FRAGILITY OF INORGANIC GLASSES AND ITS STRUCTURAL ORIGIN

摘要

Analysis of relaxation properties demonstrates that inorganic glasses can be divided into fragile (weak )and nonfragile (strong) glasses. The former include linear inorganic polymers such as vitreors selenium, and the latter include cross-linked silicon-oxygen glasses (silica and silicates). The fragility parameter D is found to correlate with the parameters T_0 and U∞:at D=0, the relaxation properties of the melt near Tg vary most rapidly, whereas D= ∞ corresponds to the lowest fragility glasses ,with Arrhenius behavior of relaxation properties, temperature-independent activation energy, and Vogel temperature T_0=0. Fragile glasses are characterized by significant brittleness and low strength because the molecular mobility responsible for the glass transition is fully suppressed below Tg and T_0 ≈Tg.This implies that the brittle temperature of highly fragile glasses coincides with the glass-transition temperature.