Single-step solution combustion synthesis of porous 1393-B3 glass powders and structural characterization via solid-state NMR spectroscopy

During the last few decades, considerable progress has been made in designing novel boron-containing bioglasses for soft tissue regeneration applications. For this purpose, conventional glass synthesis procedures such as meltquenching and sol-gel synthesis have been explored extensively. However, both methods are time and energyconsuming and need expensive materials and equipment. The current study demonstrates that straightforward and low-cost solution combustion synthesis (SCS) can produce highly porous 1393-B3 borate-based glasses employing urea and sucrose as novel fuels. Thermal analysis shows that the glass transition temperatures of the produced specimens are between 650 and 680 degrees C. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were used to confirm the absence of crystalline impurity phases and to show the highly porous microstructure of the glasses, respectively. The effect of the initial synthesis temperature (T0) on the glass structure of the obtained powders was investigated in detail via vibrational and NMR spectroscopies. The results indicate that optimum T0 values are achieved at temperatures ranging from 500 to 700 degrees C using urea and 400-750 degrees C using sucrose as fuel. Increasing the temperature beyond these limits results in the partial devitrification of the parent glass. FT-IR, Raman, 11B MAS, and 3QMAS NMR spectroscopies demonstrate that the glass structure is dominated by multiple distinct BO4 and BO3 units, i.e., neutral (B3n) and anionic (B3a, B4) borate units. Increasing T0 values reduce the fraction of the four-coordinated boron (N4) from about 60 to 35% under the transformation of B4 units into B3a units, while the overall amount of neutral B3 species stays nearly constant. The possibility of fine-tuning the boron speciation in the resulting glasses through the synthesis parameters demonstrates that SCS is a promising process for the scalable production of 1393-B3 glass powders with tailored physical properties.