Corrosion Behavior of Pure Iron by Different Droplet Volume of Sulfuric Acid Solution

Abstract

The influence of volume of aqueous sulfuric acid solution on the corrosion behavior of pure iron during the initial 0.6 ks was investigated by potentiostat and atomic force microscope (AFM). Three types of volume of solution, i.e., bulk solution, macro-droplet (millimeter size) and micro-droplet (micrometer size), were used.
A micro-droplet with diameter of 1∼10 μm can be placed on a pre-assigned target micro-zone of specimen by the cantilever tip of AFM. The corrosion behavior beneath the droplet can be investigated using both the contact mode and the a.c. non-contact mode of AFM. The corrosion rate in bulk solution is much higher than that beneath a micro-droplet of sulfuric acid solution. In the case of a micro-droplet, the corrosion rate is smaller for the smaller droplet. The drying of the micro-droplet to a solid corrosion product in 25–30%RH condition is faster than that in 50–70%RH condition.