Ag/Na ion exchange in soda-lime glasses and the formation of small Ag nanoparticles

We investigated the formation of very small Ag nanoparticles of 1–2 nm size in soda-lime glass with enhanced amounts of iron oxide by Ag/Na ion exchange procedures. The duration of ion exchange has been chosen between 20 and 600 h to study the processes systematically. It could be shown that structural relaxations take place as the Ag+ ions were incorporated into the glass replacing the Na+ of the original matrix. X-ray absorption spectroscopy at the Fe K-edge demonstrated that polyvalent Fe ions served as thermosensitive reductive during the ion exchange well below the glass transformation temperature. The transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) experiments revealed the formation of Ag nanoparticles of sizes from 1.4 to 1.8 nm in surface-near regions for exchange periods up to 400 h at 330 °C. By combination of TEM and EXAFS also the presence of metastable particles like, e.g., argentous species in the process of precipitation of very small particles has been indicated. These silver containing precipitates were transformed into crystalline silver nanoparticles for a prolonged ion exchange duration of ≈600 h.