Quasi-equilibhum in silicate glasses

Abstract

Inhomogeneity in glasses detected as a composition fluctuation with a wavelength of about 0.1 to 1.0 mm is assumed to be an inherent property of common silicate glasses caused by the circumstances of glass melting. After a single-phased melt is formed from a heterogeneous system of raw materials the component diffusion decreases the inhomogeneity This process is slowed down and practically stopped when the so-called quasi-equilibrium has been reached. In this state the chemical potendal of a given i-th component is approximately constant, i.e. µi(x,y,z) ≈ const, instead of µi{x,y,z) ≈ const, for, at least, two components. While this equation is only valid for one or two (rarely more) fixed compositions, the former one allows the coexistence of all conceivable compositions within a given range. Thus, the inhomogeneity can be preserved, especially when a long wave fluctuation prevails. The effect of the inhomogeneity on the properties of glass is emphasized.