SEARCH · Engineering Papers
Results for “PHASE STABILITY”
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.
Influence of microstructure and phase morphology on the stability of high temperature irradiation resistant thermocouples
Not Available
Lead-Free Semiconductors: Phase-Evolution and Superior Stability of Multinary Tin Chalcohalides
Not Available
Stability of the fcc phase in shocked nickel up to 332 GPa
Despite making up 5-20 wt.% of Earth’s predominantly iron core, the melting properties of elemental nickel at core conditions remain poorly understood, due largely to a dearth of experimental data. We present here an in situ X-ray diffraction study performed on laser shock-compressed samples of bulk nickel, reaching pressures up to ~ 500 GPa. Hugoniot states of nickel were targeted using a flat-top laser drive, with in situ X-ray diffraction data collected using the Linac Coherent Light Source. Rietveld methods were used to determine the densities of the shocked states from the measured diffraction data, while peak pressures were determined using a combination of measured particle velocities, shock transit times, hydrodynamic simulations, and laser intensity calibrations. We observed solid compressed face-centered cubic (fcc) Ni up to at least 332 ± 30 GPa along the Hugoniot—significantly higher than expected from the majority of melt lines that have been proposed for nickel. We also bracket the partial melting onset to between 377 ± 38 GPa and 486 ± 35 GPa.
Formation and stability of gas-phase o -benzoquinone from oxidation of ortho -hydroxyphenyl: A combined neutral and distonic radical study
Gas-phase product detection studies of o-hydroxyphenyl radical and O 2 are reported at 373, 500, and 600 K, at 4 Torr (533.3 Pa), using VUV time-resolved synchrotron photoionisation mass spectrometry. The dominant products are assigned as o-benzoquinone (C 6 H 4 O 2 , m/z 108) and cyclopentadienone (C 5 H 4 O, m/z 80). It is concluded that cyclopentadienone forms as a secondary product from prompt decomposition of o-benzoquinone (and dissociative ionization of o-benzoquinone may contribute to the m/z 80 signal at photon energies ≳9.8 eV). Ion-trap reactions of the distonic o-hydroxyphenyl analogue, the 5-ammonium-2-hydroxyphenyl radical cation, with O 2 are also reported and concur with the assignment of o-benzoquinone as the dominant product. In addition, the ion-trap study also provides support for a mechanism where cyclopentadienone is produced by decarbonylation of o-benzoquinone. Kinetic studies compare oxidation of the ammonium-tagged o-hydroxyphenyl and o-methylphenyl radical cations along with trimethylammonium-tagged analogues. Reaction efficiencies are found to be ca. 5% for both charge-tagged o-hydroxyphenyl and o-methylphenyl radicals irrespective of the charged substituent. G3X-K quantum chemical calculations are deployed to rationalise experimental results for o-hydroxyphenyl + O 2 and its charge-tagged counterpart. The prevailing reaction mechanism, after O 2 addition, involves a facile 1,5-H shift in the peroxyl radical and subsequent elimination of OH to yield o-benzoquinone that is reminiscent of the Waddington mechanism for β-hydroxyperoxyl radicals. These results suggest o-hydroxyphenyl + O 2 and decarbonylation of o-benzoquinone serve as plausible OH and CO sources in combustion.
Weak ferromagnetism and nanodimensional ferroelectric domain structure stabilized in the polar phase of Bi{sub 1−x}Nd{sub x}FeO{sub 3} multiferroics via Ti doping
Crystal structure, microstructure, local ferroelectric, and magnetic properties of the Bi{sub 0.9}Nd{sub 0.1}Fe{sub 1−x}Ti{sub x}O{sub 3} samples have been investigated at room temperature to reveal the effect of Ti{sup 4+} doping on the multiferroic behavior of the lanthanide-modified compound representing a polar (space group R3c) antiferromagnetic phase of the Bi{sub 1−x}Ln{sub x}FeO{sub 3} perovskites. Ti doping results in a gradual suppression of the rhombohedral distortions, however, symmetry of the crystal structure remains the same in the entire concentration range allowing the single-phase perovskites to be obtained (x ≤ 0.08). The doping tends to reduce existing lone-pair cation-driven polar displacements, thus giving rise to a decrease of the ferroelectric polarization in the Bi{sub 0.9}Nd{sub 0.1}Fe{sub 1−x}Ti{sub x}O{sub 3} (x→0.08) series. A drastic (from ∼10 μm for x = 0 to ∼1 μm for 0.02 ≤ x ≤ 0.08) decrease of the average grain size induced by the doping is accompanied by the formation of a ferroelectric domain structure with the average domain width of ∼40 nm. Finally, the doping was shown to induce an antiferromagnetic to weak ferromagnetic transformation. The maximum remanent magnetization observed in the Bi{sub 0.9}Nd{sub 0.1}Fe{sub 1−x}Ti{sub x}O{sub 3} series at x ∼ 0.05 coincides with the locked magnetization releasing upon the magnetic field-induced suppression of the magnetic cycloid in pure BiFeO{sub 3}.
Collective modes in excitonic insulators: Effects of electron-phonon coupling and signatures in the optical response
Here, we consider a two-band spinless model describing an excitonic insulator (EI) on the two-dimensional square lattice with anisotropic hopping parameters and electron-phonon (el-ph) coupling, inspired by the EI candidate Ta 2 NiSe 5 . We systematically study the nature of the collective excitations in the ordered phase which originates from the interband Coulomb interaction and the el-ph coupling. When the ordered phase is stabilized only by the Coulomb interaction (pure EI phase), its collective response exhibits a massless phase mode in addition to the amplitude mode. We show that in the BEC regime, the signal of the amplitude mode becomes less prominent and that the anisotropy in the phase-mode velocities is reduced. Through coupling to the lattice, the phase mode acquires a mass and the signal of the amplitude mode becomes less prominent. Importantly, the character of the softening mode at the boundary between the normal semiconductor phase and the ordered phase depends on the parameters. In particular, we point out that even for el-ph coupling smaller than the Coulomb interaction, the mode that softens to zero at the boundary can have a phonon character. We also discuss how the collective modes can be observed in the optical conductivity. Furthermore, we study the effects of nonlocal interactions on the collective modes and show the possibility of realizing a coexistence of an in-gap mode and an above-gap mode split off from the single-amplitude mode in the system with local interactions only.
Vacuum stability, fixed points, and phases of QED 3 at large N f
Not Available
Quantum stabilization of unexpected ordered phases on the honeycomb lattice
In this work, I discuss and showcase the utility of the method called minimally-augmented spin-wave theory (MAGSWT) as a relatively simple semi-analytical approach to the phase diagrams of quantum magnets. It complements numerical methods by providing physical insight into which states are competitive and by yielding approximate phase boundaries that agree well with much more numerically intensive calculations. This approach enabled me to construct the faithful phase diagrams of two paradigmatic honeycomb-lattice models in the quantum S=1/2 limit, the J 1 –J 3 FM-AF and J 1 –J 2 AF models, for the collinear quantum phases that replace or extend the classical ones. The results are in good qualitative and semi-quantitative agreement with state-of-the-art numerical studies for these models, correctly capturing the emergence of unexpected quantum phases and the suppression of classically favored spiral orders by quantum fluctuations. This study provides a much-needed important guidance to the ongoing theoretical and experimental searches of the unconventional quantum states. This work will be of significant and timely interest to both theorists and experimentalists in the field of quantum magnetism, broadly defined.
Multiple Stable Oscillators Referenced to the Same Multimode AlN/Si MEMS Resonator with Mode-Dependent Phase Noise and Frequency Stability
Explore the source record for details and available documents.
Phase composition and radiation stability of matrices for isolation of REE-actinide waste
Safe treatment with highly radioactive wastes from processing of irradiated fuel is a key problem at the final stage of the nuclear energy cycle. The waste prod ucts are currently immobilized in glassy matrices for loading in underground storage [1]. Glasses are insuf ficiently stable for isolation of long living radionu clides, including actinides. It is suggested to fraction ate such wastes and include long living nuclides in the most stable crystalline matrices in order to increase safety [2]. The available technologies allow us to sepa rate actinides (U, Np, Pu), the REE–actinide compo nent, and products of decay.
Development of an All-Aqueous Thermally Regenerative Redox Flow Battery to Support Fossil Fuel Assets
Low-temperature thermal energy, a largely untapped resource, holds significant promise for large-scale electrical power generation globally. Various stationary sources, including industrial entities and thermal power plants, emit considerable low-temperature heat that currently remains unutilized. This energy is often overlooked because its low temperature renders it unsuitable for efficient power generation using conventional methods. However, current research is exploring diverse technologies capable of converting low-temperature heat into grid-scale power, aiming to enhance grid efficiency, further decarbonization initiatives, and facilitate a shift toward more decentralized power systems. One such innovative technology is the thermally regenerative battery (TRB), noted for its high power and energy densities compared to similar technologies, positioning it as a potential game-changer in power generation. TRBs integrate two scalable and well-established unit operations: a redox flow battery and a distillation column. This integration suggests that once an effective TRB chemistry is established, the pathway to commercialization could be expedited. The copper-based thermally regenerative ammonia battery (Cu aq -TRAB) stands out as the first TRB that circumvents electrodeposition/dissolution reactions, stabilizing Cu(I) and Cu(II) within the electrolyte and maintaining stability of all electroactive species in an aqueous phase. This stabilization has led to improvements in coulombic efficiency, open circuit potential, and copper solubility, thereby enhancing power density, energy density, and overall energy efficiency. Preliminary tests were conducted to determine the effects of various electrolyte species on the performance metrics of the battery, both theoretically and experimentally. These tests revealed that the solubility of copper in the Cu aq -TRAB electrolyte was constrained by the Cu(I)-NH 3 complex. Adjusting the background electrolyte to 5 M NH4Br and the ligand concentration to 4 M NH 3 enabled the copper concentration to reach a maximum of 0.6 M. This modification led to an estimated theoretical maximum energy density of 9.5 Wh L -1 for the Cu aq -TRAB. Additionally, full cell testing indicated a tradeoff between peak power and energy density with varying copper and ammonia concentrations. Increasing the applied current density during discharge linearly raised the average power output, with a minimal reduction in energy density due to a balance between higher ohmic overpotential and reduced time for undesirable ammonia crossover. Furthermore, a comprehensive numerical sensitivity analysis of the complete Cu aq -TRAB system was performed. This analysis aimed to assess how the battery and the distillation column responded to changes in system input parameters, providing insights into optimal research directions for enhancing system performance. The analysis revealed that at room temperature, battery power was significantly more sensitive to ohmic losses than to mass transfer, with reaction rates having minimal impact. This trend continued even at higher temperatures. Also, the thermal energy required for ammonia separation was studied, showing that increased temperatures generally reduced energy requirements, except in low-pressure scenarios above 65 °C. An investigation into membrane performance in the Cu aq -TRAB was undertaken, given the significant impact of ammonia transport control and ohmic losses on system performance. Various membranes were evaluated to identify key performance metrics. Among the tested membranes, Selemion CMVN exhibited the highest performance, with a peak power density of 84 mW cm -2 and average values of 26 ± 6.8 mW cm -2 for power density and 2.9 Wh L -1 for energy density at an applied current density of 50 mA cm -2 . An economic assessment indicated a levelized cost of storage at $410 per MWh under optimal conditions, highlighting the commercial potential of the Cu aq -TRAB when utilizing cost-effective, readily available materials.
Stabilization of high Tc phase in bismuth cuprate superconductor by lead doping
It has been widely ascertained that doping of lead in Bi-Sr-Ca-Cu-O systems promotes the growth of high T sub c (110 K) phase, improves critical current density, and lowers processing temperature. A systematic study was undertaken to determine optimum lead content and processing conditions to achieve these properties. A large number of samples with cationic compositions of Bi(2-x)Pb(x)Sr2Ca2Cu3 (x = 0.2 to 2.0) were prepared by conventional solid state reaction technique. Samples of all compositions were annealed together at a temperature and characterized through resistance temperature (R-T) measurements and x ray diffraction to determine the zero resistance temperature, T sub c(0) and to identify presence of phases, respectively. The annealing temperature was varied between 790 and 880 C to optimize processing parameters. Results are given. In brief, an optimum process is reported along with composition of leaded bismuth cuprate superconductor which yields nearly a high T sub c single phase with highly stable superconducting properties.
Formation and stability of gas-phase o-benzoquinone from oxidation of ortho-hydroxyphenyl: a combined neutral and distonic radical study
Explore the source record for details and available documents.
Grain boundary segregation as a route to stabilize nanocrystalline alloys: A phase field study.
Abstract not provided.
The Stability of Magnesium Hydroxychloride Phases And Their Role in SCC.
Abstract not provided.