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Synthesizing Diamond From Liquid Feedstock

Precise proportioning of feedstock gases is not necessary. A relatively economical method of chemical vapor deposition (CVD) has been developed for synthesizing diamond crystals and films. Unlike prior CVD methods for synthesizing diamond, this method does not require precisely proportioned flows of compressed gas feedstocks or the use of electrical discharges to decompose the feedstocks to obtain free radicals needed for deposition chemical reactions. Instead, the feedstocks used in this method are mixtures of common organic liquids that can be prepared in advance, and decomposition of feedstock vapors is effected simply by heating.

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Modifying Silicates for Better Dispersion in Nanocomposites

Processability and final material properties are improved. An improved chemical modification has been developed to enhance the dispersion of layered silicate particles in the formulation of a polymer/silicate nanocomposite material. The modification involves, among other things, the co-exchange of an alkyl ammonium ion and a monoprotonated diamine with interlayer cations of the silicate. The net overall effects of the improved chemical modification are to improve processability of the nanocomposite and maximize the benefits of dispersing the silicate particles into the polymer.

Posted in: Briefs, TSP, Materials

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Better End-Cap Processing for Oxidation-Resistant Polyimides

Cross-linking in an inert atmosphere (as opposed to air) yields better results. A class of end-cap compounds that increase the thermo-oxidative stability of polyimides of the polymerization of monomeric reactants (PMR) type has been extended. In addition, an improved processing protocol for this class of endcap compounds has been invented. The class of end-cap compounds was described in “End Caps for More Thermo-Oxidative Stability in Polyimides” (LEW-17012), NASA Tech Briefs, Vol. 25, No. 10 (October 2001), page 32. To recapitulate: PMR polyimides are often used as matrix resins of high-temperature- resistant composite materials. These end-cap compounds are intended to supplant the norbornene end cap (NE) compound that, heretofore, has served to limit molecular weights during oligomerization and, at high temperatures, to form cross-links that become parts of stable network molecular structures. NE has been important to processability of high-temperature resins because (1) in limiting molecular weights, it enables resins to flow more readily for processing and (2) it does not give off volatile byproducts during final cure and, therefore, enables the production of voidfree composite parts. However, with respect to ability of addition polymers to resist oxidation at high temperature, NE has been a “weak link.” Consequently, for example, in order to enable norbornene-end-capped polyimide matrices to last for lifetimes up to 1,000 hours, it is necessary to limit their use temperatures to =315 °C.

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Amplifying Electrochemical Indicators

Reporter compounds can be formulated for high sensitivity and miniaturization of sensor units. Dendrimeric reporter compounds have been invented for use in sensing and amplifying electrochemical signals from molecular recognition events that involve many chemical and biological entities. These reporter compounds can be formulated to target specific molecules or molecular recognition events. They can also be formulated to be, variously, hydrophilic or amphiphilic so that they are suitable for use at interfaces between (1) aqueous solutions and (2) electrodes connected to external signal-processing electronic circuits. The invention of these reporter compounds is expected to enable the development of highly miniaturized, low-power-consumption, relatively inexpensive, mass-producible sensor units for diverse applications, including diagnoses of infectious and genetic diseases, testing for environmental bacterial contamination, forensic investigations, and detection of biological warfare agents.

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Precious-Metal Salt Coatings for Detecting Hydrazines

Colors change upon exposure to hydrazines and perhaps other hazardous gases. Substrates coated with a precious metal salt KAuCl4 have been found to be useful for detecting hydrazine vapors in air at and above a concentration of the order of 0.01 parts per million (ppm). Upon exposure to air containing a sufficient amount of hydrazine for a sufficient time, the coating material undergoes a visible change in color. Although the color change is only a qualitative indication, it can serve as an alarm of a hazardous concentration of hydrazine or as advice of the need for a quantitative measurement of concentration. Detection of hydrazine vapors by this technique costs much less and takes less time than does laboratory analysis of sorbent tubes using high-performance liquid chromatography, which is the technique used heretofore to detect hydrazines at concentrations down to 0.01 ppm.

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Nanocarpets for Trapping Microscopic Particles

Properties of nanocarpets can be tailored for selective trapping. Nanocarpets — that is, carpets of carbon nanotubes — are undergoing development as means of trapping microscopic particles for scientific analysis. Examples of such particles include inorganic particles, pollen, bacteria, and spores. Nanocarpets can be characterized as scaled-down versions of ordinary macroscopic floor carpets, which trap dust and other particulate matter, albeit not purposefully. Nanocarpets can also be characterized as mimicking both the structure and the particle-trapping behavior of ciliated lung epithelia, the carbon nanotubes being analogous to cilia (see figure).

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Treated Carbon Nanofibers for Storing Energy in Aqueous KOH

Treatment can increase specific capacitance by as much as 400 percent. A surface treatment has been found to enhance the performances of carbon nanofibers as electrode materials for electrochemical capacitors in which aqueous solutions of potassium hydroxide are used as the electrolytes. In the treatment, sulfonic acid groups are attached to edge plane sites on carbon atoms.

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