Encyclopedia of Glass Science, Technology, History, and Culture. Группа авторов

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Valence Z Ionic distance for oxides, Å Coordination number Field strength, 1/Ų Bond strength, kJ/mol Function Si 4 1.60 4 1.57 443 Network formers: F~1.5–2.0 B 3 1.50 3 1.63 498 4 4 1.34 372 P 5 1.55 4 2.1 368–464 Ti 4 1.96 4 1.25 455 Intermediates: F~0.5–1.0 4 1.96 6 1.04 304 Al 3 1.77 4 0.96 335–423 3 1.89 6 0.84 224–284 Fe 3 1.88 4 0.85 3 1.99 6 0.76 Be 2 1.53 4 0.86 263 Zr 4 6 0.84 338 4 2.28 8 0.77 255 Mg 2 2.03 4 0.53 2 2.10 6 0.45 155 Network modifiers: F~0.1–0.4 Pb 2 6 0.34 310 2 2.74 8 0.27 151 Ca 2 2.48 8 0.33 134 Sr 2 2.69 8 0.28 134 Li 1 2.10 6 0.23 151 Na 1 2.30 6 0.19 84 K 1 2.77 8 0.13 54 Cs 1 12 0.10 42

Table 3 Hausdorff dimensionality of the bonding system at glass transition.

Amorphous material	Below Tg (glasses)	Above Tg (supercooled melts)
Broken bonds – configurons	0	2.5a
Chemical bonds backbone cluster	3	3
Chemical bonds	3	2.5a

      ^a Experimental dimensionality – 2.4–2.8.

      Most experimental T_g data have been obtained by differential thermal analysis (DTA), differential scanning calorimetry (DSC), or dilatometry [30], where T_g is generally defined as the temperature at which the tangents to the glass and liquid curves of the relevant property intersect (Chapter 3.2). Heating (cooling) rates for DTA/DSC measurements are typically as high as 10 K/min whereas they are in 3–5 K/min range in dilatometry. As already stated, the glass transition is not abrupt but typically occurs over a few tens of degrees. For not very high cooling rates (q), its dependence on q is given by the Bartenev–Ritland equation:

(11)

where a₁ and a₂

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