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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Thermal stability of intermetallic phases in Fe-rich Fe-Cr-Ni-Mo alloys

Understanding the stability of precipitate phases in the Fe-rich Fe-Cr-Ni-Mo alloys is critical to the alloy design and application of Mo-containing Austenitic steels. Coupled with thermodynamic modeling, stability of the chi and Laves phases in two Fe-Cr-Ni-Mo alloys were investigated at 1000, 850 and 700 °C for different annealing time. The morphologies, compositions and crystal structures of the matrix and precipitate phases were carefully examined by Scanning Electron Microscopy, Electron Probe Microanalysis, X-ray diffraction and Transmission Electron Microscopy. The two key findings resulted from this work. One is that the chi phase is stable at high temperature and transformed into the Laves phase at low temperature. The other is that both the chi and Laves phases have large solubilites of Cr, Mo and Ni, among which the Mo solubility has a major role on the relative stability of the precipitate phases. The developed thermodynamic models were then applied to evaluating the Mo effect on the stability of precipitate phases in AISI 316 and NF709 alloys.

36 MATERIALS SCIENCE↗
NASA NTRS1981

The NATO III 5 MHz Distribution System

A high performance 5 MHz distribution system is described which has extremely low phase noise and jitter characteristics and provides multiple buffered outputs. The system is completely redundant with automatic switchover and is self-testing. Since the 5 MHz reference signals distributed by the NATO III distribution system are used for up-conversion and multiplicative functions, a high degree of phase stability and isolation between outputs is necessary. Unique circuit design and packaging concepts insure that the isolation between outputs is sufficient to quarantee a phase perturbation of less than 0.0016 deg when other outputs are open circuited, short circuited or terminated in 50 ohms. Circuit design techniques include high isolation cascode amplifiers. Negative feedback stabilizes system gain and minimizes circuit phase noise contributions. Balanced lines, in lieu of single ended coaxial transmission media, minimize pickup.

Vulcan, A.↗
DOE OSTI2017

Computation of entropies and phase equilibria in refractory V-Nb-Mo-Ta-W high-entropy alloys

Here, we have applied the first-principles phonon method to the refractory V-Nb-Mo-Ta-W high-entropy alloys (HEAs) to predict the major phase separations in the temperature-compositional space and hence the associated entropy changes within the systems, taking into account vibrational, electronic, and configurational contributions to the total entropy. The first-principles calculations covered 178 phases ranging from pure elements, the ordered B2, B32, B2 3 , B2 2 , hR8, hR7, tI6, C15, and D0 3 binary phases, two ordered MoNbTaW quaternary phases, and the partially disordered and completely disordered bcc phases. By sorting their relative phase stabilities with the Dantzig's simplex minimization algorithm, the possibilities of phase separation for the refractory quaternary and quinary HEAs were thermodynamically found in the temperature range of 500e907 K.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Experimental formation enthalpies for intermetallic phases and other inorganic compounds

The standard enthalpy of formation of a compound is the energy associated with the reaction to form the compound from its component elements. The standard enthalpy of formation is a fundamental thermodynamic property that determines its phase stability, which can be coupled with other thermodynamic data to calculate phase diagrams. Calorimetry provides the only direct method by which the standard enthalpy of formation is experimentally measured. However, the measurement is often a time and energy intensive process. We present a dataset of enthalpies of formation measured by high-temperature calorimetry. The phases measured in this dataset include intermetallic compounds with transition metal and rare-earth elements, metal borides, metal carbides, and metallic silicides. These measurements were collected from over 50 years of calorimetric experiments. The dataset contains 1,276 entries on experimental enthalpy of formation values and structural information. Most of the entries are for binary compounds but ternary and quaternary compounds are being added as they become available. In conclusion, the dataset also contains predictions of enthalpy of formation from first-principles calculations for comparison.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Combustion synthesis of nanoscale magnesium borides with improved hydrogen uptake and release

The overarching goal of the reported project was to develop reversible metal hydrides that can be dehydrogenated and recharged at relatively low temperatures and pressures. The project complemented the research on reversible metal hydrides for hydrogen storage conducted by the Hydrogen Materials – Advanced Research Consortium (HyMARC). The students involved were trained at both the University of Texas at El Paso (UTEP) and Sandia National Laboratories (SNL). The research objectives were to fabricate nanoscale magnesium boride powders with different B/Mg atomic ratios and to investigate the effects of B/Mg ratio and particle size on the hydrogenation properties of the obtained materials. Magnesium diboride (MgB 2 ) and tetraboride (MgB 4 ) were synthesized by using combustion synthesis and by heating in a tube furnace. The latter method resulted in materials with significantly reduced impurity levels. An effective method for the removal of magnesium oxide impurities was identified. High-energy ball milling produced submicron MgB 2 and MgB 4 powders. However, hydrogenation experiments at pressures up to 700 bar have not shown any uptake of hydrogen. Thermogravimetric analysis of the decomposition of the obtained MgB 2 and MgB 4 demonstrated higher thermodynamic stability of the latter. Thus, the boron-rich nature and phase stability of magnesium borides with high B/Mg ratios make them poor candidates for direct hydrogenation. However, the synthesized MgB 4 is a promising energetic additive to solid fuels for high-speed air-breathing propulsion as it offers a lower oxidation onset temperature and greater energy density than MgB 2 .

08 HYDROGEN↗
NASA NTRS1990

Adaptive noncolocated velocity feedback for vibration damping

A method is proposed for adaptive noncolocated velocity feedback control of flexible structure vibrations. The approach, denoted as auto-tuning, is to drive the system into a sequence of controlled oscillations to provide accurate knowledge of the plant characteristics in the vicinity of the phase cross-over frequencies. An allpass phase notch filter cascade is used as the control architecture to phase stabilize each destabilizing mode in the plant transfer function. The allpass phase notch filter cascade is tuned precisely by the information extracted from the controlled oscillations.

Bayard, David S.↗
NASA NTRS2005

Thermal Characterization of Fe3O4 Nanoparticles Formed from Poorly Crystalline Siderite

Increasing interest in environmental geochemistry has led to the recognition that crystals with sizes in the nanometer range (e.g., colloids and nanoscale precipitates) and poorly crystalline compounds (e.g., ferrihydrites) may comprise the majority of reactive mineral surface area near the Earth s surface. When the diameters of individual particles are in the range of 100 nm or less, the surface energy contribution to the free energy modifies phase stability. This results in stabilization of polymorphs not normally encountered in the macrocrystal domain. These phases potentially have very different surface-site geometries, adsorptive properties, and growth mechanisms, and exhibit size-dependent kinetic behavior. Thus nanophases dramatically modify the physical and chemical properties of soils and sediments. In a more general sense, the characteristics of nanocrystals are of intense technological interest because small particle size confers novel chemical, optical, and electronic properties. Thus, nanocrystalline materials are finding applications as catalytic substrates, gas phase separation materials, and even more importantly in the field of medicine. This is an opportune time for mineral physicists working on nanocrystalline materials to develop collaborative efforts with materials scientists, chemists, and others working on nanophase materials of technological interest (e.g., for magnetic memories). Our objective in this study was to synthesize submicron (<200 nm) magnetite and to study their thermal and particle size properties.

Lauer, H. V., Jr.↗
NASA NTRS2007

Initial Ares I Bending Filter Design

The Ares-I launch vehicle represents a challenging flex-body structural environment for control system design. Software filtering of the inertial sensor output will be required to ensure control system stability and adequate performance. This paper presents a design methodology employing numerical optimization to develop the Ares-I bending filters. The filter design methodology was based on a numerical constrained optimization approach to maximize stability margins while meeting performance requirements. The resulting bending filter designs achieved stability by adding lag to the first structural frequency and hence phase stabilizing the first Ares-I flex mode. To minimize rigid body performance impacts, a priority was placed via constraints in the optimization algorithm to minimize bandwidth decrease with the addition of the bending filters. The bending filters provided here have been demonstrated to provide a stable first stage control system in both the frequency domain and the MSFC MAVERIC time domain simulation.

Jang, Jiann-Woei↗
DOE OSTI2016

Li 3 Y(PS 4 ) 2 and Li 5 PS 4 Cl 2 : New Lithium Superionic Conductors Predicted from Silver Thiophosphates using Efficiently Tiered Ab Initio Molecular Dynamics Simulations

We report two novel, earth-abundant lithium superionic conductors, Li3Y(PS4)2 and Li5PS4Cl2, that are predicted to satisfy the necessary combination of good phase stability, high Li+ conductivity, wide band gap and good electrochemical stability for solid electrolyte applications in all-solid-state rechargeable lithium-ion batteries. These candidates were identified from a high-throughput first-principles screening of the Li–P–S ternary and Li–M–P–S (where M is a non-redox-active element) quaternary chemical spaces, including candidates obtained by replacing Ag with Li in the Ag–P–S and Ag–M–P–S chemical spaces. An efficient tiered screening strategy was developed that combines topological analysis with ab initio molecular dynamics simulations to exclude rapidly candidates unlikely to satisfy the stringent conductivity requirements of lithium superionic conductors. In particular, we find Li3Y(PS4)2 to be an extremely promising candidate exhibiting a room-temperature Li+ conductivity of 2.16 mS/cm, which can be increased multifold to 7.14 and 5.25 mS/cm via aliovalent doping with Ca2+ and Zr4+, respectively. More critically, we show that the phase and electrochemical stability of Li3Y(PS4)2 is expected to be better than current state-of-the-art lithium superionic conductors.

Zhu, Zhuoying↗
DOE OSTI2014

Misfit strain-temperature phase diagrams and domain stability of asymmetric ferroelectric capacitors: Thermodynamic calculation and phase-field simulation

Thermodynamic calculation and phase-field simulation have been conducted to investigate the misfit strain-temperature phase diagrams, dielectric property, and domain stability of asymmetric ferroelectric capacitors (FCs), with considering the effects of dissimilar screening properties and work function steps at the two interfaces. The distinct features of asymmetric FCs from their symmetric counterparts have been revealed and discussed. Polar states with nonzero out-of-plane polarization in parallel with the built-in field are found preferential to form in asymmetric FCs. Meanwhile, the built-in field breaks the degeneracy of states with out-of-plane polarization in anti-directions. This leads to the necessity of redefining phases according to the bistability of out-of-plane polarization. Moreover, the phase stability as well as the dielectric behavior can be significantly controlled by the properties of electrodes, misfit strain, and temperature. The phase-field simulation result also shows that polydomain instability would happen in asymmetric FCs as the equivalence of domain stability in anti-directions is destroyed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Investigation of Zr-doped BSCF perovskite membrane for oxygen separation in the intermediate temperature range

The series of (Ba₀.₅Sr₀.₅)(Co₀.₈Fe₀.₂){sub 1–z}Zr{sub z}O{sub 3–δ} (z=0, 0.01, 0.03, 0.05, 0.07, and 0.09) was synthesized by a sol–gel method. The materials with a zirconium content up to 3 mol% were found to be single phase. Further increase results in formation of a mixed (Ba,Sr)ZrO₃ by-phase, which was found along the grain boundaries and in the grains. With increasing zirconium content the oxygen permeation flux decreases considerably. The effect of the zirconium substitution on the long-term phase stability was investigated by long-term oxygen permeation experiments and X-ray diffraction. A slight stabilization of the oxygen flux of (Ba₀.₅Sr{sub 0.5})(Co₀.₈Fe₀.₂)₀.₉₇Zr₀.₀₃O{sub 3–δ} was found after 180 h at 1023 K. However, all compositions show a decrease in permeation flux with time, but the pure BSCF membrane exhibited the strongest drop after 180 h of operation. The decomposition products of the cubic perovskite phase were found to be a hexagonal Ba{sub 0.5±x}Sr{sub 0.5±x}CoO₃ and a rhombohedral Ba{sub 1–x}Sr{sub x}Co{sub 2–y}Fe{sub y}O{sub 5–δ}. - Graphical abstract: Backscattered-electron channeling contrast image of BSCF membrane cross-section after long-term oxygen permeation at 1023 K showing different phases in different colors. Highlights: • Ba₀.₅Sr₀.₅Co₀.₈Fe₀.₂O{sub 3–δ} systematically doped with increasing amount of zirconium. • Cubic single-phase materials up to 3 wt% zirconium. • Mixed (Ba,Sr)ZrO₃ by-phase formed mainly in the grain boundaries. • Jänecke prism was proposed by XRD and EDXS data. • (Ba₀.₅Sr₀.₅)(Co₀.₈Fe₀.₂)₀.₉₇Zr₀.₀₃O{sub 3–δ} showed a slight stabilization of oxygen flux as compared to pure Ba₀.₅Sr₀.₅Co₀.₈Fe₀.₂O{sub 3–δ}.

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

The effect of native point defect thermodynamics on off-stoichiometry in beta-Mg17Al12

The mechanical strength of Mg-Al-Zn alloys can be affected by a fine spatial dispersion of {beta}-Mg{sub 17}Al{sub 12} precipitates in the Mg matrix. In an effort to understand the phase stability and the unusual asymmetric off-stoichiometry observed in {beta}-Mg{sub 17}Al{sub 12}, we have performed a series of first-principles density functional theory (DFT) calculations of bulk and defect properties of Mg{sub 17}Al{sub 12}. Specifically, we consider native point defects (i.e. vacancies and anti-sites) in all four sublattices of Mg{sub 17}Al{sub 12}, i.e. 2a, 8c, 24g (Mg) and 24g (Al). The T = 0 K static energies of defect Mg{sub 17}Al{sub 12} supercells indicate that anti-site defects are energetically favored over vacancies, and the lowest anti-site defect formation energies are in 24g sites for both Al{sub Mg} and Mg{sub Al}. These Al-rich and Mg-rich anti-site defect formation energies are similar in magnitude, and thus do not explain the asymmetric off-stoichiometry of Mg{sub 17}Al{sub 12}. We also investigate the effect of atomic vibrations via DFT phonon calculations on native point defect free energies of Mg{sub 17}Al{sub 12} and combine these entropic contributions with the point defect formation energies to evaluate the thermodynamics of off-stoichiometry in this phase. We find that the formation of the Al{sub Mg} anti-site is not strongly stabilized by vibrational entropy. Thus, we conclude that the observed asymmetry in the off-stoichiometry of the {beta}-Mg{sub 17}Al{sub 12} phase in the Mg-Al phase diagram is not explained by simple native point defect thermodynamics, and must involve a more complicated defect formation mechanism, such as multi-defect clustering.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1976

Phase transformation and stabilization of a high strength austenite

An investigation of the phase transformation and the austenite stabilization in a high strength austenite has been made. An Fe-29Ni-4.3Ti austenite age-hardened by gamma-prime (Ni3Ti) precipitates showed a further increase of strength after martensitic and reverse martensitic phase transformations. The stability of ausaged austenite as well as ausaged and transformation-strengthened austenite was improved significantly through an isothermal treatment at 500 C. The Ms temperature of the strengthened austenite was restored to nearly that of annealed austenite while the austenite was hardened to R(C) 41 through precipitation and phase transformations. The observed austenite stabilization is attributed to the formation of GP zones or short-range order of less than about 10A in size.

Jin, S.↗
DOE OSTI2017

Thermodynamics of concentrated solid solution alloys

This study reviews the three main approaches for predicting the formation of concentrated solid solution alloys (CSSA) and for modeling their thermodynamic properties, in particular, utilizing the methodologies of empirical thermo-physical parameters, CALPHAD method, and first-principles calculations combined with hybrid Monte Carlo/Molecular Dynamics (MC/MD) simulations. In order to speed up CSSA development, a variety of empirical parameters based on Hume-Rothery rules have been developed. Herein, these parameters have been systematically and critically evaluated for their efficiency in predicting solid solution formation. The phase stability of representative CSSA systems is then illustrated from the perspectives of phase diagrams and nucleation driving force plots of the σ phase using CALPHAD method. The temperature-dependent total entropies of the FCC, BCC, HCP, and σ phases in equimolar compositions of various systems are presented next, followed by the thermodynamic properties of mixing of the BCC phase in Al-containing and Ti-containing refractory metal systems. First-principles calculations on model FCC, BCC and HCP CSSA reveal the presence of both positive and negative vibrational entropies of mixing, while the calculated electronic entropies of mixing are negligible. Temperature dependent configurational entropy is determined from the atomic structures obtained from MC/MD simulations. Current status and challenges in using these methodologies as they pertain to thermodynamic property analysis and CSSA design are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2017

An Enantiotropic Disorder–Partial Order Solid-State Transformation in a Molecular Solid Involving a Phase with Z ' = 12

A structural study of the complex aminated stereotriads, [( tert -butyldimethylsilyl)oxy]-4-ethynyl-4-(1-fluorohexyl)-1,2,3-oxathiazocane-2,2-dione (1) and its reduced analogue, [( tert -butyldimethylsilyl)oxy]-4-ethenyl-4-(1-fluorohexyl)-1,2,3-oxathiazocane-2,2-dione (2), revealed a k 12-type second-order phase transition in 1 and phase stability of 2 over the temperature range 100–400 K. The observed phase change in 1 has been linked to the partial ordering of the extensive positional disorder of the high temperature phase upon cooling as revealed by single-crystal X-ray diffraction. The ordering breaks the translational symmetry, introduces differences in the molecular volumes of the packed species, and results in a low-temperature crystal structure with Z '=12. The in situ powder X-ray diffraction studies suggest that the transition occurs between 237 K and 180 K upon cooling, but complete amorphization in the range of 244–274 K during heating complicated the assignment of the transition temperature. Lastly, the observed loss of crystallinity has been linked to the phase transition and implies that the loss of long range order is due to the crystallites undergoing the transformation independently from one another.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Autogenic succession and deterministic recovery following disturbance in soil bacterial communities

The response of bacterial communities to environmental change may affect local to global nutrient cycles; however the dynamics of these communities following disturbance are poorly understood, and are generally attributed to abiotic factors. Here, we subjected soil microcosms to a heat disturbance and followed the community composition of active bacteria over 50 days of recovery. Phylogenetic turnover patterns indicated that biotic interactions shaped the community during recovery, and that the disturbance imposed a strong selective pressure that persisted for up to 10 days, after which the importance of stochastic processes increased. Three successional stages were detected: a primary response (1-4 days after disturbance) in which surviving taxa increased in abundance; a secondary response phase (10-29 days), during which community dynamics slowed down, and a stability phase (after 29 days), during which the community tended towards its original composition. Furthermore, soil bacterial communities, despite their extreme diversity and functional redundancy, respond to disturbances like many macroecological systems and exhibit path-dependent, autogenic dynamics during secondary succession.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Perovskite Quantum Dots: A New Absorber for Perovskite-Perovskite Tandem Solar Cells: Preprint

The nanoscale phase stabilization of CsPbI3 quantum dots allows for the advantageous manipulation of its phase diagram. We show that these all inorganic halide perovskite nanocrystals can be used to fabricate colloidal perovskite quantum dot solar cells with incredibly low voltage losses. Despite recently emerging on the photovoltaic scene, CsPbI3 quantum dot solar cells have already achieved approximately 85% of their Shockley-Quessier limit open-circuit voltage, among the lowest voltage loss achieved for any material with a band gap of 1.7 eV, excepting III-V semiconductors. The low losses in these devices recently led to a world record certified quantum dot solar cell efficiency of 13.4%. While single junction thin film perovskite solar cells have surpassed 22% power conversion efficiency, perovskite-perovskite tandem solar cells offer the potential for power conversion efficiencies exceeding 30%. However, to accomplish this ambitious goal, perovskite solar cells must be designed with incredibly low losses and the appropriate band gaps, which differ from the ideal band gap for single junction perovskite solar cells. In this respect, the incredibly low voltage loss and tunable band gap of CsPbI3 quantum dots make them ideally suited for all-perovskite tandem solar cell applications.

14 SOLAR ENERGY↗
DOE OSTI2012

Dolomite III: A new candidate lower mantle carbonate

Dolomite is a major constituent of subducted carbonates; therefore evaluation of its phase stability and equation of state at high pressures and temperatures is important for understanding the deep Earth carbon cycle. X-ray diffraction experiments in the diamond anvil cell show that Ca{sub 0.988}Mg{sub 0.918}Fe{sub 0.078}Mn{sub 0.016}(CO{sub 3}){sub 2} dolomite transforms to dolomite-II at {approx}17 GPa and 300 K and then upon laser-heating transforms to a new monoclinic phase (dolomite-III), that is observed between 36 and 83 GPa. Both high-pressure polymorphs are stable up to 1500 K, indicating that addition of minor Fe stabilizes dolomite to Earth's deep-mantle conditions.

58 GEOSCIENCES↗