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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Thermophysical Property Measurements of Silicon-Transition Metal Alloys

Metals and metallic alloys often have high melting temperatures and highly reactive liquids. Processing reactive liquids in containers can result in significant contamination and limited undercooling. This is particularly true for molten silicon and it alloys. Silicon is commonly termed "the universal solvent". The viscosity, surface tension, and density of several silicon‐transition metal alloys were determined using the Electrostatic Levitator system at the Marshall Space Flight Center. The temperature dependence of the viscosity followed an Arrhenius dependence, and the surface tension followed a linear temperature dependence. The density of the melts, including the undercooled region, showed a linear behavior as well. Viscosity and surface tension values were obtain for several of the alloys in the undercooled region.

Banish, R. Michael↗
NASA NTRS1989

Ellipsometric method for the measurement of temperature and optical constants of incandescent transition metals

The development of a unique noncontact temperature measurement device utilizing rotating analyzer ellipsometry is described. The technique circumvents the necessity of spectral emissivity estimation by direct measurement concomitant with radiance brightness. Simultaneous determinations of dielectric constants and refractive indices allow changes in the physical and chemical state of a heated surface to be monitored. The results of optical property measurements at 633 nm as functions of temperature between 1000 and 2500 K for eight transition metals including Hf, Ir, Mo, Nb, Pd, Pt, Ta, and V are presented together with preliminary results of oxidation studies on iridium.

Hansen, George P.↗
NASA NTRS1978

Partitioning of transition metals between diopside and coexisting silicate liquids. I - Nickel, cobalt, and manganese

Distribution coefficients have been found for the partitioning of Ni, Co, and Mn between calcium-rich clinopyroxenes and coexisting silicate liquids. Values are found for the 1110-1360 C temperature range. The breakdown of Henry's Law was not observed. The measured clinopyroxene/liquid distribution coefficients ranged from 1.5-14.0 for Ni, 0.5-2.0 for Co, and 0.3-1.2 for Mn. Analyses of pyroxenes grown from charges differing in the amounts of transition metals indicate that Ni and Co occupy the M1 site of diopside and that Mn occupies the M1 and M2 sites. Equilibrium constants were found in terms of the activities of the components in the liquid and solid phases. These activities are based on the mole fractions. An activity/concentration model was used for the liquid phase in order to explain the variations in the clinopyroxene/liquid coefficients due to bulk composition.

Lindstrom, D. J.↗
NASA NTRS1992

Equilibrium properties of transition-metal ion-argon clusters via simulated annealing

The geometrical structures of M(+) (Ar)n ions, with n = 1-14, have been studied by the minimization of a many-body potential surface with a simulated annealing procedure. The minimization method is justified for finite systems through the use of an information theory approach. It is carried out for eight potential-energy surfaces constructed with two- and three-body terms parametrized from experimental data and ab initio results. The potentials should be representative of clusters of argon atoms with first-row transition-metal monocations of varying size. The calculated geometries for M(+) = Co(+) and V(+) possess radial shells with small (ca. 4-8) first-shell coordination number. The inclusion of an ion-induced-dipole-ion-induced-dipole interaction between argon atoms raises the energy and generally lowers the symmetry of the cluster by promoting incomplete shell closure. Rotational constants as well as electric dipole and quadrupole moments are quoted for the Co(+) (Ar)n and V(+) (Ar)n predicted structures.

Asher, Robert L.↗
NASA NTRS1993

Transition metals in superheat melts

A series of experiments with silicate melts doped with transition element oxides was carried out at atmospheric pressures of inert gas at temperatures exceeding liquidus. As predicted from the shape of fO2 buffer curves in T-fO2 diagrams the reducing conditions for a particular oxide-metal pair can be achieved through the T increase if the released oxygen is continuously removed. Experimental studies suggest that transition metals such as Cr or V behave as siderophile elements at temperatures exceeding liquidus temperatures if the system is not buffered by the presence of other oxide of more siderophile element. For example the presence of FeO prevents the reduction of Cr2O3. The sequence of decreasing siderophility of transition elements at superheat conditions (Mo, Ni, Fe, Cr) matches the decreasing degree of depletion of siderophile elements in mantle rocks as compared to chondrites.

Jakes, Petr↗
NASA NTRS1992

The role of the molecular-metallic transition of hydrogen in the evolution of Jupiter, Saturn, and brown dwarfs

An equation of state for hydrogen which predicts a molecular-metallic phase transition at finite temperatures has become available recently. The effect of this phase transition on the cooling histories of these two giant planets and of substellar brown dwarfs is studied. The phase transition alters the present age of Jupiter and of Saturn by a few percent. Interestingly, the cooling of brown dwarfs is most strongly affected at the time when the interior adiabat crosses the critical point of the phase transition.

Saumon, Didier↗
NASA NTRS2021

Semiconductor to Metal Transition in the Solids/Melts of Te and Pseudo-Binary of Hg1-xCdxTe for x = 0, 0.1 and 0.2

This paper reports the experimentally measured thermal and electrical conductivities from which the Lorenz numbers as functions of temperature were derived for the solids and melts of elemental Te and samples of Hg1-xCdxTe of x = 0, 0.1 and 0.2. The structural changes in the vicinity of the solid-liquid phase transition of elemental Te and various Hg1-xCdxTe solid solutions were assessed by closely examining these experimental properties and the derived Lorenz numbers. The values of Lorenz numbers for the solids of these samples were higher than the value of L0, i.e., the Lorenz number for the free electron gas derived by Sommerfeld, implying the characteristics of non-degenerate semiconductor. With the increasing value of x, or the larger bandgap, the materials become more non-degenerate with larger deviation from L0. As the solids started to melt, the measured values of Lorenz number for all samples started to decrease and eventually reached and maintained at values close to L0 at higher temperatures. The trend of the Lorenz number indicates that the transition from non-degenerate semiconductor of the solid samples to metal or degenerate semiconductor when the samples temperature reached above their liquidus temperatures.

thermal conductivity↗
NASA NTRS1991

Heteronuclear transition metal diatomics - The bonding and electronic structure of ScNi, YNi, ScPd, and YPd

High quality ab initio calculations show that ScNi, YNi, ScPd, and YPd all have 2Sigma(+) ground states in agreement with electron spin resonance experiments. For ScNi and YNi, this is expected based on the lowest atomic asymptote. For ScPd and YPd, the lowest atomic asymptote would give the order of stability 2Delta greater than 2Pi equal to about 2Sigma(+), but the calculations show that mixing in of the excited asymptotes preferentially lowers the 2Sigma(+) state. The calculations show that the quartet states are about 20-30 kcal/mol above the ground state, and therefore probably do not contribute significantly to the unexpected g(vertical) values found in experiment. Calculations of excited states for YPd reveal some strong transitions that should be amenable to spectroscopic studies.

Faegri, Knut, Jr.↗
NASA NTRS2018

Transition Metal Oxides as Cathodes in Li-O2 battery: A First Principles Investigation

Li-O2 batteries have traditionally used carbon based electrodes (graphite, buckypaper) as the cathode of choice due to its good electrical conductivity, stability against non-aqueous electrolytes like Dimethyl ether (DME) and ease of handling. But, the carbon cathode also leads to formation of carbonate by-products that increase overpotentials during charging leading to degradation of cathode and reduction of cyclability. In this work, we investigate some of the well-known oxides as cathodes with focus on the interface between the oxide surfaces and the discharge product: Li2O2, in the Li-O2 battery using first principles computations. Our results show that attention must be paid on choosing the appropriate surface of the oxides. We extend the analysis to suggest other possible oxide chemistries that should be investigated as cathodes in Li-O2 batteries.

Li-O2 battery↗