Search NASA⌕ Search

SEARCH · Search NASA

Results for “Microprobe”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Characterization of crust formation on a parent body of achondrites and the moon by pyroxene crystallography and chemistry

Single crystal X-ray diffraction and electron microprobe techniques were used to study lunar crustal pyroxenes in a cataclastic norite, a pyroxene-rich clast, and anorthosite lunar samples, and also in meteorites including diogenites, eucrites, and the Yamoto (1) howardite. The crystallographic and chemical characteristics of pyroxenes in these materials are compared and are discussed in terms of the lower stability limit of pigeonite. A mechanical mixing model of howardite is proposed.

Takeda, H.↗
NASA NTRS1977

Mechanism of beneficial effect of tantalum in hot corrosion of nickel-base superalloys

X-ray diffraction and electron microprobe analyses were used to examine a prominent NaTaO3 pattern formed in a number of nickel-base superalloys. It is found that a beneficial effect of tantalum with respect to hot corrosion attack arises from the ability of Ta2O5 to tie up Na2O and prevent the formation of a molten Na2MoO4 phase.

Fryburg, G. C.↗
NASA NTRS1977

The metallic microstructures and thermal histories of severely reheated chondrites

The metallographic structures of eight severely reheated chondrites - Farmington, Ramsdorf, Orvinio, Wickenburg, Lubbock, Rose City, Arapahoe, and Tadjera - were studied using optical, SEM and electron microprobe techniques. The following metallographic criteria were used to estimate the post-shock residual temperature of the chondrites: melted metal-troilite appearance, presence of martensite, phosphorus enrichment of metal and averaging of central metal grain compositions. The presence of phosphides and secondary kamacite are due to slow post-shock cooling rates. Ni rim gradients indicate both extensive remelting of metal grains and relatively fast cooling.

Smith, B. A.↗
NASA NTRS1977

Rare accessory uraninite in a Sierran granite

One grain of uraninite was found in a single thin-section of Sierran granite. Electron and ion microprobe analysis were used to determine the composition. Since the U-Pb age calculated for the uraninite does not differ greatly from the K-Ar age of the unit in which it occurs, it is suggested that the mineral is primary and not reworked from a preexisting rock. No uraninite has been detected in heavy mineral concentrates from other rocks of the local area.

Snetsinger, K. G.↗
NASA NTRS1977

Ion-beam-induced atomic mixing

Calculations based on the diffusion model are presented of atomic mixing by ion bombardment. This mixing is assumed to have its basis, as does sputtering, in the collision cascades generated by the primary beam. Sharp interfaces within a target are seen to be smoothed by ion bombardment. Mixing may place fundamental limits on the resolution of ion microprobes.

Haff, P. K.↗
NASA NTRS1977

Metallic phases in the Luna 24 soil samples

The metal and sulfide phases in the Luna 24 soil samples were studied with the optical microscope and the electron microprobe. The compositions of the metal particles fall into three groups based on their Ni and Co contents: (1) Samples of meteoritic composition which have undergone metamorphism on the lunar surface. (2) Samples of submeteoritic, low Ni and low Co contents, including most of the metal particles observed. These particles are contained in glass and agglutinate particles and were probably formed by the mixing of meteoritic metal with lunar metal produced by the reduction of silicates during shock-impact. (3) Samples of high-CO content probably formed by mixing of meteoritic material with high-Co metal from the mare basalt or by fractional crystallization from a metal silicate melt. The sulfide minerals were also studied. These are almost pure FeS, and crystallized from a late stage liquid in the mare basalt. Three high-Ni sulfides were also found in the glass phase of agglutinates.

Friel, J. J.↗
NASA NTRS1977

Chemical and petrographic constraints on the origin of chondrules and inclusions in carbonaceous chondrites

Bulk chemical compositions of the various petrographic types of chondrules and inclusions in Type 3 carbonaceous chondrites (excluding those affected by metamorphism) have been determined by microprobe defocused-beam analysis. Inclusion compositions follow approximately the theoretical compositional trajectory for equlibrium condensation. Chondrules occurring in the same meteorites have higher silica contents and show only slight overlap with inclusion compositions. Dust fusion is apparently an inadequate mechanism for producing the wide chemical variations observed among chondrules. Impact-melting models require sampling of complex target rocks which are unknown as components of meteorites; this mechanism also demands efficient mechanical processing of chondrules before accretion. A genetic relationship between chondrules and inclusions in carbonaceous chondrites is suggested by the compositional continuum between these objects. A condensation sequence which dips into the liquid stability field at lower temperatures is advocated for the production of both inclusions and chondrules. Textural relationships between intergrown chondrules and inclusions support such a sequence. This model suggests that the assembled components (inclusions and chondrules) of carbonaceous chondrites are related by a common process.

Mcsween, H. Y., Jr.↗
NASA NTRS1978

The room-temperature dissociation of the compound Au3Si

Three gold-18.6 at.% silicon specimens which were solidified by quenching from above the liquidus temperature have been reexamined after being stored at room temperature for about 8 years. It was found that the 'metastable' compound Au3Si formed on quenching had begun to dissociate by a surface nucleated, solid-state reaction. The reaction front had advanced about 0.2 mm from the surface, leaving a rim of dissociation products. These dissociation products were studied using optical and scanning electron microscopy, electron beam microprobe analysis and an X-ray micro-diffraction technique. It was concluded that the reaction produces elemental gold and silicon, as at higher reaction temperatures, but that the scale of dispersion is so extremely fine that the resulting microstructure cannot be resolved by scanning electron microscopy.

Bhattacharya, D.↗
NASA NTRS1975

Anomalous low-K silicate melt inclusions in ilmenite from Apollo 17 basalts

Primary silicate melt inclusions in ilmenite crystals in seven mare basalt samples were analyzed by electron microprobe, and analyses were made of their host and associated phases. Two distinct and restricted chemical composition ranges are drawn: high-K and low-K. The high-K samples are nearly identical with the granitic residual liquid, averaging a weight percentage of 6.27% K20, 76.3% SiO2, plus 82% normative quartz and orthoclase. It is noted that no low-K melt was found as a re-entrant or interstitial inclusion in any sample; only as isolated inclusions in illmenite.

Roedder, E.↗
NASA NTRS1975

Minor elements in lunar olivine as a petrologic indicator

Accurate electron microprobe analyses (approximately 50 ppm) were made for Al, Ca, Ti, Cr, Mn, and Ni in Mg-rich olivines which may derive from early lunar crust or deeper environments. Low-Ca contents consistently occur only in olivines from dunitic and troctolitic breccia: spinel troctolite and other rock types have high-Ca olivines suggesting derivation by near-surface processes. Rock 15445 has olivine with distinctly low CaO (approximately 0.01 wt.%). Chromium ranges to higher values (max.0.2 oxide wt.%) than for terrestrial harzburgites and lherzolites but is similar to the range in terrestrial komatiites. Divalent chromium may be indicated over trivalent Cr because olivines lack sufficient other elements for charge balance of the latter. NiO values in lunar specimens range from 0.00 to 0.07 wt.% and a weak anticorrelation with Cr2O3 suggests an oxidation state effect. Al2O3 values are mostly below 0.04-wt.% and show no obvious correlation with fragment type. TiO2 values lie below 0.13-wt.% and seem to correlate best with crystallization rate and plagioclase content of the host rock. High values of Al2O3 and TiO2 reported by other workers have not been confirmed, and are probably wrong.

Steele, I. M.↗
NASA NTRS1975

Petrography and petrology of basaltic achondrite polymict breccias /Howardites/

The reported investigation is based on the results from petrographic observations, electron microprobe analyses of constituent phases, and defocused beam analyses of clasts and glasses. Howardites consist of mostly angular-to-rounded mineral, rock, and breccia clasts compacted in variable grain-sized matrices of finely comminuted materials. Attention is given to ophitic and subophitic rocks, granular basalts and microgabbros, mafic rocks, Al-rich rocks, breccia clasts, impact melt rocks, glasses, meteorite clasts, bulk composition, particle size distribution, howardite component composition, questions of breccia formation, and parent body implications. It is found that the four main rock types found in howardites do have certain analogies to lunar rocks. It is tempting to speculate that both the moon and the basaltic achondrite parent body formed similar rock suites in their evolutionary processes.

Bunch, T. E.↗
NASA NTRS1975

Surface morphology and chemistry of rusty particle 60002,108

Scanning electron microscope, energy dispersive X-ray, and microprobe analyses of the surface of rusty colored particle 60002,108 from deep core 60002 reveal the particle to be basically metallic Ni-Fe that probably grew in contact with silicate minerals, principally plagioclase and pyroxene, and was later partially oxidized and hydrated. A yellowish wrinkled and 'shatter cone' like granular material that is either iron oxide or oxyhydrate may have formed while the particle was in the lunar environment. Ruby-red mounds of lawrencite formed, and the reaction of lawrencite, metallic Ni-Fe, and water vapor resulted in aprons of iron oxyhydrate that surrounds these mounds and flows out over the preexisting yellowish granular substrate. The observations do not allow one to distinguish unequivocally between the initiation of hydration of the ruby-red lawrencite mounds in the lunar environment followed by reaction in the terrestrial and/or spacecraft environment or only reaction in the terrestrial and/or spacecraft environment. The relationship of the lawrencite-rich mounds to the yellowish granular substrate favors the first possibility.

Carter, J. L.↗
NASA NTRS1975

Relative cooling rates of mare basalts at the Apollo 12 and 15 sites as estimated from pyroxene exsolution data

X-ray single-crystal diffraction studies, supplemented by electron microprobe analyses of core pigeonites and rim augites from rocks 12031, 15085, 15475, and 15495, have been used to suggest cooling rates for these and other Apollo 12 and 15 rocks studied by similar methods. The extent of subsolidus phase separation of pyroxenes is used as a measure of the cooling rate. The results were interpreted in terms of model cooling histories of a lava flow whose thickness was estimated from the absolute cooling rates obtained by cooling rate experiments and by temperature-time variation through an extrusive flow computed by employing simplified theory of Jaeger. All available data on the exsolution and cation distributions of pyroxenes from Apollo 12 and 15 samples at present are consistent with the hypothesis that these rocks were derived from the top and interior of lava flows with thicknesses of 4-10 m. A process for exsolution of augite from a host pigeonite on (100) has been related to its low-calcium content.

Takeda, H.↗
NASA NTRS1975

Density, chemistry, and size distribution of interplanetary dust

Depth/diameter ratios measured for 98 craters in lunar glass targets reveal a broad distribution with a single strong peaking between 0.55 and 0.8. The measured values indicate a mean meteoroid density greater than 1 g/cu cm and probably less than 4 g/cu cm. Microprobe analyses show that typical glass pit liners on silicate targets contain only approximately 0.1% or less of meteoritic material. The size-frequency distribution of meteoroids was analyzed for a fractured glass surface of 60095, and a very steep size distribution of submicron meteoroids is indicated. As in the case of 15205, a dip at approximately 5 micron in the size-frequency distribution is detected.

Brownlee, D. E.↗
NASA NTRS1975

Ion-probe studies of artificially implanted ions in lunar samples

The ion microprobe at the Johnson Space Center was used to study depth profiles of artificially implanted ions in lunar samples. Five polished sections of typical mare basalts (12040 and 12018) were irradiated with nine different elements at two energies and the resulting concentrations were measured as a function of depth in the minerals plagioclase, pyroxene, and ilmenite. These preliminary simulation experiments were undertaken to determine whether the ion probe can be used to measure solar-wind-implanted elements on the surface of lunar rock crystals and soil grains and to study mechanisms for the redistribution. The results obtained so far demonstrate that depth profiles can indeed be measured with the ion probe. From estimated exposure times of mature soil grains and selected vug crystals, it appears possible (if difficult) to detect several solar-wind-implanted elements.

Zinner, E.↗
NASA NTRS1978

Studies of Brazilian meteorites. XIV - Mineralogy, petrology, and chemistry of the Conquista, Minas Gerais, chondrite

The Conquista chondrite is described and classified as an H4. The mineral composition is reported. H-group classification is based on described microscopic, electron microprobe, and bulk chemical studies. The evidence for petrologic type 4 classification includes the pronounced well-developed chondritic texture; the slight compositional variations in constituent phases; the high Ca contents of pyroxene and the presence of pigeonite; glassy to microcrystalline interstitial material rich in alkalis and SiO2; and twinned low-Ca clinopyroxene.

Keil, K.↗
NASA NTRS1979

An experimental, low-cost, silicon slurry/aluminide high-temperature coating for superalloys

A duplex silicon-slurry/aluminide coating has been developed and cyclically tested in Mach 1 combustion gases for oxidation and thermal fatigue resistance at 1093 C and in Mach 0.3 gases for hot-corrosion resistance at 900 C. The base-metal superalloys were VIA and B-1900. The coated B-1900 specimens performed much better in oxidation than similar specimens coated with aluminides and almost as well as the more-expensive Pt-Al and MCrAlY (where M is Ni and/or Co) coatings deposited by the physical vapor deposition process. The coating also provided good hot-corrosion protection. Metallographic, X-ray, and electron microprobe studies were made to characterize the coating, determine failure mechanisms, and study some of the changes due to exposure.

Young, S. G.↗
NASA NTRS1978

The hot corrosion of Co-25Cr-10Ni-5Ta-3Al-0.5Y alloy /S-57/

A cobalt-base alloy, Co-25Cr-10Ni-5Ta-3Al-0.5Y (S-57), was subjected to hot corrosion in Mach 0.3 burner-rig combustion gases at maximum alloy temperatures of 900 and 1000 C. Various salt concentrations were injected into the burner: 0.5, 2,5, and 10 parts per million synthetic sea salt and 4 parts per million sodium sulfate (Na2SO4). The extent of corrosion was determined by measuring the maximum depth of corrosion in the alloy, and the corrosion process was studied by metallography, X-ray diffraction, scanning electron microscopy, and electron microprobe analysis. While S-57 was found to possess only moderate oxidation resistance at these temperatures, this alloy resisted significant hot corrosion attack under all but the most severe test conditions. The process of hot corrosion attack under the most severe conditions of this study was primarily sulfidation.

Santoro, G. J.↗