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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Investigation of the hydrochlorination of SiCl4

The hyrochlorination of SiC14 and m.g. silicon metal to produce SiHC13, was investigated. Reaction kinetic measurements were carried out to collect additional rate data at 525 C and 550 C. A theoretical study was carried out to provide a kinetic model and a rate equation for the hydrochlorination reaction. Results of this preliminary study show that the rate of formation of SiHC13 follows a pseudo first order kinetics. The rate constants were measured at three temperatures, 550 C, 500 C and 450 C, respectively. The activation energy was determined from the Arrhenius plot to give a value of 13.2 Kcal/mole. The design of a quartz reactor to measure reaction rates and equilibrium conversion of SiHC13 at reaction temperature up to 650 C was completed.

Mui, J. Y. P.↗
NASA NTRS1992

Preferential hydrophobic interactions are responsible for a preference of D-amino acids in the aminoacylation of 5'-AMP with hydrophobic amino acids

We have studied the chemistry of aminoacyl AMP to model reactions at the 3' terminus of aminoacyl tRNA for the purpose of understanding the origin of protein synthesis. The present studies relate to the D, L preference in the esterification of 5'-AMP. All N-acetyl amino acids we studied showed faster reaction of the D-isomer, with a generally decreasing preference for D-isomer as the hydrophobicity of the amino acid decreased. The beta-branched amino acids, Ile and Val, showed an extreme preference for D-isomer. Ac-Leu, the gamma-branched amino acid, showed a slightly low D/L ratio relative to its hydrophobicity. The molecular basis for these preferences for D-isomer is understandable in the light of our previous studies and seems to be due to preferential hydrophobic interaction of the D-isomer with adenine. The preference for hydrophobic D-amino acids can be decreased by addition of an organic solvent to the reaction medium. Conversely, peptidylation with Ac-PhePhe shows a preference for the LL isomer over the DD isomer.

Non-NASA Center↗
NASA NTRS1982

Investigation of the hydrochlorination of SiCL4

Reaction kinetic measurements on the hydrochlorination of SiCl4 and metallurgical grade (m.g.) silicon metal were made at a wide range of experimental variables. The effect of pressure on the reaction rate was studied at 25 psig, 100 psig, 150 psig and 200 psig, respectively. Results of these experiments show a large pressure effect on the hydrochlorination reaction. As expected, higher pressures produce a higher equilibrium SiHC13 conversion, since the hydrochlorination reaction results in a net volume contraction as product SiHC1 is formed. However, the reaction rate, namely, the rate at which the hydrochlorination reaction reaches its equilibrium SiHC13 conversion, was found to be much faster at low pressures.

Mui, J. Y. P.↗
NASA NTRS1974

Measurements of ion-molecule reactions of He plus, H plus, HeH plus with H sub 2 and D sub 2

A drift tube mass spectrometer apparatus has been used to determine the rate coefficient, energy dependence and product ions of the reaction He(+) +H2. The total rate coefficient at 300 K is 1.1 plus or minus 0.1) 10 to minus 13th power cu cm/sec. The reaction proceeds principally by dissociative charge transfer to produce H(+), with the small remainder going by charge transfer to produce H2(+) and by atom rearrangement to produce HeH(+). The rate coefficient increases slowly with increasing ion mean energy, reaching a value of 2.8 x ten to the minus 13th power cu cm sec at 0.18 eV. The corresponding reaction with deuterium, He(+) + D2, exhibits a value (5 plus or minus 1) x 10 to the minus 14th cu cm/sec at 300K. The reaction rates for conversion of H(+) and HeH(+) to H3(+) on collisions with H2 molecules are found to agree well with results of previous investigations.

Johnsen, R.↗
NASA NTRS1975

Hot hydrogen in prebiological and interstellar chemistry

Two articles discuss the recent experimental work of Hong et al. on the production of amino acids and gas-phase organic compounds from the ultraviolet irradiation of simple gases, with hot hydrogen atoms used as the principal energy conversion agent. The reaction possibilities involving frozen ices are mentioned in both articles, as well as the significance of three-body collisions in this situation.

Sagan, C.↗
NASA NTRS2012

Performance Evaluation of Staged Bosch Process for CO2 Reduction to Produce Life Support Consumables

Utilizing carbon dioxide to produce water and hence oxygen is critical for sustained manned missions in space, and to support both NASA's cabin Atmosphere Revitalization System (ARS) and In-Situ Resource Utilization (ISRU) concepts. For long term missions beyond low Earth orbit, where resupply is significantly more difficult and costly, open loop ARS, like Sabatier, consume inputs such as hydrogen. The Bosch process, on the other hand, has the potential to achieve complete loop closure and is hence a preferred choice. However, current single stage Bosch reactor designs suffer from a large recycle penalty due to slow reaction rates and the inherent limitation in approaching thermodynamic equilibrium. Developmental efforts are seeking to improve upon the efficiency (hence reducing the recycle penalty) of current single stage Bosch reactors which employ traditional steel wool catalysts. Precision Combustion, Inc. (PCI), with support from NASA, has investigated the potential for utilizing catalysts supported over short-contact time Microlith substrates for the Bosch reaction to achieve faster reaction rates, higher conversions, and a reduced recycle flows. Proof-of-concept testing was accomplished for a staged Bosch process by splitting the chemistry in two separate reactors, first being the reverse water-gas-shift (RWGS) and the second being the carbon formation reactor (CFR) via hydrogenation and/or Boudouard. This paper presents the results from this feasibility study at various operating conditions. Additionally, results from two 70 hour durability tests for the RWGS reactor are discussed.

Vilekar, Saurabh A.↗
NASA NTRS2001

The sugar model: catalysis by amines and amino acid products

Ammonia and amines (including amino acids) were shown to catalyze the formation of sugars from formaldehyde and glycolaldehyde, and the subsequent conversion of sugars to carbonylcontaining products under the conditions studied (pH 5.5 and 50 degrees C). Sterically unhindered primary amines were better catalysts than ammonia, secondary amines, and sterically hindered primary amines (i.e. alpha-aminoisobutyric acid). Reactions catalyzed by primary amines initially consumed formaldehyde and glycolaldehyde about 15-20 times faster than an uncatalyzed control reaction. The amine-catalyzed reactions yielded aldotriose (glyceraldehyde), ketotriose (dihydroxyacetone), aldotetroses (erythrose and threose), ketotetrose (erythrulose), pyruvaldehyde, acetaldehyde, glyoxal, pyruvate, glyoxylate, and several unindentified carbonyl products. The concentrations of the carbonyl products, except pyruvate and ketotetrose, initially increased and then declined during the reaction, indicating their ultimate conversion to other products (like larger sugars or pyruvate). The uncatalyzed control reaction yielded no pyruvate or glyoxylate, and only trace amounts of pyruvaldehyde, acetaldehyde and glyoxal. In the presence of 15 mM catalytic primary amine, such as alanine, the rates of triose and pyruvaldehyde of synthesis were about 15-times and 1200-times faster, respectively, than the uncatalyzed reaction. Since previous studies established that alanine is synthesized from glycolaldehyde and formaldehyde via pyruvaldehyde as its direct precursor, the demonstration that the alanine catalyzes the conversion of glycolaldehyde and formaldehyde to pyruvaldehyde indicates that this synthetic pathway is capable of autocatalysis. The relevance of this synthetic process, named the Sugar Model, to the origin of life is discussed.

Acetaldehyde/analogs & derivatives/chemistry↗
NASA NTRS1982

Flat-plate solar array project. Task 1: Silicon material. Investigation of the hydrochlorination of SiC14

A two inch diameter stainless steel reactor was designed and built to operate at pressures up to 500 psig for the experimental studies on the hydrochlorination of SiCl4 and metallurgical grade (m.g.) silicon metal to SiHCl3. In order to clearly see the effect of pressure, the experiments were carried out at low reactor pressures of 73 psig and 150 psig, respectively. A large pressure effect on the hydrochlorination reaction was observed between the results of the low pressure experiments and the results of the high pressure experiments. In general, higher pressure produces a higher conversion of SiHCl3, but at a lower reaction rate. The effect of temperature on the reaction rate was studied at 73 psig. Higher reaction temperature gave a higher conversion and a higher reaction rate. Samples of the materials used to construct the hydrochlorination reactor were prepared for corrosion tests.

Mui, J. Y. P.↗
NASA NTRS2017

Modeling Chemical Reactions in Classical Molecular Dynamics Simulations

An algorithm capable of incorporating multi-step reaction mechanisms into atomistic molecular dynamics (MD) simulations using traditional fixed valence force fields is proposed and implemented within the framework of LAMMPS (Large-scale Atomic Molecular Massively Parallel Simulator). This extension, referred to as fix bond/react, enables bonding topology modifications during a running MD simulation using pre- and post-reaction bonding templates to carry out a pre-specified reaction. Candidate reactants are first identified by interatomic separation, followed by the application of a generalized topology matching algorithm to confirm they match the pre-reaction template. This is followed by a topology conversion to match the post-reaction template and a dynamic relaxation to minimize high energy configurations. Two case studies, the condensation polymerization of nylon 6,6 and the formation of a highly-crosslinked epoxy, are simulated to demonstrate the robustness, stability, and speed of the algorithm. Improvements which could increase its utility are discussed.

Jacob R Gissinger↗
NASA NTRS1993

(abstract) Experimental and Modeling Studies of the Exchange Current at the Alkali Beta'-Alumina/Porous Electrode/Alkali Metal Vapor Three Phase Boundary

The microscopic mechanism of the alkali ion-electron recombination reaction at the three phase boundary zone formed by a porous metal electrode in the alkali vapor on the surface of an alkali beta'-alumina solid electrolyte (BASE) ceramic has been studied by comparison of the expected rates for the three simplest reaction mechanisms with known temperature dependent rate data; and the physical parameters of typical porous metal electrode/BASE/alkali metal vapor reaction zones. The three simplest reactions are tunneling of electrons from the alkali coated electrode to a surface bound alkali metal ion; emission of an electron from the electrode with subsequent capture by a surface bound alkali metal ion; and thermal emission of an alkali cation from the BASE and its capture on the porous metal electrode surface where it may recombine with an electron. Only the first reaction adequately accounts for both the high observed rate and its temperature dependence. New results include crude modeling of simple, one step, three phase, solid/solid/gas electrochemical reaction.

conversion↗
NASA NTRS1986

Calculated potential surfaces for the reactions: O + N2 yields NO + N and N + O2 yields NO + O

Complete Active Space SCF/Contracted CI (CASSCF/CCI) calculations, using large Gaussian basis sets, are presented for selected portions of the potential surfaces for the reactions in the Zeldovich mechanism for the conversion of N2 to NO. The N + O2 reaction is exoergic by 32 kcal/mole and is computed to have an early barrier of 10.2 kcal/mole for the (sup 2)A(sup prime) surface and 18.0 kcal/mole for the (sup 4)A(sup prime) surface. The O + N2 reaction is endoergic by 75 kcal/mole. The (sup 3)A(sup double prime) surface is calculated to have a late barrier of 0.5 kcal/mole, while the (sup 3)A(sup prime) surface is calculated to have a late barrier of 14.4 kcal/mole.

Walch, Stephen P.↗
NASA NTRS1987

Calculated potential surfaces for the reactions - O + N2 - NO + N and N + O2 - NO + O

Complete active space SCF/contracted CI calculations using large Gaussian basis sets are presented for selected portions of the potential surfaces for reactions in the Zeldovich mechanism for the conversion of N2 to NO. The N + O2 reaction is exoergic by 32 kcal/mol and is computed to have an early barrier of 10.2 kcal/mol for the 2A-prime surface and 18.0 kcal/mol for the 4A-prime surface. The O + N2 reaction is endoergic by 75 kcal/mol. The 3A-double prime surface is calculated to have a late barrier of 0.5 kcal/mol, while the 3A-prime surface has a late barrier of 14.4 kcal/mol relative to NO + N. These results are significant for determining the physical and chemical conditions which aeroassisted orbital transfer vehicles will encounter while transferring between high and low altitude earth orbits.

Walch, Stephen P.↗
NASA NTRS1992

Reactant conversion in homogeneous turbulence: Mathematical modeling, computational validations and practical applications

Closed form analytical expressions are obtained for predicting the limited rate of reactant conversion in a binary reaction of the type F + rO yields (1 + r) Product in unpremixed homogeneous turbulence. These relations are obtained by means of a single point Probability Density Function (PDF) method based on the Amplitude Mapping Closure. It is demonstrated that with this model, the maximum rate of the reactants' decay can be conveniently expressed in terms of definite integrals of the Parabolic Cylinder Functions. For the cases with complete initial segregation, it is shown that the results agree very closely with those predicted by employing a Beta density of the first kind for an appropriately defined Shvab-Zeldovich scalar variable. With this assumption, the final results can also be expressed in terms of closed form analytical expressions which are based on the Incomplete Beta Functions. With both models, the dependence of the results on the stoichiometric coefficient and the equivalence ratio can be expressed in an explicit manner. For a stoichiometric mixture, the analytical results simplify significantly. In the mapping closure, these results are expressed in terms of simple trigonometric functions. For the Beta density model, they are in the form of Gamma Functions. In all the cases considered, the results are shown to agree well with data generated by Direct Numerical Simulations (DNS). Due to the simplicity of these expressions and because of nice mathematical features of the Parabolic Cylinder and the Incomplete Beta Functions, these models are recommended for estimating the limiting rate of reactant conversion in homogeneous reacting flows. These results also provide useful insights in assessing the extent of validity of turbulence closures in the modeling of unpremixed reacting flows. Some discussions are provided on the extension of the model for treating more complicated reacting systems including realistic kinetics schemes and multi-scalar mixing with finite rate chemical reactions in more complex configurations.

Madnia, C. K.↗
NASA NTRS1981

Formation of the thioester, N,S-diacetylcysteine, from acetaldehyde and N,N'-diacetylcystine in aqueous solution with ultraviolet light

The thioester, N,S-diacetylcysteine, is formed during the illumination of phosphate buffered (pH 7.0) aqueous solutions of acetaldehyde and N,N'-diacetylcystine with ultraviolet light. The yield of N,S-diacetylcysteine relative to N-acetylcysteine and unidentified products progressively increases as ultraviolet light below 239 nm, 253 nm and 281 nm is cut off with optical filters. When ultraviolet light below 320 nm is removed with an optical filter, there is no detectable reaction. Illumination of 0.025 M N,N'-diacetylcystine with 0.5 M and 1.0 M acetaldehyde with filtered ultraviolet light gives, respectively, 20% and 80% yields of N,S-diacetylcysteine. In the reaction with 1.0 M acetaldehyde, N-acetylcysteine forms early in the reaction and later decreases with its conversion to N,S-diacetylcysteine. The prebiotic significance of these reactions is discussed.

Weber, A. L.↗
NASA NTRS1986

The reaction H + C4H2 - Absolute rate constant measurement and implication for atmospheric modeling of Titan

The absolute rate constant for the reaction H + C4H2 has been measured over the temperature (T) interval 210-423 K, using the technique of flash photolysis-resonance fluorescence. At each of the five temperatures employed, the results were independent of variations in C4H2 concentration, total pressure of Ar or N2, and flash intensity (i.e., the initial H concentration). The rate constant, k, was found to be equal to 1.39 x 10 to the -10th exp (-1184/T) cu cm/s, with an error of one standard deviation. The Arrhenius parameters at the high pressure limit determined here for the H + C4H2 reaction are consistent with those for the corresponding reactions of H with C2H2 and C3H4. Implications of the kinetic carbon chemistry results, particularly those at low temperature, are considered for models of the atmospheric carbon chemistry of Titan. The rate of this reaction, relative to that of the analogous, but slower, reaction of H + C2H2, appears to make H + C4H2 a very feasible reaction pathway for effective conversion of H atoms to molecular hydrogen in the stratosphere of Titan.

Nava, D. F.↗