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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Time exposure studies on stress corrosion cracking of aluminum 2014-T6, 2219-T87, 2014-T651, 7075-T651, and titanium 6Al-4V

The effect of a constant applied stress in crack initiation of aluminum 2014-T6, 2219-T87, 2014-T651, 7075-T651 and titanium 6Al-4V has been investigated. Aluminum c-ring specimens (1-inch diameter) and u-band titanium samples were exposed continuously to a 3.5% NaCl solution (pH 7) and organic fluids of ethyl, methyl, and iso-propyl alcohol (reagent purity), and demineralized distilled water. Corrosive action was observed to begin during the first and second day of constant exposure as evidenced by accumulation of hydrogen bubbles on the surface of stressed aluminum samples. However, titanium stressed specimens showed no reactions to its environment. Results of this investigation seems to suggest that aluminum 2014-T6, aluminum 7075-T651 and aluminum 2014-T651 are susceptible to stress corrosion cracking in chloride solution (NaCl), while aluminum 2219-T87 seem to resist stress corrosion cracking in sodium chloride at three levels of stress (25%, 50%, and 75% Y.S.). In organic fluids of methyl, ethyl, and iso-propyl alcohol, 2014-T6 and 7075-T651 did not fail by SCC; but 2014-T651 was susceptible to SCC in methly alcohol, but resistant in ethyl alcohol, iso-propyl alcohol and demineralized distilled water.

Terrell, J.↗
NASA NTRS1973

Ultrafiltration by a compacted clay membrane. I - Oxygen and hydrogen isotopic fractionation. II - Sodium ion exclusion at various ionic strengths.

Laboratory experiments were carried out to determine the magnitude of the isotopic fractionation of distilled water and of 0.01N NaCl forced to flow at ambient temperature under a hydraulic pressure drop of 100 bars across a montmorillonite disk compacted to a porosity of 35% by a pressure of 330 bars. The ultrafiltrates in both experiments were depleted in D by 2.5% and in O-18 by 0.8% relative to the residual solution. No additional isotopic fractionation due to a salt-filtering mechanism was observed at NaCl concentrations up to 0.01N. Adsorption is most likely the principal mechanism which produces isotopic fractionation, but molecular diffusion may play a minor role. The results suggest that oxygen and hydrogen isotopic fractionation of ground water during passage through compacted clayey sediments should be a common occurrence, in accord with published interpretations of isotopic data from the Illinois and Alberta basins. It is shown how it is possible to proceed from the ion exchange capacity of clay minerals and, by means of the Donnan membrane equilibrium concept and the Teorell-Meyer-Siever theory, develop a theory to explain why and to what extent ultrafiltration occurs when solutions of known concentration are forced to flow through a clay membrane.

Coplen, T. B.↗
NASA NTRS1974

Scattering of helium nozzle beams from LiF/001/ and NaCl/001/ crystal surfaces. I - Elastic and inelastic transitions

Nozzle-type atomic beams and time-of-flight detection methods are employed in studies of the scattering of thermal-energy He-4 atoms from LiF (001) and NaCl (001) surfaces under conditions where diffraction is observed and where substantial inelastic scattering occurs. Intensity and speed-distribution measurements are obtained for the portion of the scattering within the plane of incidence. For these measurements, incident-beam orientation with respect to target (polar angle and azimuth), incident-beam de Broglie wavelength (0.38-0.60 A), and crystal temperature (300-1000 K) are varied. For LiF, the measured intensity distributions exhibit sharp peaks comprised essentially of elastically scattered atoms and corresponding to up to third-order diffraction, inelastic scattering in the form of local dispersion about each of the elastic peaks, and a component of nominally diffuse scattering distributed below and between the peaks. For NaCl, the same general types of scattering are observed, with elastic scattering less prevalent, intensity peaks not as sharp, and dispersions of inelastic scattering harder to resolve.

Bledsoe, J. R.↗
NASA NTRS1977

Gaseous sodium sulfate formation in flames and flowing gas environments

Formation of Na2SO4(g) in flames and hot flowing gas systems was studied by high pressure, free-jet expansion, modulated molecular beam mass spectrometric sampling. Fuel-lean CH4-O2 flames doped with SO2, H2O and NaCl yielded the gaseous Na2SO4 molecule in residence times of less than one millisecond. Intermediate species NaSO2(g) and NaSO3(g) were also observed and measured. Composition profiles were obtained for all reaction products. Nonflame flowing gas experiments showed that Na2SO4 and NaSO3 gaseous molecules were formed at 1140 C in mixtures of O2, H2O(g), SO2 and NaCl(g). Experimental results are compared with calculated equilibrium thermodynamic predictions.

Stearns, C. A.↗
NASA NTRS1977

Study of palladium plating components

Palladium deposits were prepared by electrolysis for evaluation as catalytic materials. Electrolysis was carried out in acidic solutions consisting of either 1.0 M in NaCl and 0.01 M PdCl2 or 1.0 M NaCl and 0.04 M PdCl2. It was during the preparation of the palladium deposits that unexpected observations were made that led to the request for analytical services. The analyses did not, nor were they intended to, answer all of the questions. They did, however, shed light on the nature and magnitude of some of the contaminants in the solutions and in the palladium electrodes, as well as characterize the forms of the palladium deposits. Results of analyses are grouped into solution, deposit, and electrode categories for comparison purposes.

Source record↗
NASA NTRS1977

Gaseous sodium sulfate formation in flames and flowing gas environments

Formation of Na2SO4(g) in flames and hot flowing gas systems was studied by high pressure, free-jet expansion, modulated molecular beam mass spectrometric sampling. Fuel-lean CH4-O2 flames doped with SO2, H2O and NaCl yielded the gaseous Na2SO4 molecule in residence times of less than one millisecond. Intermediate species NaSO2(g) and NaSO3(g) were also observed and measured. Composition profiles were obtained for all reaction products. Non-flame flowing gas experiments showed that Na2SO4 and NaSO3 gaseous molecules were formed at 1140 C in mixtures of O2, H2O(g), SO2 and and NaCl(g). Experimental results are compared with calculated equilibrium thermodynamic predictions.

Stearns, C. A.↗
NASA NTRS1977

The effect of NaCl/g/ on the Na2SO4-induced hot corrosion of NiAl

Studies have been performed to examine the effect of NaCl vapor on the Na2SO4-induced hot corrosion of the alumina former NiAl. In the incubation period associated with such hot corrosion, NaCl(g) has been shown to be effective in removing aluminum from below the protective alumina scale and redepositing it as Al2O3 whiskers on the surface of the Na2SO4-coated sample. Similar effects seen in simple oxidation are associated with isothermal rupturing of the protective alumina scale.

Smeggil, J. G.↗
NASA NTRS1978

Experimental Studies of the Formation/Deposition of Sodium Sulfate in/from Combustion Gases

Processes related to the hot corrosion of gas turbine components were examined in two separate investigations. Monochromatic laser light was used to probe condensation onset and condensate film growth (via interference of reflected light) on electrically heated ribbons immersed in seeded, flat flame combustion product gases. Boron trichloride is used as the seed gas in these preliminary experiments conducted to obtain precise measurements of the dew point/deposition rates. Because of the importance of gaseous Na(g) as a precursor to NaSO4 formation, the kinetics and mechanisms of the heterogeneous reaction H(g) + NaCl(s) yields Na(g) + HCl(g) was studied using atomic absorption spectroscopy combined with microwave discharge-vacuum flow reactor techniques at moderate temperatures. Preliminary results indicate the H-atom attack of solid NaCl vaporization is negligible; hence the corresponding gas phase (homogeneous) reaction no role in the observed Na(g) production.

Rosner, D. E.↗
NASA NTRS1978

High pressure phase transitions in tetrahedrally coordinated semiconducting compounds

New experimental results are reported for structural transitions at high pressure in several III-V compounds and two II-VI compounds. These data, together with earlier results, are then compared with the predictions of model calculations of Van Vechten. Experimental transition pressures are often at variance with calculated values. However, his calculation assumes that the high pressure phase is metallic, with the beta-Sn structure. The present results show that several compounds assume an ionic NaCl structure at high pressure, while others have neither the beta-Sn nor NaCl structure.

Yu, S. C.↗
NASA NTRS1980

Na+ and Ca2+ ingestion - Plasma volume-electrolyte distribution at rest and exercise

The effects of hypernatremia and hypercalcemia on plasma volume and electrolyte distribution during rest, exercise and recovery in cool and hot environments are investigated. Plasma volume, protein and electrolytes were measured in two groups of five men in the supine position during rest, exercise at 40-47% maximal oxygen consumption and recovery in 26.5 C and 39.4 C environments, after ingestion in the rest period of 16-17 ml/kg hypertonic NaCl, isotonic NaCl or hypertonic calcium gluconate solutions. During the rest period, it is found that the hypertonic Ca drink prevents any rise in plasma volume in both cool and hot environments, while hypertonic Na retarded hypervolemia only in the cool environment and consumption of both isotonic and hypertonic Na in the heat resulted in a hypervolemic response twice as great as that in the cool environment. During exercise and recovery, plasma volume is found to be greatest after drinking hypertonic Na in the heat, while the normal hypervolemic responses during exercise were not influenced by drink composition. Results suggest that hypertonic drinks may be better for maintaining plasma volumes during exercise in the heat.

Greenleaf, J. E.↗
NASA NTRS1980

Extracellular hyperosmolality and body temperature during physical exercise in dogs

The purpose of this study was to test the hypothesis that thermoregulation during exercise can be affected by extracellular fluid hyperosmolality without changing the plasma Na(+) concentration. The effects of preexercise venous infusions of hypertonic mannitol and NaCl solutions on rectal temperature responses were compared in dogs running at moderate intensity for 60 min on a treadmill. Plasma Na(+) concentration was increased by 12 meq after NaCl infusion, and decreased by 9 meq after mannitol infusion. Both infusions increased plasma by 15 mosmol/kg. After both infusions, rectal temperature was essentially constant during 60 min rest. However, compared with the noninfusion exercise increase in osmolality of 1.3 C, rectal temperature increased by 1.9 C after both postinfusion exercise experiments. It was concluded that inducing extracellular hyperosmolality, without elevating plasma, can induce excessive increases in rectal temperature during exericse but not at rest.

Kozlowski, S.↗
NASA NTRS1980

The effect on the kinetics of pack aluminization of varying the activator

The effect on the kinetics of pack aluminization of nickel of varying the activator type was investigated using AlF3, NaF, NaCl and NaI as activators. The rate of aluminization was highest in packs activated with AlF3 and NaF, and lowest in those activated with NaCl and NaI. The results were in good accordance with predictions of the combined gas-solid diffusion theory of pack aluminization.

Gupta, B. K.↗
NASA NTRS1982

The stress-corrosion behavior of Al-Li-Cu alloys: A comparison of test methods

Two powder metallurgy processed (Al-Li-Cu) alloys with and without Mg addition were studied in aqueous 3.5% NaCl solution during the alternate immersion testing of tuning fork specimens, slow crack growth tests using fracture mechanics specimens, and the slow strain rate testing of straining electrode specimens. Scanning electron microscopy and optical metallography were used to demonstrate the character of the interaction between the Al-Li-Cu alloys and the selected environment. Both alloys are susceptible to SC in an aqueous 3.5% NaCl solution under the right electrochemical and microstructural conditions. Each test method yields important information on the character of the SC behavior. Under all conditions investigated, second phase particles strung out in rows along the extrusion direction in the alloys were rapidly attacked, and played principal role in the SC process. With time, larger pits developed from these rows of smaller pits and under certain electrochemical conditions surface cracks initiated from the larger pits and contributed directly to the fracture process. Evidence to support slow crack growth was observed in both the slow strain rate tests and the sustained immersion tests of precracked fracture mechanics specimens. The possible role of H2 in the stress corrosion cracking process is suggested.

Rizzo, P. P.↗
NASA NTRS1983

Investigation into the role of sodium chloride deposited on oxide and metal substrates in the initiation of hot corrosion

Sodium chloride is deposited on the surface of alumina substrates and exposed to air containing 1% SO2 at temperatures between 500 C and 700 C. In all cases the sodium chloride was converted to sodium sulfate. The volatilization of sodium chloride from the original salt particles was responsible for the development of a uniform coating of sodium sulfate on the alumina substrate. At temperatures above 625 C, a liquid NaCl-Na2SO4 autectic was formed on the substrate. The mechanisms for these reactions are given. One of the main roles of NaCl in low temperature hot corrosion lies in enabling a corrosive liquid to form.

Birks, N.↗
NASA NTRS1983

Band-overlap metallization of BaS, BaSe and BaTe

The insulator-metal transition volumes for BaS, BaSe, and BaTe are calculated for the first time, using the self-consistent augmented spherical wave technique. The metallized transition volumes are smaller than those corresponding to the NaCl yields CsCl structural transitions, but, 10 to 15% larger than those obtained by the Herzfeld dielectric theory. The calculated equilibrium energy gaps in the NaCl structure underestimate the measured ones by 50 to 60%.

Carlsson, A. E.↗
NASA NTRS1986

Growth of high-quality thin-film Ge single crystals by plasma-enhanced chemical vapor deposition

Thin-film Ge single crystals (approx. 10 microns) have been epitaxially grown on polished NaCl(100) substrates at 450C by using plasma-enhanced chemical vapor deposition. Films on approximately 1 sq cm and larger were separated from the NaCl by either melting the salt or by differential shear stress upon cooling to room temperature. The ordered growth of the Ge was found to be most sensitive to the initial plasma power and to the continuum flow dynamics within the carbon susceptor. The films were visually specular and exhibited a high degree of crysalline order when examined by X-ray diffraction. The films were found to be p-type with a carrier concentration of approximately 3 x 10 to the 16th power/cu cm, a resistivity of 0.11 ohm-cm, and a Hall hole mobility of 1820 sq cm/v/s at room temperature. Vacuum firing minimized the primary contaminant, Na, and corresponding lowered the carrier concentration to 4 x 10 to the 14th power/cu cm.

Outlaw, R. A.↗
NASA NTRS1986

Corrosion fatigue of 2219-T87 aluminum alloy

Corrosion fatigue studies were conducted on bare, chemical conversion coated, and anodized 2219-T87 aluminum alloy. These tests were performed using a rotating beam machine running at a velocity of 2500 rpm. The corrosive environments tested were distilled water, 100 ppm NaCl, and 3.5 percent NaCl. Results were compared to the endurance limit in air. An evaluation of the effect of protective coatings on corrosion fatigue was made by comparing the fatigue properties of specimens with coatings to those without.

Mcmillan, V. C.↗
NASA NTRS1987

On the role of convective motion during dendrite growth: Experiments under variable gravity, revised

Experiments show the effect of self induced convection on individual dendrite growth in uniformly supercooled samples and solidification of the resulting mush under conditions of high and low g. Convection is visualized by a Schlieren optical system or a Mach Zender interferometer. For ice crystals growing from the vapor in air, a slight reduction in linear growth rate occur under low g. For ice crystals growing from NaCl solution, dendrite tip velocities are unchanged, but subsequent mush solidification is enhanced through drainage channels under higher g. By contrast, sodium sulfate decahydrate dendrites growing from solution produce convective plumes which lead to higher tip growth rate only as the crystal growth direction approaches that of gravity. Convective plumes are laminar for small crystals under conditions of these experiments; the rise velocity of such plumes is greater than individual vortex rings under identical conditions. Convection effects are only present in solution under a critical supercooling less than about 5 C for sodium sulfate and 2 C for ice in NaCl since at higher supercooling the crystallization velocity, proportional to the square of the supercooling, exceeds the convective velocity, proportional to the square root of the supercooling. The role of convective velocity in bulk solidification is to give a large scale flow which under extreme cases may lead to extensive secondary crystal production, which alters the resulting crystal texture of the completely solidified melt.

Hallett, J.↗