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
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
  • C09D5/44—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications
  • C09D5/4476—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes for electrophoretic applications comprising polymerisation in situ
• • 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
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/02—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using non-aqueous solutions
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D9/00—Electrolytic coating other than with metals
  • C25D9/02—Electrolytic coating other than with metals with organic materials
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31536—Including interfacial reaction product of adjacent layers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/31504—Composite [nonstructural laminate]
  • Y10T428/31678—Of metal

Definitions

• the subject of the invention is a metallic material whose surface is modified, its method of preparation and the use of the modified material.
• the invention particularly relates to the grafting of aromatic groups on the surface of metallic material.
• the invention particularly relates to the grafting, stable over time, of aromatic groups on the surface of a metallic material.
• the invention relates to a metallic material whose surface is modified, by bonding aromatic groups to said surface, optionally substituted by functional groups.
• aromatic group is understood to mean a radical derived from a cyclic compound comprising one or more independent or condensed benzene rings, and / or one or more complex rings derived from benzene. This radical can of course also include heterocyclic rings and / or various substituents as well as hydrocarbon chains optionally comprising heteroatoms such as N, O and S.
• metal material whose surface is modified by bonds of aromatic groups to said surface means that on the surface of the metallic material is grafted a layer which can have a minimum thickness of approximately 10 ⁇ , that is to say be a monolayer.
• the layers grafted onto the surface of the metallic material according to the invention have a thickness varying from approximately 10 ⁇ to approximately 1 mm.
• aromatic groups optionally substituted by functional groups means that the grafted aromatic groups can undergo subsequent chemical transformations as it appears during the description which follows.
• the nature of the bond between the surface and the aromatic groups which modify it is a carbon-metal bond of covalent type, and is in particular such that it resists washing by ultrasound.
• carbon-metal of covalent type signifies a strong nonionic bond obtained by covering the orbitals of carbon and metal.
• the aromatic group is an aromatic C 6 -C 14 residue, optionally substituted by one or more functional substituents or a heteroaromatic residue of 4 to 14 atoms, optionally substituted by one or more functional substituents, comprising one or more heteroatoms chosen from oxygen, nitrogen, sulfur or phosphorus.
• the aromatic group comprises one or more substituents chosen from the group consisting of:
• aliphatic radicals linear or branched from 1 to 20 carbon atoms, optionally comprising one or more double (s) or triple (s) bond (s), optionally substituted by carboxyl radicals, NO 2 , disubstituted protected amino, a protected mono-substituted ino, cyano, diazonium, alkoxy of 1 to 20 carbon atoms, alkoxycarbonyl of 1 to 20 carbon atoms, alkylcarbonyloxy of 1 to 20 carbon atoms, optionally fluorinated or allyl vinyl, halogen atoms,
• aryl radicals optionally substituted with carboxyl radicals, NO 2 , disubstituted protected amino, protected monosubstituted amino, cyano, diazonium, alkoxy of 1 to 20 carbon atoms, alkoxycarbonyl of 1 to 20 carbon atoms, alkylcarbonyloxy of 1 to 20 atoms carbon, possibly fluorinated or allyl vinyl, halogen atoms,
• the metallic material according to the invention is such that the aromatic group comprises one or more substituents capable of reacting directly with a substrate, or one or more precursor substituents which, after transformation, are capable of reacting with a substrate, said substrate being chosen in the group consisting of organic resins, biological molecules, chemical molecules or complexing agents.
• the aromatic group comprises one or more substituents capable of reacting directly with a biological molecule and chosen from the group consisting of (CH 2 ) n -COOH, (CH 2 ) n -NH 2 , n being an integer between 0 and 10, or one or more precursor substituents capable of reacting after transformation with a biological molecule and chosen from the group consisting of NO 2 , N 2 + , (CH 2 ) n -CN, (CH 2 ) n -CHO, (CH 2 ) n -COOPr, Pr being a protective group, n being an integer between 0 and 10.
• the aromatic group comprises one or more substituents capable of reacting directly with functional organic molecules and chosen from the group consisting of NO 2 , (CH 2 ) n -CONH 2 , (CH 2 ) n -CN, (CH 2 ) n -CHO, (CH 2 ) n -COOH, (CH 2 ) n - CH 2 OH, (CH 2 ) n -NH 2 , n being an integer between 0 and 10, SO 2 H, SO 3 H, SO 2 R, SO 3 R, R being an aliphatic or aromatic carbon chain from 1 to 20 carbon atoms, or one or more precursor substituents capable of reacting after transformation with functional organic molecules and chosen from the group consisting of NO 2 , (CH 2 ) n -CONH 2 , (CH 2 ) n -COOPr, Pr being a protective group, (CH 2 ) n -NHP'r, (CH 2 ) n -N (P
• diazonium salts will be identified by their number, as indicated as above.
• the metal is chosen from pure metals or alloys, and in particular iron, nickel, platinum, gold, copper, zinc, cobalt, titanium, chromium, silver, stainless steels, titanium alloys, cobalt chromium alloys, molybdenum, manganese, vanadium.
• a process which consists in fixing an aromatic group on the surface of this material, by electrochemical reduction of a diazonium salt comprising this aromatic group, by bringing the material into contact metallic with a solution of the diazonium salt in a solvent and by negatively polarizing the metallic material with respect to an anode also in contact with the solution of the diazonium salt, the anode and the cathode possibly being separable one of the other, for example by a diaphragm or a membrane.
• grafting aryl groups on carbon carbon-carbon bonds are obtained which are the usual bonds of organic chemistry.
• diazonium salts are based on the fact that they are more easily reducible than the radical to which they give rise. According to the invention, it is therefore necessary that the reduction potential of the diazonium salt used is less negative than the reduction potential of the free radical Ar * corresponding to the aromatic group of this diazonium salt.
• the anode and the cathode are not separated.
• the anode the cathode immerse in the solution containing the diazonium salt.
• Two electrodes are enough to work in intentiostatic mode.
• a reference electrode must be added immersing in the same solution if working in potentiostatic mode.
• the anode and the cathode are separated, for example by a diaphragm or a membrane.
• the invention also relates to a method in which the electrochemical reduction takes place in the presence of an electrolyte, the anode and cathode compartment being optionally separated, the anode compartment comprising the solvent and the electrolyte, the cathode compartment comprising the solvent, the electrolyte and diazonium salt.
• the electrochemical reduction can take place in the presence of an electrolyte.
• the anode and the cathode may not be separated. Both immersed in the solution. Two electrodes are sufficient in intentiostatic mode. A reference electrode must be added in potentiostatic mode. According to another embodiment of the invention, the anode and the cathode can be separated, by a membrane or a diaphragm. Two electrodes are sufficient in intentiostatic mode. On the other hand, in potentiostatic mode, it is necessary to add a reference electrode in the cathode compartment.
• the diazonium salt corresponds to the formula ArN 2 + X " , in which Ar represents the aromatic group and X represents an anion and in that this diazonium salt has a reduction potential less negative than the reduction potential of the free radical Ar ° corresponding to the aromatic group of the diazonium salt, the anion X " of the diazonium salt being advantageously chosen from halogens, sulfates, phosphates, perchlorates, tetrafluoroborates, carboxylates, hexafluorophosphates.
• the reduction is carried out by repetitive cyclic voltammetry in a potential range where the diazonium salts are reduced or by electrolysis to a more negative potential than the reduction potential of the salt of diazonium, or constant current (intentiostatic mode).
• the reduction of the diazonium salt is carried out by repetitive cyclic voltammetry in a potential range where the diazonium salts are reduced
• the cathode potential is then placed at the level of the reduction wave of the diazonium salt or at a more negative potential than the potential of the reduction wave of the diazonium salt.
• the electrolysis current is fixed at a value such that only the diazonium salt is reduced.
• the concentration of diazonium salts is between 10 "3 and 10 " 'mol / 1.
• the aromatic diazonium salt is substituted by a nitro radical and the electrochemical reduction is maintained until the nitro radical is reduced to the amino radical in the acidic aqueous medium.
• the electrochemical reduction of the diazonium salt takes place in an aprotic solvent, in particular chosen from the group comprising acetonitrile, dimethylformamide, dimethylsulfoxide and benzonitrile.
• the solution of the diazonium salt comprises a support electrolyte consisting of a quaternary ammonium salt or a lithium salt, in particular a tetralkylammonium tetrafluoborate.
• the electrochemical reduction of the organic diazonium salt can take place in a protic solvent in an acid medium.
• the protic solvent is chosen from the group consisting of water, methanol, ethanol or their mixtures, or in that the protic solvent is in admixture with an aprotic solvent being it is understood that the resulting mixture has the characteristics of a protic solvent.
• the acid is chosen from sulfuric, hydrochloric, nitric, nitrous, phosphoric or tetrafluoroboric acids.
• the pH of the solution is less than 2.
• the invention also relates to a metallic material as obtained by implementing the method described above.
• the metallic material according to the invention can be characterized in that the bond between its surface and the aromatic groups which modify it is such that, when an anodic scanning is carried out from the corrosion potential of the metal forming the surface of the material metallic, there is at least one potential responsible for dissolving a detectable amount of the above metal but which does not destroy the above bond.
• the metallic material according to the invention can also be characterized by the fact that the nature of the bond between its surface and the aromatic groups which modify it is such that, when an anode sweep is applied ranging from the corrosion potential to a more anodic of approximately 75 mV, to the metallic material whose surface is modified, there is no rupture of the above-mentioned bond, but dissolution of a detectable quantity of the metal forming the surface of the metallic material.
• the diazonium salt is either prepared independently and before its addition, in a reactor, with a view to modifying the surface of the metallic material, or is is prepared in situ, by bringing together, in a reactor, the components necessary for its formation, according to the conventional methods of the prior art.
• the invention also relates to any use of the metallic materials defined above and in particular the following uses:
• bone morphogenic protein (Bone Morphogenic Protein) capable of stimulating bone growth.
• FIGS. 2a, 2b Cyclic voltammogram of a) an iron electrode modified by anthraquinone groups and transferred to an ACN + 0.1 M NB 11 4BF4 solution and b) an iron electrode in an ACN + 0.1 M NB114BF4 + 3 mM an t hraquinone solution.
• v 0.2 V / s. DHW reference.
• Figures 6a, 6b, 6c, 6d XPS spectra of: a) a clean mild steel plate, b) a mild steel plate grafted with 4-nitrophenyl groups, c) with 4-carboxyphenyl groups and d) with 4-iodophenyl groups.
• FIG. 7 Impedance diagram in H2SO4 0.1N of a) an iron electrode and b) an iron electrode modified by 4-hexadecyloxyphenyl groups.
• FIGS 9a, 9b Noltamogram in AC ⁇ + O.IM ⁇ B114BF4 a) of a carbon electrode in the presence of nitrobenzene, b) of a grafted zinc electrode (in ACN +
• DHW reference, v 0.2 V / s
• FIGS. 13a, 13b Cyclic voltammetry of a cobalt electrode a) in an ACN + 0.1M solution NBU4BF4 b) after grafting the electrode (in ACN + 0.1M
• DHW reference, v 0.2 V / s
• Figures 15a, 15b, 15c Cyclic voltammetry on a platinum electrode in an ACN + O solution.
• FIGS 17a, 17b, 17c Cyclic voltammetry on a stainless steel electrode in an ACN + O.IM solution NBu 4 BF 4j a) in the presence of 4-nitrobenzenediazonium tetrafluoroborate 1, b) after grafting the electrode (in ACN + O.IM
• the AC ⁇ comes from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2SO4 from Merck (Uvasol), H2
• Diazonium salts 1 and 11 are of commercial origin (Aldrich), the synthesis of 3 has been described [1 c J; 2, 3-6, 9, 10 were obtained from commercial amines by standard methods. [27]. Diazonium salts are stored in the refrigerator.
• the electrodes were prepared from metal wire for example, 1mm diameter wire (Johnson-Matthey 99.99%) sealed in epoxy resin or from 3mm diameter soft iron buttons held in a clamp in Teflon. Mild steel plates (containing Fe: 95.68%; C: 0.31%; Mn: 2.03%; P: 0.05%; S:
• Electrochemical equipment The electrochemical curves were obtained using a potentiostat built in the laboratory or a Versastat II system from EGG.
• Electrochemical evidence of grafting The grafting reaction was studied both in an aprotic medium [Acetonitrile (ACN) + 0.1 M NB114BF4] and in an acidic aqueous medium (the diazonium salts are not stable in an aqueous medium above pH 2).
• an iron electrode has an electroactivity range which is between -0.1 and -2.3V / ECS; in dilute sulfuric acid (0.1 N) this domain is reduced to nothing.
• the open circuit potential (corrosion potential) t 10 J is located at -0.58 V / DHW; it corresponds to a mixed potential since the reduction and oxidation reactions are different.
• the anodic or cathodic partial current which circulates at this potential is called the corrosion current (I CO rr) -
• the corrosion current of iron predominates whereas it is the reduction protons or oxygen which predominates when the potential is shifted to negative values t 1 1 ].
• the only general way of grafting aryl groups on the surface of the iron is to fix the potential at a value more negative than -0.5 V / ECS in a solution containing the diazonium salt and at a value close to the potential.
• corrosion in H2SO4 0.1N (we will see later that it is possible to determine an optimal potential of -0.75 V / DHW in this solvent). In doing so, it is assumed that the diazonium salts are reduced to neighboring potentials on carbon and on iron.
• the reduction potential of diazonium salts and the oxidation potential of iron in an aqueous medium makes the reduction of diazonium salts by iron thermodynamically possible.
• the first wave is reversible since an anode wave is observed at -1.00 V / DHW during the reverse sweep.
• FIGS 2a, 2b show the results obtained with the diazonium salt 11 which is a commercial diazonium salt of anthraquinone.
• an iron electrode modified by reduction of diazonium salt 11 to E -0.5 V / DHW in 0.1 N H2SO4, carefully rinsed and transferred to an ACN + 0.1 M solution NB114BF4 has a slightly reversible voltammogram (E pc ⁇ -0.9 V / DHW and E pa ⁇ -0.6 V / DHW) at E °
• Vibration spectra of the organic layer As in the case of organic monolayers on carbon, it is difficult to obtain infrared spectra of monolayers by reflection. However, this can be done by PMIRRAS
• the analysis shows that the grafting is homogeneous over the entire surface of the sample and remains stable under the ion beam.
• the optimal value of the potential is -0.75 V / DHW corresponding to a maximum surface concentration; at more positive potentials the grafting competes with the oxidation of the surface and with the reduction of the protons to more negative potentials.
• the surface concentrations will be discussed later.
• Photoelectron X (XPS) spectroscopy It should be noted that RBS and XPS spectroscopy are complementary surface analysis methods since the sampling depth of the first is about two orders of magnitude less than that of the second.
• Figures 6a, 6b, 6c, 6d show the full spectrum of a mild steel plate (Figure 6a) and plates grafted with 4-nitrophenyl (Figure 6b), 4-carboxyphenyl (Figure 6c) and 4- iodophenyl (Figure 6d). All these general spectra show the peaks C [i s ], O [i s ], F [2p] at energies of 285, 530 and 710 eV.
• Figure 6b clearly shows the grafting of diazonium salt 1 after electrochemical treatment. This grafting results in a clear increase in the relative intensity of the peak C [ls] and in a small peak at around 400eV.
• Capacity of the electrode The attachment of an organic layer to the surface of the electrode should decrease the capacity of this electrode by adding an additional insulating layer in series with the double layer. Capacity can be measured by an impedance method; we recorded the Nyquist diagram (Z ⁇ vs Z Re ) ( Figure 7). It is then possible from the maximum frequency to obtain C d [15]
• the capacity of a pure iron electrode 3mm in diameter in H2SO4 0.1N is 207 ⁇ F / cm 2 .
• Two methods can be used to measure the surface concentration of aryl groups. The first requires to measure (after a complete rinsing of the electrode and transfer of this one in ACN + O.IM solution NBU4BF4) the charge used to reduce the nitro group grafted to the surface (according to a monoelectronic transfer). This amounts to the integration of the voltammogram drawn using an electrode modified by 4-nitrophenyl groups.
• One of the difficulties of this method is that it requires the estimation of a baseline and the final potential of integration.
• the second method is based on the integration of the RBS spectra, in this case, it must be certain that only the grafted area of the electrode is included in the beam and that the surface is stable under the ion beam.
• the two methods provide values which are relative to the geometric surface (ie 1 cm 2 for a plate of 1 cm x 1 cm) of the electrode previously polished with diamond paste of 1 ⁇ m.
• the surface concentrations are higher than the values obtained in H2SO4 0.1N, this may be due to the oxidation of the surface in sulfuric acid which decreases the surface available for grafting aryl groups, or to hydrogen atoms formed on the surface or having penetrated into the metal [161 and which changing the properties of the surface would make the electrochemical reaction more difficult.
• the surface concentrations in Table 1 can be compared with those previously measured on carbon and in particular on HOPG (the geometric surface of which is very close to the real surface).
• the effect of the organic layer was estimated by measuring two parameters: the polarization resistance R-, and the corrosion current i cor
• the polarization resistances were obtained either from the slope of the curve obtained by anodically and cathodically scanning the potentials at 0.1 mV / s using the Stern and Geary ⁇ ' J method or from the impedance diagrams.
• the real and imaginary impedances were obtained from Nyquist diagrams (Z ⁇ as a function of Z Re for variable values of the signal frequency). These diagrams make it possible to obtain the polarization resistance at low frequency and the capacity at the maximum of Z ta [20,21] ( Figure 7).
• diazonium salts (5, 6, 7, 8) comprising long alkyl chains have been chosen such that the long chains provide a hydrophobic barrier which can limit the diffusion of oxygen and protons.
• compound 9 should constitute a very hydrophobic barrier.
• an anodic sweep of 75 mV corresponds to the consumption of 9.8 mC or 5 10 "8 moles of dissolved iron (which was verified by assaying the solution by atomic absorption spectroscopy This shows that during an anode sweep the organic groups are detached from the surface at the same time as iron atoms.
• the organic layer is not firmly grafted and can be removed in an ultrasonic tank, while the layer grafted according to the method of the invention resists.
• the metal surfaces (Fe, Ni, Pt) have also been covalently modified by electrochemical reduction of vinyl monomers such as acrylonitrile, methacrylonitrile or butenenitrile.
• Thin films of polymer ( ⁇ IO 50 nm) covalently bound to the surface have been carefully studied [24,25] e ⁇ [ ⁇ t s is a proven effective in protecting against corrosion. p6].
• the grafted layer is of the alkyl type
• the first carbon bonded to the metal is an aliphatic saturated carbon whereas according to the invention it is an aromatic carbon which is linked to metal.
• the two processes are very different; the process of the invention does not make it possible to graft an aliphatic carbon since the aliphatic diazonium salts are unstable and the process using vinyl monomers does not allow to graft an aromatic carbon.
• the invention makes it possible to graft unpolymerized monolayers while the organic layer obtained from vinyl monomers is necessarily a polymer; b) the process using vinyl monomers involves the use of a polymerizing monomer, whereas the invention makes it possible to preform the polymer (which allows all variations in structure), put it in solution and then attach it by chemical reaction on an organic layer previously grafted on the surface of the metal c) the invention makes it possible to preform a polymer having aminophenyl groups, transform these amino functions into diazonium salts and then graft the polymer thus functionalized which is impossible in the case the use of vinyl monomers.
• the organic films obtained by reduction of the diazonium salts therefore reduce the corrosion as seen in Table 2; they are stable and resist an anodic excursion of 75mV.
• Zinc grafting On this metal which is used in electrogalvanized mild steel sheets for automobiles, the grafting of compounds 1, 5, 10 has been studied. The first and the last are easily characterized while the diazonium salt 5 can provide hydrophobic protection of the metal against corrosion.
• Figures 8a, 8b, 8c show the voltamogram of anthracene (in ACN +
• FIG. 10a, 10b and 1a, 11b show a copper electrode in a solution of anthraquinone and nitrobenzene respectively and then the same electrode grafted with anthraquinone and nitrophenyl groups.
• the similarity of the potentials of the reversible systems testifies to the grafting of copper.
• FIGS. 12a, 12b similar to FIGS. 1a, 11b on copper show the grafting on a nickel surface (we observe on the grafted electrode a prevalence at a less negative potential than the wave of the 4-nitrophenyl group). The similarity of the potentials of the reversible systems indicates that on nickel, the grafting takes place.
• V / ECS can be confirmed by XPS as shown in Table 3: the nitrogen of the NO2 group at 406 eV is clearly observed, which increases in grazing incidence, which shows that it is outside the layer and the almost total disappearance of the platinum signal, masked by the organic layer.
• the XPS spectrum of the surface confirms the grafting of the surface by the 4-nitrophenyl groups.
• Table 4 XPS spectra of a titanium surface grafted with 4-nitrophenyl groups.
• Figures 17a, 17b, 17c similarly show the voltammogram of 1 on a 316 stainless steel electrode ( Figure 17a), 4-nitrophenyl groups grafted by electrolysis in ACN + 0.1M NB114BF4 + 2 mM 1 at -0.2 V / ECS ( Figure 17b) and nitrobenzene in the same solution ( Figure 17c).
• the XPS spectrum confirms the grafting.
• Figure 19 is obtained by sweeping the iron electrode between -0.6V and -1.8V in the presence of nitrobenzene (concentration 1 mM) in a solution of acetonitrile + bottom salt (0.1 MN 4 BuF 4 ). Twenty scans are then carried out between the same potentials. The process used is the same as that used to graft the diazonium salts.
• Figure 21B is obtained by sweeping the iron electrode between -0.6V and -1.6 V in the presence of p-nitrophenol (concentration 1 mM) in a solution of acetonitrile + bottom salt (0.1 MN 4 BuF 4 ) . Twenty scans are then carried out between the same potentials. The process used is the same as that used to graft the diazonium salts. ( Figure 21 A corresponds to the white of the electrode).

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