Effect of boron oxide addition on the viscosity-temperature behaviour and structure of phosphate-based glasses

In this study, nine phosphate-based glass formulations from the system P₂ O₅ -CaO-Na₂ O-MgO-B₂ O₃ were prepared with P₂ O₅ content fixed as 40, 45 and 50 mol%, where Na₂ O was replaced by 5 and 10 mol% B₂ O₃ and MgO and CaO were fixed to 24 and 16 mol%, respectively. The effect of B₂ O₃ addition on the viscosity-temperature behaviour, fragility index and structure of the glasses was investigated. The composition of the glasses was confirmed by ICP-AES. The viscosity-temperature behaviour of the glasses were measured using beam-bending and parallel -plate viscometers. The viscosity of the glasses investigated was found to shift to higher temperature with increasing B₂ O₃ content. The kinetic fragility parameter, m and F_1/2 , estimated from the viscosity curve were found to decease with increasing B₂ O₃ content. The structural analysis was achieved by a combination of Fourier transform infrared spectroscopy and solid state nuclear magnetic resonance. ³¹ P solid-state magic-angle-spinning nuclear magnetic resonance (MAS-NMR) showed that the local structure of the glasses changes with increasing B₂ O₃ content. As B₂ O₃ was added to the glass systems, the phosphate connectivity increases as the as the Q¹ units transforms into Q² units. The ¹¹ B NMR results confirmed the presence of tetrahedral boron (BO₄ ) units for all the compositions investigated. Structural analysis indicates an increasing level of cross-linking with increasing B₂ O₃ content. Evidence of the presence of P-O-B bonds was also observed from the FTIR and ³¹ P NMR analysis. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 764-777, 2017.