Pressure vitrification

Angell, C. A., and Qing, Z., Glass in a stretched state formed by negative-pressure vitrification ... 

The pressure vitrification process not only decreases the volume of the glass but it also depresses the mechanical and dielectric loss processes and increases the dielectric constant, compressive modulus and the compressive yield stress [3,11]. In addition to these changes in properties, glasses prepared under pressure exhibit time dependent changes in both the volume and enthalpy which are distinctly different from the thermal annealing... 

Sartori N, Richter K and Dobochet J 1993 Vitrification depth can be increased more than 10-foid by high pressure freezing J. Microsc. 172 55-61... 

The use of inorganic ion exchangers to solidify liquid radioactive waste followed by pressure sintering to produce a ceramic waste form appears to be a viable alternative to calcina-tion/vitrification processes. Both the process and waste form are relatively insensitive to changes in the composition of the waste feed. The stability of the ceramic waste form has been shown to be superior to vitrified wastes in leaching studies at elevated temperatures. Further studies on the effects of radiation and associated transmutation and the influence of temperature regimes associated with potential geologic repositories are needed for a more definitive comparison of crystalline and amorphous waste forms. 

Abstract—A theory is proposed of the behaviour of the hydrogen bonds in the course of vitrification caused by the decrease of temperature or the increase of pressure. This theory is based on the kinetical theory of vitrification developed earlier. It is shown that vitrification is connected with the freezing of the equilibrium between free and associated hydroxyl groups. s... 

The vitrification of liquids and polymers can be effected not only by the decrease of temperature but also by the increase of pressure [4]. Shishkin and Novak [5] obser ved the dependence of free hydroxyl concentration upon pressure. This effect can be described by Eq. (6) or (8) in the same way as the course of vitrification upon decreasing temperature. 

The hydrogen bonds play the most important role in the process of the vitrification of liquids and polymers. This process is characterized by the sharp increase of the relaxation times with the decrease of temperature or the increase of pressure and is determined in many systems by the existence of hydrogen bonds. 

An aspect that has not received enough attention is the influence of pressure on the vitrification curve (Chapter 10). For some processes that operate at very high pressures there is a significant shift of the vitrification curve to lower temperatures for example, in the processing of phenolic molding compounds, where the polymerization may be arrested by vitrification at much lower temperatures than those predicted using Tg vs conversion values determined at ambient pressure. 

The best evidence so far for the glassy nature of HDA was provided (1) by measurements of the dielectric relaxation time under pressure at 140 K [206, 251], (2) by the direct vitrification of a pressurized liquid water emulsion to HDA [252], and (3) by a high-pressure study of the glass >liquid transition using differential thermal analysis (DTA) [253], We note here that these studies probe structurally relaxed HDA (eHDA) rather than unrelaxed HDA. It is possible that structurally relaxed HDA behaves glass like, whereas structurally uHDA shows a distinct behavior. Thus, more studies are needed in the future, which directly compare structurally relaxed and unrelaxed HDA. 

The overfiring point represents that condition at which the clay shows excessive vitrification and softening under pressure. Most clays at this point begin to evolve gases which cause the structure to become vesicular or spongy. This state usually marks the end of the usefulness of the clay by itself. 

The properties of the JG relaxation discussed in Sections V.A-V.E call to mind the properties of the structural a-relaxation associated with vitrification. The properties discussed in Sections V.A, V.C, V.D, and V.E indicate that pressure P,... 

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