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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Development and Testing of High Surface Area Iridium Anodes for Molten Oxide Electrolysis

Processing of lunar regolith into oxygen for habitat and propulsion is needed to support future space missions. Direct electrochemical reduction of molten regolith is an attractive method of processing, because no additional chemical reagents are needed. The electrochemical processing of molten oxides requires high surface area, inert anodes. Such electrodes need to be structurally robust at elevated temperatures (1400-1600?C), be resistant to thermal shock, have good electrical conductivity, be resistant to attack by molten oxide (silicate), be electrochemically stable and support high current density. Iridium with its high melting point, good oxidation resistance, superior high temperature strength and ductility is the most promising candidate for anodes in high temperature electrochemical processes. Several innovative concepts for manufacturing such anodes by electrodeposition of iridium from molten salt electrolyte (EL-Form? process) were evaluated. Iridium electrodeposition to form of complex shape components and coating was investigated. Iridium coated graphite, porous iridium structure and solid iridium anodes were fabricated. Testing of electroformed iridium anodes shows no visible degradation. The result of development, manufacturing and testing of high surface, inert iridium anodes will be presented.

Shchetkovskiy, Anatoliy↗
NASA NTRS1994

Oxidation performance of platinum-clad Mo-47Re alloy

The alloy Mo-47Re has favorable mechanical properties at temperatures above 1400 C, but it undergoes severe oxidation when used in air with no protective coating. To shield the alloy from oxidation, platinum cladding has been evaluated. The unprotected alloy undergoes catastrophic oxidation under static and dynamic oxidation conditions. The platinum cladding provides good protection from static and dynamic oxidation for moderate times at 1260 C. Samples tested for longer times under static oxidation conditions experienced severe oxidation. The data suggest that oxidation results from the transport of oxygen through the grain boundaries and through the pinhole defects of the platinum cladding.

Clark, Ronald K.↗
NASA NTRS2015

Cyclic Oxidation and Hot Corrosion of NiCrY-Coated Disk Superalloy

Powder metallurgy disk superalloys have been designed for higher engine operating temperatures through improvement of their strength and creep resistance. Yet, increasing disk application temperatures to 704 C and higher could enhance oxidation and activate hot corrosion in harmful environments. Protective coatings could be necessary to mitigate such attack. Cylindrical coated specimens of disk superalloys LSHR and ME3 were subjected to thermal cycling to produce cyclic oxidation in air at a maximum temperature of 760 C. The effects of substrate roughness and coating thickness on coating integrity after cyclic oxidation were considered. Selected coated samples that had cyclic oxidation were then subjected to accelerated hot corrosion tests. The effects of this cyclic oxidation on resistance to subsequent hot corrosion attack were examined.

Hot corrosion↗
NASA NTRS1977

Studies of silicon pn junction solar cells

Modifications of the basic Shockley equations that result from the random and nonrandom spatial variations of the chemical composition of a semiconductor were developed. These modifications underlie the existence of the extensive emitter recombination current that limits the voltage over the open circuit of solar cells. The measurement of parameters, series resistance and the base diffusion length is discussed. Two methods are presented for establishing the energy bandgap narrowing in the heavily-doped emitter region. Corrections that can be important in the application of one of these methods to small test cells are examined. Oxide-charge-induced high-low-junction emitter (OCI-HLE) test cells which exhibit considerably higher voltage over the open circuit than was previously seen in n-on-p solar cells are described.

Lindholm, F. A.↗
NASA NTRS1985

Derivation and test of elevated temperature thermal-stress-free fastener concept

Future aerospace vehicles must withstand high temperatures and be able to function over a wide temperature range. New composite materials are being developed for use in designing high-temperature lightweight structures. Due to the difference between coefficients of thermal expansion for the new composite materials and conventional high-temperature metallic fasteners, innovative joining techniques are needed to produce tight joints at all temperatures without excessive thermal stresses. A thermal-stress-free fastening technique is presented that can be used to provide structurally tight joints at all temperatures even when the fastener and joined materials have different coefficients of thermal expansion. The derivation of thermal-stress-free fasteners and joint shapes is presented for a wide variety of fastener materials and materials being joined together. Approximations to the thermal-stress-free shapes that result in joints with low-thermal-stresses and that simplify the fastener/joint shape are discussed. The low-thermal-stress fastener concept is verified by thermal and shear tests in joints using oxide-dispersion-strengthened alloy fasteners in carbon-carbon material. The test results show no evidence of thermal stress damage for temperatures up to 2000 F and the resulting joints carried shear loads at room temperature typical of those for conventional joints.

Sawyer, J. W.↗
NASA NTRS1974

Investigation of the oxidation behavior of dispersion stabilized alloys when exposed to a dynamic high temperature environment

The oxidation behavior of TD-NiCr and TD-NiCrAlY alloys have been studied at 2000 and 2200 F in static and high speed flowing air environments. The TD-NiCrAlY alloys preoxidized to produce an Al2O3 scale on the surface showed good oxidation resistance in both types of environments. The TD-NiCr alloy which had a Cr2O3 oxide scale after preoxidation was found to oxidize more than an order of magnitude faster under the dynamic test conditions than at comparable static test conditions. Although Cr2O3 normally provides good oxidation protection, it was rapidly lost due to formation of volatile CrO3 when exposed to the high speed air stream. The preferred oxide arrangement for the dynamic test consisted of an external layer of NiO with a porous mushroom type morphology, an intermediate duplex layer of NiO and Cr2O3, and a continuous inner layer of Cr2O3 in contact with the alloy substrate. An oxidation model has been developed to explain the observed microstructure and overall oxidation behavior of all alloys.

Tenney, D. R.↗
NASA NTRS1999

Predicting Slag Generation in Sub-Scale Test Motors Using a Neural Network

Generation of slag (aluminum oxide) is an important issue for the Reusable Solid Rocket Motor (RSRM). Thiokol performed testing to quantify the relationship between raw material variations and slag generation in solid propellants by testing sub-scale motors cast with propellant containing various combinations of aluminum fuel and ammonium perchlorate (AP) oxidizer particle sizes. The test data were analyzed using statistical methods and an artificial neural network. This paper primarily addresses the neural network results with some comparisons to the statistical results. The neural network showed that the particle sizes of both the aluminum and unground AP have a measurable effect on slag generation. The neural network analysis showed that aluminum particle size is the dominant driver in slag generation, about 40% more influential than AP. The network predictions of the amount of slag produced during firing of sub-scale motors were 16% better than the predictions of a statistically derived empirical equation. Another neural network successfully characterized the slag generated during full-scale motor tests. The success is attributable to the ability of neural networks to characterize multiple complex factors including interactions that affect slag generation.

Wiesenberg, Brent↗
NASA NTRS1984

Oxidation and corrosion resistance of candidate Stirling engine heater-head-tube alloys

Sixteen candidate iron base Stirling engine heater head tube alloys are evaluated in a diesel fuel fired simulator materials test rig to determine their oxidation and corrosion resistance. Sheet specimens are tested at 820 C for 3500 hr in 5 hr heating cycles. Specific weight change data and an attack parameter are used to categorize the alloys into four groups; 10 alloys show excellent for good oxidation and corrosion resistance and six alloys exhibit poor or catastrophic resistance. Metallographic, X-ray, and electron microprobe analyses aid in further characterizing the oxidation and corrosion behavior of the alloys. Alloy compositions, expecially the reactive elements aluminum, titanium, and chromium, play a major role in the excellent oxidation and corrosion behavior of the alloys. The best oxidation resistance is associated with the formation of an iron nickel aluminum outer oxide scale, an intermediate oxide scale rich in chromium and titanium, and an aluminum outer oxide scale adjacent to the metallic substrate, which exhibits a zone of internal oxidation of aluminum and to some extent titanium.

Stephens, J. R.↗
NASA NTRS1987

An evaluation of candidate oxidation resistant materials

Ground based testing of materials considered for Kapton solar array blanket protection, graphite epoxy structural member protection, and high temperature radiators was performed in an RF plasma asher. Ashing rates for Kapton were correlated with rates measured on STS-8 to determine the exposure time equivalent to one year in low Earth orbit (LEO) at a constant density space station orbital flux. Protective coatings on Kapton from Tekmat, Andus Corporation, and LeRC were evaluated in the plasma asher and mass loss rates per unit area were measured for each sample. All samples evaluated provided some protection to the underlying surface but ion beam sputter deposited samples of SiO2 and SiO2 with 8% polytetrafluoroethylene (PTFE) showed no evidence of degradation after 47 hours of exposure. Mica paint was evaluated as a protective coating for graphite epoxy structural members. Mica appears to be resistant to attack by atomic oxygen but only offers some limited protection as a paint because the paint vehicles evaluated to date were not resistant to atomic oxygen. Four materials were selected for evaluation as candidate radiator materials: stainless steel, copper, niobium-1% zirconium, and titanium-6% aluminum-4% vanadium. These materials were surface textured by various means to improve their emittance. Emittances as high as 0.93 at 2.5 microns for stainless steel and 0.89 at 2.5 microns for Nb-1 Zr were obtained from surface texturing. There were no significant changes in emittance after asher exposure.

Rutledge, Sharon↗
NASA NTRS1995

Trimethoxymethane: A Fuel For Direct-Oxidation Fuel Cells

Trimethoxymethane (TMM) identified as high-energy fuel for direct-oxidation fuel cells. Synthesized from natural gas (methane) and handled easily because non-toxic, low-vapor-pressure liquid. Data obtained from both half-cell and full-cell tests indicate that TMM oxidized at very high rates. Considered excellent candidate for use in direct-oxidation fuel cells in vehicles and portable power supplies

Olah, George A.↗
NASA NTRS1982

Testing of fuel/oxidizer-rich, high-pressure preburners

Results of an evaluation of high pressure combustion of fuel rich and oxidizer rich LOX/RP-1 propellants using 4.0 inch diameter prototype preburner injectors and chambers are presented. Testing covered a pressure range from 8.9 to 17.5 MN/square meters (1292 to 2540 psia). Fuel rich mixture ratios ranged from 0.238 to 0.367; oxidizer rich mixture ratios ranged from 27.2 to 47.5. Performance, gas temperature uniformity, and stability data for two fuel rich and two ozidizer rich preburner injectors are presented for a conventional like-on-like (LOL) design and a platelet design injector. Kinetically limited combustion is shown by the excellent agreement of measured fuel rich gas composition and C performance data with kinetic model predictions. The oxidizer rich test results support previous equilibrium combustion predictions.

Lawver, B. R.↗
NASA NTRS1997

The Effect of Solid Constituent Particle Size Distributions on TP-H1148 Propellant Slag

Special aluminum and ammonium perchlorate (AP) particle size distributions were prepared for a matrix of five-inch diameter, center-perforated (CP) motor tests to measure the aluminum oxide slag response in Space Shuttle Reusable Solid Rocket Motor (RSRM) propellant. Previous tests of TP-H1148 propellant in five-inch CP spin motors have shown a correlation between aluminum particle size and generated slag. The motors for this study were cast from thirteen five-gallon propellant mixes which used five particle size levels of aluminum powder, five of unground AP and three of ground AP. Aluminum had the greatest effect on slag formation, the more coarse fractions causing greater slag quantities and larger slag particles. Unground AP had about half the effect of aluminum with the coarser fractions again producing more and larger sized slag particles. The variation in ground AP did not have a significant effect on slag formation. Quench bomb tests showed the same trends as the spin motors, that is, larger aluminum and AP particle size distributions generated larger slag particles leaving the propellant surface. Cured propellant mechanical properties were also impacted by particle size variation.

May, Douglas H.↗
NASA NTRS1982

Increased capabilities of the Langley Mach 7 Scramjet Test Facility

An experimental research program which explored the potential for expanding the operating range of NASA Langley's Mach 7 Scramjet Test Facility is described. The facility uses electric arc-heated air as the test gas and is configured for testing airframe-integrated scramjet engine models at conditions duplicating flight velocities and temperatures. Previous scramjet testing in this facility was limited to a single simulated flight condition of Mach 6.9 at 115,300 ft. altitude. The present arc heater research demonstrated that the facility can be used for scramjet testing at simulated flight conditions from Mach 4 (at altitudes from 77,000 to 114,000 ft.) to Mach 7 (at altitudes from 108,000 to 149,000 ft.). Flow quality was established from the uniformity of measured total temperature profiles. In addition, nitrogen oxide levels in the test stream were determined for relating engine test data to expected flight performance. The test frequency and reliability of the facility were also improved by a novel redesign of the heater downstream electrode and by defining limits for stable arc operation.

Thomas, S. R.↗
NASA NTRS1972

The oxidation behavior of Ni-Cr-Al-2ThO2 alloys at 1093 and 1204 C.

A pack diffusion process has been developed which permits the introduction of nearly 6 wt % Al into solid solution in the near surface region of TDNiCr (Ni-20 wt % Cr-2 vol % ThO2) and Ni-20Cr. Alumina scales, adherent under cyclic heating and cooling conditions, were produced on TDNiCr-5.86Al upon exposure to an environment of 1330 N/sq m (10 torr) or 101,000 N/sq m (760 torr) air at temperatures of 1093 and 1204 C. While the same oxidation kinetics were observed in isothermal tests for Ni-14.6Cr-5.86Al as were obtained for the TDNiCr-5.86Al, the dispersion-strengthened alloy exhibited superior oxide scale adhesion during cyclic testing. At 1204 C, continuous weight gains were observed under all test conditions for TDNiCr-5.86Al, in contrast to the weight loss with time which occurred several hours after exposure of TDNiCr to an oxidizing environment. TDNiCr with an initial aluminum surface concentration of 4.95 wt % has nearly comparable oxidation resistance to the TDNiCr-5.86Al alloy.

Seltzer, M. S.↗
NASA NTRS2009

Alloy Design Challenge: Development of Low Density Superalloys for Turbine Blade Applications

New low density single crystal (LDS) alloys have been developed for turbine blade applications, which have the potential for significant improvements in the thrust to weight ratio over current production alloys. An innovative alloying strategy was identified to achieve high temperature creep resistance, alloy density reductions, microstructural stability, and cyclic oxidation resistance. The approach relies on the use of molybdenum (Mo) as a potent solid solution strengthener for the nickel (Ni)-base superalloy; Mo has a density much closer to Ni than other refractory elements, such as rhenium (Re) or tungsten (W). A host of testing and microstructural examinations was conducted on the superalloy single crystals, including creep rupture testing, microstructural stability, cyclic oxidation, and hot corrosion. The paper will provide an overview of the single crystal properties that were generated in this new superalloy design space. The paper will also demonstrate the feasibility of this innovative approach of low density single crystal superalloy design. It will be shown that the best LDS alloy possesses the best attributes of three generations of single crystal alloys: the low density of first-generation single crystal alloys, the excellent oxidation resistance of second-generation single crystal alloys, and a creep strength which exceeds that of second and third generation alloys.

MacKay, Rebecca A.↗