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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Atmospheric degradation mechanisms of hydrogen containing chlorofluorocarbons (HCFC) and fluorocarbons (HFC)

The current knowledge of atmospheric degradation of hydrogen containing chlorofluorocarbons (HCFC 22 (CHClF2), HCFC 123 (CHCl2CF3), HCFC 124 (CHClFCF3), HCFC 141b (CFCl2CH3), HCFC 142b (CF2ClCH3)) and fluorocarbons (HFC 125 (CHF2CF3), HFC 134a (CH2FCF3), HFC 152a (CHF2CH3)) is assessed. Except for the initiation reaction by OH radicals, there are virtually no experimental data available concerning the subsequent oxidative breakdown of these molecules. However, from an analogy to the degradation mechanisms of simple alkanes, some useful guidelines as to the expected intermediates and final products can be derived. A noteable exception from this analogy, however, appears for the oxi-radicals. Here, halogen substitution induces new reaction types (C-Cl and C-C bond ruptures) which are unknown to the unsubstituted analogues and which modify the nature of the expected carbonyl products. Based on an evaluation of these processes using estimated bond strength data, the following simplified rules with regards to the chlorine content of the HCFC's may be deduced: (1) HCFC's containing one chlorine atom such as 22 and 142b seem to release their chlorine content essentially instantaneous with the initial attack on the parent by OH radicals, and for HCFC 124, such release is apparently prevented; (2) HCFC's such as 123 and 141b with two chlorine atoms are expected to release only one of these instantaneously; and the second chlorine atom may be stored in potentially long-lived carbonyl compounds such as CF3CClO or CClFO.

Zellner, Reinhard↗
NASA NTRS1991

Polyimides containing pendent siloxane groups

The incorporation of siloxane units into the backbone of aromatic polyimides has been shown to impart certain advantages over the unmodified polyimides. These include enhanced solubility, lower moisture adsorption, lower dielectric constant, improved toughness and surface modification. Also, when exposed to an atomic oxygen environment these materials form an in-situ silicate (SiO2) surface coating which protects the underlying material from further erosion. These unique advantages make polyimide-siloxanes useful in a variety of electronic and aerospace applications. As part of an effort on high performance polymeric materials for potential aerospace applications, polyimides containing pendent siloxane groups are under study. These materials were prepared by reacting a functionalized siloxane compound with polyimides containing benzhydrol groups. Thin films of the polymers exhibited glass transition temperatures ranging from 167 to 235 C. Tensile strengths and moduli measured at 23 C ranged from 11 to 14 ksi and 250 to 450 ksi, respectively. The dielectric constant was lowered substantially from that of the unmodified polyimide.

Connell, John W.↗
NASA NTRS1992

Nature of fluid flows in differentially heated cylindrical container filled with a stratified solution

Semiconductor crystals such as Hg(1-x)Cd(x)Te grown by unidirectional solidification Bridgmann method have shown compositional segregations in both the axial and radial directions. Due to the wide separation between the liquidus and the solidus of its pseudobinary phase diagram, there is a diffusion layer of higher HgTe content built up in the melt near the melt-solid interface which gives a solute concentration gradient in the axial direction. Because of the higher thermal conductivity in the melt than that in the crystal there is a thermal leakage through the fused silica crucible wall near the melt-solid interface. This gives a thermal gradient in the radial direction. Hart (1971), Thorpe, Hutt and Soulsby (1969) have shown that under such condition a fluid will become convectively unstable as a result of different diffusivities of temperature and solute. It is quite important to understand the effects of this thermosolute convection on the compositional segregation in the unidirectionally solidified crystals. To reach this goal, we start with a simplified problem. We study the nature of fluid flows of a stratified solution in a cylindrical container with a radial temperature gradient. The cylindrical container wall is considered to be maintained at a higher temperature than that at the center of the solution and the solution in the lower gravitational direction has higher solute concentration which decrease linearly to a lower concentration and then remain constant to the top of the solution. The sample solution is taken to be salt water.

Wang, Jai-Ching↗
NASA NTRS1993

Oxygen plasma resistant phosphine oxide containing imide/arylene copolymers

A series of oxygen plasma resistant imide/arylene ether copolymers were prepared by reacting anhydride-terminated poly(amide acids) and amine-terminated polyarylene ethers containing phosphine oxide units. Inherent viscosities for these copolymers ranged from 0.42 to 0.80 dL/g. After curing, the resulting copolymers had glass transition temperatures ranging from 224 C to 228 C. Solution cast films of the block copolymers were tough and flexible with tensile strength, tensile moduli, and elongation at break up to 16.1 ksi, 439 ksi, and 23 percent, respectively at 25 C and 9.1 ksi, 308 ksi and 97 percent, respectively at 150 C. The copolymers show a significant improvement in resistance to oxygen plasma when compared to the commercial polyimide Kapton. The imide/arylene ether copolymers containing phosphine oxide units are suitable as coatings, films, adhesives, and composite matrices.

Jensen, Brian J.↗
NASA NTRS1993

Polyimides containing the cyclobutene-3,4-dione moiety

In the present invention, linear aromatic polyimides containing the cyclobutene-3,4-dione moiety were produced from the reaction of a substituted or unsubstituted 1,2-bis(4-aminoanilino) cyclobutene-3,4-dione (SQDA) with various aromatic dianhydrides. These polymers had high molecular weights and their glass transition temperatures (Tgs) were greater than 500 C. Despite the very high Tg, these polymers exhibited excellent adhesion to glass. In addition, the films of these polyimides increased in flexibility with increasing cure temperatures. The novelty of this invention lies in the linear aromatic polyimide containing the cyclobutene-3,4-dione moiety. The presence of this moiety causes such changes in properties as Tgs greater than 500 C, excellent adhesion to glass, and increased flexibility with increasing cure temperatures.

St.clair, Terry L.↗
NASA NTRS1993

Polyimides containing pendent trifluoromethyl groups

Several new polyimides containing trifluoromethyl groups were prepared from the reaction of various aromatic dianhydrides and two new diamines containing trifluoromethyl groups, 4,4'-bis(3-amino-5-trifluoromethylphenoxy)biphenyl and l,4-bis(3-amino-5-trifluoromethylphenoxy)benzene. The diamines were prepared from the aromatic nucleophilic displacement of the disodium salts of 4,4'-biphenol or hydroquinone with 3,5-dinitrobenzotrifluoride followed by hydrogenation of the resultant dinitro compounds. The thermally cured polyimides exhibited glass transition temperatures between 186 and 262 C. By thermogravimetric analysis, the polyimides exhibited 5 percent weight losses at 484-527 C in nitrogen and 452-506 C in air.

Havens, S. J.↗
NASA NTRS1994

Polyimides Containing Pendent Ethynyl Groups

Series of novel diamines containing pendent ethynyl groups synthesized and reacted with various dianhydrides to form polyamide acids cyclodehydrated to form polyimides containing pendent ethynyl groups. Copolyimides of these diamines and other diamines also prepared. Upon heating, ethynyl groups in these polymers react with one another to form cross-linked molecular structures. As result of curing reaction, resistance to solvents, glass-transition temperature, and modulus of elasticity of polymer of this type generally increase, accompanied by corresponding decrease in tensile elongation and toughness. Cured polymers used as films, moldings, adhesives, and composite matrices.

Hergenrother, Paul M.↗
NASA NTRS1994

Aromatic Polyimides Containing Meta-Biphenoxy Moieties

Synthesis of two novel monomers and subsequent incorporation into aromatic polyimides yields polyimides containing meta-biphenoxy moieties exhibiting stability at high temperatures and having glass-transition temperatures lower than state-of-the-art polyimides containing para-biphenoxy moieties. Because of outstanding thermal stability, low density, resistance to radiation, electrical-insulating capability, toughness, and flexibility, linear aromatic polyimides used increasingly for applications in aerospace and electronics industries and possibly in others.

St. Clair, Terry L.↗
NASA NTRS1993

Polyimides containing amide and perfluoroisopropylidene connecting groups

New, thermooxidatively stable polyimides were prepared from the reaction of aromatic dianhydrides containing isopropylidene bridging groups with aromatic diamines containing amide connecting groups between the rings. Several of these polyimides were shown to be semi-crystalline as evidenced by wide angle x ray scattering and differential scanning calorimetry. Most of the polyimides form tough, flexible films with high tensile properties. These polyimide films exhibit enhanced solubility in organic solvents.

Dezern, James F.↗
NASA NTRS1993

Feasibility study: Monodisperse polymer particles containing laser-excitable dyes

The objective was to determine the feasibility of the preparation of monodisperse spherical poly(methyl methacrylate) and polystyrene particles that contain laser-excitable dyes in the size range 0.1 microns to 1 cm. Poly(methyl methacrylate) and polystyrene were chosen because of their excellent optical properties. The sphericity was required for uniformity of spectral output of re-irradiated light from the dye-containing particles. The monodispersity was required to give each particle the same optical properties when exposed to laser light.

Vanderhoff, John W.↗
NASA NTRS1994

Space Station Freedom solar array containment box mechanisms

Space Station Freedom will feature six large solar arrays, called solar array wings, built by Lockheed Missiles & Space Company under contract to Rockwell International, Rocketdyne Division. Solar cells are mounted on flexible substrate panels which are hinged together to form a 'blanket.' Each wing is comprised of two blankets supported by a central mast, producing approximately 32 kW of power at beginning-of-life. During launch, the blankets are fan-folded and compressed to 1.5 percent of their deployed length into containment boxes. This paper describes the main containment box mechanisms designed to protect, deploy, and retract the solar array blankets: the latch, blanket restraint, tension, and guidewire mechanisms.

Johnson, Mark E.↗
NASA NTRS1994

Copper-containing ceramic precursor synthesis: Solid-state transformations and materials technology

Three copper systems with relevance to materials technology are discussed. In the first, a CuS precursor, Cu4S1O (4-methylpyridine)(sub 4)- (4-MePy), was prepared by three routes: reaction of Cu2S, reaction of CuBr-SMe2, and oxidation of copper powder with excess sulfur in 4-methylpyridine by sulfur. In the second, copper powder was found to react with excess thiourea (H2NC(S)NH2) in 4-methylpyridine to produce thiocyanate (NCS(-)) complexes. Three isolated and characterized compounds are: Cu(NCS)(4-MePy)(sub 2), a polymer, (4-MePy-H)(Cu(NCS)(sub 3)(4-MePy)(sub 2)), a salt, and t-Cu(NCS)(sub 2)(4-MePy)(sub 4). Finally, an attempt to produce a mixed-metal sulfide precursor of Cu and Ga in N-methylimidazole (N-MeIm) resulted in the synthesis of a Cu-containing polymer, Cu(SO4)(N-MeIm). The structures are presented; the chemistry will be briefly discussed in the context of preparation and processing of copper-containing materials for aerospace applications.

Hepp, Aloysius F.↗
NASA NTRS1995

ROSAT observations of the unusual supernova remnant CTB 80 containing the pulsar PSR 1951 + 32

The unusal supernova remnant CTB, 80 containing the 39.5 ms pulsar PSR 1951 + 32, has been observed with the Position Sensitive Proportional Counter (PSPC) and the High Resolution Imager (HRI) aboard ROSAT. The HRI image, centered on the pulsar, is composed of a bright compact core of approximately 1 arcminute radius containing the pulsar and a compact nebula, as well as a diffuse nebula extending approximately 5 arcminutes eastward of the pulsar. The PSPC allowed us to model the spectra of the point source, the compact nebula and the 5 arcminute diffuse nebula. For a power-law spectrum with photon index Gamma approximately 2 and an interstellar column density of N(sub H) approximately 3 x 10(exp 21)/cm(exp 21) the derived luminosities are approximately 2.3 x 10(exp 33) d(sub 2.5)(exp 2) ergs/s from the pointlike source, approximately 3.9 x 10(exp 33) d(sup 2.5)(exp 2) ergs/s from the compact nebula, and approximately 1.8 x 10(exp 33) d(sub 2.5)(exp 2) ergs/s from the 5 arcminutes diffuse nebula. In addition, the 2 deg diameter circular field of view of the PSPC reveals a hard emission feature southeast of the pulsar with a conical geometry extending out to the edge of the detector. The spectrum from this region is well described by a two-temperature Raymond-Smith thermal plasma with an average temperature of approximately 10(exp 7) K and a luminosity of approximately 10(exp 34)d(sub 2.5)(exp 2) ergs/s. Pulsations from the 39.5 ms puslar, PSR 1951 + 32, are detected at the 99% confidence level. The implied pulsed fration is approximately 35% with a complicated energy-dependent behavior. The compact core and the extended diffuse nebula can be explained as synchrotron radiation from the relativistic pulsar wind confined by the ram pressure of the surrounding inhomgeneous medium. The conelike feature detected southeast of PSR 1951 + 32 is consistent with emission from an optically thin SNR in the radiative cooling phase of its evolution.

Safi-Harb, Samar↗
NASA NTRS1994

Structure-property relationships in addition polyimides. 1: Resins from four-ring aromatic diamines containing carbonyl and methylene groups

In an effort to improve the processing characteristics of addition-type polyimide resins the use of flexibilized four-ring aromatic diamine moieties was investigated. A series of 12 diamines containing carbonyl and methylene, as well as oxo and thio bridging groups, was synthesized. The diamines were polymerized with the dimethyl ester of 3.3', 4.4' - benzophenonetetracarboxylic acid (BTDE), using the monomethyl ester of nadic acid (NE) as an end-cap. The effect of diamine structure on the solubility and rheological properties during cure was determined. This paper also describes the effect of diamine structure and formulated molecular weight on the glass transition temperature and thermo-oxidative stability at elevated temperatures after various post-cure regimes. The results indicate that polyimides from some of the diamines containing methylene connecting groups have potential as matrix resins for long-term applications at temperatures up to 300 C.

Delvigs, Peter↗
NASA NTRS1995

Fixture For Sampling Volatile Materials In Containers

Fixture based on T-connector enables mass-spectrometric analysis of volatile contents of cylindrical containers without exposing contents to ambient conditions. Used to sample volatile contents of pressurized containers, contents of such enclosed processing systems as gas-phase reactors, gases in automotive emission systems, and gas in hostile environments.

Melton, Donald↗
NASA NTRS1993

Simulation of sloshing dynamics induced forces and torques actuated on dewar container driven by gravity gradient and jitter accelerations in microgravity

Some experimental spacecraft use superconducting sensors for gyro read-out and so must be maintained at a very low temperature. The boil-off from the cryogenic liquid used to cool the sensors can also be used, as the Gravity Probe B (GP-B) spacecraft does, as propellant to maintain attitude control and drag-free operation of the spacecraft. The cryogenic liquid for such spacecraft is, however, susceptible to both slosh-like motion and non-axisymmetric configurations under the influence of various kinds of gravity jitter and gravity gradient accelerations. Hence, it is important to quantify the magnitude of the liquid-induced perturbations on the spacecraft. We use the example of the GP-B to investigate such perturbations by numerical simulations. For this spacecraft disturbances can be imposed on the liquid by atmospheric drag, spacecraft attitude control maneuvers, and the earth's gravity gradient. More generally, onboard machinery vibrations and crew motion can also create disturbances. Recent studies suggest that high frequency disturbances are relatively unimportant in causing liquid motions in comparison to low frequency ones. The results presented here confirm this conclusion. After an initial calibration period, the GP-B spacecraft rotates in orbit at 0.1 rpm about the tank symmetry axis. For this rotation rate, the equilibrium liquid free surface shape is a 'doughnut' configuration for all residual gravity levels of 10(exp -6) g(sub 0) or less, as shown by experiments and by numerical simulations; furthermore, the superfluid behavior of the 1.8 K liquid helium used in GP-B eliminates temperature gradients and therefore such effects as Marangoni convection do not have to be considered. Classical fluid dynamics theory is used as the basis of the numerical simulations here, since Mason's experiments show that the theory is applicable for cryogenic liquid helium in large containers. To study liquid responses to various disturbances, we investigate and simulate three levels of gravity jitter (10(exp -6), 10(exp -7), and 10(exp -8) g(sub 0)) each at three predominant frequencies (0.1, 1.0, and 10 Hz), combined with a gravity gradient appropriate for the GP-B orbit. Dynamical evolution of sloshing dynamics excited fluid forces and torque fluctuations exerted on the dewar container driven by the combined gravity gradient and jitter accelerations are also investigated and simulated.

Hung, R. J.↗
NASA NTRS1996

Physics of systems containing neutron stars

This grant dealt with several topics related to the dynamics of systems containing a compact object. Most of the research dealt with systems containing Neutron Stars (NS's), but a Black Hole (BH) or a White Dwarf (WD) in situations relevant to NS systems were also addressed. Among the systems were isolated regular pulsars, Millisecond Pulsars (MSP's) that are either Single (SMP's) or in a binary (BMP's), Low Mass X-Ray Binaries (LMXB's) and Cataclysmic Variables (CV's). Also dealt with was one aspect of NS structure, namely NS superfluidity. A large fraction of the research dealt with irradiation-driven winds from companions which turned out to be of importance in the evolution of LMXB's and MSP's, be they SMP's or BMP's. While their role during LMXB evolution (i.e. during the accretion phase) is not yet clear, they may play an important role in turning BMP's into SMP's and also in bringing about the formation of planets around MSP's. Work was concentrated on the following four problems: The Windy Pulsar B197+20 and its Evolution; Wind 'Echoes' in Tight Binaries; Post Nova X-ray Emission in CV's; and Dynamics of Pinned Superfluids in Neutron Stars.

Ruderman, Malvin↗
NASA NTRS1996

Polyimides That Contain Pendent Siloxane Groups

Polyimides containing pendent siloxane groups (PISOXs) synthesized from polyimides containing hydroxy groups (PIOHs) according to either of two alternative approaches. Addition of pendent siloxane groups to polyimide decreases dielectric constant, and decreases absorption of moisture: these changes in properties advantageous in some electronic applications. Also enhance resistance to atomic oxygen in that they undergo slight degradation to form thin protective silicon oxide coats when exposed to atomic oxygen.

Connell, John W.↗