Small-angle X-ray scattering and scattering of visible light by phase-separated glasses

Abstract

Modern theory and the experimental method of small angle X-ray scattering (SAXS) permit one to find, without any a priori suppositions and with sufficient accuracy, a series of integral structural characteristics of the sub-micro-inhomogeneous (supra-molecular) structure of glass. The temperature dependence of the principal characteristics gives the possibility of describing the change of a glass structure during its heat treatment with great reliability. For example, the area of the geometrical surface separating two phases has been determined, and the change of the “bidispersive structure” with the heat treatment has been studied; it was thereby proved that the high dispersive structure is a result of the terminal velocity of cooling from high temperatures and that it also has a phase-separation nature (the secondary phase separation). Two methods—SAXS and scattering of visible light—have been used as experimental checks of the theory of spinodal decomposition, taking as an example sodium silicate glass, containing 12.5 % sodium oxide. Disagreement of the experimental results with the theoretical predictions has been found. This fact has been explained by the dependence of the diffusion coefficient and some other parameters upon the concentration which have been disregarded in the approximate variant of the theory. The main SAXS characteristics of the inhomogeneous glass structure have been defined, viz., the mean-square electron density fluctuation, the effective size and area of inhomogeneous regions and the distance between their centres.