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High temperature dielectric properties of Apical, Kapton, Peek, Teflon AF, and Upilex polymers
Reliable lightweight systems capable of providing electrical power at the magawatt level are a requirement for future manned space exploration missions. This can be achieved by the development of high temperature insulating materials which are not only capable of surviving the hostile space environment but can contribute to reducing the mass and weight of the heat rejection system. In this work, Apical, Upilex, Kapton, Teflon AF, and Peek polymers are characterized for AC and DC dielectric breakdown in air and in silicone oil at temperatures up to 250 C. The materials are also tested in terms of their dielectric constant and dissipation factor at high temperatures with an electrical stress of 60 Hz, 200 V/mil present. The effects of thermal aging on the properties of the films are determined after 15 hours of exposure to 200 and 250 C, each. The results obtained are discussed and conclusions are made concerning the suitability of these dielectrics for use in capacitors and cable insulations in high temperature environments
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Apparatus to Determine the Heat Capacity and Thermal Conductivity of a Material From 1 to 300 K in Magnetic Fields Up to 9 T
Magnetic refrigeration is a new technology that potentially offers refrigeration efficiencies > 50% of Carnot, compactness, and high reliability. Studies indicate that approx. 35% of Carnot efficiency is generally the best that is now possible for gas compression/expansion systems and, at that, only for very large plants; for smaller machines, the fraction of Carnot efficiency can become very small, e.g., 1-W refrigerators generally operate at 2 to 8% of Carnot efficiency. For magnetic refrigerators, the compression/expansion processes are replaced by a cycle involving the application/removal of a magnetic field to either a paramagnetic or ferromagnetic material (generally, paramagnets are used below approx. 20K and ferromagnets above). The thermodynamic cycles in gas and magnetic systems are analogous. Central to the development of magnetic refrigerators is the characterization of magnetic working substances. Among the key properties for which we require data are the heat capacity (from which we derive the entropy) and the thermal conductivity as functions of temperature and magnetic field. Accordingly, at the Los Alamos National Laboratory, we have designed and constructed an apparatus to make measurements of these quantities over the range 1 to 300 K at fields up to 9 T. We describe the methodology of these measurements, the versatile apparatus for making them, and results on GdNi, the first sample measured
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