Wettability studies of LiCl-KCl and FLiNaK on metal and non-metal substrates

This study examines the wettability characteristics of molten LiCl-KCl and LiF-NaF-KF (FLiNaK) salts on a variety of metal and non-metal substrates, including C276, stainless steel 304 (SS 304), stainless steel 316 (SS 316), Alloy 617, molybdenum (Mo), nickel (Ni), tantalum (Ta), IG110, glassy carbon, MACOR and quartz, which are relevant for applications in molten salt reactors (MSRs) and differential scanning calorimetry (DSC) analysis. Contact angle measurements were conducted from room temperature up to 700 °C using the sessile drop method, revealing increased wettability of both salts as temperature increases. For LiCl-KCl tests, the contact angles on each substrate are in descending order as follows: θ_IG110 > θ_{glassy carbon} > θ_Mo > θ_{SS 304} > θ_C276 > θ_MACOR > θ_{SS 316} > θ_{Alloy 617} > θ_quartz ≈ θ_Ni > θ_Ta. For FLiNaK, the measured contact angles follow a similar trend: θ_IG110 > θ_{SS 304} > θ_quartz > θ_C276 > θ_{SS 316} > θ_Ta. The wetting of FLiNaK on the same substrate tends to be higher than that of LiCl-KCl, likely due to the larger surface tension between LiCl-KCl and substrates. The work of adhesion calculated from the contact angles shows an increase in adhesion force with increasing temperature for most substrates, indicating stronger contact between the salts and substrates. Contact angle is shown to be correlated with the corrosion resistance of pure metals, but this correlation is not observed in alloys due to their complex chemical compositions. The application of contact angle in the selection of DSC container materials is also suggested to ensure proper contact and uniform thickness.