Materials

Multifunctional, High-Temperature Nanocomposites

Electrical and thermal conductivities increase with proportions of nanotubes. In experiments conducted as part of a continuing effort to incorporate multifunctionality into advanced composite materials, blends of multi-walled carbon nanotubes and a resin denoted “PETI-330” (wherein “PETI” is an abbreviation for “phenylethynyl- terminated imide”) were prepared, characterized, and fabricated into moldings. PETI-330 was selected as the matrix resin in these experiments because of its low melt viscosity (<10 poise at a temperature of 280 °C), excellent melt stability (lifetime >2 hours at 280 °C), and high temperature performance (>1,000 hours at 288 °C). The multi-walled carbon nanotubes (MWCNTs), obtained from the University of Kentucky, were selected because of their electrical and thermal conductivity and their small diameters. The purpose of these experiments was to determine the combination of thermal, electrical, and mechanical properties achievable while still maintaining melt processability.

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Increasing Durability of Flame-Sprayed Strain Gauges

Low-oxygen heat treatments and internal platinum oxygen-diffusion barriers extend lifetimes. Thermally sprayed dielectric ceramic coatings are the primary means of attaching strain and temperature gauges to hot-section rotating parts of turbine engines. As hot-section temperatures increase, lifetimes of installed gauges decrease, and seldom exceed one hour above 2,000 °F ( ≈1,100 °C). Advanced engine components are expected to operate at temperatures approaching 2,200 °F ( ≈1,200 °C), and the required high-temperature lifetime is 10 hours minimum.

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Electrodialysis To Remove Ammonium Ions From Wastewater

A simple treatment removes most of the ammonium content. Electrodialysis has been shown to be an effective means for removing ammonium ions from wastewater without use of consumable chemicals and without adding other substances to the treated water. Provided that continuing efforts to develop efficient electrodialysis equipment prove successful, it should be possible to apply this treatment principle to wastewater streams to be recycled in life-support systems for spacecraft and other closed habitats. Effluents from some industrial processes that generate high concentration of ammonium ions may also be treatable by this principle.

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Making Carbon-Nanotube Arrays Using Block Polymers: Part II

A nanoscale phase separation would be utilized to form regularly spaced catalytic dots. Some changes have been incorporated into a proposed method of manufacturing regular arrays of precisely sized, shaped, positioned, and oriented carbon nanotubes. Such arrays could be useful as mechanical resonators for signal filters and oscillators, and as electrophoretic filters for use in biochemical assays.

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Formulations for Stronger Solid Oxide Fuel-Cell Electrolytes

Alumina is added to yttria-stabilized zirconia. Tests have shown that modification of chemical compositions can increase the strengths and fracture tough- nesses of solid oxide fuel-cell (SOFC) electrolytes. Heretofore, these solid electrolytes have been made of yttria- stabilized zirconia, which is highly conductive for oxygen ions at high temp- eratures, as needed for operation of fuel cells. Unfortunately yttria-stabilized zirconia has a high coefficient of thermal expansion, low resistance to thermal shock, low fracture toughness, and low mechanical strength. The lack of strength and toughness are especially problematic for fabrication of thin SOFC electrolyte membranes needed for contemplated aeronautical, automotive, and stationary power-generation applications.

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Liquid-Crystal Thermosets, a New Generation of High-Performance Liquid-Crystal Polymers

Liquid-crystal polymers can now be used as resins in textile composites. One of the major challenges for NASA's next-generation reusable-launch-vehicle (RLV) program is the design of a cryogenic lightweight composite fuel tank. Potential matrix resin systems need to exhibit a low coefficient of thermal expansion (CTE), good mechanical strength, and excellent barrier properties at cryogenic temperatures under load. In addition, the resin system needs to be processable by a variety of non-autoclavable techniques, such as vacuum-bag curing, resin-transfer molding (RTM), vacuum-assisted resin-transfer molding (VaRTM), resin-film infusion (RFI), pultrusion, and advanced tow placement (ATP).

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Nonlinear Thermoelastic Model for SMAs and SMA Hybrid

This model captures essential mechanics with fundamental engineering property input. A constitutive mathematical model has been developed that predicts the nonlinear thermomechanical behaviors of shape-memory alloys (SMAs) and of shape- memory-alloy hybrid composite (SMAHC) structures, which are composite-material structures that contain embedded SMA actuators. SMAHC structures have been investigated for their potential utility in a variety of applications in which there are requirements for static or dynamic control of the shapes of structures, control of the thermoelastic responses of structures, or control of noise and vibrations. The present model overcomes deficiencies of prior, overly simplistic or qualitative models that have proven ineffective or intractable for engineering of SMAHC structures. The model is sophisticated enough to capture the essential features of the mechanics of SMAHC structures yet simple enough to accommodate input from fundamental engineering measurements and is in a form that is amenable to implementation in general-purpose structural analysis environments.

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