Vogel-Tamann-Fulcher

The experimentally established viscosity curve of the Si02 Al203-Mg0-Na20-K20-F glass (Fig. 1-42) was adapted according to a regression analysis of the Vogel-Fulcher-Tamann equation that corresponds to the values A = -2.105 B = 6780 and = 177.9°C. 

Figure 1-42 Viscosity of the SiOj-AlgOg-MgO-NagO-I O-F glass as a function of the temperature. The circles represent experimental datas and the curve was calculated after the Vogel-Fulcher-Tamann equation.

The temperature dependence of a structural relaxation process is in some cases of the Arrhenius type like in the case in 1,5-pentanediol. Very often we observe, however, a much stronger dependence especially at low temperatures. This has been succes-fully described by the Vogel-Fulcher-Tamann (VFT) equation involving an additional parameter, the T temperature, which is related to the glass temperature T °... 

Glass Formation and Glassy Behavior Vogel/ Fulcher/" Tamann and (VFTH) equation... 

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