FR2981366A1 - METHOD FOR THE ANTICORROSIVE TREATMENT OF A SOLID METAL SUBSTRATE AND A TREATED SOLID METAL SUBSTRATE WHICH CAN BE OBTAINED BY SUCH A METHOD - Google Patents

Abstract

The invention relates to an anticorrosive treatment method in which a solution, called a liquid treatment solution, is applied to an oxidizable surface of a solid metal substrate, comprising: O at least one alkoxysilane, and O at least one cerium cation ( This); in a liquid hydro-alcoholic composition, said treatment solution being adapted to form on the surface of the solid metal substrate, a hybrid matrix by hydrolysis / condensation of each alkoxysilane (s) and each cerium cation (Ce); the treatment solution having a molar ratio (Si / Ce) of silicon element of the alkoxysilane (s) relative to the cerium (Ce) cation (s) of between 50 and 500; characterized in that the cation (s) of the cerium (Ce) has a concentration of between 0.005 mol / L and 0.015 mol / L in the treatment solution.

Description

The invention relates to a method for the anticorrosion treatment of a solid metal substrate, in particular of a solid metal substrate, and especially to a method for the anti-corrosion treatment of a solid metal substrate, in particular of a solid metal substrate. an aluminum or aluminum alloy substrate. The invention further relates to a corrosion-resistant solid metal substrate obtainable by such a method. Such an anticorrosive treatment method has applications in the general field of surface treatment of solid metal substrates, especially metal parts. Such a method has its applications in the field of transport vehicles, including ships, motor vehicles and aircraft in which the problem of the fight against corrosion of metal parts arises. Methods for surface treatment of a solid metal substrate in which chromium-based reagents are used are already known. Such reagents are toxic to the environment and to human health and their use is regulated. To overcome the disadvantages associated with the use of chromium, it has been proposed (Pepe et al., 2004, Journal of Non-Crystalline Solids, 348, 162-171) to form a surface silica gel coating. of an aluminum alloy substrate by a sol / gel process. Such treatment is carried out by soaking and shrinking ("dip-coating") of the aluminum alloy substrate in a hybrid solution of tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) containing cerium nitrate. Such a process does not make it possible to obtain an anticorrosive coating which, at the same time, exhibits improved mechanical strength properties, in particular improved tearing resistance, and also improved healing properties and barrier effect. The invention aims to overcome the disadvantages mentioned above by proposing a method of anticorrosion treatment of a solid metal substrate which does not require the use of chromium derivatives, in particular chromium VI, which is carcinogenic, mutagenic and reprotoxic. It is an object of the invention to provide an anticorrosive treatment method adapted to form a surface anticorrosion coating of a solid metal substrate which is of high mechanical strength. The invention also aims at providing such an anticorrosion treatment method which makes it possible to obtain a layer of anti-corrosive coating of controlled thickness, in particular between 1 and 15 gm, and compatible with industrial recommendations, particularly in the field. aeronautics. Another object of the invention is to provide a method for the anticorrosion treatment of a solid metal substrate - particularly metallic parts for aeronautics - adapted to allow the formation of an anticorrosion coating of said solid metal substrate which is substantially homogeneous thickness on the surface of the solid metal substrate, which is covering and which is also leveling. By leveling, it is meant that such a coating has a free outer surface-i.e., opposed to the substrate-which is substantially planar regardless of the presence of structural defects on the surface of the underlying solid metal substrate. In particular, the invention aims to provide such a method adapted to allow the formation of an anticorrosion coating having no cracking at said structural defects. The invention also aims at such a process which is adapted to allow the formation of an anticorrosion layer which is resistant to cracking. The invention furthermore aims at such a method adapted to allow the formation of a surface anticorrosion coating of a solid metal substrate having at the same time passive protection properties - in particular, by barrier effect of said substrate vis-à-vis -vis of a corrosive external environment and active healing protection properties and limiting the progression of corrosion at the level of an accidental bite that may affect the anticorrosive coating. The invention is also directed to such an anti-corrosive treatment method adapted to be applied to a polished solid metal substrate or an unpolished solid metal substrate. The invention also aims to achieve all these objectives at lower cost, by proposing a method which is simple and which requires for its implementation that steps of contacting a solid metal substrate and liquid solutions.

The invention also aims and more particularly to provide such a method that is compatible with the constraints of safety and respect for the environment. The invention further aims to provide such a solution that preserves the work habits of staff, is easy to use, and imply 10 for its implementation that few manipulations. The invention also aims at such an anticorrosion treatment method using a treatment solution that is simple in its composition compared to liquid treatment solutions of the state of the art.

The invention therefore also relates to an anticorrosive coating having improved protective properties compared to anti-corrosion coatings of the state of the art, including anti-corrosion properties which are improved over time. To this end, the invention relates to an anticorrosive treatment method in which a solution, called a liquid treatment solution, is applied to an oxidizable surface of a solid metal substrate, comprising: at least one alkoxysilane, and at least one cation of cerium (Ce); in a liquid hydro-alcoholic composition, said treatment solution being adapted to form on the surface of the solid metal substrate, a hybrid matrix by hydrolysis / condensation of each alkoxysilane (s) and each cerium cation (Ce); the treatment solution having a molar ratio (Si / Ce) of silicon element of the alkoxysilane (s) relative to the cerium (Ce) cation (s) of between 50 and 500, in particular between 80 and 500; and 250; Characterized in that the cation (s) of cerium (Ce) has a concentration of between 0.005 mole / L and 0.015 mole / L, in particular between 0.005 mole / L and 0.01 mole / L, preferably of the order of 0.010 mol / L- in the treatment solution.

The inventors have observed that the selection of concentration values of the cerium cations in the treatment solution does not constitute an arbitrary selection of concentration, but on the contrary that this selection provides a surprising result, totally unpredictable, not described in the state. of the technique and according to which the selected concentration of the cerium (Ce) cation in the anticorrosion treatment solution of a solid metal substrate simultaneously makes it possible (1) to obtain optimum adhesion of the surface treatment solution of the substrate solid metal, (2) the formation of a hybrid matrix of passive protection of said solid metal substrate by barrier effect adapted to limit the formation of corrosion products of the solid metal substrate - in particular of a solid metallic substrate having a puncture -, and (3) forming such a hybrid protective matrix having physical strength properties. ue to mechanical aggression -including resistance to delamination, resistance to cracking, and plastic deformation- and corrosion resistance-at 1 day, 7 days and 14 days of corrosive treatment by immersion in a corrosive solution of NaCt at 0.05 mol / L in water which are improved. Such properties of physical resistance to mechanical attack are evaluated in particular by techniques known in themselves to those skilled in the art, in particular by nanoindentation for the evaluation of Young's modulus of elasticity and hardness ( for example, nano-hardness of Vickers) - or by progressive scratching ("nano-scratch") for the evaluation of the adhesion and the resistance to delamination of the anticorrosion coating on the surface of the solid metal substrate. Advantageously, the cerium cation is a single cerium cation and the concentration of the single cerium cation in the treatment solution 2981366 is between 0.005 mole / L and 0.015 mole / L, in particular between 0.005 mole / L and 0 , 01 mol / L, preferably of the order of 0.01 mol / l. Advantageously, the cerium cation is a composition comprising a plurality of distinct cerium cations and the cumulative concentration of the plurality of distinct cerium cations in the treatment solution is itself between 0.005 mole / L and 0.015 mole / L , in particular between 0.005 mol / l and 0.01 mol / l, preferably of the order of 0.01 mol / l. An anticorrosive coating according to the invention, that is to say a coating obtained with a treatment solution comprising a concentration of cerium cation, especially in Cen.sub.1 between 0.005 mol / l and 0.015 mol / l, presents: critical value (Hv) of plastic deformation measured by nano-indentation which is maximum and of the order of 39 for a cerium concentration of 0.01 mol / L in the treatment solution; A delamination critical load value FD (mN) of the corrosion-resistant coating on the solid metal substrate which is maximum and of the order of 24 mN for a cerium concentration of 0.01 mol / L in the treatment solution; a critical cracking load value Ff (mN) of the anticorrosion coating which is maximum and of the order of 15 mN for a cerium concentration of 0.01 mol / l in the treatment solution, and; a peak load value of plastic deformation without cracking FDp (mN) of the order of 6 mN for a cerium concentration of 0.01 mol / l in the treatment solution.

The inventors have observed that a concentration of cerium cation in the treatment solution of between 0.005 mol / l and 0.015 mol / l according to the invention gives the corrosion-resistant coating of a solid metal substrate a resistance against corrosion which is optimal after deposition and before immersion in a corrosive solution. On the other hand, a concentration of cerium cation in the treatment solution of greater than 0.015 mol / L leads to a significant degradation of the barrier effect of the protective layer and a resistance to reduced corrosion screw before immersion in a corrosive solution. The surface resistance in a corrosive medium of such a protective layer of 6.3 μm thick, obtained by an anticorrosion treatment of a solid metal substrate with a treatment solution containing 0.05 mol / l of cerium cation , and immediately after immersion of said metal substrate in the corrosive medium is of the order of 2.8 × 10 6 n.cm2. The surface resistance in corrosive medium of such a protective layer of 6.3 mm thick, obtained by an anticorrosion treatment of a solid metal substrate with a treatment solution containing 0.1 mol / l of cerium cation, and immediately after immersion of said metal substrate in the corrosive medium is of the order of 2.0 × 10 5 ac m 2 as measured by electrochemical impedance spectroscopy (EIS). In addition, a concentration of cerium cation in the treatment solution of between 0.005 mole / L and 0.015 mole / L according to the invention allows: - a decrease in the contact angle of the treatment solution on the metal substrate solid resulting in improved wettability of the surface of the solid metal substrate vis-à-vis the processing solution and improved application of said treatment solution to the surface of the solid metal substrate; an improved anchoring of the hybrid matrix obtained from the treatment solution on the surface of the solid metal substrate; - Improved grounding of the surface treatment solution of the solid metal substrate. Such weight gain reveals a structuring effect of the treatment solution and the hybrid matrix obtained from the treatment solution, and; - to favor the Celn at the expense of the Ceiv in the treatment solution and in the hybrid soil. We measure the distribution. Ceill / Ceiv by X-ray photoelectron spectrometry (XPS) known in itself to those skilled in the art.

The inventors have observed that such a concentration of cerium cations of between 0.005 mol / l and 0.015 mol / l in the treatment solution is adapted to at least preserve the mechanical properties of the hybrid matrix obtained from the treatment solution, to impart to the treatment solution rheological qualities and surface adhesion of the solid metal substrate which are improved over a treatment solution not having such a concentration, while conferring on said hybrid matrix passive protection properties of the solid metal substrate by barrier effect.

Advantageously and according to the invention, each alkoxysilane is selected from the group formed: tetraalkoxysilanes of the following general formula (I); If (O-R 1) 4 (I), wherein: o Si is the silicon element, O is the oxygen element; R1 is selected from the group consisting of: a hydrocarbon group - especially methyl or ethyl - of the formula [-CnH2, i + 1], n being an integer greater than or equal to 1, of the group 2- hydroxyethyl (HO-CH2-CH2-), and; An acyl group of the general formula -CO-R'1 in which R'1 is a hydrocarbon group -not a methyl, an ethyl- of formula [-C ,, H2n + 1], n being a whole number greater than or equal to 1, and; alkoxysilanes of the following general formula (II): Si (O-R 2) 4-a (R 3) a (II); Wherein R 2 is selected from the group consisting of a hydrocarbon group-especially methyl, ethyl of formula [-C n E 1 2 n + 1], where n is an integer greater than or equal to 1, of the group 2- hydroxyethyl (HO-CH2-CH2-), and; An acyl group of the general formula -CO-R'1 in which R'1 is a hydrocarbon group -not a methyl, an ethyl- of formula [-Cii112 ', 1], n being a higher integer or equal to 1, and; o R3 is an organic group -notamment an organic group consisting of carbon atom (s), hydrogen atom (s) and, if appropriate, nitrogen atom (s), atom (s) of oxygen and optionally of sulfur atom (s) and phosphorus atom (s) bound to the silicon (Si) element of the alkoxysilane by an Si-C oa bond is a natural whole number of interval] 0; 4 [, preferably 10, 1-. Advantageously, in a first variant of a process according to the invention, each alkoxysilane is selected from the group consisting of tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), tetraacetoxysilane (TAOS) and tetra-2-hydroxyethoxysilane (THEOS). .

Advantageously, in a second variant of a process according to the invention, the R 3 group of each alkoxysilane is selected from the group consisting of methacrylates, acrylates, vinyls, epoxyalkyls and epoxyalkoxyalkyls in which the group (s) ( s) alkyl has from 1 to 10 carbon atoms and is (are) selected from linear alkyl groups, branched alkyl groups and cyclic alkyl groups. Advantageously, the R 3 group of each alkoxysilane is selected from the group consisting of 3,4-epoxycyclohexylethyl and glycidoxypropyl. Advantageously, each alkoxysilane is selected from the group consisting of glycidoxypropyltrimethoxysilane (GPTMS), glycidoxypropylmethyldimethoxysilane (MDMS), glycidoxypropylmethyldiethoxysilane (MDES) of glycidoxypropyltriethoxysilane (GPTES), methyltriethoxysilane (MTES), dimethyldiethoxysilane (DMDES), metacryloxypropyltrimethoxysilane (MAP ), 3- (trimethoxysilyl) propylamine (APTMS), 2- (3,4-epoxycyclohexyl) ethyltriethoxysilane (ECHETES), 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane (ECHETMS) , 6-epoxyhexyltriethoxysilane (ENTES). In this second variant of a process according to the invention, an organic / inorganic hybrid matrix is formed by hydrolyzing the condensation of each alkoxysilane. Advantageously and according to the invention, the treatment solution comprises a single alkoxysilane. Advantageously and according to the invention, the treatment solution comprises at least one metal alkoxide.

Advantageously and according to the invention, each metal alkoxide has the following general formula (VII): M '(O-R9), f, (VII), in which: M' is a metal element selected from the group consisting of Aluminum (At), vanadium (V), titanium (Ti) and zirconium (Zr), where R9 is an aliphatic hydrocarbon group of formula [-CnE12.1] -particularly selected from the group consisting of methyl, ethyl, propyl, butyl, in particular secondary butyl of formula [CH 3 -CH 2 - (CH 3) CH -] - in which n is a whole number greater than or equal to at 1, and; In a process according to the invention, each alkoxysilane and each metal alkoxide are hydrolyzed by reacting homogeneously distributed reactive species in the reaction solution of the metal element M '. The process is thus capable of polymerizing and forming an organic / inorganic hybrid matrix, thereby forming an organic / inorganic hybrid matrix by hydrolyzing the condensation of each alkoxysilane and each metal alkoxide Advantageously, each metal alkoxide is selected from the group consisting of alkoxides. of aluminum, especially aluminum tri (t-butoxide), aluminum tri (n-butoxide), aluminum tri (ethoxide), aluminum tri (ethoxyethoxyethoxide) and tri ( aluminum isopropoxide), titanium alkoxides -including titanium tetra (n-butoxide), titanium tetra (isobutoxide), titanium tetra (isopropoxide), titanium tetra (methoxide) and titanium. titanium tetra (ethoxide), vanadium alkoxides, especially tri (isobutoxide) vanadium oxide and tri (isopropoxide) vanadium oxide and zirconium alkoxides, especially tetra (ethoxide) zirconium, tetra (zirconium isopropoxide), zirconium tetra (n-propoxide), zirconium tetra (n-butoxide) and zirconium tetra (t-butoxide). Advantageously, each metal alkoxide is an aluminum alkoxide of the following general formula (III): ## STR3 ## wherein: At and O are respectively the aluminum and oxygen elements, and R4 is an aliphatic hydrocarbon group having 1 to 10 carbon atoms, especially selected from the group consisting of methyl, ethyl, propyl, butyl, especially secondary butyl; of formula [CH3-CH2 (CH3) -CH-] -; o n is a natural integer representing the valency of the aluminum element (At). Advantageously and according to the invention, the treatment solution comprises a single metal alkoxide. An inorganic hybrid matrix is thus formed by condensation hydrolysis of each alkoxysilane and the single metal alkoxide. Advantageously, the treatment solution comprises a single metal alkoxide and a single alkoxysilane. An inorganic hybrid matrix is thus formed by condensation hydrolysis of the single alkoxysilane and the single metal alkoxide. Advantageously, the treatment solution comprises, as a single metal alkoxide, a single aluminum alkoxide.

Thus, a treatment solution comprising a metal alkoxide, especially a single alkoxide of aluminum and a single alkoxysilane, is formed, said treatment solution being of great simplicity in its composition and nevertheless adapted to provide a high performance anticorrosive coating. Advantageously, the single aluminum alkoxide is selected from the group consisting of aluminum tri (s-butoxide), aluminum tri (n-butoxide), aluminum tri (ethoxide), tri ( aluminum ethoxyethoxyethoxide) and aluminum tri (isopropoxide). Advantageously, the molar ratio of the alkoxysilanes with respect to the metal alkoxides in the treatment solution is between 99/1 and 50/50. Advantageously, the molar ratio of all the alkoxysilanes relative to the total of metal alkoxides in the treatment solution is between 99/1 and 50/50. Advantageously and according to the invention, the molar ratio of the alkoxysilanes and metal alkoxides-in particular of the aluminum alkoxide-in the treatment solution is between 85/15 and 6/4, in particular between 8/2 and 64. / 36. Advantageously, the molar ratio of all the alkoxysilanes relative to the total of metal alkoxides in the treatment solution is between 8/2 and 6/4. Advantageously and according to the invention, the solid metal substrate 20 is formed from a material chosen from the group consisting of oxidizable materials-in particular aluminum (for example alloy 2024T3), titanium (for example alloy TA6V ), magnesium (for example, the AZ30 alloy) and their alloys. Advantageously and according to the invention, the treatment solution is applied by soaking / removal of the solid metal substrate in said treatment solution. Advantageously, the solid metal substrate is removed from the treatment solution with a predetermined speed of between 5 cm / min and 10 cm / min. Advantageously and according to the invention, the atmospheric spray treatment solution 30 is applied to the surface of the solid metal substrate.

The inventors have observed that it is possible to control the thickness of the hybrid matrix by the rate of removal of the solid metal substrate from the treatment solution. According to the Landau-Levich law (Landau LD and Levich BG, (1942), Acta Physiochim, USSR, 17, 42-54), it is possible for a known viscosity treatment solution to vary the thickness of the hybrid anti-corrosion matrix of a value of 1 grn for a withdrawal speed of 1 cm / min, up to a value of 14 gm for a shrinkage speed of 20 cm / min. In particular, a withdrawal speed of 7 cm / min makes it possible to obtain a hybrid matrix with a thickness of 5 μm.

The thickness of the hybrid matrix is measured by methods known in themselves to those skilled in the art, in particular by interferometric profilometry or by measurement of induced eddy currents. Advantageously, the treatment solution further comprises a plasticizer selected from the group consisting of PEG.

Advantageously, the liquid treatment solution comprises a dye. Such a dye is selected from the group consisting of rhodamine B (CAS 81-88-9), malachite green ("brilliant green", CAS 633-03-4) and xylene cyanole (CAS 2850-17-1). ). Advantageously, rhodamine B is used at a concentration in the liquid treatment solution of between 5 × 10 -4 mol / l and 10 3 mol / l, the malachite green at a concentration in the liquid treatment solution of between 5 × 10 -4 mol / l. 4 mol / L and 10-3 mol / L and xylene cyanole at a concentration in the liquid treatment solution of between 5.10-4 mol / L and 10-3 mol / L. Advantageously, in an anticorrosion treatment process according to the invention, the treatment solution comprises a nanoparticle feedstock formed of a colloidal dispersion of boehmite in the treatment solution, ie solid boehmite nanoparticles. of general formula [-AlO (OH) -] forming a colloidal dispersion of boehmite nanoparticles in the treatment solution.

In an anticorrosive treatment process according to the invention, in order to prepare a treatment solution, each alkoxysilane, each aluminum alkoxide and, where appropriate, each metal alkoxide in an alcohol is dissolved-notably selected from the group consisting of ethanol, propanol-1 and propano-2-then a quantity of water or, where appropriate, an amount of an aqueous solution containing at least one lanthanide cation and / or or colloidal boehmite so as to form an anti-corrosion treatment solution. Advantageously, alkoxysilane (s) and the metal (s) alkoxide (s) and an amount of water or, if appropriate, an amount of an aqueous solution, are added to an alcoholic solution. containing at least one lanthanide cation and / or colloidal boehmite nanoparticles so as to substantially retain the rheological and thixotropic properties of the treatment solution. Advantageously, in a third variant of an anticorrosion treatment process according to the invention, a treatment solution comprising boehmite nanoparticles of general formula A10 (OH) and having a surface distribution of lanthanide cations-notably cations is formed. of cerium- and / or vanadate. Such boehmite nanoparticles, called physisorbed boehmite nanoparticles, are obtained by a process known in itself to those skilled in the art and in particular adapted from a process described by Yoldas (Yoldas BE et al., (1975), J. Mater Sci., 10, 1856).

In this third variant of a method according to the invention, the inventors have found an improvement in the corrosion resistance of a solid metal substrate treated with a treatment solution subjected to immersion in a corrosive NaCl bath at 0.degree. , 05 mole / L. Advantageously, in a fourth variant of an anticorrosion treatment process according to the invention, a treatment solution is formed comprising boehmite nanoparticles, called doped boehmite, of the following general formula (VIII): Ati, (X) xO ( OH) (VIII), wherein: - X is an element, referred to as a doping element, selected from the group consisting of trivalent lanthanides, especially trivalent cerium, and; 14 2 9 8 1 3 6 6 - x is a relative number between 0.002 and 0.01. Such doped boehmite nanoparticles are obtained by a process in which a solution of at least one aluminum precursor - notably At (OC 4 H 9) 3 - in water and a solution of a cation of a doping element selected from the group consisting of a nitrate, a sulfate, an acetate and a chloride of the doping element. In this fourth variant of a method according to the invention, the inventors have found an improvement in the corrosion resistance of a solid metal substrate treated with a treatment solution subjected to immersion in a corrosive bath of NaCl at 0.degree. , 05 mole / L. Advantageously, the physisorbed boehmite nanoparticles and the doped boehmite nanoparticles have a larger dimension and two smaller dimensions, perpendicular to each other and perpendicular to said larger dimension, said larger dimension is less than 200 nm, in particular less than 100. nm, particularly less than 50 nm, preferably between 5 nm and 20 nm-, and the two smaller dimensions are less than 10 nm, preferably of the order of 3 nm. Advantageously and according to the invention, the treatment solution comprises a charge of hollow boehmite nanoparticles.

Advantageously and according to the invention, after the application of the treatment solution, a heat treatment of the metal substrate adapted to allow the formation of the hybrid matrix and the evaporation of the solvents is carried out. Advantageously in a process according to the invention, before applying the treatment solution, said oxidizable surface of the solid metal substrate is immersed in a so-called conversion solution solution, a liquid formed of at least one corrosion inhibitor in the wherein said corrosion inhibitor is selected from the group consisting of lanthanide cations and said oxidizable surface of the solid metal substrate is maintained in contact with the conversion solution for a period of time suitable to form a conversion layer formed from said bound lanthanide; by at least one covalent bond to the oxidizable surface and extending at the surface of the solid metal substrate. In a fifth variant of an anticorrosion treatment process according to the invention, a conversion layer is first formed on the oxidizable surface of a solid metal substrate by contacting said oxidizable surface with the conversion solution. A treatment with such a conversion solution constitutes an anticorrosion treatment in that it allows the formation of a surface conversion layer of the solid metal substrate, instead of a metal oxide layer of the solid metal substrate. , said conversion layer exhibiting a resistance to corrosion - in particular measured by electrochemical impedance spectroscopy (EIS) - which is increased with respect to the resistance to corrosion of the coating layer. oxide formed naturally on the surface of the solid metal substrate. In fact, the inventors have observed that an anticorrosion treatment according to the invention in which a surface conversion layer of a solid metal substrate is first formed, then a treatment solution comprising at least one alkoxysilane is applied, a cerium cation at a concentration of between 0.005 mol / l and 0.015 mol / l and, if appropriate, at least one metal alkoxide, makes it possible to increase the resistance to corrosion of the oxidizable surface of a solid metal substrate, even after immersing the oxidizable surface of the solid metal substrate for a predetermined period of time - especially a time greater than 1 hour - in a corrosion bath, especially an aqueous bath of NaCC 0.05 mol / L. The inventors assume that the treatment of the oxidizable surface of the solid metal substrate with the conversion solution results in the formation of an increased corrosion resistance layer with respect to the metal oxide layer. solid metal substrate not treated with the conversion solution. Such a conversion layer is characterized, according to a representation, called "Nyquist" representation, of the electrochemical impedance diagram by a value Z '(w) of surface resistance (û.cm2) increased with respect to the value Z' (w) surface resistance of a solid metal oxide layer naturally formed on the surface of a solid metal substrate. The impedance measurements Z (co) are carried out in potentiostatic mode around the free potential, with a sinusoidal disturbance. The sinusoidal disturbance amplitude is set at 10 mV to satisfy the linearity conditions. The frequencies scanned during impedance measurements are between 65 kHz and 10 mHz with 10 points per decade. The inventors have shown by Energy Dispersive Spectroscopy (EDS) that this conversion layer consists of mixed oxides of lanthanide and the constituent metal of the oxidizable surface of the solid metal substrate. Advantageously, the conversion layer extending at the surface of the solid metal substrate has an average thickness of between 1 nm and 200 nm. The inventors have observed that increasing the immersion time of a solid metal substrate in a conversion solution according to the invention makes it possible to increase the value of the surface area resistance which goes beyond the value. limit of the surface resistance of the layer of aluminum oxide formed naturally on the surface of an aluminum alloy piece.

In addition, the inventors have also observed that such a treatment of the oxidizable surface of a solid metal substrate by a conversion solution does not lead to any detectable increase in the mass of the substrate. Such a conversion layer does not correspond to a crystallization of lanthanide oxides / hydroxides on the surface of the solid metal substrate.

In particular, the treatment of the oxidizable surface of the solid metal substrate by the conversion solution allows the formation of an active protection conversion layer and surface healing of the solid metal substrate by forming a plurality of covalent bonds involved. between the lanthanide element (Ln) corrosion inhibitor and a metal element (M) of the solid metal substrate. The inventors have shown by chemical analysis of the binding energies - in particular by X-ray photoelectron spectrometry (XPS) - that this covalent bond is of the M-O-Ln-O- type in which M represents a metallic element of the metallic substrate. solid, 0 is an oxygen atom and Ln represents the corrosion inhibiting element chosen from lanthanides. In a process according to the invention, the solid metal substrate, and optionally the surface of the conversion layer, is treated with a treatment solution consisting of an organic / inorganic hybrid soil of at least an alkoxysilane, in particular an alkoxysilane carrying an organic group, a cerium cation at a concentration of between 0.005 mol / l and 0.015 mol / l, and, if appropriate, at least one metal alkoxide, adapted to form by hydrolysis / condensation of alkoxysilane (s), metal alkoxide (s) and cerium cation an organic / inorganic hybrid matrix formed of inorganic atomic chains (-) Si-O-Si-) and organic hydrocarbon chains. The inventors have observed that immersing a solid metal substrate in a conversion solution allows not only the formation of such a conversion layer and the active protection of the solid metal substrate from corrosion, but furthermore allows an improvement in the adhesion of a hybrid soil at the surface of the solid metal substrate and an improvement in the passive protection properties of said solid metal substrate 20 with respect to corrosion. Advantageously and according to the invention, each corrosion inhibitor of the conversion solution is selected from the group consisting of lanthanum (La) cations, cerium (Ce) cations, praseodymium (Pr) cations, neodymium cations. (Nd), samarium (Sm) cations, europium (Eu) cations, gadolinium (Gd) cations, terbium (Tb) cations, dysprosium (Dy) cations, holmium (Ho), erbium cations (Er), thulium cations (Tm), ytterbium cations (Yb) and lutetium cations (Lu). Advantageously and according to the invention, each corrosion inhibitor of the conversion solution is selected from the group consisting of lanthanide chlorides, lanthanide nitrates, lanthanide acetates, and lanthanide sulfates. Advantageously, each corrosion inhibitor of the conversion solution is selected from the group consisting of lanthanum chloride (LaCt3), cerium chloride (CeCt3), yttrium chloride (YCt3), cerium sulphate (Ce2 (SO4) 3), cerium acetate (Ce (CH3COO) 3), praseodymium chloride (PrCt3), neodymium chloride (NdCt3) Advantageously and according to the invention, each corrosion inhibitor of the solution of The conversion is a cerium cation-notably cerium nitrate (Ce (NO3) 3), cerium acetate (Ce (CH3COO) 3), cerium sulphate (Ce2 (SO4) 3) and cerium chloride. (CeCt3) - wherein the cerium element is of valence III (Cern). Advantageously and according to the invention, the cerium (Ce) cation of the treatment solution is chosen from the group consisting of cerium chlorides and cerium nitrates. In particular, the corrosion inhibitor of the conversion solution is cerium nitrate Ce (NO3) 3. The inventors have shown that the conversion layer consists of mixed oxides of cerium and the constituent metal of the oxidizable surface of the solid metal substrate. Chemical analysis by Energy Dispersive Spectroscopy (EDS) has La and Ma lines characteristic of cerium at the surface of the solid metal substrate. The inventors have observed that such an anticorrosion treatment method makes it possible to form an anticorrosion coating formed of a conversion layer comprising at least one corrosion inhibitor and adapted to allow self-healing of the solid metal substrate, said conversion layer being itself protected by the cerium-rich hybrid matrix having an optimal barrier effect. But the inventors have also observed in a totally surprising manner that the conversion layer 30 does not alter the mechanical properties of delamination resistance and adhesion of the hybrid matrix to the solid metal substrate; 19 2 9 8 1 3 6 6 - does not alter the barrier properties of the hybrid matrix, as measured by SIE can slow down the loss of corrosion resistance of the solid metal substrate during a prolonged immersion thereof in a corrosion bath, and - delays the appearance of corrosion products on metal substrates undergoing a point of corrosion. The presence of a conversion layer rich in corrosion inhibitor located at the interface between the solid metal substrate and the hybrid matrix 10 provides additional active protection, which adds to the protective effect of the hybrid matrix. . Advantageously and according to the invention, the conversion solution has a concentration of corrosion inhibitor - in particular cerium (Ce) - of between 0.001 mol / l and 0.5 mol / l, in particular between 0.05 mol / l and 0 mol. , 3 mol / L, in particular of the order of 0.1 mol / L. Advantageously, the conversion solution has a concentration of corrosion inhibitor - in particular cerium (Ce) - of between 0.01 mole / L and 0.5 mole / L, preferably between 0.1 mole / L and 0.5 mol / L.

Advantageously, the oxidizable surface of the solid metal substrate is maintained in contact with the conversion solution for a predetermined period of between 1 s and 30 min, in particular between 1 s and 300 s, preferably between 1 s and 15 s, in particular between 1 s and 10 s, more preferably between 1 s and 3 s.

Advantageously, after the step of contacting the oxidizable surface of the solid metal substrate and the conversion solution, the solid metal substrate is dried at a predetermined temperature of less than 100 ° C., in particular of the order of 50 ° C. C-, so as to form on the surface of the solid metal substrate, a layer, referred to as the conversion layer, of the corrosion inhibiting element Ln (lanthanide) bonded to a metal element M of the solid metal substrate by a connection of the type MO. -ln-O-.

Advantageously, the conversion solution has a pH substantially of the order of 4. Advantageously, the pH of the conversion solution is adjusted by the addition of a mineral acid-in particular nitric acid- to the conversion solution.

The inventors have observed that a method for the corrosion treatment of a solid metal substrate in two stages according to the invention not only allows active protection, in particular by healing, of the solid metal substrate with respect to corrosion. but also provides passive protection against said corrosion.

Advantageously and according to the invention, the liquid aqueous-alcoholic composition is formed of water and at least one alcohol, in particular selected from the group consisting of ethanol, propanol-1 and propanol-2-. The inventors have observed that a method for the corrosion treatment of a solid metal substrate in two stages according to the invention not only allows active protection, in particular by healing, of the solid metal substrate with respect to corrosion. but also provides passive protection against said corrosion. Advantageously, the conversion solution has a pH substantially of the order of 4. Advantageously, the pH of the conversion solution is adjusted by addition of a mineral acid - especially nitric acid - to the conversion solution. Advantageously, the doped and / or physisorbed boehmite nanoparticles have a larger dimension and two smaller dimensions, perpendicular to each other and perpendicular to said larger dimension, said larger dimension is less than 200 nm, in particular less than 100 nm, especially less than 50 nm, preferably between 5 nm and 20 nm-, and the two smaller dimensions are less than 10 nm, preferably of the order of 3 min. Advantageously and according to the invention, the treatment solution comprises a charge of hollow boehmite nanoparticles.

The invention also provides an anticorrosive coating obtainable by a method according to the invention. The invention extends, moreover, to an anticorrosive coating of a solid metal substrate formed by a hybrid matrix extending at the surface of the solid metal substrate and obtained by hydrolysis / condensation of at least one alkoxysilane, said hybrid matrix. having a (Si / Ce) molar ratio of silicon element of (the) alkoxysilane (s) relative to at least one cation of cerium (Ce) between 50 and 500, in particular between 80 and 250.

This Ce / Si ratio is determined by methods known in themselves to those skilled in the art, in particular by RBS (Rutherford Backscattering Spectrometry) analysis of the elastic diffusion of the ions of an incident ion beam adapted to be able to measure the amount of a heavy element in a light hybrid matrix.

The invention extends in particular to an anticorrosion coating in which the hybrid matrix extending in contact with a solid metal substrate and obtained by hydrolysis / condensation of at least one alkoxysilane and, where appropriate, from minus a metal alkoxide and comprising: o at least one inorganic group of general formula (IX): -A-O-B- (IX), wherein: O is the oxygen element, A and B are independently selected from each other in the group formed of Si and M ', and; At least one organic group of general formula (XI): -DO-R10-O- E- (XI), in which O is the oxygen element, and D and E are independently selected from one of another in the group consisting of Si, M 'and Ce, and; R10 is a hydrocarbon group.

Advantageously, the anticorrosion coating has a thickness of between 1 μm and 15 μm. The invention furthermore extends to an anticorrosive coating having at least one of the following characteristics: the hybrid matrix of the anticorrosive coating is formed of a composite material comprising a hybrid xerogel - in particular an organic / inorganic hybrid xerogel and a physisorbed boehmite nanoparticle feed dispersed in the hybrid xerogel - the hybrid matrix of the anticorrosive coating is formed of a composite material comprising a hybrid xerogel - especially an organic / inorganic hybrid xerogel - and a doped boehmite nanoparticle feed. general formula (VIII) At 1, (X) x 0 (OH), (VIII) wherein: X is an element, referred to as a doping element, selected from the group consisting of trivalent lanthanides, especially trivalent cerium, and ; o x is a relative number between 0.002 and 0.01; said filler being dispersed in the hybrid xerogel; the hybrid matrix of the anticorrosive coating is formed of a composite material comprising a hybrid xerogel-especially an organic / inorganic hybrid xerogel-and a charge of hollow boehmite nanoparticles dispersed in the hybrid xerogel; the solid nanoparticles of the charge of physisorbed boehmite nanoparticles and the charge of doped boehmite nanoparticles having a larger dimension and two smaller dimensions, perpendicular to each other and perpendicular to said larger dimension, the largest dimension is smaller; at 200 nm, in particular less than 100 nm, particularly less than 50 nm, preferably between 5 nm and 20 nm, and the two smaller dimensions are less than 10 nm, preferably of the order of 3 nm; The solid nanoparticles of the charge of hollow boehmite nanoparticles are of substantially spherical shape and have a mean diameter of the order of 30 nm. Advantageously, the conversion layer of the anticorrosive coating has a thickness of between 1 nm and 200 nm. The invention also extends to a metal surface coated with an anticorrosion coating obtained by a method according to the invention. The invention also relates to a process characterized in combination by all or some of the characteristics mentioned above or hereinafter. Other objects, features and advantages of the invention will appear on reading the following description which refers to the appended figures representing preferred embodiments of the invention, given solely by way of non-limiting examples, and in which: FIG. 1 is a schematic out-of-proportion representation of a variant of an anticorrosion coating according to the invention; - Figure 2 in a scanning electron microscope (SEM) view of a cross section of an anticorrosion coating of a solid metal substrate obtained by a method according to the invention; FIG. 3 is a comparative graphical representation of the evolution of the surface resistance with respect to the corrosion of a solid metal substrate treated according to two variants of a method according to the invention; FIG. 4 is a graphical representation of the surface resistance (n.cm2) of an anticorrosive coating as a function of the cerium concentration in the treatment solution; FIG. 5 is a graphical representation of the Vickers nano-hardness of an anticorrosion coating as a function of the cerium concentration in the treatment solution; FIG. 6 is a graphical representation of the variation of the value of the Young, in GPa, determined by nano-indentation measurements; FIG. 7 is a graphical representation of the value of the critical load (mN) of delamination (o), cracking (A) and plastic deformation (o), determined by nano-nano-scratch, of a anticorrosion coating according to the concentration of cerium in the treatment solution; Fig. 8 is a Nyquist representation of the electrochemical impedance of a treated (o) or untreated solid metal substrate (A) with a conversion solution; 9 is a spectrum of chemical surface analysis by electron dispersion spectroscopy ("EDP") of a solid metal substrate treated with a conversion solution according to the invention. The invention shown in Figure 1 is supported on a metal substrate 2 formed of metallic elements M. Such an anticorrosion coating is formed of an optional conversion layer 3 in which corrosion inhibiting elements Ln are linked by covalent bonds MO In addition, Ln elements in the conversion layer corrosion inhibitors form covalent bonds with Si elements and, if appropriate, metal elements M 'chosen from the group. formed from aluminum (A 0, vanadium (V), titanium (Ti) and zirconium (Zr) and the cerium element (Ce) from the hybrid matrix 4 on the surface of the conversion layer 3. FIG. 2 represents a scanning electron microscope (SEM) section of an aluminum substrate 2 treated with a variant of a method according to the invention and comprising a conversion layer (optional) 25 extending to interface between the aluminum substrate 2 and the hybrid matrix 4. In a variant of a method for the anticorrosion treatment of a solid metal substrate according to the invention, a preparative surface treatment of a piece of rolled 2024 T3 aluminum alloy is first carried out. Such preparative treatment, given solely by way of nonlimiting example, has the objective of removing from the surface of the solid metal substrate any trace of oxidation of the alloy or of dirt which may be detrimental to the application of the alloy. 9 8 1 3 6 6 of the conversion solution and of the treatment solution on the surface of the substrate during its deposition ("dip-coating", "spray") and the anchoring of the hybrid anti-corrosion matrix obtained in surface of the substrate. Degreasing the solid metal substrate with an organic solvent The preparative treatment comprises a first step of degreasing the surface of the solid metal substrate, during which the surface of said substrate is placed in contact with a degreasing solvent. This degreasing step is carried out by methods known in themselves to those skilled in the art, in particular by soaking the surface of the substrate in the degreasing solvent or by spraying said surface with the degreasing solvent. As examples, the degreasing solvent may be stabilized pure methylene chloride (marketed under the trademark Methoklone) or pure acetone. In this case, this degreasing step is carried out at a temperature of less than 42 ° C. and for a duration of between 5 seconds and 3 minutes. It is possible to subject the solid metal substrate to ultrasonic treatment during this first degreasing step. Degreasing of the solid metal substrate with an alkaline solution The preparative treatment of the solid metal substrate comprises a second successive step of degreasing the surface of said substrate, in which the surface of the substrate is placed in contact with an alkaline preparation, in particular sold under the brand name. TURCO 4215 (HENKEL, Boulogne-Billancourt, France). This alkaline degreasing step is carried out by methods known in themselves to those skilled in the art, in particular by soaking the surface of the substrate in the alkaline preparation or by spraying said surface with said preparation for a period of time of between 10 minutes. and 30 min. Preferably, this alkaline degreasing step is carried out at a temperature of between 50 ° C. and 70 ° C. It is possible to subject the substrate to ultrasonic treatment during this second degreasing step with an alkaline solution.

The solidification of the solid metal substrate by an alkaline solution The preparative treatment according to the invention comprises a third successive step of pickling the surface of the substrate in which the surface of the substrate is placed in contact with a substrate. alkaline preparation, in particular an aqueous solution of sodium hydroxide at a concentration of between 30 g / l and 70 g / l. This alkaline pickling step is carried out by methods known in themselves to those skilled in the art, in particular by soaking the surface of the substrate in the concentrated alkaline preparation or by spraying said surface with said concentrated alkaline preparation for a period of time between 10 sec and 3 min. Preferably, this alkaline pickling step is carried out at a temperature of between 20 ° C. and 50 ° C. It is possible to subject the solid metal substrate to ultrasonic treatment during this second etching step with a concentrated alkaline solution.

At the end of this third successive step of treating the surface of the solid metal substrate, a powdery layer of oxides covering the surface of the solid metal substrate is observed. Stripping the solid metal substrate with an acidic solution The preparative treatment according to the invention comprises a fourth successive step of dissolving the oxide layer extending over the surface of the solid metal substrate at which the surface of said substrate is contact with an acidic preparation, for example TURCO LIQUID Smut-Go NC (HENKEL, Boulogne-Billancourt, France) or ARDROX 295 GD (Chemetal GmbH, Frankfurt, Germany).

This dissolution step is carried out for a period of between 1 minute and 10 minutes at a temperature of between 10 ° C. and 50 ° C. with an aqueous solution comprising between 15% (v / v) and 25% (v / v). from TURCO LIQUID Scout-Go NC. Alternatively, this dissolution step is carried out for a period of between 1 minute and 10 minutes at a temperature of between 10 ° C. and 30 ° C. with an aqueous solution comprising between 15% (v / v) and 30%. (v / v) of ARDROX 295 GD. At the end of this step the surface of the solid metal substrate is adapted to be treated according to an anticorrosion treatment 5 according to the invention. In a variant of a method of anticorrosion treatment of a solid metal substrate according to the invention, a step of forming a surface conversion layer of the solid metal substrate is carried out. A piece of aluminum (At 2024-T3) is immersed by "dip-coating" in an aqueous conversion solution containing a concentration of between 0.001 mol / l and 0.5 mol / l of Ce (NO 3) 3, the pH is adjusted to a value of 4 by adding nitric acid. After immersion and shrinkage, the aluminum piece is dried for 10 minutes at 50 ° C. At the end of this treatment with the conversion solution, no weight gain of said aluminum part is measured. In a method of anticorrosion treatment of a solid metal substrate, a treatment solution is prepared according to the following four steps: (a) elaboration of a treatment solution as described in (A) below; (b) developing a colloidal dispersion of physisorbed boehmite nanoparticles as described in (B) below; (c) developing a colloidal dispersion of doped boehmite nanoparticles as described in (C) hereinafter; (d) elaboration of hollow aluminum oxyhydroxide nanoparticles containing a corrosion inhibitor as described in (D) below; (e) developing a colloidal anticorrosive dispersion from the compositions as described in (A) above, (B), (C) and (D) below; (F) depositing the colloidal anticorrosive treatment dispersion on the solid metal substrate; and (g) heat treatment. A - Elaboration of an epoxy sol / epoxy solubilization solution GPTMS / ASB / Ce (NO3) 3 In a first embodiment, to prepare 1 L of epoxide sol, 107.4 g (0.43 g moles) of aluminum tri (s-butoxide) (ASB) in 34.8 mL of 1-propanol by stirring - in particular by magnetic stirring for 10 minutes at room temperature. 470 mL (2.13 moles) of 3- (glycidoxypropyl) trimethoxysilane (GPTMS) are then added. The molar proportion of GPTMS and ASB is 83/17. An aqueous solution of cerium (III) (Ce (NO 3) 3) is also prepared at a concentration of between 0.02 mol / l and 0.5 mol / l and a volume of this aqueous solution of cerium is added to the solution of precursor (ASB / GPTMS) so as to cause hydrolysis / condensation of the precursors. The epoxy sol obtained is stirred for a period of time necessary for a thermal decline to ambient temperature. The final concentration of cerium in the epoxy sol is 0.01 mol / L. The epoxy sol is deposited on an At 2024-T3 aluminum substrate pretreated as described above by dipping / removing the substrate in said epoxy sol. The withdrawal speed is 20 cm / min. The coated solid metal substrate is heated to a temperature of between 95 ° C. and 180 ° C., in particular 110 ° C., for a period of between 1 hour and 5 hours, in particular 3 hours. The formation of a 6 μm thick hybrid matrix is observed at the surface of the solid metal substrate having a salt spray resistance of between 96 and 800 hours. A2 - TEOS / MAP / Ce epoxy sol (NO3b In a second embodiment, to prepare 1 L of hybrid sol 230 ml of tetraethoxysilane (TEOS) is added in 600 ml of ethanol, 30 ml of methacryloxypropyltrimethoxysilane (MAP) are subsequently added. ), followed by an aqueous solution of cerium (III) (Ce (NO 3) 3) at a concentration of 4.32 g / L so as to cause hydrolysis / condensation of the TEOS and MAP precursors. The pH of the sol obtained is 4.5 and its viscosity is 3 mPa.s.B - Development of physisorbed colloidal boehmite nanoparticles 5 Such a colloidal dispersion of surface-functionalized boehmite nanoparticles (called physisorbed) is produced in two Steps described below in which a colloidal solution of boehmite nanoparticles is first formed, then said boehmite nanoparticles are functionalized with a corrosion inhibitor.

B1 - Colloidal Boehmite Condensation hydrolysis of aluminum tri-secbutoxide (ASB, At (OH) x (OC 4 H 9) 3) is carried out according to the method described by Yoldas BE (J. Mater Sci., (1975) 10, 1856), wherein an amount of water previously heated to a temperature above 80 ° C is added to aluminum tri-butoxide. The resulting solution is left stirring for 15 minutes. By way of example, such an aluminum tri (s-butoxide) solution is placed at a concentration of 0.475 mol / l (-117 g / l) in water at a temperature of 80 ° C. for duration of 15 min. A step, called the peptization step, is then carried out, during which triflutoxide is added to the hydrolysis solution a volume of between 1.4 ml and 2.8 ml of a 68% nitric acid solution. %. The mixture is placed at 85 ° C. in an oil bath for a period of 24 hours. A colloidal dispersion of aluminum oxyhydroxide (boehmite) in water is obtained. The concentration of nitric acid in the colloidal dispersion is between 0.033 mole / L and 0.066 mole / L. Alternatively, it is possible to concentrate the colloidal dispersion to a concentration of aluminum oxyhydroxide of the order of 1 mol / L. Other inorganic or organic acids may be used during this peptization step, in particular hydrochloric acid and acetic acid. A transparent and stable colloidal substrate having, by X-ray diffraction, the characteristic lines of boehmite as described in JCPDS sheet 21-1307 is obtained. B2 - Functionalization of the Boehmite Nanoparticles, To a colloidal dispersion as obtained according to the preceding step B1 and having an aluminum concentration of between 0.5 mol / l and 0.8 mol / l, is added, as appropriate a nonionic surfactant -particularly a nonionic surfactant selected from Pluronic®, P-123, Pluronic® F 127 (BASF, Mount Olive, New Jersey, USA), Brij 58 and Brij 52 in a mass proportion between 1% and 5%. An amount of a corrosion inhibitor, in particular cerium (III) nitrate (Ce (NO 3) 3) or sodium vanadate, is then added to a final concentration of between 0.001 mol / l and 0.5 mol / l. . This preparation is stirred at room temperature for 6 hours. A colloidal dispersion of surface-functionalized boehmite nanoparticles-said physisorbed boehmite nanoparticles-is obtained. Such a preparation is present in infrared spectroscopy by using the Diffuse Reflectance Infra-Red Fourier Transform (DRIFT) technique for vibrating bands at 1460 cm -1 and 1345 cm -1, which are characteristic of the coordination of cerium with nitrate ions. C - Elaboration of a colloidal dispersion of doped boehmite nanoparticles A colloidal dispersion of boehmite nanoparticles doped in two stages, described below, in which the hydrolysis / condensation of a precursor (I) is carried out is carried out. In particular, an alkoxide-aluminum and a corrosion inhibitor are used, followed by a step (C2), called a peptization step, of treatment in an acidic medium so as to form doped boehmite nanoparticles.Cl - Hydrolysis / condensation of ASB and (Ce (NO3) 3). The hydrolysis / condensation of a mixture of aluminum precursor - in particular an aluminum alkoxide, in particular tri (s-butoxide) is carried out. aluminum (ASB) - and a corrosion inhibitor - in particular cerium (III) nitrate (Ce (NO3) 3) - by adding to this mixture a minimum of water heated to 85 ° vs. This hydrolysis / condensation mixture is stirred for 15 minutes. The final concentration of ASB in the hydrolysis / condensation mixture is 0.475 mole / L and the final concentration of corrosion inhibitor in the hydrolysis / condensation mixture is 0.002 mole / cm 2. L and 0.01 mol / L. C2-Peptization An acidified aqueous solution (notably 1.4 ml to 2.8 ml of a 68% nitric acid solution) is added to the hydrolysis / condensation mixture and the acidified mixture is placed at room temperature. 85 ° C in an oil bath for a period of 24 hours. The concentration of nitric acid in the acidified mixture is between 0.033 mol / L and 0.066 mol / L. Alternatively, it is possible to concentrate the colloidal dispersion to a concentration of aluminum oxyhydroxide of the order of 1 mol / L. A transparent and stable colloidal sol having, by X-ray diffraction, the characteristic lines of boehmite as described in JCPDS sheet 21-1307 is obtained. D - Preparation of hollow aluminum oxyhydroxide (boehmite) nanoparticles containing the corrosion inhibitor. Such hollow aluminum oxyhydroxide nanoparticles containing the corrosion inhibitor are produced by formation of an inverse microemulsion (Daniel H ., et al (2007), Nano Lett., 7; 11, 3489-3492) and simultaneous encapsulation of the corrosion inhibitor. An apolar phase is prepared by mixing an alcohol, particularly hexanol, an alkane, especially dodecane, and a surfactant, especially hexadecyltrimethylammonium bromide (CTAB). A polar phase comprising water, an alcohol, in particular methanol, and a corrosion inhibitor, in particular cerium nitrate, is also prepared. The polar phase and the apolar phase are mixed and this mixture is stirred for 30 minutes to form a reverse microemulsion of water in the apolar phase. A solution of an aluminum alkoxide - especially aluminum tri (s-butoxide) (ASB) in a volume of the alkane - especially dodecane - is prepared. The aluminum alkoxide solution is introduced with stirring into the inverse microemulsion. The mixture is allowed to stand for 12 hours. A pellet containing hollow nanoparticles of aluminum oxyhydroxide is centrifuged off. After washing this pellet with diethylene glycol, a powder of 32 2981366 hollow aluminum oxyhydroxide nanoparticles containing the corrosion inhibitor is obtained. E-Elaboration of a Colloidal Solution for Anti-Corrosion Treatment A colloidal anti-corrosion treatment dispersion is prepared by mixing an amount of a treatment solution (hybrid soil) as prepared in (A), an amount of colloidal dispersion of physisorbed boehmite nanoparticles as prepared in (B) and / or an amount of a colloidal dispersion of doped boehmite nanoparticles as prepared in (C) and / or an amount of a dispersion of hollow boehmite nanoparticles. The concentration of aluminum and silicon in the colloidal anti-corrosion treatment dispersion is between 1.66 mol / l and 2 mol / l. The aluminum concentration provided by the colloidal dispersion of surface-functionalized boehmite nanoparticles in the hybrid soil is between 0.1 mole / L and 0.13 mole / L. The aluminum concentration provided by the colloidal dispersion of doped boehmite nanoparticles in hybrid soil is between 0.1 mol / l and 0.13 mol / l. The hybrid soil thus obtained is allowed to stand at ambient temperature for a period of 24 hours. In an advantageous variant according to the invention, an alcoholic solution containing at least one alkoxysilane and at least one aluminum alkoxide is prepared, then an amount of the colloidal dispersion of physisorbed boehmite nanoparticles and / or nanoparticles is added to said alcoholic solution. doped boehmite and / or hollow boehmite nanoparticles. In this way, the viscosity of the treatment solution (dispersion) decreases with the addition of the colloidal boehmite dispersion. This controls the thickness of the hybrid gel deposited on the surface of the solid metal substrate, in particular as a function of the rate of removal of the solid metal substrate from the treatment solution (dispersion). F - Deposition of the Colloidal Dispersion on the Solid Metal Substrate 33 2981366 A step is performed for depositing the colloidal anticorrosive treatment dispersion on a surface of a solid metal substrate, in particular a piece of a 2024 aluminum alloy. Laminated T3 having previously undergone a preparative treatment as described above. During this deposition step, a portion of the solvent of the hybrid composite soil evaporates and simultaneously the hydrolysis / condensation of (the) alkoxysilane (s) and (s) alkoxide (s) metal (s) allows the formation a composite hybrid anti-corrosion matrix on the surface of the solid metal substrate. The presence of cerium as a corrosion inhibitor, in particular free cerium (Cell1), in the treatment solution allows the formation during the deposition of said solution of a chemically stable conversion layer in a corrosive medium. Such a conversion layer is in particular formed from the hydroxyl groups of an element M constituting the solid metal substrate and forming an M-O-Ce- bond with cerium.

The presence of physisorbed boehmite nanoparticles and doped boehmite nanoparticles in the treatment solution is adapted to allow the formation of corrosion inhibitor reservoirs in the composite hybrid matrix constituting the anticorrosion coating, said reservoirs being adapted to allow a release. time-controlled corrosion inhibitor. The application of the surface treatment solution of the solid metal substrate is carried out by any means known in itself to those skilled in the art, in particular by soaking / shrinking ("dip coating"), by spraying ("spray-coating "), or by brush, pad or brush application for localized uses as a coating repair of the surface of the solid metal substrate. For the soaking / shrinking technique, the shrinkage rate makes it possible to control the thickness of the deposition of the treatment solution for a viscosity of the given treatment solution. Typically the shrinkage rate varies between 2 and 53 cm / min. The application of several successive layers by successive soaking / withdrawal operations, each soaking / removal operation followed by a drying step, allows the formation, if necessary, of a coating of increased thickness. It is also possible, during the soaking step, to impose a residence time of the solid metal substrate in the treatment solution which is prolonged in order to promote the chemical reactions between the solid metal substrate and the treatment solution. . For example, the extended residence time may vary between 1 and 300 seconds. For the spraying technique, the thickness of the deposits is controlled by the viscosity of the treatment solution, the sputtering parameters, especially the pressure, the flow rate, the geometric characteristics of the spray nozzles, and the speed of the spray. moving the nozzles facing the surface of the solid metal substrate and the number of nozzles passing the surface of the solid metal substrate. The application of the treatment solution can be carried out manually or be robotized according to conventional techniques. For the technique of manual application by brush, pad or brush, the thickness of the deposit is controlled by the viscosity of the treatment solution and by the number of successive applications on the surface of the solid metal substrate.

It is possible to carry out this step of depositing the treatment solution on a surface of a solid metal substrate in an enclosure under controlled atmosphere and humidity, in particular so as to limit the too rapid evaporation of the solvent (s). and in order to limit the pollution of the atmosphere. In a process according to the invention, it is also possible to carry out this step of depositing the treatment solution in the open air, in particular by spraying in the open air. G - Heat treatment A heat treatment of the treatment solution applied on the surface of the solid metal substrate is carried out so as to remove by evaporation the residual solvent (s) from the treatment solution and to allow its polymerization into a composite hybrid matrix. In particular, such a thermal treatment comprises two successive steps in which the solid metal substrate coated with the treatment solution is first subjected to a first heating step at a temperature of between 50.degree. 70 ° C for a period of time between 2 h and 24 h, said first heating step being adapted to allow removal of aqueous and / or organic solvents, then to a second heating step at a temperature between 110 ° C and 180 ° C for a period between 3 h and 16 h, said second heating step being adapted to complete the polymerization of the treatment solution and to improve the mechanical properties of the composite hybrid matrix.

FIG. 3 represents the variation of the surface resistance of a solid metal substrate treated by a process according to the invention as a function of the immersion time of this solid metal substrate in a corrosion bath (NaCt 0.05 mol / L in the water). Curve (0) represents the variation of the surface resistance of a solid metal substrate treated according to a process according to the invention consisting in the successive application of a cerium-rich conversion solution (0.1 mol / L) then a treatment solution comprising cerium (0.01 mol / L). It is observed that the surface resistance of the treated solid metal substrate (.) Decreases more slowly than the surface resistance of a solid metal substrate (A) treated with the same treatment solution (0.01 mol / L of Ce) but free of conversion layer. The numerical values are given in Table 1 below. Immersion time, h Surface resistance, û.cm2 With layer of Without conversion conversion layer 1 7870000 8080000 5 7710000 7760000 24 5280000 3980000 48 4050000 2120000 72 2750000 1111000 148 1310000 1080000 240 1180000 1030000 336 1190000 1020000 Table 1 36 2981366 We observe in particular, after 48 hours of immersion in the corrosion bath, the surface resistance of the untreated substrate (A) reaches a value of the order of 2.12 × 10 6 acm2, whereas the surface resistance of the substrate (* ) treaty remains of the order of. 4.05 106 acm2. After 72 h of immersion in the corrosion bath, the surface resistance of the untreated substrate (A) reaches a limit value of the order of 1.10 6 ncm 2, whereas the surface resistance of the substrate (*) treated remains of the order of 2.75 106 acm2. The inventors have also observed, in a completely surprising and unexpected manner, that the anticorrosion treatment of a solid metal substrate according to the invention with a treatment solution comprising a cerium concentration of between 0.005 mol / l and 0.015 mol / l makes it possible not only to obtain a surface resistance of the anticorrosive coating, measured by electrochemical impedance spectroscopy (FIG. 4), which is optimal for an immersion time of the solid metal substrate in a 1 day corrosion bath (A), 7 days (o) and 14 days (Ib) in an aqueous solution of 0.05 mol / L NaCl, but that such a treatment also makes it possible to obtain a nano-hardness (FIG. 5), a Young's modulus (FIG. 6) and a delamination resistance (o, FIG. 7), a crack resistance (A, FIG. 7) and a limit value of resistance to plastic deformation (FIG. 7) which are also maximum.

Electrochemical impedance spectroscopy is used to analyze the corrosion resistance of an M 2024-T3 solid metal substrate treated or not with a conversion solution according to a process according to the invention then exposed to a step of corrosion by immersion in an aqueous solution of 0.05 mol / L NaCl. The results are presented in Figure 8 according to the Nyquist representation. The treatment of a piece of aluminum 2024-T3 treated with a conversion solution according to the invention by immersion in a corrosion solution (NaCt 0.05 mol / L) for 30 minutes at room temperature gives the latter a resistance. Z 'surface in representation of "Nyquist" of the order of 4.104 Slcm2 (o, Figure 8). By way of comparison, the treatment of a piece of raw 2024-T3 aluminum (i.e., untreated with a conversion solution 2981366 according to the invention) by immersion in a corrosion solution (NaCE 0 , 05 mole / L) gives the latter a surface resistance Z 'in the representation of "Nyquist" of the order of 5.103 n.cm2 (A, Figure 8). By way of comparison, the treatment of an aluminum 2024-T3 piece previously immersed in a conversion solution of water and cerium (0.01 mol / L) and without immersion in a bath of corrosion, confers a surface resistance Z 'in the representation of "Nyquist" with a value greater than 6.105 n.cm2. Increasing the immersion time in the corrosion bath up to 168 hours reduces the surface resistance of the aluminum part to the characteristic value of the aluminum oxide layer of the order of 5 × 10 3 Si. .CM2. Increasing the concentration of cerium in the conversion solution and increasing the immersion time of the aluminum metal part in the conversion solution lead to an increase in the surface resistance of the metal part of the conversion solution. aluminum. In particular, the residual surface resistance Z 'measured as a "Nyquist" representation of such an aluminum piece after 1 hour of immersion in the corrosion solution (NaCE 0.05 mol / L) is of the order of 1.10.10 acm2 for a cerium concentration of 0.01 mol / l in the conversion solution and a conversion treatment time of 1 s, of the order of 2.104 acm2 for a cerium concentration of 0.05 mol. / L in the conversion solution and a conversion treatment duration of 1 s and of the order of 3.3 × 10 4 ac m 2 for a cerium concentration of 0.1 mole / L in the conversion solution and a treatment duration of 1 s conversion.

The residual surface resistance Z 'measured in the "Nyquist" representation of an aluminum piece after 1 h of immersion in the corrosion solution (0.05 mol / L NaCE) is of the order of 1.104. acm2 for a cerium concentration of 0.01 mol / L in the conversion solution and a conversion treatment time of 1 s, of the order of 2.104 acm2 for a cerium concentration of 0.01 mol / L in the conversion solution and a conversion time of 60 s and of the order of 3.8 × 10 4 ac m 2 for a cerium concentration of 0.01 mol / l in the conversion solution and a conversion processing time of 300 s. The residual surface resistance Z 'measured in the "Nyquist" representation of an aluminum piece after 1 hour of immersion in the corrosion solution (NaCt 0.05 mmol / L) is of the order of 3.2 × 10 4 acm2 for a cerium concentration of 0.1 mol / L in the conversion solution and a conversion treatment duration of 1 s, of the order of 4.0 × 10 4 acm2 for a cerium concentration of 0.1 mol / L in the conversion solution and a conversion treatment time of 60 s and of the order of 9.0 × 10 -4 μCm2 for a cerium concentration of 0.1 mol / L in the conversion solution and a treatment time conversion rate of 300 s. Prolonged immersion in the corrosion bath leads to a decrease in the surface resistance value which reaches the value of the surface resistance of the aluminum oxide in 10 hours.

The surface resistance Z 'of a piece of aluminum treated with a conversion solution containing cerium at a concentration of 0.5 mol / l for a period of 1 s, 60 s and 300 s remains greater than 1 × 10 4 Si. cm2 during 40 hours, 70 hours and 90 hours immersion in the corrosion bath, respectively.

Chemical analyzes (FIG. 9) by EDS make it possible to show the presence of Ce (III) cerium at the surface of the solid metal substrate treated for 300 sec with a conversion solution containing cerium at a concentration of 0.5 mol / l. The majority signal is characteristic of the aluminum substrate. 25

Claims (1)

CLAIMS1 / A method of anticorrosive treatment in which is applied to an oxidizable surface of a solid metal substrate a so-called liquid solution treatment solution comprising: at least one alkoxysilane, and o at least one cerium cation (Ce); in a liquid hydro-alcoholic composition, said treatment solution being adapted to form at the surface of the solid metal substrate, a hybrid matrix by hydrolysis / condensation of each alkoxysilane (s) and each cerium cation (Ce); the treatment solution having a molar ratio (Si / Ce) of silicon element of the alkoxysilane (s) relative to the cerium (Ce) cation (s) of between 50 and 500; Characterized in that the cation (s) of the cerium (Ce) has a concentration of between 0.005 mole / L and 0.015 mole / L in the treatment solution. 2 / A method according to claim 1, characterized in that each alkoxysilane chosen in the group formed: - tetraalkoxysilanes of the following general formula (I); If (O-R 1) 4 (I), wherein: o If is the silicon element, O is the oxygen element; R1 is selected from the group consisting of: a hydrocarbon group of formula [-Cal2n + 1] n being an integer greater than or equal to 1, and; ^ grouping 2-hydroxyethyl (HO-CH 2 -CH 2 -), and; an acyl group of general formula -CO-R'1 in which R'1 is a hydrocarbon group of formula [-CL, H2n + 1], n being an integer greater than or equal to 1, and; Alkoxysilanes of the following general formula (II): ## STR2 ## in which: R 2 is chosen from the group consisting of: C'H2 ', 1], n being an integer greater than or equal to 1, and; 2-hydroxyethyl group (HO-CH 2 -CH 2 -), and; an acyl group of general formula -CO-R'1 in which R'1 is a hydrocarbon group of formula [-C.H2n + 1], n being an integer greater than or equal to 1, and; R 3 is an organic group bonded to the silicon (Si) element of the alkoxysilane via an Si-C bond; o a is a natural integer of the interval] 0; 4 [. 3 / A method according to one of claims 1 or 2, characterized in that the treatment solution comprises at least one metal alkoxide. 4 / A method according to claim 3, characterized in that each metal alkoxide has the following general formula (VII): M '(O-R9) n, (VII), wherein: M' is a metal element selected from the group consisting of aluminum (At), vanadium (V), titanium (Ti) and zirconium (Zr), where R9 is an aliphatic hydrocarbon group of formula [-C.H2n + 1] in which n is an integer greater than or equal to 1, and 1 is a natural integer representing the valence of the metal element M. 5 / A method according to one of claims 3 or 4, characterized in that each metal alkoxide is an aluminum alkoxide of the general formula (III ) at (OR4) n (III), wherein: O and O are respectively the aluminum and oxygen elements, and R4 is an aliphatic hydrocarbon group having from 1 to 10 atoms carbon is a natural integer representing the valency of the aluminum element (At) 6 6 / A method according to one of claims 1 to 5, characterized in that the solid metal substrate is formed of a material chosen from the group consisting of oxidizable materials 7 / A method according to one of claims 1 to 6, characterized in that, before applying the treatment solution, said oxidizable surface of the solid metal substrate is immersed in a solution, said solution of conversion, liquid formed of at least one corrosion inhibitor in water, said corrosion inhibitor being selected from the group consisting of lanthanide cations and maintaining said oxidizable surface of the solid metal substrate in contact with the conversion solution for a period of time suitable for forming a conversion layer formed of said lanthanide bonded by at least one covalent bond to the oxidizable surface and extending at the surface of the solid metal substrate. 8 / A method according to claim 7, characterized in that the conversion solution has a corrosion inhibitor concentration of between 0.001 mol / L and 0.5 mol / L. 9 / A method according to one of claims 1 to 8, characterized in that the treatment solution is applied by soaking / removal of the solid metal substrate in said treatment solution. 10 / A method according to one of claims 1 to 8, characterized in that the application of atmospheric spray treatment solution of the surface treatment solution of the solid metal substrate. 11 / A method according to one of claims 1 to 10, characterized in that the hydro-alcoholic composition is formed of water and at least one alcohol. 12 / A method according to one of claims 1 to 11, characterized in that the cerium cation of the treatment solution is selected from the group consisting of cerium chlorides and cerium nitrates.13 / Anti-corrosion coating of a solid metal substrate formed of a hybrid matrix extending at the surface of the solid metal substrate and obtained by hydrolysis / condensation of at least one alkoxysilane; said hybrid matrix having a molar ratio (Si / Ce) of silicon element of the alkoxysilane (s) with respect to at least one cerium (Ce) cation of between 50 and 500. 14 / Coating according to claim 13 , characterized in that it has a thickness of between 1 pin and 15 pm.