Critical analysis of viscosity data of thermal argon plasmas at atmospheric pressure

Reliable values of the viscosity in thermal argon plasmas are most important for our understanding of the momentum transfer and for realistic modeling of various plasma applications. Despite numerous attempts to determine reliable viscosity values over the last three decades, discrepancies still exist among the data reported by different authors. In this paper, a critical analysis is undertaken of calculated and experimental data of the argon viscosity based on recent publications. Our recalculation of viscosities in thermal argon plasmas are performed by using Lennard-Jones, Morse, Aziz, and exponential repulsive potentials for Ar-Ar atom interactions in different temperature ranges from 300 to 20,000 K. The contributions of elastic collisions of e-Ar, e-Ar⁺, and Ar⁺-Ar, as well as charge exchange of Ar⁺-Ar, to the viscosity become important with increasing temperature and degree of ionization in argon plasmas. Based on a critical analysis and recalculations, improved values of the argon viscosity are recommended, covering temperatures from 300 to 20,000 K. Polynomial expressions have been developed for calculating argon viscosities, which will be useful for numerical work and other applications of thermal argon plasmas at atmospheric pressure.     

Transport coefficients of argon,nitrogen, oxygen,argon-nitrogen,and argon-oxygen plasmas

Calculated values of the viscosity, thermal conductivity, and electrical conductivity of argon, nitrogen, and oxygen plasmas, and mixtures of argon anti nitrogen and of argon anti oxygen, are presented. In addition, combined ordinary, pressure, and thermal diffusion coefficients are given for the gas mixtures. These three combined diffusion coefficients fully describe di fusion of the two gases, irrespective of their degree of dissociation or ionizati on. The calculations, which assume local thermodynamic equilibrium, are performed! for atmospheric-pressure plasmas in the temperature range /torn 300 to 30,000 K. A number of the collision integrals used in calculating the transport coefficients are significantly more accurate than values used in previous theoretical studies, resulting in more reliable values of the transport coefficients. The results are compared with those of published theoretical and experimental studies.     

Behavior and surface energies of polybenzoxazines formed by polymerization with argon,oxygen, and hydrogen plasmas

Polybenzoxazine (PBZZ) thin films can be fabricated by the plasma‐polymerization technique with, as the energy source, plasmas of argon, oxygen, or hydrogen atoms and ions. When benzoxazine (BZZ) films are polymerized through the use of high‐energy argon atoms, electronegative oxygen atoms, or excited hydrogen atoms, the PBZZ films that form possess different properties and morphologies in their surfaces. High‐energy argon atoms provide a thermodynamic factor to initiate the ring‐opening polymerization of BZZ and result in the polymer surface having a grid‐like structure. The ring‐opening polymerization of the BZZ film that is initiated by cationic species such as oxygen atoms in plasma, is propagated around nodule structures to form the PBZZ. The excited hydrogen atom plasma initiates both polymerization and decomposition reactions simultaneously in the BZZ film and results in the formation of a porous structure on the PBZZ surface. We evaluated the surface energies of the PBZZ films polymerized by the action of these three plasmas by measuring the contact angles of diiodomethane and water droplets. The surface roughness of the films range from 0.5 to 26 nm, depending on the type of carrier gas and the plasma‐polymerization time. By estimating changes in thickness, we found that the PBZZ film synthesized by the oxygen plasma‐polymerization process undergoes the slowest rate of etching in CF₄ plasma. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4063–4074, 2004     

Modeling and experimental study of a transferred arc stabilized with argon and flowing in a controlled-atmosphere chamber filled with argon at atmospheric pressure

For a transferred arc with a flat anode working at atmospheric pressure in an argon atmosphere, the influence of the gas injector design close to the cathode tip has been systematically studied for arc currents below 300 A, gas flowrates between 5 and 60 slm, and anode-cathode distances between 10 and 46 mm. Two types of injector configurations hare been studied: a cylindrical one with its wall parallel to the cathode axis and a conical one with the same cone angle as that of the cathode tip. The arc temperature was measured using flit, absolute intensity of ArI and ArII lines. Beside the roltagc and arc current, the losses at the cathode and at the anode were continuously recorded. An elliptic model was used to calculate the flow velocity, the temperature, and the current density close to the cathode and in the arc column. This model was either laminar or turbulent (K - ), with the empirical constants being functions of the Reynolds nunther of turbulence. A cathode sheath with nonequilibrium conditions was used to obtain accurate cathode boundary conditions. Experiments and modeling hart shown the benefits of using conical injectors which constrict drasfically the plasma_ flow and enhance the gas velocity and the current density, thus increasing the heat flux to the anode. With the cylindrical injector, recirculations close to the cathode lip modify deeply its heating and reduce the plasma jet constriction: velocities and temperatures are lower when the recirculation velocity is higher. This results in lower heat fluxes to the anode compared to the conical injector.     

Thin film deposition from plasmas of tetramethylsilane–helium–argon mixtures with oxygen and with nitrogen

Films were produced by plasma enhanced chemical vapor deposition (PECVD) of tetramethylsilane (TMS)–helium–argon mixtures with either oxygen or nitrogen in a vacuum system fed with radiofrequency power. Actinometric optical emission spectroscopy was used to determine trends in the concentrations of plasma species of interest (H, CH, O, CO, and CN) as a function of the ratio of the inorganic reactive gas (oxygen or nitrogen) to the monomer (TMS) in the system feed. As the ratio of oxygen to TMS in the feed is increased, the degree of oxygenation of the deposited material, as revealed by transmission infrared spectroscopy, is also increased. Similarly, the degree of nitrogenation of the films increases with increasing nitrogen to monomer ratio in the feed. Strong correlations exist between the plasma concentrations of the above-mentioned plasma species and film structure and composition. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1873–1879, 1998     

The dehydrogenation of isopropanol on a nickel-manganese catalyst subjected to treatment in glow-discharge oxygen,argon, and hydrogen plasmas

The dependence of the activity of the (Ni 20 wt %-Mn 4 wt %)/SiO₂ catalyst on the treatment of its surface in glow-discharge oxygen, argon, and hydrogen plasmas was studied. Catalytic experiments were performed in a flow reactor and under static conditions in a vacuum. The highest activity was observed after catalyst treatment in an argon plasma. Glow-discharge plasma treatment changed the structure and number of active centers, which resulted in a change in the reaction mechanism. Ab initio quantum-chemical calculations were performed using the Hartree-Fock (UHF) method for the Ni₅ cluster. The results substantiated the suggested that the active center contained the hydrogen atom.     

The role played by chain avalanches in the developed burning of hydrogen mixtures with oxygen and air at atmospheric pressure

The role of competition between reaction chain branching and termination at various burning stages accompanied by reaction mixture self-heating was studied by mathematically modeling combustion of hydrogen mixtures with air and oxygen at a 1 bar initial pressure. An algorithm was suggested that allowed chair branching to be switched off at various time moments during calculations with retaining all the other, including thermal, parameters. It was shown that the switching off of chain avalanches at any process stage resulted in virtually instantaneous burning termination no matter what level of reaction mixture self-heating was reached.     

Excess Volumes of Ternary Mixtures Containing N-Methylcyclohexylamine,Benzene with 1-Alkanols at 303.15 K

Abstract

New excess volume data have been measured for three ternary mixtures at 303.15 K. The mixtures included N-methylcyclohexylamine and benzene as common components. 1-propanol, 1-butanol and 1-pentanol were chosen as non-common components. The data were compared with those predicted by empirical relations. The experimental results have been analysed in terms of intermolecular interactions between unlike molecules.     

Chemical‐surface modification of polymers using atmospheric pressure nonequilibrium plasmas and comparisons with vacuum plasmas

We demonstrate that stable microwave‐coupled atmospheric pressure nonequilibrium plasmas (APNEPs) can be formed under a wide variety of gas and flow‐rate conditions. Furthermore, these plasmas can be effectively used to remove surface contamination and chemically modify polymer surfaces. These chemical changes, generally oxidation and crosslinking, enhance the surface properties of the materials such as surface energy. Comparisons between vacuum plasma and atmospheric plasma treatment strongly indicate that much of the vacuum‐plasma literature is pertinent to APNEP, thereby providing assistance with understanding the nature of APNEP‐induced reactions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 95–109, 2002     

Plasma reactions of methane in nitrogen and nitrogen/oxygen carriers by matrix isolation FTIR spectroscopy

The plasma-induced reactions of traces of methane in nitrogen and nitrogen/oxygen carriers have been investigated by freezing the products onto a 10 K CsI substrate and performing FTIR analysis on the product mixture. Isotopic substitution studies have been used to assist in identification of reaction intermediates and final products. A combination of low (10 mTorr) and high (2 Torr) pressure discharges has also been used to help in the identification of these products. Oxygen concentration was increased in a stepwise fashion to determine its effect on the reaction product distribution. In the present work, methyl radical was the principal product in low-pressure N₂/CH₄ plasmas, and small amounts of HCN and NH₃ were also produced. In the higher-pressure plasmas, HCN and NH₃ were the principal products. As O₂ was added to the plasmas, CO, H₂O, CO₂, N₂O, NO, O₃, HONO, and HNO₃ were produced in approximately the order shown, i.e., CO was formed in good yield at low oxygen partial pressures, but HNO₃ was produced only in slight yield even at the highest oxygen pressures used in this work. These results are discussed in terms of the development of a plasma device having potential application for destruction of environmentally hazardous materials and how trace organic pollutants might react in such a system.     

Cathode erosion on copper electrodes in steam,hydrogen, and oxygen plasmas

Experimental data are presented for cathode erosion rates on copper cathodes (or magnetically rotated arcs in steam, and mixtures of steam, hydrogen, and oxygen with argon. Measurements were also made of the arc voltage and velocity. The erosion rates for steam and oxygen plasmas were significantly lower than those .16r argon and hydrogen. Pure steam and 10% oxygen in argon gave erosion rates of 2.3 and 6.1 g/ C respectively while pure argon and 70% hydrogen in argon gave rates of 14.8 and 13.0 g/C respectively. Erosion rates decreased with increasing are velocities. The variation of arc velocity with operating conditions is described in terms of both aerodynamic and surface drag on the arc and arc root respectively.     

Reactions of primary and secondary butoxy radicals in oxygen at atmospheric pressure

The reaction pathways of n-butoxy and s-butoxy radicals have been investigated by TLC and HPLC analysis of end products, particularly peroxides and carbonyl compounds. The butoxy radicals were produced by the pyrolysis of very low concentrations of the corresponding dibutylperoxide in an atmosphere of oxygen and nitrogen, at atmospheric pressure. The decomposition reaction (3) s-BuO → C₂H₅ + CH₃CHO and the reaction (2) s-BuO + O₂ → HO₂ + CH₃COC₂H₅ have been studied, and the ratio k₃/k₂ has been determined in the temperature range 363–503 K by kinetic modeling of the formation of the observed acetaldehyde and methylethylketone. The rate constant k₃ obtained was: A good agreement was observed between experimental data and RRKM theory. The implications of the results for atmospheric chemistry and combustion are discussed. At room temperature, the reaction with O₂, yielding HO₂ radicals and methylethylketone is, by far, the main channel for s-BuO radicals. In the field of low temperature combustion, the decomposition of s-BuO radicals producing C₂H₅ and CH₃CHO is the main pathway; the route s-BuO + O₂ decreases tremendously in importance as the temperature is raised above 393 K.     

Using the van der Waals broadening of spectral atomic lines to measure the gas temperature of an argon–helium microwave plasma at atmospheric pressure

The applications of plasmas generated with gas mixtures have become increasingly common in different scientific and technological fields. In order to understand the advantages of these discharges, for instance in chemical analysis, it is necessary to know the gas temperature (T_g, kinetic energy of the heavy particles) since it has a great influence on the atomization reactions of the molecules located in the discharge, along with the dependence of the reaction rate on this parameter. The ro-vibrational emission spectra of the molecular species are usually used to measure the gas temperature of a discharge at atmospheric pressure although under some experimental conditions, these are difficult to detect. In such cases, the gas temperature can be determined from the van der Waals broadening of the emitted atomic spectral lines related to this parameter. The method proposed is based on the van der Waals broadening taking into account two perturbers.     

Theoretical prediction of surface tension of ternary liquid system (nitrogen + oxygen + argon) at elevated temperature and different pressure

The surface tension of a ternary liquid mixture of nitrogen, oxygen, and argon has been calculated by a new approach using critical constants Pc, Vc, and Tc at temperatures ranging from 90 to 110 K and pressure up to 865 kPa. New formalism has been made by modifying the Brock-Bird relation. The computed values are compared with the experimental findings. Satisfactory results have been obtained.     

Solubility of carbon dioxide,ethane, methane,oxygen, nitrogen,hydrogen, argon,and carbon monoxide in 1-butyl-3-methylimidazolium tetrafluoroborate between temperatures 283 K and 343 K and at pressures close to atmospheric

Experimental values for the solubility of carbon dioxide, ethane, methane, oxygen, nitrogen, hydrogen, argon and carbon monoxide in 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF₄] – a room temperature ionic liquid – are reported as a function of temperature between 283 K and 343 K and at pressures close to atmospheric. Carbon dioxide is the most soluble gas with mole fraction solubilities of the order of 10⁻². Ethane and methane are one order of magnitude more soluble than the other five gases that have mole fraction solubilities of the order of 10⁻⁴. Hydrogen is the less soluble of the gaseous solutes studied. From the variation of solubility, expressed as Henry’s law constants, with temperature, the partial molar thermodynamic functions of solvation such as the standard Gibbs energy, the enthalpy, and the entropy are calculated. The precision of the experimental data, considered as the average absolute deviation of the Henry’s law constants from appropriate smoothing equations is of 1%.     

FT-IR study of the interaction of oxygen,argon, helium,nitrogen and xenon with hydroxyl groups in H-Y zeolite at low temperatures

Adsorptions of O₂, Ar, He, N₂ and Xe on H-Y zeolite at low temperatures were studied by transmission Fouriertransform infrared spectroscopy. For the O₂ adsorption, a weak v(OO) band was observed at 1550 cm⁻¹. The formation of a weak hydrogen-bonding of O₂ and Ar with the bridging OH-groups in the supercage was observed, while these molecules did not interact chemically nor physically with the bridging OH-groups in the small cavities. These results indicate that O₂ and Ar can approach the acid sites in the supercages, but cannot approach those in the small cavities. However, a slight physical interaction (not the H-bonding) of He with the OH groups in the small cavities was observed, suggesting that He would be able to approach near the sites. N₂ adsorption gave two v(NN) bands at 2353 and 2338 cm⁻¹, which have been attributed to the N2 species adsorbed on Lewis acid sites and on Br0nsted acid sites, respectively. It was observed that N₂ and Xe interact strongly with the bridging OH-groups in the supercages as well as weakly with the silanol groups. On the basis of the IR-spectroscopic data on the strength of the interaction with the small and nonpolar gases, the acidic properties of H-Y was compared with those of H-MOR and H-ZSM-5.     

Ultrasonic Studies of Binary Mixtures of p-Chlorotoluene with l-Alcohols at 303.15 K

Abstract

Ultrasonic sound velocities and densities were measured for the binary mixtures of p-chlorotoluene with l-alcohols. The alcohols included: l-propanol, l-butanol, l-pentanol, l-hexanol and l-heptanol. Isentropic compressibilities, k_s and deviation in isentropic compressibility, K_s from ideal behaviour have been calculated from the results. The deviation in isentropic compressibility has been ascribed to competition between structure-breaking and structural effects to different extents.     

煤在合成气、氢气和氮气气氛下的热解研究

采用固定床反应器，在合成气气氛下对中国寻甸褐煤、蒙古Shiveeovoo褐煤和Khoot油页岩进行了热解研究。升温速率10 ℃/min，褐煤热解温度400 ℃～800 ℃，油页岩热解温度300 ℃~600 ℃，研究结果与氢气和氮气气氛下的热解进行了比较。结果表明,与加压热解不同，褐煤在不同气氛下常压热解半焦和焦油收率差别不大，但对油页岩，合成气和氢气气氛下热解焦油收率高于氮气，气体收率低于氮气。黄铁矿硫在不同气氛下热解均极易脱除，并部分转化为有机硫。油页岩的总硫脱除率远低于褐煤，与油页岩的高灰分含量有关。与氮气甚至氢气相比，合成气下寻甸褐煤的高总硫脱除率和低有机硫含量与合成气中的CO有关。但CO在油页岩热解脱硫中不起作用，也与油页岩高灰分含量有关。研究结果也表明合成气可代替氢气进行加氢热解。     

Microcalorimetric study of argon,oxygen, nitrogen and carbon monoxide adsorption on crystalline zirconia

The adsorption of argon, oxygen, nitrogen and carbon monoxide at 77 K on crystalline zirconia and microporous zirconia gels has been studied by adsorption volumetry and isothermal microcalorimetry.The microporous structure of the zirconia gel may explain the higher enthalpy of adsorption obtained for argon. Both crystalline samples are mesoporous and in each case, the polar sites on the surface give specific interactions with dipolar (CO) or quadrupolar (N₂, O₂) molecules, which can be deduced from the adsorption isotherms and the corresponding differential enthalpy curves.M. J. T. acknowledges for a 2 month invited professorship at Université de Provence.