Electrical properties 278 INDEX

Many grades of acetal resins are Hsted in Underwriters Eaboratories (UL) Kecogni d Component Directory. UL assigns temperature index ratings indicating expected continuous-use retention of mechanical and electrical properties. UL also classifies materials on the basis of flammability characteristics homopolymer and copolymer are both classified 94HB. 

The Underwriters Laboratories (UL) tests are recognized by various industries to provide continuous temperature ratings, particularly in electrical applications. These ratings include separate listings for electrical properties, mechanical properties including impact, and mechanical properties without impact. The temperature index is important if the final product has to receive UL recognition or approval. 

Electrically conductive rubber, 20 247 Electrically conductive resins, 7 7 840 Electrically stimulated drug delivery systems, 9 59-61, 81 Electrical mineral size reduction, 76 613 Electrical Patents Index (EPI), 18 222 Electrical properties... 

For the same grade with the same thickness, the three indices can be identical (for example, a polyethylene grade with a 50° C UL index temperature) or different (for example, a polyamide grade with a temperature index varying from 75°C for the electrical and mechanical properties, impact included, up to 105°C for the electrical properties only). 

The properties of polymers vary considerably, making the match between polymer and application a sort through such characteristics as density, tensile and impact strength, toughness, melt index, creep, elasticity, heat and chemical stability, electrical properties, flammability, and price. 

Highly pure lanthanum oxide is used to make optical glass of high refractive index for camera lenses. It also is used to make glass fibers. The oxide also is used to improve thermal and electrical properties of barium and strontium titanates. Other applications are in glass polishes carbon arc electrodes fluorescent type phosphors and as a diluent for nuclear fuels. In such apph-cations, lanthinum oxide is usually combined with other rare earth oxides. 

Carbon-fluorine bonds also have unusual electrooptical properties. Fluoropolymers are often used to provide favorable electrical properties such as low dielectric constants. The low dielectric constants are another consequence of the relatively low polarizability of C—F bonds. Polarizability a is related to index of refraction n through the following equation ... 

Fluorinated polymers are considered high value-added materials, due to their outstanding properties which open up various applications [1-9]. Such polymers exhibit high thermostability and chemical inertness, low refractive index and coefficient of friction, good water and oil repellence, low surface energy and valuable electrical properties. In addition, they are non-sticky and resistant to UV, ageing, and to concentrated mineral acids and alkalies. 

The interactions between the molecule and the environment can lead to distortions in the electrical properties due to the susceptibility of the molecules and the properties of the host matrix. The refractive index of the matrix acts as a screening factor, modifying the optical spectra and interaction between charges or dipoles embedded within it. Local field effects change the interaction with an electromagnetic field and should be considered along with orientation factors in the dipolar interaction. 

In view of the experimental difficulties a theory for radiation properties is desirable. The classical theory of electromagnetic waves from J.C. Maxwell (1864), links the emissivity e x with the so-called optical constants of the material, the refractive index n and the extinction coefficient k, that can be combined into a complex refractive index n = n — ik. The optical constants depend on the temperature, the wavelength and electrical properties, in particular the electrical resistivity re of the material. In addition, the theory delivers, in the form of Fresnel s equations, an explicit dependence of the emissivity on the polar angle / , whilst no dependence on the circumferential angle ip appears, as isotropy has been assumed. 

The two compounds which contain glass- and mineral-fillers provide the best arc resistance and tracking Index. All three materials provide a good balance of electrical properties. 

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