Airborne contaminants from fires containing nuclear waste represent significant health hazards and shape the design and operation of nuclear facilities. Much of the data used to formulate DOE-HDBK-3010-94, “Airborne Release Fractions/Rates and Respirable Fractions for Nonreactor Nuclear Facilities,” from the U.S. Department of Energy, were taken over 40 years ago. The objectives of this study were to reproduce experiments from Pacific Northwest Laboratories conducted in June 1973 employing current aerosol measurement methods and instrumentation, develop an enhanced understanding of particulate formation and transport from fires containing nuclear waste, and provide modeling and experimental capabilities for updating current standards and practices in nuclear facilities. A special chamber was designed to conduct small fires containing 25 mL of flammable waste containing lutetium nitrate, ytterbium nitrate, or depleted uranium nitrate. Carbon soot aerosols showed aggregates of primary particles ranging from 20 to 60 nm in diameter. In scanning electron microscopy, ~200-nm spheroidal particles were also observed dispersed among the fractal aggregates. The 200-nm spherical particles were composed of metal phosphates. Airborne release fractions (ARFs) were characterized by leaching filter deposits and quantifying metal concentrations with mass spectrometry. The average mass-based ARF for 238U experiments was 1.0 × 10−3 with a standard deviation of 7.5 × 10−4. For the original experiments, DOE-HDBK-3010-94 states, “Uranium ARFs range from 2 × 10−4 to 3 × 10−3, an uncertainty of approximately an order of magnitude.” Thus, current measurements were consistent with DOE-HDBK-3010-94 values. ARF values for lutetium and ytterbium were approximately one to two orders of magnitude lower than 238U. Metal nitrate solubility may have varied with elemental composition and temperature, thereby affecting ARF values for uranium surrogates (Yb and Lu). In addition to ARF data, solution boiling temperatures and evaporation rates can also be deduced from experimental data.
This Part 2 study examined the microstructural characteristics of braze joints made between two KOVarTM base materials using the filler metals, Ag-xAl, having x = 0, 2, 5, and 10 wt.% Al additions. Brazing processes had temperatures of 965°C (1769°F) and 995°C and brazing times of 5 and 20 min. All brazing was performed under high vacuum.
Pressure losses and aerosol collection efficiencies were measured for fibrous filter materials at air-flow rates consistent with high efficiency filtration (hundreds of cubic feet per minute). Microfiber filters coated with nanofibers were purchased and fabricated into test assemblies for a 12-inch duct system designed to mimic high efficiency filtration testing of commercial and industrial processes. Standards and specifications for high efficiency filtration were studied from a variety of institutions to assess protocols for design, testing, operations and maintenance, and quality assurance (e.g., DOE, ASHRAE, ASME). Three materials with varying Minimum Efficiency Reporting Values (MERV) were challenged with sodium chloride aerosol. Substantial filter loading was observed where aerosol collection efficiencies and pressure losses increased during experiments. Filter designs will be optimized and characterized in subsequent years of this study. Additional testing will be performed with higher hazard aerosols at Oak Ridge National Laboratory.
This study examined the cause of nonwetted regions of the gold (Au) finish on iron-nickel (Fe-Ni) alloy lids that seal ceramic packages using the 80Au-20Sn solder (wt %, abbreviated Au-Sn) and their impact on the final lid-to-ceramic frame solder joint. The Auger electron spectroscopy (AES) surface and depth profile techniques identified surface and through-thickness contaminants in the Au metallization layer. In one case, the AES analysis identified background levels of carbon (C) contamination on the surface; however, the depth profile detected Fe and Ni contaminants that originated from the plating process. The Fe and Ni could impede the completion of wetting and spreading to the edge of the Au metallization. The Au layer of lids not exposed to a Au-Sn solder reflow step had significant surface and through-thickness C contamination. Inorganic contaminants were absent. Subsequent simulated reflow processes removed the C contamination from the Au layer without driving Ni diffusion from the underlying solderable layer. An Au metallization having negligible C contamination developed elevated C levels after exposure to a simulated reflow process due to C contamination diffusing into it from the underlying Ni layer. However, the second reflow step removed that contamination from the Au layer, thereby allowing the metallization to support the formation of lid-to-ceramic frame Au-Sn joints without risk to their mechanical strength or hermeticity.
The run-out phenomenon was observed in Ag-Cu-Zr active braze joints made between the alumina ceramic and Kovar™ base material. Run-out introduces a significant yield loss by generating functional and/or cosmetic defects in brazements. A prior study identified a correlation between run-out and the aluminum (Al) released by the reduction/oxidation and the latter’s reaction with the Kovar™ base material. A study was undertaken to understand the fundamental principles of run-out by examining the interface reaction between Ag-xAl filler metals (x=2, 5, and 10 wt.%) and Kovar™ base material. Sessile drop samples were fabricated using brazing temperatures of 965°C or 995°C and times of 5 min or 20 min. The correlation was made between the degree of wetting-and-spreading by the sessile drops and the run-out phenomenon. Wetting-and-spreading increased with Al content (x) of the Ag-xAl filler metal, but was largely insensitive to the brazing process parameters. The increased Al concentration resulted in higher Al contents of the (Fe, Ni, Co)xAly reaction layer. Run-out was predicted when the filler metal has a locally-elevated, Al content exceeding 2 – 5 wt.%. Lastly, several mitigation strategies were proposed, based upon these findings.
Ultrafast optical microscopy of metal z-pinch rods pulsed with megaampere current is contributing new data and critical insight into what provides the fundamental seed for the magneto-Rayleigh-Taylor (MRT) instability. A two-frame near infrared/visible intensified-charge-coupled device gated imager with 2-ns temporal resolution and 3-μm spatial resolution captured emissions from the nonuniformly Joule heated surfaces of ultrasmooth aluminum (Al) rods. Nonuniform surface emissions are consistently first observed from discrete, 10-μm scale, subelectronvolt spots. Aluminum 6061 alloy, with micrometer-scale nonmetallic resistive inclusions, forms several times more spots than 99.999% pure Al 5N; 5-10 ns later, azimuthally stretched elliptical spots and distinct strata (40-100μm wide by 10μm tall) are observed on Al 6061, but not on Al 5N. Such overheat strata, which are aligned parallel to the magnetic field, are highly effective seeds for MRT instability growth. These data give credence to the hypothesis that early nonuniform Joule heating, such as the electrothermal instability, may provide the dominant seed for MRT.
Ferroelastic domain walls provide opportunities for deterministically controlling mechanical, optical, electrical, and thermal energy. Domain wall characterization in micro- and nanoscale systems, where their spacing may be of the order of 100 nm or less is presently limited to only a few techniques, such as piezoresponse force microscopy and transmission electron microscopy. These respective techniques cannot, however, independently characterize domain polarization orientation and domain wall motion in technologically relevant capacitor structures or in a non-destructive manner, thus presenting a limitation of their utility. In this work, we show how backscatter scanning electron microscopy utilizing channeling contrast yield can image the ferroelastic domain structure of ferroelectric films with domain wall spacing as narrow as 10 nm. Combined with electron backscatter diffraction to identify grain orientations, this technique provides information on domain orientation and domain wall type that cannot be readily measured using conventional non-destructive methods. In addition to grain orientation identification, this technique enables dynamic domain structure changes to be observed in functioning capacitors utilizing electrodes that are transparent to the high-energy backscattered electrons. This non-destructive, high-resolution domain imaging technique is applicable to a wide variety of ferroelectric thin films and a multitude of material systems where nanometer-scale crystallographic twin characterization is required.
This report describes a new, bio-inspired approach to electrical energy storage, based on the generation, maintenance, and discharge of ion concentration gradients. This approach was investigated as part of a Laboratory Directed Research and Development program at Sandia National Laboratories in Albuquerque, NM between October 2012 and September 2015. In particular, this report describes the development of ion-selective nanoporous membranes, controlled through pore morphology and Sandia-developed electrochemical functionalization. In addition, it describes a potential avenue to functionalize synthetic polymer membranes in a way that facilitates oriented ion pump binding to polymer surfaces. Finally, it highlights a number of new computational findings central to the understanding and ultimate design of synthetic ion channels and ion gates needed for biomimetic ion-based electrochemical energy storage.
We examined amorphous titania thin films for use as the active material in a polarimetry based HF sensor. The amorphous titania films were found to be sensitive to vapor phase HF and the reaction product was identified as a hydronium oxofluorotitanate phase, which has previously only been synthesized in aqueous solution. The extent of reaction varied both with vapor phase HF concentration, relative humidity, and the exposure time. HF concentrations as low as 1 ppm could be detected for exposure times of 120 h.
Three balance of systems (BOS) connector designs common to industry were investigated as a means of assessing reliability from the perspective of arc fault risk. These connectors were aged in field and laboratory environments and performance data captured for future development of a reliability model. Comparison of connector resistance measured during damp heat, mixed flowing gas and field exposure in a light industrial environment indicated disparities in performance across the three designs. Performance was, in part, linked to materials of construction. A procedure was developed to evaluate new and aged connectors for arc fault risk and tested for one of the designs. Those connectors exposed to mixed flowing gas corrosion exhibited considerable Joule heating that may enhance arcing behavior, suggesting temperature monitoring as a potential method for arc fault prognostics. These findings, together with further characterization of connector aging, can provide operators of photovoltaic installations the information necessary to develop a data-driven approach to BOS connector maintenance as well as opportunities for arc fault prognostics.
Magnetically driven implosions (MDIs) on the Z Facility assemble high-energy-density plasmas for radiation effects and ICF experiments. MDIs are hampered by the Magneto-Rayleigh-Taylor (MRT) instability, which can grow to large amplitude from a small seed perturbation, limiting achievable stagnation pressures and temperatures. The metallic liners used in Magnetized Liner Inertial Fusion (MagLIF) experiments include astonishingly small (-10 nm RMS) initial surface roughness perturbations; nevertheless, unexpectedly large MRT amplitudes are observed in experiments. An electrothermal instability (ETI) may provide a perturbation which exceeds the initial surface roughness. For a condensed metal resistivity increases with temperature. Locations of higher resistivity undergo increased Ohmic heating, resulting in locally higher temperature, and thus still higher resistivity. Such unstable temperature (and pressure) growth produces density perturbations when the locally overheated metal changes phase, providing the seed perturbation for MRT growth. ETI seeding of MRT on thick conductors carrying current in a skin layer has thus far only been inferred by evaluating MRT amplitude late in the experiment. A direct observation of ETI is vital to ensure our simulation tools are accurately representing the seed of the deleterious MRT instability. In this LDRD project, ETI growth was directly observed on the surface of 1.0-mm-diameter solid Al rods which were pulsed with 1 MA of current in 100 ns. Fine structures resulting from ETI-driven temperature variations were observed directly through high resolution gated optical imaging. Data from two Aluminum alloys (6061 and 5N) and a variety fabrication techniques (conventional machining, single-point diamond turned, electropolished) enable evaluation of which imperfections provide a seed for ETI growth and subsequent plasma initiation. Data is relevant to the early stages of MagLIF liner implosions, when the ETI seed of MRT may be initiated, and provides a fundamentally new dataset with which to test our state-of-the-art simulation tools.
Modification of the dipeptide of phenylalanine, FF, with a boronic acid (BA) functionality imparts unique aqueous self-assembly behavior that responds to multiple stimuli. Changes in pH and ionic strength are used to trigger hydrogelation via the formation of nanoribbon networks. Furthermore, we show for the first time that the binding of polyols to the BA functionality can modulate a peptide between its assembled and disassembled states.
Dynamic control of thermal transport in solid-state systems is a transformative capability with the promise to propel technologies including phononic logic, thermal management, and energy harvesting. A solid-state solution to rapidly manipulate phonons has escaped the scientific community. We demonstrate active and reversible tuning of thermal conductivity by manipulating the nanoscale ferroelastic domain structure of a Pb(Zr0.3Ti0.7)O3 film with applied electric fields. With subsecond response times, the room-temperature thermal conductivity was modulated by 11%.
The ability to integrate ceramics with other materials has been limited due to high temperature (>800°C) ceramic processing. Recently, researchers demonstrated a novel process, aerosol deposition (AD), to fabricate ceramic films at room temperature (RT). In this process, sub-micron sized ceramic particles are accelerated by pressurized gas, impacted on the substrate, plastically deformed, and form a dense film under vacuum. This AD process eliminates high temperature processing thereby enabling new coatings and device integration, in which ceramics can be deposited on metals, plastics, and glass. However, knowledge in fundamental mechanisms for ceramic particles to deform and form a dense ceramic film is still needed and is essential in advancing this novel RT technology. In this work, a combination of experimentation and atomistic simulation was used to determine the deformation behavior of sub-micron sized ceramic particles; this is the first fundamental step needed to explain coating formation in the AD process. High purity, single crystal, alpha alumina particles with nominal sizes of 0.3 µm and 3.0 µm were examined. Particle characterization, using transmission electron microscopy (TEM), showed that the 0.3 µm particles were relatively defect-free single crystals whereas 3.0 µm particles were highly defective single crystals or particles contained low angle grain boundaries. Sub-micron sized Al2O3 particles exhibited ductile failure in compression. In situ compression experiments showed 0.3µm particles deformed plastically, fractured, and became polycrystalline. Moreover, dislocation activity was observed within these particles during compression. These sub-micron sized Al2O3 particles exhibited large accumulated strain (2-3 times those of micron-sized particles) before first fracture. In agreement with the findings from experimentation, atomistic simulations of nano-Al2O3 particles showed dislocation slip and significant plastic deformation during compression. On the other hand, the micron sized Al2O3 particles exhibited brittle fracture in compression. In situ compression experiments showed 3µm Al2O3 particles fractured into pieces without observable plastic deformation in compression. Particle deformation behaviors will be used to inform Al2O3 coating deposition parameters and particle-particle bonding in the consolidated Al2O3 coatings.