Effect of Experimental Parameters on Simultaneous Thermal Analysis

Abstract

Differential Scanning Calorimeter (DSC) is a very effective way to measure both the heat capacity and the phase transition temperature in thermal processes. With the continued development of computational models of thermal processes, the accuracy of the thermophysical data plays an increasingly key role in the final simulation results. However, since DSC is a transient measurement process and a relative technique, the experimental parameters must be carefully considered. This study combined DSC with Thermogravimetric Analysis (TGA) to examine the influence of the various interrelated measurement parameters. This thesis consists of two sections: First, the experimental parameters of the heating rate and specimen characteristics (mass and geometry) and their effects on measurements of the transition temperature and enthalpy are considered and appropriate calibration factors determined. This is followed by an examination of the effect of oxidation on the measurements. In the first part of this work, the effects of several factors on the phase transition temperature and the transition enthalpy were examined, separately. To determine the effect of experimental parameters on the phase transition temperature, a deviation method is proposed to determine the initial phase transition temperature rather than the onset temperature as is typically used in the literature. Next, a study of the effect of sample geometry indicated that the measured phase transition temperature is reduced with decreasing particle size, but the effect from the sample mass is not significant. The phase transition enthalpy decreased with both the heating rate and the total surface area of the sample, suggesting that the oxidation of samples in the measuring process should be taken into account. The second section of this research focused on analyzing the effect of oxidation on specific heat capacity (Cp) measurements. The contribution of sample oxidation to the deviation of the heat capacity measurement could be classified in term of two factors: one being the amount of oxide generated and the other the heat released by the oxidation reaction. The results revealed that the influence of the heat capacity from the reaction enthalpy was more significant than that from the generated oxide.