Soda-lime glasses viscosity

The viscosity of liquid silicates such as drose containing barium oxide and silica show a rapid fall between pure silica and 20 mole per cent of metal oxide of nearly an order of magnitude at 2000 K, followed by a slower decrease as more metal oxide is added. The viscosity then decreases by a factor of two between 20 and 40 mole per cent. The activation energy for viscous flow decreases from 560 kJ in pure silica to 160-180kJmol as the network is broken up by metal oxide addition. The introduction of CaFa into a silicate melt reduces the viscosity markedly, typically by about a factor of drree. There is a rapid increase in the thermal expansivity coefficient as the network is dispersed, from practically zero in solid silica to around 40 cm moP in a typical soda-lime glass. 

Fig. 3. Viscosity-temperature relationship of a typical commercial soda-lime glass...

We have chemically analyzed the glass spheres and from this estimated the viscosity at 800 and 850 C by means of the correlation equations of Lyon ( ) The range of viscosity thus obtained over the above temperature range is 6.3 X 10 to 2.9 X 10 poises. This is near the geometric mean of the viscosities at the softening and working temperatures of soda-lime glass ( ). 

Figure 6.18 (a) Viscosity versus temperature for a typical soda-lime glass and (b) plot of In (viscosity) versus... 

The temperature at which any glass reaches the requisite viscosity depends on its composition.] The variation of viscosity with temperature for a soda-lime glass is plotted in Figure 6.18(a). 

The viscosity of a soda-lime glass is given in Table 6.7. Estimate the glass transition temperature. 

Table 3.4-3 Average composition in wt% and viscosity data, for soda-lime glass, container glass, and Borofloat glass...

The U.S. Bureau of Mines has employed glass for forming ceramic materials at high temperatures (75). The viscosity curve for a soda—lime—siUca glass in Figure 19 indicates the high viscosity available at hot forming temperatures. 

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

N. H. Burlingame, A. K. Varshneya, and K. Freders, Viscosity Measurement of NIST Soda-Lime Standard 710A Glass Using a Parallel Plate Viscometer , Report to the Industry-University Center for Glass Research, Alfred University, Alfred, NY (1990). 

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. 

Fig. 2 Viscosity versus temperature characteristics for various glass compositions [7]. 1, Fused silica 2, 96% silica 3, soda lime (plate glass) 4, lead silicate (electrical) 5, high-lead 6, borosilicate (low expansion) 10. aluminosilicate...

A number of specific viscosities have been designated as reference points on the viscosity/temperature curve for melts. These particular viscosities have been chosen because of their importance in various aspects of commercial or laboratory processing of glass forming melts. Several other reference temperatures which occur at approximate viscosities are also routinely used by glass technologists. These reference points are summarized in Table 6.1, and are shown on a typical curve of viscosity versus temperature for a soda-lime-silica melt in Figure 6.1. 

Water diffusion and solubility have been measured for a wide range of glass compositions, including a number of studies for vitreous silica, alkali silicates and aluminosilicates, soda-lime-silicates, and alkali borates and germanates. Early models for diffusion suggested that the diffusivity of water in melts was controlled entirely by the viscosity of the melt, as predicted by the Stokes-Einstein equation. This equation predicts that the diffusivity of a spherical particle in a liquid is inversely proportional to the viscosity. This hypothesis has been shown to be quantitatively incorrect by 4 orders of magnitude, to predict a much... 

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