Thermogravimetry quasi-isothermal

P. Staszczuk, D. Stemik, G. W. Ch dzyhski Application of quasi-isothermal thermogravimetry and sorptometry for estimation of heterostructure and fractal dimension of high temperature superconductors. J. Therm. Anal. Cal. (2003) in print. 

Paulik F and Paulik J (1971) Quasi-isothermal thermogravimetry. Analytica Chimica Acta 56 328-331. 

Figure 2.1. Three modes of thermogravimetry. (c) Isothermal thermogravimetry (6) quasi-isothermat thermogravimetry (c) dynamic thermogravimetry.

Paulik F, Paulik J, Erdey L (1958) The Derivatograph. I. An Automatic Recording Apparatus for Simultaneously Conducting Differential Thermal Analysis, Thermogravimetry, and Derivative Thermogravimetry. Z anal Chem 160 241-252. For standardization, quasi-isothermal and isobaric analyses and some example research with the Derivatograph see also (1966) Anal Chim Acta 34 419-426 Paulik F, Paulik J (1973) J Thermal Anal 5 253-270 (1975) 8 557-576. 

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... 

It has already been stated that SCTA envelopes the original CRTA techniques. Essentially, there are two forms of CRTA - the quasi-isothermal/quasi-isobaric methods (Paulik) and the constant rate method (Rouquerol). The Paulik method is based on thermogravimetry (TG) and is known as Q-TG . It depends on a control system that maintains a constant rate of mass loss and the measured parameter is temperature as a function of time. CRTA relies on using a transducer to monitor the pressure of evolved gas in a continuously evacuated chamber. The sample is heated in such a way as to maintain the monitored gas pressure constant. Since the pressure is maintained constant, the rate of gas pump-off is maintained constant and thus the rate of mass loss (when a single gas is evolved) is also maintained constant. Hence, CRTA is effectively vacuum thermogravimetry. The similarity between the Paulik and Rouquerol techniques is immediately apparent. Both maintain the reaction rate constant and both control the pressure of the evolved species in the reaction environ ment. Hence, the differences in the techniques are purely semantic. These techniques allow a precise... 

Thermoanalytical methods comprise calorimetry (Differential Scanning Calorimetry, DSC) and thermogravimetry (TG) [3]. Mostly, the temperature of the sample is increased linearly and peaks of the sample temperature in comparison to a reference sample are recorded (Differential Thermal Analysis, DTA). In thermogravimetry the mass loss is observed. In this way the content of adsorbed liquids can be determined and the desorption kinetics can be observed. For special tasks also a quasi-isothermal treatment may be applied [4]. The most important standards on such methods are summarized in Table 2. 

Isa and Oruno describe a method that enables identification of intermediates (in the gypsum dehydration process) more easily. The method involves the use of simultaneous TG-DTG-DTA under various sealed atmospheres corresponding to three systems—open completely, sealed, and quasi-sealed. Endothermic DTA peaks appear earlier (129 and 133°C) than the point of decreasing TG. This technique, resembling the quasi-isothermal and isobaric thermogravimetry (Q-TG), is superior to the latter in that it needs less of the sample. 

---