Atm Of Air Research Articles

Absorption diagnostics and modeling investigations of RDX flame structure

Absorption spectroscopy has been applied to low-pressure, self-deflagrating RDX flames in an attempt to refine the database for evaluation of detailed-chemistry combustion models. Semi-empirically determined production rates of reactants from the solid propellant surface together with a detailed gas-phase elementary reaction set were used to develop a model that minimizes the effect of uncertainties in the description of solid-phase processes. The spatial profiles of two low-concentration, highly reactive, short-lived diatomic species, CN and NH, were obtained at pressures varying from 1 to 2 atm in air. Two major species, NO and OH were also profiled using this technique. Resultant absorption spectra of the B 2Σ + − X 2Σ + transitions for CN, A 3Π − X 3Σ − transitions for NH, and the A 2Σ + − X 2Π transitions for NO and OH were least-squares fitted to obtain best values for concentration and/or temperature. Peak CN mole fractions of about 200 ppm are obtained from “snapshot” absorption spectra of RDX burning in 1 atm air, mole fractions for NH are about a factor of 2 lower. As the pressure is increased, the CN and NH species peak closer to the combusting surface and reside over a smaller spatial extent. Peak concentrations drop for these higher pressures, but may be due, at least in part, to limitations of the spatial resolution of the pressurized absorption experiment chamber. Results from high-resolution absorption measurements instituted to overcome these limitations reveal CN concentrations of 140 ppm with more consistent peak positions, widths, and CN to NH peak ratios. Measurements of the concentration of NO species show a peak concentration of 25 mole-percent occurring at a position of 0.12 mm above the surface of the propellant. In the final flame region, measured OH concentrations of 1.7 mole-percent agree well with adiabatic calculations performed with the NASA-Lewis thermochemical equilibrium code. Calculated profiles of NO and OH are in good agreement with these measurements. The model peak positions and relative concentrations of CN and NH are also in good agreement with experiment. During the course of these spectroscopic measurements, burning rates for RDX over a pressure range of 1 to 2 atm have also been determined. These values range from 0.23 mm/s at atmospheric pressure to 0.50 mm/s for 2 atm and are noticeably lower than some of the other published measurements. Calculations stemming from the proposed model predict a burning rate of 0.29 mm/s and 0.54 mm/s for the same pressure levels.

The Effect of Si3N4 Additions on the Oxidation Resistance of TiAl Alloys

The oxidation kinetics of TiAl alloys with and without 3 and 5 wt.%additions of Si3N4 particles were studied at 1173 and1273 K in 1 atm of air. The Si3N4 dispersions wereunstable in the matrix phase, so that some of them reacted with titaniumduring sintering to form Ti5Si3 and dissolvednitrogen. The oxide scale formed on TiAl–Si3N4alloys consisted of an outer TiO2, an intermediate(Al2O3+TiO2), and an inner(TiO2+Al2O3) mixed layers. The enhancedalumina-forming tendency, the presence of discrete SiO2 particlesbelow the outer TiO2 layer, and the improved scale adhesion bySi3N4 dispersions were attributable mainly to theincreased oxidation resistance compared to the Si3N4-freeTiAl alloys. Marker experiments showed that, for TiAl–Si3N4 alloys, the primary mode of scale growth was the outward diffusion oftitanium ions for the outer scale and the inward transport of oxygen ionsfor the inner scale.

Action of a self-sustained glow discharge in atmospheric pressure air on biological objects

This paper presents the results of experimental investigations of the action on biological objects of high pressure (/spl sim/1 atm) air excited in a discharge chamber. E. Coli and Staphylococcus bacteria in concentrations of -10/sup 5/ cm/sup 3/ were used for the biological cultures and Aspergillus and Penicilium were used with the granular substances. Bactericidal properties were observed up to 80 mm from the nearest electrode of the glow discharge device.

Improvement of hardness and resistance to oxidation by electric arc alloying on ferritic steels

This study has shown that it is possible to elaborate interesting surface alloys by electric arc with special electrode on ferritic steels. The surface deposition of a Fe-30Cr-4C alloy on the VCO and VH13 steels is efficient in increasing the surface hardness and wear resistance of these steels due to high (Fe, Cr){sub 7}C{sub 3} carbide precipitation. The surface alloy also leads to an excellent resistance to oxidation at high temperature in isothermal conditions. The protection against the oxidation is assured, essentially, by a microcrystallized chromium oxide layer, which is formed due to the high chromium content in the surface alloy. Consequently, the surface alloy presents a stainless steel behavior with a reduction in the oxidation rate by a factor of 35 and 50, respectively, on the VH13 and VCO steels after 50 hours of oxidation (1 atm air) at 950 C.

Characterization of HOCl Using Atmospheric Pressure Ionization Mass Spectrometry

HOCl is an important intermediate in stratospheric and tropospheric chemistry. Although it can be readily measured in laboratory systems at low pressures ({le}20 Torr) using conventional electron impact ionization mass spectrometry, there is a need for a measurement technique that can operate at higher pressures, up to 1 atm in air. One such technique seeing increasing use is atmospheric pressure ionization mass spectrometry (API-MS). The authors report here studies of the API-MS of {approximately}0.5--50 ppm HOCl at a total pressure of 1 atm and room temperature. Major peaks from the ion-adducts with Cl{sup {minus}} and OCI{sup {minus}} were observed. The Br{sup {minus}} adduct of HOCl can also be generated using bromoform in the discharge region of the ion source. At the lower range of HOCl concentrations studied in air, the O{sub 2}{sup {minus}} adduct and small parent peaks assigned to HOCl{sup {minus}} were observed. The species present as minor impurities in the HOCl source (Cl{sub 2}, Cl{sub 2}O and HCl) can be readily distinguished through identification of the parent ion for Cl{sub 2}, or as their adducts with Cl{sup {minus}} and Br{sup {minus}} for Cl{sub 2}O and HCI. The identification of HOCl was confirmed using electron impact ionization time-of-flight massmore » spectrometry (El-MS). HOCl was quantified using EI-MS to measure the Cl{sub 2} generated when the HOCl reacted heterogeneously on a water-ice/HCl surface and independently by photolysis of the HOCl to generate atomic chlorine, which was trapped using propene and measured as chloroacetone. The implications for the use of API-MS for measuring HOCl in laboratory systems and in ambient air are discussed.« less

Joint performance of DSA++ MAC protocol and SR/D-ARQ protocol for wireless ATM under realistic traffic and channel models

This paper describes the protocol stack for an ATM air interface that is able to efficiently support all ATM service categories. The multiplexing of ATM cells on the radio link is controlled by a service strategy that optimizes the resource allocation based on the negotiated quality of service. A medium access control (MAC) protocol realizes the transmission order of ATM cells given by the service strategy. The paper focuses on a strategy for transmission of acknowledgments of an automatic repeat request (ARQ) protocol and on a collision resolution algorithm for transmission of capacity requests over the uplink. The performance of the overall protocol stack is evaluated under realistic traffic and channel models by means of an integrated stochastic simulation model.

Atmospheric Chemistry of Cyclohexane: UV Spectra of c-C6H11• and (c-C6H11)O2• Radicals, Kinetics of the Reactions of (c-C6H11)O2• Radicals with NO and NO2, and the Fate of the Alkoxy Radical (c-C6H11)O•

A pulse radiolysis technique was used to measure the UV absorption spectra of c-C6H11• and (c-C6H11)O2• radicals over the ranges 230−290 and 220−300 nm, σ(c-C6H11•)250 nm = (7.0 ± 0.8) × 10-18 and σ((c-C6H11)O2•)250 nm = (5.7 ± 0.6) × 10-18 cm2 molecule-1. The rate constant for the self-reaction of c-C6H11• radicals was k3 = (3.0 ± 0.4) × 10-11 cm3 molecule-1 s-1. The addition reaction of c-C6H11• radicals with O2 proceeds with a rate constant k2 = (1.3 ± 0.2) × 10-11 cm3 molecule-1 s-1. Rate constants for reactions of (c-C6H11)O2• radicals with NO and NO2 were k4 = (6.7 ± 0.9) × 10-12 and k5 = (9.5 ± 1.5) × 10-12 cm3 molecule-1 s-1, respectively. FTIR−smog chamber techniques were used to record the IR spectrum of the peroxynitrate (c-C6H11)O2NO2, determine that the reaction between (c-C6H11)O2• radicals and NO produces a (16 ± 4)% yield of the nitrate (c-C6H11)ONO2, and study the atmospheric fate of cyclohexoxy radicals. Decomposition via C−C bond scission and reaction with O2 are competing fates of the cyclohexoxy radical. In 700−750 Torr total pressure at 296 ± 2K, the rate constant ratio kdecomp/kO2 = (8.1 ± 1.5) × 1018 molecule cm-3. At 296 K in 1 atm of air, 61% of cyclohexoxy radicals decompose and 39% react with O2. These results are discussed with respect to the literature data concerning the atmospheric chemistry of cyclohexane and analogous compounds.

Kinetics of Catalyzed Liquid-Phase Oxidation of p-Nitrotoluene by Air in Basic Medium

An alternative method for the oxidation of nitrotoluenes is described, using air with a cobalt catalyst in basic medium. Different process parameters were studied to realize the true kinetics of the process. At 28 °C and 16 atm air pressure, 96% selectivity at a conversion level of 40% for p-nitrotoluene was achieved in 18 h using cobalt phthalocyanine. For a given initial concentration of p-nitrotoluene, the reaction was found to be of first-order kinetics.

A new strategy for alkane oxidation with O2 using N-hydroxyphthalimide (NHPI) as a radical catalyst

A practical catalytic method to convert alkanes into the corresponding oxygen‐containing compounds with O2 under mild conditions using N‐hydroxyphthalimide (NHPI) in the presence or absence of a transition metal was developed. Thus, cyclohexane was successfully converted into adipic acid in good conversion and selectivity by a combined catalytic system consisting of NHPI and Mn(acac)2. Lower alkane such as isobutane was converted into t‐butyl alcohol (83%) under 10 atm of air by NHPI‐Co(OAc)2 system. Alkylbenzene such as toluene was oxidized to benzoic acid in high yield (81%) under normal temperature and pressure of dioxygen in the presence of a catalytic amount of NHPI and Co(OAc)2. ESR measurements showed that phthalimide‐N‐oxyl generated from NHPI under dioxygen atmosphere is a key species in this oxidation and functions as a radical catalyst.

Isothermal Tetragonal to Monoclinic Phase Transition around Room Temperature in 2.0 mol% Yittria-doped Zirconia Ceramics.

The tetragonal to monoclinic (t-m) phase transition in 2.0 mol% yttria-doped tetragonal zirconia polycrystals (2Y-TZP) was studied by use of XRD and FT-IR diffuse scattering (DRIFT) measurements. The phase transition occurred isothermally when the 2Y-TZP powder after calcining at temperatures below 1200°C was annealed in air even at room temperature, and more than 90% of the monoclinic phase was obtained after a long period of annealing. However only about several percent and about 40% of the monoclinic phase were formed after the annealing treatments under vacuum and 1 atm air separately sealed in a 5 ml Pyrex tube, respectively. On the other hand, no phase transition occurred in air around room temperature in the 2Y-TZP powder after being calcined at temperatures above 1300°C. A broad band around 3300 cm-1 due to the existence of adsorbed water was observed in the FT-IR DRIFT spectra of the 2Y-TZP powder only after calcination below 1200°C. The t-m transition behavior of 2Y-TZP powder after calcination below 1200°C differed with that after calcination above 1300°C. The existence of adsorbed water on 2Y-TZP was essential for the t-m phase transition of 2Y-TZP to take place in air around room temperature. The amount of transformed monoclinc phase was determined by the amount of adsorbed water on 2Y-TZP and supplied water from annealing atmosphere.

Numerical Study of Scram Accelerator Starting Characteristics

A numerical study is carried out to investigate the ignition and the detonation initiation process in a scram accelerator operating at a superdetonative mode. To simulate the scram accelerator launching process, a conical projectile is considered, injected with an initial velocity of 2500 m/s from the 1 atm air into a 25 atm 2H 2 + O 2 + mN 2 mixture. As a dilution gas, nitrogen is selected and assumed to be inert. The time accurate solutions of Reynolds averaged Navier-Stokes equations for chemically reacting flows are obtained by using a point-implicit method and an upwind-biased third-order scheme with a steady-state solution for airflow as an initial condition. To examine combustion characteristics and ram-accelerator operation limits, mixture compositions are varied from 2H 2 + O 2 + 3.76N 2 to 2H 2 + O 2 + 9N 2 by changing the amount of N 2 . The flowfield results show the detailed ignition mechanism, the initiation process of the oblique detonation, and the staring characteristics of the scram accelerator. The results also identify clearly the combustion characteristics of the operational failures at lower and upper dilution limits that have been observed in experiments

High Jc YBCO films on biaxially textured Ni with oxide buffer layers deposited using electron beam evaporation and sputtering

Epitaxial buffer layers of CeO 2 and yttria-stabilized ZrO 2 (YSZ) have been deposited on biaxially textured nickel using conventional electron beam evaporation and r-f sputtering. Epitaxial films of YBa 2Cu 3O 7− δ (YBCO) have been then grown on these buffered substrates using pulsed laser deposition (PLD). Despite intermittent exposure of the buffered substrates to 1 atm air, the resulting YBCO conductors exhibited transport critical current densities ( J c) of 0.8 MA/cm 2 at 77.3 K and H=0 T. The dependence of J c of these conductors on temperature and magnetic field is similar to that of conductors prepared solely by in situ PLD. These results suggest that it may be possible to use more flexible and easily scalable fabrication methods for preparing long YBCO conductors.

Wireless ATM LAN with and without infrastructure

We consider wireless ATM concepts for small LANs, especially for SOHO and future consumer applications. We describe a wireless ATM LAN framework architecture that supports wireless ATM communications in environments with and without fixed ATM infrastructure. For the configuration with an ATM infrastructure, a distributed ATM switched backbone is proposed, which enables a smart ATM switching element to be embedded in every wireless and fixed access point. For bandwidth efficiency and ease of operation (place-and-play), we also propose an ad hoc wireless ATM LAN concept based on the same 5 GHz wireless ATM air interface as is currently under standardization in the ETSI/BRAN and ATM Forum. Unlike CSMA-based ad hoc systems such as HIPERLAN and IEEE802.11, our ad hoc wireless ATM system makes QoS management feasible in an infrastructureless environment by using resource reservation and scheduled medium access protocol. Since cost scalability is essential throughout our system design, we consider forwarding between ad hoc subnets and interworking with the fixed network as important but optional features.

Atmospheric Chemistry of CH3I: Reaction with Atomic Chlorine at 1−700 Torr Total Pressure and 295 K

The title reaction was studied using long path length FTIR spectroscopy coupled to a smog chamber. In 1 Torr of N2 diluent at 295 K a large kinetic isotope effect was observed, kH/kD = 6, suggesting that the reaction of Cl atoms with CH3I proceeds via H atom abstraction to give CH2I radicals and HCl with a rate constant of (9.0 ± 1.8) × 10-13 cm3 molecule-1 s-1. In 700 Torr total pressure of N2, O2, and air diluents the reactivity of Cl toward CH3I was 50% greater than that at 1 Torr. The increase in reactivity is ascribed to the formation of the CH3I−Cl adduct. In 700 Torr of O2 the majority (≈98%) of the adduct decomposes back to reactants, and a small fraction (≈2%) is lost via one or more processes that do not regenerate reactants. In 1 atm of air at 295 K the reaction of Cl atoms with CH3I produces less than 20% yield of CH3Cl. The potential role of the title reaction in atmospheric chemistry is discussed.

Gas Phase Reaction of Alkenes with Ozone: Formation Yields of Primary Carbonyls and Biradicals

The gas phase reaction of ozone with alkenes plays a major role in tropospheric chemistry including urban air quality. The reaction of trans-2,2-dimethyl-3-hexene and 2,4-dimethyl-2-pentene with ozone has been studied at ambient temperature and p = 1 atm of air (RH = 55% ± 10%) with sufficient cyclohexane added to scavenge the hydroxyl radical. Carbonyl products have been identified, and their formation yields are reported. The results are compared to those previously obtained for 35 other alkenes under the same conditions. For these alkenes, the sums of the formation yields of the primary carbonyls are close to the value of 1.0 that is consistent with the following reaction mechanism: O3 + R1R2CCR3R4 → α(R1COR2 + R3R4COO) + (1 − α)(R1R2COO + R3COR4), where R1COR2 and R3COR4 are the primary carbonyls and R1R2COO and R3R4COO are the corresponding biradicals. For 26 nonsymmetrical alkenes, the coefficients α range from 0.28 to 0.82 and indicate preferential formation of the more substituted biradicals and of the biradicals that bear the less bulky substituents. The results are directly relevant to the atmospheric chemistry of alkenes and to their role in oxidant and aerosol formation.

Atmospheric Chemistry of Dimethoxymethane (CH3OCH2OCH3): Kinetics and Mechanism of Its Reaction with OH Radicals and Fate of the Alkoxy Radicals CH3OCHO(•)OCH3 and CH3OCH2OCH2O(•)

The rate constant for the reaction of dimethoxymethane (DMM) with OH radicals was determined to be (4.6 ± 1.6) × 10-12 at 346 ± 3 K using a pulse radiolysis/transient UV absorption absolute rate technique and (5.3 ± 1.0) × 10-12 cm3 molecule-1 s-1 at 295 ± 2 K using an FTIR-smog chamber relative rate technique. The reaction of OH radicals with DMM occurs via an H-atom abstraction mechanism with 76% of the attack occurring on the −CH3 end groups and 24% on the central −CH2− unit. The atmospheric fate of the alkoxy radicals CH3OCH2OCH2O(•) and CH3OCHO(•)OCH3 at 296 K in 700 Torr of air was investigated using an FTIR-smog chamber technique. The sole atmospheric fate of CH3OCHO(•)OCH3 radicals is reaction with O2 to give dimethyl carbonate (CH3OC(O)OCH3) and HO2 radicals. At least three loss processes were identified for CH3OCH2OCH2O(•) radicals. In 1 atm of air at 295 K, 84 ± 4% of the CH3OCH2OCH2O(•) radicals react with O2 while 7 ± 3% undergo H-atom elimination; the fate of the remaining 9% is unclear. OH radical-initiated oxidation of DMM in 1 atm of air at 296 K results in a yield of 24% dimethyl carbonate and 69% methoxymethyl formate; the oxidation mechanism of the remaining 7% of DMM is unclear. Relative rate techniques were used to measure rate constants for the reaction of Cl atoms with CH3OCH2OCH3 and CH3OCH2OCHO of (1.4 ± 0.2) × 10-10 and (3.6 ± 0.6) × 10-11 cm3 molecule-1 s-1, respectively. Results are discussed in the context of the atmospheric chemistry of DMM.

Gas-phase UV spectroscopy of anthracene, xanthone, pyrene, 1-bromopyrene and 1,2,4-trichlorobenzene at elevated temperatures

We present quantitative UV-absorption spectra in the wavelength range 200 to 400 nm and the temperature range 150 to 600 °C for anthracene, xanthone, pyrene, 1-bromopyrene and 1,2,4-trichlorobenzene obtained at 1 atm of air in a slowly flowing gas mixture. As a general trend, the spectra shift to the red with increasing temperature and decrease in peak intensity thus leading to a loss of the characteristic structure of the spectrum. The absorption integrated over a particular band generally stays constant or slightly decreases with increasing temperature.

Mechanistic aspects of the oxidation of phosphines and related substrates by trans-Ru VI(TMP)(O) 2; TMP = dianion of 5,10,15,20-tetramesitylporphyrin

The stoichiometric oxidations of some P( p-X-C 6H 4) 3 compounds (X = OMe, Me, H, F, Cl and CF 3), AsPh 3 and SbPh 3 by trans-Ru VI(TMP)(O) 2 ( 1) in benzene solution generate the corresponding oxides and Ru II(TMP)(L) species (L = P( p-X-C 6H 4) 3, AsPh 3, SbPh 3). Stopped-flow kinetic data are consistent with a mechanism involving formation (within a k 1 step) of Ru IV(TMP)(O)(OL) which then reversibly dissociates the OL ligand to generate Ru IV(TMP)(O); this disproportionates to Ru VI(TMP)(O) 2 and Ru II(TMP), which forms Ru II(TMP)(L). ΔH ‡ 1 values for the phosphine systems vary from 18 to 21 kJ mol −1, increasing with decreasing electron density at the phosphorus, while ΔS ‡ 1 values become more favorable (−94 to −78 J mol −1 K −1) with increasing molecular mass of the substituent. Preliminary kinetic data on the O 2-oxidations of the substrates catalyzed by ( 1) under 1 atm of air are presented.

Kinetics and Mechanism of the Reaction of Cl Atoms with 2-Methyl-1,3-butadiene (Isoprene) at 298 K

The reaction of chlorine atoms with isoprene (2-methyl-1,3-butadiene) may be important in the marine boundary layer. The kinetics and mechanisms of this reaction have been studied at 760 Torr and 298 K using the photolysis of Cl2 as the chlorine atom source. Product studies in air were carried out using 40 m path length FTIR spectrometry. Rate constants were determined in either air or N2 using a relative rate technique and GC-FID to follow the decay of isoprene relative to n-butane. For comparison, the kinetics of the chlorine atom reactions with isoprene-d8, 1,3-butadiene, and 1,3-butadiene-d6 were also studied at 1 atm in air or N2 at 298 K. The rate constant ratios determined with n-butane as the reference compound are as follows: isoprene (2.16 ± 0.17); isoprene-d8 (1.79 ± 0.22), 1,3-butadiene (2.01 ± 0.11); 1,3-butadiene-d6 (1.85 ± 0.10) (±2σ). The corresponding absolute rate constants, based on a value for n-butane of 2.11 ± 0.18 × 10-10 cm3 molecule-1 s-1, are as follows: isoprene (4.6 ± 0.5); isoprene-d8 (3.8 ± 0.6); 1,3-butadiene (4.2 ± 0.4); 1,3-butadiene-d6 (3.9 ± 0.4) (±2σ), all in units of 10-10 cm3 molecule-1 s-1. Both the kinetics studies and the HCl yields determined using FTIR show that the net abstraction of an allylic hydrogen is a small but significant fraction, 15 ± 4% (±2σ), of the overall reaction at 1 atm. The major organic products appear to be unsaturated chlorine-containing carbonyl compounds which remain unidentified. The atmospheric implications are discussed.

A kinetic and product study of the gas-phase reaction of ozone with vinylcyclohexane and methylene cyclohexane

The gas-phase reaction of ozone with vinylcyclohexane and methylene cyclohexane has been investigated at ambient T and p=1 atm of air in the presence of sufficient cyclo-hexane or 2-propanol added to scavenge OH. The reaction rate constants, in units of 10−18 cm3 molecule−1 s−1, are 7.52±0.97 for vinylcyclohexane (T=292±2 K) and 10.6±1.9 for methylene cyclohexane (T=293±2 K). Carbonyl reaction products were cyclohexyl meth-anal (0.62±0.03) and formaldehyde (0.47±0.04) from vinylcyclohexane and cyclohexanone (0.55±0.10) and formaldehyde (0.60±0.05) from methylene cyclohexane, where the yields given in parentheses are expressed as carbonyl formed, ppb/reacted ozone, ppb. The sum of the yields of the primary carbonyls is close to the value of 1.0 that is consistent with the simple mechanisms: O3+cyclo(C6H11)−CH(DOUBLEBOND)CH2→α(HCHO+cyclo(C6H11)CHOO)+(1−α)(HCHOO+cyclo(C6H11)CHO) for vinylcyclohexane and O3+(CH2)5C(DOUBLEBOND)CH2→α(HCHO +(CH2)5COO)+(1−α)(HCHOO+(CH2)5C(DOUBLEBOND)O) for methylene cyclohexane. The coefficients α are 0.43±0.10 for vinylcyclohexane and 0.52±0.05 for methylene cyclohexane, i.e., (formaldehyde+the substituted biradical) and (HCHOO+cyclohexyl methanal or cyclo-hexanone) are formed in ca. equal yields. Reaction rate constants, carbonyl yields, and reaction mechanisms are compared to those for alkene structural homologues. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 855–860, 1997