Argon Pressure Research Articles

An improved conversion of the microwave energy into plasma in an optimized microwave plasma sheet source at 2.45 GHz designed for surface treatment

Efficient conversion of the microwave energy into an atmospheric-pressure argon plasma in a microwave plasma sheet source (MPSS) operating at 2.45 GHz in ambient air is the subject of this work. The MPSSs, capable of providing an atmospheric pressure plasma in the shape of a narrow sheet are an innovative technology for variety of surface treatments with no impact on the environment. The existing designs of the MPSS exhibit unsatisfactory efficiency of the conversion of microwave energy produced by the microwave source into the microwave plasma (about 80%), which hinders implementation of the MPSSs in the industry. In this paper, after an analytical approach based on the equivalent electrical circuit method we proposed an optimization of the design of MPSS in terms of the microwave energy conversion efficiency. The MPSS design improvement consisted in reducing the electrical impedance in the input plane of the MPSS by introducing a capacitive diaphragm into the MPSS transmission line, which compensated the inductive character of the plasma sheet. The experimental measurement of the electrodynamic characteristics of the MPSS with diaphragm showed that using the diaphragm significantly decreased the microwave power losses due to the microwave reflection from about (20–30)% to a level of several percent. This substantially increased the MPSS energy conversion efficiency up to about 97%, 93% and 87% for incident powers P I of 500 W, 750 W and 1000 W, respectively. The electrodynamic characteristics of the MPSS appeared a very convenient tool for determining the conditions of maximum efficiency of conversion of the microwave energy into the microwave plasma. The electrodynamic characteristics were measured at argon flow rate of 20 Nl min−1. The analysis of the calculated input impedances of the MPSSs with and without diaphragm, based on the equivalent electrical circuits of both MPSSs confirmed that the change of the character of the input reactance of the MPSS from inductive to capacitive after introducing the diaphragm is the cause of the increase in the MPSS energy conversion efficiency. The MPSSs having the energy conversion efficiency such high as presented in this paper appears to be attractive innovative technology for economic use in industrial applications.

Evolution of the microstructure of sputter deposited TaAlON thin films with increasing oxygen partial pressure

Abstract Recently, quaternary oxynitrides of transition metals and aluminum have attracted increasing interest due to their tunable properties. Within the present work, a series of TaAl(O)N films was sputter deposited using constant nitrogen and varying oxygen partial pressures. The films were grown from single element Ta and Al targets. The deposition parameters were adjusted to obtain a Ta/Al atomic ratio of ~50/50 for the oxygen-free film and were held constant for the following depositions, with the exception of the increasing oxygen partial pressure and compensatory decreasing argon partial pressure. Elastic recoil detection analysis revealed oxygen contents of up to ~26 at.%, while the nitrogen content decreased from ~47 at.% in the oxygen-free film to ~35 at.% in the film with the highest oxygen content, resulting in a significant decrease of the metal/non-metal ratio with increasing oxygen partial pressure. The micro- and bonding structures of the films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and transmission electron microscopy. All films exhibited a dominating face-centered cubic TaN-based structure with indications for additional nanocrystalline and amorphous phase fractions in the oxygen containing films. In addition, the mechanical properties were evaluated by nanoindentation, yielding a decreasing hardness and elastic modulus with increasing oxygen content.

Assessment of quality and safety of pork treated with low-temperature atmospheric-pressure plasma

It is known that processing methods ensuring partial or full microbial inactivation are quite limited. Therefore, it is of great interest to develop technique and technologies allowing the effective action on microorganisms without a significant influence on product properties. The use of cold plasma can be one of the promising methods of meat product treatment by cold sterilization. The present work examines a possibility of chilled meat treatment with low-temperature atmospheric-pressure plasma to increase its stability to microbial spoilage and extend shelf life. To obtain low temperature plasma, the equipment developed by the designing department “Plasmamed” was used. Chilled meat was treated with low-temperature atmospheric-pressure argon plasma for 5, 10, 20 and 30 min. Samples were stored at a temperature of 2–4 °C for 10 days. Organoleptic indices, moisture weight fraction, changes in pH and water activity were analyzed before treatment and during storage. Sanitary microbiological analyses were carried out by the following indicators: quantity of mesophilic aerobic and facultative anaerobic microorganisms (QMAFAnM), the presence and quantity of coliforms, Salmonella, Escherichia coli, Listeria monocytogenes, Proteus. It was shown that meat cold treatment with argon plasma inhibited the development of mesophilic microorganisms. The colony forming units detected in the samples after ten days of storage were determined by the duration of exposure to plasma. It was proved that meat treatment for 15 and 30 min had the bactericidal effect and facilitated an improvement in meat color during storage. The organoleptic indices of the samples treated with plasma corresponded to the requirements of standards and approved consumer characteristics.

Gas pressure measurement using micro-corona-discharging effect in surface acoustic wave resonators

This paper reports a gas pressure sensor using surface acoustic wave resonator (SAWR) based on both the field-induced electron emission and the micro-corona-discharging (MCD) phenomena. With the micron-scale finger-gap of electrodes covered with SiO2 passivation layer, the enhanced field-effect emission (FEE) at electrodes result in the micro-corona-discharging and thus the change in the dynamic resistance of SAWR. A high Q-factor SAWR was fabricated on ST-cut quartz substrate using microelectronics processing technology, and the gas-pressure-dependent return-loss was tested, and the MCD theory and the equivalent circuit model of SAWR were used to analyze the test results. Under argon pressure range from 0 to 601 kPa, the dynamic resistance of the SAWR varies from 24.569 to 41.589 Ω at 25 °C. The resistance rate reaches 69.3%, which is far higher than that of traditional piezoresistive pressure sensors. At the same time, the oxygen pressure was also tested by the SAWR as a comparison. The SAW-based gas pressure sensors have the potential for measurement of the super-high pressure.

On the Insignificant Role of the Oxidation Process on Ultrafast High-Spatial-Frequency LIPSS Formation on Tungsten.

The presence of surface oxides on the formation of laser-induced periodic surface structures (LIPSS) is regularly advocated to favor or even trigger the formation of high-spatial-frequency LIPSS (HSFL) during ultrafast laser-induced nano-structuring. This paper reports the effect of the laser texturing environment on the resulting surface oxides and its consequence for HSFLs formation. Nanoripples are produced on tungsten samples using a Ti:sapphire femtosecond laser under atmospheres with varying oxygen contents. Specifically, ambient, 10 mbar pressure of air, nitrogen and argon, and 10−7 mbar vacuum pressure are used. In addition, removal of any native oxide layer is achieved using plasma sputtering prior to laser irradiation. The resulting HSFLs have a sub-100 nm periodicity and sub 20 nm amplitude. The experiments reveal the negligible role of oxygen during the HSFL formation and clarifies the significant role of ambient pressure in the resulting HSFLs period.

Argon pressure dependent optoelectronic characteristics of amorphous tin oxide thin films obtained by non-reactive RF sputtering process

In this work, amorphous tin oxide thin films were deposited by non-reactive radio frequency magnetron sputtering. A ceramic $${\text{SnO}}_2$$ target was used, while different working pressures were employed. The target to substrate distance was fixed to 17 cm, and the substrate was not intentionally heated. The properties of $${\text{SnO}}_2$$ (thickness, refractive index dispersion, optical band gap, resistivity, free carriers concentration, carriers mobility, carriers majority type and their scattering time) have been inferred from spectroscopic ellipsometry, conventional UV-Vis spectroscopy and specific Hall electrical measurements. Thickness and refractive index are slightly dependent on the deposition conditions, while the optical band gap, free carriers concentration and their mobilities are changing from sample to sample. The evolution of the optical band gap and carriers concentration is correlated to the active defects concentration. Amorphous $${\text{SnO}}_2$$ films grown at 0.4 Pa have the lowest resistivity of $$0.86\,\Omega \, \hbox {cm}$$ , a carrier concentration of $$1.05 \times 10^{18}\,\hbox {cm}^{-3}$$ , and a Hall mobility of $$6.8\,\hbox {cm}^{2}$$ / Vs. The average optical transmittance in visible spectrum is 76%.

Susceptibility of Staphylococcus epidermidis to Argon Cold Plasma Jet by Oxygen Admixture

Cold atmospheric pressure sterilization is one of the nominated and efficient techniques to prevent the spread of diseases. Reactive species such as O and OH and other radicals play a major role in the mechanism of plasma sterilization. Therefore, in this work, oxygen was mixed with different parentage from (0.2 to 1.2%) to argon to enhance the generation of the reactive species and increase the argon atmospheric pressure plasma sterilization efficacy. The emission spectra from the jet increase the radicle line intensities by increasing the percentage admixture of O2 with the argon gas to reach a maximum power at 0.8; then, it gradually decreases with a higher O2 percentage. The OH band intensity decreases with increasing the admixture of O2. The jet with different O2 percentages was tested against Gram-positive S. epidermidis, which is the causal agent of nosocomial infections. The maximum reduction in colony-forming units (CFU) was observed at 0.2% O2. No bacterial growth was observed at the later concentration applied for 8 min and the same case was detected at 0.4% O2 applied to 16 min.

Studying the in vitro corrosion response of nanostructured TaN coatings in Hank's physiological solution

AbstractThe goal of this research is to determine the effect of N2 pressure to argon pressure on the microstructural analysis and corrosion behavior of nanostructured TaN deposited coatings using a reactive DC‐magnetron sputtering (RDCMS) technique. The samples coated microstructure was studied by the X‐ray diffraction (XRD) and scanning electron microscope (SEM), and elemental distribution was studied using energy‐dispersive X‐ray spectroscopy (EDS). To investigate the corrosion behavior of nanostructured TaN coatings, the potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests were performed in Hank's physiological solution. The results of different tests revealed that the coating with a content of 17.6% PN2/PAr consisted of hexagonal and orthorhombic TaN phases and had denser microstructure and free pores. This coating showed superior corrosion behavior in comparison to the other ones. Also, the corrosion resistance of this coating raised by increasing the time of immersion from 48 to 168 h.

GROWTH RATE OF DIAMOND-LIKE COATINGS SYNTHESIZED IN RF DISCHARGE AT VARIOUS RATIOS OF THE CONCENTRATIONS OF Ar AND C6H6

Diamond-like coatings (DLC) synthesized by plasma-chemical deposition from a vapor mixture of C6H6 and Ar have been investigated. The growth rate of the coating was measured, which showed a nonlinear dependence on the partial pressure of Ar. The mathematical model of the deposition has been developed, which qualitatively and quantitatively describes the dependence of the ion flux density and deposition rate on the partial pressure of argon.

Numerical/experimental investigation of bulge tests on a localized laser heat-treated magnesium alloy AZ31 sheet

Lightweight alloys can be considered among the most promising materials thanks to their capability to reduce the environmental impact, without affecting mechanical properties. In addition, when very complex shapes are required, a viable strategy could be represented by the adoption of non-conventional forming processes applied to tailored blanks that allow to obtain local variation of the material properties. In fact, referred to the Mg alloys, both grain size and temperature strongly influence the deformation behavior, as well as the mechanical properties. In this work, the effects of a selective Laser Heat Treatment (LHT) on a Mg AZ31B-H24 alloy sheet were investigated both numerically and experimentally. Experimental tests were performed, using a Diode laser source and keeping a square spot stationary in the center of the sample. The microstructure evolution was evaluated by means of light microscopy. Subsequently, the heat-treated samples were subjected to bulge tests under superplastic conditions (450°C) and using pressurized argon gas. The experimental microstructure distributions obtained were used for the numerical bulge tests analyses performed in the same conditions of the experimental trials. Experimental LHT results showed the capability to locally modify the microstructure when suitable temperatures and interaction times are selected. Regarding the bulge tests, the obtained results showed the possibility to effectively affect the thickness distribution of the final shapes.

Tunable hydrophilicity in a surface nano-textured stainless steel thin film deposited by DC magnetron sputtering

In this article a series of Stainless steel thin films are fabricated by DC power magnetron sputtering of a SUS316 stainless steel target at various argon working pressure. The sample film compositions retain that of an austenitic stainless steel, while XRD spectra reveal that all films possess a single phase, body-centered cubic ferrite crystal structure. At working pressure 6 mTorr and above, the film exhibits a textured surface morphology made up of nano-sized pyramids. Cross-sectional images show that increasing argon pressure cause a microstructural evolution from dense, fibrous grain to coarse tapered grains. This observation agrees with the prediction by Thornton's structural zone model and causes a drastic reduction in static water contact angle (WCA) from ~65° to ~17°. With further increase of argon pressure, a minimum WCA of 11° at 8 mTorr can be achieved. In addition, our textured film deposited at 12 mTorr exhibits both excellent hydrophilicity and low contact angle hysteresis (CAH) at the same time. In summary, this work reports a convenient way of depositing a stainless steel-like hydrophilic coating, in which the wetting properties are tunable via working pressure control.

Comparison of atmospheric pressure argon producing O(1S) and helium plasma jet on methylene blue degradation

A solution of methylene blue dye was degraded under an atmospheric pressure plasma jet operating in a linear field configuration with pure argon or pure helium as working gases. Optical emission spectroscopy was carried out to understand the reactive species present with and without dye treatment. Both plasma jets contain reactive species such as OH, N2, and atomic oxygen (O). However, atomic oxygen takes a greatly different form depending on the working gas. In the argon plasma jet, we observe that most of the atomic oxygen produced is the O(1S)–O(1D) transition that also leads to the green colored plasma plume. On the other hand, the helium plasma jet produces the well known triplet states of oxygen at 777 and 844 nm. The absorption spectra confirmed the faster and more energy efficient degradation of the methylene blue dye when treated by the argon plasma jet. Argon plasma with enhanced atomic oxygen content can be utilized as a cheaper and efficient method for waste water treatment.

Micro-arc method for the synthesis of silicon nanostructures

This paper presents the results of plasma synthesis of silicon nanostructures in an air-argon medium. The synthesis of silicon nanostructures was carried out in a vacuum chamber at a gas mixture pressure of 500 Torr, with partial pressures of argon and air in the ratio of 4:1. Molybdenum and silicon embedded in a copper tube were used as electrodes. Current and voltage were maintained in the range of 8-25 A and 30-50 V, corresponding. As a result of experiments, silicon nanostructures were deposited on the surface of the electrodes. Nanostructures were studied by optical and electron microscopes. Forms of silicon nanostructures were mainly in the form of nanotubes. Their diameters range from 200 nm to 500 nm, and their length reaches 1 mm. On the surface of these nanotubes, nanovilli with a diameter of about 5 nm and a length of 100 nm are observed.

Temperature dependence of tellurium fugacity for the kotulskite (PdTe)–merenskyite (PdTe2) equilibrium determined by the method of a solid-state galvanic cell

The thermodynamic properties of the kotulskite (PdTe)/merenskyite (PdTe2) equilibrium in the Ag-Pd-Te system were determined for the first time by the electromotive force (EMF) method. The thermodynamic properties were calculated from the temperature dependence of the EMF in a completely solid-state electrochemical cell with a common gas space: $$\left( - \right){\text{C}}_{{({\text{graphite}})}} \left| {{\text{Ag}}} \right|{\text{RbAg}}_{{4}} {\text{I}}_{{5}} \left| {{\text{Ag}}_{{2}} {\text{Te}},{\text{PdTe}},{\text{PdTe}}_{{2}} } \right|{\text{C}}_{{({\text{graphite}})}} \left( + \right),$$ following a virtual chemical reaction: $${\text{2Ag}} + {\text{PdTe}}_{{2}} \leftrightarrow {\text{Ag}}_{{2}} {\text{Te}} + {\text{PdTe}}.$$ The measurements were carried out in the temperature range of 371–488 K at the atmospheric pressure of pure argon. As a result, the thermodynamic properties for the reaction PdTe + Te = PdTe2 at a pressure of 1 bar (105 Pa) were determined as: ΔrGo/J·mol−1 = − 27,639; ΔrS/J mol−1 K−1 = − 21.98; ΔrHo/J·mol−1 = − 34,176. Fugacity of gaseous tellurium (Te2) over the PdTe + 1/2Te2 ↔ PdTe2 equilibrium was also calculated: log f Te2 = (9.205 ± 0.072) − (11.44 ± 0.03)·(1000/T), (371.7 < T/K < 493.6).

Combined Toxicity of Gas Plasma Treatment and Nanoparticles Exposure in Melanoma Cells In Vitro.

Despite continuous advances in therapy, cancer remains a deadly disease. Over the past years, gas plasma technology emerged as a novel tool to target tumors, especially skin. Another promising anticancer approach are nanoparticles. Since combination therapies are becoming increasingly relevant in oncology, both gas plasma treatment and nanoparticle exposure were combined. A series of nanoparticles were investigated in parallel, namely, silica, silver, iron oxide, cerium oxide, titanium oxide, and iron-doped titanium oxide. For gas plasma treatment, the atmospheric pressure argon plasma jet kINPen was utilized. Using three melanoma cell lines, the two murine non-metastatic B16F0 and metastatic B16F10 cells and the human metastatic B-Raf mutant cell line SK-MEL-28, the combined cytotoxicity of both approaches was identified. The combined cytotoxicity of gas plasma treatment and nanoparticle exposure was consistent across all three cell lines for silica, silver, iron oxide, and cerium oxide. In contrast, for titanium oxide and iron-doped titanium oxide, significantly combined cytotoxicity was only observed in B16F10 cells.

Plasma medicine and wound management: Evaluation of the antibacterial efficacy of a medically certified cold atmospheric argon plasma jet

Objectives: A major problem for wound healing is contamination with bacteria, often resulting in biofilm formation and wound infection, which, in turn, needs immediate intervention such as surgical debridement and through irrigation. A topical treatment with cold atmospheric pressure plasma (CAP) for wound disinfection may present an alternative and less painful approach.Methods: This study investigated the antibacterial effects of a cold atmospheric pressure argon plasma jet (kINPen® MED) as a CAP source, using the three-dimensional Staphylococcus aureus immunocompetent biofilm system hpBIOM in addition to a standard planktonic test. Furthermore, skin cell compatibility was evaluated using a keratinocyte (HaCat) model.Results: CAP treatment (0–240 s) followed by incubation (15, 120 min) within the CAP-treated media showed slight bactericidal efficacy under planktonic conditions but no effect on biofilms. However, indirect CAP treatment of keratinocytes performed under the same conditions resulted in a significant decrease in metabolic activity. Short CAP treatment and exposure time (30 s; 15 min) induced a slight increase in the metabolic activity; however, longer treatments and/or exposure times led to pronounced reductions up to 100%. These effects could partially be reversed by addition of catalase, indicating a dominant role of CAP-generated hydrogen peroxide.Conclusions: These results indicate that plasma treatment does not lead to the desired disinfection or significant reduction in the bacterial burden of Staphylococcus aureus in a wet milieu or in biofilms. Thus, treatment with CAP could not be recommended as a single anti-bacterial therapy for wounds but could be used to support standard treatments.

Investigation of Micro-Hole Quality in Drilled CFRP Laminates Through CO2 Laser

Carbon fiber-reinforced polymer (CFRP) composites are increasingly replacing the metals and other composites in automotive and aerospace industries due to their excellent properties. These application components have required micro-holes on CFRP for joining different components. In the present work, micro-holes are fabricated on CFRP using CO2 laser for achieving the high-quality-dimensional precision and accurate hole. The input parameters such as laser power, cutting velocity and argon pressure were varied. The responses such as heat-affected zone, kerf width, kerf angle and aspect ratio were measured using video measurement system. Besides, analyses of variances, regression modeling and microstructural analysis were presented. Results showed that the cutting velocity is most influential factor that affecting the heat-affected zone and kerf width and followed by power.

Hydrophilic modification of poly(ether)sulfone membrane by atmospheric pressure argon jet plasma: pH dependence of ultrafiltration performance and cleaning efficiency

AbstractThe studies focused on plasma surface modification of poly(ether)sulfone (PES) ultrafiltration (UF) membrane show its potent effect on antifouling propensity but there are few data on the pH dependence of superior surface character achieved. This study examined UF performance and cleaning efficiency of atmospheric pressure argon jet plasma (AP‐AJP) modified PES membrane in whey concentration at various operation pH compared to the plain membrane (UP020). The highest initial permeate flux for the UP020 at pH of 6.4 increased the cake layer formation and the irreversible fouling resistance. The plasma action led to greater intrinsic membrane resistance causing low water permeability compared with the UP020. This effect reduced cake layer resistance despite the fact that the irreversible fouling was more severe at all operation pH. The increase in pH caused to decrease in contribution of fouling to total resistance. For the UP020, the shift in operation pH from acidic point to neutral reduced the recovery in hydraulic permeability after chemical cleaning. The plasma action induced greater cleaning efficiency, which is the most obvious at pH of 6.4. The overall results showed that the AP‐AJP may have the potential to maintain profit‐making UF process in whey concentration at broad range of pH.Practical ApplicationsIn the industrial point of view, cost friendly, and sustainable operation in valorization of whey can be achieved by fouling resistant membranes. Atmospheric pressure argon jet plasma provides extremely hydrophilic character to poly(ether)sulfone membrane. The plasma action decreases fouling resistance and especially cake layer formation. This effect broadens the operating pH of whey without any pre‐adjustment and results in easy to clean membrane surfaces.

Enhancement of hydrogen peroxide production from an atmospheric pressure argon plasma jet and implications to the antibacterial activity of plasma activated water

We explore how to configure an argon atmospheric-pressure plasma jet for enhancing its production of hydrogen peroxide (H2O2) in deionised water (DIW). The plasma jet consists of a quartz tube of 1.5 mm inner diameter and 3 mm outer diameter, with an upstream internal needle electrode (within the tube) and a downstream external cylindrical electrode (surrounding the tube). The plasma is operated by purging argon through the glass tube and applying a sinusoidal AC voltage to the internal needle electrode at 10 kV (peak–peak) with a frequency of 23.5 kHz. We study how the following operational parameters influence the production rate of H2O2 in water: tube length, inter-electrode separation distance, distance of the ground electrode from the tube orifice, distance between tube orifice and the DIW, argon flow rate and treatment time. By examining the electrical and optical properties of the plasma jet, we determine how the above operational parameters influence the major plasma processes that promote H2O2 generation through electron-induced dissociation reactions and UV photolysis within the plasma core and in the plasma afterglow; but with a caveat being that these processes are highly dependent on the water vapour content from the argon gas supply and ambient environment. We then demonstrate how the synergistic action between H2O2 and other plasma generated molecules at a plasma induced low pH in the DIW is highly effective at decontaminating common wound pathogens Gram-positive Staphylococus aureus and Gram-negative Pseudomonas aeruginosa. The information presented in this study is relevant in the design of medical plasma devices where production of plasma reactive species such as H2O2 at physiologically useful concentrations is needed to help realise the full clinical potential of the technology.

Plasma-assisted ITO sol coating for optimizing the optoelectronic properties of ITO glass

The argon atmospheric pressure plasma treatment is combined with the conventional sol-gel dip-coating process for fabricating ITO thin films to improve the electrical property of the ITO glass. The increase of the surface free energy of the ITO layer by plasma treatment improves the adhesion of the pre-annealed ITO layer, thereby increasing the thickness of the ITO film without significantly losing the light transmittance. While increasing the plasma treatment time up to 240 s, both the thickness and surface free energy of the ITO layer are increased, and the sheet resistance of the thin film is rapidly decreased. The ITO layer plasma-treated for 240 s with the thickness of 360 nm exhibits the lowest sheet resistance of 126.5 Ω/sq and the highest surface free energy of 79.45 mJ/m2. However, the increase of the plasma treatment time over 240 s do not affect the increase of film thickness, but the increase of sheet resistance. X-ray photoelectron spectroscopy depth profile reveals the decrease of the level of the oxygen vacancies with increasing plasma treatment time over 240 s. It results from the diffusion of oxygen from the surface into the bulk and explains the increase of the sheet resistance.