Radiation-induced electrical property changes in polymeric solids
Radiation induced electric property changes in organic insulating polymeric solids
SOLIDS↗
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Process for the preparation of polycarboranylphosphazenes
A process for the preparation of polycarboranylphosphazenes is described. Polydihalophosphazenes are allowed to react at ambient temperatures for at least one hour with a lithium carborane in a suitable inert solvent. The remaining chlorine substituents of the carboranyl polyphosphazene are then replaced with aryloxy or alkoxy groups to enhance moisture resistance. The polymers give a high char yield when exposed to extreme heat and flame and can be used as insulation.
Allcock, H. R.↗
Improvements to the Synthesis of Polyimide Aerogels
Cross-linked polyimide aerogels are viable approach to higher temperature, flexible insulation for inflatable decelerators. Results indicate that the all-polyimide aerogels are as strong or stronger than polymer reinforced silica aerogels at the same density. Currently, examining use of carbon nanofiber and clay nanoparticles to improve performance. Flexible, polyimide aerogels have potential utility in other applications such as space suits, habitats, shelter applications, etc. where low dusting is desired
Meador, Mary Ann B.↗
Crosslinking of loose insulating powders
Described herein are materials and methods useful in the field of insulation, including building materials, refrigeration, cryogenics, and shipping, amongst others. Advantageously, the provided materials and method provide low thermal conductivities and increased mechanical strength, allowing for efficient insulating in a diverse range of applications. The provided materials and methods include individual particles connected by a polymer network that links individual particles and may include hollow or evacuated capsules and various strengthening agents.
Simpson, Lin Jay↗
Achieving Flat-on Primary Crystals by Nanoconfined Crystallization in High-Temperature Polycarbonate/Poly(vinylidene fluoride) Multilayer Films and Its Effect on Dielectric Insulation
To meet the stringent requirements of next-generation film capacitors for power electronics, multilayer films (MLFs) are fabricated with the advantage of achieving high temperature rating, high energy density, and reasonably low loss simultaneously. In this study, a high permittivity polar polymer, poly(vinylidene fluoride) (PVDF), is multilayered with a linear, low loss dielectric polymer such as high-temperature polycarbonate (HTPC). However, the dielectric loss of these MLFs was still high as compared with current state-of-the-art biaxially oriented polypropylene (BOPP) films. The goal of this work is to decrease the dielectric loss and enhance dielectric insulation by achieving flat-on primary PVDF crystals in MLFs via nanoconfined melt-recrystallization. Based on simultaneous small- and wide-angle X-ray scattering experiments, edge-on lamellar crystals were observed for all as-extruded MLFs, regardless of different PVDF layer thicknesses. However, after melting at 180 °C followed by recrystallization, flat-on primary crystals were successfully achieved when the PVDF layer thickness was below 39 nm. Above 78 nm for the PVDF layer, major edge-on primary crystals with minor flat-on secondary crystals were observed. Furthermore, from leakage current, breakdown, lifetime, and electric displacement-electric field loop studies, MLFs with the flat-on primary crystals exhibited reduced loss and enhanced dielectric insulation as compared to as-extruded MLFs and those with edge-on primary/flat-on secondary crystals. This was attributed to the effective blockage of charge carriers by the flat-on PVDF primary crystals and their reduced ferroelectric switching.
36 MATERIALS SCIENCE↗
Review of Current State of the Art and Key Design Issues With Potential Solutions for Liquid Hydrogen Cryogenic Storage Tank Structures for Aircraft Applications
Due to its high specific energy content, liquid hydrogen (LH2) is emerging as an alternative fuel for future aircraft. As a result, there is a need for hydrogen tank storage systems, for these aircraft applications, that are expected to provide sufficient capacity for flight durations ranging from a few minutes to several days. It is understood that the development of a large, lightweight, reusable cryogenic liquid storage tank is crucial to meet the goals of and supply power to hydrogen-fueled aircraft, especially for long flight durations. This report provides an annotated review (including the results of an extensive literature review) of the current state of the art of cryogenic tank materials, structural designs, and insulation systems along with the identification of key challenges with the intent of developing a lightweight and long-term storage system for LH2. The broad classes of insulation systems reviewed include foams (including advanced aerogels) and multilayer insulation (MLI) systems with vacuum. The MLI systems show promise for long-term applications. Structural configurations evaluated include single- and double-wall constructions, including sandwich construction. Potential wall material candidates are monolithic metals as well as polymer matrix composites and discontinuously reinforced metal matrix composites. For short-duration flight applications, simple tank designs may suffice. Alternatively, for longer duration flight applications, a double-wall construction with a vacuum-based insulation system appears to be the most optimum design. The current trends in liner material development are reviewed in the case that a liner is required to minimize or eliminate the loss of hydrogen fuel through permeation.
Mital, Subodh K.↗
Engineered Interfaces in Extruded Polyphenylsulfone-Boron Nitride Composite Insulation
Improving matrix-filler interactions is critical for optimizing dielectric performance in composite insulation; however, the technique used to introduce inorganic fillers into an organic matrix varies in its ability to satisfactorily reduce the size of cavities and interfaces. This study reports effects from changing the filler incorporation strategy on the rheology, dielectric performance and thermal conductivity of extruded polyphenylsulfone (PPSU) – hexagonal boron nitride (hBN) composite insulation. Depending on the technique used to introduce BN into the host matrix, the viscosity, torque, and melt viscosity temperature of the polymer were reduced, enabling better mixing, heat transfer, and smaller voids. This corresponded to an increase in dielectric strength compared to other formulations at either a similar or lower filler loading. On the other hand, the thermal conductivity in these specimens shifted further away from the thermal conductivity target of 1 W/m·K, which was an indication of a larger separation distance between the particles in samples with smaller interfaces. A trade-off between dielectric strength and thermal conductivity may exist when maximizing thermal conduction without sacrificing dielectric strength.
Polyphenylsulfone↗
Advancing high-temperature electrostatic energy storage via linker engineering of metal–organic frameworks in polymer nanocomposites
Linker engineering of the UiO-66-based metal–organic framework series reveals its untapped potential as nanofillers for boosting the heat-resistant electrostatic energy storage performance of polyetherimide at 200 °C.
Xie, Zongliang [Materials Sciences Division, Lawre↗
Heterogeneous Integration of Flipped Oxide Heterostructure Membranes for Nanoelectronics
Freestanding complex oxide membranes enable the release and transfer of epitaxial films, offering new design freedoms for next‐generation electronics. While the LaAlO 3 /SrTiO 3 (LAO/STO) heterostructure exhibits remarkable tunable conductivity at its interface, the active interface remains buried beneath the substrate, limiting access to this functionality. Here, we demonstrate how the LAO/STO heterostructure, in membrane form, can be flipped and precisely positioned on silicon and other platforms using polymer‐free micromanipulation. The transferred membranes preserve atomically smooth surfaces, high crystallinity, and key electronic properties. Through the 44‐nm insulating STO layer, ultra‐low‐voltage electron‐beam lithography (ULV‐EBL) writes conductive nanostructures at the now‐accessible STO/LAO interface, offering the potential to function as programmable local gates that modulate charge carriers in the underlying silicon. The platform establishes a general strategy for integrating complex oxide heterostructures with semiconductors, quantum materials, and flexible substrates, enabling new architectures for reprogrammable nanoelectronic devices.
36 MATERIALS SCIENCE↗
Performance of an ablator for Space Shuttle inorbit repair in an arc-plasma airstream
An ablator patch material performed well in an arc plasma environment simulating nominal Earth entry conditions for the Space Shuttle. Ablation tests using vacuum molded cones provided data to optimize the formulation of a two part polymer system for application under space conditions. The blunt cones were made using a Teflon mold and a state of the art caulking gun. Char stability of formulations with various amounts of catalyst and diluent were investigated. The char was found to be unstable in formulations with low amounts of catalyst and high amounts of diluent. The best polymer system determined by these tests was evaluated using a half tile patch in a multiple High Temperature Reusable surface Insulation tile model. It was demonstrated that this ablator could be applied in a space environment using a state of the art caulking gun, would maintain the outer mold line of the thermal protection system during entry, and would keep the bond line temperature at the aluminum tile interface below the design limit.
Stewart, D. A.↗
Fluorinated Poly(Phenylene Ether Ketones)
Fluorinated poly(phenylene ether ketones) are colorless, transparent, low-dielectric-constant, highly thermally stable polymers. Particularly suitable for use as film and coating materials in electronic and thermal-control applications such as; passivant insulating coats and interlevel dielectrics in microelectronic circuits, or as protective transparent coats on solar cells or mirrors. Solubility and transparency of 12F-PEK along with its lower dielectric constant and other properties make it more useful as dielectric film and coating material in many applications.
St. Clair, Anne K.↗
Vaporizable Scaffolds for Fabricating Thermoelectric Modules
A process for fabricating thermoelectric modules with vacuum gaps separating the thermoelectric legs has been conceived, and the feasibility of some essential parts of the process has been demonstrated. The vacuum gaps are needed to electrically insulate the legs from each other. The process involves the use of scaffolding in the form of sheets of a polymer to temporarily separate the legs by the desired distance, which is typically about 0.5 mm. During a bonding subprocess that would take place in a partial vacuum at an elevated temperature, the polymer would be vaporized, thereby creating the vacuum gaps.
Sakamoto, Jeffrey↗
Carboranylcyclotriphosphazenes and their polymers
Carboranyl-substituted polyphosphazenes are prepared by heat polymerizing a carboranyl halocyclophosphazene at 250 C for about 120 hours in the absence of oxygen and moisture. The cyclophosphazene is obtained by allowing a lithium carborane, e.g., the reaction product of methyl-o-carborane with n-butyllithium in ethyl ether, to react with e.g., hexachlorocyclotriphosphazene at ambient temperatures and in anhydrous conditions. For greater stability in the presence of moisture, the chlorine substituents of the polymer are then replaced by aryloxy or alkoxy groups, such as CF3CH2O. The new substantially inorganic polymers are thermally stable materials which produce a high char yield when exposed to extreme temperatures, and can thus serve to insulate less heat and fire resistant substances.
Allcock, H. R.↗
Making Conductive Polymers By Arc Tracking
Experimental technique for fabrication of electrically conductive polymeric filaments based on arc tracking, in which electrical arc creates conductive carbon track in material that initially was insulator. Electrically conductive polymeric structures made by arc tracking aligned along wire on which formed. Alignment particularly suited to high conductivity and desirable in materials intended for testing as candidate superconductors.
Daech, Alfred F.↗
Heating and Cooling Efficiency for Homes
Over 40 years ago, NASA developed Radiant Barrier technology to protect astronauts in the Apollo Program from temperatures that ranged from 250 F above to 400 F below zero Fahrenheit. This feat in temperature control technology enabled the astronauts to work inside the Apollo Command Module wearing short-sleeve shirts, with temperatures similar to those of a regular business office. The Radiant Barrier has been applied to virtually all spacecraft since then, including unmanned spacecraft with delicate instruments that need protection from temperature extremes. It is also applied to the astronauts space suits, protecting them during space walks. Made of aluminized polymer film, the Radiant Barrier both bars and lets in heat to maintain a consistent temperature in an environment where ordinary insulation methods will not suffice. The aluminization of the material provides a reflective surface that keeps more than 95 percent of the radiated energy in space from reaching the spacecraft s interior. In space suits, the thin and flexible material reflects the astronauts body heat back to them for warmth, while at the same time reflecting the sun s radiation away from them to keep them cool. Using conventional insulation, a space suit would have required a 7-foot-thick protective layer.
Source record↗
Mullite Whiskers and Mullite-whisker Felt
The Naval Surface Warfare Center has developed processes for the preparation of mullite (3(Al2O3)(dot)2(SiO2)) whiskers and mullite-whisker felt. Three patents on the technology were issued in 1990. The processes are based on chemical reactions between AlF3, Al2O3, and SiO2. The felt is formed in-situ during the processing of shaped powdered precursors. It consists of randomly oriented whiskers which are mutually intergrown forming a rigid structure. The microstructure and properties of the felt and size of the whiskers can be modified by varying the amount of Al2O3 in the starting mixture. Loose mullite whiskers can be used as a reinforcement for polymer-, metal-, and ceramic-matrix composites. The felt can be used as preforms for fabricating composite materials as well as for thermal insulation and high temperature, chemically stable filters for liquids (melts) and gases.
Talmy, Inna G.↗
Mechanically Strong, Polymer Cross-linked Aerogels (X-Aerogels)
Aerogels comprise a class of low-density, high porous solid objects consisting of dimensionally quasi-stable self-supported three-dimensional assemblies of nanoparticles. Aerogels are pursued because of properties above and beyond those of the individual nanoparticles, including low thermal conductivity, low dielectric constant and high acoustic impedance. Possible applications include thermal and vibration insulation, dielectrics for fast electronics, and hosting of functional guests for a wide variety of optical, chemical and electronic applications. Aerogels, however, are extremely fragile materials, hence they have found only limited application in some very specialized environments, for example as Cerenkov radiation detectors in certain types of nuclear reactors, aboard spacecraft as collectors of hypervelocity particles (refer to NASA's Stardust program) and as thermal insulators on planetary vehicles on Mars (refer to Sojourner Rover in 1997 and Spirit and Opportunity in 2004). Along these lines, the X-Aerogel is a new NASA-developed strong lightweight material that has resolved the fragility problem of traditional (native) aerogels. X-Aerogels are made by applying a conformal polymer coating on the surfaces of the skeletal nanoparticles of native aerogels (see Scanning Electron Micrographs). Since the relative amounts of the polymeric crosslinker and the backbone are comparable, X-Aerogels can be viewed either as aerogels modified by the templated accumulation of polymer on the skeletal nanoparticles, or as nanoporous polymers made by remplated casting of polymer on a nanostructured framework. The most striking feature of X-Aerogels is that for a nominal 3-fold increase in density (still a ultralighweight material), the mechanical strength can be up to 300 times higher than the strength of the underlying native aerogel. Thus, X-Aerogels combine a multiple of the specific compressive strength of steel, with the the thermal conductivity of styrofoam. X-Aerogels have been demonstrated with several polymers such as polyurethanes/polyureas, epoxies and polyolefins, while crosslinking of approximately 35 different oxide aerogels yields a range of dimensionally stable, porous lightweight materials with unique combinations of structural, magnetic and optical properties. The main theme in materials development for space exploration is multifunction. For example, use of one material for thermal insulation/structural component will free weight for useful payload. In that regard, X-aerogels are evaluated at NASA for cryogenic fuel storage tanks and for spacesuits. Along the same lines, major impact fro X-Aerogels is also expected in commercial applications for thermal/acoustic insulation, in catalytic reformers and converters, in filtration membranes and membranes for fuel cells, as platforms for optical, electrical and magnetic sensors, and as lightweight structural component for aircraft and satellites.
Leventis, Nicholas↗
Improved Thermal Design of a Compression Mold
A compression tool used to make 1-in. (2.5-cm) diameter disks of high-temperature polymers was designed to be shorter and of larger diameter than conventional tools to reduce heat loss to the surrounding air, thus making more efficient use of applied heat. This system is less sensitive to the amount and quality of insulation than previous tools, provides more repeatable processing, and improves the quality of the samples produced. These improvements come without increasing the weight of the punch portion of the tool over that of a conventional version, an important quality when handling lower-viscosity resins. In use, the base and body of the tool are assembled, and the polymer to be processed is placed into the body of the tool. The punch is inserted, and the assembled tool is placed into the press. A temperature/ pressure profile appropriate to the nature of the polymer is applied. A series of computational and experimental runs were made using a conventional tool to validate the computational model. The new tool design was then modeled, and when the performance showed a marked improvement, the new tool was manufactured. A new series of experimental runs showed that the thermal performance of the new tool agreed well with model predictions.
Kuczmarski, Maria A.↗