I am trying to do some basic electrochemical corrosion tests (OCP, EIS, LPR) on steel samples in an oil-based lubricant. The resistivity of the oil poses a problem for the measurements of potential and impedance. So to minimize this, I coated a silver wire with AgCl and use it bare in the lubricant as a reference electrode. I am using a graphite rod as a counter electrode and there is about 0.5 cm of space between the sample and reference electrode and the same between the counter and reference.
I ran OCP and EIS. The results are noisy and inconsistent. OCP is giving huge ranges of -10V-3V and EIS gives impedances at 1 Hz ranging from 4-400 GOhm. My questions are:
1. Is the use of a AgCl electrode bare (without KCl surrounding it) viable?
2. Are there other options to get accurate measurements in an oil-based lubricant?
1. I think you should use the conventional Ag/AgCl electrode for your analysis
2. the oil may foul the surface of your graphite counter electrode (just my opinion here) perhaps you should try platinum rod/wire
3. You should alternate try altering the amplitude in your EIS.
4. you may try running the PEIS at some impressed voltage wrt ocp rather than just at OCP
you may also try to run Galvabistatic EIS instead and also tweak the test parameters like in 3.
Dear Kai,
A vital part of any electrochemical sensing system is the reference electrode, which is a probe that is capable of measuring the potential on the solution side of an electrochemical interface. Common method, the silver/silver-chloride electrode is by far the most common type of electrode used in research and industry due to its simple construction. Silver wire coated with silver chloride, immersed in a Cl− ion rich solution in a glass tube and separated from the test solution via a membrane as well as a salt bridge. But if problem comes, optional is iridium electrode.
(1) If data problems are coming use pseudo reference electrode system iridium/iridium oxide. Typically, the set-up consists of an iridium metal which is then modified with an oxidizing agent to form an oxide coating.
(2) Micro Ag/AgCl Electrodes in Capillaries/ Microfabricated Ag/AgCl with Filling Solution, attach dynamic methods include impedance measurement may be suitable for analysis.
Ashish
What is the t main intention of using an electrochemical method for corrosion testing in an oil-based lubricant? Keep in mind that the potentiostat cannot control (or measure) the potential between your reference and working electrodes, unless a very small current flows through the circuit. I know that modern potentiostats work with extremely low currents. But I think, like some others have already stated, that you are pushing the limits of the experiment too far. What is the conductivity/resistivity of your oil? Can you add some organic electrolyte to it? I know this would alter the original idea of your corrosion test. But, if your experiment seems fine after adding some electrolyte, then you can be sure that you are facing a potential control problem due to the extremely high resistiviy of the oil. Try some of the suggestions from Artur Braun too.
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