Method for determining a physical property of a substrate coating by electrochemical measurement

Abstract

The invention relates to a method for determining a physical property of a coating deposited on a substrate, the method including the following steps: a) placing the coating in contact with an impregnation solution containing a redox species referred to as probe species in order to define an impregnation zone of the coating; b) leaving the coating in contact with the impregnation solution so that the probe species impregnates the coating over a predefined impregnation time; c) halting the contact with the impregnation solution once the impregnation time has been reached; d) placing the coating in contact with a release solution in order to extract the probe species from the coating; e) concomitantly with step d), carrying out, by electrochemical means, a measurement of an electrical current generated by the amount of probe species extracted from the coating into the release solution; and f) deducing therefrom the desired physical property of the coating.

Description

[0001] DESCRIPTION

[0002] TITLE: METHOD FOR DETERMINING A PHYSICAL PROPERTY OF A SUBSTRATE COATING BY ELECTROCHEMICAL MEASUREMENT

[0003] Technical field of the invention

[0004] The invention relates to the field of corrosion risk analysis of a substrate, typically a metallic substrate, protected by a coating.

[0005] More specifically, the invention relates to the determination of a physical property of the coating, for example its porosity or permeability in order to analyze corrosion risks.

[0006] Technical background

[0007] The corrosion of metallic materials leads to significant economic losses, but can also pose serious safety risks. Methods of protecting metallic materials against corrosion rely primarily on solutions based on organic coatings, electrochemical protection, and corrosion inhibition.

[0008] Among these options, organic coating protection is widely used due to its low cost and ease of application. The coating limits contact between the corrosive environment and the metallic material by providing a barrier.

[0009] However, microscopic defects inevitably exist within the coating, which cannot completely prevent the intrusion of corrosive media. Therefore, the coating only reduces the corrosion rate of the metallic material. Furthermore, the coating is subject to aging and may have been improperly applied or undergone degradation, whether intentional or unintentional. All of this results in reduced protective performance and a shortened protection cycle.

[0010] All these phenomena ultimately result in increased porosity or permeability in the coating.

[0011] Also, evaluating a physical property of the coating, such as its porosity or permeability, is very useful to check if it has been correctly applied or degraded, to study how a coating can age and more broadly, for the development of new coatings.

[0012] Several methods exist to determine such physical properties of the coating. One known solution is to use a porosimeter.

[0013] The approach involves passing a porosimeter (for example, the Elcometer 236) in front of the coating to be tested. The porosimeter is equipped with a probe powered by a high voltage (the Elcometer 236 is available in two versions: one at 15 kV and the other at 30 kV) and a direct current. When the probe passes over a coating defect, a spark occurs and an alarm is triggered. Direct current detectors, such as the Elcometer 236, require the porosimeter to be directly connected to the conductive substrate (the metallic material covered by the coating). This technique can be used to test coatings up to 7.5 mm thick. It is a technique widely used for inspecting pipelines and protective coatings of metallic materials in general. With this porosimeter, porosity is therefore detected indirectly, by detecting a spark.

[0014] Another solution involves using a pressurization system to adsorb a gas into the coating, then using a piston to measure the amount of species released when the piston is pulled near the coating. This is, for example, what is proposed in document CN113552058A. This approach, limited to gases, does not work with a species in solution.

[0015] There are also solutions based on measuring the mass gain of the coating related to water penetration into the coating. This is proposed, for example, in the article by Ismail Kada et al., "Effect of the organic coating thickness on water uptake measurements by EIS," Progress in organic coatings 197 (2024), 108823, pp. 1-11.

[0016] (https: / / doi.Org / 10.1016 / j.porgcoat.2024.108823).

[0017] Yet another solution is to perform an electrochemical impedance measurement.

[0018] Electrochemical impedance measurement allows the electrical conductivity (which can be related to porosity or permeability) of a coating to be measured by applying a sinusoidal electrochemical signal of varying frequency. This signal relies on a coating response that remains constant throughout the measurement period. This is, for example, the method proposed in document CN114609028A.

[0019] Electrochemical impedance measurement can also be used to measure the double-layer capacitance associated with the coating. For example, see the article by Mehrdad Hoseinpoo et al., Simplified approach to assess water uptake in protective organic coatings by parallel plate capacitor method, Materialstoday communications (26), March 2021 (https: / / d0i.0rg / l 0.1016 / j.mtcomm.2020.101858).

[0020] Document EP 2 603 801 B1 proposes an electrochemical probe. A general overview of currently available solutions reveals that, aside from some being destructive or inapplicable to certain substrates, their accuracy is insufficient.

[0021] One objective of the invention is to offer an improved solution.

[0022] Summary of the invention

[0023] To achieve the aforementioned objective, the invention proposes a method for determining a physical property of a coating covering a substrate, said method being characterized in that it comprises the following steps: a) placing the coating on its substrate in contact with a solution, called the impregnation solution, containing a redox species called the probe species to define a first impregnation zone of the coating; b) leaving the substrate in contact with the impregnation solution so that the probe species impregnates the coating for a predefined impregnation time; c) stopping the contact of the coating with the impregnation solution once the impregnation time has been reached; d) placing the coating impregnated by the probe species in contact with another solution, called the salting-out solution, to extract the probe species from the coating;e) concurrently with step d), perform, by electrochemical means, an electrical intensity measurement generated by the quantity of probe species extracted from the coating in the release solution, and f) deduce the desired physical property of the coating, from the measurement performed in step e).;

[0024] The invention therefore consists of exposing the coating to a solution containing a redox species that acts as a probe (impregnation step), during which the probe species penetrates the coating, and then measuring an electrical current generated by the amount of probe species extracted from the coating during a subsequent step (release step). Detection is achieved by placing an electrochemical probe opposite the exposed area and ensuring the release of the species through a change in the composition of the solution to which the coating is exposed.

[0025] The process according to the invention may include at least one of the following additional steps, taken alone or in combination: the impregnation solution is based on water, N,N-dimethylformamide, or acetonitrile. The probe species is selected from: ferrocene, ferrocenemethanol, KsFeCNe, K2FeCN6, or Cl3RuNH6. Between steps c) and d), a rinsing step, possibly followed by a drying step. Before step f), a step is carried out to measure the coating thickness. Step f) then consists of determining the relative porosity of the coating, the porosity of the coating, and / or the permeability of the coating. Step a) consists of placing the substrate with its coating in the impregnation solution, and in this case, step c) consists of removing the substrate with its coating from the impregnation solution.step a) consisting of placing only a part of the substrate with its coating in a vertical position in the impregnation solution, said process includes, between steps b) and c), the following additional steps.

[0026] A) place the substrate with its coating deeper in the impregnation solution, at a second predefined depth, the difference in depth between the second depth and the first depth allowing to define a second impregnation zone of the coating;

[0027] B) leave the substrate in the impregnation solution so that the probe species impregnates the coating over a second predefined impregnation time;

[0028] C) optionally, repeat steps A) and B) N times, where N is a non-zero natural number, to define other depths, other coating impregnation zones and other predefined impregnation times, step e) then being implemented with a plurality of measurement electrodes, independent of each other and arranged in parallel along the same horizontal direction so as to measure the electrical intensity generated by the amount of probe species released by each of the different impregnation zones;

[0029] - step a) consists of spraying, for example in the form of a spray, the coating with the impregnation solution and in this case, step c) consists more precisely of stopping spraying the coating with the impregnation solution.

[0030] The invention also provides a device for implementing the method according to the invention, the device comprising:

[0031] - a first tank intended to receive the impregnation solution containing a redox species known as the probe species, and

[0032] - a second tank intended to receive the release solution, the second tank housing an electrochemical probe equipped with at least one measuring electrode. The device may include at least one of the following features, taken alone or in combination: another tank intended to receive a rinsing solution; the electrochemical probe includes at least one second measuring electrode, independent of said at least one measuring electrode and arranged in its extension; the electrochemical probe includes a plurality of measuring electrodes, independent of each other and arranged in parallel.

[0033] Brief description of the figures

[0034] Other objects and features of the invention will become clearer in the following description, made with reference to the accompanying figures, in which:

[0035] Figure 1 is a diagram representing the different stages of a process according to the invention;

[0036] Figure 2 is a first example of a device for implementing the process according to the invention;

[0037] Figure 3 shows, in perspective view, an electrochemical probe that can be used in the device of Figure 2;

[0038] Figure 4 represents a means of pressing a coated substrate against the electrochemical probe shown in Figure 2;

[0039] Figure 5 shows another way to plate a coated substrate against the electrochemical probe shown in Figure 2;

[0040] Figure 6 shows another electrochemical probe that can be used with the device in Figure 2;

[0041] Figure 7 is a second example of a device for implementing the method according to the invention;

[0042] Figure 8 represents an example of a measurement carried out with the device of Figure 2, representing the electrical intensity measured by the electrochemical probe as a function of time.

[0043] Detailed description of the invention

[0044] Figure 1 schematically represents the main steps of a process according to the invention. The invention relates to a process for determining a physical property of a coating covering a substrate, said process comprising the following steps: a) bringing the coating into contact with a solution, called the impregnation solution, containing a redox species, called the probe species, to define a first impregnation zone of the coating; b) leaving the substrate in contact with the impregnation solution so that the probe species impregnates the coating for a predefined impregnation time; c) stopping contact between the coating and the impregnation solution once the impregnation time has been reached; d) bringing the coating impregnated by the probe species into contact with another solution, called the salting-out solution, to extract the probe species from the coating;e) concurrently with step d), perform, by electrochemical means, an electrical intensity measurement generated by the quantity of probe species extracted from the coating in the release solution; and f) deduce the desired physical property of the coating from the measurement performed in step e).

[0045] We understand that the probe species is in solution in the impregnation solution.

[0046] The electrical current measurement performed in step e) is carried out electrochemically. In practice, this can be implemented with an electrochemical probe having one or more electrodes, where, depending on the case, an oxidation or reduction reaction occurs with the probe species (which is a redox species). This allows us to determine the amount of probe species released from the coating and therefore the amount of probe species previously impregnated in the coating during step b). The sign of the electrical current is determined by the nature of the detection process (oxidation or reduction).

[0047] Step a) may consist of spraying the coating with the impregnation solution, for example using a spray gun. In this case, step c) specifically consists of stopping the spraying of the coating with the impregnation solution.

[0048] Alternatively, step a) can consist of placing the substrate with its coating into the impregnation solution. In this case, step c) more specifically consists of removing the substrate with its coating from the impregnation solution.

[0049] Step a) can be carried out with various types of probe (redox) species, for example, but not limited to: ferrocene, ferrocenemethanol, KsFeCNe, K2FeCNe, or ChRuNHe. Furthermore, various types of solutions can be used, for example, but not limited to: water, N,N-dimethylformamide (DMF), or acetonitrile. In a specific case, step a) may consist of holding the substrate, with its coating, horizontally in the impregnation solution (not shown).

[0050] In a particular case, step a) may consist of placing only a portion of the coated substrate and holding it in a vertical position within the impregnation solution. In this case, the process may include the following additional steps between steps b) and c)

[0051] A) place the substrate with its coating deeper in the impregnation solution, at a second predefined depth, the difference in depth between the second depth and the first depth allowing to define a second impregnation zone of the coating;

[0052] B) leave the substrate in the impregnation solution so that the probe species impregnates the coating over a second predefined impregnation time;

[0053] C) optionally, repeat steps A) and B) N times, where N is a non-zero natural number, to define other depths, other coating impregnation zones and other predefined impregnation times, step e) then being implemented with a plurality of independent measuring electrodes arranged in parallel along the same horizontal direction so as to determine the electric intensity generated by the amount of probe species released by each of the different impregnation zones.

[0054] Here, we understand that the first impregnation zone has an impregnation time corresponding to the sum of the first impregnation time t1 and the second impregnation time t2, while the second impregnation zone is only impregnated in the shorter time of the second impregnation time t2.

[0055] Step C), which is optional, simply generalizes this for additional impregnation areas.

[0056] In this specific context, the electrochemical probe therefore consists of electrodes that are independent of each other and arranged parallel to each other in the same horizontal direction so that each of them is positioned opposite an impregnation zone. A more detailed description is provided below.

[0057] As for step d), one way of proceeding is to place the substrate with its coating impregnated by the probe species in the impregnation solution.

[0058] Advantageously, the process may include, between steps c) and d), a rinsing step, possibly followed by a drying step. Rinsing can be carried out in various ways: spraying with a cleaning solution (water, for example) or soaking in a cleaning solution. As for drying, when implemented, it may be manual drying with absorbent paper, drying by airflow, or another method.

[0059] It is from the measurement carried out in step e) that we can finally deduce the desired physical property of the coating (step f)), for example its porosity (relative to a reference coating or intrinsic / absolute) or its permeability.

[0060] For example, it is then possible to compare the porosity Pi, P2 (relative determination) of two coatings Ri, R2 (coating 1 / coating 2) of respective thicknesses ei, e2, noting that (relation RLT1): [Maths 1] Q2 represent the charges

[0061] P 2 Q2 e l obtained for the measurements carried out according to the invention for the coatings Ri, R2 respectively.

[0062] For each Ri, R2 coating, the corresponding charge can be obtained by integrating the electrical current measured using the method according to the invention over the considered release time. Furthermore, the thickness ei, 62 of an Ri, R2 coating can be measured with a thickness gauge, such as the PCE-CT 26FN offered by PCE Instruments or the Daroplo HW300 Max, both commercially available.

[0063] We can thus determine the relative porosity of the R2 coating compared to a reference, which would be the Ri coating.

[0064] In another example, it is possible to determine the intrinsic porosity of a coating (absolute determination, without comparison to another coating). This requires knowing V u , the volume occupied by a molecule of the probe species (unit: m 3The simplest approach is to consider that at a concentration Co (unit: mol / m3) of the probe species in the impregnation solution, the occupied volume V u is expressed (relation RLT2): [Maths 2] V u =

[0065] N HAS C O where / VA is Avogadro's constant (unit: mol -1 ).

[0066] From the amount of charge measured during release, we can then evaluate the free volume VL per unit area of ​​the coating (or free volume surface density, unit: m) in the coating according to (relation RLT3): [

[0067] L Maths 3 n, the number of electrons exchanged during the measurement carried out by electrochemical means according to the invention (oxidation or reduction) for a probe species molecule, Q, the charge determined over a predefined release time of the electrical intensity measured in step e)

[0068] F, Faraday's constant (F= 96500 C.mol' 1 ) S, the electrode surface that is in the impregnation zone analyzed during release (m 2 ), Fcoi, the electrode collection factor

[0069] The collection factor depends on the geometric parameters of the chosen measurement configuration, which can be determined separately—it is dimensionless. For a given area, the collection factor can be defined as the ratio between the quantity of species detected by the electrode and the quantity of species released by the substrate coating. Protocols for measuring the collection factor of a measurement electrode are available in the literature, for example (https: / / doi.org / 10.1016 / j.jelechem.2012.06.024).

[0070] Using relation RLT2, the reformulated relation RLT3 can then be written:

[0071] [Maths 4] V L law

[0072] CoFcolFSn

[0073] The porosity Po of the coating in question, of thickness e (which, as previously indicated, can be known elsewhere with a thickness gauge such as PCE-CT 26FN offered by PCE Instruments) can then be deduced by the relation (relt4 relation):

[0074] [Maths 5] P Q = y (unitless).

[0075] Furthermore, it is possible to deduce the PM permeability (unit: m 2 / s), which is expressed (relation RLT5): [Maths 6] P M = P0- D e ff where CU / r is the effective diffusion coefficient of the probe species in the coating (m 2 / s).

[0076] We can calculate the diffusion coefficient (D e ff, unit m 2 / s) based on Cottrell's law. Cottrell's equation is valid after a certain amount of analysis time, as can be seen in the concrete example provided below.

[0077] Cottrell's law is expressed in the form (relation RLT6): [Maths 7] with :

[0078] / , the electric intensity measured with the electrochemical measurement according to the invention (A) Fcoi, the electrode collection factor (unitless) F, the Faraday constant (96500 C.mol' 1 )

[0079] S, the electrode surface that is in the impregnation zone analyzed during release (m 2 )

[0080] From , the diffusion coefficient of the probe species in the coating (m 2 / s) Ceff, the concentration of the probe species in the coating (mol.L -1) which is equal to Cen = Po.Co where Co is the concentration of the probe species in the impregnation solution t, and the time elapsed since the beginning of the release (s) (= release time). In practice, the electrical current I is therefore the object of the electrochemical measurement carried out within the framework of the invention over the release time t. The other parameters F, F co i, S, and Cef are known or determinable from other sources. For example, for C e tf, we have Cen = Po.Co where Po can be determined by the reformulated RLT3 relation and the RLT4 relation, knowing the thickness e. Moreover, Co is known.

[0081] We can therefore deduce the diffusion coefficient D e ff of relation RLT 6.

[0082] Since the thickness e of the coating is known from elsewhere (see above, use of a commercially available thickness gauge), the RLT5 relationship then allows us to obtain the PM permeability of the coating.

[0083] It can be mentioned that numerical simulations using Fick's law in the coating and in the release solution would be a more appropriate model for interpreting the results at short times.

[0084] Figures 2 to 4 represent a first example of a device capable of implementing the process according to the invention.

[0085] In Figure 2, device D comprises a first tank PB for receiving the impregnation solution containing a redox species, referred to as the probe species, a second tank DB for receiving the salting-out solution, and an electrochemical probe SEC equipped with at least one measuring electrode EM facing the inside of the second tank DB. Also shown in this figure is a sample ECH of a substrate with its coating, about to be immersed in the impregnation solution, as well as a rinsing tank BR, located between the first tank PB and the second tank DB. On the left, an optional storage tank BS is shown, which allows for the storage of various samples for which the coating permeability needs to be determined.

[0086] Figure 3 shows the SEC electrochemical probe visible in Figure 2 from a front view showing the EM measuring electrode, looking into the inside of the second DB tank.

[0087] EM measurement electrodes can vary in size depending on the requirements. A large electrode has a larger collection area (and therefore more signal to measure), but also more noise. Conversely, with a small electrode, noise is reduced, but the collection area is smaller. However, solutions exist to reduce noise, regardless of electrode size.

[0088] As can be seen in Figure 3, the SEC electrochemical probe advantageously includes an RBD rim of predefined height H (with reference to the plane of the EM measuring electrode). This provides support for the ECH sample, which can be pressed against the rim, thus controlling the distance between the measuring electrode and the sample coating. Typically, the height H can range from 10 microns to 1 mm, for example, 100 microns.

[0089] The ECH sample can be pressed against the RBD rim of the SEC electrochemical probe in several ways. For example, in Figure 4, the clamp P, which holds the sample vertically, is used to also perform lateral positioning. This can be automated, with control along at least two spatial directions, X and Z. Another option, shown in Figure 5, involves an additional PLQ plate equipped with CR spring components. The PLQ plate is housed in the second DB tray, and the CR spring components then press the sample against the RBD rim of the SEC electrochemical probe. Other solutions are, of course, also possible.

[0090] Figure 6 shows another electrochemical probe SEC' comprising several EM1, EM2 measuring electrodes, independent of each other and arranged in parallel, allowing measurements to be taken on different impregnation areas of the coating, having different impregnation times as explained previously.

[0091] In Figure 6, it can be seen that the electrochemical probe SEC' also includes at least one second measuring electrode EM', independent of the aforementioned at least one measuring electrode EM and arranged in its extension. When the sample is progressively inserted to obtain several impregnation times during a single detection sequence, this allows for a doubled measurement.

[0092] It should be noted that an electrochemical SEC probe can be provided with two independent electrodes EM, EM' in line with each other without parallel electrodes EM1, EM2 (case not shown in the attached drawings).

[0093] Figure 7 represents a second example of a device capable of implementing the process according to the invention.

[0094] In this example, a set of tanks is used, including a first tank PB for receiving the impregnation solution containing a redox species, called the probe species, and a second tank DB for receiving the release solution and housing the electrochemical probe. These tanks are arranged around a robotic arm BRT capable of picking up a substrate with its coating and placing it in the appropriate location. The tanks act as reservoirs, and the impregnation solution can be applied to the coating by spraying, for example, using a spray gun. This figure also shows rinsing zones 5, 7 (by spraying and soaking), a drying zone 6, and various substrate storage zones 1, 4, 8, 10, for holding between the different processing stations. A human-machine interface 11 controls the movements of the robotic arm BRT.

[0095] Example

[0096] A sample consisting of a metallic substrate coated with a commercial anti-corrosion coating (with undercoat, stated corrosion resistance: 10 years) was tested according to the method of the invention, using the apparatus shown schematically in Figures 2 to 4. An impregnation tank contained an impregnation solution of water and KsFeCNe (concentration Ci) (step a) for impregnation. The sample was impregnated for 12 hours (step b). A rinsing step was then performed, in this case consisting of two successive immersions in a rinsing tank containing water, each lasting 10 seconds, followed by drying by manual wiping with absorbent paper.The sample was then placed in the release tank with its release solution (0.1 M KCl electrolytic solution) by placing an electrochemical probe having a single analysis zone (electrode) 100 microns from the surface of the coating, and polarizing it at 0V vs Ag / AgCl.

[0097] The different parameters involved in the reformulated RLT3 relationship and the RLT4 relationship are as follows:

[0098] Painting

[0099] It is then necessary to determine the charge Q involved in the reformulated RLT3 relationship, by integrating the electric intensity over the release time.

[0100] The measurement of electrical intensity as a function of time is provided in Figure 8.

[0101] The test results are presented in curve C1. For this curve C1, the signal has been corrected for the current measured before exposure of the coating in the release solution (correction: -29 nA, called baseline).

[0102] A control measurement was also performed using the C2 curve. To obtain this C2 curve, the sample was impregnated for a very short time, namely 2 seconds. The signal was corrected for the current measured before the coating was exposed to the release solution (correction: -32 nA). Over such short periods, impregnation does not have time to occur. Therefore, what is measured in this case during release corresponds a priori to an adsorption phenomenon of the probe species within the coating. In any case, by not allowing the KsFeCNe time to impregnate the coating, only a weak signal is observed.

[0103] The difference between curves C1 (test) and C2 (control) therefore comes from the penetration effect of KsFeCNe (probe species) in the coating.

[0104] To obtain the charge Q, we integrate the current (curve C1) over the release time, which here is between the initial time: 405s and the final time: 30000s (the time at which we return to the baseline): we then obtain Q = -2.8 x 10⁻¹⁰⁸⁴ 4 C. To be more precise, it would be necessary to subtract from this value the charge obtained for the curve C2 by a calculation of the corresponding intensity between the same integration limits, but this would change the value marginally and does not provide anything further to explain the method used.

[0105] We can then deduce the porosity Po of the coating: Po = 2.7 x 10 -4 .

[0106] We can also go further by determining the PM permeability of this same coating. For this purpose, we start with Cottrell's law (relation RLT 6 presented above). Cottrell's law corresponds to curve C3 in Figure 8 (dotted line). As can be seen, this law is valid for long times, namely here to = 1500s, because it is only from this value that it correctly approximates curve C1 (test). By implementing a fitting procedure for curve C3 with respect to curve C1 (test), we can then express the

[0107] 1 2 10 -6 Cottrell's law in the form: [Maths 8] I = In this case, identification with the relation

[0108] RLT6 allows us to express the diffusion coefficient D e ff in the form: [Maths 9] D eff = ( — - ) . n being recalled that Cen = Po.Co where Po = 2.7.10 -4As previously determined, colPSP0C0et Co = 100 g / L, given the molar mass M(K3FECNe) = 329.24 g / mol, gives a value of 303.729 mol / m³ 3 which is the unit to be taken into consideration here.

[0109] We deduce C f = 3.8 x 10 -7 m 2 / s then, by application of relation RLT5, PM = 1.026.10' 10 m 2 / s.

[0110] It should be noted that the sensitivity of the detection method according to the invention is very high, typically on the order of tens of nanoamperes. This means that the method makes it possible, for example, to detect a release of 3 x 10⁻¹⁰⁸ m³. 10 g over a duration of 10s of the probe species for a K3FECN6 salting-out solution in water, with M(K3FECNe) = 329.24 g / mol.

[0111] End of example.

Claims

DEMANDS 1. A method for determining a physical property of a coating covering a substrate, said method being characterized in that it comprises the following steps: a) placing the coating on its substrate in contact with a solution, called the impregnation solution, containing a redox species called the probe species to define a first impregnation zone of the coating; b) leaving the substrate in contact with the impregnation solution so that the probe species impregnates the coating for a predefined impregnation time; c) stopping contact between the coating and the impregnation solution once the impregnation time has been reached; d) placing the coating impregnated by the probe species in contact with another solution, called the salting-out solution, to extract the probe species from the coating;e) concurrently with step d), perform, by electrochemical means, an electrical intensity measurement generated by the quantity of probe species extracted from the coating in the release solution, and f) deduce the desired physical property of the coating, from the measurement performed in step e).; 2. A process according to claim 1, wherein the impregnation solution is based on water, N,N-dimethylformamide (DMF) or acetonitrile.

3. A method according to any one of the preceding claims, wherein the probe species is selected from: Ferrocene, Ferrocenemethanol, KsFeCNe, K2FeCNe or ChRuNHe.

4. A method according to any one of the claims comprising, between step c) and step d), a rinsing step optionally followed by a drying step.

5. A method according to any one of the preceding claims, wherein, before step f), a step is implemented consisting of measuring a thickness of the coating.

6. Method according to the preceding claim, wherein step f) then consists of deducing a relative porosity of the coating, a porosity of the coating and / or a permeability of the coating.

7. A method according to any one of the preceding claims, wherein step a) consists of placing the substrate with its coating in the impregnation solution and in In this case, step c) consists of removing the substrate with its coating from the impregnation solution.

8. A method according to the preceding claim, wherein step a) consisting of placing only a portion of the substrate with its coating in a vertical position in the impregnation solution, said method comprises, between steps b) and c), the following additional steps: A) place the substrate with its coating deeper in the impregnation solution, at a second predefined depth, the difference in depth between the second depth and the first depth allowing to define a second impregnation zone of the coating; B) leave the substrate in the impregnation solution so that the probe species impregnates the coating over a second predefined impregnation time; C) optionally, repeat steps A) and B) N times, where N is a non-zero natural number, to define other depths, other coating impregnation zones and other predefined impregnation times, step e) then being implemented with a plurality of independent measuring electrodes arranged in parallel along the same horizontal direction so as to measure the electrical intensity generated by the amount of probe species released by each of the different impregnation zones.

9. A method according to any one of claims 1 to 6, wherein step a) consists of spraying, for example in the form of a spray, the coating with the impregnation solution and in this case, step c) consists more specifically of stopping spraying the coating with the impregnation solution.

10. Device (D) for implementing the process according to one of the preceding claims, the device comprising: a first tank (PB) intended to receive the impregnation solution containing a redox species called the probe species, and a second tank (DB) intended to receive the release solution, the second tank housing an electrochemical probe (SEC) equipped with at least one measuring electrode (EM).

11. Device (D) according to the preceding claim, further comprising another container (BR) intended to receive a rinsing solution.

12. Device (D) according to any one of claims 10 or 11, wherein the electrochemical probe (SEC) comprises at least one second measuring electrode (EM'), independent of said at least one measuring electrode (EM) and arranged in its extension.

13. Device (D) according to any one of claims 10 to 12, wherein the electrochemical probe (ECP) comprises a plurality of measuring electrodes (EM, EM1, EM2), independent of each other and arranged in parallel.

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