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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Effect of non-axisymmetric arc on microstructure, texture and properties of variable polarity plasma arc welded 5A06 Al alloy

Highlights: • Variable polarity plasma arc welding of 5A06 Al alloy was carried out under the condition of non-axisymmetric arc. • Deformation bands formed in the weld joint were due to microstructural inhomogeneities. • Tensile fracture occurred along the deformation bands in the TZ/HAZ fusion boundary on the side of “lower arc”. • The weld zones are harder than the BM due to dislocation sub-structure, deformation bands and ultrafine subgrain. - Abstract: Microstructure, texture and mechanical properties in the weld joint of variable polarity plasma arc welding of 5A06 Al alloy under the condition of non-axisymmetric arc have been investigated. The weld joint are characterized by elongated structure in the base material (BM), the heat affected zone (HAZ) and the transition zone (TZ) and equiaxed structure in the fusion zone (FZ). Microstructure of the weld joint is asymmetrical and inhomogeneous leading to deformation bands. Deformation texture and recrystallization texture were developed in the weld zones. The FZ center was dynamic recrystallized due to severe deformation. Materials in the TZ have undergone dynamic recovery. The weld zones are harder than the BM due to dislocation sub-structure, deformation bands and ultrafine subgrains. Microhardness distribution was homogeneous in the regions without deformation bands. Tensile fracture occurred along the deformation bands on the side of “lower arc” exhibiting ductile fracture, while the BM is less ductile.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Arc-Fault Primer: Numerical, Analytical, and Experimental Characteristics of Initiation and Sustainment of Arc Plasmas (DRAFT)

While arc-faults are rare in electrical installations, many documented events have led to fires that resulted in significant damage to energy-generation, commercial and residential systems, as well as surrounding structures, in both the United States and abroad. Arc-plasma discharges arise over time due to a variety of reliability issues related to cable material degradation, electrical and mechanical stresses or acute conductive wiring dislocations. These may lead to discontinuity between energized conductors, facilitating arcing events and fires. Arc-flash events rapidly release significant energy in a localized volume, where the electric arc experiences a reduction in resistance. This facilitates a reduction in electrical resistance as the arc temperature and pressure can increase rapidly. Strong pressure waves, electromagnetic interference (EMI), and intense light from an arc pose a threat to electrical worker safety and system equipment. This arc-fault primer provides basic fundamental insight into arc-fault plasma discharges, and an overview of direct current (DC) and alternating current (AC) arc-fault phenomena. This primer also covers pressure waves and EMI arc-fault hazard analyses related to incident energy prediction and potential damage analysis. Mitigation strategies are also discussed related to engineering design and employment of protective devices including arc-fault circuit interrupters (AFCIs). Best practices related to worker safety are also covered, especially as they pertain to electrical codes and standards, particularly Institute of Electrical and Electronics Engineers (IEEE) 1584 and National Fire Protection Agency (NFPA) 70E. Throughout the primer various modelling and test capabilities at Sandia National Laboratories are also covered, especially as they relate to novel methods of arc-fault/arc-flash characterization and mitigation approaches. Herein, this work describes methods for producing and characterizing controlled, sustained arcs at atmospheric pressures as well as methods for mitigation with novel materials.

42 ENGINEERING↗
DOE OSTI2017

Generation of High Charge State Metal Ions in an Arc Plasma

Generation of high charge state metal ions in arc plasma is investigated and methods of elevation of the average ion charge state are analyzed. To realize multiple ionization of the arc plasma, a strong magnetic field in the arc cathode area, an ark current spike, an injection of a high-current electron beam or a high-power microwave radiation flow into the plasma, and a creation of a short high-current arc are realized. For each method, the main features are considered and the maximum ion charge states are determined.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Peculiarities of Magnetic Behavior of CuO Nanoparticles Produced by Plasma-Arc Synthesis in a Wide Temperature Range

Copper oxide nanoparticles, produced by direct plasmochemical synthesis in a low-pressure arc discharge plasma, show a wide variety of magnetic properties depending on the strength of the external magnetic field and the temperature. At low strength of the field and throughout the studied temperature range, the ferromagnetic state dominates. This state is caused by disordering of the spins on the surface of the nanoparticles. At high strength of the field and under temperatures of less than 200 K, nanoparticles exhibit a paramagnetic state due to the spin-glass behavior of copper atoms. At high strength of the field (more than 3 kOe) and under temperatures of above 300 K, the diamagnetic state of nanoparticles is observed, due to local eddy currents caused by oxygen vacancies. The temperature of antiferromagnetic ordering under study is significantly lowered (down to ∼ 100 K).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Reconfiguration of an Electrothermal-Arc Plasma Source for In Situ PMI Studies

An electrothermal-arc plasma source (ET-Arc) has been developed to produce transient plasma heat and particle fluxes similar to those produced by edge localized modes onto divertor plasma-facing components in tokamaks. The ET-Arc utilizes a capacitive discharge to send current through a 4-mm-diameter, 9-cm-long capillary source liner. The liner material is ablated to form a high-velocity plasma jet that impacts the target downstream. With the current discharge circuit configuration, pulse lengths are 1 to 2 ms in duration and deliver heat fluxes of 0.25 to 2.1 GW m-2. The plasma was previously characterized with optical emission spectroscopy (OES) on helium emission lines. The He I line ratios were interpreted with collisional radiative analysis to calculate ne and Te. The electron temperature and electron density ranged from Te = 1 to 5 eV and ne = 1022 to 1028 electrons/m3, respectively.

Lindquist, Elizabeth G.↗
DOE OSTI2019

Deoxidation of Ti Melt by Newly Developed Two-Step Plasma Arc Melting Process Using Hydrogen

A two-step plasma arc melting process, comprising a first step under Ar-30 pct H{sub 2} gas flow and the second step under Ar gas flow, has been newly developed for the deoxidation of Ti melts. The oxygen content after this process depended on the depth probed in the Ti melt. Decrease in the oxygen content from 1.5 to 0.7 mass pct in the surface region of the Ti melt occurred in the second step.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Final Technical Report: Plasma Arc Gasification Based Rare Earth Element Recovery from Coal Fly Ash

Southern Research, as the primary awardee, with sub-awardees ArcSec Technologies, LLC (ArcSec) and Reaction Engineering International (REI) have investigated a plasma arc based thermal process intended to concentrate rare earth elements (REE) from coal fly ash. Successful demonstration of the technology would contribute to the effort for realizing a competitive, domestic REE value chain thereby reducing U.S. dependence on foreign supply, maintaining national security interests, and creating opportunities for economic growth. The originally proposed concept included two technology options – 1) a smelting process and 2) a smelting plus vaporization and condensation process. For both options, coal fly ash would be smelted in a plasma arc heated furnace under reducing conditions to separate ash into molten slag and reduced metal (primarily iron) phases. During smelting, it was expected that the REE would also be reduced to metals and partition mostly to the iron phase. During the first year of work, sample coal ash feedstocks were acquired and characterized, feasibility of the smelting process was evaluated in bench-scale experiments, and the vaporization/condensation process was investigated through equilibrium and CFD modeling studies. From the feedstock characterization, REE content for the coal ash samples obtained was measured to be in the range of 302 – 1219 ppm with average at 537 ppm. Though it was successfully demonstrated that ash could be separated into slag and metal phases, the bench-scale experiments were only marginally successful at collecting REE in the metal phase. Producing REE concentrates near the DOE goal of 2%, however, has not been achieved. From the modeling studies, the vaporization/condensation process was predicted to be effective for separating individual REE and producing enriched metal fractions with total REE content higher than 2%, provided the smelting process performed as intended. Supplemental smelting experiments and thermodynamic modeling studies, conducted during the second year of work, indicated a number of technical modifications that could lead to producing higher REE concentrates from coal ash. The strategy shifted to reducing as much of the ash oxides to metals as possible, leaving the REE more concentrated in the remaining slag. Results from later experiments based on the modified approach showed improvements in REE recovery and concentration levels in smelted products. SEM-EDS analyses on product specimens showed agglomerations of reduced metal REE crystals at much larger length-scales as compared to REE content in raw ash.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2018

Microstructure and Mechanical Properties of Al-Mg-Sc-Zr Alloy Variable Polarity Plasma Arc Welding Joint

Al-Mg-Sc-Zr alloy plates were welded by variable polarity plasma arc welding (VPPAW) with Sc-containing filler wire. The microstructure and mechanical properties were investigated. Results show that the weld zone and heat-affected zone (HAZ) are narrow due to the high concentrated heat input of VPPAW. Primary Al{sub 3}(Sc,Zr) particles are nice nucleating sites for α-Al, which can significantly refine the grains of α-Al, helping the weld zone maintain an outstanding strength. The unmelted Al{sub 3}(Sc,Zr) precipitates of the base metal aggregated near the fusion boundary result in the formation of a fine equiaxed grains zone, which improves the bonding degree between the weld zone and the base metal. The Al{sub 3}(Sc,Zr) precipitates in the HAZ have excellent inhibition effect on recrystallization. According to the observed microhardness distribution and microstructure characteristics, the microstructure model of welded joint is obtained. The fractured position of welded joint locates in the weld zone. The tensile strength of the welded joint without reinforcing rib is 330 MPa. The welding coefficient reaches 74%.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A 6 MW/m 2 High Heat Flux Testing Facility of Irradiated Materials Using Infrared Plasma-Arc Lamps

Assessing the effect of neutron irradiation of plasma-facing materials has been challenging due to both the technical and radiological challenges involved. In an effort to address the radiological challenges, a facility was developed to conduct high heat flux testing (HHFT) of inherently small samples of neutron-irradiated materials. A new line-focus reflector was designed and fabricated at Oak Ridge National Laboratory for a plasma-arc lamp (PAL) to attain a source heat flux of 12 MW/m 2 . The new reflector was fabricated with two ports for monitoring specimen condition during HHFT. At the same operational conditions for PAL, the absorbed heat flux in tungsten was increased from 1.39 MW/m 2 with the uniform irradiance reflector to 5.12 MW/m 2 for the line-focus reflector. This fourfold increase in the heat flux, at the same PAL electrode lifetimes, enabled cost-effective facility operation for a high number of cyclic high heat flux tests. Specifically, the test section is confined to a hemispherical dome, and specimens are bolted directly to a water-cooled copper alloy rod. Temperature measurement in the PAL facility was a main challenge due to a limited line of sight. For the first time in a PAL facility operating at high heat fluxes, the specimen surface temperature was directly measured during HHFT with a pyrometer. Finally, the HHFT data, which were obtained in this upgraded PAL facility, demonstrated the facility readiness for irradiated materials.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Mechanism of Desulfurization from Liquid Iron by Hydrogen Plasma Arc Melting

In this study, desulfurization from liquid iron by Ar and (10 to 40 pct)H{sub 2} + Ar plasma arc melting (HPAM) was examined. The experimental results show that the rate of desulfurization increases as hydrogen is added proportionally to plasma gas. The thermodynamic analysis suggests that the interaction of activated atomic hydrogen and dissolved sulfur in liquid iron, [S]+2H=H{sub 2}S, could be taking place. The kinetic analysis confirms that the desulfurization from liquid iron obeys a first-order rate law.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Investigation of flow regimes in arc plasma–gas interactions using a two-temperature arc in crossflow model

The perpendicular impingement of a gas stream on an electric arc, a configuration known as the arc in crossflow, is of primary relevance in the study of plasma-gas interactions, as well as in industrial applications such as circuit breakers and wire-arc spraying. The flow dynamics in the arc in crossflow are the result of coupled fluid-thermal-electromagnetic phenomena accompanied by large property gradients, which can produce significant deviations from Local Thermodynamic Equilibrium (LTE) among electrons and gas species. These characteristics can lead to the establishment of distinct flow regimes depending on the relative values of the controlling parameters of the system, such as inflow velocity, arc current, and inter-electrode spacing. A two-temperature non-LTE (NLTE) model is used to investigate the arc dynamics and the establishment of flow regimes in the arc in crossflow. The plasma flow model is implemented within a nonlinear Variational Multiscale (VMS) numerical discretization approach that is less dissipative, and hence better suited to capture unstable behavior, than traditional VMS methods commonly used in computational fluid dynamics simulations. The Reynolds and the Enthalpy dimensionless numbers, characterizing the relative flow strength and arc strength, respectively, are chosen as the controlling parameters of the system. Simulation results reveal the onset of dynamic behavior and the establishment of steady, periodic, quasi-periodic, and chaotic or potentially turbulent, regimes, as identified by distinct spatiotemporal fluctuations. The computational findings reveal the role of increasing the relative arc strength on enhancing flow stability by delaying the growth of fluctuating and unstable flow behavior.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Unipolar arc plasmas on nanostructured tungsten surfaces under perpendicular magnetic field

Abstract Unipolar arcing is an important phenomenon in terms of wall erosion and the subsequent plasma contamination in nuclear fusion devices. In this study, unipolar arc plasmas are experimentally explored under the presence of the external magnetic field perpendicular to a tungsten (W) sample on which a ‘fuzz’ nanostructure surface is formed. It is found that the fuzz layer thickness, d fuzz , plays a dominant role in determining the motion of arc spots, the arc ignition probability, and arc plasma parameters. High-speed imaging reveals that the motion of arc spots becomes more collective, as d fuzz increases. Interestingly, arc spots make a circle while moving outward. With increasing d fuzz , the amount of eroded W atoms increases, as indicated from an observed increase in the total visible emission intensity, while the arc ignition probability is found to drop. The physical mechanisms are discussed, in detail, based on spectroscopic measurements of the electron temperature, obtained from Boltzmann plots of both W I and W II, and the electron density, determined from Stark broadening of W I lines.

Physics↗
DOE OSTI2019

Microstructure and Work Hardening Behavior of Micro-plasma Arc Welded AISI 316L Sheet Joint

The aim of this research is to investigate the microstructural changes and work hardening behavior of AISI 316L 0.5-mm-thick sheet due to micro-plasma arc welding. AISI 316L similar sheets were welded in single-pass square butt joint configuration. The microstructure in the fusion zone typically contains a variety of complex δ-ferrite-austenitic structure, which significantly increased hardness value compared to the base material because of rapid solidification of the weld pool. Systematic tensile test was performed to investigate strain rate sensitivity of the welded joint under quasi-static loading conditions. The multistage work hardening behavior was determined by Kocks–Mecking (K–M) model and differential Crussard–Jaoul analysis. In both the cases, stage III work hardening behavior and stage IV work hardening behavior were observed. The stress–strain curves of welded specimen at different strain rates were analyzed in terms of Hollomon, Ludwik and Swift equations to determine work hardening exponent values. The welded joints were ruptured in the transition zone of heat affected and fusion zones. The fractographic observation exhibited variation in dimple and void density over strain rate from 0.0001 to 0.0015 s{sup −1}.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Life cycle analysis of hydrogen production via methane pyrolysis using plasma arc

Steam methane reforming of natural gas is the primary method of producing hydrogen in the United States, accounting for 95% of all hydrogen produced there. Methane pyrolysis, an alternative production pathway that decomposes natural gas into solid carbon and hydrogen, both eliminates CO 2 emissions associated with methane reforming and allows for additional income from carbon black. A life-cycle inventory of this process has been developed using ASPEN Plus to model the methane pyrolysis (plasma arc) process. From well to gate, hydrogen production via methane pyrolysis produces 2.78 kg CO 2 e/kg H 2 of greenhouse gas emissions using mass allocation of emissions between hydrogen and carbon black coproducts. The well-to-gate emissions are mainly driven by electricity consumption (∼38 kW h/kg H 2 ), which accounts for 81% of the emissions; if renewable electricity is used, well-to-gate emissions can be reduced to −0.448 kg CO 2 e/kg H 2 .

08 HYDROGEN↗
DOE OSTI2020

Erosion and cathodic arc plasma of Nb–Al cathodes: composite versus intermetallic

Many properties of cathodic arcs from single-element cathodes show a correlation to the cohesive energy of the cathode material. For example, the burning voltage, the erosion rate, or, to a lesser extent, plasma properties like electron temperatures or average ion energy and charge states. For multi-element cathodes, various phases with different cohesive energies can initially be present in the cathode, or form due to arc exposure, complicating the evaluation of such correlations. To test the influence of morphology and phase composition of multi-element cathodes on cathodic arc properties, a Nb–Al cathode model system was used that includes: pure Nb and Al cathodes; intermetallic Nb 3 Al, Nb 2 Al and NbAl 3 cathodes; and three composite Nb–Al cathodes with atomic ratios corresponding to the stoichiometric ratios of the intermetallic phases. Pulsed cathodic arc plasmas from these cathodes were examined using a mass-per-charge and energy-per-charge analyzer, showing that charge-state-resolved ion energy distributions of plasmas from the intermetallic and corresponding composite cathodes are nearly identical. An examination of converted layers of eroded cathodes using x-ray diffraction and scanning electron microscopy indicates the formation of a surface layer with similar phase composition for intermetallic and their corresponding composite cathode types. The average arc voltages do not follow the trend of cohesive energies of Nb, Al and intermetallic Nb–Al phases, which have been calculated using density functional theory. Possible reasons for this effect are discussed based on the current knowledge of multi-element arc cathodes and their arc plasma available in literature.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Thermo-Mechanical Distortion of Tungsten-Coated Steel During High Heat Flux Testing Using Plasma Arc Lamps

An experimental setup and a test section were designed and fabricated for high heat flux testing (HHFT) of neutron-irradiated specimens using water-wall plasma arc lamps. Because of the radiological considerations and limitations of reactor irradiation, the size of the test articles was limited to disks less than 10 mm in diameter. The specimen was clamped onto an actively cooled block, and clamping allowed the insertion of several thermocouples on the back surface of the specimen through a copper (Cu) block. Five vacuum plasma sprayed tungsten (W)–coated F82H steel specimens were subjected to HHFT. Surface profilometry measurements, which were conducted after HHFT, revealed central bowing of the top W surface. This type of residual distortion occurred for all of the specimens, and the larger the specimens were, the larger was the distortion.In an attempt to understand specimen distortion and address the science questions related to the testing of subsize specimens during HHFT, a simplified thermo-mechanical model was developed. By using a measured temperature in the Cu as an isothermal boundary condition, the model eliminated the need for coupling cooling fluid flow models with stress models, greatly simplifying the analysis. The main variable in the proposed model is hC, i.e., the thermal contact conductance between the F82H and the Cu washer. Inelastic properties, including hardening properties, were considered for F82H steel and Cu. Numerical simulation results demonstrated a buildup of residual deformation during HHFT and a very complex state of stress and deformation during typical heat flux (HF) cycling. Additionally, hoop stress evolution during a high heat flux cycle reveals that F82H at an interface with W would be mainly in compression during HF application and experienced a transition to a tension state during cooldown. Also, specimen distortion evolves during each HF cycle, as the specimen bows downward during HF application and upward during the cooldown period between HF cycles. The final specimen distortion, i.e., upward bowing of the specimen center, was qualitatively predicted for hC values of 4000 to 5000 W/(m 2 ·K). This hC range of values, for which bulging is obtained, is at the lower spectrum of the range of values for hC, consistent with the low thermal contact conductance expected from the unpolished F82H surface.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

DU Processing Efficiency and Reclamation: Plasma Arc Melting

The work described here corresponds to one piece of a larger effort to increase material usage efficiency during DU processing operations. In order to achieve this goal, multiple technologies and approaches are being tested. These technologies occupy a spectrum of technology readiness levels (TRLs). Plasma arc melting (PAM) is one of the technologies being investigated. PAM utilizes a high temperature plasma to melt materials. Depending on process conditions, there are potential opportunities for recycling and material reclamation. When last routinely operational, the LANL research PAM showed extremely promising results for recycling and reclamation of DU and DU alloys. The current TRL is lower due to machine idleness for nearly two decades, which has proved difficult to restart. This report describes the existing results, promising techniques, and the process of bringing this technology back to readiness at LANL.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Plasma-arc lamp high heat flux cycling exposure of neutron irradiated tungsten materials

Thick plate, unalloyed W was neutron irradiated in the High Flux Isotope Reactor (HFIR) at 550 °C to a fast fluence of 1.24 × 10 25 n m -2 E > 0.1 MeV (~0.24 dpa). Unirradiated and irradiated specimens of the material were high heat flux (HHF) tested in the Plasma Arc Lamp (PAL) facility. The PAL uses a high-power photon source to provide a broad and even heat distribution on the sample surface. To simulate on/off cycling of normal operating plasma, the samples were exposed to approximately 800 cycles at 4.73 MW m -2 absorbed heat flux (incident heat fluxes of 10.95 MW m -2 ). Additionally, after PAL exposure, slight changes were observed on the surfaces of the samples with SEM. The samples showed some annealing in the near surface polished region, but they were all below the damage threshold for cracking or other destructive features. The PAL has a large parameter space for future testing. The use of the HFIR and PAL to sequentially expose neutron irradiated samples to HHF will be a powerful tool for understanding materials behavior in a fusion-like environment.

36 MATERIALS SCIENCE↗