Materials

Incorporating Functional Fillers into Silicone Elastomer Systems

Silicones can be developed into fluids, gels, adhesives, elastomers, and resins designed with unique properties that make them ideal for specific application uses in the defense and aerospace industries. Silicones are most widely known for their ability to maintain elastomeric properties in extreme conditions, but an additional benefit of these materials is the ability to incorporate large amounts of fillers that can impart properties such as electrical and thermal conductivity, and radar-absorbing characteristics. Silicone materials appear in a wide variety of material compositions, and this broad range of material compositions makes silicone a viable option to endless numbers of optic applications.

Posted in: Briefs, Materials, Optics, Composite materials, Elastomers, Materials properties, Silicon alloys
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Gold-Based Nanoparticle Liquids for Electronic Applications

Electrically conductive, solventless nanoparticle liquids, consisting of gold nanoparticles chemically functionalized with large organic molecular groups, have been investigated for potential utility in electronic and electrical applications. These and other solventless nanoparticle liquids, including electrically nonconductive ones, have been topics of recent research directed toward understanding and exploiting their unusual properties. The most obvious unusual property is that a collection of nanoparticles of this type can flow in a liquid-like fashion, notwithstanding the absence of free solvent molecules. By modifying the attractive and repulsive forces between the nanoparticles through modifications of the surface chemistry of the organic ligands, the properties of the resulting nanoparticle liquids can be tailored for specific applications.

Posted in: Briefs, Materials
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Dimensional Stabilization of Composite Space Structures

A research project has yielded progress on several fronts toward the goal of minimizing thermal and aging distortions of composite-material (specifically, polymer- matrix/graphite-fiber) outer-space structures that are required to retain precise dimensions and shapes. The achievements of this project are also applicable to terrestrial composite-material structures to the extent to which various environmental effects can be properly taken into account. Examples include effects of expansion caused by absorption of atmospheric moisture (similar to effects of purely thermal expansion) and effects of outgassing of volatile constituents of polymers (effects of out-gassing are more pronounced in the outer-space vacuum).

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Less-Polluting Resins for Molding Composite Structures

Liquid resins that are suitable for use in molding composite- material structural panels and that contain and emit smaller amounts of air-polluting volatile organic compounds than do corresponding commercial resins have been invented. In particular, these resins are under study as less-polluting potential substitutes for commercial vinyl ester and unsaturated polyester resins heretofore used in making lightweight composite panels for some military vehicles.

Posted in: Briefs, Materials, Volatile organic compounds, Product development, Composite materials, Lightweight materials, Resins, Military vehicles and equipment
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Some Advances in High-Temperature Superconductor Coatings

Several advances were made in a program focused on the science and technology of high-temperature superconductors [especially yttrium barium copper oxide ("YBCO")] deposited on normal electrical conductors. This program was part of a continuing effort to develop superconductor-coated normal conductors for use in electric-power systems of interest to the Air Force.

Posted in: Briefs, Materials, Electrical systems, Coatings Colorants and Finishes, Conductivity, Heat resistant materials, Military aircraft, Military vehicles and equipment
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Continuous Carbon Nanofibers for Structural Composites

A program of research has addressed key issues in the production of continuous carbon nanofibers and the utilization of carbon nanofibers as the reinforcing components in matrix/fiber composite materials. The goal of this research is to contribute to the development of advanced lightweight structural composites in which the exceptionally high strengths of carbon nanofibers are exploited to obtain mechanical strengths, delamination toughnesses, and fatigue lives greater than would otherwise be possible.

Posted in: Briefs, Materials, Fabrication, Composite materials, Fibers, Lightweight materials, Nanomaterials
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High-Strain-Rate Tests of Epoxy/Aluminum-Powder Composites

Initial tests have been performed in a continuing experimental study to determine selected mechanical properties, at high strain rates, of an epoxy and of composite materials consisting of the epoxy filled with aluminum powders. These composites are examples of the large variety of polymer-matrix/particlefilling composites in general, which are widely used in military and civilian applications. The properties of such composites can be tailored for specific applications through appropriate choices of constituent materials, the proportions of the constituent materials, and the sizes of the particles. Especially in aerospace structural applications, the composites are exposed to complex, temporally varying loads. Therefore, the mechanical properties of such composites’ high strain rates are of increasing importance.

Posted in: Briefs, Materials
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High-Temperature Resins for Composite Materials

Improved, readily processable thermosetting polymer resins are being developed for use as matrix materials in composite-material structures in applications in which there are requirements for thermal stability and hot-wet performance. Heretofore, the development and utilization of polymer resins for such applications have been limited by adverse characteristics that include (1) toxicity of many of the chemicals used to make the resins; (2) poor performance during fires (excessive flame and smoke, dripping, and generation of hazardous substances); (3) significant absorption of water in humid environments, linked to delamination during rapid heating; and (4) in the cases of many of the polymers suitable for use at the highest temperatures, difficulties in the use of newer, less expensive fabrication techniques.

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Making Ultra-Hydrophobic Textured Silicone-Rubber Surfaces

Silicone-rubber surfaces microscopically textured in such a manner as to render them ultra-hydrophobic have been fabricated by a method in which breath figures are utilized. Originally, “breath figures” signified fog-like patches formed by condensation of microscopic droplets of water from air exhaled onto cooler surfaces. Now, “breath figures” refers more generally to patches formed by condensation, whether from natural breath or artificial sources. The essence of the method is to use a breath figure to form a pattern of microscopic, approximately hemispherical pits (each pit corresponding to a condensed water droplet) on the surface of a layer of polystyrene, then use the pitted polystyrene surface as a template to cast the silicone rubber having a surface pattern of nanometer- or micron-sized pillars corresponding to the pits.

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Alloys for Nozzles of Hypersonic Wind Tunnels

Alloys are being developed for nozzles of hypersonic wind tunnels to be used in testing components of future hypersonic missiles, aircraft, and space transportation systems. The nozzle components made from these alloys will be required to retain sufficient strength to withstand stresses of as much as 600 MPa at throat surface gas temperatures as high as 1,700 K while resisting erosion and oxidation by impinging hypersonic flows of air and possibly other gases. In some applications, back-side cooling or film/transpiration cooling may be used to reduce the temperature rises in nozzles. Alternatively, in some applications, nozzles may be used, without active cooling, in either of two heat-sink modes. In one mode, exposure time would be limited in order to limit the maximum temperature rise. In the other mode, denoted the self-limiting heat-sink mode, a nozzle throat would be exposed long enough to come into thermal equilibrium with the gas, and, hence, the nozzle throat material must be chosen to withstand the maximum surface gas temperature (e.g., 1,700 K) for an indefinite time.

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