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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

The impact of rare earth cobalt permanent magnets on electromechanical device design

Specific motor designs which employ rare earth cobalt magnets are discussed with special emphasis on their unique properties and magnetic field geometry. In addition to performance improvements and power savings, high reliability devices are attainable. Both the mechanism and systems engineering should be aware of the new performance levels which are currently becoming available as a result of the rare earth cobalt magnets.

Fisher, R. L.↗
NASA NTRS1972

Rare earths and other trace elements in Luna 16 soil.

An analysis has been made of four small samples of material brought to earth by the Luna 16 mission, with the aim to determine rare earths and other trace elements in these samples. The analytical results are tabulated, and the rare earth abundances are compared with the average for chondrites. A comparison is also made with the results of similar analyses of Apollo samples.

Helmke, P. A.↗
NASA NTRS2011

Improved Rare-Earth Emitter Hollow Cathode

An improvement has been made to the design of the hollow cathode geometry that was created for the rare-earth electron emitter described in Compact Rare Earth Emitter Hollow Cathode (NPO-44923), NASA Tech Briefs, Vol. 34, No. 3 (March 2010), p. 52. The original interior assembly was made entirely of graphite in order to be compatible with the LaB6 material, which cannot be touched by metals during operation due to boron diffusion causing embrittlement issues in high-temperature refractory materials. Also, the graphite tube was difficult to machine and was subject to vibration-induced fracturing. This innovation replaces the graphite tube with one made out of refractory metal that is relatively easy to manufacture. The cathode support tube is made of molybdenum or molybdenum-rhenium. This material is easily gun-bored to near the tolerances required, and finish machined with steps at each end that capture the orifice plate and the mounting flange. This provides the manufacturability and robustness needed for flight applications, and eliminates the need for expensive e-beam welding used in prior cathodes. The LaB6 insert is protected from direct contact with the refractory metal tube by thin, graphite sleeves in a cup-arrangement around the ends of the insert. The sleeves, insert, and orifice plate are held in place by a ceramic spacer and tungsten spring inserted inside the tube. To heat the cathode, an insulating tube is slipped around the refractory metal hollow tube, which can be made of high-temperature materials like boron nitride or aluminum nitride. A screw-shaped slot, or series of slots, is machined in the outside of the ceramic tube to constrain a refractory metal wire wound inside the slot that is used as the heater. The screw slot can hold a single heater wire that is then connected to the front of the cathode tube by tack-welding to complete the electrical circuit, or it can be a double slot that takes a bifilar wound heater with both leads coming out the back. This configuration replaces the previous sheathed heater design that limited the cycling-life of the cathode.

Goebel, Dan M.↗
NASA NTRS1999

Rare Earth Doped Yttrium Aluminum Garnet (YAG) Selective Emitters

As a result of their electron structure, rare earth ions in crystals at high temperature emit radiation in several narrow bands rather than in a continuous blackbody manner. This study presents a spectral emittance model for films and cylinders of rare earth doped yttrium aluminum garnets. Good agreement between experimental and theoretical film spectral emittances was found for erbium and holmium aluminum garnets. Spectral emittances of films are sensitive to temperature differences across the film. For operating conditions of interest, the film emitter experiences a linear temperature variation whereas the cylinder emitter has a more advantageous uniform temperature. Emitter efficiency is also a sensitive function of temperature. For holminum aluminum garnet film the efficiency is 0.35 at 1446K but only 0.27 at 1270 K.

Chubb, Donald L.↗
NASA NTRS1995

Radiative and Nonradiative Transitions of the Rare-Earth Ions Tm(3+) and Ho(3+) in Y3AI5O12 and LiYF4

The optical spectra of rare earth ions in solids arise primarily from electric and magnetic dipole transitions between stark split multiplets of the 4f(sup N) electronic configuration. Electric dipole transitions are parity forbidden between levels of the 4f(sup N) configuration, while those of magnetic dipole origin are allowed. It is known from experiment, however, that the significant contributions to the intensities of most transitions are electric dipole in nature. Judd and Ofelt developed the theory of forced electric dipole transitions of rare-earth ions. This study is devoted to determining electric dipole transition probabilities and branching ratios for Tm(3+) and Ho(3+) ions in Yttrium Aluminum Garnet (YAG) and Yttrium Lithium Fluoride (YLF) using the theory of Judd and Ofelt. The radiative rates determined from the Judd-Ofelt analysis are used with measured lifetimes to find nonradiative rates of relaxation.

Walsh, Brian M.↗
NASA NTRS1985

Oxidation of silicon nitride sintered with rare-earth oxide additions

The effects of rare-earth oxide additions on the oxidation of sintered Si3N4 were examined. Insignificant oxidation occurred at 700 and 1000 C, with no evidence of phase instability. At 1370 C, the oxidation rate was lowest for Y2O3 and increased for additions of La2O3, Sm2O3, and CeO2, in that order. Data obtained from X-ray diffraction, electron microprobe analysis, and scanning electron microscopy indicate that oxidation occurs via diffusion of cationic species from Si3N4 grain boundaries.

Mieskowski, D. M.↗
NASA NTRS2021

Thermodynamics of the Lu2O3 – SiO2 system and comparison to other Rare Earth Silicates

Environmental barrier coatings are necessary to protect SiC based ceramics and composites from water vapor degradation in harsh engine environments. Currently, rare earth (RE) silicates are the most promising systems to protect SiC based ceramics and composites. This protection is largely based on reduced silica activity in these rare earth silicates which results in a lowered reactivity with water vapor. To that end, previous Knudsen effusion mass spectrometry (KEMS) studies have explored RE = Yb, Y silicates to measure the reduced silica activity and subsequent water vapor reactivity. Similarly, this work employs the KEMS technique to measure the SiO(g) vapor pressure in Lu containing RE silicates to calculate the activity of silica within the monosilicate [log(a(SiO2)) = -2351.1*1/T-1.6731] and the disilicate (log(a(SiO2)) = -4884.0*1/T + 2.2208) as a function of temperature. The enthalpies of formation for Lu monosilicate from the oxides and the elements were calculated to be -45±3 kJ/mol at 1550 K and -2831.1±12 kJ/mol at 298 K, respectively. The measured enthalpy of formation and those found in literature are compared to modeled values from density functional theory and those estimated using electronegativity.

Knudesen Effusion Mass Spectrometry↗
NASA NTRS1976

Rare earth element abundances in rocks and minerals from the Fiskenaesset Complex, West Greenland

The paper reports activation-analysis determinations of rare-earth-element (REE) and other trace-element concentrations in selected rocks, plagioclase, and mafic separates from the Fiskenaesset Complex. The REE abundances are found to be very low and atypical in comparison with other terrestrial anorthosites. The plagioclases are shown to be characterized by a deficiency in heavy RE elements relative to light ones and a positive Eu anomaly, while the mafic separates are enriched in heavy rare earths and have no Eu anomaly, except in one sample. It is found that the bulk and trace-element abundances of the plagioclases are similar to those observed in some lunar anorthosites, but the degree of Eu anomaly is less in the plagioclases. The data are taken as confirmation of the idea that fractionation processes were involved in the origin of the Complex, and it is concluded that the Complex may have been produced from a magma generated by partial melting of a garnet-bearing source.

Henderson, P.↗