Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/125—Process of deposition of the inorganic material
  • C23C18/1254—Sol or sol-gel processing
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/1204—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material inorganic material, e.g. non-oxide and non-metallic such as sulfides, nitrides based compounds
  • C23C18/1208—Oxides, e.g. ceramics
  • C23C18/1216—Metal oxides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/1229—Composition of the substrate
  • C23C18/1241—Metallic substrates
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/02—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition
  • C23C18/12—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by thermal decomposition characterised by the deposition of inorganic material other than metallic material
  • C23C18/125—Process of deposition of the inorganic material
  • C23C18/1279—Process of deposition of the inorganic material performed under reactive atmosphere, e.g. oxidising or reducing atmospheres

Definitions

• the invention relates to the field of protection against corrosion of metal substrates.
• the invention may for example be used to manufacture anticorrosion coatings in the primary or secondary fluid circuits of a nuclear power plant, or in the field of aeronautics or the protection of installations at the seaside as tidal turbines or wind turbines. More broadly, the invention relates to any field requiring the protection of metals or metal alloys against generalized corrosion, pitting corrosion or stress corrosion.
• the protection of metal substrates against corrosion occurs in many areas. It can intervene in industries such as building, civil engineering, transport and can affect industrial facilities such as thermal or nuclear power plants.
• primary, secondary and tertiary thermal circuits are subject to corrosion by the fluid circulating in these circuits.
• the constituent material of these circuits is generally a stainless steel alloy for coating the reactor vessel and pipes, or nickel-based alloys for the steam generators.
• the primary circuit requires an optimal resistance to corrosion. Indeed, the corrosion products can be activated under neutron flux, be redeposited in the circuit and increase the radiological risk in the installation.
• the tertiary circuit is open to the environment, and can lead to unwanted pollution. Corrosion of brass condensers in this circuit may, for example, give rise to unwanted copper rejection.
• the use of stainless steel instead of brass can have an impact on the development of pathogenic microorganisms.
• the stainless alloys of these facilities are often protected by a passive oxide film that forms a protective film on the surface of the metal substrate.
• this film is likely to destabilize when the chemistry of the medium evolves, and lead to widespread or localized corrosion of the substrate. Pitting corrosion, crevice corrosion, intergranular corrosion or stress corrosion can then propagate cracks in the substrate. It has been proposed to stabilize passive film by adding film-forming elements such as chromium, molybdenum, titanium, aluminum or silicon. This solution is however expensive and modifies the metallurgical structure and the mechanical properties of the material.
• Another solution is to control the chemistry of the corrosive medium to prevent degradation of the passive film. This solution is however not practical and imposes a strong operating constraint.
• Another possibility is to manufacture a coating in the form of nano-oxide film on the metal substrate, chemically stable in the corrosive environment and resistant to temperatures involved in industrial installations, such as TiO 2 nano-films, Zr0 2 , A1 2 0 3 , Ce0 2 .
• Document FR 13 62541 proposes a sol-gel process for treating a metal substrate by depositing a metal oxide film.
• a sol-gel process also called “solution-gelling” process has the advantage of being used with large sizes of substrate. It is also implemented at low temperature, is inexpensive to implement, and allows the production of thin films of a thickness. typically between about ten and one hundred nanometers and with a controlled composition.
• a colloidal suspension of oligomers whose diameter is a few nanometers is transformed during a hydrolysis-condensation process in the presence of water to form a viscous network called "gel ".
• the solution contains a precursor of the metal oxide in the form of alkoxides [M (OR) z ] n where M is a metal of valence z, R is an organic compound and n refers to the possibility of having precursors under form of polymers or oligomers (when n is different from 0).
• the solution further contains a non-aqueous solvent, water and may contain additives such as inhibitors or reaction catalysts.
• the hydrolysis-condensation process is carried out in solution by adding liquid water, before depositing the solution on the substrate, preferably during a maturation stage which may last several hours with stirring.
• This type of sol-gel method for depositing an anticorrosion coating on a metal substrate has the disadvantage of requiring homogenization of the solution during the maturation step, at the risk of seeing inhomogeneities in the oxide network formed by hydrolysis-condensation.
• this maturation step gives the hydrolysed solution a limited life beyond which it can no longer be used to make a deposit. Maturation therefore adds a time constraint in the use of the solution to make a deposit, which leads to an increase in the operating cost when unused solution must be discarded or recycled.
• the present invention proposes a sol-gel process for producing an anticorrosion coating consisting of at least one layer of an oxide on a metal substrate, the process comprising successively:
• Idl Perform a film stabilization treatment on the surface of the substrate
• the sol-gel process of the present invention allows a finer and more precise control of the hydrolysis-condensation process, the latter being carried out in situ directly on the metal substrate after the deposit of the non-aqueous solution. This process makes it possible in particular to considerably increase the duration of use of the solution which is maintained in unhydrolyzed form, the hydrolysis only taking place after the deposit of the solution on the sample.
• contacting the film comprising the precursor of the oxide with a moist atmosphere ensures a more homogeneous distribution of the moisture, which diffuses through a thin film to the metal substrate, avoiding a local accumulation of water likely to create a heterogeneous hydrolysis-condensation.
• This approach differs significantly from that involving a ripening step as proposed in application FR 13 62541. Indeed, when the hydrolysis is initiated by adding water to the liquid solution, a local accumulation of water can cause hydrolysis condensation heterogeneous leading to an inhomogeneous density oxide network.
• the approach proposed in the present invention ensures a better homogeneity to the oxide network, and therefore a higher quality in the anticorrosion coating manufactured.
• the use of a humid atmosphere makes it possible to control finely the course of the hydrolysis-condensation. Parameters such as the moisture content and the exposure time of the film to the humid atmosphere can influence the course of this chemical reaction.
• the contact with a humid atmosphere also makes it possible to overcome the disadvantages related to the differences in the reactivity of the components present in the solution. Indeed, not all precursors react with the same reaction kinetics in solution. In the case of maturation by adding water in solution, these kinetic differences are not controllable, while the exposure to an atmosphere wet a thin film, about a hundred nanometers thick, allows to adjust the moisture content and the duration of exposure depending on the reactivity of the precursor.
• the approach of the invention by initiating ⁇ hydrolysis-condensation directly in situ by contacting with a humid atmosphere, offers the advantage of eliminating the maturation stage, which reduces the duration of implementation of the process. process of several hours.
• the invention also allows greater control over the properties of the anticorrosive coating produced by providing an intermediate step of stabilizing treatment of the film comprising the oxide network.
• This stabilization treatment makes it possible to evacuate any organic matter possibly present in the film, and can also be used to reduce the porosity of the film, in the case of an ultraviolet treatment in particular.
• the presence of this intermediate step makes it possible in particular to avoid the appearance of cracks or cracks during the subsequent heat treatment phase of the film, by consolidation of the film.
• steps I 1 to / d / may be repeated to deposit more than one layer on the metal substrate.
• steps Ibl to lel it is possible to deposit several layers of one or more oxides to provide better protection against corrosion.
• the use of a stack of several oxide layers can in particular guarantee better protection against pitting corrosion.
• a multilayer stack can also eliminate defects such as cracks or gaps in lower coatings.
• the stabilization treatment may comprise an exposure of the film to a gas stream heated to a temperature above room temperature and below 200 ° C. By heating the film at these temperatures, any organic material present in the film can be evaporated, regardless of the geometry of the metal substrate on which the film is deposited.
• the stabilizing treatment may comprise exposure of the film to ultraviolet radiation.
• the exposure of the film to ultraviolet radiation makes it possible to decompose organic compounds possibly present in the film, such as, for example, complexing agents, alkoxides or surfactants, by means of the photocatalytic properties of the oxide precursor used, such as, for example titanium oxide.
• the irradiance control and the spectrum of the radiation used reduce the porosity of the film, especially when this step is carried out while the condensation of the oxide precursor is not yet complete.
• a typical irradiance of 225 mW / cm 2 with radiation comprising UVa (typically between 315 nm and 400 nm wavelength) and UVb (wavelength typically between 280 nm and 315 nm) is particularly suitable for reducing the porosity of the film.
• the decomposition of organic compounds under ultraviolet radiation is amplified under a humid atmosphere.
• the stabilizing treatment may be selected from a microwave assisted film processing and an induction film treatment at a temperature above room temperature and below 200 ° C.
• the use of microwaves makes it possible to effectively evaporate any organic material that may be present in the film, for any geometry of metal substrates on which the film is deposited.
• the microwaves also promote condensation and crystallization of the oxides.
• the precursor of the oxide may be chosen from a titanium precursor, a zirconium precursor, a chromium precursor, an yttrium precursor, a cerium precursor and an aluminum precursor.
• the precursor of the oxide may be chosen from: titanium ethoxide, titanium n-propoxide, titanium s-butoxide, titanium n-butoxide, titanium t-butoxide and isobutoxide of titanium, titanium isopropoxide, tetrabutyl orthotitanate, tetra-tert-butyl orthotitanate, poly (dibutyltitanate), zirconium n-propoxide, zirconium n-butoxide, zirconium t-butoxide, zirconium ethoxide, the 2- zirconium methoxymethyl-2-propoxide, zirconium 2-methyl-2-butoxide, zirconium isopropoxide, yttrium isopropoxide, yttrium n-butoxide, titanium triisopropoxide methacrylate, bis (tetramethylheptanedionate) diisopropoxide ) of titanium, titanium 2,4-p
• the solution of the precursor of the oxide may comprise, for one mole of the precursor of the oxide, 0 to 2 moles of complexing agent and 10 to 50 moles of ethanol.
• Such a composition is particularly suitable for producing anticorrosive coatings with a thickness of between 50 nm and 150 nm.
• the control of the composition of the solution is an adjustable parameter of the thickness. Indeed, the higher the ethanol content, the lower the thickness of the coating obtained, since for the same amount of deposited solution, there will be fewer precursor molecules of the oxide.
• the amount of complexing agents present in the solution makes it possible to modulate the reactivity of the various constituents of the solution. In particular, these complexing agents make it possible to control more finely the hydrolysis-condensation process during the deposition, and to make the solution more stable over time and more homogeneous.
• the presence of complexing agents also makes it possible to substantially modify the microporosity of the coating, in particular the quantity of pores with a diameter of less than 2 nm.
• the solution of the precursor of the oxide may further comprise, for one mole of the precursor of the oxide, up to 0.2 moles of a surfactant.
• the presence and the relative amount of surfactants in the solution make it possible to adjust the porosity of the coating.
• the more surfactants in the solution the greater the porosity of the coating.
• the amount of surfactant indicated for one mole of the precursor of the oxide makes it possible to obtain a porosity typically representing 40% to 50% by volume of the coating. This proportion can then be reduced by means of a stabilization treatment by applying ultraviolet radiation to the film.
• pores in the film can contribute to making the anticorrosive coating more mechanically resistant, especially by making it more flexible, which reduces the risk of occurrence of cracks due to differences in thermal expansion between the metal substrate and the anticorrosive coating.
• the presence of pores also makes it possible to more effectively confine the corrosion products and reduce the migration of constituent metallic elements of the substrate.
• the step Ibl can be implemented by a technique chosen from: a soak-removal of the surface in the solution, the shrinkage being carried out at a speed of between 0.5 mm / s and 20 mm / s; spraying the solution on the surface with a controlled spray rate and a relative speed of controlled movement of a sprayer relative to the surface; evaporation of the solution in an enclosure containing the surface and under controlled temperature and pressure.
• Soak-shrinkage also called “dip-withdraw” or “dip-coating” according to the English terminology
• the thickness of the coating is controllable by the rate of removal of the metal substrate from the solution.
• the deposition of the non-aqueous solution with a soaking-removal method is carried out by drainage, by obeying a so-called "Landau Levich” regime rather than by capillarity.
• Spraying the solution on the surface of the metal substrate is more suitable for metal substrates of complex geometrical shape, such as ducts cylindrical bent for example.
• the speed of movement of the sprayer, as well as the flow rate make it possible to adjust the thickness of the coating thus obtained.
• Evaporation of the solution in an enclosure under controlled pressure and temperature is an advantageous variant to the spray for depositing the solution on metal substrates of complex geometric shape.
• the step Ibl can be carried out by placing the surface in contact with a sponge element impregnated with the solution and diffusing the solution by capillarity on the surface.
• the diffusion of the solution by the spongy element makes it possible to deposit the solution on the surface.
• the step Ibl can be performed by contacting the surface with a predetermined volume of solution confined at least partially by a sealed membrane, the waterproof membrane being able to slide by translation along the surface. , a controlled displacement of the waterproof membrane allowing the formation of a controlled film thickness on the surface.
• Such a way of depositing the solution on the metal substrate has the advantage of allowing a particularly fine control of the amount of solution deposited, as well as to marry the surface of the metal substrate.
• the thickness of the deposited film essentially depends on the speed of translation of the sealed membrane.
• this deposition technique reduces the amount of solution needed to deposit a precursor film on the surface.
• the waterproof membrane can be movable in translation along an axis of the cylindrical substrate.
• the steps Ibl to lel are implemented on a production line making a relative displacement of the metal substrate relative to animated modules arranged to perform the deposition of the solution on the surface, the exposure of the film in a humid atmosphere, the exposure of the film to a stabilizing treatment and the exposure of the film to a heat treatment.
• the various steps of the anticorrosive coating manufacturing method can be carried out on the same production line, in which the various actions described above are carried out by modules fed to the metal substrate by the production line. In such a production line, each module can perform an action on the metal substrate in accordance with the steps described above.
• the heat treatment is carried out at a temperature of between 300 ° C. and 500 ° C. These temperatures can be applied for about 30 minutes to crystallize the metal oxide to conclude the synthesis of the anticorrosive coating.
• the invention also relates to a metal substrate comprising an anticorrosion coating obtained by the implementation of the process described above.
• FIG. 1 is a flow chart showing five steps of the method of manufacturing an anticorrosive coating according to the invention
• FIGS. 2a and 2b are diagrammatic representations of a soak-removal method of a metal substrate in a non-aqueous solution for depositing an oxide precursor film on a surface of the substrate;
• FIG. 3 is a schematic representation of a method of depositing the non-aqueous solution on the surface of the metal substrate by evaporation of the solution in an enclosure under controlled temperature and pressure;
• FIG. 4 is a schematic representation of the deposition of a non-aqueous solution of an oxide precursor on the inner surface of a cylindrical metal substrate by means of a membrane movable in translation along the axis of the substrate;
• FIG. 5 is a diagrammatic representation of a cylindrical metal substrate of fluidic pipe type comprising an anticorrosion coating on its inner surface;
• FIG. 6 is a schematic representation of a production line scrolling modules applying a method of manufacturing an anticorrosive coating on a metal substrate
• FIGS. 7a and 7b are graphs respectively representing the results of electrochemical measurements at ambient temperature in a corrosive environment rich in chloride ions in the form of polarization curves (FIG. 7a) and in the form of a Bode diagram (FIG. 7b).
• a substrate comprising a titanium oxide coating and a substrate comprising a zirconium oxide coating.
• the present invention provides a method for producing an anticorrosion coating consisting of at least one layer of an oxide on a metal substrate.
• a possible application of the invention is the protection of primary, secondary and tertiary circuit conduits of thermal or nuclear power plants. In this particular context, an optimal protection is sought to avoid any degradation following the corrosion likely to increase the radiological risk or the environmental impact.
• Another application is the protection of facilities subject to a corrosive environment, such as aeronautical industry machinery, seaside facilities (wind turbines, tidal turbines, subject to wet and chlorinated environments) for example.
• a corrosive environment such as aeronautical industry machinery, seaside facilities (wind turbines, tidal turbines, subject to wet and chlorinated environments) for example.
• the invention consists of a simple method to implement, which can be applied to large areas of metal substrate of any shape.
• the quality of the coating obtained makes it possible to improve by a factor of 100 to 1000 the protection against corrosion of a metal substrate, thereby lengthening the service life of the metal substrate.
• Figure 1 shows a flowchart illustrating five steps of the method of the invention.
• This method is a sol-gel process involving a first step S 1 for preparing the sol-gel solution comprising a precursor of an oxide intended to form a coating on the metal substrate, a second step S 2 of depositing the solution on a surface of the metal substrate for forming a film of the precursor of the oxide, a third step S3 of initiating the hydrolysis-condensation by exposing the film to a humid atmosphere, with a view to creating an oxide network in the film . Then, a fourth stabilization treatment step S4 aims at evaporating any organic component that may be present in the film, and at promoting condensation reactions that also make it possible to eliminate organic compounds. Finally, a step S5 corresponding to a crystallization heat treatment of the oxide network to form the anticorrosive coating.
• a non-aqueous solution containing a precursor of the oxide is prepared.
• the precursor of the oxide is typically an alkoxide type transition metal oxide precursor of the general formula [M (OR) z ] n , where M is a metal of valence z, R is an organic compound. It is also possible to produce a composition comprising a plurality of different oxide precursors, for example a mixture comprising a precursor of zirconium oxide and a precursor of titanium oxide.
• the oxide precursor may typically be a precursor of titanium oxide or zirconium oxide, which are metals particularly suitable for use as a coating in nuclear installations.
• Zirconium oxide also has the advantage of having a high coefficient of expansion, which naturally protects it against the appearance of cracks during the crystallization of the oxide network on metal substrates, which takes place at a high temperature. temperature between 300 ° C and 500 ° C.
• oxide precursors may be used as precursors of chromium or yttrium.
• Yttrium can be used to stabilize cubic zirconia in particular.
• the R group is generally an alkyl group preferably comprising 1 to 4 carbon atoms such as a methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl or t-butyl group.
• the precursor may, for example, be chosen from the following compounds: titanium ethoxide Ti (OC 2 H 5 ) 4 , titanium propoxide Ti (OC 3 H 7 ) 4 , titanium isopropoxide Ti [OCH ( CH 3 ) 2 ] 4 , titanium butoxide Ti (OCH 2 CH 2 CH 2 CH 3 ) 4 , zirconium butoxide Zr (OC 4 H 9 ) 4 , zirconium propoxide Zr (OCH 2 CH 2 CH 3 ) 4 , acetylacetonate chromium Cr (C 5 H 7 O 2 ) 3 , yttrium butoxide Y (OC 4 H 9 ) 3 , yttrium isopropoxide Y (OCH (CH 3 ) 2 ) 3 .
• the precursor may be chosen from: titanium isobutoxide, poly (dibutyltitanate), zirconium ethoxide, 2-methoxymethyl-2-zirconium propoxide, zirconium 2-methyl-2-butoxide, zirconium isopropoxide.
• the non-aqueous solution typically comprises a mixture in which, for one mole of metal oxide precursor, 10 to 50 moles of ethanol (non-aqueous solvent) and advantageously 0 to 2 moles of complexing agent are added.
• the complexing agent is an additive which makes it possible to stabilize the precursor in the solution, insofar as the alkoxides are very reactive, which affects the quality of the oxide network obtained during the hydrolysis-condensation of the solution.
• the metal oxide precursor has the general chemical formula L x [M (OR) z ] n-Xi where L is a monodentate or polydentate ligand such as the carboxylic acid at C. % such as acetic acid, a ⁇ -diketone, preferably in Cs -2 o, such as acetoacetone or dibenzoylmethane, a ⁇ -ketoester preferably in Cs -2 o such as methyl acetoacetate, a ⁇ -ketoamide preferably C 5 -2 o, such as N-methylacetoacetamide, a? or? -hydroxiacide preferably of C 3-2 o such as lactic acid or salicylic acid, an amino acid such as alanine or a polyamine as diethylenetriamine (DETA).
• L is a monodentate or polydentate ligand such as the carboxylic acid at C. % such as acetic acid, a ⁇ -diketone, preferably in Cs
• the compounds incorporating a ligand may especially be chosen from: titanium triisopropoxide methacrylate, titanium bis (tetramethylheptanedionate) diisopropoxide, titanium 2,4-pentanedionate, diisopropoxy-bis (ethylacetoacetato) titanate, di-n-butoxide (bis-2,4-pentanedionate) titanium, 2-ethylhexoxide titanium, titanium bis (acetylacetonate) oxide, bis (2,2,6,6-tetramethyl-3,5-heptanedionato) oxotitane, bis (ammonium lactate) titanium dihydroxide, zirconium bis (diethyl citrato) dipropoxide, zirconyl propionate, chromium acetate.
• the non-aqueous solution may in particular also contain a surfactant element used to modify the porosity of the metal oxide film obtained.
• the surfactant is present in the solution in such proportions that for one mole of the precursor of the oxide there is up to 0.2 mole of the surfactant.
• the surfactant is typically selected from nonionic amphiphilic surfactants. They may be amphiphilic molecules or macromolecules such as polymers.
• the molecular nonionic amphiphilic surfactants may, for example, be C 12-22 ethoxylated linear alcohols comprising from 2 to 30 ethylene oxide units, or fatty acid esters containing from 12 to 22 carbon atoms, and sorbitan.
• the surfactants available as Brij®, Span® and Tween® may be used.
• Polymeric nonionic amphiphilic surfactants may be any amphiphilic polymer having both a hydrophilic character and a hydrophobic character.
• these surfactants may be chosen from fluorinated copolymers such as CH 3 - [CH 2 -CH 2 -CH 2 -CH 2 -0] "- CO-R 1 with or C 8 F 17 , block copolymers comprising two blocks, three blocks of type ABA or ABC or four blocks.
• the following compounds may be selected: copolymers based on poly (meth) acrylic acid, polydiene-based copolymer, copolymers based on hydrogenated diene, copolymers based on poly (propylene oxide), copolymers based on poly (ethylene oxide), copolymers based on polyisobutylene, copolymers based on polystyrene, copolymers based on poly (2-vinyl-naphthalene), copolymers based on poly (vinyl pyrrolidone), and block copolymers consisting of poly (alkylene oxide) chains, each block consisting of a poly (alkylene oxide) chain, the alkylene having a number of different carbon atom according to each chain.
• one of the two blocks may comprise a poly (alkylene oxide) chain of hydrophilic nature while the other block may comprise a poly (oxide) chain. alkylene) of hydrophobic nature.
• two of the blocks may be hydrophilic in nature while the other block, located between the two hydrophilic blocks, may be hydrophobic in nature.
• the hydrophilic poly (alkylene oxide) chains are poly (ethylene oxide) chains noted (POE) u and (POE) w and the Poly (alkylene oxide) chains of hydrophobic nature are chains of poly (propylene oxide) denoted (POP) v or chains of poly (butylene oxide), or mixed chains in which each chain is a mixture of several monomers of alkylene oxides.
• POP polypropylene oxide
• a compound of formula (POE) u - (POP) v - (POE) w with 5 ⁇ u ⁇ 106, 33 ⁇ v ⁇ 70 and 5 ⁇ w ⁇ 106 can be used.
• the molar proportion of surfactant in the non-aqueous solution controls the amount of pores in the oxide precursor film.
• complexing agents and surfactants can also contribute to increasing the thickness of the anticorrosive coating while rendering it more porous.
• the non-aqueous solution 1 may furthermore comprise nanoparticles of titanium oxide or of zirconium oxide. These nanoparticles can serve as a seed crystal to promote the crystallization of the anticorrosive coating during the heat treatment step of the latter. The addition of nanoparticles can also help densify the anticorrosive coating and limit the formation of cracks.
• the second step S2 consists of depositing the non-aqueous solution on at least one surface of the metal substrate to form a film comprising the precursor of the oxide on this metal substrate. This step can be implemented in different ways, as explained in particular in FIGS. 2a, 2b, 3 and 4.
• a means for depositing the non-aqueous solution 1 on the surface 11 of the metal substrate 10 consists in carrying out dip-withdrawing ("dip-withdraw” or “dip-coating” according to the English terminology ).
• this step is performed by dipping the metal substrate into the solution and then removing the metal substrate from the solution as shown in Figure 2b.
• the thickness of the film comprising the precursor of the oxide depends in particular on the speed of the withdrawal step of FIG. 2b.
• a withdrawal speed of between 0.5 mm / s and 20 mm / s should be provided.
• the soaking-shrinking at these speeds is done by drainage and not by capillarity.
• the higher the rate of shrinkage the greater the thickness of the film obtained.
• Another parameter influencing the thickness of the film obtained is the molar proportion of ethanol in the non-aqueous solution 1. In fact, the more ethanol there is in the solution, the less precursor of the oxide there is. volume unit in the solution and more the deposited film is fine.
• FIGS. 2a and 2b show a soak-withdrawal in which the solution is kept in a fixed position while the substrate is displaced in the solution
• an alternative configuration allowing a relative movement of the substrate with respect to the solution can also be set implemented.
• the non-aqueous solution 1 may, for example, be moved a first time until it coats the surface 11 of the metal substrate 10 and then moved again to release the metal substrate 10 from the non-aqueous solution 1 at a controlled rate. .
• Soak-shrink is a suitable method for depositing the solution on metal substrates of simple geometrical shape. However, more complex surfaces may benefit from more suitable methods such as spraying.
• Spraying can alternatively be effected by means of a movable pulverizer with respect to the metal substrate 10, whose displacement speed and ejected flow rate are controllable to obtain a desired film thickness.
• FIG. 3 schematically shows an example of deposition of the non-aqueous solution 1 on the metal substrate 10 by evaporation of the solution in an enclosure containing the surface 11 and under controlled temperature and pressure.
• a carrier gas inlet 2 can contribute to transport the solution and bring it onto the surface 11 of the metal substrate 10.
• Figure 4 shows a cylindrical vessel 100 comprising the metal substrate 20 as a cylindrical pipe.
• a waterproof membrane 44 is fixed to an axis 45 of the cylindrical tank 100.
• a section 412 located above the membrane has a predefined volume of non-aqueous solution 1.
• the membrane 44 slides in translation along the axis 45 maintaining a sealed contact with the walls of the metal substrate 10.
• the displacement of the sealed membrane 44 may in particular be provided by a pulling ring 43 connected to the waterproof membrane 44.
• the mass of this traction ring 43, as well as the volume of solution in section 41 are parameters for controlling the thickness of the film 20 deposited on the metal substrate 10.
• the section 40 located above the section 41 is devoid of non-aqueous solution 1 but is already coated with the film 20.
• the section 42 located under the section 41 will be treated by the deposition of a film 20 when the waterproof membrane 44 has moved to its level.
• An excess of non-aqueous solution 1 can be discharged through openings provided in a central element 46 whose dimensions are adapted to maintain a predetermined volume of non-aqueous solution above the membrane 44.
• a third step S3 of the anticorrosive coating manufacturing process is to initiate hydrolysis of the oxide precursor in the film by exposure of the film to gaseous water present in a humid atmosphere.
• An originality of the invention lies in the fact that this step S3, making it possible to increase the viscosity of the film 20 and form an oxide network in the film 20, is performed after the film 20 has been deposited on the surface 11 of the metal substrate 10 in step S2.
• the diffusion of the water in gaseous form avoids the local appearance of a large quantity of water capable of producing a heterogeneous oxide network during the hydrolysis and the condensation that follows.
• the invention also eliminates the need for a maturation step in the non-aqueous solution, which is a long step in the processes of the prior art.
• an initialization of the gaseous hydrolysis in a humid atmosphere makes it possible to compensate for the high reactivity of the oxide precursors by exposing them in a progressive and controlled manner to the moisture which diffuses through the thickness of the film 20.
• the initiation of hydrolysis by exposure to a humid atmosphere proves particularly effective because of the film thicknesses involved in the process, of the order of one hundred nanometers, which facilitates the permeation of the film. water through the film 20.
• the moisture content of the atmosphere can be controlled, and is advantageously between 20% and 80%. Higher humidity can lead to condensation on film 20, which is not desired.
• the duration of exposure to this humid atmosphere can typically be between 30 seconds, especially for high humidity levels, and 5 minutes, especially for low humidity levels.
• the temperature during step S 3 is a parameter that can influence the hydrolysis-condensation kinetics.
• a temperature of between 15 ° C and 35 ° C is preferred.
• step S4 of FIG. 1 the film 20 comprising the oxide network is subjected to a stabilization treatment making it possible to promote the condensation reactions leading to elimination of any organic component remaining in the film 20, and to avoid appearance of cracks in the film during the subsequent heat treatment step S5.
• step S4 The stabilization treatment of step S4 can be carried out in different ways.
• this treatment can be carried out by means of simple exposure to a temperature above room temperature, and preferably below 200 ° C, in an oven.
• a temperature above room temperature and preferably below 200 ° C
• Such an approach is particularly suitable for homogeneous stabilizing treatment in the case of metal substrates 10 of complex shape, such as, for example, bent pipes with a length of up to 10 m.
• Another approach is to circulate a gas heated to a temperature above room temperature, and preferably below 200 ° C around the metal substrate 10.
• this stabilization of the film for consolidating the inorganic part of the oxide network may be carried out by microwave application or by induction, at a temperature above room temperature and below 200 ° C.
• the consolidation of the film can be performed by applying ultraviolet radiation.
• This solution has the advantage of also allowing a reduction of the porosity of the film, and therefore of densifying the film 20 comprising the oxide network.
• An exposure time of between 30 seconds and 10 minutes at a radiation of wavelengths between 280 nm and 400 nm (so-called UVa and UVb radiation) with an irradiance of about 225 mW / cm 2 is particularly effective. to stabilize a film 20 with a thickness of about 100 nm.
• Step S4 can be implemented at least in part while step S3 is still in progress.
• more than one protective layer has to be made, which is particularly advantageous for providing good protection against pitting corrosion, it is possible to repeat the previous steps on an existing coating.
• the process can even be completely repeated (steps S1-S5) during the deposition of each coating layer.
• Figure 5 shows schematically the section of a tube 3 of fluid circuit in top view.
• the metal substrate 10 is covered on an inner surface of the tube 3 by two layers 31, 32 of different metal oxides. It is also possible to provide only one layer for the anticorrosive coating, which can be beneficial to avoid excessive thickness for the anticorrosive coating, and reduce the time and cost necessary for the total treatment of the substrate.
• Step S5 consists in applying to the film 20 comprising the stabilized oxide network a heat treatment at a temperature typically between 300 ° C. and 500 ° C. This step is preferably carried out under a controlled atmosphere to prevent oxidation of the substrate disturbing the crystallinity of the coating. Through this step the oxide network of the film 20 is crystallized to form the final anti-corrosion coating.
• the process described above eliminates the need for a long stage of maturation of the non-aqueous solution 1, thanks to hydrolysis-condensation in the vapor phase in a humid atmosphere.
• the invention may in particular be carried out on an industrial production line, such as that shown schematically in FIG.
• FIG. 6 proposes placing the metal substrate 10 in a fixed position, and scrolling modules animated by a line 60 in the direction of the metal substrate 10.
• a first module 61 may for example be used to polish the surface 11 to prepare it treatment. This preparation can be mechanical etching, mechanical polishing or chemical etching for example.
• a module 62 can then carry out a cleaning of the polished surface 11, for example by rinsing.
• the module 63 deposits the sol-gel solution by one of the processes described above for example. In Figure 6, this deposit is made by a spongy element.
• a module 64 exposes the film 20 of the surface 11 to a humid atmosphere.
• the module 65 performs the stabilization treatment (for example by exposure to ultraviolet radiation), then the module 66 performs the treatment to crystallize the anticorrosive coating.
• the line 60 can be used to transport the various modules towards the metal substrate 10, and can also include arrivals of water, electricity and non-aqueous solution for example, in order to feed the different modules.
• the metal substrate equipped with the anticorrosion coating obtained by the process described above has a corrosion resistance 100 to 1000 times greater than a metal substrate without such a coating.
• the corrosion current of a metal substrate comprising the anticorrosive coating is at least a factor of at least 10 less than a corrosion current of a metal substrate having no anticorrosive coating.
• Comparative measurements were carried out on a inconel 690 metal substrate, without anticorrosive coating and with an anticorrosive coating of Ti0 2 and Zr0 2 , in the presence of a corrosive environment comprising chloride ions.
• Figure 7a shows polarization curves for these three samples in a solution containing NaCl at a concentration of 0.05 mol / L.
• FIG. 7a shows a cathode Tafel domain on the left side of the figure and an anode Tafel domain on the right side of the figure.
• the Tafel straight line method makes it possible to determine the corrosion current density, indicated for each sample in FIG. 7a by the name Icorr. These curves show a significantly lower corrosion current density and corrosion potential in FIG. presence of anticorrosion coating, which confirms the effectiveness of the method described above. In particular, the corrosion current density is 10 to 100 times smaller in the presence of a coating of titanium oxide and zirconium oxide.
• Figure 7b shows impedance spectroscopy measurements performed on these same samples.
• the effectiveness of the coating vis-à-vis corrosion is reflected in particular by an increase in the module of the impedance Z at low frequencies.

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