Densified glass

The concept of a single structural transition in amorphous material, i.e., an amorphous-amorphous transition, was coined in 1985 by Mishima et al. [25] on the example of water. Today, in many respects the nature of pressure- and/or temperature-induced transformations in glasses and amorphous solids remains unclear. In most cases, the pressure treatment of glasses and amorphous solids results in residual densification. In the process, the densified glasses and... 

The maximum densification of 18-20% is achieved after a pressure of 16-20 GPa—room temperature treatment or after 5-8 GPa—800-1000 K treatment. The densified glasses have predominantly tetrahedral coordination of silica atoms, Z 4-4.5 [14, 71, 88], Elastic moduli and optical characteristics of densified glasses are distinctly different from those of pristine silica glasses. 

Naoki, M. Mori, H. Owada, A., "Equation of State of Pressure-Densified Glasses of Poly(vinyl chloride)," Macromolecules, 14, 1567 (1981). 

In this chapter, I focus on works concerning the atomic structures of diaplectic glass and shock-wavc-densified glasses in order to understand the for-... 

In addition to temperature, pressure can also be introduced as a variable. Three types of volume-recovery experiments can be considered in which the pressure is different from, or is not maintained at, 1 bar. In the first, the temperature is stepped up or down at constant pressure but for pressures exceeding 1 bar in the second, the pressure is stepped at constant temperature and in the third, volume recovery is examined for densified glasses formed by compressing the liquid, cooling it to below Tg, and then releasing the pressure [Robertson et al., 1985]. For the first two... 

FIGURE 4.11 Paths for attaining equilibrium volume below the glass transition temperature at atmospheric pressure with densified glass. (Adapted from Robertson et al. [1985].)... 

In the computation of the volume-recovery curves in Figures 4.12 and 4.13, only thermal agitation, or Brownian motion, was assumed for the driving force for recovery. Stress field effects were not taken into account. However, the release of pressure from the densified glass is equivalent to an application of a negative pressure (i.e., an... 

Figure 6.124 shows for polystyrene cooled at atmospheric pressure the typical DSC trace of enthalpy relaxation for a sample cooled slowly and heated fast. This experiment represents the typical hysteresis or enthalpy relaxation described in Fig. 6.6. Carrying out the same DSC experiments with a pressure-densified glass instead of a slowly cooled glass leads to the much different response of the upper curves in Fig. 6.124. The beginning of the glass transition is shifted considerably...

Vg = glass specific volume V( = equilibrium volume of densified glass. The imrelaxed volume disappears at the glass-transition temperature. 

Grand S., Costa L. Lanthanide-doped Si02-Al203 aerogels and densified glasses. J. Non-Cryst. 

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