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At least 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Cosmogenic Be-10, Al-26, and He-3 in olivine from Maui lavas

This paper reports the presence of cosmogenic Be-10 and Al-26 in olivines from the Maui Haleakala basalts in which cosmogenic He-3 and Ne-21 were discovered. Based on production-rate calibrations in quartz crystals from late Pleistocene granite exposures in the Sierra Nevada, the Haleakala crater erosion rates derived from Be-10 and Al-26 concentrations agree within 10 percent and give a mean rate of 12 m/Myr, about 40 percent greater than the rate of 8.5 m/Myr previously derived from He-3 measurements. These results establish the feasibility of the simultaneous use of radioactive and stable cosmogenic nuclides for studies of exposure-ages and erosion-rates in basaltic and andesitic terrains.

Nishiizumi, K.↗
NASA NTRS1991

GRIS observations of Al-26 gamma-ray line emission from two points in the Galactic plane

Both of the Gamma-Ray Imaging Spectrometer (GRIS) experiment's two observations of the Galactic center region, at l = zero and 335 deg respectively, detected Al-26 gamma-ray line emission. While these observations are consistent with the assumed high-energy gamma-ray distribution, they are consistent with other distributions as well. The data suggest that the Al-26 emission is distributed over Galactic longitude rather than being confined to a point source. The GRIS data also indicate that the 1809 keV line is broadened.

Teegarden, B. J.↗
NASA NTRS1989

Cryogenic mechanical properties of low density superplastically formable Al-Li alloys

The aerospace industry is considering the use of low density, superplastically formable (SPF) materials, such as Al-Li alloys in cryogenic tankage. SPF modifications of alloys 8090, 2090, and 2090+In were tested for strength and Kahn tear toughness. The results were compared to those of similar tests of 2219-T87, an alloy currently used in cryogenic tankage, and 2090-T81, a recently studied Al-Li alloy with exceptional cryogenic properties (1-9). With decreasing temperature, all materials showed an increase in strength, while most materials showed an increase in elongation and decrease in Kahn toughness. The indium addition to 2090 increased alloy strength, but did not improve the strength-toughness combination. The fracture mode was predominantly intergranular along small, recrystallized grains, with some transgranular fracture, some ductile rupture, and some delamination on large, unrecrystallized grains.

Verzasconi, S. L.↗
NASA NTRS1991

The effect of TiB2 reinforcement on the mechanical properties of an Al-Cu-Li alloy-based metal-matrix composite

Weldalite 049, an Al-base Cu-Li-Mg-Ag-Zr alloy, achieves 700 MPa tensile strengths in the near-peak-aged temper in virtue of the nucleation of a T(1)-type platelike strengthening precipitate. Attention is presently given to the possibility that the alloy's modulus could be further increased through the addition of high-modulus TiB2 particles, using the 'XD' process, due to TiB2's good wettability with liquid Al. An 8-percent modulus increase is obtained with 4 vol pct TiB2.

Langan, T. J.↗
NASA NTRS1990

The roles of Zr and Mn in processing and superplasticity of Al-Mg alloys

Processing studies have been conducted on two alloys, of nominal compositions Al-10Mg-0.1Zr or Al-10Mg-0.5Mn, in order to clarify the role of the dispersoid forming Zr or Mn additions. Mechanical property data reveal that the Mn-containing alloy has a lower maximum elongation but exhibits superplastic response over a broader range of temperature. Microstructural investigations and texture analyses were utilized to assess the effect of the presence of Al8Mg5 precipitates in combination with either Al3Zr or Al6Mn dispersoid particles during isothermal rolling at 300 C and subsequent tensile deformation at temperatures from 200-425 C.

Mcnelley, Terry R.↗
NASA NTRS1991

Comment on 'The Space Shuttle's impact on the stratosphere' by Michael J. Prather et al

Prather et al. (1990) argued that no local hole in column ozone could occur above the launch site of the Space Shuttle because (1) the HCl in the exhaust would require some time to be converted into more catalytically active forms, (2) the Shuttle trajectory is not vertically aligned, and (3) the corridor of exhaust gases is laterally spread over more than 1000 km in a day. In contradiction to these arguments, it is maintained here that assumption (1) is inconsistent with the empirical evidence, rendering (2) and (3) insufficient to maintain the claim that no local hole in column ozone could occur. In a reply, ozone image data from the TOMS on Nimbus 7 is used to support the argument of Prather et al.

Aftergood, Steven↗
NASA NTRS1992

Formation of a metastable ferromagnetic tau phase during containerless melt processing and rapid quenching in Mn-Al-C alloys

Solidification of selected Mn-Al-C alloys during containerless levitation and rapid quenching has yielded the first report for a ferromagnetic metastable tau phase formed directly from the melt. Complete solidification to tau phase was interrupted by the competitive evolution of an equilibrium epsilon phase during recalescence. The amount of undercooling required to produce the metastable ferromagnetic tau phase in a Mn(0.55)Al(0.433)C(0.017) alloy during solidification was estimated as approximately 470 K based on differential thermal analysis results. When the alloy carbon content was increased to 3.4 at. pct, transition in structure development occurred so that the samples exhibited gamma 2 phase formation as well as tau and epsilon phases.

Kim, Y. J.↗
NASA NTRS1992

Aerodynamics of the advanced launch system (ALS) propulsion and avionics (P/A) module

This paper discusses the design and testing of candidate Advanced Launch System (ALS) Propulsion and Avionics (P/A) Module configurations. The P/A Module is a key element of future launch systems because it is essential to the recovery and reuse of high-value propulsion and avionics hardware. The ALS approach involves landing of first stage (booster) and/or second stage (core) P/A modules near the launch site to minimize logistics and refurbishment cost. The key issue addressed herein is the aerodynamic design of the P/A module, including the stability characteristics and the lift-to-drag (L/D) performance required to achieve the necessary landing guidance accuracy. The reference P/A module configuration was found to be statically stable for the desired flight regime, to provide adequate L/D for targeting, and to have effective modulation of the L/D performance using a body flap. The hypersonic aerodynamic trends for nose corner radius, boattail angle and body flap deflections were consistent with pretest predictions. However, the levels for the L/D and axial force for hypersonic Mach numbers were overpredicted by impact theories.

Ferguson, Stan↗
NASA NTRS1991

The bonding of multiple ligands to Mg(+) and Al(+)

The bonding of one to four waterligands to Mg(+) and Al(+) is studied. The bonding is very different from that found for multiple ligands bound to Na(+) or Cu(+). All the waters bind on the same side of the Mg or Al because of the polarization of the 3s orbital away from the ligands. Two benzene and methanol molecules also have a ligand-Mg-ligand angle of less than 180 deg with the angle determined by ligand-ligand repulsion.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1993

Built-up Al-Li structures for cryogenic tank and dry bay applications

The objectives are: (1) to demonstrate the cost benefits of built-up cryotank and dry bay structures; (2) to study of benefits of using Al alloys; (3) to study of benefit of using Al-Li alloys; (4) to evaluate alternative low-cost stiffener and joining concepts.

Lisagor, W. Barry↗
NASA NTRS1993

Control of interfaces in Al-C fibre composites

The interface of Al-C fiber composite was modified by coating a silver layer on the surface of carbon fibres prior to making composites, in an attempt to improve the wettability between molten aluminum and carbon fibers during infiltration. An electroless plating technique was adopted and perfected to provide a homogeneous silver coating on the carbon fiber surface. Al-C fiber composites were prepared using a liquid infiltration technique in a vacuum. It was found that silver coating promoted the wetting between aluminum and carbon fibers, particularly with polyacrylonitrile-base carbon fibers. However, due to rapid dissolution of silver in molten aluminum, it was believed that the improved infiltration was not due to the wetting behavior between molten aluminum and silver. The cleaning of the fiber surface and the preservation of the cleaned carbon surface with silver coating was considered to be the prime reason for the improved wettability. Interfacial reactions between aluminum and carbon fibers were observed. Amorphous carbon was found to react more with aluminum than graphitic carbon. This is believed to be because of the inertness of the graphitic basal planes.

Warrier, S. G.↗
NASA NTRS1993

Ca-,Al-rich inclusions in the unique chondrite ALH85085 - Petrology, chemistry, and isotopic compositions

A comprehensive study is performed for the Ca-,Al-rich inclusions (CAIs) in the unique chondrite ALH85085. The ALH85085 inclusions are smaller (5-80 microns) and more refractory than their counterparts in carbonaceous chondrites. The study includes 42 inclusions for petrography and mineralogy, 15 for bulk major and minor element chemical composition, six for Mg-Al isotopic systematics, 10 for Ca isotopes, nine for Ti isotopes, and six for trace element abundances. In addition, oxygen-isotopic compositions were determined in minerals from a single inclusion. No correlation is found between mineralogy, major element chemistry, and trace element abundances. It is further shown that the high-temperature geochemical behavior of ultrarefractory trace elements is decoupled from that of the major elements Ca and Ti (Ti is correlated with the relatively volatile elements Nb and Yb) implying that perovskite is of only minor importance as carrier of ultrarefractories.

Kimura, Makoto↗
NASA NTRS1993

H4 and H5 chondrites from the Rub'al Khali desert

Based on texture and mineral composition, the highly weathered al-Jimshan chondrite is classed as an S2-shock stage H4 chondrite. The Bir-Hadi and ad-Dahbubah H chondrites are probably not paired with al-Jimshan, and are here respectively classified as H5, shock stage S3 and H5, shock stage S2.

Krot, Aleksandr N.↗
NASA NTRS1993

Intrinsic fatigue crack growth rates for Al-Li-Cu-Mg alloys in vacuum

The influences of microstructure and deformation mode on inert environment intrinsic fatigue crack propagation were investigated for Al-Li-Cu-Mg alloys AA2090, AA8090, and X2095 compared to AA2024. The amount of coherent shearable delta-prime (Al3Li) precipitates and extent of localized planar slip deformation were reduced by composition (increased Cu/Li in X2095) and heat treatment (double aging of AA8090). Intrinsic growth rates, obtained at high constant K(max) to minimize crack closure and in vacuum to eliminate any environmental effect, were alloy dependent; da/dN varied up to tenfold based on applied Delta-K or Delta-K/E. When compared based on a crack tip cyclic strain or opening displacement parameter, growth rates were equivalent for all alloys except X2095-T8, which exhibited unique fatigue crack growth resistance. Tortuous fatigue crack profiles and large fracture surface facets were observed for each Al-Li alloy independent of the precipitates present, particularly delta-prime, and the localized slip deformation structure. Reduced fatigue crack propagation rates for X2095 in vacuum are not explained by either residual crack closure or slip reversibility arguments; the origin of apparent slip band facets in a homogeneous slip alloy is unclear.

Slavik, D. C.↗
NASA NTRS1993

The Al Rais meteorite: A CR chondrite or close relative?

Although the classificational group 'CR' was first put forth by McSween more than 10 years ago, it included only the Al Rais and Renazzo meteorites. It has only been the relatively recent discovery of several CR-related chondrites in Antarctica and the Sahara that has provided the necessary research material for an extensive group description and classification. Some 22 separate specimens representing at least 6 falls are now purportedly members of the CR group. In light of all this new data, an old question can once again be raised as to whether or not Al Rais should be classified in the same distinct group as Renazzo. This paper explores that question.

Kallemeyn, G. W.↗
NASA NTRS1993

Lattice-mismatched In(0.40)Al(0.60)As window layers for indium phosphide solar cells

The efficiency of indium phosphide (InP) solar cells is limited by its high surface recombination velocity (approximately 10(exp 7) cm/s). This might be reduced by a wide-bandgap window layer. The performance of InP solar cells with wide-bandgap (1.8 eV) lattice-mismatched In(0.40)Al(0.60)As as a window layer was calculated. Because the required window layer thickness is less than the critical layer thickness, growth of strained (pseudomorphic) layers without interfacial misfit dislocations should be possible. Calculations using the PC-lD numerical code showed that the efficiencies of baseline and optimized p(+)n (p-on-n) cells are increased to more than 22 and 24 percent, (air mass zero (AMO), 25 C), respectively for a lattice-mismatched In(0.40)Al(0.60)As window layer of 10-nm thickness. Currently, most cell development work has been focused on n(+)p (n-on-p) structures although comparatively little improvement has been found for n(+)p cells.

Jain, Raj K.↗
NASA NTRS1994

Partition coefficients for Al, Ca, Ti, Cr, and Ni in olivine obtained by melting experiment on an LL6 chondrite

We report the partition coefficients for Ca, Al, Ti, Cr, and Ni in olivine obtained through a series of melting experiments on an LL6 chondrite under varying conditions of temperature and oxygen fugacity. It is necessary to examine the variation of partition coefficients up to extremely reducing conditions in order to study meteoritic olivines. For Ca, Al, and Cr, the partition coefficients tend to decrease as temperature increases, but do not change even under extremely reducing conditions.

Miyamoto, M.↗
NASA NTRS1994

COMPTEL observations of the 1.809 MeV gamma-ray line from galactic Al-26

The COMPTEL experiment on the Compton Gamma-Ray Observatory (CGRO) has been demonstrated to be capable of imaging the Galaxy within its field of view of about 1 steradian in the 1.809 MeV gamma-ray line originating from radioactive Al-26. The combined data from the CGRO sky survey in 1991/1992 have been analyzed to provide a first map of the inner Galaxy in this gamma-ray line. The 1.809 MeV emission appears extended along the inner 70 deg of the Galactic plane, with a relatively sharp falloff outside this regime. Correlations with massive stars and supernova remnants as possible tracers of the candidate Al-26 sources are discussed.

Diehl, R.↗