SOME COMMENTS ON THE THERMODYNAMIC ASPECTS OF GLASS-FORMATION IN FLUORIDE SYSTEMS

By contrast with oxide glasses, only BeF2 among the single fluorides v itrifies upon cooling. However, when two or more fluorides are mixed, glasses are formed more easily. The heavy metal fluoride glasses are t ypical examples. In the present paper correlations between viscosity, thermodynamics, glass stability and glass composition are discussed wi th special emphasis on ZrF4- and BeF2-based glasses. The molten fluori de mixtures are treated in terms of chemical thermodynamics which focu s on the enthalpy and entropy of mixing. Further, the glass formation is discussed in light of the thermodynamics of the solid state. The au thors believe that a better understanding of the equilibrium thermodyn amic properties of fluoride systems is helpful as a guideline for the development of new fluoride glass compositions, or when changes in gla ss compositions are needed.