Strong and Fragile Liquids

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. 

Angell CA (1985) Strong and fragile liquids in relaxations in complex systems. In Nagai K, Wright GB (eds) National Technical Information Service, US Department of Commerce, p 1... 

The concept of fragility is a qualitative one and is related to deviations of the relaxation time of a liquid from Arrhenius-like behavior and to the topology of the potential energy landscape of the system. The classification of liquids into strong and fragile thus provides a fundamental framework for quantitatively describing equilibrium and dynamical properties of supercooled liquids and glassy states of matter [1-6,8,9,22,37,38,52,54—56,88-91,103]. 

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. 

Angell C, Scamehom C, Phifer C, Khadiyala R, Cheeseman P (1982) Pressure enhancement of ion mobilities in liquid silicates from computer simulation studies to 800 kilobars. Science 218 885-887 Angell C (1985) Strong and fragile hquids. In Ngai K, Wright G (eds) Relaxation in complex systems. 

Senapati U. and Varshne3ra A. K., Viscosity of chalcogenide glassforming liquids an anomaly in the strong and fragile classification./. 

Figure 10.3 Viscosities of a variety of glass-forming systems as a function of reduced reciprocal temperature (Kelvin) Tg/r, where 7g is defined as the temperature when the viscosity t = 10 Pas. The difference in temperature-dependent behaviour between strong and fragile glass-forming liquids is clear (8).

Figure 4.5 Viscosity versus inverse temperature for glass-forming liquids, showing behavior classified as strong, typified by open tetrahedral networks, to fragile, typical of ionic and molecular liquids. Here Tg is defined by the criterion that nlT ) = 10 P. For most of the liquids, the viscosities seem to extrapolate to a common value of around 10" P at high temperatures, corresponding to a fundamental molecular vibrational frequency of around 10 sec-i. (Reprinted from J. Non-Cryst. -Solids, 73 1, Angell (1985), with kind permission from Elsevier Science—NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.)...

It describes the temperature dependence of viscosity in an undercooled liquid, where rjo and are constants, and D is the fragility parameter. Undercooled liquids with large D values (>50) are referred to as strong , and those with low D values (<10) as fragile . Molecular mobility behaves in a similar way and t, the mean relaxation time, may also be described in a similar fashion ... 

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