Indium and aluminum (calibration standards, purity > 99.999 %)
Standards for temperature calibration
Measuring cell: TGA850
Pan: Alumina 70 µl
Sample preparation: Two indium pellets, one piece of aluminum wire. The metals are pressed flat. Weight of each sample approx. 12 mg. The pure metals are put in the pan well separated from each other.
TGA measurement: Heating from 100 °C to 200 °C at 10 K/min, from 200 °C to 600 °C at 50 K/min, from 600 °C to 700 °C at 10 K/min (indium-aluminium check).
Atmosphere: Nitrogen, 20 cm3/min
The SDTA signal shows the melting of both metals. The automatic evaluation determines the melting points (onsets) of both metals and compares them with the reference values. If the deviations are too large then the appropriate message is displayed. In this example the results lie within the specifications. The two peaks at 230 °C and 600 °C are caused by the change of heating rate.
The weight curve is not shown because no effects would be observed.
Determination of the melting points (onsets) of indium and aluminum using the SDTA curve.
Indium measured | Ref. value | Aluminum measured | Ref. value | |
---|---|---|---|---|
Melting point 1) | 156.5 | 156.6 +/- 1 | 660.3 | 660.3 +/- 1.5 °C |
Melting point 2) | 156.7 | 156.6 +/- 1 | 660.4 | 660.3 +/- 3 °C |
1) based on the thermocouple of the sample holder (sample temperature)
2) based on the thermocouple of the furnace (abscissa unit)
The so called indium-aluminium check is a quick and easy method to check the temperature calibration of the thermobalance. If the measured values lie outside the given tolerances, then the settings can be adjusted. If the thermobalance (as in the case of the TGA850 or TGA/SDTA851e) is equipped with a suitable sample temperature sensor, then the check is performed using the melting of known standards. Otherwise the method using the Curie point transition temperatures of different metals is used.
TGA Calibration, Temperature | Thermal Analysis Application No. HB844 | Application published in METTLER TOLEDO TA Application Handbook Pharmaceuticals