Materials & Coatings

Coating Thermoelectric Devices To Suppress Sublimation

Thermoelectric materials are covered with adherent, chemically stable metal outer layers. A technique for suppressing sublimation of key elements from skutterudite compounds in advanced thermoelectric devices has been demonstrated. The essence of the technique is to cover what would otherwise be the exposed skutterudite surface of such a device with a thin, continuous film of a chemically and physically compatible metal. Although similar to other sublimation- suppression techniques, this technique has been specifically tailored for application to skutterudite antimonides.

Posted in: Briefs, TSP, Materials, Powder metallurgy, Coatings, colorants, and finishes, Materials properties, Metals


Rapid Fabrication of Carbide Matrix/Carbon Fiber Composites

Melt infiltration offers advantages over chemical vapor infiltration. Composites of zirconium carbide matrix material reinforced with carbon fibers can be fabricated relatively rapidly in a process that includes a melt infiltration step. Heretofore, these and other ceramic matrix composites have been made in a chemical vapor infiltration (CVI) process that takes months. The finished products of the CVI process are highly porous and cannot withstand temperatures above 3,000 °F (≈1,600 °C). In contrast, the melt-infiltration-based process takes only a few days, and the composite products are more nearly fully dense and have withstood temperatures as high as 4,350 °F (≈2,400 °C) in a highly oxidizing thrust chamber environment. Moreover, because the meltinfiltration- based process takes much less time, the finished products are expected to cost much less.

Posted in: Briefs, Materials, Fabrication, Composite materials


Ultrahigh-Temperature Ceramics

Materials are being developed to withstand temperatures above 1,650 °C. Figure 1. Examples of UHTC Components areshown that have been tested in the NASA AmesArc Jet facility to evaluate the materialsresponse in a simulated reentry environment.The cone and wedge models are representativeof the scale and geometries anticipated for useon UHTC sharp leading-edge vehicles.Ultrahigh temperature ceramics (UHTCs) are a class of materials that include the diborides of metals such as hafnium and zirconium. The materials are of interest to NASA for their potential utility as sharp leading edges for hypersonic vehicles. Such an application requires that the materials be capable of operating at temperatures, often in excess of 2,000 °C. UHTCs are highly refractory and have high thermal conductivity, an advantage for this application. UHTCs are potentially applicable for other high- temperature processing applications, such as crucibles for molten-metal processing and high-temperature electrodes.

Posted in: Briefs, TSP, Materials


Improved C/SiC Ceramic Composites Made Using PIP

These materials are expected to remain strong for longer times at high temperatures. Improved carbon-fiber- reinforced SiC ceramic-matrix composite (C/SiC CMC) materials, suitable for fabrication of thick-section structural components, are producible by use of a combination of raw materials and processing conditions different from such combinations used in the prior art. In comparison with prior C/SiC CMC materials, these materials have more nearly uniform density, less porosity, and greater strength. The majority of raw-material/processing-condition combinations used in the prior art involve the use of chemical vapor infiltration (CVI) for densifying the matrix.

Posted in: Briefs, Materials, Ceramics, Composite materials, Polymers


Coating Carbon Fibers With Platinum

Uniform coats are produced relatively inexpensively. A process for coating carbon fibers with platinum has been developed. The process may also be adaptable to coating carbon fibers with other noble and refractory metals, including rhenium and iridium. The coated carbon fibers would be used as ingredients of matrix/fiber composite materials that would resist oxidation at high temperatures. The metal coats would contribute to oxidation resistance by keeping atmospheric oxygen away from fibers when cracks form in the matrices.

Posted in: Briefs, Materials, Coatings, colorants, and finishes, Fibers, Metals


Nanorod-Based Fast-Response Pressure-Sensitive Paints

Improved, nanostructured coatings could be used to measure rapid pressure fluctuations. A proposed program of research and development would be devoted to exploitation of nanomaterials in pressuresensitive paints (PSPs), which are used on wind-tunnel models for mapping surface pressures associated with flow fields. Heretofore, some success has been achieved in measuring steady-state pressures by use of PSPs, but success in measuring temporally varying pressures has been elusive because of the inherent slowness of the optical responses of these materials.

Posted in: Briefs, Materials, Coatings, colorants, and finishes, Materials properties, Nanomaterials


Photocatalytic/Magnetic Composite Particles

Magnetic agitation enhances effectiveness. Photocatalytic/ magnetic composite particles have been invented as improved means of exploiting established methods of photocatalysis for removal of chemical and biological pollutants from air and water. The photocatalytic components of the composite particles are formulated for high levels of photocatalytic activity, while the magnetic components make it possible to control the movements of the particles through the application of magnetic fields. The combination of photocatalytic and magnetic properties can be exploited in designing improved air- and water-treatment reactors.

Posted in: Briefs, Materials, Air pollution, Catalysts, Water pollution, Composite materials, Magnetic materials


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