Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “eds”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Revealing Possible Coherence Limiting Sources in Superconducting Qubit with Advanced Electron Microscopy

Superconducting materials hold great potential for solid-state quantum computing. Their fabrication relies on established semiconductor fabrication techniques, such as thin film deposition and lithography, but the complex processing steps can result in defects at the qubits' interfaces and surfaces that can negatively impact coherence time. To improve superconducting qubit performance, it is essential to understand the structural features, at the atomic scale, that may act as sources of decoherence limiting factor in both the Josephson junction (JJ) and resonators, which are key components of superconducting qubit. This talk will present our recent studies on the microstructures in a 2D-transmon, with an emphasis on the JJ. For this research, a combination of advanced microscopy techniques, including high-resolution (S)TEM imaging, and spectroscopy (EDS and EELS) are used to identify possible coherence-limiting defects or structural features.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Quench dynamics of two-component dipolar fermions subject to a quasiperiodic potential

Motivated by recent experiments in fermionic polar gases, we study the nonequilibrium dynamics of two-component dipolar fermions subject to a quasiperiodic potential. We investigate the localization of charge and spin degrees of freedom time evolving with a long-range spin-SU(2) symmetric fermionic Hamiltonian by calculating experimentally accessible dynamical observables. To study the nonequilibrium dynamics, we start the time evolution with two initial states at half-filling: (i) product state with doublons |↑↓0↑↓0↑↓0↑↓0↑↓$\rangle$ and (ii) product state with singlons |↑↓↑↓↑↓↑↓↑↓$\rangle$. We carried out the real-time evolution via the fermionic Hamiltonian using exact diagonalization (ED) and the time-dependent variational principle (TDVP) for finite matrix product states (MPS), within experimentally relevant timescales. For the product state with doublons, we observe a delocalized to localized phase transition varying disorder strengths by monitoring the decay of charge imbalance with time. For the long-range interacting Hamiltonian of our focus, and in the presence of strong enough disorder, starting the time evolution with singlons we find a strong reduction in the spin delocalization, contrary to results of previous studies using the disordered short-range (on-site) Hubbard model with SU(2) symmetry. In addition to the quench dynamics, we also demonstrate the localization of charge and spin in the full energy spectrum of the long-range spin-SU(2) symmetric Hamiltonian by monitoring spin and charge autocorrelation functions. Finally, our predictions for localization of both charge and spin should be observable in ultracold experiments with fermionic dipolar atoms subject to a quasiperiodic potential.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Mn(Pt 1–x Pd x ) 5 P: Isovalent tuning of Mn-sublattice magnetic order

Here, e report the growth and characterization of MnPd 5 P, a rare-earth-free ferromagnet, with T C ≈ 295 K and planar anisotropy, and conduct a substitutional study with its antiferromagnetic analogue MnPt 5 P. We provide a solution route to grow large single crystals of MnPd 5 P and the series Mn(Pt 1–x Pd x ) 5 P by adding Mn into Pd-P and (Pt 1–x Pd x )-P based melts. All compounds in the family adopt the layered anti-CeCoIn5 type structure with the space group P4/mmm, and EDS and X-ray diffraction results indicate that MnPt 5 P and MnPd 5 P form a complete solid solution. Based on measurements of the temperature- and field-dependent magnetization and resistance, we construct a temperature-composition (T-x) phase diagram for Mn(Pt 1–x Pd x ) 5 P and demonstrate that the initial antiferromagnetic order found in MnPt 5 P is extraordinarily sensitive to Pd substitution. At low Pd fractions (x < 0.010), the single antiferromagnetic transition in pure MnPt 5 P splits into a higher temperature ferromagnetic transition followed first, upon cooling, by a lower temperature ferromagnetic to antiferromagnetic transition and then by a re-entrant antiferromagnetic to ferromagnetic transition at even lower temperatures. The antiferromagnetic region makes up a bubble phase that persists up to x ≈ 0.008-0.009 for T ≈ 150 K, with all samples x < 0.008 recovering their initial ferromagnetic state upon further cooling to base temperature. Over the same low substitution range we find a non-monotonic change in the room temperature value of the unit cell volume, further suggesting that pure MnPt 5 P is very close to an instability. Once x > 0.010, Mn(Pt 1–x Pd x ) 5 P undergoes a only single transition into the ferromagnetic phase. The Curie temperature initially increases rapidly with x, rising from T C ≈ 197 K at x = 0.013 to a maximum of T C ≈ 312 K for x ≈ 0.62, and then falling back to T C ≈ 295 K for pure MnPd 5 P (x = 1.00). Given that Pt and Pd are isoelectronic, this work raises questions as to the origin of the extreme sensitivity of the magnetic ground state in MnPt 5 P upon introducing Pd.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Measures of complexity and entanglement in many-fermion systems

There is no unique and widely accepted definition of the complexity measure (CM) of a many-fermion wave function in the presence of interactions. The simplest many-fermion wave function is a Slater determinant. In shell-model or configuration interaction (CI) and other related methods, the state is represented as a superposition of a large number of Slater determinants, which in the case of CI calculations reaches about 20 billion terms [Johnson, arXiv:1809.07869]. Although in practice this number has been used as a CM for decades, it is ill defined: it is not unique, and it depends on the particular type and the number of single-particle wave functions used to construct the Slater determinants. Further, the canonical wave functions and/or natural orbitals [Löwdin, Adv. Phys. 5, 1 (1956); Löwdin and Shull, Phys. Rev. 101, 1730 (1956); Bardeen et al., Phys. Rev. 108, 1175 (1957); N. N. Bogoljubov, Il Nuovo Cimento 7, 794 (1958); Valatin, Il Nuovo Cimento 7, 843 (1958); de Gennes, Superconductivity of Metals and Alloys (CRC Press, Boca Raton, FL, 1999); Ring and Schuck, The Nuclear Many-Body Problem, 1st ed. (Springer-Verlag, Berlin, 2004)] and their corresponding occupation probabilities are intrinsic properties of any many-body wave function, irrespective of the representation, and they provide a unique solution to characterize the CM. The non-negative orbital entanglement entropy, which vanishes for a Slater determinant, provides the simplest CM, while a more complete measure of complexity is the entanglement spectrum. We illustrate these aspects in the case of a complex nonequilibrium time-dependent process, induced nuclear fission described within a real-time density functional theory framework extended to superfluid systems, which can describe simultaneously the long-range and the short-range correlations between fermions. The orbital entanglement entropy of the fissioning nucleus illustrates the localization mechanism of the many-body wave function in Fock and/or Hilbert space. The (minimal) number of Slater determinants required to represent such a complex many-body wave function with a well-defined number of particles in the case presented here is about 10 500 . The realistic case of the highly nonequilibrium nuclear fission process illustrated here is equivalent to a system of 23.328×10 9 interacting quantum spin-1/2 particles, a very large system for the study of quantum entanglement.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

High-temperature ferromagnetism in Cr 1+x Pt 5-x P

In this work, we present the growth and basic magnetic and transport properties of Cr 1+x Pt 5-x P. We show that single crystals can readily be grown from a high-temperature solution created by adding dilute quantities of Cr to Pt-P based melts. Like other 1-5-1 compounds, Cr 1+x Pt 5-x P adopts a tetragonal P4/mmm, structure composed facesharing CrPts like slabs that are broken up along the c-axis by sheets of P atoms. EDS and X-ray diffraction measurements both suggest Cr 1+x Pt 5-x P has mixed occupancy between Cr and Pt atoms, similar to what is found in the closely related compound CrPtg, giving real compositions of Cr 1.5 Pt 4.5 P (x = 0.5). We report that Cr 1.5 Pt 4.5 P orders ferromagnetically at T c = 464.5 K with a saturated moment of ≈ 2.1 μs/Cr at 1.8 K. Likely owing to the strong spin-orbit coupling associated with the large quantity of high Z, Pt atoms, Cr 1.5 Pt 4.5 P has exceptionally strong planar anisotropy with estimated anisotropy fields of 345 kOe and 220 kOe at 1.8 K and 300 K respectively. The resistance of Cr 1.5 Pt 4.5 P has a metallic temperature dependence with relatively weak magnetoresistance. Electronic band structure calculations show that CrPt 5 P has a large peak in the density of states near the Fermi level which is split into spin majority and minority bands in the ferromagnetic state. Furthermore, the calculations suggest substantial hybridization between Cr-3d and Pt-5d states near the Fermi level, in agreement with the experimentally measured anisotropy.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Superspin renormalization and slow relaxation in random spin systems

We develop an excited-state real-space renormalization group (RSRG-X) formalism to describe the dynamics of conserved densities in randomly interacting spin-12 systems. Our formalism is suitable for systems with U(1) and Z2 symmetries, and we apply it to chains of randomly positioned spins with dipolar XX+YY interactions, as arise in Rydberg quantum simulators and other platforms. The formalism generates a sequence of effective Hamiltonians that provide approximate descriptions for dynamics on successively smaller energy scales. These effective Hamiltonians involve “superspins”: two-level collective degrees of freedom constructed from (anti)aligned microscopic spins. Conserved densities can then be understood as relaxing via coherent collective spin flips. For the well-studied simpler case of randomly interacting nearest-neighbor XX+YY chains, the superspins reduce to single spins. Our formalism also leads to a numerical method capable of simulating the dynamics up to an otherwise inaccessible combination of large system size and late time. Focusing on disorder-averaged infinite-temperature autocorrelation functions, in particular the spin survival probability Sp¯(t), we demonstrate quantitative agreement between our algorithm and exact diagonalization (ED) at low but nonzero frequencies. Such agreement holds for chains with nearest-neighbor, next-nearest-neighbor, and long-range dipolar interactions. Our results indicate decay of Sp¯(t) slower than any power law and feature no significant deviation from the ∼1/ln2(t) asymptote expected from the infinite-randomness fixed-point of the nearest-neighbor model. We also apply the RSRG-X formalism to two-dimensional long-range systems of moderate size and find slow late-time decay of Sp¯(t).

Zhao, Yi J↗
DOE OSTI2024

Correlative X-ray micro-nanotomography with scanning electron microscopy at the Advanced Light Source

Geological samples are inherently multi-scale. Understanding their bulk physical and chemical properties requires characterization down to the nano-scale. A powerful technique to study the three-dimensional microstructure is X-ray tomography, but it lacks information about the chemistry of samples. To develop a methodology for measuring the multi-scale 3D microstructure of geological samples, correlative X-ray micro- and nanotomography were performed on two rocks followed by scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) analysis. The study was performed in five steps: (i) micro X-ray tomography was performed on rock sample cores, (ii) samples for nanotomography were prepared using laser milling, (iii) nanotomography was performed on the milled sub-samples, (iv) samples were mounted and polished for SEM analysis and (v) SEM imaging and compositional mapping was performed on micro and nanotomography samples for complimentary information. Correlative study performed on samples of serpentine and basalt revealed multiscale 3D structures involving both solid mineral phases and pore networks. Significant differences in the volume fraction of pores and mineral phases were also observed dependent on the imaging spatial resolution employed. This highlights the necessity for the application of such a multiscale approach for the characterization of complex aggregates such as rocks. Information acquired from the chemical mapping of different phases was also helpful in segmentation of phases that did not exhibit significant contrast in X-ray imaging. Adoption of the protocol used in this study can be broadly applied to 3D imaging studies being performed at the Advanced Light Source and other user facilities.

58 GEOSCIENCES↗
DOE OSTI2021

Detection of diffusion limited oxidation in thermally aged ethylene propylene rubber cable insulation material

The lifetime prediction of electrical cable insulation in nuclear power plants (NPPs) is primarily based on accelerated aging. Polymeric insulation exposed to accelerated aging at high temperatures may demonstrate diffusion limited oxidation (DLO) where oxygen within the material is consumed faster than can be supplied by diffusion from the surrounding air. This situation leads to equilibrium oxidation at the exposed surfaces and limited oxidation away from the surfaces. Therefore, DLO results in a heterogeneously aged material which can lead to underestimation of lifetime for in-service cable insulation. In this study, the presence of inhomogeneous aging caused by DLO was evaluated on cross-sectioned cable insulation specimens made of ethylene propylene rubber (EPR). The studies were performed on thermally aged specimens (165 °C, 1 day and 165 °C, 16 days) using local measurement techniques including nanoindentation, micro-Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) - energy dispersive spectroscopy (EDS). All the results indicate some degree of heterogenous aging, with 165 °C, 16 days, aging demonstrating highest degree of oxidative degradation on the inside edges presumably caused due to copper catalyzed oxidation.

Pallaka, Madhusudhan Reddy↗
DOE OSTI2025

Diagnosis of PV Cell Antireflective Coating Degradation Resulting From Hot-Humid High-Voltage Potential Aging

Corrosion of the antireflective coating on a photovoltaic cell ("ARc corrosion") has previously been observed in studies using hot-humid test conditions with external high-voltage (HV) bias. This study primarily focuses on known vulnerable legacy aluminum back surface field cells in mini-modules (MiMos) put through comparative stepped stress tests. Each cell type had MiMos at +1500 V, -1500 V, or unbiased ("Voc") potential, which were sequentially subjected to test conditions of 60 degrees C/60% relative humidity (RH) for 96 h, as in International Electrotechnical Commission Technical Specification 62804-1; 70 degrees C/70% RH for 200 h; and 85 degrees C/85% RH for 200 h. Characterizations at each step included visual camera and electroluminescence (EL) imaging, colorimetry, and current-voltage curve tracing. Final characterizations included: Suns-Voc, spatial mapping of external quantum efficiency, high-resolution photoluminescence, EL, and dark lock-in thermography imaging. Forensics were performed on extracted cores, including scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy, and scanning Auger microscopy (SAM). Forensics were also conducted on MiMos from previous studies that underwent stepped HV aging and separate outdoor aged full-sized modules. ARc corrosion was specifically seen for the glass/encapsulant/cell side of the +1500 V (HV+) stressed MiMos and modules. Appearance, color, and reflectance were the most distinguishing characteristics relative to glass corrosion, gridline corrosion and delamination, and other concurrent degradation modes. SEM/EDS and SAM identified the conversion of silicon nitride to hydrated silica, hydrous silica, or hydrated amorphous silica, which preferentially occurred at the edges and tips of the pyramidal textured cell surface.

14 SOLAR ENERGY↗
DOE OSTI2021

Reliability Implications of Solder in Multiwire Modules under Dynamic Mechanical Loading

Two generations of multiwire modules were studied under dynamic mechanical loading (DML) with in-situ differential conductance (dG) and electroluminescence (EL) imaging. Energy-dispersive x-ray spectroscopy (EDS) was used to identity the solder alloys. The earlier generation module was found to use an In-based solder alloy, and the current generation a Bi-based alloy. The earlier generation module degraded significantly under DML with increasing resistance, while the current generation module did not demonstrate degradation under DML. Atomic force microscopy scratch testing was used to probe the wear resistance of each solder alloy. These results indicate that current multiwire designs may have higher mechanical durability than earlier generations.

atomic force microscopy↗
DOE OSTI2021

Differences in c-Si Solar Cell Metallization and Susceptibility to Series Resistance Degradation

In this case study, we investigate a degradation mode occurring at the cell level in fielded multi-Si modules. Affected cells in the module show a progressive, series-resistance-related power degradation observed in module- and cell-level IV curves along with EL and PL imaging at the module, cell, and cell core sample scale. SEM and elemental analysis via EDS reveal a difference in the oxides in the silver paste used in screen printing of the finger contacts. This suggests that the cells were screen printed with different silver paste compositions and possibly firing conditions. One of these combinations leads to degradation of the contact at the interface between the cell and contact finger, causing severe series resistance across the cell that continues to progress over time.

acetic acid↗
DOE OSTI2022

Impact of Indium Chloride Treatment on the Properties of CuInSe 2 Thin Films

Copper Indium diselenide (CIS) semiconductor thin films were deposited by single-stage process. Following the deposition, annealing and recrystallization of CIS was carried out in the presence of InCl 3 at different temperatures. Increase in grain size was observed by SEM in all cases. Increase in peak intensity was observed by XRD after treatment, correlating well with the SEM results. Measurements of the composition by both XRF and EDS indicate significant changes, notably a decrease in copper content. Here, this will likely be an issue for device performance and will need to be addressed.

14 SOLAR ENERGY↗
DOE OSTI2024

Diagnosis of PV Cell Passivation Degradation Resulting from Hot-Humid, High Voltage Potential Aging

Corrosion of the antireflective coating on the cell ("AR c corrosion") was previously observed in studies using hot-humid test conditions with external high voltage (HV) bias. Because AR c corrosion is not well understood, mini-modules (MiMos) were examined in a comparative experiment using PERC and PERT as well as legacy Al-BSF cells. For separate MiMos with the cell circuit electrical at +1500 V, -1500 V, or unbiased "V oc", test conditions in the comparative study included 60degrees C/60% RH for 96 h, as in IEC TS 62804-1; 70degrees C/70%RH for 200 h; and 85degrees C/85% RH for 200 h. Characterizations at each read point included: camera and electroluminescence (EL) imaging, colorimetry, and I-V curve tracing. Characterizations at the final read point included: SunsVoc; spatially mapping external quantum efficiency (EQE); high resolution: photoluminescence (PL), EL, and dark lock-in thermographic (DLIT) imaging. Forensics were performed on extracted cores, including scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) and scanning Auger microscopy (SAM). Forensics were also conducted on MiMos (stepped HV aging) and full-sized modules (outdoor aging) from previous studies. AR c corrosion was specifically observed for the glass/encapsulant/cell side of +1500 V (HV+) stressed MiMos, where appearance, color, and reflectance were the characteristics most distinguished relative to simultaneously occurring degradation modes. SEM/EDS and SAM identified conversion of silicon nitride to silicon oxide or hydrous silica, preferentially occurring at the edges and tips of the pyramidal textured cell surface.

aging↗
DOE OSTI2021

Multimaterial Aerosol Jet Printed Magnetic Nanocomposites for Microwave Circuits

Here this article demonstrates the process and characterization of additively manufactured polymer-matrix magnetic nanocomposites. These nanocomposites are composed of nickel-zinc ferrite (Ni 0.5 Zn 0.5 Fe 2 O 4 ) nanoparticles in a polyimide matrix. These materials are printed using multimaterial aerosol jet printing where aerosols of nickel-zinc ferrite and polyimide inks are mixed in place to fabricate structures with nonunity relative permeability. To characterize these materials, we use energy-dispersive X-ray spectroscopy to estimate the content of ferrite in the composite, fitted simulation models, and ring resonator measurements to estimate the permeability. In fully aerosol jet printed 1-mm 2 inductors, we demonstrate an increase in inductance density of 40% in a 4.5-turn microstrip spiral inductor using this printed composite. These fully printed inductors demonstrate an inductance density of 4.2-nH/mm 2 . EDS analysis shows films with 18 wt.% Ni 0.5 Zn 0.5 Fe 2 O 4 . Finally, we show microstrip transmission lines on printed composite compared to the same on polyimide subjected to a dc magnetic bias, displaying a magnetic resonance behavior.

42 ENGINEERING↗
DOE OSTI2022

Crystal Ball: A Naturalist Perspective of Microbiology: Examples from Methanogenic Archaea

Storytelling has been the primary means of knowledge transfer over human history. The effectiveness and reach of stories are improved when the message is appropriate for the target audience. Oftentimes, the stories that are most well received and recounted are those that have a clear purpose and that are told from a variety of perspectives that touch on the varied interests of the target audience. Whether scientists realize or not, they are accustomed to telling stories of their own scientific discoveries through the preparation of manuscripts, presentations, and lectures. Perhaps less frequently, scientists prepare review articles or book chapters that summarize a body of knowledge on a given subject matter, meant to be more holistic recounts of a body of literature. Yet, by necessity, such summaries are often still narrow in their scope and are told from the perspective of a particular discipline. In other words, interdisciplinary reviews or book chapters tend to be the rarity rather than the norm. Naturalists are scientists that tell stories of organisms and their natural environment within a historical context and from an interdisciplinary perspective. Such stories interweave observations of biological subjects from disparate disciplines into a cohesive story. To this end, the success of naturalists in recounting compelling natural history stories is enhanced when they allow themselves to become vulnerable by knowingly entering a literature base full of unfamiliar ways of observing and describing such subjects. When successful, this approach can broaden the scope of the story, making it of interest to a larger audience and attracting further recounting of that story (e.g., citations). To this end, when we look into our crystal ball, we see a need to tell more holistic stories of microorganisms and their functions from an interdisciplinary, naturalist perspective that combines what is known of their contemporary ecology, physiology, and biochemistry with their evolutionary history thereby placing them within a historical Earth context. With this conviction in mind, we take the opportunity to look back on the natural history of methanogens to identify some of their most profound biochemical innovations and their impact on the trajectory of life and the planet. Our approach was to integrate knowledge from the fields of biochemistry, physiology, ecology, evolution, geochemistry, and atmospheric sciences. We start with the origin of the first autotrophic cells and how this set Earth on a path towards biomass expansion and functional diversification. Next, we discuss the importance of iron and sulfur in methanogen metabolism, and how their innovative ways of accessing these elements allowed for expanded use of iron-sulfur clusters ([Fe-S]) as nanoscale catalysts that power(ed) Earth’s biochemical cycles. We next discuss the origin and evolution of [NiFe]-hydrogenase and how this versatile enzyme chassis was co-opted by a variety of anaerobes and aerobes as the foundation for respiratory complexes capable of sustaining higher forms of life, including humans. Lastly, we discuss the evolution of the enzyme molybdenum nitrogenase, and how this allowed the biosphere to overcome fixed nitrogen limitation by tapping the seemingly endless reserve of atmospheric dinitrogen (N 2 ). In telling these stories, we aimed to generate template(s) to motivate future interdisciplinary natural history studies focused on other organisms and processes. Further, we hope to stimulate scientific discourse and provide impetus to become vulnerable and peruse literature of relevance to understanding the causes and consequences of the evolution of your favorite microorganism or biochemical process.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Organic preservation of vase‐shaped microfossils from the late Tonian Chuar Group, Grand Canyon, Arizona, USA

Abstract Vase‐shaped microfossils (VSMs) are found globally in middle Neoproterozoic (800–730 Ma) marine strata and represent the earliest evidence for testate (shell‐forming) amoebozoans. VSM tests are hypothesized to have been originally organic in life but are most commonly preserved as secondary mineralized casts and molds. A few reports, however, suggest possible organic preservation. Here, we test the hypothesis that VSMs from shales of the lower Walcott Member of the Chuar Group, Grand Canyon, Arizona, contain original organic material, as reported by B. Bloeser in her pioneering studies of Chuar VSMs. We identified VSMs from two thin section samples of Walcott Member black shales in transmitted light microscopy and used scanning electron microscopy to image VSMs. Carbonaceous material is found within the internal cavity of all VSM tests from both samples and is interpreted as bitumen mobilized from Walcott shales likely during the Cretaceous. Energy dispersive X‐ray spectroscopy (EDS) and wavelength dispersive X‐ray spectroscopy (WDS) reveal that VSM test walls contain mostly carbon, iron, and sulfur, while silica is present only in the surrounding matrix. Raman spectroscopy was used to compare the thermal maturity of carbonaceous material within the samples and indicated the presence of pyrite and jarosite within fossil material. X‐ray absorption spectroscopy revealed the presence of reduced organic sulfur species within the carbonaceous test walls, the carbonaceous material found within test cavities, and in the sedimentary matrix, suggesting that organic matter sulfurization occurred within the Walcott shales. Our suite of spectroscopic analyses reveals that Walcott VSM test walls are organic and sometimes secondarily pyritized (with the pyrite variably oxidized to jarosite). Both preservation modes can occur at a millimeter spatial scale within sample material, and at times even within a single specimen. We propose that sulfurization within the Walcott Shales promoted organic preservation, and furthermore, the ratio of iron to labile VSM organic material controlled the extent of pyrite replacement. Based on our evidence, we conclude that the VSMs are preserved with original organic test material, and speculate that organic VSMs may often go unrecognized, given their light‐colored, translucent appearance in transmitted light.

58 GEOSCIENCES↗
DOE OSTI2022

Impact of non‐framework cation mixing on the structure and crystallization behavior of model high‐level waste glasses

Abstract Spinel crystallization is known to be detrimental to the operation of Joule heated ceramic melters during the vitrification of iron‐rich high‐level nuclear wastes (HLW) into borosilicate glasses. The literature on this subject focuses on tackling the problem by developing empirical constraints to design compositions, which limit the fraction of spinels formed in the melter or by developing empirical models to predict the settling behavior of spinels in the melter as a function of the glass composition. While these empirical models can predict the behavior of most of the compositions, they are not failsafe as there are always some compositions, whose behavior is beyond the predictive ability of these models. This can lead to undesirable situations during the vitrification of the nuclear waste, and therefore an in‐depth investigation of the chemo‐structural descriptors controlling the crystallization behavior in these glasses is warranted. Accordingly, the present study aims to understand the impact of non‐framework cation mixing (i.e., Li + /Na + and Ca 2+ /Na + ) on the structure (through Raman spectroscopy and Mössbauer spectroscopy) and crystallization behavior (through XRD, SEM‐EDS, and vibrating sample magnetometry) of iron‐rich model HLW glasses in the system: (mol.%) x M y O–(25− x ) Na 2 O–9.12 B 2 O 3 –6.4 Al 2 O 3 –51.25 SiO 2 –7.22 Fe 2 O 3 –0.38 MnO–0.08 Cr 2 O 3 –0.55NiO (M y O = Li 2 O or CaO).

Balasubramanya, Nikhila↗
DOE OSTI2026

Alkali Vapor Corrosion of Spinel (MgAl 2 O 4 ) and Gahnite (ZnAl 2 O 4 ) Refractories—A Comparative Study

Alkali vapor corrosion is critical for refractories used in the kilns and furnaces of diverse high-temperature processing and manufacturing sectors such as gasifiers, cement production, and glass making. Gahnite (ZnAl 2 O 4 ) is being investigated as a potential chrome-free refractory because of its similarity with the structure and properties of magnesium aluminate (MgAl 2 O 4 ) spinel. The alkali vapor corrosion of ZnAl 2 O 4 , MgAl 2 O 4 , and Mg 0.5 Zn 0.5 Al 2 O 4 was studied, according to ASTM C987-10, at 1371°C for 24 h using sodium carbonate (Na 2 CO 3 ). The surface and the polished cross-sections of the corroded ZnAl 2 O 4 , MgAl 2 O 4 , and Mg 0.5 Zn 0.5 Al 2 O 4 specimens were analyzed using x-ray diffraction (XRD), microscopy, and energy-dispersive spectroscopy (EDS) techniques. MgO in MgAl 2 O 4 , ZnO in ZnAl 2 O 4 , Mg 0.77 Zn 0.23 O, and NaAlO 2 were detected as the corrosion products for these specimens. The extent of corrosion substantially varied among the specimens despite the similarity in the corrosion products. The corrosion resistance increased in the following order: Mg 0.5 Zn 0.5 Al 2 O 4 > MgAl 2 O 4 > ZnAl 2 O 4 . The formation of a dense MgO and Mg 0.77 Zn 0.23 O layer for MgAl 2 O 4 and Mg 0.5 Zn 0.5 Al 2 O 4 , respectively, contributed to their superior resistance to alkali vapor corrosion. The underlying corrosion mechanisms are discussed based on experimental observations supported by thermodynamic analysis. Additionally, the results suggest that a partial Zn 2+ substitution for Mg 2+ in MgAl 2 O 4 can enhance the resistance to alkali vapor corrosion.

alkali corrosion↗