METHOD AND DEVICE FOR ELECTRODEPOSITING A COATING ON THE SURFACE OF AN ELECTRODE

Abstract

The present invention relates to a method for electrodepositing a coating on the surface of an electrode, comprising the following steps: (a) providing, in an electrolytic solution containing charged species, a first electrode and a second electrode coaxial with the first electrode and placed inside the first electrode, the shape of the inner surface of the first electrode being complementary to the shape of the outer surface of the second electrode, one of the first and second electrodes being porous;and (b) applying a potential difference between said first electrode and said second electrode such that, when the species contained in said electrolytic solution are positively charged, the porous electrode is the anode and, when the species contained in said electrolytic solution are negatively charged, the porous electrode is the cathode, whereby a coating is electrodeposited at the surface of the electrode opposite the porous electrode. The present invention also relates to a device for carrying out such a method. Abstract figure = Fig. 1;

Description

Title of the invention: METHOD AND DEVICE FOR ELECTRODEPOSITING A COATING ON THE SURFACE OF AN ELECTRODE Technical field

[0001] The present invention belongs to the field of surface coatings and in particular to the field of electrodeposited surface coatings, i.e. deposited electrochemically.

[0002] The present invention provides a method and a device for obtaining a coating, in particular a homogeneous coating and, in particular, a homogeneous coating of micrometric or nanometric particles on an electrically conductive substrate, regardless of the shape of the surface of the substrate to be coated. To achieve this aim, the method according to the present invention uses a device comprising two electrodes arranged coaxially, the first being hollow and the second placed inside the first, one of the two electrodes being porous. STATE OF THE PRIOR ART

[0003] One of the techniques currently used to make homogeneous deposits on a substrate is electrophoresis, also called electrodeposition. This electrochemical deposition technique allows charged particles to be deposited in colloidal solution on an electrically conductive support. The method is based on the movement of particles in solution when they are subjected to an electric field generated between two electrodes.

[0004] In practice, the electrodes are parallel, flat and immersed in the solution containing the particles to be deposited and the electric field causes the particles to migrate towards the substrate. In particular, if the particles are positively charged, they will be deposited on the cathode and therefore, this technique is called cataphoresis. On the contrary, if the particles are negatively charged, they will be deposited on the anode by anaphoresis.

[0005] The advantage of this technique is that it allows for the deposition of thin layers, most often on a silicon wafer. However, if one wants to cover a sample with a different geometric shape such as, for example, a sample with a curved, cylindrical, convex, concave or etched surface, a three-dimensional sample, a sample with a high aspect ratio (length » width) such as a cylinder 1 cm long and 2 mm in diameter for example, it is difficult to obtain a homogeneous deposit all around the lateral surface of the sample.

[0006] Utility model CN ​​205443493 [1] proposes to solve this technical problem by using a motor to rotate the sample, thus making it possible to make three-dimensional deposits around the latter.

[0007] In another technical field, patent application JP-H04202790 [2] proposes to separate and purify samples such as proteins or blood components using the principle of electrophoresis. To do this, a negative electrode is arranged inside a cylindrical electrophoresis tank whose inner peripheral surface corresponds to the positive electrode, the two electrodes being coaxial. When a sample containing different components is introduced into the electrophoresis tank, the components of the sample are moved, as they descend into the electrophoresis tank, towards the side of the positive electrode by means of an electric field formed between the two electrodes.The different components are separated by the difference in the speed of electrical movement of each of them, depending on their size and charge, towards the positive electrode and are then extracted by means of separate extraction tubes.

[0008] In summary, existing solutions for making electrodepositions on electrodes only offer a system of flat and parallel electrodes and therefore, to be able to make a deposit on the entire lateral surface of a parallelepiped, spherical or cylindrical sample, it is necessary to insert a rotation motor to rotate the sample or change the geometry and arrangement of the electrodes.

[0009] The inventors therefore set themselves the goal of proposing a rapid, easy-to-implement process making it possible to obtain, by electrodeposition, a coating and in particular a homogeneous coating on the surface of a conductive substrate regardless of the shape of this surface. Statement of the invention

[0010] The present invention makes it possible to achieve the aim set by the inventors since the latter propose a method implementing an electrophoresis device with an electrode system which can be arranged in an electrophoresis tank characterized by the presence of an external electrode, surrounding an internal electrode, one of the two electrodes being porous and the sample to be coated being the surface of the electrode opposite the porous electrode.

[0011] This device is clearly distinguished from the device described in patent application JP-H04202790 [2] since, in the latter, none of the electrodes are porous.

[0012] Furthermore, the device implemented in the method according to the invention is much simpler to use in comparison with that described in the utility model CN ​​205443493 [1] which has a rotation motor. It should be noted that the device implemented implemented in the method according to the invention is a compact and portable device, not commercially available at the date of the invention.

[0013] The method according to the invention can be generalized to any type of electrode regardless of the shape of the face of the electrode to be coated, i.e. whether this shape is curved, cylindrical, convex, concave or etched or whether this electrode has a high aspect ratio.

[0014] More particularly, the present invention relates to a method for electrodepositing a coating on the surface of an electrode, comprising the following steps:

[0015] a) arranging, in an electrolytic solution containing charged species, a first electrode and a second electrode coaxial with the first electrode and placed inside the first electrode,

[0016] the shape of the internal surface of the first electrode being complementary to the shape of the external surface of the second electrode,

[0017] one of the first and second electrodes being porous; and

[0018] b) applying a potential difference between said first electrode and said second electrode such that, when the species contained in said electrolytic solution are positively charged, the porous electrode is the anode and, when the species contained in said electrolytic solution are negatively charged, the porous electrode is the cathode, whereby a coating is electrodeposited at the surface of the electrode opposite the porous electrode.

[0019] In order for the method according to the present invention to be feasible, it is obvious that the first electrode also designated, in the present description, as the outer electrode and the second electrode also designated, in the present description, as the inner electrode must be spaced from each other.

[0020] In a first embodiment, the method according to the invention comprises the following steps:

[0021] al) arranging, in an electrolytic solution containing charged species, a first porous electrode and a second electrode coaxial with the first electrode and placed inside the first electrode,

[0022] the shape of the inner surface of the first electrode being complementary to the shape of the outer surface of the second electrode; and

[0023] bl) applying a potential difference between said first electrode and said second electrode such that, when the species contained in said electrolytic solution are positively charged, said first electrode is the anode and, when the species contained in said electrolytic solution are negatively charged, said first electrode is the cathode, whereby a coating is electrodeposited at the external surface of the second electrode.

[0024] In a second embodiment, the method according to the invention comprises the following steps:

[0025] a2) placing, in an electrolytic solution containing charged species, a first electrode and a second electrode coaxial with the first electrode, placed inside the first electrode, this second electrode being hollow and porous,

[0026] the shape of the internal surface of the first electrode being complementary to the shape of the external surface of the second electrode; and

[0027] b2) applying a potential difference between said first electrode and said second electrode such that when the species contained in said electrolytic solution are positively charged, said second electrode is the anode and when the species contained in said electrolytic solution are negatively charged, said second electrode is the cathode, whereby a coating is electrodeposited at the inner surface of the first electrode.

[0028] With the two-electrode device, the method according to the invention makes it possible to obtain, quickly and easily, a coating and in particular a homogeneous coating on one of the two electrodes since a homogeneous electric field is created, directed from one of the electrodes towards the other.

[0029] Furthermore, the use of a porous electrode makes it possible to obtain a flow of particles contained in the electrolytic solution and intended to form the coating, without exhaustion or modification of the composition at the level of the electrode opposite the electrode to be coated.

[0030] The method according to the present invention uses at least two electrodes which have essential characteristics, namely (i) one of the two electrodes must be porous, (ii) the two electrodes must be coaxial (i.e. the axis of the electrodes is the same) and (iii) the two electrodes must have surfaces facing each other, i.e. the internal surface of the first electrode and the external surface of the second electrode, which are complementary.

[0031] On the other hand, there is no constraint as to the materials of the electrodes used in the present invention; the latter can be made of any electrically conductive material known to those skilled in the art.

[0032] Similarly, there is no constraint as to the electrolytic solution to be used in the context of the method according to the invention. The electrolytic solution contains charged species which may be ions and / or charged particles. A person skilled in the art will be able to determine the components of the latter depending on the material of the coating to be electrodeposited and the nature of the electrodes and in particular the electrode to be coated used.

[0033] Regarding feature (iii), the shape of the inner surface of the first electrode and the shape of the outer surface of the second electrode are identical to a ready homothety ratio. Therefore, the space between the inner surface of the first electrode and the outer surface of the second electrode has a thickness that is substantially invariable in the circumferential direction and in the axial direction of this space.

[0034] By "porous electrode" is meant an electrode having a plurality of longitudinal pores. When the outer electrode is porous or the inner electrode is porous and hollow, the plurality of longitudinal pores extends from the inner surface to the outer surface of the outer electrode or the inner electrode, the pores being perpendicular or substantially perpendicular to the inner surface and the outer surface of the porous outer electrode or the porous and hollow inner electrode.

[0035] The pores of the porous electrode implemented in the invention may have circular, rectangular, square, polygonal cross sections such as, for example, hexagonal or even a mixture of at least two of these types of section.

[0036] The distribution of the pores presented by the porous electrode implemented in the present invention may be random, homogeneous (the distance between two consecutive pores is substantially identical) or even staggered. In a particular embodiment, the porous electrode implemented in the present invention may be in the form of a grid. In the case where it is the outer electrode which is in the form of a grid, the latter surrounds the inner electrode.

[0037] Furthermore, the pores that the porous electrode has may have average dimensions, generally defined by the diameter of their cross-sections, which may be identical or different. Advantageously, the pores that the porous electrode has have a substantially identical average dimension. A person skilled in the art will be able to choose, without inventive effort, the average dimension, i.e. the diameter of their cross-section, most suitable for the pores of the porous electrode depending in particular on the compounds present in the electrolytic solution and the distance between the inner electrode and the outer electrode. For this purpose, a person skilled in the art may refer to the work of the inventors presented in the experimental part below.

[0038] Typically and in particular in terms of mechanical strength constraints, the porosity of the porous electrode defined as the ratio of the volume of the pores to the total volume of the porous electrode used in the present invention is between 20% and 80%.

[0039] In a particular embodiment, the first electrode is in the form of a hollow cylinder and the second electrode is cylindrical and, if it is the porous electrode, it is also hollow, the assembly therefore being cylindrical with a symmetry of revolution. In other words, the first electrode and the second electrode are in the form of two concentric cylinders.

[0040] As shown in [Fig.l], in this embodiment applied to the first embodiment as previously defined, the first electrode or outer electrode (1) which is porous surrounds a second electrode or inner electrode (2). The first electrode (1) has a plurality of through pores (12) and an inner surface (11) facing the outer surface (21) of the second electrode (2). These two concentric cylindrical electrodes are contained in a container or bottle (3), immersed in an electrolytic solution (4) of the dissolution type containing charged species such as, for example, charged luminescent particles (5).

[0041] In step (b) of the method according to the present invention, a voltage difference is applied between the two electrodes whereby an electric field is created between them.

[0042] In the case presented in [Fig.l], the positive terminal is placed on the porous outer electrode (anode) and the negative terminal on the inner electrode (cathode), thus there will be an electric field directed from the outer electrode to the inner electrode. These electrodes are immersed in a container, with a solution containing charged species such as charged particles. If these species are positively charged, they will follow the direction of the electric field, which will allow the outer surface of the inner electrode to be completely covered.

[0043] Alternatively, but still with an electrolytic solution comprising positive charges, a deposit can also be made on the internal surface of the external electrode. In this case, the voltage difference must be reversed, that is, the positive terminal must be placed on the internal electrode, which is porous and hollow (anode), and the negative terminal on the external electrode (cathode) to have an electric field directed from the internal electrode to the external electrode.

[0044] As a further variant, if an electrolytic solution comprising negative charges is used, a coating can be formed:

[0045] - at the level of the external surface of the internal electrode, if the terminal is placed positive on the inner electrode (anode) and the negative terminal on the porous outer electrode (cathode) to have an electric field directed from the inner electrode to the outer electrode; or

[0046] - at the level of the internal surface of the external electrode, if the terminal is placed positive on the outer electrode (anode) and the negative terminal on the inner electrode which is porous and hollow (cathode) to have an electric field directed from the outer electrode to the inner electrode.

[0047] In other words, there are several situations within the scope of the present invention:

[0048] 1) a voltage of x V is applied to the external electrode (anode) and a voltage of -x V on the inner electrode (cathode) to produce an electric field from the outer electrode to the inner electrode (x can, for example, be 6),

[0049] 1.1) If the particles of the electrolytic solution are positively charged, they will follow the electric field and we will therefore have a coating on the external surface of the internal electrode, or

[0050] The sample to be coated is the inner electrode and the outer electrode is hollow and porous,

[0051] 1.2) If the particles are negatively charged, they will move in the direction opposite to the electric field and we will therefore have a coating on the internal surface of the external electrode.

[0052] The sample is the outer electrode which is a hollow cylinder and the inner electrode is hollow and porous.

[0053] 2) A voltage of -x V is applied to the external electrode (cathode) and a voltage of x V on the inner electrode (anode) to produce an electric field from the inner electrode to the sample outer electrode (x can, for example, be 6).

[0054] 2.1) If the particles of the electrolytic solution are positively charged, they will follow the electric field and we will therefore have a coating on the internal surface of the outer electrode. The sample is the outer electrode which is a hollow cylinder and the inner electrode is hollow and porous.

[0055] 2.2) If the particles are negatively charged, they will move in the direction opposite to the electric field and we will therefore have a coating on the external surface of the inner electrode. The sample is the inner electrode and the outer electrode is hollow and porous.

[0056] The homogeneity of the deposit and therefore of the coating depends strongly on the homogeneity of the electric field.

[0057] It must be taken into account that there are curvatures of the electric field on the ends of the sample (i.e. the electrode to be coated) and therefore inhomogeneities on the deposit. These inhomogeneities cannot be avoided.

[0058] Furthermore, there are also curvatures of the electric field between the two electrodes along the sample (i.e. the electrode to be coated) due to the existence of pores on the other electrode. These curvatures can, however, become negligible if the porosity of the porous electrode and the distance between the electrodes are correctly adjusted. The experimental part below illustrates how this adjustment can be carried out by a person skilled in the art.

[0059] In addition, inhomogeneities in the deposit can be reduced, for example, by adapting the size of the inner and outer electrodes.

[0060] For a coating to be electrodeposited at the external surface of the inner electrode, the latter advantageously has a height lower than the height of the outer electrode. Typically, the height of the inner electrode will be at least 10%, at least 20%, at least 30% or at least 40% lower than the height of the outer electrode. In particular, the height of the inner electrode corresponds to half the height of the outer electrode.

[0061] Alternatively, for a coating to be electrodeposited at the internal surface of the outer electrode, the latter advantageously has a height less than the height of the inner electrode. Typically, the height of the outer electrode will be at least 10%, at least 20%, at least 30% or even at least 40% lower than the height of the inner electrode. In particular, the height of the outer electrode corresponds to half the height of the inner electrode.

[0062] In other words, between the first electrode and the second electrode, the height of the porous electrode is at least 10%, at least 20%, at least 30% or at least 40% greater than the height of the other electrode. In particular, between the first electrode and the second electrode, the height of the porous electrode is twice as great as the height of the other electrode.

[0063] In this case, it is also possible to obtain a homogeneous deposit at the surface of the base of the electrode to be coated.

[0064] In another embodiment, during step (b) of the method according to the invention, one between the outer electrode and the inner electrode is kept fixed and the other is moved along the axis of the electrodes. In other words, to homogenize the coating, it is possible

[0065] - either to make the inner electrode go back and forth and to keep it fixed the outer electrode;

[0066] - or, conversely, to keep the inner electrode fixed and move vertically (ie along the axis of the electrodes) the outer electrode.

[0067] It should, however, be noted that the homogeneity of the deposit may not be complete because the time of presence of the ends to be treated in the electric field is shorter than in the central part: the thickness of the deposit should vary accordingly.

[0068] This embodiment can also be used when one between the outer electrode and the inner electrode is very long compared to the other and in particular when the electrode to be coated is very long compared to the porous electrode.

[0069] Whatever the application of this embodiment, the relative movement of the inner electrode (or the outer electrode) with respect to the outer electrode (or the inner electrode) is carried out at a speed which depends on the length of the electrodes and the duration of T electrodeposition. Typically, this speed is slow, i.e. less than or equal to 5 mm / min, in particular less than or equal to 3 mm / min, in particular, less than or equal to 2 mm / min and, more particularly, of the order of 1 mm / min (i.e. 1 mm / min ± 0.5 mm / min).

[0070] In another embodiment, it is possible, within the scope of the present invention, to evaluate the thickness of the coating by measuring the variation in resistance between the inner electrode and the outer electrode. The experimental part below illustrates this aspect.

[0071] In another embodiment, a third porous electrode, coaxial with the first electrode and the second electrode, is arranged between the first electrode and the second electrode, the shape of the internal surface of this third electrode is complementary to the shape of the external surface of the second electrode and the shape of the external surface of this third electrode is complementary to the shape of the internal surface of the first electrode.

[0072] What has been previously explained regarding the complementarity of the shape of the inner surface of the first electrode and the shape of the outer surface of the second electrode applies mutatis mutandis to the complementarity of the shape of the inner surface of the third electrode and the shape of the outer surface of the second electrode as well as to the complementarity of the shape of the outer surface of the third electrode and the shape of the inner surface of the first electrode.

[0073] The pore size of the third electrode may be the same as or different from the pore size of the porous electrode (first or second electrode). Similarly, the pore distribution of the third electrode may be the same as or different from the pore distribution of the porous electrode (first or second electrode). Advantageously, the pore size and distribution of the third electrode are the same as the pore size and distribution of the porous electrode.

[0074] During step (b) of the method, the third electrode is at the same potential as that of the porous electrode and slides between the first electrode and the second electrode, whereby the porosity is open or closed. As a result, the porosity is adjustable, thus making it possible to obtain a coating with patterns.

[0075] The present invention also relates to the device implemented during the method for electrodepositing a coating on the surface of an electrode, said device comprising said first electrode and said second electrode as previously defined. This device may further comprise a third electrode as previously defined.

[0076] The present invention also relates to the use of a hollow and porous electrode 1 for electrodepositing a coating on the surface of an electrode 2 which is coaxial with it, the shape of the surfaces of the hollow and porous electrode 1 and of the electrode 2 facing each other being complementary. In this use, it is clear that the hollow and porous electrode 1 can be the outer electrode (or the inner electrode) such that previously defined and therefore that electrode 2 can be the inner electrode (or the outer electrode) as previously defined.

[0077] Other characteristics and advantages of the present invention will become apparent to those skilled in the art upon reading the examples below given for illustrative and non-limiting purposes, with reference to the appended figures. Brief description of the drawings

[0078] [Fig. 1] already presented illustrates the physical principle of cataphoresis with the assembly of the electrodes proposed in the present invention (sectional view).

[0079] [Fig.2] shows the dimensions of the device simulated on COMSOL Multiphysics.

[0080] [Fig.3] shows the electric potential on the yz plane for x = 0.0 using a non-porous or porous outer electrode with pores of diameter 1 mm, 2 mm or 4 mm.

[0081] [Fig.4] shows the comparison of the electric potential as a function of z, for x = 0.0 mm and y = 2.0 mm, using a non-porous or porous outer electrode with pores of diameter 1 mm, 2 mm or 4 mm.

[0082] [Fig.5] shows the electric potential as a function of z, for x = 0.0 mm and y = 2.0 mm, in the case where the outer electrode has pores with a diameter of 1 mm. The squares show the position of the pores seen from the profile.

[0083] [Fig.6] corresponds to the results presented in [Fig.4] (comparison of the electric potential as a function of z, for x = 0.0 mm and y = 2.0 mm, using a non-porous or porous external electrode with pores of diameter of 1 mm, 2 mm or 4 mm) with in addition the confidence interval of 10% around the value of 6 V applied to the external electrode.

[0084] [Fig.7] shows the comparison of the electric field as a function of z, for x = 0.0 mm and y = 2.0 mm, using a non-porous or porous outer electrode with pores of diameter 1 mm, 2 mm or 4 mm.

[0085] [Fig.8] shows the comparison of the electric potential as a function of z, for x = 0.0 mm and y = 2.0 mm, for different distances between electrodes (0.5 mm, 1 mm and 1.5 mm).

[0086] [Fig.9] shows the thickness of the deposit as a function of time from the measurement of the resistance between the electrodes.

[0087] [Fig. 10] shows the photograph of a deposit of Y2O3:Eu3+ on an electrically conductive sample 2 mm in diameter and 10 mm in length in accordance with the method according to the invention, observed under UV light (254 nm).

[0088] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0089] I. Parameters of the method according to the present invention.

[0090] 1.1. Porosity of the external electrode.

[0091] As mentioned above, it is possible to vary the porosity of the outer electrode to reduce field curvatures due to pores.

[0092] Different simulations on COMSOL Multiphysics were carried out to visualize the effect of pores on the potential and electric field. To do this, a cylindrical container with a diameter of 20 mm and a height of 60 mm was simulated. This container contains only water, no charged particles, in order to study the effect of porosity on the potential and the electric field. The electrode system, composed of an outer electrode with an internal diameter of 4 mm, thickness 1 mm, height 12.5 mm and an inner electrode with a diameter of 2 mm and height 12.5 mm are immersed in the container, as shown in [Fig.2].

[0093] In all the cases studied, a voltage of 6 V and a voltage of -6 V were applied respectively to the outer electrode and to the inner electrode to produce an electric field from the outer electrode to the sample, i.e. the inner electrode.

[0094] First, a simulation was performed where the outer electrode has no porosity and then the electrical potential obtained in this case was compared with those obtained by adding different porosities, more precisely pores with cross-sectional diameters of 1 mm, 2 mm and 4 mm. [Fig.3] shows this comparison of the electrical potential on the yz plane for x = 0.0 mm (axis of axial symmetry).

[0095] All these potentials can be compared for the value y = 2.0 mm, that is, on the internal surface of the outer electrode. The results are shown in [Fig.4]. A constant value of the potential set at 6 V is obtained when the outer electrode has no porosity. In the case where the outer electrode has pores of 1 mm diameter, the position of the pores was fixed for the simulation so as to have 1.5 mm between the centers of the pores and 1.0 mm between the end of the electrode and the center of the first and last pore. In this way, it can be observed on the graph of [Fig.5] that the potential peaks coincide perfectly with the position of the pores.

[0096] Generalizing for all the cases shown in [Fig.4], it can be confirmed that when the pore size increases, the curvatures of the electric potential also increase. It is therefore advisable to reduce the pore size, and even to use a metal grid as an external electrode, to have a potential with the least curvatures, provided that the pore size still allows the passage of charged elements contained in the electrolytic solution such as particles.

[0097] For example, if we want to make a luminescent deposit with quantum dots of the AgInS2 type, these particles have a size of a few nm (around 12 nm) whereas If we want to use phosphors of the Y2O3:Eu3 + type, these are larger particles, rather micrometric (8 pm).

[0098] To choose a size for the pores of the outer electrode, it is possible to establish a confidence interval of 10% around the value of 6 V fixed at the outer electrode (typical but not restrictive value). [Fig.6] shows this confidence interval and it can be observed that, when the diameter of the pores is greater than 1 mm, we are outside this interval. Thus, for a luminescent deposit with quantum dots, the diameter of the pores will be between 40 pm (to ensure that a phosphor particle passes without problem) and 1 mm maximum.

[0099] Finally, the electric field was also studied. [Fig.7] shows the electric field as a function of z (electrode height) for x = 0.0 mm and y = 2.0 mm, by analogy with [Fig.4] for the electric potential.

[0100] In this figure, we notice that the field is practically constant in all cases and that its value is approximately 8500 V / m. We recall that we apply a voltage of 6 V to the outer electrode and -6 V to the inner electrode, so that we have 12 V in a space of 1 mm (distance between the two electrodes). In other words, we would have a maximum electric field of 12,000 V / m, so the value of 8,500 V / m is reasonable.

[0101] 1.2. Distance between electrodes.

[0102] Furthermore, the variation of the electric potential was studied for different distances between electrodes. [Fig.8] shows the potential for three different distances between electrodes (0.5 mm, 1.0 mm and 1.5 mm) and for the same pore diameter (1.0 mm):

[0103] For the smallest distance between electrodes, the curvatures of the potential are the most marked. If this distance is increased from 0.5 mm to 1.0 mm, these curvatures are less strong. On the other hand, if we continue to increase this distance, it seems that these curvatures become stronger again. In this case, the most suitable distance between the electrodes is an intermediate distance and in particular the distance of 1.0 mm.

[0104] 1.3. Control of the thickness of the deposit.

[0105] The thickness of the deposit can be determined from the resistance: 1. The thickness of the deposit is optically measured for a certain duration of the deposit. For example, for tduration = 10 s, we obtain a thickness e = 10 pm (typical but not restrictive values), 2. The thickness is measured for a second duration of the deposit: for tduration = 100 s, we obtain a thickness e = 250 pm, 3. The variation in resistance between the electrodes is measured when a constant voltage difference is applied to create the deposit, 4. The correlation is made between the resistance measured after the application of a voltage for a time tduration and its deposit thickness, which makes it possible to know the variation of the deposit thickness as a function of time ([Fig.9]).

[0106] II. Deposition of a luminescent material according to the method of the invention.

[0107] The present invention was experimentally tested by depositing a luminescent material of Y2O3:Eu3+ commercially obtained from Phosphor Technology Ltd (EIA-WTDS P56-RF, PTL GRADE QK63 / N-C1) on a conductive cylindrical sample with a gold deposit of 2 mm in diameter and 10 mm in length. The porous outer electrode, made of steel, is 12 mm in height, 5 mm in outer diameter and 4 mm in inner diameter. The procedure was as follows:

[0108] - prepare a solution with 1 g of luminescent particles in suspension, 0.8 ml of cations (11.4 mg of magnesium nitrate hexahydrate Mg(NO3)2 6H2O solubilized in a mixture of 0.1 ml of ionized water and 0.7 ml of ethanol) to positively charge the solution, 0.4 ml of deionized water and 20 ml of ethanol to disperse the particles well;

[0109] - pour the solution into a small container and stir with a magnetic stirrer for 2 minutes to homogenize the solution;

[0110] - arrange the sample in the external electrode coaxially;

[0111] - apply a voltage difference of 12 V for a duration of 45 s (even if electrolysis of water occurs at 1.23 V, it is possible to apply 12 V without risk since the solution contains a greater proportion of ethanol than water, 20 ml against 0.4 ml);

[0112] - remove the sample from the dissolution and allow the coating to dry thoroughly for 2 minutes.

[0113] To check that there has been a homogeneous deposit on the sample, it is placed under UV light (254 nm) and we see that, indeed, there is a luminescent layer around the sample, as shown in [Fig. 10]. Bibliographic reference

[0114] [1] Utility model CN ​​205443493 published on August 10, 2016.

[0115] [2] Patent application JP-H04202790 published on July 23, 1992.

Claims

Claims

1. A method for electrodepositing a coating on the surface of an electrode, comprising the following steps: a) arranging, in an electrolytic solution containing charged species, a first electrode and a second electrode coaxial with the first electrode and placed inside the first electrode, the shape of the inner surface of the first electrode being complementary to the shape of the outer surface of the second electrode, one of the first and second electrodes being porous;and b) applying a potential difference between said first electrode and said second electrode such that, when the species contained in said electrolytic solution are positively charged, the porous electrode is the anode and, when the species contained in said electrolytic solution are negatively charged, the porous electrode is the cathode, whereby a coating is electrodeposited at the surface of the electrode opposite the porous electrode.;

2. A method according to claim 1, characterized in that said method comprises the following steps: a1) arranging, in an electrolytic solution containing charged species, a first porous electrode and a second electrode coaxial with the first electrode and placed inside the first electrode, the shape of the inner surface of the first electrode being complementary to the shape of the outer surface of the second electrode; and b1) applying a potential difference between said first electrode and said second electrode so that, when the species contained in said electrolytic solution are positively charged, said first electrode is the anode and, when the species contained in said electrolytic solution are negatively charged, said first electrode is the cathode, whereby a coating is electrodeposited at the outer surface of the second electrode.

3. Method according to claim 1, characterized in that said method comprises the following steps: a2) arranging, in an electrolytic solution containing charged species, a first electrode and a second electrode coaxial with the first electrode, placed inside the first electrode, this second electrode being hollow and porous, the shape of the internal surface of the first electrode being complementary to the shape of the external surface of the second electrode;and b2) applying a potential difference between said first electrode and said second electrode such that, when the species contained in said electrolytic solution are positively charged, said second electrode is the anode and, when the species contained in said electrolytic solution are negatively charged, said second electrode is the cathode, whereby a coating is electrodeposited at the inner surface of the first electrode.;

4. Method according to any one of claims 1 to 3, characterized in that the porosity of said porous electrode is between 20% and 80%.

5. Method according to any one of claims 1 to 4, characterized in that said first electrode and said second electrode are in the form of two concentric cylinders.

6. Method according to any one of claims 1 to 5, characterized in that, between said first electrode and said second electrode, the height of the porous electrode is twice as great as the height of the other electrode.

7. Method according to any one of claims 1 to 5, characterized in that, during said step (b), one between said first electrode and said second electrode is kept fixed and the other is moved along the axis of said electrodes.

8. Method according to claim 7, characterized in that the relative displacement of said second electrode (or said first electrode) with respect to said first electrode (or said second electrode) is carried out at a speed less than or equal to 5 mm / min, in particular less than or equal to 3 mm / min, in particular less than or equal to 2 mm / min and, more particularly, of the order of 1 mm / min (i.e. 1 mm / min ± 0.5 mm / min).

9. Method according to any one of claims 1 to 8, characterized in that the thickness of said coating is evaluated by measuring the variation in resistance between said second electrode and said first electrode.

10. Method according to any one of claims 1 to 9, characterized in that a third porous electrode, coaxial with said first electrode and said second electrode is arranged between said first electrode and said second electrode, the shape of the internal surface of the third electrode being complementary to the shape of the external surface of said second electrode and the shape of the external surface of the third electrode being complementary to the shape of the internal surface of said first electrode.

11. A method according to claim 10, characterized in that, during said step (b), said third electrode is at the same potential as the porous electrode and slides between said first electrode and said second electrode whereby the porosity is opened or closed.

12. Device implemented during a method as defined in any one of claims 1 to 11, said device comprising a first electrode as defined in any one of claims 1 to 6 and a second electrode as defined in any one of claims 1 to 6.

13. Device according to claim 12, characterized in that it further comprises a third electrode as defined in claim 1 A.

14. 1U. Use of a hollow and porous electrode 1 for electrodepositing a coating on the surface of an electrode 2 which is coaxial with it, the shape of the surfaces of the porous and hollow electrode 1 and of the electrode 2 facing each other being complementary.

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