Degradation of materials in molten salts
Molten salts have been widely used in the industry. Some examples are molten chloride salt mixtures as baths for alloying surface treatments and fluoride salts as solvents. More recently molten nitrate and nitrite mixtures hav been becoming more attractive due to their application as heat transfer fluid (HTF) and thermal storage for the power industry.
Driven by the long-term need of utilization of fluctuating regenerative energy resources Fraunhofer IWM invests in the development of methods for assessment and qualification of materials to be used in the molten salt environment of high temperature storage systems of solar power plants (TES Thermal Energy Storage, CSP concentrated solar power plants). These activities are included in the Fraunhofer project Supergrid (Project management: Fraunhofer Institute for Solar Energy Systems ISE), which comprises additional aspects of integration fluctuating regenerative energy resources into a trans-European power grid (DESERTEC).
For the cost-efficient optimisation and reliability of high temperature storage and piping systems, there is a need of comprehensive material characterization and assessment. In the field of heat exchangers the appearance of complex and cyclic thermal-mechanical stresses under the chemical influence of the molten salts can cause a critical degradation of the material resulting in failure of the system.
Fraunhofer IWM has qualified and experienced staff (physicists, engineers and chemists) for the study of the degradation mechanisms, the material selection and optimisation, the development of protective systems and the evaluation life time prediction methods. Moreover Fraunhofer IWM is currently working on the design and building of new testing facilities for the mechanical characterization of materials exposed to molten salt environments at high temperature. These facilities include: