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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Mechanical characterization of unnotched SCS6/Ti-15-3 metal matrix composites at room temperature

The Ti-15-3 metal matrix composites containing silicon-carbide (SCS6) fibers, in five different lay-ups, have been tested at room temperature to determine static strengths and mechanical properties. Experimental data and predicted values of the laminate properties and strengths showed good correlation. The off-axis laminate plies (that is, 90 and 45 deg) suffered fiber/matrix interface failures at stress levels as low as 20 ksi, thus significantly affecting the mechanical properties of the laminate. Edge replicas were used to verify the fiber/matrix separations. Microscopic examinations determined that the fiber/matrix failures were occurring in the titanium/silicon reaction layer. Fatigue tests were performed on unnotched specimens to determine the number of cycles to failure versus cyclic stress level. It was found that the stress in the 0 deg fiber could be used to correlate the fatigue life of different laminates containing 0 deg plies.

Johnson, W. S.↗
NASA NTRS1989

Threshold analysis of pulsed lasers with application to a room-temperature Co:MgF2 laser

Rate-equation calculations are used to model accurately the near-threshold behavior of a Co:MgF2 laser operating at room temperature. The results demonstrate the limitations of the conventional threshold analysis in cases of practical interest. This conclusion is applicable to pulsed solid-state lasers in general. The calculations, together with experimental data, are used to determine emission cross sections for the Co:MgF2 laser.

Harrison, James↗
NASA NTRS1989

Tribological reactions of perfluoroalkyl polyether oils with stainless steel under ultrahigh vacuum conditions at room temperature

The reaction between three types of commercial perfluoroalkyl polyether (PFPE) oils and stainless steel 440C was investigated experimentally during sliding under ultrahigh vacuum conditions at room temperature. It is found that the tribological reaction of PFPE is mainly affected by the activity of the mechanically formed fresh surfaces of metals rather than the heat generated at the sliding contacts. The fluorides formed on the wear track act as a boundary layer, reducing the friction coefficient.

Mori, Shigeyuki↗
NASA NTRS2019

Room Temperature Radiation Testing of a 500 °C Durable 4H-SiC JFET Integrated Circuit Technology

Total ionizing dose (TID) and single-event effect (SEE) room-temperature radiation test results are presented for developmental prototype 4H-SiC junction field effect transistor (JFET) semiconductor integrated circuits (ICs) that have demonstrated prolonged operation in extremely high-temperature (500 °C) environments. The devices tested demonstrated over 7 Mrad(Si) TID tolerance and no destructive SEE susceptibility.

Lauenstein, Jean-Marie↗
NASA NTRS1991

Effect of Fiber Strength on the Room Temperature Tensile Properties of Sic/Ti-24Al-11Nb

SCA-6 SiC fibers of known strength were incorporated into SiC/Ti-24Al-11Nb (at. percent) composites and the effect of fiber strength variability on room temperature composite strength was investigated. Fiber was etched out of a composite fabricated by the powder cloth technique and the effect of the fabrication process on fiber strength was assessed. The strength of the composite was directly correlated with the strength of the as-received fiber. The strength of composite plates containing mixed fiber strengths was dominated by the lower strength fiber. Fabrication by the powder cloth technique resulted in only a slight degradation of fiber strength. The strength of the composite was found to be overestimated by the rule of mixtures strength calculation. Examination of failed tensile specimens revealed periodic fiber cracks and the failure mode was concluded to be cumulative. With the variation in fiber strength eliminated, the composite UTS was found to have a positive correlation with volume fraction of fiber.

Draper, S. L.↗
NASA NTRS1979

Room-temperature bonding of thin plastic sheets

Thin sheets of plastic are bonded together, without heat, by depositing metal films on plastic and applying light pressure. Films are pressed together at room temperature, technique which makes it possible to join organic material without high temperatures necessary for conventional adhesive bonding.

Frazer, R. E.↗
NASA NTRS1989

Notch effects on room temperature tensile and bend properties of Ni3Al and Ni3Al+B

The notched mechanical properties of Ni3Al and Ni3Al+B prepared by powder metallurgy techniques have been determined in both tension and bending at room temperature. Tensile tests performed using double-notched specimens containing relatively blunt notches produced intergranular fracture in both Ni3Al and Ni3Al+B, with evidence of fracture initiating in an intergranular manner ahead of the blunt notch in both cases. Estimates of notched fracture toughness from bend tests and of local grain boundary fracture stress from the notched tensile tests suggest an increase in these values with boron addition.

Khadkikar, P. S.↗
NASA NTRS1998

Room Temperature Tensile Behavior and Damage Accumulation of Hi-Nicalon Reinforced SiC Matrix Composites

Composites consisting of woven Hi-Nicalon fibers, BN interphases, and different SiC matrices were studied in tension at room temperature. Composites with SiC matrices processed by CVI and melt infiltration were compared. Monotonic and load/unload/reload tensile hysteresis experiments were performed. A modal acoustic emission (AE) analyzer was used to monitor damage accumulation during the tensile test. Post test polishing of the tensile gage sections was performed to determine the extent of cracking. The occurrence and location of cracking could easily be determined using modal AE. The loss of modulus could also effectively be determined from the change in the velocity of sound across the sample. Finally, the stresses where cracks appear to intersect the load-bearing fibers correspond with high temperature low cycle fatigue run out stresses for these materials.

Morscher, G. N.↗
NASA NTRS1974

Trapping of hydrogen atoms in X-irradiated salts at room temperature and the decay kinetics

The salts (hypophosphites, formates, a phosphite, a phosphate, and an oxalate) were X-irradiated, whereby hydrogen formed chemically by a radiolytic process becomes trapped in the solid. By room temperature vacuum extraction, the kinetics for the evolution of this trapped hydrogen was studied mass spectrometrically. All salts except two exhibited second-order kinetics. The two exceptions (NaH2PO2(H2O) and K2HPO4) showed first-order kinetics. Based on experimental results, the escape of hydrogen involves three steps: the diffusion of hydrogen atoms from the bulk to the surface, association of these atoms on the surface (rate controlling step for second-order hydrogen evolution), and the desorption of molecular hydrogen from the surface. The hydrogen does not escape if the irradiated salt is stored in air, apparently because adsorbed air molecules occupy surface sites required in the escape mechanism.

May, C. E.↗
NASA NTRS1986

Room-Temperature Deposition of NbN Superconducting Films

Films with high superconducting transition temperatures deposited by reactive magnetron sputtering. Since deposition process does not involve significantly high substrate temperatures, employed to deposit counter electrode in superconductor/insulator/superconductor junction without causing any thermal or mechanical degradation of underlying delicate tunneling barrier. Substrates for room-temperature deposition of NbN polymeric or coated with photoresist, making films accessible to conventional lithographic patterning techniques. Further refinements in deposition technique yield films with smaller transition widths, Tc of which might approach predicted value of 18 K.

Thakoor, S.↗
NASA NTRS1990

Static compression of Ca(OH)2 at room temperature - Observations of amorphization and equation of state measurements to 10.7 GPa

X-ray diffraction measurements are reported for Ca(OH)2 portlandite as it is compressed to 37.6 GPa in the diamond cell at room temperature. Between 10.7 and 15.4 GPa crystalline Ca(OH)2 transforms to a glass, and on decompression the glass recrystallizes between 3.6 and 5.1 GPa. Below pressures of 10.7 GPa the elastic compression of crystalline Ca(OH)2 was measured. A finite strain analysis of these data shows that the isothermal bulk modulus and its pressure derivative are 37.8 + or - 1.8 GPa and 5.2 + or - 0.7 at zero pressure. The change in the unit cell dimensions indicates that the linear incompressibilities of Ca(OH)2 differ by a factor of three.

Meade, Charles↗
NASA NTRS1991

Spatial variations in ac susceptibility and microstructure for the YBa2Cu3O(7-x) superconductor and their correlation with room-temperature ultrasonic measurements

The spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu3O(7-x) specimens over the pore fraction range of 0.10 to 0.25 was examined. The viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability was determined. Spatial variations in superconductor properties were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in alternating-current shielding and loss behavior. Optical quantitative image analysis on sample cross-sections revealed pore fraction to be the varying microstructural feature.

Roth, Don J.↗
NASA NTRS1991

Spatial variations in a.c. susceptibility and microstructure for the YBa2Cu3O(7-x) superconductor and their correlation with room-temperature ultrasonic measurements

The spatial (within-sample) uniformity of superconducting behavior and microstructure in YBa2Cu30(7-x) specimens over the pore fraction range of 0.10 to 0.25 was examined. The viability of using a room-temperature, nondestructive characterization method (ultrasonic velocity imaging) to predict spatial variability was determined. Spatial variations in superconductor properties were observed for specimens containing 0.10 pore fraction. An ultrasonic velocity image constructed from measurements at 1 mm increments across one such specimen revealed microstructural variation between edge and center locations that correlated with variations in alternating-current shielding and loss behavior. Optical quantitative image analysis on sample cross-sections revealed pore fraction to be the varying microstructural feature.

Roth, Don J.↗
NASA NTRS1992

Long-term storage of salivary cortisol samples at room temperature

Collection of saliva samples for the measurement of cortisol during space flights provides a simple technique for studying changes in adrenal function due microgravity. In the present work, several methods for preserving saliva cortisol at room temperature were investigated using radioimmunoassays for determining cortisol in saliva samples collected on a saliva-collection device called Salivettes. It was found that a pretreatment of Salivettes with citric acid resulted in preserving more than 85 percent of the salivary cortisol for as long as six weeks. The results correlated well with those for a sample stored in a freezer on an untreated Salivette.

Chen, Yu-Ming↗
NASA NTRS2014

Room Temperature Carbon Nanotube Based Sensor for Carbon Monoxide Detection

Sulfonated single-walled carbon nanotubes have been used in an integrated electrode structure forthe detection of carbon monoxide. The sensor responds to 0.5 ppm of CO in air at room temperature. All eightsensors with this material in a 32-sensor array showed good repeatability and reproducibility, with response andrecovery times of about 10 s. Pristine nanotubes generally do not respond to carbon monoxide and the resultshere confirm sulfonated nanotubes to be a potential candidate for the construction of an electronic nose thatrequires at least a few materials for the selective detection of CO.

Nanomaterial functionalization↗
NASA NTRS1988

Room-temperature codeposition growth technique for pinhole reduction in epitaxial CoSi2 on Si (111)

A solid-phase epitaxy has been developed for the growth of CoSi2 films on Si (111) with no observable pinholes (1000/sq cm detection limit). The technique utilizes room-temperature codeposition of Co and Si in stoichiometric ratio, followed by the deposition of an amorphous Si capping layer and subsequent in situ annealing at 550-600 C. CoSi2 films grown without the Si cap are found to have pinhole densities of (1-10) x 10 to the 7th/sq cm when annealed at similar temperatures. A CF4 plasma-etching technique was used to increase the visibility of the pinholes in the silicide layer.

Lin, T. L.↗
NASA NTRS1989

Room-temperature InGaAs detector arrays for 2.5 microns

This paper describes new alloy heterojunction detectors of In(.8)Ga(.2)As/InAs(.6)P(.4) which can detect light between 1.7 and 2.6 microns with 50 percent quantum efficiency and 5 mA/sq cm dark current (-1 V) density at room temperature. Wafer probe data showed that over 50 good contiguous 100 micron diameter devices (spaced 400 microns) could be made on a 25 x 30 mm wafer with overall yield above 93 percent. The ability to operate under -1 V reverse bias makes these devices ideally compatible with existing commercial multiplexer readouts.

Olsen, G. H.↗