Materials

Improved BN Coatings on SiC Fibers in SiC Matrices

Outside debonding would be favored over inside debonding. Modifications of BN-based coatings that are used as interfacial layers between the fibers and matrices of SiC-fiber/SiC-matrix composite materials have been investigated to improve the thermomechanical properties of these materials. Such interfacial coating layers, which are also known as interphases (not to be confused with "interphase" in the biological sense), contribute to strength and fracture toughness of a fiber/matrix composite material by providing for limited amounts of fiber/matrix debonding and sliding to absorb some of the energy that would otherwise contribute to the propagation of cracks.

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Composite-Material Tanks With Chemically Resistant Liners

Liner materials are chosen for compatibility with reactive and/or unstable fluids. Lightweight composite-material tanks with chemically resistant liners have been developed for storage of chemically reactive and/or unstable fluids — especially hydrogen peroxide. These tanks are similar, in some respects, to the ones described in — Lightweight Composite-Material Tanks for Cryogenic Liquids — (MFS-31379), NASA Tech Briefs, Vol.25, No.1 (January, 2001), page 58; however, the present tanks are fabricated by a different procedure and they do not incorporate insulation that would be needed to prevent boil-off of cryogenic fluids.

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Brazing SiC/SiC Composites to Metals

Success depends on suitable process conditions and adequate titanium contents in brazing alloys. Experiments have shown that active brazing alloys (ABAs) can be used to join SiC/SiC composite materials to metals, with bond strengths sufficient for some structural applications. The SiC/SiC composite coupons used in the experiments were made from polymer-based SiC fiber preforms that were chemical-vapor- infiltrated with SiC to form SiC matrices. Some of the metal coupons used in the experiments were made from 304 stainless steel;others were made from oxygen-free, high-conductivity copper.

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Improved Charge-Transfer Fluorescent Dyes

Improved charge- transfer fluorescent dyes have been developed for use as molecular probes. These dyes are based on benzofuran nuclei with attached phenyl groups substituted with, variously, electron donors, electron acceptors, or combi- nations of donors and acceptors. Optionally, these dyes could be incorporated as parts of polymer backbones or as pendant groups or attached to certain surfaces via self-assembly-based methods.

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Wipes, Coatings, and Patches for Detecting Hydrazines

With suitable reformulation, other hazardous substances could also be detected. Three color-indicating devices have been conceived as simple, rapid, inexpensive means of detecting hazardous liquid and gaseous substances in settings in which safety is of paramount concern and it would be too time-consuming or otherwise impractical to perform detection by use of such instruments as mass spectrometers. More specifically, these devices are designed for detecting hypergolic fuels (in particular, hydrazines) and hypergolic oxidizers in spacecraft settings, where occasional leakage of these substances in liquid or vapor form occurs and it is imperative to take early corrective action to minimize adverse health effects. With suitable redesign, including reformulation of their color indicator chemicals, these devices could be adapted to detection of other hazardous substances in terrestrial settings (e.g., industrial and military ones).

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Improved Small-Particle Powders for Plasma Spraying

Minimum layer thicknesses needed for complete coverage are reduced. Improved small-particle powders and powder-processing conditions have been developed for use in plasma spray deposition of thermal-barrier and environmentalbarrier coatings. Heretofore, plasmasprayed coatings have typically ranged in thickness from 125 to 1,800 µm. As explained below, the improved powders make it possible to ensure complete coverage of substrates at unprecedentedly small thicknesses — of the order of 25 µm.

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Advanced Metal Foam Structures for Outer Space

A document discusses a proposal to use advanced materials — especially bulk metallic glass (BMG) foams — in structural components of spacecraft, lunar habitats, and the like. BMG foams, which are already used on Earth in some consumer products, are superior to conventional metal foams: BMG foams have exceptionally low mass densities and high strength-to-weight ratios and are more readily processable into strong, lightweight objects of various sizes and shapes. These and other attractive properties of BMG foams would be exploited, according to the proposal, to enable in situ processing of BMG foams for erecting and repairing panels, shells, containers, and other objects. The in situ processing could include (1) generation of BMG foams inside prefabricated deployable skins that would define the sizes and shapes of the objects thus formed and (2) thermoplastic deformation of BMG foams. Typically, the generation of BMG foams would involve mixtures of precursor chemicals that would be subjected to suitable pressure and temperature schedules. In addition to serving as structural components, objects containing or consisting of BMG foams could perform such functions as thermal management, shielding against radiation, and shielding against hypervelocity impacts of micrometeors and small debris particles.

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