Devitrification behavior and preferred crystallization mechanism of glasses based on fluorrichterite (Na2CaMg5Si8O22F2) composition

Abstract

This paper reports on the effect of different contents of fluorine on the thermal stability of glasses in the SiO2–MgO–CaO–Na2O–F system. Four glass compositions, with experimental fluorine contents varying from 2.12 to 4.39wt.%, were studied using differential scanning calorimetry (DSC). The devitrification behavior was assessed through the evaluation of both the glass stability (GS) and glass-forming ability (GFA) using different parameters calculated from the characteristic temperatures in non-isothermal DSC curves. The predominant crystallization mechanism was determined by the difference in the crystallization temperature (ΔTp) between fine and coarse glass samples. The results indicate that the studied melts exhibit a low tendency to devitrify during cooling, although this trend is increased with the fluorine content. The glass thermal stability is affected by the particle size, with it being easier to crystallize a glass powder sample than a coarse glass sample. The surface crystallization mechanism is predominant at the beginning of the devitrification process; however, the volume crystallization acquires importance with an increase in the fluorine content.