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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Calculation methods for compressible turbulent boundary layers

Calculation procedures for non-reacting compressible two- and three-dimensional turbulent boundary layers were reviewed. Integral, transformation and correlation methods, as well as finite difference solutions of the complete boundary layer equations summarized. Alternative numerical solution procedures were examined, and both mean field and mean turbulence field closure models were considered. Physics and related calculation problems peculiar to compressible turbulent boundary layers are described. A catalog of available solution procedures of the finite difference, finite element, and method of weighted residuals genre is included. Influence of compressibility, low Reynolds number, wall blowing, and pressure gradient upon mean field closure constants are reported.

Bushnell, D. M.↗
NASA NTRS1967

Infusible silazane polymer and process for producing same

Coatings of high thermal and chemical stability for application to metal, glass, ceramics, and other surfaces are formed by reacting diphenyldichlorosilane in the presence of triethylamine with a nitrogen base selected from the group consisting of ammonia and methylamine. The pl polymeric, noncrystalline reaction product is heated in a reaction zone open to the atmosphere at a temperature ranging from approximately 250 C to 450 C until the infusible polymer is formed.

Burks, R. E., Jr.↗
NASA NTRS1968

Fluorine-containing polyformals

A fluorine-containing polymeric polyformals is described which has the repeating unit O CH2 O CH2 (CF2) sub n CH2 wherein n is an integer of from about 3 to about 6 prepared by reacting trioxane with a diol having the formula HO CH2 (CF2) sub n CH2 OH. These polymeric polyformals are useful directly for impervious coatings on metals and the like.

Trischler, F. D.↗
NASA NTRS1979

Preparation of heterocyclic block copolymer from perfluoroalkylene oxide alpha, omega-diamidoximes

Diamidoxime monomers are intermolecularly and thermally condensed to form a heat and chemical resistant polymer containing 1,2,4-oxadiazole linkages with identical bivalent organic radicals or any combination of bivalent organic radicals selected from the group consisting of -(CX(sub 2))p-, wherein P ranges from 2 to 8 when X is fluorine and 2 to 18 when X is hydrogen, chlorine, nitro or aryl; arylene; and an oligometric or polymeric radical prepared by reacting a dicarboxylic acid halide with a fluorinated epoxide and having the formula: (CFY(OCF(sub 2)CFY)sub m)O(CX(sub 2))(sub p)O(CFYCF(sub 2)O)(sub n)CFY wherein Y is flourine or tryifluoromethyl, X is nitro, aryl, hydrogen, chlorine or fluorine, preferably the latter, p ranges from 1 to 18 and m+n ranges from 2 to 7.

Ross, L. O.↗
NASA NTRS1979

Development of a model and computer code to describe solar grade silicon production processes

Mathematical models, and computer codes based on these models were developed which allow prediction of the product distribution in chemical reactors in which gaseous silicon compounds are converted to condensed phase silicon. The reactors to be modeled are flow reactors in which silane or one of the halogenated silanes is thermally decomposed or reacted with an alkali metal, H2 or H atoms. Because the product of interest is particulate silicon, processes which must be modeled, in addition to mixing and reaction of gas-phase reactants, include the nucleation and growth of condensed Si via coagulation, condensation, and heterogeneous reaction.

Srivastava, R.↗
NASA NTRS1979

A throat-bypass stability-bleed system using relief valves to increase the transient stability of a mixed-compression inlet

A stability-bleed system was installed in a YF-12 flight inlet that was subjected to internal and external airflow disturbances in the NASA Lewis 10 by 10 foot supersonic wind tunnel. The purpose of the system is to allow higher inlet performance while maintaining a substantial tolerance (without unstart) to internal and external disturbances. At Mach numbers of 2.47 and 2.76, the inlet tolerance to decreases in diffuser-exit corrected airflow was increased by approximately 10 percent of the operating-point airflow. The stability-bleed system complemented the terminal-shock-control system of the inlet and did not show interaction problems. For disturbances which caused a combined decrease in Mach number and increase in angle of attack, the system with valves operative kept the inlet started 4 to 28 times longer than with the valves inoperative. Hence, the stability system provides additional time for the inlet control system to react and prevent unstart. This was observed for initial Mach numbers of 2.55 and 2.68. For slow increase in angle of attack at Mach 2.47 and 2.76, the system kept the inlet started beyond the steady-state unstart angle. However, the maximum transient angles of attack without unstart could not be determined because wind-tunnel mechanical-stop limits for angle of attack were reached.

Neiner, G. H.↗
NASA NTRS1979

The influence of ionization events on atmospheric ozone

Atmospheric ionization events can modify the concentration of neutral species in the stratosphere and mesosphere. In particular, ozone is destroyed because of the production of significant quantities of odd nitrogen and hydrogen compounds which react photochemically to destroy ozone. Direct evidence of ozone depletion comes from data taken during and following two solar flares generating large fluxes of 10-100 Mev protons, which bombarded the polar stratosphere and mesosphere. Observations of ozone taken during X-ray emission by solar flares and energetic electron precipitation during aurorae indicates ozone destruction above 50 km by ionization produced odd hydrogen. Lightning is apparently a large contributor to the tropospheric odd nitrogen budget. Ion propulsion induced dumping of the inner proton radiation belt represents a human activity which may influence stratospheric NOx.

Aikin, A. C.↗
NASA NTRS1979

Semiconductor Grade, Solar Silicon Purification Project

A low cost by-product, SiF4, is reacted with mg silicon to form SiF2 gas which is polymerized. The (SiF2)x polymer is heated forming volatile SixFy homologues which disproportionate on a silicon particle bed forming silicon and SiF4. The silicon analysis procedure relied heavily on mass spectroscopic and emission spectroscopic analysis. These analyses demonstrated that major purification had occured and some samples were indistinguishable from semiconductor grade silicon (except possibly for phosphorus). However, electrical analysis via crystal growth reveal that the product contains compensated phosphorus and boron.

Ingle, W. M.↗
NASA NTRS1979

The chemistry of sodium chloride involvement in processes related to hot corrosion

Thermodynamic and mass transport calculations, and laboratory experiments elucidating the behavior of sodium chloride in combustion environments, in the deposition process, and in reactions with certain oxides on the surfaces of superalloys are summarized. It was found that some of the ingested salt is separated out of the air stream by the compressor. However, sodium chloride does pass from the compressor to the combustor where numerous chemical reactions take place. Here some of the salt is vaporized to yield gaseous sodium chloride molecules. Hydrogen and oxygen atoms present in the combustion products react with some sodium chloride to yield other gaseous species such as sodium, and a fraction of the salt remains as particulates. Both the gas phase and condensed sodium chloride can lead to sodium sulfate formation by various routes, all of which involve reaction with sulfur oxides and oxygen. In addition to contributing to the formation of sodium sulfate, the sodium chloride can contribute to corrosion directly.

Stearns, C. A.↗
NASA NTRS1979

Application of a finite element method for computing grazing incidence wave structure in an impedance tube - Comparison with experiment

The acoustic performance of a liner specimen, in a grazing incidence impedance tube, is analyzed using a finite element method. The liner specimen was designed to be a locally reacting, two-degree-of-freedom type with the resistance and reactance provided by perforated facesheets and compartmented cavities. Measured and calculated wave structures are compared for both normal and grazing incidence from 0.3 to 1.2 kHz. A finite element algorithm was incorporated into an optimization loop in order to predict liner grazing incidence impedance from measured SWR and null position data. Results suggest that extended reaction effects may have been responsible for differences between normal and grazing incidence impedance estimates.

Lester, H. C.↗
NASA NTRS1979

The role of phosphorus in the upper atmosphere of Jupiter

The reaction of elemental phosphorus and H atoms to form PH3 was observed and should be a major factor in the recycling of PH3 in the stratosphere of Jupiter. The formation of PH3 in this manner should predominate at high altitudes where, due to the very low temperatures, reactions that require higher activation energies than these atom reactions cannot occur. At lower altitudes, in the troposphere, the rapid formation of H atoms from the strong absorption of light by NH3 will contribute to phosphine production also in this same manner. Recent experiments have also shown that elemental phosphorus reacts readily with aqueous ammonia to form PH3. This reaction may also be important in the recycling of PH3 in the upper troposphere of Jupiter if water-ammonia clouds, as had been previously thought, exist. Considerations of the coloration of the Great Red Spot have been made based upon the nature of the phosphorus obtained by decomposition of the phosphine.

Howland, G. R.↗
NASA NTRS1979

Status review of PMR polyimides

In the NASA developed PMR (polymerization of monomer reactants) the reinforcing fibers are impregnated with a solution containing a mixture of monomers dissolved in a low boiling point alkyl alcohol solvent, with the monomers reacting in situ at elevated temperatures to form a thermo-oxidatively stable polyimide matrix. The current status of first and second generation PMR polyimides is reviewed, considering synthesis and properties, processing, and applications. It is concluded that the PMR approach offers various significant advantages, especially superior high temperature properties and processing versatility, to fabricators and users of polyimide/fiber composites.

Serafini, T. T.↗
NASA NTRS1978

Reactively evaporated films of copper molybdenum sulfide

Films of superconducting Chevrel-phase copper molybdenum sulfide CuxMo6S8 were deposited on sapphire substrates by reactive evaporation using H2S as the reacting gas. Two superconducting temperatures (10.0 K and 5.0 K) of the films were found, corresponding to two different phases with different copper concentrations. All films were superconducting above 4.2 K and contained Chevrel-phase compound as well as free molybdenum. The critical current was measured as a function of applied field. One sample was found to deviate from the scaling law found for co-evaporated or sputtered samples, which possibly indicates a different pinning mechanism or inhomogeneity of the sample.

Chi, K. C.↗
NASA NTRS1979

The catalysis of nucleotide polymerization by compounds of divalent lead

The nonenzymatic, nontemplate catalysis of nucleotide polymerization by Pb(2+) ions, a possible prebiotic catalyst, is reported. Adenosine and uridine phosphoimidazoles were reacted in buffered solutions of lead salts and products were analyzed by means of paper chromatography and electrophoresis. In the presence of Pb(2+) ion at pH 8.0 and 7.0 the reaction is found to progress rapidly with excellent yields of oligomers, with optimal yields observed at pH 8.0. Little temperature dependence in the range 0 to 30 C is observed, however hydrolysis of the reaction products is minimal when the reaction is carried out at 0 C. Results show that the yield of oligomers is insensitive to mixing or the source of lead ions, indicating that naturally occurring minerals or precipitates could be a source of Pb(2+) ions under prebiotic conditions.

Sleeper, H. L.↗
NASA NTRS1979

Approximate convective heating equations for hypersonic flows

Laminar and turbulent heating-rate equations appropriate for engineering predictions of the convective heating rates about blunt reentry spacecraft at hypersonic conditions are developed. The approximate methods are applicable to both nonreacting and reacting gas mixtures for either constant or variable-entropy edge conditions. A procedure which accounts for variable-entropy effects and is not based on mass balancing is presented. Results of the approximate heating methods are in good agreement with existing experimental results as well as boundary-layer and viscous-shock-layer solutions.

Zoby, E. V.↗
NASA NTRS1978

Polyglutaraldehyde - A new reagent for coupling proteins to microspheres and for labeling cell-surface receptors

Glutaraldehyde polymerized in basic aqueous solutions was found to react with low molecular weight amines, immunoglobulins and hemoglobin. The polyglutaraldehyde was covalently bound to hydrophilic microspheres. The rate of addition of proteins to the polyglutaraldehyde-derivatized microspheres was investigated spectrophotometrically as a function of pH and temperature. The reaction of polyglutaraldehyde was found to be faster than that of the monomer. The findings led to successful labeling of human lymphocyte subpopulations.

Rembaum, A.↗
NASA NTRS1980

Double metalization for VLSI

Postsintering process increases yield of double-layer metal conductors to almost 100 percent. When wafers containing double-metalized chips are sintered, metal layers react with oxide film remaining in insulation layer holes, breaking it up so that it no longer impedes electric current. Cooling also mechanically disrupts oxide film.

Trotter, J. D.↗
NASA NTRS1981

Heat resistant polyphosphazene polymers

Polymers of carboranyl substituted polyphosphazene are stable at high temperatures and produce insulating char upon pyrolysis. Substituted compounds are prepared by heat polymerizing carboranyl halophosphazene, which is obtained by reacting lithium carborane with, for example, hexachlorocyclotriphosphazene under anhydrous conditions. Chlorine of polymer may be replaced by aryloxy and alkoxy groups.

Fewell, L. L.↗