reverse sputtering time on the structure and performance of the Cr porous coatings was investigated systematically. The thickness of Cr diffusion layers increased from 13 μm to 28 μm as the reverse sputtering time increased to 45 min. The friction behavior was revealed by wear test, demonstrating prominent improvement of wear resistance. Meanwhile, the as-prepared micro-nano structured Cr coatings exhibited superhydrophobic properties with ultrahigh adhesion.

Optimization for solderability of large-size single-crystal diamond with heterogeneity alloys by tantalum coating

To ameliorate the solderability of single-crystal diamond with heterogeneity metals/alloys, tantalum (Ta) coatings were prepared on the diamond by utilizing the double glow plasma surface metallurgy (DGPSM) technique. Using Ag-Cu-Ti solder, the Ta-coated single-crystal diamonds were soldered onto cemented carbide (WC-Co) matrixes. The effects of metallization temperatures on the microstructure, phase, and solderability of the Ta-coated diamond were investigated. The results show that uniform and compact Ta coatings with increased thicknesses are obtained with increasing metallization temperatures. Besides, under all the temperatures, the diffusion layers composed of Ta2C and TaC could be formed at the Ta/diamond interface, which is beneficial to enhance the coating adhesion. The average shear strength of the soldered joint with Ta-coating increases first and then decreases with the increase of temperature. The maximum value is 118.7 MPa on the soldered joint with 850 °C Ta coating, which is approximately 57% higher than without Ta coating. Three failure modes occur during the shear process, including the ductile fracture of the soldered seam, brittle fracture in the interior of Ta carbides at the Ta/diamond interface, and brittle fracture of the single-crystal diamond itself. Among them, the ductile fracture of the soldered seam is the dominant fracture mode.

The Improvement of Reserve Polysaccharide Glycogen Level and Other Quality Parameters of S. cerevisiae Brewing Dry Yeasts by Their Rehydration in Water, Treated with Low-Temperature, Low-Pressure Glow Plasma (LPGP)

The increasing popularity of active dry yeast arises from its properties, such as ease of storage, and simplicity of preparation and dosing. Herein, we elaborate on the effect of plasma-treated water (PTW) under air atmosphere (PTWAir) and nitrogen (PTWN) on the improvement of the reserve polysaccharide glycogen level and other quality parameters of S. cerevisiae brewing dry yeast in comparison with the non plasma-treated water (CW). For this purpose, strains of top-fermenting (S. cerevisiae T58 (poor quality), S33 (poor quality)) and bottom-fermenting (S. pastorianus W30/70 (poor quality)) yeast stored one year after opening and S. cerevisiae US-05 (fresh strain) were selected to examine the influence of PTWs toward the quality parameters of yeast biomass after the rehydration and fermentation process. The obtained results showed that in the case of poor quality yeast strains, PTWAir increased glycogen content after the rehydration and fermentation process, which was a favorable trend. A similar increase was observed for the trehalose content. Results showed that PTWN significantly reduced the number of yeast cells in ale strains and the viability of all analyzed samples. The lowest viability was observed in Sc S33 strain for PTWAir (41.99%), PTWN (18.6%) and CW (22.86%). PTWAir did not contribute to reducing the analyzed parameter; in particular, the results of Sc T58 yeast strain’s viability are shown: PTWAir (58.83%), PTWN (32.28%) and CW (43.56%). The obtained results suggest that rehydration by PTWN of dry yeast with a weakened condition is not recommended for both qualitative and cost-related reasons, while PTWAir significantly contributed to the improvement of some yeast parameters after rehydration and fermentation (higher glycogen and trehalose content).

A modern-day alchemy: Double glow plasma surface metallurgy technology

In the long history of science and technology development, one goal is to diffuse solid alloy elements into the surface of steel materials to form surface alloys with excellent physical and chemical properties. On the basis of plasma nitriding technology, double glow plasma surface metallurgy technology has answered this challenge. This technology, which seems to be a modern-day alchemy, can use any element in the Periodic Table of chemical elements, including solid metal elements and their combinations, to form many types of surface alloyed layers with high hardness, wear resistance, corrosion resistance, and high temperature oxidation resistance on various metal materials. For example, nickel base alloys, stainless steels, and high speed steels are formed on the surfaces of ordinary carbon steels; high hardness, wear resistance, and high temperature oxidation resistance alloys are formed on the surface of the titanium alloy. This article briefly introduces the formation and principle of double glow plasma surface metallurgy technology and summarizes the experimental results and industrial applications. The significance and development prospect of this technology are discussed.

Anodic growth of copper oxide nanostructures in glow discharge

Purpose: Application of plasma glow discharge to copper oxide nanostructure growth is studied. The simplicity of the proposed technique may be beneficial for the development of new plasma reactors for large-scale production of diverse metal oxide nanostructures. Design/methodology/approach: Copper sample was placed on anode of a setup designed to ignite plasma glow discharge. The proposed approach allows eliminating the negative effects of ion bombardment, like sputtering and generation of defects on a surface of the growing nanostructures, but preserves the advantages of thermal growth. The growth process was explained in terms of thermal processes interaction occurring on a surface of the anode with the glow discharge plasma. Findings: Plasma treatment resulted in generation of reach and diverse nanostructures that was confirmed by SEM images. Nanowire-like, flower-like, anemone-like nanostructures and nanodisks composed into the nanoassemblies are observed; the nanostructures are associated with microbabbles on CuO layer. These findings allow concluding about the possible implementation of the proposed method in industry. Research limitations/implications: The main limitation is conditioned by the lack of heat supplied to the anode, and absence of independent control of the heat and ion fluxes; thus, the additional heater should be installed under the anode in order to expand the nomenclature of the nanospecies in the future studies. Practical implications: High-productivity plasma process in copper oxide nanostructures synthesis was confirmed in this research. It may be applied for field emitter and supercapacitor manufacturing. Originality/value: Oxide nanostructure synthesis is conducted by use of a simple and well-known glow discharge technique in order to expand the production yield and diversity of nanostructure obtained in the processes of thermal growth.

Specific Way of Controlling Composition of Cannabinoids and Essential Oil from Cannabis sativa var. Finola

Recently, a series of papers reported preparation and physicochemical properties of various kinds of water treated in contact with various gases with low-temperature, low-pressure glow plasma of low frequency (LPGP). Consecutive papers presented results of watering numerous herbal plants with those kinds of water in planting of numerous herbal plants. Always, the watering influenced the yield and quality of the crops and considerably changed the composition of the essential oils extracted from the watered plants. This paper provides the effects of watering of Cannabis sativum var. Finola with water LPGP-treated either in the air (LPGPA), under molecular nitrogen (LPGPN) or carbon dioxide (LPGPC). Cannabis sativa, particularly its botanic class called hemp, attracts great attention for its numerous applications. They include rope, textiles, clothing, shoes, food, paper, bioplastics, insulation, biofuel and industrial fibre. The watering was maintained for 12 weeks. Regardless of the kind of the used plasma-treated water, a considerable increase in the plant crop yield was noted for first 7 weeks. Further cultivation resulted in a minute increase in the yield. The watering with LPGPC offered the highest crop yield, followed by nontreated water, LPGPN and LPGPA. The yield of essential oil per 1 g of plant was independent of the used kind of plasma-treated water. Watering Finola with LPGPA resulted in a decrease in the level of cannabidivarin (CBD V) and considerable increase in the deal of Δ 9-tetrahydrocannabinol (Δ9-THC). The levels of the remaining components of the essential oil slightly decreased with respect to that in the control sample. Almost identical trends in the influence of watering upon the composition of essential oil were observed in the case of LPGPN. However, an unusually strong decrease in the level of CBD V accompanied by a very high increase in the level of Δ9-THC could be noted. The performed study provided strong evidence that watering seeds and plants of Finola with various kinds of the LPGP-treated water could modulate and even tailor the crop yield, functional properties of the plant and essential oils extracted from it. The composition of the essential oil isolated from the plant watered with LPGPN suggests its application as a substitute of medical marijuana (medical cannabis).

Role of the nitrogen ratio on mechanical properties and wear resistance of CrN/Fe functionally graded coating produced by double glow plasma alloying

The hard ceramic coating under the external load tends to show cracking and spallation due to the mismatch of deformation between coating and substrate. To moderate the property difference, a CrN/Fe gradient coating was fabricated by double glow plasma alloying at different Ar/N2 ratios. The thermodynamically favorable reaction between Cr and N ensured the spatially gradient structure of CrN and (Fe, Cr) phase without Fe nitrides. The outmost CrN phase possessed over-stoichiometry of N atoms, leading to the N1s spectrum shifted to the lower binding energy. The increased N2 ratio made the nitride content increase from 53.4, 73.6 to 74.0 %. Various volume gradients of nitride/metal contributed to different mechanical behavior of coatings, such as the enhanced hardness (16.3 to 21.5 GPa) and Young’s Modulus. Two indexes, H/E and H3/E2, showed an increasing trend with the increasing N2, which meant better toughness and adequate elastic abilities to suppress radial cracks. Compressive residual stress in these coating ranging from −1.06, −1.16 to −1.44 GPa, also restrained the radial cracks and accelerated the formation of circumferential cracks. Introducing nitride-metal transitional structure lowered the probability of cracks and spallation in the wear test.

A functionally graded coating from ZrN to Ti: Experimental characterization, erosion behavior and design concept

In functionally graded coatings (FGCs), the elemental composition, or structure, within a coating changes progressively as a function of depth, allowing for the property gradual transition from coating to matrix. One method for preparing FGCs with continuous component distribution is double glow plasma alloying (DGPA) technique. In this work, a sandwich-like ZrN/Ti FGC was fabricated, consisting of a single ZrN ceramic layer on the topmost layer, a ceramic/metal intermediate transition layer, and a metallic Ti layer in the inner layer. The transition layer derived from atom diffusion made the metallurgical bonding for entire coating, which endowed the coating with high adhesion. The erosion tests exhibited that the coating improved the erosion resistance of substrate effectively, which was attributed to the high hardness and elastic work consumption. Besides, the transition layer with coexistence of metal and ceramic phases deflected the radial crack propagation, and thus increased the plastic work consumption. The thermodynamic calculation using two sub-lattice and Miedema models showed that controlling the Zr diffusion thickness over N diffusion thickness can increase the ZrN phase content and reduce the unfavorable TiN and Ti2N phase. The experiment results and design concept described herein for characterizing FGCs can be used to promote the understanding and design of other FGCs.

Application of Water Treated with Low-Temperature Low-Pressure Glow Plasma (LPGP) in Various Industries

Plasma processing is now a key technology across the world, and nonthermal low-temperature plasmas are being increasingly used. This situation can be explained by a rapidly growing interest in the optimization of existing methods, as well as the development of new ones. Over the last few years, the production of plasma-treated water (PTW) by low-temperature low-pressure glow plasma (LPGP) under an atmosphere of various gases has been increasingly gaining in popularity. Research has been conducted on producing plasma-treated water in the presence of air, nitrogen, ammonia, carbon dioxide, and methane. All the obtained results show that the changed physicochemical properties of the water depend on the type of gas used and the duration of the plasma treatment. New research is emerging on the possibility of using this water in plant breeding, animal husbandry, cosmetology, medicine, and food. For the first time, plasma-treated water has also been tested for use in the brewing industry at the raw material preparation stage. The results obtained in all branches of science are very promising, contributing to the growing interest in plasma-treated water within the scientific community.

Tribological behaviors of HfC coating prepared on 45 steel via double glow plasma surface metallurgy technique

Purpose45 steel is a common material for the manufacture of various components such as shafts or gears. However, its poor surface properties often limit its applications. The purpose of this paper is to find a way to enhance the surface performance of 45 steel, which is expected to improve the wear resistance of 45 steel.Design/methodology/approachDouble glow plasma surface metallurgy technique was used to prepare hafnium carbide (HfC) coatings on the surface of the 45 steel with two preparation process; one is to diffuse two elements together, while the other is to diffuse step by step. The scanning electronic microscopy and the X-ray diffraction were used to analyze the morphology and phase of the HfC coatings. And then the wear tests were carried out for this coating.FindingsCoating diffused step by step shows better performance; it has a 15-µm alloyed layer which is uniform and dense and its hardness can reach up to 1326.5 Vickers-hardness (HV). While the coating fabricated by diffusing elements together owns a 10-µm alloyed layer and its hardness is 1204.1 HV. According to the wear test results, both coatings have a protective effect on the substrate and the coating prepared by step-by-step diffusion process has less wear volume, indicating that it possesses better friction reduction.Originality/valueA new method which diffuses elements together was successfully used to prepare compound HfC coating, which can reduce the cost of coating preparation and improve the efficiency of coating preparation.

Characterization of Quasi-Static/Dynamic Contact Mechanical Properties of Mo Surface-Modified TC4

By using the double glow plasma surface alloying technique, a Mo surface-modified layer is prepared on Ti6Al4V(TC4). The element concentration and microstructure are characterized with a glow-discharge optical emission spectroscope and a scanning electron microscope. The results indicate that the Mo modified layer is compact in structure and gradation in composition, which consists of a pure Mo deposition layer and a thick Mo diffusion layer. Nanoindentation test results indicate that the surface hardness of TC4 is significantly improved after surface modification. Therefore, the initial part of the Mo diffusion layer has higher hardness than the Mo deposition layer. The impact tests for 10,000 cycles at different loads demonstrate that impact load 100 N only causes small plastic deformation, while impact loads 300 N and 500 N could result in cracks. Combining nanoindentation test with finite element reverse analysis, plastic parameters of the Mo modified layer are quantitatively determined. By using the impact test and finite element forward analysis, the dynamic contact mechanical properties of Mo surface-modified TC4 are characterized. When the impact cycles are fixed, ring cracks firstly occur and then radial cracks occur with the impact load increase on the graded layer. The ring cracks are mainly caused by impact stretch fatigue and corresponding cyclic stress is between 3.53 and 2.62 GPa. The radial cracks are mainly related to the tension-compression fatigue and corresponding cyclic stress is between 3.92 and −0.97 GPa.

Performance recovery of plasma actuators in wet conditions

Plasma actuators have been extensively studied for flow control applications over the past two and a half decades. While these studies have been traditionally focused on characterizing their performances as flow control devices, the performance of plasma actuators under adverse conditions such as dew or light rain remains to be less explored. This paper seeks to study the effects of water adhesion from droplets directly sprayed on to a plasma actuator using thrust recovery as the performance metric. It was found in all tests that wet actuators quickly recover plasma glow, before gradually regaining performance comparable to the dry actuator. The measured thrust for the wet actuator after 5 s of operation recovered by 46% and 42% of the thrust of the dry actuator for 50.0–62.5 g m−2 and 125–150 g m−2 of sprayed water droplets, respectively. At 22.5 kVpp and 14 kHz, the highest thrust recovery was recorded at 84% of that of the dry actuator after 80 s of operation. For 17.5 kVpp and 14 kHz the wet thrust recovered by 79%, while for 22.5 kVpp and 10 kHz the wet thrust recovered by 68% of their dry counterpart in 80 s. For 17.5 kVpp and 14 kHz, the thrust almost fully recovered in comparison to the dry actuator after about 290 s of operation. These results indicate that both applied voltage and operating frequency plays a critical role in the performance recovery while the latter may have a stronger influence. Performance recovery for a wet serpentine shaped plasma actuator is also included for general applicability. The power data in all cases show that wet actuators consume more power which with time gradually approach the dry actuator power data. This is because during the initial stages of operation, the rolling mean current of the wet actuator is higher than the dry actuator even though the ionization spikes of dry actuator is stronger.

Positive column dynamics of a low-current atmospheric pressure discharge in flowing argon

We present the results of studies of a cold-plasma atmospheric pressure discharge in argon flow, in both DC and pulse-periodic modes. The burning voltage and the discharge current were 200 V and 15 mA in continuous mode; in pulse-periodic mode the voltage was 220 V and the current 15 mA for a pulse repetition rate of 100 kHz. Special attention was given to the positive column dynamics during the discharge stages of initiation, burning, and extinction. The main method of investigation employed optical diagnostics of the plasma in the visible range with high time resolution. The positive discharge column is shown to be a constricted current channel in the form of an elongated loop. In continuous mode, the length of the positive column, from anode attachment to inflection point outside the discharge system, is several millimeters. In pulsed mode, the positive column is an unsteady plasma formation, the length of which increases at about 4 m s−1, and reaches the same dimension over a time of order 1 ms. We find that the positive column plasma includes hydroxyl molecules OH, nitrogen N2, and atomic oxygen O I, along with atoms of the working gas argon. Observation of the time evolution of the optical emission from the plasma-forming gas shows that the plasma glow of the positive column is mainly determined by argon Ar I radiation, with maximum intensity at the trailing edge of the current pulse.

Tribological characteristics of samples made from titanium alloy VT5 nitrided in plasma glow discharge

The effect of nitriding of VT5 alloy (3.7115) in the plasma of a glow discharge excited in a hollow cathode on its tribological characteristics in pairs with different materials in jet fuel TS-1 and under dry sliding conditions has been studied. For research and tribological tests, samples of VT5 alloy were nitrided in the plasma of a glow discharge excited in a hollow cathode at a temperature of 975 ± 15 °C and a pressure of 58 ± 2 Pa in a nitrogen-argon gas mixture with a nitrogen content of 78 vol. %. Tribological tests were performed on a friction machine 2070 SMT-1 according to the scheme "cube-roller". Tests under conditions of sliding with jet fuel TS-1 were performed at a load of 200 N. The sliding speed during the tests was 1.3 m/s, and the test time was 75 s. The test under dry sliding conditions was carried out at a load of 100 N and a sliding speed of 0.785 m/s. The test time was 30 minutes. It is shown that the nitrided VT5 alloy in friction pairs with several materials has rather low wear values (≤ 2.26 × 10–6 mm3/Nm), as well as a coefficient of friction at the level of 0.08 to 0.12.