Calibration and Adjustment of Sample Temperature for the DMA Tension Sample Holder - METTLER TOLEDO

Calibration and Adjustment of Sample Temperature for the DMA Tension Sample Holder

The DMA/SDTA861e has a thermocouple that is used to measure the sample temperature near the sample. The measured sample temperature can of course be calibrated and adjusted. In this article, we show how this is done for the large or small tension sample holders.

 

Introduction

In the DMA/SDTA861e, the sample temperature is measured by a thermocouple. This sample thermocouple (STC) can be separately calibrated and adjusted for each sample holder. This is particularly easy to do with the shear sample holder because the STC is in direct contact with the sample holder and is always reproducibly in the same position relative to the position of the sample.

Besides this, the thermal mass of the sample holder is large and the sample and sample holder are in close thermal contact. This guarantees that the measured sample temperature agrees very well with the actual sample temperature in shear experiments. Furthermore, the calibration substances (indium, zinc, water) normally employed in the thermal analysis can be used.

The situation with bending, tension and compression is somewhat different. Here the STC is not in direct contact with the sample holder but is positioned as near as possible. The measured sample temperature includes an uncertainty contribution that is mainly determined by the reproducibility involved in positioning the STC.

In addition, it is not quite so easy to use the above-mentioned calibration substances. In this article, we will describe how samples for calibration and adjustment of the STC can be prepared for tension experiments and what the uncertainty of the measured sample temperature is. The methodology can be used for both the large and small tension sample holders (tension clamps).

 

Experimental Details

The experiments described here were performed in the large tension sample holder (sample length 10.5 mm). The measurements were carried out using the default STC adjustment parameters. The heating rate was 3 K/min...

Melting points of different reference materials 



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Conclusions and Final Comments

The calibration and adjustment of the sample thermocouple (STC) in the DMA/SDTA861e can be performed separately for each sample holder. In the tension sample holder, calibration and adjustment of the STC is performed using the melting points (onset) of reference materials measured by the SDTA sensor.

With suitable sample preparation, the temperature curve of the storage modulus of water can also be used (onset of the step in the storage modulus). The onset temperatures of the SDTA melting peaks and the step in the storage modulus curve agree well for water. In the temperature range –100 °C to +200 °C, the uncertainty in the measured sample temperature using the default calibration of the STC is about 5.4 K. If the STC is adjusted, the uncertainty is reduced to about 3.7 K.

For the large tension sample holder in particular, the measured melting points are very dependent on the heating rate used. At heating rates above 3 K/min, deviations between the measured sample temperature and the actual sample temperatures can be significantly greater than the values given here.

For the small tension sample holder, the same reference materials with the same types of sample preparation can be used (“crucible method”, “foil method”, “paper method”, “fiber method”). The advantage of the small tension sample holder is that the STC can be positioned with better reproducibility.

The sample is also better shielded from the furnace and is therefore in an environment that is thermally more stable. For the small tension sample holder, with the default adjustment we expect an uncertainty (s2) in the sample temperature of about ±3 K. If the STC is adjusted, the uncertainty of the sample temperature (s1) is reduced to ±2 K.


Calibration and Adjustment of Sample Temperature for the DMA Tension Sample Holder | Thermal Analysis Application No. UC354 | Application published in METTLER TOLEDO Thermal Analysis UserCom 35