© 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Thermal plasma-assisted processing is an effective process for the synthesis of gas (CO and H2) and carbonaceous materials production from industrial waste. In this paper, a DC plasma torch designed with two vortices chambers has been developed, and its characteristics have been experimentally tested. The plasma torch operates with different plasma working gases, including steam. The results of coal tar pitch (CTP) processing will be presented as a possible ecological application. CTP is a waste from the steel industry mainly composed of polycyclic aromatic hydrocarbons. The experimental results will be discussed with thermodynamic calculations and numerical simulation of the heat and mass transfer in the DC plasma torch and the chemical reaction chamber. The simulations were carried out to clarify the regions of gas flow and temperatures for producing synthesis gas and carbon nanomaterial. The results enable one to predict the produced gas composition and carbon nanomaterial properties. The physicochemical properties of carbon nanomaterial and synthesis gas show high efficiency in converting CTP into high-value-added products.

© 2022 Society.This is an experimental study on the decolorization efficiency and the degradation of organic compounds from textile wastewater by the ozonation process in a batch system. The effects of different sample volumes of textile wastewater over time were investigated. The experiments were performed in a 1 L glass reactor with a magnetic stirrer and a bubble diffuser at the bottom to feed the ozone. The applied cumulative ozone dosage varied at 120 gO3 L−1, 60 gO3 L−1, and 30 gO3 L−1, and the total interaction time for each test was 1 h. To investigate the physicochemical properties of the textile wastewater (solid and liquid phases) before and after the treatment, multiple analytical characterization methods were used: Thermal Gravimetric Analysis, Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy, X-ray diffraction, Fourier Transform Infrared spectroscopy, and Spectrophotometer. The most perceptive change was observed in the color of the liquid medium, which turned from black to transparent, and a visual color number indicator known as DurchsichtFarbZahl (DFZ) was used for the evaluation of this process. Absorbance values decreased about 3.5 times after 5 min of treatment with a 0.15 L sample volume, and these values differed for tests with larger sample volumes. FTIR spectroscopy demonstrated that the bands’ intensities associated with the C − H, C − N, and C − O decrease during treatment. On the other hand, it was possible to conclude that combining treatment methods to improve the degradation of persistent compounds after the ozonation process is necessary. Finally, the ozonation of the textile wastewater proved to be effective at removing color due to its high reaction capacity.

© 2021 Informa UK Limited, trading as Taylor & Francis Group.The processing of coal tar pitch (CTP) to produce clean fuel gas and carbon black (CB) is studied in a plasma reactor equipped with a direct-current plasma torch. The composition of the gas produced and energy costs were estimated theoretically for the CTP pyrolysis and gasification processes by two oxidants, namely oxygen and water vapor. We have found that the main gaseous compounds obtained in the pyrolysis and gasification processes are hydrogen (H2), carbon monoxide (CO), and very often carbon dioxide (CO2). For the pyrolysis case, the mean value of the synthesis gas concentration reaches a major value of 98 vol.% (H2–81 vol.%, CO–17. vol.%). However, only 23% of the initial CTP is transformed into gas phase at 1100 K and its content increases up to 37.4% at a temperature of 3000 K. For oxygen gasification, the syngas quantity is little less compared to the pyrolysis case and attains 96.6 vol.% (H2–26.5 vol.%, CO–70.1 vol.%) for T > 1100 K. An intermediate syngas content for the water steam gasification is 97.8 vol.% (with H2–55.8 vol.% and CO–42.0 vol.%). The CB produced was composed of well-defined spherical particles of 30-nm size. Furthermore, it is composed of carbon (98.2%), and followed by oxygen (1.8%) with a surface area of 97 m2 g−1. The thermal plasma system shows high efficiency in conversion of CTP into high-value-added products.

© 2022 Elsevier B.V.Polyaniline (PAni) widely studied conductive polymer due to its incredible versatility, electrical properties, and low cost. PAni usually is produced by chemical or electrochemical synthesis. However, these processes either generate a large amount of waste or are expensive and produce a small amount. The catalytic system incorporated into the PAni synthesis can be a strategic way to develop clean and low-cost processes. Therefore, we propose a synthesis of PAni catalyzed by carbon fiber (CF) reported for the first time. The procedure is to immerse the CF in an aqueous solution of aniline and H2SO4, at room temperature, in an open flask. Tests were carried out to investigate the CF as a catalyst and the molecular oxygen as an oxidant in the polymerization reaction. The samples were characterized by scanning electron microscopy, Raman spectroscopy, infrared spectroscopy, and X-ray photoelectron spectroscopy. According to the analyses, the reaction catalysts are heteroatoms on the fiber surface. Molecular oxygen present in atmospheric air is the oxidant of the reaction. The method is environmentally friendly, simple, and economical route to produce a conductive form of PAni on carbon fiber. The composite produced was evaluated as a possible electrode for a supercapacitor, and presented interesting results for application in energy storage devices.

© 2021 Wiley-VCH GmbHThis study applies a proof of concept for future applications in controlling the microbiota in tubes and tracheal appliances used in the respiratory tract. Therefore, the physical–chemical parameters of the plasma-activated and nebulized water (NPAW) are measured in a nebulizer tube with different lengths between 0.1 and 3.0 m. The pH values and oxidation–reduction potential (ORP) do not change during nebulization of PAW over a 1.0 m tube. However, for longer lengths, there is an increase in pH and a decrease in ORP. At 3.0 m, the pH increases approximately 16% compared with the 1.0 m position with a 20% decrease in the ORP values. Hydrogen peroxide (H2O2) measured quantitatively using test strips presents values between 0.5 and 2.0 mg/L for condensed NPAW in different tube lengths between 0.1 and 3.0 m, and maintains the approximate value of 2.0 mg/L in tubes up to 1.0 m, with a reduction proportional to the increase in the length of the tube. The antimicrobial efficacy of NPAW applied for 15 min shows the inactivation of Staphylococcus aureus and Escherichia coli but without significant inactivation of Candida albicans.

© 2021 Elsevier LtdThermal plasma technology is a process that demonstrates high performance for the processing of different types of waste. This technology can also be applied in the treatment of radioactive wastes, which requires special care. Beyond that, volumetric reduction, inertization, as well as a cheap and efficient process are necessary. In this context, the purpose of this paper is to demonstrate the application of thermal plasma technology for the treatment of solid radioactive waste. For this, stable Co and Cs were used to simulate compactable and non-compactable radioactive waste; about 0.8 g Co and 0.6 g Cs were added in each experimental test. The experimental tests were conducted using plasma of transferred arc electric discharge generated by the graphite electrode inside the process reactor. The behavior and distribution of the radionuclides present in the waste were assessed during the plasma process. The results show that the significant amounts of Co and Cs leave the melt by volatilization and are transferred to the gas phase with a small portion retained in the molten slag. The retention rate of Co in the slag phase is about 0.03% and 0.30% for compactable and non-compactable waste, respectively. On the other hand, Cs is completely transferred to the gas phase when added to the compactable waste. Conversely, when in the non-compactable waste, only 1.4% Cs is retained.

© 2021, Associação Brasileira de Engenharia Química.Mercury and its compounds are very dangerous to environmental and human health. Methods to contain and/or limit its emission through the filters, gas cleaning systems, and alternative processes for purification of industrial residues are necessary. This study focused on mercury removal from diatomite sorbent samples–used as a filter in chemical industries–using an oxygen low-pressure hollow cathode discharge (HCD). The effects of the exposure time and temperature were investigated. Thermal desorption (at 500 and 650 °C) and plasma oxidation were performed at low pressures (between 36 and 80 Pa). The results show a considerable acceleration of the diatomite decontamination to a temperature of 650 °C, bringing the concentration of mercury below 100 µg/kg after 10 min and 39 µg/kg after 110 min of HCD exposure time. A comparative analysis of the virgin diatomite characteristics used in the filter press and after treatment show the possibility of recycling this material. Additionally, the mercury extracted by condensation in the vacuum line (by using a dry ice trap) can be purified for reuse and returned to the industrial process.

© 2021 Elsevier LtdNb2O5 polymorphism and defect chemistry depend on the temperature, pressure, atmosphere composition and the initial crystallography. Plasma spray of Nb2O5 is a pathway to form coatings with in-situ metastable and nonstoichiometric phases, however so far unexplored. This study aimed to understand the phase evolution of plasma sprayed Nb2O5 coatings, and its effect on their morphology and properties. Phase evolution from H-Nb2O5 in the feedstock, to T-Nb2O5, TT-Nb2O5, N-Nb2O5, H-Nb2O5, Nb12O29 and NbO2 in the coatings depends on the plasma Ar/H2 ratio and its related enthalpy. The microstructure shows a layered distribution of nonstoichiometric phases at the splat boundaries and splat cores composed of T-Nb2O5 or TT-Nb2O5. The presence and distribution of these phases are related to the thermomechanical and electrical properties. The mechanisms driving the formation of these coatings are based on the Nb2O5 incongruent vaporization which promote retention of nonstoichiometric phases and the rapid solidification of metastable phases.

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.The garment industry demands stamping processes that are increasingly more agile and less damaging to the environment. In this scenario, digital printing, with the sublimation transfer printing technique, presents itself as a viable option for synthetic textile substrates. Among the synthetic fibres, polyamide (P.A.) fibres stand out, as they are light, soft, durable, and boast moderate sweat absorption; however, before sublimation, superficial treatment is necessary in order to present good results such as withstanding washing and maintaining colour intensity. This study addresses the surface modification of the PA6.6 textile substrate by activating non-thermal plasma at atmospheric pressure to receive dye through the sublimation method with dispersed dye. The knitted PA6.6 fabric surface treatment was performed with plasma application at atmospheric pressure using air in the Plasmatreater AS400 equipment. The sublimation transfer effects were evaluated by wash fastness and colourimetric tests. To assess the wettability effect of the control and treated samples, a contact angle test was carried out on PA6.6 samples. Fourier transform infrared spectroscopy (FTIR) proved the changes in chemical functional groups in the fibres. The results showed a decrease in the contact angle of the textile surface, 4–5 grayscale results for colour change and transfer for washing, and an increase in colour strength. In the FTIR tests, there is an increase in the transmittance value of aromatic, carboxylic groups (C=O, 580 cm−1), amides (N=H, 1630 cm−1), and methyl groups (CH 1369 to 1463 cm−1) as well as the presence of new functional groups in the 3064 cm−1 and 2860 cm−1 bands. These conditions allowed sublimation in the knitted PA6.6 fabric and showed increased colour strength and good wash fastness.

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.In this study, the potential antimicrobial activity of plasma-activated tap water (PAW) was evaluated against Staphylococcus aureus, Escherichia coli, and Candida albicans. For this, PAW was prepared in a gliding arc plasma system using two treatment conditions: stagnant water and water stirring by a magnetic stirrer, called moving water. Subsequently, their oxidation-reduction potential (ORP), pH, electrical conductivity (σ), and total dissolved solids (TDS) were monitored in different areas of the sample divided according to the depth of the beaker. It was observed that PAW obtained in dynamic conditions showed a more uniform acidity among the evaluated areas with pH 3.53 and ORP of 215 mV. Finally, standardized suspensions of Staphylococcus aureus (ATCC 6538), Escherichia coli (ATCC 10799), and Candida albicans (SC 5314) were treated with PAW, and the reduction of viable cells determined the antimicrobial effect. Our results indicate that the tap water, activated by plasma treatment using gliding arc, is an excellent inactivation agent in the case of Staphylococcus aureus and Escherichia coli. On the other hand, no significant antimicrobial activity was achieved for Candida albicans.

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.The chemical, structural, morphological, and optical properties of Al-doped TiO2 thin films, called TiO2/Al2O3 nanolaminates, grown by plasma-enhanced atomic layer deposition (PEALD) on p-type Si <100> and commercial SLG glass were discussed. High-quality PEALD TiO2/Al2O3 nanolam-inates were produced in the amorphous and crystalline phases. All crystalline nanolaminates have an overabundance of oxygen, while amorphous ones lack oxygen. The superabundance of oxygen on the crystalline film surface was illustrated by a schematic representation that described this phenomenon observed for PEALD TiO2/Al2O3 nanolaminates. The transition from crystalline to amorphous phase increased the surface hardness and the optical gap and decreased the refractive index. Therefore, the doping effect of TiO2 by the insertion of Al2O3 monolayers showed that it is possible to adjust different parameters of the thin-film material and to control, for example, the mobility of the hole-electron pair in the metal-insulator-devices semiconductors, corrosion protection, and optical properties, which are crucial for application in a wide range of technological areas, such as those used to manufacture fluorescence biosensors, photodetectors, and solar cells, among other devices.

© 2020 International Ozone Association.The purpose of the current study was to investigate the effect of ozone exposure on the process of water uptake and germination of lentil (Lens culinaris) seeds. For this, a commercial ozone generator that provides a concentration of 1 g/m3 generated from atmospheric air was used. In the experiments 10 lentil seeds were used per treatment carried out at different times of exposure to ozone: 2, 3, 5, 10 and 15 min. Imbibition curves were performed following the seed mass for 180 min. For germination tests, wet neutral pH germination paper was used where, every 24 h, the mass, root size and stem size of the plant were measured over 7 days. Furthermore, contact angle analysis and Fourier transform infrared spectroscopy (FT-IR) were performed on the seeds. The maximum water uptake in the seeds as a function of the imbibition time was optimum for the samples treated with 3 and 5 min. This fact was reflected in the growth rates of the stem, root and mass that were significantly higher than the control sample, after 7 days of germination. The FT-IR analysis indicated the formation of bands in 1345 cm−1 (NO3−) related to ethylene ozonolysis. Also, it was observed a reduction of the N-H band (amide II) at 1551–1550 cm−1 and increase of the C-H bond at 1543 cm−1, evidencing a possible action of ozone on lentil proteins. This fact is probably related to the enhancement of the seed germination process, allowing the germination rates to be 90% for samples treated with ozone for 3 and 10 min.

© 2020 Elsevier B.V.The demand for the development of more efficient, low emission, and high-performance aircraft have required new methods to obtain lighter materials, with higher temperature resistance and chemical stability. For these purposes, Environmental Barrier Coatings (EBC) are largely studied. EBC's are commonly obtained through Atmospheric Plasma Spray, where the process parameters, as well as the precursor characteristics, and its interaction with the plasma jet influence the properties of the deposited material. In this context, this work aims to deposit EBC on C/C composites through the high-velocity plasma spray (HVPS) using a new concept of hybrid SiO2 + ZrO2 precursor. For this, a solid load of 7% yttria-stabilized zirconia (7YSZ) is mixed in a Si(OH4) solution with concentrations of 10, 20, and 30 g/L. From Raman and XRD analyses, ZrSiO4 and SiC were identified, its formations occur due to the reactions of SiO2 with ZrO2 (7YSZ) and the SiO2 precursor with C/C substrate. Finally, we demonstrate the versatility of the HVPS process using a hybrid precursor, capable of producing micro/nanostructured EBC coatings.

© 2020 by the authors.This work proposes the use of a dielectric barrier discharge (DBD) reactor operating at atmospheric pressure (AP) using air and sub-atmospheric pressure (SAP) using air or argon to treat polyamide 6.6 (PA6.6) fabrics. Here, plasma dosages corresponding to 37.5 kW·min·m-2 for AP and 7.5 kW·min·m-2 for SAP in air or argon were used. The hydrophilicity aging effect property of untreated and DBD-treated PA6.6 samples was evaluated from the apparent contact angle. The surface changes in physical microstructure were studied by field emission scanning electron microscopy (FE-SEM). To prove the changes in chemical functional groups in the fibers, Fourier transform infrared spectroscopy (FTIR) was used, and the change in surface bonds was evaluated by energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). In addition, the whiteness effect was investigated by the color spectrophotometry (Datacolor) technique. The results showed that the increase in surface roughness by the SAP DBD treatment contributed to a decrease in and maintenance of the hydrophilicity of PA6.6 fabrics for longer. The SAP DBD in air treatment promoted an enhancement of the aging effect with a low plasma dosage (5-fold reduction compared with AP DBD treatment). Finally, the SAP DBD treatment using argon functionalizes the fabric surface more efficiently than DBD treatments in air.

© 2019, Springer Nature B.V.Abstract: Dielectric Barrier Discharge (DBD) can be used to produce a large volume of non-thermal plasma at atmospheric pressure. Such plasmas are sources of highly reactive species (radicals, ozone, atoms, ions and excited molecules). Due to its characteristics, the DBD plasma can be applied for the pretreatment of lignocellulosic materials, in order to extract lignin that prevents the access to remained fermentable sugars in the biomass. In this context, an alternative method for pretreatment of lignocellulosic material in an in-liquid DBD plasma reactor using non-contact electrodes, working with atmospheric air, has been proposed. After the pretreatment, the solids were washed and submitted to enzymatic hydrolysis with a commercial enzyme complex, at 10 FPU/g of pretreated biomass and 50 g/L solids concentration (dry basis), for 72 h. The release of fermentable sugars was measured, comparing the samples obtained with and without plasma treatment. The highest sugar release was achieved using the plasma-in-liquid pretreatment in a single step, with glucose and xylose yields of 51.3 and 38.5%, respectively, after enzymatic hydrolysis. Thus, an effective pretreatment was developed to be applied to biomass such as: corn cob, sugarcane bagasse, bamboo, eucalyptus, etc., in order to reduce the environmental impact and, at the same time, produce biofuels. Graphic Abstract: [Figure not available: see fulltext.]

Copyright © 2020 by ASME.In this study, a hypersonic plasma setup was constructed based on a vortex plasma heater with prenozzle gas-dynamic insertion. The prenozzle allows the improvement of the characteristics of the vacuum system according to the necessities of the experiments. The plasma setup produces a hypersonic thermal flow, which is capable to test the thermal oxidation of ultrahigh temperature ceramics (UHTC) composites, such as zirconium diboride (ZrB2). Thereby, ZrB2 samples were prepared with a variation of 10, 20, and 30% of silicon carbide (SiC) in volume, in order to investigate the oxidation mechanisms and microstructural properties of the samples tested under hypersonic thermal flow. The results of the oxidation tests showed that the samples with 10 and 30% of SiC undergo to the active oxidation and forms an unstable and fragile ZrO2 oxide. The formed ZrO2 does not withstand the drag force and the thermal flux of the hypersonic plasma jet, partially volatilizing the oxide layer, causing an accentuated loss of mass. For the oxidation tests of the sample with 20% of SiC, the gain of mass was observed due to the formation of ZrSiO4 passivation layer, which is a stable oxide and promotes mechanical resistance, and low degradation rate. These results can be associated with the variation of SiC, which demonstrates an ideal proportion of 20% of SiC in ZrB2, which influences the oxidation mechanisms and produce a protective layer.

© 2020, Akadémiai Kiadó, Budapest, Hungary.In this paper, a review of radioactive wastes treatment using thermal plasma technology is presented as a treatment method for radioactive waste management.Virtually all waste streams can be treated by the thermal plasma technologies, resulting in a conditioned product, free from organics and liquids, definitely meeting the acceptance criteria for safe storage and disposal. The application of the thermal plasma system in the nuclear area is still one of the current research topics due to the theoretical and practical complexity of the treatment. This paper discusses the performance of the thermal plasma systems, addressing the advantages and limitations of the method.

© 2020 by the authors. Licensee MDPI, Basel, Switzerland.Black TiO2 materials have been quite widely explored due to their large solar absorption and superior photocatalytic activity. In this paper, the blackening process of titanium dioxide (TiO2) thin film using the hollow cathode hydrogen plasma (HCHP) technique is reported. First, pristine anatase TiO2 films were grown by magnetron sputtering onto silicon and cover glass substrates and then annealed at 450◦C for 2 h. Then, the as-grown TiO2 films were treated with HCHP for 15 min. The physical, chemical and morphological properties of the films were analyzed by profilometry, X-ray diffraction (XRD), UV-Vis spectrophotometry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. Electrical and photocatalytic measurements were performed by four-point probe and methylene blue UV degradation assays, respectively. The results showed that the black TiO2 film is highly absorbent in the UV-visible region, has low electrical resistance and greater surface area compared to the non-treated TiO2 film. These properties of black TiO2 film, as well as its performance as a photocatalytic agent, were investigated, indicating the superior quality of this material in thin film form and the promising potential of the HCHP treatment to produce hydrogenated TiO2 in short process time.

© 2019Nuclear reactors, hospitals, industries and research institutes generate considerable amounts of radioactive waste every day. To dispose this waste in a safe and cost-effective manner, it must be treated by immobilising the radionuclides and, for better stocking capacity, it must be volumetrically reduced as much as possible. To this end, plasma technology, among other promising technologies for radioactive waste treatment, exposes radioactive waste to temperatures above 1400 °C, thereby substantially reducing its volume. In the planning and managing of radioactive waste, the challenges related to plasma technology are presented as a motivation factor for the possible implantation of plasma reactors in nuclear plants and research centres, thereby improving radioactive waste management. In this study, a thermal plasma treatment process was established, and a plasma reactor was used for compactable waste processing. After 30 min of thermal plasma treatment, the volume reduction factor reached 1:99. The results demonstrate the viability of using a thermal plasma process for the volumetric reduction of radioactive waste in a safe and cost-effective manner.

© 2020 Elsevier Ltd. All rights reserved.An experimental study on the degradation of organic compounds from radioactive oil sludge by the ozonation process is presented. The effects of different concentrations of ozone in the oil sludge degradation over time were investigated. The experiments were performed in a 0.125 L glass reactor with magnetic stirring and a diffuser plate at the bottom to feed the ozone. The ozone concentration varied from 13 to 53 mg L-1 and the total interaction time was 1 h. To investigate the physicochemical properties of the oil sludge (solid and liquid components) prior to and after the treatment, multiple analytical characterization methods were used: Thermal Gravimetric Analysis, X-ray diffraction, Scanning Electron Microscopy coupled with Energy-Dispersive X-ray Spectroscopy, Fourier Transform Infrared spectroscopy, Spectrophotometer, and Residual Gas Analyzer. The most perceptive change is in the color of the liquid medium turned from dark brown to light yellow, especially under ozone concentrations higher than 33 mg L-1. Absorbance values decreased about 3.5 times after 30 min of treatment with [O3] =53 mg L-1. FTIR spectroscopy showed that the bands associated with the CH3 and CeH in CH2 disappeared during treatment. On the other hand, a greater presence of C]C aromatics was observed. By residual gas analysis, various organic and inorganic gases were identified during the treatment, such as CH4, H2, CO2, and H2S. Finally, the ozonation of the oil sludge proved to be effective, due to its high reaction capacity.

© 2020 Universidade Federal de Sao Carlos. All rights reserved.In this study, the hybrid corona-dielectric barrier discharge plasma treatment was employed to modify the physical, chemical and morphological characteristics of a half-knitted fabric composed of 92% polyamide 6.6 and 8% elastane (PA). These properties of the fabric were evaluated by the water contact angle, x-ray diffraction, infrared spectroscopy, scanning electron microscopy and atomic force microscopy techniques. In addition, the dyeing and washing processes were also investigated. A significant reduction of the contact angle was observed for plasma-treated PA. Infrared spectroscopy analyses indicated that C-H, N-H, and N-O groups in PA increased after plasma treatment, explaining the improved coloring strength for the plasma-treated samples when dyed with reactive and acid dyes. A better fixation of dye was also observed after the atmospheric plasma treatment. Furthermore, dyeing with a basic and acid dye caused the dyeability increases for the plasma-treated sample compared with the untreated sample.

© 2020 The Author(s). Published by IOP Publishing Ltd.The development of efficient, reliable and affordable propulsion units is one of the main objectives in the development of aerospace technology. Typically the final cost of the vehicle is deeply affected by this subsystem. In this study, a hybrid combination of the ablative chamber is presented where graphite nozzles coated with chemical vapor deposited Silicon Carbide (CVD-SiC) is submitted to the ablative environment, generated by a DC plasma torch operating at a power of 35 kW and homogeneous heat flow of 0.75 MW m-2. The ablative properties of the samples were evaluated by measuring the weight loss as a function of the exposure time, weight loss of 0.11% after 70 s of exposition due to the formation of SiO gas was observed. The microstructure characteristics of SiC coating before and after ablation tests were carried out by SEM and XRD showing that it goes to scale oxidation to forming of SiO2 (β-quartz) and SiC (β to α) phase transformation. Whereas the ablation mechanism showed to be dependent on the initial coating thickness and exposure time.

© 2019, Springer Science+Business Media, LLC, part of Springer Nature.The use of materials for aerospace devices, such as rocket nozzles and thermal shields, depends primarily on their thermal and structural characteristics. Ceramic materials and carbon composites have been studied for this purpose. This work measures and investigates the ablation and thermal diffusivity of hybrid matrix composites of carbon–silicon carbide matrix reinforced by carbon fiber (C/C-SiC). Silicon powder was added to a phenolic thermoset matrix with proportions of 5, 10, and 20 %. In addition, the liquid polymer infiltration (LPI) process using a silicone polymer was used to produce the same composites. A thermal plasma torch was used to obtain the ablation and effective thermal diffusivity characteristics of the materials. The morphologies, microstructures, and chemical compositions of the samples were investigated by scanning electron microscopy and energy-dispersive spectrometry (SEM/EDS) and X-ray diffraction (XRD). The thermal diffusivities of the composites were found to be in the range of 0.2–1.5 × 10−6 m2·s−1 from 700 °C to 1000 °C, respectively. The void volume fraction of the composites was approximately 20 % and decreased the thermal diffusivity.

© 2019 IOP Publishing Ltd.Organic contaminants (for example in wastewater effluents) cause serious health and environmental problems due to their high chemical oxygen demand (COD), low biodegradability, and toxicity. Non-equilibrium and thermal plasmas were actively studied and numerous reactor geometries were developed to induce chemical reactions in treated liquids. Thermal plasma, because of its elevated temperatures and presence of highly active radicals, accelerates kinetics of chemical reactions and achieve high destruction efficiencies in processing of gaseous, liquids and solid materials. In this work, a plasma-chemical reactor, with submerged plasma jet for treatment of liquid residues, is presented and applied for treatment of water contaminated with glycerine. A distinctive feature of submerged plasma treatment is the high local plasma temperature and low treated liquid temperature, which promotes high quenching rate that preserves radical concentration and promotes advanced oxidation of aqueous effluents in highly turbulence flow. This work presents the main functioning characteristics of the reactor and the effect of specific energy input on glycerine degradation by thermal plasma.

© 2019, Springer Nature Switzerland AG.Titanate nanorod synthesis method is extremely important due to their large application in electronic, catalysis, and biological areas. However, works reporting the influence of synthesis parameters on the structure, morphology, and properties of titanate nanorods are still rare. Therefore, this work aims to analyze the preparation of titanate nanorods from TiO2 nanoparticles via hydrothermal reaction. The microstructure and morphological properties were evaluated as a function of time, temperature and precursor nature (anatase or anatase/rutile mixture) by X-ray powder diffraction, Raman spectroscopy, transmission electron microscopy and field-emission scanning electron microscopy. The crystallinity of the precursor was the main parameter for the titanate nanorods formation. Besides, temperature has also a direct influence in the fibril morphology. The use of low temperature and anatase/rutile mixture was not able to produce titanate nanorods. Only the use of higher temperatures and pure anatase resulted in rod-like titanates, which showed higher methylene blue photodegradation efficiency than TiO2 nanoparticles.

© 2018 IOP Publishing Ltd.Candida spp are present in 70%-90% of invasive infections and non-thermal plasmas operated at atmospheric pressure have been gaining attention as a new antimicrobial strategy for medical devices. This work presents studies on the inactivation efficacy of biofilms of Candida albicans grown in polyurethane (PU), main constituent of central venous catheter, by atmospheric gliding arc plasma jet operated at different process parameters: gas chemistry/flow(argon, helium, or its mixture with air) and plasma pulsing. The investigation was performed in the post-discharge region of the plasma jet. After plasma treatment, the colony-forming units(CFU)were counted, and the chemical bonding (FT-IR) and morphological (SEM) analyses of the surface of the biofilm plus PU substrate were investigated. Furthermore, optical emission spectroscopy (OES) technique was applied to characterize the plasma chemistry and measure the OH concentration and rotational temperature, together with thermal analyses of the substrate during treatment. CFU results showed that gliding arc plasma jet was efficient for the inactivation of C. albicans biofilms. It obtained a maximum CFU reduction of 100% and 98% for 4 L min-1 air/6 L min-1 He and 99% and 98% for 4 L min-1 air/6 L min-1 Ar in continuous and pulsed mode, respectively. SEM and FT-IR analyses corroborate with results of % CFU reduction, showing a reduction of the biofilm constituents on the substrate surface. From OES and substrate thermal analyses, it was possible to verify that, although the OH concentration and rotational temperature of air/He plasma jet are lower in comparison to the air/Ar, a drastic increase of the substrate temperature during the treatment (up to 70 °C)was observed for this plasma chemistry.

© 2018 IEEE.Titanium dioxide (TiO(2) thin films were deposited on conductive (titanium and fluorine tin oxide glass), insulant (mica, cover glass and thermal SiO(2 thin film on silicon) and semiconductive (silicon (100) and 4H-SiC) substrates by atomic layer deposition (ALD) technique. The metal and ligand precursors used were titanium tetrachloride and water, respectively. Grazing incidence X-ray diffraction (GIXRD) analysis was performed to investigate the dependence of crystalline phase of the as-deposited thin films on different substrates for process temperatures ranging from 150-450 °C. Results indicate that the ALD TiO(2 crystalline phase is dependent on the substrate nature which modifies the required temperature for phase change, i.e. from amorphous to anatase to rutile. For example, for conductive substrates the temperature for formation of rutile phase is around 350 °C while for semiconductor substrates it was observed only from 400 °C. By other hand, when the substrate has an amorphous structure there is not a common rule, i.e. for mica and thermal SiO(2 thin film on silicon only anatase phase was formed in all temperature range investigated while, for cover glass, it was possible to observe all stages of TiO(2 phase change, highlighting the formation of brookite phase for temperatures between 300 and 350 °C. Moreover, it is shown that rutile phase can be obtained, in pure phase, at temperatures higher than 400 °C, however only for glass and titanium substrates. These results allow us to infer that less expensive Ti thin film could act as a good seed layer for growth of good quality rutile TiO(2 phase, by using ALD process on Si substrate and using precursors such as TiCl4 and H2O.

© 2018 IOP Publishing Ltd.Materials used in space vehicles components are subjected to thermally aggressive environments when exposed to atmospheric reentry. In order to protect the payload and the vehicle itself, ablative composites are employed as TPS (Thermal Protection System). The development of TPS materials generally go through phases of obtaining, atmospheric reentry tests and comparison with a mathematical model. The state of the art presents some reentry tests in a subsonic or supersonic arc-jet facility, and a complex type of mathematical model, which normally requires large computational cost. This work presents a reliable method for estimate the performance of ablative composites, combining empirical and experimental data. Tests of composite materials used in thermal protection systems through exposure to a plasma jet are performed, where the heat fluxes emulate those present in atmospheric reentry of space vehicles components. The carbon/phenolic material samples have been performed in the hypersonic plasma tunnel of Plasma and Process Laboratory, available in Aeronautics Institute of Technology (ITA), by a plasma torch with a 50 kW DC power source. The plasma tunnel parameters were optimized to reproduce the conditions close to the critical re-entry point of the space vehicles payloads developed by the Aeronautics and Space Institute (IAE). The specimens in study were developed and manufactured in Brazil. Mass loss and specific mass loss rates of the samples and the back surface temperatures, as a function of the exposure time to the thermal flow, were determined. A computational simulation based in a two-front ablation model was performed, in order to compare the tests and the simulation results. The results allowed to estimate the ablative behavior of the tested material and to validate the theoretical model used in the computational simulation for its use in geometries close to the thermal protection systems used in the Brazilian space and suborbital vehicles.

© Sociedade Brasileira de Física 2018. Hollow cathode discharge (HCD) is widely used in material processing and plasma emission spectroscopy due to several advantages over other plasma sources. Basically, the HCD consists of a cathode with a hollow structure (cavity, hole, or parallel faces) and an anode of arbitrary shape. In this investigation, experimental studies on low-pressure plane-parallelHCD operated at different process conditions are reported. Herein, we investigate the dependence of the discharge current on the product of the gas pressure and intercathode distance (pD). In addition, the electron temperature and density were inferred from the current-voltage characteristics of a single cylindrical Langmuir probe positioned between the cathodes, on the discharge axis. The measurements were carried out at different gas pressures, magnetic field intensities, working gases, inter-cathode distances, cathode materials, and discharge voltages. The results showed that, at different gas pressures, the maximum discharge current (I d,max ) is not only a function of the product pD, but also of the pressure itself. Application of a uniform longitudinalmagnetic field improved plasma confinement between cathodes, leading to a substantial increase in I d,max in most of the situations considered in this study. However, for oxygen discharge, a strong discharge current reduction after the application of the magnetic field was observed. In relation to the Langmuir probe studies, it was observed that the uniform longitudinal magnetic field reduced the electron temperature, but this behavior depends strictly on pD. The typical values of electron density and electron temperature in the case of the nitrogen discharge were n e = 10 17 m −3 and T e = 2.5 eV, respectively. Finally, our experiments showed that the pD range for hollow cathode effects was between 0.2–5 Pa m.

© 2018 ASM International® All rights reserved.The plasma torch design affects the particle-plasma interaction, in-flight properties and the coating microstructure. When spraying metallic powders, the in-flight oxidation as well as the particle velocity and temperature determine the mechanical, corrosion and oxidation properties, which have a major impact on the in-service degradation of bond coats. This study aims to determine the microstructural and mechanical properties of as-sprayed CoNiCrAlY coatings deposited on the Inconel 718 alloy. Depositions were made using a High Velocity Plasma Spray Process (HVPS), which is based on a special plasma torch design. In-flight particle characteristics were determined to elucidate the kinetic and thermal regime of HVPS process.

© 2017 Elsevier Ltd and Techna Group S.r.l.Carbon/carbon (C/C) composites are widely used in structural components, particularly in the aerospace and aeronautics sectors. However, the application of C/C composites is limited by low oxidation resistance at high temperatures. In order to overcome this problem, graded SiO2/SiC coatings were deposited on C/C composites by a high-velocity solution plasma spray (HVSPS) process. Graded coatings were formed by reactions between the Si(OH)4 sprayed liquid precursor and the C/C substrate; these reactions were promoted by the high temperature of the plasma torch. The morphologies, microstructures, and chemical compositions of the coatings were investigated by X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy. By altering the deposition time, the coating thickness was controlled, therefore demonstrating SiC formation and realizing graded SiO2/SiC coatings.

© 2017, Springer Science+Business Media B.V.The thermochemical decomposition of sunflower oil cake (SuOC) with ZnCl2 and AlCl3 additives was studied by thermogravimetric (TG) analysis at a heating rate of 5 °C/min under a controlled nitrogen atmosphere with flow value of (20 mL/min). The present study focused on the development of evaluation criteria of the thermal decomposition of SuOC with additives. Evaluation criteria were suggested based on a comparison of kinetic data of an actual mixture with that of a corresponding reference mechanical mixture (RMM). Assessment of the additives influences on the thermal behaviour of SuOC showed that AlCl3 provided up to a 70% enhancement of devolatilization in comparison with the RMM and a 7.5–10% decrease of activation energy at the low pyrolysis temperature of 242 °C by providing a biomass conversion degree of α = 60–70%. In contrast, the ZnCl2 provided the same value of biomass conversion degree, but only in the temperature range of 450–550 °C.

© 2017, ASM International.Plasma spray is a versatile technology used for production of environmental and thermal barrier coatings, mainly in the aerospace, gas turbine, and automotive industries, with potential application in the renewable energy industry. New plasma spray technologies have been developed recently to produce high-quality coatings as an alternative to the costly low-pressure plasma-spray process. In this work, we studied the properties of as-sprayed CoNiCrAlY coatings deposited on Ti-6Al-4V substrate with smooth surface (Ra = 0.8 μm) by means of a plasma torch operating in supersonic regime at atmospheric pressure. The CoNiCrAlY coatings were evaluated in terms of their surface roughness, microstructure, instrumented indentation, and phase content. Static and dynamic depositions were investigated to examine their effect on coating characteristics. Results show that the substrate surface velocity has a major influence on the coating properties. The sprayed CoNiCrAlY coatings exhibit low roughness (Ra of 5.7 μm), low porosity (0.8%), excellent mechanical properties (Hit = 6.1 GPa, Eit = 155 GPa), and elevated interface toughness (2.4 MPa m1/2).

© 2017 The Author(s).Results of experimental investigations of a new-type generator of an arc water plasma Having a high thermal efficiency close to 100% Are presented This generator represents a system comprising a vortex arc plasma generator In which an electric arc is stabilized by water vapor and a straight-through-flow tubular electric steam generator Such a high effi ciency of the plasma generator system was achieved due to the refi nement of the internal gas dynamics of the plasma generator and the heat and mass transfer in its discharge channel as a result of the improvement of the vortex stabilization and thermal insulation of an arc discharge in it by the specially organized ″instantly permeable″ channel wall cooled by only the working water used for generation of the plasma.

© 2017, Springer Science+Business Media New York.The motion of particles axially injected into the plasma spray process has been studied using a one-dimensional model. The effect of the initial particle velocity and particle diameter on the final particle velocity and temperature was evaluated. The aim of the work is to optimize the spraying process by defining the favorable particle injection velocity, considering a wide range of velocity and temperature of the plasma jet.

© 2016 Elsevier B.V.This work presents a plasma torch able to operate at supersonic regime with axial injection of feedstock. In contrast to commonly used linear scheme, the principal axis of the plasma torch is perpendicular to feedstock injection direction, which is aligned with coming out plasma jet. The plasma torch has slightly ascending current voltage characteristics and fixed arc length. Electrical, thermal and kinetic characteristics outlined from comparison with conventional linear plasma spray torches are intermediate between APS, HVOF and VPS. The plasma torch developed in this work has an elevated arc voltage (370 V) and low arc current (100 A), which contribute to increase the electrode life and decrease the arc voltage relative fluctuation (10%). According to in-flight particle monitoring the CoNiCrAlY particles were sprayed at 500 m/s and temperature of 2400 °C, whereas the 7%YSZ at 491–683 m/s and 2535–2636 °C.

© 2016 American Chemical Society.In this study, the authors have presented a numeric model (NM) for application to naphthalene (C10H8) conversion via ionization reaction in a microwave air plasma torch. The NM has included a pressure-independent enhanced electron energy distribution function (EEDF) and cross-section calculation, enhanced by a new formula of phase shift determination. Based on the validated NM, electron density ne and O2+, O-, C10H8, N2, and O2 particles densities were calculated, as well as the conversion rate of C10H8 molecules was predicted. The predicted results showed that the ionization impact on C10H8 molecules conversion has not exceeded 0.81 × 10-10%. Based on the calculated collision cross-section of each species (O2, N2, and C10H8) of carrier gas, the authors suggested using cubic polynomial approximations of the cross-section curves with R-Square (COD) parameter R2 = 99%. MW power increasing in the range 1.75-20 kW has raised the electron density in the range (0.5-4.5) × 1012 m-3. The maximal effect of electron density decreasing with pressure increasing was simulated at values of MW power greater than 7.5 kW. Herewith, pressure increasing and MW power increasing have not had any significant effect on the average electron energy.

© 2016 American Chemical Society.In this paper, a naphthalene (C10H8) thermal cracking model is presented. The model is based on a simple model that takes into account the microwave (MW) plasma thermal influence on naphthalene cracking, accompanying its steam reforming reactions. The temperature level of 1573 K was established for complete C10H8 cracking at 1.75 kW plasma power. High conversion efficiency of C10H8 is achieved varying the air flow rate in the range of 0.6-1.2 m3/h. The model approximates the characteristics of the considered MW plasma to thermal plasma in local thermodynamic equilibrium (LTE). Experimental data have good agreement with calculated data at the cited region of the air flow rate and power. Conversion efficiency up to 99.36% was obtained.

© 1973-2012 IEEE.Total current-voltage characteristics (CVCs) of a transferred arc plasma torch were determined for the case of oxidative plasma type, steam and air, by the application of the anisotropic analytical model to dc electric arc. The model takes into account the arc radiation reabsorption in the approximation of radiant thermal conductivity and is based on the power function approximation of temperature dependence on plasma electrical conductivity with different exponents along the longitudinal and transversal coordinates. The experimental data generalization for a 50-kW plasma torch was obtained in a simple form of dimensionless expression with a high statistically acceptable level. The electric resistance of arc as a generalized function πdep is mainly affected by convection number of the energy transfer πconv. This generalized characteristic can be used with subsequent application in the design of steam-and air-transferred arc plasma torches at a wide range of dimensionless numbers: πdep between 90 and 932, πconv from 5.16 10-5 to 1.76 × 10-3 , and the Reynolds number from 526 to 2212.

© 2015 IEEE.Thermochemical assessment of the gasification of the biomass waste composed of sugarcane bagasse aiming for practical applications of an electric arc or radio frequency plasma reactors for the syngas production was carried out, considering different gasifying agents and their mixture (steam + air). The analysis of the calculations in the thermodynamic equilibrium shows that steam is the most efficient oxidant. In this case, the predicted optimum regime corresponds to the value of steam-biomass ratio of 0.4 at the temperature 1000 K (at ambient pressure), and for these conditions the maximum value of the energy efficiency is 0.91 and the value of the exergy efficiency is 0.84.

© 2015 IEEE.Gliding arc discharges have been utilized in plasma-assisted combustion processes, among various other applications, due to their chemical properties. In this paper, an ac-powered gliding arc discharge having a reverse vortex flow configuration (tornado) was experimentally studied in air and in air-natural gas mixtures. A new method is proposed for the generalization of power characteristics of this type of discharge, based on similarity theory. The application of this method is demonstrated to be efficient for gliding arc discharges with tornado effect, using dimensional numbers. Regression dependences for discharges in air and in mixtures of air and natural gas were obtained in a form of simple power function equations (using the concept of equivalence ratio), which can be applied for the design of different gliding arc equipments for plasma-assisted combustion and related technologies.

© 2015 by Nova Science Publishers, Inc. All rights reserved.Thermal plasma gasification technologies are the last two decades in commercialization stage for industrial wastes as, municipal solid waste (MSW), ash residues, low grade coals and biomass. These can be used to produce a high calorific syngas (HHV ≥ 20 MJ/kg) at low operating cost. Consequently, the potential market of the plants for Waste-to-Energy plasma gasification will increase during the next period. Joint project of Westinghouse Plasma Corporation and of Geoplasma in Florida USA is an example of efficient facility with middle-scale productivity up to 600 tons/day, for thermal plasma gasification of the solid waste. This chapter presents the assessment of thermal plasma gasification of Brazilian industrial wastes as low grade coal and biomass sugar cane bagasse. Based on the parametric analysis of the air and steam plasma gasification with using thermochemical simulation methods, the results show that the gasification of both feedstock using air as gasifying agent is more efficient on such output parameter as energy efficiency, which is higher at the optimal temperature level of 1250 K, and the ratio of mass flow rates of the feedstock to air up to 0.65 for the bagasse and up to 0.79 for the coal.

© 2014 The Brazilian Society of Mechanical Sciences and Engineering.This paper presents the analysis of ecological and economical availability for using syngas from gasification of biomass waste or other solid fuels into diesel with ICE-based combined cycle (CC). The new approach is proposed to improve the ecological efficiency of the CC system and decrease the cost of electricity which can be produced with electric generator. For optimization of design of the combined system the new diagrams were obtained to determine characteristics of mixed fuel (diesel + syngas) for the engine at varied syngas fuel parameters after the gasifier with steam agent (plasma or other type). Based on these diagrams it is possible to obtain total reducing CO2emission in atmosphere of ~1.5 times in the CC system with biomass gasifier.

In this work, mass spectrometry and optical emission spectroscopy techniques were used to monitor the molecular and atomic neutral species during SF6/CF4, SF6/O2 and CF 4/O2 plasmas generated in a radio-frequency Hollow Cathode Reactive Ion Etching (HCRIE) reactor keeping constant the following operational conditions: total gas flow rate, gas pressure, and discharge power. The investigations were aimed to understand the chemistry behavior of plasmas generated with SF6 and CF4 mixtures or mixed separately with O2. The neutral mass spectrometry analysis showed a high concentration of gas species namely SF5+ (parent specie = SF6), SF3+ (SF4), CF 3+ (CF4) and HF+ (HF) in SF 6/CF4 plasmas, SF5+, SF 3+, O2+ (O2), F + (F) and HF+ in SF6/O2 plasmas and CF3+, O2+, CO2 + (CO2) and HF+ in CF4/O2 plasmas. The presence of other species was observed in quantities lower than 1% of total gas pressure. It was used the actinometry method to monitor the atomic fluorine (F) concentration during discharge operation. Higher density of F was observed in all experiments, varying from (2.8-9.5) × 1019 m-3 in SF6/CF4 plasmas, (0.2-1.7) × 1020 m-3 in SF6/O2 plasmas and (0.06-1.17) × 1020 m-3 in CF4/O 2 plasmas. The addition of CF4 in SF6 plasma reduces monotonically the F concentration when compared with the SF 6/O2 and CF4/O2 plasmas that promotes an increase of F for low O2 concentrations. This effect shows the importance of oxygen species in the dissociative processes of the fluorine-based plasma also for this type of plasma reactor. Moreover, it is highlighted the higher concentrations of HF in gas phase that promotes reactions paths that decrease the F species in gas/plasma phase. © 2014 Elsevier Ltd. All rights reserved.

In this paper, we report on the existence of two electron temperature populations in the low pressure expanding dc plasma jet through the investigation of the spatial evolution of EEDF measured by a single Langmuir probe system. It was observed that for argon the plasma jet is Maxwellian type in all discharge axes. However, when an electronegative gas was inserted/replaced the EEDF turns 'two-temperature' Maxwellian type or is deformed, increasing the high energy electron population. Finally, the effect of gas discharge power shows different behaviors when an electropositive gas was replaced by an electronegative gas. © 2013 IEEE.

In this work the chemistry of CF4 capacitive plasma is studied. For this, experimental measurements were made by mass spectrometry technique which allowed the analysis of neutral species generated during the fragmentation of the source gas by the electrical gas discharge. Additionally, we use global model simulations in order to complement the experimental results, allowing to discern the main chemical processes occurring in the CF4 plasma. The global model developed here considers the main chemical reactions in CF 4 plasma: momentum transfer, vibrational, ionization, dissociation, electron attachment and loss, recombination between charged and neutral species in the gas phase and the reactor walls. © 2013 IEEE.

This chapter presents the investigations about the characteristics of the cathode sheath generated in an argon low-pressure hollow cathode discharge (HCD). The theoretical model for the cathode sheath is considered to be non-collisional. Secondary electrons emitted from the cathode surface are taken into account in the discharge model and their influence on the theoretical sheath potential profile is investigated. The plasma parameters and the floating potential profile along the discharge axis were inferred from the current-voltage characteristics of a single Langmuir probe positioned at the inter-cathode space of the HCD. For a low pressure HCD, typical values of the electron density and electron temperature are ne ≈ 1016 m-3 and Te = 4 eV, respectively. By using the probe data, the floating potential profile was determined to verify the position of the plasma-cathode sheath interface and to promote a qualitative discussion between theoretical and experimental results. © 2013 by Nova Science Publishers, Inc. All rights reserved.

This chapter presents the chemistry studies of low-pressure electrical discharges generated with argon gas. This noble gas is widely used in gas-discharge lamps, as sputtering gas for deposition and/or etching processes, arc welding, among others. Especially, in the semiconductor industry, this gas is present in most of the processing steps of a chip or a micro device. The magnetron sputtering reactor, designed for the deposition of thin films, and the reactive ion etching reactor, designed for etching process of materials at micro/nano scale level are among the most common equipment that use argon-based plasma environment. Moreover, microplasma reactors can currently generate plasmas at pressures of the order of tens of Torr. In order to tune or better understand these plasmas, it is necessary to investigate the chemistry occurring in their generation and during the self-sustained discharge. Experimental diagnostic tools, such as Langmuir probe and optical emission spectroscopy, are used to determine plasma/gas parameters namely electron density, electron temperature, argon ion density, metastable species, gas temperature, etc. In argon discharges, several excited and metastable species are observed, and they affect the physics and chemistry of the medium due to occurrence of multistep and Penning ionization processes. These ionization modes appear commonly when discharge parameters such as pressure or power are increased, but are strongly dependent on the concentration and distribution of the metastable species as well as reactor geometry. Thus, simulation tools are essential to complement the experimental data and explain the discharge mechanisms. In this work, some primarily results of plasma simulations with collisional-radiative model are presented. Moreover, a revised set of collisional-radiative reactions are presented and discussed. Finally, for the case of magnetron sputtering plasma, a brief discussion about the influence of argon gas incorporation in the properties of the grown thin films by this technique is presented. © 2013 by Nova Science Publishers, Inc. All rights reserved.

In this paper, the anisotropic model for the dc electric arc was expanded, which allows the obtaining of power function generalized expressions for calculating the characteristics of the electric discharge into the dc plasma torch channel without using a large number of experimental studies. The model is based on the power law approximation of temperature dependence of the plasma electrical conductivity σ with different exponents along the longitudinal and transversal coordinates. The approximation of the dependence for σ of steam plasma was obtained in simple linear forms σ = 0.221 ΔS and as the power approximation σ = 44.51 ΔS0.484 [where ΔS is increment of thermal conductivity function (TCF)]. The comparison of the obtained dependences with referenced data shows such moderate difference between the calculated approximations for σ of steam and the data of recent publications for this plasma as 15%-25% throughout the vast ranges of the plasma parameters T (temperature) and S (TCF). © 1973-2012 IEEE.

In this work an oxygen asymmetric capacitive radio frequency discharge was investigated with numerical global model and Langmuir Probe to evaluate the behavior of the electron density (ne) and the electron temperature (Te) as a function of input power and gas pressure. The experimental Langmuir probe measurements show that Te increases for pressures below 30 mTorr, which corresponds to low ne, as usual for Reactive Ion Etching type reactor. Moreover, the experimental and simulated electron temperature are in good agreement for gas pressure values above 25 mTorr, because in this case the electron energy distribution function (EEDF) is Maxwellian, according to assumption made in the global model, for the rate coefficient calculation. For electron density the discrepancy is higher for all pressure range, probably because the effect of secondary electron emission that is not considered in our global model simulations. © The Electrochemical Society.

In this work is proposed the automation of a gas injection (mass flow) system in order to generate timemultiplex SF6/CH4 radiofrequency plasma applied for silicon (Si) etching process. The control of the gas injection system is important in order to better control the process anisotropy, i.e., the high-aspect-ratio of mask pattern transfer to substrate surface. In other words, this control allows the attainment of deep Si etching process. Here, the automation of the gas injection system was realized through the interface between a computer and a data acquisition board. The automation software developed allows controlling the gas flow rate switching it on and off during whole process through the use of a square waveform routine, intermittent flow, beyond the conventional condition of a fixed value for gas flow rate, continuous flow. In order to investigate the time-multiplex SF6/CH4 plasma etching of Si, the residual gas analysis was performed. The investigations were made keeping the following process parameters: flow of SF6: 10 sccm, flow of CH4: 6 sccm, 100 W rf power, wave period: 20 sec. It were monitored the partial pressure of SF+ 5 (parent neutral specie: SF6), CH+4 (CH4) and SiF+ 3 (SiF4) species as a function of time for different gas flow switching and duty cycle. The results showed that with the generation of plasma occurs a drastic change in behavior of partial pressures of SF+ 5 and CH+4 species. Moreover, it is evidenced that the interactions between the SF6 and CH4 fragments promotes a high production rate of HF molecule and consequently a decrease of atomic fluorine, mainly when plasma is on. Finally, the behavior of partial pressure of SiF+ 3 specie for alternatively intermittent SF6 and CH4 flow operation shows us that both the etching processes and the deposition of a polymer passivation layer are occurring alternatively, a desirable feature for multi-step etching process. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In this work, a theoretical model for the cathode sheath using experimental data of a low pressure hollow cathode discharge (HCD) is derived considering it to be non-collisional. Secondary electrons emitted from the cathode surface are taken into account on the discharge model and their influence on the theoretical sheath potential profile is investigated. The plasma parameters and the floating potential profile along the discharge axis were inferred from the current-voltage characteristics of a single Langmuir probe positioned at the inter-cathode space of the HCD. For a low pressure HCD, typical values of the electron density and electron temperature are ne ≈ 1016 m-3 and Te = 4 eV, respectively. By using the probe data the floating potential profile was determined to verify the position of the plasma-cathode sheath interface and to promote a qualitative discussion between theoretical and experimental results.

In this work, the surface of silicon etched by sulphur hexafluoride (SF6) and carbon tetrafluoride (CF4) plasma jet, pure or mixed with oxygen gas (O2), was investigated by scanning electron microscope (SEM), optical perfilometry and x-ray photoelectron spectroscopy (XPS). Through these techniques it was possible to investigate the etching rate, etched surface roughness and chemistry on Si surface as a function of O 2 concentration in the SF6+O2 and CF 4+O2 mixture. The results indicate high etching rates of up to 1.0 μm/min obtained for rf power and operating pressure at about 150W and 3.2 mTorr, respectively. The conditions whose etched profile showed higher anisotropy were obtained with CF4. Regarding the chemical analysis of the etched Si surface it was possible to identify elements of the sample surface such as F, C, N and O, as well as, their respective bonds with the Si. ©The Electrochemical Society.

In this work, electrical and optical studies of SF6 and SF 6/O2 plasmas generated in a hollow cathode reactive ion etching reactor were performed using the Langmuir probe and optical emission spectroscopy techniques, respectively. We carried out an investigation aimed at understanding the influence of radio-frequency power, gas pressure and O 2 gas mixing ratio on plasma parameters, namely electron temperature, electron density and electronegativity, and also atomic fluorine density. The results indicate an increase of up to one order of magnitude in electron density and atomic fluorine in the overall gas volume when compared with a conventional reactive ion etching plasma generated under the same operation conditions. © 2010 IOP Publishing Ltd.

The structure of molecular oxygen discharge generated by a capacitively coupled reactor was experimentally investigated using a Langmuir probe and the results were compared to the Particle-inCell (PIC) simulation. The electron energy distribution functions (EEDF) were measured for a pressure range of 10 to 100 mTorr, keeping the power injected into the plasma at about 50 and 200W. The simulation calculated the EEDFs taking into account three main charged particle species presented in oxygen plasma: electron, O- and O 2+. The PIC simulation gives the specie profiles; however is time-consuming for discharges with many species such as oxygen discharges. Despite that, the order of magnitude is the same as the experimental data. The simulation results show that the cold and hot electron temperatures are in a good agreement with the experimental data. Moreover, the results indicate mat the EEDFs measured at lower pressures are bi-Maxwellian distributions. ©The Electrochemical Society.

A volume-averaged global model for inductively coupled carbon tetrafluoride (CF4) plasma was used to study the role of the different processes of production and loss of atomic fluorine on the two different ways to vary the gas pressure: under variable or constant gas flow rate. The results obtained by plasma modeling confirm the behavior of atomic fluorine density with pressure observed in others studies (1-3) when the gas flow rate effect is considered. It's noticeable that the fluorine atoms are created mainly by dissociative processes and lost by recombination to the reactor walls for both gas flow conditions. The relative reaction rate for dissociative processes presents a similar behavior to the fluorine density with the variation of the gas pressure. We also note that the applied power has an important role in reducing the recombination of atomic fluorine to the walls, but does not affect me flow rate effect. ©The Electrochemical Society.

A stationary experiment was performed to study the degradation of carbon-based materials by immersion in a plasma jet. In the experiment, graphite and C/C composite were chosen as the target materials, and the reactive plasma jet was generated by an air plasma torch. For macroscopic study of the material degradation, the sample's mass losses were measured as function of the exposure time under various temperatures on the sample surface. A microscopic analysis was then carried out for the study of microscopic aspects of the erosion of material surface. These experiments showed that the mass loss per unit area is approximately proportional to the exposure time and strongly depends on the temperature of the material surface. The mass erosion rate of graphite was appreciably higher than the C/C composite. The ablation rate in the carbon matrix region in C/C composite was also noticeably higher than that in the fiber region. In addition, the latter varied according to the orientation of fibers relatively to the flow direction. These tests indicated an excellent ablation resistance of the C/C composite, thus being a reliable material for rocket nozzles and heat shielding elements of the protection systems of hypersonic apparatuses from aerodynamic heating.

A formula for quick calculation of thermal characteristics of materials used for thermal protection is proposed. The mode of heating of the sample external surface (subjected to thermal exposure) is approximated by two regions, which differ by corresponding boundary conditions on the heating surface: Tf = cτ (linear growing with time) and Tf = const (with permanent temperature of destruction). That approximation permits to obtain an analytical solution in integral form. In order to simplify and accelerate data treatment, a simple empirical formula is proposed. A contribution of each thermal region is proportional to the regime duration. A good agreement with an analytical solution is shown. © (2010) Trans Tech Publications.

The results of experimental investigations of electrical and thermal characteristics of a vortex plasma torch with a reverse vortex, generated in a hollow blind-end electrode, are presented. It is shown that the reverse vortex essentially improves the performance of the plasma torch and contributes to an increase in the thermal efficiency and enthalpy of the plasma jet. © 2009 IOP Publishing Ltd.

Quartz phenolic composites have been applied to thermal protection systems (TPSs) for reentry vehicles since the late fifties due to their excellent ablative resistance and mechanical performance. TPSs must withstand the aggressive reentry environment, such as atomic oxygen, when submitted to very high temperatures (> 1000° C) and heat flux. The ablative performance of composites is influenced by both base materials and environmental parameters during the ablation process. For TPS systems phenolic resin is usually used as the base matrix due to its ability to form a stable char during decomposition. This char plays an important role in the absorption of the heat generated during the ablation process. During re-entry, parts of the charred matrix can be abrasively removed by shear force due to high pressure and velocity. In this work the ablative and mechanical properties of quartz phenolic composites were evaluated in order to identify the range of properties suitable for the use of these materials as thermal protection systems for space vehicles. Quartz fabric 2 having an areal weight of 680 g/m2 and a resole-type phenolic resin were used to prepare the composites. The resin has a viscosity of 165 MPa at 20°C. The prepreg material was cured by heating under pressure of 100 bar in a mold. The resin content of the prepreg obtained was about 50 per cent. The mechanical properties evaluated were, tensile, shear and flexural strength. The results obtained showed that this material has average values of 38.5 MPa, 52 MPa and 85 MPa for tensile, shear and flexural strength, respectively. The ablative tests were carried out in a high-energy air plasma in ambient atmosphere and the mass losses were measured for different exposure time.

In this work the applicability of a low pressure sulphur hexafluoride (SF6) plasma jet for silicon etching was investigated by optical emission spectroscopy (OES) technique. Through the use of actinometry method the density of atomic fluorine was obtained as a function of process parameters namely radio-frequency (rf) power, axial magnetic field, SF6 gas pressure and flow rate, and O2 concentration in the SF 6+O2 mixture. The results indicate large fluorine concentrations (>10% in overall plasma volume) for the conditions studied. To confirm the applicability of these results for microelectronic material processing, we performed the etching of masked silicon (Si) substrates under some optimum process conditions. Etch rates of up to 1.2 μm/min were obtained for rf power of about 150W and operating pressures about 3.1 mTorr. These values of etching rates are comparable with those obtained in inductively coupled plasma (ICP) systems operating at similar process conditions. © The Electrochemical Society.

An arc-heated experimental setup for producing hypersonic plasma jet developed in ITA is presented. Setup permits gas-dynamic control of enthalpy of plasma jet in addition to common control of the regimes of plasma heater. This allows variation of the main parameters including enthalpy of plasma jet within wider range than during changing only the regime of plasma heater. In addition, this allows to adjust the necessary parameters of vacuum system to the regimes of operation of the plasma heater. Method is based on the controlled outflow upstream the nozzle of the part of vortex flow from the colder boundary layer at the walls of arc stabilizing channel into atmosphere with minimal heating. The facility and measurement techniques are described. The facility during testing is capable of producing Mach numbers up to 5, enthalpy from 1 to 13 MJ/kg, heat fluxes up to 3 MWm-2 and stagnation pressures in the range of 0.01 to 1 atm. By considering the levels of heat fluxes, enthalpy and stagnation pressure, the setup is able of simulating conditions of re-entry of the Brazilian satellite SARA (satellite of atmospheric re-entry) for the most crucial part of reentry trajectory, approximately from 42 to 34 km of altitude.

This paper presents the initial studies carried out in materials used as thermal protection systems (TPS) in reentry atmospheric vehicles (e.g reusable satellites) and in rocket nozzles. In the experiment, graphite and C/C composite are chosen as the target materials. For macroscopic aspect evaluation of the material degradation, the mass losses are measured against the exposure time by changing the material surface temperature. From the microscopic aspect, the eroded surfaces of materials by reactive air plasma are observed with a scanning electron microscope (SEM).

Thick composite materials are used as liners in rocket nozzles, due to its structural strength, low density and very high thermal insulation property. Carbon fiber and silica fiber based composite structures are used in the nozzles of large solid rocket motors. Since these are multiple layer structures, the commonly observed defects are delaminations, lack of adhesive material, porosity between layers, etc. In this work quartz-phenolic resin based ablative composites have been characterized, with the intention to evaluate composite materials for thermal protection systems. The study used as parameters the resin concentration in the composite and the characteristics of the quartz fabric. These materials had been processed with different phenolic resin concentrations (20, 32 and 42%) using woven and chopped fabric configurations. The option for studying different configurations of fabric and concentrations of resin lies in the possibility to solve problems of delamination and molding in thermal protection systems of large dimensions and complex formats. Therefore we focussed our interest in the evaluation of the effects of the characteristics of woven mesh quartz fibers (weaved with aligned fibers in a single plan) and chopped mesh quartz fibers (with random domains of orientation of fibers) over their ablative, thermal and microstructural properties. The processed materials had been submitted to a non transferred arc plasma torch operating in air with a flow of 5.4. 10-3 kg/s and 30 kW power transferred to the jet, that corresponds to an enthalpy of ∼5.5 of MJ/kg. The samples had been exposed to thermal flows between 0.5 and 1.7 MW/m2 during 30 seconds, and we evaluated the loss of specific mass of the samples. To study its microscopic aspects, the samples were analyzed, after the ablation process, with a scanning electron microscope (SEM). The thermal insulation properties of the samples were evaluated by measuring the temperature at some internal positions in the samples using thermocouples inserted at distances of 2, 4 and 8mm of the sample surface, where the temperature was measured using an optical pyrometer. The diffusivity of the samples was measured in a graphite furnace "Flashline 5000" from room temperature to 1500° C.

This paper describes the effect of the SF 6 gas residence time on the morphology of silicon (1 0 0) samples etched in a reactive ion etching system. Profilometry and atomic force microscopy techniques were used to characterize the etching process focusing attention on the evolution of the surface morphology. Under the condition of variable pressure and gas flow rate, the decrease of the residence time leads to an increase of the silicon etch rate concomitantly with an increase of the surface roughness. Contrary fact is observed when the gas flow is fixed and the pressure is varied. Here, the increasing of residence time leads to a constant increase of silicon etch rate with small variations in final surface roughness. To better understanding this resident time effect, mass spectrometry analyses were realized during the discharge for both gas flow conditions. © 2008 Elsevier B.V. All rights reserved.

Amorphous and crystalline AlN thin films were deposited on Si (100) substrates by off-axis hollow cathode magnetron technique. The evolution of the crystalline orientation and the morphology of AlN thin films have been investigated depending on the nitrogen concentration. It has been demonstrated by using a combination of mass spectrometry, X-ray diffraction and atomic force microscopy techniques, that the film crystallinity and surface roughness are related with the nitrogen concentration. The results show that the monitoring of Al+ and AlN+ species by mass spectrometry proved to be an important new method to prescribe the plasma conditions for growing amorphous or crystalline films. © 2006 Elsevier B.V. All rights reserved.

A new de hollow cathode plasma source has been assembled whith a conventional planar magnetron cathode used together with another plane cathode plate to form a hollow cathode cavity. The system comprises two cathode plates of aluminium separated by a distance d, one of them acting as target of the magnetron cathode, the other being an ordinary plate. The discharge anode is a metallic flange of the vacuum chamber. This leads to enhanced ionization in the cathode cavity region and enables the discharge to operate at significantly lower pressures than for a typical planar magnetron configuration. As a consequence, sputtered atoms can reach a substrate with minimum energy loss due to collisions with filling gas atoms. The discharge gas was a mixture of argon and nitrogen. AlN thin films were grown on silicon substrates, at ambient temperature, and characterized with respect to the structure and morphology by XRD and AFM analyses respectively. The structure and roughness of the AlN films were studied as a function of the deposition parameters.

Sized PAN-based carbon fibers were treated with hydrochloric and nitric acids, as well as argon and oxygen cold plasmas, and the changes on their surfaces evaluated. The physicochemical properties and morphological changes were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), tensile strength tests and Raman spectroscopy. The nitric acid treatment was found to cause the most significant chemical changes on the carbon fiber surface, introducing the largest number of chemical groups and augmenting the roughness. The oxygen plasma treatments caused ablation of the carbon fiber surface, removing carbon atoms such as CO and CO2 molecules. In addition, the argon plasma treatment eliminated defects on the fiber surface, reducing the size of critical flaws and thus increasing the fiber's tensile strength.

The electrical breakdown has been investigated for low-pressure argon and nitrogen discharges under the influence of an external longitudinal magnetic field. Plane-parallel aluminum electrodes (5 cm diameter) separated by a variable distance d (4.0 cm < d < 11.0 cm) were sustained with a dc voltage (0 < V < 1 kV). A Helmholtz coil was used to produce an uniform magnetic field(B) parallel to the discharge axis. Paschen curves were obtained and the secondary electron emission coefficient (γ), the first Townsend ionization coefficient (α) and the ionization efficiency(η), were plotted with respect to the variation of the reduced field (E/P). To observe the effect of the magnetic field these curves were plotted for fixed values of B=0 and B=350 Gauss. As consequence of the longitudinal magnetic field, the free paths of the electrons in the Townsend discharge are lengthened and their lateral diffusion is reduced, thus reducing electron losses to the walls. The data presented in this paper give a quantitative description of the B-field effect on the Townsend's coefficients and overall it is concluded that the DC electrical breakdown of the gases is facilitated if a longitudinal magnetic field is applied along the discharge axis.

Experimental studies of the formation of electrostatic double layers (DLs) and electron-holes (e-holes) are reported. The measurements were performed in the positive column of a mercury arc discharge operating in the low-pressure range of (2.0-14.0) × 10-2 Pa with current density in the range of (3.0-8.0) × 103 A m-2. Stable and unstable modes of the discharge were identified as the current was gradually increased, keeping constant the vapour pressure. The discharge remains stable until a critical current from which a slight increase of the current leads to an unstable regime characterized by high discharge impedance and strong oscillations. This mode ceased after a DL was formed in the plasma column. To induce the DL formation and to transport it smoothly along the discharge column, a low intensity B -field (7-10) × 10-3 T produced by a movable single coil was used. The fi-field locally increases the electron current density and makes the DL form at the centre of the magnetic constriction where it remained at rest. Electrostatic potential structures compatible with ordinary DLs and multiple-layers could be formed in the plasma column by dealing with the combined effects of the operational parameters of the discharge. It is noticeable that a pure e-hole, which is a symmetric triple-layer having a bell shape potential profile, could easily be formed by means of this experimental technique. A partial kinetic description, based on the space charge structure derived from an experimental e-hole, is presented in order to infer the charged particle populations that could contribute to the space charge of the e-hole. Evidence is shown that strong e-hole formation might be driven by an ion beam, therefore it could not be formed in isolation since its formation requires a nearby ion accelerating potential structure. Probe measurements of the plasma properties, at various radial positions of the stable positive column, are also presented. In the stable mode, prior to current limitation, the probe data reveal a substantial radial decrease of the electron drift velocity. This result calls for a review of the free fall theories of low pressure plasma columns to take into account this non-uniformity of the electron drift velocity.

A theoretical and experimental study was developed about the applicability of a double probe system consisting of two directional Langmuir probes, both probes being located separately in a plasma column. The current-voltage characteristic of the double probe was obtained considering a plasma with a drifting maxwellian electron velocity distribution function and stationary ion background. In deriving the characteristic of the double probe, the plasma parameters, namely, electron temperature (Te), electron density (Ne), electron drift velocity (Vde) and plasma potential (Vp) are assumed to be non-uniform. The double probe characteristic is also dependent on the angle between the axial direction of the electron drift and the normal to the collecting area of the probe. Each probe can be rotated such that this angle can be varied between zero and 180 degrees. Various probe characteristics were simulated using plasma parameters obtained by independent single probe measurements in the positive column of a low-pressure arc discharge in mercury vapor. Typical parameters of the positive column, used in the simulation, are: Te = 5 eV, Ne = 1017 m-3, vde = 8x105 ms -1. Experimental characteristics of the double probe were obtained and compared with the simulated results, showing good agreement. It is concluded that this directional probe system can be a reliable diagnostic tool especially for studies of non-uniform plasmas.

The present research has been conducted aiming the study of mechanical characteristic improvement of Ti6Al4V alloy surface. The proposed process is based on an ion nitriding method performed in a low intensity plasma jet reactor. An objective of the study is to enlarge the applicability of this alloy in several industrial areas, mainly foccusing the biomedical applications. The reactor of low intensity nitrogen plasma jet is a system governed by principle of gas expansion through a constriction orifice. The whole device is constituted by a plasma source chamber maintained at relatively high pressure and a vacuum chamber where the nitriding is processed, both chambers being separated by a wall having one central orifice. The D.C. electric discharge is run between a cathode located in the source chamber and the wall of the processing chamber playing the role of anode. The reactive plasma jet of nitrogen emerges from the constriction and expands into the vacuum chamber, where the sample is placed to intercept the plasma jet. The nitrided surfaces of Ti6Al4V samples are characterized by means of structural and physical analyses to formulate the correlations between surface characteristics and process parameters. © 2002 Elsevier Science Ltd. All rights reserved.