Thermal properties electrical insulators

Electrical insulation Thermal properties Service temperature, F Fair Good Very good Good Fair to good... 

General-Purpose Polystyrene. Polystyrene is a high molecular weight M = 2 — 3 x 10 ), crystal-clear thermoplastic that is hard, rigid, and free of odor and taste. Its ease of heat fabrication, thermal stabiUty, low specific gravity, and low cost result in mol dings, extmsions, and films of very low unit cost. In addition, PS materials have excellent thermal and electrical properties that make them useful as low cost insulating materials (see Insulation, ELECTRIC Insulation, thermal). 

IEC 60216, Electrical insulating materials - Properties of thermal endurance, 1990-2001. 

The photocrosslinking of polymer materials continues to be attractive in many applications for electronic, electrical, insulation and property enhancements. iV-isopropylacrylamide with di-methylmaleinimidoacrylamide has been crosslinked to produce thermally sensitive nano-gels. These gels, made in micellar media, exhibited major changes in the hydrodynamic diameter in the vicinity of the phase-transition temperature of the polymer, with increases of temperature, micellar concentration and chromophore content all decreasing... 

Silicones appear in various compositions from thin fluids up to polymers that act as elastomers or thermosetting rigid plastomers. Silicones excel in weather durability, water repellency and in electrical and thermal properties. Silicone resins or coatings have heat-distortion temperatures up to 450 C. They are much used in aviation and the space industry as electrical insulation for motors, glue, protective coatings, a premium elastomer or as additives in construction. 

TABLE 6.2 Variation of Electrical and Thermal Properties of Coimnon Insulators as a Function of Temperature... 

DIN EN 60216 Electrical insulating materials — Properties of thermal endurance (lEC 60216) German version EN 60216... 

Composite bipolar plates are designed to provide high mechanical, electrical, and thermal properties by adding highly conducting fillers such as metals or carbon in an insulating base such as polymers. While metallic composites... 

Electrical Properties. Polytetrafluoroethylene is an excellent electrical insulator because of its mechanical strength and chemical and thermal stabihty as well as excellent electrical properties (Table 6). It does not absorb water and volume resistivity remains unchanged even after prolonged soaking. The dielectric constant remains constant at 2.1 for a temperature range of —40 to 250°C and a frequency range of 5 Hz to 10 GHz. 

Poly(phenylquinoxaline—arnide—imides) are thermally stable up to 430°C and are soluble in polar organic solvents (17). Transparent films of these materials exhibit electrical insulating properties. Quinoxaline—imide copolymer films prepared by polycondensation of 6,6 -meth5lene bis(2-methyl-3,l-benzoxazine-4-one) and 3,3, 4,4 -benzophenone tetracarboxyUc dianhydride and 4,4 -oxydianiline exhibit good chemical etching properties (18). The polymers are soluble, but stable only up to 200—300°C. 

PPQs possess a stepladder stmcture that combines good thermal stabiUty, electrical insulation, and chemical resistance with good processing characteristics (81). These properties allow unique appHcations in the aerospace and electronics industries (82,83). PPQ can be made conductive by the use of an electrochemical oxidation method (84). The conductivities of these films vary from 10 to 10 S/cm depending on the dopant anions, thus finding appHcations in electronics industry. Similarly, some thermally stable PQs with low dielectric constants have been produced for microelectronic appHcations (85). Thin films of PQs have been used in nonlinear optical appHcations (86,87). 

Cases can be classified as either hermetic or nonhermetic, based on their permeabiUty to moisture. Ceramics and metals are usually used for hermetic cases, whereas plastic materials are used for nonhermetic appHcations. Cases should have good electrical insulation properties. The coefficient of thermal expansion of a particular case should closely match those of the substrate, die, and sealing materials to avoid excessive residual stresses and fatigue damage under thermal cycling loads. Moreover, since cases must provide a path for heat dissipation, high thermal conductivity is also desirable. 

Highly desirable properties of PPS include excellent chemical resistance, high temperature thermal stabiUty, inherent flame resistance, good inherent electrical insulating properties, and good mechanical properties. 

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