METHOD FOR SELF-REPAIRING OF DAMAGE TO INORGANIC PROTECTIVE LAYER ON METAL SURFACE

Abstract

Disclosed is a method for self-repairing of damage to an inorganic protective layer on a metal surface. The method includes: placing a metal with the inorganic protective layer having a damaged surface in a chloride ion solution, and performing self-repairing, wherein the metal with the inorganic protective layer comprises a metal substrate and a layered double hydroxide protective layer intercalated by acid anions covering a surface of the metal substrate; and the acid anions are selected from the group consisting of phosphate anions and molybdate anions.

Description

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to the Chinese Patent Application No. CN2023111553093, filed with the China National Intellectual Property Administration (CNIPA) on Sep. 7, 2023, and entitled “METHOD FOR SELF-REPAIRING OF DAMAGE TO INORGANIC PROTECTIVE LAYER ON METAL SURFACE”, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure belongs to the technical field of self-repairing of materials, and specifically relates to a method for self-repairing of damage to an inorganic protective layer on a metal surface.

BACKGROUND

Reinforced concrete has been widely used in the field of civil engineering due to that rebar has good mechanical properties and can be effectively combined with concrete. However, rebar has very poor corrosion resistance, and the corrosion of rebar seriously affects the use of infrastructure and national economic development in China.

Layered double hydroxide (LDH) as an inorganic material is a promising material in the field of metal corrosion prevention due to its good physical barrier properties and exchangeability characteristics of interlayer anions. However, with the prolongation of the service time, once the layered double hydroxide on the metal surface is damaged, it is difficult to play the effect of corrosion prevention on the metal, which makes the time limit of metal corrosion prevention shorter.

SUMMARY

An object of the present disclosure is to provide a method for self-repairing of damage to an inorganic protective layer on a metal surface, which realizes self-repairing of damaged inorganic protective layer on the metal surface and improves the time limit of the metal corrosion protection.

In order to realize the above object, the present disclosure provides the following technical solutions:

The present disclosure provides a method for self-repairing of damage to an inorganic protective layer on a metal surface, including:

• • placing a metal with the inorganic protective layer having a damaged surface in a chloride ion solution, and performing self-repairing;
  • wherein the metal with the inorganic protective layer includes a metal substrate and a layered double hydroxide (LDH) protective layer intercalated by acid anions covering a surface of the metal substrate; and the acid anions are selected from the group consisting of phosphate anions and molybdate anions.

In some embodiments, the metal substrate includes one selected from the group consisting of steel material, zinc material, magnesium material, aluminum material, and copper material.

In some embodiments, the layered double hydroxide protective layer intercalated by acid anions has a thickness of less than or equal to 50 micrometers.

In some embodiments, the metal with the inorganic protective layer is prepared by a process including the following steps:

• • mixing a first divalent metal salt, aluminium nitrate and water to obtain a mixed solution;
  • taking the mixed solution as a deposition solution, constructing a three-electrode system with a metal substrate as a working electrode, and performing electrodeposition with the three-electrode system to obtain a post-deposition metal substrate;
  • mixing a second divalent metal salt, aluminium nitrate, an acid anion source and water to obtain a mixture, and adding ammonia water to the mixture to adjust a pH value thereof to 9-12 to obtain a hydrothermal reaction solution; and
  • placing the post-deposition metal substrate in the hydrothermal reaction solution, and performing hydrothermal reaction to obtain the metal with the inorganic protective layer;
  • wherein the first divalent metal salt and the second divalent metal salt are each independently selected from the group consisting of zinc nitrate and magnesium nitrate; and the acid anion source includes one selected from the group consisting of a dihydrogen phosphate or a molybdate.

In some embodiments, the chloride ion solution includes a sodium chloride solution; and the sodium chloride solution has a concentration of 3.5 wt %.

In some embodiments, the self-repairing is performed at room temperature.

The present disclosure provides a method for self-repairing of damage to an inorganic protective layer on a metal surface, including: placing a metal with the inorganic protective layer having a damaged surface in a chloride ion solution and performing self-repairing, wherein the metal with the inorganic protective layer includes a metal substrate and a layered double hydroxide protective layer intercalated by phosphate anions or molybdate anions covering a surface of the metal substrate. In the present disclosure, when the LDH protective layer intercalated by phosphate anions or molybdate anions is damaged, the metal substrate is corroded, and metal cations are released into the environment. At this moment, the phosphate anions or the molybdate anions between the LDH layers combine with the escaped metal cations to form a precipitate that covers the corroded site(s), thereby repairing the damaged protective layer. Meanwhile, anionic vacancies are formed between the LDH layers, which adsorb and capture chloride anions, inhibiting further corrosion development, thereby realizing the self-repairing effect of coating. In the present disclosure, the method could achieve the self-repairing of damaged inorganic protective layer on the metal surface and improve the time limit of the metal corrosion protection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the self-repairing mechanism of the rebar covered by a ZnAl-LDH protective layer intercalated by phosphate anions.

FIG. 2 shows an X-ray diffraction pattern of the rebar covered by a ZnAl-LDH protective layer intercalated by phosphate anions prepared in Example 1.

FIG. 3 shows a Fourier infrared spectrum of the rebar covered by a ZnAl-LDH protective layer intercalated by phosphate anions prepared in Example 1.

FIG. 4 shows the microstructure of the ZnAl-LDH protective layer intercalated by phosphate anions prepared in Example 1.

FIG. 5 shows immersion impedance changes of the rebar covered by a ZnAl-LDH protective layer intercalated by phosphate anions and the original rebar in a 3.5 wt % NaCl solution before and after applying artificial scratches.

FIG. 6A to FIG. 6E show the optical pattern of the ZnAl-LDH protective layer intercalated by phosphate anions with artificial scratches before and after immersion in a 3.5 wt % NaCl solution, and the microstructure and elemental scanning results of the scratch area, wherein FIG. 6A shows the optical pattern of the ZnAl-LDH protective layer intercalated by phosphate anions with artificial scratches before and after immersion in a 3.5 wt % NaCl solution; FIG. 6B shows the microstructure of the scratch area; FIG. 6C shows the Fe elemental scanning result of the scratch area; FIG. 6D shows the O elemental scanning result of the scratch area; and FIG. 6E shows the P elemental scanning result of the scratch area.

FIG. 7A to FIG. 7C show the microstructure and the elemental composition of the scratch area and non-scratch area of the ZnAl-LDH protective layer intercalated by phosphate anions with artificial scratches after immersion in a 3.5 wt % NaCl solution, wherein FIG. 7A shows the microstructure of the scratch area and non-scratch area of the ZnAl-LDH protective layer intercalated by phosphate anions with artificial scratches after immersion in a 3.5 wt % NaCl solution; FIG. 7B shows the elemental composition of the Point 1; and FIG. 7C shows the elemental composition of the Point 2.

FIG. 8 shows an X-ray diffraction pattern of the rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions prepared in Example 2.

FIG. 9 shows a Fourier infrared spectrum of the rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions prepared in Example 2.

FIG. 10 shows immersion impedance changes of the rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions prepared in Example 2 and the original rebar in a composite environment of simulated concrete hole solution (saturated calcium hydroxide solution) and a 3.5 wt % NaCl solution.

FIG. 11A to FIG. 11B show the microstructure and the elemental composition table of the rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions in the artificial scratch area, wherein FIG. 11A shows the microstructure of the rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions in the artificial scratch area; and FIG. 11B shows the elemental composition table of the rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions in the artificial scratch area.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure provides a method for self-repairing of damage to an inorganic protective layer on a metal surface, including:

• • placing a metal with the inorganic protective layer having a damaged surface in a chloride ion solution, and performing self-repairing;
  • wherein the metal with the inorganic protective layer includes a metal substrate and a layered double hydroxide protective layer intercalated by acid anions covering a surface of the metal substrate; and the acid anions are selected from the group consisting of phosphate anions and molybdate anions.

In the present disclosure, the LDH protective layer intercalated by acid anions is in-situ grown on a surface of the metal substrate.

In some embodiments of the present disclosure, the metal substrate includes one selected from the group consisting of steel material, zinc material, magnesium material, aluminum material, and copper material, and preferably a rebar or a steel sheet.

In some embodiments of the present disclosure, the LDH protective layer intercalated by acid anions has a thickness of less than or equal to 50 micrometers, and preferably 15 micrometers.

In some embodiments of the present disclosure, the metal with the inorganic protective layer is prepared by a process including the following steps:

• • mixing a first divalent metal salt, aluminium nitrate and water to obtain a mixed solution;
  • taking the mixed solution as a deposition solution, constructing a three-electrode system with a metal substrate as a working electrode, and performing electrodeposition with the three-electrode system to obtain a post-deposition metal substrate;
  • mixing a second divalent metal salt, aluminium nitrate, an acid anion source and water to obtain a mixture, and adding ammonia water to the mixture to adjust a pH value thereof to 9-12 to obtain a hydrothermal reaction solution; and
  • placing the post-deposition metal substrate in the hydrothermal reaction solution, and performing hydrothermal reaction to obtain the metal with the inorganic protective layer,
  • wherein the first divalent metal salt and the second divalent metal salt are each independently selected from the group consisting of zinc nitrate and magnesium nitrate; and the acid anion source includes selected from the group consisting of a dihydrogen phosphate or a molybdate.

In some embodiments of the present disclosure, a first divalent metal salt, aluminium nitrate and water are mixed to obtain a mixed solution. In some embodiments of the present disclosure, the first divalent metal salt is selected from the group consisting of zinc nitrate and magnesium nitrate. In some embodiments of the present disclosure, a molar ratio of the first divalent metal salt to aluminium nitrate is in a range of 2-4:1, preferably 2.5-3.5:1, and more preferably 3:1. In the present disclosure, the molar ratio of the first divalent metal salt to aluminium nitrate is limited within the above range, which could regulate the structure of the LDH and improve corrosion resistance. In some embodiments of the present disclosure, water is deionized water.

In some embodiments of the present disclosure, the first divalent metal salt in the mixed solution has a concentration of 40 mmol/L to 50 mmol/L, preferably 42 mmol/L to 48 mmol/L, and more preferably 45 mmol/L. In the present disclosure, the concentration of the first divalent metal salt in the mixed solution is limited within the above range, which could make the seed crystal of the LDH generated in the process of electrodeposition have a better quality and make the subsequently formed protective layer of the LDH not easy to fall off.

In the present disclosure, after obtaining the mixed solution, the mixed solution is taken as a deposition solution, a three-electrode system with a metal substrate as a working electrode is constructed, and electrodeposition is performed with the three-electrode system to obtain a post-deposition metal substrate. In some embodiments of the present disclosure, the metal substrate is pretreated before the electrodeposition. In some embodiments of the present disclosure, the pretreatment is performed by acid washing, water washing, and air drying in sequence. In some embodiments of the present disclosure, a washing liquid for the acid washing is dilute hydrochloric acid. In some embodiments, the dilute hydrochloric acid has a mass fraction of 7.5%. In some embodiments of the present disclosure, the acid washing is performed under an ultrasonic condition. In some embodiments, the acid washing is performed for 10 min.

In some embodiments of the present disclosure, a counter electrode of the three-electrode system is a platinum sheet. In some embodiments, a reference electrode of the three-electrode system is Ag/AgCl.

In some embodiments of the present disclosure, the electrodeposition is performed at a voltage of −1.2 V to −1.4 V, and preferably −1.3 V. In some embodiments, the electrodeposition is performed for 200 s to 800 s, preferably 300 s to 700 s, and more preferably 400 s to 600 s. In the present disclosure, the voltage and time for the electrodeposition are limited within the above ranges, which could improve the quality of the generated LDH seed crystal and make the LDH protective layer not easy to fall off. In the present disclosure, during the electrodeposition process, the first divalent metal salt reacts with aluminum nitrate to form a seed crystal of LDH, which could crystallize and grow in the subsequent hydrothermal reaction to form an LDH protective layer.

In some embodiments of the present disclosure, a second divalent metal salt, aluminium nitrate, an acid anion source and water are mixed to obtain a mixture, and ammonia water is added to the mixture to adjust a pH value thereof to 9-12 to obtain a hydrothermal reaction solution. In some embodiments of the present disclosure, the second divalent metal salt is selected from the group consisting of zinc nitrate and magnesium nitrate. In some embodiments of the present disclosure, a molar ratio of the second divalent metal salt to aluminium nitrate is in a range of 2-4:1, preferably 2.5-3.5:1, and more preferably 3:1.

In some embodiments of the present disclosure, the acid anion source is selected from the group consisting of a dihydrogen phosphate or a molybdate. In some embodiments of the present disclosure, the dihydrogen phosphate is sodium dihydrogen phosphate. In some embodiments of the present disclosure, the molybdate is sodium molybdate. In the present disclosure, the dihydrogen phosphate is used to provide phosphate anions and the molybdate is used to provide molybdate anions, which could replace nitrate anions between the LDH layers to obtain the LDH protective layer intercalated by phosphate anions or molybdate anions, so as to realize the purpose of self-repairing. In some embodiments of the present disclosure, a molar ratio of the acid anion source to the second divalent metal salt in the hydrothermal reaction solution is in a range of 1-2:1, preferably 1.2-1.8:1, and more preferably 1.5-1.7:1. In the present disclosure, the molar ratio of dihydrogen phosphate to the second divalent metal salt in the hydrothermal reaction solution is limited within the above ranges, which could adjust the type and number of anions in the interlayer of the LDH protective layer and further improve the self-repairing effect thereof.

In the present disclosure, the molar ratio of the second divalent metal salt to aluminum nitrate in the hydrothermal reaction solution is the same as that in the mixed solution mentioned above.

In some embodiments of the present disclosure, the second divalent metal salt in the hydrothermal reaction solution has a concentration of 55 mmol/L to 65 mmol/L, preferably 58 mmol/L to 62 mmol/L, and more preferably 60 mmol/L. In the present disclosure, the concentration of the second divalent metal salt in the hydrothermal reaction solution is limited within the above ranges, which is beneficial to the crystal growth of the seed crystals of the LDH and further improves the performance of the LDH protective layer.

In some embodiments of the present disclosure, a pH value of the hydrothermal reaction solution is in a range of 9 to 12, and preferably 10 to 11. In the present disclosure, the pH value of the hydrothermal reaction solution is limited within the above ranges, which could adjust the microstructure of the LDH protective layer and further improve the performance of the LDH protective layer.

In some embodiments of the present disclosure, nitrogen gas is introduced continuously during the mixing process. In the present disclosure, the continuous introduction of nitrogen could prevent carbon dioxide in the atmosphere from dissolving into the solution and prevent the introduction of carbonate anions into the LDH.

In some embodiments of the present disclosure, the hydrothermal reaction solution is prepared on the spot, to prevent the hydrothermal reaction liquid from absorbing carbon dioxide in the air, which otherwise results in that the product contains carbonate anions.

In some embodiments of the present disclosure, after obtaining the post-deposition metal substrate and the hydrothermal reaction solution, the post-deposition metal substrate is placed in the hydrothermal reaction solution, and hydrothermal reaction is performed to obtain the metal with the inorganic protective layer. In some embodiments of the present disclosure, when the hydrothermal reaction is carried out, the post-deposition metal substrate is placed perpendicular to a bottom of a hydrothermal reaction container. There is no special limitation on the dosage of the hydrothermal reaction solution as long as the hydrothermal reaction solution can submerge the post-deposition metal substrate.

In some embodiments of the present disclosure, the hydrothermal reaction is performed at a temperature of 90° C. to 140° C., and preferably 90° C. to 120° C. In some embodiments, the hydrothermal reaction is performed for 12 h to 24 h, and preferably 15 h to 18 h. In the present disclosure, the temperature and time for the hydrothermal reaction are limited within the above range, which could make the seed crystal of the LDH fully mature and grow to form an LDH protective layer, adjust the morphology of the LDH protective layer, and further improve the performance of the LDH protective layer.

In some embodiments of the present disclosure, after the hydrothermal reaction is finished, the product from the hydrothermal reaction is washed alternately with water and ethanol to obtain a metal with an inorganic protective layer.

After obtaining the metal with an inorganic protective layer, the metal with an inorganic protective layer having a damaged surface is placed in a chloride ion solution for self-repairing. In some embodiments of the present disclosure, the chloride ion solution includes a sodium chloride solution. In some embodiments, the sodium chloride solution has a concentration of 3.5 wt %. In some embodiments of the present disclosure, the chloride ion solution further includes calcium hydroxide.

In some embodiments of the present disclosure, the self-repairing is performed at room temperature. In the present disclosure, under the condition that the chloride ion solution contains calcium hydroxide, the self-repairing includes: placing the metal with an inorganic protective layer having a damaged surface in a saturated calcium hydroxide solution, and performing first immersion, then adding sodium chloride particles thereto until a concentration of sodium chloride is 3.5 wt %, and performing second immersion. In some embodiments of the present disclosure, the first immersion is performed for 1 day to 7 days, and preferably 3 days. In some embodiments of the present disclosure, the second immersion is performed for 17 days. In the present disclosure, the saturated calcium hydroxide solution is used to simulate a concrete pore solution, which can prove that the method provided by the present disclosure could realize the self-repairing of the rebar in concrete.

The technical solutions of the present disclosure will be clearly and completely described below with reference to the examples of the present disclosure. Apparently, the described examples are merely a part rather than all of the examples of the present disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.

Example 1

(1) A rebar was ultrasonically cleaned with a 7.5 wt % dilute hydrochloric acid for 10 min, and then washed with water and dried in air. The rebar (10 mm×30 mm) was used as a working electrode, a platinum sheet was used as a counter electrode, Ag/AgCl was used as a reference electrode, and a mixed solution of zinc nitrate and aluminum nitrate was used as an electrodeposition solution. The mixed solution of zinc nitrate and aluminum nitrate was prepared by the following steps: zinc nitrate, aluminum nitrate and water were mixed, and stirred until the solids were completely dissolved to form a clear and transparent solution, obtaining the mixed solution, in which the zinc nitrate concentration was 45 mmol/L, and the aluminum nitrate concentration was 15 mmol/L. A white LDH seed crystal layer was formed on a surface of the rebar by electrodeposition for 400 s at a constant voltage of −1.3 V by chronoamperometry.

(2) Zinc nitrate, aluminum nitrate, sodium dihydrogen phosphate and water were mixed, obtaining a mixture. Then ammonia water was added to the mixture to adjust the pH value thereof to 10, obtaining a hydrothermal reaction solution, in which the zinc nitrate concentration was 60 mmol/L, the aluminum nitrate concentration was 20 mmol/L, and the sodium dihydrogen phosphate concentration was 100 mmol/L. During the preparation process, nitrogen was continuously introduced. The resulting rebar with a surface covered by an LDH seed crystal layer was transferred to a reaction kettle, the hydrothermal reaction solution was added to the reaction kettle, and the hydrothermal reaction was performed at 90° C. for 18 h. After the reaction was finished, the resulting product was washed with water and ethanol alternately, obtaining a rebar covered by a ZnAl-LDH protective layer intercalated by phosphate anions.

(3) An artificial scratch with a width of 50 μm was applied to a surface of the rebar covered by a ZnAl-LDH protective layer intercalated by acid anions. The scratch penetrated deep into the rebar matrix. The rebar was immersed in a 350 mL NaCl solution with a concentration of 3.5 wt % for 36 h, and a self-repairing was performed at room temperature. During the self-repairing process, the electrochemical performance was tested every fourth hour. The results are shown in FIG. 5.

Test Example 1

The ZnAl-LDH protective layer intercalated by phosphate anions in the rebar covered by a ZnAl-LDH protective layer intercalated by phosphate anions prepared in Example 1 had a thickness of 15 micrometers.

FIG. 1 is a diagram showing the self-repairing mechanism of the rebar covered by a ZnAl-LDH protective layer intercalated by phosphate anions. It can be seen from FIG. 1 that the LDH protective layer releases phosphate anions, which further form ferric phosphate precipitates in defect areas, thereby realizing the repairing of the defect areas.

FIG. 2 shows an X-ray diffraction pattern of the rebar covered by a ZnAl-LDH protective layer intercalated by phosphate anions prepared in Example 1. It can be seen from FIG. 2 that the ZnAl-LDH protective layer intercalated by phosphate anions has been successfully synthesized on the surface of the rebar.

FIG. 3 shows a Fourier infrared spectrum of the rebar covered by a ZnAl-LDH protective layer intercalated by phosphate anions prepared in Example 1. As can be seen from FIG. 3, the infrared vibration signal attributed to phosphate anions can be clearly observed, indicating that the anions synthesized between the LDH layers are indeed phosphate anions.

FIG. 4 shows the microstructure of the ZnAl-LDH protective layer intercalated by phosphate anions prepared in Example 1. A typical LDH nanosheet structure can be seen from FIG. 4.

FIG. 5 shows immersion impedance changes of the rebar covered by a ZnAl-LDH protective layer intercalated by phosphate anions and the original rebar in a 3.5 wt % NaCl solution before and after applying artificial scratches. After the first electrochemical impedance test (0 h) of the whole sample, one artificial scratch was immediately applied to the surface of the sample. The sample was immersed in a 3.5 wt % NaCl solution, and the electrochemical impedance change was tested every fourth hour. It can be seen from FIG. 5 that after the artificial scratches were applied to the surface of the rebar with a ZnAl-LDH protective layer intercalated by phosphate anions for 4 h, the impedance decreases significantly, and then the impedance value gradually increases with the extension of the immersion time, indicating that the phosphate anions play a self-repairing role in the protective layer.

FIG. 6A to FIG. 6E show the optical pattern of a ZnAl-LDH protective layer intercalated by phosphate anions with artificial scratches before and after immersion in a 3.5 wt % NaCl solution and the microstructure and elemental scanning results of the scratch area. As can be seen from FIG. 6A to FIG. 6E, the scratch area is filled with a repairing substance and major elements such as Fe, P and O are present in the scratch area.

FIG. 7A to FIG. 7C show the microstructure and the elemental composition table of the scratch area and non-scratch area of the ZnAl-LDH protective layer intercalated by phosphate anions with artificial scratches after immersion in a 3.5 wt % NaCl solution. FIG. 7A to FIG. 7C show that phosphate anions are adsorbed in the scratch area and form a repairing substance that inhibits anode reaction.

Example 2

(1) A rebar was ultrasonically cleaned with a 7.5% dilute hydrochloric acid for 10 min, and then washed with water and dried in air. The rebar (10 mm×30 mm) was used as a working electrode, a platinum sheet was used as a counter electrode, Ag/AgCl was used as a reference electrode, and a mixed solution of magnesium nitrate and aluminum nitrate was used as an electrodeposition solution. The mixed solution of magnesium nitrate and aluminum nitrate was prepared by the following steps: magnesium nitrate, aluminum nitrate and water were mixed, and stirred until the solids were completely dissolved to form a clear and transparent solution, obtaining the mixed solution, in which, the magnesium nitrate concentration was 45 mmol/L, and the aluminum nitrate concentration was 15 mmol/L. An LDH seed crystal layer was formed on a surface of the rebar by electrodeposition for 300 s at a constant voltage of −1.5 V by chronoamperometry.

(2) Magnesium nitrate, aluminum nitrate, sodium molybdate and water were mixed, obtaining a mixture. Then ammonia water was added to the mixture to adjust the pH value thereof to 10, obtaining a hydrothermal reaction solution, in which, the magnesium nitrate concentration was 60 mmol/L, the aluminum nitrate concentration was 20 mmol/L, and the sodium molybdate concentration was 100 mmol/L. During the preparation process, nitrogen was continuously introduced. The resulting rebar with a surface covered by an LDH seed crystal layer was transferred to a reaction kettle, the hydrothermal reaction solution was added to the reaction kettle, and the hydrothermal reaction was performed at 90° C. for 18 h. After the reaction was finished, the resulting product was washed with water and ethanol alternately, obtaining a rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions.

(3) An artificial scratch with a width of 50 μm was applied to a surface of the rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions. The rebar was immersed in a 350 mL saturated calcium hydroxide solution for 3 days, and then NaCl particles were added thereto until the sodium chloride concentration reached 3.5 wt %. The rebar was immersed in a composite solution of saturated calcium hydroxide and NaCl for 17 days, and a self-repairing was performed at room temperature.

Test Example 2

The MgAl-LDH protective layer intercalated by molybdate anions in the rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions prepared in Example 2 had a thickness of 15 micrometers.

FIG. 8 shows an X-ray diffraction pattern of the rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions prepared in Example 2. It can be seen from FIG. 8 that a MgAl-LDH protective layer intercalated by molybdate anions has been successfully synthesized on the surface of the rebar.

FIG. 9 shows a Fourier infrared spectrum of the rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions prepared in Example 2. As can be seen from FIG. 9, the infrared vibration signal attributed to molybdate anions can be clearly observed, indicating that the anions synthesized between the LDH layers are indeed molybdate anions.

FIG. 10 shows immersion impedance changes of the rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions prepared in Example 2 and the original rebar in a composite environment of simulated concrete hole solution (saturated calcium hydroxide solution) and a 3.5 wt % NaCl solution. As can be seen from FIG. 10, the impedance value of the rebar grown with the MgAl-LDH protective layer intercalated by molybdate anions gradually increases with the extension of the immersion time and tends to be constant, indicating that molybdate anions have played a self-repairing role in the protective layer.

FIG. 11A to FIG. 11B show the microstructure and the elemental composition table of the rebar covered by a MgAl-LDH protective layer intercalated by molybdate anions in the artificial scratch area. As can be seen from FIG. 11A to FIG. 11B, the major elements such as Fe, Mo, and O in the scratch area are observed, indicating that molybdate anions are adsorbed in the scratch area and form a repairing substance that inhibits anode reaction.

The above descriptions are merely preferred embodiments of the present disclosure. It should be noted that a person of ordinary skill in the art may further make several improvements and modifications without departing from the principle of the present disclosure, but such improvements and modifications should be deemed as falling within the protection scope of the present disclosure.

Claims

1. A method for self-repairing of damage to an inorganic protective layer on a metal surface, comprising:

placing a metal with the inorganic protective layer having a damaged surface in a chloride ion solution, and performing self-repairing,

wherein the metal with the inorganic protective layer comprises a metal substrate and a layered double hydroxide protective layer intercalated by acid anions covering a surface of the metal substrate; and

the acid anions are selected from the group consisting of phosphate anions and molybdate anions.

2. The method of claim 1, wherein the metal substrate comprises one selected from the group consisting of steel material, zinc material, magnesium material, aluminum material, and copper material.

3. The method of claim 1, wherein the layered double hydroxide protective layer intercalated by acid anions has a thickness of less than or equal to 50 micrometers.

4. The method of claim 1, wherein the metal with the inorganic protective layer is prepared by a process comprising the following steps:

mixing a first divalent metal salt, aluminium nitrate and water to obtain a mixed solution;

taking the mixed solution as a deposition solution, constructing a three-electrode system with a metal substrate as a working electrode, and performing electrodeposition with the three-electrode system to obtain a post-deposition metal substrate;

mixing a second divalent metal salt, aluminium nitrate, an acid anion source and water to obtain a mixture, and adding ammonia water to the mixture to adjust a pH value thereof to 9-12 to obtain a hydrothermal reaction solution; and

placing the post-deposition metal substrate in the hydrothermal reaction solution, and performing hydrothermal reaction to obtain the metal with the inorganic protective layer,

wherein the first divalent metal salt and the second divalent metal salt are each independently selected from the group consisting of zinc nitrate and magnesium nitrate; and

the acid anion source comprises one selected from the group consisting of a dihydrogen phosphate or a molybdate.

5. The method of claim 1, wherein the chloride ion solution comprises a sodium chloride solution; and the sodium chloride solution has a concentration of 3.5 wt %.

6. The method of claim 1, wherein the self-repairing is performed at room temperature.

7. The method of claim 2, wherein the metal with the inorganic protective layer is prepared by a process comprising the following steps:

mixing a first divalent metal salt, aluminium nitrate and water to obtain a mixed solution;

taking the mixed solution as a deposition solution, constructing a three-electrode system with a metal substrate as a working electrode, and performing electrodeposition with the three-electrode system to obtain a post-deposition metal substrate;

mixing a second divalent metal salt, aluminium nitrate, an acid anion source and water to obtain a mixture, and adding ammonia water to the mixture to adjust a pH value thereof to 9-12 to obtain a hydrothermal reaction solution; and

placing the post-deposition metal substrate in the hydrothermal reaction solution, and performing hydrothermal reaction to obtain the metal with the inorganic protective layer,

wherein the first divalent metal salt and the second divalent metal salt are each independently selected from the group consisting of zinc nitrate and magnesium nitrate; and

the acid anion source comprises one selected from the group consisting of a dihydrogen phosphate or a molybdate.

8. The method of claim 3, wherein the metal with the inorganic protective layer is prepared by a process comprising the following steps:

mixing a first divalent metal salt, aluminium nitrate and water to obtain a mixed solution;

taking the mixed solution as a deposition solution, constructing a three-electrode system with a metal substrate as a working electrode, and performing electrodeposition with the three-electrode system to obtain a post-deposition metal substrate;

mixing a second divalent metal salt, aluminium nitrate, an acid anion source and water to obtain a mixture, and adding ammonia water to the mixture to adjust a pH value thereof to 9-12 to obtain a hydrothermal reaction solution; and

placing the post-deposition metal substrate in the hydrothermal reaction solution, and performing hydrothermal reaction to obtain the metal with the inorganic protective layer,

wherein the first divalent metal salt and the second divalent metal salt are each independently selected from the group consisting of zinc nitrate and magnesium nitrate; and

the acid anion source comprises one selected from the group consisting of a dihydrogen phosphate or a molybdate.