Tellurite And Fluorotellurite Glasses For Active And Passive

4. Thermal properties and glass stability; MDO 87
The first endotherm at around 250°C is the glass transition temperature (Tg). The onset of
this temperature was obtained by interpolating the straight line just before the transition
and the straight line which occurs after the initial change in gradient as shown in fig.
(4.3) 1 .
←← Endothermic ∆∆T / °C Exothermic →
T g
200 210 220 230 240 250
Temperature / °C
260 270 280 290 300
Fig. (4.3): DTA trace of glass MOF005 (70TeO2-10Na2O-20ZnF2 (mol. %)), showing
interpolation of the onset of the glass transition temperature, Tg.
The first exotherm on fig. (4.2) at around 425°C was due to crystallization event in the
glass. The onset of crystallization, Tx, was obtained by plotting the ‘lift-off’ point from
the baseline before the crystallisation event. Fig. (4.4) illustrates this. With Tx and Tg
known, a crude measure of glass stability can be calculated: Tx–Tg.
1 Transformations obtained using the DSC were identified using the same methods described here.