Search NASA⌕ Search

SEARCH · Search NASA

Results for “in situ crystallization”

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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Petrology and thermal history of type IA chondrules in the Semarkona (LL3.0) chondrite

Detailed petrologic studies have been made of 15 type IA, Fe-poor, porphyritic olivine chondrules in Semarkona (LL3.0). Major and minor element concentrations in olivines, pyroxenes, and mesostases, and bulk composition so the chondrules are measured along with zoning profiles in the olivine and pyroxene crystals. The mineral compositions and textures are best interpreted in terms of closed system crystallization in which the olivines and pyroxenes crystallized in situ from a melt corresponding to the bulk composition of the chondrule. Relict olivine grains are not found in the chondrules. Crystallization probably occurred at a cooling rate of the order of 1000 C/hr. Precursor materials of the chondrules were composed of two components, one refractory Ca-, Al-, and Ti-rich, and one less refractory Si-, Fe-, Cr-, and Mn-rich. The evidence is consistent with Semarkona being one of the least metamorphosed ordinary chondrites.

Jones, R. H.↗
NASA NTRS1984

Relict and other anomalous grains in chondrules - Implications for chondrule formation

Relict olivine and pyroxene grains have been identified in chondrules from ordinary and carbonaceous chondrites that probably did not crystallize in situ. Some of these olivines are clear, but others contain fine-grained Fe, Ni ('dusty olivines') and resemble previously described occurrences in ordinary chondrites. There are also chondrules in which all olivine is dusty. It is concluded that: (1) not all relict olivines are dusty, (2) not all dusty olivines crystallized outside the chondrule in which they occur, and (3) some dusty olivines were produced during chondrule formation by a reduction process that affected the whole chondrule. The occurrence of dusty olivines and relict pyroxenes and olivines in chondrules from carbonaceous as well as ordinary chondrites supports the argument that chondrules from all chondrites had similar origins and histories. It is proposed that chondrules and mineral fragments were transported across f(O2) gradients in the solar nebula while they were hot, or were reheated in an environment different from the one in which they formed. Partially molten chondrules sometimes incorporated mineral grains or chondrules with different redox states, producing compound chondrules and chondrules containing anomalous grains. Dusty olivines may also have formed when hot chondrules were transported to regions of lower oxygen fugacity.

Kracher, A.↗
NASA NTRS2013

Timescale of Petrogenetic Processes Recorded in the Mount Perkins Magma System, Northern Colorado River Extension Corridor, Arizona

The Miocene Mt. Perkins Pluton is a small composite intrusive body emplaced in the shallow crust as four separate phases during the earliest stages of crustal extension. Phase 1 (oldest) consists of isotropic hornblende gabbro and a layered cumulate sequence. Phase 2 consists of quartz monzonite to quartz monzodiorite hosting mafic microgranitoid enclaves. Phase 3 is composed of quartz monzonite and is subdivided into mafic enclave-rich zones and enclave-free zones. Phase 4 consists of aphanitic dikes of mafic, intermediate and felsic compositions hosting mafic enclaves. Phases 2-4 enclaves record significant isotopic disequilibrium with surrounding granitoid host rocks, but collectively enclaves and host rocks form a cogenetic suite exhibiting systematic variations in Nd-Sr-Pb isotopes that correlate with major and trace elements. Phases 2-4 record multiple episodes of magma mingling among cogenetic hybrid magmas that formed via magma mixing and fractional crystallization at a deeper crustal. The mafic end-member was alkali basalt similar to nearby 6-4 Ma basalt with enriched OIB-like trace elements and Nd-Sr-Pb isotopes. The felsic end-member was a subalkaline crustal-derived magma. Phase 1 isotropic gabbro exhibits elemental and isotopic compositional variations at relatively constant SiO2, suggesting generation of isotropic gabbro by an open-system process involving two mafic end-members. One end-member is similar in composition to the OIB-like mafic end-member for phases 2-4; the second is similar to nearby 11-8 Ma tholeiite basalt exhibiting low epsilon (sub Nd), and depleted incompatible trace elements. Phase 1 cumulates record in situ fractional crystallization of an OIB-like mafic magma with isotopic evidence of crustal contamination by partial melts generated in adjacent Proterozoic gneiss. The Mt Perkins pluton records a complex history in a lithospheric scale magma system involving two distinct mantle-derived mafic magmas and felsic magma sourced in the crust. Mixing and fractional crystallization of these magmas at various levels in the crust generated a suite of intermediate composition magmas. U-Pb zircon SHRIMP ages of phase 1 (15.7 +/- 0.2 Ma), phase 3 (15.8 +/- 0.2 Ma) and phase 4 (15.4 +/- 0.3 Ma) document a 100-300k year timescale for petrogenetic processes recorded in the Mt Perkins magma system.

Danielson, Lisa R.↗
NASA NTRS1994

Relict grains in chondrules: Evidence for chondrule recycling

The presence of relict grains in chondrules, which offers some insight into the degree to which chondrule material was recycled in the chondrule-forming region, is discussed in this report. Relics are grains that clearly did not crystallize in situ in the host chondrule. They represent coarse-grained precursor material that did not melt during chondrule formation, and provide the only tangible record of chondrule precursor grains. Relics are commonly identified by a large difference in size, textural differences, and/or significant compositional differences compared with normal grains in the host chondrule. Two important types of relics are: (1) 'dusty,' metal-bearing grains of olivine and pyroxene; and (2) forsterite (Mg-rich olivine) grains present in FeO-rich chondrules.

Jones, R. H.↗
NASA NTRS1994

The Divnoe meteorite: Petrology, chemistry, oxygen isotopes and origin

The Divnoe meteorite is an olivine-rich primitive achondrite with subchondritic chemistry and mineralogy. It has a granoblastic, coarse-grained, olivine groundmass (CGL: coarse-grained lithology) with relatively large pyroxene-plagioclase poiklitic patches (PP) and small fine-grained domains of an opaque-rich lithology (ORL). Both PP and ORL are inhomogeneously distributed and display reaction boundaries with the groundmass. Major silicates, olivine Fa(20-28) and orthopyroxyene Fs(20-28 Wo(0.5-2.5), display systematic differences in composition between CGL and ORL as well as a complicated pattern of variations within CGL. Accessory plagioclase has low K content and displays regular igneous zoning with core compositions An(40-45) and rims An(32-37). The bulk chemical composition of Divnoe is similar to that of olivine-rich primitive achondrites, except for a depletion of incompatible elements and minor enrichment of refractory siderophiles. Oxygen isotope compositions for whole-rock and separated minerals from Divnoe fall in a narrow range, with mean delta O-18 = +4.91, delta O-17 = +2.24, and Delta O-17 = -0.26 +/- 0.11. The isotopic composition is not within the range of any previously recognized group but is very close to that of the brachinites. To understand the origin of Divnoe lithologies, partial melting and crystallization were modelled using starting compositions equal to that of Divnoe and some chondritic meteorites. It was found that the Divnoe composition could be derived from a chondritic source region by approximately 20 wt% partial melting at Ta approximately 1300 C and log(fO2) = IW-1.8, followed by approximtely 60 wt% crystallization of the partial melt formed, and removal of the still-liquid portion of the partial melt. Removal of the last partial melt resulted in depletion of the Divnoe plagioclase in Na and K. In this scenario, CGL represents the residue of partial melting, and PP is a portion of the partial melt that crystallized in situ. The ORL was formed during the final stages of partial melting by reaction between gaseous sulfur and residual olivine in the source region. A prominent feature of Divnoe is fine micron-scale chemical variations within olivine grains, related to lamellar structures the olivines display. The origin of these structures is not known.

Petaev, M. I.↗
NASA NTRS1994

Igneous petrology of the new ureilites Nova 001 and Nullarbor 010

The Nova 001 (= Nuevo Mercurio (b)) and Nullarbor 010 meteorites are ureilites, both of which contain euhedral graphite crystals. The bulk of the meteorites are olivine (Fo79) and pyroxenes (Wo9En73Fs18, Wo3En77Fs20), with a few percent graphite and minor amounts of troilite, Ni-Fe metal, and possibly diamond. The rims of olivine grains are reduced (to Fo91) and contain abundant blebs of Fe metal. Silicate mineral grains are equant, anhedral, up to 2 mm across, and lack obvious preferred orientations. Euhedral graphite crystals (to 1 mm x 0.3 mm) are present at silicate grain boundaries, along boundaries and protruding into the silicates, and entirely within silicate mineral grains. Graphite euhedra are also present as radiating clusters and groups of parallel plates grains embedded in olivine; no other ureilite has comparable graphite textures. Minute lumps within graphite grains are possible diamond, inferred to be a result of shock. Other shock effects are limited to undulatory extinction and fracturing. Both ureilites have been weathered significantly. Considering their similar mineralogies, identical mineral compositions, and identical unusual textures, Nova 001 and Nullarbor 010 are probably paired. Based on olivine compositions, Nova 001 and Nullarbor 010 are in Group 1 (FeO-rich) of Berkley et al. (1980). Silicate mineral compositions are consistent with those of others known ureilites. The presence of euhedral graphite crystals within the silicate minerals is consistent with an igneous origin, and suggests that large proportions of silicate magma were present locally and crystallized in situ.

Triman, Allan H.↗
NASA NTRS2004

Forsterite and Olivine in Sahara-97210 (LL3.2) and Chainpur (LL3.4) Chondrules: Compositional Evolution and the Influence of Melting

It is generally accepted that chondrules contain relict grains that did not crystallize in situ, and that forsterite is one type of relict grain which is a likely precursor for chondrules. Chemically and morphologically similar forsterite is also found as "isolated grains", especially in carbonaceous chondrites. Using SIMS, we analyzed forsterite, ferrous overgrowths around forsterite, and coexisting normal olivine in 5 chondrules and 2 isolated grains in the Sahara-97210 ('Sahara") LL3.2 chondrite. We earlier used the same methods to study olivine in 3 Chainpur chondrules that contain relict forsterite. Our new data for Sahara provide additional insight into the processes affecting chondrules and their precursors.

Ruzicka, A.↗
NASA NTRS2004

Relict Forsterite in Chondrules: Implications for Cooling Rates

Forsterite (Fo(sub 99-100)) is often present in chondrules as relict grains that did not crystallize in situ and as isolated grains outside of chondrules; both are surrounded by ferrous overgrowths which clearly formed at a later time, probably during chondrule formation. We performed microprobe analyses across forsterite-overgrowth interfaces in 12 chondrules and 4 isolated grains in the Sahara-97210 LL3.2 (Sahara), Wells LL3.3, and Chainpur LL3.4 chondrites and modelled diffusional exchange between forsterite and overgrowths, with the goal of constraining the thermal histories during chondrule formation. The cooling rates experienced by chondrules provide an important constraint on the origin and setting of these objects.

Greeney, S.↗
NASA NTRS1999

Crystal Growth Using MEPHISTO

The shuttle flight experiment "In Situ Monitoring of Crystal Growth Using MEPHISTO" was accomplished during STS-87 as part of the fourth flight of the United States Microgravity Payload (USMP-4), which was flown from November 19 to December 5, 1997. The data returned from that flight are just now beginning to yield quantitative results. This project is an international collaboration: the furnace system known as MEPHISTO was built in France by CNES (French National Space Agency) and CEA (French Atomic Energy Commission); the principal investigator, Prof. Reza Abbaschian, is from the University of Florida at Gainesville; and numerical and analytical modeling support includes collaborators from the University of New South Wales, Australia, the University of Wisconsin at Milwaukee, the National Institute of Standards and Technology, and the NASA Lewis Research Center. MEPHISTO is a French acronym that translates into English as Materials for the Study of Interesting Phenomena of Solidification on Earth and in Orbit. Since this was the fourth flight of the MEPHISTO furnace, the experiment is referred to as MEPHISTO-4. MEPHISTO-4 was a directional solidification experiment that studied the liquid-to-solid transformation of bismuth alloyed with tin. Directional solidification is a freezing technique common to the processing of the electronic materials used in integrated circuits and detectors, such as silicon and germanium. When liquids are frozen on Earth, they must be cooled. The cooling causes stirring because of density variations in the liquid. This stirring, known as natural convection, influences the quality of the resulting solid. During freezing, regions of high and low concentrations of tin are created. This introduces another important phenomenon: diffusion, or the movement by molecular action of matter from regions of high concentration to regions of lower concentration. In MEPHISTO-4, it is tin that diffuses from the high-concentration region in front of the solid-liquid interface to more distant low-concentration regions.

deGroh, Henry C., III↗
NASA NTRS2009

On the Importance of Small Ice Crystals in Tropical Anvil Cirrus

In situ measurements of ice crystal concentrations and sizes made with aircraft instrumentation over the past two decades have often indicated the presence of numerous relatively small (< 50 m diameter) crystals in cirrus clouds. Further, these measurements frequently indicate that small crystals account for a large fraction of the extinction in cirrus clouds. The fact that the instruments used to make these measurements, such as the Forward Scattering Spectrometer Probe (FSSP) and the Cloud Aerosol Spectrometer (CAS), ingest ice crystals into the sample volume through inlets has led to suspicion that the indications of numerous small ]crystals could be artifacts of large ]crystal shattering on the instrument inlets. We present new aircraft measurements in anvil cirrus sampled during the Tropical Composition, Cloud, and Climate Coupling (TC4) campaign with the 2 ] Dimensional Stereo (2D ]S) probe, which detects particles as small as 10 m. The 2D ]S has detector "arms" instead of an inlet tube. Since the 2D ]S probe surfaces are much further from the sample volume than is the case for the instruments with inlets, it is expected that 2D ]S will be less susceptible to shattering artifacts. In addition, particle inter ]arrival times are used to identify and remove shattering artifacts that occur even with the 2D ]S probe. The number of shattering artifacts identified by the 2D ]S interarrival time analysis ranges from a negligible contribution to an order of magnitude or more enhancement in apparent ice concentration over the natural ice concentration, depending on the abundance of large crystals and the natural small ]crystal concentration. The 2D ]S measurements in tropical anvil cirrus suggest that natural small ]crystal concentrations are typically one to two orders of magnitude lower than those inferred from CAS. The strong correlation between the CAS/2D ]S ratio of small ]crystal concentrations and large ]crystal concentration suggests that the discrepancy is likely caused by shattering of large crystals on the CAS inlet. We argue that past measurements with CAS in cirrus with large crystals present may contain errors due to crystal shattering, and past conclusions derived from these measurements may need to be revisited. Further, we present correlations between CAS spurious concentration and 2D ]S large ]crystal mass from spatially uniform anvil cirrus sampling periods as an approximate guide for estimating quantitative impact of large ]crystal shattering on CAS concentrations in previous datasets. We use radiative transfer calculations to demonstrate that in the maritime anvil cirrus sampled during TC4, small crystals indicated by 2D ]S contribute relatively little cloud extinction, radiative forcing, or radiative heating in the anvils, regardless of anvil age or vertical location in the clouds. While 2D ]S ice concentrations in fresh anvil cirrus may often exceed 1 cm.3, and are observed to exceed 10 cm.3 in turrets, they are typically ~0.1 cm.3 and rarely exceed 1 cm.3 (<1.4% of the time) in aged anvil cirrus. We hypothesize that isolated occurrences of higher ice concentrations in aged anvil cirrus may be caused by ice nucleation driven by either small ]scale convection or gravity waves. It appears that the numerous small crystals detrained from convective updrafts do not persist in the anvil cirrus sampled during TC ]4.

Jensen, E. J.↗
NASA NTRS2004

In-situ Optical Waveguides for Monitoring and Modifying Protein Crystal Growth

The use of electric fields in the growth of protein crystals was investigated, both theoretically and experimentally. We used dc, ac and optical fields to change the spatial distribution of proteins. Dc fields had only local effects, due to the conductivity of the growth solution. We found that for low frequency fields, movement of the buffer and salt ions dominated, and that for high frequency ac fields, &electrophoretic effects could be useful for relocating growing protein crystals. The most promising result was that for optical fields, a large gradient in the field could be used to capture a crystal, and observe growth in-situ. This concept could be developed into an experimental setup compatible with automated x-ray diffraction measurements in microgravity.

Gibson, Ursula↗
NASA NTRS1995

Remote sensing of cirrus cloud optical and microphysical properties using AVHRR data

The importance of understanding the radiative and microphysical properties of cirrus clouds in weather and climate research has been articulated by Liou (1986). This importance has also been recognized in view of the intensive field observations that have been conducted as a major component of the First ISCCP Regional Experiment (FIRE) in October-November 1986 (Starr 1987) and more recently in November-December 1991 (FIRE-II) as well as the European experiments on cirrus (ICE/EUCREX) that has been carried out in 1989. One of the fundamental objectives of the FIRE program has been and is to apply the field campaign and theoretical results to develop and verify improved techniques for the inference of cloud radiative and microphysical properties from satellite and surface-based data. A program is designed for the validation of the satellite retrived optical depth and mean effective ice crystal size utilizing in situ replicator observations for ice crystal size distributions and shapes. To minimize the effect of the horizontal size variability of the microphysical structure and the problem associated with collocation and coincidence, an averaging procedures was developed for both the satellite retrieved cloud parameters and the measured ice crystal data.

Liou, K. N.↗
NASA NTRS1999

In-Situ Partial Pressure Measurements and Visual Observation during Crystal Growth of ZnSe by Seeded Physical Vapor Transport

An in-situ monitoring furnace was constructed with side windows to perform partial pressure measurements by optical absorption and visual observation of the growing crystal. A fused silica -rowth ampoule with a 4.5 cm long square tube between the source and the seed was prepared for the optical absorption measurements. A ZnSe crystal was grown by the seeded physical vapor transport (PVT) technique in the horizontal configuration. The growth temperature was 1120 C and the furnace translation rate was 3nmVday. Partial pressures of Se2, P(sub Se2), at three locations along the length of the growth ampoule were measured at 90 min intervals during the growth process. The measured P (sub Se2) were in the range of 2.0 to 6.5 x 10(exp -3) atm. The P(sub Se2) results indicated that the partial pressure profile was inconsistent with the results of the one-dimensional diffusion mass transport model and that the source composition shifted toward Se-rich during the run, i.e. the grown crystal was more Zn-rich than the source. The visual observation showed that the seed crystal first etched back, with greater thermal etching occurring along the edges of the seed crystal. Once the growth started, the crystal crew in a predominately contactless mode and facets were evident during growth. The crystal did not grow symmetrically which is believed to be due to the unintentional asymmetry of the radial thermal profile in the furnace.

Su, Ching-Hua↗
NASA NTRS2004

Methods for Validation and Intercomparison of Remote Sensing and In situ Ice Water Measurements: Case Studies from CRYSTAL-FACE and Model Results

Remote sensing observations, such as those from AURA, are necessary to understand the role of cirrus in determining the radiative and humidity budgets of the upper troposphere. Using these measurements quantitatively requires comparisons with in situ measurements that have previously been validated. However, a direct comparison of remote and in situ measurements is difficult due to the requirement that the spatial and temporal overlap be sufficient in order to guarantee that both instruments are measuring the same air parcel. A difficult as this might be for gas phase intercomparisons, cloud inhomogeneities significantly exacerbate the problem for cloud ice water content measurements. The CRYSTAL-FACE mission provided an opportunity to assess how well such intercomparisons can be performed and to establish flight plans that will be necessary for validation of future satellite instruments. During CRYSTAL-FACE, remote and in situ instruments were placed on different aircraft (NASA's ER-2 and WB-59, and the two planes flew in tandem so that the in situ payload flew in the field of view of the remote instruments. We show here that, even with this type of careful flight planning, it is not always possible to guarantee that remote and in situ instruments are viewing the same air parcel. We use ice water data derived from the in situ Harvard Total Water (HV-TW) instrument, and the remote Goddard Cloud Radar System (CRS) and show that agreement between HV-TW and CRS is a strong function of the horizontal separation and the time delay between the aircraft transects. We also use a cloud model to simulate possible trajectories through a cloud and evaluate the use of statistical analysis in determining the agreement between the two instruments. This type of analysis should guide flight planning for future intercomparison efforts, whether for aircraft or satellite-borne instrumentation.

Sayres, D.S.↗
NASA NTRS1988

Fatique crack growth behavior of a single crystal alloy as observed through an in situ fatigue loading stage

An in situ fatigue loading stage inside a scanning electron microscope (SEM) was used to determine the fatigue crack growth behavior of a PWA 1480 single-crystal nickel-based superalloy. The loading stage permits real-time viewing of the fatigue damage processes at high magnification. The PWA 1480 single-crystal, single-edge notch specimens were tested with the load axis parallel to the (100) orientation. Two distinct fatigue failure mechanisms were identified. The crack growth rate differed substantially when the failure occurred on a single slip system in comparison to multislip system failure. Two processes by which crack branching is produced were identified and are discussed. Also discussed are the observed crack closure mechanisms.

Telesman, Jack↗
NASA NTRS1988

Fatigue crack growth behavior of a single crystal alloy as observed through an in situ fatigue loading stage

An in situ fatigue loading stage inside a scanning electron microscope (SEM) was used to determine the fatigue crack growth behavior of a PWA 1480 single-crystal nickel-based superalloy. The loading stage permits real-time viewing of the fatigue damage processes at high magnification. The PWA 1480 single-crystal, single-edge notch specimens were tested with the load axis parallel to the (100) orientation. Two distinct fatigue failure mechanisms were identified. The crack growth rate differed substantially when the failure occurred on a single slip system in comparison to multislip system failure. Two processes by which crack branching is produced were identified and are discussed. Also discussed are the observed crack closure mechanisms.

Telesman, Jack↗
NASA NTRS1988

Application of Hoffman modulation contrast microscopy coupled with three-wavelength two-beam interferometry to the in situ direct observation of the growth process of a crystal in microgravity

Direct visualization of three dimensional transfer process of both heat and mass around a growing crystal and mono-molecular growth layers on the surface is possible in situ by means of high resolution Hoffman modulation contrast microscopy coupled with three wavelength two beam Mach-Zehnder interferometry. This in situ observation is very suitable for the verification of the growth mechanism of a crystal in a solution or a melt in microgravity.

Tsukamoto, Katsuo↗