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At least 1,045 records · Page 58

All sources NASA NTRS DOE OSTI

DOE OSTI2016

Aerosol detection efficiency in inductively coupled plasma mass spectrometry

We used an electrostatic size classification technique to segregate particles of known composition prior to being injected into an inductively coupled plasma mass spectrometer (ICP-MS). Moreover, we counted size-segregated particles with a condensation nuclei counter as well as sampled with an ICP-MS. By injecting particles of known size, composition, and aerosol concentration into the ICP-MS, efficiencies of the order of magnitude aerosol detection were calculated, and the particle size dependencies for volatile and refractory species were quantified. Similar to laser ablation ICP-MS, aerosol detection efficiency was defined as the rate at which atoms were detected in the ICP-MS normalized by the rate at which atoms were injected in the form of particles. This method adds valuable insight into the development of technologies like laser ablation ICP-MS where aerosol particles (of relatively unknown size and gas concentration) are generated during ablation and then transported into the plasma of an ICP-MS. In this study, we characterized aerosol detection efficiencies of volatile species gold and silver along with refractory species aluminum oxide, cerium oxide, and yttrium oxide. Aerosols were generated with electrical mobility diameters ranging from 100 to 1000 nm. In general, it was observed that refractory species had lower aerosol detection efficiencies than volatile species, and there were strong dependencies on particle size and plasma torch residence time. Volatile species showed a distinct transition point at which aerosol detection efficiency began decreasing with increasing particle size. This critical diameter indicated the largest particle size for which complete particle detection should be expected and agreed with theories published in other works. Aerosol detection efficiencies also displayed power law dependencies on particle size. Aerosol detection efficiencies ranged from 10 -5 to 10 -11 . Free molecular heat and mass transfer theory was applied, but evaporative phenomena were not sufficient to explain the dependence of aerosol detection on particle diameter. Additional work is needed to correlate experimental data with theory for metal-oxides where thermodynamic property data are sparse relative to pure elements. Finally, when matrix effects and the diffusion of ions inside the plasma were considered, mass loading was concluded to have had an effect on the dependence of detection efficiency on particle diameter.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Grain refinement in heavy rare earth element-free sintered Nd–Fe–B magnets by addition of a small amount of molybdenum

We employed a modified refractory-metal-addition method to achieve higher coercivity and remanence in heavy rare earth element (HREE)-free Nd–Fe–B sintered magnets. This process involved inducing the formation of a homogeneous secondary phase at the grain boundaries during sintering, making it possible to control the intergrain diffusion by adding small amounts of Mo, a refractory metal. To control the microstructure of the secondary phase effectively, a metal organic compound of the refractory metal was coated on the surfaces of the particles of an HREE-free Nd–Fe–B powder. The average grain size after this process was 5.60 μm, which was approximately 1.8 μm smaller than that of the HREE-free sintered Nd–Fe–B magnets (7.4 μm). The coercivity of the magnets prepared through this process could be increased from 11.88 kOe to 13.91 kOe without decreasing their remanence.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

NEUTRAL Na IN COMETARY TAILS AS A REMNANT OF EARLY AQUEOUS ALTERATION

Observations of comet C/1995O1 Hale-Bopp during the spring of 1997 led to the discovery of a neutral sodium tail whose origin is still not clearly understood. Here, we propose an interpretation for the origin of this sodium tail, which is based upon chemical grounds. Starting from Na{sup +} trapped chemically during the condensation of refractory material in the protosolar nebula to its incorporation in the building blocks of comets and its transfer from refractory to volatile phases in the nucleus due to aqueous alteration, we follow the chemical path of sodium until its transformation into a neutral atom when released from the sublimating cometary ice. We propose that two Na reservoirs should coexist in a comet: one coming from the refractory dust, the other one from the icy matrix. Their relative importance would depend on the extent of the zone where liquid water formed within the nucleus and the time during which water remained liquid, thus favoring the Na{sup +} exchange between rocks and ice. These two key parameters would in turn strongly depend on the thermal history of the comet (amounts of radiogenic nuclides, orbital history, etc.). If our model is correct, the detection of Na originating from water ice would be a testimonial of the past aqueous alteration of the comet or its parent body.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Crystallization In High Level Waste (HLW) Glass Melters: Operational Experience From The Savannah River Site

processing strategy for the Hanford Tank Waste Treatment and Immobilization Plant (WTP). The basis of this alternative approach is an empirical model predicting the crystal accumulation in the WTP glass discharge riser and melter bottom as a function of glass composition, time, and temperature. When coupled with an associated operating limit (e.g., the maximum tolerable thickness of an accumulated layer of crystals), this model could then be integrated into the process control algorithms to formulate crystal tolerant high level waste (HLW) glasses targeting higher waste loadings while still meeting process related limits and melter lifetime expectancies. This report provides a review of the scaled melter testing that was completed in support of the Defense Waste Processing Facility (DWPF) melter. Testing with scaled melters provided the data to define the DWPF operating limits to avoid bulk (volume) crystallization in the un-agitated DWPF melter and provided the data to distinguish between spinels generated by K-3 refractory corrosion versus spinels that precipitated from the HLW glass melt pool. This report includes a review of the crystallization observed with the scaled melters and the full scale DWPF melters (DWPF Melter 1 and DWPF Melter 2). Examples of actual DWPF melter attainment with Melter 2 are given. The intent is to provide an overview of lessons learned, including some example data, that can be used to advance the development and implementation of an empirical model and operating limit for crystal accumulation for WTP. Operation of the first and second (current) DWPF melters has demonstrated that the strategy of using a liquidus temperature predictive model combined with a 100 °C offset from the normal melter operating temperature of 1150 °C (i.e., the predicted liquidus temperature (TL) of the glass must be 1050 °C or less) has been successful in preventing any detrimental accumulation of spinel in the DWPF melt pool, and spinel has not been observed in any of the pour stream glass samples. Spinel was observed at the bottom of DWPF Melter 1 as a result of K-3 refractory corrosion. Issues have occurred with accumulation of spinel in the pour spout during periods of operation at higher waste loadings. Given that both DWPF melters were or have been in operation for greater than 8 years, the service life of the melters has far exceeded design expectations. It is possible that the DWPF liquidus temperature approach is conservative, in that it may be possible to successfully operate the melter with a small degree of allowable crystallization in the glass. This could be a viable approach to increasing waste loading in the glass assuming that the crystals are suspended in the melt and swept out through the riser and pour spout. Additional study is needed, and development work for WTP might be leveraged to support a different operating limit for the DWPF. Several recommendations are made regarding considerations that need to be included as part of the WTP crystal tolerant strategy based on the DWPF development work and operational data reviewed here. These include: Identify and consider the impacts of potential heat sinks in the WTP melter and glass pouring system; Consider the contributions of refractory corrosion products, which may serve to nucleate additional crystals leading to further accumulation; Consider volatilization of components from the melt (e.g., boron, alkali, halides, etc.) and determine their impacts on glass crystallization behavior; Evaluate the impacts of glass REDuction/OXidation (REDOX) conditions and the distribution of temperature within the WTP melt pool and melter pour chamber on crystal accumulation rate; Consider the impact of precipitated crystals on glass viscosity; Consider the impact of an accumulated crystalline layer on thermal convection currents and bubbler effectiveness within the melt pool; Evaluate the impact of spinel accumulation on Joule heating of the WTP melt pool; and Include noble metals in glass melt experiments because of their potential to act as nucleation sites for spinel crystallization.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2016

Arctic Black Carbon Loading and Profile Using the Single-Particle Soot Photometer (SP2) Field Campaign Report

One of the major issues confronting aerosol climate simulations of the Arctic and Antarctic cryospheres is the lack of detailed data on the vertical and spatial distribution of aerosols with which to test these models. This is due, in part, to the inherent difficulty of conducting such measurements in extreme environments. However given the pronounced sensitivity of the polar regions to radiative balance perturbations, it is incumbent upon our community to better understand and quantify these perturbations, and their unique feedbacks, so that robust model predictions of this region can be realized. One class of under-measured radiative forcing agents in the polar region is the absorbing aerosol—black carbon and brown carbon. Black carbon (BC; also referred to as light-absorbing carbon [LAC], refractory black carbon [rBC], and soot) is second only to CO2 as a positive forcing agent. Roughly 60% of BC emissions can be attributed to anthropogenic sources (fossil fuel combustion and open-pit cooking), with the remaining fraction being due to biomass burning. Brown carbon (BrC), a major component of biomass burning, collectively refers to non-BC carbonaceous aerosols that typically possess minimal light absorption at visible wavelengths but exhibit pronounced light absorption in the near-ultraviolet (UV) spectrum. Both species can be sourced locally or be remotely transported to the Arctic region and are expected to perturb the radiative balance. The work conducted in this field campaign addresses one of the more glaring deficiencies currently limiting improved quantification of the impact of BC radiative forcing in the cryosphere: the paucity of data on the vertical and spatial distributions of BC. By expanding the Gulfstream aircraft (G-1) payload for the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility-sponsored ACME-V campaign to include the Single-Particle Soot Photometer (SP2)) and leveraging the ACME-V campaign’s deployment within the Arctic Circle during the summer of 2015 (Deadhorse, Alaska [70° 12' 20" N, 148° 30' 42" W]), the truly unique opportunity presented itself to acquire profile data on BC loading at little additional cost. Since the SP2 is a particle-resolved measurement, the resulting data set provides refractory black carbon (rBC) mass loadings, size and mass distributions, and rBC-containing particle mixing state, all of which are expected to readily find value in the modeling community. As part of the ACME-V (http://www.arm.gov/campaigns/aaf2014armacmev) campaign, CO, CO2, and CH4 were also measured, providing the unique opportunity for carbon closure. We will also work closely with modelers who require such data and expect this collaboration will lead directly to a better understanding of the climate impacts of BC in the Arctic. The primary measurement objective was to acquire airborne data on the vertical and spatial distributions of refractory black carbon (rBC) loading, size and mass distribution, and particle mixing state. The primary scientific objective was to provide a targeted data set of rBC particle distributions to better understand and constrain the impact of black carbon radiative forcing in the cryosphere. The SP2-based data set during this campaign is available in the DOE-ARM archive (http://www.arm.gov/campaigns/aaf2015abclp).

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2015

Improved High-Alkali Low-Activity Waste Formulations (Final Report, Rev. 0)

High waste loading LAW glass formulations developed for ORP by VSL and EnergySolutions contain about 0.5 wt% Cr 2 O 3 as an additive to control K-3 refractory corrosion by the glass. However, addition of Cr 2 O 3 also increases the tendency for formation of sulfate/chromate secondary phases and therefore such additions become increasingly undesirable as the ratio of sulfate to sodium in the LAW stream increases. Therefore, for such LAW streams, removal of Cr 2 O 3 as an additive could potentially increase sulfate loading in the LAW glasses, provided that K-3 refractory corrosion can be controlled by other means. The present work was directed towards developing LAW glasses with high alkali concentrations (> 24 wt%) without the use of Cr 2 O 3 as an additive. The results of the work clearly show that LAW glasses with high alkali concentrations that meet all of the WTP requirements, including K-3 refractory corrosion, can be formulated without the use of Cr 2 O 3 as an additive.

Muller, Isabelle S.↗

DOE OSTI2022

Cooperative Research and Development Agreement between National Energy Technology Laboratory and ATI Specialty Alloys & Components (Abstract)

The National Energy Technology Laboratory (NETL) and ATI will collaborate on improving the computational capabilities for predicting elevated temperature strength and phase stability for refractory-based alloys. Increasing the efficiency and decreasing harmful emissions from turbines for power generation and aviation applications will require materials beyond superalloys to accommodate higher turbine combustion and inlet temperatures. Higher strength refractory alloys are a potential enabling technology for these highly efficient, low emission, advanced turbines. The development of higher strength refractory alloys will be aided by improved and validated computational models to predict elevated temperature strength.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Inhibited Surface Diffusion in Nanoporous Multi-Principal Element Alloy Thin Films Prepared by Vacuum Thermal Dealloying

Nanoporous structures with 3D interconnected networks are traditionally made by dealloying a binary precursor. Certain approaches for fabricating these materials have been applied to refractory multi-principal element alloys (RMPEAs), which can be suitable candidates for high-temperature applications. In this study, nanoporous refractory multi-principal element alloys (np-RMPEAs) were fabricated from magnesium-based thin films (VMoNbTaMg) that had been prepared by magnetron sputtering. Vacuum thermal dealloying (VTD), which involves sublimation of a higher vapor pressure element, is a novel technique for synthesizing nanoporous refractory elements that are prone to oxidation. When VMoNbTaMg was heated under vacuum, a nanoporous structure was created by the sublimation of the highest vapor pressure element (Mg). X-ray photoelectron spectroscopy depth profiling indicated significantly less ligament oxidation during VTD as compared to traditional dealloying methods. Furthermore, np-RMPEAs exhibited outstanding stability against coarsening, retaining smaller ligaments (~25 nm) at elevated temperature (700 °C) for a prolonged period (48 h).

Das Gupta, Tibra (ORCID:0000000317103025)↗

NASA NTRS1969

Study of high temperature bearing materials

Experimental investigation identifies materials suitable for use in potassium lubricated turbo-generator journal bearing and shaft applications at high temperatures. Attention is given to nonrefractory metals and alloys, refractory metals and alloys, Fe-Ni-Co bonded carbides, refractory compounds, and refractory metal bonded carbides.

Frank, R. G.↗

NASA NTRS1968

Brazing alloy Patent

Brazing alloy adapted for brazing corrosion resistant steel to refractory metals, also for brazing refractory metals to other refractory metals

Smith, D.↗

NASA NTRS1974

Effects of composition and testing conditions on oxidation behavior of four cast commercial nickel-base superalloys

Four cast nickel-base superalloys were oxidized at 1000 and 1100 C for times up to 100 hr in static air and a Mach 1 gas stream. The oxidation resistance was judged by weight change, metal thickness loss, depletion-zone formation, and oxide formation and morphology. The alloys which formed mostly nickel aluminate (NiAl2O4) and aluminum oxide (Al2O3) (B-1900, VIA, and to a lesser extent 713C) were more oxidation resistant. Poorer oxidation resistance was associated with the appearance of chromium sesquioxide (Cr2O3) and chromite spinel (738X). Refractory metal content had little effect on oxidation resistance. Refractory metals appeared in the scale as tapiolite (NiM2O6, where M represents the refractory metal). Thermal cycling in static air appeared to supply sufficient data for the evaluation of oxidation resistance, especially for alloys which form oxides of low volatility. For alloys of higher chromium levels with high propensities toward forming a chromium-bearing scale of higher volatility, testing under conditions of high gas velocity is necessary to assess fully the behavior of the alloy.

Lowell, C. E.↗

NASA NTRS1974

Chemical fractionation in the solar nebula

The sequence of condensation of minerals from a cooling gas of solar composition has been calculated from thermodynamic data assuming complete chemical equilibrium is maintained. The results suggest that the Ca-Al-rich inclusions in Allende and other carbonaceous chondrites are aggregates of the highest temperature condensates. Complete condensation of these elements is followed 100 deg later, by the onset of the crystallization of nickel-iron, forsterite and enstatite. Transport of Ca-Al-rich refractory condensates from one part of the nebula to another before the condensation of these lower-temperature phases may have been responsible for the refractory element fractionations between the different classes of chondrites and possibly for the inferred refractory element enrichment of the moon.

Grossman, L.↗

NASA NTRS1976

Method of making an apertured casting

An apertured casting is made by first forming a duplicate in the shape of the finished casting, positioning refractory metal bodies such as wires in the duplicate at points corresponding to apertures or passageways in finished products, forming a ceramic coating on the duplicate, removing the duplicate material, firing the ceramic in a vacuum or inert atmosphere, vacuum casting the metal in the ceramic form, removing the ceramic form, heating the cast object in an atmospheric furnace to oxidize the refractory metal bodies and then leaching the oxidized refractory bodies from the casting with a molten caustic agent or acid solution.

Terray, A.↗

NASA NTRS1977

Chemical fractionation in the solar nebula

The sequence of condensation of minerals from a cooling gas of solar composition has been calculated from thermodynamic data over the pressure range 0.001-0.00001 atm, assuming that complete chemical equilibrium is maintained. The results suggest that the Ca-Al-rich inclusions Allende and other carbonaceous chondrites are aggregates of the highest temperature condensates. Complete condensation of these elements is followed, 100 deg later, by the onset of the crystallization of nickel-iron, forsterite and enstatite. Transport of Ca-Al-rich refractory condensates from one part of the nebula to another before the condensation of these lower-temperature phases may have been responsible for the refractory element fractionations between the different classes of chondrites and possibly for the inferred refractory element enrichment of the Moon. The temperature gap between the condensation temperatures of nickel-iron and forsterite increases with increasing total pressure. Because pressure and temperature probably increased with decreasing heliocentric distance in the solar nebula, Mercury may have accreted from a condensate assemblage having a higher metal/silicate ratio than Venus or Earth which may, in turn, have formed from less oxidized material than Mars.

Grossman, L.↗

NASA NTRS1977

High temperature materials for space power systems

Future space power systems will largely be nuclear-driven or solar-driven Brayton cycle or thermionic converter systems. This paper presents some of the limited data available on the long-time properties of the superalloys and refractory metals that will have to be used in large parts of these systems. These data include vaporization rates of pure metals as a function of temperature, extrapolated stress for 1 percent creep in 10 years for selected superalloys, vacuum creep behavior of Mar M-509 at 900 C and 110 MN/sq m, extrapolated stress for 1 percent creep in 10 years for refractory alloys, and approximate useful temperature ranges for superalloys and refractory metals.

Gangler, J. J.↗

NASA NTRS1979

Adherence of sputtered titanium carbides

Sputtered coatings of the refractory metal carbides are of great interest for applications where hard wear-resistant materials are desired. The usefulness of sputtered refractory carbides is often limited, in practice, by spalling or interfacial separation. In this work improvements in the adherence of refractory carbides on iron, nickel and titanium based alloys were obtained by using oxidation, reactive sputtering or sputtered interlayers to alter the coating-substrate interfacial region. X-ray photoelectron spectroscopy and argon ion etching were used to characterize the interfacial regions, and an attempt was made to correlate adherence as measured in wear tests with the chemical nature of the interface.

Brainard, W. A.↗

NASA NTRS1979

Trace elements in the Allende meteorite. IV - Amoeboid olivine aggregates

INAA data for Ca, Sc, Hf, La, Ce, Sm, Eu, Tb, Yb, Lu, Os, Ir, Ru, Na, Cl, Br, Fe, Mn, Cr, Co, Au, As, and Sb are presented for ten amoeboid aggregates from the Allende meteorite. Only one lacks olivine. Seven of the remainder, as a group, have cosmic proportions of refractory lithophile and siderophile elements and appear to have formed when coarse-grained Allende inclusion material underwent partial reaction with a low-temperature nebular gas and mixture with FeO-rich olivine. The other two have highly fractionated abundances of refractory elements relative to one another compared to Cl chondrites, including Group II REE patterns, and probably formed by the mixing of fine-grained Allende inclusion material with FeO-rich olivine. Non-refractory siderophile components are also different in composition in each type of amoeboid olivine aggregate.

Grossman, L.↗

NASA NTRS1984

Inorganic composites for space applications

The development of inorganic composite materials for space applications is reviewed. The composites do not contain any organic materials, and therefore, are not subject to degradation by ultraviolet radiation, volatilization of constituents, or embrittlement at low temperatures. The composites consist of glass, glass/ceramics or ceramic matrices, reinforced by refractory whiskers or fibers. Such composites have the low thermal expansion, refractories, chemical stability and other desirable properties usually associated with the matrix materials. The composites also have a degree of toughness which is extraordinary for refractory inorganic materials.

Malmendier, J. W.↗