Corrosion of Alloys in a Chloride Molten Salt (NaCl-LiCl) for Solar Thermal Technologies

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Abstract

Next-generation solar power conversion systems in concentrating solar power (CSP) applications require high-temperature advanced fluids in the range of 600-800 °C. Current commercial CSP plants use molten nitrate salt mixtures as the heat transfer fluid and the thermal energy storage (TES) media while operating with multiple hours of energy capacity and at temperatures lower than 565 °C. At higher temperatures, the nitrates cannot be used because they decompose. Molten chloride salts are candidates for CSP applications because of their high decomposition temperatures and good thermal properties; but they can be corrosive to common alloys used in vessels, heat exchangers, and piping at these elevated temperatures. In this article, we present the results of the corrosion evaluations of several alloys in eutectic 34.42 wt% NaCl - 65.58 wt% LiCl at 650-700 °C in nitrogen atmosphere. Electrochemical evaluations were performed using open-circuit potential followed by a potentiodynamic polarization sweep. Corrosion rates were determined using Tafel slopes and Faraday's law. A temperature increase of as little as 50 °C more than doubled the corrosion rate of AISI stainless steel 310 and Incoloy 800H compared to the initial 650 °C test. These alloys exhibited localized corrosion. Inconel 625 was the most corrosion-resistant alloy with a corrosion rate of 2.80±0.38 mm/year. For TES applications, corrosion rates with magnitudes of a few millimeters per year are not acceptable because of economic considerations. Additionally, localized corrosion (intergranular or pitting) can be catastrophic. Thus, corrosion-mitigation approaches are required for advanced CSP plants to be commercially viable.

Original languageAmerican English
Pages (from-to)234-244
Number of pages11
JournalSolar Energy Materials and Solar Cells
Volume157
DOIs
StatePublished - 1 Dec 2016

Bibliographical note

Publisher Copyright:
© 2016 Elsevier B.V. All rights reserved.

NREL Publication Number

  • NREL/JA-5500-66629

Keywords

  • Chlorides
  • Concentrating solar power
  • Corrosion
  • Heat transfer fluid
  • Molten salts
  • Thermal energy storage

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