Effect of Na2CO3 as foaming agent on dynamics and structure of foam glass melts

• Foam glass is obtained from waste glass and Na2CO3 at 923–1173 K.
• For high [Na2CO3] Tg of foam glass strongly depends on treatment temperature.
• Tg drops by ~ 120 K within 5 min; afterwards Tg increases slightly with time.
• The Tg change is related to inhomogeneous incorporation of Na2O in the glass structure.

We investigate the kinetics and dynamics of the reaction between Na2CO3 and the cathode ray tube panel glass powder at 923–1173 K. The reaction causes foaming of the glass melt. After the reaction, the Tg decreases with increasing Na2CO3 content and reaches a minimum value of Tg. However, this Tg value is even lower than that of the homogeneous bulk glass with the same chemical composition. The lower Tg of the foam glass could be attributed to inhomogeneous incorporation of Na in the glass, leading to Na-rich domains that cause an overall decrease of Tg. Remarkably, after 5 min treatment at 1073 K, the Tg drops by 120 K, indicating that the reaction between Na2CO3 and glass is very fast. Increasing treatment duration causes a slight increase of Tg likely due to both a more homogeneous Na distribution and the compositional change of the glass as a result of Na2SrSi2O6 crystal formation.