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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Kinetics of the Cl(2)P(J)) + CH4 Reaction: Effects of Secondary Chemistry Below 300 K

Absolute rate data for the Cl(2)P(J) + CH4 yields HCl + CH3 reaction have been obtained from 218 to 298 K by using the discharge-flow resonance fluorescence technique at I Torr total pressure. The result at 298 K is (10.1 +/- 0.6) x 10(exp -14) cu cm/molecule/s. The temperature dependence in Arrhenius form is (6.5 +/- 0.9 ) x 10(exp -12) exp[(-1235 +/- 34 )/T]. The errors given are one standard deviation; overall experimental error is estimated at +/- 15%. Because of the relatively large disagreement among earlier measurements at low temperatures, the results were examined for possible effects of non-Boltzmann spin distribution and vibrational excitation of CH4, secondary chemistry of CH3 radicals, and impurities in the CH4 source. There was no significant change in the observed rate constant when an efficient spin quencher, CF4, was added and estimates indicate that vibrational partitioning in CH4 should be at the ambient reactor temperature before the start of the reaction. The results were also independent of the source of Cl atoms (microwave discharge or thermal decomposition of Cl2) and whether CH4 was purified in-situ. However, the observed rate constant did depend on initial Cl atom concentrations and to a lesser extent on CH4 concentrations. Numerical simulations were used to assess the importance of secondary chemistry over a range of reactant concentrations

Wang, J. J.↗
NASA NTRS1997

Kinetics of the Reactions of O((sup 3)P) and Cl((sup 2)P) with HBr and Br2

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of reactions (1)-(4) as a function of temperature. (1) O((sup 3)P) + Br2 yields BrO + Br((sup 2)P(sub 3/2)) at 255-350 K; (2) Cl((sup 2)P) + Br2 yields BrCl + Br((sup 2)P(sub 3/2)) at 298-401 K; (3) O((sup 3)P) + HBr yields OH + Br((sup 2)P(sub J)) at 250-402 K; (4) Cl((sup 2)P) + HBr yields HCl + Br((sup 2)P(sub J)) at 257-404 K. In all cases, the concentration of the excess reagent, i.e, HBr or Br2, was measured in situ in the slow flow system by UV-visible photometry. Heterogeneous dark reactions between XBr (X equals H or Br) and the photolytic precursors for Cl((sup 2)P) and O((sup 3)P) (Cl2 and O3, respectively) were avoided by injecting minimal amounts of precursor into the reaction mixture immediately upstream from the reaction zone. The following Arrhenius expressions summarize our results (errors are 2 sigma and represent precision only, units are cu cm/(molecule.s): k(sub 1) = (1.76 +/- 0.80) x 10(exp -11 exp[(40 +/- 100)/T]; k(sub 2) = (2.40 +/- 1.25) x 12(exp -10) exp[-(144 +/- 176)/T]; k(sub 3) = (5.11 +/- 2.82) x 10(exp -12) exp[-(1450 +/- 160)/T]; k(sub 4) = (2.25 +/- 0.56) x 10(exp -11) exp[-(400 +/- 80)/T]. The consistency (or lack thereof) of our results with those reported in previous kinetics and dynamics studies of reactions (1)-(4) is discussed.

Nicovich, J. M.↗
NASA NTRS1997

Kinetics of the Reactions of F((sup 2)P) and Cl((sup 2)P) with HNO3

The kinetics of the reactions of HNO3 with fluorine (k(sub 1)) and Chlorine (k(sub 2)) atoms have been studied by using a time-resolved long-path laser absorption technique to monitor the appearance of product NO3 radicals following 351-nm pulsed laser photolysis of X2/HNO3/He mixtures (X = F,Cl). Absolute rate coefficients for the F((sup 2)P) + HNO reaction have been determined over the temperature range 260-373 K. Between 260 and 320 K, the data are adequately represented by the Arrhenius expression k(sub 1)(T) = (6.0 +/- 2.6) x 10(exp -12) exp[(40 +/- 120)/T]cu cm/(molecule.s). Between 335 and 373 K, the rate coefficient is found to be (2.0 +/- 0.3) x 10(exp -11)cu cm/(molecule.s) independent of temperature. The observed temperature dependence suggests that reaction proceeds via competing direct abstraction and complex pathways. No NO3 production was observed in the experiments with X equals Cl, thus establishing that k(sub 2)(298 K) is less than 2 x 10(exp -16) cu cm/(molecule.s). The Cl((sup 2)P) + HNO reaction was also investigated by using a pulsed laser photolysis-resonance fluorescence technique to monitor the decay of Cl((sup 2)P). Upper limit values for k(sub 2) obtained from these experiments, in units of 10(exp -16)cu cm/(molecule.s), are 13 at 298 K and 10 at 400 K.

Wine, P. H.↗
NASA NTRS1997

Kinetics and Thermochemistry of Reversible Adduct Formation in the Reaction of Cl((sup 2)P(sub J)) with CS2

Reversible adduct formation in the reaction of Cl((sup 2)P(sub J)) with CS2 has been observed over the temperature range 193-258 K by use of time-resolved resonance fluorescence spectroscopy to follow the decay of pulsed-laser-generated Cl((sup 2)P(sub J)) into equilbrium with CS2Cl. Rate coefficients for CS2Cl formation and decomposition have been determined as a function of temperature and pressure; hence, the equilbrium constant has been determined as a function of temperature. A second-law analysis of the temperature dependence of Kp and heat capacity corrections calculated with use of an assumed CS2Cl structure yields the following thermodynamic parameters for the association reaction: Delta-H(sub 298) = -10.5 +/- 0.5 kcal/mol, Delta-H(sub 0) = -9.5 +/- 0.7 kcal/mol, Delta-S(sub 298) = -26.8 +/- 2.4 cal/mol.deg., and Delta-H(sub f,298)(CS2Cl) = 46.4 +/- 0.6 kcal/mol. The resonance fluorescence detection scheme has been adapted to allow detection of Cl((sup 2)P(sub J)) in the presence of large concentrations of O2, thus allowing the CS2Cl + Cl + O2 reaction to be investigated. We find that the rate coefficient for CS2Cl + O2 reaction via all channels that do not generate Cl((sup 2)P(sub J)) is less than 2.5 x 10(exp-16) cu cm/(molecule.s) at 293 K and 300-Torr total pressure and that the total rate coefficient is less than 2 x 10 (exp -15) cu cm/(molecule.s) at 230 K and 30-Torr total pressure. Evidence for reversible adduct formation in the reaction of Cl((sup 2)P(sub J)) with COS was sought but not observed, even at temperatures as low as 194 K.

Nicovich, J. M.↗
NASA NTRS1972

Energy distribution among reaction products. V.

Discussion of three reactions, one point of theoretical interest being the predicted correlation between barrier height and barrier location. The H + Br 2 reaction having a lower activation barrier than H + Cl 2, should have an earlier barrier, and hence a greater percentage attractive energy release and higher efficiency of vibrational excitation. Information is developed concerning the effect of isotopic substitution in the pair of reactions H + Cl 2 and D + Cl 2. The 'arrested relaxation' method was used. Essentially, the method involves reacting two diffuse reagent beams in a reaction vessel with background pressure less than 0.001 torr, and with walls cooled by liquid nitrogen or liquid helium.

Anlauf, K. G.↗
NASA NTRS1988

Simulation of the transport of halogen species from the equatorial and mid-latitude stratosphere to the polar stratosphere in a two-dimensional model

The bulk of O sub 3 destruction in the Antarctic stratosphere takes place in the lower stratosphere between 15 and 25 km. Both O sub 3 and the halogen reservoir species have their origins in the higher altitude region (20 to 30 km) in the equatorial and mid-latitude stratosphere. Using the Caltech-JPL two-dimensional residual circulation model, researchers investigate the growth of stratospheric halogen due to the increase of CFCl sub 3 and CF sub 2 Cl sub 2.

Yung, Yuk L.↗
NASA NTRS1997

Kinetics of the Reactions of Cl((sup 2)P(sub J)) and Br((sup 2)P(sub 3/2)) with O3

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the important stratospheric reactions Cl((sup 2)P(sub J)) + O3 yields ClO + O2 and Br((sup 2)P(sub 3/2)) + O3 yields BrO + O2 as a function of temperature. The temperature dependence observed for the Cl((sup 2)P(sub J)) + O3 reaction is nonArrhenius, but can be adequately described by the following two Arrhenius expressions (units are cu cm/(molecule.s), errors are 2 sigma and represent precision only): k(sub 1)(T) = (1.19 +/- 0.21) x 10(exp -11) exp[(-33 +/- 37)/T] for T = 189-269 K and k(sub 1)(T) = (2.49 +/- 0.38) x 10(exp -11) exp[(-233 +/- 46)/T] for 269-385 K. At temperatures below 230 K, the rate coefficients determined in this study are faster than any reported previously. Incorporation of our values for k(sub 1)(T) into stratospheric models would increase calculated ClO levels and decrease calculated HCI levels; hence the calculated efficiency of ClO catalyzed ozone destruction would increase. The temperature dependence observed for the Br((sup 2)P(sub 3/2)) + O3 reaction is adequately described by the following Arrhenius expression (units are cu cm/(molecule.s), errors are 2 sigma and represent precision only): k(sub 2)(T) = (1.50 +/- 0.16) x 10(exp -11)exp[(-775 +/- 30)/T for 195-392 K. While not in quantitative agreement with Arrhenius parameters reported in most previous studies, our results almost exactly reproduce the average of all earlier studies and therefore will not affect the choice of k(sub 2)(T) for use in modeling stratospheric BrO2 chemistry.

Nicovich, J. M.↗
NASA NTRS1997

Kinetics and Thermochemistry of the Cl((sup 2)P(sub J)) + C2Cl4 Association Reaction

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the Cl(sup 2)P(sub j) + C2Cl4 association reaction as a function of temperature (231-390 K) and pressure (3-700 Torr) in nitrogen buffer gas. The reaction is found to be in the falloff regime between third and second order over the range of conditions investigated, although the second-order limit is approached at the highest pressures and lowest temperatures. At temperatures below 300 K, the association reaction is found to be irreversible on the experimental time scale of approximately 20 m-s. The kinetic data at T is less than 300 K have been employed to obtain falloff parameters in a convenient format for atmospheric modeling. At temperatures above 330 K, reversible addition is observed, thus allowing equilibrium constants for C2Cl5 formation and dissociation to be determined. Second- and third-law analyses of the equilibrium data lead to the following thermochemical parameters for the association reaction: Delta-H(298) = -18.1 +/- 1.3 kcal/mol, Delta-H(0) = -17.6 +/- 1.3 kcal/mol, and Delta-S(298) = -27.7 +/- 3.0 cal/mol.K. In conjunction with the well-known heats of formation of Cl((sup 2)P(sub j)) and C2Cl4 the above Delta-H values lead to the following heats of formation for C2Cl5, at 298 and 0 K: Delta-H(f,298) = 8.0 +/- 1.3 kcal/mol and Delta-H(f,0) = 8.1 +/- 1.5 kcal/mol. The kinetic and thermochemical parameters reported above are compared with other reported values, and the significance of reported association rate coefficients for understanding tropospheric chlorine chemistry is discussed.

Nicovich, J. M.↗
NASA NTRS2000

Through form to function: root hair development and nutrient uptake

Root hairs project from the surface of the root to aid nutrient and water uptake and to anchor the plant in the soil. Their formation involves the precise control of cell fate and localized cell growth. We are now beginning to unravel the complexities of the molecular interactions that underlie this developmental regulation. In addition, after years of speculation, nutrient transport by root hairs has been demonstrated clearly at the physiological and molecular level, with evidence for root hairs being intense sites of H(+)-ATPase activity and involved in the uptake of Ca(2+), K(+), NH(4)(+), NO(3)(-), Mn(2+), Zn(2+), Cl(-) and H(2)PO(4)(-).

Review, Tutorial↗
NASA NTRS2023

Effect of the Electrostatic Field due to the Surface Monolayer Metal Atoms on the Dissociation of Homonuclear Diatomic Gases in Gas-Metal Surface Reactions

The present paper examines the role of an electrostatic field generated by the outermost monolayer of metal ions prior to gas adsorption in aiding the dissociation of homonuclear diatomic gas molecules. The interaction of five homonuclear diatomic gases, Cl 2 , F 2 , H 2 , N 2 and O 2 , with several pure metals are examined using Coulomb’s law to calculate the attractive and repulsive forces between the electrons or ions in the gas molecule and the free surface metallic electrons or ions assuming a Bohr model. These calculations demonstrate that the total energy of the electrostatic fields from the metals can exceed the molecular binding energies of Cl 2 , F 2 , and O 2 at some distance from the metallic surface thereby suggesting that these gases interact primarily with the metallic surface in their atomic states after molecular bond dissociation prior to reaction. In contrast, H 2 and N 2 gases do not dissociate prior to reaching the metal surface due to the fact that the effective charge of the gas ions is less than the total electron charge at the outermost electronic shell. The present results correlate linearly with the electrochemical series standard reduction potential as well as with the Pauling electronegativity for several metals.

Gas-metal reactions↗
NASA NTRS1988

Particulate emissions from a mid-latitude prescribed chaparral fire

Particulate emission from a 400-acre prescribed chaparral fire in the San Dimas Experimental Forest was investigated by collecting smoke aerosol on Teflon and glass-fiber filters from a helicopter, and using SEM and EDAX to study the features of the particles. Aerosol particles ranged in size from about 0.1 to 100 microns, with carbon, oxygen, magnesium, aluminum, silicon, calcium, and iron as the primary elements. The results of ion chromatographic analysis of aerosol-particle extracts (in water-methanol) revealed the presence of significant levels of NO2(-), NO3(-), SO4(2-), Cl(-), PO4(3-), C2O4(2-), Na(+), NH4(+), and K(+). The soluble ionic portion of the aerosol was estimated to be about 2 percent by weight.

Cofer, Wesley R., III↗
NASA NTRS1988

Stability and photochemistry of ClO dimers formed at low temperature in the gas phase

The recent observations of elevated concentrations of the ClO radical in the austral spring over Antarctica have implicated catalytic destruction by chlorine in the large depletions seen in the total ozone column. One of the chemical theories consistent with an elevated concentration of the ClO is a cycle involving the formation of the ClO dimer through the association reaction: ClO + ClO = Cl2O2 and the photolysis of the dimer to give the active Cl species necessary for O3 depletion. Here, researchers report experimental studies designed to characterize the dimer of ClO formed by the association reaction at low temperatures. ClO was produced by static photolysis of several different precursor systems: Cl sub 2 + O sub 3; Cl sub 2 O sub 2; OClO + Cl sub 2 O spectroscopy in the U.V. region, which allowed the time dependence of Cl sub 2, Cl sub 2 O, ClO, OClO, O sub 3 and other absorbing molecules to be determined.

Cox, R. A.↗
NASA NTRS1992

We can't explore space without it - Common human space needs for exploration spaceflight

An overview is conducted of physiological, psychological, and human-interface requirements for manned spaceflight programs to establish common criteria. Attention is given to the comfort levels relevant to human support in exploration mission spacecraft and planetary habitats, and three comfort levels (CLs) are established. The levels include: (1) CL-1 for basic crew life support; (2) CL-2 for enabling the nominal completion of mission science; and (3) CL-3 which provides for enhanced life support and user-friendly interface systems. CL-2 support systems can include systems for EVA, workstations, and activity centers for repairs and enhanced utilization of payload and human/machine integration. CL-3 supports can be useful for maintaining crew psychological and physiological health as well as the design of comfortable and earthlike surroundings. While all missions require CL-1 commonality, CL-2 commonality is required only for EVA systems, display nomenclature, and restraint designs.

Daues, K. R.↗
NASA NTRS1997

New Fluorinated Polymers

This report summarizes progress during 1996 in our research effort along with a description of additional results associated with a TAG supplement to this grant (items 2 and 5 below). Progress is reported in five areas: 1) Polyamides Derived from [(p-HOOCC6H4)](sub 2)C(CF3)X (X= -CF3, OCH3, Cl); 2) Phosphorus-containing '12F-PEK' - Effect of Systematic Replacement of [(p-FC6H4COC6H4)](sub 2)C[(CF3)](sub 2) Monomer by [(p-FC6H4)](sub 2)(C6H5)PO; 3) Poly(ether ketone)s Derived from [(p-FC6H4COC6H4)](sub 2)(C6H5)PO; 4) New CF3-containing Organosilane Monomers and; 5) New Monomers for 12F-PEK Analogues with Improved Processability and Solubility.

Fitch, John W., III↗
NASA NTRS1990

Measurements and mechanisms of localized aqueous corrosion in aluminum-lithium alloys

Like most heat treatable aluminum alloys, localized corrosion and stress corrosion of Al-Li-Cu alloys is strongly dependent on the nature and distribution of second phase particles. To develop a mechanistic understanding of the role of localized corrosion in the stress corrosion process, bulk samples of T(sub 1) (Al2CuLi) and a range of Al-Cu-Fe impurity phases were prepared for electrochemical experiments. Potentiodynamic polarization and galvanic couple experiments were performed in standard 0.6 M NaCl and in simulated crevice solutions to assess corrosion behavior of these particles with respect to the alpha-Al matrix. A comparison of time to failure versus applied potential using a constant load, smooth bar SCC test technique in Cl(-), Cl(-)/CrO4(2-), and Cl(-)/CO3(2-) environments shows that rapid failures are to be expected when applied potentials are more positive than the breakaway potential (E sub br) of T(sub 1) (crack tip) but less than E(sub br) of alpha-Al (crack walls). It is shown that this criterion is not satisfied in aerated Cl(-) solutions. Accordingly, SCC resistance is good. This criterion is satisfied, however, in an alkaline isolated fissure exposed to a CO2 containing atmosphere. Rapid failure induced by these fissures was recently termed preexposure embrittlement. Anodic polarization shows that the corrosion behavior of T(sub 1) is relatively unaffected in alkaline CO3(2-) environments but the alpha-Al phase is rapidly passivated. X ray diffraction of crevice walls from artificial crevices suggests that passivation of alpha-Al occurs as hydrotalcite-type compound (LiAl2(OH)6)2(+) - CO3(2-) - nH2O.

Buchheit, Rudolph G., Jr.↗