Reproducible Growth of High-Quality Cubic-SiC Layers

Cubic SiC could be used to improve high-power and harsh-environment electronic devices.

Semiconductor electronic devices and circuits based on silicon carbide (SiC) are being developed for use in high-temperature, high-power, and/or high-radiation conditions under which devices made from conventional semiconductors cannot adequately perform. The ability of SiC-based devices to function under such extreme conditions is expected to enable significant improvements in a variety of applications and systems. These include greatly improved high-voltage switching for saving energy in public electric power distribution and electric motor drives; more powerful microwave electronic circuits for radar and communications; and sensors and controls for cleaner-burning, more fuel-efficient jet aircraft and automobile engines.

Posted in: Briefs, TSP, Materials, High voltage systems, Integrated circuits, Semiconductor devices, Switches, High voltage systems, Integrated circuits, Semiconductor devices, Switches, Silicon alloys, Durability, Durability

Nonlinear Thermoelastic Model for SMAs and SMA Hybrid

This model captures essential mechanics with fundamental engineering property input.

A constitutive mathematical model has been developed that predicts the nonlinear thermomechanical behaviors of shape-memory alloys (SMAs) and of shape- memory-alloy hybrid composite (SMAHC) structures, which are composite-material structures that contain embedded SMA actuators. SMAHC structures have been investigated for their potential utility in a variety of applications in which there are requirements for static or dynamic control of the shapes of structures, control of the thermoelastic responses of structures, or control of noise and vibrations. The present model overcomes deficiencies of prior, overly simplistic or qualitative models that have proven ineffective or intractable for engineering of SMAHC structures. The model is sophisticated enough to capture the essential features of the mechanics of SMAHC structures yet simple enough to accommodate input from fundamental engineering measurements and is in a form that is amenable to implementation in general-purpose structural analysis environments.

Posted in: Briefs, TSP, Materials, Mathematical models, Thermodynamics, Thermodynamics, Composite materials, Smart materials

Liquid-Crystal Thermosets, a New Generation of High-Performance Liquid-Crystal Polymers

Liquid-crystal polymers can now be used as resins in textile composites.

One of the major challenges for NASA's next-generation reusable-launch-vehicle (RLV) program is the design of a cryogenic lightweight composite fuel tank. Potential matrix resin systems need to exhibit a low coefficient of thermal expansion (CTE), good mechanical strength, and excellent barrier properties at cryogenic temperatures under load. In addition, the resin system needs to be processable by a variety of non-autoclavable techniques, such as vacuum-bag curing, resin-transfer molding (RTM), vacuum-assisted resin-transfer molding (VaRTM), resin-film infusion (RFI), pultrusion, and advanced tow placement (ATP).

Posted in: Briefs, Materials, Polymers, Refractory materials, Resins, Fuel tanks, Reusable launch vehicles and shuttles

Formulations for Stronger Solid Oxide Fuel-Cell Electrolytes

Alumina is added to yttria-stabilized zirconia.

Tests have shown that modification of chemical compositions can increase the strengths and fracture toughnesses of solid oxide fuel-cell (SOFC) electrolytes. Heretofore, these solid electrolytes have been made of yttria- stabilized zirconia, which is highly conductive for oxygen ions at high temperatures, as needed for operation of fuel cells. Unfortunately yttria-stabilized zirconia has a high coefficient of thermal expansion, low resistance to thermal shock, low fracture toughness, and low mechanical strength. The lack of strength and toughness are especially problematic for fabrication of thin SOFC electrolyte membranes needed for contemplated aeronautical, automotive, and stationary power-generation applications.

Posted in: Briefs, TSP, Materials, Solid propellants, Fabrication, Composite materials, Electrolytes, Durability, Durability

Making Carbon-Nanotube Arrays Using Block Polymers: Part II

A nanoscale phase separation would be utilized to form regularly spaced catalytic dots.

Some changes have been incorporated into a proposed method of manufacturing regular arrays of precisely sized, shaped, positioned, and oriented carbon nanotubes. Such arrays could be useful as mechanical resonators for signal filters and oscillators, and as electrophoretic filters for use in biochemical assays.

Posted in: Briefs, TSP, Materials, Fabrication, Biomaterials, Chemicals, Nanotechnology, Polymers

Rod/Coil Block Copolyimides for Ion-Conducting Membranes

Lithium cells and fuel cells could function over wider temperature ranges.

Rod/coil block copolyimides that exhibit high levels of ionic conduction can be made into diverse products, including dimensionally stable solid electrolyte membranes that function well over wide temperature ranges in fuel cells and in lithium-ion electrochemical cells. These rod/coil block copolyimides were invented to overcome the limitations of polymers now used to make such membranes. They could also be useful in other electrochemical and perhaps some optical applications, as described below.

Posted in: Briefs, TSP, Materials, Conductivity, Materials properties, Polymers

Processable Polyimides Containing APB and Reactive End Caps

Properties can be tailored through choice of proportions of dianhydrides and APB.

Imide copolymers that contain 1,3-bis (3- aminophenoxy) benzene (APB) and other diamines and dianhydrides and that are terminated with appropriate amounts of reactive end caps have been invented. The reactive end caps investigated thus far include 4-phenylethynyl phthalic anhydride (PEPA), 3-amino- phenoxy-4'- phenylethynyl benzophenone (3-APEB), maleic anhydride (MA), and 5-norbornene-2,3-dicarboxylic anhydride [also known as nadic anhydride (NA)]. The advantage of these copolyimides terminated with reactive groups, relative to other polyimides terminated with reactive groups, is a combination of (1) higher values of desired mechanical-property parameters and (2) greater ease of processing into useful parts.

Posted in: Briefs, TSP, Materials, Fabrication, Materials properties, Polymers

Liquid Coatings for Reducing Corrosion of Steel in Concrete

Structures could be protected more easily and less expensively.

Inorganic coating materials are being developed to slow or stop corrosion of reinforcing steel members inside concrete structures. It is much simpler and easier to use these coating materials than it is to use conventional corrosion-inhibiting systems based on impressed electric currents. Unlike impressed electrical corrosion-inhibiting systems, these coatings do not require continuous consumption of electrical power and maintenance of power-supply equipment. Whereas some conventional systems involve the use of expensive arc-spray equipment to apply the metallic zinc used as the sacrificial anode material, the developmental coatings can be applied by use of ordinary paint sprayers.

Posted in: Briefs, Materials, Energy conservation, Coatings Colorants and Finishes, Coatings, colorants, and finishes, Corrosion, Inorganic chemicals, Steel

Less-Toxic Coatings for Inhibiting Corrosion of Aluminum

It is no longer necessary to use highly toxic and carcinogenic chromates.

Two recently invented families of conversion- coating processes have been found to be effective in reducing or preventing corrosion of aluminum alloys. These processes offer less-toxic alternatives to prior conversion-coating processes that are highly effective but have fallen out of favor because they generate chromate wastes, which are toxic and carcinogenic. Specimens subjected to these processes were found to perform well in standard salt-fog corrosion tests.

Posted in: Briefs, Materials, Aluminum alloys, Coatings Colorants and Finishes, Coatings, colorants, and finishes, Corrosion

Organic/Inorganic Hybrid Polymer/Clay Nanocomposites

The exfoliation and dispersion of clay particles are improved.

A novel class of polymer/clay nanocomposites has been invented in an attempt to develop transparent, lightweight, durable materials for a variety of aerospace applications. As their name suggests, polymer/clay nanocomposites comprise organic/ inorganic hybrid polymer matrices containing platelet- shaped clay particles that have sizes of the order of a few nanometers thick and several hundred nanometers long. Partly because of their high aspect ratios and high surface areas, the clay particles, if properly dispersed in the polymer matrix at a loading level of 1 to 5 weight percent, impart unique combinations of physical and chemical properties that make these nanocomposites attractive for making films and coatings for a variety of industrial applications. Relative to the unmodified polymer, the polymer/clay nanocomposites may exhibit improvements in strength, modulus, and toughness; tear, radiation, and fire resistance; and lower thermal expansion and permeability to gases while retaining a high degree of optical transparency.

Posted in: Briefs, Materials, Product development, Coatings Colorants and Finishes, Coatings, colorants, and finishes, Composite materials, Nanomaterials, Polymers

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