Materials Degradation Phenomena of High Temperature Alloys by Molten Salts (MaDMoS)

• Applicants: Dr. Thomas Bauer, since 3/2024; Professor Dr.-Ing. Ulrich Krupp; Dr. Srinivasan Swaminathan, since 3/2023
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Metallurgical, Thermal and Thermomechanical Treatment of Materials
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 455432503

The societal challenge for enhanced usage of alternative power sources has driven the development of concentrating solar power plants (CSP). CSP plants offer intrinsic compatibility with thermal storage and their integration allows for the generation of dispatchable electricity. Two-tank thermal energy storage systems based on molten Solar Salt, a mixture of 60 wt.% NaNO3 and 40 wt.% KNO3, operate at temperatures up to 560 °C and have proven most advantageous in terms of operating temperature, fluid dynamics and costs. In direct storage configurati on the molten salt acts as heat transfer fluid and storage medium, simultaneously. Structural materials applied in the central receiver must meet certain requirements:• Manufacturability: The alloy must be processed to thin wall tubes, since as thinner the wall the higher the transfer area and the higher the heat flux. • Mechanical performance and corrosion resistance as a result of manufacturing in a molten salt environment.Previous studies demonstrate the challenging balance act to fulfill the mentioned requirements, which is of vital importance, to make the CSP technology competitive. The research project aims to further design salt chemistry and stainless steels in a knowledge-based feedback loop and to assess the lifetime by a combined experimental and semi-quantitative life prediction approach. Although corrosion rates are known for many materials, there is a partial lack of mechanistic understanding of the processes that can promote or inhibit corrosion. Analysis of structure and chemistry at the interfaces is thereby the key to understand these processes. Previous studies mainly used classical metallographic and microscopic analysis to tackle the corrosion processes. The interfacial structure-chemistry-transport property relations were not addressed, previously. They will be evaluated in the proposed project applying sophisticated analysis techniques such as X-ray absorption spectroscopy (XAS) comparatively to metallographic and microscopic analysis. The project aims in a comprehensive understanding of degradation mechanisms proceeding in the salt and on the alloy side, driven by interfacial diffusion-reaction mechanisms and focuses on the following objectives:A) Elucidate corrosion product formation.B) Identify key parameters for salt and material degradation.C) Elucidate material degradation under cyclic load.The key part to fulfill these objectives is the design and evaluation of an analysis routine for materials degradation by superimposed mechanical-thermal and chemical load (RWTH). To extract the information achieved by the multiple material exposure approach different sub topics, analyzing the degradation processes within the salt (DLR/BAM) and especially at the interfaces between the material and the salt (BAM) are addressed.

• DFG Programme: Research Grants
• Ehemalige Antragstellerinnen / Ehemalige Antragsteller: Dr. Alexander Bonk, until 3/2024; Dr. Axel Kranzmann, from 10/2021 until 3/2023; Professorin Dr. Christiane Stephan-Scherb, until 9/2021