Oxidizing Gas Mixture Research Articles

Influence of oxidizing and Nitriding parameters on nitrogen concentration of electrical steels

The influence of oxidizing and nitriding parameters on the nitrogen concentration of grain-oriented electrical steels preliminary to the development of the final Goss texture was explored. Results show that the nitrogen enrichment is driven by a ferrite to austenite transformation during thermochemical treatments. Such a transformation is promoted by (i) a redistribution of ferrite-forming elements close to the surface during oxidizing prior to nitriding, (ii) the oxygen content within the oxide layer prior to nitriding, (iii) the temperature of oxidizing and nitriding, and (iv) the nitrogen enrichment during nitriding. Optimization of the nitrogen content, and thus the precipitation kinetics of alloying elements nitrides (e.g. inhibitors) required for the development of the final Goss texture can be controlled by an optimization of the oxide layer growth, the temperatures and gas mixture of nitriding.

Application of Ethylene Oxide Gas and Argon Gas Mixture System Method for Scale Deacidification of Cellulose-Based Cultural Heritage Collections

Deacidification plays an important role in the conservation of paper-based cultural heritage objects. Herein, a novel approach for the conservation of scale paper-based cultural heritage objects is proposed using a mixture of argon and ethylene oxide (EO-Ar) for the first time. The optimum process conditions for deacidification of ethylene oxide and argon mixture system are determined by orthogonal testing. To evaluate the stabilization effect of paper treated with EO-Ar, the degradation of the mechanical properties (tensile strength, folding endurance and tearing strength tests) of paper after artificial aging was evaluated. The results show that the treated paper had better durability with respect to tensile strength, folding endurance and tearing strength. Additionally, thermal stability, crystallinity and fiber wall thickness increased after EO-Ar treated, which was determined by scanning electron microscope (SEM), diffraction of X-rays (XRD), and thermo gravimetric (TG) analysis. Some compounds, such as polyethylene glycol, organic acids, esters, were detected by GC-MS after treatment with EO-Ar. Two hundred and forty books including acidic, weak acidic and alkaline books were successfully deacidified, resulting in pH values of paper ranges suitable for paper preservation. Finally, a possible mechanism of deacidification of EO-Ar was proposed.

The effects of differential diffusion in counter-flow premixed flames with dilution and hydrogen enrichment

The effects of differential diffusion on local flamelet velocities, turbulent burning rates, and structure of lean turbulent premixed flames in the thin reaction zone regime are investigated using aerodynamically stabilized flames in a counter-flow apparatus. Various fuel–oxidizer–inert mixtures with different transport properties, representative of distinct effective Lewis numbers, are studied. In order to minimize the effects of mixture reactivity in these experiments, unstretched laminar flame speed is kept constant during mixture dilution, and hydrogen enrichment of hydrocarbon flames, through changing the mixture equivalence ratio. Furthermore, bulk-flow properties and stagnation surface temperature are kept constant; hence, the study focuses on the effects of differential diffusion, which is the change in transport properties of the mixture, i.e., fuel and heat diffusivities, in the context of fuel flexibility. Highly strained laminar flame measurements are also reported as a reference of comparison. Local instantaneous statistics of various flame parameters within the imaged plane, such as flame location, flame velocity, and flame-front topology, are quantified using high-speed particle image velocimetry (PIV) and Mie scattering flame tomography at two levels of turbulence intensity. These parameters are presented as probability density functions using sufficiently large data sets to ensure statistical accuracy. The results for various flame-parameter statistics, which are measured over a wide range of Lewis numbers, show that the effects of differential diffusion are important in turbulent flames in the thin reaction zone regime. At constant turbulence intensity, differential diffusion increases the burning rates of turbulent flames in thermo-diffusively unstable mixtures through two main mechanisms: (1) increasing local flamelet displacement velocity, and (2) increasing flame-surface area. The relative contribution of these two parameters in increasing turbulent burning rates is approximately 76% and 24%, respectively, which is not dependent on the fuel, oxidizing-gas mixture, or turbulence intensity, and the results overlap over a wide range of Lewis numbers.

Experimental and modelling study of treatment and regeneration of ferrous-nitrilotriacetate solution scrubbed with nitric oxide by an up-flow anaerobic biofilm reactor

This paper deals with an integrated biochemical process for the treatment of stationary gaseous emissions containing nitric oxide. The process involves absorption of nitric oxide in a solution of ferrous nitrilotriacetate, followed by regeneration of the solution by microbial reduction of nitrosyl adduct of ferrous nitrilotriacetate and ferric nitrilotriacetate present in the solution generated during absorption. A laboratory-scale up-flow anaerobic biofilm reactor using polyurethane foam cubes as support matrix for biofilm was employed for the treatment of 20 mM ferrous nitrilotriacetate solution scrubbed with synthetic nitric oxide gas mixture. The biofilm was developed by fed-batch operation for 30 days by using enriched bacterial culture capable of reducing nitrosyl adduct and ferric nitrilotriacetate using ethanol as organic electron donor. Under steady-state conditions, the nitrosyl adduct reduction efficiency reached >90% at a loading rate of 0.24 mML−1 h−1 while ferric nitrilotriacetate reduction efficiency was 15–20%. The average biofilm thickness was about 550 μm, decreasing the porosity of the matrix. Reactor hydrodynamics was studied by tracer (methyl orange) experiments. The analysis based on residence time distribution theory involved axial dispersion flow model and tracer diffusion with linear adsorption inside the biofilm. Peclet number value of 28 was obtained allowing the plug-flow assumption for the reactor model. The experimental profiles of the nitrosyl adduct reduction in the reactor were explained by using a kinetic model of first order reaction coupled with NO diffusion inside the biofilm.

Aging, re-dispersion, and catalytic oxidation characteristics of model Pd/Al2O3 automotive three-way catalysts

Thermal aging characteristics of model automotive Pd/Al2O3 catalyst materials were examined under simulated aging and light-off conditions as a function of aging temperature (up to 1000°C) in both reducing and oxidizing gas mixtures, and in the presence and absence of steam. The catalysts were characterized by static H2 chemisorption, thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), and both CO as well as propylene light-off experiments. Aging-induced changes in the Al2O3 support were modest and limited to slight loss of BET area and transition from predominantly γ-phase (as received) to θ-phase (after 1000°C aging). The main deactivation mode of aging was loss of Pd surface area via metallic Pd sintering, especially above the PdO decomposition temperature, as evidenced by higher light-off temperatures. Aging gas composition also impacted the Pd particle size, with more pronounced growth in rich gas (H2) mixtures. In contrast, particle growth was minimal in lean (O2) gas mixtures below the PdO decomposition temperature, and sintered Pd particles could be modestly re-dispersed by treating below the PdO decomposition temperatures in O2 and in the absence of steam. The study suggests strategies for operating vehicles in ways that mitigate or reverse aging effects related to Pd particle growth.

Preparation and characterization of TiO2-based plasma-sprayed coatings for NOx abatement

To minimize the formation of environmentally hazardous emissions, the catalytic reduction of NO by CO at metal oxide surfaces deposited by plasma spray technology on a Fe–Cr alloy support was studied. The paper outlines an experiment performed on a bench-scale reactor, describes the preparation of a catalytic monolithic reactor, the operating conditions as well as the properties of new-type catalytic coatings. As noted earlier in [1], the catalytic coatings containing an active component CuO effectively reduce the content of CO in the exhaust gas by over 90%. To enhance the NOx reduction by CO on the catalyst, TiO2 as a promoter and Ni powder as a catalyst were additionally incorporated in the initial mixture for catalytic coating formation. The structural and functional properties of the active layer – substrate system were analysed by methods of scanning electron microscopy (SEM), BET surface area, thermal analysis (DSC-TG), X-ray diffraction (XRD) and determination of roughness parameters. All the obtained coatings showed a good density, thermal stability and physical strength. However, irregularly agglomerated metal oxide layers had been formed in some places. The most active catalytic coating of Ni–Cu/TiO2–Al2O3 type showed an 80–90% removal for both NO and CO (CO/NO=3) in the oxidizing gas mixture.

Methane oxidation on Pd/YSZ by electrochemical promotion

Electrochemical investigations have been carried out on Pd/YSZ catalyst-electrodes for deep oxidation of methane in excess of oxygen. A wet impregnation technique has been used to achieve highly active Pd catalyst films. It was found that co-feeding of ethylene in oxidizing gas mixtures enhances the rate of methane conversion and allows for electrochemical promotion of methane oxidation at temperatures as low as 320°C. The electrochemical promotion behavior has been studied with long term potentiostatic transients together with AC impedance measurements during polarization.

Evaluation of hydrogen generation test using redox reaction

The hydrogen energy society is desirable to mitigate global warming. The redox reaction of iron oxide Fe3O4 which can generate 4·8 wt% hydrogen for metallic iron is considered as one of means to store and supply it. However, this reaction is known to be significantly retarded because of sintering of solid particles. Toward solving these problems, our previous research proved alumina coating on the surface of fine iron oxide particles could improve the reaction efficiency most drastically. In this work, a lot of small pellets made of 1·25 mol% alumina coating fine particles Fe2O3 (0·1 μm dia.) by means of hydrometallurgy were prepared. Then, hydrogen generation using redox reaction in the packed bed of these pellets was tested under electric heating by gas chromatography of exit gas. Based on steam conversion degrees at 350°C with oxidation time after H2 reduction at 500°C, it was found that less steam flow rates in H2O-N2 oxidizing gas mixture (a constant N2 flow rate) provided higher steam conversion degrees near 100% and the theoretical total hydrogen generation degrees were mostly realized, independently of steam flow rates. The results were overall investigated with the view point of potential application to fuel cell.

Thermophoresis effect on volatile particle concentration in micro-organic dust flame

In this paper, a mathematical model is proposed for the study of the structure of an upward-propagating flame that contains uniformly distributed volatile fuel particles in an oxidizing gas mixture. In order to obtain an appropriate model, the flame's front zone (the unburned zone) is divided into two zones: preheat and vaporization. In this research, physical phenomena such as thermophoretic effect, vaporization process and particle radius changes have been studied in the two mentioned zones. The vaporization process across the flame front leads to particle radius reduction, which can affect the particles' hydrodynamic behavior. As the thermophoretic force progressively increases by approaching the flame, it reaches a critical magnitude that just balances the gravity and buoyancy forces of the particles. At this point, the particle cloud remains stationary where the particles accumulate, and as a result, the volume fraction of particles reaches its maximum value. Particle size can strongly affect the hydrodynamic behavior of dust, and it can be stated that the increase of the radius of particles could lead to the reduction of the distance between the stagnation point (where the particle volume fraction is maximum) and the flame. The theoretical results show reasonable correlation with the experimental data.

Experimental study of diffusion instability in three-component gas mixture without density gradient

The process of binary (propane-nitrous oxide) gas mixture diffusion into carbon dioxide was experimentally studied in a two-compartment setup at various component concentrations and pressures. Regimes of mixing are determined depending on the initial concentrations of binary mixture components.

Electrochemical promotion of the SO2 oxidation over thin Pt films interfaced with YSZ in a monolithic electropromoted reactor

The effect of electrochemical promotion of catalysis on the SO2 oxidation reaction was investigated over thin (∼40nm) Pt catalyst electrodes interfaced with YSZ, in a monolithic electrochemically promoted (MEP) reactor equipped with five or twenty-two electrocatalytic plates. A mildly oxidizing gas mixture was used at temperatures from 330 to 370°C and flowrates between 1 and 30Lmin−1.It was found that positive potential application, i.e. O2− supply to catalyst surface, can cause an increase of up to 200% in the catalytic oxidation rate of SO2 with Faradaic efficiency values up to 30 at flowrates as high as 30Lmin−1 which corresponds to 3×104h−1 space velocity or 0.1s residence time.The results show the strong potential of MEP reactors for practical applications of the electrochemical promotion of catalysis (EPOC) effect, in gas treatment units and chemical synthesis and destruction processes.

Novel analytical model for predicting the combustion characteristics of premixed flame propagation in lycopodium dust particles

This paper presents the effects of the temperature difference between gas and particle, different Lewis numbers, and heat loss from the walls in the structure of premixed flames propagation in a combustible system containing uniformly distributed volatile fuel particles in an oxidizing gas mixture. It is assumed that the fuel particles vaporize first to yield a gaseous fuel, which is oxidized in a gas phase. The analysis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number is large. The structure of the flame is composed of a preheat zone, reaction zone, and convection zone. The governing equations and required boundary conditions are applied in each zone, and an analytical method is used for solving these equations. The obtained results illustrate the effects of the above parameters on the variations of the dimensionless temperature, particle mass friction, flame temperature, and burning velocity for gas and particle.

Functionalization of Copper Surfaces by Plasma Treatments to Improve Adhesion of Epoxy Resins

AbstractAdhesion of epoxy resins on copper foils for printed circuit board (PCB) applications is improved by nearly a factor of 5, using surface cleaning and deposition of a 15‐nm‐thick film in a low‐pressure remote plasma‐enhanced chemical vapor deposition process. The cleaning pretreatment, using an N2–O2 oxidizing gas mixture with moderate heating (343 K), gives the best results. This pretreatment removes the carbonaceous contaminants present on the topmost surface of the sample and slightly oxidizes the copper into CuO. This oxide is then reduced during the deposition treatment, presumably by reaction with the aminopropyltrimethoxysilane (APTMS) precursor. The surface roughness is unchanged after treatment, thereby showing that the improvement of the copper/epoxy adhesion is only due to the chemistry of the plasma coating. Applying these results to dielectric barrier discharges allows us to achieve the same level of adhesion, which, therefore, does not depend on the process.

Modeling combustion of lycopodium particles by considering the temperature difference between the gas and the particles

The effect of the temperature difference between the gas and the particles on propagation of premixed flames in a combustible mixture containing volatile fuel particles uniformly distributed in an oxidizing gas mixture is analyzed in this paper. It is presumed that the fuel particles vaporize first to yield a gaseous fuel, which is oxidized in the gas phase. The analysis is performed in the asymptotic limit, where the value of the characteristic Zel’dovich number is large, which implies that the reaction term in the preheating zone is negligible. Required relations between the gas and the particles are derived from equations for premixed flames of organic dust. Subsequently, the governing equations are solved by an analytical method. Finally, the variation of the dimensionless temperatures of the gas and the particles, the mass fraction of the particles, the equivalence ratio ϕ g as a function of ϕ u , the flame temperature, and the burning velocities of the gas and the particles are obtained. The analysis shows that the calculated value of ϕ g is smaller than unity for certain cases, even though ϕ u ⩾1.

Magnitude of the Second Gas Effect on Arterial Sevoflurane Partial Pressure

A number of studies have demonstrated a faster rate of increase in end-expired partial pressure as a fraction of inspired (Pa/Pi) for volatile agents in the presence of high concentrations of nitrous oxide, consistent with the second gas effect. However, no study has demonstrated a similar effect on arterial blood concentrations. The authors compared arterial and end-tidal partial pressures of sevoflurane (Pa/Pisevo and Pa/Pisevo) in 14 patients for 30 min after introduction of either 70% nitrous oxide or nitrous oxide-free gas mixtures to determine the magnitude of the second gas effect. Blood partial pressures were measured using a double headspace equilibration technique. Both Pa/Pisevo and Pa/Pisevo were significantly higher in the nitrous oxide group than in the control group (P < 0.001 on two-way analysis of variance). This difference was significantly greater (P < 0.05) for Pa/Pisevo (23.6% higher in the nitrous oxide group at 2 min, declining to 12.5% at 30 min) than for Pa/Pisevo (9.8% higher in the nitrous oxide group at 2 min) and was accompanied by a significantly lower Bispectral Index score at 5 min (40.7 vs. 25.4; P = 0.004). Nitrous oxide uptake exerts a significant second gas effect on arterial sevoflurane partial pressures. This effect is two to three times more powerful than the effect on end-expired partial pressures. The authors explain how this is due to the influence of ventilation-perfusion scatter on the distribution of blood flow and gas uptake in the lung.

Effect of treating atmosphere in plasma post-oxidation of nitrocarburized AISI 5115 steel

In this study quenched and tempered AISI 5115 steel was plasma-nitrided and nitrocarburized at 550 °C for 5 h in atmospheres of 80% N 2 balanced with various amounts of CO 2 and H 2 gases. The amount of CO 2 varied from 0 to 10 vol%. The highest amount of ε phases was formed in the compound layer after treating in atmosphere containing 7 vol% CO 2. Optimized compound layer was post-oxidized for 1 h at 450 °C under O 2/H 2 volume ratios of 1/1 and 3/1 as well as 100% oxygen. The treated samples were characterized using metallographic techniques, XRD, SEM, roughness measurement and potentiodynamic methods. The results showed that the growth rate of the oxide layer increased with increasing O 2 in the oxidizing gas mixture. X-ray diffraction analysis of oxidized layers confirmed the formation of highest amount of magnetite at post-oxidation in an atmosphere with the O 2/H 2 volume ratio of 1/1. Electrochemical polarization tests proved the enhancement of corrosion resistance by plasma post-oxidation and the highest corrosion resistance obtained after oxidizing under an O 2/H 2 volume ratio of 1/1.

Methane Cracking over a Bituminous Coal Char

Methane cracking over a bed of Chinese bituminous coal char was studied using a fixed-bed reactor at atmospheric pressure and temperatures between 1073 and 1223 K. Methane conversion over the fresh char increased with increasing temperature to 90% at 1223 K. Hydrogen was the only gas-phase product that was detected during the experimentation. The char was shown to exert a significant catalytic effect on methane cracking by comparing results from experiments with the raw char and demineralised char as well as from blank experiments using quartz. It was further shown that the ash was not the source of the catalytic effect of the char. However, both methane conversion and hydrogen yield decreased with increasing reaction time, irrespective of other experimental conditions, indicating that the char rapidly became deactivated following the exposure to methane. It was speculated that the deposition of carbon from methane cracking was responsible for this deactivation, which is supported by scanning electron microscopy (SEM) image analysis. It was demonstrated that the catalytic activity of the deactivated char can be partially recovered by burning off the carbon deposits with an oxidizing gas mixture containing 0.46% oxygen.

The development of new microelectrode gas sensors: An odyssey: Part V. Simultaneous electrochemical determination of oxygen, carbon dioxide and nitrous oxide gas mixtures in a non-aqueous solvent using membrane shielded gold microelectrodes

The simultaneous electrochemical reduction of oxygen, carbon dioxide and nitrous oxide was investigated at Au microelectrodes (5 μm, diam.) in dimethyl sulfoxide (DMSO) solvent, using both voltammetric and potential step chronoamperometric techniques. In agreement with previous voltammetric studies, carbon dioxide is shown to react with the superoxide anion radical, formed from the electro-reduction of oxygen (−1.3 V vs. Ag). This cross-interference reaction complicates the simultaneous detection of all three gases. The presence of nitrous oxide, however, appears to give rise to no deleterious cross-interference reactions with either oxygen or carbon dioxide. By contrast, the use of potential step, chronoamperometric techniques are shown to effectively collapse the deleterious cross-interference reaction between superoxide and carbon dioxide (current enhancement <2%). In addition, potential step interrogation of the carbon dioxide reduction signal indicates a linear dependence on the concentrations of both oxygen and nitrous oxide. Meanwhile, interrogation of the nitrous oxide reduction signal reveals a proportional current enhancement with the stepwise addition of oxygen but no dependence on the concentration of carbon dioxide. In addition, a “proof of principle” practical sensor design incorporating a polytetrafluoroethylene (PTFE, Teflon ®) membrane-covered gold microelectrode is described for the simultaneous measurement of oxygen, carbon dioxide and nitrous oxide over a wide concentration range.

Decarburization of Fe/C melts in a crucible: Effects of gas flow rate and composition

Decarburization of iron–carbon melts contained in a bath has been experimentally investigated. In some experiments controlled Fe/C melts were used whereas in others commercial type metal containing some impurities was used. The effects of a wide range of gas injection flowrates, percentage composition of the decarburizing component and nature of the decarburizing gas were investigated. The presence of nitrogen or argon as inert gas has also been investigated. Results showed that decarburization rate increases with an increase in the concentration of O2 or CO2 in the decarburizing gas. It was also observed that higher decarburization rate and more vigorous reaction were observed when O2 was used as oxidizing gas instead of CO2. Finally, the presence of N2 instead of Ar as inert gas in the oxidizing gas mixture, did not make any significant difference to the decarburization rate.

Studies on nitric oxide removal in simulated gas compositions under plasma-dielectric/catalytic discharges

Application of pulsed electrical discharges for gas cleaning is gaining prominence, mainly from the energy consideration point of view. This present paper presents recent work on applying the electrical discharge plasma technology for treating gaseous pollutants, in general, and nitric oxide, in particular, as this is one of the major contributors to air pollution. The present work focuses attention on pulsed electrical discharge technique for nitric oxide removal from simulated gas compositions and study of effect of packed dielectric pellets, with and without a coating of catalyst, on the removal process. Experiments were conducted in a cylindrical corona reactor energized by repetitive high voltage pulses. The effects of various parameters, viz. pulse voltage magnitude, pulse frequency, initial nitric oxide concentration and gas mixture composition on nitric oxide removal efficiency, are discussed. When the reactors were filled with different dielectric pellets like, barium titanate, alumina, and alumina coated with palladium catalyst, the improvement in nitric oxide removal efficiency is studied and discussed. The power dissipated in the reactor and the energy consumed per nitric oxide molecule removed was calculated. Further results and comparative study of various cases are presented in the paper.