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Hot fixed points

Especially interesting for:

  • material scientists
  • production and process engineers

To improve the energy efficiency of power plants, motors and thermal process engineering facilities, ever higher process temperatures are required which, however, make great demands on the materials used. For temperatures up to more than 2000 °C, the measuring methods used so far did not allow the thermo-physical properties of these materials to be determined with sufficient accuracy. In a cooperation with an industrial consortium, PTB scientists now succeeded in improving the uncertainty of the temperature measurement in devices for dynamic scanning calorimetry with the aid of high-temperature fixed points to values below 1 K.

Industrial and scientific applications at very high temperatures (e.g. in power plants and in aviation and aerospace for reentry and turbine technologies) require the optimization of materials with respect to energy efficiency and reliability. In such cases, the specific heat capacity is an important thermo-physical material property. In commercial instruments it is determined by measuring a differential temperature between two samples with a thermocouple. As the stability of the thermocouple decreases at temperatures above 1000 °C, an insitu calibration of the thermocouple is required.

Within the scope of a project funded by the BMWi, PTB is developing – in cooperation with Netzsch Gerätebau GmbH and with the support of Techno-Team Bildverarbeitung GmbH, HTM Reetz GmbH and ifa GmbH – novel calibration fixed points on the basis of eutectic metal-carbon alloys. In the project it has been possible to prove the suitability of these material combinations for fixed point standards in the temperature range from 1100 °C to 2300 °C. These fixed points now allow the in-situ calibration of the temperature of apparatuses for differential scanning calorimetry.

For temperatures up to above 1600 °C, the uncertainty of the temperature measurement in dynamic differential calorimetry has been improved to values below 1 K. Analogous to the ultrahigh-purity fixed points, these standards are being made available to the users as reference samples. A patent for the procedure has already been applied for and the method shall, in future, also be used in other devices for thermo-physical material investigations.

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