Viscosity technical glasses

Fig. 3.4-13 Viscosity-temperature curves for some important technical glasses. 1, fused silica 2, 8405 3, 8330 4, 8248 5, 8350 6, 8095 7, 8465. Glasses with steep gradients (such as 7) are called short glasses, and those with relatively shallow gradients (such as 4) are called long glasses...

Experimental measures of molecular mobility within glasses have proven technically difficult because of the long time spans required. General behavior is described by the Vogel-Tamman-Fulcher (VTF) Model, valid for temperatures near Tg, where viscosity increases in a double exponential relationship with decreasing temperature (Angell, 1991) ... 

By incorporating fluorine, Beall (1991) managed to develop new crystal phases that could not be formed in the pure ternary system. In addition, it was relatively easy to melt glasses of this composition, since the viscosity curve was approximately 150 C lower than that of technical soda-lime silicate bulk glass. 

Fragile polymeric materials, since they exhibit larger and quicker changes, particularly of their viscosity, near Tg, are excellent prototype systems for the experimental investigation of the glass transition. From the point of view of technical applications, these compounds are very suitable to develop heating-based nanofabrication processes, including many methods used to produce nanofibers. In particular, as is well known the simplest model that one can... 

Technically, a glass is a material that can be cooled from the melt without crystallizing. Since it does not crystallize, there is no distinct melting point. Instead, the viscosity... 

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