Low-pressure Plasma Research Articles

Characteristics of low-pressure-plasma-processed NiRu-MOFs/nickel foam for Hydrogen evolution reaction

NiRu bimetallic metal–organic frameworks (NiRu-MOFs) are grown by a simple hydrothermal method on nickel foam (NF) as an the electrocatalyst for the hydrogen evolution reaction. Low-pressure plasmas of pure Ar, 95%Ar + 5%H2, and 95% Ar + 5%O2 are used for the post-treatment of the NiRu-MOFs. NiRu-MOFs-AO with post-plasma treatment with 95%Ar + 5%O2 show the lowest overpotential of 123.3 mV at a current density of 10 mA cm−2 and a Tafel slope of 72.0 mV dec−1 in 1 M KOH electrolyte. Electrochemical impedance spectroscopy results indicate that post-plasma treatment can further reduce the charge transfer resistance. Moreover, the electric double-layer capacitance (Cdl) is calculated based on the cyclic voltammetry results, and the electrocatalyst subjected to 95%Ar + 5%O2 post-plasma treatment shows a 2Cdl value of 3.69 mF/cm2, suggesting a larger electrochemically active surface area after oxygen-containing-plasma treatment.

Surface modification of natural leather using RF plasma discharge

Radiofrequency (RF) low-pressure plasma has been applied to improve natural leather's wettability and water absorption. The plasma was generated using RF discharge of the Ar-He gas mixture at 60 and 120 W power using different treatment times (30, 60, 120, 180, and 300s). Before and after treatment, the contact angle, surface free energy, and water absorption ratio were measured. It was observed that a 300s plasma treatment time and plasma power 60 and 120 W is enough to decrease the water contact angle from 83.56 for an untreated sample to 0°. The surface-free energy and the water absorption ratio increase with an increase in the treatment time and plasma power. The findings demonstrate that plasma treatment increases the wettability of the surface of leather samples. In addition, the change in leather properties was analyzed by scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry, Fourier transform infrared spectroscopy.

Enhanced high temperature ablation resistance of dense ZrB2–Al2TiO5 composite coating by very low-pressure plasma spraying

ZrB2-based composite coatings with addition of Al2TiO5 were prepared via very low-pressure plasma spraying using mechanically mixed powder of ZrB2 and Al2O3-40 wt%TiO2 (AT40). The ablation behavior of the composite coating was investigated using a high temperature plasma jet at a temperature of ∼2500oC. Results demonstrate the addition of AT40 improved the ablation resistance of the ZrB2 coatings at high temperatures. The coating with 17 vol%AT40 addition exhibited the lowest ablation rate, approximately 1.33 μm/s, which is only one-third of that of the pure ZrB2 coating. The added AT40 filled the pores between ZrO2 crystals during ablation, reducing oxygen penetration and lowering the ablation rate. However, excessive addition of AT40 hindered gaseous B2O3 release and thus led to large pore formation, impairing the protective effect. The ZrB2-AT40 coating is a promising candidate for high-temperature applications.

Evaluation of Low-Pressure Cold Plasma Effect on Phytonutrients, Drying and Microstructural Characteristics, and Changes in Microbial Load of Fresh and Hot-Air-Dried ‘Heidi’ Mango

AbstractAlternative pre-treatment strategies before drying offer the prospect to minimize drying time, replacing the use of chemicals, and preserving quality of dried fresh products. This study explored the application of low-pressure atmospheric cold plasma (CP) for 5- and 10 min (CP5 and CP10) as pre-treatments prior to processing and hot air drying (60 °C) of ‘Heidi’ mango, while non-treated samples served as control. Changes in tissue microstructure and physicochemical properties, bioactive compounds, and microbial load were evaluated, and seven thin layer drying models were applied. Scanned electron microscope images showed that CP pre-treatments altered the tissue microstructure of dried mango slices compared to control. ‘Heidi’ mango slices with the initial moisture content of 80 ± 0.2% on a wet basis was reduced by 81% and 76% in dried CP5 and CP10 samples, respectively. Drying time was reduced by 20% for CP pre-treated samples in comparison to control samples, and the drying behavior of ‘Heidi’ mango slices was best described by the Logarithmic model (R2, 0.9999 and RMSE, 0.0122). Colour attributes were best retained by sodium metabisulphite (SMB) pre-treated samples, followed by CP5 pre-treated, which performed better than CP10 and control (p ≤ 0.05). Highest total flavanols (15.0 ± 0.4 mg CE 100 g−1) and higher total phenolics (1528.2 ± 23.6 mg GA 100 g−1) were found in CP5 pre-treated samples compared to the control (p ≤ 0.05). Lowest antioxidant activities were found in CP10 pre-treated samples compared to the control (p ≤ 0.05). CP-pretreatment and drying resulted in ≥ 2 Log reduction in microbial load on mango slices. These results demonstrate to the role players in mango value addition chain, the potential of low-pressure CP pretreatment in enhancing/maintaining the bioactive compounds, reducing drying time and microbial load.

Trapping and actively transporting single particles of arbitrary properties in low-pressure rf plasmas with and without a magnetic field

We report the experimental realization of optical trapping and controlled manipulations of single particles of arbitrary properties, e.g., nano- to micrometer in size, transparent spheres to strongly light absorbing nonspherical particles, in low-pressure rf plasmas. First, we show optical trapping and transport of single particles in an unmagnetized rf plasma. Then, we show similar observations in a weakly magnetized rf plasma. This is the first demonstration of actively transporting (pushing and pulling) light-absorbing, nonspherical single particles in plasmas. The result suggests that optically trapped, actively controlled, single plasma dust particles (not limited to those externally sampled spheres) could be an in situ micro-probe for dusty plasma and magnetized dusty plasma diagnostics.

Sporadic regional re-emergent cholera: a 19th century problem in the 21st century.

Cholera, caused by Vibrio cholerae, is a severe diarrheal disease that necessitates prompt diagnosis and effective treatment. This review comprehensively examines various diagnostic methods, from traditional microscopy and culture to advanced nucleic acid testing like polymerase spiral reaction and rapid diagnostic tests, highlighting their advantages and limitations. Additionally, we explore evolving treatment strategies, with a focus on the challenges posed by antibiotic resistance due to the activation of the SOS response pathway in V. cholerae. We discuss promising alternative treatments, including low-pressure plasma sterilization, bacteriophages, and selenium nanoparticles. The paper emphasizes the importance of multidisciplinary approaches combining novel diagnostics and treatments in managing and preventing cholera, a persistent global health challenge. The current re-emergent 7th pandemic of cholera commenced in 1961 and shows no signs of abeyance. This is probably due to the changing genetic profile of V. cholerae concerning bacterial pathogenic toxins. Given this factor, we argue that the disease is effectively re-emergent, particularly in Eastern Mediterranean countries such as Lebanon, Syria, etc. This review considers the history of the current pandemic, the genetics of the causal agent, and current treatment regimes. In conclusion, cholera remains a significant global health challenge that requires prompt diagnosis and effective treatment. Understanding the history, genetics, and current treatments is crucial in effectively addressing this persistent and re-emergent disease.

Nanoparticles synthesis in microwave plasmas: peculiarities and comprehensive insight

Low-pressure plasma processes are routinely used to grow, functionalize or etch materials, and thanks to some of its unique attributes, plasma has become a major player for some applications such as microelectronics. Plasma processes are however still at a research level when it comes to the synthesis and functionalization of nanoparticles. Yet plasma processes can offer a particularly suitable solution to produce nanoparticles having very peculiar features since they enable to: (i) reach particle with a variety of chemical compositions, (ii) tune the size and density of the particle cloud by acting on the transport dynamics of neutral or charged particles through a convenient setting of the thermal gradients or the electric field topology in the reactor chamber and (iii) manipulate nanoparticles and deposit them directly onto a substrate, or codeposit them along with a continuous film to produce nanocomposites or (iv) use them as a template to produce 1D materials. In this article, we present an experimental investigation of nanoparticles synthesis and dynamics in low-pressure microwave plasmas by combining time-resolved and in-situ laser extinction and scattering diagnostics, QCL absorption spectroscopy, mass spectrometry, optical emission spectroscopy and SEM along with a particle transport model. We showed for the first time the thermophoresis-driven dynamic of particle cloud in electrodless microwave plasmas. We showed that this effect is linked to particular fluctuations in the plasma composition and results in the formation of a void region in the bulk of the plasma surrounded by a particle cloud in the peripherical post-discharge. We also reveals and analyze the kinetics of precursor dissociation and molecular growth that result in the observed nanoparticle nucleation.

Real-time in situ monitoring of dust particle growth in a low-pressure nanodusty plasma based on laser-induced photodetachment

Particulate matter air pollution in the form of ultrafine dust is a growing global concern. In this Letter, we will use a nanodusty Ar/HMDSO plasma as a model system for a heavily contaminated gas and we present the development of a technique for real-time in situ measurements of the dust particle size. The method is based on laser-induced photodetachment of bound electrons from the surface of dust particles. These photo-released electrons are measured as an increase in the free electron density of the plasma using microwave cavity resonance spectroscopy. We show that instead of reconstructing the entire resonance profile, the temporal response of a single microwave frequency was enough to perform the measurements. More specifically, the decay timescale of the cavity response can be interpreted as the re-charging timescale of the dust particles. Then, using a stochastic model, this timescale can be modeled, which eventually retrieves the dust particle size. We found good agreement between the predicted dust particle size and the average dust particle size obtained from ex situ scanning electron microscopy measurements. This method allows for the real-time monitoring of the dust particle size and a controlled production of nanometer-scale dust particles, which gives opportunities both for fundamental dusty plasma physics and models, as well as for applications in monitoring ultrafine dust air pollution.

Modeling and experimental comparison of pulsed-DC driven low-pressure plasma discharge in a metal tube

High-voltage pulsed-DC can be used to deposit films on the inner surfaces of tubes and pipes. However, the characteristics of the plasma discharge in the tubes and mechanisms of film deposition are not well understood. In this study, a discharge is formed in a metal tube inserted with a coaxial anode by microsecond (μs) pulsed power to explore the influence of the pulse parameters on the plasma characteristics, including the temporal and spatial evolution near the tube walls experimentally and by simulation. The discharge waveform is monitored by a voltage-current probe to analyze the impact of the electrical characteristics on the plasma. The plasma properties are diagnosed by a Langmuir probe and numerically calculated by the fluid model. The source voltage and current jointly influence the plasma density and electron temperature, and secondary electron emission by energetic ion bombardment affects not only the distribution of electron density measured by the probe, but also the temporal distribution during the pulse-on and pulse-off time. The electron temperature varies conversely with the density from the plasma zone to the cathode suggesting the typical glow discharge in the pulsed-DC tube. Secondary electron emission is created at a higher discharge frequency, and a sustained plasma between pulse cycles appears to be produced at a higher frequency. The results impart information about the pulsed-DC driven plasma discharge at low pressure as well as the role energetic ions play on the cathode and elucidate the mechanisms of plasma deposition on the interior tube wall.

Adhesion characteristics of plasma-treated flax fabrics and elastoplastic properties of their biocomposites

ABSTRACT Recently, there has been growing interest in replacing synthetic fibers with natural fibers in polymer composites due to several advantages of natural fibers over synthetic ones, such as low cost, low density, sustainability, and biodegradability. However, a significant drawback of natural fibers is their high capillary water absorption, worsened by waxes and atmospheric pollutants, resulting in weak adhesion with polymer matrices. Surface treatments, including plasma treatments, have shown promise in improving this interfacial bonding. In this study, woven flax fabrics (FFs) were treated with two plasma techniques: atmospheric pressure plasma torch (APPT) and low-pressure plasma (LPP). The plasma effects on the fibers’ surface, wettability, and surface energy were assessed through X-ray photoelectron spectroscopy and contact angle measurements, respectively. Subsequently, the treated fibers were utilized to fabricate biopolymer composites using polyamide1 (PA11), green low-density polyethylene (GPE), and polybutylene succinate (PBS) as matrices. The adhesion strength and elastoplastic behavior of the biocomposites were compared by peel-off test and plasticity index measurement. The results indicated that both treatments successfully improved the FFs’ surface characteristics, resulting in increased wettability and surface energy. The higher peeling strengths and lower plasticity indices confirmed the improvement in the adhesion of treated FFs with the biopolymer matrices.

Nanoscale dielectric properties of TiO2 in SiO2 nanocomposite deposited by hybrid PECVD method

In this paper, nanocomposites (TiO2 in SiO2) are produced by an advanced hybrid aerosol-PECVD method based on direct liquid injection of a non-commercial colloidal solution in an O2 / hexamethyldisiloxane (HMDSO) low-pressure plasma. Dielectric properties are investigated at nanoscale using techniques derived from Atomic Force Microcopy in terms of relative dielectric permittivity, charge injection and transport. Results show that a concentration in TiO2 up to 14% by volume makes it possible to increase the relative dielectric permittivity up to 4.8 while maintaining the insulating properties of the silica matrix. For a TiO2 concentration in the range 15%–37% by volume, the relative dielectric permittivity increases (up to 11 for 37% TiO2 by volume) and only few agglomerated nanoparticles lowering the insulating properties are observed. For TiO2 concentration above 40% by volume, the relative dielectric permittivity still increases but the quantity of agglomerated nanoparticles is very high, which greatly increases the charge transport dynamic and degrades the insulating properties. Finally, 37% of TiO2 by volume in the SiO2 matrix appears to be the best compromise, between high dielectric permittivity and low leakage current for the MIM applications aimed.

Handling Nanoparticle Content in Nanocomposite Thin Films Deposited by Misty Plasma Processes through Controlled Flash Boiling Atomization.

Misty plasma processes based on colloidal solutions sprayed into low-pressure plasmas have recently shown great potential for multifunctional thin film deposition. In such processes, nanoparticle accumulation in ring-shaped structures remains the main obstacle to the synthesis of high-quality coatings containing abundant, small-scale, and evenly dispersed nanoparticles. These local buildups appear after a colloidal droplet evaporates from a substrate. Accordingly, controlling the droplets' size in the spray is of key importance to ensure a uniform nanoparticle content in the plasma-deposited nanocomposite film. In this work, it is shown that the use of more volatile solvents produces finer droplets on the substrate, thereby improving nanoparticle dispersion in the matrix. A one-dimensional evaporation model is further developed and used to show that, contrary to what one might expect, this result cannot be attributed to faster evaporation during droplet transport in the low-pressure plasma. Instead, a so-called "flash" boiling atomization mechanism is discussed to support the experimental findings.

Adhesive bonding of glass-fibre thermoplastic composite: process optimisation and sustainability analysis using LCA methodology

In recent years, great attention has been paid to the challenge of integrating more sustainable circular approaches to manufacturing, which involve optimising the entire product cycle, from design to fabrication, assembly and eventual reuse/recycling. In this context, the use of thermoplastic composite materials in combination with adhesive bonding is attracting increasing attention to achieve this dual objective. Therefore, the proposed research focuses on the experimental and statistical optimisation of an adhesive bonding process for glass-fibre–reinforced composite substrates with polypropylene matrix, with the aim of comparing its performance with that of joints made using more conventional configurations, i.e. utilising thermosetting substrates. A low-pressure plasma pre-bonding surface treatment is adopted, and its effectiveness in enhancing joint performance compared to more conventional preparations for plastics is discussed. By varying plasma parameters according to the design of experiments statistical approach, the joint response is studied in terms of tensile shear strength and modelled in accordance with the response surface methodology to identify the optimum condition of process parameters within the established system boundaries. The study found that with optimised pre-treatment, adhesive joints of glass-fibre–reinforced composites with thermoplastic matrices (first scenario) can achieve tensile shear strength (TSS) comparable to that of thermoset composites (second scenario), making them viable options in various applications. Two alternative scenarios—namely, joints with thermoplastic composite or thermoset composite substrates—are then analysed by the life cycle assessment methodology and compared according to their relative environmental impact, demonstrating that glass-fibre thermoplastic composite joints are competitive alternatives to thermoset joints in terms of mechanical static performance achieved, but significantly preferable with regard to environmental sustainability.

A hybrid plasma model for Cr thin film deposition by deep oscillation magnetron sputtering

A time-dependent hybrid plasma model composed of a zero-dimensional global model and a two-dimensional fluid model is proposed for simulation of plasma chemistry and transportation of plasma during Cr thin film deposition by deep oscillation magnetron sputtering (DOMS). The global model deals with plasma reactions in the ionization region near the target with discharge voltage and current waveforms as inputs. The temporal plasma characteristics calculated by the global model are utilized as a boundary condition for the two-dimensional fluid model to simulate high-density plasma transportation in the diffusion region through the entire macropulse period. The full momentum equation taking inertia force into consideration is applied for ion momentum conservation in the fluid model instead of using the drift-diffusion approximation, which ensures validity of the simulation for low-pressure plasmas. The deposition flux as well as the kinetic and potential energy fluxes transferred to the growing films are calculated by the hybrid model. Microstructure evolution of the DOMS deposited Cr thin films from zone I to zone T is attributed to the growing kinetic and potential energies as the charging voltage increases according to the structure zone diagram. The deposition rate loss in DOMS is explained by the back attraction effect, sputtering yield effect, and densification of the films.

Effect of Heat Treatment on Microstructure of Silicon-containing CrFeCoNi High Entropy Alloys Produced by Low-Pressure Plasma Spraying

Effect of Heat Treatment on Microstructure of Silicon-containing CrFeCoNi High Entropy Alloys Produced by Low-Pressure Plasma Spraying

Tailoring surface energy of cellulose nanocrystals (CNCs) via low-pressure plasma polymerization to control the interfacial properties in polycaprolactone (PCL)/CNC nanocomposite

Tailoring surface energy of cellulose nanocrystals (CNCs) via low-pressure plasma polymerization to control the interfacial properties in polycaprolactone (PCL)/CNC nanocomposite

Kinetic simulations of low-pressure inductively coupled plasma: an implicit electromagnetic PIC/MCC model with the ADI-FDTD method

Low-pressure inductively coupled plasma (ICP) is promising for space electric propulsion. For the first time, an implicit electromagnetic particle-in-cell Monte Carlo collision model based on the alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method is developed to investigate low-pressure xenon plasma characteristics of a miniature ICP source. The induced simulated electric field is well consistent with that calculated by the finite element method, indicating that this method can provide an accurate estimation of the electromagnetic field. The simulation time step used in the ADI-FDTD method is no longer restricted by the Courant–Friedrichs–Lewy constraints. Compared with the FDTD method, the ADI-FDTD method increases the size of the time step and significantly improves computational efficiency. The method is validated by comparing the simulated and measured electron density and plasma potential profile and reasonable agreement is reached. Therefore, the model is used to investigate the temporal and spatial distribution of plasma properties and the influence of the current amplitude of radio frequency (RF) coil, applied frequency of RF coil and neutral gas pressure on the plasma dynamics in the ionization chamber of a miniature gridded RF ion thruster. To explain the influence of the operating parameters, a concept called ‘the energy relaxation characteristics of electrons in response to the change of electric field’ is proposed and verified. The simulations also find that the oscillation frequency of plasma properties is twice the applied frequency of RF coil. The oscillation characteristics reveal the dynamic energy balance in the ICP. The experiment on the gridded RF ion thruster BHRIT-4 confirms the oscillation by measuring the plasma sheath potential.

Measurement of the main neutral species densities and temperatures in iodine plasmas using optical absorption techniques

Iodine is a promising propellant for future plasma thrusters used in space propulsion. It is therefore important to understand the basic physics and chemistry of low-pressure iodine plasmas. In the present work, optical absorption methods are used to measure the densities of iodine molecules, I2, and iodine atoms, I, the translational temperature of the atoms and the dissociation fraction. The plasma is generated in a long quartz tube by a capacitively coupled RF discharge, and the pressure is varied between a few Pa and a few tens of Pa. The translational temperature of the atom vapour increases both with RF power and with pressure and reaches 1000 K at 50 W and 25 Pa. The molecules appear to be efficiently dissociated, with a dissociation fraction found above 65%, on average along the line-of-sight, at 120 W and 5 Pa. The population of the upper, 2P1/2∘ , fine-structure level of the atomic ground term is found to be negligible, which confirms the existence of a high quenching rate, due to collisions with molecules and/or atoms. These measurements can be helpful for chemistry models of iodine plasmas.

Effect of low-pressure plasma treatment on the thermal behaviour of organo-modified montmorillonite nanoclay

The thermal behaviour of nanoclay can be considered an important factor in obtaining high-performance polymer nanocomposite. Thus, the current study aims to investigate the effect of plasma treatment on the thermal stability of two organically modified nanoclays, Cloisite 30B (C30B) and Nanomer I.34TCN (I.34TCN), compared with pristine NaMMT.The nanoclays were studied and characterised using Thermogravimetric Analysis (TGA). TGA was used to measure the weight loss of the plasma-treated and untreated nanoclays (C30B, I.34TCN, and NaMMT nanoclays) over a 30-630 C temperature range.Based on TGA results, the decomposition of all plasma-treated nano clays (C30B, I.34TCN and pristine NaMMT) was shifted to a lower temperature than in the untreated ones at all those stages. Thus, plasma treatment was successfully used as a convenient method to alter the chemical structure and surface morphology of MMT nanoclays for better thermal behaviour and filling distribution.This hypothesis can be corroborated by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) for a better understanding of the structural and surface changes that occurred due to the plasma action, which can provide an interpretation of the changes in the thermal behaviour of nanoclays.The plasma treatment, therefore, can improve the thermal stabilisation of the nanocomposite powders for the LS fabricated parts and even for the surrounding powder for the recovery process. Plasma-treated nano clay, therefore, can be used to reinforce polymers with an expectation of increasing the thermal stability of the resultant composites. Thus, the plasma-treated composite can be fabricated for laser sintering applications in fields that require high thermal stability.The surface modification of nanoclay powders via plasma treatment can be used as a convenient method to alter the chemical structure and surface morphology for better thermal behaviour and filling distribution.

Improvement of the durability of thermal barrier coating by pre-oxidation

To suppress thermally grown oxides (TGO) in thermal barrier coatings (TBCs), the effect of pre-oxidation treatment was investigated for different thermal spray processes, such as high-velocity oxy-fuel spraying (HVOF) and low-pressure plasma spray (LPPS). A pre-oxidation treatment was applied before or after the top coat processing. When the pre-oxidation treatment was applied before top coat processing, TGO growth was suppressed during isothermal oxidation compared to when pre-oxidation was applied after the top coat process. Thermal spray processing did not affect the TGO growth behavior.