Students working in a group (c) Jonas Kron

OptiMa

Optical differential calorimetry for state-of-the-art materials research at high temperatures

Short Facts

  • Duration: 01/10/2021 – 30/09/2024
  • Funded by: Federal Ministry of Education and Research
  • Project partner(s): Techno Team Bildverarbeitung GmbH in Ilmenau, Heitronics Infrarot Messtechnik GmbH in Wiesbaden, Netzsch-Gerätebau GmbH in Selb, Morgan Advanced Materials Haldenwanger GmbH, Ariane Group, Technische Universität Berlin, Center for Applied Energy Research e.V., Physikalisch-Technische Bundesanstalt

     

Summary

Methods of modern material development demand exact knowledge of specific material properties for the preliminary simulation and validation of achievable component and process properties. Especially in Industry 4.0, innovative methods of laser-based, additive manufacturing for the layer-by-layer production of complex components and innovative structures are used increasingly. Such methods work with very high temperatures, far above the melting point of the materials processed, where there is little knowledge about the material properties. However, they are of vital importance. For making exact predictions on the functionality and quality of the components produced according to this method, as well as on safety margins, material data at these high temperatures need to be available at sufficient accuracy. The OptiMa project pursues the innovative approach of carrying out the differential temperature measuring and temperature control of the DSC method contactless through optical methods.

Project goals and contents

Thermal conductivity and specific heat are important thermo-physical material properties, which determine, e.g., the maximum temperature during a selective laser melting process. While there are valid measuring techniques for the thermal conductivity at high temperatures >2000 °C, such methods are unavailable for the specific heat at high temperatures, limiting especially the modelling of the selective laser melting process. As a secured method for determining the specific heat at temperatures <1000 °C, the Differential Scanning Calorimetry (DSC) has been established. DSC records the temperature change of a reference sample and of a test sample that is heated in the same process as function of the temperature. So far, this method has only been reliably usable to temperatures of <1000 °C, as the thermocouples used for measuring the temperature lose accuracy and stability at higher temperatures and induce unknown heat losses, which makes it harder to take valid measurings and makes it impossible to take measurings above 1.500 °C. In addition, the costly tungsten/rhenium thermocouple used at these temperatures only have a lifetime of a few days. Thus, they are only used by well-established metrological institutes.

To solve this problem, there have been attempts in recent times to develop alternative methods to DSC, which, however, were not successful so far. It was also tried to extend the DSC method to higher temperatures, but also with only very little success. The crucial problem in the measuring of thermophysical properties at high temperatures is thus the conventional, contact temperature measuring with thermocouples. The OptiMa project pursues the innovative approach of carrying out the differential temperature measuring and temperature control of the DSC method contactless through optical methods. For this purpose, punctiform and imaging methods are used. The contactless temperature measuring enables to go without delicate thermocouples and allows it to increase the DSC working temperature to >1000 °C up to >2000 °C. In addition, the contactless measuring technique minimises unwanted heat losses, and the imaging method can quantify the remaining losses. Following the method, first, a dynamic calorimeter apparatus based on optical measuring techniques is set up in the laboratory, which is in short the optical lab DSC (opLa-DSC), for which a contactless heat source (inductive or optical) is also planned. The opLa-DSC is also intended to be used for larger samples, e.g. to determine the specific heats of phase change materials (PCM), or for the calorimetry of accumulators. At high temperatures, PCM are suitable as innovative storage materials for electrical energy that has been renewably converted, in particular metal-carbon alloys, which are currently under intensive study.

Project contact(s)