Materials & Coatings

Increasing Durability of Flame-Sprayed Strain Gauges

Low-oxygen heat treatments and internal platinum oxygen-diffusion barriers extend lifetimes.

Thermally sprayed dielectric ceramic coatings are the primary means of attaching strain and temperature gauges to hot-section rotating parts of turbine engines. As hot-section temperatures increase, lifetimes of installed gauges decrease, and seldom exceed one hour above 2,000 °F ( ≈1,100 °C). Advanced engine components are expected to operate at temperatures approaching 2,200 °F ( ≈1,200 °C), and the required high-temperature lifetime is 10 hours minimum.

Posted in: Briefs, Materials, Ceramics, Coatings, colorants, and finishes, Gas turbines, Test equipment and instrumentation

Multifunctional, High-Temperature Nanocomposites

Electrical and thermal conductivities increase with proportions of nanotubes.

In experiments conducted as part of a continuing effort to incorporate multifunctionality into advanced composite materials, blends of multi-walled carbon nanotubes and a resin denoted “PETI-330” (wherein “PETI” is an abbreviation for “phenylethynyl- terminated imide”) were prepared, characterized, and fabricated into moldings. PETI-330 was selected as the matrix resin in these experiments because of its low melt viscosity (<10 poise at a temperature of 280 °C), excellent melt stability (lifetime >2 hours at 280 °C), and high temperature performance (>1,000 hours at 288 °C). The multi-walled carbon nanotubes (MWCNTs), obtained from the University of Kentucky, were selected because of their electrical and thermal conductivity and their small diameters. The purpose of these experiments was to determine the combination of thermal, electrical, and mechanical properties achievable while still maintaining melt processability.

Posted in: Briefs, TSP, Materials, Product development, Molding, Composite materials, Conductivity, Nanomaterials, Resins

Multilayer Impregnated Fibrous Thermal Insulation Tiles

Temperature rises are limited by transpiration cooling.

The term “secondary polymer layered impregnated tile” (“SPLIT”) denotes a type of ablative composite-material thermal- insulation tiles having engineered, spatially non-uniform compositions. The term “secondary” refers to the fact that each tile contains at least two polymer layers wherein endothermic reactions absorb considerable amounts of heat, thereby helping to prevent overheating of an underlying structure. These tiles were invented to afford lighter-weight alternatives to the reusable thermal-insulation materials heretofore variously used or considered for use in protecting the space shuttles and other spacecraft from intense atmospheric- entry heating. Tiles of this type could also be useful on Earth as relatively lightweight components of fire-retardant structures.

Posted in: Briefs, TSP, Materials, Composite materials, Insulation, Polymers, Lightweighting, Rescue and emergency vehicles and equipment, Spacecraft

Accounting for Uncertainties in Strengths of SiC MEMS Parts

Fracture strength of a part can be predicted as one statistical distribution.

A methodology has been devised for accounting for uncertainties in the strengths of silicon carbide structural components of microelectromechanical systems (MEMS). The methodology enables prediction of the probabilistic strengths of complexly shaped MEMS parts using data from tests of simple specimens. This methodology is intended to serve as a part of a rational basis for designing SiC MEMS, supplementing methodologies that have been borrowed from the art of designing macroscopic brittle material structures.

Posted in: Briefs, TSP, Materials, Finite element analysis, Microelectromechanical devices, Prognostics, Materials properties, Silicon alloys

Lithium Dinitramide as an Additive in Lithium Power Cells

This inorganic additive appears to act as a superior SEI promoter.

Lithium dinitramide, LiN(NO2)2 has shown promise as an additive to nonaqueous electrolytes in rechargeable and non-rechargeable lithium-ion-based electrochemical power cells. Such non-aqueous electrolytes consist of lithium salts dissolved in mixtures of organic ethers, esters, carbonates, or acetals. The benefits of adding lithium dinitramide (which is also a lithium salt) include lower irreversible loss of capacity on the first charge/discharge cycle, higher cycle life, lower self-discharge, greater flexibility in selection of electrolyte solvents, and greater charge capacity.

Posted in: Briefs, Materials, Battery cell chemistry, Lithium-ion batteries

Ion-Conducting Organic/Inorganic Polymers

Properties can be tailored through a choice of starting alkoxysilane and diamine ingredients.

Ion-conducting polymers that are hybrids of organic and inorganic moieties and that are suitable for forming into solidelectrolyte membranes have been invented in an effort to improve upon the polymeric materials that have been used previously for such membranes. Examples of the prior materials include perfluorosulfonic acid-based formulations, polybenzimidazoles, sulfonated polyetherketone, sulfonated naphthalenic polyimides, and polyethylene oxide (PEO)-based formulations. Relative to the prior materials, the polymers of the present invention offer greater dimensional stability, greater ease of formation into mechanically resilient films, and acceptably high ionic conductivities over wider temperature ranges. Devices in which films made of these ion-conducting organic/ inorganic polymers could be used include fuel cells, lithium batteries, chemical sensors, electrochemical capacitors, electrochromic windows and display devices, and analog memory devices.

Posted in: Briefs, TSP, Materials, Performance upgrades, Conductivity, Materials properties

MoO₃ Cathodes for High-Temperature Lithium Thin-Film Cells

Cycle lives of these cathodes exceed those of LiCoO2 and LiMn2O4 cathodes.

MoO3 has shown promise as a cathode material that can extend the upper limit of operating temperature of rechargeable lithium thin-film electrochemical cells. Cells of this type are undergoing development for use as energy sources in cellular telephones, wireless medical sensors, and other, similarly sized portable electronic products. The LiCoO2 and LiMn2O4 cathodes heretofore used in these cells exhibit outstanding cycle lives (of the order of hundreds of thousands of cycles) at room temperature, but operation at higher temperatures reduces their cycle lives substantially: for example, at a temperature of 150 °C, cells containing LiCoO2 cathodes lose half their capacities in 100 charge/discharge cycles.

Posted in: Briefs, TSP, Materials, Battery cell chemistry, Lithium-ion batteries, Thermal testing

Elastic Memory Composite Hinges Tested on Shuttle

TEMBO® Elastic Memory Composite Hinges (EMCH) Composite Technology Development (CTD) Lafayette, CO 303-664-0394

Elastic Memory Composite Hinges (EMCH) were developed by CTD for deploying solar arrays, communications, and optical systems in space. They are designed to drive and dampen the deployment of a structure and hold the structure firmly at the end of deployment with no dead band. Combining carbon fiber reinforcement and shape-memory polymers, the hinges are constructed of TEMBO® composites, which replace complex mechanical deployment systems with lighter ones.

Posted in: Application Briefs, Materials, Composite materials, Smart materials, Parts, Reusable launch vehicles and shuttles

Progressive Failure Analysis of Composite Structures with FEA Software

A combination of analysis programs simulates the stochastic nature of fiber breakage in composites.

The Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) is core technology in a software suite called ImMAC, developed at NASA’s John Glenn Research Center. An abbreviation for Integrated Multiscale Micromechanics Analysis Code, ImMAC is used in the design and analysis of advanced composite structures.

Posted in: Briefs, Materials, Finite element analysis, Computer software and hardware, Microelectromechanical devices, Composite materials

Ceramic Paste for Patching High-Temperature Insulation

Repairs can be performed by use of simple techniques.

A ceramic paste that can be applied relatively easily, either by itself or in combination with one or more layer(s) of high temperature ceramic fabrics, such as silicon carbide or zirconia, has been invented as a means of patching cracks or holes in the reinforced carbon-carbon forward surfaces of a space shuttle in orbit before returning to Earth. The paste or the paste/fabric combination could also be used to repair rocket-motor combustion chambers, and could be used on Earth to patch similar high-temperature structures.

Posted in: Briefs, Materials, Maintenance, repair, and service operations, Ceramics, Fabrics, Insulation, Reusable launch vehicles and shuttles

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