DSC Measurements of Metals by DSC and TGA/DSC

DSC measurements can be performed up to about 700 °C using conventional DSC instruments. If higher temperatures are required, DSC curves can be measured up to 1600 °C using the TGA/DSC. This article compares DSC and TGA/DSC measurements and discusses how quantitative calorimetric measurements are possible in the high temperature region.

Introduction

Thermal analysis methods have been used for the analysis of metals since the end of the 19th century. The first measurements with controlled heating and cooling rates were carried out by differential thermal analysis (DTA). This method allows transition temperatures to be determined. However, the determination of quantitative thermodynamic quantities such as transition enthalpies or specific heat capacities requires a calorimeter.

In the low and medium temperature range, good accuracy can be obtained using conventional DSC. DSC measurements above 700 °C can be performed using simultaneous thermal analysis (TGA/DSC) and the appropriate sensor. The technique allows measurements to be performed from room temperature to 1600 °C.

In this article, we compare DSC and DSC/ TGA and show the possibilities of DSC measurement at high temperatures using metals and metal alloys as examples.

Measurement of the heat flow curve by TGA/DSC

Basic principles

The classical method used for measuring thermal events is DTA (Differential Thermal Analysis). A DTA measuring cell consists of a pair of thermoelements for measuring the temperature difference between a crucible containing a sample and a reference measuring point, both of which are in a furnace whose temperature is controlled (Figure 1a).

The measurement signal is the temperature difference ΔT (or sometimes the voltage) between the sample and the reference. The measurement assumes that the sample and the reference are subjected to the identical temperature program and that the thermal losses are about the same. The measurement curve shows the temperatures and the transitions. Quantitative calorimetric data cannot however be obtained.

Summary and conclusions

The temperature range of a conventional DSC (about 700 °C) is sufficient to investigate some metal alloys. However, the measurement possibilities are considerably expanded when the temperature range is increased to 1600 °C.

Instruments for simultaneous measurements (TGA/DSC3+) are available that can measure up to this temperature. There are also several sensors to measure heat flow.

In this article, we have discussed the socalled DTA sensor, which it is in fact a true DSC sensor, and have shown that quantitative DSC measurements up to 1600 °C are possible. Temperature-modulated measurements are recommended in order to obtain precise measurements of specific heat capacity.

_{DSC measurements of metals by DSC and TGA/DSC | Thermal Analysis Application No. UC 462 | Application published in METTLER TOLEDO Thermal Analysis UserCom 46}