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All sourcesNASA NTRSDOE OSTI
NASA NTRS2008

Adsorption of Water on Simulated Moon Dust Samples

A lunar regolith simulant dust sample (JSC-1a) supported on a silica wafer (SiO2/Si(111)) has been characterized by scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), and Auger electron spectroscopy (AES). The adsorption kinetics of water has been studied primarily by thermal desorption spectroscopy (TDS) and also by collecting isothermal adsorption transients. The support has been characterized by water TDS. JSC-1a consists mostly of aluminosilicate glass and other minerals containing Fe, Na, Ca, and Mg. The particle sizes span the range from a few microns up to 100 microns. At small exposures, H2O TDS is characterized by broad (100 to 450 K) structures; at large exposures distinct TDS peaks emerge that are assigned to amorphous solid water (145 K) and crystalline ice (165 K). Water dissociates on JSC-1a at small exposures but not on the bare silica support. It appears that rather porous condensed ice layers form at large exposures. At thermal impact energies, the initial adsorption probability amounts to 0.92+/-0.05.

Goering, John P.↗
NASA NTRS2008

Desert Dust Aerosol Air Mass Mapping in the Western Sahara, Using Particle Properties Derived from Space-Based Multi-Angle Imaging

Coincident observations made over the Moroccan desert during the Sahara mineral dust experiment (SAMUM) 2006 field campaign are used both to validate aerosol amount and type retrieved from multi-angle imaging spectroradiometer (MISR) observations, and to place the suborbital aerosol measurements into the satellite s larger regional context. On three moderately dusty days during which coincident observations were made, MISR mid-visible aerosol optical thickness (AOT) agrees with field measurements point-by-point to within 0.05 0.1. This is about as well as can be expected given spatial sampling differences; the space-based observations capture AOT trends and variability over an extended region. The field data also validate MISR s ability to distinguish and to map aerosol air masses, from the combination of retrieved constraints on particle size, shape and single-scattering albedo. For the three study days, the satellite observations (1) highlight regional gradients in the mix of dust and background spherical particles, (2) identify a dust plume most likely part of a density flow and (3) show an aerosol air mass containing a higher proportion of small, spherical particles than the surroundings, that appears to be aerosol pollution transported from several thousand kilometres away.

Kahn, Ralph↗
NASA NTRS2011

Preliminary Examination of Particles Recovered from the Surface of the Asteroid Itokawa by the Hayabusa Mission

The Hayabusa spacecraft arrived at S-type Asteroid 25143 Itokawa in November 2006, and reveal astounding features of the small asteroid (535 x 294 x 209 m). Near-infrared spectral shape indicates that the surface of this body has an olivinerich mineral assemblage potentially similar to that of LL5 or LL6 chondrites with different degrees of space weathering. Based on the surface morphological features observed in high-resolution images of Itokawa s surface, two major types of boulders were distinguished: rounded and angular boulders. Rounded boulders seem to be breccias, while angular boulders seem to have severe impact origin. Although the sample collection did not be made by normal operations, it was considered that some amount of samples, probably small particles of regolith, was collected from MUSES-C regio on the Itokawa s surface. The sample capsule was successfully recovered on the earth on June 13, 2010, and was opened at curation facility of JAXA (Japan Aerospace Exploration Agency), Sagamihara, Japan. A large number of small particles were found in the sample container. Preliminary analysis with SEM/EDX at the curation facility showed that at least more than 1500 grains were identified as rocky particles, and most of them were judged to be of extraterrestrial origin, and definitely from Asteroid Itokawa. Minerals (olivine, low-Ca pyroxene, high-Ca pyroxene, plagioclase, Fe sulfide, Fe-Ni metal, chromite, Ca phosphate), roughly estimated mode the minerals and rough measurement of the chemical compositions of the silicates show that these particles are roughly similar to LL chondrites. Although their size are mostly less than 10 m, some larger particles of about 100 m or larger were also identified. A part of the sample (probably several tens particles) will be selected by Hayabusa sample curation team and examined preliminary in Japan within one year after the sample recovery in prior to detailed analysis phase. Hayabusa Asteroidal Sample Preliminary Examination Team (HASPET) has been preparing for the preliminary examination with close cooperation with the curation team.

Tsuchiyama, A.↗
DOE OSTI2014

The appearance of plasticity on the blocks surfaces in geological media

In present the elasticity and plasticity are absolutely different models of solids, which are not relate to each other. The experimental observations show, that the plasticity arrives and localizes on the surfaces of structures, which contain solid samples. The transition in special state, where a small part of solid volume is in plastic state, while the main part of volume is in elastic state not be describe by classical continuum Cauchy and Poisson model. This classical model requires two alternative states. Either is elastic state in the all volume or plastic one for all elementary volume too. However, the structured model of space gives us a possibility to describe this complicate state. In this paper shown that the sliding surfaces divided to each other by distances equal to the average sizes of microstructures, in the contrary of classical plasticity, where they have not characteristic distance. The energy of plastic transition is very small, because the main part of volume is elastic body. This description means the smooth transition from elasticity to plasticity in vicinity of sliding surfaces.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Porosity and mechanical properties of zirconium ceramics

Has been studied a porous ceramics obtained from ultra-fine powders. Porous ceramic ZrO{sub 2}(MgO), ZrO{sub 2}(Y{sub 2}O{sub 3}) powder was prepared by pressing and subsequent sintering of compacts homologous temperatures ranging from 0.63 to 0.56 during the isothermal holding duration of 1 to 5 hours. The porosity of ceramic samples was from 15 to 80%. The structure of the ceramic materials produced from plasma-sprayed ZrO{sub 2} powder was represented as a system of cell and rod structure elements. Cellular structure formed by stacking hollow powder particles can be easily seen at the images of fracture surfaces of obtained ceramics. There were three types of pores in ceramics: large cellular hollow spaces, small interparticle pores which are not filled with powder particles and the smallest pores in the shells of cells. The cells generally did not have regular shapes. The size of the interior of the cells many times exceeded the thickness of the walls which was a single-layer packing of ZrO{sub 2} grains. A distinctive feature of all deformation diagrams obtained in the experiment was their nonlinearity at low deformations which was described by the parabolic law. It was shown that the observed nonlinear elasticity for low deformation on deformation diagrams is due to mechanical instability of the cellular elements in the ceramic carcass.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Vitrification of Hanford Tank Waste 241-AP-105 in a Continuous Laboratory-Scale Melter

Low-activity waste (LAW) stored in underground tanks on the Hanford site in Washington State is planned to be filtered for solids removal and processed through ion exchange columns for cesium removal at the Low-Activity Waste Pretreatment System facility. These pretreatment steps will allow the waste to be transferred to the Hanford Tank Waste Treatment and Immobilization Plant LAW facility for immobilization into glass. The liquid waste will be combined with glass-forming chemicals (GFCs) to form a waste feed slurry that can be fed to electric melters for vitrification. The process of continuously converting the aqueous feed slurry into a melt is dynamic and includes multiple reactions, degassing, and dissolution processes that depend on heat from the melt below. In this conversion process, waste components are partitioned into one of two streams: glass and off-gas. Processing information and chemical information associated with these waste product streams has been requested by Washington River Protection Solutions for actual tank waste from tank 241-AP-105 (referred to as AP-105). To acquire this type of information, a small-scale melter system was desired that would not require high volumes of input waste or the large resource commitment of a full-scale melter system, while also providing dynamic information that would be difficult to determine from batch reactions in a crucible system. A continuous laboratory-scale melter (CLSM), has been designed to operate with a continuous feeding process, while periodically pouring glass product and collecting off-gas. The CLSM vessel has been sized to collect the relevant process and chemical information from obtainable volumes of AP-105 waste samples. Two CLSMs were constructed: one in a non-radioactive environment for processing waste simulants and another in a fume hood capable of handling radioactive material for processing actual Hanford tank waste. This dual-system setup allowed for comparison between simulated and real tank waste with essentially identical test equipment. AP-105 waste simulant was first tested in the non-radioactive CLSM to determine the processability and desired operating window for the actual tank waste. Rhenium (Re) was added to the simulant to act as a surrogate for technetium-99 ( 99 Tc), a key waste component found in the actual tank waste. The partitioning of Re into the glass and off-gas products during the continuous feeding of simulant was determined, which allowed the Re retention, the mass flow rate of Re out of the CLSM via the glass product with respect to the mass flow rate of Re into the CLSM via the feed slurry, to be calculated. Key processing results and the average Re retention, from the CLSM test run with AP-105 simulant feed slurry are shown in Table ES.1.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Vitrification of Hanford Tank Waste 241-AP-107 in a Continuous Laboratory-Scale Melter

Low-activity waste (LAW) stored in underground tanks on the Hanford Site in Washington State is planned to be filtered for solids removal and processed through ion exchange columns for cesium removal. These pretreatment steps will allow the waste to be transferred to the Hanford Tank Waste Treatment and Immobilization Plant’s LAW Facility for immobilization into glass. The liquid waste will be combined with glass-forming chemicals (GFCs) to form a waste feed slurry that can be fed to electric melters for vitrification. The process of continuously converting the aqueous feed slurry into a melt is dynamic and includes multiple reactions, degassing, and dissolution processes that depend on heat from the melt below. In this conversion process, waste components are partitioned into one of two streams: glass and off-gas. Washington River Protection Solutions has requested processing information and chemical information associated with these waste products for actual waste from Hanford tank 241-AP-107 (referred to herein as AP-107). To acquire this type of information, a small-scale melter system was designed that would not require high volumes of input waste or the large resource commitment of a full-scale melter system, while also providing dynamic information that would be difficult to determine from batch reactions in a crucible system. A continuous laboratory-scale melter (CLSM) has been designed to operate with a continuous feeding process while periodically pouring glass product and collecting off-gas. The CLSM vessel has been sized to collect the relevant process and chemical information from obtainable volumes of AP-107 waste samples. A total 8.6 L of actual AP-107 tank waste were received after filtering for solids removal and ion exchange for cesium removal. This volume of AP-107 waste was mixed with GFCs to form an estimated 11.8 L of melter feed slurry. A mass of 7.01 kg of glass product were poured from the CLSM vessel during 10.07 hours of charging the AP-107 melter feed, indicating that about 15.0 kg of melter feed was vitrified into glass. The CLSM system was also designed with the capability to fully divert the flow of off-gas produced in the CLSM vessel to a sampling line that could capture the volatile species of interest, such as technetium-99 ( 99 Tc). This novel sampling system avoided the difficulties of slipstream sampling and could be activated once the feeding reached a steady state within the CLSM vessel. Off-gas product samples captured via high-efficiency particulate air (HEPA) filters using this method, as well as selected glass product samples were sent to an analytical lab for chemical analysis.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Colloidal Synthesis of Bulk-Bandgap Lead Selenide Nanocrystals

Lead selenide quantum dots (QDs) are low-bandgap IV-VI semiconducting nanomaterials that have been studied for a variety of applications. Their preparation using colloidal methods can create small spherical to larger cubic nanocrystals, with an upper limit of ~17 nm reported to date. Here we describe methods for preparing cubic PbSe nanocrystals over a 20–40 nm size range using a twostep procedure. Specifically, ~10 nm PbSe QDs are generated using the rapid injection method, the products from which are overcoated with additional lead and selenium precursors. The use of two lead reagents were studied; lead oleate resulted in a maximum of 20 nm cubes, while more reactive lead hexyldecanoate resulted in much larger nanomaterials with bulk bandgaps. However, PbSe samples prepared with lead hexyldecanoate also contained agglomerates. Special care must be taken when characterizing larger strained nanomaterials with X-ray powder diffraction, for which the Scherrer equation is inadequate. A more rigorous approach using the Williamson–Hall method provides characterizations that are consistent with electron microscopy analysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2004

The Wide-Field Imaging Interferometry Testbed: Progress and Plans

We describe the technique of wide field mosaic imaging for optical/IR interferometers and present early experimental results from a laboratory instrument designed to validate, experiment with, and refine the technique. A conventional single-detector stellar interferometer operating with narrow bandwidth at center wavelength lambda is limited in its field of view to the primary beam of the individual telescope apertures, or approx. lambda/D(sub tel) radians, where is the telescope diameter. Such a field is too small for many applications; often one wishes to image extended sources. We are developing and testing a technique analogous to the mosaic method employed in millimeter and radio astronomy, but applicable to optical/IR Michelson interferometers, in which beam combination is done in the pupil plane. An N(sub pix) x N(sub pix) detector array placed in the image plane of the interferometer is used to record simultaneously the fringe patterns from many contiguous telescope fields, effectively multiplying the field size by N(sub pix)/2, where the factor 2 allows for Nyquist sampling. This mosaic imaging technique will be especially valuable for far IR and submillimeter interferometric space observatories such as the Space Infrared Interferometric Telescope (SPIRIT) and the Submillimeter Probe of the Evolution of Cosmic Structure (SPECS). SPIRIT and SPECS will be designed to provide sensitive, high angular resolution observations of fields several arcminutes in diameter, and views of the universe complementary to those provided by HST, NGST, and ALMA.

Rinehart, S. A.↗
DOE OSTI2012

The Multi Optical Transition Radiation System

The determination and monitoring of the transverse phase space in ATF2 is crucial in order to meet their performances specifications. Since the beam sizes at the Interaction Point (IP) depend strongly on the aberrations in the Final Focus System (FFS), accurate measurement upstream of the FFS is required to tune the beam sizes at the IP. The beam sizes as well as the emittance are measured in several locations in the beam diagnostic section of the Extraction Line (EXT line) of ATF2. The vertical beam sizes in the diagnostic section are of the order of 10 {mu}m this means that the devices have to image spot sizes as small as 5 {mu}m, with 10% accuracy a 2 {mu}m resolution device is necessary. The ATF2 EXT line is a beam line with low power and low repetition rate that make usable devices using solid targets. In contrast to a ring machine, where an individual bunch can be measured many times as it passes around the ring, the beam size and the emittance measurement in the LC or in the beam lines have to be performed in a single pass. This requires that the wire scan device types (laser or solid) sample across successive bunches within a train, often with an over-estimation of the beam size due to beam position and intensity jitter, and can take up to half a minute to complete the measurement. Although some of these effects could be corrected, as the jitter effect could be subtracted by using the nearby BPMs signals, this can be avoided by using Optical Transition Radiation (OTR) Monitors. These monitors are based on the transition radiation effect, a light cone emitted when the charged particle crosses a metallic interface. This light is emitted in a specular fashion so it can be focused on to a CCD and produces an image of the beam. OTRs are able to take many fast measurements and therefore to measure the emittance with high statistics, giving a low error and a good understanding of the emittance jitter. In this article, simulations of the expected beam sizes and emittance, along with a technical description of the system, its hardware and software implementation are described. Additionally first measurement of the beam size and emittance of the Multi Optical Transition Radiation System located in the Extraction Line of ATF2 are presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

A SUPER-SOLAR METALLICITY FOR STARS WITH HOT ROCKY EXOPLANETS

Host star metallicity provides a measure of the conditions in protoplanetary disks at the time of planet formation. Using a sample of over 20,000 Kepler stars with spectroscopic metallicities from the LAMOST survey, we explore how the exoplanet population depends on host star metallicity as a function of orbital period and planet size. We find that exoplanets with orbital periods less than 10 days are preferentially found around metal-rich stars ([Fe/H] ≃ 0.15 ± 0.05 dex). The occurrence rates of these hot exoplanets increases to ∼30% for super-solar metallicity stars from ∼10% for stars with a sub-solar metallicity. Cooler exoplanets, which reside at longer orbital periods and constitute the bulk of the exoplanet population with an occurrence rate of ≳90%, have host star metallicities consistent with solar. At short orbital periods, P<10 days, the difference in host star metallicity is largest for hot rocky planets (<1.7 R{sub ⊕}), where the metallicity difference is [Fe/H] ≃ 0.25 ± 0.07 dex. The excess of hot rocky planets around metal-rich stars implies they either share a formation mechanism with hot Jupiters, or trace a planet trap at the protoplanetary disk inner edge, which is metallicity dependent. We do not find statistically significant evidence for a previously identified trend that small planets toward the habitable zone are preferentially found around low-metallicity stars. Refuting or confirming this trend requires a larger sample of spectroscopic metallicities.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

Lunar and martian meteorite delivery services

Launch mechanisms for lunar and martian meteorites have been investigated, by integrating physical modeling constraints, geochemical cosmic-ray exposure (CRE) constraints, and petrologic constraints. The potential source region for lunar meteorites is remarkably small compared to the final crater volume. CRE constraints indicate that most launches start at depths of less than or equal to 3.2 m, and cratering theory implies derivation of suitably accelerated objects from a subvolume with diameter only about 0.3 x the final crater diameter. The shallow depth provenance is probably related to shock-wave interference, enhanced by the lunar regolith's extremely low compressional wave velocity. CRE constraints alone imply that four to five separate launch events are represented among the eight well-studied lunar meteorites. Most of the lunar meteorites are regolith breccias, which tend to show only limited compositional diversity within any kilometer-scale region of the Moon. Several others are polymict breccias, which also show relatively subdued compositional diversity, compared to igneous rocks. The observed diversity among these samples in terms of abundances of mare basalt and KREEP, and in Mg/(Mg + Fe) ratio, implies that among eight well-studied lunar meteorites only two potential source craters pairings are plausible: between Asuka-881757 + Y-793169 (most probable) and between Y-793274 + EET875721. Altogether, these eight lunar meteorites apparently represent at least six separate source craters, including three in the past 10(exp 5) years and five in the past 10(exp 6) years. CRE constraints imply that SNC meteorites are launched from systematically greater than lunar meteorites. SNCs are also systematically bigger, and all nine well-studied SNCs are uncommonly young (by martian standards) mafic igneous rocks. Comparison between Viking and Apollo results reveals that rocks the size of common meteorites are remarkably scarce in the martian regolith, probably due to pervasive weathering. A plausible explanation for these trends is that most old, small, and shallow rocks on Mars have been weakened by a two-stage process of brecciation followed by pervasive weathering, to the point where they seldom survive the stresses of spallation off the planet. The scarcity of source-crater pairing among the lunar meteorites implies that these objects can be launched from craters much smaller than previously estimated and tends to support the suggestion of Rabinowitz (1993) that present-day cratering rates for the Earth-Moon region may be higher than previously estimated.

Warren, Paul H.↗
DOE OSTI2015

Grain orientation effects on dynamic strength of FCC multicrystals at low shock pressures: a hydrodynamic instability study

Variability in local dynamic plasticity due to material anisotropy in polycrystalline metals is likely to be important on damage nucleation and growth at low pressures. Hydrodynamic instabilities could be used to study these plasticity effects by correlating measured changes in perturbation amplitudes at free surfaces to local plastic behaviour and grain orientation, but amplitude changes are typically too small to be measured reliably at low pressures using conventional diagnostics. Correlations between strength at low shock pressures and grain orientation were studied in copper (grain size ≈ 800 μm) using the Richtmyer–Meshkov instability with a square-wave surface perturbation (wavelength = 150 μm, amplitude = 5 μm), shocked at 2.7 GPa using symmetric plate impacts. A Plexiglas window was pressed against the peaks of the perturbation, keeping valleys as free surfaces. This produced perturbation amplitude changes much larger than those predicted without the window. Amplitude reductions from 64 to 88% were measured in recovered samples and grains oriented close to $\langle$0 0 1$\rangle$ parallel to the shock had the largest final amplitude, whereas grains with shocks directions close to $\langle$1 0 1$\rangle$ had the lowest. Finite element simulations were performed with elastic-perfectly plastic models to estimate yield strengths leading lead to those final amplitudes. Anisotropic elasticity and these yield strengths were used to calculate the resolved shear stresses at yielding for the two orientations. In conclusion, results are compared with reports on orientation dependence of dynamic yielding in Cu single crystals and the higher values obtained suggest that strength estimations via hydrodynamic instabilities are sensitive to strain hardening and strain rate effects.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Developing quantitative capabilities for a scanning microwave impedance microscope

Currently no instrument exists to quantitatively measure electrical properties (dielectric constant and conductivity) on sub-micron regions, a capability of extreme importance to measure the functioning of sub-micron structures and devices. In particular, such electrical measurements could support the development and manufacture of advanced energy related materials used in technologies such as photovoltaic cells, fuel cells and advanced batteries, thereby increasing performance and/or lowering production costs. The goal of this project is to develop microwave imaging add-on modules and probes capable of quantitatively measuring the electrical properties of small regions of a material using microwaves. These modules for scanning probe microscopes, such as atomic force microscopes, make use of the near-field interaction between the exciting microwaves and a material and can resolve regions 10 nanometers in size (less than a million atoms) with little perturbation of the material. In Phase 1 commercial probes and modified hardware were used to establish the feasibility of using microwave imaging systems to quantify local permittivity and conductivity. Repeatable measurements that vary in a systematic way with electrical parameters were obtained from a variety of samples. In Phase 2 research prototypes of the needed hardware and probes were developed and their performance against test structures and real-world samples was demonstrated. Result of this research project include demonstration of quantification of both permittivity and doping level at precisions up to 10% using multiple technical approaches. The level of performance and ease of use meets market expectations and the technology and protocols researched under this grant are currently being commercialized. Quantitative capabilities of this sort will provide a key capability to energy related technologies, and to a wide variety of semiconductor, biological, and materials science applications. Applications include both materials research in academic and industrial labs, as well as manufacturing applications. In a manufacturing environment the quantitative measurement and imaging capabilities could be used both as metrology for process control and as a tool for failure analysis and yield improvement.

36 MATERIALS SCIENCE↗
NASA NTRS2002

Argus: a new instrument for the measurement of the stratospheric dynamical tracers, N2O and CH4

We describe here a new instrument for the simultaneous, in situ measurement of the stratospheric tracer molecules, nitrous oxide (N2O) and methane (CH4). Argus is unique in its small size making it well suited for limited payload atmospheric research platforms. Argus employs second harmonic spectroscopy using tunable lead-salt diode lasers emitting in the mid-infrared. We first explain the Argus design philosophy followed by detailed descriptions of the instrument's optical, mechanical, and thermal sub-systems. Argus employs an in-flight calibration system providing real time calibrations and tightly constrained uncertainty estimates of the returned data. Data analysis is carried out using non-linear least-squares model fits to the acquired second harmonic spectra. A sampling of Argus data acquired on a recent stratospheric research campaign in the Arctic winter is presented.

Methane/analysis↗
NASA NTRS2012

Herschel Discovery of a New class of Cold, Faint Debris Discs

We present Herschel PACS 100 and 160 micron observations of the solar-type stars alpha Men, HD 88230 and HD 210277, which form part of the FGK stars sample of the Herschel Open Time Key Programme (OTKP) DUNES (DUst around NEarby Stars). Our observations show small infrared excesses at 160 micron for all three stars. HD 210277 also shows a small excess at 100 micron. while the 100 micron fluxes of a Men and HD 88230 agree with the stellar photospheric predictions. We attribute these infrared excesses to a new class of cold, faint debris discs. alpha Men and HD 88230 are spatially resolved in the PACS 160 micron images, while HD 210277 is point-like at that wavelength. The projected linear sizes of the extended emission lie in the range from approximately 115 to <= 250 AU. The estimated black body temperatures from the 100 and 160 micron fluxes are approximately < 22 K, while the fractional luminosity of the cold dust is L(dust)/ L(star) approximates 10(exp -6), close to the luminosity of the Solar-System's Kuiper belt. These debris discs are the coldest and faintest discs discovered so far around mature stars and cannot easily be explained by invoking "classical" debris disc models.

Eiroa, C.↗
NASA NTRS2011

Herschel Discovery of a New Class of Cold, Faint Debris Discs

We present Herschel PACS 100 and 160 micron observations of the solar-type stars alpha Men, HD 88230 and HD 210277, which form part of the FGK stars sample of the Herschel Open Time Key Programme (OTKP) DUNES (DUst around NEarby Stars). Our observations show small infrared excesses at 160 m for all three stars. HD 210277 also shows a small excess at 100 micron, while the 100 micron fluxes of alpha Men and HD 88230 agree with the stellar photospheric predictions. We attribute these infrared excesses to a new class of cold, faint debris discs. alpha Men and HD 88230 are spatially resolved in the PACS 160 m images, while HD 210277 is point-like at that wavelength. The projected linear sizes of the extended emission lie in the range from approx 115 to <= 250 AU. The estimated black body temperatures from the 100 and 160 micron fluxes are approx < 22 K, while the fractional luminosity of the cold dust is L(sub dust) / L(*) approx 10 (exp 6) close to the luminosity of the Solar-System's Kuiper belt. These debris discs are the coldest and faintest discs discovered so far around mature stars and cannot easily be explained by invoking "classical" debris disc models.

Eiroal, C.↗
NASA NTRS2000

Creep Properties of NiAl-1Hf Single Crystals Re-Investigated

NiAl-1Hf single crystals have been shown to be quite strong at 1027 C, with strength levels approaching those of advanced Ni-based superalloys. Initial testing, however, indicated that the properties might not be reproducible. Study of the 1027 C creep behavior of four different NiAl-1Hf single-crystal ingots subjected to several different heat treatments indicated that strength lies in a narrow band. Thus, we concluded that the mechanical properties are reproducible. Recent investigations of the intermetallic NiAl have confirmed that minor alloying additions combined with single-crystal growth technology can produce elevated temperature strength levels approaching those of Ni-based superalloys. For example, General Electric alloy AFN 12 {Ni-48.5(at.%) Al-0.5Hf-1Ti-0.05Ga} has a creep rupture strength equivalent to Rene 80 combined with a approximately 30-percent lower density, a fourfold improvement in thermal conductivity, and the ability to form a self-protective alumina scale in aggressive environments. Although the compositions of strong NiAl single crystals are relatively simple, the microstructures are complex and vary with the heat treatment and with small ingot-toingot variations in the alloy chemistry. In addition, initial testing suggested a strong dependence between microstructure and creep strength. If these observations were true, the ability to utilize NiAl single-crystal rotating components in turbine machinery could be severely limited. To investigate the possible limitations in the creep response of high-strength NiAl single crystals, the NASA Glenn Research Center at Lewis Field initiated an in depth investigation of the effect of heat treatment on the microstructure and subsequent 1027 C creep behavior of [001]-oriented NiAl-1Hf with a nominal chemistry of Ni-47.5Al-1Hf-0.5Si. This alloy was selected since four ingots, grown over a number of years and possessing slightly different compositions, were available for study. Specimens taken from the ingots were subjected to several heat treatment schedules, examined by transmission electron microscopy, and tested in both compression and tension. An example of the microstructure found in a [001]-oriented NiAl-1Hf specimen after a solution treatment at 1317 C for 50 hr followed by air cooling is illustrated in the image on the left, where the NiAl matrix contains a uniform distribution of nanometer-scale Gphase (Ni16Hf6Si7) precipitates. Other heat treating schedules produced microstructures with nanometer-sized G-phase cubes and plates or, in an extreme case, produced a microstructure with all the G-phase converted to Heusler (Ni2AlHf) particles. The results of 1027 C creep strength and strain rate testing are illustrated which summarizes data from tensile and compressive testing of samples cut from all four NiAl-1Hf ingots and subjected to a variety of heat treatment schedules. With one exception, all the strength values lie in a narrow band that spans six orders of magnitude in strain rate. The only factor that produced results outside of this band was the heat treatment schedule that dissolved all the G-phase and replaced it with Heusler precipitates. The results portrayed in this figure lead to the important practical conclusion that the elevated-temperature creep properties of NiAl-1Hf single crystals are reproducible and are not affected by small variations in alloy chemistry from ingot to ingot or by different initial distributions of G-phase in the heat-treated alloy. The only variable in this study that produced a significant and delerious effect on mechanical strength was a post-solution heat treatment that lead to the complete disappearance of the G-phase in favor of Heusler precipitates.

Whittenberger, J. Daniel↗