Pressure Plasma Torch Research Articles

Two-photon laser-induced fluorescence study of the CO B 1Σ+ (v' = 0) state in a 4850K plasma plume: Modified molecular constants, evidence of predissociation, and J'-dependent photoionization.

We report the two-photon absorption laser-induced fluorescence rotational spectrum of the CO B 1Σ+ ← X 1Σ+ Hopfield-Birge system (v' = 0, v″ = 0) Q-branch in an ∼4850K, atmospheric pressure plasma torch plume at thermal equilibrium in both the quenching-dominated (low laser intensity) and photoionization-dominated (high laser intensity) regimes. We provide a detailed analysis of the photophysics in these two regimes using a rate equation approach and propose modeling considerations for them as well. In the experimental spectra, distinct rotational transitions up to J″ = 83 are observed, allowing analysis over a very large range of rotational states. Evidence of predissociation is observed for J' ≥ 64 and is likely due to the interaction with the D'1Σ+ electronic state, which has been proposed in the literature but never observed in the v' = 0 state. The line positions of higher rotational states show disagreement with line positions calculated from molecular constants in the available literature, suggesting the need for modifications to the constants, which are reported here. A shift in the B 1Σ+ ← X 1Σ+ absorption spectrum toward higher two-photon energy as a result of the second-order Stark shift was observed in the photoionization-dominated spectrum, and the second-order Stark shift cross section was estimated to be 7 ± 3 × 10-18 cm2. The mean photoionization cross section of the excited upper state was inferred by comparing the line broadening of the two spectra and was estimated to be 11 ± 7 × 10-18 cm2. In addition, weak J'-dependent variations of the photoionization cross section were observed and are reported here.

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.

Measurements and Modeling of Air Plasma Radiation in the VUV

Measurements of high-temperature air emission spectra between 150 and 250 nm (VUV/UV) are presented. These measurements are calibrated in absolute intensity. The high-temperature air was produced using an atmospheric pressure plasma torch facility. The centerline temperature of the plasma jet is approximately 6700 K. A VUV emission spectroscopy system was adapted to the plasma torch facility to acquire spectra from 150 to 250 nm. Absolute intensity spectra were obtained in this wavelength range. They were compared with numerical predictions of the line-by-line spectroscopy code SPECAIR. The overall agreement between the SPECAIR predictions and measurements is good, particularly above 180 nm. Several modifications to the SPECAIR radiation code were carried out in order to improve agreement with experiments. These modifications significantly improved agreement though, at lower wavelengths, the data indicate that a source of emission remains unaccounted for by SPECAIR. Several possibilities for this missing source of emission are discussed, including photodissociation of the nitric oxide molecule.

Experimental and numerical studies of polyamide 11 and 12 surfaces modified by atmospheric pressure plasma treatment

Polyamide 11 and 12 (PA11 and PA12) have been applicable in various industries, including automotive, oil and gas, and sporting goods, over the past 70 years. Although they have good dyeability, their adhesion to other materials is limited due to relatively poor surface properties, which can be promoted by good wettability and high surface energy. This study aims to improve the surface properties of PA11 and PA12 by employing the advanced method of Atmospheric Pressure Plasma Torch (APPT) treatment. In this regard, the adhesion strengths of four commercially available adhesives were evaluated with the pull-off test on PAs plates before and after APPT treatment. The numerical simulation of this test was carried out in commercial finite element software using a cohesive zone model (CZM) to predict the fracture of adhesively bonded joints. Moreover, the modified PAs were analyzed using XPS, DSC, ATR-FTIR, optical profilometer and surface energy measurement. The results indicated that the surface properties, including wettability, polar surface energy and adhesion bonding, improved by employing the plasma treatment on PAs surfaces. The numerical simulation outcomes showed that the pull-off test might be a viable alternative to determine the CZM laws for fracture mode I.

Influence of surface treatment on strength and adhesion between flax natural fibres and a thermoplastic matrix

Composites of thermoplastics reinforced with natural fibres have been widely used in recent years. Natural fibres are considered as a greener substitute due to their advantages over conventional fibres such as low cost, low density, high availability, excellent mechanical properties, biodegradability and to be environmentally friendly. However, they present an important limitation, the weak interaction between fibres and matrix. Therefore, surface treatments on natural fibres are very common in order to increase wettability and surface energy and thus to promote good fibre-matrix adhesion. The objective of this work is to study adhesion between flax fibres, under different surface treatments, and LDPE matrix. Pull-out tests were carried out with flax fibres yarns treated with low pressure plasma, atmospheric pressure plasma torch,silane coating and different alkaline treatments as well as with untreated fibres.  Afterwards,  composites materials were manufactured using unidirectional flax fabric and LDPE in a hot plate press. Finally, mechanical properties of each composite material were evaluated by tensile tests using an universal test machine. In this way, a greater interaction between LDPE and flax fibres can be compared with the final properties.

Characterisation of a Cold Atmospheric Pressure Plasma Torch for Medical Applications: Demonstration of Device Safety

The safety and effectiveness of plasma devices are of crucial importance for medical applications. This study presents the novel design of an atmospheric plasma torch (SteriPlas) and its characterisation. The SteriPlas was characterised to ascertain whether it is safe for application on human skin. The emission spectrum discharged from the SteriPlas was shown to be the same as the emission from the MicroPlaSter Beta. The UV emitted from the SteriPlas was measured, and the effective irradiance was calculated. The effective irradiance enabled the determination of the maximum UV exposure limits, which were shown to be over two hours: significantly longer than the current two-minute treatment time. The use of an extraction system with a higher flow rate appears to reduce slightly the effective irradiance at the treatment area. The NOx and ozone emissions were recorded for both SteriPlas configurations. The NOx levels were shown to be orders of magnitude lower than their safety limits. The ozone emissions were shown to be safe 25 mm from the SteriPlas cage. A discussion of how safety standards differ from one regulatory body to another is given.

AP-PACVD plasma printer: investigating the influence of gas flow rates to printing resolution in parallel with CFD simulation

A coaxial shaped atmospheric pressure plasma torch has been used to deposit the millimetric scale plasma polymer. A detailed experiment has revealed the appearance of three different kinetic regimes with distinct coating morphology: no deposition, circular dot and circular ring formation. The ratio of precursor carrier gas flow to the plasma species carrier gas flow has been identified as crucial factor to separate the three regimes. Further experiments regarding the influence of precursor mass fraction on the dimension and deposition rates has been performed for a circular dot regime to get more insights into the coating shape, size and volume and its relation to gas flow dynamics. A side by side computational fluid dynamic simulation coupled with species transport module has been performed to understand the influence of flow dynamics on coating morphology. The appearance of recirculatory vortices in-between the nozzle and substrate and its role on confinement of precursor at specific region and mixing of plasma species to precursor has been highlighted. A good correlation in between the diameter of thus coated plasma polymer in circular dot regime and the simulated confinement zone is here reported.

Characterization of hybrid biocomposite Poly-Butyl-Succinate/Carbon fibers/Flax fibers

The investigation of renewable and recyclable materials becomes more critical every day due to the high levels of waste and carbon emissions and their impact on the environment. The use of eco-friendly materials, such as natural fibers and bioplastics, is increasingly important, and their use is always more popular. The aim of this research is to evaluate the changes in properties of composite materials made of Poly-Butyl-Succinate (PBS), a biodegradable thermoplastic matrix, and carbon fiber when some layers of carbon fiber are replaced by some layers of flax fiber to create a hybrid composite; in order to obtain a material more environmentally friendly with similar mechanical properties. To modify the flax fiber's surface energy and improve the wettability with the PBS matrix, an Atmospheric Pressure Plasma Torch (APPT) treatment was performed. The fibers' surfaces were characterized by measuring the contact angle; the contact angle values confirmed the wettability and accordingly, adhesion increased after plasma treatment. Different experiments were performed after substituting carbon fibers to evaluate the changes in the composite material's mechanical and thermal properties: tensile test, three-point bending test, impact tests and differential scanning calorimetry. Replacing the carbon fiber core layer with one or two flax fiber layers did not compromise the thermal stability. It led to the manufacturing of a hybrid composite with improved mechanical properties and higher impact resistance.

Silicon Dioxide Deposited Using Atmospheric Pressure Plasma Chemical Vapor Deposition for Improved Adhesion and Water Intrusion Resistance for Lightweight Manufacturing

This work aims to demonstrate the barrier coating, and adhesion promoting properties of silica-based coatings deposited using an atmospheric pressure plasma torch (APPT). This is achieved by applying an industrial grade adhesive to silica thin films deposited, on the surfaces to be joined, using atmospheric pressure plasma chemical vapor deposition (APP-CVD), to make single joint lap shear samples of different metal combinations commonly found in lightweight manufacturing, such as aluminum and magnesium as well as steel. To deposit these thin films, two separate silicon based organic precursors, hexamethyldisiloxane (HMDSO), and tetraehylorthosilicate (TEOS), are used. Samples are bonded using DuPont Betamate 1486 adhesive, and the lap shear results for these films are compared to the lap shear results of a chemically cleaned control using the same adhesive. The APPT uses a microwave power supply and gas mixtures of N2 and Ar. The adhesion of the films are tested using lap shear, and elevated temperature water soaks are conducted on the joints as well to simulate environmental exposure. Lap shear results, from samples with silica thin films, have an increase of max shear stress of 25%-115% compared to control samples depending on material. After exposure to water soak the max shear strength of the joints decreased by less than 15%, which demonstrates the films capabilities as a water barrier. Film morphology is examined using Scanning Electron Microscopy (SEM), and the film's composition and approximate thickness are obtained using Rutherford Backscattering Spectroscopy (RBS).

Effect of APPT Treatment on Mechanical Properties and Durability of Green Composites with Woven Flax.

Through this study, two different natural fibres green composites were characterised from the point of view of mechanical properties and durability. These green polymers allow manufacturing with a respectful life cycle due to their biodegradable or recyclable character. Composite materials were prepared in a hot plates press with two biopolymeric matrices, green low density polyethylene (GPE) and polybutylene succinate (PBS). As reinforcement, Atmospheric Pressure Plasma Torch (APPT) treated and untreated unidirectional woven flax were used. Mechanical properties were evaluated by tensile tests and the adhesion between matrices and reinforcement by peeling tests. The durability of each composite was analysed by water absorption measurements, Fourier Transform Infrared Spectroscopy (FTIR) analysis and tensile tests, during several aging times, up to 60 days, under high temperature and humidity conditions. The influence of the Atmospheric Pressure Plasma Torch treatment (APPT) was evaluated in all studies. It was found that GPE composites present better durability against aging conditions than PBS materials, due to the tendency of polyester to hydrolyse compared to the good resistance to humidity of polyolefins. The adhesion between matrices and reinforcement improves with APPT treatment. This improvement is more evident by avoiding the absorption of water than in the mechanical properties results, where only a slightly improvement is shown.

Measurements and modeling of CO 4th positive (A–X) radiation

We present absolute intensity measurements of CO 4th positive emission from a CO2/Ar plasma jet produced using an atmospheric pressure plasma torch facility. The centerline temperature of the plasma jet is approximately 6300 K. A VUV emission spectroscopy system was adapted to the plasma torch facility to measure spectrally resolved emission down to 140 nm. The emission from the plasma in the VUV, UV and near IR is consistent with thermochemical equilibrium. Carbon lines in the UV and VUV are found to be optically thick and their amplitude is therefore substantially affected by the line broadening parameters used for the calculation. For the CO 4th positive emission, these measurements test the performance of various models for the electronic transition moment function (ETMF). These ETMFs are used to calculate sets of Einstein coefficients that are used by SPECAIR to calculate the spectrally resolved emission of the plasma for comparison with experiments. We find that the EMTF of Kirby and Cooper and Spielfiedel accurately reproduce the measured emission from 150–215 nm.

Novel application of a thermoplastic composite with improved matrix-fiber interface

Ornamental materials are widely used in many fields such as construction. However, they have a main issue: up to 60% of processed marble pieces break due to their low toughness. In this work, an externally bonded reinforcement which can cope with this problem is presented. It must absorb the shock energy when marble is subjected to an impact without increasing severely the production cost. A thermoplastic polymer matrix composite is proposed due to its high toughness compared with conventional thermoset polymer matrix composites. However, thermoplastics present an issue related to the adhesion with the reinforcement, therefore fibers must be treated to solve this matter. Atmospheric pressure plasma torch offers a time saving and environmental friendly solution for improving adhesion between the fibers and the matrix. Finally, when marble is reinforced with the composite an important increase in absorbed energy is found in both, Charpy and drop tower test.

Development and diagnosis of an atmospheric pressure plasma torch for investigating magnetohydrodynamic instabilities

The development and diagnosis of an atmospheric pressure, non-transferred, DC arc plasma torch for investigating magnetohydrodynamic experiments is presented. Utilizing a custom AC starter circuit coupled with a high power DC power supply a long, laminar plasma jet was successfully generated by adjusting voltage and current characteristics, gas flow rates, and torch geometry (nozzle diameter and length). A complete and detailed description of the design and operation conditions of our torch is presented such that our results may be reproduced. Utilizing copper, aluminum, and tungsten alloy electrode components in conjunction with an electrically isolated water cooling system allows for continuous torch operation. The 50 kV AC starter circuit is coupled with a 15 kW DC power supply via a series injection transformer as a part of the custom arc starter circuit components. Axial and tangential gas flow, with nitrogen as the working gas, is regulated to generate a stable, laminar, atmospheric plasma torch with a jet length of over 80 cm under ideal operating conditions. To visualize the plasma interface in magnetohydrodynamics experiments, a technique was developed to image the cylindrical plasma jet in both the R-Z plane (axial) and R-θ plane (cross sectional) using planar-laser Mie scattering from particles added to the surrounding gas. Plasma emission wavelengths are filtered out allowing scattered light from the particle laden-flow field illuminated at 532 nm by an Nd:YAG laser, to be isolated. Plasma electron temperature and degree of ionization were estimated using a technique based on the well-known Fowler–Milne spectroscopic method. Electron temperatures of up to 14 000 K and degree of ionization up to 27% at the torch exit were obtained.

Environmentally Friendly Plasma Activation of Acrylonitrile–Butadiene–Styrene and Polydimethylsiloxane Surfaces to Improve Paint Adhesion

Generally, polymeric materials present an issue related to their low surface energy: low painting ability. The main aim of this work is to improve the adhesion between polymeric surfaces (polydimethylsiloxane (PDMS), and acrylonitrile-butadiene-styrene (ABS)) and paints (epoxy (EP), and polyurethane (PU)-based). In order to increase adhesion, hydrophilic modification of surfaces by atmospheric pressure plasma torch treatment (APPT) was proposed. Furthermore, it can permit dissimilar joints, i.e., ABS with a metal joined by a silicone (based PDMS), to be painted. The surface modifications were characterized by measurements of surface energy and roughness. In addition, the effectiveness of the pre-treatment on improving paint adhesion was confirmed by scratch, cross-cut, and adhesion tests. Results showed the possibility of coating both ABS and PDMS with a PU-based paint when treated with plasma. As a novel result, polymer and metal panels joined by silicone were able to be painted with the PU paint.

Comparative surface and adhesion properties of mechanical abrasion, flame and radiation-based surface treated wood plastic composites made with different polymers

Wood plastic composites (WPCs) show low surface energy and poor adhesion properties, and they can be improved by applying surface treatment. In this study three WPCs made with polyethylene, polypropylene and poly(vinyl chloride) have been treated by mechanical abrasion, flame and radiation-based (UV/ozone, atmospheric pressure plasma torch, Ar:O2 low pressure plasma) treatments. The influence of the wood content and polymer nature in the WPC on the surface modifications and adhesion properties produced by the surface treatments has been assessed. The surface treatments by mechanical abrasion and flame produced slight changes in the WPC surface, mainly in roughness, irrespective of the wood content and polymer nature in the WPC. The radiation-based surface treatments were the most efficient in increasing the surface energy (particularly the polar component) and produced ablation and surface oxidation of the WPC, the most noticeable modifications were obtained in the WPCs made with polyolefin. The adhesion (180° peel strength and cross-hatch adhesion) of the WPCs made with polyolefin was enhanced by surface treatment with both plasmas, irrespective of the adhesive or coating nature, and a relationship between the surface modifications produced by the plasma treatments and the adhesion was found. The surface modifications by the different treatments were less marked for the WPC made with poly(vinyl chloride) due to its smooth surface, low wood content and the existence of carbonate filler in its composition; furthermore, lower adhesion than for the surface treated WPCs made with polyolefin was obtained, and the highest 180° peel strength and cross-hatch adhesion were obtained with different surface treatments, the adhesion also depended on the coating nature. The effectiveness of the surface treatment in improving the adhesion of the WPCs depended on their wood content, polymer nature and surface roughness.

Characterization of high microwave power atmospheric pressure plasma torch

An atmospheric pressure microwave plasma torch operating at 2.45 GHz frequency using a surfaguide waveguide fed by argon gas at a constant rate is characterized at various microwave power settings. Coarse optical emission spectroscopy technique is used to diagnose the plasma parameters. The Boltzmann plot method is implemented to measure the electron temperature. Using the Doppler shift of the strong argon atomic spectral lines, the plasma velocity is determined. These results are in good agreement with earlier studies conducted on similar microwave plasma torches at a lower power setting. In this study, we exceed the previous power limitations observed in earlier studies and scan the microwave power in increments up to 2 kW.

Contribution of optical emission spectroscopy measurements to the understanding of TiO2 growth by chemical vapor deposition using an atmospheric-pressure plasma torch

The plasma jet of an atmospheric-pressure chemical vapor deposition system, namely, the axial injection torch, was diagnosed by optical emission spectroscopy (OES) in the conditions corresponding to titanium oxide deposition. Titanium tetraisopropoxide (TTIP) was used as the Ti organometallic precursor. The determination of the spatially-resolved excitation temperatures in the discharge allowed the determination of relative concentrations of atomic emitting species. The entrainment of air was estimated by measuring the relative quantity of N and O atoms in the discharge. The decomposition of TTIP was estimated by measuring the relative concentration of atomic Ti. It was shown that the air is rapidly introduced and distributed in the discharge while TTIP is progressively decomposed. Space-resolved OES measurements allowed to highlight titanium-depletion regions in the discharge. In light of previous results, it was suggested that these Ti-depletion regions reflect TiO2 gas phase nucleation processes. They are thus expected to affect the deposition growth mechanisms: Ti-rich regions would contribute to surface deposition (heterogeneous phase reactions) whereas Ti-depletion regions would contribute to the TiO2 particles deposition (homogeneous phase reactions).

Effect of atmospheric plasma torch on ballistic woven aramid

Atmospheric pressure plasma torch (APPT) is a cold plasma technique that can be used to treat materials with a polymeric surface in an environmentally friendly way. The treatment modifies the topography and chemistry of the surfaces. The effect of APPT on woven aramid is studied with the aim of enhancing its impact strength for ballistic applications. The shielding, laminated with several layers of woven and resin, can better resist projectile penetration. Woven aramid has low wettability due to its low polarity. Therefore adhesives penetrate the woven fibers with difficulty. APPT treatment considerably increases the polar component of the surface energy and the wettability is improved. Changes in the micro-topography and chemical composition that generate enhanced adhesion are investigated. The adhesion ability was determined by adhesion pull-off test, T-peel test, and impact test. Two types of adhesives were used: an elastic one (polyurethane-based, with elastoplastic mechanical behavior) and a rigid one (epoxy-based). Composites made with woven aramid treated with APPT exhibit an enhanced resistance to impact in terms of elastic energy recovery due to the greater degree of adhesive penetration between the woven fibers of each layer and better transfer of loads.

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters.

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a stable and continuous operation of the plasma is possible and the plasma torch can be used for many different applications. On one hand, the hot (3,600 K gas temperature) plasma can be used for chemical processes and on the other hand the cold afterglow (temperatures down to almost RT) can be applied for surface processes. For example chemical syntheses are interesting volume processes. Here the microwave plasma torch can be used for the decomposition of waste gases which are harmful and contribute to the global warming but are needed as etching gases in growing industry sectors like the semiconductor branch. Another application is the dissociation of CO2. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 to CO and O2. The CO can be further processed to gaseous or liquid higher hydrocarbons thereby providing chemical storage of the energy, synthetic fuels or platform chemicals for the chemical industry. Applications of the afterglow of the plasma torch are the treatment of surfaces to increase the adhesion of lacquer, glue or paint, and the sterilization or decontamination of different kind of surfaces. The movie will explain how to ignite the plasma solely by microwave power without any additional igniters, e.g., electric sparks. The microwave plasma torch is based on a combination of two resonators - a coaxial one which provides the ignition of the plasma and a cylindrical one which guarantees a continuous and stable operation of the plasma after ignition. The plasma can be operated in a long microwave transparent tube for volume processes or shaped by orifices for surface treatment purposes.

Evaluation of Adhesion Improvement of a GFRP Treated with Atmospheric Plasma Torch

The applications (and repair) of glass fiber reinforced epoxy composites are increasing in different industries (wind turbines, boats, chassis of buses, etc.) due to specific strength and low cost. Their major disadvantage is the difficulty to shape complex components. This problem can be solved manufacturing different parts, being adhesively bonded afterwards. This work studies the effect of atmospheric pressure plasma torch compared to grit-blasting to improve adhesion. After surface treating different parts, the changes of wettability and surface energy were measured. Treated samples were bonded with polyurethane and epoxy adhesives, and the quality of the bond was evaluated using pull-off adhesion tests and fracture strength test under cleavage loads. Obtained results allow to select the most adequate treatment in terms of mechanical requirements.