Special Coverage

Converting from Hydraulic Cylinders to Electric Actuators
Automating Optimization and Design Tasks Across Disciplines
Vibration Tables Shake Up Aerospace and Car Testing
Supercomputer Cooling System Uses Refrigerant to Replace Water
Computer Chips Calculate and Store in an Integrated Unit
Electron-to-Photon Communication for Quantum Computing
Mechanoresponsive Healing Polymers
Variable Permeability Magnetometer Systems and Methods for Aerospace Applications
Evaluation Standard for Robotic Research

SiC Composite Turbine Vanes

Y-cloth was conceived to provide fiber reinforcement for sharp trailing edges.

Turbine inlet guide vanes have been fabricated from composites of silicon carbide fibers in silicon carbide matrices. A unique design for a cloth made from SiC fibers makes it possible to realize the geometric features necessary to form these vanes in the same airfoil shapes as those of prior metal vanes.

Posted in: Briefs, TSP, Materials, Forming, Composite materials, Fabrics, Silicon alloys, Fans, Gas turbines

Thermoelectric Inhomogeneities in (Ag1-SbTe2)x(PbTe)1-x

A document presents a study of why materials of composition (Ag1–ySbTe2)0.05 (PbTe)0.95 [0=y=1] were previously reported to have values of the thermoelectric figure of merit [ZT (where Z = a2/??, a is the Seebeck coefficient, ? is electrical resistivity, ? is thermal conductivity, and T is absolute temperature)] ranging from 2. In the study, samples of (AgSbTe2)0.05(PbTe)0.95, (Ag0.67SbTe2)0.05 (PbTe)0.95, and (Ag0.55SbTe2)0.05(PbTe)0.95 were prepared by melting followed, variously, by slow or rapid cooling. Analyses of these samples by x-ray diffraction, electron microscopy, and scanning microprobe measurements of the Seebeck coefficient led to the conclusion that these materials have a multiphase character on a scale of the order of millimeters, even though they appear homogeneous in x-ray diffraction and electron microscopy. The Seebeck measurements showed significant variations, including both n-type and p-type behavior in the same sample. These variations were found to be consistent with observed variations of ZT. The rapidly quenched samples were found to be less inhomogeneous than were the furnace-cooled ones; hence, rapid quenching was suggested as a basis of research on synthesizing more nearly uniform high-ZT samples.

Posted in: Briefs, TSP, Materials, Heat transfer, Thermodynamics, Composite materials, Test procedures, Thermal testing

Oxygen-Permeable, Hydrophobic Membranes of Silanized α-Al2O3

These membranes perform better than do organic polymer oxygen-diffusion membranes.

Membranes made of silanized alumina have been prepared and tested as prototypes of derivatized ceramic membranes that are both highly permeable to oxygen and hydrophobic. Improved oxygen-permeable, hydrophobic membranes would be attractive for use in several technological disciplines, including supporting high-temperature aqueous-phase oxidation in industrial production of chemicals, oxygenation of aqueous streams for bioreactors, and oxygenation of blood during open-heart surgery and in cases of extreme pulmonary dysfunction. In comparison with organic polymeric oxygen-permeable membranes now commercially available, the derivatized ceramic membranes are more chemically robust, are capable of withstanding higher temperatures, and exhibit higher oxygen-diffusion coefficients.

Posted in: Briefs, Materials, Product development, Aluminum alloys, Ceramics, Materials properties, Performance tests

Lower-Conductivity Ceramic Materials for Thermal-Barrier Coatings

Thermal conductivities of certain pyrochlore oxides can be reduced by doping.

Doped pyrochlore oxides of a type described below are under consideration as alternative materials for high temperature thermal barrier coatings (TBCs). In comparison with partially yttria stabilized zirconia (YSZ), which is the state of the art TBC material now in commercial use, these doped pyrochlore oxides exhibit lower thermal conductivities, which could be exploited to obtain the following advantages:

Posted in: Briefs, TSP, Materials, Thermal management, Ceramics, Coatings, colorants, and finishes, Conductivity

Improving Thermomechanical Properties of SiC/SiC Composites

A heat treatment increases thermal conductivity and increases creep resistance.

Today, a major thrust toward improving the thermomechanical properties of engine components lies in the development of fiber-reinforced silicon carbide matrix composite materials, including SiC-fiber/SiC-matrix composites. These materials are lighter in weight and capable of withstanding higher temperatures, relative to state-of-the-art metallic alloys and oxide-matrix composites for which maximum use temperatures are in the vicinity of 1,100 °C. In addition, the toughness or damage tolerance of the SiC-matrix composites is significantly greater than that of unreinforced silicon-based monolithic ceramics.

Posted in: Briefs, TSP, Materials, Thermodynamics, Forming, Metallurgy, Composite materials, Fibers, Materials properties

Patches for Repairing Ceramics and Ceramic Matrix Composites

Patches are simply pressed in place, then heated.

Patches consisting mostly of ceramic fabrics impregnated with partially cured polymers and ceramic particles are being developed as means of repairing ceramics and ceramic-matrix composites (CMCs) that must withstand temperatures above the melting points of refractory metal alloys. These patches were conceived for use by space-suited, space-walking astronauts in repairing damaged space-shuttle leading edges: as such, these patches could be applied in the field, in relatively simple procedures, and with minimal requirements for specialized tools. These design characteristics also make the patches useful for repairing ceramics and CMCs in terrestrial settings.

Posted in: Briefs, Materials, Maintenance, repair, and service operations, Ceramics, Composite materials

4-Vinyl-1,3-Dioxolane-2-One as an Additive for Li-Ion Cells

Low-temperature charge/discharge capacity is increased.

Electrolyte additive 4-vinyl-1, 3-dioxolane-2-one has been found to be promising for rechargeable lithium-ion electrochemical cells. This and other additives, along with advanced electrolytes comprising solutions of LiPF6 in various mixtures of carbonate solvents, have been investigated in a continuing effort to improve the performances of rechargeable lithium-ion electrochemical cells, especially at low temperatures. In contrast to work by other researchers who have investigated the use of this additive to improve the high-temperature resilience of Li-ion cells, the current work involves the incorporation of 4-vinyl-1,3-dioxolane-2-one into quaternary carbonate electrolyte mixtures, previously optimized for low-temperature applications, resulting in improved low temperature performance.

Posted in: Briefs, TSP, Materials, Battery cell chemistry, Lithium-ion batteries, Thermal management, Electrolytes

Aerogel/Particle Composites for Thermoelectric Devices

Shrinkage is reduced through addition of titania powder.

Optimizing solution chemistry and the addition of titania and fumed silica powder reduces shrinkage. These materials would serve to increase thermal efficiency by providing thermal insulation to suppress lateral heat leaks. They would also serve to prolong operational lifetime by suppressing sublimation of certain constituents of thermoelectric materials (e.g., sublimation of Sb from CoSb3) at typical high operating temperatures. [The use of pure silica aerogels as cast-in-place thermal-insulation and sublimation-suppression materials was described in “Aerogels for Thermal Insulation of Thermoelectric Devices” (), NASA Tech Briefs, Vol. 30, No. 7 (July 2006), page 50.]

Posted in: Briefs, TSP, Materials, Powder metallurgy, Composite materials, Insulation, Reliability

Vaporizable Scaffolds for Fabricating Thermoelectric Modules

Thermoelectric legs would be separated by precise gaps.

A process for fabricating thermoelectric modules with vacuum gaps separating the thermoelectric legs has been conceived, and the feasibility of some essential parts of the process has been demonstrated. The vacuum gaps are needed to electrically insulate the legs from each other. The process involves the use of scaffolding in the form of sheets of a polymer to temporarily separate the legs by the desired distance, which is typically about 0.5 mm. During a bonding subprocess that would take place in a partial vacuum at an elevated temperature, the polymer would be vaporized, thereby creating the vacuum gaps. If desired, the gaps could later be filled with an aerogel for thermal insulation and to suppress sublimation of thermoelectric material, as described in “Aerogels for Thermal Insulation of Thermoelectric Devices” (), NASA Tech Briefs, Vol. 30, No. 7 (July, 2006), page 50.

Posted in: Briefs, TSP, Materials, Fabrication, Insulation, Polymers, Electro-thermal engines

Stability Enhancement of Polymeric Sensing Films Using Fillers

Enhanced stability of polymer sensing films is achieved by adding colloidal fillers.

Experiments have shown the stability enhancement of polymeric sensing films on mixing the polymer with colloidal filler particles (submicron-sized) of carbon black, silver, titanium dioxide, and fumed silicon dioxide. The polymer films are candidates for potential use as sensing media in micro/nano chemical sensor devices. The need for stability enhancement of polymer sensing films arises because such films have been found to exhibit unpredictable changes in sensing activity over time, which could result in a possible failure of the sensor device.

Posted in: Briefs, TSP, Materials, Sensors and actuators, Composite materials, Materials properties, Nanotechnology, Polymers

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