Hot corrosion behavior of commercial alloys in thermal energy storage material of molten MgCl2/KCl/NaCl under inert atmosphere

Re‐establishing the paradigm for evaluating halide salt compatibility to study commercial chloride salts at 600°C–800°C

“…The salt components KCl and NaCl are some of the most stable chlorides followed by MgCl 2 , that is, they have the most negative Gibbs energy relative to elements in the standard state. Some of the minor alloy additions such as Al and Mn are next followed by Cr, which is expected to be selectively attacked . Some of the least stable chlorides are Ni and Mo.…”

“…The characterization of these specimens is still in progress, but the results indicate that it is possible to improve the compatibility of Cl salts and achieve much lower corrosion rates than reported in the literature. To compare these results to the recent literature, the mass change was converted to metal loss using the alloy density and linear kinetics were assumed. The largest mass loss amounts in the TCL correspond to a 9 µm/yr corrosion rate, which suggests that this commercial salt can be compatible with alloy 600 at up to 700°C.…”

“…A recent literature review concluded that purified salts and sealed containers had a significant effect on corrosion rates . Also, in the recent chloride salt literature, it is common to extrapolate isothermal results and report an annualized rate of attack (i.e., µm/yr) as a performance metric . That is inappropriate for two main reasons: first, an assumption must be made about the kinetics and the assumption of a linear extrapolation is not based on any mechanistic understanding or data.…”

“…While a variety of thermal storage concepts can be considered, one strategy is to select a salt with higher temperature capabilities, such as chloride or fluoride salts, with chloride salts being favored due to lower costs . However, numerous recent isothermal assessments have indicated that chloride salts can be extremely corrosive to structural alloys at ≥600°C . But these results need to be considered in the context of how fluoride salts (e.g., FLiBe) were evaluated for and deployed in the molten salt reactor experiment conducted at Oak Ridge National Laboratory (ORNL) from 1965 to 1969 .…”

Enabling chloride salts for thermal energy storage: implications of salt purity

“…High temperature molten salts exhibit properties ideally suited for use as heat transfer uids (HTFs) in solar thermal collectors, nuclear reactors, and heat recovery systems in factories. [1][2][3][4][5][6][7] Mixed molten salts have high heat-capacity, are chemically stable at elevated temperatures, and exhibit a tailorable melting point through compositional changes. A large body of work has been performed on uoride, nitrate, and carbonate salt mixtures, such as lithium beryllium uoride (FLiBe), [8][9][10][11] sodium potassium nitrate (NaNO 3 -KNO 3 ), 7,[12][13][14] lithium potassium carbonate (LiKCO 3 ), 15,16 and many others.…”