U.S. Department of Energy - Energy Efficiency and Renewable Energy

SunShot Initiative

Degradation Mechanisms for Thermal Energy Storage and Heat Transfer Fluid Containment Materials

National Renewable Energy Laboratory logo Graph of a chart with three sets of three lines that curve downward to the right.

Schematic of the electrochemical system. 1: crucible furnace 2: silica liner 3: three-electrode arrangement (working-electrode/sample, reference electrode, and counter-electrode) 4: molten salt (carbonates or chlorides) 5: alumina crucible 6; thermocouple 7: furnace controller with over-temperature control 8: potentiostat/power-supply 9: purge gas inlet 10: argon tank 11: off-gas outlet 12: chlorine compounds trap (MgO pellets) 13: water removal trap (anhydrous CaSO4) 14: water reflux trap 15: NaOH scrubber 16: exhaust gases 17: thermocouple for overheating control Image from NREL

The National Renewable Energy Laboratory (NREL), with support from the University of Wisconsin and Sandia National Laboratories, under the National Laboratory R&D competitive funding opportunity, is investigating the effects of high-temperature salt and supercritical carbon dioxide (s-CO2) on various alloys and developing protective methods and coatings for thermal energy storage (TES) and heat transfer fluid (HTF) containment materials. By reducing both the cost of materials used in concentrating solar power (CSP) systems and the risk of using the materials under investigation in CSP plants, this research will significantly reduce the cost and the investment risk of CSP plants.

Approach

Next-generation solar power conversion systems require high-temperature, advanced fluids operating at temperatures between 600°C and 900°C as HTF and TES materials. The three major advanced fluid groups—s-CO2, liquid metal alloys, and molten salts—are corrosive to common alloys used in vessels, heat exchangers, and piping at these temperatures.

The research team will use electrochemical techniques to understand and control the corrosion mechanisms of molten salts, immersion degradation to evaluate these mechanisms for liquid metal alloys, and autoclave and flow tests to evaluate the corrosion mechanisms of s-CO2. The team will also evaluate protective coatings containing materials such as graphite and alumina in an effort to reduce the corrosive effects of molten salts, liquid metals, and s-CO2. The overall objective of the project is to produce material systems and conditions (i.e., coatings and surface modification techniques) that result in a corrosion or degradation rate of less than 30 micrometers per year.

Innovation

Currently there are no protection methods or advanced materials for TES and HTF containment that resist corrosion at temperatures between 600°C and 900°C. This project will evaluate novel approaches such as the use of protective coatings that are resistant to aggressive fluids and will study the self-healing behavior of silicon coatings in liquid aluminum-silicon alloys. The team will also use first principles density functional theory modeling to determine which doping elements could be used to improve the properties of the containment materials.

Publications, Patents, and Awards

At this time, this project does not have published articles, patents, or awards.

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Progress Reports
January 2013

Learn about other DOE competitive awards for concentrating solar power research that are in progress.