Abstract
Passive films were formed on A508-3 steel (A508-3), 304L stainless steel (304L) and Incoloy 800 (In800) with blank/zinc/zinc–aluminum treatments in air at 300 °C. The electrochemical corrosion behaviors of different metals were investigated through potentiodynamic polarization, electrochemical impedance spectroscopy and the Mott–Schottky technique. The morphology and composition of passive films were analyzed using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The zinc–aluminum treatment effectively reduced the corrosion current and increased the impedance of A508-3 and 304L, but had a weak effect on In800. The zinc–aluminum treatment reduced the carrier concentration of A508-3 and changed the semiconductor property of 304L and In800. The order of zinc–aluminum treatment for improving the corrosion resistance of three metals was: A508-3 > 304L > In800. In addition, the zinc–aluminum treatment enhanced the density and smoothness of passive films. According to the composition analysis, spinel ZnAl2O4 was formed on three metals; however, the amount of spinel varied with the content of nickel and chromium in different metals, which affected the results of using this technology.
Highlights
The main structural materials in the primary circuit of pressurized water reactor (PWR) nuclear power plants are composed of stainless steel, nickel alloy and low alloy ferritic steel [1,2,3,4,5]
It could be seen from the n value of Qout in the G(blank) and G(40Zn) of A508-3 that the outer layers of the passive films formed on A508-3 with the blank treatment and zinc treatment were close to the Warburg impedance caused by semi-infinite diffusion, which indicates that concentration polarization occured on the surface of passive films fomed on A508-3
Compared with the zinc treatment, the zinc–aluminum treatment could further reduce the corrosion current density and increase the impedance of the passive films formed on A508-3 and
Summary
The main structural materials in the primary circuit of pressurized water reactor (PWR) nuclear power plants are composed of stainless steel, nickel alloy and low alloy ferritic steel [1,2,3,4,5]. Researchers proposed that aluminum could combine with zinc to participate in the formation of the passive film to make the morphology of the passive film denser, and to generate a ZnAl2 O4 phase with extremely low solubility and high stability, which enhances the corrosion resistance of the passive film This technology was used to conduct pre-experiments on different metals in laboratory conditions. It was not possible to rely on simple polarization curves and visual observations to determine whether the simultaneous injection of zinc and aluminum could generate key substances (ZnAl2 O4 ) in passive films on different metals If this technology could generate ZnAl2 O4 on the surface of highly corrosion-resistant metals and form a dense passive film, it would have a certain protective effect for the equipment in long-term service, and have a guiding significance for subsequent research and applications. The morphology and composition of passive films on different metal surfaces were comparatively analyzed using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS)
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