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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 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Premelting, Melting, and Degradation Properties of Molten Alkali Nitrates: LiNO{sub 3}, NaNO{sub 3}, KNO{sub 3}, and Binary NaNO{sub 3}-KNO{sub 3}

A simultaneous thermal analyzer (STA) was used to observe the transition and degradation events of LiNO{sub 3}, NaNO{sub 3}, KNO{sub 3}, and binary NaNO{sub 3}-KNO{sub 3} salts for potential use as phase change materials (PCMs) and heat transfer fluid (HTF). Samples were heated from 50 °C to 800 °C at 10 °C/min scanning rate in three atmospheres (argon, air, and oxygen) using an STA to observe decomposition behavior. Thermal stability increased for all salts at high partial pressure of O{sub 2} (P{sub O{sub 2}}= 1.0) compared to inert argon (P{sub O{sub 2}}= 0). O{sub 2}, N{sub 2}, NO, N{sub 2}O, and NO{sub 2} were main evolved gases during nitrate decomposition. NO and O{sub 2} started to evolve at approximately the same temperature after melting, indicating that primary and secondary decomposition reactions were concurrent and overlapping. The solid-solid transition, liquidus and solidus temperatures, heat of transition, heat of melting, and heat of solidification were obtained at various heating-cooling rates (1, 2, 4, 5, 6, 8, 10, and 15 °C/min) using an STA. At all heating-cooling rates, a small gap exists between liquidus and solidus temperatures for all samples due to the salts exhibiting supercooling phenomena. This study showed that the degradation point depends on the blanket atmosphere top of the molten salts and that heating rates have a minor effect on transition events (peaks height, peaks width, and transition enthalpies).

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Binary Alkali Nitrate and Chloride Phase Diagrams: NaNO{sub 3}-KNO{sub 3}, LiNO{sub 3}-NaNO{sub 3}, LiNO{sub 3}-KNO{sub 3}, and NaCl-KCl

LiNO{sub 3}-NaNO{sub 3}, LiNO{sub 3}-KNO{sub 3,} NaNO{sub 3}-KNO{sub 3}, and NaCl-KCl phase relations were formulated using the regular solution model to obtain desired compositions for their potential application as a heat transfer fluid. The simultaneous nonlinear equations formed were solved numerically using a contour plot technique in Matlab. An algorithm was developed to determine the real roots of the coupled nonlinear equations and subsequent phase diagrams were constructed. The phase diagrams were compared with those predicted using FactSage thermochemical package and literature data from experimental studies. The calculated NaNO{sub 3}-KNO{sub 3} phase diagram shows that this system has a eutectic point at 0.5 mole fraction of KNO{sub 3} with a eutectic temperature of 220.85 °C, while the LiNO{sub 3}-KNO{sub 3} system was found to have a eutectic point at 0.44 mole fraction LiNO{sub 3} at 137 °C. The LiNO{sub 3}-NaNO{sub 3} system shows a eutectic at 0.524 mole fraction LiNO{sub 3} at 192.8 °C, and finally the NaCl-KCl system has a eutectic point at 0.48 mole fraction NaCl at 634 °C. The liquidus and solidus curves obtained fitted close against values obtained from the quasi-chemical model used in FactSage and experimental values from the literature. This study showed that the regular solution model combined with the contour plots approach can sufficiently describe the liquidus–solidus curves of the alkali binary nitrate and chloride systems and could be a useful method for predicting the phase diagrams for higher order alkali nitrates and chlorides.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Calculating Ti-6Al-4V β Transus Through a Chemistry-Based Equation Derived from Combined Element Binary Phase Diagrams

A mathematical model was developed to correlate the relationship between titanium alloying elements (Al, O, N, C, V, and Fe) in Ti-6Al-4V, and the resulting beta transus temperature (β{sub t}). The model was produced by analyzing the slope of the lines separating the alpha + beta (α + β) and beta (β) phase fields on combined element binary phase diagrams generated through the Pandat modeling software. Experimental results showed a strong agreement between the baseline data, obtained through differential thermal analysis (DTA), and the calculated β{sub t}, determined by measuring the chemistry at a location adjacent to the DTA sample. The difference between the calculated β{sub t} and the baseline DTA data was approximately ± 10 °F (± 5.56 °C). The thermodynamically ideal β{sub t} temperature was additionally modeled for each set of chemistries through the Pandat software. These results were compared to the β{sub t} temperatures determined through the chemistry-based equation and DTA methods.

36 MATERIALS SCIENCE↗
DOE OSTI2024

First Principles Evaluation of Phase Stability in the In-Sn Binary System

Abstract The In-Sn binary alloy system exhibits several unusual features that challenge crystallographic and thermodynamic expectations. We combine first principles total energy calculation with simple thermodynamic modeling to address two key points. First, we evaluate energies along the Bain path to interpret the discontinuous transition between the phases α-In (Pearson type tI2) and β-In 3 Sn (also Pearson type tI2) that are identical in symmetry. Second, we demonstrate that the solid solution phases β-In 3 Sn and γ-InSn 4 (Pearson type hP1) exist at high temperatures only, and they exhibit eutectoid decompositions at low temperatures.

Chemistry↗
DOE OSTI2024

Evaluation of sintered bauxite proppant for binary enhanced geothermal systems

Abstract Solid granular proppant particles are widely used in oil and gas development to sustain permeability through fractures after hydraulic stimulation. Similar proppants are of interest for geothermal applications where the goal of sustaining permeability is the same, but the harsh geothermal environment risks rapid proppant degradation that will reduce fracture permeability. Here, we present proppant conductivity experiments using saw cut granite, tensile fractured granite, and aluminum control specimens packed with sintered bauxite ceramic proppants at concentrations of 0.0, 0.1, and 1.0 kg/m 2 . Simulated geothermal conditions included temperatures up to 130 °C and normal closure stresses up to 60 MPa. Compared to unpropped specimens, peak fracture conductivity enhancement was up to 6 orders of magnitude. At simulated geothermal conditions, proppants were able to sustain fracture conductivity over 60 h, but chemical dissolution and decreasing permeability over time were evident. Irreversible conductivity reductions with crushing and embedment of proppants during loading stages were also observed. Overall, sintered bauxite proppant remains a promising option for low-temperature binary-cycle enhanced geothermal systems.

58 GEOSCIENCES↗
DOE OSTI2013

Stability of binary nanocrystalline alloys against grain growth and phase separation

Grain boundary segregation has been established through both simulation and experiments as a successful approach to stabilize nanocrystalline materials against grain growth. However, relatively few alloy systems have been studied in this context; these vary in their efficacy, and in many cases the stabilization effect is compromised by second phase precipitation. We address the open-ended design problem of how to select alloy systems that may be stable in a nanocrystalline state. We continue the development of a general “regular nanocrystalline solution” model to identify the conditions under which binary nanocrystalline alloy systems with positive heats of mixing are stable with respect to both grain growth (segregation removes the grain boundary energy penalty) and phase separation (the free energy of the nanocrystalline system is lower than the common tangent defining the bulk miscibility gap). We calculate a “nanostructure stability map” in terms of alloy thermodynamic parameters. Three main regions are delineated in these maps: one where grain boundary segregation does not result in a stabilized nanocrystalline structure, one in which macroscopic phase separation would be preferential (despite the presence of a nanocrystalline state stable against grain growth) and one for which the nanocrystalline state is stable against both grain growth and phase separation. Additional details about the stabilized structures are also presented in the map, which can be regarded as a tool for the design of stable nanocrystalline alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Hardening in thermally-aged Fe–Cr binary alloys: Statistical parameters of atomistic configuration

Through exploiting Monte Carlo methodology and molecular dynamics, we computationally simulate the spinodal decomposition of iron–chromium binary alloys and analyze the relationship between the increase of yield strength induced by the phase separation phenomenon, and statistical parameters of the atomistic configuration. We successfully model the experimentally-discovered proportional relationship between the hardness and the variation parameter (or V), and also found that the adequacy of the parameter V as an empirical indicator of hardening is limited, because it does not properly capture short-range atomistic configurations that influence the hardening. We anticipate that the short-range-order parameter has more potential to become universal descriptor of the phenomenon.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Phase stability of γ'-Ni 2 Cr and α-Cr in the Ni-Cr binary

For this study, the stability of the γ'-Ni 2 Cr long-range order (LRO) phase present on the Ni-Cr binary phase diagram was examined in a Ni-55Cr (wt. %) alloy. It is shown that the γ'-Ni 2 Cr phase is metastable, and that the two-phase γ-Ni + α-Cr phase field extends to room temperature. The as-cast alloy consisted of a typical dendritic microstructure, with Cr-rich primary α-Cr dendrites and a Cr-lean, γ-Ni interdendritic. Annealing the as-cast alloy at 500°C for 1000 h (γ'-Ni 2 Cr + α-Cr phase field) resulted in pockets of α-Cr and γ-Ni + γ'-Ni 2 Cr at the dendritic/interdendritic interface, with little change to the interdendritic γ-Ni microstructure. Annealing at 900°C for 4 h (γ-Ni + α-Cr phase field) resulted in the interdendritic precipitation of α-Cr, both as a continuous and discontinuous precipitate. Annealing at 900°C for 4 h followed by 500°C for 1000 h resulted in the interdendritic precipitation of α-Cr at 900°C, but no precipitation of γ'-Ni 2 Cr during subsequent annealing at 500°C. This behavior suggests that the γ'-Ni 2 Cr phase is not the equilibrium phase, but rather a metastable transition phase. Furthermore, it is speculated that this phase in more complex alloys (i.e. Alloy 690) is also metastable, and its metastability should be considered in applications involving long-term, high temperature exposures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Helium irradiated cavity formation and defect energetics in Ni-based binary single-phase concentrated solid solution alloys

In this study, binary single-phase concentrated solid solution alloys (SPCSAs), including Ni 80 Co 20 , Ni 80 Fe 20 , Ni 80 Cr 20 , Ni 80 Pd 20 , and Ni 80 Mn 20 (in atomic percentage), were irradiated with 200 keV He + ions at 500 °C. He cavity size and density distribution were systematically investigated using transmission electron microscope. Here we show that alloying elements have a clear impact on He cavity formation. Cavity size is the smallest in Ni 80 Mn 20 but the largest in Ni 80 Co 20 . Alloying elements could also substantially affect cavity density profile. In-depth examination of cavities at peak damage region (~500 nm) and at low damage region (~300 nm) demonstrates that cavity size is depth (damage) dependent. Competition between consumption and production of vacancies and He atoms could lead to varied cavity size. Density functional theory (DFT) calculations were performed to obtain the formation and migration energies of interstitials and vacancies. Combined experimental and simulation results show that smaller energy gap between interstitial and vacancy migration energies may lead to smaller cavity size and narrower size distribution observed in Ni 80 Mn 20 , comparing with Ni 80 Co 20 . Finally, the results of this study call attention to alloying effects of specific element on cavity formation and defect energetics in SPCSAs, and could provide fundamental understanding to predict radiation effects in more complexed SPCSAs, such as high entropy alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Anisotropic Cahn-Hilliard free energy and interfacial energies for binary alloys with pairwise interactions

The original Cahn-Hilliard derivation of the contribution of compositional inhomogeneity to the free energy of a binary alloy with pairwise interactions is extended to include higher-order inhomogeneity terms. For alloys on a cubic lattice, the coefficient of the first inhomogeneity is a second-rank tensor and reduces to a scalar, but it is shown that the second order and the third order inhomogeneity terms are weighted by fourth-rank and sixth-rank tensors, thus resulting in anisotropic contributions. Furthermore, each interaction shell generates a unique set of inhomogeneity coefficients that is determined by the set of vectors connecting an atom to its neighbors on that shell. These coefficients are calculated for fcc and bcc alloys with interactions up fourth nearest neighbors. Phase field simulations based on these extended Cahn-Hilliard free energies are performed to measure interface free energies along specific crystallographic directions as a function of temperature, and to obtain the equilibrium shape of precipitates. Interface free energies, and the resulting anisotropies, are compared to those obtained by discrete models and Monte Carlo simulations.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Topological defect formation in rotating binary dipolar Bose–Einstein condensate

We investigate the topological defects and spin structures of a rotating binary Bose–Einstein condensate, which consists of both dipolar and scalar bosonic atoms confined in spin-dependent optical lattices, for an arbitrary orientation of the dipoles with respect to their plane of motion. Our results show that the tunable dipolar interaction, especially the orientation of the dipoles, can be used to control the direction of stripe phase and its related half-vortex sheets. In addition, it can also be used to obtain a regular arrangement of various topological spin textures, such as meron, circular and cross disgyration spin structures. We point out that such topological defects and regular arrangement of spin structures arise primarily from the long-range and anisotropic nature of dipolar interaction and its competition with the spin-dependent optical lattices and rotation. - Highlights: • Effects of both strength and orientation of the dipoles are discussed. • Various topological defects can be formed in different parameter regions. • Present one possible way to obtain regular arrangements of spin textures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Testing claims of the GW170817 binary neutron star inspiral affecting β-decay rates

On August 17, 2017, the first gravitational wave signal from a binary neutron star inspiral (GW170817) was detected by Advanced LIGO and Advanced VIRGO. Here we present radioactive β-decay rates of three independent sources 44 Ti, 60 Co and 137 Cs, monitored during the same period by a precision experiment designed to investigate the decay of long-lived radioactive sources. We do not find any significant correlations between decay rates in a 5 h time interval following the GW170817 observation. This contradicts a previous claim published in this journal of an observed 2.5σ Pearson Correlation between fluctuations in the number of observed decays from two β-decaying isotopes ( 32 Si and 36 Cl) in the same time interval. By correcting for the choice of an arbitrary time interval, we find no evidence of a correlation above 1.5σ confidence. In addition, we argue that such analyses on correlations in arbitrary time intervals should always correct for the so-called Look-Elsewhere effect by quoting the global significance.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

First-principles calculations and thermodynamic modeling of the Yb-Ni binary system

A complete thermodynamic description of the Yb-Ni binary system is developed by means of the CALculation of PHAse Diagram (CALPHAD) method in combination with first-principles calculations based on density functional theory (DFT) and available experimental data in the literature. Finite temperature thermodynamic properties of the Yb-Ni intermetallic compounds are predicted using the quasi-harmonic approach, where first-principles phonon calculations are performed to calculate the lattice vibrational entropy. Here, the associate solution model is used to describe the complex thermodynamic behavior of the liquid phase. The calculated phase diagram agrees well the experimental phase equilibrium data in the literature. By the coupling of CALPHAD modeling with first-principles calculations, the present work provides a more thermodynamically accurate model of the Yb-Ni system when compared to previous models.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Ab initio simulations on the pure Cr lattice stability at 0K: Verification with the Fe-Cr and Ni-Cr binary systems

Significant discrepancies have been observed and discussed on the lattice stability of Cr between the predictions from the ab initio calculations and the CALPHAD approach. In the current work, we carefully examined the possible structures for pure Cr and reviewed the history back from how Kaufman originally determined the Gibbs energy of FCC-Cr in the 1970s. The reliability of Cr lattice stability derived by the CALPHAD and ab initio approaches was systematically discussed. It is concluded that the Cr lattice stability based on the CALPHAD approach has large uncertainty. Meanwhile, we cannot claim that the ab initio H FCC-Cr is error-free as FCC-Cr is an unstable phase under ambient conditions. The present work shows that the ab initio HFCC-Cr can be a viable scientific approach. As both approaches have their limitations, the present work propose to integrate the ab initio results into the CALPHAD platform for the development of the next generation CALPHAD database. As a result, the Fe-Cr and Ni-Cr binary systems were chosen as two case studies demonstrating the capability to adopt the ab initio Cr lattice stability directly into the current CALPHAD database framework.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Perrhenate incorporation into binary mixed sodalites: The role of anion size and implications for technetium-99 sequestration

Perrhenate (ReO 4 - ), as a TcO 4 - analogue, was incorporated into mixed-anion sodalites from binary solutions containing ReO 4 - and a competing anion X n- (Cl - , CO 3 2- , SO 4 2- , MnO 4 - , or WO 4 2- ). For this study, our objective was to determine the extent of solid solution formation and the dependence of competing ion selectivity on ion size. Using equivalent aqueous concentrations of the anions (ReO 4 - /X n- molar ratio = 1:1), we synthesized mixed-anion sodalites from zeolite and NaOH at 90 °C for 96 h. The resulting solids were characterized by bulk chemical analysis, powder X-ray diffraction, scanning electron microscopy, and X-ray absorption near edge structure (XANES) spectroscopy to determine crystal structure, chemical composition, morphology, and rhenium (Re) oxidation state. Rhenium in the solid phase occurred predominately as Re(VII)O 4 - in the sodalites, which have a primitive cubic pattern in the space group P43n. The refined unit-cell parameters of the mixed sodalites ranged from 8.88 to 9.15 Å and showed a linear dependence on the size and mole fraction of the incorporated anion(s). The ReO 4 - selectivity, represented by its distribution coefficient (K d ), increased in the following order: Cl - < NO 3 - < MnO 4 - and CO 3 2- < SO 4 2- < WO 4 2- for the monovalent and divalent anions, respectively. The relationship between the ReO 4 - distribution coefficient and competing anion size was nonlinear. When the difference in ionic radius (DIR) between ReO 4 - and X n - (n = 1 or 2) was greater than ~ 12%, then ReO 4 - incorporation into sodalite was insignificant. The results imply that anion size is the major factor that determines sodalite anion compositions. Given the similarity in chemical behavior and anion size, ReO 4 - serves as a suitable analogue for TcO 4 - under oxidizing conditions where both elements are expected to remain as oxyanions in the + 7 oxidation state.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Autoignition study of binary blends of n- dodecane/1-methylnaphthalene and iso- cetane/1-methylnaphthalene

An experimental study on autoignition of two binary blends, n-dodecane/1-methylnaphthalene and iso-cetane/1-methylnaphthalene, has been conducted using a rapid compression machine. Specifically, the ignition delays of the stoichiometric blend+air mixtures were measured at elevated pressures of P C = 15 bar and 30 bar, compressed temperatures of T C = 626–944 K, and varying blending ratios of the constituents. For a given set of P C and T C , a nonlinear response of the blend reactivity with respect to the relative amount of the constituents was observed. Since a comprehensive chemical kinetic model for the blends investigated here is under development, the current ignition delay datasets serve as the needed targets for model validation. For selected conditions, ignition delay simulations were conducted to highlight and discuss the deficiencies of the literature models and the potential areas for model improvements, especially at low temperatures. In conclusion, further chemical kinetic analyses were conducted to gain understanding of the blending behavior predicted by the available model.

1-methylnaphthalene↗
DOE OSTI2021

A multi-phase-field model of topological pattern formation during electrochemical dealloying of binary alloys

Porous metal structures produced by electrochemical dealloying have been extensively studied for use in various applications that require high surface areas. A new comprehensive multi-phase-field (MPF) model is proposed to study topological porous patterns formed by spontaneously etching a bulk binary alloy that involves electrochemical reactions, bulk and surface diffusion, ion transport, applied electrode potential, and charge conservation. The governing equations for the alloy-porous cluster-electrolyte system account for a generalized Butler-Volmer electrochemical reaction and are in accordance with the classical nucleation theory. Based on a quantitative examination of the effects of electrode potential and precursor composition, the simulation results reproduce typical phenomena including passive surface dealloying, active porosity evolution, critical potential, and characteristic length scale in two-dimension (2-D) and three-dimension (3-D). To consider more complicated dealloying systems, the evolutions of a bimodal porous metal structure, nanocomposite, and nested porous network with a structured hierarchy are investigated. Finally, the proposed model can be a useful tool for understanding and predicting the morphology evolution of diverse porous structures during electrochemical dealloying.

Hierarchical porous structure↗
DOE OSTI2024

Ab initio property predictions of quinary solid solutions using small binary cells

The Set of Small Ordered Structures (SSOS) approach is an ab initio technique for modelling random solid solutions in which many small structures are averaged so that their correlation functions match those of a desired composition. SSOS has been shown to be effective in reducing the cost of density functional theory calculations relative to other well-known techniques such as cluster expansions and special quasirandom structures for modelling solid solutions. Here in this work, we demonstrate that SSOS’s can be constructed using cells with only a subset of elements while still accurately modelling multi-component systems. Specifically, we show that small binary cells can effectively model two quinary high entropy alloys – NbTaTiHfZr and MoNbTaVW – accurately capturing properties such as formation energy, lattice parameters, elastic constants, and root-mean-square atomic displacements. Overall, this insight is useful for those looking to construct databases of such small structures for predicting the properties of multi-component solid solutions, as it greatly decreases the number of structures that needs to be considered.

36 MATERIALS SCIENCE↗