Formation of Akaganeite in Atmospheric Corrosion of Carbon Steel Induced by NaCl Particles in an 85% RH Environment

Akaganeite is the most destructive corrosion product in a rust layer, and it accelerates the corrosion rate of steel in certain atmospheres. Until now, considerable controversy has existed regarding the conditions required for its formation and its mechanism of formation. In this work, the formation of akaganeite in the specific corrosion process, which was atmospheric corrosion induced by NaCl deliquescence, was investigated through simulated experiments in a laboratory setting. Stereoscopic microscopy and scanning electron microscopy were employed to characterize the morphologies of the corrosion products, which could illuminate the morphological features of the electrolyte induced by the NaCl particles. The constituents of rust in a single droplet were analyzed by micro-Raman spectroscopy, and the components of the corrosion phases on a macroscopic scale were analyzed by XRD. The results indicate that the deliquescence of NaCl particles caused droplets to form around them, and atmospheric corrosion occurred in each droplet independently. Akaganeite can form during atmospheric corrosion induced by NaCl particles in the early stage within 12 h. The initial corrosion products, lepidocrocite and magnetite, increase the amount of akaganeite formed. The amount of salt deposited also plays an essential role in the formation of akaganeite on a macroscopic scale.