Materials & Coatings

Nanotip Carpets as Antireflection Surfaces

Reflectance less than 10–3 is readily achieved.

Carpetlike random arrays of metal-coated silicon nanotips have been shown to be effective as antireflection surfaces. Now undergoing development for incorporation into Sun sensors that would provide guidance for robotic exploratory vehicles on Mars, nanotip carpets of this type could also have many uses on Earth as antireflection surfaces in instruments that handle or detect ultraviolet, visible, or infrared light.

Posted in: Briefs, TSP, Materials, Optics, Optics, Materials properties, Nanomaterials
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Nano-Engineered Catalysts for Direct Methanol Fuel Cells

Small particle sizes and large surface areas can be produced economically and consistently.

Nano-engineered catalysts, and a method of fabricating them, have been developed in a continuing effort to improve the performances of direct methanol fuel cells as candidate power sources to supplant primary and secondary batteries in a variety of portable electronic products. In order to realize the potential for high energy densities (as much as 1.5 W•h/g) of direct methanol fuel cells, it will be necessary to optimize the chemical compositions and geometric configurations of catalyst layers and electrode structures. High performance can be achieved when catalyst particles and electrode structures have the necessary small feature sizes (typically of the order of nanometers), large surface areas, optimal metal compositions, high porosity, and hydrophobicity.

Posted in: Briefs, TSP, Materials, Catalysts, Fuel cells, Methanol, Fabrication, Nanotechnology
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Making More-Complex Molecules Using Superthermal Atom/Molecule Collisions

Atoms adsorbed on cold surfaces react with energetic impinging atoms.

A method of making more-complex molecules from simpler ones has emerged as a by-product of an experimental study in outer-space atom/ surface collision physics. The subject of the study was the formation of CO2 molecules as a result of impingement of O atoms at controlled kinetic energies upon cold surfaces onto which CO molecules had been adsorbed. In this study, the O/CO system served as a laboratory model, not only for the formation of CO2 but also for the formation of other compounds through impingement of rapidly moving atoms upon molecules adsorbed on such cold interstellar surfaces as those of dust grains or comets. By contributing to the formation of increasingly complex molecules, including organic ones, this study and related other studies may eventually contribute to understanding of the origins of life.

Posted in: Briefs, TSP, Materials, Carbon dioxide, Fabrication, Test procedures
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Improved Silica Aerogel Composite Materials

Shrinkage and cracking are greatly reduced.

A family of aerogel-matrix composite materials having thermal-stability and mechanical-integrity properties better than those of neat aerogels has been developed. Aerogels are known to be excellent thermal- and acoustic-insulation materials because of their molecular-scale porosity, but heretofore, the use of aerogels has been inhibited by two factors:

Their brittleness makes processing and handling difficult. They shrink during production and shrink more when heated to high temperatures during use. The shrinkage and the consequent cracking make it difficult to use them to encapsulate objects in thermal-insulation materials.
Posted in: Briefs, TSP, Materials, Composite materials, Materials properties
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Nematic Cells for Digital Light Deflection

Smectic A (SmA) prisms can be made in a variety of shapes and are useful for visible spectrum and infrared beam steerage.

Smectic A (SmA) materials can be used in non-mechanical, digital beam deflectors (DBDs) as fillers for passive birefringent prisms based on decoupled pairs of electrically controlled, liquid crystalline polarization rotators, like twisted nematic (TN) cells and passive deflectors. DBDs are used in free-space laser communications, optical fiber communications, optical switches, scanners, and in-situ wavefront correction.

Posted in: Briefs, TSP, Materials, Optics, Optics, Materials properties
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Precipitation-Strengthened, High-Temperature, High-Force Shape Memory Alloys

Shape memory alloys capable of performing up to 400 °C have been developed for use in solidstate actuator systems.

Shape memory alloys (SMAs) are an enabling component in the development of compact, lightweight, durable, high-force actuation systems particularly for use where hydraulics or electrical motors are not practical. However, commercial shape memory alloys based on NiTi are only suitable for applications near room temperature, due to their relatively low transformation temperatures, while many potential applications require higher temperature capability. Consequently, a family of (Ni,Pt)1–xTix shape memory alloys with Ti concentrations x ≤ 50 atomic percent and Pt contents ranging from about 15 to 25 at.% have been developed for applications in which there are requirements for SMA actuators to exert high forces at operating temperatures higher than those of conventional binary NiTi SMAs. These alloys can be heat treated in the range of 500 °C to produce a series of fine precipitate phases that increase the strength of alloy while maintaining a high transformation temperature, even in Ti-lean compositions.

Posted in: Briefs, TSP, Materials, Sensors and actuators, Sensors and actuators, Heat treatment, Alloys, Smart materials
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Heat-Storage Modules Containing LiNO3•3H2O and Graphite Foam

Heat capacity per unit volume has been increased.

A heat-storage module based on a commercial open-cell graphite foam (PocoFoam or equivalent) imbued with lithium nitrate trihydrate (LiNO3•3H2O) has been developed as a prototype of other such modules for use as short-term heat sources or heat sinks in the temperature range of approximately 28 to 30 °C. In this module, the LiNO3•3H2O serves as a phase-change heat-storage material and the graphite foam as thermally conductive filler for transferring heat to or from the phase-change material. In comparison with typical prior heat-storage modules in which paraffins are the phase-change materials and aluminum fins are the thermally conductive fillers, this module has more than twice the heat-storage capacity per unit volume.

Posted in: Briefs, Materials, Energy storage systems, Energy storage systems, Heating, ventilation, and air conditioning systems (HVAC), Heating, ventilation, and air conditioning systems (HVAC), Foams, Graphite
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Polymer-Based Composite Catholytes for Li Thin-Film Cells

It should be possible to increase charge capacities and cycle lives.

Polymer-based composite catholyte structures have been investigated in a continuing effort to increase the charge/ discharge capacities of solid-state lithium thin-film electrochemical cells. A cell according to this concept contains the following layers (see figure):

An anode current-collecting layer, typically made of Cu; An Li metal anode layer; A solid electrolyte layer of Li3.3PO3.8N0.22 (“LiPON”) about 1 to 2 μm thick; The aforementioned composite catholyte layer, typically about 100 μm thick, consisting of electronically conductive nanoparticles in an Li-ion- conductive polymer matrix; and A metallic cathode current collector, typically made of Mo and about 0.5 μm thick.
Posted in: Briefs, TSP, Materials, Battery cell chemistry, Battery cell chemistry, Composite materials, Lithium, Polymers
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Using ALD To Bond CNTs to Substrates and Matrices

CNT-based field emitters could be made more durable.

Atomic-layer deposition (ALD) has been shown to be effective as a means of coating carbon nanotubes (CNTs) with layers of Al2O3 that form strong bonds between the CNTs and the substrates on which the CNTs are grown. It should also be possible to form strong CNT/ substrate bonds using other coating materials that are amenable to ALD — for example, HfO2, Ti, or Ta. Further, it has been conjectured that bonds between CNTs and matrices in CNT/matrix composite materials could be strengthened by ALD of suitable coating materials on the CNTs.

Posted in: Briefs, Materials, Joining, Coatings Colorants and Finishes, Coatings, colorants, and finishes, Nanomaterials
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Alternating-Composition Layered Ceramic Barrier Coatings

These coatings are expected to be more durable, relative to prior thermal/environmental barrier coatings.

Ceramic thermal and environmental barrier coatings (T/EBCs) that contain multiple layers of alternating chemical composition have been developed as improved means of protecting underlying components of gas-turbine and other heat engines against both corrosive combustion gases and high temperatures. A coating of this type (see figure) is configured using the following layers:

An outer, or top oxide layer that has a relatively high coefficient of thermal expansion (CTE) and serves primarily to thermally protect the underlying coating layers and the low-CTE ceramic substrate structural material (the component that is ultimately meant to be protected) from damage due to exposure at the high temperatures to be experienced in the application; An inner, or bottom silicon-containing/ silicate layer, which is in contact with the substrate, has a low CTE and serves primarily to keep environmental gases away from the substrate; and Multiple intermediate layers of alternating chemical composition (and, hence, alternating CTE).
Posted in: Briefs, TSP, Materials, Thermal management, Thermal management, Ceramics, Chemicals, Coatings Colorants and Finishes, Coatings, colorants, and finishes, Engine mechanical components
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