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At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Acid droplet generation in SRM exhaust clouds

A free energy analysis is applied to the co-condensation/evaporation of H2O and HCl vapors on wettable particles in open air in order to model droplet nucleation in solid rocket motor (SRM) exhaust clouds. Formulations are defined for the free energy change, the drop radius, the saturation ratio, the total number of molecules, and the mean molecular radius in solution, as well as the molecular volume and the concentration range. The free energy release in the phase transition for the AL2O3 nuclei in the SRM exhaust is examined as a function of the HCl molefraction and nucleating particle radius, based on Titan III launch exhaust cloud conditions 90 sec after ignition. The most efficient droplet growth is determined to occur at an HCl molefraction of 0.082 and a particle radius of 0.0000013 cm, i.e. a molality of 5.355.

Dingle, A. N.↗
NASA NTRS1984

Aluminum chloride formation on Space Shuttle aluminum oxide

Samples of particulates collected from the exhaust of Space Shuttle launches STS-1, -4, -5, -6, and -7 were analyzed. Scanning electron microscopy and X-ray diffractometry of these samples indicated that the particulates were spherical and predominantly composed of aluminum oxide. The water-soluble weight fraction, pH, acid-soluble weight fraction, and insoluble weight fraction were determined for each sample. Water-soluble weight fractions averaged about 7 percent of the total sample weight, were generally very acidic, and contained significantly elevated concentrations of chloride and aluminum (III) ion. The high concentrations of soluble aluminum (III) and chloride ions observed suggested that aluminum chlorides and/or oxychlorides had formed on the surface of the alumina particulates. More than 72 percent by weight of each sample was insoluble in either water or strong mineral acid, and was identified as alpha-Al2O3. The results from these analyses suggest that the surface of Space Shuttle exhaust alumina particulates will be highly acidic and heavily chlorided, and that a substantial amount of the surface chloride may be chemically associated with aluminum (III) ions rather than just physically adsorbed as HCl.

Cofer, W. R., III↗
NASA NTRS1983

Comparison of seal materials for use in Stirling engines

In a dry, reciprocating sliding test, rods of 12 different surface materials rubbed against a glass filled PTFE gas seal. To simulate operation in a Stirling engine a gas (N2) pressure of 1 MPa differential pressure was applied across the seal. Gas leakage rates, rods surface temperatures, changes in the surface finish of the rod, surface hardness of the rod and wear rate of the seals were measured. The rod surface materials that produced the least seal were: plasma sprayed molybdenum (75 Mo 18 Ni 4 Cr), gas nitrided steel, and plasma sprayed aluminum oxide (94 Al2O3 6 TiO2). In contrast to almost all other mating surfaces, the surface roughness of the rods coated with Mo did not decrease during wear. This property is very important for the formation of a PTFE transfer film on the mating surface. The presence of a stable transfer film gives a low PTFE wear rate.

Lundholm, G.↗
NASA NTRS1984

Two forsterite-bearing FUN inclusions in the Allende meteorite

Two forsterite-, fassaite-, spinel-rich inclusions in Allende which share common mineralogy and texture with three previously described inclusions are described. These inclusions were at least partially molten at temperatures over 1400 C, and their crystallization sequence was spinel, olivine, fassaite, and Mg-rich melilite. At least some of them experienced partial volatilization of MgO and SiO2 from their outer margins. At least one of the inclusions is highly enriched in MgO relative to CaO and Al2O3 compared to Allende coarse-grained inclusions, although it is just as strongly enriched in refractory trace elements as the latter, relative to C1 chondrites. Two of the objects are FUN inclusions on the basis of their oxygen, magnesium, and silicon isotopic compositions.

Clayton, R. N.↗
NASA NTRS1984

Al-rich objects in ordinary chondrites - Related origin of carbonaceous and ordinary chondrites and their constituents

A description is given of 169 Al-rich objects (arbitrarily defined as having 10 wt pct or more of Al2O3) from 24 ordinary chondrites of types 3 and 4, five regolith breccias containing unequilibrated material, the unique meteorite Kakangari, and a few ordinary chondrites of types 5 and 6. On the basis of shape and texture, the Al-rich objects are divided into chondrules (round, with igneous textures), irregularly shaped inclusions (similar to type F and spinel-rich complex Ca-Al-rich inclusions), and fragments (probably fragments of Al-rich chondrules and inclusions). For descriptive purposes, the Al-rich chondrules are further subdivided into compositional subgroups, although they are entirely transitional.

Bischoff, A.↗
NASA NTRS1984

Solute transport and the prediction of breakaway oxidation in gamma + beta Ni-Cr-Al alloys

The Al transport and the condition leading to breakaway oxidation during the cyclic oxidation of gamma + beta NiCrAl alloys have been studied. The Al concentration/distance profiles were measured after various cyclic oxidation exposures at 1200 C. It was observed that cyclic oxidation results in a decreasing Al concentration at the oxide/metal interface, maintaining a constant flux of Al to the Al2O3 scale. It was also observed that breakaway oxidation occurs when the Al concentration at the oxide/metal interface approaches zero. A numerical model was developed to simulate the diffusional transport of Al and to predict breakaway oxidation in gamma + beta NiCrAl alloys undergoing cyclic oxidation. In a comparison of two alloys with similar oxide spalling characteristics, the numerical model was shown to predict correctly the onset of breakaway oxidation in the higher Al-content alloy.

Nesbitt, J. A.↗
NASA NTRS1983

Space Shuttle Environmental Effects: The First 5 Flights

Environmental effects associated with the first five Space Shuttle flights were monitored by the National Aeronautics and Space Administration (NASA) and the U.S. Air Force (USAF). Results and interpretations from this effort were reported at the December 1982 joint NASA-USAF conference. The conference proceedings are presented in this document. Most of the monitoring activity was focused on the launch cloud, emphasizing surface effects on the biota and air quality, model prediction of surface concentrations of HCl gas and Al2O3 dust, and airborne measurements of cloud composition. In general, assessments and predictions made in the April 1978 Final Environmental Impact Statement for the Space Shuttle Program were verified. Fallout of acidic mist and dust within 3 mi to 5 mi of the launch pad was the only unexpected effect of the launch. Atomization of deluge water in the Shuttle exhaust is considered to be the most probable cause of this effect. Sonic booms were monitored for several landings at Edwards Air Force Base, California; results agreed well with model predictions.

Potter, A.↗
NASA NTRS1984

Ceramic powder for sintering materials

Surface activity of ceramic powders such as MgO and Al2O3, for use in sintering with sp. emphasis on their particle size, shape, particle size distribution, packing, and coexisting additives and impurities are reviewed.

Akiya, H.↗
NASA NTRS1984

Structural changes during milling of aluminum oxide powders

The mechanical activation of four fused corundum powders and a calcined Al2O3 powder was studied. The milled powders were characterized by their structural properties, crystallite size, and lattice distortions. Structural changes during milling, detected by X-ray line broadening analysis, gave information about the enhanced activity of the powders caused by the lattice distortions and by the decreasing crystallite size during milling. The structural changes during milling, under the same milling conditions, can be quite different for the same ceramic material, but with different characteristics in the as received state.

Ziepler, G.↗
NASA NTRS1984

Bulk compositions of Al-rich chondrules in ordinary and carbonaceous chondrites: Variations and similarities

An extended study of ordinary chondrites revealed that chondrules exist which are transitional in composition between Al-rich and Mg-Fe-rich types in contrast to the finding of Wlotzka, who inferred a gap in compositions between the Ca-Al-rich and Mg-Fe-rich chondrules. Transitional chondrule bulk compositions are plotted. They show that no compositional gap exists between the Mg-Fe-rich and Al-rich chondrules. Chondrules with Na2O-contents 3.0 wt.% are indicated. Variable CaO/Na2O-ratios for chondrule bulk compositions exist, similar to what was described for the subgroups of Al-rich chondrules. Al-rich and transitional chondrules similar to those described above were found also in carbonaceous chrondrites. Thirty-nine chondrules from the carbonaceous chondrites Leoville, Allende, Vigarano and Colony were investigated. Their bulk compositions in terms of Al2O3 vs. CaO were plotted.

Bischoff, A.↗
NASA NTRS1984

Transformation toughened ceramics for the heavy duty diesel engine technology program

The objective of this program is to develop an advanced high temperature oxide structural ceramic for application to the heavy duty diesel engine. The approach is to employ transformation toughening by additions of ZrO.5HfO.5O2 solid solution to the oxide ceramics, mullite (2Al2O3S2SiO2) and alumina (Al2O3). The study is planned for three phases, each 12 months in duration. This report covers Phase 1. During this period, processing techniques were developed to incorporate the ZrO.5HfO.5O2 solid solution in the matrices while retaining the necessary metastable tetragonal phase. Modulus of rupture and of elasticity, coefficient of thermal expansion, fracture toughness by indent technique and thermal diffusivity of representative specimens were measured. In Phase 2, the process will be improved to provide higher mechanical strength and to define the techniques for scale up to component size. In Phase 3, full scale component prototypes will be fabri-]cated.

Musikant, S.↗
NASA NTRS1984

Material growth and characterization for solid state devices

Manganese was used as the dopant for p-type InGaAs layers grown on semi-insulating (Fe-doped) and n-type (Sn-doped) InP substrates. Optical, electrical (Hall) and SIMS measurements were used to characterize the layers. Mn-diffusion into the substrate (during the growth of In GaAs) was observed only when Fe-doped substrates were used. Quaternary layers of two compositions corresponding to wavelengths (energy gaps) of approximated 1.52 micrometers were successfully grown at a constant temperature of 640 C and InP was grown in the temperature range of 640 C to 655 C. A study of the effect of pulses on the growth velocity of InP indicated no significant change as long as the average applied current was kept constant. A system for depositing films of Al2O3 by the pyrolysis of aluminum isopropoxide was designed and built. Deposited layers on Si were characterized with an ellipsometer and exhibited indices of refraction between 1.582 and 1.622 for films on the order of 3000 A thick. Undoped and p-type (Mn-doped) InGaAs epitaxial layers were also grown on Fe-doped InP substrates through windows in sputtered SiO2 (3200 A thick) layers.

Stefanakos, E. K.↗
NASA NTRS1985

Particle size, number, composition and velocity from solid rocket motors

The damage potentials to the space shuttle orbiter caused by the high velocity particles contained in the exhaust plume of an upper stage is discussed. In particular, the particle size distribution and composition, the velocity of the particles and the expected contribution from shuttle launched upper stages are addressed. Particle size estimates based on historical data are compapred with those derived from upper stage motor performance testing. The particle velocities as determined by the best available plume computational technique are presented. The shuttle is scheduled to launch approximately 135 upper-stages over its lifetime looking at the currently scheduled flights and averaging over a yearly basis yields the contribution of particulates from the uper-stages. On the average, 91,645 llbs of Al2O3 will be ejected on each launch. The analysis to determine how much of this 91,645 lbs will remain in orbit or the decay rate is yet to be accomplished.

Roberts, B. B.↗
NASA NTRS1985

The Geology of East Butte, a Rhyolitic Volcanic Dome on the Eastern Snake River Plain, Idaho

East Butte is a prominent volcanic dome located on the eastern Snake River Plain. It is situated 51 km west of Idaho Fallls in the southeast corner of the Idaho National Engineering facility. East Butte rises 350 meters above the Quaternary basalt flows which encircle its 2.4 kilometer diameter base. Its maximum elevation is 2003 meters above sea level. East Butte is composed dominantly of rhyolite. Armstrong and others (1975) determined a K-Ar age of 0.6 +/- m.y. for a rhyolite sample from East Butte. Detailed geologic mapping revealed East Butte to be a single, large cumulo-dome composed dominantly of rhyolite. Major element geochemical analyses indicate that the rhyolite of East Butte is mildly peralkaline (molecular excess of Na2O and K2O over Al2O3 and compositionally homogeneous. Color variations in the East Butte rhyolite result from varying amounts of chemical and physical weathering and to the degree of devitrification that the glass in the groundmass of the rhyolite underwent.

Bretches, J. E.↗
NASA NTRS1985

Ion beam sputter-deposited thin film coatings for protection of spacecraft polymers in low Earth orbit

Ion beam sputter-deposited thin films of Al2O3, SiO2, and a codeposited mixture of predominantly SiO2 with small amounts of a fluoropolymer were evaluated both in laboratory plasma ashing tests and in space on board shuttle flight STS-8 for effectiveness in preventing oxidation of polyimide Kapton. Measurements of mass loss and optical performance of coated and uncoated polyimide samples exposed to the low Earth orbital environment are presented. Optical techniques were used to measure loss rates of protective films exposed to atomic oxygen. Results of the analysis of the space flight exposed samples indicate that thin film metal oxide coatings are very effective in protecting the polyimide. Metal oxide coatings with a small amount of fluoropolymer codeposited have the additional benefit of great flexibility.

Banks, B. A.↗
NASA NTRS1984

Moderate temperature sodium cells. V - Discharge reactions and rechargeability of NiS and NiS2 positive electrodes in molten NaAlCl4

NiS2 and NiS have been characterized as high energy density rechargeable positive electrodes for moderate-temperature Na batteries of the configuration, Na(1)/beta double prime-Al2O3/NaAlCl4(1), NiSx. The batteries operate in the temperature range 170 - 190 C. Positive electrode reactions during discharge/charge cycles have been characterized. Excellent rechargeability of the batteries has been demonstrated by extended cell cycling. A Na/NiS2 cell, operating at 190 C, exceeded 600 deep discharge/charge cycles with practically no capacity deterioration. The feasibility of secondary Na/NiSx batteries with specific energies equal to or greater than 50 Wh/lb and cycle lifes exceeding 1000 deep discharge/charge cycles has been demonstrated.

Abraham, K. M.↗
NASA NTRS1984

Electromagnetic modes of the asymmetric metal-oxide-metal tunnel junction

The characteristics of the modes of an Al-Al2O3-Ag tunnel junction are analyzed, and the way in which the field profiles, the propagation constant, and the attenuation depend on the thickness of the oxide layer is described. The significance of these results for investigations of light emission from metal-oxide-metal tunnel junctions is discussed.

Kurdi, B. N.↗
NASA NTRS1984

Cyclic oxidation behavior of beta+gamma overlay coatings on gamma and gamma+gamma-prime alloys

Detailed experimental studies of the cyclic oxidation behavior of low-pressure plasma sprayed beta+gamma coasting on gamma-phase Ni-Cr-Al alloys have shown the correlation of weight change, oxide type, and Cr and Al concentration-distance profiles as a function of oxidation time. Of special interest was the transition to breakway oxidation due to the loss of the Al flux to the oxide and the failure of the coated alloy to form an Al2O3-rich oxide scale. The experimental results on beta+gamma/gamma coating systems were used as the basis of a numerical model (ternary, semi-infinite, finite-difference analysis) which accurately predicted changes in Cr and Al concentration-distance profiles. The model was used to study parameters critical to enhancing the life of coatings which fail by a combination of Al loss in forming the oxide scale and Al loss via interdiffusion with the substrate alloy. Comparisons of beta+gamma/gamma coating behavior are made to the oxidation of coated gamma+gamma-prime substrates, both ternary Ni-Cr-Al alloys and Mar-M 247-type alloys.

Nesbitt, J. A.↗