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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Self-diffusion of carbon and oxygen in dolomite.

Self-diffusion of carbon and oxygen in dolomite was measured by isotopic exchange with CO2 at 645-785 C at 120-935 bars pressure. Several runs were also made with calcite under comparable experimental conditions. The principal findings of this study are that (1) the self-diffusion coefficients of both carbon and oxygen in dolomite are approximately 100 times larger than the values in calcite over the temperature range investigated and (2) oxygen self-diffusion in calcite is accelerated by high CO2 pressure.

Anderson, T. F.↗
NASA NTRS1972

Diffusion in the system K2O-SrO-SiO2. II - Cation self-diffusion coefficients.

The self-diffusion coefficients were measured by introducing a slab of glass previously irradiated in a reactor between two slabs of unirradiated glass. By heating the specimens, etching them sequentially and determining the radioactivity, self-diffusion coefficients for K and Sr were measured. It is pointed out that the results obtained in the investigations appear to support the proposal that the network of the base glass predominantly controls the activation energy for the diffusion of ions.

Varshneya, A. K.↗
NASA NTRS1967

Self-diffusion in simple fluids.

Self-diffusion coefficients of simple liquids as predicted by Rice-Allnatt theory, noting friction coefficient and correlation function

CORRELATION FUNCTION↗
NASA NTRS1974

M558 radioactive tracer diffusion

This experiment was performed in Skylab 3 with two objectives in mind. First, the experimental self-diffusion coefficients for liquid zinc were to be determined in a convection-free environment. Secondly the reduction in convective mixing in earth gravity by going into the zero-gravity environment of space was to be estimated. The experiment was designed to utilize high temperatures and linear thermal gradients provided by the M518 Multipurpose Electric Furnace, and the radioactivity of zinc-65 of 245-day half-life to investigate self-diffusion in liquid zinc. The distribution of zinc-65 tracer, after melting, maintaining at soak temperature for 1 hour of soak time and then resolidifying, was obtained by sample sectioning. The concentration of activity of each section (microcurie-gram) was plotted against positions along the sample axial and radial position. Experimental data and theoretical results from solution of Fick's law of diffusion in one dimensional were compared. Samples tested on earth showed very rapid diffusion. Diffusion coefficient in unit gravity was 50 times the zero-gravity diffusion coefficient of Skylab.

Ukanwa, A. O.↗
NASA NTRS1960

Vacancy-Vacancy Interaction in Copper

The binding energy of two vacancies in a static lattice as a function of their separation and the positions of their displaced neighboring atoms has been calculated using a Morse potential function model for copper. It was found that two vacancies attract one another at separation less than about 7 A. At separations greater than 7 A the vacancies do not interact appreciably. The most stable separation was found to be the first nearest- neighbor separation or the divacancy configuration, for which the binding energy was found to be 0.64 ev. Based on these calculations, it is shown that third-stage annealing in irradiated copper may be accounted for by divacancy migration. The role of the divacancy in copper self-diffusion is also explained.

Girifalco, L. A.↗
NASA NTRS1971

The creep properties of dispersion-strengthened silver-gallium oxide alloys.

Steady-state creep rates were measured for two preparations of a dispersion-strengthened alloy of silver with 1 mol % gallium oxide. One preparation, an internally-oxidized type, had a grain size 40 times that of the other preparation, which was a consolidated-powder type of alloy. The temperature and stress dependence of the steady-state creep rate differs widely for the two alloys and must be attributed to the difference in grain size. The activation energy for steady-state creep of the internally-oxidized coarse grained material is near that for self-diffusion of silver, which strongly indicates a creep process controlled by dislocation climb.

Lenel, F. V.↗
NASA NTRS1973

O(minus 2) grain boundary diffusion and grain growth in pure dense MgO

Grain growth behavior in fully dense compacts of MgO of very high purity was studied, and the results compared with other similar behaving materials. The activation energy for the intrinsic self-diffusion of Mg(2minus) is discussed along with the grain boundary diffusion of O(2minus). Grain boundary diffusion of O(2minus) is proposed as the controlling mechanism for grain growth.

Kapadia, C. M.↗
NASA NTRS1972

Thermal conductivity in vibrationally excited gases.

Comparisons between experimental and theoretical values of the thermal conductivity for a series of nonpolar polyatomic gases show large discrepancies at higher temperatures where the vibrational contribution becomes increasingly important. Examination of various theoretical approaches indicates that the discrepancies can be attributed to approximating the coefficient characterizing the diffusion of vibrational energy, D sub vib, by the self-diffusion coefficient. The present theories cannot accurately predict D sub vib, and its measurement is extremely difficult. Consequently, the approach adopted by the author is to obtain D sub vib by using experimental values of the thermal conductivity. An attempt is made to correlate these values of D sub vib with vibrational relaxation time, so that values of D sub vib can be obtained for all nonpolar polyatomic gases.

Ahtye, W. F.↗
NASA NTRS1973

Equilibrium properties of a one-dimensional kinetic system.

One-dimensional systems of N = 500 and 250 particles in equilibrium are numerically simulated utilizing the method of molecular dynamics. Periodic boundary conditions are imposed. The classical two-body interaction potential is short range, repulsive and has a corresponding finite force. The equations of state are determined for densities both less and greater than one. Corresponding theoretical isochores are determined from models based on nearest-neighbor interactions and on a truncated virial expansion, and a comparison is made with the experimental isochores. Time independent radial distributions are constructed numerically and discussed. A change of state from a solidlike state to a fluid-gas state based on the penetrability of the particles is predicted. The transition temperatures are estimated from the radial distribution functions and the nearest-neighbor model. Self-diffusion is observed and the corresponding constants are determined from the velocity autocorrelation functions.

Williams, J. H.↗
NASA NTRS1976

Extended analysis of Skylab experiment M558 data

A careful review of the data from Skylab M558 was made in an effort to explain the apparent anomaly of the existence of radial concentration gradients whereas none should bave been observed. The very close modelling of the experimental axial concentration profiles by the unsteady-state one-dimensional solution of Fick's Law of self-diffusion in liquid zinc, and the condition of initial uniform concentration in the radioactive pellet portion of the experimental specimens would have precluded the appearance of such radial concentration gradients. Statistical analyses were used to test the significance of the observed deviation from radial-concentration homogeneity. A student t-distribution test of significance showed that, at 90% or even at 80% level of significance, there were no significant deviations from uniformity in radial concentrations. It was also concluded that the two likely causes of any deviation that existed were the zinc to zinc-65 bonding procedure and surface phenomena such as surface tension and capillary action.

Ukanwa, A. O.↗
NASA NTRS1975

The elastic modulus correction term in creep activation energies Applied to oxide dispersion strengthened superalloy

The effect of elastic modulus and the temperature dependence of elastic modulus on creep activation energies for an oxide dispersion strengthened nickel-base superalloy are investigated. This superalloy is commercially known as Inconel Alloy MA 753, strengthened both by gamma-prime precipitates and by yttria particles. It is shown that at intermediate temperatures, say below 1500 F, where elastic modulus is weakly dependent on temperature, the modulus correction term to creep activation energy is small. Accordingly, modulus corrections are insignificant for the superalloy considered, which shows high apparent creep activation energies at this temperature. On the contrary, at very high temperatures, the elastic modulus correction term can be significant, thus reducing the creep activation energy to that of vacancy self-diffusion. In order to obtain high-temperature creep resistance, a high-value elastic modulus with a weak dependence on temperature is required.

Malu, M.↗
NASA NTRS1976

Diffusion in mixed solvents. III - The heat of mixing parameter and the Soret coefficient

New evidence is presented that for aqueous glycerol solutions, the Soret coefficient of glycerol, sigma sub 1 = D sub 1 T/D sub 1 (where D sub 1 T and D sub 1 are the thermal and self-diffusion coefficients, respectively, of glycerol in aqueous solutions), is an integral part of the heat of mixing parameter. Expressions are presented indicating the importance of the Soret coefficients to correlations for diffusion processes in glycerol water solvents.

Carapellucci, P. A.↗