Isothermal and cyclic corrosion behaviour of Ni-based alloys in an electrochemical reduction process

Abstract

In this study, the isothermal and cyclic corrosion behaviours of Haynes 282 and Haynes 214 in a lithium molten salt were investigated at 650°C for 168 h and 7 thermal cycles, respectively; this was achieved by measuring the mass changes, surface and cross-sectional morphologies with their elemental distributions, and compositional changes in the subscale, substrate and spalled oxide scale. The weight loss of Haynes 282 comprising an external corrosion layer was approximately four times lower than that of Haynes 214 with a spalled external corrosion layer, depending on the effects of their alloying elements and the preservation, spallation and dissolution of the corrosion layer. After 168 h and 7 thermal cycles, corrosion products of Haynes 282 were Cr 2 O 3 and CoCr 2 O 4 and those of Haynes 214 were Cr 2 O 3 , LiFeO 2 and FeCr 2 O 4 . In addition, the internal corrosion layers of Haynes 282 and Haynes 214 exhibited localised and uniform corrosion behaviours, respectively.

Cyclic oxidation and hot corrosion performance of direct metal laser sintered and wrought alloy 718 at 800°C in air and molten salts containing Na2SO4, V2O5 and NaCl

“…Mo gets oxidised, and it has resulted in MoO 2 formation. Further, MoO 2 is converted into MoO 3, which is not identified by XRD due to volatilisation at 800°C [22–26].…”

“…Due to the high partial pressure of O at 800°C, metal chlorides were evaporated as gas because of their volatile nature. Based on the Equations ( 12)-( 15), the remaining metal chlorides reacted with O to develop porous scales and Cl (Here, M refers to Ni and Cr) [24][25][26][27][28]. Chloride deposits could form the low melting eutectic phase, which dissolves the scales and produce gaseous chlorides, and porous scales are known as active oxidation.…”

Effect of reaction temperature on the corrosion behaviour of Inconel alloys in lithium molten salt under an oxidising atmosphere

“…The ones mentioned above will be discussed in more detail in Corrosion behaviours. Furthermore, Figure 5 shows the attack depth after 24 h (Figure 5 25,39 ; therefore, Cr 2 O 3 is initially formed as a corrosion product. In case of FeCr 2 O 4 (spinel-type), given that the diffusion coefficient of metal ions in the oxide is Fe 3+ > Fe 2+ > Ti 3+ > Ni 2+ > Cr 3+ , 40 the Fe-based oxide appears to be formed via an external diffusion of the Fe ions through the initially formed Cr-based oxide layer, and subsequently, FeCr 2 O 4 is considered to be formed by a solid-state reaction with the corresponding oxide (FeO and Cr 2 O 3 ).…”

“…22 Specifically, during the electrolytic reduction of spent oxide nuclear fuel in a molten lithium salt system containing highly corrosive and strongly basic Li 2 O, the oxygen generated at the anode and resulting high-temperature molten lithium salt can lead to a chemically aggressive environment, which is excessively corrosive for ordinary structural materials. 2,[24][25][26][27][28] Hence, studies on the hot corrosion of Ni-base alloys, which are used to fabricate the equipment related to the handling of high-temperature molten salts owing to their excellent resistance to corrosion at elevated temperatures, [29][30][31][32][33][34][35] have been conducted. In addition, long-term corrosion resistance is an important parameter, which is used to determine the suitability of structural materials requiring continuous exposure to high-temperature molten salts.…”

“…Few reports on the high-temperature corrosion behaviours of Ni-base alloys in a LiCl-Li 2 O molten salt are available. [24][25][26][27][28] According to these reports, in addition to the formation, maintenance and spalling of the external corrosion layer and the shape and growth of the internal corrosion layer, the depletion region of major alloying elements formed beneath the corrosion layer has a significant effect on the weight loss of the alloy. Many alloys for hightemperature applications are based on Ni and/or Co due to their better corrosion resistance and rely on the formation of Cr 2 O 3 layers for protection against corrosion.…”