No abstract

The properties of the oxide films formed on solution-annealed and cold-worked 316L stainless steel (SS) specimens with and without charged hydrogen in deaerated pressurized water reactor primary water at 300°C were investigated. The outer oxide layers of all specimens were composed of magnetite (Fe 3 O 4 ) and NiFe 2 O 4 . Charged hydrogen resulted in larger outer iron-bearing oxide particles forming due to hydrogen-enhanced outward diffusion of iron cations. Prior cold-work accelerates the oxidation was observed. Charged hydrogen led to local cracks in the oxide film and enhanced the penetration oxidation beneath the metal/oxide interface. The Cr-rich inner oxide layer grown on the prior cold-worked specimen with charged hydrogen was thicker than that on the cold-work specimen or the hydrogen-charged specimen, revealing the combined effects of charged hydrogen and prior cold-work on the acceleration of the oxidation process. The working mechanism of the solid-state hydrogen effect on the oxide film was discussed.

Effects of diffusing hydrogen atoms on anodic processes and pitting corrosion for iron in chloride-bearing bicarbonate solutions were studied with a dual cell for realizing the hydrogen diffusing and electrochemical measurements simultaneously. A high concentration of chloride in solution, pre-cleaning and diffusing hydrogen in iron can move the open circuit state from passive state to active dissolution state. Potentodynamic anodic polarization curves show that the effect of diffusing hydrogen is strongly dependent on the chloride concentration in the solution. The diffusing hydrogen atoms enhance the anodic reaction before the oxygen evolution potential when the chloride concentration is low while enhance the anodic reaction in the overall potential range when the chloride concentration is high. In addition, diffusing hydrogen atoms slow down the anodic reaction in the first current plateau regime if the chloride concentration is sufficiently high. For the hydrogen-diffusing electrode, the occurrence of the active dissolution regime is mainly from the surface cleaning effect, and the enhanced anodic reaction in the transition regime, pre-passive regime, passive film growth regime, passive regime, and in some cases, transpassive regime is due to both the electrode kinetics and the surface cleaning effect. Diffusing hydrogen would retard the anodic reaction in a specific potential regime through its combined effect with high concentration chlorides. More severe pitting is generally observed for the precleaned electrodes and the hydrogen diffusing than for the non-charged electrode. Depending on the applied potential and time as well as the chloride concentration, the hydrogen-diffusing electrode would show more extensive or severe pitting than the precleaned electrode, with some exceptions showing less severe pitting.