Applications of Thermogravimetry

Three detailed applications of thermogravimetry are described with more quantitative interpretations, i.e., efforts are made to develop information on the kinetics and equilibrium. The calcium oxalate/carbonate decomposition is treated first. The lithium hydrogen phosphate polymerization has been discussed above as a step-reaction in Sect. 3.1 (Figs. 3.16-22). Finally, the method and some examples of lifetime determinations based on TGA are shown at the end of this section. 

Calcium oxalate/carbonate decomposition follows the chemical reactions  

These reactions have been frequently analyzed and also often used as a calibration standard. The TGA curves are taken with the infrared image furnace shown in Fig. 4.184. A general kinetics equation can be written as  

The curves of Fig. 4.194 were taken on 14 mg of the monohydrate at a nitrogen flow rate of 90 cm min with a quite fast heating rate. The first step is assigned to the water loss, the second, to the conversion of the oxalate to carbonate, the last step is the loss of CO2 in the reaction that forms calcium oxide. From the DTA trace the first and last reactions seem to be simple, endothermic reactions. The DTA trace of the loss of CO indicates an initial exothermic reaction onto which an endothermic 

6tudy of the Decomposition in the System Calcium Oxalate/Carbonate 

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Applications. Some of the applications of thermogravimetry are of particular importance to the analyst. These are ... 

Wiedemann, H.G. (1972) Application of thermogravimetry for vapor pressure determination. Thermochim. Acta 3, 355-366. 

Trends and Applications of Thermogravimetry Hans G. Wiedemann and Gerhard Bayer 67... 

This is another example of the application of thermogravimetry for determination of equilibrium temperatures in dissociation studies. This also enables one to calculate the heat of dissociation from the linear relation between log of dissociation pressure and 1/T. Determination of the specific heat by means of DTA was used afterwards for conversion of the heat of dissociation into the standard values of formation at 298 °K. Ba02 was chosen for these investigation56 because it has been investigated in the past by calorimetric methods and therefore gives a possibility for comparing those values obtained from static methods with those obtained from values from dynamic methods. 

The present work demonstrates the application of thermogravimetry for vapor pressure determination62,63. The optimum use of the apparatus by automation of the measuring program, collection of the data and possible sources for errors will be discussed with some examples. 

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