Materials & Coatings

Regenerable Trace-Contaminant Sorbent for the Primary Life Support System (PLSS)

This technology has applications in air-revitalization systems on spacecraft, submarines, automobiles, and commercial aircraft. Lyndon B. Johnson Space Center, Houston, Texas The NASA objective of expanding the human experience into the far reaches of space requires the development of regenerable life support systems. This work addresses the development of a regenerable air-revitalization system for trace-contaminant (TC) removal for the spacesuit used in extravehicular activities (EVAs). Currently, a bed of granular activated carbon is used for TC control. The carbon is impregnated with phosphoric acid to enhance ammonia sorption, but this also makes regeneration difficult, if not impossible. Temperatures as high as 200 °C have been shown to be required for only partial desorption of ammonia on time scales of 18,140 hours. Neither these elevated temperatures nor the long time needed for sorbent regeneration are acceptable. Thus, the activated carbon has been treated as an expendable resource, and the sorbent bed has been oversized in order to last throughout the entire mission.

Posted in: Briefs, TSP

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Lithium Fluoride as a Polysulfide Shuttle Inhibitor for Lithium Sulfur Chemistry

This invention imparts properties such as reinforcement, enhanced tensile strength, and/or electrical and thermal conductivity to composites. Lyndon B. Johnson Space Center, Houston, Texas In a lithium sulfur cell, the reduction of sulfur to lithium sulfide is a critical series of reactions that provides a large theoretical capacity of 1,672 mAh/g sulfur. One of many challenges in this system is the solubility of generated lithium polysulfides during the charge/discharge process. These polysulfides derived from the reduction of elemental sulfur are soluble in organic electrolytes, and can be reduced at the anode, causing an undesired reaction. Polysulfide species can also accumulate at the surface of the cathode and be further reduced to lower-order polysulfides such as Li2S2 or Li2S. The insulating nature of these lower-order polysulfides blocks the electron pathway on the carbon cathode.

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White, Electrically Conductive, Radiation-Stable, Thermal Control Coating

Goddard Space Flight Center, Greenbelt, Maryland A highly reflective, white conductive coating system was developed using a layered approach with a combination of commercially available white conductive pigments within a conductive binder system. The top coating is a space-stable, radiation-resistant, highly reflective coating that has been tailored to provide optimum reflectance properties and meet vacuum thermal surface resistivities. The combined layer is a mixture of a highly reflective, electrically dissipative coating and a moderately reflective but highly conductive pigment in a conductive binder. A second, underlying layer of conductive white coating offers optimum adhesion to metal substrates and the topcoat. The system vacuum resistivity at room temperature is approximately 1 × 109 ohms/sq, and has a solar absorptance of less than 0.13 as measured on a Cary 5000 spectrophotometer.

Posted in: Briefs, TSP, Thermoelectrics, Coatings & Adhesives

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Plasma-Assisted Thin Film Coatings to Create Highly Hydrophobic Porous Structures

Multiple samples can be coated in this manner. John H. Glenn Research Center, Cleveland, Ohio Gas-distribution layers (GDLs) are water-management structures used in fuel cells and electrolyzers. GDLs are critical components that prevent flooding of the fuel cell electrode by product water, thus preserving open channels for reactant gas to reach the electrode. Typically, GDLs are electrically conductive papers (metal or carbon) having a fine pore structure. Extremely fine pores in some GDL materials are difficult to fully infiltrate with Teflon (PTFE). These materials are typically wet-proofed by coating with hydrophobic materials (e.g. PTFE). This is usually accomplished by immersing the raw paper in a PTFE emulsion. Completeness of wet-proofing by immersion in emulsion can be limited, because fine pores will filter out the PTFE particles.

Posted in: Briefs, TSP, Coatings & Adhesives

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Modeling Transmission Effects on Multilayer Insulation

New mathematical modeling of multilayer insulation performance extends over a much wider range of performance criteria than other known models. John F. Kennedy Space Center, Florida Recent experimental results within the NASA community have shown apparent degradation in the performance of multilayer insulation (MLI) when used in low-temperature applications, e.g., in liquid hydrogen tanks. There was speculation that this degradation was due to the appearance of radiative transmission of energy at these low temperatures since the black-body emission curve at low temperatures corresponds to long wavelengths that might be able to partially pass through the MLI sheets. The standard models for MLI could not be extended to include transmission effects, so a new mathematical system was developed that generalizes the description of the performance of this insulation material.

Posted in: Briefs, TSP, Coatings & Adhesives

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Innovative, Low-CTE, Lightweight Structures with Higher Strength

These composites feature controllable properties and strength. Goddard Space Flight Center, Greenbelt, Maryland A series of lightweight (density below 2.0 gm/cm3) composites has been manufactured that have controllable properties. The core composite has been improved to provide higher strength (similar to aluminum), extremely low density, receptivity to exterior coatings, and highly designable properties. The composite is made in days, is machinable and formable, can be joined/threaded, can be exposed to various environments (temperature, radiation), and is easily made into many parts. Lightweight mirrors for space and IR applications are extremely important. The goal of this work was to create lightweight multifunctional composites for replacement of titanium, beryllium, Invar, aluminum, rubber, and graphite epoxy for structural, mirror, and non-structural components. The key characteristics of this tailorable composite are low density, high stiffness (up to 25 MSI modulus), variable/low coefficient of thermal expansion (CTE) (2 to 7 ppm/°C), high temperature refractory materials and variable thermal conductivity. The composites are easily made (time to completion of 7 to 10 days), joinable, threadable, machinable to 80 mils, durable to resist FOD (foreign object damage), ductile enough to behave like a metal, and relatively low in cost.

Posted in: Briefs, TSP, Coatings & Adhesives, Composites

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Negative Dielectric Constant Material Based on Ion-Conducting Materials

Langley Research Center, Hampton, Virginia Metamaterials, or artificial negative index materials (NIMs), have generated great attention due to their unique and exotic electromagnetic properties. A negative dielectric constant material, which is an essential key for creating the NIMs, was developed by doping ions into a polymer, a protonated poly(benzimidazole) (PBI).

Posted in: Briefs, TSP, Energy Storage, Sensors

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