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At least 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

The chemical composition of soil from the Apollo 16 and Luna 20 sites.

The concentrations of the rare earth elements K, Rb, Sr, Ba, U, Zr, and Cr for the Luna 20 soil and four different Apollo 16 soils are reported. These trace element abundances imply: (1) that the lunar highlands consist of a mixture of rocks rich in large ion lithophile (LIL) elements and LIL-element improverished anorthosites; or (2) that the bulk of the aluminum-rich crust did not originate by upward segregation of plagioclase in a primitive liquid shell. The Luna 20 soil is distinguished from the Apollo 16 soil by lower aluminum and LIL element abundances.

Bansal, B. M.↗
NASA NTRS1973

Lunar evolution - How well do we know it now.

The currently known astronomical, chemical, and magnetic data are not uniquely indicative of an extensively and globally molten moon. It is argued that an accretional layering occurred in the moon, but at temperatures below solidus. The excess mass in the near side of the moon compatible with a 2-km displacement in the center of mass relative to the center of figure and the moment of inertia data is considered to be due to Fe-FeS liquid formation and inhomogeneous segregation. These Fe-FeS bodies, termed 'fescons,' are shown to be capable of accounting for the presently available magnetization data, by acting as small regenerative dynamos with a time-stability less than that of the terrestrial equivalent. The chemical characteristics of the highly differentiated materials, are considered to be due to small-scale localized melting caused by collisional events, from sources in which accessory phases play a significant role. Mare basalts are considered to be melts in the overlying material produced at a later time by K-40 radioactivity in the fescons. Some consequences of the present hypothesis are suggested. It is concluded that these and other characteristics of the lunar materials are reconcilable with a 'cold' moon, such as discussed by Urey over the past two decades.

Murthy, V. R.↗
NASA NTRS1972

The origin and chemical composition of the earth's core

The process of core formation in the earth is subject to the constraints that it be nearly simultaneous with accretion and yet occur in a manner that the mantle retains radiogenic Xe-129 produced from the extinct radioactivity of I-129 with a half life of 17.6 million y. From these constraints, it appears that the only feasible mechanism is the segregation of an Fe-FeS melt. Trace element abundances in major classes of meteorites and the silicate fractions of the earth show that not only there is a high depletion of sulphur in the crust and the mantle, but that it is even more highly depleted than the rare gases, water and the halogens. From the nature of this depletion pattern and the fact that any model of accretion of the earth will necessarily produce an Fe-FeS melt, it is concluded that the light element in the core is largely sulphur with minor amounts of carbon. A consequence of this mode of core formation is found to be the availability of K-40 radioactive heat production in the liquid core, estimated at about 10 to the 19th power erg/s at the present time.

Murthy, V. R.↗
NASA NTRS1974

The effect of grain boundaries on the resistivity of polycrystalline silicon

The electrical resistivity of polycrystalline silicon films was investigated. The films were grown by the chemical vapor decomposition of silane on oxidized silicon wafers. The resistivity was found to be independent of dopant atom concentration in the lightly doped regions but was a strong function of dopant levels in the more heavily doped regions. A model, based on high dopant atom segregation in the grain boundaries, is proposed to explain the results.

Fripp, A. L., Jr.↗
NASA NTRS1974

Concentration changes during eutectic solidification

Thermotransport (or thermal diffusion, Soret effect) is shown to cause significant amount of segregation during the directional solidification of aluminum-copper eutectic. The concentration changes are predicted quantitatively and they are a function of temperature gradient, rate of melting and solidification and the time of soaking. There is a fair agreement between the experiments and calculations. A process is suggested where these concentration changes may be minimized.

Bhat, B. N.↗
NASA NTRS1974

Effect of gravity on liquid phase sintering

The unique conditions offered by the earth orbital environment in material processing involving both solid and liquid phases, such as liquid phase sintering, were studied. An experimental development program involving both test and theoretical work was initiated. Experimental work using material combinations selected such that maximum information about the effect of gravity can be derived has been conducted. Wetting of the solid phase by the liquid during sintering is an important phenomenon in liquid phase sintering, and gravity has influence on both capillary phenomenon and density segregation; hence, material combinations were selected such that these two effects can be suitably studies. The experimental work is meant to form the basis for similar comparative work done under low-g conditions. The part of the model dealing with the capillary phenomenon, as related to liquid phase sintering and the effect of gravity on it, suggest that gravity will have negligible effect on the Bond number and that the cohesive force is dependent on both the amount of liquid phase and the angle of contact.

Mookherji, T.↗
NASA NTRS1974

Energy impact of short-haul STOL systems

An analysis has been made to evaluate the impact on fuel requirements of a segregated short-haul system. A comparison has been made between two alternate scenarios: one with STOL, and the other without STOL. For the New York to Washington, D.C. city pair the results show: (1) the modal efficiency approach, while indicating the with STOL scenario requires more fuel than the without STOL scenario, is of questionable validity because it does not account for various effects which exist in realistic scenarios; (2) evaluation of fuel requirements based on more detailed modeling indicates that while a STOL scenario requires more fuel than without STOL when an idealized CTOL system is postulated, the STOL scenario requires less fuel than without STOL when the CTOL system has even moderate delays. These results are due to a combination of effects: the closer and more convenient locations of STOL ports to the traveler, congestion at the CTOL airports, and the impact of the through passenger traffic. Sensitivity of results to STOL aircraft block fuel and to CTOL congestion delays are considered.

Stewart, E. C.↗
NASA NTRS1974

Liquid-metal atomization for hot working preforms

Rapid quenching of a liquid metal by atomization or splat cooling overcomes the major limitation of most solidification processes, namely, the segregation of alloying elements, impurities, and constituent phases. The cooling rates of different atomizing processes are related to the dendrite arm spacings and to the microstructure of the atomized powders. The increased solubility limits and the formation of metastable compounds in splat-cooled alloys are discussed. Consolidation of the powders by hot isostatic compaction, hot extrusion, or hot forging and rolling processes yields billets with properties equivalent to or better than those of the wrought alloys. The application of this powder processing technology to high-performance alloys is reviewed.

Grant, N. J.↗
NASA NTRS1974

Liquid phase sintered compacts in space

A model that will explain the effect of gravity on liquid phase sintering was developed. Wetting characteristics and density segregation which are the two important phenomena in liquid phase sintering are considered in the model development. Experiments were conducted on some selected material combinations to study the gravity effects on liquid phase sintering, and to verify the validity of the model. It is concluded that: (1) The surface tension forces acting on solid particles in a one-g environment are not appreciably different from those anticipated in a 0.00001g/g sub 0 (or lower) environment. (2) The capillary forces are dependent on the contact angle, the quantity of the liquid phase, and the distance between solid particles. (3) The pores (i.e., bubbles) do not appear to be driven to the surface by gravity-produced buoyancy forces. (4) The length of time to produce the same degree of settling in a low-gravity environment will be increased significantly. (5) A low gravity environment would appear to offer a unique means of satisfactorily infiltrating a larger and/or complex shaped compact.

Mookherji, T. K.↗
NASA NTRS1975

Effects of alloy composition in alleviating embrittlement problems associated with the tantalum alloy T-111

The causes of aging embrittlement in T-111 (Ta-8W-2Hf) and the effect of alloy modification were investigated. Results show that T-111 possesses a critical combination of tungsten and hafnium that leads to loss in ductility at -196 C after aging near 1040 C. It was found that this occurs because tungsten enhances hafnium segregation to grain boundaries, which also leads to increased susceptibility to hydrogen embrittlement. Aging embrittlement was not observed in tantalum alloys with reduced tungsten or hafnium contents; most of the alloys studied have lower strengths than T-111 and exhibit susceptibility to hydrogen embrittlement.

Stephens, J. R.↗
NASA NTRS1975

Dependence of resistivity on the doping level of polycrystalline silicon

The electrical resistivity of polycrystalline silicon films has been studied as a function of doping concentration and heat treatment. The films were grown by the chemical vapor decomposition of silane on oxidized silicon wafers. The resistivity of the as-deposited films was widely scattered but independent of dopant atom concentration at the lightly doped levels and was strong function of dopant level in the more heavily doped regions. Postdeposition heat treatments in an oxidizing atmosphere remove scatter in the data. The resultant resistivity for dopant levels less than 10 to the 16th atoms/per cu cm was approximately equal to that of intrinsic silicon. In the next 2 orders of magnitude increase in dopant level, the resistivity dropped 6 orders of magnitude. A model, based on high dopant atom segregation in the grain boundaries, is proposed to explain the results.

Fripp, A. L.↗
NASA NTRS1975

On the 'Seyfert Sextet', VV 115

Radial velocity observations and red shift determinations of some galaxies east of the Seyfert Sextet are discussed. It is suggested that the Sextet may be a condensation in an extended group of galaxies. The velocities of galaxies in this region are segregated into three main groups, corresponding to the redshifts of the Hercules cluster, the group including the Seyfert Sextet, and a third group as indicated by the velocities of NGC 6035 and Mark 294.

Chincarini, G.↗
NASA NTRS1975

Superconducting properties of Pb-Sn-In alloys directionally solidified aboard Skylab

Superconducting alloys of Pb-Sn-In were directionally solidified in the absence of gravity-induced convection and segregation by processing in a near weightless condition aboard Skylab. Lead-rich and tin-rich lamellar structures were obtained with both high and low G/R (temperature gradient/solidification rate) samples processed at 0-g and at 1-g in a ground-based laboratory. Thinner, higher density lamellae were found with the 0-g specimens. Magnetization curves at 4.2 K showed hysteresis effects with large areas under the curves indicating magnetic flux pinning by the normal state tin-rich phase.

Anderson, W. T., Jr.↗
NASA NTRS1974

A study of Pb-204 partition in lunar samples using terrestrial and meteoritic analogues

Pb-204, Bi, Tl, and Zn have been measured in Apollo 16 samples and Apollo 17 orange soil. These data in addition to already reported Apollo 14 and 15 Pb-204 results and literature data are used to support the Pb-204-metallic phase coherence. The partition of Pb-204 into very fine metallic grains appears to be the result of an impact process rather than metal segregation in a magma.

Allen, R. O., Jr.↗
NASA NTRS1975

Origin of titaniferous lunar basalts

Delineation of low pressure phase equilibria in the composition space relevant to titaniferous lunar basalts demonstrates a significant degree of control by those equilibria on the compositions of the basalts. The existence of two distinct chemical groups of basalts (high and low K) which cannot be related one to the other by fractional crystallization at any pressure, suggests that melting is responsible for the two groups. Consideration of the pressure shift required to produce the differences between groups constrains magma segregation to have occurred in the outer 150 km of the moon. It is difficult to relate low-Ti and high-Ti basalts to the same source region. The preferred source region of high-Ti basalts, based on phase equilibrium considerations, is a late ilmenite-rich cumulate produced from the residual liquid of the primordial differentiation of the outer portions of the moon. This ilmenite-rich layer is sandwiched between the lunar feldspathic crust and a complementary mafic cumulate.

Walker, D.↗
NASA NTRS1975

A study of reactive turbulent mixing

This paper describes the development of a probe to study turbulent reactive mixing of two hypergolic streams of gas. The streams contain CO and O2 respectively and are mixed at 1400 K. The probe is a water cooled sonic orifice probe followed by a Fanno duct. Tests showed that it rapidly quenched the reaction, and that time-average, ingested gas composition accurately reflected the time-average composition at the sampling point. A new way to measure mixedness to the molecular level in a reactive flow situation is described, based on time-average compositions at the probe. This definition is compared to the definition of intensity of segregation which can be used for unreactive mixing situations. Finally, the probe is used to examine centerline composition in a confined coaxial mixing situation.

Roler, M. A.↗
NASA NTRS1976

Growing crystals from eutectic melts

Inverted Bridgman Method yields crystals of higher homogeneity and better structure than those grown by ordinary Bridgman method. Process controls thermotransport by holding molten alloy in known temperature for known period of time. Rapid cooling quenches in state of segregation. Method is applicable to other eutectiferous systems where thermotransport is appreciable.

Bhat, B. N.↗