Glass Activation Energy Lab Report

The glass transition activation energy, Et, is among the important characteristic parameters of the glasses. Et is defined as the amount of energy absorbed by a group of atoms in the glassy region and therefore, a jump from one metastable state to another is possible. In addition, the activation energy of glass transition can be obtained as a function of the glass transition temperature, Tg, using the second approach proposed by Kissinger [26]: (16) where R is the universal gas constant. The plots of versus 1000/Tg for different compositions are shown in Fig.7. The values of the activation energy for the glass transition of the studied glasses calculated from
Strong glasses exhibit resistance to structural degradation and generally with a small enthalpy of the structural relaxation kinetics (glass-transition kinetics). The glassy materials with a higher fragility show a relatively narrow glass transition temperature range, while those with low fragility have a comparatively broad glass transition temperature range. Furthermore, Fragility describes the anomalous non-Arrhenius transport behavior of glassy materials close to the randomness breaking glass-transition region. Using the activation energy of the glass transition Et and the glass-transition temperature, Tg, the fragility index (Fi) is calculated using the following relation [27]. (17)
The low value of Fi (Fi ≈ 16) defines strong glass-forming liquids [28], while a high value of Fi (Fi ≈ 200) represents fragile glass-forming liquids [29]. The values of Fi for all composition were obtained at all heating rates using Eq. 17 and are listed in Table 3. Since these values of Fi shown in Table 3 are within the above-mentioned limit, it is reasonable to state that the prepared (As50Se50)100-xAgx (0 ≤ x ≤ 25) glasses are obtained from strong glass-forming liquids.
Fig. 8 shows the relation between vs. for the studied compositions. The values of the activation energy, Ec, and frequency factor, Ko, evaluated by least squares fitting method are given in Table 4.
The activation energy of crystallization for the studied glasses has also been obtained using the method proposed by Gao et al. according the following relation [31]: (19) where χ is the volume fraction of crystallization, and ln(dχ/dt)p is the maximum crystallization rate. Fig. 9 shows the plot of ln(dχ/dt)p against 1000/Tp. The Ec values for all investigated compositions are given in Table 4. We found that the values of both Ec and Ko decrease with increasing Ag content. The decrease in the activation energy of crystallization with increasing the Ag content could be attributed to the fact that the addition of more Ag results in heavy cross-linked structure due to the cross-linking of Ag with other elements and thereby reducing the tendency of