• Soares, Roque S.
• Lopes, Andreia A. S.
• Lima, Maria Margarida Rolim Augusto
• Monteiro, R. C. C.

Abstract

The glass transition and crystallization kinetics of a glass with a molar composition 60BaO- 30B2O3-10SiO2 were investigated by differential scanning calorimetry (DSC) under non-isothermal conditions. DSC curves exhibited an endothermic peak associated with the glass transition and two partially overlapped exothermic peaks associated with the crystallization of the glass. The dependence of the glass transition temperature (Tg) and of the maximum crystallization temperature (Tp) on the heating rate was used to determine the activation energy associated with the glass transition (Eg), the activation energy for crystallization (Ec), and the Avrami exponent (n). X-ray diffraction (XRD) revealed that barium borate (b-BaB2O4) was the first crystalline phase to be formed followed by the formation of barium silicate (Ba5Si8O21). The variations of activation energy for crystallization and of Avrami exponent with the fraction of crystallization (v) were also examined. When the crystallization fraction (v) increased from 0.1 to 0.9, the value of local activation energy (Ec(v)) decreased from 554 to 458 kJ/mol for the first exothermic peak and from 1104 to 831 kJ/mol for the second exothermic peak. The value determined for the Avrami exponent was near 2 indicating a similar one-dimensional crystallization mechanism for both crystalline phases. This was confirmed by the morphological studies performed by scanning electron microscopy (SEM) on glass samples heat-treated at the first and at the second crystallization temperatures

Topics

• scanning electron microscopy
• x-ray diffraction
• crystalline phase
• glass
• glass
• thermogravimetry
• glass transition temperature
• differential scanning calorimetry
• activation
• crystallization
• one-dimensional
• crystallization temperature
• Barium