Strong glass formers

Figure 2 Sketch of typical temperature dependencies of the viscosity r of glass-forming systems. The viscosimetric Tg of a material is defined by the viscosity reaching 1013 Poise. Strong glass formers show an Arrhenius temperature dependence, whereas fragile glass formers follow reasonably well a Vogel-Fulcher (VF) law predicting a diverging viscosity at some temperature T0.

Molten silica (SiO2) is often considered the prototypical strong glass former (Angell, 1988). Its density is relatively constant in the supercooled range (<1700°C), and in that range the Arrhenius form (39) provides a good description for A numerical fit for that viscosity leads to the results (Mackenzie, 1961)... 

For m>30 and Dj-kIO liquids are considered fragile whereas m<30 and Oj > 10 there are encountered to strong glass formers, with d5mamics closer to the Arrhenius pattern. In supercooled liquids at least two dynamical domains with the crossover at r(jg)< are considered. ... 

Fig. 1.10 Example of an Angell plot for typical glasses. Line a represents a strong glass former (m = 25), b represents a medium glass former (m = 50), and c represents a weak glass former...

Since the bonding network of both the crystalline and amorphous phases mostly consists of four-membered rings, it has been suggested that the crystallization should require few bonds breaking which would make the transformation particularly fast [13-15]. This has to be contrasted with the behavior of a strong glass former such as... 

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