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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

High-Strength, Low-Shrinkage Ceramic Tiles

Addition of refractory fibers and whiskers to insulating tiles composed primarily of fibrous silica, such as those used on the skin of Space Shuttle orbiter, greatly improves properties. New composition suitable for lightweight, thermally-stable mirror blanks and as furnace and kiln insulation. Improved tiles made with current tile-fabrication processes. For given density, tiles containing silicon carbide and boron additives stronger in flexure than tiles made from silica alone. In addition, tiles with additives nearly immune to heat distortion, whereas pure-silica tiles shrink and become severely distorted.

Wheeler, W. H.↗
NASA NTRS1984

Inorganic composites for space applications

The development of inorganic composite materials for space applications is reviewed. The composites do not contain any organic materials, and therefore, are not subject to degradation by ultraviolet radiation, volatilization of constituents, or embrittlement at low temperatures. The composites consist of glass, glass/ceramics or ceramic matrices, reinforced by refractory whiskers or fibers. Such composites have the low thermal expansion, refractories, chemical stability and other desirable properties usually associated with the matrix materials. The composites also have a degree of toughness which is extraordinary for refractory inorganic materials.

Malmendier, J. W.↗
NASA NTRS1986

High-resolution Surface Analysis by Microarea Auger Spectroscopy: Computerization and Characterization

A custom scanning Auger electron microscope (SAM) capable of introducing a 3-5 keV electron beam of several nA into a 30 nm diameter sample area was fitted with a sample introduction system and was fully computerized to be used for materials science research. The method of multispectral Auger imaging was devised and implemented. The instrument was applied to various problems in materials science, including the study of the fiber/matrix interface in a SiC reinforced titanium alloy, the study of SiC whiskers in Al alloy 2124 (in cooperation with NASA-Langley), the study of NiCrAl superalloys (in collaboration with NASA-Lewis), the study of zircalloy specimens (in collaboration with Stanford University), and the microstructure of sintered SiC specimens (in collaboration with NASA-Lewis). The report contains a number of manuscripts submitted for publication on these subjects.

Browning, R.↗
NASA NTRS1985

Design, fabrication, and performance of a whiskerless Schottky diode for millimeter and submillimeter wave applications

Design considerations, fabrication techniques, and performance predictions are presented for a planar whiskerless Schottky diode to be used (in radio astronomy applications) at 100-300 GHz. The anode and ohmic contacts are on the same side of the device, and proton bombardment is used to establish the divided surface (by making some regions of the GaAs wafer semiinsulating) prior to definition of a B-doped SiO2 finger, ohmic contacting, anode formation, and anode contact metallization (all using photolithographic techniques). The contributions of parasitic elements are calculated for a device with a 3.5-micron-deep n(+) layer doped at 2 x 10 to the 18th/cu cm, a 250-nm-thick epitaxial layer doped at 5 x 10 to the 16th/cu cm, and a 1-micron-radius anode (providing zero-bias junction capacitance 7 fE). It is predicted that such a device would have total series resistance 12.58 ohm and total shunt capacitance 1.37 fF, compared with 14.27 ohm and 0.93 fF for the corresponding whiskered device.

Mckinney, K.↗
NASA NTRS1987

Ceramic Parts for Turbines

Abilities of ceramics to serve as turbine blades, stator vanes, and other elements in hot-gas flow of rocket engines discussed in report. Ceramics prime candidates, because of resistance to heat, low density, and tolerance of hostile environments. Ceramics considered in report are silicon nitride, silicon carbide, and new generation of such ceramic composites as transformation-toughened zirconia and alumina and particulate- or whisker-reinforced matrices. Report predicts properly designed ceramic components viable in advanced high-temperature rocket engines and recommends future work.

Jones, R. D.↗
NASA NTRS1987

Composites review

The properties and applications of composite materials are reviewed. Glass, carbon, Kevlar, ceramic, whisker, and metal fibers are discussed along with polyester, epoxy, polyimide, Peek, carbon, ceramic, and metal matrices. The quantitative distribution of high technology fiber in various applications is given. The role of aerospace industry in the development and promotion of composite utilization is discussed. Consumption trends indicate a rapid development of the composite market.

Hordonneau, A.↗
NASA NTRS1987

Analytical electron microscopy of fine-grained phases in primitive interplanetary dust particles and carbonaceous chondrites

In order to describe the total mineralogical diversity within primitive extraterrestrial materials, individual interplanetary dust particles (IDPs) collected from the stratosphere as part of the JSC Cosmic Dust Curatorial Program were analyzed using a variety of AEM techniques. Identification of over 250 individual grains within one chondritic porous (CP) IDP shows that most phases could be formed by low temperature processes and that heating of the IDP during atmospheric entry is minimal and less than 600 C. In a review of the mineralogy of IDPs, it was suggested that the occurrence of other silicates such as enstatite whiskers is consistent with the formation in an early turbulent period of the solar nebula. Experimental confirmation of fundamental chemical and physical processes in a stellar environment, such as vapor phase condensation, nucleation, and growth by annealing, is an important aspect of astrophysical models for the evolution of the Solar System. A detailed comparison of chondritic IDP and carbonaceous chondrite mineralogies shows significant differences between the types of silicate minerals as well as the predominant oxides.

Mackinnon, Ian D. R.↗
NASA NTRS1987

Polyphase alloys as rechargeable electrodes in advanced battery systems

The rechargeability of electrochemical cells is often limited by negative electrode problems. These may include loss of capacity, increased impedance, macroscopic shape change, dendrite growth, or a tendency for filamentary or whisker growth. In principle, these problems can be reduced or eliminated by the use of alloys that undergo either displacement or insertion reactions at reactant species activities less than unity, rather than pure elements. The fundamental reasons for some of these problems with elemental electrodes, as well as the basic principles involved in the different behavior of alloys, are briefly discussed. More information is now available concerning the thermodynamic and kinetic properties of a number of alloys of potential interest for use as electrodes in elevated temperature lithium battery systems. Recent results have extended these results down to ambient temperatures, indicating that some such materials may be of interest for use with new low temperature molten salt electrolytes, or with organic solvent electrolytes. The all solid mixed conductor matrix concept is also reviewed.

Huggins, Robert A.↗
NASA NTRS1986

Laboratory measurement of the rotational spectrum of the OH radical with tunable far-infrared research

Rotational and fine-structure transitions between the low rotational levels of the OH radical in its X 2Pi state have been observed in absorption in the laboratory. It has thus been possible to measure the frequencies of these transitions directly. The observations were made with tunable far-infrared radiation generated by mixing two chosen CO2 laser frequencies in a metal-insulator-metal diode; the far-infrared difference frequency was radiated from the diode's whisker antenna. The measurements have an accuracy of a few hundred kHz. They both confirm and improve on the best previous estimates, which were obtained by extrapolation of laser magnetic resonance data.

Brown, J. M.↗
NASA NTRS1986

International SAMPE Symposium and Exhibition, 31st, Los Angeles, CA, April 7-10, 1986, Proceedings

The present conference on the development status of advanced structural materials considers topics arising in such areas as automated structural manufacturing, advanced material and structure design techniques, environmental effects on materials, composite matrix processing, computer modeling for materials and processes, materials development trends in Europe and in Japan, fiber and whisker reinforcement development status, and novel thermoplastic materials and their applications. Also discussed are pressure-sensitive adhesive systems, materials suitable for space applications, polyimide resin systems, electronic materials, novel resin chemistries, ceramic and metallic systems, and the impact performance of state-of-the-art materials.

Bauer, J. L.↗
NASA NTRS1988

Improved Consolidation Of Silicon Carbide

Colloidal techniques used to improve dispersion and suspension of SiC in water. In combination with slurry pressing, resulted in increase in strength of sintered SiC by 87 percent over SiC sintered after dry pressing. Improvement due to reduced porosity and reflected in improved densities of "green" and sintered specimens. Smaller sizes of pores, and reduced sizes of critical flaws contributed to increase in strength. Useful for making parts from particulate-, transformation-, and whisker-toughened ceramics and monolithic ceramics. Provides avenue for study of variables contributing to reliability of current structural ceramics.

Freedman, Marc R.↗
NASA NTRS1988

Fracture criteria for discontinuously reinforced metal matrix composites

The effect of sample configuration on the details of initial crack propagation in discontinuously whisker reinforced aluminum metal matrix composites was investigated. Care was taken to allow direct comparison of fracture toughness values utilizing differing sample configurations and orientations, holding all materials variables constant, e.g., extrusion ration, heat treatment, and chemistry.

Rack, H. J.↗
NASA NTRS1988

A dual-frequency 183/380 GHz receiver for airborne applications

A complete dual-frequency cryogenic heterodyne receiver operating at 183 and 380 GHz is described. The cooled mixers are whisker-contacted GaAs Schottky diodes mounted in reduced-height fundamental-mode waveguide. The local oscillators are Gunn-oscillator-driven multipliers using GaAs varactor diodes as the harmonic generators. Quasi-optical techniques are used extensively for coupling the remote and local oscillator signals into the mixers. The overall system double side-band (DSB) noise temperature is 320 K for the 183-GHz receiver and 650 K for the 380 GHz receiver.

Batelaan, Paul D.↗
NASA NTRS1988

Transmission electron microscopy of composites

Since interphase-interfaces are often both the structurally weakest and chemically least stable regions of a composite material, they are critical determinants of such macrostructural characteristics as tensile strength and fracture toughness. Attention is presently given to the use of TEM for the study of interfaces between dissimilar materials; electron-diffraction, analytical, and high-resolution forms of TEM are employed, for the cases of both structural and semiconductor composites. The materials studied are SiC/Si, GaP/Si, and SiC fiber- and whisker-reinforced Si3N4.

Pirouz, P.↗
NASA NTRS1988

Dynamic fracture toughness of ceramic composites

The dynamic fracture toughness vs crack velocity relationships of TiB2 particulate-reinforced SiC-matrix and SiC whisker-reinforced Al2O3-matrix composites were determined at both room temperature and 1200 C with impacted, single-edge notched three-point bend specimens. Rapid crack initiation and propagation were monitored by a laser interferometric-displacement gage system. A FEM model that transmitted the measured outside-impact load to the specimen within the furnace was used to characterize the entire loading system-specimen unit. Small differences were measured between the room temperature and 1200 C dynamic responses.

Yang, K. H.↗
NASA NTRS1989

A corner-reflector mixer mount for far infrared wavelengths

A new type of corner-reflector mixer mount, which has the advantages of ease of fabrication and assembly as well as frequency versatility, has been designed and constructed. The predicted response patterns have been experimentally verified for various antenna lengths and operating frequencies between 800 and 2000 GHz. An important design feature is the incorporation of a microstrip matching network which eliminates IF impedance mismatch and provides mechanical isolation for the whisker antenna.

Zmuidzinas, J.↗
NASA NTRS1989

Thermal expansion and elastic anisotropies of SiC as related to polytype structure

The concept of the fraction of hexagonal stacking is used to describe the anisotropic thermal expansion coefficients of polytypes of SiC. The single crystal elastic anisotropy for the SiC polytype structures and the temperature dependencies of the anisotropies are examined. The anisotropic thermoelastic stress index for the 3C and 6H SiC polytypes are illustrated graphically. It is shown that this index is useful for predicting the most desirable crystal growth orientations for SiC whisker incorporation into composite matrices.

Li, Z.↗
NASA NTRS1989

EDM machinability of SiCw/Al composites

Machinability of high temperature composites was investigated. Target materials, 15 and 25 vol pct SiC whisker-2124 aluminum composites, were machined by electrodischarge sinker machining and diamond saw. The machined surfaces of these metal matrix composites were examined by SEM and profilometry to determine the surface finish. Microhardness measurements were also performed on the as-machined composites.

Ramulu, M.↗