• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
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    • 专利摘要:
    Conversion layer generation procedure with corrosion resistance properties. The present invention refers to a process of forming conversion layers with corrosion resistance properties by thermally activated chemical reactions at high pressure for magnesium parts or powders or of a magnesium alloy, including pure or almost pure magnesium and all their combinations with other elements in any proportion, using a solution of one or more metal salts, one of them being, a rare earth salt in a deep eutectic solvent. (Machine-translation by Google Translate, not legally binding)
    公开号:ES2745873A1
    申请号:ES201830863
    申请日:2018-09-03
    公开日:2020-03-03
    发明作者:Diego Ignacio García；Del Campo Ana Conde；Vara María Angeles Arenas；González Juan José Damborenea；De La Rosa Silvia Morales；Martín José Miguel Campos
    申请人:Consejo Superior de Investigaciones Cientificas CSIC；
    IPC主号:
    专利说明:

    [0001]
    [0002] Conversion Layer Generation Procedure with Corrosion Resistance Properties
    [0003]
    [0004] The present invention relates to a process of forming conversion layers with corrosion resistance properties by high pressure thermally activated chemical reactions for parts or powder of magnesium or magnesium alloys, including pure or near-pure magnesium and all combinations thereof. with other elements in any proportion, using a solution of one or more metal salts, one of them being a rare earth salt in a deep eutectic solvent.
    [0005]
    [0006] BACKGROUND OF THE INVENTION
    [0007]
    [0008] Magnesium and its alloys have a high mechanical resistance and the lowest density among all metallic materials, which makes them very attractive. Unfortunately, its low resistance to corrosion and its high chemical reactivity have prevented its widespread use in many fields. The reason for the low corrosion resistance of magnesium and its alloys lies in two aspects: the oxide layer that forms naturally on the surface is not protective; and, it is very susceptible to galvanic corrosion caused by impurities or secondary phases of the alloys (such as Mg17Al12, AlMn, Al8Mn5, etc.). These limitations therefore make it necessary to modify its surface to improve the corrosion resistance of magnesium alloys.
    [0009]
    [0010] Conventionally, various techniques have been used for coating deposition-based magnesium alloys [CD Gu et al. Electroless Ni-P plating on AZ91D magnesium alloy from a sulfate solution, J. Alloys Compd., 391 (2005), pp. 104-109], anodized [GL Song et al., Corrosion mechanism and evaluation of anodized magnesium alloys, Corros. Sci., 85 (2014), pp. 126-140], superhydrophobic coatings [Q. Chu et al., Facile fabrication of a robust superhydrophobic surface on magnesium alloy, Colloids Surf. A, 443 (2014), pp. 118-122], sputtering [SK Wu et al., A study of rf-sputtered Al and Ni thin films on AZ91D magnesium alloy, Surf. Coat. Technol., 200 (2006), pp. 2769-2774] and chemical conversion. The latter is one of the most common methods of protection to increase the corrosion resistance of magnesium alloys. These conversion layers are grown by chemical treatment of the metal surface to produce a surface layer of fundamentally different types of oxides chemically bonded to the surface [JE Gray et al., Pmtective coatings on magnesium and its alloys — a critica! review, J. Alloys Compd., 336 (2002), pp. 88-113]. Traditional conversion coatings were based on hexavalent chromium compounds and have been widely used to protect magnesium alloys [P. Schmutz et al., Influence of Dichromate Ions on Corrosion Processes on Pure Magnesium, J. Electrochem. Soc. 2003 volume 150, issue 4, B99-B110]. However, growing safety concerns regarding highly toxic chromate-based compounds have motivated researchers and industries to develop chromate-free conversion coating methods such as tin-based [F. Zucchi, et al., Stannate and permanganate conversion coatings on AZ31 magnesium alloy, Corros. Sci., 49 (2007), pp. 4542 4552], zinc phosphate [LY Niu et al., A study and application of zinc phosphate coating on AZ91D magnesium alloy, Surf. Coat. Technol., 200 (2006), pp. 3021-3026] and, very promisingly, those based on rare earth elements [T. Takenaka, et al., Improvement of corrosion resistance of magnesium alloys by surface film with rare earth elements, Mater. Trans., 49 (2008), pp. 1071-1076; X. Jiang et al., Microstructure and corrosion resistance of Ce-V conversion coating on AZ31 magnesium alloy, Appl. Surf. Sci., 341 (2015), pp. 166-174].
    [0011]
    [0012] The typical process for the production of conversion layers of rare earth elements to magnesium or magnesium alloys consists of immersing the parts in an aqueous solution of a rare earth element salt, typically Ce (NO3) 3 or CeCl3, for a prolonged time of several minutes or hours that can be shortened by raising the temperature of the solution or adding an oxidant, typically H2O2, that accelerates the oxidation and precipitation of cerium oxides or compounds. The growth of the conversion layer is closely related to the pH changes that occur in the metal substrate during immersion in the conversion bath and to the formation of cerium compounds with different states of valence. The steps that take place during the formation of the conversion layer in a conventional aqueous medium are the following [MF Montemor et al., Characterization of rare-earth conversion films formed on the AZ31 magnesium alloy and its relation with corrosion protection, Appl. Surf. Sci., 253 (2007), p.6922]:
    [0013] • Dissolution of the native oxide layer, accompanied by the formation of hydroxyl ions and an increase in pH.
    [0014] • Growth of the first layers composed of Ce (IV) and Ce (III) hydroxides, mixed with Mg hydroxides
    [0015] • Thickening of the surface film and slowing down of the increase in pH that lead to the preferential deposition of Ce (OH) 4 and its conversion into CeO2, forming an outer layer, richer in Ce (IV) species.
    [0016]
    [0017] In aqueous media, the growth of the first layers and the subsequent thickening of the film are favored in CeCl3 solutions. This behavior suggests that chloride ions induce a faster surface attack and pH increase compared to the action of other salt anions [M.F. Montemor et al., Composition and corrosion resistance of cerium conversion films on the AZ31 magnesium alloy and its relation to the salt anion, Applied Surface Science, Volume 254, Issue 6, 2008, Pages 1806-1814].
    [0018]
    [0019] The processes for obtaining conversion layers with rare earths on magnesium or its alloys in aqueous media are very inefficient and the thicknesses obtained are very limited, on the order of nanometers.
    [0020]
    [0021] Ionic Liquid (IL) refers to a class of organic salts that are entirely composed of ions. Due to its organic nature, typically at least one of the cations or anions has a bulky and asymmetric structure that prevents strong interaction between ions [M. Armand et al. lonic-liquid materials for the electrochemical challenges of the future. Nature Materials 8 (2009) 621-629]. Unlike sodium chloride, which melts at elevated temperature (800 ° C) ILs can exist in a liquid state at temperatures below 100 ° C. A particular class of IL with a melting point below 25 ° C is called Ionic Liquids at Room Temperature (RTIL). Because ILs are composed solely of ions, they have very interesting properties compared to water or other solvents such as having low melting points, very low volatility (negligible vapor pressure), good thermal stability, and high ionic conductivity. , which makes them ideal electrolytes for many applications.
    [0022] Recent work has demonstrated new applications of IL, including protection against reactive metal corrosion, the benefits of which lie in the intrinsic properties of IL. Almost all of the initial work involving IL treatments for corrosion protection focused on trihexyl (tetradecyl) phosphonium bis (trifluoromethylsulfonyl) amide ([P6,6,6,14] [NTf2]) IL, due to its commercial availability and its advantageous electrochemical properties, using a simple immersion treatment. Subsequently, and as new ILs were synthesized, numerous works have been carried out using various anions and processes to accelerate the formation of the conversion layer by increasing the temperature, the treatment time, the percentage of water in the IL or the application of anode potentials. Among them all, the fluorinated and organophosphate ILs the mentioned trihexyl (tetradecyl) phosphonium bis (trifluoromethylsulfonyl) amide ([P6,6,6,14] [NTf2] and the trihexyl (tetradecyl) phosphonium diphenyl phosphate [P6,6,6 , 14] [dpp]) are among the best performing. These studies have also shown that there is a critical treatment time, as long treatment times often lead to thick, cracked and poorly protective films. The presence of equilibrium amounts of water with the IL and the treatment at 50 ° C improved the quality and the corrosion protection of the generated film [P. Huang et al. A review of ionic liquid surface film formation on Mg and its alloys for improved corrosion performance, Electrochimica Acta, Volume 110, 2013, pages 501-510].
    [0023]
    [0024] Particularly interesting is the proposal to increase the process temperature to reach the decomposition temperature of IL [US9435033B2]. The method involves contacting the magnesium-containing surface with an ionic liquid under conditions that result in decomposition of the ionic liquid to produce a conversion layer on the magnesium or magnesium alloy with a significant improvement in resistance to corrosion. The temperatures for the degradation of the ionic liquid are between, at least, 100 ° C and 300 ° C. For example, the conversion layer can be obtained by applying a layer of the ionic liquid tetraoctylammonium bis (2-ethylhexyl) phosphate [N8888] [DEHP] on the surface of the sample and then heat treating the sample at 300 ° C in an oven for 7 minutes. The conversion layer has a thickness of 80-100 nm and is composed of elements of the magnesium alloy, oxides and phosphates.
    [0025] A method similar to that previously described has been recently proposed, but performing the treatment in deep eutectic solvents (DES). Unlike conventional ILs, DESs are commonly defined as systems composed of a mixture of at least two components, a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD), which are capable of self-associating to form a new eutectic phase characterized by a melting point (below 100 ° C) lower than that of each individual component. These constituent components of DES must also have safe, low-toxicity, renewable and biodegradable characteristics, as well as a significantly lower cost than ILs. The number of possible combinations of HBA and HBD that can form eutectic mixtures is extremely high, and to rationalize the properties and behavior of these solvents, classification into four types of DES has been often considered according to the two components that make it up: Type I (quaternary salt and metal halide), Type II (quaternary salt and hydrated metal halide), Type III (quaternary salt and hydrogen bond donor) and type IV (metal halide and hydrogen bond donor) [LIN Tomé et al., Deep eutectic solvents for the production and application of new materials, Applied Materials Today, Volume 10, 2018, Pages 30-50].
    [0026]
    [0027] Said proposed process for the formation of conversion layers with DES on magnesium alloys is based on the interaction of a deep eutectic solvent (DES) with the substrate. Upon heating, the choline chloride / urea mixture-based DES reacts with the magnesium alloy surface to form a promising anticorrosion conversion film. The chemical conversion film is mainly composed of the MgH2 and MgCO3 phases. Electrochemical tests and visual inspections indicated that the corrosion resistance of the magnesium alloy was enhanced by the presence of a conversion coating [Gu et al., Corrosion resistance of AZ31B magnesium alloy with a conversion coating produced from a choline chloride — Urea based deep eutectic solvent, Corrosion Science 106, May 2016, Pages 108-116].
    [0028]
    [0029] As an alternative to its application to generate coatings or conversion layers, different hydrothermal synthesis processes [M. Hirano et al., Hydrothermal Synthesis of Nanocrystalline Cerium ( IV) Oxide Powders, Journal of the American Ceramic Society 82, 3, (1999) pp 786-788], solvothermic [RI Walton, Solvothermal synthesis of cerium oxides, Progress in Crystal Growth and Characterization of Materials, Volume 57, Issue 4, 2011, Pages 93-108] and more recently, ionotherms in ionic liquids [T. Brezesinski et al. , Mesostructured crystalline ceria with a bimodal pore system using block copolymers and ionic liquids as rational templates, Chem Mater, 17 (2005), p. 1683] and in deep eutectic solvents [Hammond et al., Deep eutectic-solvothermal synthesis of nanostructured ceria, Nature Communications volume 8, Article number: 14150 (2017)], have proposed routes for the generation of Ce oxide nano crystalline powder (IV), CeO2, for various applications. In all of these synthesis processes, including recent DES work, the cerium or rare earth precursor usually in the form of chloride, sulfate, or nitrate dissolves in the solvent (water, an organic solvent, an IL, or a DES) and is raise the temperature and pressure until nanometric crystals of CeO2 or some cerium compound are precipitated, which is subsequently calcined in an oven to form CeO2.
    [0030]
    [0031] DETAILED DESCRIPTION OF THE INVENTION
    [0032]
    [0033] The present invention relates to a method of generating conversion layers with, mainly, corrosion resistance properties on the surface of magnesium or magnesium alloys characterized in that it comprises immersing said magnesium or said magnesium alloy, in any geometric shape including in powder form of any particle size, in a non-aqueous solution consisting of one or more metal salts, one of which is a rare earth element salt, at a temperature equal to or greater than 100 ° C in a reactor high pressure, preferably at pressures between 1 and 30 atmospheres.
    [0034]
    [0035] Said dissolution includes:
    [0036] - a deep eutectic solvent of the general formula Cat + X-zY, where Cat + is an organic cation such as ammonium, sulfonium or phosphonium and X - is a Lewis base, generally a halide anion of the salt, Y is a Lewis base or Bronsted, and z is the number of molecules of Y,
    [0037] - one or more metallic salts of the metal or metals of general formula M + X -where M is the metal with which you want to form the conversion layer on the part and X - is the same halide anion of the deep eutectic solvent being minus one of the salts a salt of the elements known as rare earths (cerium, lanthanum, etc.)
    [0038] A sufficiently high temperature must be applied under conditions of high pressure and limited humidity for decomposition of the solution of the salt or metal salts in the deep eutectic solvent to occur, in turn reacting with the surface of the magnesium alloy forming a layer of metal oxides, oxy-carbonates and hydroxides of the metals present in the solution and of the metallic elements of the magnesium alloy themselves, obtaining conversion layers of homogeneous thickness and composition that have properties as good or even superior to those obtained by other procedures in for example corrosion protection applications of magnesium alloys or in manufacturing applications of oxide coated powders for catalysis applications.
    [0039]
    [0040] The metal salt selected from the rare earth elements may be present in a concentration of between 5-10.7 and 1.5 M, preferably in a concentration of between 0.01 and 1 M, and more preferably between 0.1 and 0.5 M.
    [0041] In the process of the invention, said rare earth inorganic salt can be a lanthanide or actinide element, preferably a halide salt of the chemical element Lanthanum or Cerium, and more preferably CeCl3.
    [0042]
    [0043] The process can be performed with only said salt of a rare earth element or in a mixture of said salt with other metallic salts. The selected inorganic metal salt may be present in a concentration of between 5-10.7 and 1.5M, preferably in a concentration of between 0.01 and 1M, and more preferably between 0.1 and 0.5M.
    [0044]
    [0045] The metal salt may be of a metal selected from the alkali, alkaline earth, or transition metals, or a salt of another lanthanide or actinide element, and preferably a halide salt of a transition metal.
    [0046]
    [0047] In the process of the invention, the DES deep eutectic solvent where the metal salts are dissolved is a mixture of at least two components, a hydrogen bridge bond acceptor compound (HBA) and a hydrogen bridge bond donor compound ( HBD) that form a new phase eutectic with a melting temperature lower than the melting temperature of both compounds and in turn lower than 100 ° C or even lower than 25 ° C.
    [0048]
    [0049] The deep eutectic solvent of the process of the invention can be described with the general formula Cat + X "zY, where Cat + is the cation of any ammonium, sulfonium or phosphonium salt (ammonium, sulfonium, or phosphonium) and X - is a base of Lewis, generally a halide anion of the salt, Y is a Lewis or Bronsted base, and z is the number of molecules of Y. In the process of the invention the DES employed comprises a halide salt of a quaternary amine and an amide, carboxylic acid or alcohol as a donor of hydrogen bridge bonds, and preferably, the DES formed by choline chloride and urea as HBD and preferably, in a 1: 2 molar ratio to form the eutectic phase. Both components are safe, cheap and non-toxic.
    [0050] In the process of the invention DES is generated in the usual way by mechanically mixing the two elements (HBA and HBD) at a temperature between 50 and 80 ° C until the formation of the eutectic phase.
    [0051]
    [0052] In the process of the invention the rare earth element salt, together with the additional metal salt or salts, are added to the previously formed DES in anhydrous or hydrated form at room temperature or preferably at a temperature between room temperature and 100 ° C or more preferably between 50 and 80 ° C to accelerate dissolution.
    [0053]
    [0054] In the process of the invention, the solution formed by DES and the metal salt or salts are subjected to a vacuum drying process at a temperature between 50 and 80 ° C for at least 12 hours, preferably 24 hours or the time necessary to reach the minimum amount of dissolved water, and in any case less than 500 ppm.
    [0055]
    [0056] As indicated above, the procedure is applied to the surface of magnesium or magnesium alloys, which can occur:
    [0057] - in the form of a solid or porous piece with dimensions greater than one millimeter. - in the form of powder of any size between one millimeter and one nanometer.
    [0058] In a possible embodiment of the process of the invention, the part to be coated is chemically pure magnesium or magnesium with a purity greater than 99%. Alternatively, the part is made of a magnesium alloy.
    [0059]
    [0060] In some embodiments, the magnesium or magnesium alloy is subjected to a stage, prior to treatment with the dissolution of the metal salts in the DES, of roughing and / or sanding and / or polishing by mechanical means until a homogeneous surface is obtained and free from organic or inorganic contamination.
    [0061]
    [0062] In some embodiments, the magnesium or magnesium alloy is subjected to an acid pickling process, prior to treatment with dissolution of the metal salts in the DES. In this acid pickling step, the magnesium or magnesium alloy surface is contacted with one or more acids, which can be inorganic or organic acids. Some examples of inorganic pickling acids include hydrohalogenated acids (eg, HF, HCl, HBr, HI), nitric acid, sulfuric acid, and phosphoric acid. Some examples of organic pickling acids include carboxylic acids (eg, acetic or propionic acid and fluorinated versions, eg, trifluoroacetic acid) and sulfonic acids (eg, methylsulfonic or triflic acids). In further embodiments, an alkaline conditioning step may be employed after the acid pickling step and prior to treatment with dissolution of the metal salts in DES. In the alkaline conditioning step, the magnesium or magnesium alloy surface is contacted with one or more alkaline substances, typically in the form of an alkaline aqueous solution. Some examples of alkaline compounds that can be used in the alkaline conditioning step include metal hydroxides (eg, sodium hydroxide), carboxylate salts, metal carbonates, or bicarbonates (eg, sodium or bicarbonate carbonate), and amines. (for example, dimethyl or trimethylamine). In further embodiments, a surface activation step may be employed after the acid pickling or alkaline conditioning step and immediately prior to treatment with dissolution of the metal salts in DES. In the surface activation step, the magnesium or magnesium alloy surface is contacted with hydrohalogenated acids (eg, HF).
    [0063] In the process of the invention, the magnesium or magnesium alloy part or powder, previously subjected to the mechanical or chemical cleaning process, is introduced into a high pressure reactor with an internal Teflon coating and filled up to half its volume with the dissolution of the salt or metallic salts in the DES previously dried in vacuum until obtaining a humidity value of less than 500 ppm. The reactor is then closed and heated to a temperature at which decomposition of DES and metal salt or salts occurs, preferably at a temperature between 100 and 300 ° C, and more preferably between 150 and 180 ° C, and more preferably even at 160 ° C, for a time of between 1 and 12 hours, preferably between 1 and 6 hours, and more preferably between 2 and 3 hours.
    [0064]
    [0065] BRIEF DESCRIPTION OF THE FIGURES
    [0066]
    [0067] Figure 1 . Image obtained by a Scanning Electron Microscope of the surface of the piece of AZ31 treated in Example 1. a) x1000 magnification, b) x3000 magnification, c) x10000 magnification, d) x30000 magnification.
    [0068]
    [0069] Figure 2. Image obtained by a Scanning Electron Microscope of the surface of the piece of AZ31 treated in Example 1. a) x8000 increases, b) x5000 increases.
    [0070]
    [0071] Figure 3. Image and elemental composition obtained by a Scanning Electron Microscope of the surface of the piece of AZ31 treated in Example 1. a) image at x8000 magnifications with the relative profiles of composition obtained by X-ray Energy Dispersion Spectroscopy. EDX, b) carbon EDX profile, c) oxygen EDX profile, d) magnesium EDX profile, e) cerium EDX profile.
    [0072]
    [0073] Figure 4. X-ray diffraction diagram in incidence of grazing angle of the sample from Example 1.
    [0074]
    [0075] Figure 5. XPS spectra of the energy levels (a) C1s (b) Ce3d of the sample of example 1.
    [0076]
    [0077] Figure 6. Polarization curves in 1% NaCl by weight of an AZ31 sample treated according to Example 1 and an untreated AZ31 sample.
    [0078] Figure 7. Volume of hydrogen evolved during immersion in NaCI 1% by weight of a sample of AZ31 treated according to Example 1 and a sample of AZ31 untreated. Average values of 3 samples.
    [0079]
    [0080] Figure 8. Image obtained by a Scanning Electron Microscope of the surface of the piece of AZ31 treated in Example 3. a) x1000 increases, b) x3000 increases.
    [0081]
    [0082] Figure 9. EDX spectra obtained by a Scanning Electron Microscope of the surface of: a) the piece of AZ31 treated in Example 1, b) the piece of AZ31 treated in Example 3.
    [0083]
    [0084] EXAMPLES
    [0085]
    [0086] Example 1.
    [0087] Conversion layer on a piece of AZ31 magnesium alloy obtained with a 0.1 M solution of CeCl3-7H2O in the DES choline-urea chloride.
    [0088] A 24mm diameter, 2mm thick disc of AZ31 magnesium alloy is subjected to a conventional solvent cleaning treatment with acetone for 5 minutes, manually roughened with # 2000 particle size SiC paper, rinsed with distilled water for about 2 minutes and with ethanol for 30 seconds.
    [0089]
    [0090] DES is prepared by mixing choline chloride, solid, with urea, solid, in the proportion of 1 mole of choline chloride with 2 moles of urea and heating it to 50 ° C while mechanically stirring until a liquid phase is formed. colorless chute urea chloride eutectic.
    [0091]
    [0092] 100 cm3 of the resulting DES are measured and 3.74 g of CeCl3 heptahydrate are added to obtain a solution with a concentration of 0.1M CeCl3 in the DES. The dissolution process is carried out at a temperature of 60 ° C with mechanical stirring until complete dissolution.
    [0093]
    [0094] The CeCl3 solution in the DES choline-urea chloride is heated at 80 ° C under vacuum <10 mbar for 24 hours to minimize, by means of selective evaporation, the water contained in the solution.
    [0095] The AZ31 disk is introduced into an internal Teflon-lined high pressure reactor with a capacity of approximately 100 cm3 and approximately 50 cm3 of the previously prepared solution of CeCl3 is poured into the DES of cholineurea chloride. The rector is hermetically closed and placed in an oven previously heated to 160 ° C. It is kept at 160 ° C for 2 hours. Remove from oven and cool with water to room temperature.
    [0096]
    [0097] The AZ31 disk is removed from the reactor and the remains of the CeCl3 solution in the choline-urea chloride DES are cleaned with distilled water and dried with warm air.
    [0098]
    [0099] After cleaning, the surface of the AZ31 disc has a homogeneous black-brown color. Figure 1 shows an image taken in a Scanning Electron Microscope MEB where it is observed that the surface is covered by a homogeneous layer that presents a network of cracks typical of the rare earth conversion layers on magnesium or aluminum alloys obtained by methods conventional in aqueous solutions.
    [0100]
    [0101] Figure 2 shows an image taken by MEB where it is observed that the coating obtained in AZ31 has approximately a thickness of 4 microns, substantially greater than the thickness obtained by conventional means in aqueous solutions. Cracks observed on the surface run through the entire coating. The microstructure of the coating is dense and there is a good bond with the AZ31 substrate.
    [0102]
    [0103] Figure 3 shows superimposed on image 2 the relative distribution of the chemical elements that make up the coating obtained by X-ray Energy Dispersion Spectroscopy in the MEB. It is observed that the coating is composed of Magnesium, Cerium, Oxygen and Carbon. The shallowest part of the coating is relatively richer in cerium and the inner part is richer in magnesium, demonstrating that a reaction has occurred between CeCl 3 and DES with the magnesium alloy surface itself.
    [0104] Figure 4 shows the X-ray Diffraction (XRD) diagram obtained by the angle of the sample. The coating is predominantly amorphous with three crystalline phases that can be identified as cerium, magnesium, and oxy-carbonate dioxide. cerium. Semiquantitatively, the composition of the crystalline phases is 66.3% cerium oxycarbonate, 25.8% magnesium and 8.1% cerium dioxide.
    [0105]
    [0106] The superficial analysis of the samples by means of X-ray photoelectron spectroscopy (XPS), shows that the cerium present on the surface is exclusively as Ce (III), while most of the carbon is in the form of carbonate (Figure 5 ).
    [0107]
    [0108] The results indicate that a homogeneous, dense and adherent coating approximately 4 microns thick, amorphous and nano crystalline, is obtained, composed mainly of cerium (III) oxy-carbonate.
    [0109]
    [0110] Example 2.
    [0111] Corrosion resistance properties in NaCl of an AZ31 magnesium alloy disc treated in Example 1.
    [0112]
    [0113] An AZ31 magnesium alloy disc treated following the method described in Example 1 herein was subjected to electrochemical measurements of corrosion resistance in an aggressive medium consisting of a 1% by weight solution of NaCl in distilled water. A conventional three-electrode cell was used for this type of electrochemical measurements, the disc treated according to Example 1 being the working electrode, a platinum wire the counter electrode and a silver / silver chloride electrode the reference electrode. After 900 s of immersion in the NaCl solution, a potential sweep was made from the open circuit potential to more anodic (positive) values collecting the current density. In another area of the disc treated according to Example 1, the same procedure was performed but scanning the potential from the open circuit potential towards more cathodic (negative) values. For reference, the same procedures were performed on a pretreated AZ31 alloy disc.
    [0114] Figure 6 shows the results of current density versus potential (polarization curves or power-dynamic curves) of a disc treated according to Example 1 and of an untreated AZ31 alloy disc. The corrosion potential of the sample treated according to Example 1 is observed to be more negative than that of the AZ31 alloy, -1.66 V vs REF and -1.52 V vs REF respectively. It is further observed that the corrosion density, taken as the extrapolated current density of the branch The cathodic corrosion potential is significantly lower in the AZ31 sample treated according to Example 1 compared to an AZ31 sample without treatment, 1.6 10-5 A / cm2 and 1,310-4 A / cm2 respectively. This implies that the corrosion rate of the AZ31 alloy is reduced by an order of magnitude thanks to the method described in Example 1 of this invention.
    [0115]
    [0116] However, magnesium and magnesium alloys are known to have an anomalous corrosion mechanism that does not allow a corrosion rate to be inferred directly in terms of loss of mass or thickness from the electrochemical values [A. Atrens et al., Review of Recent Developments in the Field of Magnesium Corrosion, Advanced Engineering Materials, vol 17, issue 4 (2015) pp 400-453]. Therefore, the method for measuring the evolution of hydrogen during immersion in a 1% by weight NaCl solution in distilled water was used. AZ31 disks treated by the process described in Example 1 of the present invention were immersed in the NaCl solution at room temperature and the evolved hydrogen was collected for a total of 72 hours. Figure 7 shows the volume of accumulated hydrogen formed by the corrosion process of untreated and treated AZ31 according to the method of example 1. It is observed how the hydrogen evolution is significantly less on the surface of the AZ31 alloy treated according to example 1 Since each mole of hydrogen formed by the corrosion reactions corresponds to one mole of metallic magnesium that has been oxidized, the values in figure 7 can be transformed into values of magnesium thickness lost by corrosion per year using the expression given by Atrens et to the. [TO. Atrens et al., Review of Recent Developments in the Field of Magnesium Corrosion, Advanced Engineering Materials, vol 17, issue 4 (2015) pp 400-453]. Therefore, it is concluded that the treatment described in Example 1 notably reduces the corrosion rate to 0.32 mm / year with respect to the value of 0.75 mm / year of the AZ31 alloy without treatment.
    [0117]
    [0118] Example 3.
    [0119] Conversion layer on a piece of AZ31 magnesium alloy obtained with a 0.1 M solution of CeCl3-7H2O and 0.1 M CaCl2 in the DES choline-urea chloride.
    [0120]
    [0121] An AZ31 magnesium alloy disc was treated following the method described in Example 1 herein except that 1.11 g of CaCl2 is added to the DES of choline chloride and urea to obtain a solution with a concentration of 0.1M of CeCl3 and 0.1M CaCl2 in DES. The dissolution process is carried out at a temperature of 60 ° C with mechanical stirring until complete dissolution.
    [0122]
    [0123] After treatment with the same parameters as Example 1, the AZ31 disk is removed from the reactor and the remains of the solution of CeCl 3 and CaCl 2 are cleaned in the DES choline-urea chloride with distilled water and dried with air tempered.
    [0124]
    [0125] Figure 8 shows an image taken in a Scanning Electron Microscope MEB where it is observed that the surface is covered by a homogeneous layer that presents a crack network typical of the rare earth conversion layers similar to that obtained following the procedure of the example 1 (figure 1).
    [0126]
    [0127] Figure 9 shows by comparison the results of X-ray Energy Dispersion Spectroscopy (EDX) in the MEB of the layer obtained on an AZ31 disc treated according to Example 1 and treated according to Example 3. It is observed that the coating obtained in Example 1 is composed of Magnesium, Aluminum, Cerium, Oxygen and Carbon, while the coating obtained in Example 3 also shows the presence of Calcium. This shows that there has also been a reaction between CaCl2 and DES with the very surface of the magnesium alloy through which Calcium has become part of the coating formed.
    [0128]
    [0129] The semi-quantitative composition of the coating of Example 1 obtained by EDX is (in atomic%) 60.5% Oxygen, 21.8% Carbon, 8.1% Cerium, 7.0% Magnesium, and 2.7% Aluminum. The semi-quantitative composition of the coating of Example 3 obtained by EDX is (in atomic%) 63.1% Oxygen, 21.6% Carbon, 11.6% Cerium, 1.9% Magnesium, 1.2% Aluminum, and 0, 6% Calcium.
    权利要求:
    Claims (26)
    [1]
    1. A method of generating conversion layers with corrosion resistance properties on a magnesium or magnesium alloy surface comprising a step of dipping a magnesium or magnesium alloy part or powder in a non-aqueous solution of at least one metallic salt, at a temperature equal to or greater than 100 ° C in a high pressure reactor, characterized in that said non-aqueous solution comprises:
    - a deep eutectic solvent of the general formula Cat + X-zY, where Cat + is the cation of any ammonium, sulfonium or phosphonium salt and X - is a Lewis base, preferably a halide anion of the salt, Y is a base of Lewis or Bronsted, and z is the number of molecules of Y,
    - at least one metal salt of general formula M + X - where M is the metal with which you want to form the conversion layer on the piece and X - is the same Lewis base, preferably the same halide anion of the deep eutectic solvent and M being a rare earth element.
    [2]
    2. The conversion layer generation process according to claim 1, characterized in that said deep eutectic solvent comprises a halide salt of a quaternary amine and an amide, carboxylic acid or alcohol.
    [3]
    3. Method for generating conversion layers according to any one of claims 1 or 2, characterized in that said DES is the one formed between choline chloride and urea in a 1: 2 molar ratio to form the eutectic phase.
    [4]
    4. Method for generating conversion layers according to any one of claims 1 to 3, characterized in that the salt of rare earth elements is a halide of a lanthanide or actinide element.
    [5]
    5. The method of generating conversion layers according to claim 4, characterized in that the salt of rare earth elements is a cerium or lanthanum halide.
    [6]
    6. The method of generating conversion layers according to claim 5, characterized in that the salt of rare earth elements is cerium chloride.
    [7]
    7. Method for generating conversion layers according to any one of claims 1 to 6, characterized in that in addition to the salt of a rare earth element, a halide salt of an alkaline element is added.
    [8]
    Process for generating conversion layers according to any one of claims 1 to 6, characterized in that in addition to the salt of a rare earth element, a halide salt of an alkaline-earth element is added.
    [9]
    9. A process for generating conversion layers according to any one of claims 1 to 6, characterized in that in addition to the salt of a rare earth element, a halide salt of a transition metal is added.
    [10]
    10. Method for generating conversion layers according to any one of claims 1 to 9, characterized in that the concentration of the rare earth element salt is between 0.01 and 1 M.
    [11]
    11. The method for generating conversion layers according to claim 10, characterized in that the concentration of the salt of the rare earth element is between 0.1 and 0.5 M.
    [12]
    12. Process for generating conversion layers according to any one of claims 1 to 11, characterized in that the concentration of the additional salt of halides of alkali, alkaline earth or transition metal elements is between 0.01 and 1 M.
    [13]
    13. The conversion layer generation process according to claim 12, characterized in that the concentration of the additional salts of alkali, alkaline earth elements or transition metal is between 0.1 and 0.5 M.
    [14]
    14. Process for generating conversion layers according to any one of claims 1 to 13, characterized in that decomposition of the solution of salts in the DES occurs and the reaction with the surface of magnesium or magnesium alloy to a temperature between 100 ° C and 300 ° C in a high pressure reactor.
    [15]
    15. The conversion layer generation process according to claim 14, characterized in that the decomposition of the solution of salts in the DES occurs and the reaction with the magnesium or magnesium alloy surface at a temperature between 150 and 180 ° C.
    [16]
    16. The conversion layer generation process according to claim 15, characterized in that the decomposition of the salt solution in the DES occurs and the reaction with the magnesium or magnesium alloy surface at a temperature of 160 ° C.
    [17]
    17. Process for generating conversion layers according to any one of claims 14 to 16, characterized in that the decomposition of the solution of salts in the DES occurs and the reaction with the surface of magnesium or magnesium alloy for a time reaction time between 1 and 12 hours.
    [18]
    18. Process for generating conversion layers according to claim 17, characterized in that the decomposition of the solution of salts in the DES occurs and the reaction with the magnesium or magnesium alloy surface during a reaction time between 2 and Three hours.
    [19]
    19. Method for generating conversion layers according to any one of claims 1 to 18, characterized in that the part to be coated is chemically pure magnesium or magnesium with a purity greater than 99%.
    [20]
    20. Method for generating conversion layers according to any one of claims 1 to 18, characterized in that the part to be coated is a magnesium alloy.
    [21]
    21. Method for generating conversion layers according to any one of claims 19 or 20, characterized in that the magnesium or the magnesium alloy is in the form of a solid or porous piece with dimensions greater than one millimeter.
    [22]
    22. Method for generating conversion layers according to any one of claims 19 or 20, characterized in that the magnesium or the alloy of Magnesium is in the form of a powder of any size between one millimeter and one nanometer.
    [23]
    23. Method for generating conversion layers according to any one of claims 1 to 22, characterized in that the magnesium or the magnesium alloy is previously subjected to a surface preparation by mechanical means until a clean and homogeneous surface is obtained.
    [24]
    24. Process for generating conversion layers according to any one of claims 1 to 22, characterized in that the magnesium or the magnesium alloy is previously subjected to cleaning and pickling in an acid bath.
    [25]
    25. Process for generating conversion layers according to any one of claims 1 to 22, characterized in that the magnesium or the magnesium alloy has been previously cleaned and pickled in an acid bath and conditioned in an alkaline bath.
    [26]
    26. Method for generating conversion layers according to any one of claims 23 to 25, characterized in that the magnesium or magnesium alloy, previously cleaned and mechanically or chemically pickled, is activated in hydrofluorinated acid.
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    同族专利:
    公开号 | 公开日
    ES2745873B2|2020-07-15|
    WO2020049199A1|2020-03-12|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US20150090369A1|2013-10-02|2015-04-02|Ut-Battelle, Llc|Corrosion prevention of magnesium surfaces via surface conversion treatments using ionic liquids|
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    PCT/ES2019/070569| WO2020049199A1|2018-09-03|2019-08-20|Method for generating conversion layers with corrosion-resistant properties|
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