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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Processing and properties of SiC whisker- and particulate-reinforced reaction bonded Si3N4

The microstructure and mechanical properties of reaction bonded Si3N4 (RBSN) reinforced with SiC whiskers of particles were investigated using RBSN composites made from colloidally pressed octanol dispersions of high-purity Si powders mixed with either SiC whiskers or alpha-SiC particles. Results of investigations, revealing high conversions of Si to Si3N4, specific surface areas, and constant relative densities and strengths, showed that the uniform microstructure and small flaw size of the matrix were maintained in the composites and that no degradation of the reinforcements was taking place. Neither the monolithic nor the composite materials exhibited R-curve behavior. A modest increase in fracture toughness was observed only in the RBSN containing 33 vol pct SiC(p).

Lightfoot, A.↗
NASA NTRS1992

Strength, toughness and R-curve behaviour of SiC whisker-reinforced composite Si3N4 with reference to monolithic Si3N4

The flexural strength and fracture toughness of 30 vol pct SiC whisker-reinforced Si3N4 material were determined as a function of temperature from 25 to 1400 C in an air environment. It was found that both strength and toughness of the composite material were almost the same as those of the monolithic counterpart. The room-temperature strength was retained up to 1100 C; however, appreciable strength degradation started at 1200 C and reached a maximum at 1400 C due to stable crack growth. In contrast, the fracture toughness of the two materials was independent of temperature with an average value of 5.66 MPa sq rt m. It was also observed that the composite material exhibited no rising R-curve behavior at room temperature, as was the case for the monolithic material. These results indicate that SiC whisker addition to the Si3N4 matrix did not provide any favorable effects on strength, toughness and R-curve behavior.

Choi, S. R.↗
NASA NTRS1992

Whisker growth studies under conditions which resemble those available on an orbiting space station

Minimal funding was provided by NASA with one designated 'mission' being the clear demonstration of the relevance of previously supported whisker growth studies to microgravity research. While in one sense this work has shown the converse, namely, that ambient gravitational fields as high as 1 Earth normal have no relevance to growth of whiskers by hydrogen reduction of metal halides, a case is made that this does not demonstrate lack of relevance to microgravity research. On the contrary, the driving forces for this growth are precisely those which must be understood in order to understand growth in microgravity. The results described suggest that knowledge gained from this work may be highly fundamental to our understanding of the genesis of metal crystals. Time and money ran out before this work could be considered complete. At least another year's study and analysis will be required before publications could be justified.

Hobbs, Herman H.↗
NASA NTRS2007

Space Shuttle Program Tin Whisker Mitigation

The discovery of tin whiskers (TW) on space shuttle hardware led to a program to investigate and removal and mitigation of the source of the tin whiskers. A Flight Control System (FCS) avionics box failed during vehicle testing, and was routed to the NASA Shuttle Logistics Depot for testing and disassembly. The internal inspection of the box revealed TW growth visible without magnification. The results of the Tiger Team that was assembled to investigate and develop recommendations are reviewed in this viewgraph presentation.

Nishimi, Keith↗
NASA NTRS2009

Tin Whisker Electrical Short Circuit Characteristics

Existing risk simulations make the assumption that when a free tin whisker has bridged two adjacent exposed electrical conductors, the result is an electrical short circuit. This conservative assumption is made because shorting is a random event that has an unknown probability associated with it. Note however that due to contact resistance electrical shorts may not occur at lower voltage levels. In our first article we developed an empirical probability model for tin whisker shorting. In this paper, we develop a more comprehensive empirical model using a refined experiment with a larger sample size, in which we studied the effect of varying voltage on the breakdown of the contact resistance which leads to a short circuit. From the resulting data we estimated the probability distribution of an electrical short, as a function of voltage. In addition, the unexpected polycrystalline structure seen in the focused ion beam (FIB) cross section in the first experiment was confirmed in this experiment using transmission electron microscopy (TEM). The FIB was also used to cross section two card guides to facilitate the measurement of the grain size of each card guide's tin plating to determine its finish.

Courey, Karim J.↗
NASA NTRS2015

Silicon Whisker and Carbon Nanofiber Composite Anode

A carbon nanofiber can have a surface and include at least one crystalline whisker extending from the surface of the carbon nanofiber. A battery anode composition can be formed from a plurality of carbon nanofibers each including a plurality of crystalline whiskers.

Ma, Junqing↗
NASA NTRS1963

Metal whiskers

Metal whiskers - induced growth, growth mechanism, energy sources for growth, magnetic properties, and radiation effects

WHISKER↗
NASA NTRS1971

Growth of In2Bi whiskers

In-Bi whisker growth by squeeze technique, measuring crystal structure by X ray analysis and melting point method

Davis, J. H.↗
NASA NTRS1979

Whiskers, cones and pyramids created in sputtering by ion bombardment

A thorough study of the role which foreign atoms play in cone formation during sputtering of metals revealed many experimental facts. Two types of cone formation were distinquished, deposit cones and seed cones. Twenty-six combinations of metals for seed cone formation were tested. The sputtering yield variations with composition for combinations which form seed cones were measured. It was demonstrated that whisker growth becomes a common occurrence when low melting point material is sputter deposited on a hot nonsputtered high melting point electrode.

Wehner, G. K.↗