Quench rate and temperature effects on boron coordination in aluminoborosilicate melts

The effect of temperature on the structure of aluminoborosilicate liquids has been studied by 11B MAS NMR, 11B 3QMAS NMR, 23Na and 27Al MAS NMR spectroscopies using glass samples prepared with different cooling rates and thus different fictive temperatures. The abundance of BO3 group and non-bridging oxygen (NBO) increases with increasing fictive temperature, indicating that the reaction BO4 ↔ BO3 + NBO shifts to the right with increasing temperature. The observed temperature dependence of BO4 species abundance allows us to estimate the ∆H of this reaction to be 24 to 50 kJ mol−1 in different glass compositions, and closely related with the amount of NBOs in the glass. Configurational heat capacities have been measured by differential scanning calorimetry (DSC). We found that the redistribution of boron species (BO4/BO3) contributes a varying range of configurational heat capacity, from 7% to 30%, with different glass compositions. 11B 3QMAS NMR indicates two different BO3 sites, the populations of which are also affected by fictive temperature. The exchange between two different BO3 sites should also contribute to configurational heat capacity.