Molecular dynamics simulation of thermodynamic and structural properties of silicate glass: Effect of the alkali oxide modifiers

• Glass state of silica is characterized by fictive temperature.
• Kind and molar fraction of alkali oxides effect on Tg.
• Alkali atoms, in the case of Na and Li, organize them-selves in forms of channels.
• Simulated structures of silicates agree with experimental results.
• Shift of potential energy implying more cohesive structure and decreasing Tg.

Molecular dynamics simulation was applied to elucidate the effect of adding alkali oxides (M2O)X(SiO2)(1 − X)with M = (Na, Li or K) into silicate glass matrix. We are interested in the study of this effect particularly on structural and thermodynamic properties of the material. Some interesting results were obtained given a new insight on the bridging process and its reliability to the observed depolymerization phenomena affecting the existing SiO network and depending on both the kind of the alkali modifier and its molar fraction. We observed that the thermodynamic properties are influenced by these structural modifications. Indeed, the glass transition temperature Tg has been found to decrease as the molar fraction of modifier increases depending strongly on the alkali modifier kind. On the other hand, we extracted the fictive temperature from the calculated total energy of the system and determined the glass transition by studying the variation of the fictive temperature as a function of the conventional one using different cooling and heating rates.