JP7356705B2 - Rust prevention sheet and rust prevention method - Google Patents

Description

The present invention relates to a rust-preventing sheet with excellent rust-preventing ability, and a rust-preventing method using the rust-preventing sheet.

The main cause of metal deterioration is corrosion induced by chloride ions. Corrosion occurs when the passive film on the metal surface is destroyed by chloride ions, and the metal dissolves from inside as ions. Corrosion of reinforcing steel inside the concrete of a building is considered to be a serious problem because it can cause cracks and destruction of the building.

One possible way to deal with this problem is to remove chloride ions from the metal surface using a material that has a high binding capacity for chloride ions, that is, a chloride absorbent. Research has been conducted using various materials to remove chloride ions, and layered double hydroxide (LDH) is attracting attention as one of the materials.

A typical LDH has the formula [M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] ^x+ [A ^n- _x/n・yH ₂ O] ^x- (where M ²⁺ is a divalent metal cation , M ³⁺ represents a trivalent metal cation, and A ^n- represents an n-valent anion), and is a layered inorganic compound having an anion exchange ability. Since the hydroxide has a structure in which a part of the divalent metal cations (M ²⁺ ) are substituted with trivalent metal cations (M ³⁺ ) in a non-stoichiometric ratio, it is positively charged. Therefore, exchangeable anions (A ^{n -} ) can be taken in and retained between its own layers for charge compensation. Known uses include anion exchangers, catalysts, electrochemical sensors, and bioactive materials. Using this anion exchange ability, chloride ions can be absorbed between layers, so it is expected to be effective as a chloride absorbent.

For example, in Patent Documents 1 to 3, a surface treatment film is formed on the surface using a surface treatment composition in which an organic phosphoric acid compound and an inorganic phosphoric acid compound are added in a predetermined ratio to a specific titanium-based aqueous liquid, Furthermore, on top of that, a zinc-based or aluminum-based plated steel sheet is formed with an upper layer film made of a coating composition containing a solid lubricant consisting of a non-chromium rust preventive additive and a crystalline layered double hydroxide in a resin. Disclosed. Patent Document 4 and Patent Document 5 disclose that an anticorrosion primer containing an organic resin and at least one synthetic layered double hydroxide having an organic anion is applied directly onto a metal substrate, and then the anticorrosion primer is applied to a polymer coating. A method of making a film-forming anticorrosive coating is disclosed.

In these prior art, the layered double hydroxide was recognized as a solid lubricant component and was also used as a material that incorporates organic anions.

Conventional methods for synthesizing layered double hydroxides include the coprecipitation method, sol-gel method, urea method, hydrothermal method, and redeposition method, but these methods have limitations on substrates and crystallinity. It has disadvantages such as low Therefore, the present inventor has proposed a method using a liquid phase deposition method (LPD method) (Non-Patent Document 1). The LPD method is divided into two reactions: a ligand exchange reaction and a fluorine scavenging reaction. By adding aluminum or boric acid, which are fluorine scavengers, to a metal fluoro complex, a stable complex is formed with free fluorine ions. This method shifts the equilibrium of the phase exchange reaction toward the hydroxide precipitation side, and deposits metal hydroxide on the substrate. In the LPD method, a thin film is deposited uniformly and stably on the substrate surface, and can be synthesized only in a reaction vessel at room temperature and pressure.

JP2012-77368A Japanese Patent Application Publication No. 2012-77369 Japanese Patent Application Publication No. 2012-77370 Special Publication No. 2015-504448 Special Publication No. 2016-511300

H. Maki et al., ACS Appl. Master. Interfaces, 7, 17188 (2015)

As mentioned above, anticorrosive coatings containing layered double hydroxides have been known. However, general metal materials are painted after removing rust and then applying anti-rust paint. Anti-corrosion coating must be removed. On the other hand, if it takes a long time between removing the rust and applying the anti-rust paint, there is a risk of rust forming. Further, there is a demand for further improvement in rust prevention performance.
Therefore, the present invention provides a rust prevention sheet that can at least temporarily cover a metal material for rust prevention and has excellent rust prevention performance, and a rust prevention method using the rust prevention sheet. The purpose is to

The present inventor has conducted extensive research in order to solve the above problems. As a result, the present invention was completed by discovering that an extremely excellent rust-preventing effect can be exhibited by coating a metal material with a rust-preventing sheet containing a layered double hydroxide containing nitrite ions.
The present invention will be described below.

[1] Contains resin and layered double hydroxide,
A rust-preventing sheet characterized in that at least some of the anions contained in the layered double hydroxide are nitrite ions.
[2] The anticorrosive sheet according to [1] above, wherein the layered double hydroxide is represented by the following formula (I).
[M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] ^x+ [A ^n- _x/n・yH ₂ O] ^x- (I)
[In the formula, M ²⁺ represents a divalent metal cation, M ³⁺ represents a trivalent metal cation, A ^n- represents an n-valent anion, and at least a part of the n-valent anion is a nitrite ion. , x is in the range of 0.1 or more and 0.33 or less. ]
[3] The divalent metal cation is zinc ion, magnesium ion, calcium ion, copper ion, nickel (II) ion, cobalt (II) ion, iron (II) ion, manganese (II) ion, cadmium ion, lead. ions, and one or more divalent metal cations selected from strontium ions, and the trivalent metal cations include aluminum ions, bismuth ions, iron (III) ions, chromium ions, gallium ions, nickel (III) ions, The anticorrosive sheet according to [2] above, which is one or more trivalent metal cations selected from cobalt (III) ions, manganese (III) ions, vanadium ions, cerium ions, and lanthanum ions.
[4] The anticorrosive sheet according to any one of [1] to [3] above, wherein the resin is polyacrylic acid or a salt thereof.
[5] A rust prevention method comprising the step of coating at least a portion of the surface of a metal material to be rust-proofed with the rust-proof sheet according to any one of [1] to [4] above.

The layered double hydroxide contained in the rust-preventing sheet of the present invention is capable of taking in chloride ions, etc. that cause corrosion due to its anion exchange action, as well as nitrite ions, which are probably excellent in rust-preventing performance. Due to this action, it exhibits extremely excellent rust prevention performance. More specifically, when repainting a corroded area of metal, by applying the rust prevention sheet according to the present invention after polishing the corroded area, chloride ions, etc. remaining in the pitting corrosion can be removed by anion exchange action. It can be removed and exhibits excellent rust prevention effects. Moreover, at the time of repainting, the anticorrosive sheet according to the present invention can be easily removed. Further, according to the rust prevention method of the present invention, excellent rust prevention is achieved by coating the surface of a metal material with a rust prevention sheet that exhibits excellent rust prevention performance while producing a highly crystalline layered double hydroxide. The effect is demonstrated. Therefore, the present invention is industrially useful as a technique that can effectively suppress rusting of metal products.

Figure 1 shows as-dep. This is a SEM image of LDH. FIG. 2 shows as-dep. The results of elemental analysis of LDH by SEM-EDX line analysis are shown. FIG. 3 shows as-dep. The results of XRD measurement of LDH are shown. FIG. 4 shows as-dep. The XRD measurement results of LDH, OH ^- -LDH, and NO ₂ ^- -LDH and the interlayer distance in the (003) plane direction are shown. FIG. 5 is a schematic diagram of a three-electrode electrochemical measurement cell used to measure the corrosion-inhibiting effect of the corrosion-inhibiting sheet. FIG. 6 shows a representative example of Tafel plot obtained by electrochemical measurements.

The anticorrosion sheet of the present invention contains a resin and a layered double hydroxide.

The resin is not particularly limited as long as it forms the matrix of the anti-corrosion coating and can fix layered double hydroxide on the surface of the metal material to be anti-corrosion, such as acrylic resin, epoxy resin, urethane resin, polyalginic acid, Polyalkylene glycol and the like can be used.

Acrylic resins have excellent transparency, and some have excellent dispersibility in solvents. In addition to (meth)acrylic acid polymers, acrylic resins are copolymers of (meth)acrylic acid and itaconic acid, fumaric acid, crotonic acid, citraconic acid, vinyl sulfonic acid, (meth)allylsulfonic acid, etc. There may be. Furthermore, salts of poly(meth)acrylic acid such as sodium poly(meth)acrylate have excellent affinity with aqueous solvents. As the acrylic resin, polyacrylic acid or a salt thereof is preferable. Examples of the polyacrylate include sodium polyacrylate, in which all the carboxy groups may be in a salt state, or only some carboxy groups may be in a salt state.

Examples of the epoxy resin include various epoxy resins of bisphenol A type, bisphenol F type, phenoxy type, novolac type, aliphatic type, and glycidylamine type. Preferred epoxy resins include bisphenol A type and bisphenol F type epoxy resins, with bisphenol A type epoxy resins being particularly preferred. Particularly preferred phenolic resins include resol type phenolic resins.

Polyurethane resin is a reaction product of a polyisocyanate component and a polyol component, and has excellent adhesion to metal materials. In addition, polyalkylene glycols such as polyethylene glycol have a high affinity for water and water-miscible organic solvents, and are easy to form gel-like antirust sheets.

The resin preferably has a high affinity for water and water-miscible organic solvents. By increasing the proportion of the solvent in the rust preventive sheet according to the present invention using such a resin, it becomes possible to make the rust preventive sheet into a so-called gel-like state and improve its adhesion to the metal material to be rust prevented. From this point of view, acrylic resins, polyalginic acids, polyalkylene glycols, and the like are preferred. Furthermore, the rust-preventing sheet according to the present invention has excellent rust-preventing performance due to its absorption of chloride ions and nitrite ions, so it exhibits excellent rust-preventing effects even when it contains water. The water-miscible solvent mentioned above refers to an organic solvent that has a high affinity with water and is miscible with water without restriction, such as alcohol solvents such as methanol, ethanol, and isopropanol; polyhydric alcohol solvents such as ethylene glycol and glycerin. ; Examples include ketone solvents such as acetone and methyl ethyl ketone.

Water-soluble acrylic resin, polyalginic acid, polyalkylene glycol, etc. are crosslinked and insolubilized by ions of group 2 elements such as calcium and magnesium; polyvalent metal ions such as aluminum; and crosslinking agents such as boric acid to form gels. It is also possible to do so.

Layered double hydroxide is a compound that has a structure in which regular octahedral basic layers made of metal hydroxide and intermediate layers made of anions and water are alternately laminated, and the regular octahedral basic layer consists of metal ions It has a positive charge as a result of being replaced by a more multivalent metal ion, and to compensate for this charge, anions are incorporated into the intermediate layer to maintain electrical neutrality.

A general layered double hydroxide is represented by the following formula in which the divalent metal cation of the basic layer consisting of a divalent metal hydroxide is replaced with a trivalent metal cation. In general layered double hydroxides, trivalent metal cations can replace divalent metal cations up to a maximum molar ratio of divalent metal cations:trivalent metal cations=2:1.
[M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] ^x+ [A ^n- _x/n・yH ₂ O] ^x-
[In the formula, M ²⁺ represents a divalent metal cation, M ³⁺ represents a trivalent metal cation, A ^n- represents an n-valent anion, and x is in the range of 0.1 or more and 0.33 or less. be. ]

In addition, Mg-Al-Zr ⁴⁺ -based layered double hydroxides and Zn-Ti ⁴⁺ -based layered double hydroxides in which some or all of the trivalent metal cations are replaced with tetravalent metal cations are also known. .

Examples of the divalent metal cations include zinc ions, magnesium ions, calcium ions, copper ions, nickel (II) ions, cobalt (II) ions, iron (II) ions, manganese (II) ions, cadmium ions, and lead. ions, and one or more divalent metal cations selected from strontium ions, with preference given to one or more divalent metal cations selected from zinc ions, magnesium ions, calcium ions, and nickel (II) ions. .

The trivalent metal cations include aluminum ions, bismuth ions, iron (III) ions, chromium ions, gallium ions, nickel (III) ions, cobalt (III) ions, manganese (III) ions, vanadium ions, cerium ions, and lanthanum ions, and one or more trivalent metal cations selected from aluminum ions, chromium ions, cobalt (III) ions, manganese (III) ions, and vanadium ions. Metal cations are preferred, and aluminum ions and/or chromium ions are more preferred.

Examples of guest anions contained in the layered double hydroxide include OH ^- , F ^- , Cl ^- , Br ^- , NO ₃ ^- , CO ₃ ^2- , and SO ₄ ^2- , which are used in the present invention. The layered double hydroxide contains nitrite ion (NO ₂ ⁻ ) as a guest anion. Nitrite ions exhibit excellent anticorrosion performance, and it is thought that nitrite ions are released from layered double hydroxides and contribute to corrosion protection of metal materials.

When x is in the range of 0.1 or more and 0.33 or less, good ion exchange capacity tends to be imparted to the layered ascites oxide according to the present invention. As x, 0.15 or more and 0.25 or less are more preferable. Further, the ion exchange capacity, assuming that anions are exchanged to OH ^- , is preferably 1.0 mol/kg or more and 3.8 mol/kg or less. If the ion exchange capacity is 1.0 mol/kg or more, a sufficient amount of nitrite ions, which are important for rust prevention performance, can be contained through ion exchange, and if the ion exchange capacity is 3.8 mol/kg or less, it is caused by excessive anion exchange. Destabilization of layered ascites oxide can be more reliably suppressed. The ion exchange capacity is more preferably 1.6 mol/kg or more and 2.8 mol/kg or less.

The larger the negative charge density, that is, the smaller the ionic radius and the larger the negative charge, the easier it is to be incorporated into the layered double hydroxide. For example, while OH ^- and F ^- are easily incorporated, nitrite ions are relatively less likely to be incorporated into the layered double hydroxide. It can be said that it is difficult to be taken in. However, since the anticorrosion performance of nitrite ions is excellent, it is thought that the anticorrosion performance can be exhibited even in small amounts. Specifically, about 5 mmol or more and 50 mmol or less of nitrite ions may be contained per 1 g of the layered double hydroxide.

The amount of layered double hydroxide to be used may be adjusted as appropriate, and may be, for example, 0.1 times or more and 5 times or less by mass of the resin constituting the anticorrosion sheet. If the ratio is 0.1 times by mass or more, the rust preventive effect of the rust preventive sheet will be more reliably exhibited. On the other hand, if the ratio is 5 times by mass or less, falling off of the layered double hydroxide from the anticorrosion sheet can be more reliably suppressed. The ratio is preferably 0.2 times by mass or more, preferably 2 times by mass or less, and more preferably 1 times by mass or less.

Although the method for producing the layered double hydroxide according to the present invention is not particularly limited, it can be produced by, for example, a liquid phase precipitation method (LPD method). More specifically, by adding trivalent metal ions to a fluoride complex solution of divalent metal ions, a complex is formed between the fluoride ions and the trivalent metal ions, consuming the fluoride ions, and dissolving the divalent metal ions. The ligand bonded to the ion is exchanged from fluoride ion to hydroxide ion, and the hydroxide of the divalent metal ion is precipitated. At this time, some of the divalent metal ions are exchanged with trivalent metal ions, and the hydroxide as a whole takes on a positive charge, resulting in layered double hydroxide containing guest anions between the layered hydroxide layers. An oxide (LDH) is formed.

The reaction formula of the above mechanism when Ni ²⁺ is used as the divalent metal ion and Al ³⁺ is used as the trivalent metal ion is shown below.
[Ligand exchange reaction]
(NiF ₆ ) ^4- + 2H ₂ O ⇔ Ni(OH) ₂ + 6F ^- + 2H ⁺ ... Formula 1
[Fluorine scavenging reaction]
Al + 6HF ⇔ H ₃ AlF ₆ + 3/2H ₂ ... Formula 2

As shown in the above reaction formula, it is thought that by adding Al as a fluorine scavenger, free fluorine ions form a stable fluoride complex, so the equilibrium in Formula 1 shifts to the right and nickel hydroxide precipitates.

The ratio of divalent metal cations and trivalent metal cations in the solution is determined by considering the ratio of divalent metal cations and trivalent metal cations in the desired layered double hydroxide, and at the same time, is sufficient to form a complex with fluoride ions. It is preferable to determine the amount of trivalent metal cations in consideration of the amount of trivalent metal cations. For example, the ratio of trivalent metal ions to the total of divalent metal ions and trivalent metal ions in the above formula (I) is 20 mol% or more and 33 mol% or less. In addition to this ratio, the amount of trivalent metal ions to be used may be determined by taking into account sufficient capture of free ionic fluorine.

Further, a carrier may be added to the solution. Although a layered double hydroxide can be formed in the absence of a carrier, the particle size may be non-uniform, so it is preferable to use a carrier to grow crystals of the layered double hydroxide on the carrier. Examples of the carrier include alumina, ceria, zirconia, and ceria-zirconia composite oxide powder.

After the reaction, general post-treatment may be performed. For example, the produced layered double hydroxide may be filtered and washed with water or the like. In addition, in order to perform the subsequent ion exchange smoothly, the obtained layered double hydroxide may be precipitated in water as it is.

The guest anions contained in the LDH produced in the above reaction include hydroxide ions, fluoride ions, and counter anions constituting water-soluble salts of divalent metal cations and/or trivalent metal ions. Such counter anions include nitrate ions, chloride ions, sulfate ions, and the like. Therefore, guest anions may be unified by immersing LDH in an excess aqueous anion solution. Specifically, the generated LDH crystals may be collected by filtration, washed and dried, and then LDH may be immersed in an aqueous solution of a desired anion salt, and then filtered and washed again. In order to smoothly carry out the subsequent ion exchange, the obtained layered double hydroxide may be precipitated in water as it is.

Next, at least a portion of the guest anions are replaced with nitrite ions. Specifically, the layered double hydroxide may be immersed in an aqueous solution of a water-soluble salt of nitrite ions such as sodium nitrite, followed by filtering, washing, and drying. The content of nitrite ions can be measured by a conventional method. For example, when some of the hydroxide ions in a layered double hydroxide containing only hydroxide ions as guest anions are replaced with nitrite ions, a layered double hydroxide containing only hydroxide ions and nitrite ions The hydroxide ion content of the layered double hydroxide containing the hydroxide is measured by neutralization titration or the like, and the nitrite ion content is determined from the difference between the measured values.

Next, the obtained layered double hydroxide containing nitrite ions is mixed with a resin in a solvent. Examples of the solvent include water; alcohol solvents such as methanol, ethanol, and isopropanol; polyhydric alcohol solvents such as ethylene glycol and glycerin; ketone solvents such as acetone and methyl ethyl ketone; and mixed solvents of two or more of these solvents. .

The nitrite ion-containing layered double hydroxide may be mixed into a resin solution, dispersion, or gel. The ratio of the nitrite ion-containing layered double hydroxide may be adjusted as appropriate, and may be, for example, 0.05 times or more and 1 times the weight of the resin. When a resin solution or dispersion is used, a gel-like sheet may be obtained by distilling off the solvent.

It is known that layered double hydroxides can be prepared by the sol-gel method, coprecipitation method, etc. in addition to the liquid phase precipitation method described above (Julia Prince et al., Chem. Mater. ., Vol. 21, No. 24, pp. 5826-5835 (2009), etc.). These manufacturing methods may use precursor solutions containing organic substances or coexisting ions that are not included in the composition of the layered double hydroxide, but these may cause poor results. be. The reason for this is that organic molecules and coexisting ions that coexist during the reaction may distort the crystal structure or impede good crystal growth. However, the layered double hydroxide according to the present invention only needs to contain nitrite ions by ion exchange, and if there is no problem in maintaining the structure containing nitrite ions, the layered double hydroxide by these manufacturing methods may be used. Hydroxides may also be used.

The rust-preventing sheet according to the present invention exhibits a rust-preventing effect by coating at least a portion of the surface of a metal material to be rust-prevented. In the present invention, the term "sheet" refers to something that can exist independently, unlike a coating formed on the surface of a metal material. Therefore, in general, rust is removed from the surface of a metal material by polishing, etc., then an anti-rust paint is applied and then painted again. Oxidation begins the moment the rust is removed, and the longer it takes to apply the anti-corrosion paint, the worse the rust will become. Although it is possible to coat the surface of a metal material with an anti-rust coating before applying the anti-rust paint, it takes time and effort to remove it. Therefore, for example, if a rust-preventive coating layer is formed after polishing the surface of a metal material and before painting it, corrosion may occur during the removal process, or corrosion may occur on the rust-preventive coating layer. I'll have to paint it. Therefore, by removing rust from the surface of the metal material and then coating it with the rust prevention sheet according to the present invention, rust formation can be effectively suppressed. Rust sheets can be easily peeled off. Furthermore, since the rust preventive sheet according to the present invention can remove chloride ions, etc. present in pitting corrosion, metal materials are unlikely to rust even after the rust preventive sheet according to the present invention is peeled off. I can say that.

The metal material to which the anticorrosive sheet according to the present invention is applied is not particularly limited as long as rusting is a problem. For example, metal materials constituting the metal material include iron, zinc, aluminum, magnesium, copper, nickel, chromium, tin, and alloys thereof. Further, metal materials include not only metal products and metal parts, but also existing buildings made of metal materials.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the Examples below, and modifications may be made as appropriate within the scope of the spirit of the preceding and following. Of course, other implementations are also possible, and all of them are included within the technical scope of the present invention.

Example 1: Production of anticorrosion sheet (1) As-dep. by liquid phase precipitation method. Production of LDH Nickel (II) nitrate hexahydrate (Ni(NO ₃ ) _{2.6H 2} O, manufactured by Nacalai Tesque) was mixed with deionized distilled water (hereinafter referred to as "distilled water") at a concentration of approximately 20% by mass. After dissolving in nickel hydroxide, β-nickel hydroxide was precipitated by adding 20 vol% ammonia water and adjusting the pH to about 7.5. The generated precipitate was collected by suction filtration, washed, and then dissolved in a 10 mol/L hydrofluoric acid aqueous solution. This solution was used as a film-forming reaction mother liquor, and the Ni concentration in the mother liquor was determined using an ICP-AES spectrometer ("ULTIMA 2000" manufactured by Horiba, Ltd., hereinafter referred to as "ICP") to determine the concentration of the mother liquor.
A solution of aluminum nitrate nonahydrate (Al(NO ₃ ) ₃ ·9H ₃ O, manufactured by Nacalai Tesque) dissolved in distilled water at a concentration of 0.2 mol/L was used as a fluoride ion scavenger.
The above membrane forming reaction solution and 10 mol/L hydrofluoric acid aqueous solution were mixed so that [Ni ²⁺ ] = 12 mmol/L, [F ^- ] = 200 mmol/L, [Al ³⁺ ] = 2.0 mmol/L. After adding 10 mg of fumed alumina ("AEROXIDE ^(R) Alu130" manufactured by Nippon Aerosil Co., Ltd.) to the solution whose pH was adjusted to 8.20 by further adding 20 vol% ammonia water, the above Al(NO ₃ ) ₃ aqueous solution was added. was added to prepare a reaction solution. This reaction solution (100 mL) was reacted at 50° C. for 6 to 48 hours in a constant temperature bath. After the reaction, the produced precipitate was collected by filtration, washed, and dried, and the resultant product was called as-dep. It was set as LDH.

(2) Synthesis of NO ₂ ^- -LDH Distilled water was boiled for 15 minutes and cooled while bubbling with nitrogen to obtain degassed water. Potassium hydroxide (manufactured by Nacalai Tesque) was dissolved in degassed water at a concentration of about 6.0 mol/L to obtain a KOH aqueous solution.
under nitrogen atmosphere, as-dep. After anion exchange was performed by immersing LDH in a stirred approximately 6.0 mol/L aqueous KOH solution for 24 hours, the product was filtered, washed, and dried to obtain OH ^- -LDH.
Sodium nitrite (NaNO ₂ , manufactured by Nacalai Tesque) was dissolved in distilled water, and the Na concentration in the solution was determined by ICP and used as an aqueous NaNO ₂ solution.
After performing anion exchange by immersing OH ^- -LDH in a stirred approximately 1.0 mol/L NaNO ₂ aqueous solution or approximately 7.0 mol/L NaNO ₂ aqueous solution for 24 hours under a nitrogen atmosphere, it was collected by filtration, washed and After drying, NO ₂ ⁻ -LDH was obtained.

(3) Synthesis of sodium polyacrylate gel Sodium polyacrylate ((C ₃ H ₃ NaO ₂ ) _n , manufactured by Toagosei Co., Ltd., 1.14 g), glycerin (manufactured by Nacalai Tesque Co., Ltd., 5.7 g), and hydroxide Aluminum (Al(OH) ₃ , manufactured by Nacalai Tesque, 0.057 g) was mixed, and further tartaric acid ((CH(OH)COOH) ₂ , manufactured by Nacalai Tesque, 0.057 g) and distilled water (12.046 g) were mixed. By adding and mixing, a sodium polyacrylate gel was obtained. Furthermore, OH ^- -LDH or NO ₂ ^- -LDH (0.50 g) was added to obtain OH ^- -LDH gel and NO ₂ ^- -LDH gel.

Test Example 1: as-dep. Shape observation of LDH by SEM and elemental analysis by SEM-EDX As-dep. The shape of the LDH sample was observed using a field emission scanning electron microscope ("JSM-6335F" manufactured by JEOL Ltd., hereinafter abbreviated as "SEM"). The accelerating voltage of the electron beam was 15 kV, and in order to prevent charge-up on the sample surface, a carbon coater ("CC-40FM" manufactured by Meiwa Shoji Co., Ltd.) or a platinum coater ("SC-701" manufactured by Sanyu Denshi Co., Ltd.) was applied to the sample surface. was pre-coated with carbon or platinum. The results are shown in Figure 1.
In the liquid phase deposition method (LPD method), a stable fluoro complex is formed by adding a fluorine scavenger to an aqueous solution containing a metal fluoride complex, thereby shifting the equilibrium to the oxide side and depositing oxidation on the substrate. This is a film-forming method in which a thin film of a compound or oxyhydroxide is deposited and grown. The reaction by the LPD method is divided into a ligand exchange reaction and a fluorine trapping reaction, and the precipitation mechanism when Al is used as a fluoride ion trapping agent is proposed as shown in the following equation.
[Ligand exchange reaction]
(NiF ₆ ) ^4- + 2H ₂ O ⇔ Ni(OH) ₂ + 6F ^- + 2H ⁺ ... Formula 1
[Fluorine scavenging reaction]
Al + 6HF ⇔ H ₃ AlF ₆ + 3/2H ₂ ... Formula 2
It is believed that by adding Al as a fluorine scavenger, free fluorine ions form a stable fluoride complex, so that the equilibrium of Equation 1 shifts to the right, and a film of nickel hydroxide is deposited on the substrate. In the case of this experiment, part of the Al used as a fluorine scavenger replaced part of the Ni constituting the nickel hydroxide crystal, giving it a positive charge as a whole, resulting in a layered Ni-Al water crystal. It is thought that a layered double hydroxide containing a guest anion between the oxide layers was formed.
Figure 1 shows as-dep. A SEM image of LDH is shown. When the reaction time was 12 hours or more, a network structure peculiar to Ni-Al LDH was observed, and it was also confirmed that the longer the reaction time, the more the LDH particles grew.

In addition, using an energy dispersive X-ray spectrometer ("JED-2200" manufactured by JEOL Ltd., hereinafter abbreviated as "SEM-EDX"), as-dep. Elemental qualitative analysis of LDH samples was performed.
FIG. 2 shows as-dep. The results of elemental analysis of LDH by SEM-EDX line analysis are shown. These results confirmed that Ni element and Al element were present on the network-structured precipitate, and it became clear that this precipitate was Ni-Al LDH.

Test Example 2: As-dep. Quantification of LDH as-dep. A solution obtained by dissolving LDH in 0.1 mol/L nitric acid was quantified using an ICP-AES spectrometer ("ULTIMA2000 model" manufactured by HORIBA, hereinafter abbreviated as "ICP"), and the elements of Ni and Al were determined. The content ratio was determined. As concentration standard solutions, 1000 ppm nickel standard solution and aluminum standard solution (manufactured by Nacalai Tesque) diluted with distilled water were used.
As a result, the substitution rate of Al in the LDH formula [M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] ^x+ "A ^n- _x/n・yH ₂ O] ^x- is x=0.24 It became clear.

Test Example 3: Identification of sample by XRD measurement In order to analyze the surface of the synthesized Ni-Al LDH and calculate the interlayer distance, a fully automated multi-purpose horizontal X-ray diffraction device (“SmartLab” manufactured by Rigaku Corporation, hereinafter referred to as “XRD”) was used. X-ray diffraction measurements were performed using The apparatus settings were a tube voltage of 45 kV, a tube current of 200 mA, and a parallel method 2θ scan using a CuKα1 (λ=1.541 Å) ray as an X-ray source. The measurement conditions were θ=5° to 80°, scan speed 2.0°/min, and scan step 0.01°.
FIG. 3 shows as-dep. The results of XRD measurement of LDH are shown. Diffraction peaks were confirmed around 11.4°, 22.8°, 34.5°, 38.5°, 45.9°, 60.7°, and 61.9°, respectively, and the ( 003) plane, (006) plane, (012) plane, (015) plane, (018) plane, (101) plane, and (113) plane. This result also revealed that Ni--Al LDH was deposited on the fumed alumina.
FIG. 4 shows as-dep. The XRD measurement results of LDH, OH ^- -LDH, and NO ₂ ^- -LDH and the interlayer distance in the (003) plane direction are shown. Table 1 also shows the ionic radii of F ^- , OH ^- and NO ₂ ^- . Bragg's formula: 2dsinθ=nλ (d: lattice constant, θ: scattering angle, n: integer, λ: wavelength) was used to calculate the interlayer distance.

As shown in FIG. 4, as-dep. While the interlayer distance of LDH and OH ^- -LDH remained almost unchanged, the peak position of NO ₂ ^- -LDH shifted slightly to the left, confirming an increase in the interlayer distance. It was confirmed that this result was in good agreement with the ionic radii of F ^- , OH ^- and NO ₂ ^- shown in Table 1. This result also revealed that NO ₂ ^- was inserted between the layers of LDH.

Test Example 4: Determination of OH ^- concentration in each solution by neutralization titration After drying oxalic acid dihydrate ((COOH) _{2.2H 2} O, manufactured by Nacalai Tesque Co., Ltd.) at 120°C for 2 hours, distillation was performed. It was dissolved in water to prepare 0.5 mmol/L and 0.05 mol/L (COOH) ₂ aqueous solutions.
The KOH aqueous solution and the NaNO ₂ aqueous solution used in the anion exchange were subjected to neutralization titration using a (COOH) ₂ aqueous solution. By immersing in a KOH aqueous solution to perform anion exchange, first, F ^- , NO ₃ ^-, etc. that are thought to be contained between the layers are replaced with OH ^- , and then by immersing in a NaNO ₂ aqueous solution, OH ^- is replaced with NO ₂ ^- . The amount of substituted anions was measured by quantifying the amount of change in OH ^- concentration in the KOH aqueous solution and the NaNO ₂ aqueous solution.
As-dep. As a result of neutralization titration of the KOH aqueous solution after immersing LDH using a 0.05 mol/L (COOH) ₂ aqueous solution, it was confirmed that the OH ⁻ concentration in the KOH aqueous solution decreased before and after immersion. From this result, as-dep. It was revealed that 20 mmol of OH ^- per gram was inserted between the layers of LDH.
Next, as a result of neutralization titration of the NaNO ₂ aqueous solution after immersing the OH ^- -LDH using a 0.5 mmol/L (COOH) ₂ aqueous solution, it was found that the OH ^- concentration in the NaNO ₂ aqueous solution before and after immersion was It was confirmed that there was a decrease. From this result, when a 1 mol/L NaNO ₂ aqueous solution is used, 20 μmol of NO ₂ ^- is inserted per 1 g between the OH ^- -LDH layers, and when a 7 mol/L NaNO ₂ aqueous solution is used, 133 μmol of NO 2 - is inserted per 1 g. It became clear that NO ₂ ^- had been inserted.
Since the ionic radius of NO ₂ ^- is slightly larger than that of OH ^- , the charge density is also lower, and it is thought that it was difficult to insert between the layers compared to OH ^- .

Test Example 5: Electrochemical measurements (1) Preparation of KCl salt bridge Potassium chloride (manufactured by Nacalai Tesque) was dissolved in distilled water to obtain a saturated KCl aqueous solution.
Agar (for vegetable culture medium, manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in a saturated KCl aqueous solution and distilled water, mixed, poured into an acrylic tube, cooled, and used as a KCl salt bridge.

(2) Preparation of Pt Plate Electrode A mixture of sulfuric acid (H ₂ SO ₄ , manufactured by Nacalai Tesque) and hydrogen peroxide (manufactured by Nacalai Tesque) at a ratio of 3:1 was used as a piranha solution.
A 15 mm x 25 mm platinum plate was immersed in a piranha solution for 20 minutes and then washed. A copper wire was soldered to a cleaned platinum plate and adhered with an epoxy resin-based reactive adhesive, which was used as a Pt plate electrode.

(3) Preparation of Ag/AgCl electrode Potassium chloride (manufactured by Nacalai Tesque) was dissolved in distilled water at a concentration of 0.1 mol/L and used as a KCl aqueous solution.
Nitric acid (HNO ₃ , manufactured by Nacalai Tesque) was mixed with distilled water at a concentration of 1.0 mol/L and used as an aqueous HNO ₃ solution.
A 50 mm silver wire was soldered to a copper wire, washed by immersing it in an HNO ₃ aqueous solution for 1 minute, then covered with a glass tube and glued with an epoxy resin-based reactive adhesive, and a current of 1 mA was applied for 45 minutes in a KCl aqueous solution. By applying this method, an Ag/AgCl electrode was prepared.

(4) Electrochemical measurement In order to measure the corrosion inhibition effect of the obtained sample, a three-electrode electrochemical measurement cell was prepared and Linear Sweep measurement was performed. Specifically, as shown in FIG. 5, the reference electrode was Ag/AgCl, the working electrode was an Fe plate (manufactured by Nilaco, purity: 99.5%), the counter electrode was a Pt plate, and the electrolyte was the same as in Example 1. A saturated KCl aqueous solution was used for the reference electrode side of the rust preventive sheet, and a KCl salt bridge was used for the salt bridge. Before the measurement, an aqueous NaCl solution was added to the anticorrosive sheet to contain 3.5% by mass of NaCl. Further, a rust preventive sheet was molded so that the reaction area of the working electrode was 1 cm ² . "Compact Stat Plus" (manufactured by IVIUM) was used as a constant potential electrolysis device, and the scanning range was set to -1.0 V to 1.0 V, and the scan rate was set to 10 mV/s.
First, the spontaneous potential was measured over 600 seconds by transients measurement. Subsequently, Linear Sweep measurement was performed to sweep from the measured natural potential to -1.0V, then from -1.0V to +1.0V, and Tafel plot was performed. For comparison, a similar experiment was conducted using a sodium polyacrylate gel containing no LDH and containing 3.5% by mass of NaCl. A typical example of Tafel plot is shown in FIG. From this result, the corrosion potential E _corr and the corrosion current I _corr can be determined from the intersection of the straight line portion of the reduction current and the straight line portion of the oxidation current. Table 2 shows the corrosion current I _corr , corrosion potential E _corr , and pitting potential E _pit determined from the Tafel plot obtained for each sample. The pitting potential was determined from the potential at the end of the passive region of the Tafel plot.

According to the results shown in Table 2, the corrosion current is reduced when using a gel containing OH ^- -LDH or NO ₂ ^- -LDH compared to a sodium polyacrylate gel that does not contain LDH. It was revealed. In particular, in the case of NO ₂ ^- -LDH gel, a significant decrease in corrosion current was observed, confirming that it has a high corrosion inhibiting effect. Subsequently, the passive area, expressed as pitting potential-corrosion potential (E _pit -E _corr ), was increased nearly 10 times for the LDH-containing gel. This is considered to be the result of a decrease in the chloride ion concentration on the metal surface due to some of the chloride ions being incorporated into the LDH, making it difficult for passivation breakdown to occur. There is an increase in the passivation region especially for NO ₂ ^- -LDH, and this result can be attributed to the repassivation of iron by nitrite ions.
Furthermore, when comparing 1 mol/L NO ₂ ^- -LDH and 7 mol/L NO ₂ ^- -LDH, no significant change was observed. This is probably because even though the content of nitrite ions increased, the value itself was small, so the effect on the corrosion inhibition effect was small.
From the above, the corrosion inhibiting effect of LDH alone was confirmed, but it became clear that the insertion of nitrite ions had an even more corrosion inhibiting effect. Considering that nitrite ions are contained in only tens to hundreds of μmol in 1 g of LDH, it was confirmed that even a small amount of nitrite ions has a corrosion inhibiting effect.

Summary It was confirmed that it is possible to precipitate Ni-Al LDH on fumed alumina by the liquid phase precipitation method, and that the particles become larger as the reaction time increases.
In the synthesized Ni-Al LDH, it was confirmed that nitrite ions were inserted, albeit in small amounts, through anion exchange.
In addition, it was confirmed that LDH alone has a corrosion inhibiting effect, suggesting that it functions as a chloride absorbent, but the results show that further corrosion inhibition can be expected by inserting nitrite ions between the layers. Ta.

Claims (5)

a resin , a layered double hydroxide , and water or a water-miscible organic solvent and water ;
A gel-like rust-preventive sheet characterized in that the layered double hydroxide is represented by the following formula (I) .
[M ²⁺ _1-x M ³⁺ _x (OH) ₂ ] ^x+ [A ^n- _x/n ・yH ₂ O] ^x- (I)
[In the formula, M ²⁺ represents a divalent metal cation, M ³⁺ represents a trivalent metal cation, A ^n- represents an n-valent anion, and at least a part of the n-valent anion is a nitrite ion. , x is in the range of 0.1 or more and 0.33 or less. ] The divalent metal cations include zinc ions, magnesium ions, calcium ions, copper ions, nickel (II) ions, cobalt (II) ions, iron (II) ions, manganese (II) ions, cadmium ions, lead ions, and one or more divalent metal cations selected from strontium ions; the trivalent metal cations include aluminum ions, bismuth ions, iron (III) ions, chromium ions, gallium ions, nickel (III) ions, cobalt (III) ions; ) ion, manganese (III) ion, vanadium ion, cerium ion, and lanthanum ion. The gel- like anticorrosive sheet according to claim 1 or 2, wherein the resin is polyacrylic acid or a salt thereof , polyalginic acid, or polyalkylene glycol . The gel-like anticorrosion sheet according to any one of claims 1 to 3, wherein the ratio of the layered double hydroxide to the resin is 0.05 times or more and 1 times or less by mass. A rust prevention method comprising the step of coating at least a portion of the surface of a metal material to be rust-prevented with the gel -like rust prevention sheet according to any one of claims 1 to 4.

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