The Application of Thermo-analytical Methods in Environment Protection

4 The Application of Thermo-analytical Methods in Environment Protection 

Thermogravimetry (TG) is defined by ICTAC (International Confederation for Thermal Analysis and Calorimetry) as a technique in which the mass change of a substance is measured as a function of temperature whilst the substance is subjected to a controlled temperature programme. In TG experiment, the sample is placed in a crucible which is positioned in a furnace balance detects the mass loss, while the results are presented as a plot of mass against temperature (T) or time (t). The alternative presentation is the derivative of the original experimental curve dm/dt (or dm/dT) plotted against temperature T or time t. 

Mass loss is only noticed if a volatile component is lost in the investigated process. Therefore, the processes which happen without mass loss can not be investigated by TG. For these kinds of processes, other thermal techniques such as DTA or DSC are available. The term differential emphasises an important feature of these techniques—two identical measuring sensors are used one for the sample and the other for the reference the signal from the instrument depends on the difference between the responses of the two sensors. 

The practical distinction between DTA and DSC is in the nature of the signal obtained from the equipment. In the case of DTA it is proportional to the temperature difference established between the sample and an inert reference when both are subjected to the same temperature program AT = - T (subscripts S and 

R indicate the sample and reference respectively). DSC signal can be regarded as proportional to the difference in thermal power between the sample and reference dAq/dt. The results from DTA and DSC experiments are displayed as a thermal analysis curve in which the instrument signal is plotted against temperature (usually the sample temperature) or time. Combining different heating or cooling rates with isothermal periods is also possible and often employed. 

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