Glasses dielectric properties

The dielectric properties of polar materials will depend on whether or not the dipoles are attached to the main chain. When they are, dipole polarisation will depend on segmental mobility and is thus low at temperatures below the glass transition temperatures. Such polymers are therefore better insulators below the glass temperature than above it. 

A recent competitor to CVD in the planarization of silicon dioxide is the sol-gel process, where tetraethylorthosilicate is used to form spin-on-glass (SOG) films (see Appendix). This technique produces films with good dielectric properties and resistance to cracking. Gas-phase precipitation, which sometimes is a problem with CVD, is eliminated. 

An alternative electrical method that has been used in the study of glass-ionomer cements has been the measurement of dielectric properties. Tay Braden (1981, 1984) measured the resistance and capacitance of setting cements at various times from mixing. From the results obtained, relative permittivity and resistivity were calculated. In general, as these cements set, their resistivity was found to fall rapidly, then to rise again. Both these results and the results of relative permittivity measurements were consistent with the cements comprising highly ionic and polar structures. 

Tay, W. M. Braden, M. (1981). Dielectric properties of glass-ionomer cements. Journal of Dental Research, 60, 1311-14. 

The Hamaker constant A can, in principle, be determined from the C6 coefficient characterizing the strength of the van der Waals interaction between two molecules in vacuum. In practice, however, the value for A is also influenced by the dielectric properties of the interstitial medium, as well as the roughness of the surface of the spheres. Reliable estimates from theory are therefore difficult to make, and unfortunately it also proves difficult to directly determine A from experiment. So, establishing a value for A remains the main difficulty in the numerical studies of the effect of cohesive forces, where the value for glass particles is assumed to be somewhere in the range of 10 21 joule. 

D-glass with high dielectric properties, transparent to electromagnetic waves. The principal applications relate to the manufacture of radomes, electromagnetic windows and high-tech printed circuit boards. 

Glass fibers are the most common reinforcing fiber due to their excellent combination of mechanical properties, dielectric properties, thermal stability and relatively low cost. As a result, there are many different types of silicate glass fibers, all with varying properties designed for various applications (see Table 1.32). The majority... 

Many of the fundamental relationships and concepts governing the electrical properties of materials have been introduced in the previous section. In this section, we elaborate upon those topics that are more prevalent or technologically relevant in ceramics and glasses than in metals, such as electrical insulation and superconductivity, and introduce some topics that were omitted in Section 6.1.1, such as dielectric properties. 

Dielectric Properties of Glass-Fiber-Reinforced Polymers. As... 

The most noticeable difference between syntactic foams with the same filler but different binders is seen in the tangent of the dielectric loss angle (Table 25)11(. If glass microspheres replace organosilicon ones for the same binder, not only tan 8, but also e decrease 1). But also the dielectric properties and the concentration of the binder affect the final foam s e (Fig. 18) n). 

Table 25. Dielectric properties of syntactic foams with glass microspheres111 ...

Table 26. Superhigh-Frequency Dielectric Properties of Epoxy Syntactic Foams using Glass Microspheres...

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