E. A. Karfidov, E. V. Nikitina
ABSTRACT
The effect of temperature in the range from 500 to 800°C on nickel (N1) corrosion was studied during testing in a salt melt of a eutectic mixture of lithium and potassium chlorides, with the addition of lanthanum trichloride from 0.5 to 2 mol. %. The corrosion rate of nickel increases with increasing temperature, the addition of lanthanum chloride reduces the corrosion rate at 500–650°C (inhibition of the shielding type due to the subsequent chemical reaction). The corrosion potential of nickel is approximately –0.5 V relative to the silver chloride electrode at a temperature of 500°C and decreases slightly with increasing temperature, and does not depend on the concentration of lanthanum chloride. To concretize the mechanism of corrosion damage, the current-voltage curves were taken with the content of lanthanum chloride 0.5 and 2 mol. % at sweep speeds of 10 and 20 mV/s. X-ray phase and micro X-ray spectral analysis methods were used. The sweep speed does not affect the course of the irreversible electrochemical oxidation process, and the addition of lanthanum chloride increases the current density in the anode region tenfold. Comparison of corrosion rates obtained by gravimetric and chemical-analytical methods, allows us to speak about the electrochemical mechanism of corrosion.
KEYWORDS nickel, chloride melt, corrosion, lanthanum trichloride, temperature, surface morphology
DOI: 10.1134/S0235010619040078