Materials

High-Performance Polymers Having Low Melt Viscosities

Mixtures of differently shaped molecules have properties superior to the corresponding linear polymers. High-performance polymers that have improved processing characteristics, and a method of making them, have been invented. One of the improved characteristics is low (relative to corresponding prior polymers) melt viscosities at given temperatures. This characteristic makes it possible to utilize such processes as resin transfer molding and resin-film infusion and to perform autoclave processing at lower temperatures and/or pressures. Another improved characteristic is larger processing windows — that is, longer times at low viscosities. Other improved characteristics include increased solubility of uncured polymer precursors that contain reactive groups, greater densities of cross-links in cured polymers, improved mechanical properties of the cured polymers, and greater resistance of the cured polymers to chemical attack.

Posted in: Materials, Briefs, TSP

Read More >>

Low-Density, Aerogel-Filled Thermal- Insulation Tiles

Aerogel fillings have been investigated in a continuing effort to develop low-density thermal-insulation tiles that, relative to prior such tiles, have greater dimensional stability (especially less shrinkage), equal or lower thermal conductivity, and greater strength and durability. In preparation for laboratory tests of dimensional and thermal stability, prototypes of aerogel-filled versions of recently developed low-density tiles have been fabricated by impregnating such tiles to various depths with aerogel formations ranging in density from 1.5 to 5.6

Posted in: Materials, Briefs

Read More >>

Glass Frit Filters for Collecting Metal

Filter disks made of glass frit have been found to be effective as means of high throughput collection of metal oxide particles, ranging in size from a few to a few hundred nanometers, produced in gas phase condensation reactors. In a typical application, a filter is placed downstream of the reactor and a valve is used to regulate the flow of reactor exhaust through the filter. The exhaust stream includes a carrier gas, particles, byproducts, and unreacted particle precursor gas. The filter selectively traps the particles while allowing the carrier gas, the byproducts, and, in some cases, the unreacted precursor, to flow through unaffected. Although the pores in the filters are much larger than the particles, the particles are nevertheless trapped to a high degree: Anecdotal information from an experiment indicates that 6-nm-diameter particles of MnO2 were trapped with >99-percent effectiveness by a filtering device comprising a glass-frit disk having pores 70 to 100 µm wide immobilized in an 8-cm-diameter glass tube equipped with a simple twist valve at its downstream end.

Posted in: Materials, Briefs

Read More >>

Anhydrous Proton-Conducting Membranes for Fuel Cells

Operating temperatures could be as high as 200 °C. Polymeric electrolyte membranes that do not depend on water for conduction of protons are undergoing development for use in fuel cells. Prior polymeric electrolyte fuel-cell membranes (e.g., those that contain perfluorosulfonic acid) depend on water and must be limited to operation below a temperature of 125 °C because they retain water poorly at higher temperatures. In contrast, the present developmental anhydrous membranes are expected to function well at temperatures up to 200 °C.

Posted in: Materials, Briefs, TSP

Read More >>

Patched Off-Axis Bending/Twisting Actuators for Thin Mirrors

Two documents present updates on thin-shell, adjustable, curved mirrors now being developed for use in spaceborne imaging systems.  These mirrors at an earlier stage of development were reported in “Nanolaminate Mirrors With Integral Figure-Control Actuators” (NPO-30221), NASA Tech Briefs, Vol. 26, No. 5 (May 2002), page 80. To recapitulate: These mirrors comprise metallic film reflectors on nanolaminate substrates that contain “in-plane” actuators for controlling surface figures with micronlevel precision. The actuators are integral parts of the mirror structures, typically fabricated as patches that are bonded onto the rear (nonreflective) surfaces of the mirror shells. The current documents discuss mathematical modeling of mirror deflections caused by actuators arranged in unit cells distributed across the rear mirror surfaces. One of the documents emphasizes an actuator configuration in which a mirror surface is divided into hexagonal unit cells. Each unit cell contains four rectangular actuator patches in an off-axis cruciform pattern to induce a combination of bending and twisting. For deflections to reduce certain optical aberrations, it is found that, relative to other configurations, this configuration involves a smaller areal density of actuators.

Posted in: Materials, Briefs, TSP

Read More >>

Nickel-Tin Electrode Materials for Nonaqueous Li-Ion Cells

Capacity densities exceed those of materials now commercially available for the same purpose. Experimental materials made from mixtures of nickel and tin powders have shown promise for use as the negative electrodes of rechargeable lithium-ion electrochemical power cells. During charging (or discharging) of a lithiumion cell, lithium ions are absorbed into (or desorbed from, respectively) the negative electrode, typically through an intercalation or alloying process. The negative electrodes (for this purpose, designated as anodes) in state-of-the-art Li-ion cells are made of graphite, in which intercalation occurs. Alternatively, the anodes can be made from metals, in which alloying can occur. For reasons having to do with the electrochemical potential of intercalated lithium, metallic anode materials (especially materials containing tin) are regarded as safer than graphite ones; in addition, such metallic anode materials have been investigated in the hope of obtaining reversible charge/discharge capacities greater than those of graphite anodes. However, until now, each of the tin-containing metallic anode formulations tested has been found to be inadequate in some respect.

Posted in: Materials, Briefs

Read More >>

Isogrid Membranes for Precise, Singly Curved Reflectors

Reinforcing meshes of fibers would prevent wrinkles and ripples. A new type of composite material has been proposed for membranes that would constitute the reflective surfaces of planned lightweight, single curvature (e.g., parabolic cylindrical) reflectors for some radar and radio communication systems. The proposed composite materials would consist of polyimide membranes containing embedded grids of high strength (e.g., carbon) fibers. The purpose of the fiber reinforcements, as explained in more detail below, is to prevent wrinkling or rippling of the membrane.

Posted in: Materials, Briefs, TSP

Read More >>

White Papers

UV-/Light-Curing Adhesives Improve Manufacturing Productivity
Sponsored by DELO
Introduction to Hypervisor Technology
Sponsored by Curtiss-Wright Controls Embedded Computing
Solar Electric Systems – Power Reliability
Sponsored by SunWize
How to Avoid Bearing Corrosion
Sponsored by Kaydon
Designing Ring Projections for Hermetic Sealing
Sponsored by Miyachi Unitek
Fundamentals of Vector Network Analysis Primer
Sponsored by Rohde and Schwarz

White Papers Sponsored By: