Materials & Coatings

Integrated Multilayer Insulation

IMLI offers several potential advantages over conventional MLI.

Integrated multilayer insulation (IMLI) is being developed as an improved alternative to conventional multilayer insulation (MLI), which is more than 50 years old. A typical conventional MLI blanket comprises between 10 and 120 metallized polymer films separated by polyester nets. MLI is the best thermal-insulation material for use in a vacuum, and is the insulation material of choice for spacecraft and cryogenic systems. However, conventional MLI has several disadvantages: It is difficult or impossible to maintain the desired value of gap distance between the film layers (and consequently, it is difficult or impossible to ensure consistent performance), and fabrication and installation are labor-intensive and difficult. The development of IMLI is intended to overcome these disadvantages to some extent and to offer some additional advantages over conventional MLI.

Posted in: Briefs, Materials, Performance upgrades, Product development, Insulation

Polyimide/Glass Composite High-Temperature Insulation

This composite was found to exhibit an unexpectedly high degree of fire resistance.

Lightweight composites of RP46 polyimide and glass fibers have been found to be useful as extraordinarily fire-resistant electrical-insulation materials. RP46 is a polyimide of the polymerization of monomeric reactants (PMR) type, developed by NASA Langley Research Center. RP46 has properties that make it attractive for use in electrical insulation at high temperatures. These properties include high-temperature resistance, low relative permittivity, low dissipation factor, outstanding mechanical properties, and excellent resistance to moisture and chemicals. Moreover, RP46 contains no halogen or other toxic materials and when burned it does not produce toxic fume or gaseous materials.

Posted in: Briefs, Materials, Composite materials, Glass fibers, Insulation, Polymers, Fire prevention

Damage Detection and Self-Repair in Inflatable/Deployable Structures

Integrated sensors and self-repairing materials provide structural health management.

Inflatable/deployable structures are under consideration for applications as varied as expansion modules for the International Space Station to destinations for space tourism to habitats for the lunar surface. Monitoring and maintaining the integrity of the physical structure is critical, particularly since these structures rely on non-traditional engineering materials such as fabrics, foams, and elastomeric polymers to provide the primary protection for the human crew. The closely related prior concept of monitoring structural integrity by use of built-in or permanently attached sensors has been applied to structures made of such standard engineering materials as metals, alloys, and rigid composites. To effect monitoring of flexible structures comprised mainly of soft goods, however, it will be necessary to solve a different set of problems — especially those of integrating power and data-transfer cabling that can withstand, and not unduly interfere with, stowage and subsequent deployment of the structures. By incorporating capabilities for self-repair along with capabilities for structural health monitoring, successful implementation of these technologies would be a significant step toward semi-autonomous structures, which need little human intervention to maintain. This would not only increase the safety of these structures, but also reduce the inspection and maintenance costs associated with more conventional structures.

Posted in: Briefs, Materials, Finite element analysis, On-board diagnostics, On-board diagnostics (OBD), Maintenance, repair, and service operations, Elastomers, Fabrics, Gases

Nanocomposite Strain Gauges Having Small TCRs

Usefully large gauge factors and acceptably small drifts should also be attainable.

Ceramic strain gauges in which the strain-sensitive electrically conductive strips made from nanocomposites of noble metal and indium tin oxide (ITO) are being developed for use in gas turbine engines and other power-generation systems in which gas temperatures can exceed 1,500°F (about 816°C). In general, strain gauges exhibit spurious thermally induced components of response denoted apparent strain. When temperature varies, a strain-gauge material that has a nonzero temperature coefficient of resistance (TCR) exhibits an undesired change in electrical resistance that can be mistaken for the change in resistance caused by a change in strain. It would be desirable to formulate strain-gauge materials having TCRs as small as possible so as to minimize apparent strain.

Posted in: Briefs, TSP, Materials, Sensors and actuators, Ceramics, Composite materials, Nanotechnology, Semiconductors, Gas turbines

A Simplified Diagnostic Method for Elastomer Bond Durability

Less time and equipment are needed.

A simplified method has been developed for determining bond durability under exposure to water or high humidity conditions. It uses a small number of test specimens with relatively short times of water exposure at elevated temperature. The method is also gravimetric; the only equipment being required is an oven, specimen jars, and a conventional laboratory balance.

Posted in: Briefs, TSP, Materials, Diagnostics, Elastomers, Durability

Very High Output Thermoelectric Devices Based on ITO Nanocomposites

Thermocouples based on this material perform better than precious-metal thermocouples.

A material having useful thermoelectric properties was synthesized by combining indium-tin-oxide (ITO) with a NiCoCrAlY alloy/alumina cermet. This material had a very large Seebeck coefficient with electromotive- force-versus- temperature behavior that is considered to be excellent with respect to utility in thermocouples and other thermoelectric devices. When deposited in thin-film form, ceramic thermocouples offer advantages over precious-metal (based, variously, on platinum or rhodium) thermocouples that are typically used in gas turbines. Ceramic thermocouples exhibit high melting temperatures, chemical stability at high temperatures, and little or no electromigration. Oxide ceramics also resist oxidation better than metal thermocouples, cost substantially less than precious-metal thermocouples, and, unlike precious-metal thermocouples, do not exert catalytic effects.

Posted in: Briefs, Materials, Ceramics, Composite materials, Materials properties, Nanomaterials, Semiconductors

Complex Multifunctional Polymer/Carbon-Nanotube Composites

CNTs are treated and incorporated into composites to obtain enhanced properties.

A methodology for developing complex multifunctional materials that consist of or contain polymer/ carbon-nanotube composites has been conceived. As used here, “multifunctional” signifies having additional and/or enhanced physical properties that polymers or polymer- matrix composites would not ordinarily be expected to have. Such properties include useful amounts of electrical conductivity, increased thermal conductivity, and/or increased strength. In the present methodology, these properties are imparted to a given composite through the choice and processing of its polymeric and CNT constituents.

Posted in: Briefs, Materials, Forming, Composite materials, Nanomaterials, Polymers

Gadolinia-Doped Ceria Cathodes for Electrolysis of CO2

These electrodes have relatively low area-specific resistances.

Gadolinia-doped ceria, or GDC, (Gd0.4Ce0.6O2–δ, where the value of δ in this material varies, depending on the temperature and oxygen concentration in the atmosphere in which it is being used) has shown promise as a cathode material for high- temperature electrolysis of carbon dioxide in solid oxide electrolysis cells. The polarization resistance of a GDC electrode is significantly less than that of an otherwise equivalent electrode made of any of several other materials that are now in use or under consideration for use as cathodes for reduction of carbon dioxide. In addition, GDC shows no sign of deterioration under typical temperature and gas-mixture operating conditions of a high-temperature electrolyzer.

Posted in: Briefs, TSP, Materials, Carbon dioxide, Fuel cells, Electrolytes, Materials properties, Parts

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.

Posted in: Briefs, Materials, Lithium-ion batteries

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.

Posted in: Briefs, TSP, Materials, Carbon dioxide, Methane, Life support systems

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