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Total Pressure (total + pressure)
Selected AbstractsRheological characteristics of solid,fluid transition in dry granular dense flows: A thermodynamically consistent constitutive model with a pressure-ratio order parameterINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2010Chung Fang Abstract Dry granular flows are characterized as quasi-static, dense and collisional states by the interactions among the grains, which is indexed macroscopically by an internal variable, called the order parameter defined as the square root of the static pressure to the total pressure. The solid,fluid state transition is regarded as a second-order phase transition process, and is described by a kinematic evolution of the order parameter. The thermodynamic analysis, based on the Müller,Liu entropy principle, is employed to deduce the equilibrium responses of the constitutive equations, while the dynamic responses are postulated on the basis of a quasi-linear and the second-order Ginzburg,Landau phase transition theories. The obtained model is applied to study the rheological characteristics of a dry granular dense flow between two infinite parallel plates, of which the results are compared with those from DEM simulations to estimate the model validity. The present study provides a general framework for the theoretical justifications on the thermodynamic consistencies of order-parameter-based constitutive models, and can be extended to flows in quasi-static or collisional states. Copyright © 2009 John Wiley & Sons, Ltd. [source] Rate constants for the gas-phase reactions of nitrate radicals with geraniol, citronellol, and dihydromyrcenol,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2010Joel C. Harrison Terpenes and terpene alcohols are prevalent compounds found in a wide variety of consumer products including soaps, flavorings, perfumes, and air fresheners used in the indoor environment. Knowing the reaction rate of these chemicals with the nitrate radical is an important factor in determining their fate indoors. In this study, the bimolecular rate constants of k (16.6 ± 4.2) × 10,12, k (12.1 ± 3) × 10,12, and k (2.3 ± 0.6) × 10,14 cm3 molecule,1 s,1 were measured using the relative rate technique for the reaction of the nitrate radical (NO3,) with 2,6-dimethyl-2,6-octadien-8-ol (geraniol), 3,7-dimethyl-6-octen-1-ol (citronellol), and 2,6-dimethyl-7-octen-2-ol (dihydromyrcenol) at (297 ± 3) K and 1 atmosphere total pressure. Using the geraniol, citronellol, or dihydromyrcenol + NO3, rate constants reported here, pseudo-first-order rate lifetimes (k,) of 1.5, 1.1, and 0.002 h,1 were determined, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 669,675, 2010 [source] ,-Ionone reactions with the nitrate radical: Rate constant and gas-phase productsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2009Joel C. Harrison The bimolecular rate constant of k (9.4 ± 2.4 × 10,12 cm3 molecule,1 s,1 was measured using the relative rate technique for the reaction of the nitrate radical (NO3,) with 4-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3-buten-2-one (,-ionone) at (297 ± 3) K and 1 atmosphere total pressure. In addition, the products of ,-ionone + NO3, reaction were also investigated. The identified reaction products were glyoxal (HC(O)C(O)H), and methylglyoxal (CH3C(O)C(O)H). Derivatizing agents O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine and N,O-bis(trimethylsilyl)trifluoroacetamide were used to propose the other major reaction products: 3-oxobutane-1,2-diyl nitrate, 2,6,6-trimethylcyclohex-1-ene-carbaldehyde, 2-oxo-1-(2,6,6-trimethylcyclohex-1-en-1-yl)ethyl nitrate, pentane-2,4-dione, 3-oxo-1-(2,6,6-trimethylcyclohex-1-en-1-yl)butane-1,2-diyl dinitrate, 3,3-dimethylcyclohexane-1,2-dione, and 4-oxopent-2-enal. The elucidation of these products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible ,-ionone + NO3, reaction mechanisms based on previously published volatile organic compound + NO3, gas-phase mechanisms. The additional gas-phase products 5-acetyl-2-ethylidene-3-methylcyclopentyl nitrate, 1-(1-hydroxy-7,7-dimethyl-2,3,4,5,6,7-hexahydro-1 H-inden-2-yl)ethanone, 1-(1-hydroxy-3a,7-dimethyl-2,3,3a,4,5,6,-hexahydro-1 H-inden-2-yl)ethanone, and 5-acetyl-2-ethylidene-3-methylcyclopentanone are proposed to be the result of cyclization through a reaction intermediate. © 2009 Wiley Periodicals, Inc., Int J Chem Kinet 41: 629,641, 2009 [source] The hydroxyl radical reaction rate constant and products of 3,5-dimethyl-1-hexyn-3-ol,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2004J. R. Wells A bimolecular rate constant,kDHO, of (29 ± 9) × 10,12 cm3 molecule,1 s,1 was measured using the relative rate technique for the reaction of the hydroxyl radical (OH) with 3,5-dimethyl-1-hexyn-3-ol (DHO, HCCC(OH)(CH3)CH2CH(CH3)2) at (297 ± 3) K and 1 atm total pressure. To more clearly define DHO's indoor environment degradation mechanism, the products of the DHO + OH reaction were also investigated. The positively identified DHO/OH reaction products were acetone ((CH3)2CO), 3-butyne-2-one (3B2O, HCCC(O)(CH3)), 2-methyl-propanal (2MP, H(O)CCH(CH3)2), 4-methyl-2-pentanone (MIBK, CH3C(O)CH2CH(CH3)2), ethanedial (GLY, HC(O)C(O)H), 2-oxopropanal (MGLY, CH3C(O)C(O)H), and 2,3-butanedione (23BD, CH3C(O)C(O)CH3). The yields of 3B2O and MIBK from the DHO/OH reaction were (8.4 ± 0.3) and (26 ± 2)%, respectively. The use of derivatizing agents O -(2,3,4,5,6-pentalfluorobenzyl)hydroxylamine (PFBHA) and N,O -bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible DHO/OH reaction mechanisms based on previously published volatile organic compound/OH gas-phase reaction mechanisms. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 534,544, 2004 [source] Validation of a thermal decomposition mechanism of formaldehyde by detection of CH2O and HCO behind shock wavesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2004Gernot Friedrichs The thermal decomposition of formaldehyde was investigated behind shock waves at temperatures between 1675 and 2080 K. Quantitative concentration time profiles of formaldehyde and formyl radicals were measured by means of sensitive 174 nm VUV absorption (CH2O) and 614 nm FM spectroscopy (HCO), respectively. The rate constant of the radical forming channel (1a), CH2O + M , HCO + H + M, of the unimolecular decomposition of formaldehyde in argon was measured at temperatures from 1675 to 2080 K at an average total pressure of 1.2 bar, k1a = 5.0 × 1015 exp(-308 kJ mol,1/RT) cm3 mol,1 s,1. The pressure dependence, the rate of the competing molecular channel (1b), CH2O + M , H2 + CO + M, and the branching fraction , = k1a/(kA1a + k1b) was characterized by a two-channel RRKM/master equation analysis. With channel (1b) being the main channel at low pressures, the branching fraction was found to switch from channel (1b) to channel (1a) at moderate pressures of 1,50 bar. Taking advantage of the results of two preceding publications, a decomposition mechanism with six reactions is recommended, which was validated by measured formyl radical profiles and numerous literature experimental observations. The mechanism is capable of a reliable prediction of almost all formaldehyde pyrolysis literature data, including CH2O, CO, and H atom measurements at temperatures of 1200,3200 K, with mixtures of 7 ppm to 5% formaldehyde, and pressures up to 15 bar. Some evidence was found for a self-reaction of two CH2O molecules. At high initial CH2O mole fractions the reverse of reaction (6), CH2OH + HCO , CH2O + CH2O becomes noticeable. The rate of the forward reaction was roughly measured to be k6 = 1.5 × 1013 cm3 mol,1 s,1. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 157,169 2004 [source] Rate coefficients and mechanisms of the reaction of cl-atoms with a series of unsaturated hydrocarbons under atmospheric conditionsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2003John J. Orlando Rate coefficients and/or mechanistic information are provided for the reaction of Cl-atoms with a number of unsaturated species, including isoprene, methacrolein (MACR), methyl vinyl ketone (MVK), 1,3-butadiene, trans -2-butene, and 1-butene. The following Cl-atom rate coefficients were obtained at 298 K near 1 atm total pressure: k(isoprene) = (4.3 ± 0.6) × 10,10cm3 molecule,1 s,1 (independent of pressure from 6.2 to 760 Torr); k(MVK) = (2.2 ± 0.3) × 10,10 cm3 molecule,1 s,1; k(MACR) = (2.4 ± 0.3) × 10,10 cm3 molecule,1 s,1; k(trans -2-butene) = (4.0 ± 0.5) × 10,10 cm3 molecule,1 s,1; k(1-butene) = (3.0 ± 0.4) × 10,10 cm3 molecule,1 s,1. Products observed in the Cl-atom-initiated oxidation of the unsaturated species at 298 K in 1 atm air are as follows (with % molar yields in parentheses): CH2O (9.5 ± 1.0%), HCOCl (5.1 ± 0.7%), and 1-chloro-3-methyl-3-buten-2-one (CMBO, not quantified) from isoprene; chloroacetaldehyde (75 ± 8%), CO2 (58 ± 5%), CH2O (47 ± 7%), CH3OH (8%), HCOCl (7 ± 1%), and peracetic acid (6%) from MVK; CO (52 ± 4%), chloroacetone (42 ± 5%), CO2 (23 ± 2%), CH2O (18 ± 2%), and HCOCl (5%) from MACR; CH2O (7 ± 1%), HCOCl (3%), acrolein (,3%), and 4-chlorocrotonaldehyde (CCA, not quantified) from 1,3-butadiene; CH3CHO (22 ± 3%), CO2 (13 ± 2%), 3-chloro-2-butanone (13 ± 4%), CH2O (7.6 ± 1.1%), and CH3OH (1.8 ± 0.6%) from trans -2-butene; and chloroacetaldehyde (20 ± 3%), CH2O (7 ± 1%), CO2 (4 ± 1%), and HCOCl (4 ± 1%) from 1-butene. Product yields from both trans -2-butene and 1-butene were found to be O2 -dependent. In the case of trans -2-butene, the observed O2 -dependence is the result of a competition between unimolecular decomposition of the CH3CH(Cl)CH(O,)CH3 radical and its reaction with O2, with kdecomp/kO2 = (1.6 ± 0.4) × 1019 molecule cm,3. The activation energy for decomposition is estimated at 11.5 ± 1.5 kcal mol,1. The variation of the product yields with O2 in the case of 1-butene results from similar competitive reaction pathways for the two ,-chlorobutoxy radicals involved in the oxidation, ClCH2CH(O,)CH2CH3 and ,OCH2CHClCH2CH3. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 334,353, 2003 [source] Kinetics of the reaction of OH radicals with acetylene in 25,8000 torr of air at 296 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2003M. Sørensen Relative rate techniques were used to study the kinetics of the reaction of OH radicals with acetylene at 296 K in 25,8000 Torr of air, N2/O2, or O2 diluent. Results obtained at total pressures of 25,750 Torr were in good agreement with the literature data. At pressures >3000 Torr, our results were substantially (,35%) lower than that reported previously. The kinetic data obtained over the pressure range 25,8000 Torr are well described (within 15%) by the Troe expression using ko = (2.92 ± 0.55) × 10,30 cm6 molecule,2 s,1, k, = (9.69 ± 0.30) × 10,13 cm3 molecule,1 s,1, and Fc = 0.60. At 760 Torr total pressure, this expression gives k = 8.49 × 10,13 cm molecule,1 s,1. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 191,197, 2003 [source] Modeling of coupled mass and heat transfer through venting membranes for automotive applicationsAICHE JOURNAL, Issue 2 2009Amine Barkallah Abstract Experimental and theoretical approaches based on a mathematical model, have been developed to study the evolution of environmental parameters (temperature, total pressure, relative humidity, and water vapor partial pressure) inside a housing of an electronic device with a window containing a macroporous membrane. The model was based on the coupling of mass and heat transfer taking into account the effects of polarization of concentration in boundary layers. Membranes have been characterized by mercury porosimetry, liquid entry pressure measurements, scanning electron microscopy, and gas permeation. Once the model was experimentally validated, it was applied to investigate the influence of membranes on heat and mass transfer and to study the impact of the boundary layers on the global mass transport. The results demonstrated the importance of the membrane choice and dimensions to get the best temperature regulation and avoid water condensation inside an automotive electronic control unit (ECU). © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Propylene/propane separation by vacuum swing adsorption using 13X zeoliteAICHE JOURNAL, Issue 2 2001Francisco A. Da Silva A vacuum swing adsorption process using 13X zeolite pellets with five steps was designed to split an equimolar mixture of propylene/propane: pressurization with feed; high-pressure feed; high-pressure purge with product; cocurrent blowdown; and counter-current vacuum blowdown, where the enriched propylene product is withdrawn. In the process, the partial pressure of the C3 -mixture is controlled with nitrogen, which is used as inert gas. With an equimolar feed of C3 diluted to 50% with nitrogen, the column is fed at 5 bar and 423 K, and the product is obtained when the total pressure is lowered to 0.1 bar. After 15,20 cycles, the cyclic steady-state condition is achieved, a propylene-enriched stream of 98% mol relative to propylene/propane mixture, with 3.2% of nitrogen, a recovery of 19% (molar basis), and a productivity of 0.785 mol/kg·h is obtained. The experimental work was complemented with numerical simulations, and the effect of different operating parameters on the performance of the VSA was considered. [source] CH3CH2SCH3,+,OH radicals: temperature-dependent rate coefficient and product identification under atmospheric pressure of air,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2010Gabriela Oksdath-Mansilla Abstract Relative rate coefficients have been determined for the gas-phase reaction of hydroxyl (OH) radicals with ethyl methyl sulfide (EMS) using isobutene as a reference compound. The experiments were performed in a 1080,L quartz glass photoreactor in the temperature range of 286,313,K at a total pressure of 760,±,10,Torr synthetic air using in situ FTIR absorption spectroscopy to monitor the concentration-time behaviors of reactants and products. OH radicals were produced by the 254,nm photolysis of hydrogen peroxide (H2O2). The kinetic data obtained were used to derive the following Arrhenius expression valid in the temperature range of 286,313,K (in units of cm3,molecule,1,s,1): The rate coefficient displays a negative temperature dependence and low pre-exponential factor which supports the existence of an addition mechanism for the reaction involving reversible OH-adduct formation. The results are compared with previous data of other sulfides from the literature and are rationalized in terms of structure,reactivity relationships. Additionally, product identification of the title reaction was performed for the first time by the FTIR technique under atmospheric conditions. Sulfur dioxide, formaldehyde, and formic acid were observed as degradation products in agreement with the two possible reaction channels (addition/abstraction). Copyright © 2010 John Wiley & Sons, Ltd. [source] Water Vapor Corrosion Behavior of Scandium Silicates at 1400°CJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2009Zhiliang Hong The corrosion behavior of scandium silicates with different scandia contents were investigated in an atmosphere of 50%H2O,50%O2 water vapor with a total pressure of 1 atm at 1400°C. The weight changes of scandium silicates as a function of annealing time were recorded to illustrate the corrosion behavior of these materials. The phases of as-prepared and corroded materials were compared by using X-ray diffraction and Fourier transform infrared spectroscopy. The results indicate that the water vapor does not corrode the scandium disilicate. The weight gain during corrosion is attributed to the hydroxylation of free scandia. [source] Alumina Volatility in Water Vapor at Elevated TemperaturesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2004Elizabeth J. Opila The volatility of alumina in high-temperature water vapor was determined by a weight loss technique. Sapphire coupons were exposed at temperatures between 1250° and 1500°C, water partial pressures between 0.15 and 0.68 atm in oxygen, a total pressure of 1 atm, and flowing gas velocities of 4.4 cm/s. The water vapor pressure dependence of sapphire volatility was consistent with Al(OH)3(g) formation. The enthalpy of reaction to form Al(OH)3(g) from sapphire and water vapor was determined to be 210 ± 20 kJ/mol, comparing favorably to other studies. Microstructural examination of tested sapphire coupons revealed surface rearrangement consistent with a volatilization process. [source] Effectiveness of platinum and iridium in improving the resistance of Ni-Al to thermal cycling in air,steam mixturesMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 6 2008R. Kartono Abstract The aim of this work was to assess the value of platinum and iridium additions, with and without hafnium, to binary Ni-Al alloys, intended to act as models for aluminide coatings. Attention was focused on a (,,+,,,) Ni-22Al alloy, but comparisons were made with , -Ni-50Al. All compositions are given in at%. Alloys were exposed to flowing gases at a total pressure of 1 bar for one thousand 1 h cycles at 1200,°C. Compared to binary Ni-Al alloys, the Pt-modified alloys performed much better (with or without Hf) in dry air. Thermal cycling in air,+,12% H2O led to more rapid weight losses, due to enhanced spalling. Again, the addition of Pt was beneficial, but weight losses were still significant in the absence of Hf additions. A Ni-22Al-15Pt,+,Hf alloy slowly lost weight by scale spallation over 1000 cycles, but a Ni-22Al-30Pt,+,Hf alloy resisted weight loss. Partial substitution of Ir for Pt was beneficial in both wet and dry air. However, in the case of wet air, Hf additions were necessary to prevent slow spallation losses. [source] Study of Inductive Coupled Hydrogen and Argon Plasma Interaction with SiO2 GlassPLASMA PROCESSES AND POLYMERS, Issue S1 2009Atis Skudra Abstract This work is devoted to the diagnostics of interaction between hydrogen and argon with the surface of SiO2 glass walls. For diagnostics of the interaction, special high-frequency electrodeless light sources were prepared, filled with pure argon of 1,Torr or argon-hydrogen of total pressure of 1,Torr (Ar/H2 mixing ratio is 9:1). Besides the mostly used spherical and cylindrical lamps, dumbbell type lamps have also been investigated. The spectroscopic and AFM measurements showed that in comparison with pure argon plasma, the argon-hydrogen plasma causes non-uniform changes of the SiO2 surface. For these modifications active OH are primarily responsible molecules, created in the reactions of hydrogen molecules with oxygen molecules, adsorbed from the walls. [source] Polymerization in Nanocrystalline Diamond Films by Oxygen IncorporationPLASMA PROCESSES AND POLYMERS, Issue 9 2006Kungen Teii Abstract Summary: Structure and resistivity of nanocrystalline diamond films deposited using microwave Ar-rich/O2/CH4 plasmas have been examined as a function of the O2/CH4 ratio from 0 to 0.53. Addition of O2 to Ar-rich/CH4 plasmas likely reduced the density of C2 radicals due to loss reactions of O atoms with CH4 and CHx radicals. The Raman peak of diamond at 1,332 cm,1 was overlapped by the D peak of sp2 -bonded, disordered carbon and its intensity was a little enhanced by the O2 addition, while the average size of sp2 -bonded carbon clusters in nondiamond phases was increased. Oxygen was incorporated into the films in forms of CO bonds, which bridged the carbon clusters themselves, and formed polymer-like, large-unit structures. The resistivity of the films was drastically increased from the order of 10,4 up to 104 ,,·,m with a small O2 addition (1.2 vol.-% in total pressure), providing novel sensor and storage applications based on oxygen incorporation and desorption. Decomposition of a Raman spectrum showing the diamond, D and G modes of amorphous carbon, and trans -polyacetylene peaks. The insert represents a typical SEM image showing a film surface. [source] Association between Attributes of a Cyclist and Bicycle Seat PressureTHE JOURNAL OF SEXUAL MEDICINE, Issue 10 2010Eadric Bressel PhD ABSTRACT Introduction., Bicycle seat pressure is thought to be the principal risk factor for bicycle seat injuries such as erectile dysfunction; however there is a lack of understanding regarding the characteristics of a cyclist that predict bicycle seat pressure. Aim., The purpose of this study was to determine if select attributes of a cyclist are associated with seat pressure during stationary bicycling. A secondary purpose was to determine which of the associated attributes were the best predictors of seat pressure and if they were consistent between two different seats. Methods., There were two data collection phases to this correlational study in which 40 males between the ages 20 and 50 years volunteered. For the first phase, select attributes of the cyclist (age, weight, flexibility, experience level, and ischial tuberosity width) were measured. The second phase required participants to ride a stationary cycle ergometer while pelvic tilt angles and seat pressures were measured on two different traditional seats. Main Outcome Measure., The main outcome is the mean and peak bicycle seat interface pressure over the anterior and total seat. Results., Body weight explained up to 50% of the variance in mean total seat pressure (P = 0.001). Regarding peak total pressure, pelvic tilt angle and flexibility explained 43% and 17% of the variance, respectively, for the two seats tested (P = 0.01). Conclusion., These results indicate that predictors of mean seat pressure are not the same for peak pressure. Body weight alone accounted for the most variance in mean pressure whereas pelvic tilt and flexibility accounted for the most variance in peak pressure. These variables related to seat pressure may give some guidance to cyclists and clinicians who intend to prevent or alleviate the symptoms associated with bicycle seat injuries that include erectile dysfunction. Bressel E, Nash D, and Dolny D. Association between attributes of a cyclist and bicycle seat pressure. J Sex Med 2010;7:3424,3433. [source] Fed-Batch Cultivation of Saccharomyces cerevisiae in a Hyperbaric BioreactorBIOTECHNOLOGY PROGRESS, Issue 2 2003I. Belo Fed-batch is the dominating mode of operation in high-cell-density cultures of Saccharomyces cerevisaein processes such as the production of bakerapos;s yeast and recombinant proteins, where the high oxygen demand of these cultures makes its supply an important and difficult task. The aim of this work was to study the use of hyperbaric air for oxygen mass transfer improvement on S. cerevisiaefed-batch cultivation. The effects of increased air pressure up to 1.5 MPa on cell behavior were investigated. The effects of oxygen and carbon dioxide were dissociated from the effects of total pressure by the use of pure oxygen and gas mixtures enriched with CO2. Fed-batch experiments were performed in a stirred tank reactor with a 600 mL stainless steel vessel. An exponential feeding profile at dilution rates up to 0.1 h,1 was used in order to ensure a subcritical flux of substrate and, consequently, to prevent ethanol formation due to glucose excess. The ethanol production observed at atmospheric pressure was reduced by the bioreactor pressurization up to 1.0 MPa. The maximum biomass yield, 0.5 g g,1 (cell mass produced per mass of glucose consumed) was attained whenever pressure was increased gradually through time. This demonstrates the adaptive behavior of the cells to the hyperbaric conditions. This work proved that hyperbaric air up to 1.0 MPa (0.2 MPa of oxygen partial pressure) could be applied to S. cerevisiaecultivation under low glucose flux. Above that critical oxygen partial pressure value, i.e., for oxygen pressures of 0.32 and 0.5 MPa, a drastic cell growth inhibition and viability loss were observed. The increase of carbon dioxide partial pressure in the gas mixture up to 48 kPa slightly decreased the overall cell mass yield but had negligible effects on cell viability. [source] Shock-tube and modeling study of acetaldehyde pyrolysis and oxidationINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2008Kenji Yasunaga Pyrolysis and oxidation of acetaldehyde were studied behind reflected shock waves in the temperature range 1000,1700 K at total pressures between 1.2 and 2.8 atm. The study was carried out using the following methods, (1) time-resolved IR-laser absorption at 3.39 ,m for acetaldehyde decay and CH-compound formation rates, (2) time-resolved UV absorption at 200 nm for CH2CO and C2H4 product formation rates, (3) time-resolved UV absorption at 216 nm for CH3 formation rates, (4) time-resolved UV absorption at 306.7 nm for OH radical formation rate, (5) time-resolved IR emission at 4.24 ,m for the CO2 formation rate, (6) time-resolved IR emission at 4.68 ,m for the CO and CH2CO formation rate, and (7) a single-pulse technique for product yields. From a computer-simulation study, a 178-reaction mechanism that could satisfactorily model all of our data was constructed using new reactions, CH3CHO (+M) , CH4 + CO (+M), CH3CHO (+M) , CH2CO + H2(+M), H + CH3CHO , CH2CHO + H2, CH3 + CH3CHO , CH2CHO + CH4, O2 + CH3CHO , CH2CHO + HO2, O + CH3CHO , CH2CHO + OH, OH + CH3CHO , CH2CHO + H2O, HO2 + CH3CHO , CH2CHO + H2O2, having assumed or evaluated rate constants. The submechanisms of methane, ethylene, ethane, formaldehyde, and ketene were found to play an important role in acetaldehyde oxidation. © 2007 Wiley Periodicals, Inc. 40: 73,102, 2008 [source] Kinetics of the reaction of OH radicals with acetylene in 25,8000 torr of air at 296 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2003M. Sørensen Relative rate techniques were used to study the kinetics of the reaction of OH radicals with acetylene at 296 K in 25,8000 Torr of air, N2/O2, or O2 diluent. Results obtained at total pressures of 25,750 Torr were in good agreement with the literature data. At pressures >3000 Torr, our results were substantially (,35%) lower than that reported previously. The kinetic data obtained over the pressure range 25,8000 Torr are well described (within 15%) by the Troe expression using ko = (2.92 ± 0.55) × 10,30 cm6 molecule,2 s,1, k, = (9.69 ± 0.30) × 10,13 cm3 molecule,1 s,1, and Fc = 0.60. At 760 Torr total pressure, this expression gives k = 8.49 × 10,13 cm molecule,1 s,1. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 191,197, 2003 [source] The fate of the hydroxyalkoxy radical in the OH-initiated oxidation of isopreneINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2002June E. Reitz Rate constants for several intermediate steps in the OH-initiated oxidation of isoprene were determined using laser-photolysis/laser-induced fluorescence of OH radicals at total pressures between 3 and 4 Torr at 295 K. The rate constant for decomposition of the hydroxyalkoxy radical was determined to be (3.0 ± 0.5) × 104 s,1 in this pressure range, which is in fair agreement with previous work. The presence of a prompt alkoxy decomposition pathway was also investigated and found to contribute less than 10% to the total hydroxyalkoxy radical decomposition. The rate constant for the reaction of the hydroxyperoxy radical with NO was determined to be (2.5 ± 0.5) × 10,11 cm3 molecule,1 s,1, which is moderately higher than previously reported. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 255,261, 2002 [source] Non-mass-dependent oxygen isotopic fractionation in smokes produced in an electrical dischargeMETEORITICS & PLANETARY SCIENCE, Issue 7-8 2007Yuki Kimura The smokes were formed at the Goddard Space Flight Center (GSFC) at total pressures of just under 100 Torr in an electrical discharge powered by a Tesla coil, were collected from the surfaces of the copper electrodes after each experiment and sent to the University of California at San Diego (UCSD) for oxygen isotopic analysis. Transmission electron microscopy studies of the smokes show that they grew in the gas phase rather than on the surfaces of the electrodes. We hypothesize at least two types of fractionation processes occurred during formation of the solids: a mass-dependent process that made isotopically lighter oxides compared to our initial oxygen gas composition followed by a mass-independent process that produced oxides enriched in 17O and 18O. The maximum ,17O observed is + 4.7, for an iron oxide produced in flowing hydrogen, using O2 as the oxidant. More typical displacements are 1,2, above the equilibrium fractionation line. The chemical reaction mechanisms that yield these smokes are still under investigation. [source] | ||||||||||||||||