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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Thermodynamics and kinetics of reactions in protective coating systems

Investigations of fluoride activated packs with Al:Ni ratios greater than 50 a/o prove that the specimen surface is not in equilibrium with the pack at high Al:Ni ratios but that an activity gradient exists between pack and specimen. Therefore, gaseous diffusion and possibly surface reactions play a role in determining the overall rate of Al deposition in such packs. Noticeable differences in coating behavior have been obtained in packs activated with chloride and iodide, and it appears that poorest results are obtained with iodides, better with chlorides, and best with fluorides. A numerical method has been perfected for calculating rates of solid-state diffusion controlled coating formation, allowing for the variation of diffusivity with composition in the NiAl phase. Layer growth rates can now be accurately predicted from a knowledge of the surface and substrate compositions. Furthermore, the correct diffusion profiles are obtained by this method. These differ substantially from the profile obtained when the diffusivity is assumed constant.

Gupta, B.↗
NASA NTRS1975

Oxygen reduction of several gold alloys in 1-molar potassium hydroxide

With rotated disk-and-ring equipment, polarograms and other electrochemical measurements were made of oxygen reduction in 1-molar potassium hydroxide on an equiatomic gold-copper (Au-Cu) alloy and a Au-Cu alloy doped with either indium (In) or cobalt (Co) and on Au doped with either nickel (Ni) or platinum (Pt). The results were compared with those for pure Au and pure Pt. The two-electron reaction dominated on all Au alloys as it did on Au. The polarographic results at lower polarization potentials were compared, assuming exclusively a two-step reduction. A qualified ranking of cathodic electrocatalytic activity on the freshly polished reduced disks was indicated: anodized Au Au-Cu-In Au-Cu Au-Cu-Co is equivalent or equal to Au-Pt Au-Ni. Aging in distilled water improved the electrocatalytic efficiency of Au-Cu-Co, Au-Cu, and (to a lesser extent) Au-Cu-In.

Miller, R. O.↗
NASA NTRS1974

Experimental investigation and model development of the Skylab ATM secondary nickel-cadmium batteries

The performance of a Ni-Cd battery was evaluated and the cyclic battery controls to be used on the ATM batteries were determined. Cell and battery performance models were developed which to predict the performance of the secondary Ni-Cd batteries on the ATM. Capacity degradation and charge acceptance characteristics were considered. Mathematical models for each of these operating areas were developed based on data from two separate test programs. The capacity degradation model describes the expected usable battery capacity as a function of time, temperature, and depth-of-discharge. The charge acceptance model describes the cell charge acceptance as a function of charge rate, temperature, and state of charge. The models were designed for computer use and to facilitate possible battery modification. They can be used to predict expected performance or to compare real time performance during flight.

Kirsch, W. W.↗
NASA NTRS1974

Bio-conversion of water hyacinths into methane gas, part 1

Bio-gas and methane production from the microbial anaerobic decomposition of water hyacinths (Eichhornia crassipes) (Mart) Solms was investigated. These experiments demonstrated the ability of water hyacinths to produce an average of 13.9 ml of methane gas per gram of wet plant weight. This study revealed that sample preparation had no significant effect on bio-gas and/or methane production. Pollution of water hyacinths by two toxic heavy materials, nickel and cadmium, increased the rate of methane production from 51.8 ml/day for non-contaminated plants incubated at 36 C to 81.0 ml/day for Ni-Cd contaminated plants incubated at the same temperature. The methane content of bio-gas evolved from the anaerobic decomposition of Ni-Cd contaminated plants was 91.1 percent as compared to 69.2 percent methane content of bio-gas collected from the fermentation of non-contaminated plants.

Wolverton, B. C.↗
NASA NTRS1975

Thermal expansion in the nickel-chromium-aluminum and cobalt-chromium-aluminum systems to 1200 degrees C

Thermal expansion data were obtained on 12 Ni-Cr-Al and 9 Co-Cr-Al alloys by high temperature X-ray diffraction. The data were computer fit to an empirical thermal expansion equation developed in the study. It is shown that the fit is excellent to good, and that the expansion constants depend on phase but not on composition. Phases for the Ni-Cr-Al system and Co-Cr-Al system are given. Results indicate that only alpha Cr has an expansion constant low enough to minimize oxide spalling or coating cracking induced by thermal expansion mismatch.

Lowell, C. E.↗
NASA NTRS1975

Solar flare particles - Energy-dependent composition and relationship to solar composition

Plastic and glass track detectors on rockets and Apollo spacecraft have been used to determine the composition of particles from He to Ni at energies from 0.1 to 50 MeV per nucleon in several solar flares of widely varying intensities. At low energies the composition of solar particles is enriched in heavy elements by an amount, relative to the asymptotic high-energy composition, that increases with atomic number from Z = 2 up to at least Z = 50, that decreases with energy, and that varies from flare to flare. At high energies (usually beyond an energy of 5 to 20 MeV per nucleon) the composition becomes independent of energy and, though somewhat variable from flare to flare, approximates the composition of the solar atmosphere. A table of abundances of the even-Z elements from He to Ni (plus N) in solar particles is constructed by averaging the asymptotic high-energy abundances in several flares.

Crawford, H. J.↗
NASA NTRS1974

Forbidden-line excitation data for certain coronal lines

Some new data pertinent to forbidden transitions for coronal lines of S XII, Ca XIII, K XI, Mn XIII, Fe XIV, Co XV, Ni XVI, N XV, Cr IX, Fe X, and Ni XII are presented. We include additional calculations of collision strengths for a number of ions and then set up and solve the equations of statistical equilibrium in the limiting approximations in which contributions to level population by cascade from higher levels are neglected. We then calculate volume emissivities per ion as a function of density and temperature.

Czyzak, S. J.↗
NASA NTRS1975

Paleomagnetic systematics of ordinary chondrites

The investigation shows that the decrease in intensity and the increase in stability of natural remanent magnetization (NRM) to alternating field (AF) demagnetization roughly parallel the decrease in Ni-Fe metal content and the corresponding enrichment of the metal phases in Ni. The stability of NRM within a chemical type appears to decrease with increasing degree of metamorphism, a feature interpretable in terms of composition, size, and shape of metal grains. Paleofield intensities required to imprint the NRM as thermo-chemical remanence are in the range from 0.01 to 0.3 Oe.

Brecher, A.↗
NASA NTRS1975

Classification and properties of iron meteorites

The paper describes the general requirements for a genetically significant scheme for classifying iron meteorites. Some of the properties which may be used to classify iron meteorites are reviewed, and a classification scheme based on Ga-Ni and Ge-Ni plots, taxonomic properties, and chemical properties is proposed. It is found that 95% of the irons can be assigned to a genetic group or an anomalous class.

Scott, E. R. D.↗
NASA NTRS1976

Oxide dispersion strengthened nickel produced by nonreactive milling

It is shown that oxide dispersion strengthened alloys can be produced by a postulated nonreactive milling mechanism whereby the dispersoid is trapped at the interface between welding metal powder particles. This interparticle welding is possible because, without a suitable and sufficiently vigorous chemical reaction between the metal powder particles and the milling fluid, no protective, weld-preventing reaction coating is formed on these particles. Using water as the nonreactive milling fluid, Ni - 1.8-vol % thoria and Ni - 1.8-vol % yttria alloys with 1093 C tensile strengths ranging from 122.3 to 141.5 MN/sq m (17,900 to 20,500 psi) were produced by nonreactive milling.

Arias, A.↗
NASA NTRS1976

Alloy and structural optimization of a directionally solidified lamellar eutectic alloy

Mechanical property characterization tests of a directionally solidified Ni-20 percent Cb-2.5 percent Al-6 percent Cr cellular eutectic turbine blade alloy demonstrated excellent long time creep stability and indicated intermediate temperature transverse tensile ductility and shear strength to be somewhat low for turbine blade applications. Alloy and structural optimization significantly improves these off-axis properties with no loss of longitudinal creep strength or stability. The optimized alloy-structure combination is a carbon modified Ni-20.1 percent Cb-2.5 percent Al-6.0 percent Cr-0.06 percent C composition processed under conditions producing plane front solidification and a fully-lamellar microstructure. With current processing technology, this alloy exhibits a creep-rupture advantage of 39 C over the best available nickel base superalloy, directionally solidified MAR M200+ Hf. While improved by about 20 percent, shear strength of the optimized alloy remains well below typical superalloy values.

Sheffler, K. D.↗
NASA NTRS1976

Formation of iron sulphide in solar nebula

Noting that the iron sulfide in the Orgueil carbonaceous meteorite is an Fe-deficient monosulfide (pyrrhotite), it is suggested that such mineral chemistry is inconsistent with equilibrium condensation of the solar nebula and that the course of condensation may have been modified by kinetic effects. The effect of Ni on the reaction between Fe and S to produce FeS is examined, and possible reasons are considered for the fact that the cited meteorite differs in both crystal structure and Ni content from the predictions of equilibrium condensation. It is proposed that sulfide formation in the solar nebula may have been inhibited by sluggish diffusion, so that sulfur began to react with previously condensed troilite to form pyrrhotite. On this basis, observations of the Orgueil sulfides are shown to suggest that the course of solar-system condensation was modified by kinetic effects below about 700 K and that equilibrium may not have been achieved.

Kerridge, J. F.↗
NASA NTRS1976

The lithium-like 2s 2S-2p 2P transition in solar flares

Accurate wavelengths of the Fe XXIV lithium-like doublet at 192 and 255 A are derived from measurements made in a sample of four solar flares observed with a spectroheliograph aboard Skylab and selected to minimize systematic effects. The mean value of the Fe XXIV doublet interval is determined, and new members of the lithium isoelectronic sequence are identified, including Cr XXII, Mn XXIII, and Ni XXVI. Doublet splitting along the lithium sequence is analyzed in terms of the experimental screening factor, it is found that the doublet separations increase smoothly with charge number along the sequence, and the doublet interval in Ni XXVI is accurately extrapolated. The experimental screening factors are compared with the values predicted by Snyder's (1971) relativistic screening theory, and excellent agreement is found.

Widing, K. G.↗
NASA NTRS1976

Explanation for the very low Ga and Ge concentrations in some iron meteorite groups

Parallels between the abundance patterns of moderately volatile elements in iron meteorites and ordinary chondrites are pointed out and discussed in relation to condensation processes in the solar nebula. The discussion is centered around a graph in which As, Cu, Ga, Ge to Ni ratios, normalized to CI chondrites, are compared for IVB, IVA, IVB, and IIIAB irons and H-group ordinary chondrites. The patterns suggest that the same volatile loss mechanism was at work for both IVB irons and ordinary chondrites, but was more efficient in the IVB process. A picture for the process at the IVB location is proposed, according to which condensation occurred when temperature decreased rapidly and trace metals condensed as a fine aerosol that was later blown away by a T-Tauri solar storm. Condensation at the H-group location was more complete because of a less rapid temperature decrease, allowing trace metals to diffuse deeper into Fe-Ni grains. Possible ways in which IVA conditions may have differed from IIIAB or H conditions are also proposed and discussed.

Wasson, J. T.↗
NASA NTRS1976

Effect of adsorbed films on friction of Al2O3-metal systems

The kinetic friction of polycrystalline Al2O3 sliding on Cu, Ni, and Fe in ultrahigh vacuum was studied as a function of the surface chemistry of the metal. Clean metal surfaces were exposed to O2, Cl2, C2H4, and C2H3Cl, and the change in friction due to the adsorbed species was observed. Auger electron spectroscopy assessed the elemental composition of the metal surface. It was found that the systems exposed to Cl2 exhibited low friction, interpreted as the van der Waals force between the Al2O3 and metal chloride. The generation of metal oxide by oxygen exposures resulted in an increase in friction, interpreted as due to strong interfacial bonds established by reaction of metal oxide with Al2O3 to form the complex oxide (spinel). The only effect of C2H4 was to increase the friction of the Fe system, but C2H3Cl exposures decreases friction in both Ni and Fe systems, indicating the dominance of the chlorine over the ethylene complex on the surface

Pepper, S. V.↗
NASA NTRS1976

On the kinetics of the pack - Aluminization process

An investigation has been made of the aluminization of unalloyed Ni in fluoride-activated packs of varying Al activity. In packs of low Al activity, in which the ratio of Al to Ni was less than 50 at. pct, the specimen surface quickly came to equilibrium with the pack and remained close to equilibrium for the duration of normal coating runs. In these packs the kinetics of aluminization was controlled by diffusion in the solid. In packs of higher Al activity the surface of the specimen did not come to equilibrium with the pack and the kinetics of the process was governed by a combination of solid and gas diffusion rates. Under most conditions however, the surface composition was time-invariant and a steady-state appeared to exist at the pack-coating interface. By combining Levine and Caves' model for gaseous diffusion in pure-Al packs with calculations of solid diffusion rates some success has been achieved in explaining the results.

Sivakumar, R.↗
NASA NTRS1977

Creep degradation in oxide-dispersion-strengthened alloys

Oxide dispersion strengthened Ni-base alloys in wrought bar form are studied for creep degradation effects similar to those found in thin gage sheet. The bar products evaluated included ODS-Ni, ODS-NiCr, and three types of advanced ODS-NiCrAl alloys. Tensile test specimens were exposed to creep at various stress levels at 1365 K and then tensile tested at room temperature. Low residual tensile properties, change in fracture mode, the appearance of dispersoid-free bands, grain boundary cavitation, and internal oxidation in the microstructure were interpreted as creep degradation effects. This work showed that many ODS alloys are subject to creep damage. Degradation of tensile properties occurred after very small amounts of creep strain, ductility being the most sensitive property. All the ODS alloys which were creep damaged possessed a large grain size. Creep damage appears to have been due to diffusional creep which produced dispersoid-free bands around boundaries acting as vacancy sources. Low angle and possibly twin boundaries acted as vacancy sources.

Whittenberger, J. D.↗
NASA NTRS1977

Processing eutectics in space

The examination of the Ni-Mo-Al system is discussed. Experiments were performed to examine the role of thermal gradient magnitude at the solidifying interface on the geometrical regularity of the microstructure. The difficulty in measuring the thermal gradient in the melt using superheat temperatures as high as 1800 C resulted in the examination of three liquid temperature gradient ranges. Examination of the microstructure from directionally solidified ingots using transverse sections indicated that the highest gradient runs produced microstructure of no greater regularity than runs made at lower gradients. For the Ni-Al-Mo monovariant eutectic system, the magnitude of the thermal gradient at the solidifying interface is not a controlling parameter with respect to the geometrical regularity of the microstructure, provided it is sufficient to satisfy the gradient/rate ratio needed to produce a planar interface growth.

Douglas, F. C.↗