The Effect of Time in the Anodizing Process on the Coating Characteristics and Corrosion Behavior of Zirconium Metal

Abstract

Zirconium and its alloys are the standard material for nuclear fuel cladding in Pressurized Water Reactors (PWR) due to their low neutron absorption cross-section, excellent mechanical properties, and good corrosion resistance in high-temperature water. However, the operational environment of a PWR imposes severe conditions that can degrade the cladding integrity over time, including oxidation, hydriding, and mechanical damage such as scratching or denting during fuel refueling operations. These surface defects can act as initiation sites for localized corrosion, potentially compromising the primary containment barrier. This study investigates the effectiveness of electrochemical anodizing as a surface modification technique to enhance the performance of Zirconium. The anodizing process was conducted at a constant voltage of 30 V with varying durations of 10, 15, and 20 minutes. The resulting surface characteristics were evaluated using Optical Microscopy, Digital Microscopy for roughness analysis, and X-Ray Diffraction (XRD). Mechanical reliability was assessed via Vickers Microhardness testing, while Corrosion behavior was studied in a 3.5% NaCl solution using Open Circuit Potential (OCP), Potentiodynamic Polarization (PDP), and Electrochemical Impedance Spectroscopy (EIS). The results demonstrated that increasing the anodizing time significantly improved the surface quality, reducing the arithmetic mean roughness Ra from 0.53 µm (10 min) to 0.24 µm (20 min). XRD analysis confirmed the formation of a crystalline ZrO₂ oxide layer. Electrochemical tests revealed a substantial enhancement in corrosion resistance; the corrosion current density i_corr decreased by two orders of magnitude from 12.93 x 10^-9 A/cm² for the substrate to 0.19 x 10^-9 A/cm² for the 20-minute anodized specimen. The study concludes that a 20-minute anodizing treatment at 30 V produces a robust, smooth, and highly corrosion-resistant oxide layer suitable for mitigating degradation in nuclear fuel cladding applications.