Thermodynamic model and structural analysis of borosilicate glasses for pharmacy

Abstract A study was focused on 17 samples of borosilicate glasses, utilizing an eight-component model system representing the pharmacy vials with the following base glass composition: 75.23 mol% SiO 2 , 7.70 mol% B 2 O 3 , 4.24 mol% Al 2 O 3 , 8.02 mol% Na 2 O, 1.15 mol% CaO, 1.44 mol% K 2 O, 0.95 mol% ZnO, and 1.26 mol% BaO. The glass composition was modified through increasing and decreasing the molar amount of each oxide. For the network-forming oxides (SiO 2 , and B 2 O 3 ), and Al 2 O 3 the content was changed by ± 10 relative %. For the modifier oxides (remaining oxides), the content was either increased by ± 40 relative % or reduced to zero. Molar Gibbs energies from the FACT database were used to evaluate the Shakhmatkin-Vedishcheva thermodynamic model (SVTDM). 115 model components were considered, of which only 25 with non-negligible equilibrium molar amounts were identified. After identification of components with strongly correlated equilibrium molar amounts, only 11 independent components remained. From the SVTDM results, the distribution of Si-Q and B-Q was calculated. Multilinear regression analysis was used to describe the dependence of molar volume ( V m ) and glass transition temperature ( T g ) on the equilibrium molar amounts of significant and uncorrelated SVTDM components. After excluding statistically insignificant terms for V m , and T g , the standard deviation of approximation s apr = 0.13 cm 3 mol −1 , and s apr = 1.7 K were obtained. Subsequently, regression analysis was used to describe the dependence of V m , and T g on the molar amounts of the individual Q-units. In such a way, the compositional dependence of V m , and T g was described by a lower standard deviation of approximation; for molar volume s apr = 0.20 cm 3 mol −1 , and for glass transition temperature s apr = 6.2 K. The distribution of Q-units obtained by SVTDM was found to reliably describe the compositional dependence of the selected properties of the model borosilicate glass.