Materials & Coatings

Flat Membrane Device for Dehumidification of Air

Water vapor is not condensed; instead, it is transported to vacuum. A device based on the transport of water through a membrane to a vacuum has been developed for dehumidifying a stream of air in the life-support system of a spacecraft or space suit. The device could also be adapted to terrestrial use in dehumidification of air in an air-conditioning stream or drying of air or another gas in a chemical processing stream. The design of this device is an advance in that it decreases (relative to prior designs) the weight, power consumption, and volume of the dehumidifier in the life-support system or other gas-circulation system in which the device is used. In the case of a spacecraft or space suit, the design thereby also increases safety and health margins. Although the membranes in the device must be replaced periodically and a vacuum source is essential for its operation, no other dehumidifier works as well in a spacecraft or space suit.

Posted in: Materials, Briefs

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Nano-Engineered Catalysts for Direct Methanol Fuel Cells

Small particle sizes and large surface areas can be produced economically and consistently. Nano-engineered catalysts, and a method of fabricating them, have been developed in a continuing effort to improve the performances of direct methanol fuel cells as candidate power sources to supplant primary and secondary batteries in a variety of portable electronic products. In order to realize the potential for high energy densities (as much as 1.5 W•h/g) of direct methanol fuel cells, it will be necessary to optimize the chemical compositions and geometric configurations of catalyst layers and electrode structures. High performance can be achieved when catalyst particles and electrode structures have the necessary small feature sizes (typically of the order of nanometers), large surface areas, optimal metal compositions, high porosity, and hydrophobicity.

Posted in: Materials, Briefs, TSP

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Nanotip Carpets as Antireflection Surfaces

Reflectance less than 10–3 is readily achieved. Carpetlike random arrays of metal-coated silicon nanotips have been shown to be effective as antireflection surfaces. Now undergoing development for incorporation into Sun sensors that would provide guidance for robotic exploratory vehicles on Mars, nanotip carpets of this type could also have many uses on Earth as antireflection surfaces in instruments that handle or detect ultraviolet, visible, or infrared light.

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Directed Growth of Carbon Nanotubes Across Gaps

Single-walled carbon nanotubes grow aligned along applied electric fields. An experiment has shown that when single- walled carbon nanotubes (SWNTs) are grown by chemical vapor deposition in the presence of an electric field of suitable strength, the nanotubes become aligned along the electric field. In an important class of contemplated applications, one would exploit this finding in fabricating nanotube transistors; one would grow SWNTs across gaps between electrodes that would serve, subsequently, as source and drain contacts during operation of the transistors.

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Protective Solid Electrolyte Films for Thin Li-Ion Cells

These films would simplify fabrication and afford greater flexibility in design. Thin films of Li2CO3 are under consideration for use as passivating layers between electrodes and solid electrolytes in advanced thin-film lithium-ion electrochemical cells. By suppressing undesired chemical reactions as described below, the Li2CO3 films could help to prolong the shelf lives, increase the specific energies, and simplify the fabrication of the cells. Batteries comprising one or more cells of this type could be used as sources of power in such miniature electronic circuits as those in “smart” cards, implantable electronic medical devices, sensors, portable communication devices, and hand-held computers.

Posted in: Materials, Briefs, TSP

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Testing Soil for Electrokinetically Enhanced Bioremediation

Data from tests provide guidance for in situ treatment. The term “prefield test” denotes an in situ test of contaminated soil in preparation for in situ treatment of the soil by a method called “electrokinetically enhanced bioremediation” (EEB). A prefield test yields data that are helpful in designing and operating an efficient and cost-effective EEB system.

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Heat-Storage Modules Containing LiNO3•3H2O and Graphite Foam

Heat capacity per unit volume has been increased. A heat-storage module based on a commercial open-cell graphite foam (PocoFoam or equivalent) imbued with lithium nitrate trihydrate (LiNO3•3H2O) has been developed as a prototype of other such modules for use as short-term heat sources or heat sinks in the temperature range of approximately 28 to 30 °C. In this module, the LiNO3•3H2O serves as a phase-change heat-storage material and the graphite foam as thermally conductive filler for transferring heat to or from the phase-change material. In comparison with typical prior heat-storage modules in which paraffins are the phase-change materials and aluminum fins are the thermally conductive fillers, this module has more than twice the heat-storage capacity per unit volume.

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