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Chapter IV Thermal Studies of …..
thermodynamic properties and physical-chemical kinetics. The TGA involves
measurement of a change in weight of a system as the temperature is
increased at pre-determined rate. Changes in weight are a result of the rupture
and/or formation of various physical and chemical bonds at elevated
temperatures that lead to the evaluation of volatile products or the formation of
heavier reaction products. From such curves, parameters concerning the
thermodynamics and kinetics of the various chemical reactions can be
evaluated, reaction mechanism, the intermediate and final reaction products.
Usually, the temperature range is from ambient to 1200 C with inert or reactive
atmospheres. The derivative in TG is often used to pinpoint completion of
weight- loss steps or to increase resolution of overlapping weight-loss
occurrences.
Modern commercial variety of instruments for TGA usually consists of,
(1) a sensitive analytical balance, (2) a furnace, (3) a pure gas system (for
providing an inert or sometimes reactive gas atmosphere) and (4) a
microcomputer or microprocessor for instrumental control and data acquisition
and display. A block diagram of TGA is shown in figure (4.2).
Figure: 4.2 Components of a thermal balance. (Courtesy: Mmatter instrument corp. Hightston)
A- beam, B- sample cup and holder, C- counterweight, D- lamp and
photodiodes, E- coil, F- magnet, G- control amplifier, H- tare calculator, I-
amplifier, J- recorder.
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