Temperature and modifier cation field strength effects on aluminoborosilicate glass network structure

The effect of temperature on the structure of barium aluminoborosilicate liquids has been studied by B-11, Al-27, and O-17 MAS NMR spectroscopies using glass samples prepared with different cooling rates and thus different fictive temperatures. Concentrations of BO3 groups and of non-bridging oxygen (NBO) increase with increasing fictive temperature. The abundance of boron structural groups and NBO quantified by B-11 MAS NMR and O-17 MAS NMR confirms that the change of NBO corresponds to the boron coordination change through the structural reaction BO4 <-> BO3 + NBO, which shifts to the right at higher temperature. The reaction enthalpy of this reaction is about 40 kJ mol(-1). Configurational heat capacities have been estimated from differential scanning calorimetry (DSC) data; the redistribution of boron species (BO4/BO3) contributes about 30% to these values. Results for barium aluminoborosilicates are compared with our previous study of sodium and calcium aluminoborosilicates with same stoichiometry [1] to understand how the modifier cation field strength affects the glass network structure. The modifier with higher field strength promotes the formation of BO3 group and NBO, and the additional NBO helps to stabilize the modifier cation in the melt structure and lower the reaction enthalpy change of the speciation reaction. (C) 2012 Elsevier B.V. All rights reserved.