Electrochemical Formation Mechanism of Microdroplets on Pure Iron.

Xiao Tang,Yuan Wu,Juanjuan Li,Haiming Fan,Yan Li,Hao Hu,Chao Ran Ma

doi:10.3389/fchem.2021.610738

Abstract

The electrochemical formation mechanism of microdroplets formed around a primary droplet of 3.5% NaCl solution on an iron-plated film was investigated by quartz crystal microbalance (QCM) and concentric three-electrode array (CTEA) measurements. During the initial stage, the microdroplets mainly originate from evaporation owing to cathodic polarization and electric current of the localized corrosion cell under the primary droplet. The maximal electrochemical potential difference between the anode and cathode was measured to be 0.36 V and acted as the driving force for the formation of microdroplets. The maximums of anodic and cathodic electric current density of pure iron under the NaCl droplet are 764 and −152 μA/cm2, respectively. Propagation of microdroplets in the developing stage attributes to horizontal movement of the electrolyte, water evaporation, and recondensation from primary and capillary condensation from moist air. The results of the study suggest that the initiation and propagation of microdroplets could promote and accelerate marine atmospheric corrosion.

Highlights

Steel structures in coastal regions experience marine atmospheric corrosion, which is affected by factors such as the presence of pollutants, temperature, relative humidity (RH), and wind
The images reveal that a large number of microdroplets are formed around the primary droplet, and the size of the droplet decreases with the increase in distance from the primary droplet
The results show that the microdroplets are not separated and migrated directly from the primary droplet; otherwise, the microdroplets will appear red consistent with the primary droplet

Summary

Introduction

Steel structures in coastal regions experience marine atmospheric corrosion, which is affected by factors such as the presence of pollutants, temperature, relative humidity (RH), and wind. In a simulation of atmospheric corrosion on carbon steel, Wang et al observed the formation of tiny microdroplets around a macroscopic salt solution droplet (Wang and Tsuru, 2003). A number of investigators have focused on the microdroplet formation phenomenon, which is closely related to atmospheric corrosion. Studies on the microdroplets have been conducted from various perspectives such as chemistry and growth characteristics (Tsuru et al, 2004), electrochemical investigations (Zhang et al, 2005), microscopic observations (Bian et al, 2005), the effect of electrochemical polarization on the microdroplet formation (Wang et al, 2008), and the effect of the properties of the primary droplet on the microdroplets (Liang et al, 2006). It was found that cathodic polarization can initiate and accelerate the formation of microdroplets, whereas anodic polarization can inhibit the microdroplets formation

Objectives

Results

Discussion

Conclusion