Localized Electrochemical Corrosion Measurements - Princeton ...

Localized Electrochemical Corrosion Measurements Rob Sides, Ph.D. Princeton Applied Research www ametek com www.ametek.com

Leaders in Corrosion Control Technology

Bulk Electrochemical Corrosion Measurements • A voltage is applied to the metal sample in order to drive the corrosion reaction. • Current flows and is measured as the response response. • By knowing the electrons-per-ion ratio and material’s t i l’ physical h i l proprieties i ti ((molecular l l weight, i ht density, etc.) current is converted to a corrosion rate rate. Leaders in Corrosion Control Technology 2

Electrochemical Corrosion Measurements

Apply polarization to cause corrosion to happen happen.

Measure current (rate of electrons, thus reaction). eact o )

Convert current into corrosion rate, assuming uniform di t ib ti distribution.

Leaders in Corrosion Control Technology 3

Bulk versus Local Measurements • In Bulk experiments, experiments such as Tafel, Tafel LPR, LPR and EIS, a potentiostat measures an averaged integrated current across the averaged, entire sample. • It is not able to distinguish between electrons from an intense pit, or several less-intense pits or uniform corrosion corrosion. The electrons all look the same. Leaders in Corrosion Control Technology 4

Bulk versus Local Measurements Local measurements are made by positioning an external measurement probe close (