Thermogravimetry sample size

Mass sensitivity as a critical parameter in thermogravimetry has been considered by Cahn and Peterson (47). Greater sensitivity of the thermobalance permits the use of smaller samples, with improved determination of mass plateaus of intermediate compounds and the use of faster heating rates. However, thermobalances with sensitivities greater than I jig can be attained only under two conditions (48) (1) sample Hangdown tubes of 9 mm inside diameter or less if used at atmospheric pressure and (2) larger-diameter tubes if used at reduced pressure (41 mm id at 150 Torr). Unfortunately, the use of the 9-mm tubes limits the sample size to 15-20 mg. 

It is demonstrated that thermogravimetry data for uncalcined MCM-41 samples can be used to predict the structural quality of the calcined materials. The method is based on the comparison of weight change derivatives for a sample under study with those for a series of well-characterized samples prepared under similar conditions. Thermogravimetry data were found useful for a qualitative estimation of the overall sample quality, phase purity, degree of structural collapse and, in favorable cases, pore size of calcined MCM-41 materials. 

From the above remarks it may be seen that many factors affect the observed results. This means that although thermogravimetry can identify a substance from its decomposition temperature it should not be thought of as a finger print method like spectroscopy. In that technique a peak will always be at the same position in the spectrum, regardless of the make of the instrument or size of sample. 

The samples consist of sheets in right-angled parallelepipeds of approximate sizes 10 mm x 10 mm x 2 mm. The kinetics of the phenomenon is followed by thermogravimetry, and we finally obtain the variations of the differences in mass between times 0 and t per unit of area of the sheet versus time ... 

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