Radio Frequency Plasma Torch Research Articles

Suspension plasma sprayed copper-graphene coatings for improved antibacterial properties

Copper has a long history of use as a biocidal agent. Recent studies have demonstrated that incorporating graphene into copper coatings improves their antibacterial properties. However, the implementation of copper-graphene composite coatings is currently limited by the cost and scarcity of copper, as well as the difficulty of achieving a homogeneous distribution of graphene within the copper matrix. In this study, a new approach was developed to utilize an inductively-coupled radio frequency plasma torch to spray a uniform composite coating of copper nanoparticles and graphene nanoflakes (GNFs) onto a metal substrate. The resulting composite coatings exhibit microstructural uniformity, coating splats cohesion, and GNFs retention and dispersion within the Cu matrix. Furthermore, the Cu-GNFs coatings demonstrated strong antibacterial properties, with a 99% reduction of Escherichia coli bacteria within 1 h.

Controllable Preparation of Spherical Molybdenum Nano-Powders by One-Step Reduction of APM in Radio Frequency Hydrogen Plasma

Spherical molybdenum nano-powders were in-situ ultrafast synthesized from ammonium paramolybdate (APM) raw materials in a one-step reduction method by radio frequency (RF) hydrogen plasma. Due to the extreme conditions of the RF plasma torch such as its high temperature and large temperature gradient, the injected raw APM powder was quickly gasified and then reduced into nano-sized metal molybdenum (Mo) powder. The influences of APM powder delivery rate and H2 concentration on the properties of the obtained powders were investigated. Field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), X-ray diffraction (XRD), nanolaser particle analyzer, and specific surface area method were used to characterize the morphology, phase, and particle size distribution of the powders. The results showed that the nano-sized Mo powder obtained by hydrogen plasma treatment had a quasi-spherical morphology and an average particle size of about 30 nm. The particle size could be successfully adjusted by varying H2 concentrations. In addition, spherical nano-sized MoO3 powder could be obtained when no H2 was added into the RF plasma.

Improving the Physical and Mechanical Performance of Laminated Wooden Structures by Low-Temperature Plasma Treatment

This paper considers the effect of RF plasma on wood in improving the adhesion of binders to wood by increasing its surface wettability. Our study reveals that radiofrequency (RF) plasma treatment causes a greater than threefold decrease in the marginal wetting angle of wood. The greatest effect is achieved in RF plasma treatment in argon, which is on average 5% greater than that of RF plasma treatment in air or in propane/nitrogen mixture. In addition, the power of the RF plasma torch has the greatest influence, and the main influence comes from the voltage applied to the RF plasma torch; current does not have such a significant effect. To achieve a significant effect, the duration of exposure should be at least 5 min, with a total power of 4.05 kW. Studies have been conducted to determine the adhesive strength of wood. An increase in the strength of laminated beams made from RF-treated bars in relation to control samples was found. The greatest impact on the adhesion strength was revealed when using PVA-based glue, compared with the use of polyurethane-based adhesives and urea-formaldehyde resin.

Tuning the wicking and wettability properties of PET textiles by DBD or a remote atmospheric RF torch: A comparison

AbstractTextile industry is constantly searching for easy and rapid ways to improve the properties of textiles. In this matter, plasma treatments have already proven to be an efficient and green solution, as they proceed in a dry environment and require minimal use of chemicals. To date, most of the work on the subject has been performed with low‐pressure plasmas. Recently, atmospheric plasmas have received increasing interest, especially for industrial applications. Indeed, the possibility to avoid the use of pumping systems makes this technology easily implementable in continuous in‐line processes. For many applications, the treatment aims at modifying the textile surface to increase the overall hydrophilicity. The latter is often probed by the water contact angle, but this does not always reflect the global hydrophilic behavior of the textile as a three‐dimensional material. A complementary study of the wicking properties is important to better reflect the penetration of liquids into the textile, but it is poorly reported in the literature. The present work aims at increasing the water uptake of polyethylene terephthalate (PET) textile by direct or remote plasma treatment, which are the two main trends in this field. For this purpose, a dielectric barrier discharge (DBD) and a radiofrequency plasma torch at atmospheric pressure are used, respectively. Different plasma parameters are varied and their respective effect on the wicking properties of the fabric, assessed by an absorbency test developed ad hoc, are correlated to their surface chemical composition determined by X‐ray photoelectron spectroscopy. These results are compared with the possible changes in wetting of the fiber surface witnessed by water contact angles measured on PET foil samples submitted to the same plasma treatments. Complete wicking of water in PET textile can be obtained after 20 or 10 s of torch treatment with pure Ar plasma or Ar/O2 mixture, respectively. However, a comparable effect is detected, after 30 s of DBD Ar plasma treatment, under the used experimental conditions. Besides, the addition of O2 to the discharge has an opposite effect on the fabric wicking. These results are discussed in terms of the peculiar processes in surface activation and modification of the fabric surface triggered by the two different plasma technologies.

A High-Temperature Quenching Reactor

This article reports results of modeling, design, and experimental investigation of a heat exchanger to be used downstream of a radio frequency plasma torch for a variety of applications. A heat exchanger is designed for a plasma generator with thermal power of 30 kW and a maximum air plasma temperature of about 6000 K. The design can also be scaled to accommodate higher power plasma generators. The proposed engineering approach is double stage quenching of intermediate and unstable products from plasma chemical reactions. The design can be used in various technological processes, particularly for fixing atmospheric nitrogen and obtaining nitrogen oxides.

A novel thermal plasma-based technology for submicronic silicon carbide production at pilot scale

Abstract Submicronic powder of silicon carbide was synthesized in a pilot novel radiofrequency plasma torch reactor. The precursors were pyrolysis char and silica powders both with micrometric size. The mass rate of the precursor powder varied in the range 600-2500 g/h. The maximum test time was approximately 3 h. With the goal to increase the process yield, several technical measures were implemented. Silicon carbide yield was above 70 wt% when the plasma flame was confined by a tube that prolonged the residence time of the reactants at the useful temperature for the advancement of reaction. The silicon carbide was characterized by XRD, SEM, and DLS. Both α and β-crystalline phases were detected.

Understanding polyethylene surface functionalization by an atmospheric He/O2 plasma through combined experiments and simulations

High density polyethylene surfaces were exposed to the atmospheric post-discharge of a radiofrequency plasma torch supplied in helium and oxygen. Dynamic water contact angle measurements were performed to evaluate changes in surface hydrophilicity and angle resolved x-ray photoelectron spectroscopy was carried out to identify the functional groups responsible for wettability changes and to study their subsurface depth profiles, up to 9 nm in depth. The reactions leading to the formation of C–O, C = O and O–C = O groups were simulated by molecular dynamics. These simulations demonstrate that impinging oxygen atoms do not react immediately upon impact but rather remain at or close to the surface before eventually reacting. The simulations also explain the release of gaseous species in the ambient environment as well as the ejection of low molecular weight oxidized materials from the surface.

Characteristics of Synthesized Alumina Nanoparticles in a High-Pressure Radio Frequency Thermal Plasma Reactor

Nanophase alumina is synthesized in an atmospheric pressure radio frequency (RF) plasma reactor through melting, evaporation, and vapor phase nucleation technique. A specially designed high-pressure RF plasma reactor fitted with an indigenously built RF plasma torch converts commercially available micrometer size alumina chunks into spherical nanophase alumina in a single step under ambient quenching conditions without use of any additional quenching gas. Obtained powder contains mixed phases of α and δ -alumina as revealed by X-ray diffraction studies. Transmission Electron Microscopy analyses exhibit very small particle size (peak at 15 nm), narrow size distribution (half width ~ 24 nm), zero agglomeration, and good crystallinity. Obtained particle characteristics together with the high purity owing to inherent electrode-less feature of the RF discharge are suitable for important technological applications including fabrication of high-power ceramic laser gain media like Y3Al5O12 (YAG) from composites of Al2O3 and Y2O3. Characteristics of the synthesized alumina are compared with that of nanoalumina synthesized in atmospheric arcs.

고주파 열플라즈마 토치를 이용한 Ni 금속 입자의 나노화 공정에 대한 전산해석 연구

Numerical analysis on RF (Radio-Frequency) thermal plasma treatment of micro-sized Ni metal was carried out to understand the synthesis mechanism of nano-sized Ni powder by RF thermal plasma. For this purpose, the behaviors of Ni metal particles injected into RF plasma torch were investigated according to their diameters (), RF input power (6 ~ 12 kW) and the flow rates of carrier gases (2 and 5 slpm). From the numerical results, it is predicted firstly that the velocities of carrier gases need to be minimized because the strong injection of carrier gas can cool down the central column of RF thermal plasma significantly, which is used as a main path for RF thermal plasma treatment of micro-sized Ni metal. In addition, the residence time of the injected particles in the high temperature region of RF thermal plasma is found to be also reduced in proportion to the flow rate of the carrier gas In spite of these effects of carrier gas velocities, however, calculation results show that a Ni metal particle even with the diameter of can be completely evaporated at relatively low power level of 10 kW during its flight of RF thermal plasma torch (

RF thermal plasma treatment of dredged sediments: vitrification and silicon extraction

In the present work, dredged polluted sediments with high level of hydrocarbons and heavy metals have been treated by means of a laboratory scale radiofrequency (RF) thermal plasma source inside a graphite crucible. Two different experimental approaches have been utilized (1) to fully decontaminate and vitrify this material, and (2) to study the technical feasibility of metallurgical-grade silicon (MGS) smelting by carbothermal-reduction reactions of carbon with silica (SiO2) content in these dredged sediments. A two-dimensional model of a commercial inductively coupled RF plasma torch has been used to investigate the effects of plasma flow and temperature distributions of the plasma discharge interacting with the material inside the crucible. Samples of both vitrification and carbothermal reduction processes were characterized by scanning electron microscopy analysis (SEM), energy dispersion spectroscopy (EDS), X-ray fluorescence (XRF) and leaching tests. Results obtained showed a fully decontamination of the dredged sediments, with release values of heavy metals in leachates well below the law limits. Moreover, SEM/EDS analyses suggested that separation of MGS by carbothermal-reduction process is possible.

PTFE Surface Etching in the Post‐discharge of a Scanning RF Plasma Torch: Evidence of Ejected Fluorinated Species

AbstractThe texturization of poly(tetrafluoroethylene) (PTFE) surfaces is achieved at atmospheric pressure by using the post‐discharge of a radio‐frequency plasma torch supplied in helium and oxygen gases. The surface properties are characterized by contact angle measurement, X‐ray photoelectron spectroscopy and atomic force microscopy. We show that the plasma treatment increases the surface hydrophobicity (with water contact angles increasing from 115 to 155°) only by modifying the PTFE surface morphology and not the stoichiometry. Measurements of sample mass losses correlated to the ejection of CF2 fragments from the PTFE surface evidenced an etching mechanism at atmospheric pressure. magnified image

Application of atmospheric pressure plasma polishing method in machining of silicon ultra-smooth surfaces

The modern optics industry demands rigorous surface quality with minimum defects, which presents challenges to optics machining technologies. There are always certain defects on the final surfaces of the components formed in conventional contacting machining processes, such as micro-cracks, lattice disturbances, etc. It is especially serious for hard-brittle functional materials, such as crystals, glass and ceramics because of their special characteristics. To solve these problems, the atmospheric pressure plasma polishing (APPP) method is developed. It utilizes chemical reactions between reactive plasma and surface atoms to perform atom-scale material removal. Since the machining process is chemical in nature, APPP avoids the surface/subsurface defects mentioned above. As the key component, a capacitance coupled radio-frequency plasma torch is first introduced. In initial operations, silicon wafers were machined as samples. Before applying operations, both the temperature distribution on the work-piece surface and the spatial gas diffusion in the machining process were studied qualitatively by finite element analysis. Then the following temperature measurement experiments demonstrate the formation of the temperature gradient on the wafer surface predicted by the theoretical analysis and indicated a peak temperature about 90°C in the center. By using commercialized form talysurf, the machined surface was detected and the result shows regular removal profile that corresponds well to the flow field model. Moreover, the removal profile also indicates a 32 mm3/min removal rate. By using atomic force microscopy (AFM), the surface roughness was also measured and the result demonstrates an Ra 0.6 nm surface roughness. Then the element composition of the machined surface was detected and analyzed by X-ray photoelectron spectroscopy (XPS) technology. The results also demonstrate the occurrence of the anticipated main reactions. All the experiments have proved that this atmospheric pressure plasma polishing method has the potential to achieve the manufacture of high quality optical surfaces.

The Design of an Atmospheric Pressure Plasma Torch Used for Polishing Ultra-Smooth Surfaces

As there are always certain defects on the final surface of large-scale lightweight mirrors, which are formed in traditional mechanical polishing process, such as microcracks, lattice disturbances, plastic deformation, and so on, an atmospheric pressure plasma polishing method is a good solution to this problem. As a key component, the design of the capacitance coupling atmospheric pressure radio-frequency plasma torch is introduced. The designed torch uses water cooled coaxial aluminium electrodes with special treatment to avoid arcing between them. In normal machining process, the mixture of reaction gas and plasma gas with optimum ratio is input into the plasma torch. Then, excited by radio-frequency power, reaction gas is ionized in the plasma so as to create high density and energy reactive radicals under atmospheric pressure. The radicals cause chemical reactions with the atoms on the part surface, which performs an effective atomscale removal process. As the machining process is chemical in nature, this method avoids surface/subsurface defects mentioned above. Furthermore, initial experiment data analysis has proved that the atmospheric pressure plasma polishing method is effective and reliable, as well as demonstrates the validity of the designed plasma torch.

Flexible small size radiofrequency plasma torch for Tokamak wall cleaning

A plasma torch aiming to assist the detritiation process of Tokamak tiles in gaps and zones with difficult access, like in the divertor regions, was designed and built up. The torch operation is based on the expansion of a radiofrequency discharge constrained to burn in a limited space. The plasma torch is small size, flexible and compatible with mounting on a robotic arm, and can be operated stable both in argon and nitrogen at low and atmospheric pressure. The capability of the source in cleaning surfaces was proved by experiments on material removal from graphite and CFC tiles.

Experimental observations and nucleation and growth theory of polyhedral magnetic ferrite nanoparticles synthesized using an RF plasma torch

We have used transmission electron microscopy (TEM) to observe the morphologies of ferrite nanoparticles synthesized using a radio frequency plasma torch. These nanoparticles were faceted, having cuboctahedral polygonal growth forms with exclusively the {1 1 1} and {1 0 0} type faces. A model for the critical nucleus shapes and the growth forms of small cuboctahedral particles is proposed considering the Helmholtz free energies for nucleation and growth. The critical nucleus shape is predicted to be either a perfect cube or a perfect octahedron, while the equilibrium growth forms are the truncated shapes. High-resolution TEM observations of individual nanoparticles reveal that the smallest nanoparticles exhibit perfect octahedral shapes, while larger particles have truncated octahedral shapes. These observations are consistent with the model predictions. The morphology observations are also consistent with 0.95 < γ 1 0 0 γ 1 1 1 < 1.14 , where γ 1 0 0 and γ 1 1 1 are the surface energies of the (1 0 0) and (1 1 1) surfaces, respectively.

Neutron powder diffraction of carbon-coated FeCo alloy nanoparticles

Neutron powder diffraction is used to study the order–disorder transformation in carbon-coated FexCo1−x nanoparticles produced using a radio frequency plasma torch. The nanoparticles, nominally Fe50Co50, are produced from alloy powder and acetylene precursors by gas-phase nucleation from the plasma. The resulting nanoparticles undergo an order–disorder transformation near 730 °C, passing from an ordered B2 (CsCl) structure to a disordered A1 (body-centered-cubic) structure upon heating, similar to the transformation seen in bulk equiatomic FeCo. Although it is very difficult to quench the disordered state in bulk samples, the extreme cooling rates present in the plasma reactor produce metastable disordered nanoparticles. Neutron powder diffractograms acquired during a heating–cooling cycle at 27, 500, 710, 800, 710, and 400 °C indicate the particles relax to their equilibrium ordered state upon heating first, disorder as they pass through the transformation temperature, and reorder upon cooling.

A GENERAL MODEL FOR THE SPECTRAL CALCULATION OF OH RADIATION IN THE ULTRAVIOLET

A spectroscopic/collisional-radiative model is presented that permits the calculation of OH ( A 2Σ +− X 2Π) spectra in the ultraviolet for a wide range of gas dynamics conditions, including those observed in hypersonic flows. This requires a rotational–vibrational–electronic excitation model sufficiently general to account for the diversity of collision rates that encompasses conditions ranging from equilibrium to collisionless regimes. To this end, the proposed excitation model considers several state-specific processes, including quenching, predissociation, radiation, and vibrational–rotational exchange. Although the structure of the OH ( A→ X) spectra is complex, accurate line positions and transition probabilities are available and have been used. This paper discusses the full excitation and spectral model and provides examples that demonstrate its generality. Detailed comparisons are presented with experimental spectra measured under very different conditions. The first spectrum was measured at atmospheric pressure in a plasma generated by a 50 kW radio-frequency plasma torch. The second spectrum was measured under rarefied conditions in the bow shock of a reentering rocket.

Thermal Plasma Synthesis of γ-FeN, Nanoparticles as Precursors for the Fe16N2 Synthesis by Annealing

ABSTRACTAn ordered Fe16N2 phase has been reported with iron moments as high as 3.2 μB. It is precipitated from nitrogen martensite structures ideally containing 10.5 at.% nitrogen. Due to the highly distorted crystal structure and metastability of this phase non-equilibrium processing routes are sought to synthesize this phase. Here we report on radio frequency (RF) plasma torch synthesis which is used to produce FeN. nanoparticles quenched into a body centered tetragonal bct) structure as precursors for further annealing studies to form α“- Fe16N2 phase. We have employed a Tekna PL-50 type 50 kW, RF plasma torch. A plasma gas mixture containing 40 standard liters per minute (slpm) Ar and 8 slpm Hydrogen - 70 slpm Ar gas was used as a sheath gas. Iron powder ( &lt; 10 μm) was injected into the plasma stream using Ar flowing 15 slpm as a carrier gas. Nitrogen and Ammonia were used as a nitrogenization sources. Relatively low injection rates were used in order to achieve smaller particle sizes and thus faster quenching rates. We were able to produce particles containing up to 45 % of the quenched γ-phase. Observations based on x-ray diffraction (XRD) determination of lattice expansion and phase transition temperatures observed by differential thermal analysis (DTA) indicated that the quenched phase contains 6.5 atomic % nitrogen. Scherrer analysis of the fine particle broadening indicated that the average particle size for γ- phase is 27 nm, whereas this value is found to be 55 nm. for α-Fe. Nitrogen is well known for its grain size refinement in Fe thin films. Saturation magnetizations were found to be as low as 123 emu/g due to the presence of the nonmagnetic γ-FeNx phase.

Modelling of the heat transfer and fluid flow in a radio-frequency plasma torch with argon-hydrogen as the working gas

Modelling results concerning the heat transfer and fluid flow in a radio-frequency plasma torch with argon and hydrogen as the working gas are presented. The diffusion of hydrogen in the gas mixture due to the presence of temperature and concentration gradients within the torch has been modelled by using the combined-diffusion-coefficient approach. Included in the modelling are also the effects of the induced currents appearing in the brass probe for central gas injection on the electromagnetic fields and thus on the plasma flow and heat transfer within the plasma torch. It has been shown that the electrical conductivity of the probe affects the modelling results of the flow field and the temperature distribution in the torch. The flow rate of the central argon flow has substantial effects on the temperature, velocity and concentration fields, especially in the region near the axis of the torch. Computed temperature profiles at a few cross sections of the torch are favourably compared with corresponding experimental data for a typical case.

The deposition of chromium by the use of an inductively-coupled radio-frequency plasma torch

This paper discusses attempts to deposit a layer of hard Cr metal, with properties similar to those of layers currently obtained by electrolytic methods, onto a metallic substrate using an inductively-coupled, radio-frequency plasma torch (ICP-RF) torch. Preliminary studies indicated that it might be possible to produce a suitable layer using a number of chromium-based compounds. For this study, Cr powders and a chromium precursor were injected into the high temperature region of the plasma plume, where thermal decomposition of the feed material produced Cr atoms that deposited onto the surface of metal substrates placed below the plasma torch. The films produced were examined to determine thickness, chemical compositions, and adherence. Since the goal of the project was to develop a coating method that was not only industrially suitable but also environmentally safe, care was taken to monitor the emissions produced by the system during deposition.