In the industrial field, one of the great enemies to avoid is undoubtedly that of corrosion. This phenomenon often goes unnoticed, but it ends up costing companies a lot of money. In the best of cases, if we are lucky, the corrosion is detected in time and it is only necessary to remove or replace the corroded element. In the worst cases, it leads to the failure of the machine or the installation, having to be repaired or replaced due to the failure of a single component.
What is the potentiostat corrosion test?
The potentiostat test consists of recreating an electrical circuit, which consists of the following parts:
- Cathode: it is the positive pole of the circuit, and a material with good resistance to corrosion is usually used.
- Anode: it is the negative pole of the circuit, and in this case, the material we want to test is used.
- Electrolyte: it is the conductive liquid that puts the cathode in contact with the anode to close the electrical circuit.
During the potentiostat test, a certain voltage is normally applied and it is varied over time to measure the current passing through the circuit. The more current passes through the circuit, the more corrosion is occurring at the anode.
Types of potentiostat tests
There are different types of corrosion tests that can be done with a potentiostat:
Determination of open circuit potential “OCP”
This test is used to determine the corrosion potential of materials. To do this, you simply have to leave the anode and cathode in contact with the electrolyte and record the voltage and current in the circuit. By not applying any electrical stimulus externally, the system tends to the equilibrium point, which is the voltage at which the least current passes through the circuit.
Linear polarization curve
In this test there are two different parts. The first is a brief OCP test, to know the corrosion potential of the material to be analyzed, and then a voltage sweep is made, starting from a point close to the OCP, to know how much current is passing through the circuit with the potential difference. In this way, it is possible to know, for example, the pitting potential of a steel, or what is the same, with what voltage difference will pitting due to corrosion begin to occur in said steel.
These are the two most basic types of tests that can be performed with a potentiostat, but there are many other more specific ones, which can give us useful information depending on the application.
What is the potentiostat corrosion test for?
This type of essay provides us with a great deal of information:
It indicates how easily a material has to be corroded. In the event that there is a union of two metals in contact with an electrolyte, the one with the lowest corrosion potential will act as the anode and will therefore corrode.
Intensity at different voltages
Indicates the corrosion rate that will occur in the event that the material acts as an anode. The lower the intensity that passes through the circuit, the lower the corrosion rate. If the recorded current is low during large voltage ranges, it will indicate that, although this material acts as an anode and will corrode, this corrosion will be slow and probably less problematic.
There are certain materials that register a drastic rise in current as soon as they move slightly away from their corrosion potential. When this happens, corrosion occurs quickly. However, there are certain materials, such as some steels, that keep the current low over a wide range of voltages. In these cases, there is a drastic increase in the intensity that passes through the circuit, but at a high voltage. This voltage is called pitting potential, and it is the one that, when exceeded, pitting due to corrosion begins to appear.
Taking into account these three parameters, by doing a potentiostat test on these materials, we will be able to know which ones will be more prone to corrode when in contact and which ones will corrode faster.
In turn, the possibility of measuring these parameters when the materials are in contact with different liquids, allows to know the behavior that they will have in certain applications and circumstances, which are difficult to reproduce with other corrosion tests.
In this way, we can, for example, evaluate the corrosion resistance of a metal in contact with water with different degrees of salinity, or in contact with various liquids, such as saliva, sweat, or blood.
Differences with other corrosion tests
It is true that the potentiostat corrosion test is a very useful test, and here we present the differences that make it stand out:
- Speed: the tests are fast, being able to obtain high degrees of corrosion in less than an hour, which contrasts with the tests of the salt spray chamber, which are more expensive in time.
- Electrolyte variation: potentiostat tests allow choosing the electrolyte that is most interesting at all times, thus being able to recreate the real conditions in which the material is going to work.
- Small sample size: depending on the galvanostatic cell that the potentiostat has, it will be necessary for the tested samples to have a certain size, but it allows flexibility, being able to measure from plates of a few centimeters, to threads of a few microns thick.
- Repeatability: unlike other corrosion tests in which environmental conditions play an important factor, in the potentiostat test only the electrical properties and oxidation states of the materials influence, being able to repeat the measurements at any time and obtain the same results.
- Quantitative evaluation: many corrosion tests are evaluated visually, observing the corrosion that appears on the pieces in a qualitative way. However, the potentiostat test allows numerical values to be obtained that are used to compare the properties of materials and their resistance to corrosion in a quantitative way.
What do you think of our blog about the potentiostat corrosion test? Do you need to analyze your material to know if it is the most suitable to withstand corrosion in your application? Do you need to know if your materials can suffer corrosion when faced with a new liquid? Contact us!