Long Lasting Time Outdoor Atmospheric
Corrosion Tests: Electrochemical Analysis
Author(s)
M. Leiro & E. S. Ayllón
Abstract
When submerging a pure metal or an alloy in an aqueous solution, a migration of
metallic ions between the solid phase and the aqueous phase starts immediately.
In fact, it is a constant exchange of metallic ions in which the prevailing speed
will be the one leading to a decrease of the free energy (W) of the system.
The passing of the metallic ions to the solution will create a potential
difference in the metal-solution interface, which will hinder the passage of new
ions. A potential difference will be reached, in which the free energy variation
will be null, and a thermodynamic equilibrium will exist.
If the metal is submerged into a solution that has its own ions, the
electrochemical potential will be different in each metal. Noble metals are those
like gold (Au), and Platinum (Pt), whose ions are deposited on the metallic solid
phase thus increasing their potential with respect to the solution. The metal will
be traditionally more positive than the solution.
Those metals like Iron (Fe) and Zinc (Zn) will have a tendency to pass to a
solution, no matter their ionic concentration, getting the metallic solid phase
lower potentials than the solution, or negative potentials in contrast with noble
metals.
The direct measurement of the potential difference between the metal and the
solution is experimentally impossible. However, a cell with two electrodes can
be formed to measure the potential difference between the two. One of the
electrodes will be the pure metal or alloy, whose potential we are interested in
finding out, and the other will be an electrode with an easy-to-reproduce
potential to take it as a pattern.
Keywords
atmospheric corrosion, electrochemical analysis
Related Book
Other papers in this volume
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