Nano and microcrystallites of KSbOSiO4 in glass matrix as a source of internal strain and fatal corrosion of historic turquoise glass

Abstract

Investigating long-term fatal corrosion of turquoise lead-potassium historic glass beads, we have detected micro and nano crystallites of orthorhombic KSbOSiO 4 (KSS) in glass. We have come to conclusion that KSS precipitates and their clusters give rise to internal glass corrosion. K and Sb being glass dopants form KSS crystallites during glass melt cooling; tensile strain arising in the glass matrix during cooling gives rise to glass cracking and eventually to its rupture and formation of heterogeneous grains. The strain-induced diffusion of impurities, resembling internal gettering in the Si technology, explains changes in glass color. We have also detected Pb 2 Fe 0.5 Sb 1.5 O 6.5 nano crystallites in stable yellow lead glass beads. The number density and the sizes of these crystallites are much less than those of the KSS crystallites in turquoise lead-potassium glass, they do not form large clusters; internal cracks also has not been observed in this glass. This may explain the stability of yellow lead glass. The study may be useful for predicting long-term stability of technical glasses as well as for synthesis of nano-KSS/glass composites.