Vitrification

vitrification

[‚vi·trə·fə′kā·shən]

(engineering)

Heat treatment of a material such as a ceramic to produce a glazed surface.

(geology)

Formation of a glassy or noncrystalline material.

(medicine)

An experimental procedure for preserving human organs in which chemicals are added prior to cooling to prevent crystallization of water within and outside the cells, so that with coolings the molecules essentially become fixed in place.

Vitrification

 

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.

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Vitrification

 

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 (T_mp) 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 (T_v). Upon vitrification, a liquid retains (inherits) the structural elements that characterized the liquid at temperatures above T_v.

With an increase in viscosity from 10⁸to 10¹²newtons·sec/m²(l newton·sec/m² = 10 poises) in the T_mp – T_v 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
Glass	TV	Tmp
Window ...............	550	700
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 T_mp and T_v, 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 T_v.

N. M. PAVLUSHKIN

vitrification

Of a clay product, the condition resulting when kiln temperatures are sufficient to fuse grains and close the surface pores, making the mass impervious.