Heat capacity enhancement and thermodynamic properties of nanostructured amorphous SiO2

The heat capacity of nanostructured amorphous SiO2 (na-SiO2) has been measured by adiabatic calorimetric method over the temperature range 9–354 K. TG and differential scanning calorimeter (DSC) were also employed to determine the thermal stability. Glass transition temperature (Tg) for the two same grain sizes with different specific surface of na-SiO2 samples and one coarse-grained amorphous SiO2 (ca-SiO2) sample were determined to be 1377, 1397 and 1320 K, respectively. The low temperature experimental results show that there are significant heat capacity (Cp) enhancements among na-SiO2 samples and ca-SiO2. Entropy, enthalpy, Gibbs free energy and Debye temperature (θD) were obtained based on the low temperature heat capacity measurement of na-SiO2. The Cp enhancements of na-SiO2 were discussed in terms of configurational and vibrational entropy.