Process for coating magnesium oxide on surface of steel plate

Abstract

The invention discloses a process for coating magnesium oxide on the surface of a steel plate, which comprises the following steps: mixing silicon dioxide nanospheres with ethanol as a dispersing agent, performing ultrasonic treatment, adding a substance containing amino functional groups, and performing centrifugal washing to obtain the silicon dioxide nanospheres containing the amino functional groups; the preparation method comprises the following steps: mixing silicon dioxide nanospheres containing amino functional groups with a dispersing agent, adding magnesium nitrate, carrying out ultrasonic dispersion treatment, adjusting pH, heating and stirring, centrifuging to obtain core-shell particles, and calcining to obtain a coating with a core-shell structure; silicon steel is placed in an alkaline cleaning solution to be subjected to ultrasonic cleaning, acid pickling activation and pre-oxidation treatment; heating to a second temperature and a second atmosphere, and annealing to generate magnesium silicate crystals; spraying nano sol on the product in S5, drying, and carrying out annealing crosslinking in a third atmosphere and at a third temperature; the transition layer can absorb interface stress through progressive lattice distortion, and nucleation and expansion of cracks are remarkably inhibited.

Description

Technical Field

[0001] The present invention relates to the field of coating processes, and particularly to a magnesium oxide coating process for the surface of steel plates. Background Art

[0002] The surface coating technology of silicon steel is widely used in industry to improve the corrosion resistance, wear resistance and high-temperature resistance of materials. However, traditional coating technologies have many limitations. Especially under complex working conditions, the adhesion and durability of the coatings are difficult to meet the requirements. For example, coatings with a single reaction layer are prone to peeling due to interfacial stress concentration in high-temperature or corrosive environments, resulting in coating failure. In addition, the thermal expansion coefficient of traditional coatings does not match that of the substrate material, resulting in cracks and peeling during temperature changes, further shortening the service life of the coatings.

[0003] Currently, the surface coating technology of silicon steel mainly focuses on the coating of single materials such as alumina and zirconia. However, these coatings are prone to failure due to differences in thermal expansion coefficients in high-temperature environments. At the same time, the microstructure design of traditional coatings is relatively simple, lacking gradient design and multi-layer structures, and it is difficult to effectively disperse interfacial stress and block the penetration of corrosive media. Summary of the Invention

[0004] The present invention overcomes the deficiencies of the prior art and provides a magnesium oxide coating process for the surface of steel plates.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a magnesium oxide coating process for the surface of steel plates, comprising the following steps: S1: Mix silicon dioxide nanospheres and ethanol as a dispersant, perform ultrasonic treatment, add a substance containing an amino functional group, and perform centrifugal washing to obtain silicon dioxide nanospheres containing an amino functional group; S2: Mix the silicon dioxide nanospheres containing an amino functional group with a dispersant, add magnesium nitrate, perform ultrasonic dispersion treatment, adjust the pH, heat and stir, and centrifuge to obtain core-shell particles, and calcine to obtain a core-shell structured coating; S3: Place the silicon steel in an alkaline cleaning solution for ultrasonic cleaning, perform pickling activation and pre-oxidation treatment to obtain silicon steel with a surface oxidation; S4: Coat the core-shell structured coating on the silicon steel with a surface oxidation, and dry; S5: Anneal the product dried in S4 at a first atmosphere and a first temperature to form a magnesium silicate layer; Then raise the temperature to a second temperature and a second atmosphere for annealing to form magnesium silicate crystals; S6: Spray nano-sol on the product of S5, dry, and perform annealing crosslinking at a third atmosphere and a third temperature.

[0006] In a preferred embodiment of the present invention, in S1, the ultrasonic treatment time is 25 - 35 min, and the substance containing amino functional groups is selected as 3 - aminopropyltriethoxysilane.

[0007] In a preferred embodiment of the present invention, in S2, the dispersant is selected as a mixed solution of ethanol and water with a mixing volume ratio of 3 - 5:1; adjusting the pH specifically means adding one of ammonia water, sodium carbonate, or sodium bicarbonate to adjust the pH value to 8 - 10; the heating temperature is 50 - 70 °C, the stirring speed is 2620 - 300 rpm; the centrifugation speed is 7500 - 8500 rpm; the calcination temperature is 400 - 600 °C for 2 - 4 h, and the heating rate is 2 - 5 °C / min.

[0008] In a preferred embodiment of the present invention, in S3, the alkaline cleaning solution is selected as one of a mixed solution of sodium hydroxide with a mass fraction of 4% - 6% and sodium dodecylbenzenesulfonate with a mass fraction of 0.05% - 0.15% or a mixed solution of sodium hydroxide with a mass fraction of 4% - 6% and AEO with a mass fraction of 2% - 5%; the ultrasonic cleaning time is 5 - 15 min; pickling and activation specifically means placing the cleaned silicon steel in one of a hydrogen chloride solution, nitric acid, or hydrofluoric acid solution for 2 - 4 min to activate its surface; pre - oxidation specifically means placing the activated silicon steel in a mixed gas of nitrogen and oxygen and heating it to 550 - 650 °C at a rate of 8 - 12 °C / min and holding for 25 - 35 min.

[0009] In a preferred embodiment of the present invention, in S4, the coating thickness is 80 - 100 μm, the drying temperature is 78 - 82 °C, and the drying time is 8 - 12 min.

[0010] In a preferred embodiment of the present invention, in S5, the first atmosphere is one of a mixed gas of hydrogen and nitrogen, a mixed gas of argon and nitrogen, and a mixed gas of hydrogen and helium, the first temperature is 700 - 800 °C, and the time is 1 - 2 h.

[0011] In a preferred embodiment of the present invention, in S5, the second atmosphere is one of hydrogen, nitrogen, or helium, the second temperature is 900 - 1000 °C, and the time is 2 - 4 h.

[0012] In a preferred embodiment of the present invention, in S6, the nano - sol is selected as one of nano - alumina sol, nano - titanium dioxide sol, and nano - zirconia sol.

[0013] In a preferred embodiment of the present invention, in S6, the spraying thickness is 20 - 30 μm, the drying temperature is 78 - 82 °C, and the time is 25 - 35 min.

[0014] In a preferred embodiment of the present invention, in S6, the third atmosphere is one of a mixed gas of nitrogen and hydrogen, a mixed gas of nitrogen and argon, or a mixed gas of nitrogen and helium, the third temperature is 780 - 820 °C, and the time is 1 - 3 h.

[0015] The present invention solves the defects existing in the background art and has the following beneficial effects: (1) The present invention provides a process for coating magnesium oxide on the surface of a steel plate. By controlling the pre-oxidation temperature and the annealing process, an Fe-Si-O gradient transition layer and a magnesium silicate spinel layer can be formed on the surface of silicon steel. The formation of the Fe-Si-O gradient transition layer enables a gradual matching of the thermal expansion coefficients between the coating and the substrate, thereby effectively dispersing the interfacial stress. In the actual use process, when thermal shock occurs, this transition layer can absorb the interfacial stress through gradual lattice distortion, significantly inhibiting the nucleation and propagation of cracks. At the same time, the formation of the magnesium silicate spinel layer further enhances the bonding strength between the coating and the substrate, enabling the coating to maintain high integrity and stability in a high-temperature environment and effectively extending the service life of the coating.

[0016] (2) The present invention provides a process for coating magnesium oxide on the surface of a steel plate. Through the coordinated regulation of the calcination temperature and the annealing temperature, the pore structure of the coating is significantly optimized. During the calcination process, by controlling the temperature, magnesium hydroxide decomposes to form magnesium oxide, and through the construction of a nanofiber network structure, the size of the pores is restricted. In the annealing stage, the volume expansion effect brought about by the spinelization reaction further seals the grain boundary diffusion channels, reducing the porosity to an extremely low level. This low porosity and dense microstructure significantly improve the anti-permeation performance of the coating, effectively preventing the penetration of corrosive media. At the same time, the dense structure also enhances the mechanical strength and fracture toughness of the coating, enabling it to withstand greater stress without damage in a high-temperature environment. Through this multi-scale structural optimization, the high-temperature resistance and overall performance of the coating are significantly improved, providing reliable protection for the application of silicon steel under complex working conditions. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings; Figure 1 It is a flowchart of a preferred embodiment of the present invention. Detailed Embodiments

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0019] In the following description, many specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0020] As Figure 1 shown, a magnesium oxide coating process on the surface of a steel plate includes the following steps: S1: Mix silicon dioxide nanospheres and ethanol as a dispersant, perform ultrasonic treatment, add a substance containing an amino functional group, and perform centrifugal washing to obtain silicon dioxide nanospheres containing an amino functional group; In the present invention, in S1, the ultrasonic treatment time is 25 - 35 min, and the substance containing an amino functional group is selected as 3-aminopropyltriethoxysilane.

[0021] It should be noted that in the preparation stage of the core-shell structure, the silicon dioxide nanospheres are subjected to amino-functionalization treatment by using a surface modification technique. After dispersing the dried silicon dioxide nanospheres in an ethanol solution, 3-aminopropyltriethoxysilane is added for surface grafting reaction. This step forms an active surface with amino modification through the covalent bonding of the amino functional group of the silane coupling agent and the hydroxyl group on the surface of silicon dioxide. This surface modification not only enhances the interfacial bonding force between silicon dioxide and the subsequent coating material, but more importantly, the amino functional group can effectively capture magnesium ions in the solution through electrostatic adsorption, laying a molecular-level bonding foundation for the uniform coating of the subsequent magnesium oxide shell layer.

[0022] Through the amino-functionalization treatment of silicon dioxide nanospheres by using a surface modification technique, the key basis for the preparation of the core-shell structure is realized. After dispersing the silicon dioxide nanospheres in an ethanol solution, 3-aminopropyltriethoxysilane is added. The ethoxy group in its molecule undergoes a hydrolysis condensation reaction with the hydroxyl group on the surface of silicon dioxide to form a siloxane covalent bond, and at the same time, the exposed amino functional group endows the nanosphere surface with a positive charge property. This modification not only enhances the interfacial bonding force between silicon dioxide and the subsequent magnesium oxide shell layer through chemical bonding, but more importantly, the amino group can adsorb magnesium ions in the solution through electrostatic interaction in a weakly alkaline environment, providing molecular-level adsorption sites for subsequent uniform coating. Ultrasonic treatment for 25 - 35 minutes ensures the full dispersion of the nanospheres and avoids the problem of uneven coating caused by aggregation.

[0023] S2: Mix the amino-functionalized silica nanospheres with a dispersant, add magnesium nitrate, perform ultrasonic dispersion treatment, adjust the pH, heat and stir, and centrifuge to obtain core-shell particles, then calcine to obtain a core-shell structured coating; In the present invention, in S2, the dispersant is selected as a mixed solution of ethanol and water, and the mixing volume ratio is 3-5:1; adjusting the pH specifically means adding one of ammonia water, sodium carbonate or sodium bicarbonate to adjust the pH value to 8-10; the heating temperature is 50-70 °C, the stirring speed is 2620-300 rpm; the centrifugation speed is 7500-8500 rpm; the calcination temperature is 400-600 °C, the time is 2-4 h, and the heating rate is 2-5 °C / min.

[0024] It should be noted that the sol-gel method is used for magnesium oxide coating. The modified silica nanospheres are dispersed in an ethanol-water mixed solvent, and magnesium nitrate is added as a precursor. By controlling the amount of ammonia water added, the pH of the solution is adjusted to a weakly alkaline environment, so that magnesium ions are gradually hydrolyzed to form magnesium hydroxide precipitation and uniformly deposited on the surface of silica. In the calcination treatment stage, thermal decomposition is carried out at 400-600 °C to promote the conversion of magnesium hydroxide into a dense magnesium oxide shell layer. Controlling the heating rate at 2-5 °C / min during this process can effectively avoid the problem of shell cracking caused by thermal stress, and finally form a composite powder with a core-shell structure.

[0025] The sol-gel method is used to construct a magnesium oxide shell layer on the surface of amino-functionalized silica. The modified nanospheres are dispersed in an ethanol-water mixed solvent, and magnesium nitrate is used as a precursor to gradually hydrolyze to form magnesium hydroxide precipitation under alkaline conditions (pH 8-10). The addition of ammonia water not only adjusts the pH value, but the complex formed by it and magnesium ions can delay the precipitation rate, promoting the uniform deposition of magnesium hydroxide in the form of nanoparticles on the surface of silica. Heating and stirring at 50-70 °C (2620-300 rpm) accelerates the hydrolysis reaction and prevents particle sedimentation. Subsequent gradient calcination at 400-600 °C converts magnesium hydroxide into magnesium oxide. Controlling the heating rate at 2-5 °C / min can relieve thermal stress and avoid shell cracking, and finally form a dense core-shell structure, and the shell thickness can be precisely controlled by the concentration of magnesium nitrate and the calcination temperature.

[0026] S3: Place the silicon steel in an alkaline cleaning solution for ultrasonic cleaning, perform pickling activation and pre-oxidation treatment to obtain silicon steel with a surface oxidation; In the present invention, in S3, the alkaline cleaning solution is selected from a mixed solution of sodium hydroxide with a mass fraction of 4%-6% and sodium dodecylbenzenesulfonate with a mass fraction of 0.05%-0.15% or a mixed solution of sodium hydroxide with a mass fraction of 4%-6% and AEO with a mass fraction of 2%-5%. The ultrasonic cleaning time is 5-15 min. The pickling activation is specifically to place the cleaned silicon steel in one of the solutions of hydrogen chloride solution, nitric acid or hydrofluoric acid for 2-4 min to activate its surface. The pre-oxidation is specifically to place the activated silicon steel in a mixed gas of nitrogen and oxygen and heat it up to 550-650 °C at a rate of 8-12 °C / min and keep it warm for 25-35 min.

[0027] It should be noted that in the pre-treatment process of the silicon steel substrate, a hierarchical cleaning and activation process is adopted to ensure the cleanliness of the substrate surface. First, the surface grease and processing residues are removed by the alkaline cleaning solution. Among them, sodium hydroxide provides a strong alkaline environment to decompose organic pollutants, and sodium dodecylbenzenesulfonate, as a surfactant, enhances the decontamination effect. With the cooperation of ultrasonic vibration, the cleaning agent can fully penetrate into the microscopic depressions. The pickling activation uses hydrochloric acid solution for short-term treatment at room temperature, which not only removes the surface oxide layer but also increases the surface roughness through acid etching to improve the mechanical anchoring effect of the subsequent coating. The pre-oxidation treatment is carried out in a nitrogen-oxygen mixed atmosphere. By precisely controlling the oxygen partial pressure, a uniform and dense silicon oxide transition layer is formed on the surface of the silicon steel. This layer not only serves as a chemical bonding medium between the subsequent coating and the substrate, but its optimal thickness of about 80 nanometers can balance the interface bonding strength and stress buffering requirements.

[0028] In the alkaline cleaning solution, sodium hydroxide saponifies grease, and sodium dodecylbenzenesulfonate reduces the surface tension. With the cooperation of ultrasonic cavitation, surface pollutants are completely removed. In the pickling activation stage, hydrochloric acid reacts with the matrix iron to generate ferrous chloride and dissolve the surface oxide layer, and at the same time, a micron-scale rough structure is etched. In the pre-oxidation treatment, the temperature is raised to 550-650 °C in a nitrogen-oxygen mixed gas, which promotes the selective oxidation of the silicon steel surface to generate a uniform silicon oxide transition layer. This layer has chemical compatibility with the subsequent magnesium oxide coating, and a thickness of about 80 nanometers can effectively buffer the difference in thermal expansion coefficients.

[0029] S4: Coat the core-shell structure coating on the surface-oxidized silicon steel and dry it. In the present invention, in S4, the coating thickness is 80-100 μm, the drying temperature is 78-82 °C, and the drying time is 8-12 min.

[0030] It should be noted that the core-shell structure coating is achieved by roll coating to form a large-area uniform film. By adjusting the roller gap and the rheological properties of the coating solution, the wet film thickness is controlled within the range of 80-100 μm. This thickness design can not only ensure sufficient coating thickness but also avoid cracks during the drying process.

[0031] Controlling the wet film thickness to 80 - 100 μm can form a dense coating of about 220 - 30 μm after drying. Low-temperature drying at 78 - 82 °C avoids cracking caused by rapid solvent evaporation. At this time, the magnesium oxide shell layer in the coating is in physical contact with the substrate silicon oxide layer, laying a geometric contact condition for subsequent high-temperature reactions.

[0032] S5: Anneal the product dried in S4 at the first atmosphere and the first temperature to generate a magnesium silicate layer; Then raise the temperature to the second temperature and the second atmosphere for annealing to generate magnesium silicate crystals; In the present invention, in S5, the first atmosphere is one of a mixed gas of hydrogen and nitrogen, a mixed gas of argon and nitrogen, and a mixed gas of hydrogen and helium, the first temperature is 700 - 800 °C, and the time is 1 - 2 h; the second atmosphere is one of hydrogen, nitrogen, or helium, the second temperature is 900 - 1000 °C, and the time is 2 - 4 h.

[0033] It should be noted that the staged annealing treatment is the core innovation of this process. The first stage is medium-temperature annealing in a reducing atmosphere, which promotes the solid-phase reaction between the magnesium oxide shell layer and the silicon oxide on the surface of silicon steel to generate an interface layer of magnesium silicate layer. The generated magnesium silicate layer has excellent thermal expansion matching, and at the same time, the reducing atmosphere effectively inhibits the oxidation of the substrate iron. The second stage of high-temperature annealing is carried out in a pure hydrogen atmosphere. By increasing the reaction temperature, the core-shell structure is fully densified, and the unreacted magnesium oxide forms a continuous network structure at the grain boundaries, significantly improving the anti-permeation performance of the coating.

[0034] In the first stage at 700 - 800 °C in a reducing atmosphere, magnesium oxide reacts with the substrate silicon oxide by solid-phase reaction to generate a magnesium silicate layer. This spinel structure has a thermal expansion coefficient matching that of steel. The second stage of pure hydrogen atmosphere at 900 - 1000 °C promotes the recrystallization of the unreacted magnesium oxide to form a continuous network structure to fill the pores. At the same time, the remaining silicon dioxide core reacts with magnesium oxide to generate more magnesium silicate layers, increasing the coating density to more than 95%.

[0035] S6: Spray nano-sol on the product of S5, dry it, and carry out annealing crosslinking at the third atmosphere and the third temperature.

[0036] In the present invention, in S6, the nano-sol is selected from one of nano-aluminum oxide sol, nano-titanium dioxide sol, and nano-zirconium oxide sol; the spraying thickness is 20 - 30 μm, the drying temperature is 78 - 82 °C, and the time is 25 - 35 min; the third atmosphere is one of a mixed gas of nitrogen and hydrogen, a mixed gas of nitrogen and argon, or a mixed gas of nitrogen and helium, the third temperature is 780 - 820 °C, and the time is 1 - 3 h.

[0037] It should be noted that alumina particles with a particle size of 10 - 20 nanometers are injected into the micropores of the core - shell structure through a spraying process. The high surface energy characteristics of the nanoparticles enable them to spontaneously fill the micron - scale pores under capillary force, and during the drying process, the sol is transformed into a gel state to achieve preliminary fixation. In the final annealing stage, the pores are permanently closed through the spinelization reaction. Alumina reacts with residual magnesium oxide at 800 °C to form magnesium aluminate spinel. This spinel phase has excellent thermal stability and mechanical strength, and its volume expansion effect can further compress the pore space.

[0038] The sprayed alumina sol infiltrates into the micron - scale pores under capillary action and forms gel - state alumina after drying. When annealed at 780 - 820 °C, alumina reacts with magnesium oxide to form magnesium aluminate spinel. Its volume expansion effect further compresses the pore space, reducing the porosity of the coating. This spinel phase has a melting point as high as 2135 °C, significantly improving the high - temperature resistance of the coating. At the same time, the pinning effect of the nanoparticles increases the hardness of the coating by about 30%. The entire process realizes multi - scale synergy through molecular - level modification, interfacial reaction regulation, and nano - strengthening, and finally obtains a composite coating system with high bonding strength and low porosity.

[0039] Example 1

[0040] First, dry silica nanospheres are dispersed in the dispersant ethanol and ultrasonic - treated. Subsequently, 3 - aminopropyltriethoxysilane is added and stirred at 60 °C to introduce amino functional groups. After centrifugal washing to remove the unreacted 3 - aminopropyltriethoxysilane, the silica nanospheres are dried at 60 °C for standby. The amino functional groups adsorb magnesium ions through electrostatic interaction, thus promoting uniform coating.

[0041] Next, the magnesium oxide shell layer is coated. The modified silica nanospheres are dispersed in a dispersant of an ethanol / water mixture with a volume ratio of ethanol to water of 4:1. Magnesium nitrate is added and ultrasonically dispersed. Ammonia water is added dropwise to adjust the pH to 9, and the reaction is stirred at 60 °C with a stirring speed of 280 rpm. After the reaction is completed, the core - shell particles are collected by centrifugation at a centrifugal speed of 8000 rpm. Finally, the core - shell particles are calcined at 500 °C for 3 h with a heating rate of 3 °C / min to convert magnesium hydroxide into magnesium oxide.

[0042] The silicon steel is first ultrasonically cleaned in an alkaline cleaning solution to remove grease. The alkaline cleaning solution is a mixed solution of 5% sodium hydroxide and 0.1% sodium dodecylbenzenesulfonate by mass fraction, and the ultrasonic cleaning time is 10 min. Then, it is pickled and activated in a hydrochloric acid solution for 3 min, and finally washed with water until the conductivity is lower than 5 μS / cm. The pre - oxidation is carried out in a mixed gas of nitrogen and oxygen with a volume ratio of nitrogen to oxygen of 19:1 to form a uniform silica oxide layer on the surface of the silicon steel, and it is held at 600 °C for 30 min with a heating rate of 10 °C / min.

[0043] The prepared core - shell structure coating liquid is coated on the surface of pretreated silicon steel through a roll coater, and the wet film thickness is controlled to be 90 μm. After coating, it is dried at 80 °C for 10 min to remove moisture.

[0044] The staged annealing treatment is first carried out in a mixed atmosphere of hydrogen and nitrogen at 750 °C for 1.5 h to form an interfacial magnesium silicate layer. Subsequently, it is heated to 950 °C in a hydrogen atmosphere for 3 h in the second - stage annealing, so that the core - shell structure completely reacts to form nano - magnesium silicate grains and reduce the porosity.

[0045] For the middle filling layer coating, nano - alumina sol is selected as the filling material. The nano - alumina sol is sprayed on the core - shell structure coating with a spraying thickness of 25 μm, penetrates into the gaps, and is dried at 80 °C for 30 min, and then undergoes a third annealing at 800 °C in a mixed atmosphere of nitrogen and hydrogen for 2 h to promote the reaction of alumina with magnesia to form a spinel phase, fill the pores and enhance the interfacial bonding.

[0046] Example 2

[0047] First, dry silica nanospheres are dispersed in the dispersant ethanol and ultrasonically treated. Subsequently, 3 - aminopropyltriethoxysilane is added and stirred at 60 °C to introduce amino functional groups. After centrifugal washing to remove the unreacted 3 - aminopropyltriethoxysilane, the silica nanospheres are dried at 60 °C for standby. The amino functional groups adsorb magnesium ions through electrostatic interaction, thus promoting uniform coating.

[0048] Next, the magnesia shell layer is coated. The modified silica nanospheres are dispersed in a dispersant of ethanol / water mixture with a volume ratio of ethanol to water of 4:1, magnesium nitrate is added and ultrasonically dispersed. Ammonia water is added dropwise to adjust the pH to 9, and it is stirred and reacted at 60 °C with a stirring speed of 280 rpm. After the reaction is completed, the core - shell particles are collected by centrifugation at a centrifugal speed of 8000 rpm. Finally, the core - shell particles are calcined at 500 °C for 3 h with a heating rate of 3 °C / min to convert magnesium hydroxide to magnesia.

[0049] The silicon steel is first ultrasonically cleaned in an alkaline cleaning solution to remove grease. The alkaline cleaning solution is a mixed solution of 5% sodium hydroxide and 0.1% sodium dodecylbenzenesulfonate by mass fraction, and the ultrasonic cleaning time is 10 min. Then it is pickled and activated in a hydrochloric acid solution for 3 min, and finally washed with water until the conductivity is lower than 5 μS / cm. The pre - oxidation is carried out in a mixed gas of nitrogen and oxygen with a volume ratio of nitrogen to oxygen of 19:1 to form a uniform silica oxide layer on the surface of the silicon steel, and it is held at 550 °C for 30 min with a heating rate of 10 °C / min.

[0050] The prepared core-shell structure coating liquid is coated on the surface of the pretreated silicon steel through a roll coater, and the wet film thickness is controlled to be 90 μm. After coating, it is dried at 80 °C for 10 min to remove moisture.

[0051] The staged annealing treatment is first carried out in a mixed atmosphere of hydrogen and nitrogen at 750 °C for 1.5 h to form an interfacial magnesium silicate layer. Subsequently, it is heated to 950 °C in a hydrogen atmosphere for 3 h for the second-stage annealing, so that the core-shell structure completely reacts to form nano magnesium silicate grains and reduce the porosity.

[0052] For the middle filling layer coating, nano-alumina sol is selected as the filling material. The nano-alumina sol is sprayed on the core-shell structure coating with a spraying thickness of 25 μm, penetrates into the gaps, and is dried at 80 °C for 30 min, and then undergoes a third annealing at 800 °C in a mixed atmosphere of nitrogen and hydrogen for 2 h to promote the reaction of alumina with magnesia to form a spinel phase, fill the pores and enhance the interfacial bonding.

[0053] Example 3

[0054] First, the dried silica nanospheres are dispersed in the dispersant ethanol and ultrasonically treated, and then 3-aminopropyltriethoxysilane is added and stirred at 60 °C to introduce amino functional groups. After centrifugal washing to remove the unreacted 3-aminopropyltriethoxysilane, the silica nanospheres are dried at 60 °C for standby. The amino functional groups adsorb magnesium ions through electrostatic action, thus promoting uniform coating.

[0055] Next, the magnesium oxide shell layer is coated. The modified silica nanospheres are dispersed in a dispersant of an ethanol / water mixture with a volume ratio of ethanol to water of 4:1, magnesium nitrate is added and ultrasonically dispersed. Ammonia water is added dropwise to adjust the pH to 9, and the reaction is stirred at 60 °C with a stirring speed of 280 rpm. After the reaction is completed, the core-shell particles are collected by centrifugation at a centrifugal speed of 8000 rpm. Finally, the core-shell particles are calcined at 500 °C for 3 h with a heating rate of 3 °C / min to convert magnesium hydroxide to magnesium oxide.

[0056] The silicon steel is first ultrasonically cleaned in an alkaline cleaning solution to remove grease. The alkaline cleaning solution is a mixed solution of 5% sodium hydroxide and 0.1% sodium dodecylbenzenesulfonate by mass fraction, and the ultrasonic cleaning time is 10 min. Then it is pickled and activated in a hydrochloric acid solution for 3 min, and finally washed with water until the conductivity is lower than 5 μS / cm. The pre-oxidation is carried out in a mixed gas of nitrogen and oxygen with a volume ratio of nitrogen to oxygen of 19:1 to form a uniform silica oxide layer on the surface of the silicon steel, and it is kept at a temperature of 650 °C for 30 min at a heating rate of 10 °C / min.

[0057] The prepared core-shell structure coating solution was coated on the surface of pretreated silicon steel by a roll coater, and the wet film thickness was controlled to be 90 μm. After coating, it was dried at 80 °C for 10 min to remove moisture.

[0058] The staged annealing treatment was first carried out in a mixed atmosphere of hydrogen and nitrogen at 750 °C for 1.5 h to form an interfacial magnesium silicate layer. Subsequently, it was heated to 950 °C in a hydrogen atmosphere for 3 h in the second-stage annealing, so that the core-shell structure completely reacted to form nano magnesium silicate grains and reduce the porosity.

[0059] For the coating of the intermediate filling layer, nano-alumina sol was selected as the filling material. The nano-alumina sol was sprayed on the core-shell structure coating with a spraying thickness of 25 μm, penetrated into the gaps, and dried at 80 °C for 30 min. Then, it was annealed for 2 h at 800 °C in a mixed atmosphere of nitrogen and hydrogen to promote the reaction of alumina and magnesia to form a spinel phase, fill the pores and enhance the interfacial bonding.

[0060] Example 4

[0061] First, the dried silica nanospheres were dispersed in the dispersant ethanol and ultrasonically treated. Subsequently, 3-aminopropyltriethoxysilane was added and stirred at 60 °C to introduce amino functional groups. After centrifugal washing to remove the unreacted 3-aminopropyltriethoxysilane, the silica nanospheres were dried at 60 °C for standby. The amino functional groups adsorbed magnesium ions through electrostatic interaction, thus promoting uniform coating.

[0062] Next, the magnesia shell layer was coated. The modified silica nanospheres were dispersed in the dispersant of ethanol / water mixture with a volume ratio of ethanol to water of 4:1, magnesium nitrate was added and ultrasonically dispersed. Ammonia water was added dropwise to adjust the pH to 9, and the reaction was stirred at 60 °C with a stirring speed of 280 rpm. After the reaction was completed, the core-shell particles were collected by centrifugation at a centrifugal speed of 8000 rpm. Finally, the core-shell particles were calcined at 500 °C for 3 h with a heating rate of 3 °C / min to convert magnesium hydroxide into magnesia.

[0063] The silicon steel was first ultrasonically cleaned in an alkaline cleaning solution to remove grease. The alkaline cleaning solution was a mixed solution of 5% sodium hydroxide and 0.1% sodium dodecylbenzenesulfonate by mass fraction, and the ultrasonic cleaning time was 10 min. Then, it was pickled and activated in a hydrochloric acid solution for 3 min, and finally washed with water until the conductivity was lower than 5 μS / cm. The pre-oxidation was carried out in a mixed gas of nitrogen and oxygen with a volume ratio of nitrogen to oxygen of 19:1 to form a uniform silica oxide layer on the surface of the silicon steel, and it was held at 600 °C for 30 min at a heating rate of 10 °C / min.

[0064] The prepared core-shell structure coating liquid was coated on the surface of the pretreated silicon steel through a roll coater, and the wet film thickness was controlled to be 90 μm. After coating, it was dried at 80 °C for 10 min to remove moisture.

[0065] The staged annealing treatment was first carried out in a mixed atmosphere of hydrogen and nitrogen at 700 °C for 1.5 h to form an interfacial magnesium silicate layer. Subsequently, it was heated to 950 °C in a hydrogen atmosphere for 3 h for the second-stage annealing, so that the core-shell structure completely reacted to form nano magnesium silicate grains and reduce the porosity.

[0066] For the coating of the intermediate filling layer, nano-alumina sol was selected as the filling material. The nano-alumina sol was sprayed on the core-shell structure coating with a spraying thickness of 25 μm, penetrated into the gaps, and dried at 80 °C for 30 min, and then the third annealing was carried out at 800 °C in a mixed atmosphere of nitrogen and hydrogen for 2 h to promote the reaction of alumina and magnesia to form a spinel phase, fill the pores and enhance the interfacial bonding.

[0067] Example 5

[0068] First, the dried silica nanospheres were dispersed in the dispersant ethanol and ultrasonically treated, and then 3-aminopropyltriethoxysilane was added and stirred at 60 °C to introduce amino functional groups. After centrifugal washing to remove the unreacted 3-aminopropyltriethoxysilane, the silica nanospheres were dried at 60 °C for standby. The amino functional groups adsorbed magnesium ions through electrostatic interaction, thus promoting uniform coating.

[0069] Next, the magnesium oxide shell layer was coated. The modified silica nanospheres were dispersed in a dispersant of ethanol / water mixture with a mixing volume ratio of ethanol to water of 4:1, magnesium nitrate was added and ultrasonically dispersed. Ammonia water was added dropwise to adjust the pH to 9, and the reaction was stirred at 60 °C with a stirring speed of 280 rpm. After the reaction was completed, the core-shell particles were collected by centrifugation at a centrifugal speed of 8000 rpm. Finally, the core-shell particles were calcined at 500 °C for 3 h with a heating rate of 3 °C / min to convert magnesium hydroxide to magnesium oxide.

[0070] The silicon steel was first ultrasonically cleaned in an alkaline cleaning solution to remove grease. The alkaline cleaning solution was a mixed solution of 5% sodium hydroxide and 0.1% sodium dodecylbenzenesulfonate by mass fraction, and the ultrasonic cleaning time was 10 min. Then it was pickled and activated in a hydrochloric acid solution for 3 min, and finally washed with water until the conductivity was lower than 5 μS / cm. The pre-oxidation was carried out in a mixed gas of nitrogen and oxygen with a volume ratio of nitrogen to oxygen of 19:1 to form a uniform silica oxide layer on the surface of the silicon steel, and it was kept at 600 °C for 30 min at a heating rate of 10 °C / min.

[0071] The prepared core-shell structure coating solution was coated on the surface of pretreated silicon steel by a roll coater, and the wet film thickness was controlled to be 90 μm. After coating, it was dried at 80 °C for 10 min to remove moisture.

[0072] The staged annealing treatment was first carried out in a mixed atmosphere of hydrogen and nitrogen at 800 °C for 1.5 h to form an interfacial magnesium silicate layer. Subsequently, it was heated to 950 °C in a hydrogen atmosphere for 3 h for the second-stage annealing, so that the core-shell structure completely reacted to form nano magnesium silicate grains and reduce the porosity.

[0073] For the middle filling layer coating, nano-alumina sol was selected as the filling material. The nano-alumina sol was sprayed on the core-shell structure coating with a spraying thickness of 25 μm, penetrated into the gaps, and dried at 80 °C for 30 min. Then, it was annealed for the third time at 800 °C in a mixed atmosphere of nitrogen and hydrogen for 2 h to promote the reaction of alumina and magnesia to form a spinel phase, fill the pores and enhance the interfacial bonding.

[0074] Example Six

[0075] First, the dried silica nanospheres were dispersed in the dispersant ethanol and ultrasonically treated. Subsequently, 3-aminopropyltriethoxysilane was added and stirred at 60 °C to introduce amino functional groups. After centrifugal washing to remove the unreacted 3-aminopropyltriethoxysilane, the silica nanospheres were dried at 60 °C for standby. The amino functional groups adsorbed magnesium ions through electrostatic interaction, thus promoting uniform coating.

[0076] Next, the magnesium oxide shell layer was coated. The modified silica nanospheres were dispersed in the dispersant of the ethanol / water mixture with a volume ratio of ethanol to water of 4:1, magnesium nitrate was added and ultrasonically dispersed. Ammonia water was added dropwise to adjust the pH to 9, and it was stirred and reacted at 60 °C with a stirring speed of 280 rpm. After the reaction was completed, the core-shell particles were collected by centrifugation at a centrifugal speed of 8000 rpm. Finally, the core-shell particles were calcined at 500 °C for 3 h with a heating rate of 3 °C / min to convert magnesium hydroxide into magnesium oxide.

[0077] The silicon steel was first ultrasonically cleaned in an alkaline cleaning solution to remove grease. The alkaline cleaning solution was a mixed solution of 5% sodium hydroxide and 0.1% sodium dodecylbenzenesulfonate by mass fraction, and the ultrasonic cleaning time was 10 min. Then, it was pickled and activated in a hydrochloric acid solution for 3 min, and finally washed with water until the conductivity was lower than 5 μS / cm. The pre-oxidation was carried out in a mixed gas of nitrogen and oxygen with a volume ratio of nitrogen to oxygen of 19:1 to form a uniform silica oxide layer on the surface of the silicon steel, and it was kept at 550 °C for 30 min at a heating rate of 10 °C / min.

[0078] The prepared core-shell structure coating liquid was coated on the pretreated silicon steel surface by a roller coater, and the wet film thickness was controlled to be 90 μm. After coating, it was dried at 80° C. to remove moisture for 10 minutes.

[0079] The staged annealing treatment was first carried out at 650°C for 1.5 hours in a mixed atmosphere of hydrogen and nitrogen to form an interface magnesium silicate layer. The temperature was then raised to 950°C in a hydrogen atmosphere for 3 hours for the second stage annealing to completely react the core-shell structure to form nano-magnesium silicate grains and reduce the porosity.

[0080] Nano-alumina sol is selected as the filling material for the intermediate filling layer coating. The nano-alumina sol is sprayed on the core-shell structure coating with a thickness of 25 μm, penetrated into the gap, and dried at 80°C for 30 minutes, and annealed for the third time at 800°C in a nitrogen and hydrogen mixed atmosphere for 2 hours to promote the reaction of alumina and magnesium oxide to form a spinel phase, fill the pores and enhance the interface bonding.

[0081] Experiment 1 Now, the silicon steel is coated according to the six groups of coating processes of Examples 1 to 6, and the coated silicon steel is placed in a muffle furnace for high-temperature heating. When the temperature is heated to 800°C, the heat is maintained for 20 minutes, and then the silicon steel is taken out and placed in 25°C water for quenching. This cold and hot cycle is performed 50 times and 100 times respectively. The coating shedding area of ​​the detector is measured, and the shedding area percentage (the entire shedding area / silicon steel coating area) is calculated. See Table 1 for details. Table 1

[0082] It can be seen from Table 1 that in the process of silicon steel surface treatment, the selection of 600℃ pre-oxidation temperature in the S3 stage is essentially achieved by precisely controlling the diffusion dynamics of the three elements of iron, silicon and oxygen. When the temperature rises to 600℃, the silicon atoms in the silicon steel preferentially diffuse outward in the oxidizing environment and combine with oxygen to form an amorphous silicon dioxide network, while the iron atoms diffuse through the grain boundaries to form nanoscale Fe-O clusters. At this time, the combined effect of oxygen partial pressure and temperature makes the diffusion rate of silicon and the oxidation rate of iron reach a dynamic equilibrium, and finally forms a Fe-Si-O gradient transition layer. The special feature of this transition layer is the coherent connection between silicon oxygen tetrahedron and iron oxygen octahedron in its microstructure. This atomic-scale topological continuity makes its thermal expansion coefficient (CTE=4.5×10 -6 / ℃) is just between the matrix (CTE=12×10 -6 / ℃) and magnesium oxide coating (CTE = 8×10 -6 / ℃), and about 72% of the interface stress is absorbed by progressive lattice distortion during the thermal shock process.

[0083] When the system enters the annealing stage at 750 °C in the S5 stage, SiO in the transition layer 2 undergoes a solid-phase reaction with MgO in the coating. At this temperature, the diffusion activation energy of magnesium ions is significantly reduced, enabling to penetrate the oxygen vacancy defects in the SiO 2 network and undergo a charge compensation reaction with tetrahedra. Specifically, it is manifested as substituting sites in the network to form structural units. At the same time, the excess positive charge reaches electrical neutrality through the electron compensation of oxygen vacancies. This process reconstructs the interfacial chemical environment at the atomic scale and generates magnesium silicate with a spinel structure. In this compound, bonds and bonds cooperate to form a three-dimensional cross-linked network, and stress release is achieved through dislocation slip and grain boundary migration. At this time, the chemical bond type at the interface changes from being dominated by van der Waals forces to a covalent-ionic mixed bond, and the binding energy increases.

[0084] The Fe-Si-O layer formed by pre-oxidation at 600 °C acts as a "buffer pad", and its amorphous / nanocrystalline composite structure dissipates thermomechanical stress through viscoelastic deformation; while the layer generated by annealing at 750 °C acts as a "chemical anchor", forming an interdiffusion zone with a width of about 5 nm at the interface. In this region, the concentrations of Fe, Mg, Si, and O show an exponential gradient distribution, and a continuous electron cloud is constructed through the edge sharing and corner sharing of metal-oxygen polyhedra, enabling the overlap of the electron density of states near the Fermi level, significantly enhancing the interfacial electron conductivity. Effectively inhibiting the nucleation and propagation of cracks during thermal shock, and finally achieving strong bonding strength still maintained after thermal shock cycles.

[0085] Experiment Two Taking the coating process of Example 1 as the control group, the calcination temperature of S2 and the annealing temperature of S6 in the coating process of the control group were respectively changed, and silicon steel was coated accordingly to obtain several experimental groups. The products obtained from the experimental groups and the control group were respectively placed in a dilatometer, sealed and connected to a mercury porosimeter. The dilatometer was evacuated to remove the gas on the surface and in the pores of the sample, and mercury was filled under a low pressure of 0.1 pai to determine the sample skeleton volume V s , gradually pressurized to 33000 psi, corresponding to pore diameters of 3 nm - 360 μm, pressurized in stages according to ASTM standards, and the mercury intrusion volume at each pressure point was recorded. The instrument automatically accumulated the mercury intrusion volume to generate a pore size distribution curve and the total pore volume V p , , where V p is the mercury volume accumulated by the mercury porosimeter (i.e., the total open pore volume), and V tThe geometric volume of the sample (or the actual volume calibrated by mercury displacement method using a dilatometer), as shown in Table 2 specifically Table 2

[0086] As can be seen from Table 2, during the calcination process at 500 °C in the S2 stage, the decomposition kinetics of magnesium hydroxide and temperature control played a decisive role. When the temperature rose to 500 °C, the decomposition reaction converted into magnesium oxide and water and entered the rapid stage. At this time, the dehydration rate and the grain growth rate reached a dynamic equilibrium. Through the stepwise heating strategy, the (200) crystal plane of MgO grains preferentially grew during the calcination process, forming an interlaced nanofiber network structure. The particularity of this structure lies in that the diameter of a single MgO fiber is about 20 - 30 nm, and the fibers form a three-dimensional continuous skeleton through bridging grain boundaries, and the pore size is limited within the range of 100 - 500 nm. At the same time, the precise control of the calcination temperature avoided the sudden change of grain boundary mobility caused by local overheating, making the residual stress inside the shell (calculated by XRD full width at half maximum analysis to be about 120 MPa) always lower than the yield strength of MgO (about 300 MPa), thus ensuring the integrity of the shell structure and reducing the initial porosity from more than 15% in the traditional process to 8 - 12%.

[0087] After annealing at 800 °C in the S6 stage, the filling and reaction mechanism of nano-alumina sol further optimized the pore structure. At this temperature, boehmite ( ) in the sol dehydrated to form , and at the same time, the surface hydroxyl groups reacted with the residual MgO at the interface. Specifically, aluminum ions diffused into the MgO lattice through oxygen vacancies, triggering the spinelization reaction: every 1 mol of magnesium oxide reacted with 1 mol of aluminum oxide to generate 1 mol of magnesium aluminate spinel, and this process was accompanied by a 5.8% volume expansion. This expansion effect microscopically manifested as the mechanical extrusion of the newly formed spinel relative to the pore space - after the pores of the original 100 nm level were filled with the expanding substance, the pore diameter shrank to less than 20 nm, and a closed pore structure was formed in three-dimensional space. More importantly, the formation of the spinel phase was not evenly distributed, but preferentially nucleated in the dislocation core region at the MgO grain boundaries (it was observed by TEM that the spinel phase density at the grain boundaries was more than 3 times higher than that in the grains), and this selective growth effectively blocked the grain boundary diffusion channels, further compressing the porosity to less than 5%.

[0088] The three-dimensional framework structure formed by the nanoscale spinel phase (30 - 50 nm) not only improves the material density but also significantly enhances the fracture toughness through multiple toughening mechanisms. Analyzed from the perspective of micro mechanics, when a crack propagates into the spinel phase region, lattice distortion and branching occur at the crack tip. Specifically, spinel grains absorb approximately 35% of the fracture energy through stress-induced phase transformation (tetragonal phase → cubic phase); meanwhile, the residual stress field (about 200 MPa) between nanograins forces the crack path to deflect, with an average deflection angle of 22.5°, making the crack propagation require an additional energy barrier of 2.4×10³ J / m² to overcome. This multi-scale synergistic toughening effect improves the fracture toughness B of the material compared to traditional processes, which is equivalent to an increase in the critical crack length that can be tolerated under the same load. In addition, the high-temperature stability of the spinel framework (melting point of 2135 °C) ensures that the pore structure of the coating can maintain long-term stability even during subsequent service with thermal cycling.

[0089] Based on the inspiration of the ideal embodiments of the present invention, through the above description, relevant personnel can make various changes and modifications completely within the scope of not deviating from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A magnesium oxide coating process for a steel plate surface, comprising the following steps: S1: mixing silica nanospheres with ethanol as a dispersant, ultrasonically treating, adding a substance containing an amino functional group, centrifuging and washing, and obtaining silica nanospheres containing an amino functional group; S2: mixing the silicon dioxide nanospheres containing amino functional groups with a dispersant, adding magnesium nitrate, performing ultrasonic dispersion treatment, adjusting the pH, heating and stirring, centrifuging to obtain core-shell particles, and calcining to obtain a coating with a core-shell structure; S3: placing the silicon steel in an alkaline cleaning solution for ultrasonic cleaning, performing pickling activation, and pre-oxidation treatment to obtain silicon steel with surface oxidation; S4: coating the core-shell structure coating on the surface oxidized silicon steel and drying; S5: annealing the dried product of S4 in a first atmosphere and at a first temperature to form a magnesium silicate layer; Then the temperature is raised to a second temperature and annealed in a second atmosphere to generate magnesium silicate crystals; S6: spraying the nano sol on the product of S5, drying, and performing annealing and cross-linking in a third atmosphere and a third temperature.

2. A magnesium oxide coating process for steel plate surface according to claim 1, characterized in that: In the S1, the ultrasonic treatment time is 25-35 min, and the substance containing amino functional group is 3-aminopropyltriethoxysilane.

3. A magnesium oxide coating process for steel plate surface according to claim 1, characterized in that: In S2, the dispersant is a mixed solution of ethanol and water, and the mixing volume ratio is 3-5:1; the pH is adjusted by adding one of ammonia water, sodium carbonate or sodium bicarbonate, and the pH value is adjusted to 8-10; the heating temperature is 50-70°C, the stirring speed is 2620-300rpm; the centrifugal speed is 7500-8500rpm; the calcination temperature is 400-600°C, the time is 2-4h, and the heating rate is 2-5°C / min.

4. A magnesium oxide coating process for steel plate surface according to claim 1, characterized in that: In S3, the alkaline cleaning solution is selected from a mixed solution of 4%-6% sodium hydroxide and 0.05%-0.15% sodium dodecylbenzene sulfonate or a mixed solution of 4%-6% sodium hydroxide and 2%-5% AEO, and the ultrasonic cleaning time is 5-15 minutes; the pickling activation is specifically placing the cleaned silicon steel in a solution of hydrogen chloride solution, nitric acid or hydrofluoric acid for 2-4 minutes to activate its surface; the pre-oxidation is specifically placing the activated silicon steel in a mixture of nitrogen and oxygen, heating to 550-650°C at a rate of 8-12°C / min, and keeping warm for 25-35 minutes.

5. The magnesium oxide coating process for steel plate surface according to claim 1, characterized in that: In the S4, the coating thickness is 80-100 μm, the drying temperature is 78-82° C., and the drying time is 8-12 min.

6. A magnesium oxide coating process for steel plate surface according to claim 1, characterized in that: In S5, the first atmosphere is one of a mixed gas of hydrogen and nitrogen, a mixed gas of argon and nitrogen, and a mixed gas of hydrogen and helium, the first temperature is 700-800°C, and the time is 1-2h.

7. The magnesium oxide coating process for steel plate surface according to claim 1, characterized in that: In the step S5, the second atmosphere is one of hydrogen, nitrogen or helium, the second temperature is 900-1000°C, and the time is 2-4h.

8. The magnesium oxide coating process for steel plate surface according to claim 1, characterized in that: In S6, the nano-sol is selected from one of nano-alumina sol, nano-titania sol and nano-zirconia sol.

9. The magnesium oxide coating process for steel plate surface according to claim 1, characterized in that: In the S6, the spraying thickness is 20-30 μm, the drying temperature is 78-82° C., and the drying time is 25-35 min.

10. The magnesium oxide coating process for steel plate surface according to claim 1, characterized in that: In S6, the third atmosphere is one of a nitrogen and hydrogen mixed gas, a nitrogen and argon mixed gas or a nitrogen and helium mixed gas, the third temperature is 780-820°C, and the time is 1-3h.

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