Tech Briefs

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

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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

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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

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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

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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

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Measurement of Model Noise in a Hard-Wall Wind Tunnel

Spurious noise is suppressed in processing of digitized microphone outputs. Identification, analysis, and control of fluid mechanically generated sound from models of aircraft and automobiles in special low-noise, semi-anechoic wind tunnels are an important research endeavor. Such studies can also be done in aerodynamic wind tunnels that have hard walls if phased microphone arrays are used to focus on the noise source regions and reject unwanted reflections or background noise. Although it may be difficult to simulate the total flyover or drive-by noise in a closed wind tunnel, individual noise sources can be isolated and analyzed.

Posted in: Briefs, Mechanical Components, Mechanics

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Tilt/Tip/Piston Manipulator With Base-Mounted Actuators

The geometry and kinematics of this manipulator would afford advantages for some applications. A proposed three degree of freedom (tilt/tip/piston) manipulator, suitable for aligning an optical or mechanical component, would offer several advantages over prior such manipulators:

Posted in: Briefs, TSP, Mechanical Components, Mechanics

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