Initial Gas Composition Research Articles

Interaction of SF6 Multiple PhotonDissociation Products With Siliconand SiO2 Surfaces

Experiments on etching Si and SiO2 by the multiple photon dissociation products of SF6 molecule in IR laser field have been carried out. These experiments showed that the etching of Si and SiO2 is the result of two qualitatively different processes and high selectivity (>103) can be achieved. The dependences of the etching process of the initial gas mixture pressure and composition, on the laser intensity and the number of laser pulses and on the direction of laser radiation have been studied. It has been found out that the etching rates of “a monolayer per pulse” for Si and ~100 Å/min for SiO2 are comparable to the rates achieved in low‐temperature plasma technique. Possible mechanisms and chemical reactions which can cause Si and SiO2 etching are discussed. It has been concluded that under the experimental conditions multiple photon dissociation forms the basis for the etching process.

CO oxidation on LnCoO 3 perovskite oxides: Effect of initial total pressure and gas composition

The kinetics of oxidation of CO on LnCoO 3 (Ln ≡ La, Nd, Sm, Gd) were studied in the temperature range 150–360 °C. These systems show an abrupt gradient change in the Arrhenius plots for CO oxidation at about 200 °. The adsorption isobars constructed for the total amount of gas mixture adsorbed show either a maximum or a minimum at the same temperature, indicating that the change in the mode of adsorption of the reactants is the cause for the break in the Arrhenius plots. The effect of the initial total pressure and an excess of CO or oxygen on the rate of the reaction was studied and the intrinsic rate constants were calculated.

Kinetics Study on the Reaction of Carbon with Carbon Dioxide in a Batchwise Reactor

This is a proposal of new method for kinetics study on the reaction of artificial graphites with carbon dioxide.In order to investigate the gasification of artificial graphites, the reaction rates were measured in a batchwise reactor connected with circulation system.Five artificial graphite samples were used in this experiments, i.e., PGX (UCC), ATJ (UCC), H-451 (GLCC), IG-11 (A), (B) (TOYO TANSO).These samples were allowed to react with carbon dioxide at 1000°C. The initial gas composition in a system was carbon dioxide only or carbon dioxide and nitrogen mixture.During the reaction, carbon monoxide increased progressively and total volume increased.However, the pressure in the reactor was maintained at atmospheric pressure with the aid of a variable Tedlar bag fitted with the circulation system.Oxygen partial pressure Po2 in the system was measured by means of a oxygen concentration cell (stabilized ZrO2) heated at 950°C, so that Pco2 /Pco ratio was determined.On the basis of Boudouard reaction, the rates of reaction expressed as burn-off per unit time were calculated from the ratio Pco2 /Pco and initial amount of carbon dioxide, and sample weight.Results obtained in this study were seen to obey the Langmuir-Hinshelwood equation.

A theory of nondilute spray evaporation based upon multiple drop interactions

A theory of nondilute spray evaporation has been developed which takes into account the separation distance between drops. This theory is based upon the global conservation equations for the two-phase mixture and the conservation equations for a drop evaporating in finite surroundings. Results obtained for n-decane using this theory show that as the equivalence ratio of the two-phase mixture decreases from 200 to 10 −2, four universal regimes are identified: (1) a regime of lean overall mixtures and dilute sprays where nondilute and dilute spray theories agree, (2) a regime where although both theories predict complete evaporation before saturation, the ratio of the evaporation times (onndilute/dilute) predicted by the two theories is a function of the equivalence ratio, (3) a regime where the nondilute spray theory predicts saturation before complete evaporation, whereas the dilute spray theory predicts the opposite, and (4) a regime where both theories predict saturation before complete evaporation, but at different residual drop sizes. In regimes 1 and 2 the evaporation time is a decreasing function of the equivalence ratio, whereas in regimes 3 and 4 it becomes an increasing function of the equivalence ratio. Parametric variations of the initial gas composition show that departures from the predictions of the dilute spray theory are obtained even for very dilute sprays if the overall mixture is rich. This implies that the dilute spray theory cannot adequately describe evaporation of drops injected during the later part of injection, or of larger-than-average drops in polydisperse sprays. Other departures from the dilute spray theory are obtained for sprays injected into relatively hot gases and for dense sprays initially composed of relatively cold drops. It was also shown that the evaporation time of a spray is a decreasing, nearly linear function of the initial drop temperature.

Gas absorption in the middle ear.

The middle ear (ME) pressure of alert and anesthetized rhesus monkeys was monitored by serial tympanograms in order to determine the gas absorption process in the ME cavity. During the four-hour observation period the ME pressure showed small, random fluctuations around zero pressure in the alert animals, whereas in the anesthetized animals, following an initial positive pressure phase, the ME pressure reached a plateau at an average pressure of -60 mm H2O. The ME gas composition was changed by air or oxygen gas politzerization in anesthetized animals to determine the effect of different initial gas compositions on the rate of absorption of the gas and on the magnitude of ME pressure. Politzerization with air and with oxygen gas resulted in average maximum ME pressures of -400 and -730 mm H2O, respectively. The experimental evidence suggested that the physiological composition of ME gases is nearly that of the surrounding environment and that the rate of gas absorption is low. When the gas composition of the ME is changed, the ME pressure decreases considerably. Based on these findings, a possible mechanism for the development of negative ME pressure is proposed.

Models for interpreting deposition rate data from a closed chemical vapour deposition system

Two models for interpreting deposition rate data from a closed chemical vapour deposition system were developed and were applied to the chemical vapour deposition of boron. In the quasi-kinetics model the deposition rate k is expressed by k = k 0(1− m m 0 ) n where k 0 is a rate constant, n is the order of the reaction, m is the amount of deposited boron and m 0 is the maximum available amount of boron from the vapour. Introduction of the temperature dependence of k 0 (Arrhenius equation) yields k = Ae − E A RT (1− m m 0 ) n All the deposition rate data are well described using n = 1.0. The apparent activation energies are in the range 115–135 kJ mol −1 for the four initial gas compositions investigated. In the diffusion model the deposition rate is described by a product function which contains the temperature T and the partial pressure difference ΔP i of the gaseous species i ( T r ΔP i , where r is a real number). By utilizing this function the deposition rate data from various experimental series can be brought to a common basis, provided that the initial compositions of the reaction gas mixtures in the series are the same, that only one solid reaction product (amorphous or crystalline boron) is formed and that the diffusing gaseous species is hydrogen or hydrogen chloride.

A study of the thermal decomposition of gaseous Si-B bromides under reduced pressure

We studied the pyrolysis of a BBr 3-SiBr 4 mixture under a reduced pressure. The yield and the silicon content of the deposits were determined as functions of the temperature, the pressure and the initial gas composition. This allowed us to define optimum conditions for the preparation of materials with good thermoelectrical performance at high temperatures.

Fuel content characterization and pressure retention measurements of DT-filled laser fusion microballoon targets

We have developed a nondestructive assay of the fule content of deuterium-tritium (DT) -filled microballoon laser fusion targets, which is based on β-particle counting rates. Using a model employing transmission measurements of kilovolt electrons through thin films, observed count rates are correlated with the amount of tritium in the glass walls and hollow interior of the microballoons. It has been shown that gas pressure in balloons can be calculated from tritium content and a knowledge of the initial gas composition since D and T were found to leak at the same rate. This assay technique is primarily applicable for balloons with glass wall thicknesses <1.5 μm where the number of escaping β particles is large compared with the number of x-ray photons generated in the glass. The technique has been applied to measure the pressure retention characteristics of individual targets. At room temperature, the balloons exhibited widely diverse and rapid leakage rates which could not be correlated with a model based on molecular diffusion and the assumption that all balloons had a homogeneous composition. Cryogenic storage greatly reduced the leakage rates with pressure retention half-lives ranging from 5 to approximately 12 years. Finally, it was determined that tritium in the glass wall is trapped and evidence is presented to support the hypothesis that it is uniformly distributed across the shell.

Multifactor optimization of a carbon dioxide gasdynamic laser. II. Specific power optimization

Methods for calculation of the output power of a carbon dioxide gasdynamic laser are discussed. The optimal conditions are found for maximum specific power on the assumption of one-dimensional flow of an inviscid gas ignoring changes in the chemical composition. The optimization is performed simultaneously with respect to the initial temperature, pressure, gas composition (carbon dioxide, nitrogen, helium, water vapor), nozzle profile, and resonator characteristics. The shape of the surface in the multidimensional space of the parameters being optimized is found. The nature of changes in the parameters near the optimal points is investigated.

Species composition in a CO2laser discharge

Recent experimental studies have shown that small quantities of nitrogen oxides can seriously effect discharge stability and power output in flowing CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> discharge lasers. In the present study, the formation of these oxides was measured in a sealed-off discharge tube under operating conditions similar to those in CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> lasers. The gas composition was sampled with a modulated molecular beam, low-voltage ionizer, quadrupole mass spectrometer. The combined use of low ionizer voltage and phase sensitive detection eliminated extraneous mass peaks caused by background gases and dissociative ionization in the analyzer itself. Equilibrium and time-varying measurements were made of neutral and ionix species. Two initial gas compositions were used 1) 71.8 percent He, 15.5 percent N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , 12.7 percent CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , and 2) 87.2 percent He, 12.8 percent CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . Measurements were made in a discharge tube 2.2 cm inside diameter, 26 cm between electrodes. The system was pumped to approximately 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> mm Hg between data runs. Total pressure was varied from 1 to 8 mm Hg and discharge current from 0 to 80 mA. Typical CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> dissociation data at 40 mA and 4 mm Hg indicate an initial rate of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7(\pm0.5) \times 10^{-2}</tex> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with an equilibrium value of approximately 65 percent dissociation in the He/ N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> /CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> mixture and slightly lower vatues in the He/CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> mixture. Under the same conditions, nitric oxide (NO) exhibited a buildup rate of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8(\pm1) \times 10^{-2}</tex> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with an equilibrium value of approximately 0.1 percent of total gas composition. Nitrogen diozide (NO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ) was detected by comparing the relative amounts of mass numbers 45 and 46. Data indicate that in the He/N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> / CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> mixture the NO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> component of mass 46 can be as high as 0.12 percent of total mixture with an initial buildup rate of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7(\pm2) \times 10^{-2}</tex> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 80 mA discharge current. Measurement of the ion spectra at the cathode indicate that CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + is the major initial ion in the He/N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> /CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> mixture, but decays with a rate of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5 (\pm.5) \times 10^{-1}</tex> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and is replaced by NO <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> at approximately the same rate. In the He/CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> mixture CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + is replaced as the major ion by O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> + , with with slightly lower rates than those measured in the mixtures containing N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> .

Computer calculated concentrations in the reactions of nitrogen and oxygen

The efficiencies of the reaction between nitrogen and oxygen to form NO at high temperatures and the further oxidation of NO to NO2 at low temperatures can be calculated as a function of the initial gas composition, temperature, and pressure.

Co60 γ‐radiation‐induced copolymerization of ethylene and carbon monoxide

AbstractThe γ‐radiation‐induced free‐radical copolymerization of ethylene and CO has been investigated over a wide range of pressure, initial gas composition, radiation intensity, and temperature. At 20°C., concentrations of CO up to 1% retard the polymerization of ethylene. Above this concentration the rate reaches a maximum between 27.5 and 39.2% CO and then decreases. The copolymer composition increases only from 40 to 50% CO when the gas mixture is varied from 5 to 90% CO. A relatively constant reactivity ratio is obtained at 20°C., indicating that CO adds 23.6 times as fast as an ethylene monomer to an ethylene free‐radical chain end. For a 50% CO gas mixture, the above value of 23.6 and the copolymerization rate decrease with increasing temperature to 200°C. The kinetic data indicate a temperature‐dependent depropagation reaction. Infrared examination of copolymers indicates a polyketone structure containing CH2CH2 and CO units. The crystalline melting point increases rapidly from 111 to 242°C., as the CO concentration in the copolymer increases from 27 to 50%. Molecular weight of copolymer formed at 20°C. increased with increasing CO, indicating M̄n values &gt;20,000. Increasing reaction temperature results in decreasing molecular weight. Onset of decomposition for a 50% CO copolymer was measured at ≈250°C.

鉄の酸化還元速度および酸化物融体の酸素分圧測定について

The change of oxygen pressure in the waste gas of CO-CO2 mixture after the oxidation or reduction of iron or iron oxides has been continuously measured. From this change, the rate of oxidation or reduction has been calculated, knowing the initial gas composition of CO-CO2 mixture flown into the reaction chamber.It is shown that the oxygen concentration cells or the oxygen gauge can be used for the continuous measurement of the change in the gas compositon. Thus, the rates of the reactions relating to the change of oxygen pressure, in general, can be determined by the oxygen concentration cells with a solid electrolyte, Zr02 CaO. The used cell is:_??_The equilibrium oxygen pressure in a liquid PbO-Si02 binary solution equilibrated with liquid lead has been measured at 800°C, 900°C, 1000°C, and 1100°C by the following cell:_??_EMFThe equilibrium oxygen pressure in the PbO-SiO2 binary solution increased at higher temperatures, and decreased with anincrease in the silica content of the solution.The chemical activity of PbO was calculated from the equilibrium oxygen pressure.The activity of PbO deviated in a negative direction from the Raoultian law, with the deviation increasing with a lowering temperature. The activity of SiO2 was determined by the Gibbs-Duhem equation.The activity of SiO2 deviates in a negative direction from ideality if the silica content is less than 0.38 mole fraction, above which the activity of silica deviates in a positive direction. The deviation becomes less at higher temperatures.The free energy of mixing of PbO-Si02 system has minimum values at Nsio2 0.38, asΔFmix=-2.2Kcal/mole, -2.3Kcal/mole, and -2.45Kcal/mole at 900°C, 1000°C, and 1100°C, respectively.The minimum enthalpy of mixing is about-700 Cal/mole at Nsio2=0.32 and the maximum entropy of mixing is about 1.3 entropy units/mole at Nsio2=0.38.

Aerothermodynamic and Electrical Properties of Some Gas Mixtures to Mach 20

Pressure, temperature, chemical composition and electrical conductivity data are presented for gas mixtures behind strong air shocks and detonations of hydrogen-air and acetylene-air mixtures up to Mach 20. A digital computer program has been developed which solves the simultaneous aerodynamic and chemical equilibrium equations. The latest thermodynamic and collision crosssection data are used. Data are also presented wherein the initial gas composition was varied to obtain the maximum electrical conductivity for a given shock or detonation strength.

Application of the Temkin kinetic equation to ammonia synthesis in large-scale reactors

The rate of reaction in an industrial, high pressure ammonia synthesis reactor is expressed in terms of the kinetic equation formulated by T emkin and P yzhev. An estimate of catalyst activity is derived, affording a means of comparing different catalysts, and of measuring catalyst deterioration. Optimum temperatures giving maximum rates of reaction are estimated for certain conditions of catalyst activity and initial gas composition. A reasonable approach to optimum conditions is calculated for a particular design of catalyst bed, fitted with a means of removing some of the heat of reaction. Incorporation of the design in a plant reactor showed that the best operating conditions conformed closely to those calculated.