Materials & Coatings

Gas Sensors Based on Coated and Doped Carbon Nanotubes

Large specific surface areas of nanotubes could enable attainment of high sensitivities.

Efforts are underway to develop inexpensive, low-power electronic sensors, based on single-walled carbon nanotubes (SWCNTs), for measuring part-per-million and part-per-billion of selected gases (small molecules) at room temperature. Chemically unmodified SWCNTs are mostly unresponsive to typical gases that one might wish to detect. However, the electrical resistances of SWCNTs can be made to vary with concentrations of gases of interest by coating or doping the SWCNTs with suitable materials. Accordingly, the basic idea of the present development efforts is to incorporate thus-treated SWCNTs into electronic devices that measure their electrical resistances.

Posted in: Briefs, Materials, Sensors and actuators, Gases, Nanomaterials

Photochemically Synthesized Polyimides

Single monomers are polymerized by exposure to ultraviolet light, without heating.

An alternative to the conventional approach to synthesis of polyimides involves the use of single monomers that are amenable to photopolymerization. Heretofore, the synthesis of polyimides has involved multiple-monomer formulations and heating to temperatures that often exceed 250 °C. The present alternative approach enables synthesis under relatively mild conditions that can include room temperature.

Posted in: Briefs, TSP, Materials, Forming, Productivity, Polymers

Hydroxide-Assisted Bonding of Ultra-Low-Expansion Glass

Preparation of bond surfaces is critical to success.

A process for hydroxide-assisted bonding has been developed as a means of joining optical components made of ultra-low-expansion (ULE) glass, while maintaining sufficiently precise alignment between. The process is intended mainly for use in applications in which (1) bonding of glass optical components by use of epoxy does not enable attainment of the required accuracy and dimensional stability and (2) conventional optical contacting (which affords the required accuracy and stability) does not afford adequate bond strength.

Posted in: Briefs, Materials, Optics, Joining, Glass

Optimized Carbonate and Ester-Based Li-Ion Electrolytes

This technology can be used in portable electronics, cell phones, and electric vehicles.

To maintain high conductivity in low temperatures, electrolyte co-solvents have been designed to have a high dielectric constant, low viscosity, adequate coordination behavior, and appropriate liquid ranges and salt solubilities. Electrolytes that contain ester-based co-solvents in large proportion (>50 percent) and ethylene carbonate (EC) in small proportion (<20 percent) improve low-temperature performance in MCMB carbon-LiNiCoO2 lithium-ion cells. These co-solvents have been demonstrated to enhance performance, especially at temperatures down to –70 °C. Low-viscosity, ester-based co-solvents were incorporated into multi-component electrolytes of the following composition: 1.0 M LiPF6 in ethylene carbonate (EC) + ethyl methyl carbonate (EMC) + X (1:1:8 volume percent) [where X = methyl butyrate (MB), ethyl butyrate EB, methyl propionate (MP), or ethyl valerate (EV)]. These electrolyte formulations result in improved low-temperature performance of lithium-ion cells, with dramatic results at temperatures below –40 °C. [See “Ester-Based Electrolytes for Low-Temperature Li-Ion Cells,” (NPO-41097) NASA Tech Briefs, Vol 29, No. 12 (December, 2005), p. 59.]

Posted in: Briefs, TSP, Materials, Optimization, Lithium-ion batteries, Electrolytes, Materials properties

LiCoPO₄ Cathode Layers for Thin-Film Batteries

Highest voltage thin-film batteries ever reported are demonstrated at low current densities.

LiCoPO4 has been found to be a promising active cathode material for high-energy-density, thin-film, rechargeable electrochemical power cells. The potential of the charge/discharge plateau of a cell containing an LiCoPO4 cathode is 4.8 V — a value that compares favorably with the corresponding value of 3.8 V of a state-of-the art cell containing an LiCoO2 cathode.

Posted in: Briefs, TSP, Materials, Lithium-ion batteries, Materials properties

High-Temperature SMAs for Actuator Applications

Work output is comparable to conventional SMA alloys but with transition temperatures significantly exceeding those of conventional materials.

Compositions and production processes have been developed for making NiTi-based shape-memory alloys (SMAs) that can be tailored for use as actuator materials at temperatures exceeding those of conventional alloys. Whereas conventional shape-memory alloys are limited to use at temperatures well below 100 °C due to low transformation temperatures, these high-temperature shape-memory alloys (HTSMAs) have transformation temperatures exceeding 300 °C while maintaining many of the other attributes associated with NiTi alloys, most importantly high work output (see Figure 1). Other attractive properties of this family of NiTiPt HTSMAs include usefully high values of tensile ductility, relatively narrow hysteresis, good oxidation resistance up to 600 °C, and excellent thermal and dimensional stability. Just as important, these alloys can be readily processed into various structural forms such as thin rod and fine-diameter wire by conventional processes (see Figure 2). These materials hold promise for expanding the variety of applications in which SMAbased actuators could be used.

Posted in: Briefs, TSP, Materials, Sensors and actuators, Heat resistant alloys, Materials identification

NASA-Inspired Shape-Sensing Fibers Enable Minimally Invasive Surgery

Minimally Invasive Surgery (MIS) is a new class of surgical procedures in which the operation is performed with surgical instruments inserted through small incisions in the body. In contrast to open surgery, in which the organ or tissue is exposed through large incisions in the body, MIS procedures generally allow for faster recovery time, less pain and trauma, reduced risk of infection, and shorter hospital stays.

Posted in: Articles, Materials, Medical, Sensors, Surgical procedures, Fibers

Low-Pt-Content Anode Catalyst for Direct Methanol Fuel Cells

The costs of fuel-cell anodes could be reduced substantially.

Combinatorial experiments have led to the discovery that a nanophase alloy of Pt, Ru, Ni, and Zr is effective as an anode catalyst material for direct methanol fuel cells. This discovery has practical significance in that the electronic current densities achievable by use of this alloy are comparable or larger than those obtained by use of prior Pt/Ru catalyst alloys containing greater amounts of Pt. Heretofore, the high cost of Pt has impeded the commercialization of direct methanol fuel cells. By making it possible to obtain a given level of performance at reduced Pt content (and, hence, lower cost), the discovery may lead to reduction of the economic impediment to commercialization.

Posted in: Briefs, TSP, Materials, Catalysts, Fuel cells, Methanol, Alloys, Nanotechnology

Atomized BaF₂-CaF₂ for Better-Flowing Plasma-Spray Feedstock

Water atomization is better suited to high-volume production of metal fluoride than conventional methods.

Atomization of a molten mixture of BaF2 and CaF2 has been found to be superior to crushing of bulk solid BaF2- CaF2 as a means of producing eutectic BaF2-CaF2 powder for use as an ingredient of the powder feedstock of a hightemperature solid lubricant material known as PS304. Developed to reduce friction and wear in turbomachines that incorporate foil air bearings, PS304 is applied to metal substrates by plasma spraying. The constituents of PS304 are:

Posted in: Briefs, TSP, Materials, Lubricants, Powder metallurgy, Production, Bearings

Nanophase Nickel-Zirconium Alloys for Fuel Cells

Corrosion resistance can be achieved at lower cost.

Nanophase nickel- zirconium alloys have been investigated for use as electrically conductive coatings and catalyst supports in fuel cells. Heretofore, noble metals have been used because they resist corrosion in the harsh, acidic fuel-cell interior environments. However, the high cost of noble metals has prompted a search for less-costly substitutes.

Posted in: Briefs, TSP, Materials, Fuel cells, Nanotechnology, Nickel alloys

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