Effects of Zinc Surface Acid-Based Properties on Formation Mechanisms and Interfacial Bonding Properties of Zirconium-Based Conversion Layers

This study investigates the surface characteristics and deposition procedure of zirconium-based conversion layers on pure zinc substrates. The topography and composition of a set of pure zinc samples treated in alkaline, neutral, and acid solutions before and after deposition of the conversion layers were evaluated using X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM). Additionally, the depth profiles of the elements across the thickness of conversion layers as well as the deposition kinetics were characterized by means of Auger Election Spectroscopy (AES) depth profiling and recording the Open Circuit Potential (OCP), respectively. The acid-based properties of the obtained conversion layers were probed by adsorption of succinic acid molecules. The results revealed that the surface composition and deposition procedure of conversion layers strongly depend on the initial surface composition and roughness. Additionally, the adsorption of the succinic molecules was found to correlate to the surface hydroxyl fraction on the conversion layers, which in turn varied with the initial hydroxyl fraction on the based zinc substrates.