Tellurite And Fluorotellurite Glasses For Active And Passive

4. Thermal properties and glass stability; MDO 83
4.1. Experimental
4.1.1. Method, instrumentation and theory of operation
4.1.1.1. DTA
In this study, Perkin Elmer DTA7 equipment was used with unlidded platinum crucibles
and holders. The DTA curves were recorded under a flowing BOC argon atmosphere (20
ml.min. -1 ) at heating rates of 10°C.min. -1 (unless stated) on glass chips of around 2mm in
diameter with a mass of around 35mg. The extrapolated onset glass transition
temperature (Tg) was measured with a repeatability of +3°C, onset of the first
crystallisation above Tg (Tx) +1°C, and stability (Tx-Tg) +4°C. Characteristic temperatures
were obtained using Perkin Elmer software (see later in this section for further details).
DTA measures the difference in temperature between a sample and reference which are
subjected to the same heating schedule by symmetrically arranging them in relation to the
furnace of the equipment [3]. The reference can be any material with approximately the
same thermal mass as the sample, which undergoes no transformations in the range of
temperatures being measured. In this study an empty platinum crucible was used as the
reference. A baseline run, measured using empty platinum sample and reference
crucibles, was subtracted from the data obtained for each DTA run. The temperature of
the sample and sample crucible will have differed slightly with respect to the empty
reference crucible, due to the difference in thermal mass, and hence heat capacity; this