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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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A superconducting comb structure as a slow-wave element in a traveling-wave maser will significantly improve maser noise temperature and gain by reducing the insertion loss. The results of the insertion loss measurements of superconducting niobium slow-wave structures subjected to maser operating conditions at X-Band frequencies are presented.
Lines of the first multiplet of niobium are strong in R And and HR 1105. These lines are also present in other S stars: HR 8714, R Cam, V Cnc, R CMi, and T Sgr. They are also visible in the M stars, Beta-Peg and Mu-UMa. An approximation to the abundance ratio, Nb/Fe, has been deduced from pairs of lines having nearly equal intensity. In R And, the ratio is about 200 times the solar value. It is hoped that good plates will soon be obtained for the near infrared region, so that the significant Nb/Rb abundance ratio may be determined.
The 100 meter drop tube at NASA's Marshall Space Flight Center has been used for a series of experiments with niobium-germanium alloys. These experiments were conducted with electromagnetic levitation melting in a 200 torr helium environment. Liquid alloys experienced large degrees of undercooling prior to solidification in the drop tube. Several interesting metastable structures were observed. However, the recalescence event prevented extended solid solubility of germanium in the A-15 beta phase. Liquids of eutectic composition were found to undercool in the presence of solid alpha and solid Nb5Ge3.
A niobium alloy with 1 percent zirconium and 0.063 percent carbon by weight was investigated in the as-rolled and annealed conditions, and after high-temperature (1350 and 1400 K) exposure with and without an applied stress. In the as-rolled and annealed conditions, large metastable carbides were observed in addition to a regular distribution of small particles. During the high-temperature exposure, the majority of the large carbides were dissolved and a more stable carbide phase formed. This finely dispersed phase had a composition determined to be approximately 70 percent ZrC and approximately 30 percent NbC and showed some evidence of an orientation relationship with the matrix. The precipitates appeared to coarsen slightly after approximately 5000 hr exposure in the presence of an applied stress resulted in a decrease in the size and in the interparticle spacing of the stable precipitates. However, the composition of the precipitate phase and its ability to pin dislocations were not affected by the temperature or stress conditions.
Chemical compatibility of several reinforcement materials with three niobium aluminides, Nb3Al, Nb2Al, and NbAl3, were examined from thermodynamic considerations. The reinforcement materials considered in this study include carbides, borides, nitrides, oxides, silicides, and Engel-Brewer compounds. Thermodynamics of the Nb-Al system were reviewed and activities of Nb and Al were derived at desired calculation temperatures. Criteria for chemical compatibility between the reinforcement material and Nb-Al compounds have been defined and several chemically compatible reinforcement materials have been identified.
The mechanical and electrical quality factors of a 10-g niobium resonator were measured at 4.4 K and were found to be 8.1 x 10 to the 6th, and 3.8 x 10 to the 6th, respectively. The value for the electrical quality factor is high enough for a system operating at 50 mK at a sensitivity level of one phonon. The resonator's low damping properties make it suitable for use as a transducer for a cryogenic three-mode gravitational radiation detector. A practical design is given for the mounting of the resonator on a 2400-kg aluminum-bar detector. Projections are made for the sensitivity of a 2400-kg bar instrumented as a three-mode system with this resonator inductively coupled to a SQUID.
Niobium triselenide cathodes in Li ambient-temperature rechargeable batteries for space applications undergo a topotactic reaction, with three equivalents of Li at high positive potential furnishing high energy density. It also yields good electronic conductivity, a long life cycle, and high diffusivity for Li. An attempt is presently made to characterize the intercalation mechanism between Li and NbSe3 by means of an ac impedance study conducted at various charge stages in the process of SbSe3 reduction. An effort is also made to predict the charge state of NbSe3 nondestructively, on the basis of the impedance parameters.
Study conducted to determine feasibility of using composite materials in advanced space power systems, described in 22-page report. Tungsten fibers reduce creep and mass in advanced power systems. Reinforcing niobium alloys with tungsten fibers increases their resistances to creep by factors of as much as 10.
Chemical compatibility of several reinforcement materials with three niobium aluminides, Nb3Al, Nb2Al, and NbAl3, were examined from thermodynamic considerations. The reinforcement materials considered in this study include carbides, borides, nitrides, oxides, silicides, and Engel-Brewer compounds. Thermodynamics of the Nb-Al system were reviewed and activities of Nb and Al were derived at desired calculation temperatures. Criteria for chemical compatibility between the reinforcement material and Nb-Al compounds have been defined and several chemically compatible reinforcement materials have been identified.
The long term interdiffusional stability of tungsten fiber reinforced niobium alloy composites is addressed. The matrix alloy that is most promising for use as a high temperature structural material for reliable long-term space power generation is Nb1Zr. As an ancillary project to this program, efforts were made to assess the nature and kinetics of interphase reaction between selected beryllide intermetallics and nickel and iron aluminides.
A magnetic field trapped in a superconducting sphere was examined at temperatures from 4.6 K to 5.5 K. The sphere was the rotor of a precision gyroscope and was made of fused quartz and coated with a sputtered niobium film. The rotor diameter was 3.8 cm. The film thickness was 2.5 microns. The tests were carried out at an ambient magnetic field of about 1 mG. Unexpected instability of the trapped field was observed. The experimental results and possible explanations are presented.
Niobium microbolometers approximately 1 micron wide x 2 micron long x 10 nm thick have been integrated at the feeds of equiangular spiral antennas made of 200 nm thick Nb. The device's current-voltage characteristics and infrared responsivity as a function of DC bias voltage were measured over a range of temperature spanning approximately plus or minus 2 percent around T(sub c). The greatest voltage responsivity occurs well below T(sub c), in a regime where the I-V curve is significantly hysteretic due to self-heating and resembles the I-V curve of a superconducting microbridge.
This article describes the successful fabrication, operation, and evaluation of a series of niobium-alloy (Nb-1 Zr and PWC-11) thermal convection loops designed to contain and circulate molten lithium at 1,350 K. These loops were used to establish the fabrication variables of significance for a nuclear power supply for space. Approximately 200 weldments were evaluated for their tendency to be attacked by lithium as a function of varying atmospheric contamination. No attack occurred for any weldment free of contamination, with or without heat treatment, and no welds accidentally deviated from purity. The threshold oxygen content for weldment attack was determined to be 170-200 ppm. Attack varied directly with weldment oxygen and nitrogen contents.
This investigation concludes a study to determine the effects of up to 25 atomic percent of 55 alloying additions on the oxidation characteristics of niobium. The alloys were evaluated by oxidizing in an air atmosphere for 4 hours at 1000 C and 2 hours at 1200 C. Titanium and chromium improved oxidation resistance at both evaluation conditions. Vanadium and aluminum improved oxidation resistance at 1000 C, even though the V scale tended to liquefy and the Al specimens became brittle and the scale powdery. Copper, cobalt, iron, and iridium improved oxidation resistance at 1200 C. Other investigations report tungsten and molybdenum are protective up to about 1000 C, and tantalum at 1100 C. The most important factor influencing the rate of oxidation was the ion size of the alloy additions. Ions slightly smaller than the Nb(5+) ion are soluble in the oxide lattice and tend to lower the compressive stresses in the bulk scale that lead to cracking. The solubility of the alloying addition also depends on the valence to some extent. All of the elements mentioned that improve the oxidation resistance of Nb fit this size criterion with the possible exception of Al, whose extremely small size in large concentrations would probably lead to the formation of a powdery scale. Maintenance of a crack-free bulk scale for as long as possible may contribute to the formation of a dark subscale that ultimately is rate- controlling in the oxidation process. The platinum-group metals, especially Ir, appear to protect by entrapment of the finely dispersed alloying element by the incoming Nb2O5 metal-oxide interface. This inert metallic Ir when alloyed in a sufficient amount with Yb appears to give a ductile phase dispersed in the brittle oxide. This scale would then flow more easily to relieve the large compressive stresses to delay cracking. Complex oxide formation (which both Ti and Zr tend to initiate) and valence effects, which probably change the vacancy concentration in the scale, are masked by the overriding tendency for a porous scale.
The copper-niobium phase diagram has been under active debate; thus, a corroboratory experimental study is needed. In this investigation, the melts of Cu-Nb alloys at compositions ranging from 5 lo 86 wt% Nb were processed in different environments and solidified at relatively low rates of 50-75 C/s to determine liquidus temperatures and to study solidification behavior. For all samples processed under very clean conditions, only Nb dendrites in a Cu matrix were observed; while in the presents of oxygen impurities, the alloys containing 5-35 wt% Nb exhibited microstructure of Nb-rich spheroids and Nb dendrites in the Cu matrix. The results obtained from clean conditions are in fair agreement with the Cu-Nb phase diagram having an S-shaped, near-horizontal appearances of the liquidus. The formation of Nb-rich droplets at slow cooling rates is discussed in terms of a stable liquid miscibility gap induced by oxygen.
The copper-niobium phase diagram has been under active debate; thus, a corroboratory experimental study is needed. In this investigation, the melts of Cu-Nb alloys at compositions ranging from 5 to 86 wt pct Nb were processed in different environments and solidified at relatively low cooling rates of 50 to 75 C/s to determine liquidus temperatures and to study solidification behavior. For all samples processed under very clean conditions, only Nb dendrites in a Cu matrix were observed; while in the presence of oxygen impurities the alloys containing 5 to 35 wt pct Nb exhibited microstructure of Nb-rich spheroids and Nb dendrites in the Cu matrix. The results obtained from clean conditions are in fair agreement with the Cu-Nb phase diagram having an S-shaped, near-horizontal appearance of the liquidus. The formation of Nb- rich droplets at slow cooling rates is discussed in terms of a stable liquid miscibility gap induced by oxygen.
Proposed concepts for an ambitious mission to explore Jupiter's three icy moons place significant demands on the various spacecraft systems. There are many challenges related to the high output power conversion systems being considered, and one example is the need to ensure system compatibility at all levels. The utilization of appropriate materials for component structures is important to ensuring long mission life. Refractory metal alloys have attractive high-temperature properties in inert environments, but these alloys are sometimes susceptible to contamination. Potential material compatibility issues exist between refractory metal candidates and more conventional alloys. Nb-1Zr has long been considered one of the most well characterized refractory alloys that is well suited for elevated-temperature use and liquid-metal compatibility. However, previous studies have suggested that niobium alloys can not co-exist in a closed system with traditional stainless steels or superalloys due to transport of contaminants. The relevance of this information to a proposed power conversion system is discussed. Also, experiments and fundamental calculations are being performed to determine contamination transport from candidate superalloys to Nb-1Zr in a closed system with an inert carrier gas. Potential protective schemes are explored to ensure system level compatibility between the refractory alloy Nb-1Zr and a nickel-based superalloy.
Cold electropolishing (EP) of a nitrogen-doped (N-doped) niobium (Nb) superconducting RF (SRF) cavity was found to improve its quality factor. In order to understand the effect of EP temperature on N-doped and undoped surfaces, a systematic EP study was conducted with 2/0 N-doped and heat-treated Nb samples in a beaker. The Nb samples were electropolished at different surface temperatures ranging from 0 to 42 C. The results showed that the doped surface was susceptible to the sample temperature during EP. EP resulted in the surface pitting on the doped samples where the number density of pits increased at a higher temperature. The surface results were compared with the surface of cutouts from a 9-cell cavity which was 2/0 N-doped and electropolished. This paper shows de-tailed surface features of the N-doped and undoped Nb surfaces electropolished at different temperatures.