Corrosion data using Electrochemistry

Sgta

Hi,

I am a Chemical Engineer but a novice in electrochemistry; hence the query might sound very basic to everyone.

We have an industrial electrochemical process (With Iron anode) and we are conducting a lab experiment to understand what is the effect of electrolyte pH on corrosion rate of Iron (this will include corrosion + electrochemical dissolution). The experiment involves using electrolyte at different pH values galvanostatically in a stirred cell (using a potentiostat) on a known weight of Fe electrode and measuring the weight loss after a period of 2-3 hours of galvanostatic operation. The working electrode in the lab is of course, the Anode (Fe).

My issue relates to the potential being measured in the lab. In our plant, the potential difference between our electrodes is between 3-4 V. In the lab experiment, the potential measured by the reference electrode is close to 6-7 V.

This makes me question :
a) Is our lab experiment at all happening under the same conditions as the plant? Since the potential is different, the corrosion/passivity reactions occurring on the lab Fe electrode might be very different from the plant.
b) If a) is right, do I need to ensure that the voltage in the lab stirred cell is close to the voltage in the plant.

Thanks,
Sgta

Borek

You need these potentials to be identical, no doubt about it. Actually to be sure you should work on having both potential difference and current density (A/cm²) similar to the production set up.

Sgta

Thanks Borek. I agree with your current density point too and are working towards it. Another question: 3-4 V is the potential difference between our electrode whereas 6-7 V is the potential measured for the working electrode i.e. it is the difference between the Anode and the solution. This means that the actual potential difference between the working and counter electrode in the lab is higher than 7 V. Is that right ?

Borek

Sorry, but I have problems following your description. In the electrochemistry world that I worked for a short time over 20 years ago we often used three electrodes setup:

- working electrode (be it anode or cathode, that depends on the system researched)

- reference electrode (one that is used to measure the potential of the working electrode)

- counter electrode (AKA auxiliary electrode) which is just a current sink - reference electrode is way too delicate to survive huge currents.

I am not sure I am able to translate your system to this one.