Materials & Coatings

Oxide Fiber Cathode Materials for Rechargeable Lithium Cells

LiCoO2 and LiNiO2 fibers have been investigated as alternatives to LiCoO2 and LiNiO2 powders used as lithium-intercalation compounds in cathodes of rechargeable lithium-ion electrochemical cells. In making such a cathode, LiCoO2 or LiNiO2 powder is mixed with a binder [e.g., poly(vinylidene fluoride)] and an electrically conductive additive (usually carbon) and the mixture is pressed to form a disk. The binder and conductive additive contribute weight and volume, reducing the specific energy and energy density, respectively.

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Electrocatalytic Reduction of Carbon Dioxide to Methane

A room-temperature electrocatalytic process that effects the overall chemical reaction CO2 + 2H2O → CH4 + 2O2 has been investigated as a means of removing carbon dioxide from air and restoring oxygen to the air. The process was originally intended for use in a spacecraft life-support system, in which the methane would be vented to outer space. The process may also have potential utility in terrestrial applications in which either or both of the methane and oxygen produced might be utilized or vented to the atmosphere.

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Progress Toward Making Epoxy/Carbon-Nanotube Composites

A modicum of progress has been made in an effort to exploit single-walled carbon nanotubes as fibers in epoxy-matrix/fiber composite materials. Two main obstacles to such use of carbon nanotubes are the following: (1) bare nanotubes are not soluble in epoxy resins and so they tend to agglomerate instead of becoming dispersed as desired; and (2) because of lack of affinity between nanotubes and epoxy matrices, there is insufficient transfer of mechanical loads between the nanotubes and the matrices.

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Heterogeneous Superconducting Low-Noise Sensing Coils

Electrically superconductive outer layers are supported by highly thermally conductive skeletons. A heterogeneous material construction has been devised for sensing coils of super-conducting quantum interference device (SQUID) magnetometers that are subject to a combination of requirements peculiar to some advanced applications, notably including low-field magnetic resonance imaging for medical diagnosis. The requirements in question are the following:

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Predicting Properties of Unidirectional-Nanofiber Composites

A theory for predicting mechanical, thermal, electrical, and other properties of unidirectional- nanofiber/matrix composite materials is based on the prior theory of micromechanics of composite materials. In the development of the present theory, the prior theory of micromechanics was extended, through progressive substructuring, to the level of detail of a nanoscale slice of a nanofiber. All the governing equations were then formulated at this level.

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Quench Crucibles Reinforced With Metal

Specimens can be quenched rapidly, without cracking ampules. Improved crucibles consisting mainly of metal-reinforced ceramic ampules have been developed for use in experiments in which material specimens are heated in the crucibles to various high temperatures, then quenched by, for example, plunging the crucibles into water at room temperature. A quench crucible of the traditional type intended to be supplanted by the improved crucibles consists mainly of a ceramic or graphite ampule inside a metal cartridge, with a gap between the metal and the cartridge, as shown on the left side of the figure.

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Adjustable Membrane Mirrors Incorporating G-Elastomers

Lightweight, flexible, large-aperture mirrors of a type being developed for use in outer space have unimorph structures that enable precise adjustment of their surface figures. A mirror of this type includes a reflective membrane layer bonded with an electrostrictive grafted elastomer (G-elastomer) layer, plus electrodes suitably positioned with respect to these layers. By virtue of the electrostrictive effect, an electric field applied to the G-elastomer membrane induces a strain along the membrane and thus causes a deflection of the mirror surface. Utilizing this effect, the mirror surface figure can be adjusted locally by individually addressing pairs of electrodes.

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