Comments from Jim Jenkins

Richard:

In addition to all of your comments, most of which I agree with, any potential measurement using a reference electrode where the absolute potential is to be determined needs to include the temperature of the reference electrode at the time of measurement. This is a bigger problem for the Cu/CuSO, than for the Ag/AgCl reference, but is a problem for both. In fact, I actually made the statement at an early RP-0169 revision meeting that "any absolute potential reading using a reference electrode where the temperature of the reference electrode is unknown is meaningless". I don't even think that using a reference electrode for potential rise or decay is valid unless the temperature of the reference electrode is known, or known not to change significantly during the measurement.

I hate zinc reference electrodes as I have found that the potential of even a freshly polished zinc reference can vary on soil by over 200 mV. It is closer for a freshly polished zinc reference in seawater ( about -1.05 V vs Ag/AgCl ) but the main problem in seawater is that the zinc always becomes more electropositive which indicates a more protected potential than would be measured when using a real reference electrode such as an Ag/AgCl. I am currently working on a project where using a zinc reference (even after I warned the owner that this is not satisfactory) to monitor a C.P. system has resulted in several millions of dollars of damage to a marine structure. Why risk structural integrity to save $ 100.00 on a reference electrode?

I plan to remain a voice in the wilderness on this and will continue to vote negative on SP-0169 until this is included. I have given my comments to NACE previously on this with my negative vote with no success.


Jim Jenkins