Heat capacity measurements of 75SiO₂–6B₂O₃–10Al₂O₃–9MO (M=Mg, Ca, Sr and Ba) glasses and melts

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Heat capacities of 75SiO₂–6B₂O₃–10Al₂O₃–9MO (M=Mg,Ca, Sr and Ba) glasses and melts were determined between 345 and 1877 K by differential scanning calorimetry and drop calorimetry. The heat capacities of glasses and melts increase with increasing field strength of alkaline-earth metals. The glass transition takes place when the heat capacity of glass reaches 95–97% of Dulong-Petit harmonic limit. The configurational contribution to the melt heat capacity is about 20% and is independent of temperature. The partial molar heat capacity of B₂O₃ (Cp_B2O₃) in borosilicate melts containing alkaline-earth metals approaches to constant value (110–120 J·K⁻¹·mol⁻¹) above 1600 K and is consistent with heat capacity of pure B₂O₃ liquid. This suggests that there are no significant differences in coordination state of boron and in B–Si ordering among Mg, Ca, Sr and Ba-bearing alumino-borosilicate melts.