Tellurite And Fluorotellurite Glasses For Active And Passive

4. Thermal properties and glass stability; MDO 98
be conducted infinitely slowly, but the sensitivity of detection is then an issue. Thus, the
DTA / DSC methods are a compromise.
4.1.5. Time-temperature-transformation (TTT) experiments (using
DSC)
TTT (time-temperature-transformation) experiments were performed in this study using a
DSC with conditions and sample preparation as described in section 4.1.1.1 unless
otherwise stated. A number of groups has performed these experiments on various glass
compositions such as aluminosilicates [5], borosilicates [6], heavy-metal-fluorides [7],
Ga-La-S [8] and tellurites [9]. The glass samples here were quenched in the DSC from
the molten state (600°C) at a rate of 300°C/min., to various temperatures between the
glass transition and the melting point to study crystallisation kinetics. The samples were
quenched from 600°C and isothermally held for 10 min. at 5°C intervals from 270 to
450°C. After each hold the sample was taken back up to 600°C and held there for 10 min.
to ensure complete remelting. The TTT diagrams were constructed by integrating the
crystallisation peak obtained from the isothermal steps using Microcal Origin software.
The time corresponding to 50% area of the integrated crystallisation isotherm was taken
as the time plotted on the TTT diagram for each isothermal temperature [7]. Fig. (4.9)
illustrates this for an isothermal hold of glass MOF005 (70TeO2-10Na2O-20ZnF2 mol. %)
at 325°C.