Glass-forming systems

The soda added to silica reacts with the O atoms at the comers of the SiO tetrahedra to break up the network, which lowers the melting temperature. This not only increases the glass forming ability but also lowers the processing cost. The calcia renders the glass insoluble in water, lliis is why soda-lime glasses are widely used for cheap glass products. 

Other additives to alter the properties of the glass are called intermediates. The addition of PbO to increase the index of refraction and to provide shielding from x-rays is an example. Aluminosilicate glasses are considerably stronger than soda-lime glasses and are used for reinforcing fibers, glass wool for insulation, as well as for optical applications. 

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Glass-forming systems other than siUca have been examined. The fraction of three- and four-coordinated boron in borate glasses can be determined by nmr (29). Both nmr and x-ray diffraction (30) results led to the suggestion that the boroxyl ring is the stmctural unit of vitreous The... 

H. Rawson, Inorganic Glass-Forming Systems, Academic Press, Inc., London, 1967. 

Carbonate Glasses. Carbonate glasses must be melted under moderate pressures to prevent the escape of carbon dioxide gas. The simplest carbonate glass forming system is K CO —MgCO. ... 

D.R. Uhlmann and NJ. Kiiedel. Glass Science and Technology, Vol. I (Glass forming systems). Academic Piess (1983) TP848 G56. 

Rawson, H. (1967). Inorganic Glass-Forming Systems, Chapter 2. London New York Academic Press. 

Fig. 6 DSC thermograms showing representative thermal transitions in frozen solutions. The top thermogram is for a mannitol solution and is characteristic of a metastable glass-forming system.

Figure 2 Sketch of typical temperature dependencies of the viscosity r of glass-forming systems. The viscosimetric Tg of a material is defined by the viscosity reaching 1013 Poise. Strong glass formers show an Arrhenius temperature dependence, whereas fragile glass formers follow reasonably well a Vogel-Fulcher (VF) law predicting a diverging viscosity at some temperature T0.

Let us now turn to a discussion of the relation of the temperature dependence of the polymer melt s configurational entropy with its glass transition and address the famous paradox of the Kauzmann temperature of glass-forming systems.90 It had been found experimentally that the excess entropy of super-cooled liquids, compared with the crystalline state, seemed... 

Before we examine in more detail the dynamics of a super-cooled melt of coarse-grained chains and of PB chains, respectively, let us first compare the structure of these two glass-forming systems. Structure is obtained experimentally from either the neutron or the X-ray structure factors. The melt (or liquid) structure factor is given as110... 

Partlow, D. E. and B. E. Yoldas. 1981. Colloidal versus polymer gels and monolithic transformation in glass forming systems. J. Non-Crystalline Solids 46 153-161. 

Fig. 4.1 a Typical time evolution of a given correlation function in a glass-forming system for different temperatures (T >T2>...>T ), b Molecular dynamics simulation results [105] for the time decay of different correlation functions in polyisoprene at 363 K normalized dynamic structure factor at the first static structure factor maximum solid thick line)y intermediate incoherent scattering function of the hydrogens solid thin line), dipole-dipole correlation function dashed line) and second order orientational correlation function of three different C-H bonds measurable by NMR dashed-dotted lines)... 

Up to date the only published work on the dynamic structure factor of a glass forming system at intermediate length scales is a study on PIB [147]. The NSE measurements explored the Q-range 0.20[Pg.136]

As had been found in the glass-forming systems, the predicted undercoolings for compounds could vary markedly both between various types alloy systems and between various competing phases in the same alloy system. 

A. A. Bobyshev, V. A. Radzig, in A. R. Silin (Ed.), Spectroscopy of Glass-Forming Systems, Latvian State University, Riga, 1988, p. 85. 

Figure 10. Nanocrystallization (a) hypothetical free energy composition diagram and (b) composition profile of a primary precipitate for an Fe based glass forming system.

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