Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “CRYSTALS”

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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Space manufacturing in an automated crystal growth facility

An account is given of a Space Station Freedom-based robotic laboratory system for crystal growth experiments; the robot must interface with both the experimental apparatus and such human input as may be required for control and display. The goal of the system is the simultaneous growth of several hundred protein crystals in microgravity. The robot possesses six degrees-of-freedom, allowing it to efficiently manipulate the cultured crystals as well as their respective growth cells; the crystals produced are expected to be of sufficiently high quality for complete structural determination on the basis of XRD.

Quinn, Alberta W.↗
NASA NTRS1990

Crystal chemical effects on the partitioning of trace elements between mineral and melt - An experimental study of melilite with applications to refractory inclusions from carbonaceous chondrites

Results are presented on the partitioning experiments for trace elements Be, Sc, Ba, La, Ce, and Tm between melilite and melt for a bulk composition relevant to Type B inclusions, using a technique, described by Brody and Flemings (1966), by which distributon coeffecients can be obtained over the entire range of crystallization from trace element analysis of a single zoned crystal. Zoned crystals of melilite were grown during controlled cooling rate experiments, and trace element concentrations were determined by SIMS. At each step in the crystal growth, trace element concentrations in the coexisting melt were determined by mass balance, using stepwise integration of a Rayleigh fractionation equation.

Beckett, John R.↗
NASA NTRS1991

Electrostatic Stabilization Of Growing Protein Crystals

Proposed technique produces large crystals in compact, economical apparatus. Report presents concept for supporting protein crystals during growth in microgravity. Yields crystals larger and more-nearly perfect than those grown on Earth. Combines best features of sandwich-drop and electrostatic-levitation methods of support. Drop of protein solution inserted between pair of glass or plastic plates, as in sandwich-drop-support method. Electrostatically charged ring confines drop laterally and shapes it, as in electrostatic technique. Apparatus also made to accommodate several drops simultaneously between same pair of supporting plates. Drops can be inserted and crystals removed through ducts in plates.

Shlichta, Paul J.↗
NASA NTRS1991

Initiating Growth Of Crystals Away From Container Walls

Nucleation controlled to obtain better crystals. In technique proposed specifically for growing large protein crystals in microgravity (where no thermal convection), small region of high supersaturation created by injection of hot concentrated solution or by use of cold probe. Crystals nucleate preferably in this small region. Also conceivable technique applied on Earth to crystallizations in melts and solutions sufficiently viscous to suppress convection to extent necessary to prevent cooling-induced nucleation in undesired sites.

Kroes, Roger L.↗
NASA NTRS1990

Crystal growing

One objective is to demonstrate the way crystals grow and how they affect the behavior of material. Another objective is to compare the growth of crystals in metals and nonmetals. The procedures, which involve a supersaturated solution of a salt that will separate into crystals on cooling and the pouring off of an eutectic solution to expose the crystals formed by a solid solution when an alloy of two metals forms a solid and eutectic solution on cooling, are described.

Neville, J. P.↗
NASA NTRS1989

Structures of cyano-biphenyl liquid crystals

The structures of p-alkyl- p'-cyano- bicyclohexanes, C(n)H(2n+1) (C6H10)(C6H10) CN (n-CCH), and p-alkyl- p'-cyano- biphenyls, C(n)H(2n+1) (C6H4)(C6H4) CN (n-CBP), were studied. It is convenient to use an x ray image intensification device to search for symmetric x ray diffraction patterns. Despite the similarities in molecular structures of these compounds, very different crystal structures were found. For the smectic phase of 2CCH, the structure is close to rhombohedral with threefold symmetry. In contrast, the structure is close to hexagonal close-packed with two molecules per unit cell for 4CCH. Since intermolecular forces may be quite weak for these liquid crystals systems, it appears that crystal structures change considerably when the alkyl chain length is slightly altered. Different structures were also found in the crystalline phase of n-CBP for n = 6 to 9. For n = 7 to 9, the structures are close to monclinic. The structures are reminiscent of the smectic-A liquid crystal structures with the linear molecules slightly tilted away from the c-axis. In contrast, the structure is quite different for n = 6 with the molecules nearly perpendicular to the c-axis.

Chu, Yuan-Chao↗
NASA NTRS1990

On the facet-skeletal transition of snow crystals - Experiments in high and low gravity

A laboratory investigation of the influence of air velocity on the growth of columnar ice crystals from the vapor over the range -3 to -5 C shows that the linear growth velocity increases and that columns transform to sheath crystals or needles as air velocity increases from a few cm/s to 40 cm/s. Comparison with a similar transition of plates to dendrites shows that, macroscopically, in both cases the facets sprout rounded tips at a critical velocity which is lower for higher ambient supersaturation. Studies in low gravity show that chamber scale convection under normal gravity may have significant influence on growth even in the absence of an imposed air velocity. Falling snow crystals become more skeletal in shape as they grow and fall with increasing velocity. This development depends critically on temperature (+ or - 0.5 C) and demonstrates that the snow crystal shape is even more dependent on environmental growth conditions that previously thought.

Alena, T.↗
NASA NTRS1991

Fracture of single crystals of the nickel-base superalloy PWA 1480E in helium at 22 C

The fracture behavior and deformation of He-charged (at 22 C) single crystals of PWA 1480E Ni-base superalloy were investigated using SEM and TEM techniques to observe the behavior of tensile fractures in notched single crystals with seven different crystal growth orientations: 100-line, 110-line, 111-line, 013-line, 112-line, 123-line, and 223-line. To identify the cleavage plane orientation, a stereoscopic technique, combined with the use of planar gamma-prime morphologies, was applied. It was found that gamma-prime particles were orderly and closely aligned with edges along the 100-line, 010-line, and 001-line-oriented directions of the gamma matrix. Different crystal growth orientations were found not to affect the morphology of gamma-prime particles. The accumulation of dislocations around gamma/gamma-prime interfaces formed strong barriers to subsequent dislocation movement and was the primary strengthening mechanism at room temperature.

Chen, P. S.↗
NASA NTRS1990

Crystallization of the Fab from a human monoclonal antibody against gp 41 of human immunodeficiency virus type I

A monoclonal IgG antibody directed against gp 41 from the human immunodeficiency virus (HIV-1) has been crystallized in both intact and Fab forms. Crystals of the intact antibody grow as tetragonal-like prisms too small for conventional X-ray analysis. However, the Fab portion of the antibody produces suitable platelike crystals which belong to the space group P2(1)2(1)2(1) with unit cell constants of a = 66.5 A, b = 74.3 A, and c = 105.3 A. There is one molecule of Fab in the asymmetric unit. The Fab crystals show diffraction to d-spacings less than 3.0 A.

Casale, Elena↗
NASA NTRS1991

A novel technique for response function determination of shear sensitive cholesteric liquid crystals for boundary layer investigations

A description of the design and setup of an experimental technique for measurement of the response function in shear sensitive liquid crystals has been reported. Utilizing the selective reflection characteristics of cholesteric liquid crystals, the method is capable of measuring the delay, rise, and relaxation times in response to a given dynamic shear stress as a function of the wavelength of the incident light. Application of a step input shear stress results in a liquid crystal time response that can be described as consisting of an initial delay, a shear induced helix deformation, and a relaxation to the initial state through diffusion processes. The method has been used for quantitative calibration of a shear sensitive liquid crystal by observing the peak in reflected light intensity, at a given wavelength, as a function of the shear stress.

Parmar, D. S.↗
NASA NTRS1991

Fracture of single crystals of the nickel-base superalloy PWA 1480E in hydrogen at 22 C

The present study investigates the hydrogen-induced fracture behavior of notched single crystals of the PWA 1480E nickel-based superalloy. Notched single crystals with seven different crystal orientations were tensile tested at 22 C in a hydrogen atmosphere at 34 MPa. Hydrogen-enhanced cleavage along 100-line planes in the notched region was found to be due to cracking along the gamma/gamma-prime interfaces. Cleavage on 111-line-type planes was observed only outside the notch region. The occurrence of 100- and 111-line-types of cleavage was independent of the single-crystal orientation. Outside the notch region, the fracture surfaces of specimens tested in hydrogen appeared very similar to those tested in helium. Differences in the fracture surfaces were located primarily near the notch region.

Chen, P. S.↗
NASA NTRS1991

Growth and characterization of high-performance photorefractive BaTiO3 crystals

Barium titanate has been used for many nonlinear optical applications primarily because it has high grain and high self-pumped phase conjugate reflectivities. However, barium titanate has had a relatively slow response time, and thus low sensitivity. Therefore, it has not been suited to real-time operations. In this report we will describe the modifications in crystal growth, doping, reduction, and poling that have produced barium titanate crystals with the fastest photorefractive response time reported to date, approximately 21 microseconds with a beam-coupling gain coefficient of 38.7 cm(exp -1) and the highest sensitivity reported to date of 3.44 cm(exp 3)/kJ. The sensitivity of these barium titanate crystals is comparable to or greater than other photorefractive oxides. We will show, for the first time, beam-coupling in barium titanate at video frame rates. We infer from response time measurements that barium titanate has a phonon limited mobility. Also, photorefractive response time measurements as a function of the crystallographic orientation and grating wave vector for our cobalt-doped oxygen reduced crystals indicate that their faster response time arise because of an increase in the free carrier lifetime.

Warde, C.↗
NASA NTRS1991

Comparative study of flux pinning, creep and critical currents between YBaCuO crystals with and without Y2BaCuO5 inclusions

In the Y-Ba-Cu-O system, YBa2Cu3O(x) phase is produced by the following peritectic reaction: Y2BaCuO5 + liquid yields 2YBa2Cu3O(x). Through the control of processing conditions and starting compositions, it becomes possible to fabricate large crystals containing fine Y2BaCuO5(211) inclusions. Such crystals exhibit Jc values exceeding 10000 A/sq cm at 77 K and 1T. Recently, researchers developed a novel process which can control the volume fraction of 211 inclusions. Elimination of 211 inclusions is also possible. In this study, researchers prepared YBaCuO crystals with and without 211 inclusions using the novel process, and compared flux pinning, flux creep and critical currents. Magnetic field dependence of Jc for YBaCuO crystals with and with 211 inclusions is shown. It is clear that fine 211 inclusions can contribute to flux pinning. It was also found that flux creep rate could be reduced by increasing flux pinning force. Critical current density estimates based on the conventional flux pinning theory were in good agreement with experimental results.

Murakami, Masato↗
NASA NTRS1992

Mercury iodide nucleation and crystal growth in vapor phase (4-IML-1)

The objectives of this experiment are to grow simultaneously three single crystals of mercuric iodide (HgI2) in an imposed temperature profile and to assess the advantages of growth in microgravity on the HgI2 crystal quality. Growth in microgravity should reduce fluctuations in HgI2 concentrations and thus decrease the resultant crystal defects. In order to test this hypothesis, a seeded growth of HgI2 crystals will be performed on International Microgravity Lab. (IML-1).

Cadoret, Robert↗
NASA NTRS1992

Holographic data storage crystals for the LDEF

Lithium niobate is a significant electro-optic material, with potential applications in ultra high capacity storage and processing systems. Lithium niobate is the material of choice for many integrated optical devices and holographic mass memory systems. For crystals of lithium niobate were passively exposed to the space environment of the Long Duration Exposure Facility (LDEF). Three of these crystals contained volume holograms. Although the crystals suffered the surface damage characteristics of most of the other optical components on the Georgia Tech tray, the crystals were recovered intact. The holograms were severely degraded because of the lengthy exposure, but the bulk properties are being investigated to determine the spaceworthiness for space data storage and retrieval systems.

Callen, W. Russell↗
NASA NTRS1990

The effects of small ice crystals on the infrared radiative properties of cirrus clouds

The effects of nonspherical small ice crystals on the IR radiative properties of cirrus clouds are investigated utilizing light scattering properties of spheroidal particles. Employing the anomalous diffraction theory for spheres and results from the exact spheroid scattering program, efficient parameterization equations are developed for calculations of the absorption and scattering properties for small ice crystals. Parameterization formulas are developed for large ice crystals employing results computed from the geometric ray-tracing method and the Fraunhofer diffraction theory for hexagonal crystals and spheroids.

Takano, Y.↗
NASA NTRS1992

Protein crystal growth aboard the U.S. Space Shuttle flights STS-31 and STS-32

Results obtained from the Shuttle flight STS-32 flown in January 1990, and preliminary results from the most recent Shuttle flight, STS-31, flown in April 1990, are presented. Crystals grown in microgravity environment include Canavalin, isocitrate lyase, human serum albumin, and Anti-HPr Fab. It is concluded that about 20 percent of proteins flown exhibit better morphologies or better quality data than their earth-grown counterparts. About 40 percent do not yield crystals at all and the remaining 40 percent yield crystals that are either too small for X-ray analysis or produce data of poorer quality than the best earth-grown crystals.

Delucas, Lawrence J.↗
NASA NTRS1991

Growth of bulk single crystals of organic materials for nonlinear optical devices - An overview

Highly perfect single crystals of nonlinear optical organic materials are required for use in optical devices. An overview of the bulk crystal growth of these materials by melt, vapor, and solution processes is presented. Additionally, methods that may be used to purify starting materials, detect impurities at low levels, screen materials for crystal growth, and process grown crystals are discussed.

Penn, Benjamin G.↗