Structural, thermal and mechanical properties of barium alumino-borosilicate glasses

Barium alumino-borosilicate glasses of composition: xAl₂O₃-(50-x)BaO-7.5B₂O₃-42.5SiO₂ (x = 5, 7.5, 10, 12.5 and 14.5 mol%) and one glass of composition: 7.5Al₂O₃-40BaO-7.5B₂O₃-45SiO₂ were prepared by melt quenching. B-O and Al-O coordination were determined by ¹¹B and ²⁷Al Magic Angle Spinning Nuclear Magnetic Resonance spectroscopy. The structure of glasses consists of AlO₄, AlO₅, BO₃ and BO₄ units. The hardness of glasses was measured by Vicker’s indentation and the longitudinal and transverse acoustic velocities by Brillouin scattering studies. The glass transition temperature increases from 643 °C to 706 ± 1 °C, density decreases from 4.107 to 3.642 ± 0.005 g·cm⁻³ and refractive index decreases from 1.58 to 1.55 ± 0.01 with an increase in Al₂O₃ concentration. Glasses have hardness in the range of 5.44–6.30 ± 0.01 GPa and Young’s modulus of: 78.42 to 84.60 ± 0.01 GPa. The enhancement of hardness and elastic moduli with increase in Al₂O₃ concentration in borosilicate network correlates directly with an increase in the glass transition temperature.