Effects of zinc–aluminium injection on corrosion behaviour and semiconductor properties of carbon steel in the PHT system of PHWR

Abstract

Carbon steel is widely used as the piping of the primary heat transport system (PHT) in pressurized heavy water reactors (PHWR). Effects of zinc/aluminum treatment and simultaneous injection of zinc and aluminum on corrosion behavior and semiconductor properties of oxide films formed on carbon steels were characterized by the gravimetric method, potentiodynamic polarization scan, EIS, Mott–Schottky test, SEM, EDS mapping, XPS analysis and photocurrent response measurement. The results showed that all the metal cation ions treatment can improve the corrosion resistance of oxide films in varying degrees. 20 ppb Zn²⁺ had the greatest enhancement in corrosion resistance, followed by 20 ppb Zn²⁺ + 20 ppb Al³⁺. ZnFe₂O₄, FeAl₂O₄ and ZnAl₂O₄ were detected to be new spinel phases generated in oxide films. The oxide films on the surface of carbon steel all demonstrated n-type semiconductor properties. It was worth noting that the total content of manganese and zinc in the oxide film played an important role in the corrosion resistance of carbon steel.