The utility of simultaneous parameter measurements in thermal analysis

Abstract

In recent years, it has become increasingly apparent that the information gleaned from conventional thermal analysis techniques such as differential scanning calorimetry (DSC) and thermogravimetry (TG) can be considerably magnified in scope by combining them with mechanistic probes which are responsive to changes taking place in the sample on a molecular level. This is particularly true in the case of naturally occurring complex materials such as coals, oil shales and tar sands. The utility of simultaneous parameter measurements was illustrated for such materials by combining dielectric measurements with differential thermal analysis (DTA) [l-3]. On the basis of this approach, it was proposed that an ideal combination would be that coupling “primary” thermal analysis techniques such as DSC (or DTA) and TG with mechanistic probes such as thermoelectrometry and thermoacoustimetry [ 41. In this communication, we present yet another piece of experimental evidence in favor of the above concept. It is shown that a combined use of the two techniques of DSC and thermoacoustimetry results in a powerful analytical tool which is responsive to changes both in the thermal as well as in the mechanical properties of the test sample as a function of temperature. More significantly, the extreme sensitivity of the thermoacoustimetric probe and the loss of valuable mechanistic information-that would have resulted from a DSC examination alone are highlighted by the present results. The proof-of-concept measurements are illustrated on a sample of Utah tar sand bitumen, although, in principle, the conclusions apply equally well to all materials. Thermoacoustimetry was carried out according to the technique and procedures outlined in a previous paper [5]. Differential scanning calorimetry was performed on a DuPont 990 Thermal Analysis System *:* equipped with the DSC accessory module. Both sets of measurements were carried out under identical conditions of heating rate, sample preparation, ambient atmosphere, etc. to eliminate artifacts in the correlation of thermoacoustimetric and DSC data. The sample of Utah tar sand bitumen (P.R. Springs, Main Canyon) was obtained from the Laramie Energy Technology Center.