Constants of Glasses

The Verdet constant of glasses varies linearly with concentration for mixtures of different rare earth ions. Since positive Verdet constants can be obtained for glasses containing Yb, Gd, or Sm, it is possible to produce glasses with a Verdet eonstant of exaetly zero by the appropriate choice of composition. 

The dielectric constant of glass-reinforced polystyrene, FEP, polypropylene, polyacetal, and modified PPO resins are relatively unaffected by frequencies of 60-10 Hz. Significant increases in dielectric constant are noted with the addition of flame retardants. ... 

Flgu re 5.369 Influence of moisture on loss factor tan 6 and dielectric constant of glass fiber-reinforced molding material, exposure at room temperature and 93% relative humidity, sheet thickness 1 mm, measurement frequency 50 Hz Curve I hot curing agent, quartz powder 150wt.%... 

Temperature. The dielectric constant of glass increases with rising temperature in proportion to the polarizability of the medium. When stability of the dielectric properties is required, glasses with rigid structures, e.g., fused silica and high-siUca glasses, are used. 

Frequency. The dielectric constant of glass decreases very slightly with increasing frequency (see Fig. 2.36). At frequencies above 50 Hz, the relatively long relaxation times typical of sihcate glass structures prevents an increase in the dielectric constant. Table 2.9 lists the dielectric constants at several frequencies for a number of commercial glasses. 

Insulator Dielectrics. Insulator thick film dielectrics are multiphase materials. The electronic, ionic, and interfacial polarization mechanisms all contribute to the dielectric constant of glass-ceramic materials. Electronic polarization is directly proportional to the density of electrons in the glass-ceramic. Thus, dielectrics based on glasses containing oxides of high atomic number elements (e.g., lead) or high density exhibit high dielectric constants. 

Dielectric Constants of Glasses, 12-56 Dielectric Strength of Insulating Materials,... 

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