Hot Corrosion of Steels In Chloride Salts For Concentrated Solar Power Generation Environments
Concentrating (or concentrated) solar power (CSP) is a method of tapping plentifully available solar energy that offers grid flexibility over photovoltaic generation. Molten salts have emerged as viable candidates for thermal energy storage in CSP. Chloride salts have many advantages such as their economic availability and their stability to temperatures around 1100°C which opens up the possibility for higher power generation efficiency. However, molten chlorides are known corrosives; therefore, proper materials selection for plant hardware is important. Nickel-based superalloys are good candidates as construction materials. However, while superalloys provide the needed corrosion resistance, they are cost prohibitive for constructing industrial scale solar power plants. Due to this restriction, many existing solar power plants use stainless steels because of the combination of low cost and appropriate mechanical properties and corrosion resistance. In this research project, two different stainless steels (UNS S30400 and UNS S31600) and a carbon steel, i.e., UNS G10180, were tested at 450, 550, & 700°C under a NaCl-KCl-MgCl₂ salt eutectic. DC electrochemical techniques were utilized to characterize the corrosion behavior of these steels. The morphology of attack was determined using optical and scanning electron microscopy coupled with energy dispersive spectroscopy (EDS). X-ray diffraction was used to characterize the corrosion products formed on the surface of the substrate. Based on these results, inferences were drawn on the corrosion resistance of these particular alloys.
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