difference ''Polarization Resistance'' and ''Electro-chemical noise'' measurement

[bert vdb]

hi all,

First, I am kind of new to corrosion and corrosion monitoring. So, my apologies in advance for maybe asking a trivial question. But any help is appreciated.

Anyway, I was wondering about the actual difference between the measurement of polarization resistance and electro-chemical noise. As I see it, electro-chemical noise is the corrosion current running from one electrode to an other due to electrons which got free from the corrosion reaction. Now, the polarization resistance is based on that same corrosion current. However, it is measured indirectly by applying an external voltage and measuring the delta current-voltage.

So my question: Is my understanding above correct? If not, what am I missing? If so, which are the drawbacks/advantages of both methods?

Thanks in advance!

 

[Chumpes]

hello

polarization resistance is the slope of the curve of electrical tension vs. curent intensity around open circuit potential (U = R.i). it is measured by applying a cyclic curent intensity (or cyclic tension) to an electrode vs. reference electrode (cyclic polarization), and to measure the resulting tension (or curent intensity) in the electrode of interest (working electrode). the more resistance you have, the less corrosion you have, as corrosion rate is proportionnal to curent intensity

electrochemical noise is totaly different. it is a measurement of the curent intensity peaks that occur between two similar working electrodes (steel for example) in electric contact when a corrosion event (pit?) occurs on one of the 2 electrodes. the number of peaks in a period of time and their intensity defines the electrochemical noise.

regards

 

[WKTaylor]

For Steels...

electrochemical noise = 'Barkhausen noise' [testing] ???

Regards, Wil Taylor

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[EdStainless]

No Barkhausen noise is an electromagnetic effect.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[bert vdb]

Thank you Chumpes, it helped me putting some things together.

One follow question I have is: if Rp low, does it mean that the metal is corroded or that the metal is corroding this instance? in other words, can Rp measure in how bad of shape the metal is (even if no corrosion is happening at that moment)?


kind regards,

Bert