High temperature molten salt corrosion of structural materials in UCl₃–LiCl–KCl

Abstract

High temperature corrosion behaviour of 2.25Cr-1Mo, 9Cr-1Mo and SS 410 in molten UCl 3 -LiCl-KCl salt at 500 and 600°C under inert and reactive atmospheres for 24 h were studied by thermogravimetry. The results indicate marginal weight gains in all the alloys. In all conditions, except at 600°C under reactive atmosphere, the weight gains were higher in initial period of exposure. The weight gain was continuous for samples studied at 600°C under reactive atmosphere. The 2.25Cr-1Mo showed higher weight gain in an inert atmosphere, whereas SS 410 showed more weight gain at 500°C and 9Cr-1Mo at 600°C under reactive atmosphere. The weight gains were attributed to the formation of γ-FeOOH, α-Fe 2 O 3 , Fe 3 O 4 , FeCr 2 O 4 and Cr 2 O 3 as confirmed by Raman spectra analysis. The oxide films formed are neither uniform as evidenced from SEM-EDS analysis nor protective, attributed to the corrosive and aggressive nature of molten chloride salts.

High-temperature electrochemical corrosion evaluation of 2.25Cr–1Mo alloy in eutectic LiCl–KCl molten salt

“…The formation of metal chlorides from the alloy matrix are also favourable at the studied temperature as the Gibb's energy of the formation of metal chlorides are more negative [42]. The formation of corrosion product regions and dissolution regions were also observed during the immersion studies of alloys in molten LiCl–KCl salt using thermogravimetry [42], in UCl 3 –LiCl–KCl salt [4,5] and weight loss measurements [3]. The monitoring of OCP indicated the formation of intermittent oxide films as indicated by the fluctuations of OCP across the total period of 200 h. The linear polarisation and impedance studies indicated the increase in corrosion of the alloy with the duration of immersion in molten salt by the reduction in the polarisation resistance values.…”

“…Furthermore, the understanding of high-temperature corrosion attacks of materials for reliability, economy, quality, safety and profitability of any industrial sector associated with the high-temperature process using molten salts is of utmost importance. The corrosion evaluation of structural materials in aggressive environments like molten salts is generally studied by carrying out immersion experiments [3][4][5], salt deposit coatings experiments [6,7] and electrochemical techniques [1,8,9] as in the case of aqueous corrosion evaluation at lower temperatures. Electrochemical methods are rapid and potential and suitable techniques for evaluating corrosion behaviour of alloys in situ compared with the conventional corrosion evaluation methods [10,11].…”