s Corrosion Behavior on Ni-base Alloys Applied with Nano-TiO2 in High Temperature Caustic Water

In Pressurized Water Reactor (PWR) power plants, Alloy 600, a Ni-Cr-Fe alloy, is used for steam generator tube materials. However, these tubes have experienced a lot of corrosion problems during their operation times. Several chemicals have been investigated for inhibitors of stress corrosion cracking (SCC) in the tube materials. Titanium dioxide (TiO2), which is sonochemically treated in water, was tested to evaluate the inhibition effect of SCC using a reverse U-bend specimen of alloy 600 under the condition of a 10% NaOH solution and a temperature of 315°C. The TiO2 particle size was reduced by ultrasonic power, and the morphology of the TiO2 powder was observed by a transmission electron microscope (TEM) based on the ultrasonic processing times. The particle size of TiO2 affects the SCC rate of the tube materials, and shows an improvement in resistance on SCC when decreasing the particle size of TiO2. When the nano-sized inhibitor is applied, the property of the oxide layer is changed to a more dense composition. The chemical composition in the oxide layer was analyzed using an X-ray photoelectron spectroscope (XPS) with a variation in the ultrasonic process times, and the difference in the Ti-compound structure between the oxide surface and inner layer of oxide was compared using XPS data.