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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Rapid Solidification of Magnetic Oxides

The enhanced control over microstructural evolution inherent in rapid solidification processing techniques are exploited to create novel ceramic magnetic materials. The great sensitivity of magnetic properties to local structure provides a powerful probe both for the study of structure and of microscopic solidification mechanisms. The first system studied is the SrO-Fe2O3 binary, which contains the commercially important hard magnetic compound strontium hexaferrite. The products were analyzed by transmission electron microscopy, Mossbauer spectroscopy, magnetic measurements, and differential thermal analysis. As-quenched ribbons contain high concentrations of super-paramagnetic particles, 80 to 250 Angstroms in diameter, in a glassy matrix. This suggests the possibility of crystallizing monodomain strontium hexaferrite during subsequent heat treatment, with a resulting increase in coercivity over conventionally processed ferrite magnets. That magnetic properties can be controlled in solidification processing by varying the quench rate is demonstrated.

Kalonji, G.↗
NASA NTRS2011

Improved Design and Fabrication of Hydrated-Salt Pills

A high-performance design, and fabrication and growth processes to implement the design, have been devised for encapsulating a hydrated salt in a container that both protects the salt and provides thermal conductance between the salt and the environment surrounding the container. The unitary salt/container structure is known in the art as a salt pill. In the original application of the present design and processes, the salt is, more specifically, a hydrated paramagnetic salt, for use as a refrigerant in a very-low-temperature adiabatic demagnetization refrigerator (ADR). The design and process can also be applied, with modifications, to other hydrated salts. Hydrated paramagnetic salts have long been used in ADRs because they have the desired magnetic properties at low temperatures. They also have some properties, disadvantageous for ADRs, that dictate the kind of enclosures in which they must be housed: Being hydrated, they lose water if exposed to less than 100-percent relative humidity. Because any dehydration compromises their magnetic properties, salts used in ADRs must be sealed in hermetic containers. Because they have relatively poor thermal conductivities in the temperature range of interest (<0.1 K), integral thermal buses are needed as means of efficiently transferring heat to and from the salts during refrigeration cycles. A thermal bus is typically made from a high-thermal-conductivity met al (such as copper or gold), and the salt is configured to make intimate thermal contact with the metal. Commonly in current practice (and in the present design), the thermal bus includes a matrix of wires or rods, and the salt is grown onto this matrix. The density and spacing of the conductors depend on the heat fluxes that must be accommodated during operation.

Shirron, Peter J.↗
NASA NTRS1972

Some aspects of flare properties versus magnetic boundary morphology.

Flares often begin near lines of zero-longitudinal magnetic field. These boundary lines between opposite polarities can have the magnetic field either parallel to or transverse to the boundary. A study of 75 flares associated with one or the other type of boundary indicates that the difference in boundary morphology is not reflected in the frequency or properties of the associated flares.

Prata, S. W.↗
NASA NTRS1989

Evidence for pigmentary hematite on Mars based on optical, magnetic, and Moessbauer studies of superparamagnetic (nanocrystalline) hematite

Samples containing variable amounts of superparamagnetic hematite (sp-Hm) were prepared by a method in which the sp-Hm particles were dispersed throughout larger particles of silica gel, and the optical and magnetic properties of these samples were compared with those of larger-diameter hematite (bulk-Hm). It is shown that the optical properties of sp-Hm are different from those of bulk-Hm. Implications of the results for mineralogical interpretations of spectral data for the Martian surface and its terrestrial analogues are discussed. It is concluded that features resulting from ferric iron in the Martian spectral data and the results of the Viking magnetic properties experiment are both consistent with hematite present as both sp-Hm and bulk-Hm; the hematite particles most likely occur in pigmentary form, i.e., as particles dispersed throughout the volume of a spectrally neutral material.

Morris, Richard V.↗
NASA NTRS1986

Directional solidification and characterization of near eutectic Sm2CO17/Co alloys

The effects of directional solidification processing on the microstructural, compositional, and magnetic properties of near eutectic Co-Sm alloys (about 9 at. pct Sm) have been studied. Initial investigations have been performed at modest thermal gradients in the liquid, G(L) less than 60 C/cm and over a range of furnace (solidification) velocities, V = 0.8 45.4 cm/h. The primary dendrite spacing for near eutectic Sm2Co17/Co scaled with 1/sq rt V and varied from about 50 microns for V greater than or equal to 20 cm/h to hundreds of microns for V less than 10 cm/h, while the rod eutectic diameter and interrod spacing were an order of magnitude smaller. For both dendritic and cooperative growth, the associated permanent magnet properties were rather poor, e.g., remanence less than 4 kG and coercive force less than 1 kOe for the smallest dendrite and rod diameter dimensions encountered, although the magnetic hardness for the rod eutetic was larger than for the dendritic microstructure. Magnetization as a function of sample orientation indicated that the easy axis of magnetization was primarily along the direction of solidification for both ferromagnetic phases.

Pirich, Ronald G.↗
NASA NTRS1991

Magnetic and electrical properties of Martian particles

The only determinations of the magnetic properties of Martian materials come from experiments on the two Viking Landers. The results suggest Martian soil containing 1 to 10 percent of a highly magnetic phase. Though the magnetic phase mineral was not conclusively identified, the predominate interpretation is that the magnetic phase is probably maghemite. The electrical properties of the surface of Mars were only measured remotely by observations with Earth based radar, microwave radiometry, and inference from radio-occultation of Mars orbiting spacecraft. No direct measurements of electrical properties on Martian materials have been performed.

Olhoeft, G. R.↗
NASA NTRS2012

Axisymmetric Flow Properties for Magnetic Elements of Differing Strength

Aspects of the structure and dynamics of the flows in the Sun's surface shear layer remain uncertain and yet are critically important for understanding the observed magnetic behavior. In our previous studies of the axisymmetric transport of magnetic elements we found systematic changes in both the differential rotation and the meridional flow over the course of Solar Cycle 23. Here we examine how those flows depend upon the strength (and presumably anchoring depth) of the magnetic elements. Line of sight magnetograms obtained by the HMI instrument aboard SDO over the course of Carrington Rotation 2097 were mapped to heliographic coordinates and averaged over 12 minutes to remove the 5-min oscillations. Data masks were constructed based on the field strength of each mapped pixel to isolate magnetic elements of differing field strength. We used Local Correlation Tracking of the unmasked data (separated in time by 1- to 8-hours) to determine the longitudinal and latitudinal motions of the magnetic elements. We then calculated average flow velocities as functions of latitude and longitude from the central meridian for approx 600 image pairs over the 27-day rotation. Variations with longitude indicate and characterize systematic errors in the flow measurements associated with changes in the signal from disk center to limb. Removing these systematic errors reveals changes in the axisymmetric flow properties that reflect changes in flow properties with depth in the surface shear layer.

Rightmire-Upton, Lisa↗
NASA NTRS1982

Influence of gravity driven convection on the directional solidification of Bi/MnBi eutectic composites

The role of gravity on Bridgman-Stockharger directional solidification of eutectic Bi/MnBi has been studied in reduced gravity aboard NASA sounding rocket SPAR flight experiments and contrasted with normal gravity investigations. The directional solidification of eutectic Bi/MnBi results in a low volume fraction, faceted/nonfaceted aligned rod eutectic whose MnBi rod size, interrod spacing, thermal and magnetic properties are sensitive functions of solidification processing conditions. The morphology of the low-gravity samples showed striking differences compared with identically processed, normal gravity samples grown in the same apparatus. The MnBi rod diameter and interrod spacing distributions were significantly smaller, approximately 50 percent, for the low gravity samples compared with identically processed one gravity samples. Accompanying the smaller MnBi rod diameters observed in the flight samples, was an increase in permanent magnet properties which reached greater than 97 percent of the theoretical maximum. Gravitationally induced thermal instabilities in one-gravity which result in irregular interface movement and associated difficulty of the faceted MnBi phase to branch are suggested to explain the morphological differences between one and low gravity solidification.

Pirich, R. G.↗
NASA NTRS1981

Hard permanent magnet development trends and their application to A.C. machines

The physical and magnetic properties of Mn-Al-C, Fe-Cr-Co, and RE-TM (rare earth-transition metal intermetallics) in polymer and soft metal bonded or sintered form are considered for ac circuit machine usage. The manufacturing processes for the magnetic materials are reviewed, and the mechanical and electrical properties of the magnetic materials are compared, with consideration given to the reference Alnico magnet. The Mn-Al-C magnets have the same magnetic properties and costs as Alnico units, operate well at low temperatures, but have poor high temperature performance. Fe-Cr-Co magnets also have comparable cost to Alnico magnets, and operate at high or low temperature, but are brittle, expensive, and contain Co. RE-Co magnets possess a high energy density, operate well in a wide temperature range, and are expensive. Recommendation for exploring the rare-earth alternatives are offered.

Mildrum, H. F.↗
NASA NTRS1969

Properties of magnetically balanced arcs

Magnetically balanced arcs in supersonic external flows, indicating central core with differential Lorentz forces analogous to Grashof number in free convection phenomena

Kuethe, A. M.↗
NASA NTRS1976

Basic properties of magnetic flux tubes and restrictions on theories of solar activity

It is shown that the mean longitudinal field in a magnetic flux tube is reduced, rather than enhanced, by twisting the tube to form a rope. It is shown that there is no magnetohydrostatic equilibrium when one twisted rope is wound around another. Instead there is rapid line cutting (neutral point annihilation). It is shown that the twisting increases, and the field strength decreases, along a flux tube extending upward through a stratified atmosphere. These facts are at variance with Piddington's (1975) recent suggestion that solar activity is to be understood as the result of flux tubes which are enormously concentrated by twisting, which consist of several twisted ropes wound around each other, and which came untwisted where they emerge through the photosphere.

Parker, E. N.↗
NASA NTRS1983

Determination of the properties of magnetic turbulence in radio sources

The transport of polarized synchrotron radiation in a source possessing a highly irregular magnetic field, as proposed by Laing has been considered. The transport equation has been solved in a special case, relating the observable correlation functions in the Stokes parameters Q and U to the correlation functions of magnetic field and plasma density in the source. A rough application of the results to observations of the radio galaxy 3C 166 indicates that the turbulent scale length may be a few percent of the lobe size.

Spangler, S. R.↗
NASA NTRS1985

Magnetic field properties of the distant magnetotail magnetopause and boundary layer

Models incorporating merging between dayside magnetosheath and magnetosphere field lines predict the location of the magnetotail boundary layer and bending of magnetotail field lines in the direction of the IMF. Previous observations supporting these models are reviewed, and a case of dense magnetotail boundary layer plasma and strongly bent field lines observed by ISEE 3 is examined. Observations of boundary layer plasma within a tangential discontinuity magnetopause are discussed. The model to explain this phenomenon requires that interconnected magnetotail and magnetosheath field lines leave the magnetotail via a narrow 'window'. Field lines in the dense boundary layer plasma veer away from the aberrated x axis more than those in the void magnetotail lobes in order to pass through the windows. Magnetosheath plasma must enter the magnetotail lobes through the windows at all downstream distances in order to supply he observed tailward flux of lobe plasma.

Sibeck, D. G.↗
NASA NTRS1987

Statistical properties of magnetic field fluctuations in the distant plasmasheet

Short (less than 1 min) and long time (greater than 5 min) variations of the plasmasheet magnetic field have been examined during all intervals when ISEE-3 was at distances x less than -200 earth radii. It is determined that short period magnetic turbulence increases by a factor of about 3 with increasing geomagnetic activity, as indicated by AE. In contrast, long period field variations with North-then-South signatures at plasmasheet entry occur about 2.5 times more frequently than South-then-North signatures. This result, combined with other previous ISEE-3 results, is in agreement with the interpretation that the North-South plasmasheet features are plasmoids propagating tailward. However, a statistical examination of the geomagnetic activity relationship indicates that there does not appear to be any substorm dependence on these North-South events.

Tsurutani, Bruce T.↗