Corrosion Under an Evans Droplet

Application ID: 113981

An Evans droplet experiment is a century-old corrosion experiment for demonstrating oxygen transport-limited corrosion. A droplet of water is placed on a metal surface, and over time the surface features differences in the radial direction of the surface in terms of amount of corroded material and deposited corrosion products.

This tutorial model defines corrosion of an iron surface in contact with a water droplet in a surrounding atmosphere containing both carbon dioxide and oxygen. The model accounts for charge and mass transport of a multitude of species as well as iron dissolution, oxygen reduction, carbonic acid equilibria and iron hydroxide formation.

The model computes the transient and spatial distributions of the various species within the droplet. A spatial gradient in pH is demonstrated and is attributed to the complex interplay between the dissolved iron and the carbonic acid.

This model example illustrates applications of this type that would nominally be built using the following products: