Effects of Nitrogen Deficiency on the Kinetics and Mechanism of Electrolytic ZrN _x Oxidation

Abstract

Use has been made of potentiodynamic polarization curves, XRD, and scanning electron microscopy (SEM) in the electrolytic oxidation in 3% NaCl solution for specimens of nitrogen-deficient zirconium nitride (ZrN_0.67, ZrN_0.77, ZrN_0.87, and ZrN_0.97), as well as pure zirconium. In all cases, the anodic polarization curves have several stages which characterize during oxidation both active dissolution of ZrN _x and Zr in the electrolyte as well as the formation of surface layers of ZrOCl₂, ZrN _x O _y , and α‐ZrO₂ of monoclinic form. The corrosion resistance of single-phase ZrN _x specimens in 3% NaCl solution decreases in the sequence ZrN_0.97 → ZrN_0.87 → ZrN_0.77, and the initial stages of interaction between the specimen surface and the electrolyte largely determine the subsequent behavior of specimens. It is found that ZrN _x containing a large number of nitrogen atom vacancies, in particular ZrN_0.77, is closer in corrosion behavior to metallic zirconium than it is to stoichiometric ZrN (the reduction in the corrosion resistance is undoubtedly due to the reduction in the ionic-covalent components of the bonds in ZrN _x ).