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change of a liquid into a glasslike state when the temperature is lowered. Vitrification occurs in plants and animals as well as in their isolated organs and tissues when they are abruptly chilled (below -20° C). Tissue thus frozen in an amorphous glasslike mass remains viable a long time; if carefully thawed, the vital activity of tis-sues and whole organisms can be restored.
the transition of a liquid to a solid glassy state as it is supercooled. In contrast to crystallization, where the liquid-crystal transition occurs in jumps at the melting point (Tmp) vitrification involves the conversion of melts of certain inorganic and organic substances (quartz, silicates, phosphates, borates, sulfur), which are undergoing cooling and a gradual increase in viscosity, to a solid state at the vitrification temperature (Tv). Upon vitrification, a liquid retains (inherits) the structural elements that characterized the liquid at temperatures above Tv.
With an increase in viscosity from 108to 1012newtons·sec/m2(l newton·sec/m2 = 10 poises) in the Tmp – Tv range, there is a continuous change in other physicochemical properties of the liquid being cooled. For example, the specific volume and conductivity in this range have smooth curves when plotted against temperature; the coefficient of thermal expansion and the index of refraction undergo changes in jumps.
|Table 1. Anomalous ranges of certain types of glass|
|Household glassware ...............||530||630|
|Optical F2 ...............||430||570|
|Vitreous silica ...............||1250||1250|
Because of the peculiarities of the changes in properties in the interval between Tmp and Tv, this range is described as anomalous. The plastic state is characteristic of various types of glass within this range (see Table 1), while the brittle state characterizes glass at temperatures below Tv.
N. M. PAVLUSHKIN