Plasma Chemistry and Plasma Processing (v.33, #1)
Streamer-Like Electrical Discharges in Water: Part I. Fundamental Mechanisms by Ravindra P. Joshi; Selma Mededovic Thagard (1-15).
Electrical discharge plasma formed in liquid water is under intensive investigation for many possible applications in biomedical, environmental and chemical engineering as well as for general scientific issues in plasma chemistry and other engineering applications. The subject of pulsed breakdown of water has additionally begun to assume importance due to growing interest in decontamination, purification of water containing chemical impurities and industrial sludge, and also in the emerging area of bio-electrics. This review paper focuses on the plasma physics (Part I) and chemistry of electrical discharges in liquid water and the chemical effects of plasmas on the degradation of organic molecules (Part II). This part discusses dielectric liquid breakdown and its mechanisms, streamer propagation and the effect of electrode polarity on streamer dynamics.
Keywords: Electrical discharge; Breakdown; Plasma; Water
Streamer-Like Electrical Discharges in Water: Part II. Environmental Applications by Ravindra P. Joshi; Selma Mededovic Thagard (17-49).
Plasmas formed in aqueous solutions dissociate water into highly oxidative and reductive radicals which can induce chemical changes in compounds present in the bulk liquid. As a result, electrical discharge plasmas have acquired significant importance in drinking and wastewater treatment. Part II of this manuscript reviews the chemistry of electrical discharges in liquid water and the chemical effects of plasmas on the degradation of organic molecules. Due to a wide range of work done with plasmas in water, this review is limited to streamer-like electrical discharges directly in water excluding the discharges with gases bubbling through the plasma zone and the presence of additives. The goal was to summarize and present major findings on the fundamental mechanisms related to the production of radicals in the plasma as well as to describe chemical pathways for the degradation of different groups of molecules.
Keywords: Electrical discharge; Organic compounds; Plasma chemistry; Water
Pulsed Corona Discharge for Degradation of Methylene Blue in Water by Monica Magureanu; Corina Bradu; Daniela Piroi; Nicolae Bogdan Mandache; Vasile Parvulescu (51-64).
A pulsed corona discharge in multiwire-plate geometry, generated above water was studied for the removal of organic compounds in liquids. The degradation of methylene blue (MB) and the formation of hydrogen peroxide (H2O2) were investigated. The MB solution was rapidly decolorized, evidencing the degradation of the dye after approximately 10 min plasma treatment. Nitrate, formate, sulphate and chlorine ions have been detected in the treated solution, explaining partly the change in the solution properties with plasma exposure, i.e. increase of electrical conductivity and decrease of pH. It was found that the concentration of H2O2 generated in water increased with plasma exposure time, reaching 200 mg/L after 30 min treatment. In the MB solution less hydrogen peroxide was detected, suggesting reactions with the dye and its degradation products. The addition of FeCl2 catalyst had a slight favorable effect on methylene blue degradation due to Fenton’s reaction. It was observed that MB and H2O2 concentrations continue to decrease after the plasma treatment was stopped, suggesting that active species which accumulate in the solution may react post-plasma with methylene blue and its degradation products.
Keywords: Water treatment; Non-thermal plasma; Pulsed corona discharge; Organic dyes
Adsorption of Acid Orange II from Aqueous Solution by Plasma Modified Activated Carbon Fibers by Du ChangMing; Huang DongWei; Li HongXia; Xiao MuDan; Wang Kui; Zhang Lu; Li ZhiYi; Chen TengFei; Mo JianMin; Gao Dong; Huang YuHao; Liu ShangKun; Yu Liao; Zhang ChuangRong (65-82).
As a main composition of dye wastewater, organic pollutant which has a negative effect on the environment can be effectively removed by active carbon adsorption. In the present work, activated carbon fiber (ACF) was modified by a novel modification technology, gilding arc discharge, while its adsorption capacity was studied with the acid orange II (AO II) solution selected as the target wastewater. Several factors, such as air flow rate, distance between samples and the discharge area, pH of the solution and plasma treating time, were investigated with respect to their effects on properties of the plasma-treated ACF, in terms of texture characteristic, surface chemical compositions and adsorption capacities. The results showed that the specific surface area and pore volume of ACF decreased after the plasma treatment, while the amounts of oxygen-containing functional groups on the surface of ACF increased compared with the raw ACF. Moreover, it was observed that the adsorption capacity of the modified ACF was improved by nearly 20.9 %, which was beneficial to the industrial application.
Keywords: Gliding arc discharge (GAD); Plasma; Acid orange II (AO II); Activated carbon fibers (ACF); Modification
High Power DC Diaphragm Discharge Excited in a Vapor Bubble for the Treatment of Water by P. Lukes; M. Clupek; V. Babicky; E. Spetlikova; I. Sisrova; E. Marsalkova; B. Marsalek (83-95).
Novel apparatus for the generation of underwater plasma based on DC diaphragm discharge excited in a vapor bubble has been developed for decontamination and disinfection of conductive water. The apparatus allows deposition of relatively high applied power into the discharge (order of kW) and the treatment of a relatively large volume of liquid (order of L/min). The apparatus is operated at the quasi-pulse regime with self-terminating discharge pulses (with a repetition rate of 15–20 Hz) generated upon the formation of the vapor bubble inside the diaphragm (capillary) and its subsequent breakdown. The effects of input power, solution conductivity and the method of liquid flow through the reactor on the plasmachemical yield of H2O2 production and degradation of phenol have been determined. The biocidal effects of the apparatus were evaluated on inactivation of bacteria E. coli and E. faecalis suspended in aqueous NaCl solutions and on growth inhibition of the cyanobacterium Planktothrix sp. in natural lake water. The apparatus proved to be capable of efficiently reducing biological contamination in water, especially when operated in the plug-flow regime (up to a 5-log reduction in bacteria after 3 passes through the reactor). In the case of cyanobacteria, the growth inhibition further proceeded after exposure to the discharge and one pass of the biomass through the reactor was sufficient to reduce the algae in the water.
Keywords: Diaphragm discharge; Water; Hydrogen peroxide; Phenol; Bacteria; Algae
Removal of Model Pollutants in Aqueous Solution by Gliding Arc Discharge: Determination of Removal Mechanisms. Part I: Experimental Study by D. Iya-Sou; S. Laminsi; S. Cavadias; S. Ognier (97-113).
The respective roles of short and long-life oxidant species in the degradation of model organic pollutants in water have been investigated in a gas–liquid gliding arc plasma reactor. Three different model pollutants were treated in two configurations: direct discharge mode and spatial post discharge mode. In each case the pollutants were classified according to their ease of removal, from easier to more difficult to remove. The results were as follows: phenol >> 1-heptanol >> pCBA. The removal mechanisms also are different depending on the characteristics of the pollutant treated. Phenol (100 % of phenol was removed for energy density = 1.20 × 105 J/L) was supposed to react strongly with NO2° radicals produced by the dissociation of N2O4 in liquid phase. The degradation of 1-heptanol would proceed by desorption of the liquid phase to the gas phase, where oxidation occurs due to the plasma active short-lived species. In the case of pCBA, oxidation occurs in the liquid solution, but the degradation is low because of its low reactivity with species such as ozone and °NO2 and insufficient production of OH° radicals in the solution.
Keywords: Non-thermal plasma; Electrical discharge; Gliding arc discharge; Water treatment; Mass transfer
Homogeneous Dielectric Barrier Discharge Reactor with Two L-Shaped Electrodes Operating at Atmospheric Pressure by M. Hur; W. S. Kang; Y. H. Song (115-129).
Homogeneous non-thermal plasma at atmospheric pressure is highly effective for surface treatment of various polymeric substrates. We propose a dielectric barrier discharge (DBD) reactor consisting of two back-to-back L-shaped electrodes, driven by bipolar voltage pulses of opposite polarity. This structure and driving scheme allow the discharge to be initiated earlier inside the reactor than outside the reactor. The plasma formed inside the reactor is ejected through a slit and moves toward the substrate. As a result, an abundance of electrons is provided to the outside region of the reactor at its breakdown stage. These electrons play a role in suppressing the filamentary mode, and hence, homogeneous discharge in He and Ar can be achieved under an open air configuration. The discharge characteristics inside and outside the reactor are analyzed by using the discharge current and the temporal evolution of emission intensity, respectively. The importance of seed electrons available at the gas breakdown stage in achieving a homogeneous discharge is discussed together with the differences between the discharge characteristics of helium and argon gases.
Keywords: Homogeneous dielectric barrier discharge; Atmospheric-pressure plasma; Surface treatment; Seed electrons
Plasma Chemical and Electrical Modeling of a Dielectric Barrier Discharge in Kr–Cl2 Gas Mixtures by A. Belasri; N. Larbi Daho Bachir; Z. Harrache (131-146).
This paper reports the study of the Kr–Cl2 plasma chemistry in terms of the homogenous model of a dielectric barrier discharge and for two kinds of the applied voltage excitation shape. The effect of Cl2 concentration in the gas mixture, as well as gas pressure and power frequency on the discharge efficiency and the 222 nm photon generation, under typical experimental operating conditions, have been investigated and discussed. Calculations suggest that the overall conversion efficiency from electrical energy to ultraviolet emission in the lamp is in the range of 4.4–12 %, and it will be very affected at high chlorine percentage (>1 %) and high gas pressure (>200 Torr). A comparison between the sinusoidal and the burst excitation waveforms reveals that the burst excitation method provides an enhanced light source performance compared to the sinusoidal wave.
Keywords: Modeling; DBDs; Excimer lamp; Kr–Cl2 mixtures; Kinetic scheme; Efficiency
Low-Pressure Plasma Polymerization of Acetylene–Ammonia Mixtures for Biomedical Applications by Angel Contreras-García; Michael R. Wertheimer (147-163).
Past research in this laboratory has focused on the deposition of nitrogen- (N)-rich thin organic coatings for biomedical applications; among usual fabrication methods are plasma polymerization (PP) at low- (“L”) or atmospheric- (high-, “H”)-pressure. In the “L” case, ethylene (“E”, C2H4)/ammonia (NH3) feed-gas mixtures with different flow ratios, R, are used, by which the nitrogen- and primary amine concentrations, [N] and [–NH2], respectively, can be reproducibly controlled. The generic symbol we use for that family of deposits is L-PPE:N. In the present research, we used acetylene (“A”, C2H2) as the hydrocarbon feed, because our earlier experience with “H”-type materials (H-PPE:N and H-PPA:N) revealed striking differences in physico-chemical (e.g. [N] and [–NH2], and solubility) characteristics, which are important for applications. We now find that such differences also exist between the L-PPA:N and L-PPE:N families of coatings. This is attributed to the fundamentally different bonding structures of “A” and “E”, namely CH≡CH and CH2=CH2; the former leads to more highly cross-linked, [NH2]-leaner deposits, as was also noted for the “H”-type deposits mentioned above.
Keywords: Plasma polymerization; Acetylene–ammonia; Surface chemistry; Ageing; Solubility
Surface Modification of Poly-ε-Caprolactone with an Atmospheric Pressure Plasma Jet by N. De Geyter; A. Sarani; T. Jacobs; A. Yu. Nikiforov; T. Desmet; P. Dubruel (165-175).
In this work, poly-ε-caprolactone samples are modified by an atmospheric pressure plasma jet in pure argon and argon/water vapour mixtures. In a first part of the paper, the chemical species present in the plasma jet are identified by optical emission spectroscopy and it was found that plasmas generated in argon/0.05 % water vapour mixtures show the highest emission intensity of OH (A–X) at 308 nm. In a subsequent section, plasma jet surface treatments in argon and argon/water vapour mixtures have been investigated using contact angle measurements and X-ray photoelectron spectroscopy. The polymer samples modified with the plasma jet show a significant decrease in water contact angle due to the incorporation of oxygen-containing groups, such as C–O, C=O and O–C=O. The most efficient oxygen inclusion was however found when 0.05 % of water vapour is added to the argon feeding gas, which correlates with the highest intensity of OH (X) radicals. By optimizing the OH (X) radical yield in the plasma jet, the highest polymer modification efficiency can thus be obtained.
Keywords: Atmospheric pressure plasma jet; Poly-ε-caprolactone; Water vapour; Contact angle; X-ray photoelectron spectroscopy; Optical emission spectroscopy
Applications of Plasma Technology in Development of Superhydrophobic Surfaces by Reza Jafari; Siavash Asadollahi; Masoud Farzaneh (177-200).
Superhydrophobic surfaces, originally inspired by nature, have gained a lot of interest in the past few decades. Superhydrophobicity is a term attributed to the low adhesion of water droplets on a surface, leading to water contact angles higher than 150°. Due to their vast variety of possible applications, ranging from biotechnology and textile industry to power network management and anti-fouling surfaces, many methods have been utilized to develop superhydrophobic surfaces. Among these methods, plasma technology has proved to be a very promising approach. Plasma technology takes advantage of highly reactive plasma species to modify the functionality of various substrates. It is one of the most common surface treatment technologies which is widely being used for surface activation, cleaning, adhesion improvement, anti-corrosion coatings and biomedical coatings. In this paper, recent advances in the applications of plasma technology in the development of superhydrophobic surfaces are discussed. At first, a brief introduction to the concept of superhydrophobicity and plasma is presented, then plasma-based techniques are divided into three main categories and studied as to their applications in development of superhydrophobic surfaces.
Keywords: Plasma polymerization; Etching; Sputtering; Superhydrophobic surfaces; Thin films; Nano-structured surfaces
Deposition of Gold Nanoparticles on Polypropylene Nonwoven Pretreated by Dielectric Barrier Discharge and Diffuse Coplanar Surface Barrier Discharge by Nina Radić; Bratislav M. Obradović; Mirjana Kostić; Biljana Dojčinović; Markéta Hudcová; Milorad M. Kuraica; Mirko Černák (201-218).
The aim of this study was to examine and compare the potentials of two different ambient air plasma treatments: volume dielectric barrier discharge and diffuse coplanar surface barrier discharge, for the activation of polypropylene (PP) nonwovens surface. This was done in order to enhance the deposition of gold nanoparticles (AuNPs) onto PP surface. AuNPs were attached onto PP surface from colloidal solution prepared without stabilizers. Scanning electron microscopy, atomic force microscopy, attenuated total reflection-Fourier transform infrared spectroscopy, water absorption, and AuNPs uptake were used to assess the surface changes due to the plasma treatment, and to evaluate the durability of the achieved treatment effects. Finally, as a very important aspiration of the research, antibacterial activity of AuNPs loaded PP nonwovens against pathogens Staphylococcus aureus and Escherichia coli was evaluated in vitro. The plasma modified PP nonwovens have highly improved wetting and sorption properties. The PP nonwovens loaded with 17–62 mg/kg AuNPs exhibit antibacterial activity against tested pathogens. Surprisingly, this activity was enhanced by the first sample rinsing.
Keywords: Polypropylene; Plasma modification; Dielectric barrier discharge; Gold nanoparticles; Antimicrobial activity
Synthesis and Swelling Behaviors of P(AMPS-co-AAc) Superabsorbent Hydrogel Produced by Glow-Discharge Electrolysis Plasma by Jie Yu; Yuanpei Pan; Quanfang Lu; Wu Yang; Jinzhang Gao; Yan Li (219-235).
Highly swelling P(2-acrylamido-2-methyl-1-propanesulfonic acid- co-acrylic acid) (P(AMPS-co-AAc)) superabsorbent hydrogel was synthesized in aqueous solution by a simple one-step using glow-discharge electrolysis plasma technique, in which N,N’-methylenebisacrylamide was used as a crosslinking agent. The structure, thermal stability and morphology of P(AMPS-co-AAc) superabsorbent hydrogel were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. A mechanism for synthesis of P(AMPS-co-AAc) superabsorbent hydrogel was proposed. The reaction parameters affecting the equilibrium swelling (i.e., discharge voltage, discharge time, macroscopic temperature of the liquid phase, mass ratio of AMPS to AAc, and content of crosslinker) were systematically optimized to achieve a superabsorbent hydrogel with a maximum swelling capacity. The hydrogel formed which absorbed about 1,685 g H2O/g dry hydrogel of the optimized product was used to study the influence of various pH values and salts solutions (NaCl, KCl, MgCl2, and CaCl2) on the equilibrium swelling. In addition, swelling kinetics in distilled water and on–off switching behavior were preliminarily investigated. The results showed that superabsorbent hydrogel was responsive to the pH and salts.
Keywords: Glow-discharge electrolysis plasma (GDEP); Acrylic acid (AAc); 2-Acrylamido-2-methyl-1-propanesulfonic acid (AMPS); Superabsorbent hydrogel; Swelling behavior
Deposition of π-Conjugated Polycyanate Ester Thin Films and Their Dielectric Properties by Xiong-Yan Zhao; Ming-Zhu Wang (237-247).
Two kinds of novel π-conjugated polycyanate esters, namely the plasma-polymerized 4-methoxyphenol cyanate ester (PPMPCE) and the plasma-polymerized 4-phenylphenol cyanate ester (PPPPCE), were successfully prepared by plasma polymerization for the first time. The structure and compositions of both plasma polycyanate esters were investigated by Fourier Transform Infrared (FT-IR), X-ray Photoelectron Spectroscopy (XPS) and UV–Visible Absorption Spectra (UV–Vis). The results show that extensively conjugated C=N double bonds were formed in the plasma-deposited cyanate ester thin films, the plasma polymerization of both monomers proceeded mainly via the opening of π-bonds of the O–C≡N functional groups which are further on being formed into a large π-conjugated system, this unique process is noticeably different from the conventional thermal polymerization reaction of cyanate ester monomers. Further dielectric measurement shows that PPPPCE thin film gives a lower dielectric constant comparing to that of the PPMPCE film, and the dielectric constant of both plasma deposited thin films decreased with an increase in measurement frequency.
Keywords: Plasma deposition; Cyanate ester; Dielectric property; Dielectric constant; Thin films
Mapping Plasma Chemistry in Hydrocarbon Fuel Processing Processes by Dae Hoon Lee; Kwan-Tae Kim; Young-Hoon Song; Woo Suk Kang; Sungkwon Jo (249-269).
A role of plasma chemistry and relative contribution to the overall reaction is explained. Considering relative contribution of thermo chemistry and plasma chemistry, reactions are classified into three different regimes. The way plasma affects kinetic pathways differs according to these regimes. This review introduces how plasma chemistry affects overall reaction and determines kinetic pathways based on the classified regimes. Among these three regimes, In the case of weakly exothermic reactions, discernible role of plasma chemistry is most confusing because plasma chemistry provokes both electron and excited species induced activation and thermal activation that are competitive and interactive. This review introduces the way how to understand the discern plasma chemistry in these reactions. There is possibility of misleading in evaluation of thermal efficiency of process if the concept of warm plasma is not defined correctly. Efficiency and process design also should be based on the classification of the regimes and this review can provide the insight on the understanding specific role and function of plasma chemistry in diverse plasma applied processes.
Keywords: Plasma chemistry; Kinetic path; Warm plasma; Hydrocarbon
Study of the Production of Hydrogen and Light Hydrocarbons by Spark Discharges in Diesel, Kerosene, Gasoline, and Methane by Muhammad Arif Malik; David Hughes; Areej Malik; Shu Xiao; Karl H. Schoenbach (271-279).
Reforming liquid fuels into hydrogen and light hydrocarbons is desirable for improving the combustion characteristics of the fuels and the production of reducing agents for applications such as the removal of nitrogen oxides. In this study, diesel, kerosene, gasoline and methane were reformed by spark discharges between needle and plate electrodes at room temperature and atmospheric pressure. The gaseous products from liquid fuels comprised 65–70 % hydrogen and 30–35 % light hydrocarbons having two carbon atoms per molecule (i.e., C2s), or three carbon atoms per molecule (i.e., C3s). The product gases were 90 % hydrogen and 10 % C2s in the case of methane reforming. The energy efficiency for the production of gaseous products was highest in the case of gasoline at 3.8 mol/kWh, followed by kerosene, diesel and methane at 3.2, 3.0, and 2.4 mol/kWh, respectively. These results were found to be comparable to those reported by others for the reforming of pure hydrocarbons by plasmas in liquids. The liquid fuels turned black due to the formation of carbonaceous products, some of which could be filtered out as solid carbon particles, but others remained dissolved and imparted color to the treated liquid.
Keywords: Spark discharges; Reforming; Diesel; Kerosene; Gasoline; Methane; Non-equilibrium plasma; Hydrogen
Experimental Investigation of Plasma Oxidization of Diesel Particulate Matter by Xiujuan Tang; Haiquan Lu; Lili Lin; Shuiliang Yao (281-292).
Particulate matter (PM) from diesel vehicles is harmful to humans and should be removed from the exhaust gases before its emission into the atmosphere. Plasma PM oxidation is an advanced method to be used for oxidative PM removal. Factors influencing plasma PM oxidation include gas temperature, gas composition, PM amount, the geometry of plasma reactors. The PM oxidation in atmospheric air discharges was carried out using a pulsed dielectric barrier discharge reactor at temperatures of 100, 150, and 200 °C. It was found that PM is oxidized to CO and CO2. CO2/CO concentration ratio is a function of PM amount in the discharge space. PM removal efficiency (PM amount oxidized per kWh energy injection) increased with increasing air temperature and PM amount in the discharge space. Water promotes PM oxidation, which suggested that oxygen atoms produced in the discharge space react with water to yield hydroxyl free radicals that are of more reactivity than oxygen atoms. The activation energy of plasma PM oxidation was kinetically calculated to be 15.4 kJ/mol.
Keywords: Particulate matter; Oxidation; Plasma; DBD; Activation energy
Degradation of PCDD/Fs in Fly Ash by Vortex-shaped Gliding Arc Plasma by Yong Ren; Xiaodong Li; Liang Yu; Kui Cheng; Jianhua Yan; Changming Du (293-305).
PCDD/Fs in fly ash from municipal solid waste incinerators (MSWIs) can be decomposed in non-thermal plasma, more in particular in a vortex-shaped gliding arc. Typical operating conditions are 10 kV voltage, 40 kΩB external current-limited resistor, 11 L/min tangential gas and 2 L/min axial carrier gas flow rates. Degradation efficiencies of PCDD/Fs are respectively 54.9, 61.7 and 66.8 % on mass basis and 60.7, 73.3 and 70.1 % on toxicity basis under N2, air and O2 condition. After treatment the morphology of fly ash has changed: needle-shaped crystals increasing, pores and fragments appearing and high-temperature melting showing which is leaded by direct contact with high-temperature core of arc. The results are explained tentatively by the creation of reactive intermediates leading to dechlorination and oxidation of PCDD/Fs and finally producing end-products such as CO2, CO, HCl and CH4.
Keywords: Vortex-shaped gliding arc plasma; PCDD/Fs; Fly ash; Degradation
Characteristics and Analysis of the Mechanism of NO Removal in Dielectric Barrier Discharge Plasma by Hydrocarbons at Varying Temperatures by Tao Wang; Bao-Min Sun; Hai-Ping Xiao (307-322).
Theoretical analysis of the electron energy distribution function by the Boltzmann equation and experimental investigations into the effect of hydrocarbons (methane, acetylene and ethylene) on NO removal efficiency are presented at varying temperatures. The experiments were carried out using dielectric barrier discharge plasmas at 298, 363 and 403 K, respectively. Ethylene greatly enhanced NO conversion because of its stronger affinity for the O radical. NO conversion in the presence of methane and acetylene was much lower than with ethylene at all temperatures. With an increase in temperature, E/N increased, the molecular ionization strengthened and the electron mean energy increased, resulting in more active species generated through ionizing and exciting reactions at the same energy density. High-energy electrons accelerated the decomposition rate of hydrocarbons, and the rate constants of some major reactions were increased, producing more strong oxidizing radicals (HO2). Therefore, NO removal efficiency was increased when the temperature was higher.
Keywords: Dielectric barrier discharge; Boltzmann equation; NO removal; Temperature; Hydrocarbons
Hydrocarbon Assisted NO Oxidation with Non-thermal Plasma in Simulated Marine Diesel Exhaust Gases by Michael Schmidt; Ralf Basner; Ronny Brandenburg (323-335).
The NO oxidation performance in a non-thermal plasma (NTP) reactor under realistic synthetic exhaust gas compositions is investigated. The gas compositions differ mainly in the NO–NO2 ratio and represent different modes of operation of a marine diesel engine. It is found that the maximum NO oxidation efficiency is independent on the NO–NO2 ratio. Up to 55 % of the NO is mainly oxidised to NO2 in all gas mixtures being analysed. However, the specific energy density needed to reach the highest NO oxidation varies with the gas composition between 15 and 60 J/L. The performance of the NTP-reactor was significantly improved by the addition of propene (C3H6) acting as an additional oxidising agent. The energy consumption for NO–NO2 conversion was found to be between 20 and 45 eV/NO, depending on the ratio of the added propene as well as the initial concentrations of nitrogen oxides.
Keywords: Non-thermal plasma; Marine; Diesel; Exhaust; NO-oxidation
Dielectric Barrier Discharge for Ammonia Production by Graciela Prieto; Kazunori Takashima; Akira Mizuno; Oscar Prieto; Carlos R. Gay (337-353).
The leading after-treatment technology for NOx removal process in Diesel engines for stationary and mobile applications is the selective catalytic reduction of oxides of nitrogen [NOx] by ammonia [NH3]. A novel non-thermal plasma electrode with a needle array in a dielectric barrier discharge reactor, powered by a high frequency neon transformer, is used for the thermal decomposition of solid urea [(NH2)CO(NH2)] to produce ammonia. The thermolysis of urea produces iso-cyanic acid [HNCO] as a byproduct, besides ammonia, which can react with water in the gas phase, thus giving carbon dioxide and more ammonia. The presence of water fed before and/or after the plasma reactor was studied to assess its effect on the amount of produced ammonia. Results clearly showed that water fed to the entrance of the reactor can efficiently promote the reaction of iso-cyanic acid to produce ammonia and this result can be improved when air is used as carrier gas for 115 V of input voltage to a neon transformer and with a gas flow rate of 4 L/min.
Keywords: Ammonia production; Urea thermolysis; DBD reactor; Non-thermal plasma; DeNOx
Fullerene C60 Trichloromethylation Through CCl4 Plasmalysis or Sonolysis by Franco Cataldo; Ornella Ursini; Pietro Ragni (355-365).
The trichloromethylation of C60 fullerene was achieved either under plasmalysis conditions, i.e. by arcing a solution of C60 in CCl4 between two graphite electrodes, or by sonolysis of C60 in CCl4. The resulting products were studied by UV–VIS and FT-IR spectroscopy as well as by thermogravimetric analysis in comparison to the trichloromethyl adducts formed by radiolysis or photolysis of C60 in CCl4. A reference study on the plasmalysis of pure CCl4 has revealed the formation of carbon soot and hexachlorobenzene. The formation of the latter compound was suppressed when C60 was present in CCl4.
Keywords: C60 ; Trichloromethylation; Plasmalysis; Arcing; Sonolysis; Ultrasonication
Influence of Partition Function and Interaction Potential on Transport Properties of Thermal Plasmas by J. Aubreton; M. F. Elchinger; P. André (367-399).
This paper, divided into two parts, is devoted to the transport properties at local thermodynamic equilibrium: the first part shows the influences of partition functions through the plasma composition and the second part the influence of interaction potentials. In the first part, for complex chemical mixtures the determination of the partition functions of different species is considered: monatomic, diatomic and polyatomic. In the plasmas the monatomic species are important; we study thoroughly the partition functions of monatomic neutrals and ions. We introduce two cut-off criteria. We test the influence of the two criteria on the partition functions and consequently onto the plasma composition and transport properties. We applied the study to Ar–Cu mixtures. In the second part, an historic study shows that the collision integrals used in calculating the transport properties become more accurate leading to more reliable values of the transport coefficients: application to N2 plasma. Now we have to calculate transport properties of complex mixtures and in these cases, for numerous interactions, a lack of data means that model potentials have to be used to determine collision integrals. In this paper, we have used two potential models: the first, for neutral–neutral and ion–neutral interactions, is an improvement of the Lennard-Jones function and the second is developed, from Stockmayer potential, for polar gases. We compare, for the collision integrals, the results obtained by these two models with those determined with more accurate potentials: applications to CO2 plasma and H2–N2 mixtures.
Keywords: Partition functions; Cut-off criteria; Plasma composition; Transport coefficients; Collision integrals; Interaction potentials; Thermal plasma; Argon–copper; Hydrogen–nitrogen; CO2
Analytical Expressions of Thermodynamic and Transport Properties of the Martian Atmosphere in a Wide Temperature and Pressure Range by G. Colonna; A. D’Angola; A. Laricchiuta; D. Bruno; M. Capitelli (401-431).
Calculation of thermodynamic and transport properties of CO2/N2/O2/Ar system (Martian atmosphere) have been performed in a wide pressure (0.01–100 bar) and temperature range (50–50,000 K). A self-consistent approach for the thermodynamic properties and higher order approximation of the Chapman–Enskog method for the transport coefficients have been used. Debye–Hückel corrections have been included in the calculation of thermodynamic properties while collision integrals derived following a phenomenological approach and accounting also for resonant processes contributions have been used. Moreover, charge–charge interactions have been obtained by using a screened Coulomb potential. Calculated values have been fitted by closed forms ready to be inserted in fluid dynamic codes in order to simulate plasma conditions for different technological applications. Comparison with data present in literature is also reported.
Keywords: Thermodynamics; Transport; Mars atmosphere; Plasma properties