Fragile liquid

C. A. Angell, Strong and Fragile Liquids, in K. L. Ngai and G. B. Wright, (eds.) Relaxation in Complex Systems, Naval Research Laboratory, Washington, 1X7, 1984. 

Figure 12.7 Configurational space explored by a fragile liquid in the vicinity of the glass transition temperature (From Ref. 2).

Fig. 4. The strong-fragile classification of liquids. This Arrhenius plot differs from Fig. 3 in that the temperature is scaled with Eg. Strong liquids display Arrhenius behavior fragile liquids do not. (From Angell, 1988.)...

Angell, C. A., Structural instability and relaxation in liquid and glassy phases near the fragile liquid limit. J. Non-Cryst Sol. 102,205 (1988). 

Description of glass transition as an isoviscous phenomenon appears to be incorrect because in a variety of fragile liquids, the calorimetric Tg (t 100 s) occurs when the liquid viscosities are as low as 10 poises (see Chapter 9). 

A// near Tg and also small values of AQ, whereas in fragile liquids these quantities have large values. 

The first-type liquids have a good glass-forming ability, while the third-type liquids are poor glass-formers. Apparently, metallic melts belong to second-type liquids. Probably, the so-called strong liquids [6.88] are the first-type liquids, and fragile liquids are the second-type liquids. 

Liquids in the Y -A CX, system do not form glasses very easily, a feature that is not just coincidental with the polyamorphic transition [115-117], Poor glass-forming ability is a feature of fragile liquids and the polyamorphic transition in Y203-A1203... 

A basic feature of the response of fragile liquids to various perturbations is the pronounced nonexponential relaxation behavior. The relaxation function typically exhibits a two-step feature. The fast relaxation at short times is generally associated with vibrational degrees of freedom. The long-time decay of the relaxation function 4>(t), which is governed by the structural relaxation, can often be described by the stretched exponential or the Kohlrausch-Williams-Watts (KWW) function... 

Figure 32. Oxygen self diffusion in silieate glasses and liquids involving interaetion with network oxygen, redrawn from Lamkin et al. (1992). Note the similarity in diffusion rates within a given temperature range for a wide variety of eompositions, and the overall Z-shaped feature eharaeterizing the glass transition. The pronounced Z-shape occurs because of over-representation of fragile liquids, studied in the glass industiy, in the data set. Sources of the data for each line or curve ate in Table 4 (see Appendix), except for [5], which is from DiMarcello (1966).

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