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Corrosion Djinn™

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Although galvanic potential difference (difference between Open Circuit Potentials, OCP) acts as a battery to drive galvanic corrosion, it is not widely realized that the corrosion rate is governed by galvanic current, which is determined by the kinetics/electrochemistry of the surface. Consequently, relying on galvanic tables as most standards and guidelines do, often results in very poor material and coating choices.

For this reason we have developed Corrosion Djinn™, a web app for engineers that quickly calculates the corrosion current generated between materials based on their full electrochemical polarization curves.  Corrosion Djinn™ is a quick and easy way to evaluate accurately the galvanic corrosion current (corrosion rate) between materials and coatings.  It is based on a database of validated, curated data obtained by members of the ONR Sea-Based Aviation Team, and has been validated against galvanic assembly corrosion data and CAE analysis models.

For example, the galvanic table in MIL-STD-889 says that putting titanium next to aluminum is a very bad idea, since these two materials are at opposite ends of the galvanic chart. Copper, on the other hand, is somewhat closer to aluminum galvanically, although still quite cathodic. Therefore the standard galvanic table says that corrosion of aluminum against titanium would be worse than against copper. A couple of minutes with Corrdesa’s new Corrosion Djinn™ web app shows how wrong this is:

Material 1 & OCP (mV, SCE)

3.5% NaCl

Material 2 & OCP (mV, SCE)

3.5% NaCl

Potential difference (mV)

Corrosion current (rate) (mA/m2)

Al 2024 (chromate converted)

-615

Copper (pure)

-248

367

150

Al 2024 (chromate converted)

-615

Ti6Al4V

33

648

1.9

Al 2024 (chromate converted)

-615

15-5PH stainless

58

673

100

 

So the galvanic interaction is almost two orders of magnitude lower with titanium than with either copper or stainless, because of surface chemistry, which controls the kinetics. This is an extreme example, to be sure, but the same approach also shows that repairing aluminum airframes in Naval aircraft with titanium instead of stainless steel bushings (as they currently do based on the galvanic table) will reduce subsequent corrosion by one or two orders of magnitude.

This calculation is illustrated in a real-time video at:

http://www.screencast.com/t/XNCfzmTDq 
and 
https://www.youtube.com/channel/UCb7Vup7hLDHFGL7xs6mv2HQ 

 
How do I get Corrosion Djinn™?

On-line version:  http://corrosiondjinn.com  Note: Corrosion Djinn™ runs on HTML 5.  It will not run on older browsers, and is best on the latest versions of Chrome, Firefox, Internet Explorer, etc.

Username/password, technical help:     

Keith Legg , (847) 219-9868
Alan Rose , (770) 683-3960

You don’t have the data for my materials

Corrosion Djinn rests on a robust database of consistent electrochemical data.  If you can supply us either with reliable polarization data taken according to our Best Practices (which we can supply), or with samples of your materials and coatings, we will take the polarization data and incorporate it into the database for free.  Please contact Alan Rose or Keith Legg to discuss incorporating your materials.