Variety Of Gas Mixtures Research Articles

Understanding the characteristics of non-equilibrium alternating current gliding arc discharge in a variety of gas mixtures (air, N2, Ar, Ar/O2, and Ar/CH4) at elevated pressures (1–5 atm)

This work aims at clarifying the fundamental mechanisms of non-equilibrium alternating current gliding arc discharge (GAD) by investigating effects of gas compositions and pressures on the GAD characteristics with electrical and optical methods. Interestingly, the glow-to-spark transition was found by adding O2 or CH4 into the argon or modulating the power supply. This transition occurs attributed to the fact that the discharge mode is largely affected by the effective electron decay time (τ) as well as the feedback response of the power supply to the free electron density in the GAD. Short τ or low free electron density tends to result in the spark-type discharge. It further implies that the power supply characteristics is crucial for discharge mode control. The pressure effects on the GAD characteristics were found to vary with gas composition when the same alternating current power supply was used. In N2 or air, the emission intensity from the plasma column increases with pressure while the mean electric field strength (E) along the plasma column decreases with pressure. Differently, in Ar, the emission intensity and E do not change much with pressure. It can be explained by the different energy partition and transfer pathways between monatomic and molecular species. The molecular gases have vibrational excitation pathways to facilitate the electronic excitation and ionization that is different from the monatomic gas.

Applications and Perspectives of Ultrasonic Multi-Gas Analysis with Simultaneous Flowmetry

We have developed ultrasonic instrumentation for simultaneous flow and composition measurement in a variety of gas mixtures. Flow and composition are respectively derived from measurements of the difference and average of sound transit times in opposite directions in a flowing process gas. We have developed a sound velocity-based algorithm to compensate for the effects of additional gases, allowing the concentrations of a pair of gases of primary interest to be acoustically measured on top of a varying baseline from ‘third party’ gases whose concentrations in the multi-gas mixture are measured by other means. Several instruments are used in the CERN ATLAS experiment. Three monitor C3F8, (R218), and CO2 coolant leaks into N2-purged environmental envelopes. Precision in molar concentration of better than 2 × 10−5 is routinely seen in mixtures of C3F8 in N2 in the presence of varying known concentrations of CO2. Further instruments monitor air ingress and C3F8 vapor flow (at high mass flows around 1.1 kg s−1) in the 60 kW thermosiphon C3F8 evaporative cooling recirculator. This instrumentation and analysis technique, targeting binary pairs of gases of interest in multi-gas mixtures, is promising for mixtures of anesthetic gases, particularly in the developing area of xenon anesthesia.

Applications and perspectives of gas analysis based on sonar instrumentation

We have developed ultrasonic instrumentation to simultaneously monitor flow and composition in a variety of gas mixtures. Flow and mixture composition are respectively derived from measurements of the difference and average of sound transit times in two opposite directions in a flowing process gas blend. Gas composition is then determined from an automated comparison of the measured sound velocities with a velocity/composition database.Continuous, real-time precision measurements of binary gas mixtures are required in many applications. While the most natural application of this instrumentation is in the analysis of such mixtures, analysis of mixtures with additional components is also possible, as discussed in this paper.In the ATLAS experiment at CERN, several instruments are presently used in the Detector Control System. Three instruments monitor octafluoropropane (C3F8, R218) and carbon dioxide (CO2, R744) coolant leaks into the nitrogen-purged envelopes surrounding elements of the inner silicon tracker. Precision in molar concentration of better than 2.10−5 is routinely seen in mixtures of C3F8 in nitrogen in the presence of known concentrations of the third party gas CO2.Two further instruments are used to monitor the new 60 kW thermosiphon C3F8 evaporative coolant recirculator which exploits the 90 m depth of the ATLAS pit to circulate coolant without the need for pumps or compressors in the primary loop. These instruments are used to verify the absence of air leaks in the thermosiphon cooling circuit and to measure the vapour-phase coolant flow in real-time.This instrumentation is also used to measure zeotropic fluorocarbon blends containing C3F8 and up to 25% hexafluoroethane (C2F6, R116), achieving a precision around 0.16% in the range 0–25% C2F6. We also report on measurements of heat transfer coefficient in these blends: our experimental data were compared to several empirical correlations, with typical differences less than 10%.This analysis technique, targeting binary pairs of gases of dissimilar molecular weight, is particularly promising for mixtures of anesthetic gases, including in the developing area of anesthesia using xenon. The instrument and its various applications will be discussed.

Identification of vapor-phase chemical warfare agent simulants and rocket fuels using laser-induced breakdown spectroscopy

Application of laser-induced breakdown spectroscopy (LIBS) to the identification of security threats is a growing area of research. This work presents LIBS spectra of vapor-phase chemical warfare agent simulants and typical rocket fuels. A large dataset of spectra was acquired using a variety of gas mixtures and background pressures and processed using partial least squares analysis. The five compounds studied were identified with a 99% success rate by the best method. The temporal behavior of the emission lines as a function of chamber pressure and gas mixture was also investigated, revealing some interesting trends that merit further study.

Gas-Phase Chemistry in Inductively Coupled Plasmas for NO Removal from Mixed Gas Systems

Inductively coupled rf plasmas were used to investigate the removal of NO from a variety of gas mixtures. Laser-induced fluorescence and optical emission spectroscopy were employed to measure the relative gas-phase density of NO as a function of the applied rf power, gas mixture, and catalytic substrate type. In general, the overall density of NO decreases as a function of applied rf power in both NO and N(2)/O(2) plasmas, but the addition of gases such as H(2)O vapor and CH(4), as well as the presence of Au-coated substrates, significantly affects the behavior of NO in these systems. Rotational and vibrational temperatures for NO were measured using laser-induced fluorescence excitation spectra and optical emission spectra. Results show NO vibrational temperatures are about a factor of 5 higher than rotational temperatures and indicate little dependence on applied rf power, feed gas composition, or overall system pressure. Possible mechanisms for the observed changes in [NO] as well as the rotational and vibrational temperature data are addressed.

Kinetic aspects of the formation of aluminium oxide by use of a microwave-induced plasma.

The oxidation of thin aluminium layers in a microwave plasma has been investigated to determine the kinetics of oxide growth. Thin Al-coatings were oxidized by means of a variety of gas mixtures, characterized by different partial pressures of oxygen, in microwave-induced plasmas of different power. To study the whole kinetic process the Al-metal and the oxide formed were investigated by means of a combination of grazing incidence X-ray reflectometry (GIXR) and grazing incidence X-ray diffractometry (GIXRD). XPS and FTIR spectroscopy confirmed the formation of stoichiometric Al(2)O(3). The alumina formed is X-ray amorphous. Quantitative description of oxide formation was achieved indirectly by determination of the decrease in the integrated intensity of the Al(111)-peak and the total thickness of the whole coating. These values enabled calculation of kinetic data. It was found that oxide growth was a combination of two simultaneous processes - diffusion and sputter processes. The diffusion coefficient D (cm(2) s(-1)) and the sputter rate S (nm s(-1)) were determined. The effect of the composition of the gas mixture, microwave power, and concentration of activated oxygen species on the oxidation process will be discussed. For calculation of the activation energy, E(A), of this plasma-enhanced diffusion process the temperature-dependence of D was investigated.

Measurement and manipulation of the partial pressure of oxygen in the rat anterior chamber

Purpose. To measure the partial pressure of oxygen in the anterior chamber of the rat eye under a variety of physiological conditions. Methods. Polarographic oxygen electrode measurements were made in methoxyflurane-anesthetized Wistar or Sprague-Dawley rats. After ketamine-xylazine or pentobarbital induction, animals were artificially ventilated with a variety of gas mixtures; gases were directed over the corneal surface during measurement of the partial pressure of oxygen in the middle of the pupil at the surface of the lens. Results. The partial pressure of oxygen in the anterior chamber of the rat eye was measured as 63 ± 9 mm Hg (mean ± S.D.). Breathing 100% oxygen and delivery of 100% oxygen to the cornea additively increased aqueous humor oxygen partial pressure to levels above 279 ± 45 mm Hg with the greatest increase coming from inhaled 100% oxygen. Conversely, inhalation and subsequent transcorneal delivery of 10% oxygen reduced levels to 22 ± 11 mm Hg. Conclusions. These results suggest that the partial pressure of oxygen in the anterior chamber is sensitive to the environment in contact with the cornea. In the rat eye, the delivery of oxygen to the anterior chamber via transcorneal diffusion may be more significant than for larger animals.

A method for correcting short-term fatigue in electrochemical gas sensors

The electrochemical fuel-cell sensor provides a reliable means of determining the concentration of a range of gases in a variety of gas mixtures. Its use in screening for breath alcohol content, evidential testing and environmental monitoring for a range of aldehydes is well established across the world. The fuel cell, in common with other types of similar sensors, when subjected to successive samples or doses, with short rest times between doses, will exhibit a variation in response due to an effect known as short-term fatigue, the extent of which is related to the sensor dose history (i.e., to the dose concentration and rest time between doses). Current practice involves allowing the cell to recover to an acceptable level before resampling but, since this limits the speed of the sampling process, for high-accuracy operation a method of fatigue correction is highly desirable. This paper describes the development of a model that approximates the relationship between dose history and response deviation. Results are presented which demonstrate that, when combined with an appropriate input function, this method has the potential for overcoming the problems associated with short-term fatigue.

In vitro accuracy of three blood O2 saturation optic catheter systems

The measure of the precision and accuracy of three optic SvO2 systems in vitro (SAT-2 Baxter, oximetrix 3 Abbott, HEMOPRO-2 Spectramed in a wide range of saturations (24-85%) and hematocrit (20-40%). In vitro comparison of the results given by a Co-Oximeter and the SvO2 systems. 144 blood samples were tonometered with a variety of gas mixtures. Measurements of SvO2 were compared to those obtained by means of a Co-Oximeter, the difference (dSO2) between paired values were calculated. Precision was evaluated from confidence intervals (2SD) and accuracy was tested using dSO2 figures. As there was no difference in either precision or accuracy among catheters for a given system, data obtained from a given system were pooled. Mean precision was 14.2%, 8.6%, 9% for the Spectramed, Baxter and Abbott systems, respectively. The rather low reliability of the optic method should be borne in mind in patients with low SvO2 and/or low hematocrit.

A SEM/AES/XPS tribometer for rolling and sliding contacts

A facility for studying the tribological performance of materials for a wide range of conditions has been established. It provides sliding, rolling and rolling-with-controlled-slip contact conditions at temperatures from liquid nitrogen to ambient in environments from ultra-high vacuum to one atmosphere of oxygen, hydrogen and a variety of gas mixtures. Parameters such as normal and friction forces, wear, temperature and speed are monitored in real-time with a computer data acquisition system. The surface topography and chemical composition are analyzed with scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and small-area multichannel X-ray photoelectron spectroscopy (XPS) incorporated in the facility. The chemical composition of the test environment and outgassed compounds from the tribomaterials are monitored with a quadrupole mass spectrometer.

Monte Carlo-fluid model of chlorine atom production in Cl2, HCl, and CCl4 radio-frequency discharges for plasma etching

Chlorine chemistries are often used for the radio-frequency (rf) discharge plasma etching of compound semiconductors, metals, and silicon. A variety of gas mixtures are used as Cl atom donors, many of which have different electron transport coefficients. In this article we computationally investigate 13.56 MHz rf discharges sustained in He/Cl2, He/HCl, and He/CCl4 gas mixtures in the context of plasma etching. The study is performed using a Monte Carlo-fluid hybrid model of rf discharges. We find that the Cl atom production efficiency is surprisingly similar in these mixtures, while the details of the electron transport (sources of ionization, locations of attachment, electronegativity) dramatically differ. We also find that even at the low pressures of interest (0.25–1 Torr) attachment in He/HCl mixtures is dominated by vibrationally excited HCl, in analogy to high-pressure discharge devices.

Human Cerebrovascular Response to Oxygen and Carbon Dioxide as Determined by Internal Carotid Artery Duplex Scanning

Alterations in arterial oxygen and carbon dioxide influence cerebrovascular resistance and therefore cerebral blood flow (CBF), but the magnitude of these CBF responses have not been well defined in normal humans. Duplex scanning (B-mode imaging and pulsed Doppler shift analysis) was used to measure internal carotid blood flow (ICBF) as an indicator of CBF in 20 normal subjects during alterations of arterial O2 and CO2. End-tidal Pco2 (PETco2) was measured by mass spectrometry, arterial oxygen saturation by pulse oximetry, and unilateral (right) ICBF by duplex scanning. A variety of gas mixtures were administered to achieve hypoxemia (Fio2 = 0.075–0.10) and hypercapnia (Fico2 = 0.05) or the subject was asked to hyperventilate to PETco2 = 16–24 mm Hg. The ICBF was determined five times in each of six conditions: (1) normoxia/normocapnia; (2) normoxia/hypercapnia; (3) normoxia/hypocapnia; (4) hypoxia/normocapnia; (5) hypoxia/hypercapnia; and (6) hypoxia/hypocapnia. During normoxia and normocapnia, the mean ICBF was 330 ± 19 (SEM) mL/min. Specific CO2 reactivity was 7.4 ± 0.7 mL/min/mmHg, which is equivalent to 2.3% ± 0.1% of normocapnic blood flow per mm Hg change in CO2. During normocapnia, ICBF increased by 2.9 ± 0.9 mL/min for each percentage decrease in oxygen saturation. Using an ANOVA with repeated measures to fit the responses, the following statistically significant relationship was found: ICBF (mL/min) = 333 + 6.3 (PETco2 - 40) + 2.7 Dso2 ± 81 where Dso2 is arterial desaturation (100 - arterial saturation). An additional “between subject” variation had a mean of 0 and a standard deviation of 82 mL/min. There was no statistically significant evidence of an interaction between O2 and CO2 response. Our data suggest that hypoxia and carbon dioxide changes will alter CBF simultaneously and additively. Duplex scanning of the internal carotid artery, which can be performed at the bedside, is sufficiently sensitive to detect changes in ICBF and internal carotid artery oxygen delivery.

Polarization Effects on Meniscus Characteristics in Molten Carbonate

Meniscus heights on a gold flag electrode partially submerged in Li/K carbonate (62/38 mole percent) at 650°C have been determined under a variety of gas mixtures at atmospheric pressure. The meniscus height as a function of electrode potential shows a characteristic minimum for each gas composition and a relatively steep increase with increasing cathodic polarization. Analysis of the near‐equilibrium data, assuming electrocapillary effects only, shows that this is consistent with specific adsorption of oxide ion on the electrode. At appreciable polarization, mass‐transfer effects as well as adsorption appear to play a role, and the approach to steady‐state conditions following a disturbance is slow.

Investigation of Cvd-Grown Diamond by Cathodoluminescence in TEM

ABSTRACTHigh resolution cathodoluminescence (CL) spectroscopy and imaging have been performed in transmission electron microscopy (TEM) to analyze defects and impurities in polycrystalline diamond films grown by chemical vapor deposition (CVD) using a variety of gas mixtures, and oxyacetylene combustion flame synthesis (CFS). The combination of CL and TEM allows a direct correlation of film microstructure with the electronic structure due to defects. The CL was found to be very nonuniformly distributed on a submicron scale reflecting different spatial distributions of N, B and Si impurities and their correlations with microstructure. Band A CL due to closely-spaced donor-acceptor (D-A) pairs was correlated with dislocations in both CVD-grown and CFS material whereas band A from widely-separated D-A pairs was uniformly distributed in the films. CL from several different N-related point-type defects was observed and found to depend on the growth gases used, although no correlation with microstructure has been observed so far. A di-Si interstitial impurity, believed to arise from the Si substrate and reactor walls, was not correlated with any microstructure but varied greatly in concentration from grain to grain and from film to Film. In addition, both highly faulted and defect-free grains were found to emit no visible CL due to mid gap states.

HUMAN CEREBROVASCULAR RESPONSE TO OXYGEN AND CARBON DIOXIDE CHANGES AS DETERMINED BY INTERNAL CAROTID ARTERY DUPLEX SCANNING

Alterations in arterial oxygen and carbon dioxide influence cerebrovascular resistance and therefore cerebral blood flow (CBF), but the magnitude of these CBF responses have not been well defined in normal humans. Duplex scanning (B-mode imaging and pulsed Doppler shift analysis) was used to measure internal carotid blood flow (ICBF) as an indicator of CBF in 20 normal subjects during alterations of arterial O2 and CO2. End-tidal PCO2 (PETCO2) was measured by mass spectrometry, arterial oxygen saturation by pulse oximetry, and unilateral (right) ICBF by duplex scanning. A variety of gas mixtures were administered to achieve hypoxemia (FIO2 = 0.075-0.10) and hypercapnia (FICO2 = 0.05) or the subject was asked to hyperventilate to PETCO2 = 16-24 mm Hg. The ICBF was determined five times in each of six conditions: (1) normoxia/normocapnia; (2) normoxia/hypercapnia; (3) normoxia/hypocapnia; (4) hypoxia/normocapnia; (5) hypoxia/hypercapnia; and (6) hypoxia/hypocapnia. During normoxia and normocapnia, the mean ICBF was 330 +/- 19 (SEM) mL/min. Specific CO2 reactivity was 7.4 +/- 0.7 mL/min/mmHg, which is equivalent to 2.3% +/- 0.1% of normocapnic blood flow per mm Hg change in CO2. During normocapnia, ICBF increased by 2.9 +/- 0.9 mL/min for each percentage decrease in oxygen saturation. Using an ANOVA with repeated measures to fit the responses, the following statistically significant relationship was found: ICBF (mL/min) = 333 + 6.3.(PETCO2 - 40) + 2.7 DSO2 +/- 81 where DSO2 is arterial desaturation (100 - arterial saturation). An additional "between subject" variation had a mean of 0 and a standard deviation of 82 mL/min. There was no statistically significant evidence of an interaction between O2 and CO2 response. Our data suggest that hypoxia and carbon dioxide changes will alter CBF simultaneously and additively. Duplex scanning of the internal carotid artery, which can be performed at the bedside, is sufficiently sensitive to detect changes in ICBF and internal carotid artery oxygen delivery.

Excimer fluorescence for display applications

Over the past decade workers have examined a variety of gas mixtures and phosphor excitation schemes in an effort to develop a viable alternative to the orange neon gas discharge display. To date no approach has been found that offers the combination of brightness, efficiency, and practicality typical of neon-based displays. In this paper we report early results of an investigation directed toward evaluation of excimer molecule fluorescence for display applications. Attention has been focused on rare gas-halide and rare gas-oxide excimers because of their favorable formation kinetics and visible emission characteristics. Modeling of kinetic processes has identified gas mixtures suitable for the generation of visible excimer fluorescence. Experimentation carried out using both a conventional ac plasma panel and a discharge test device has resulted in blue Xe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Cl emission using Ne-Xe-Cl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> mixtures, and green XeO emission using Xe-O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> mixtures. Moreover, the measured luminous intensity of these excimer mixtures was comparable to, and under some conditions greater than, that of neon-Penning mixtures excited under Similar conditions. These results indicate the possibility of developing a new class of plasma display based on the visible fluorescence of excimer molecules.

Low energy electron collision phenomena in HgBr2

Cross sections for mercuric bromide (HgBr2) dissociative attachment and ionization have been measured using an electron beam experiment. The dominant products of these reactions, as identified by mass analysis, are Br− and HgBr+2. A complementary electron swarm experiment was used to determine the ion production coefficients in a variety of gas mixtures containing HgBr2. The measured ion production coefficients were found to be in excellent agreement with the attachment and ionization coefficients computed using the measured cross sections. Additionally, analysis of the variations in the measured HgBr2 ion production coefficients along with measured electron drift velocity variations is found to be consistent with the interpretation that vibrational excitation of HgBr2 is dominated by a resonance in the 3–5 eV electron energy range for which dissociative attachment is observed to occur.

A laboratory study on the dissociative recombination of vibrationally excited O2+ ions

The production of metastable O(¹S) atoms by the dissociative recombination of O2+ ions has been studied in a laboratory plasma spectroscopy experiment. The specific dissociative recombination coefficient for O(1S) formation has a value of 2.1 × 10−8 cm3 s−1, corresponding to an O(¹S) quantum yield of 10% at an apparent temperature of 296°K, in agreement with the earlier but less comprehensive measurements of Zipf [1970]. By using a variety of gas mixtures in order to modify the vibrational population of the O2+ ions and laser‐induced photofluorescence techniques it was found that the laboratory O2+ plasmas are vibrationally excited and that O2+ ions in the υ′=4–12 vibrational levels are the chief source of the observed O(1S) atoms. The specific O(1S) dissociative recombination coefficient for O2+(2πg) ions in the lowest vibrational levels (υ′ ≤3) is much smaller (4.2 × 10−9 cm3 s−1). The implications of the quantum yield of 9.9% derived from Atmosphere Explorer data are discussed in the light of these findings. Preliminary electron‐heating experiments indicate that the specific O(¹S) recombination coefficient decreases with increasing electron temperature.

Medium Effects in NMR. III. Fluorine Resonance in Gases

The fluorine resonance of CF4, SiF4, SF6, and CHF3, and in a variety of gas mixtures have been measured at pressures up to 50 atm at room temperature. The pressure dependence of the chemical shift is much more pronounced than for protons [W. T. Raynes, A. D. Buckingham, and H. J. Bernstein, J. Chem. Phys. 36, 3481 (1962)]. The results are interpreted in the same manner as for the proton work (see reference above) in terms of a field and field square contribution to the medium shift. The field square contribution is primarily due to dispersive forces and is 15 to 44 times as large as for hydrogen in CH bonds. The polar contribution (first power of the field) for CF bonds is also larger than for CH bonds but of opposite sign, being responsible for high-field medium shifts for CF bonds.