Corrosion behavior of UCX, KHR35, and KHR45 alloys in molten nitrates

Abstract

The corrosion behavior of three high-Ni, high-Cr alloys, that is, UCX, KHR35, and KHR45 alloys, in a mixture of 60% NaNO 3-40% KNO 3 at 600°C has been evaluated by using weight loss tests, potentiodynamic polarization curves, and electrochemical impedance spectroscopy measurements. Cr contents ranged between 23.25 and 43.2 wt.%, whereas Ni ranged between 36.6 and 50.3 wt.%. For comparison, the same studies were performed on 304-type stainless steel (304SS). Tests were complemented with detailed scanning electronic microscope and X-ray diffraction studies. Results showed that that the three high-Ni, high-Cr alloys had lower weight loss than that for 304SS. Polarization tests indicated the formation of a passive layer in all cases. Electrochemical impedance spectroscopy data have shown that the corrosion mechanism for all the alloys was charge transfer from the alloy to the molten salt. Finally, X-ray patterns showed the presence of Cr 2 O 3 in all tested alloys, which is responsible for the observed passive behavior and their corrosion resistance.

Corrosion behavior and mechanism of 316 stainless steel in NaCl–KCl–FeCl3 molten salt and vapor at 300°C

“…The annual corrosion rate of the alloy is calculated in Equation () [ 24 ] $$${CR}=(K\times w)/(t\times \rho ),$$$ where CR is the corrosion rate per year (μm/year), K is a constant and is 8.76 × 10 4 , w is the mass change per unit area before and after corrosion (mg/cm 2 ), t is the corrosion time of the sample in molten salt (h), and ρ is the alloy density (g/cm 3 ).…”