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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Directionally solidified composite systems under evaluation

The directionally solidified eutectic in-situ composites being evaluated for use as turbine materials range from ductile-ductile systems, where both matrix and reinforcement are ductile, to brittle-brittle systems, where both phases are brittle. The alloys most likely to be used in gas turbine engines in the near term are the lamellar ductile-semiductile alloys gamma prime-delta, Ni3Al-Ni3Nb and gamma/gamma prime-delta Ni,Cr,Cb,Al/Ni3Al-Ni3Nb and the fibrous ductile-brittle alloys M-MC CoTaC or NiTaC and M-M7C3(Co,Cr,Al)-(Cr,Co)7C3. Gamma-prime strengthened NiTaC alloys and a (Co,Cr,Al)-(Co,Cr)7C3 have greater tensile strength than the strongest superalloys at temperatures up to about 600 C. The gamma prime-delta and gamma/gamma prime-delta alloys in the Ni,Al,Nb(Cr) systems have greater tensile strength than the superalloys at temperatures greater than 800 C. At low stresses fibrous carbide reinforced eutectic alloys have longer lives at high temperatures than the strongest superalloys. Lamellar delta, Ni3Nb reinforced eutectic alloys have longer lives at high temperatures than the strongest superalloys at all stresses.

Ashbrook, R. L.↗
NASA NTRS1977

Tables of branching ratios for electric dipole transitions between arbitrary levels of hydrogen-like atoms

The branching ratios in hydrogen-like atoms due to the electric-dipole transitions are tabulated for the initial principal and azimuthal quantum numbers n prime l prime, and final principal and azimuthal quantum numbers n l. Average values with respect to l prime are given. The branching ratios not tabulated, including the initial states n prime yields infinity l prime corresponding to the threshold of the continuum, could be obtained by extrapolation.

Omidvar, K.↗
NASA NTRS1977

Exploratory study on the effects of novel diamine curing agents and isocyanate precursors on the properties on new epoxy and urethane adhesives

Aromatic diamines based on diphenyl sulfone and benzophenone were studied as epoxy adhesive curing agents. Previously found differences in adhesive strengths for meta vs para orientation were not found in these series. The use of aluminum and alumina as fillers in a m,m prime-methylene dianiline-cured epoxy adhesive was not found to be beneficial to adhesive strength. Alumina filled adhesives had much lower strength than unfilled adhesives. The unfilled m,m prime-methylene dianiline-based epoxy adhesive had excellent resistance to moisture relative to a p,p prime-methylene dianiline-based adhesive and maintained good strengths up to 250 F. A glass fiber composite based on a m,m prime-methylene dianiline-cured epoxy appeared to be equivalent to the p,p prime-methylene dianiline-cured epoxy as judged by short beam shear tests.

Glasgow, D. G.↗
NASA NTRS1977

Effects of heat treating PM Rene' 95 slightly below the gamma' solvus

An investigation was performed on as-hot-isostatically-pressed (As-HIP) Rene' 95 to obtain additional information on the variation of the amount of gamma prime with solutioning temperatures near the gamma prime solvus temperature and the resulting effects on tensile and stress rupture strength of As-HIP Rene' 95. The amount of gamma prime phase was found to increase at a rate of about 0.5% per degree Celsius as the temperature decreased from the solvus temperature to about 50 C below the gamma prime solvus temperature. The change in the amount of gamma prime phase with decreasing solutioning temperature was observed to be primarily associated with decreasing solubilities of Al+Ti+Nb and increasing solubility of Cr in the gamma phase.

Dreshfield, R. L.↗
NASA NTRS1977

Laser-induced fluorescence of CN/X2 Sigma +/ produced by photolysis of C2N2 at 160 nm

The paper reports laser-induced fluorescence measurements of the initial product state distributions of CN(X2 Sigma +) produced during the photolysis of C2N2 at a wavelength of 160 nm. The parent molecules were photodissociated by an argon flash lamp, and saturated solutions of BBD in p-dioxane were used as a laser dye to produce radiation that excited CN radicals in the (upsilon-double-prime, N-prime) vibrational-rotational sublevels of the X state to the B-state sublevels. Spectral-line identification is discussed along with the observed rotational, electronic, and vibrational energy partitionings. The effect of added buffer gas (N2 or He) on the observed product state distributions is examined in order to monitor collisional energy transfer from CN(A2 Pi, upsilon = 0) to CN(X2 Sigma +, upsilon-double-prime = 4). It is found that both buffer gases produce population inversion between the upsilon-double-prime = 4 and upsilon-double-prime = 3 levels of the X state.

Cody, R. J.↗
NASA NTRS1982

Superalloy composition modeling

Development of a predictive method for determination of the gamma/gamma prime phase fields, i.e., gamma prime volume fraction as a function of the multicomponent composition, is described. The cluster variation method used for binary alloys in which the precipitated phase is coherent with the matrix phase is extended for application to the multicomponent coherent gamma/gamma prime nickel-based superalloys. It is shown that the cluster variation method can accurately describe the equilibrium (incoherent) gamma/gamma prime phase fields in the binary Ni-Al phase diagram. The gamma/gamma prime phase field for the Ni-Cr-Al ternary phase diagram is computed as a function of temperature. A reasonable fit results between the calculated and the experimental diagrams. The modeling of the six-component Ni-Cr-Al-Co-Mo-Ti base superalloy and the effect of Ni substitution of Co are discussed.

Barefoot, J.↗
NASA NTRS1982

Molecular processes in comets

Potential energy curves for the two lowest 2 sigma- states of OH are computed at the configuration-interaction level using four different basis sets. Electronic transition dipole moments connecting the excited 1 2 sigma- and 2(D) 2 sigma- states with each other and with he ground X2pi state are presented as functions of internuclear distance. The theoretical absorption oscillator strengths for the D 2 sigma-(v prime=0) reverser to X 2pi (v prime prime=0) transition are in good agreement with the empirical value derived from astronomical measurements. The photodissociation cross sections for absorption rom the v prime prime=0,1, and levels of the ground state into the continuum of the 1 2 sigma- state are calculated, and the interstellar and cometary photodissociation rates are derived.

Dalgarno, A.↗
NASA NTRS1985

Elevated temperature creep-rupture behavior of the single crystal nickel-base superalloy NASAIR 100

The creep and rupture behavior of 001-line-oriented single crystals of the nickel-base superalloy NASAIR 100 was investigated at temperatures of 925 and 1000 C. In the stress and temperature ranges studied, the steady state creep rate, time to failure, time to the onset of secondary creep, and the time to the onset of tertiary creep all exhibited power law dependencies on the applied stress. The creep rate exponents for this alloy were between seven and eight, and the modulus-corrected activation energy for creep was approximately 350 kjoule/mole, which was comparable to the measured activation energy for Ostwald ripening of the gamma-prime precipitates. Oriented gamma-prime coarsening to form lamellae perpendicular to the applied stress was very prominent during creep. At 1000 C, the formation of a continuous gamma-gamma-prime lamellar structure was completed during the primary creep stage. Shear through the gamma-gamma-prime interface is considerd to be the rate limiting step in the deformation process. Gradual thickening of the lamellae appeared to be the cause of the onset of tertiary creep. At 925 C, the fully developed lamellar structure was not achieved until the secondary or tertiary creep stages. At this temperature, the gamma-gamma-prime lamellar structure did not appear to be as beneficial for creep resistance as at the higher temperature.

Nathal, M. V.↗
NASA NTRS1984

On the stereoselective aminoacylation of RNA

Gabbay and Kleinman (1970) have found that stereospecific complex formation (noncovalent) occurs between nucleic acids and a number of derivatives of amino acids. However, until recently, chiral selection in any nonenzymatic RNA-aminoacylation reaction was unknown. Profy and Usher (1984) reported that aminoacylation of the 'internal' 2-prime-ester occurred with a significant amount of stereoselection. Profy and Usher (1984) have also observed that aminoacylation of the 'internal' 2-prime-hydroxyl groups of polyribonucleotides by the imidazolide of N-3,5-dinitrobenzoylalanine occurs with chiral selection. In order to obtain further information regarding the considered phenomena, a systematic investigation was initiated of the factors which contribute to the observed stereoselectivity of the aminoacylation reaction. In the present paper, the effect of a change in the amino acid from alanine to leucine is considered along with an investigation of the D- and L-alanyl internal' 2-prime esters of the dinucleoside monophosphate of 3-prime,5-prime-ApA.

Usher, D. A.↗
NASA NTRS1985

The substitution of nickel for cobalt in hot isostatically pressed powder metallurgy UDIMET 700 alloys

Nickel was substituted in various proportions for cobalt in a series of five hot-isostatically-pressed powder metallurgy alloys based on the UDIMET 700 composition. These alloys were given 5-step heat treatments appropriate for use in turbine engine disks. The resultant microstructures displayed three distinct sizes of gamma-prime particles in a gamma matrix. The higher cobalt-content alloys contained larger amounts of the finest gamma-prime particles, and had the lowest gamma-gamma-prime lattice mismatch. While all alloys had approximately the same tensile properties at 25 and 650 gamma C, the rupture lives at 650 and 760 C peaked in the alloys with cobalt contents between 12.7 and 4.3 pct. Minimum creep rates increased as cobalt contents were lowered, suggesting their correlation with the gamma-prime particle size distribution and the gamma-gamma-prime mismatch. It was also found that, on overaging at temperatures higher than suitable for turbine disk use, the high cobalt-content alloys were prone to sigma phase formation.

Harf, F. H.↗
NASA NTRS1985

The lower electronic states of ClOO - A computational investigation

Eight doublet and eight quartet states of ClOO were investigated by ab initio CI techniques. The potential energy surfaces of the four lowest energy doublet states of both A-double-prime and A-prime symmetry indicate that only the 1 2A-double-prime state is bound. In contrast to the model provided by the HO2 radical, all of the excited doublet states investigated were repulsive with respect to dissociation to Cl + O2 and metastable or bound with respect to dissociation to ClO + O. The transitions to the excited states investigated span the visible and near UV spectral regions, but the transition moments indicate that they are very weak. Since the photolysis products are the same as those of the rapid thermal dissociation, photolysis is not expected to be an important atmospheric process. The soft bending potential for the 1 2A-prime state and the shape of the 1 4A-double-prime state in the entrance channel of the ClO + O yields Cl + O2 reaction provide a qualitative explanation for the underprediction of the low temperature reaction rate by previous trajectory calculations.

Jafri, J. A.↗
NASA NTRS1989

Chemoviscosity modeling for thermosetting resin systems, 4

An experimental study on the changes of chemorheological properties has been conducted and analyzed on commercial Hercules 3501-6 resin system cured under several isothermal conditions between 375 and 435 K. For the cure temperatures equal to or greater than 385 K, the storage modulus curing curves, G prime (t), exhibited abrupt changes in slope which occurred at various times depending on the curing temperatures and were attributed to the onset of gelation reactions. The crossover points between G prime (t) and G double prime (t) curves were observed for curing temperatures equal to or greater than 400 K. The gelation and the crossover points obtained from the chemorheological measurements, therefore, defined two characteristic resin states during cure. Approximately the same value for the degree of cure was reached by the advancement of the reaction at each of these states. The temperature dependency of the viscosities for the characteristic resin states and the rate constants of increase in moduli at different stages of curing were analyzed. Various G prime (t) and G double prime (t) isothermal curing curves were also shown to be capable of being superimposed on one another by the principle of time-temperature superposition. The resultant shift factors a sub t(t) and a Eta(T) were shown to follow the Arrhenius type relationship. Values of the activation energy suggested that the reaction kinetics, instead of the diffusion mechanism, was the limiting step in the overall resin advancement for the cure at temperatures equal to or greater than 385 K.

Hou, T. H.↗
NASA NTRS1989

Mineral catalysis of the formation of the phosphodiester bond in aqueous solution - The possible role of montmorillonite clays

The possible role of montmorillonite clays in the spontaneous formation on the primitive earth of the phosphodiester bond in the presence of water was investigated in experiments measuring the binding of various nucleosides and nucleotides with Na(+)-montmorillonite 22A and the reactions of these compounds with a water-soluble carbodiimide. It was found that, at neutral pH, adenine derivatives bind stronger than the corresponding uracil derivatives, consistent with the protonation of the adenine by the acidic clay surface and a cationic binding of the protonated ring to the anionic clay surface. The reaction of the 5-prime-AMP with carbodiimide resulted in the formation of 2-prime,5-prime-pApA (18.9 percent), 3-prime,5-prime-pApA (11 percent), and AppA (4.8 percent). The yields of these oligomers obtained when poly(U) was used in place of the clay were 15.5 percent, 3.7 percent, and 14.9 percent AppA, respectively.

Ferris, James P.↗
NASA NTRS1989

Deformation behavior of NiAl-based alloys containing iron, cobalt, and hafnium

The effects of alloying additions on the mechanical properties of the B2 intermetallic NiAl have been investigated in both the melt-spun ribbon and consolidated, bulk form. The study is based on a matrix of NiAl-based alloys with up to 20 at. pct Co and Fe additions and with reduced Al levels in the range of 30-40 at. pct. Characterization of the melt-spun ribbon by optical and scanning electron microscopy indicates a range of microstructures, including single-phase beta, gamma-prime necklace phase surrounding either martensitic or beta grains, and a mixture of equiaxed martensitic and gamma-prime grains. Bend ductility is present in melt-spun and annealed ribbons exhibiting the gamma-prime necklace structure and in a single-phase beta material containing 20 at. pct Fe. The analysis of compressive flow behavior on consolidated, bulk specimens indicates that the single-phase beta alloys exhibit a continuous decrease in yield stress with increasing temperature and profuse microcracking at grain boundaries. In contrast, multiphase (gamma-prime + either martensite or beta) alloys tend to display a peak in flow stress between 600 and 800 K, with little or no signs of microcracking. In general, heat treatments which convert the martensitic grains to beta + gamma-prime result in improved strength at temperatures above 600 K and better resistance to crack initiation.

Pank, D. R.↗
NASA NTRS1990

Coarsening in high volume fraction nickel-base alloys

The coarsening behavior of the gamma-prime precipitate has been examined in high volume fraction nickel-base alloys aged at elevated temperatures for times of up to 5000 h. Although the cube rate law was observed during coarsening, none of the presently available coarsening theories showed complete agreement with the experimental particle size distributions (PSDs). These discrepancies were thought to be due to elastic coherency strains which were not considered by the available models. Increasing the Mo content significantly influenced the PSDs and decreased the coarsening rate of the gamma-prime cubes, as a result of increasing the magnitude of the lattice mismatch. After extended aging times, the gamma-prime cubes underwent massive coalescence into plates at a rate which was much faster than the cuboidal coarsening rate. Once the gamma-prime plates were formed, further coarsening was not observed, and this stabilization of the microstructure was attributed to the development of dislocation networks at the gamma-gamma-prime interfaces.

Mackay, R. A.↗
NASA NTRS1992

Microstructural observations in rapidly-solidified and heat-treated Ni3Al-Cr alloys

The microstructural development following heat treatments of several rapidly-solidified Ni3Al-Cr and Ni3Al-Cr-B alloys is presented. Depending on composition, the as-solidified samples were either 100 percent gamma-prime phase - in the form of fine antiphase domains (APD) - or a mixture of gamma-prime (APDs) and beta phases. Upon annealing, the as-solidified microstructures transform to either APD-free gamma-prime or mixtures of gamma and gamma-prime phases. For those compositions where the quenched microstructures were 100 percent gamma-prime it was observed that APD coarsening followed conventional grain-growth kinetics, but when gamma phase precipitated on the APD boundaries the rate constant changed abruptly while the time exponent remained unaffected. It was also found that alloys containing critical amounts of chromium and boron are susceptible to precipitation of the boride Cr5B3.

Carro, G.↗
NASA NTRS1994

Oscillator strengths of selected resonance transitions in neutral sulfur

Mean lives and branching ratios for the 4s (3)S(sup 0 sub 1) and 4s(double prime) (3)P(sup 0 sub 1, 2) levels of neutral sulfur were determined at the Toledo Heavy Ion Accelerator using beam-foil spectroscopic techniques. The mean lives obtained for the 4s (3)S(sup 0 sub 1) 4s(double prime) (3)P(sup 0 sub 1), and (3)P(sup 0 sub 2) levels, 1.875 +/- 0.094 ns, 2.034 +/- 0.102 ns, and 2.146 +/- 0.129 ns, respectively, represent the most accurate results available to date. Oscillator strengths for the transitions 3p(sup 4)(3)P(sub 2, 1, 0)-4s (3)S(sup 0 sub 1) and 3p(sup 4)(3)P(sub 2, 1, 0)-4s(double prime) (3)P(sup 0 sub 1, 2) were derived from these mean lives together with the measured branching ratios. For comparison with published results which present only multiplet f-values, such f-values were computed from the measured individual line oscillator strengths. The value obtained for the 3p(sup 4)(3)P-4s(sup 3)S(sup 0) multiplet at 1814 A is 0.088 +/- 0.005, in good agreement with the mean of previous experimental measurements and theoretical calculations. With the mean life for the 4s(double prime) 3P(sup 0 sub 0) level set equal to the mean of our determination for the other two 4s(double prime) (3)P(sup 0) levels (a valid assumption for LS coupling conditions, and consistent with the observed equality of the mean lives within the accuracy of our measurement), an oscillator strength for the 1299 A multiplet of 0.121 +/- 0.004 was found. Both results are in good agreement with recent large-scale theoretical calculations that incorporate the effects of configuration interaction.

Beideck, D. J.↗
NASA NTRS1995

Experimental Determination of the Electric Dipole Moment Function of the X Pi-2 Hydroxyl Radical

Laboratory infrared emission spectra of X 2piOH obtained with the Solar McMath FTS and the U. Paris (Orsay) FTS are used in an inversion procedure to experimentally determine the electric dipole moment function (EDMF) of the hydroxyl radical. The spectra produced at Kitt Peak show vibrational levels up to v = 10 and rotational lines in the range, -25.5 less than or equal to m less than or equal to 12.5. The following vibrational quantum number ranges were observed: for DELTA v = -1, v prime = 1 - 9, for DELTA v = -2, v prime = 2 - 10, and for DELTA v = - 3, v prime = 6 - 10. The spectra produced at Orsay show DELTA v = -1, with v prime = 1 - 4 and -22.5 less than or equal to m less than or equal to 9.5 as well as DELTA v = 0, with v prime= 1 - 3, and 9.5 less than or equal to m less than or equal to 25.5. The OH rovibrational wavefunctions used in the inversion procedure were calculated using a procedure which reproduces observed rotational constants with a high level of accuracy. Comparisons of our EDMF are made with previous experimental and theoretical work.

Chackerian, C., Jr.↗