EP2766508B1 - Process for the anticorrosion treatment of a solid metal substrate - Google Patents

Description

The invention relates to a method for anticorrosion treatment of a solid metal substrate, in particular an aluminum or aluminum alloy substrate. The invention further relates to a corrosion-resistant solid metal substrate obtainable by such a method.

Such an anticorrosion treatment method has applications in the general field of surface treatment of solid metal substrates, in particular 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 of 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 of using chromium, it has been proposed ( Pepe et al., 2004, Journal of Non-Crystalline Solids, 348, 162-171 ) to form a silica gel-based coating on the surface 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 method does not make it possible to obtain an anticorrosive coating which, at the same time, has improved mechanical strength properties, in particular improved tear resistance, and also improved healing properties and an improved barrier effect.

The invention aims to overcome the disadvantages mentioned above by proposing a method of anticorrosion treatment of a solid metal substrate that does not require the use of chromium derivatives-especially chromium VI- which is carcinogenic, mutagenic and reprotoxic.

We also know « Zhong et al, (2010), Progress in Organic Coatings, 69, 52-56 A process for treating an aluminum alloy in which an aqueous-alcoholic solution of γ-glycidoxypropyltrimethoxysilane (GPTMS) and of vinytriethoxysilane (VETO) is prepared, followed by hydrolysis / condensation of said aqueous-alcoholic solution in a manner to form a gel, and then added to the gel formed a quantity of cerium nitrate.

" Palomino et al, (2009), Corrosion Science, 51, 1238-1250 "describes an anticorrosion treatment of an aluminum alloy.

The object of the invention is to provide an anticorrosive treatment method adapted to form a corrosion-resistant coating on the surface 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 anticorrosion coating of controlled thickness, in particular between 1 μm and 15 μm, and compatible with the industrial recommendations, particularly in the field. aeronautics.

Another objective of the invention is to propose 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 of thickness substantially homogeneous 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-that is, 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 method 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 of an outside environment corrosive and protective active healing properties and limiting the progression of corrosion at an accidental bite likely to affect the anticorrosive coating.

The invention also aims at such an anticorrosion treatment method adapted to be applied on a polished solid metal substrate or on 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 for its implementation that little manipulation.

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 do this, the invention relates to an anticorrosion treatment method according to claim 1.

Advantageously and according to the invention, the treatment solution having a molar ratio (Si / Ce) of silicon element of (the) alkoxysilane (s) relative to the (x) cation (s) of cerium (Ce) between 50 and 500, in particular between 80 and 250. Advantageously and according to the invention, the cation (s) of cerium (Ce) present (s) a concentration of between 0.005 mol / L and 0.015 mol / L -notamment between 0.005 mol / L and 0.01 mol / L, preferably of the order of 0.010 mol / L- in the treatment solution.

In a process according to the invention, at least one alkoxysilane and at least one cerium (Ce) cation are mixed in a liquid aqueous-alcoholic solution under conditions suitable for allowing hydrolysis / condensation of said at least one alkoxysilane and said at least one a cation of cerium (Ce), and said treatment solution is applied to the oxidizable surface of a solid metal substrate so as to form on the surface of the solid metal substrate, a hybrid matrix by hydrolysis / condensation of each alkoxysilane (s) and each cation of cerium (Ce).

In a process according to the invention, the hydrolysis / condensation of each alkoxysilane (s) is carried out in the treatment solution in the presence of each cation (s) of cerium (Ce), said treatment solution having a ratio (Si / This molar element of silicon of (the) starting alkoxysilane (s) relative to the (x) cation (s) of cerium (Ce) starting between 50 and 500, in particular between 80 and 250.

The inventors have observed that the selection of a concentration value 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 FIG. state of the art and according to which the selected concentration of the cerium (Ce) cation in the solution for the corrosion treatment of a solid metal substrate at the same time allows (1) to obtain optimal adhesion of the surface treatment solution of the solid metal substrate, (2) the formation of a hybrid matrix of passive protection of said solid metal substrate by a barrier effect adapted to limit the formation of corrosion products of the solid metal substrate - in particular of a solid metal substrate having a puncture -, and (3) to form such a hybrid protection matrix having Physical resistance properties to mechanical stresses - including resistance to delamination, crack resistance, and plastic deformation and corrosion resistance - at 1 day, 7 days and 14 days corrosive treatment by immersion in a corrosive solution of NaCℓ 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 is between 0.005 mol / L and 0.015 mol / L, especially between 0.005 mol / 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 mol / L and 0.015 mol / L, in particular between 0.005 mol / L and 0.01 mol / L, preferably of the order of 0.01 mol / L.

• une valeur (Hv) critique de déformation plastique mesurée par nano-indentation qui est maximale et de l'ordre de 39 pour une concentration en cérium de 0,01 mole/L dans la solution de traitement ;
• une valeur de charge critique de délamination F_D (mN) du revêtement anticorrosion sur le substrat métallique solide qui est maximale et de l'ordre de 24 mN pour une concentration en cérium de 0,01 mole/L dans la solution de traitement ;
• une valeur de charge critique de fissuration F_f (mN) du revêtement anticorrosion qui est maximale et de l'ordre de 15 mN pour une concentration en cérium de 0,01 mole/L dans la solution de traitement, et ;
• une valeur de charge critique de déformation plastique sans fissuration F_DP (mN) maximale de l'ordre de 6 mN pour une concentration en cérium de 0,01 mole/L dans la solution de traitement.

An anticorrosion coating according to the invention, that is to say a coating obtained with a treatment solution comprising a concentration of cerium cation - in particular in Ce ^III - between 0.005 mol / l and 0.015 mol / l, presents:

• a 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 F _D (mN) of the anticorrosion 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 F _f (mN) of the anticorrosive 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 critical strain value of plastic deformation without cracking F _DP (mN) maximum 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 anticorrosion coating of a solid metal substrate a resistance towards 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 reduced resistance to corrosion 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 Ω.cm ² . The surface resistance in 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 0.1 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 Ω.cm ² as measured by electrochemical impedance spectroscopy (EIS).

• une diminution de l'angle de contact de la solution de traitement sur le substrat métallique solide traduisant une mouillabilité améliorée de la surface du substrat métallique solide vis-à-vis de la solution de traitement et une application améliorée de ladite solution de traitement sur la surface du substrat métallique solide ;
• un ancrage amélioré de la matrice hybride obtenue à partir de la solution de traitement sur la surface du substrat métallique solide ;
• une prise de masse améliorée de la solution de traitement en surface du substrat métallique solide. Une telle prise de masse révèle un effet structurant de la solution de traitement et de la matrice hybride obtenue à partir de la solution de traitement, et ;
• de privilégier le Ce^III aux dépends du Ce^IV dans la solution de traitement et dans le sol hybride. On mesure la distribution Ce^III/Ce^IV par spectrométrie photo-électronique X (XPS) de surface.

In addition, a concentration of cerium cation in the treatment solution of between 0.005 mol / l and 0.015 mol / l according to the invention allows:

• a decrease in the contact angle of the treatment solution on the solid metal substrate indicating improved wettability of the surface of the solid metal substrate with respect to the treatment solution and an improved application of said treatment solution to the solid metal substrate surface;
• improved anchoring of the hybrid matrix obtained from the treatment solution on the surface of the solid metal substrate;
• an improved grounding of the surface treatment solution of the solid metal substrate. Such a mass gain reveals a structuring effect of the treatment solution and the hybrid matrix obtained from the treatment solution, and;
• to favor Ce ^III at the expense of Ce ^IV in the treatment solution and in hybrid soil. The Ce ^III / Ce ^IV distribution is measured by surface X-ray photoelectron spectrometry (XPS).

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

• des tétraalcoxysilanes de formule générale (I) suivante ;
  
          Si(O-R₁)₄     (I),
  
  dans laquelle :
  • ∘ Si est l'élément silicium, O est l'élément oxygène ;
  • ∘ R₁ est choisi dans le groupe formé :
    • ▪ d'un groupement hydrocarboné -notamment un méthyle ou un éthyle- de formule [-C_nH_2n+1], n étant un nombre entier supérieur ou égal à 1,
    • ▪ du groupement 2-hydroxyéthyle (HO-CH₂-CH₂-), et ;
    • ▪ d'un groupement acyle de formule générale -CO-R'₁ dans laquelle R'₁ est un groupement hydrocarboné -notamment un méthyle, un éthyle- de formule [-C_nH_2n+1], n étant un nombre entier supérieur ou égal à 1, et ;
• des alcoxysilanes de formule générale (II) suivante :
  
          Si(O-R₂)_4-a(R₃)_a     (II) ;
  
  dans laquelle :
  • ∘ R₂ est choisi dans le groupe formé :
    • ▪ d'un groupement hydrocarboné -notamment un méthyle, un éthyle- de formule [-C_nH_2n+1], n étant un nombre entier supérieur ou égal à 1,
    • ▪ du groupement 2-hydroxyéthyle (HO-CH₂-CH₂-), et ;
    • ▪ d'un groupement acyle de formule générale -CO-R'₁ dans laquelle R'₁ est un groupement hydrocarboné -notamment un méthyle, un éthyle- de formule [-C_nH_2n+1], n étant un nombre entier supérieur ou égal à 1, et ;
  • o R₃ est un groupement organique -notamment un groupement organique formé d'atome(s) de carbone, d'atome(s) d'hydrogène et le cas échéant d'atome(s) d'azote, d'atome(s) d'oxygène et éventuellement d'atome(s) de soufre et d'atome(s) de phosphore- lié à l'élément silicium (Si) de l'alcoxysilane par une liaison Si-C ;
  • o a est un nombre entier naturel de l'intervalle ]0 ; 4[, -de préférence égal à 1-.

Advantageously and according to the invention, each alkoxysilane is selected from the group formed:

• tetraalkoxysilanes of the following general formula (I);
  
  If (OR ₁ ) ₄ (I),
  
  in which :
  • ∘ If is the silicon element, O is the oxygen element;
  • ∘ R ₁ is chosen from the group formed:
    • A hydrocarbon group, in particular methyl or ethyl, of formula [-C _n H _{2n + 1} ], n being an integer greater than or equal to 1,
    • ▪ the 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 - in particular a methyl, an ethyl of formula [-C _n H _{2n + 1} ], n being a higher whole number or equal to 1, and;
• alkoxysilanes of the following general formula (II):
  
  If (OR ₂ ) _4-a (R ₃ ) _a (II);
  
  in which :
  • ∘ R ₂ is chosen from the group formed:
    • A hydrocarbon group, in particular a methyl, an ethyl of formula [-C _n H _{2n + 1} ], n being an integer greater than or equal to 1,
    • ▪ the 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 - in particular a methyl, an ethyl of formula [-C _n H _{2n + 1} ], n being a higher whole number or equal to 1, and;
  • R ₃ is an organic group, in particular an organic group consisting of carbon atom (s), hydrogen atom (s) and, if appropriate, nitrogen atom (s), atom (s), ) oxygen and optionally sulfur atom (s) and phosphorus atom (s) bonded to the silicon (Si) element of the alkoxysilane via an Si-C bond;
  • oa is a natural integer of the interval] 0; 4 [, preferably equal to 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), methacryloxypropyltrimethoxysilane (MAP). , 3- (trimethoxysilyl) propylamine (APTMS), 2- (3,4-epoxycyclohexyl) ethyltriethoxysilane (ECHETES), 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane (ECHETMS) and 5,6 epoxyhexyltriethoxysilane (EHTES).

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.

• o M' est un élément métallique choisi dans le groupe formé de l'aluminium (Aℓ), du vanadium (V), du titane (Ti) et du zirconium (Zr),
• o R₉ est un groupement hydrocarboné aliphatique de formule [-C_nH_2n+1] -notamment choisi dans le groupe formé d'un méthyle, d'un éthyle, d'un propyle, d'un butyle, en particulier d'un butyle secondaire de formule [CH₃-CH₂-(CH₃)CH-]- dans laquelle n est un nombre entier supérieur ou égal à 1, et ;
• o n" est un nombre entier naturel représentant la valence de l'élément métallique M'.

Advantageously and according to the invention, each metal alkoxide has the following general formula (VII):

M '(OR ₉ ) _{n "} (VII),

in which :

• M 'is a metal element selected from the group consisting of aluminum (Aℓ), vanadium (V), titanium (Ti) and zirconium (Zr),
• R ₉ is an aliphatic hydrocarbon group of formula [-C _n H _{2n + 1} ] -particularly selected from the group consisting of a methyl, an ethyl, a propyl, a butyl, in particular of a secondary butyl of formula [CH ₃ -CH ₂ - (CH ₃ ) CH -] - in which n is an integer greater than or equal to 1, and;
• it is a natural integer representing the valence of the metal element M '.

In a process according to the invention, each reactive species homogeneously distributed in the treatment solution and able to polymerize and form an organic / inorganic hybrid matrix are formed by hydrolysis of each alkoxysilane and each metal alkoxide. An organic / inorganic hybrid matrix is thus formed by condensation hydrolysis of each alkoxysilane and each metal alkoxide.

Advantageously, each metal alkoxide is selected from the group consisting of aluminum alkoxides, especially aluminum tri ( s- butoxide), aluminum tri ( n- butoxide), aluminum tri (ethoxide), aluminum, aluminum tri (ethoxyethoxyethoxide) and aluminum tri ( iso- propoxide), titanium alkoxides -including titanium tetra ( n- butoxide), titanium tetra ( iso- butoxide), tetra ( iso- propoxide) of titanium, titanium tetra (methoxide) and titanium tetra (ethoxide), vanadium alkoxides, especially vanadium tri ( iso- butoxide) oxide and vanadium tri ( iso- propoxide) oxide and alkoxides; zirconium-especially tetra (ethoxide) zirconium, tetra (iso-propoxide) zirconium, tetra (n -propoxyde) zirconium, tetra (n-butoxide) and zirconium tetra (t -butoxide) zirconium.

• ∘ Aℓ et O sont respectivement les éléments aluminium et oxygène, et ;
• o R₄ est un groupement hydrocarboné aliphatique présentant de 1 à 10 atomes de carbone -notamment choisi dans le groupe formé d'un méthyle, d'un éthyle, d'un propyle, d'un butyle, en particulier d'un butyle secondaire de formule [CH₃-CH₂(CH₃)-CH-]- ;
• o n est un nombre entier naturel représentant la valence de l'élément aluminium (Aℓ).

Advantageously, each metal alkoxide is an aluminum alkoxide of the following general formula (III):

Aℓ (OR ₄ ) _n (III),

in which :

• ∘ Aℓ and O are respectively the elements aluminum and oxygen, and;
• R ₄ is an aliphatic hydrocarbon group having 1 to 10 carbon atoms, in particular selected from the group consisting of a methyl, an ethyl, a propyl, a butyl, in particular a secondary butyl of formula [CH ₃ -CH ₂ (CH ₃ ) -CH -] -;
• we are a natural integer representing the valency of the aluminum element (Aℓ).

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.

A treatment solution is thus formed comprising a metal alkoxide, especially a single aluminum alkoxide and a single alkoxysilane, said treatment solution being of great simplicity in its composition and still suitable for providing 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 (ethoxyethoxyethoxide) ) aluminum and tri ( iso propoxide) aluminum.

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 alkoxysilanes and metal alkoxides-in particular 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 is formed of 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 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. In accordance with 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 by a value of 1 μm for a withdrawal speed of 1 cm / min, up to a value of 14. μm for a withdrawal speed of 20 cm / min. In particular, a withdrawal rate 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 to 10 ^-3 mol / L and xylene cyanole at a concentration in the liquid treatment solution between 5.10 ^-4 mol / L to 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, that is to say solid nanoparticles of boehmite of general formula [-AlO (OH) -] forming a colloidal dispersion of boehmite nanoparticles in the treatment solution.

In an anticorrosion treatment process according to the invention, to prepare a treatment solution is dissolved each alkoxysilane, each aluminum alkoxide and, where appropriate, each metal alkoxide in an alcohol - especially chosen from the group formed by ethanol , propanol-1 and propanol-2, and then a quantity of water or, if appropriate, an amount of an aqueous solution containing at least one lanthanide cation and / or colloidal boehmite is added to form an anticorrosion treatment solution.

Advantageously, to an alcoholic solution is added alkoxysilane (s) and the (the) alkoxide (s) metal (s) and an amount of water or, if appropriate, an amount of an aqueous solution containing at least one lanthanide cation and / or nanoparticles of colloidal boehmite 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 AlO (OH) and having a surface distribution of lanthanide cations -including cerium- and / or vanadate cations. 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 bath of NaCℓ at 0, 05 mole / L.

• X est un élément, dit élément de dopage, choisi dans le groupe formé des lanthanides trivalent -notamment du cérium trivalent-, et ;
• x est un nombre relatif compris entre 0,002 et 0,01.

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 general formula (VIII) below:

Aℓ _1-x (X) _x O (OH) (VIII),

in which :

• X is an element, referred to as a doping element, selected from the group consisting of trivalent lanthanides, especially trivalent cerium, and;
• 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 Aℓ (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, 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 water said corrosion inhibitor being selected from the group consisting of lanthanide cations and said oxidizable surface of the solid metal substrate is held 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 corrosion resistance 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 layer of surface conversion of a solid metal substrate, then a treatment solution comprising at least one alkoxysilane, a cerium cation at a concentration of between 0.005 mol / L and 0.015 mol / L, and, where 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 immersion of the oxidizable surface of the solid metal substrate for a predetermined period of time -particularly a duration greater than 1 hour- in a bath of corrosion, especially an aqueous bath of NaCℓ 0.05 mol / L.

The inventors assume that the treatment of the oxidizable surface of the solid metal substrate by the conversion solution results in the formation of an increased corrosion resistance layer with respect to the metal oxide layer of the 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 '(ω) of surface resistance (Ω.cm ² ) increased compared with the value Z' (co) the 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 amplitude of sinusoidal disturbance is set at 10 mV in order 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 limit value of the surface resistance of the layer of aluminum oxide formed naturally on the surface of a piece of alloy of aluminum.

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 and healing layer on the surface of the solid metal substrate by formation of a plurality of covalent bonds occurring 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 MO-Ln-O- type in which M represents a metallic element of the solid metal substrate, O is an oxygen atom and Ln represents the corrosion inhibiting element chosen from lanthanides.

In a process according to the invention, a treatment solution formed of an organic / inorganic hybrid soil of at least one alkoxysilane is applied to the oxidizable surface of the solid metal substrate, and optionally to the surface of the conversion layer. 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 optionally at least one metal alkoxide, adapted (s). ) to form by hydrolysis / condensation of (the) 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 against corrosion, but also allows an improvement of the adhesion of a hybrid soil surface of the solid metal substrate and an improvement of passive protection properties of said solid metal substrate against 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 cations (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 chosen from the group formed by lanthanide chlorides, lanthanide nitrates, lanthanide acetates and lanthanide sulfates.

Advantageously chosen each corrosion inhibitor of the conversion solution in the group consisting of lanthanum chloride (LaCℓ _3), cerium chloride (CeCℓ _3), yttrium chloride (YCℓ _3), cerium sulfate ( Ce ₂ (SO ₄ ) ₃ ), cerium acetate (Ce (CH ₃ COO) ₃ ), praseodymium chloride (PrCℓ ₃ ), neodymium chloride (NdCℓ ₃ )

Advantageously and according to the invention, each corrosion inhibitor of the conversion solution is a cerium cation-notably cerium nitrate (Ce (NO ₃ ) ₃ ), cerium acetate (Ce (CH ₃ COO) ₃ ) , cerium sulphate (Ce ₂ (SO ₄ ) ₃ ) and cerium chloride (CeCℓ ₃ ) - in which the cerium element is of valence III (Ce ^III ).

Advantageously and according to the invention, the cerium cation (Ce) of the treatment solution is chosen from the group formed by cerium chlorides and cerium nitrates. In particular, the corrosion inhibitor of the conversion solution is cerium nitrate Ce (NO ₃ ) 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. The chemical analysis by energy dispersive spectroscopy ("EDS") shows Lα and Mα lines characteristic of cerium bound by covalent liaiasons on 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 it is protected by the cerium-rich hybrid matrix with an optimal barrier effect.

• n'altère pas les propriétés mécaniques de résistance à la délamination et d'adhésion de la matrice hybride sur le substrat métallique solide ;
• n'altère pas les propriétés barrière de la matrice hybride, telles que mesurées par SIE ;
• permet de ralentir la perte de résistance à la corrosion du substrat métallique solide durant une immersion prolongée de celui-ci dans un bain de corrosion, et ;
• retarde l'apparition des produits de corrosion sur les substrats métalliques subissant un point de corrosion.

But the inventors have also observed in a totally surprising way that the conversion layer:

• does not alter the mechanical properties of resistance to delamination and adhesion of the hybrid matrix to the solid metal substrate;
• does not alter the barrier properties of the hybrid matrix, as measured by SIE;
• slows the loss of corrosion resistance of the solid metal substrate during prolonged immersion thereof in a corrosion bath, and
• delays the appearance of corrosion products on metal substrates undergoing a corrosion point.

The presence of a corrosion inhibitor-rich conversion layer at the interface between the solid metal substrate and the hybrid matrix 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, 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 of 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. in order to form on the surface of the solid metal substrate, a layer, referred to as the conversion layer, of the corrosion inhibitor element Ln (lanthanide) bonded to a metal element M of the solid metal substrate by a bond of the MO-Ln type. O-.

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 - in particular nitric acid - to the conversion solution.

The inventors have observed that a method of anticorrosion treatment of a solid metal substrate in two stages according to the invention not only allows an 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 -notamment selected from the group consisting of ethanol, propanol-1 and propanol-2-.

Advantageously, doped and / or physisorbed boehmite nanoparticles have a larger dimension and two smaller dimensions, perpendicular to each other and perpendicular to said larger one. dimension, said largest dimension is less than 200 nm, especially 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 less than the order of 3 nm.

Advantageously and according to the invention, the treatment solution comprises a charge of hollow boehmite nanoparticles.

The invention also relates to an anticorrosion coating that can be obtained by a process according to the invention.

The invention also extends to an anticorrosion 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, 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.

• o au moins un groupement inorganique de formule (IX) générale :
  
          -A-O-B-     (IX),
  
  dans laquelle :
  • ▪ O est l'élément oxygène,
  • ▪ A et B sont choisis indépendamment l'un de l'autre dans le groupe formé de Si et de M', et ;
    • o au moins un groupement organique de formule (XI) générale :
      
              -D-O-R₁₀-O- E-     (XI),
      
      
  • ▪ dans laquelle O est l'élément oxygène,
  • ▪ D et E sont choisis indépendamment l'un de l'autre dans le groupe formé de Si, de M' et de Ce, et ;
  • ▪ R₁₀ est un groupement hydrocarboné.

The invention extends in particular to an anticorrosion coating in which the hybrid matrix extending in contact with a solid metal substrate is obtained by hydrolysis / condensation of at least one alkoxysilane and, where appropriate, at least one a metal alkoxide and comprising:

• at least one inorganic group of general formula (IX):
  
  -AOB- (IX),
  
  in which :
  • ▪ O is the oxygen element,
  • ▪ A and B are independently selected from the group consisting of Si and M ', and;
    • at least one organic group of general formula (XI):
      
      -OR ₁₀ -O- E- (XI),
      
      
  • In which O is the oxygen element,
  • D and E are independently selected from the group consisting of Si, M 'and Ce, and;
  • R ₁₀ is a hydrocarbon group.

Advantageously, the anticorrosion coating has a thickness of between 1 micron and 15 microns.

• la matrice hybride du revêtement anticorrosion est formée d'un matériau composite comprenant un xérogel hybride -notamment un xérogel hybride organique/inorganique- et une charge de nanoparticules de boehmite physisorbée dispersée dans le xérogel hybride ;
• la matrice hybride du revêtement anticorrosion est formée d'un matériau composite comprenant un xérogel hybride -notamment un xérogel hybride organique/inorganique- et une charge de nanoparticules de boehmite dopées de formule générale (VIII) :
  
          Aℓ_1-x(X)_xO(OH),     (VIII)
  
  dans laquelle :
  • o X est un élément, dit élément de dopage, choisi dans le groupe formé des lanthanides trivalents -notamment du cérium trivalent-, et ;
  • o x est un nombre relatif compris entre 0,002 et 0,01 ;
  ladite charge étant dispersée dans le xérogel hybride ;
• la matrice hybride du revêtement anticorrosion est formée d'un matériau composite comprenant un xérogel hybride -notamment un xérogel hybride organique/inorganique- et une charge de nanoparticules de boehmite creuses dispersée dans le xérogel hybride ;
• les nanoparticules solides de la charge de nanoparticules de boehmite physisorbées et de la charge de nanoparticules de boehmite dopées présentant une plus grande dimension et deux plus petites dimensions, perpendiculaires entre elles et perpendiculaires à ladite plus grande dimension, la plus grande dimension est inférieure à 200 nm -notamment inférieure à 100 nm, particulièrement inférieure à 50 nm, de préférence comprise entre 5 nm et 20 nm-, et les deux plus petites dimensions sont inférieures à 10 nm, de préférence de l'ordre de 3 nm ;
• les nanoparticules solides de la charge de nanoparticules de boehmite creuses sont de forme sensiblement sphérique et présentent un diamètre moyen de l'ordre de 30 nm.

The invention also extends to an anticorrosive coating having at least one of the following characteristics:

• the hybrid matrix of the anticorrosion coating is formed of a composite material comprising a hybrid xerogel-in particular an organic / inorganic hybrid xerogel-and a physisorbed boehmite nanoparticle filler dispersed in the hybrid xerogel;
• 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 doped boehmite nanoparticle feed of general formula (VIII):
  
  Aℓ _1-x (X) _x O (OH), (VIII)
  
  in which :
  • o X is an element, called doping element, selected from the group consisting of trivalent lanthanides, especially trivalent cerium, and;
  • ox 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-in particular 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 less than 200; nm -notamment 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 anticorrosion 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 below.

• la figure 1 est une représentation schématique hors proportion d'une variante d'un revêtement anticorrosion selon l'invention ;
• la figure 2 en une vue en microscopie électronique à balayage (MEB) d'une coupe transversale d'un revêtement anticorrosion d'un substrat métallique solide obtenu par un procédé selon l'invention ;
• la figure 3 est une représentation graphique comparative de l'évolution de la résistance surfacique vis-à-vis de la corrosion d'un substrat métallique solide traité selon deux variantes d'un procédé selon l'invention ;
• la figure 4 est une représentation graphique de la résistance surfacique (Ω.cm²) d'un revêtement anticorrosion en fonction de la concentration en cérium dans la solution de traitement ;
• la figure 5 est une représentation graphique de la nano-dureté de Vickers d'un revêtement anticorrosion en fonction de la concentration en cérium dans la solution de traitement ;
• la figure 6 est une représentation graphique de la variation de la valeur du module de Young, en GPa, déterminée par des mesures de nano-indentation ;
• la figure 7 est une représentation graphique de la valeur de la charge critique (mN) de délamination (○), de fissuration (▲) et de déformation plastique (□), déterminée par nano-nano-scratch, d'un revêtement anticorrosion en fonction de la concentration en cérium dans la solution de traitement ;
• la figure 8 est une représentation de Nyquist de l'impédance électrochimique d'un substrat métallique solide traité (○) ou non traité (▲) avec une solution de conversion ;
• la figure 9 est un spectre d'analyse chimique de surface par Spectroscopie de Dispersion Electronique ("Energy Dispersion Spectroscopy (EDS) d'un substrat métallique solide traité avec une solution de conversion selon l'invention.

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: :

• the figure 1 is a schematic representation out of proportion of a variant of an anticorrosion coating according to the invention;
• the 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;
• the figure 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 process according to the invention;
• the figure 4 is a graphical representation of the surface resistance (Ω.cm ² ) of an anticorrosive coating as a function of the cerium concentration in the treatment solution;
• the figure 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;
• the figure 6 is a graphical representation of the variation of the Young's modulus value, in GPa, determined by nano-indentation measurements;
• the figure 7 is a graphical representation of the value of the delamination (○), cracking (▲) and plastic deformation (□) critical load, determined by nano-nano-scratch, of an anticorrosion coating as a function of cerium concentration in the treatment solution;
• the figure 8 is a Nyquist representation of the electrochemical impedance of a treated (○) or untreated ()) solid metal substrate with a conversion solution;
• the figure 9 is a spectrum of surface chemical analysis by Spectroscopy of Electronic Dispersion ("Energy Dispersion Spectroscopy" (EDS)) of a solid metal substrate treated with a conversion solution according to the invention.

An anticorrosion coating 1 according to the invention represented in figure 1 is supported on a metal substrate 2 formed of metallic elements M. Such an anticorrosive coating is formed of an optional conversion layer 3 in which corrosion inhibiting elements Ln are linked by MO-Ln- covalent bonds to metallic elements M of the metal substrate 2. In addition, conversion layer corrosion inhibitor elements Ln form covalent bonds with Si elements and, where appropriate, metal elements M 'chosen from the group consisting of aluminum (Aℓ), vanadium (V ) titanium (Ti) and zirconium (Zr) and the cerium element (Ce) of the hybrid matrix 4 extending on the surface of the conversion layer 3.

The figure 2 represents a scanning electron microscopy (SEM) section of an aluminum substrate 2 treated with an alternative of a method according to the invention and comprising a conversion layer (optional) 3 extending at the 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 a preparative treatment, given solely by way of nonlimiting example, aims to eliminate from the surface of the solid metal substrate any trace of oxidation of the alloy or of staining which may hinder the homogeneous application of the conversion solution and 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 at the surface of the substrate.

Degreasing of 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 below 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 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 marketed under the trademark 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 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 an ultrasonic treatment during this second degreasing step with an alkaline solution.

Stripping the solid metal substrate with 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 an alkaline preparation, in particular an aqueous solution of sodium hydroxide at a concentration of between 30.degree. g / L at 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, there is observed a powdery layer of oxides covering the surface of the solid metal substrate.

Stripping the solid metal substrate with an acidic solution

The preparative treatment according to the invention comprises a fourth successive stage of dissolution of the oxide layer extending over the surface of the solid metal substrate in which the surface of said substrate is placed in contact with an acid 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 min and 10 min at a temperature of between 10 ° C. and 50 ° C. with an aqueous solution comprising between 15% (v / v) and 25% (v / v) of TURCO LIQUID Smut-Go NC.

Alternatively, this dissolution step is carried out for a period of between 1 min and 10 min at a temperature of between 10 ° C. and 30 ° C. with an aqueous solution comprising between 15% (v / v) and 30% (v / v). v) 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 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 (Aℓ 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 piece is measured.

• (a) élaboration d'une solution de traitement comme décrit en (A) ci-après ;
• (b) élaboration d'une dispersion colloïdale de nanoparticules de boehmite physisorbées comme décrit en (B) ci-après ;
• (c) élaboration d'une dispersion colloïdale de nanoparticules de boehmite dopée comme décrit en (C) ci-après ;
• (d) élaboration de nanoparticules d'oxyhydroxyde d'aluminium creuse contenant un inhibiteur de corrosion comme décrit en (D) ci-après ;
• (e) élaboration d'une dispersion colloïdale de traitement anticorrosion à partir des compositions comme décrit en (A), en (B), en (C) et en (D) ci-dessous ;
• (f) dépôt de la dispersion colloïdale de traitement anticorrosion sur le substrat métallique solide ;
• (g) traitement thermique.

In a method of anticorrosion treatment of a solid metal substrate, a treatment solution is prepared according to the following steps:

• (a) developing 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) below;
• (d) developing hollow aluminum oxyhydroxide nanoparticles containing a corrosion inhibitor as described in (D) hereinafter;
• (e) developing a colloidal anticorrosive dispersion from the compositions as described in (A), (B), (C) and (D) below;
• (f) depositing the colloidal anticorrosion treatment dispersion on the solid metal substrate;
• (g) heat treatment.

A - Elaboration of a treatment solution - epoxy soil A1 - GPTMS / ASB / Ce epoxy sol (NO ₃ ) ₃

In a first embodiment, to prepare 1 L of epoxide sol is dissolved 107.4 g (0.43 moles) of aluminum tri ( s- butoxide) (ASB) in 34.8 mL of propanol-1 by stirring. especially 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 ) at a concentration of between 0.02 mol / l and 0.5 mol / l is also prepared, and a volume of this aqueous solution of cerium is added to the solution. precursor (ASB / GPTMS) 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.

• en particulier 110°C- pendant une durée comprise entre 1 h et 5 h -en particulier 3 h-. On observe la formation d'une matrice hybride de 6 µm d'épaisseur en surface du substrat métallique solide présentant une durée de tenue au brouillard salin comprise entre 96 et 800 heures.

The epoxy sol is deposited on an Aℓ 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 between 95 ° C and 180 ° C

• in particular 110 ° C for a period of between 1 h and 5 h - in particular 3 h-. The formation of a hybrid matrix 6 microns thick at the surface of the solid metal substrate having a salt spray resistance time of between 96 and 800 hours is observed.

A2 - Epoxy solids TEOS / MAP / Ce (NO ₃ ) ₃

In a second embodiment, to prepare 1 L of hybrid soil is added 230 mL of tetraethoxysilane (TEOS) in 600 mL of ethanol. 30 ml of methacryloxypropyltrimethoxysilane (MAP) are then 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

Such a colloidal dispersion of surface-functionalized boehmite nanoparticles (so-called physisorbed) is produced in two steps, described below, in which a colloidal solution of boehmite nanoparticles is first formed, and then said boehmite nanoparticles are functionalized with an inhibitor of corrosion.

B1 - Colloidal Boehmite

Condensation hydrolysis of tri- sec butoxide (ASB, Al (OH) _x (OC ₄ H ₉ ) _3-x ) of aluminum is carried out according to the method described by Yoldas BE ( J. Mater. Sci., (1975), 10, 1856 ), in which an amount of water preheated to a temperature above 80 ° C is added to tri- sec- butoxide of aluminum. The resulting solution is left stirring for 15 minutes.

By way of example, such a solution of aluminum tri ( s- butoxide) at a concentration of 0.475 mol / l (~ 117 g / l) in water at a temperature of 80 ° C. for one duration of 15 min. Is then carried out step, said step of peptization, at which is added to the dry tri- butoxide hydrolysis solution a volume of between 1.4 ml and 2.8 ml of a nitric acid solution at 68 %. The mixture is placed at 85 ° C. in an oil bath for a period of 24 hours. A colloidal dispersion of oxyhydroxide is obtained aluminum (boehmite) in the water. 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 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, a nonionic surfactant, especially a non-surfactant, is added, if appropriate. ionic material chosen from Pluronic® P-123, Pluronic® F 127 (BASF, Mount Olive, New Jersey, USA), Brij 58 and Brij 52 in a final mass proportion of 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 / ml. L. This preparation is stirred at room temperature for a period of 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 of the 1460 cm ^-1 and 1345 cm ^-1 vibration bands characteristic of the coordination of cerium with nitrate ions.

C - Elaboration of a colloidal dispersion of doped boehmite nanoparticles

Such a colloidal dispersion of boehmite nanoparticles doped in two steps described below is carried out in which (C1) is carried out the hydrolysis / condensation of a precursor - in particular an aluminum alkoxide and a corrosion inhibitor. Next, a step (C2), called a step of peptization, acid treatment in order to form doped boehmite nanoparticles.

C1 - Hydrolysis / condensation of ASB and (Ce (NO ₃ ) ₃ )

The hydrolysis / condensation of a mixture of aluminum precursor - in particular an aluminum alkoxide, in particular aluminum tri ( s- butoxide) (ASB) - and a corrosion inhibitor - is carried out. in particular cerium (III) nitrate (Ce (NO ₃ ) ₃ ) - by adding to this mixture a minimum of water heated to the temperature of 85 ° C. This hydrolysis / condensation mixture is placed under stirring for 15 minutes. The final concentration of ASB in the hydrolysis / condensation mixture is 0.475 mol / L and the final concentration of corrosion inhibitor in the hydrolysis / condensation mixture is between 0.005 mol / L and 0.015 mol / L.

C2 - Peptisation

To the hydrolysis / condensation mixture is added an acidified aqueous solution - in particular 1.4 ml to 2.8 ml of a 68% nitric acid solution - and the acidified mixture is placed at a temperature of 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 - Elaboration 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, in particular hexanol, an alkane, especially dodecane, and a surfactant, especially hexadecyltrimethylammonium bromide (CTAB). We prepare also a polar phase comprising water, an alcohol - in particular methanol - and a corrosion inhibitor - in particular cerium nitrate -. 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 ( t- 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 hollow aluminum oxyhydroxide nanoparticle powder containing the corrosion inhibitor is obtained.

E - Elaboration of a colloidal solution for anticorrosive treatment

Such a colloidal anticorrosive treatment dispersion is prepared by mixing an amount of a treatment solution (hybrid sol) as prepared in (A) with 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 mol / l and 0.13 mol / 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 and then an amount of the dispersion is added to the alcoholic solution. colloidal of physisorbed boehmite nanoparticles and / or doped boehmite nanoparticles and / or hollow boehmite nanoparticles.

In this way, the viscosity of the treatment solution (dispersion) which decreases with the addition of the colloidal dispersion of boehmite is controlled in this way. 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 - Colloidal dispersion deposit on the solid metal substrate

A step is performed for depositing the colloidal anti-corrosion treatment dispersion on a surface of a solid metal substrate, in particular a part of a rolled aluminum alloy 2024 T3 having previously undergone degreasing and pickling. During this deposition step, a part of the solvent of the composite hybrid soil evaporates and simultaneously the hydrolysis / condensation of (the) alkoxysilane (s) and (s) alkoxide (s) metal (s) allows the formation of a composite hybrid anti-corrosion matrix on the surface of the solid metal substrate.

The presence of cerium as a corrosion inhibitor, especially free cerium (Ce ^III ), 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 MO-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 controlled release. in time of the 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 withdrawal speed varies between 2 and 53 cm / min. The application of several successive layers by successive dipping / withdrawal operations, each soaking / removal operation being 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, including the pressure, the flow rate, the geometric characteristics of the spray nozzles, and the speed of movement. nozzles facing the surface of the solid metal substrate and the number of passage of the nozzles in front of 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

The treatment solution applied to the surface of the solid metal substrate is heat-treated so as to evaporatively remove the residual solvent (s) from the treatment solution and allow it to polymerize into a hybrid matrix. composite. In particular, such a heat 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 between 50 ° C and 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 of time between 3 h and 16 h, said second heating step being adapted to perfect the polymerization of the treatment solution and to improve the mechanical properties of the composite hybrid matrix.

The figure 3 represents the variation of the surface resistance of a solid metal substrate treated by a method according to the invention as a function of the immersion time of this solid metal substrate in a corrosion bath (NaCℓ 0.05 mol / L in the water). The curve (●) 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 conversion solution rich in cerium (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 (Δ) 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. <u> Table 1 </ u> Immersion time, h Surface resistance, Ω.cm ² With conversion layer Without 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

It is observed in particular that after 48 hours of immersion in the corrosion bath, the surface resistance of the untreated substrate (Δ) reaches a value of the order of 2.12 10 ⁶ Ω.cm ² , while the resistance surface area (•) treated remains of the order of 4.05 10 ⁶ Ω.cm ² . After 72 hours of immersion in the corrosion bath, the surface resistance of the untreated substrate (Δ) reaches a limit value of the order of 1.1 × 10 ⁶ Ω.cm ² , whereas the surface resistance of the substrate ( ) treated remains of the order of 2.75 10 ⁶ Ω.cm ² .

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 allows not only to obtain a surface resistance of the anticorrosion coating, measured by electrochemical impedance spectroscopy ( figure 4 ), which is optimal for an immersion time of the solid metal substrate in a corrosion bath of 1 day (Δ), 7 days (○) and 14 days (●) in an aqueous solution of NaCℓ 0.05 mol / L , but that such a treatment also makes it possible to obtain a nano-hardness ( figure 5 ), a Young's module ( figure 6 ) and resistance to delamination (○, figure 7 ), resistance to cracking (▲, figure 7 ) and a limit value of resistance to plastic deformation (□, figure 7 ) also maximum.

Electrochemical impedance spectroscopy is used to analyze the corrosion resistance of a solid metal substrate Aℓ 2024-T3 treated or not with a conversion solution and then exposed to a step of corrosion by immersion in an aqueous solution of NaCℓ 0.05 mole. / L. The results are presented in figure 8 according to the representation of Nyquist.

Treatment of a piece of aluminum 2024-T3 treated with a conversion solution by immersion in a corrosion solution (NaCℓ 0.05 mol / L) for 30 minutes at room temperature gives the latter a surface resistance Z 'in representation of "Nyquist" of the order of 4.10 ⁴ Ω.cm ² (○, figure 8 ). For comparison, the treatment of a piece of raw aluminum 2024-T3 (that is to say, not treated with a conversion solution) by immersion in a corrosion solution gives the latter a surface resistance Z ' of the order of 5.10 ³ Ω.cm ² (▲, figure 8 ).

The treatment of a piece of aluminum 2024-T3 previously immersed in a conversion solution formed of water and cerium (0.01 mol / L) and without immersion in a corrosion bath, confers a surface resistance Z 'with a value greater than 6.10 ⁵ Ω.cm ² . 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 Ω .cm ² .

The increase in the concentration of cerium in the conversion solution and the increase in the immersion time of the aluminum metal part in the conversion solution lead to an increase in the surface resistance of the aluminum metal part. .

In particular, the residual surface resistance Z 'of such a piece of aluminum after 1 hour of immersion in the corrosion solution is of the order of 1.1 × 10 ⁴ Ω.cm ² for a cerium concentration of 0, 01 mole / L in the conversion solution and a conversion treatment duration of 1 s, of the order of 2.10 ⁴ Ω.cm ² 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 Ω.cm ² for a cerium concentration of 0.1 mol / L in the conversion solution and a conversion treatment duration of 1 s.

The residual surface resistance Z 'of an aluminum piece after 1 h immersion in the corrosion solution is of the order of 1.1 × 10 ⁴ Ω.cm ² for a cerium concentration of 0.01 mol / L in the solution of conversion and a conversion treatment duration of 1 s, of the order of 2.10 ⁴ Ω.cm ² for a cerium concentration of 0.01 mol / L in the conversion solution and a conversion treatment duration of 60 s and of the order of 3.8 × 10 ⁴ Ω.cm ² for a cerium concentration of 0.01 mol / L in the conversion solution and a conversion treatment time of 300 s.

The residual surface resistance Z 'of an aluminum piece after 1 hour of immersion in the corrosion solution is of the order of 3.2 × 10 ⁴ Ω.cm ² for a cerium concentration of 0.1 mol / L in the conversion solution and a conversion treatment time of 1 s, of the order of 4.0 × 10 ⁴ Ω.cm ² for a cerium concentration of 0.1 mol / L in the conversion solution and a duration of conversion treatment of 60 s and of the order of 9.0.10 ⁴ Ω.cm ² for a cerium concentration of 0.1 mol / L in the conversion solution and a conversion treatment time 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 Ω. cm ² after respectively 40 hours, 70 hours and 90 hours of immersion of the aluminum part in the corrosion bath.

Chemical analyzes ( figure 9 ) by EDS make it possible to show the presence of cerium Ce (III) 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.

Claims (12)

1. Anticorrosion treatment process in which is prepared a liquid solution, named treatment solution, comprising:

   - at least one alkoxysilane, and

   - at least one cerium (Ce) cation,

   in an alcohol-water liquid composition, then said treatment solution is applied to an oxydizable surface of a solid metal substrate, said treatment solution:

   -- being suitable for forming a hybrid matrix by hydrolysis/condensation of each alkoxysilane in the presence of each cerium (Ce) cation on the surface of the solid metal substrate, and

   -- presenting a molar (Si/Ce) ratio of the silicon element of the alkoxysilane(s) with respect to the cerium (Ce) cation(s) comprised between 50 and 500;

   characterised in that the treatment solution is prepared such that the cerium (Ce) cation(s) have a concentration comprised between 0.005 mole/L and 0.015 mole/L in the treatment solution.
2. The process according to claim 1, characterised in that each alkoxysilane is chosen from the group formed of:

   - the tetraalkoxysilanes of the general formula (I) below:
   
           Si(O-R₁)₄     (I)
   
   wherein:

   o Si is the element silicon, O is the element oxygen;

   o R₁ is chosen from the group formed of:

   ▪ a hydrocarbon group of the formula [-C_nH_2n+1], n being an integer greater than or equal to 1; and

   ▪ the group 2-hydroxyethyl (HO-CH₂-CH₂-); and

   ▪ an acyl group of the general formula -CO-R'₁ wherein R'₁ is a hydrocarbon group of the formula [-C_nH_2n+1], n being an integer greater than or equal to 1; and

   - the alkoxysilanes of the general formula (II) below:
   
           Si(O-R₂)_4-a(R₃)_a     (II)
   
   wherein:

   o R₂ is chosen from the group formed of:

   ▪ a hydrocarbon group of the formula [-C_nH_2n+1], n being an integer greater than or equal to 1; and

   ▪ the group 2-hydroxyethyl (HO-CH₂-CH₂-); and

   ▪ an acyl group of the general formula -CO-R'₁ wherein R'₁ is a hydrocarbon group of the formula [-C_nH_2n+1], n being an integer greater than or equal to 1; and

   o R₃ is an organic group bonded to the silicon element (Si) of the alkoxysilane by an Si-C bond;

   o a is a natural integer of the interval ]0 ; 4[.
3. The process according to one of claims 1 or 2, characterised in that the treatment solution comprises at least one metal alkoxide.
4. The process according to claim 3, characterised in that each metal alkoxide has the general formula (VII) below:
   
           M'(O-R₉)_n"     (VII)
   
   wherein:

   ∘ M' is a metal element chosen from the group formed of aluminium (Al), vanadium (V), titanium (Ti) and zirconium (Zr);

   ∘ R₉ is an aliphatic hydrocarbon group of the formula [-C_nH_2n+1] wherein n is an integer greater than or equal to 1; and

   ∘ n" is a natural integer representing the valence of the metal element M'.
5. The process according to one of claims 3 or 4, characterised in that each metal alkoxide is an aluminium alkoxide of the general formula (III) below:
   
           Al(OR₄)_n     (III)
   
   wherein:

   ∘ A1 and O are the elements aluminium and oxygen, respectively; and

   ∘ R₄ is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms;

   o n is a natural integer representing the valence of the aluminium element (Al).
6. The process according to any one of claims 1 to 5, characterised in that the solid metal substrate is formed of a material chosen from the group formed of the oxidizable materials.
7. The process according to any one of claims 1 to 6, characterised in that, before application of the treatment solution, said oxidizable surface of the solid metal substrate is immersed in a liquid solution, named a conversion solution, formed of at least one corrosion inhibitor in water, said corrosion inhibitor being chosen from the group formed of the lanthanide cations, and said oxidizable surface of the solid metal substrate is kept in contact with the conversion solution for a period of time adapted to form a conversion layer formed of said lanthanide bonded by at least one covalent bond to the oxidizable surface and extending over the surface of the solid metal substrate.
8. The process according to claim 7, characterised in that the conversion solution has a concentration of corrosion inhibitor of between 0.001 mol/l and 0.5 mol/l.
9. The process according to any one of claims 1 to 8, characterised in that the treatment solution is applied by dip-coating of the solid metal substrate in said treatment solution.
10. The process according to any one of claims 1 to 8, characterised in that the treatment solution is applied by atmospheric spray-coating of the treatment solution on the surface of the solid metal substrate.
11. The process according to any one of claims 1 to 10, characterised in that the hydroalcoholic composition is formed of water and at least one alcohol.
12. The process according to any one of claims 1 to 11, characterised in that the cerium cation of the treatment solution is chosen from the group formed of the cerium chlorides and cerium nitrates.

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