Phase separation of alkaline earth fluorosilicate glass: A strategy to suppress fluoride evaporation

Fluorosilicate glasses are widely applied as optical and luminescent materials to host a variety of lanthanides. However, fluorides evaporation causes notable difference between the actual composition and the nominal composition of fluorosilicate glass. In this work, a series of SiO2 - Al2O3 - MF2 (M = Ca, Sr, Ba) glasses are fabricated, and quantitative element analysis is performed to determine the actual composition of the fluorosilicate glasses through an inductively coupled plasma atomic emission spectrometer (ICP-AES) and a gas chromatography analysis. A series of molecular dynamics (MD) simulations are carried out to study the glass network microstructures. The phase separation with silicate and fluoride phases is clearly observed in the MD simulated structures and agrees well with the observed self-crystallization of fluorides in the experiments. SiF4 as well as CaF2 / SrF2 / BaF2 are confirmed as the major evaporated substances from the glass melts. The phase separation may well inhibit the evaporation of SiF4 through partitioning Si4+ and F- ions into silicate phase and fluoride phase, respectively. The phase separation may enrich the alkaline earth cations into fluoride phase thus aggravate the evaporated loss of alkaline earth elements. This study is then help to understand the mechanism of fluoride evaporation from glass melts, and quantitatively predict actual composition of the fluorosilicate glasses.