On the theory of glass solidification

Abstract

The process of glass solidification is analyzed in the context of the fundamental principles of physicochemical kinetics. The concept of the emergence of "solidification seeds", formation of "solidification layers" and their migration into the glass volume are discussed. It is demonstrated that the level of diathermancy of tinted glasses can characterize the force of the interaction between the colorant complexes and the main silicon-oxygen elements in glass and, consequently, can influence viscosity variation in solidifying. The proposed theoretical principles agree well with experimental and industrial data.The critical factor in molding glass articles is the glass solidification rate, which depends on the combination of viscosity variation depending on temperature and temperature variation in time. As a rule, published works on the kinetics of glass solidification describe qualitative results of experiments related to different diathermancy of glasses determined by introduction of colorants [1]. The new concept of glass solidification is based on fundamental principles of physics and chemistry of melts and solids, taking into account the vitreous state and the factors of surface and volumetric interactions in glass technology processes [2].Cooling and solidification of a highly viscous glass melt in the formation of glass articles proceed due to a complex heat exchange with the ambient medium with participation of thermal conductance and radiation. One should bear in mind the following specifics of industrial glass molding:-highly viscous glass melt delivered for molding is not totally homogeneous chemically, thermally, and optically; -cooling of glass melt is nonuniform; this is especially true of processes involving molds where a highly viscous glass melt contacts a heat-removing surface at a limited number of points;-cooling and solidification of glass melt starts from the surface and extends into the glass volume;.Taking into account the above specifics of glass melt cooling, it can be assumed that viscosity variations are likely to be fragmentary, both on the surface (fast process) and inside the volume (slow process).The results of the study in [3] demonstrated that a granular structure is registered in glass in forming, with a "grain" size of 4 -8 mm, parallel to the mold surfaces. The crosssection of molded articles (perpendicular to the mold surfaces) has a laminar structure with layer thickness of 2 -4 mm. Thus, the glass solidification process in molding can be represented in two stages:-emergence of "solidification seeds" (local areas of glass with increased viscosity) and the formation of a "solidification layer"; -expansion of the "solidification layer" into the volume of glass.The formation of "solidification seeds" is governed by probabilistic processes; the theoretical principles of these processes are formulated in the works of A. N. Kolmogorov (1937), M. Avramy (1939), and B. V. Erofeev (1950. According to the basic principles of these studies, the solidification rate (viscosity variation w...

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