STTR Phase I: Corrosion Inhibition of Stainless Steel Alloys in High Temperature Chloride Salts for Concentrated Solar Power Applications

The broader impact/commercial potential of this Small Business Innovation Research Phase I project is through the development of cost effective, high temperature molten salt heat transfer fluids for concentrated solar power plants that would make solar power an economical and viable source of renewable energy for mass consumption. With the worldwide growing need for energy, alternative sources of energy have been the primary focus of research over the past few decades. Molten salt heat transfer fluid used in concentrated solar power plants are one sub-area of such research. Molten salts have excellent stability at high temperature (>650C) and can be mined and easily manufactured into solar heat transfer fluids at a reasonable cost. Additionally, the developed molten salt heat transfer fluid would increase the efficiency of energy generation in solar power plants and provide potential cost savings by utilizing ubiquitous economical metals such as stainless steel. The heat transfer fluid could potentially bring the subsidy-free installed system price at the utility scale to a competitive price of 5-6 cents per kilowatt-hour. The technical objectives in this Phase I research project are to (i) develop a fundamental understanding of interfacial corrosion of 316L stainless steel in molten chloride salt compositions and (ii) inhibit this corrosion by utilizing suitable additives. It is known that chloride salts could potentially increase the operating temperatures (to 900 Celcius) and hence enhance the energy efficiency of solar power plants. However, the extreme corrosive behavior of molten chlorides towards the stainless steel pipes utilized in solar plants has prevented their usage for practical applications. With the fundamental corrosion insight gained through this research project, Dynalene intends to develop proprietary inhibitor compositions that can be added to the chloride salt in-situ during the operation of a solar power plant. These additives would minimize corrosion by forming a continuous and inert ceramic layer at the operating temperature on the stainless steel surface, and simultaneo usly strengthen the grain boundaries. Dynalene had some initial success in growing a few micron-thick inert, continuous ceramic layer on a stainless steel surface. In this project, Dynalene will develop a corrosion package that would reduce dechromatization in steel and restrict the corrosion rate of 316L stainless steel to 10 micro-meters/year