Initial Gas Mixture Research Articles

Равновесие водяного газа с углеродом

The calculated possible parameters of equilibrium of water gas with carbon are presented in the form of spatial (3-dimensional) diagram in coordinates “ xCO – xH2 – T ”,. It can be supplemented with a graph of isothermal projections of isothermal section surfaces onto the plane “ xCO – xH2 ”. Different ways of obtaining gas atmosphere with oxygen potential sufficient to reduce metal oxides are explored. The most technological method of obtaining gas mixture capable of reducing metal oxides is heating water vapour in contact with carbon. In this case the resulting water gas composition is determined by heating temperature only. Maximum concentration of hydrogen xH2 reaches 0.5 when “H2O – C” is heated to ~ 900 K, and heating to temperatures above 1100 K produces a mixture of reducing gas agents with equal concentrations xCO = xH2 = 0.5. Heating gas mixtures “H2O – CO2” in contact with carbon produces water gas with reduced concentration of H2 and increased concentration of CO. Gas atmosphere (H2 – H2O – CO – CO2) of any composition can be obtained by heating mixtures “H2 – CO” in contact with carbon. Formation of CO2 occurs as a result of the dissociation reaction of CO and water vapor by the reaction H2O + CO = H2 + CO2. A technique of quantification of the carbon gasification with water vapor H2O carbon dioxide CO2 is presented. Calculations showed that gasification reactions C + CO2 = 2CO and C + H2O = CO + H2 can occur both forth and back depending on the composition of the initial gas mixtures and temperature.

Hydrogenated silicon oxycarbonitride films. Part III. Thermodynamic modeling of the Si-C-N-O-H system

The thermodynamic modeling of the deposition of the condensed phase of a complex composition has been performed in the Si-C-N-O-H system in the broad temperature range of 300–1300 K under total pressure Ptotal0 = 6−7×10−2 Torr and residual air pressure in reactor Pres = 5 × 10−3 Torr using the initial gas mixtures of organosilicon compound, hexamethyldisilazane (HMDS), with nitrogen, oxygen, air mixture (O2 + 4N2), and a variable mixture of oxygen with nitrogen (O2 + xN2). The temperature boundaries of multiphase ranges, where one can anticipate the deposition of silicon oxycarbonitride, silicon oxycarbides, and silicon oxynitride, have been determined.

Phase composition of thin silicon carbonitride films obtained by plazma endanced chemical vapour deposition using organosilicon compounds

High-temperature silicon carbonitride films are synthesized by plasma decomposition of gas mixtures of 1,1,1,3,3,3-hexamethyldisilazane (HMDS) (the synonym used by IUPAC bis(trimethylsilyl) amine) with ammonia or helium in the temperature range of 673–1273 K. It is shown that silicon carbonitride films, obtained in high temperature processes of the plasma decomposition of organosilicon compounds, are nanocomposite. In their amorphous matrix the crystals belonging to the phases of the α-Si3−nCnN4 family and impurity graphite are embedded. To clarify the previously obtained data by means of the X-ray diffractometry using synchrotron radiation, they are compared with the published results of modeling the structure of these phases. It is shown that nanocrystals belonging to the phases of α-Si3N4, α-Si2CN4, α-SiC2N4, and α-C3N4 are present in the films. An increase in the ammonia concentration in the initial gas mixture causes a decrease in the film hardness from 24 GPa to 16 GPa due to the increased content of α-Si3N4 and α-Si2CN4 nanocrystals having a lower hardness compared to α-C3N4 and α-SiC2N4.

Kinetics of premixed acetaldehyde + air flames

Non-stretched laminar burning velocities, SL, of acetaldehyde+air mixtures at initial gas mixture temperatures, T, of 298, 318, 338, 348 and 358K are reported for the first time. The flames were stabilized on a perforated plate burner at 1atm using the heat flux method at conditions where the net heat loss from the flame to the burner is zero. Uncertainties of the measurements were analyzed and assessed experimentally. The overall accuracy of the burning velocities was estimated to be typically better than ±1cm/s. Experimental results were compared with predictions of several kinetic models from the literature. Recent model of Leplat et al. (2011) [30] developed for acetaldehyde and ethanol oxidation showed the closest agreement with the measurements as compared to the Konnov and San Diego models. The effects of initial temperature on the adiabatic laminar burning velocities of acetaldehyde were interpreted using the correlation SL=SL0 (T/T0)α. Particular attention was paid to the variation of the power exponent α with equivalence ratio. The existence of a minimum in α in the slightly rich mixtures is demonstrated experimentally and confirmed computationally. The model of Leplat et al. was further analyzed using sensitivity analysis and it was concluded that the deviation of the modelled results when comparing with experiments is not a result of the fuel specific reactions but rather the sub-mechanisms of C1 and H2/O2.

Influence of CO on Titan atmospheric reactivity

The atmosphere of Titan is mainly composed of N2 and CH4 which are the source of various CxHyNz photochemical volatiles products. Laboratory simulations of the Titan’s atmospheric reactivity were mainly interested in the study of the complex organic chemistry which leads to the formation of analogues of Titan’s aerosols, called tholins. These studies were mainly interested in the reactivity of the N2/CH4 gaseous mixture and with the primary products of reactions without oxygen. However, the atmosphere of Titan also contains oxygenated volatile species. The most abundant one to have been detected is CO with a concentration about 50ppmv. The work presented here is an experimental simulation devoted to estimate the influence of CO on the Titan’s atmospheric reactivity. With this aim, CO is introduced in a standard N2/CH4 mixture at different mixing ratio up to 4.5%. The kinetics of the methane consumption is monitored with in situ mass spectrometry and the compositions of the gaseous phase and tholins produced in the reactor are characterized ex situ with GC–MS and elemental analysis. This work shows that CO modifies the composition of the gas phase with the detection of oxygenated compounds: CO2 and N2O. The presence of CO also drastically decreases the production rate of tholins, involving also a perturbation on the methane kinetics. Tholins are produced in lower global amounts, but their sizes are found to be significantly larger than without CO. The oxygen incorporation in tholins is found to be efficient, with an oxygen content of the same order of magnitude as the amount of CO in the initial gas mixture.

Ignition delay times of shock-heated tetraethoxysilane, hexamethyldisiloxane, and titanium tetraisopropoxide

Ignition delay times of tetraethoxysilane (TEOS), hexamethyldisiloxane (HMDSO) and titanium tetraisopropoxide (TTIP) were determined from the onset of chemiluminescence in shock-tube experiments behind reflected shock waves in dry as well as in humid gas mixtures. Additionally, the ignition delay times of TEOS and HMDSO have been investigated in humid air and as a function of water vapor concentration in the initial gas mixture.

Nanocrystalline and Amorphous Silicon Semiconductors as Competing Candidates for PV Applications

The optical properties of two Hydrogenated nanocrystalline (nc-Si: H) and amorphous silicon (a-Si: H) thin film samples are investigated using conventional spectrophotometric technique. Both samples were prepared by plasma enhanced chemical vapor deposition technique (PECVD). The nc-Si: H sample prepared with 1% silicon concentration at temperature of 220˚C with ∼1 Å/s growth rate exhibits optical behavior closer to crystalline Silicon (c-Si) sample than the a-Si: H sample prepared with Helium (He) percentage of the initial gas mixture of 20 at temperature of 80˚C with increased growth rate of ∼2.8 Å/s. The optical constants, thicknesses and the energy band gap of both samples are obtained from the transmission data only. The values of refractive index within an estimated uncertainty of 1% for both a- Si: H and nc-Si: H samples are found close to those of c-Si sample in the chosen range of wavelengths. Both samples are found to have the same optical energy gap of ~1.7 eV within an uncertainty of ~ 0.03 eV and exhibit absorption features close to those of c-Si sample. The absorption behavior in the visible and near infrared regions of electromagnetic spectrum makes both samples good candidates for photovoltaic (PV) applications.

On combustion in a closed rectangular channel with initial vorticity

This article examines the detailed combustion process in a theoretical model with applicability to combustion in a wave rotor or wave disc engine. The model comprises a single channel into which an initial loading of methane and air is admitted and ignited after all inlet and exit ports have been closed. Combustion takes place at constant volume. However, the initial gaseous mixture in the channel is not at rest. The initial opening and closing of the ports generates significant vorticity which influences the evolution of the combustion process. Numerical evaluations are provided for the detailed flame shape for simplified (one-step) chemistry and a simulation using the detailed 235-step San Diego scheme. Quantities examined are the evolution of vorticity, pressure fluctuations, mass consumption rate, flame surface area and the influences on combustion of adiabatic and non-adiabatic channel walls. Combustion regimes are identified and compared with simpler model studies (no initial flow). Pointwise quantities are examined to describe the various stages of burning in the channel. The focus of the study is directed towards quantities that influence overall burning rate and completeness of combustion.

Investigating the Thermodynamic Stabilities of Hydrogen and Methane Binary Gas Hydrates

When hydrogen (H2) is mixed with small amounts of methane (CH4), the conditions required for clathrate hydrate formation can be significantly reduced when compared to that of simple H2 hydrate. With growing demand for CH4 as a commercially viable source of energy, H2 + CH4 binary hydrates may be more appealing than extensively studied H2 + tetrahydrofuran (THF) hydrates from an energy density standpoint. Using Raman spectroscopic and powder X-ray diffraction measurements, we show that hydrate structure and storage capacities of H2 + CH4 mixed hydrates are largely dependent on the composition of the initial gas mixture, total system pressure, and formation period. In some cases, H2 + CH4 hydrate kinetically forms structure I first, even though the thermodynamically stable phase is structure II.

Laminar Burning Velocities of Dimethyl Carbonate with Air

Laminar burning velocities of dimethyl carbonate (DMC) + air flames at initial gas mixture temperatures of 298, 318, 338, and 358 K are reported. Nonstretched flames were stabilized on a perforated plate burner at atmospheric pressure, and the laminar burning velocities were determined using the heat flux method. The overall accuracy of the burning velocities was evaluated to be typically better than ±1 cm/s. The effects of unburned mixture temperature on the laminar burning velocity of DMC were analyzed using the correlation SL = SL0 (Tu/Tu0)α. The present experimental results indicated that the power exponent α reaches a minimum in slightly rich mixtures corresponding to the maximum burning velocity. Modeling of these results has been attempted using the mechanism developed by Glaude et al. It was found that this model significantly overpredicts laminar burning velocities of methanol, ethanol, and DMC; however, it accurately reproduces the temperature power exponent α for dimethyl carbonate flames.

On the reactivity of plasma-treated photo-catalytic TiO2 surfaces for oxidation of C2H2 and CO

The objective of this study is to understand fundamental aspects of interactions of plasmas with catalytic surfaces. Based on this approach the reactivity of plasma treated and stimulated catalytic surfaces of TiO2 is studied by analysing the oxidation (i) of C2H2 to CO and CO2 and (ii) of CO to CO2. The inner surface of a Pyrex discharge tube is coated with TiO2 films impregnated with TiO2 nanoparticles, which provides a surface area of about 4 m2. In addition to the exposure of the TiO2 surface by low-pressure radio-frequency plasmas using O2, Ar or N2 (f = 13.56 MHz, p = 0.53 mbar, P = 17 W) the surfaces are stimulated by heating and UV radiation treatment. The temporal development of the concentrations of the precursor gases C2H2 or CO and of the reaction products is monitored using quantum cascade laser absorption spectroscopy, which provides multi-component detection in the mid-infrared spectral range. The C2H2 concentration was found to be nearly constant over time after a pre-treatment with Ar or N2 discharges using an initial gas mixture of 1% C2H2 in Ar. However, a strong decay of the concentration of C2H2 is observed for pure O2 plasma pre-treatment. In general, the decay is found to be nearly exponential with time constant in the order of about 10 min. The reactive adsorption of C2H2 molecules on the inner surface of the tube reactor showed a density of about 7.5 × 1012 C2H2 molecules cm−2. This behaviour demonstrates that the reaction produces some adsorbed intermediates, which can be thermally or photo-catalytically oxidized to CO2. In contrast, when 1% CO in Ar is used as an initial gas mixture no adsorption processes on the TiO2 surface could be detected. An effective destruction of CO took part via photo-catalytic oxidation.

Stability Assessment of Gas Mixtures Containing Monoterpenes in Varying Cylinder Materials and Treatments

Studies of climate change increasingly recognize the diverse influences exerted by monoterpenes in the atmosphere, including roles in particulates, ozone formation, and oxidizing potential. Measurements of key monoterpenes suggest atmospheric mole fractions ranging from low pmol/mol (parts-per-trillion; ppt) to nmol/mol (parts-per-billion; ppb), depending on location and compound. To accurately establish the mole fraction trends, assess the role of monoterpenes in atmospheric chemistry, and relate measurement records from many laboratories and researchers, it is essential to have good calibration standards. The feasibility of preparing well-characterized, stable gas cylinder standards for monoterpenes at the nmol/mol level was previously tested using treated (Aculife IV) aluminum gas cylinders at NIST. Results for 4 of the 11 monoterpenes, monitored versus an internal standard of benzene, indicated stability in these treated aluminum gas cylinders for over 6 months and projected long-term (years) stability. However, the mole fraction of the key monoterpene β-pinene decreased, while the mole fractions of α-pinene, d-limonene (R-(+)-limonene), p-cymene, and camphene (a terpene not present in the initial gas mixture) increased, indicating a chemical transformation of β-pinene to these species. A similar pattern of decreasing mole fraction was observed in α-pinene where growth of d-limonene, p-cymene, and camphene has been observed in treated gas cylinders prepared with a mixture of just α-pinene and benzene as the internal standard. The current research discusses the testing of other cylinders and treatments for the potential of long-term stability of monoterpenes in a gas mixture. In this current study, a similar pattern of decreasing mole fraction, although somewhat improved short-term stability, was observed for β-pinene and α-pinene, with growth of d-limonene, p-cymene, and camphene, in nickel-plated carbon steel cylinders. β-Pinene and α-pinene showed excellent stability at over 6 months in aluminum cylinders treated with a different process (Experis) than used in the original study.

Synthesis of silicon carbonitride dielectric films with improved optical and mechanical properties from tetramethyldisilazane

Films of silicon carbonitride have been obtained by the plasma chemical decomposition of a gaseous mixture of helium and a volatile organic silicon compound 1,1,3,3-tetramethyldisilazane (TMDS) in the temperature range of 373–973 K. The modeling of the processes of deposition from a gaseous mixture (TMDS + He) in the temperature range of 300–1300 K and pressures of P total 0 = 10−2–10 Torr has shown that it is possible to vary the equilibrium composition of the condensed phase depending on the synthesis temperature and the initial gaseous mixture composition. The chemical and phase compositions, as well as physicochemical and functional properties, of the films obtained in the range of 373–973 K have been studied using a complex of modern techniques, including Fourier transformed infrared (FTIR) Raman, X-ray photoelectron (XPS) and energy-dispersive spectroscopy (EDS), scanning electron (SEM) and atomic-force microscopy (AFM), X-ray diffraction using synchrotron radiation (XRD-SR), ellipsometry, and spectrophotometry. The electrophysical parameters are determined using the C-V and I-V characteristics, and the microhardness and Young’s modulus are determined by the nanoindentation method. It is established that the chemical composition of low-temperature (373–673 K) films of silicon carbonitride corresponds to a gross formula of SiC x N y O z : H, while that of high-temperature films corresponds to SiC x N y . The presence of nanocrystals with the phase composition close to the standard phase α-Si3N4 is detected in the films. It is shown that all of the films are perfect dielectrics (k = 3.8–6.4, ρ = 2.2 × 1010−1.3 × 1011 Ohm · cm), possess high transparency (∼98%) in a wide spectral range of 280–2500 nm, and have a high microhardness (3.8–36 GPa) and Young’s momentum (125–190 GPa).

Laminar burning velocities of acetone in air at room and elevated temperatures

Laminar burning velocities of acetone+air mixtures at initial gas mixture temperatures of 298, 318, 338 and 358K are reported. Non-stretched flames were stabilized on a perforated plate burner at 1atm, and laminar burning velocities were determined using the heat flux method, at conditions where the net heat loss from the flame to the burner is zero. The overall accuracy of the burning velocities was estimated to be better than ±1.0cms−1. Very good reproducibility of the results and excellent agreement with modeling using a recently updated chemical kinetic model brings confidence in the validity of the reported results. Previous determinations of laminar burning velocities for acetone have provided inconsistent results. In the present work it is suggested that this can in part be attributed to the chemically aggressive nature of acetone.

X-ray photoelectron and auger spectroscopic study of the chemical composition of BC x N y films

X-ray photoelectron and Auger spectroscopy are used to investigate the chemical composition of BCxNy films synthesized by PECVD from different initial gas mixtures in the temperature range 473–723 K. Main principles and features of the film formation are found. It is shown that the chemical composition of BCxNy films significantly depends on the synthesis parameters, which enables targeted control of their physical properties. The obtained data are discussed.

Structural features and conductivity of silicon films: Simulation and experiment

Structural and photoelectric properties of low-temperature silicon microcrystalline layers are studied. The layers are obtained by a new method of electron-beam plasma produced by the electron beam interaction with the supersonic flow of initial gas mixtures. Based on the experiments and Monte Carlo calculations it is found that the dependence of the μc-Si:H layer conductivity on the degree of crystallinity of the material is described within percolation theory.

Oxy-fuel Combustion of Ethanol in Premixed Flames

First measurements of the adiabatic laminar burning velocities of lean ethanol + oxygen + carbon dioxide flames, at 1 atm and initial gas mixture temperatures of 298, 318, and 338 K, are presented. The oxygen content O2/(O2 + CO2) in the artificial air was 35%. The laminar burning velocities were determined using the heat flux method, where a non-stretched flame is stabilized under adiabatic conditions. The measurements were found in qualitative agreement with modeling performed using the Marinov model, the San Diego model, and the model by Leplat et al. In comparison to experimental data, the Marinov model gave the best quantitative agreement. Notable quantitative differences between the models were analyzed using sensitivity analysis and reaction path diagrams. Reaction path analysis showed that the Marinov and the San Diego models have the same 12 most important species. Among the 12 most important species in the model of Leplat et al., 10 species are in common with the other two models. According to predictions of the Marinov model, combustion of ethanol in air and at oxy-fuel conditions proceeds via the same reaction path; however, the sensitivities of the key reactions are different.

Tris(diethylamino)silane—A new precursor compound for obtaining layers of silicon carbonitride

Silicon carbonitride layers have been obtained by chemical deposition from the gas phase with thermal (LPCVD) and plasma (PECVD) activation of the gas mixture of helium with the new volatile siliconorganic compound tris(diethylamino)silane (Et 2N)3SiH (TDEAS) in the temperature region 373–1173 K. Thermodynamic simulation of the deposition processes from the gas mixture (TDEAS + He) in the temperature interval 300–1300 K and pressure interval P tot 0 from 1 × 10−2 to 10 mm Hg has revealed the possibility of varying the equilibrium composition of the condensed phase depending on the synthesis temperature and the composition of the initial gas mixture. Physicochemical and functional properties of obtained layers were studied by complex of modern methods. It has been established that the chemical composition of the silicon carbonitride layers obtained by the PECVD method, depending on the deposition conditions, approaches that of silicon oxynitride or nitride, and the composition of those obtained by the LPCVD method approaches that of silicon carbide. The presence of nanocrystals with a phase composition close to the standard α-Si3N4 phase and of carbon inclusions has been found in the layers.

No evidence for superiority of air or oxygen for neonatal resuscitation: a meta-analysis

The aim of this meta-analysis was to re-evaluate the evidence in favour of oxygen or room air as the initial gas mixture for neonatal resuscitation in terms of the following outcomes: death, hypoxic/ischemic encephalopathy, need for tracheal intubation, and APGAR score-Appearance (skin color), Pulse (heart rate), Grimace (reflex irritability), Activity (muscle tone), and Respiration-at five minutes. A search with no language restriction for all available controlled clinical trials (CCT) was conducted in PUBMED, Cochrane Central Register of Controlled Trials, and EMBASE. Data were extracted independently by the two investigators. Eight CCTs were retained for analysis. They included 1,500 patients, 772 in the oxygen group and 728 in the air group. The evidence is based mainly on quasi-randomized studies (1,311/1,500) with unblinded resuscitators (1,421/1,500). The expertise/training of the resuscitators was unspecified for four of the eight studies. The risk ratio (RR) for death was 1.35 (95% confidence intervals [CI]=0.97 to 1.88; P=0.08; I-squared 0%). The RR for hypoxic/ischemic encephalopathy was 1.03 (95% CI=0.86 to 1.23; P=0.74; I-squared 0%). The RR for requiring a tracheal intubation was 0.85 (95% CI=0.69 to 1.05 [random effects model]; P=0.12; I-squared=9.51%). The literature is insufficient to make any statement regarding the superiority of oxygen or room air as the initial gas mixture for neonatal resuscitation.

Salmon in modified atmospheres using high- and low-barrier packaging materialsSalmón en atmósferas modificadas utilizando material de alta y baja barrera

The effectiveness of packaging material on the shelf-life of fresh salmon (Salmo salar) derived from aquaculture has been studied using an atmosphere rich in carbon dioxide and low in oxygen (80% CO2, 5% O2, 15% N2). Multilayer materials with different permeability to the gases (with copolymers of ethylene-vinyl alcohol or of polyethylene) were used in the upper film and/or in the packaging tray. The effect of the material on the conservation of the salmon was determined on the basis of changes in the initial gas mixture and the quantification of chemical, microbiological, and sensory variables during storage. In general, the results show small differences between the two types of packaging and their influence on salmon conservation. The sensorial parameter mean values (color, odor, flavor and texture) were favorable to the low barrier material LB/LB at the end of the storage period (day 13) when the salmon in EVOH/LB was considered as rejected. Se ha estudiado la efectividad del material de envasado en la vida útil de salmón (Salmo salar) fresco procedente de la acuicultura, utilizando una atmósfera rica en dióxido de carbono y baja en oxígeno (80% CO2, 5% O2, 15% N2). Los materiales multicapa con distinta permeabilidad a los gases (con copolímeros de etileno-alcohol vinílico o polietileno) se utilizaron en la película superior y/o en la bandeja de envasado. La valoración del efecto del material en la conservación del salmón se realizó de acuerdo a los cambios en la mezcla gaseosa inicial y a la cuantificación de variables químicas, microbiológicas y sensoriales durante el almacenamiento. En general, los resultados muestran pequeñas diferencias entre los dos tipos de envasados y su influencia en la conservación del salmón. Los valores medios de los parámetros sensoriales (color, olor, sabor y textura) fueron favorables al material de baja barrera LB/LB al final del periodo de almacenamiento (día 13), momento en que el salmón en EVOH/LB se consideró rechazado.