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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.

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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS2021

Phase Diagram, Melt Growth and Characterization of Cd0.8Zn0.2Te Crystals for X-Ray Detector

In this study, the solidus curve of the Cd0.8Zn0.2Te homogeneity range was constructed from the partial pressure measurements by optical absorption technique which provided the information of the melt growth parameters to process crystals with the required electrical resistivity. The melt growth of Cd0.8Zn0.2Te crystals were then processed by directional solidification under controlled Cd overpressure. During the growth experiments, several procedures have been developed to improve the crystalline quality: (1) minimizing the contamination of impurities (2) improving the structural defects and (3) minimizing the Te-precipitates within the grown crystals to enhance charge transport properties. Additionally, the thermal conductivity, electrical conductivity, and Seebeck coefficient of a vapor-grown CdTe and two melt-grown Cd0.8Zn0.2Te crystals were measured between 190oC and 780oC to provide an in-depth understanding of the thermal and electrical conduction mechanisms of the crystals as well as the prospect of its thermoelectric applications.

x-ray detector↗
NASA NTRS2023

Recrystallization of A Shot Peened Single Crystal Nickel-Base Superalloy

Single crystal nickel-base superalloys used as turbine engine airfoils can have much higher creep and thermal fatigue resistance required for blades and vanes than polycrystalline superalloys due to the absence of weak grain boundaries, as well as the low elastic modulus in the [001] single crystal growth direction (Refs. 1 and 2). This has allowed an increase in the turbine rim inlet temperatures for improved performance and efficiency. However, these advantages in performance require constraints on acceptable levels of single crystal defects, such as macroscopic grain boundaries at low angles to the primary grain (i.e., low angle boundaries or LAB), higher angle boundaries, small new grains nucleated at the blade surface (a.k.a. freckles), larger new grains, and also the single crystal blades’ orientation, typically degrees off of the [001] direction and the orientation of a transverse [010] direction with respect to blade geometry. Therefore, single crystal turbine airfoils, which are frequently used with as-cast surfaces, are grain etched and inspected before and after heat treatments to ensure these aspects conform to acceptability limits.

single crystal↗
NASA NTRS1972

Single crystals of selected titanates and tungstates

The compound preparation and crystal growth of a number of mixed titanate compositions was investigated. None of the compounds studied were found to melt congruently and therefore, crystal growth was extremely difficult. Various single crystal preparation methods always resulted in mixed phases from which 1-2 mm size crystals could be separated. It is concluded from this study that before successful single crystal growth can be accomplished, a detailed study of the phase diagrams in each of the systems of interest must be completed.

Loiacono, G. M.↗
NASA NTRS1972

Development of single crystal membranes

The design and construction of a high pressure crystal growth chamber was accomplished which would allow the growth of crystals under inert gas pressures of 2 MN/sq m (300 psi). A novel crystal growth technique called EFG was used to grow tubes and rods of the hollandite compounds, BaMgTi7O16, K2MgTi7O16, and tubes of sodium beta-alumina, sodium magnesium-alumina, and potassium beta-alumina. Rods and tubes grown are characterized using metallographic and X-ray diffraction techniques. The hollandite compounds are found to be two or three-phase, composed of coarse grained orientated crystallites. Single crystal c-axis tubes of sodium beta-alumina were grown from melts containing excess sodium oxide. Additional experiments demonstrated that crystals of magnesia doped beta-alumina and potassium beta-alumina also can be achieved by this EFG technique.

Stormont, R. W.↗
NASA NTRS1974

A scanning electron microscope study of olivine crystal surfaces

SEM photographs were taken of euhedral olivine grains from the Murchison C2 chondrite and several terrestrial and lunar occurrences. In general, the crystal faces of the meteorite grains are rough and uneven, with irregular growth patterns. They are very similar to crystal faces on terrestrial olivine grains that formed by sublimation from a vapor phase. They are very different from the relatively smooth and featureless surfaces of magmatic olivine crystals that precipitated from igneous melts. Qualitatively, the surface morphology of the crystal supports the contention that many euhedral crystals of olivine in C2 meteorites condensed from a gas phase.

Olsen, E. J.↗
NASA NTRS1975

Space processing of crystals for opto-electronic devices: The case for solution growth

The results obtained during a six month program aimed at determining the viability of space processing in the 1980's of dielectric-elastic-magnetic single crystals were described. The results of this program included: identification of some important emerging technologies dependent on dielectric-elastic-magnetic crystals, identification of the impact of intrinsic properties and defects in the single crystals on system performance, determination of a sensible common basis for the many crystals of this class, and identification of the benefits of micro-gravity and some initial experimental evidence that these benefits can be realized in space. It is concluded that advanced computers and optical communications are at a development stage for high demand of dielectric-elastic-magnetic single crystals in the mid-1980's. Their high unit cost and promise for significantly increased perfection by growth in space justified pursuit of space processing.

Hayden, S. C.↗
NASA NTRS1976

Evolution of major mineral compositions and trace element abundances during fractional crystallization of a model lunar composition

The evolution of major mineral compositions and trace element abundances during perfect fractional crystallization of a model lunar magma ocean was calculated. The minerals in the model lunar composition were olivine, orthopyroxene, clinopyroxene, and plagioclase. Lunar bulk composition data, major mineral/melt equilibria data, and trace element partition data were taken from published sources. The results show olivine beginning to crystallize at 1380 C. Approximately 50% of the system crystallizes as olivine. From 50 to 60% solidification, orthopyroxene crystallizes alone. During the final 40% solidification, Ca-rich clinopyroxene and plagioclase crystallize together. Various changes in composition of all these minerals are also noted during the process. Concomitant evolution of major element abundances in the melt is followed along with that of trace element abundances. Consequences of the results for constraints on some aspects of the composition of the lunar magma ocean and of the primitive moon are discussed.

Drake, M. J.↗
NASA NTRS1976

Crystallization history of lunar picritic basalt sample 12002 - Phase-equilibria and cooling-rate studies

Experimental crystallization of a lunar picrite composition (sample 12002) at controlled linear cooling rates produces systematic changes in the temperature at which crystalline phases appear, in the texture, and in crystal morphology as a function of cooling rate. Phases crystallize in the order olivine, chromium spinel, pyroxene, plagioclase, and ilmenite during equilibrium crystallization, but ilmenite and plagioclase reverse their order of appearance and silica crystallizes in the groundmass during controlled cooling experiments. The partition of iron and magnesium between olivine and liquid is independent of cooling rate, temperature, and pressure. Comparison of the olivine nucleation densities in the lunar sample and in the experiments indicates that the sample began cooling at about 1 deg C/hr. Pyroxene size, chemistry, and growth instability spacings, as well as groundmass coarseness, all suggest that the cooling rate subsequently decreased by as much as a factor of 10 or more. The porphyritic texture of this sample, then, is produced at a decreasing, rather than a discontinuously increasing, cooling rate.

Walker, D.↗
NASA NTRS1977

Crystal growth from solutions in low gravity

An experiment performed during the Apollo-Soyuz flight investigated a novel process for growing single crystals from solutions. In zero gravity, reactant solutions were allowed to diffuse slowly toward each other through a region of pure solvent in which they underwent a chemical reaction to form crystals of an insoluble material. The process is analogous to the growth of crystals in gels in normal gravity. The experiment was successful and yielded crystals of about the expected size, number, and quality. The results indicate that with further refinement the process should yield large, high quality crystals of a variety of materials.

Lind, M. D.↗
NASA NTRS1969

Method for the preparation of inorganic single crystal and polycrystalline electronic materials

Large area, semiconductor crystals selected from group 3-5 compounds and alloys are provided for semiconductor device fabrication by the use of a selective etching operation which completely removes the substrate on which the desired crystal was deposited. The substrate, selected from the same group as the single crystal, has a higher solution rate than the epitaxial single crystal which is essentially unaffected by the etching solution. The preparation of gallium phosphide single crystals using a gallium arsenide substrate and a concentrated nitric acid etching solution is described.

Groves, W. O.↗
NASA NTRS1978

Crystallization of pyroxenes in lunar KREEP basalt 15386 and meteoritic basalts

Single crystal X-ray diffraction studies and electron microprobe analyses of pyroxenes from the meteorites Pasamonte, Yamato 74450 and Yamato 74159 and in lunar KREEP basalt 15386 show similarities of pyroxene crystallization history. They each began crystallization with magnesian pyroxene (pigeonite in the meteorites, orthopyroxene in 15386) followed by strong zonation toward iron-rich and calcium-rich compositions. These data appear to be understandable in terms of dynamic crystallization experiments on liquids of similar composition to the meteorites. In contrast, pyroxene compositions in the meteorites Juvinas, Sioux County and Nuevo Laredo lie along an apparent tie line between calcium-poor and calcium-rich end members with no iron-enrichment trend. In Sioux County and Juvinas, the primary pyroxene is calcium-poor, with exsolved augite. In Nuevo Laredo, pigeonite and augite occur as separate grains with exsolution of augite in the pigeonite. The development of prominent exsolution lamellae is consistent with a long thermal annealing after the primary crystallization event, which may also explain the absence of iron/magnesium zonation in the pigeonites.

Takeda, H.↗
NASA NTRS1979

Rates and processes of crystal growth in the system anorthite-albite

The growth rates and interface morphologies of crystals of synthetic compositions in the anorthite (CaAl2Si2O8)-albite (NaAlSi3O8) plagioclase feldspar system are measured in an investigation of the crystallization of igneous rocks. Mixed plagioclase glasses with compositions of 75% and 50% anorthite were observed using the microscope heating technique as they crystallized at temperatures near the liquidus, and 75%, 50% and 20% anorthite crystals were treated by resistance heating and observed at greater degrees of undercooling. Growth rates were found to be independent of time and to decrease with increasing albite content, ranging from 0.5 to 2 x 10 to the -5th cm/min. The crystal morphologies for all compositions are faceted near the liquidus and become progressively skeletal, dendritic and fibrillar with increasing undercooling.

Kirkpatrick, R. J.↗
NASA NTRS1980

Anisotropy of nickel-base superalloy single crystals

The influence of orientation on the tensile and stress rupture behavior of 52 Mar-M247 single crystals was studied. Tensile tests were performed at temperatures between 23 and 1093 C; stress rupture behavior was examined between 760 and 1038 C. The mechanical behavior of the single crystals was rationalized on the basis of the Schmid factor contours for the operative slip systems and the lattice rotations which the crystals underwent during deformation. The tensile properties correlated well with the appropriate Schmid factor contours. The stress rupture lives at lower testing temperatures were greatly influenced by the lattice rotations required to produce cross slip. A unified analysis was attained for the stress rupture life data generated for the Mar-M247 single crystals at 760 and 774 C under a stress of 724 MPa and the data reported for Mar-M200 single crystals tested at 760 C under a stress of 689 MPa. Based on this analysis, the stereographic triangle was divided into several regions which were rank ordered according to stress rupture life for this temperature regime.

Mackay, R. A.↗
NASA NTRS1979

Free convection about a rectangular prismatic crystal growing from a solution

Sodium chlorate crystals growing from unstirred aqueous solutions were observed by Schlieren techniques. Growth rate data were best correlated by a Sherwood number with finite interface kinetics and a characteristic length equal to the crystal height plus the inverse reciprocal sum of the horizontal dimensions. The growth rate was slightly higher when the plume was laminar than when it was irregular. The horizontal growth rate was greater than the vertical growth rate, with the ratio tending to decrease with increasing plume instability. The threshold Grashof number for plume instability was greatly decreased with decreasing height for crystals with the same horizontal dimensions. The velocity of the eddies approached a constant value with increasing distance above the crystal surface, the terminal value being roughly proportional to the ratio of the square root of the Rayleigh number to the crystal characteristic length.

Chen, P.-S.↗
NASA NTRS1980

The effect of growth rate, diameter and impurity concentration on structure in Czochralski silicon crystal growth

It is demonstrated that maximum growth rates of up to 80% of the theoretical limit can be attained in Czochralski-grown silicon crystals while maintaining single crystal structure. Attaining the other 20% increase is dependent on design changes in the grower, to reduce the temperature gradient in the liquid while increasing the gradient in the solid. The conclusions of Hopkins et al. (1977) on the effect of diameter on the breakdown of structure at fast growth rates are substantiated. Copper was utilized as the test impurity. At large diameters (greater than 7.5 cm), concentrations of greater than 1 ppm copper were attained in the solid (45,000 ppm in the liquid) without breakdown at maximum growth speeds. For smaller diameter crystals, the sensitivity of impurities is much more apparent. For solar cell applications, impurities will limit cell performance before they cause crystal breakdown for fast growth rates of large diameter crystals.

Digges, T. G., Jr.↗
NASA NTRS1982

Optical crystal temperature gauge with fiber optic connections

An optical temperature gauge uses a semiconductor crystal with a band-edge shift property which is temperature dependent. An external narrow band light source provides optical excitation through a optical fiber and light energy thus passed through the crystal is conveyed by a second optical fiber to a light-to-electric transducers at an external location. The crystal can be located in cryogenic or other systems, to provide remote read-out. The light wavelength is varied (scanned) in a repetitive pattern in source with the instantaneous wavelength passing over the band-edge wavelength during each cycle of the scan. The timing of the crossover is related to the temperature of the crystal by electronic means. Several alternative elements of instrumentation are disclosed. A variation in the basic measurement apparatus is also disclosed, in which the band gap voltage of a light source such as a laser diode is evaluated at the time of band-edge crossover in the crystal and converted to a temperature value.

Sharma, M. M.↗
NASA NTRS1982

Crystal cleaving machine

A machine is disclosed for cleaving hard crystals. A typical example of which is lithium fluoride, with prcision and uniformity and includes vertical axis positioning control means for an adjustable spring tension guided hammer mechanism employed to strike an anvil. A crystal cleaving shock wave transmitted to a cleaving blade is generated having an angulated cleaving edge in contact with one corner of the crystal. Connection between the anvil and the blade is by means of a pair of vertical shafts held in substantially friction free engagement by two pairs of adjustable linear bearings. An underlying crystal holding fixture with horizontal position control means includes a zero reference stop face for the crystal and opposing spring-loaded clamping and vertical positioning elements which are precisely guided.

Hallberg, F. C.↗
NASA NTRS1982

The influence of orientation on the stress rupture properties of nickel-base superalloy single crystals

Constant load creep rupture tests were performed on MAR-M247 single crystals at 724 MPa and 774 C where the effect of anisotropy is prominent. The initial orientations of the specimens as well as the final orientations of selected crystals after stress rupture testing were determined by the Laue back-reflection X-ray technique. The stress rupture lives of the MAR-M247 single crystals were found to be largely determined by the lattice rotations required to produce intersecting slip, because second-stage creep does not begin until after the onset of intersecting slip. Crystals which required large rotations to become oriented for intersecting slip exhibited the shortest stress rupture lives, whereas crystals requiring little or no rotations exhibited the lowest minimum creep rates, and consequently, the longest stress rupture lives.

Mackay, R. A.↗