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–x Sr x Zn2Si2O7 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, evidence is given that in some cases microcrack formation starts right at the center of the crystals, where metallic particles are found.

Microstructure transformation of a crystallized glass from the system BaO‐SrO‐ZnO‐SiO2

“…Since this micrograph shows a 2D cut through the material, these needles might be plates. A detailed description of the microstructure can also be found in Thieme et al. 17 If this material is reheated to 950°C kept for 1 h, spherical islands have been formed within the volume of the material.…”