Thermogravimetry mass changes detectable

As previously mentioned, in thermogravimetry the mass-change of the sample is continuously recorded as a function of temperature. The temperature, in this definition, may be that of the furnace chamber, the temperature near the sample (i.e., in close contact with the sample container), or the temperature of the sample. These three sources of temperature detection are shown in Figure 3.10. In (a), the thermocouple is near the sample container but not in contact with it. There is a correlation between ihe temperature of the container and that detected by the thermocouple, but the thermocouple will either lead or lag behind the sample lemperature, depending on the thermochemistry of the reaction. Most thermobalances use this type of... 

The application of thermogravimetry to a particular problem is possible if a mass-change is observed on the application of heat. If no mass-change is observed, then other thermal techniques such as DTA, DSC, TMA, and so on, may have to be employed. If the mass-change is very small (< 1%), then perhaps other techniques such as evolved-gas analysis (EGA) may be more useful. Mass-changes (generally mass-losses) which can be detected by TG techniques are summarized in Figure 4.1. 

A more complex system of temperature and atmosphere control used in the study of decomposition rates is quasi-isothermal and quasi-isobaric thermogravimetry [6]. In this method a heating programme linearly increases the sample temperature until a mass change is detected. On detection of a mass... 

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. 

The common feature of these established experimental methods is their ability to detect changes in the mass (Am(t)) and/or heat (Aq(t)) of a reacting system. Let us begin the discussion with thermogravimetry, since it clearly illustrates the philosophy of the essentially thermodynamic methods. 

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