Silica glasses viscosity

Reference Point Definition Viscosity (poise) 96% Si02 glass (°C) Soda-lime-silica glass (°C)... 

Sol-gel preparations of tetraethoxysilane can be spun into fibers once the appropriate viscosity has been achieved. These fibers are only slightly weaker than silica-glass fibers. 

Density. The density of transparent vitreous silica is approximately 2.20 g/cm3. Translucent and opaque glasses have lower densities owing to the entrapped bubbles. The density of translucent Vitreosil, for example, is 2.07—2.15 g/cm3 (87,119). The density of transparent vitreous silica decreases with increasing hydroxyl content and with lower fictive (glass structure equilibrium) temperatures. The fictive temperature depends on the thermal history and on glass viscosity (120). 

FIG. 33. Viscosity of alkali-—silica glasses after various authors (from Scholze, 1965). 

FIG. 34. The changes in temperature for viscosities of 10 and dPa s due to replacing Si02 by other oxides in sodium oxide-silica glass (after Gehlhoff and Thomas, 1926). 

FIG. 35. The time dependence of viscosity for soda-— lime—silica glass in the transformation range (Lillie, 1933). 

The liquidus curves in Fig. 38 indicate the reason why industrial soda-lime-silica glasses contain small amounts of AI2O3 the liquidus temperature is thus decreased into the higher viscosity region which is favourable for machine forming. 

Figure5.2 Log viscosity as a function of temperature of a soda-lime-silica glass.

HGURE 21.4 (a) Viscosity as a function of temperature (T) for several silicate glasses units of ii are dPa s. (b) Viscosity as a function of temperature (1/7) for the main glass-forming oxides. Notice the effect that a small amount of water has on the viscosity of silica glass. 

Continuous ceramic oxide fibers have low melt viscosities and very high crystallization propensities, and therefore cannot be readily obtained directly from a melt. Solid green or precursor fibers are obtained from solutions or dispersions, respectively, and they are converted into ceramic oxide fibers (Table I). In contrast, continuous silica glass fibers can be dry spun directly from a high viscosity melt or indirectly from a viscous sol-gel (Chapter 5). 

At temperatures below 1150°C, the viscosity of the silica glass is too high and it is unable to flow into any cracks that may develop. However, it is widely used in conjunction with B. 

Figure 8.4 Viscosity-temperature relation of a soda-lime-silica glass (19). Soda-lime-silica glass is one of the commonly used glasses for windows and other items.

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