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

Barium alumino-borosilicate glasses of composition: xAl 2 O 3 -(50-x)BaO-7.5B 2 O 3 -42.5SiO 2 (x = 5, 7.5, 10, 12.5 and 14.5 mol%) and one glass of composition: 7.5Al 2 O 3 -40BaO-7.5B 2 O 3 -45SiO 2 were prepared by melt quenching. B-O and Al-O coordination were determined by 11 B and 27 Al Magic Angle Spinning Nuclear Magnetic Resonance spectroscopy. The structure of glasses consists of AlO 4 , AlO 5 , BO 3 and BO 4 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 Al 2 O 3 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 Al 2 O 3 concentration in borosilicate network correlates directly with an increase in the glass transition temperature.