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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Stability and phase transition of localized modes in Bose–Einstein condensates with both two- and three-body interactions

We investigate the stability and phase transition of localized modes in Bose–Einstein Condensates (BECs) in an optical lattice with the discrete nonlinear Schrödinger model by considering both two- and three-body interactions. We find that there are three types of localized modes, bright discrete breather (DB), discrete kink (DK), and multi-breather (MUB). Moreover, both two- and three-body on-site repulsive interactions can stabilize DB, while on-site attractive three-body interactions destabilize it. There is a critical value for the three-body interaction with which both DK and MUB become the most stable ones. We give analytically the energy thresholds for the destabilization of localized states and find that they are unstable (stable) when the total energy of the system is higher (lower) than the thresholds. The stability and dynamics characters of DB and MUB are general for extended lattice systems. Our result is useful for the blocking, filtering, and transfer of the norm in nonlinear lattices for BECs with both two- and three-body interactions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

A molecular dynamics study of phase transition in strongly coupled pair-ion plasmas

Existence of phase transition in strongly coupled pair-ion plasmas with soft core is investigated. Extensive Molecular Dynamics (MD) simulations are performed in the canonical ensemble, for such plasmas, at different temperatures, to analyze phase stability. Our studies show interesting phase co-existence between liquid-like and vapor-like phases. The different phases are identified by calculating the ensemble averaged density. This and the corresponding critical properties are calculated directly from MD simulation. The critical temperature of vapor-liquid coexistence is obtained, and the corresponding critical value of density is also estimated for different sizes of the soft core. We have used a novel method that allows the location of phase coexistence through a constant density simulation in which the temperature is changed in a single time-step (quenching) in order to place the system in a thermodynamically and mechanically unstable state, resulting in spontaneous separation of two coexisting phases. The results obtained from this temperature quench MD method also show the coexistence of vapor-liquid phase in pair-ion plasmas. The critical exponents obtained directly from MD simulation are found to be in close agreement with the values predicted by a mean-field theory.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2013

Precision phase control for the radio frequency system of K500 superconducting cyclotron at Variable Energy Cyclotron Centre, Kolkata

Variable Energy Cyclotron Centre (VECC) has commissioned K500 Superconducting cyclotron (SCC) based on MSU and Texas A and M university cyclotrons. The radio frequency (RF) system of SCC has been commissioned with the stringent requirement of various RF parameters. The three-phase RF system of Superconducting cyclotron has been developed in the frequency range 9–27 MHz with amplitude and phase stability of 100 ppm and ±0.1°, respectively. The phase control system has the option to change the relative phase difference between any two RF cavities and maintain the phase stability within ±0.1° during round-the-clock cyclotron operation. The said precision phase loop consists of both analogue In-phase/Quadrature modulator to achieve faster response and also Direct Digital Synthesis based phase shifter to achieve wide dynamic range as well. This paper discusses detail insights into the various issues of phase control for the K500 SCC at VECC, Kolkata.

43 PARTICLE ACCELERATORS↗
NASA NTRS1998

Stability and Phase Noise Tests of Two Cryo-Cooled Sapphire Oscillators

A cryocooled Compensated Sapphire Oscillator (CSO), developed for the Cassini Ka-band Radio Science experiment, and operating in the 8K - 10K temperature range was previously demonstrated to show ultra-high stability of sigma(sub y) = 2.5 x 10 (exp -15) for measuring times 200 seconds less than or equal to tau less than or equal to 600 seconds using a hydrogen maser as reference. We present here test results for a second unit which allows CSO short-term stability and phase noise to be measured for the first time. Also included are design details of a new RF receiver and an intercomparison with the first CSO unit. Cryogenic oscillators operating below about 10K offer the highest possible short term stability of any frequency sources. However, their use has so far been restricted to research environments due to the limited operating periods associated with liquid helium consumption. The cryocooled CSO is being built in support of the Cassini Ka-band Radio Science experiment and is designed to operate continuously for periods of a year or more. Performance targets are a stability of 3-4 x 10 (exp -15) (1 second less than or equal to tau less than or equal to 100 seconds) and phase noise of -73dB/Hz @ 1Hz measured at 34 GHz. Installation in 5 stations of NASA's deep space network (DSN) is planned in the years 2000 - 2002. In the previous tests, actual stability of the CSO for measuring times tau less than or equal to 200 seconds could not be directly measured, being masked by short-term fluctuations of the H-maser reference. Excellent short-term performance, however, could be inferred by the success of an application of the CSO as local oscillator (L.O.) to the JPL LITS passive atomic standard, where medium-term stability showed no degradation due to L.O. instabilities at a level of (sigma)y = 3 x 10 (exp -14)/square root of tau. A second CSO has now been constructed, and all cryogenic aspects have been verified, including a resonator turn-over temperature of 7.907 K, and Q of 7.4 x 10 (exp 8). These values compare to a turn-over of 8.821 K and Q of 1.0 x 10 (exp 9) for the first resonator. Operation of this second unit provides a capability to directly verify for the first time the short-term (1 second less than or equal to tau less than or equal to 200 seconds) stability and the phase noise of the CSO units. The RF receiver used in earlier tests was sufficient to meet Cassini requirements for tau greater than or equal to 10 seconds but had short-term stability limited to 2-4 x 10 (exp -14) at tau = 1 second, a value 10 times too high to meet our requirements. A new low-noise receiver has been designed to provide approximately equal to 10-15 performance at 1 second, and one receiver is now operational, demonstrating again short-term CSO performance with H maser-limited stability. Short-term performance was degraded in the old receiver due to insufficient tuning bandwidth in a 100MHZ quartz VCO that was frequency-locked to the cryogenic sapphire resonator. The new receivers are designed for sufficient bandwidth, loop gain and low noise to achieve the required performance.

Dick, G. John↗
DOE OSTI2019

Effects of Nb on Superelasticity and Low Modulus Properties of Metastable β-Type Ti-Nb-Ta-Zr Biomedical Alloys

In this work, a series of Ti-xNb-2Ta-3Zr (x = 25, 30, 35, 40 wt.%) alloys are designed, and the transformation of β-phase to α″ martensitic, β-phase stability, microstructure, mechanical properties and corrosion performance of these alloys are investigated. The phase analysis shows as the Nb content increases, the α″ phase in these alloys decreases, while the intensity of the two main peaks β(110) and β(211) of Ti-40Nb-2Ta-3Zr alloy is reduced. These results can be attributed to the variation of β-phase stability caused by Nb element of alloy and cold rolling process. The mechanical properties test shows that the elastic modulus (52 GPa) of the Ti-35Nb-2Ta-3Zr alloy is the lowest and the elongation (18.8%) is the maximum. In addition, the alloy is susceptible to β-phase elastic deformation and stress-induced martensitic transformation resulting in the highest recovery strain of the alloy (66.87%). The polarization curves show that the Ti-35Nb-2Ta-3Zr alloy has the highest corrosion potential (− 0.34 V) and the lowest corrosion current density (0.21 μA cm{sup −2}) exhibiting the best corrosion resistance.

36 MATERIALS SCIENCE↗
NASA NTRS2011

Simultaneous Ka-Band Site Characterization: Goldstone, CA, White Sands, NM, and Guam, USA

To statistically characterize atmospheric effects on Ka-band links at NASA operational sites, NASA has constructed site test interferometers (STI s) which directly measure the tropospheric phase stability and rain attenuation. These instruments observe an unmodulated beacon signal broadcast from a geostationary satellite (e.g., Anik F2) and measure the phase difference between the signals received by the two antennas and its signal attenuation. Three STI s have been deployed so far: the first one at the NASA Deep Space Network Tracking Complex in Goldstone, California (May 2007); the second at the NASA White Sands Complex, in Las Cruses, New Mexico (February 2009); and the third at the NASA Tracking and Data Relay Satellite (TDRS) Remote Ground Terminal (GRGT) complex in Guam (May 2010). Two station-years of simultaneous atmospheric phase fluctuation data have been collected at Goldstone and White Sands, while one year of data has been collected in Guam. With identical instruments operating simultaneously, we can directly compare the phase stability and rain attenuation at the three sites. Phase stability is analyzed statistically in terms of the root-mean-square (rms) of the tropospheric induced time delay fluctuations over 10 minute blocks. For two years, the time delay fluctuations at the DSN site in Goldstone, CA, have been better than 2.5 picoseconds (ps) for 90% of the time (with reference to zenith), meanwhile at the White Sands, New Mexico site, the time delay fluctuations have been better than 2.2 ps with reference to zenith) for 90% of time. For Guam, the time delay fluctuations have been better than 12 ps (reference to zenith) at 90% of the time, the higher fluctuations are as expected from a high humidity tropical rain zone. This type of data analysis, as well as many other site quality characteristics (e.g., rain attenuation, infrastructure, etc.) will be used to determine the suitability of all the sites for NASA s future communication services at Ka-band.

Acosta, Roberto↗
NASA NTRS1986

An explanation for the plateau phenomenon in isoelectric focusing

Isoelectric focusing of mixtures of simple ampholytes occurs in two phases, an initial rapid separation phase and a second relatively slow stabilizing phase. Transient and steady-state computer simulation data are shown to predict the development of pH plateaus around neutrality during the stabilizing phase of the focusing of such mixtures. This occurs because a nonzero electrophoretic flux is present in a pure zone of focused ampholyte, which is a function of both its isolectric point (pI) and its Delta-pK value. For an ampholyte with a pI greater than 9 or less than 5, this flux causes the development of a significant concentration gradient within its focused zone which is accompanied by a contraction of this zone along the focusing axis. Acidic and basic ampholytes are thereby displayed toward the anode and cathode respectively, creating a pH plateau in the neutral region. Thus, there will be regions of the focusing column, closer to the electrodes and containing more acidic or basic pH values, within which the resolution of samples will reach a maximum and then decrease.

Mosher, Richard A.↗
DOE OSTI2017

Structural Effects of Lanthanide Dopants on Alumina

Lanthanide (Ln 3+ ) doping in alumina has shown great promise for stabilizing and promoting desirable phase formation to achieve optimized physical and chemical properties. However, doping alumina with Ln elements is generally accompanied by formation of new phases (i.e. LnAlO3, Ln2O3), and therefore inclusion of Ln-doping mechanisms for phase stabilization of the alumina lattice is indispensable. In this study, Ln-doping (400 ppm) of the alumina lattice crucially delays the onset of phase transformation and enables phase population control, which is achieved without the formation of new phases. The delay in phase transition (θ → α), and alteration of powder morphology, particle dimensions, and composition ratios between α- and θ-alumina phases are studied using a combination of solid state nuclear magnetic resonance, electron microscopy, digital scanning calorimetry, and high resolution X-ray diffraction with refinement fitting. Loading alumina with a sparse concentration of Ln-dopants suggests that the dopants reside in the vacant octahedral locations within the alumina lattice, where complete conversion into the thermodynamically stable α-domain is shown in dysprosium (Dy)- and lutetium (Lu)-doped alumina. This study opens up the potential to control the structure and phase composition of Ln-doped alumina for emerging applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

High strain rate deformation of aged TRIP Ti-10V-2Fe-3Al (wt.%) examined by in-situ synchrotron X-ray diffraction

Transformation Induced Plasticity (TRIP) is a promising avenue for tailoring the work hardening response of metastable $β$ titanium (Ti) alloys. Here we show that aged TRIP Ti-10V-2Fe-3Al (wt.%) maintains higher elongations and flow stresses as strain rate increases, if phase stability and microstructural characteristics are tuned. Low temperature aging influences the matrix $β$ phase stability by $ω$ phase precipitation, which affords a promising way to impact the TRIP effect and obtain desirable mechanical properties, ranging from high damping capacity to good strength/ductility combinations. Although TRIP is active during quasi-static and dynamic testing up to 2000 s –1 , increasing aging time and/or strain rate reduces the overall propensity for the TRIP effect and extent of transformation, which occurs rapidly just at the onset of yielding. Importantly, TRIP with $ω$ phase precipitation provides interesting alloying, microstructure, and property design strategies for engineering applications like lightweight protective structures, where high strains and the need for energy absorption are encountered.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Polymorphism and thermodynamic ground state of silver fulminate studied from van der Waals density functional calculations

Silver fulminate (AgCNO) is a primary explosive, which exists in two polymorphic phases, namely, orthorhombic (Cmcm) and trigonal (R3{sup ¯}) forms at ambient conditions. In the present study, we have investigated the effect of pressure and temperature on relative phase stability of the polymorphs using planewave pseudopotential approaches based on Density Functional Theory (DFT). van der Waals interactions play a significant role in predicting the phase stability and they can be effectively captured by semi-empirical dispersion correction methods in contrast to standard DFT functionals. Based on our total energy calculations using DFT-D2 method, the Cmcm structure is found to be the preferred thermodynamic equilibrium phase under studied pressure and temperature range. Hitherto Cmcm and R3{sup ¯} phases denoted as α- and β-forms of AgCNO, respectively. Also a pressure induced polymorphic phase transition is seen using DFT functionals and the same was not observed with DFT-D2 method. The equation of state and compressibility of both polymorphic phases were investigated. Electronic structure and optical properties were calculated using full potential linearized augmented plane wave method within the Tran-Blaha modified Becke-Johnson potential. The calculated electronic structure shows that α, β phases are indirect bandgap insulators with a bandgap values of 3.51 and 4.43 eV, respectively. The nature of chemical bonding is analyzed through the charge density plots and partial density of states. Optical anisotropy, electric-dipole transitions, and photo sensitivity to light of the polymorphs are analyzed from the calculated optical spectra. Overall, the present study provides an early indication to experimentalists to avoid the formation of unstable β-form of AgCNO.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Anomalous grain growth in the surface region of a nanocrystalline CeO2 film under low-temperature heavy ion irradiation

Grain growth and phase stability of nanocrystalline ceria are investigated under ion irradiation at different temperatures. Irradiations at temperatures of 300 and 400 K result in uniform grain growth throughout the film. Anomalous grain growth is observed in thin films of nanocrystalline ceria under 3 MeV Au+ irradiation at 160 K. At this low temperature, significant grain growth is observed within 100 nm from the surface, no obvious growth is detected in the rest of the films. While the grain growth is attributed to a defect-stimulated mechanism at room temperature and above, a defect diffusion-limited mechanism is significant at low temperature with the primary defect responsible being the oxygen vacancy. The nanocrystalline grains remain in the cubic phase regardless of defect kinetics.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2026

Nonequilibrium defect-phase nanostructures stabilized by irradiation in undersaturated Ni-Si nanocrystalline alloy

Nanocrystalline thin films of the undersaturated alloy Ni-8.5 at% Si were subjected to 2 MeV Ti irradiation at temperatures ranging from 450˚C to 550˚C. Correlative microscopy combining transmission electron microscopy (TEM), scanning-TEM and atom probe tomography (APT revealed that large dose irradiation at 450˚C of samples with initial grain sizes below 100 nm stabilized a novel nanostructure which surprisingly contained three co-existing phases, the γ face-centered-cubic (FCC) matrix, γ' L12 ordered precipitates on intragranular dislocation loops and Ni 31 Si 12 precipitates at triple junctions (TJs). In contrast, irradiation at 550˚C and irradiation of larger grain-size samples at 450˚C only produced a γ-γ' two-phase coexistence. Analysis of the three-phase nanostructure and phase field simulations indicates that radiation-induced segregation is most pronounced at TJs, thus triggering the formation of Ni 31 Si 12 precipitates. These incoherent precipitates, in turn, are expected to stabilize the grain size under irradiation. The results are generalized using the concept of driven defect-phases. It is suggested that the stabilization of driven defect-phases may impart radiation resilience by providing localized relaxation modes to the microstructure evolution during and after temporary perturbations in irradiation conditions.

36 MATERIALS SCIENCE↗
NASA NTRS2022

On the Stability and Phase Behavior of Titan's Subsurface Liquid Columns

On Titan, liquid hydrocarbon may stay in the subsurface porous permeable crust known as the alkanofer, analogous to water in Earth’s aquifer. In addition to pressure gradient, the subsurface liquid in alkanofers is subject to vertical compositional grading due to the gravity and temperature gradient. The common wisdom is that the liquid would normally stay underground in a stability established by the pressure that increases with depth as observed in aquifers on Earth. However, Titan’s liquids consist of nitrogen and hydrocarbons, mainly methane and ethane, the behavior of which is very sensitive to temperature and pressure. Consequently, the liquid density does not always increase with depth, thus may introduce a reverse density profile that leads to vertical convective instability of the liquid column. If reverse density profiles are present, capillary pressures arising from liquid trapped within small pores in the crust can help with the column stability. The liquid held in the capillaries can seal the space below it thus helping with the stability, unless the overpressure built from underneath becomes larger than the capillary pressure, which causes leakage to allow the liquids to seep upward from the deep. This situation is analogous to hydrocarbon seeps on Earth, where oil and natural gas escape the reservoir and flow slowly through network of cracks to the surface. An algorithm based on an extended Gibbs equation commonly used in petroleum reservoir engineering is employed in this work to produce pressure, density, and compositional profiles for evaluating the stability and phase behavior of Titan’s subsurface fluids.

Sugata Tan↗
DOE OSTI2015

Magnetostructural, mechanical and electronic properties of manganese tetraboride

Magnetostructural stabilities, mechanical behaviors and electronic structures of various phases of manganese tetraboride (MnB{sub 4}) have been investigated systematically by density functional theory (DFT) based first-principles methods. It is found that MnB{sub 4} undergoes temperature-induced phase transitions from the nonmagnetic (NM) monoclinic mP20 structure to the ferromagnetic (FM) orthorhombic oP10 structure at 438 K, then to the antiferromagnetic (AFM) orthorhombic oP10 structure at 824 K. We reveal that the NM insulating mP20 phase stabilizes by the Peierls distortion breaking the structural degeneracy, while the FM and AFM metallic oP10 phases stabilize by the Stoner magnetism lifting the spin degeneracy. Furthermore, the calculated mechanical properties show that the NM mP20, FM oP10, and AFM oP10 phases exhibit low compressibility and high hardness, which originate from their three-dimensional covalent boron networks. Therefore, this unique temperature-assisted insulator-metal transition, strong stiffness and high hardness suggest that MnB{sub 4} may find promising technological applications as thermoelectric switches and field effect transistors at the extreme conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Complexions at the iron-magnetite interface

Synthesizing distinct phases and controlling crystalline defects are key concepts in materials design. These approaches are often decoupled, with the former grounded in equilibrium thermodynamics and the latter in nonequilibrium kinetics. By unifying them through defect phase diagrams, we can apply phase equilibrium models to thermodynamically evaluate defects—including dislocations, grain boundaries, and phase boundaries—establishing a theoretical framework linking material imperfections to properties. Using scanning transmission electron microscopy (STEM) with differential phase contrast (DPC) imaging, we achieve the simultaneous imaging of heavy Fe and light O atoms, precisely mapping the atomic structure and chemical composition at the iron-magnetite (Fe/Fe 3 O 4 ) interface. We identify a well-ordered two-layer interface-stabilized phase state (referred to as complexion) at the Fe[001]/Fe 3 O 4 [001] interface. Using density-functional theory (DFT), we explain the observed complexion and map out various interface-stabilized phases as a function of the O chemical potential. The formation of complexions increases interface adhesion by 20% and alters charge transfer between adjacent materials, impacting transport properties. Our findings highlight the potential of tunable defect-stabilized phase states as a degree of freedom in materials design, enabling optimized corrosion protection, catalysis, and redox-driven phase transitions, with applications in materials sustainability, efficient energy conversion, and green steel production.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Computational discovery of ultra-strong, stable, and lightweight refractory multi-principal element alloys. Part II: comprehensive ternary design and validation

Abstract Here the discovery of refractory multi-principal element alloys (MPEAs) with high-temperature strength and stability is pursued within a constrained and application-relevant design space. A comprehensive approach is developed and applied to explore all 165 ternary systems in the Al-Ce-Fe-Hf-Mo-Nb-Ta-Ti-V-W-Zr family. A subset of ternary systems that contain large areas in composition–temperature space with high strength and robust BCC phase stability is found. Twelve sets of high-performing alloys are identified, each set optimized for one combination of phase constraint, optimization target, and temperature range. Preliminary mechanical tests support the viability of the method. This work highlights the importance of considering phase stability, exploring non-equiatomic regions of composition space, and applying application-relevant constraints. Parts I and II provide three down-selection techniques for identifying high-performing BCC refractory MPEAs, design guidelines, and many candidates predicted to have BCC phase stability and strengths 2–3 times higher than any reported to date.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The CALPHAD approach for HEAs: Challenges and opportunities

Phases are key microstructural features that determine material properties. The most intuitive way of representing phase stability in a material is by its phase diagram. The vastness of the composition space is the most compelling reason for investigating high-entropy alloys (HEAs), but it also creates major challenges in controlling phases and microstructures of HEAs due to lack of experimental phase diagrams in highly concentrated multicomponent space. The CALPHAD (Calculation of Phase Diagram) approach, although it needs improvements, is the only viable way to calculate multicomponent phase diagrams. The two major property databases in CALPHAD, Gibbs energy and mobility, when coupled, can provide not only the equilibrium phase information, but also information about diffusion and kinetics. In this article, we will review the use of the CALPHAD approach in understanding phase stability and diffusion in high-entropy alloys. Finally, we will discuss the notable trend of coupling the high-throughput CALPHAD approach with machine learning in HEA design.

36 MATERIALS SCIENCE↗
DOE OSTI2016

First-principles study of crystalline and amorphous AlMgB{sub 14}-based materials

We report first-principles investigations of crystalline and amorphous boron and M1{sub x}M2{sub y}X{sub z}B{sub 14−z} (M1, M2 = Al, Mg, Li, Na, Y; X = Ti, C, Si) phases (so-called “BAM” materials). Phase stability is analyzed in terms of formation energy and dynamical stability. The atomic configurations as well as the electronic and phonon density states of these phases are compared. Amorphous boron consists of distorted icosahedra, icosahedron fragments, and dioctahedra, connected by an amorphous network. The presence of metal atoms in amorphous BAM materials precludes the formation of icosahedra. For all the amorphous structures considered here, the Fermi level is located in the mobility gap independent of the number of valence electrons. The intra-icosahedral vibrations are localized in the range of 800 cm{sup −1}, whereas the inter-icosahedral vibrations appear at higher wavenumbers. The amorphization leads to an enhancement of the vibrations in the range of 1100–1250 cm{sup −1}. The mechanical properties of BAM materials are investigated at equilibrium and under shear and tensile strain. The anisotropy of the ideal shear and tensile strengths is explained in terms of a layered structure of the B{sub 12} units. The strength of amorphous BAM materials is lower than that of the crystalline counterparts because of the partial fragmentation of the boron icosahedra in amorphous structures. The strength enhancement found experimentally for amorphous boron-based films is very likely related to an increase in film density, and the presence of oxygen impurities. For crystalline BAM materials, the icosahedra are preserved during elongation upon tension as well as upon shear in the (010)[100] slip system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗