Showing papers on "Atmospheric pressure published in 1990"

On the use of atmospheric pressure plasmas as electromagnetic reflectors and absorbers

Abstract: Tenuous man-made plasmas in the Earth's atmosphere from sea level to 100 km are discussed. An ionization source generates a tenuous plasma with an electron number density n/sub e/ that is high near the source and diminishes with distance from the source. After the source shuts off, n/sub e/ decreases as a function of time as electrons recombine with positive ions or attach to negative ions. The electromagnetic properties that are essential to an understanding of these plasmas, which can be modeled as cold collisional plasmas, is discussed. Gas and plasma characteristics, such as momentum-transfer collision rate, plasma lifetime, recombination kinetics, and the effect of noble gases, are presented. Typical collision rates and plasma lifetimes at atmospheric pressure are quantified. Applications for a plasma with a gradient are discussed. They include a high-altitude plasma that can reflect or absorb from HF to VHF and a broadband atmospheric pressure absorber. The generation and use of plasma, including electron impact ionization with a high-energy electron-beam source and UV photoionization of an alkali vapor or an organic vapor such as tetrakis (dimethylamino)ethylene (TMAE), is described. The power required to sustain a plasma is quantified, and properties such as maximum absorption and bandwidth are discussed. Tradeoffs among maximum absorption, absorption bandwidth, duty ratio, and applied power permit optimization of absorption primarily at VHF. >

Partial oxidation of methane to synthesis gas

Abstract: Partial oxidation of methane to synthesis gas has been carried out over a number of transition metal catalysts under a range of conditions. It is found that the metals Ni, Ru, Rh, Pd, Ir and Pt, either supported on alumina or present in mixed metal oxide precursors, will bring the system to equilibrium. The yield of CO and H2 improves with increasing temperature in the range 650–1050 K, and decreases with increasing pressure between 1 and 20 atm. An excellent yield (∼92%) is obtained with a 4∶2∶1 N2∶CH4∶O2 ratio at 1050 K and atmospheric pressure, with a space velocity of 4×104 hour−1.

The mechanism of the stabilisation of glow plasma at atmospheric pressure

Abstract: Some reasons are discussed for the stabilisation of a glow discharge at atmospheric pressure which was attained by controlling the following three conditions: the use of a high-frequency source, the use of He gas for dilution and the insertion of a dielectric plate between electrodes. The three conditions interact: the dielectric plate in a plasma forms the pulsed discharge from a low-frequency source, the fast duration of pulse current prevents a transition to an arc style discharge and a large volume of metastable atomic helium aids ionisation or dissociation near the electrode plate and in the flowing gas. The measurements of discharge-maintaining voltage at several hundred volts provide evidence that this is really a glow plasma at atmospheric pressure. The changes of the emission intensities of metastable helium prove indirectly that some dissociation occurs as a result of the action of the helium atom.

Silicon Dioxide Deposition by Atmospheric Pressure and Low‐Temperature CVD Using TEOS and Ozone

Abstract: We report characteristics of the film deposited by an atmospheric pressure and low‐temperature CVD process using TEOS and ozone. Nondoped silicon oxide was deposited on thermally grown oxide, silicon, and aluminum steps. The film surface was very smooth even on aluminum lines and step coverage of the films changed from isotropic to flow shape with ozone concentration increase. This is one of the largest advantages of this CVD technology and is promising for advanced VLSI device fabrication. The film has tensile stress of less than , typically , low enough to fabricate VLSI devices. Film shrinkage was 5% in the film deposited at the higher ozone concentration when annealed at 950°C, which was comparable to that of the conventionally deposited films. The largest thickness without any cracks varied depending on deposition conditions. A thickness of 2 μm without cracks was obtained at 400°C and 0.1 μm/min deposition rate with an ozone concentration of 4.8%. Particle generation was very low and the number of particles of more than 0.3 μm were less than 20 on a 6 in. diam wafer.

Effect of growth rate on the band gap of ga0.5in0.5p

Abstract: The band gap of Ga0.5In0.5P is reported as a function of growth rate and growth temperature. The Ga0.5In0.5P is grown lattice matched to 2°‐off (100) GaAs substrates by atmospheric pressure organometallic chemical vapor deposition using an inlet group V/III ratio of 65. The variation of the band gap is surprisingly complex, taking five different functional forms within the two‐dimensional parameter space. These include regions in which the band gap (1) increases with growth rate, (2) decreases with growth rate, (3) is independent of both growth rate and temperature, (4) is independent of growth rate, but dependent on growth temperature, and (5) is not measurable since three‐dimensional, instead of two‐dimensional, growth is observed. The behavior can only be explained by a theory involving competing processes. One such theory is described.

Process for increasing the reactivity of cellulose-containing materials

Abstract: This process for increasing the reactivity of cellulose-containing materials such as animal feedstuffs involves contacting the material, in a pressure vessel, with a volatile liquid swelling agent e.g. ammonia, which has a vapor pressure greater than atmospheric pressure at ambient temperatures. The contact is maintained for a time period sufficient for the agent to swell the cellulose of the material. The pressure is then rapidly reduced to atmospheric pressure, thereby causing the agent to boil and explode the material. The rapid pressure reduction also causes some freezing of the cellulose. The swelling agent is separated from said cellulose-containing material and recovered for recycling. The process also increases the water holding capacity of cellulose-containing materials.

Effect of frequency on local thermodynamic equilibrium conditions in an inductively coupled argon plasma at atmospheric pressure

Abstract: A theoretical investigation of the effect of induction frequency shows that deviations from local thermodynamic equilibrium (LTE) are strongly related to this parameter. Computations are carried out for an argon plasma at atmospheric pressure over the frequency range 3–40 MHz. Higher frequencies result in lower‐temperature levels in the torch, and also the difference between the electron and the atom/ion temperatures is increased. This is in agreement with the observations of other investigators. The results of the proposed model also show good agreement with the measured temperature profiles. Similar calculations, which are based on the LTE assumption, are reported and compared with the present non‐LTE model.

Io's atmosphere from microwave detection of So2

Abstract: The microwave detection of SO2 at 222 GHz in Io's atmosphere is reported. The observations imply an SO2 surface pressure of 4-35 nanobars, covering 3-15 percent of the surface on both leading and trailing sides of Io when illuminated by the sun. This supports atmospheric models in which the partial pressure of SO2 at the surface is determined by the Io surface temperature, favoring, in particular, the 'albedo cold-trap' models. The failure to detect H2S at 169 GHz suggests that the pressure of this gas is probably below 10 to the -10th bar. These results, taken together with Pioneer ionospheric data, suggest that an atmospheric gas other than SO2 is present. It is proposed that the locally buffered SO2 atmosphere coexists with a background atmosphere of oxygen with a partial surface pressure of about 20 nanobars.

Atomspheric plasma reaction method and apparatus therefor

Abstract: This invention provides an atmospheric plasma reaction method characterized by introducing a mixed gas of rare gas and reactive gas into a reaction vessel having a dielectric-coated electrode wherein the surface of two or more electrodes located parallel therewith are provided with solid dielectrics, exciting said mixed gas with plasma at atmospheric pressure, then transporting the active species to the downstream of the plasma and treating the surface of a substrate. This invention also provides an atmospheric plasma reaction apparatus.

InAs/InP strained single quantum wells grown by atmospheric pressure organometallic vapor phase epitaxy

Abstract: Strained InAs/InP single quantum wells of nominal thickness 1–11 monolayers have been prepared using organometallic vapor phase epitaxy in an atmospheric pressure reactor. For wells of thickness 1–3 ML grown using optimal flow modulation parameters, the surface morphology was specular and narrow single‐line photoluminescent emission was observed. For thicker wells, the evolution of additional PL features and the appearance of island‐like features on the sample surface was attributed to the onset of three‐dimensional (island) growth.

Formation of vapor bubbles in nonpolar liquids initiated by current pulses

Abstract: The electrical conduction of purified nonpolar liquids with point-plane electrode geometry was studied as a function of various parameters. For negative polarity of the point, a pulse regime has been observed which bears a great similarity to the TRICHEL pulses occurring in air, with the exception of a lack of pressure dependence. At atmospheric pressure, bubble formation was correlated with current pulse. The generation and dynamics of the bubble are studied as a function of various parameters: injected energy, hydrostatic pressure (up to 12 MPa), and the nature of the liquid (cyclohexane, n-pentane, n-decane, iso-octane, and tetramethylsilane). >

The Impact of Atmospheric Conditions on Gas Turbine Performance

Abstract: This paper is devoted to studying the impact of atmospheric conditions, such as ambient temperature, pressure, and relative humidity on gas turbine performance. A fully interactive computer program based on the derived governing equations is developed. The effects of typical variations of atmospheric conditions on power output and efficiency are considered. The thermal efficiency and specific network of a gas turbine were calculated at different values of maximum turbine inlet temperature and variable environmental conditions

Oxidation of silicon in an electron cyclotron resonance oxygen plasma: Kinetics, physicochemical, and electrical properties

Abstract: An electron cyclotron resonance (ECR) plasma system was used to oxidize single‐crystal silicon. Two distinct oxidation processes were observed, one of which was ion flux controlled. Oxidation of trench structures confirmed the existence of these two oxidation regimes. Kinetic rate studies indicated that the effective activation energies for both oxidation processes were substantially lower than the activation energy of atmospheric pressure steam or dry oxygen oxidation. The Deal–Grove linear‐parabolic rate law can be used to describe long‐time ion‐controlled oxidation rates, although the theory of Wolters–Zegers‐van Duynhoven best described the observed oxidation rates. Oxides grown in the ion flux controlled regime had growth rates and physicochemical properties nearly identical to thermal oxides grown at atmospheric pressure and above 1123 K, whereas oxides grown outside this regime were self‐limiting (≊100 A) in thickness and of poorer dielectric quality unless subjected to a post oxidation anneal. Cap...

Photoluminescence of InAsBi and InAsSbBi grown by organometallic vapor phase epitaxy

Abstract: Infrared photoluminescence (PL) from InAsBi and InAsSbBi epitaxial layers grown by atmospheric pressure organometallic vapor phase epitaxy has been studied. The PL from ternary InAsBi was investigated for Bi concentrations of ≤2.3 at. %. The peak energy decreases at a rate of 55 meV/at. % Bi with increasing Bi concentration. A study of the transmission spectra of these Bi‐containing alloys confirms the above result. The PL peak is assigned to near band edge emission for InAsBi. The value of dEg/dx=−55‐meV/at. % Bi is more than double the previously reported theoretical prediction for the band gap of InAsBi. The PL for the quaternary layer of InAsSbBi is also studied for Sb concentrations of <10 at. % and Bi concentrations of ≤1.5 at. %. Bi incorporation in InAs1−xSbx(0.07

Tensile fracture and fractographic analysis of 1045 spheroidized steel under hydrostatic pressure

Abstract: Void formation in tensile test under hydrostatic pressure is characterized through quantitative metallography, and the fracture mechanism under pressure is analyzed by fractography. Transition of the fracture surface from the cup-and-cone under atmospheric pressure to a slant structure under high pressure is explained on the basis of the void development leading to fracture and the concomitant change in fracture mechanism. The concept of “shear blocks” is introduced to illustrate the features observed on the fracture surface of specimens tested under high pressure. It is postulated that shear blocks evolve to connect the central crack regions with the shear crack initiated on neck surface due to the severe necking deformation under applied pressure.

Schlieren measurements of the hydrodynamics of excimer laser ablation of polymers in atmospheric pressure gas

Abstract: Pulsed schlieren photography and fast helium‐neon laser deflection are used to study the hydrodynamics of laser ablation of polyethyleneterephthalate and polymethylmethacrylate by pulsed KrF (248 nm) radiation in atmospheric air, Ar and N2. Schlieren measurements show the evolution of shock waves, sound waves, and reduced‐density, hot gas plumes. A transition from sound to shock at the ablation threshold for both polymers is observed. The shock velocity of PET tends to approach agreement with blast wave theory at fluences higher than 1 J/cm2. Plumes in air are consistently larger than those produced in Ar and N2 (at fluences below 5 J/cm2) suggesting that combustion may occur. Laser deflection measurements for PET at 150 mJ/cm2 indicate a plume density of 0.6 kg/m3 (50% atmospheric density).

Dynamics of heterogeneous azeotropic distillation columns

Abstract: A new dynamic model has been developed for heterogeneous azeotropic distillation columns, which is capable of automatically detecting and accounting for multiple liquid phases on trays at each instant of time. Extensive dynamic simulations have been carried out for the heterogeneous distillation of ethanol, water and benzene. Our results are in general agreement with prior work, which shows that this class of separations can be expected to exhibit multiple steady states, complex dynamic behavior, and parametric sensitivity. One of the most unexpected results was that these systems exhibit parametric sensitivity with respect to small changes in column pressure. For systems vented to the atmosphere, small increases in the barometric pressure lead to loss of interface in the decanter over a 24-hour period. If small pressure variations of this sort are left uncontrolled long enough, the entire separation will fail. Small decreases in the barometric pressure do not have such a disastrous effect.

Method and apparatus for radiation microwave energy into material containing water or mixed with water

Abstract: In order to obtain a more homogeneous energy absorption and preset maximum temperatures in an apparatus for radiating microwave energy into water-containing material or material mixed with water, which is introduced into a cavity resonator subjected to microwaves by one or more microwave generators, a pressure and/or temperature sensing device being included, the proposal is put forward that a sealable container be provided for receiving the material to be treated, which should be transparent to microwaves and resistant to gases and pressures, and whose interior should be enclosed by the cavity at a given distance, and that the pressure and/or temperature sensing device be connected with the interior of this container, and further that a device be provided for control of the energy output of the microwave generator, which device should control and maintain constant a preset interior pressure deviating from atmospheric pressure, and which should be connected to the pressure and/or temperature sensing device.

Plasma processing method and apparatus

Abstract: A plasma processing apparatus comprising: a vacuum container; an evacuation means for keeping the interior of the vacuum container at a pressure not higher than atmospheric pressure; a substrate support device for supporting a substrate to be subjected to plasma processing; an electrode for generating plasma in cooperation with the substrate support; a voltage supply for applying a voltage to the electrode; a gas introducing system for introducing a gaseous material into a space where the plasma is produced; a surrounding member for enclosing the space above the substrate support, and a drive for relatively moving the surrounding member to space an end of the surrounding member proximate from the substrate from at least one of the substrate support and the substrate supported thereon by a distance which is short enough to suppress plasma leakage during the plasma processing and to position the end of the surrounding member away from said at least one of the substrate support and the substrate thereon for charging and discharging of the substrate.

Laser in situ monitoring of combustion processes

Abstract: Several examples of laser in situ monitoring of combustion processes are presented. Using a frequency modulated (13)CO(2) waveguide laser, in situ concentrations of NH(3) down to 1 ppm were measured at temperatures up to 600 degrees C in waste incinerators and power or chemical plants. Following ignition of CH(3)OH-O(2) mixtures by a TEA CO(2) laser, gas temperature profiles were measured using rapid scanning tunable diode laser spectroscopy of CO molecules. In laminar CH(4)-air counterflow diffusion flames at atmospheric pressure absolute concentrations, temperatures, and collisional lifetimes of OH radicals were determined by 2-D and picosecond LIF and absorption spectroscopy. Two-dimensional LIF and Mie scattering were used to observe fuel injection and combustion in a diesel engine.

The physical nature of ball lightning

Abstract: Ball lightning (BL) is mathematically modelled assuming a solid, positively charged core exists at its center. The large amount of energy occasionally associated with BL is mainly due to the electrostatic (ES) energy of the charge on the core. The upper energy limit is determined by the size and strength of the core and this energy can be orders of magnitude greater than the energy which can be confined by atmospheric pressure alone. A pure electron layer and a plasma layer surround the core. The charge of the electron layer is equal in magnitude to that of the core. An electromagnetic (EM) field is completely trapped by the electron and plasma layers. The electron temperature is sufficiently high that absorption by electron-ion collisions is small, enabling the ball to have a lifetime of seconds or more. The ponderomotive force (radiation pressure) of the trapped EM field balances the ES force of the electrons toward the core plus the force of atmospheric pressure. The generation mechanism is not considered.

Radiation and self-absorption in argon-iron plasmas at atmospheric pressure

Abstract: The paper presents a theoretical study of the line and continuum radiation emitted by an argon plasma at atmospheric pressure in the presence of iron vapour at concentrations ranging from 0.001 to 10%(molar) and temperatures up to 15 000 K. The results show that the line emission is clearly the dominant mechanism due to the very rich iron spectrum. An analysis of the importance of self-absorption for the argon and iron lines indicates a strong absorption of the argon resonant lines and a significant absorption of iron lines even at low concentrations.

High growth rate diamond synthesis in a large area atmospheric pressure inductively coupled plasma

Abstract: : Diamond synthesis is demonstrated in an atmospheric pressure inductively coupled argon-hydrogen-methane plasma. The plasma generated has a free stream active area of 20 sq cm and has an equilibrium electron temperature T sub e of approximately 4000 K. Growth rates are typically in the range of 25- 50 microns/hour and are found to depend on the processing conditions and position on the substrate. Individual crystallites are analyzed by micro-raman spectroscopy. Large (50 microns) size well-faceted crystallites are found to be under a state of compression, displaying shifts in the principal phonon mode as great as 3/cm from that of smaller polycrystalline diamond clusters or secondary nucleation sites. These shifts are shown to be expected within the framework of linear thermal expansion theory and the assumption of negligible stress relief at the crystallite-substrate interface. Keywords: Diamond synthesis, Thermal plasma, Raman spectroscopy.