Materials & Coatings

Detecting Airborne Mercury by Use of Gold Nanowires

Mercury has been detected at concentrations as low as 2 ppb.

Like the palladium chloride (PdCl2) films described in the immediately preceding article, gold nanowire sensors have been found to be useful for detecting airborne elemental mercury at concentrations on the order of parts per billion (ppb). Also like the PdCl2 films, gold nanowire sensors can be regenerated under conditions much milder than those necessary for regeneration of gold films that have been used as airborne-Hg sensors. The interest in nanowire sensors in general is prompted by the expectation that nanowires of a given material covering a given surface may exhibit greater sensitivity than does a film of the same material because nanowires have a greater surface area.

Posted in: Briefs, TSP, Materials, Sensors and actuators, Sensors and actuators, Air pollution, Metals, Nanotechnology, Hazardous materials

Electrolytes for Low-Temperature Operation of Li-CFₓ Cells

A report describes a study of electrolyte compositions selected as candidates for improving the low-temperature performances of primary electrochemical cells that contain lithium anodes and fluorinated carbonaceous (CFx) cathodes. This study complements the developments reported in “Additive for Low-Temperature Operation of Li-(CF)n Cells” (NPO-43579) and Li/CFx Cells Optimized for Low-Temperature Operation (NPO-43585), which appear elsewhere in this issue of NASA Tech Briefs.

Posted in: Briefs, TSP, Materials

Polyimide-Foam/Aerogel Composites for Thermal Insulation

These composites may also afford enhanced acoustic attenuation.

Composites of specific types of polymer foams and aerogel particles or blankets have been proposed to obtain thermal insulation performance superior to those of the neat polyimide foams. These composites have potential to also provide enhanced properties for vibration dampening or acoustic attenuation. The specific type of polymer foam is denoted “TEEK-H,” signifying a series, denoted “H,” within a family of polyimide foams that were developed at NASA’s Langley Research Center and are collectively denoted “TEEK” (an acronym of the inventors’ names).

Posted in: Briefs, Materials, Thermal management, Thermal management, Performance upgrades, Composite materials, Foams, Insulation

Yb₁₄MnSb₁₁ as a High-Efficiency Thermoelectric Material

This material could supplant the state-of-theart material, SiGe.

Yb14MnSb11 has been found to be well-suited for use as a p-type thermoelectric material in applications that involve hot-side temperatures in the approximate range of 1,200 to 1,300 K. The figure of merit that characterizes the thermal-to-electric power-conversion efficiency is greater for this material than for SiGe, which, until now, has been regarded as the state-of-the art high-temperature p-type thermoelectric material. Moreover, relative to SiGe, Yb14MnSb11 is better suited to incorporation into a segmented thermoelectric leg that includes the moderate-temperature p-type thermoelectric material CeFe4Sb12 and possibly other, lower-temperature p-type thermoelectric materials.

Posted in: Briefs, Materials

Room-Temperature Ionic Liquids for Electrochemical Capacitors

A document discusses room-temperature ionic liquids (RTILs) used as electrolytes in carbon-nanotube-based, electrochemical, double-layer capacitors. Unlike the previous electrolyte (EtNB4 in acetonitrile), the RTIL used here does not produce cyanide upon thermal decomposition and does not have a moisture sensitivity.

Posted in: Briefs, TSP, Materials, Capacitors, Capacitors, Electrolytes, Nanotechnology

Ultra-Lightweight Self- Deployable Nanocomposite Structure for Habitat Applications

A document discusses self-deployable, rigidized structures that are ultra-lightweight and have gas barrier properties, space durability, and high impact resistance. Developed here are microcellular-foamed sandwich structures made from nanocomposite shape memory polymers (SMPs) with Cold-Hibernated Elastic Memory (CHEM) deployed technique for space structural components including space habitats. This type of foam sandwich also does not suffer from the toxicity problems of conventional foams, and has higher mechanical properties than those processed with conventional techniques. This design can be compacted into a very small volume for launch. Once deployed, the microcellular structure can use the heat from the Sun to recover 98 to 100 percent of its shape.

Posted in: Briefs, TSP, Materials

Room-Temperature-Cured Copolymers for Lithium Battery Gel Electrolytes

Room-temperature curing offers an important advantage in room-temperature functionality.

Polyimide-PEO copolymers (“PEO” signifies polyethylene oxide) that have branched rod-coil molecular structures and that can be cured into film form at room temperature have been invented for use as gel electrolytes for lithium-ion electric- power cells. These copolymers offer an alternative to previously patented branched rod-coil polyimides that have been considered for use as polymer electrolytes and that must be cured at a temperature of 200 °C. In order to obtain sufficient conductivity for lithium ions in practical applications at and below room temperature, it is necessary to imbibe such a polymer with a suitable carbonate solvent or ionic liquid, but the high-temperature cure makes it impossible to incorporate and retain such a liquid within the polymer molecular framework. By eliminating the high-temperature cure, the present invention makes it possible to incorporate the required liquid.

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

Catalysts for Efficient Production of Carbon Nanotubes

Some alloys have been found to work at lower temperatures.

Several metal alloys have shown promise as improved catalysts for catalytic thermal decomposition of hydrocarbon gases to produce carbon nanotubes (CNTs). Heretofore almost every experiment on the production of carbon nanotubes by this method has involved the use of iron, nickel, or cobalt as the catalyst. However, the catalytic-conversion efficiencies of these metals have been observed to be limited. The identification of better catalysts is part of a continuing program to develop means of mass production of high-quality carbon nanotubes at costs lower than those achieved thus far (as much as $100/g for purified multi-wall CNTs or $1,000/g for single-wall CNTs in year 2002).

Posted in: Briefs, TSP, Materials

Amorphous Silk Fibroin Membranes for Separation of CO₂

Amorphous silk fibroin has shown promise as a polymeric material derivable from natural sources for making membranes for use in removing CO2 from mixed-gas streams. For most applications of silk fibroin, for purposes other than gas separation, this material is used in its highly crystalline, nearly natural form because this form has uncommonly high tensile strength. However, the crystalline phase of silk fibroin is impermeable, making it necessary to convert the material to amorphous form to obtain the high permeability needed for gas separation.

Posted in: Briefs, Materials, Biomaterials, Fibers, Materials properties, Polymers, Tensile Strength

Use of Atomic Oxygen for Increased Water Contact Angles of Various Polymers for Biomedical Applications

Improved polymer hydrophilicity is beneficial for cell culturing and implant growth.

The purpose of this study was to determine the effect of atomic oxygen (AO) exposure on the hydrophilicity of nine different polymers for biomedical applications. Atomic oxygen treatment can alter the chemistry and morphology of polymer surfaces, which may increase the adhesion and spreading of cells on Petri dishes and enhance implant growth. Therefore, nine different polymers were exposed to atomic oxygen and water-contact angle, or hydrophilicity, was measured after exposure. To determine whether hydrophilicity remains static after initial atomic oxygen exposure, or changes with higher fluence exposures, the contact angles between the polymer and water droplet placed on the polymer’s surface were measured versus AO fluence. The polymers were exposed to atomic oxygen in a 100-W, 13.56-MHz radio frequency (RF) plasma asher, and the treatment was found to significantly alter the hydrophilicity of non-fluorinated polymers.

Posted in: Briefs, MDB, TSP, Briefs, TSP, Coatings & Adhesives, Materials, Bio-Medical, Medical, Medical equipment and supplies, Materials properties, Oxygen, Polymers

The U.S. Government does not endorse any commercial product, process, or activity identified on this web site.