Tellurite And Fluorotellurite Glasses For Active And Passive

4. Thermal properties and glass stability; MDO 84
will have manifested as an offset in the baseline. Fig. (4.1) shows a schematic of the DTA
cell and how the DTA curve is formed from the data recorded.
(a) (b) (c)
Fig. (4.1): (a) Schematic of DTA cell (S = sample, R = reference), (b) data recorded by
equipment, and (c) to form the DTA trace.
The temperature difference (∆T) between the sample (Ts) and the reference (TR) is
measured using a differential thermocouple, where one junction is in contact with the
bottom of the sample crucible and the other is in contact with the bottom of the reference
crucible. When the sample undergoes a transformation it either absorbs (endothermic) or
gives out (exothermic) heat. The DTA detects if the sample is cooler or hotter than the
reference and displays an exotherm or an endotherm on the trace of ∆T versus time (or
temperature if the heating rate is constant, as is the case in this study). Fig. (4.1b) shows
the temperature of the sample and reference increasing with time. The reference
temperature increases linearly (TR), however the sample temperature (Ts) undergoes a
melting transition at Tm. As melting phenomena are endothermic, the sample takes in heat
from the surroundings and the temperature plateaus for some time until melting is