Encyclopedia of Glass Science, Technology, History, and Culture. Группа авторов. Читать онлайн. Newlib. NEWLIB.NET

Автор: Группа авторов
Издательство: John Wiley & Sons Limited
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Жанр произведения: Техническая литература
Год издания: 0
isbn: 9781118799499
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rel="nofollow" href="#ulink_c09cff21-980f-5c59-bbcd-4335aec64f7e">Figure 3 Viscosity–temperature relationship of different glass‐forming systems; pure metallic melts of Ag and Fe are displayed for comparison.

      (2)equation

      where A, B, and T0 are empirical fit constants and T is expressed here in °C. The float glass DGG‐1 included in Figure 3 is a certified viscosity standard whose VFT equation has been derived from 44 measurement points. These are reproduced with the parameters A = −1.601, B = 4330.9, and T0 = 246.1 (η in dPa·s) with a standard deviation of δlog η = ± 0.16, illustrating that the VFT equation is a valuable tool for any technological purpose.

      Viscosities are in addition an indicator of crystallization tendency at the liquidus temperature Tliq, which is shown in Figure 3 on the viscosity curves. Melts with log η(Tliq) < 2.0 tend to crystallize quickly, thus requiring very high cooling rates, whereas melts with η(Tliq) > 4.0 may in contrast be vitrified at moderately low cooling rates.

      (3)equation

      where y(j) is the weight fraction of oxide j.


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Oxide j Viscosity Elastic properties
a(j) for Validity range (wt %) V(j) (cm3/mol) U(j) (GPa)
T(2.0) (°C) T(4.0) (°C) T(6.0) (°C)
SiO2 1847.80 1249.70 962.90 28.0 64.5
TiO2 −4.00 −4.00 −4.00 29.2 86.7
ZrO2 8.65 7.96 8.16 0–8b 30.2 97.1
Al2O3 8.32 5.23 4.01 0–8a 42.8 134.0
B2O3 −21.62 −11.97 −6.42 0–14a 41.6 77.8
‐ “‐ 0.5122 0.3182 0.1900
MgO −5.87 −0.12 0.91 0–6a 15.2 83.7
CaO −11.27 −3.99 −0.74 4–13a 18.8 64.9
BaO −5.67 −3.04 −1.88 0–17b 26.2 40.6