Role of Tin Oxide as a Nucleating Agent with Low Solubility in BaO–SrO–ZnO–SiO2 Glasses Studied by Electron and X-ray Microscopy

Abstract

The crystallization behavior of BaO–SrO–ZnO–SiO2 glasses containing different concentrations of SnO2 was studied using microscopic techniques as well as thermal analyses. It is shown that SnO2 triggers volume crystallization, but at low nucleation rates. During heat treatments near respective glass transition temperatures, nucleation takes place. In the course of this nucleation treatment, SnO2 added leads to the formation of small metallic particles which serve as nuclei for the growth of Ba1–xSrxZn2Si2O7 crystals. The metallic nuclei are composed of metallic Sn and Pt. The latter is introduced into the glass during synthesis in a Pt crucible as a contaminant. Besides scanning electron microscopy, also X-ray microscopy was used to study the microstructure as well as the origin of appearing cracks in three dimensions. It was found that the different morphologies detected via scanning electron microscopy are solely due to different orientations of the crystals within the glassy matrix. Furthermore, evidenc...