Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 286

According to PCT, a glass can be formed if and only if it can exist as a TD network (i.e. only if f ≥ 0). With increasingly positive values of f, however, the existing TD network becomes progressively more floppy and may crystallize beyond a certain value f(q) that depends on the cooling rate, q. Thus, glass formation is possible in the range for which 0 ≤ f ≤ f(q). With positive and increasing f, the potential energy of interaction (the chemical energy) increases because of unsatisfied chemical bonds. With decreasing and negative f, the strain energy in the system increases. In other words, an isostatic network represents a minimum in the total energy of the system. For this reason, the glass‐forming ability is best under isostatic condition (f = 0) and becomes poor as f increases. The f = 0 boundary is termed the isostatic boundary of glass formation and the f(q) boundary the kinetic boundary of glass formation.