Electrochemical Corrosion Behavior of Carbon Steel under Thin Electrolyte Layer Containing NaCl

The self-built electrochemical measurement system of thin electrolyte layer was utilized to investigate the electrochemical characteristics of carbon steel corrosion under thin electrolyte layer containing Cl- by means of polarization curves and electrochemical impedance spectroscopy. In the case of a thicker electrolyte layer, a slower corrosion rate can be observed due to the difficult oxygen diffusion. With the thinning of electrolyte layer, the diffusion of oxygen and corrosion products becomes relatively easy, which promotes the corrosion process. The corrosion current density and limiting diffusion current density reach the maximum value at 350μm in layer thickness, which reveals the easiest corrosion tendency and the biggest corrosion rate. As the thickness of the electrolyte layer is reduced, the anodic process is inhibited and the corrosion rate slows down. The Nyquist curves for initial corrosion process consists of capacity reactance arc at high frequency and diffusion impedance at low frequency. As corrosion continues, the Nyquist curve comprises capacity reactance arc at high frequency and capacity reactance arc at low frequency, and all show two time constants. Electron transfer resistance decreases, suggesting the increase of corrosion rate with corrosion time, which results from the strong attack of chloride ion and the formation of loose and porous corrosion products.