Effect of polishing on the morphology of Zircaloy-4 nanostructure: formation of a novel hexagonal nanoscale pattern

Abstract

Zircaloy-4 (Zr-4) is widely used as the cladding material in nuclear power plants (NPPs) due to its excellent corrosion resistance and low neutron absorption cross-section. Under Loss of Coolant Accident (LOCA) conditions, oxidation of Zr-4 can compromise the safety of the NPPs by accelerating hydrogen production. Therefore, enhancing the oxidation resistance of Zr-4 is a critical research focus. Surface modification through a facile method offers a promising approach to address this issue. This study explores the impact of chemical, mechanical, and electropolishing (EP) pre-treatments on Zr-4 morphology before and after anodization. EP conducted in ethylene glycol monobutyl ether–perchloric acid electrolyte produced a mirror-like surface finish with hexagonal nanopattern formation under optimized conditions, as revealed by SEM studies. Anodization of the patterned surface in a glycerol-based electrolyte resulted in a hybrid (nanoporous and nanotubular) structure, unlike the nanotubular-only morphology observed in the chemically or mechanically polished samples. EDAX and XRD analyses confirmed the formation of ZrO₂. The hexagonal nanopattern generated by EP suppressed the dissolution of the nanotube during anodization, resulting in a hybrid nanostructure. Additionally, the chemical polishing of EP-treated Zr-4 in HF : HNO₃ : H₂O generated a porous particulate structure due to selective etching. This work demonstrates that the surface pre-treatment significantly influences the morphology of anodized Zr-4 nanostructures and suggests the potential use of EP in other materials for hexagonal nanopattern generation.