Phase Transformations, Thermodynamics and Structural Relaxation of Phase Separated (9⩽x⩽20) Glasses
- Conference date: 7–9 October 2009
- Location: Baroda (India)
The present paper reports the investigations on structural relaxation of (9⩽x⩽20) glasses through the study of phase transformation and thermodynamics carried out using differential scanning calorimetry (DSC). The DSC thermograms at constant heating rates exhibit single glass transition and double crystallization on heating, indicating the occurrence of phase separation in these glasses. It has been found through the X‐ray diffraction (XRD) that glasses get crystallized into and PbSe/Se phases after annealing for 2 hrs at an intermediate temperature between first and second crystallization. Kinetics of phase transformation of these glasses studied earliar through the kinetic parameters like activation energy of glass transition and crystallization, avrami exponent, dimensionality of growth show that increase in lead (Pb) contents increases the thermal stability of the glassy samples.
The thermodynamic study made through the determination of parameters like specific heat, entropy difference between metastable states as well as glass and crystalline state, Gibbs free energy difference between glass and crystalline state and enthalpy released during phase transformation (glassy to crystalline) reveals that glass has highest thermal stability among the other samples if the series.
An effort has also been made to study the structural relaxation in the vicinity of glass transition in these glasses. The structural relaxation of ( 18) glassy samples has been studied in terms of excess specific heat and excess enthalpy in the glass transition region. Excess specific heat has been obtained using the specific heat of the as‐prepared sample and that obtained by annealing the sample at two different temperatures below glass transition temperature. The values of excess enthalpy show that glass is more stable than glass, a conclusion which has already been drawn from the study of kinetics of phase transformations and thermodynamics.
- Glass transitions
- Phase transitions
- Heat capacity
- Crystal structure
- Differential scanning calorimeters
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