Corrosion Behavior and Mechanism of Fe-14Cr-Mn Alloy in Molten Eutectic NaCl-MgCl 2 at Different Temperatures

Abstract

Operating temperature waves around the melting temperature of molten eutectic NaCl-MgCl2 which is thermal storage media at medium-high temperature. But the corrosion behavior of the molten salt on metal at different temperatures is not clear. In the present paper, the corrosion behavior and mechanism of the molten salt on Fe-14Cr-Mn alloy were studied by an immersion salt corrosion method at 718, 768 and 818 K. Results show that corrosion rate increases lightly with the increase of corrosion temperature. Corrosion kinetics characteristics obey the linear law (slope k≈-4.806×10-4). At the early stage of corrosion, there are lots of vacuoles, while a large number of pit holes are formed after corroding for 80 h. Corrosion products are mainly Fe, Fe-Cr and MgO. Corrosion mechanism is as follows: absorbed oxygen on molten salt surface and oxygen atom that is introduced in the form of moisture-absorbed MgCl2 are as depolarizing agents. Chlorides of Cr and Mn are got when oxide of Cr and Mn react with Cl-. The chlorides of Cr and Mn with water, e.g. CrCl3• 6(H2O) and MnCl2• n(H2O) that have low melting point would escape from corrosion system. In addition, there is a salt crust that is composed of MgCl2• (H2O)6, NaCl and MgO on molten salt upper surface, while NaCl coexists with NaMgCl3 inside mixture salt.

Effect of Molten Salts Composition on the Corrosion Behavior of Additively Manufactured 316L Stainless Steel for Concentrating Solar Power

“…The corrosion process followed an active oxidation mechanism in which a chlorine cycle is assumed to have been involved due to the molten salt's presence, where MgO originated from the spontaneous decomposition of MgOHCl, which was generated from the hydrolysis of hydrated MgCl 2 as MgCl 2 •H 2 O, following reaction (5). Then, chlorine reacted with metal elements to produce volatile metal chlorides via reaction (6), escaping the corrosion system [52]. In this context, some alloying elements like Cr, which has lower standard electrode potential in molten chlorides compared with Fe or Ni, could not avoid the corrosion process [53].…”