Glass Forming Melts

Figure 7.10. This figure shows the molar volume as a function of temperature for a glass forming melt being cooled. If the...

When compared with current liquids, crystallization processes in glass-forming melts are slowed down considerably by the high viscosity,which is the main reason for their ready undercooling to the glassy state. The rate of crystal growth is so low that within relatively short periods of time, glass fails to crystallize perceptibly even in cases when the melt contains nuclei or a phase boundary which may assume the function of the former. 

Mazurin O. V. et al., The Properties of Glasses and Glass-Forming Melts (in Russian), Part I—III., Nauka, Leningrad 1973, 1975, 1979... 

Most of the liquids obey Eq. (9.2) if the temperature interval is not too large. However, for glass-forming melts, the viscosity of which ranges from 1 Pa to 10 " Pa, the Vogel-Fulcher-Tamman equation is frequently used... 

Figure 2.16 Variation of volume of a simple glass forming melt along with that of the crystal. The cooling rate for curve a is higher than that for curve h (schematic).

Figure 2.17 Variation of Cp of a glass forming melt and a crystal.

The behavior of entropy and enthalpy of glass-forming melts is very similar. Discrete changes are observed at T in both enthalpy (A//) and entropy (A5) for the crystalline phase, but for the glass, a continuous change occurs at Tg with only a change of slope. 

MD has been used very effectively to elucidate vibrational spectra. Garofalini (1982) reported vibrational modes at 400, 800 and 1100 cm in vitreous Si02 compared to 450, 800 and 1050 cm observed in Raman and 465, 800 and 1100 cm observed in IR and 350, 800 and 1080 cm observed in inelastic neutron scattering. Experimental observation such as non-Newtonian behaviour of glass forming melts (Simmons et al., 1982), brittle fracture of Si02 (Ochoa et al., 1991) are only some of the other successful simulations using this powerful technique. 

Schaeffer HA (1984) Diffusion-controlled processes in glass forming melts. J Non-Ciystalline Sohds 67 19-33... 

High-Temperature Sensors for Oxidic Glass-Forming Melts.1155... 

Intrinsic Redox System of Oxidic Glass-Forming Melts. 1156... 

Study of Metal Electrodes in Nonisothermal Glass-Forming Melts. .. 1178... 

It was essential for the application of the cell for scientific and technical purposes to confirm its correct and reversible response with respect to the intrinsic redox system, Oj/O ", of glass-forming melts. Since, however, melts are open systems with respect to dissolved gases and standard melts with defined oxygen contents are not available, the correct functioning was verified on a thermodynamic basis [S]. 

The quantity (d Th,m/dr) in the integral of Equation (26-36) is defined standard Seebeck coefficient and is a characteristic property of a glass-forming melt. It is determined by means of zirconia microelectrodes (Figure 26-14), which eliminate temperature-dependent redox potentials inherently included in the emf if platinum electrodes were applied to these measurements [12]. The cell scheme for measuring standard Seebeck coefficients according to Figure 26-14 is... 

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