A Magnesium Oxide Coating Process for Steel Plate Surfaces

Abstract

The invention discloses a magnesium oxide coating process for steel plate surfaces, comprising: mixing silicon dioxide nanospheres and ethanol as a dispersant, ultrasonically treating, adding a substance containing an amino functional group, and centrifugally washing to obtain silicon dioxide nanospheres containing amino functional groups; mixing the silicon dioxide nanospheres containing amino functional groups with the dispersant, adding magnesium nitrate, ultrasonically dispersing, adjusting pH, heating and stirring, and centrifuging to obtain core-shell particles, and calcining to obtain a coating with a core-shell structure; placing silicon steel in an alkaline cleaning solution for ultrasonic cleaning, performing acid washing activation, and performing a pre-oxidation treatment; then heating to a second temperature and a second atmosphere for annealing to generate magnesium silicate crystals; spraying a nanosol on the S5 product, drying, and annealing and cross-linking in a third atmosphere and a third temperature; the transition layer can absorb interface stress through progressive lattice distortion, thereby significantly inhibiting the nucleation and expansion of cracks.

Description

Technical Field

[0001] The present invention relates to the field of coating technology, in particular to a magnesium oxide coating technology for steel plate surfaces. Background Art

[0002] Silicon steel surface coating technology is widely used in industry to improve the material's corrosion resistance, wear resistance, and high-temperature performance. However, traditional coating technologies have numerous limitations, particularly in complex operating conditions, where coating adhesion and durability struggle to meet requirements. For example, single-layer coatings are susceptible to flaking due to interfacial stress concentration in high-temperature or corrosive environments, leading to coating failure. Furthermore, the thermal expansion coefficient of traditional coatings does not match that of the substrate, leading to cracking and delamination during temperature fluctuations, further shortening the coating's service life.

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

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

[0005] To achieve the above object, the technical solution adopted by the present invention is: a magnesium oxide coating process on the surface of a steel plate, comprising the following steps:

[0006] S1: mixing silica nanospheres with ethanol as a dispersant, ultrasonically treating, adding a substance containing an amino functional group, and centrifuging and washing to obtain silica nanospheres containing an amino functional group;

[0007] S2: mixing silica 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 core-shell structure coating;

[0008] S3: placing the silicon steel in an alkaline cleaning solution for ultrasonic cleaning, performing pickling activation, and pre-oxidation treatment to obtain surface-oxidized silicon steel;

[0009] S4: coating the core-shell structure coating on the surface of oxidized silicon steel and drying;

[0010] S5: annealing the dried product of S4 in a first atmosphere and at a first temperature to form a magnesium silicate layer;

[0011] Then, the temperature is raised to a second temperature and annealed in a second atmosphere to generate magnesium silicate crystals;

[0012] S6: spraying the nanosol on the product of S5, drying, and performing annealing and cross-linking in a third atmosphere and a third temperature.

[0013] 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 3-aminopropyltriethoxysilane.

[0014] In a preferred embodiment of the present invention, 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.

[0015] In a preferred embodiment of the present invention, in S3, the alkaline cleaning solution is selected from a mixed solution of 4%-6% sodium hydroxide and 0.05%-0.15% sodium dodecylbenzenesulfonate 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 placed 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 placed in a mixture of nitrogen and oxygen, heated to 550-650°C at a rate of 8-12°C / min, and kept warm for 25-35 minutes.

[0016] 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.

[0017] In a preferred embodiment of the present invention, in S5, the first atmosphere is one of a mixture of hydrogen and nitrogen, a mixture of argon and nitrogen, and a mixture of hydrogen and helium, the first temperature is 700-800°C, and the time is 1-2h.

[0018] 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 hours.

[0019] In a preferred embodiment of the present invention, in S6, the nanosol is selected from one of nano-alumina sol, nano-titania sol and nano-zirconia sol.

[0020] 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 drying time is 25-35 min.

[0021] In a preferred embodiment of the present invention, 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.

[0022] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0023] (1) The present invention provides a magnesium oxide coating process for steel plate surfaces. By controlling the pre-oxidation temperature and annealing process, a Fe-Si-O gradient transition layer and a magnesium silicate spinel layer can be formed on the silicon steel surface. The formation of the Fe-Si-O gradient transition layer enables a progressive matching of the thermal expansion coefficients between the coating and the substrate, thereby effectively dispersing the interfacial stress. In the event of thermal shock during actual use, this transition layer can absorb the interfacial stress through progressive lattice distortion, significantly inhibiting the nucleation and expansion 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, allowing the coating to maintain a high degree of integrity and stability in a high-temperature environment, effectively extending the service life of the coating.

[0024] (2) The present invention provides a magnesium oxide coating process for steel plate surfaces, which significantly optimizes the pore structure of the coating by coordinating the calcination temperature and the annealing temperature. During the calcination process, magnesium hydroxide is decomposed to form magnesium oxide by controlling the temperature, and the pore size is limited by constructing a nanofiber network structure. During the annealing stage, the volume expansion effect brought about by the spinelization reaction further blocks the grain boundary diffusion channel and reduces the porosity to an extremely low level. This low porosity and dense microstructure significantly improve the anti-penetration performance of the coating and effectively prevent 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 high temperature environments. 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments described in the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0026] Figure 1 is a flow chart of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0029] like Figure 1 As shown, a magnesium oxide coating process for a steel plate surface comprises the following steps:

[0030] S1: mixing silica nanospheres with ethanol as a dispersant, ultrasonically treating, adding a substance containing an amino functional group, and centrifuging and washing to obtain silica nanospheres containing an amino functional group;

[0031] In the present invention, in S1, the ultrasonic treatment time is 25-35 min, and the substance containing amino functional group is 3-aminopropyltriethoxysilane.

[0032] It should be noted that during the core-shell structure preparation stage, the silica nanospheres were treated with amino functionalization using surface modification technology. After the dried silica nanospheres were dispersed in an ethanol solution, 3-aminopropyltriethoxysilane was added for surface grafting. This step forms an amino-modified active surface through covalent bonding of the amino functional groups of the silane coupling agent with the hydroxyl groups on the silica surface. This surface modification not only enhances the interfacial bonding between the silica and subsequent coating materials, but more importantly, the amino functional groups can effectively capture magnesium ions in the solution through electrostatic adsorption, laying the molecular foundation for the subsequent uniform coating of the magnesium oxide shell.

[0033] The key foundation for the preparation of core-shell structure was achieved by amino functionalization of silica nanospheres through surface modification technology. After dispersing the silica nanospheres in ethanol solution, 3-aminopropyltriethoxysilane was added. The ethoxy group in its molecule reacted with the hydroxyl group on the silica surface to form a siloxane covalent bond. At the same time, the exposed amino functional group gave the surface of the nanospheres positive charge characteristics. This modification not only enhances the interfacial bonding between silica and the subsequent magnesium oxide shell through chemical bonding, but more importantly, the amino group can adsorb magnesium ions in the solution through electrostatic effects in a weakly alkaline environment, providing molecular-level adsorption sites for subsequent uniform coating. Ultrasonic treatment for 25-35 minutes ensures that the nanospheres are fully dispersed to avoid uneven coating caused by agglomeration.

[0034] S2: mixing silica 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 core-shell structure coating;

[0035] In the present invention, 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.

[0036] It should be noted that magnesium oxide coating is achieved using a sol-gel method. The modified silica nanospheres are dispersed in an ethanol-water mixed solvent. Magnesium nitrate is added as a precursor. The pH of the solution is adjusted to a weakly alkaline environment by controlling the amount of ammonia added. This allows the magnesium ions to gradually hydrolyze to form magnesium hydroxide precipitates, which are evenly deposited on the silica surface. During the calcination stage, thermal decomposition is carried out at 400-600°C, promoting the conversion of magnesium hydroxide into a dense magnesium oxide shell. During this process, the heating rate is controlled at 2-5°C / min to effectively avoid shell cracking caused by thermal stress, ultimately forming a composite powder with a core-shell structure.

[0037] A sol-gel method was used to construct a magnesium oxide shell on the surface of amino-modified silica. The modified nanospheres were dispersed in an ethanol-water mixture. Magnesium nitrate, a precursor, was gradually hydrolyzed under alkaline conditions (pH 8-10) to precipitate magnesium hydroxide. The addition of ammonia not only adjusted the pH but also formed a complex with magnesium ions, slowing the precipitation rate, promoting the uniform deposition of magnesium hydroxide nanoparticles on the silica surface. Heating and stirring at 50-70°C (2620-300 rpm) accelerated the hydrolysis reaction while preventing particle sedimentation. Subsequent calcination at a gradient of 400-600°C dehydrated the magnesium hydroxide into magnesium oxide. A controlled heating rate of 2-5°C / min alleviated thermal stress and prevented shell cracking, ultimately forming a dense core-shell structure. The shell thickness can be precisely controlled by the magnesium nitrate concentration and calcination temperature.

[0038] S3: placing the silicon steel in an alkaline cleaning solution for ultrasonic cleaning, performing pickling activation, and pre-oxidation treatment to obtain surface-oxidized silicon steel;

[0039] In the present invention, in S3, the alkaline cleaning solution is selected from a mixed solution of 4%-6% sodium hydroxide and 0.05%-0.15% sodium dodecylbenzenesulfonate 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 placed 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 placed in a mixture of nitrogen and oxygen, heated to 550-650°C at a rate of 8-12°C / min, and kept warm for 25-35 minutes.

[0040] It should be noted that in the pretreatment stage of silicon steel substrates, a graded cleaning and activation process is used to ensure the cleanliness of the substrate surface. First, an alkaline cleaning solution is used to remove surface grease and processing residues. Sodium hydroxide provides a strong alkaline environment to decompose organic pollutants, and sodium dodecylbenzene sulfonate is used as a surfactant to enhance the decontamination effect. Ultrasonic vibration is used to allow the cleaning agent to fully penetrate into the microscopic depressions. Acid pickling activation uses hydrochloric acid solution for a short time at room temperature, which not only removes the surface oxide layer but also increases the surface roughness through acid etching, thereby improving the mechanical anchoring effect of subsequent coatings. The pre-oxidation treatment is carried out in a nitrogen and oxygen mixed atmosphere. The precise control of the oxygen partial pressure causes a uniform and dense silicon oxide transition layer to form on the silicon steel surface. 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.

[0041] The alkaline cleaning solution contains sodium hydroxide to saponify grease, sodium dodecylbenzenesulfonate to reduce surface tension, and ultrasonic cavitation to thoroughly remove surface contaminants. During the pickling activation phase, hydrochloric acid reacts with the iron substrate to form ferrous chloride, dissolving the surface oxide layer while simultaneously etching away a micron-scale rough structure. Pre-oxidation treatment involves heating the steel surface to 550-650°C in a nitrogen and oxygen mixture, selectively oxidizing the surface to form a uniform silicon oxide transition layer. This layer is chemically compatible with the subsequent magnesium oxide coating, and its approximately 80-nanometer thickness effectively mitigates differences in thermal expansion coefficients.

[0042] S4: coating the core-shell structure coating on the surface of oxidized silicon steel and drying;

[0043] 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.

[0044] It should be noted that the core-shell structure coating adopts a roller coating process to achieve large-area uniform film formation. The wet film thickness is controlled in the range of 80-100μm by adjusting the roller gap and the rheological properties of the coating liquid. This thickness design can not only ensure sufficient coating thickness but also avoid cracks during the drying process.

[0045] Controlling the wet film thickness to 80-100μm results in a dense coating of approximately 220-30μm after drying. Low-temperature drying at 78-82°C prevents rapid solvent volatilization and cracking. At this point, the magnesium oxide shell in the coating is in physical contact with the substrate silicon oxide layer, establishing the geometric contact conditions for subsequent high-temperature reactions.

[0046] S5: annealing the dried product of S4 in a first atmosphere and at a first temperature to form a magnesium silicate layer;

[0047] Then, the temperature is raised to a second temperature and annealed in a second atmosphere to generate magnesium silicate crystals;

[0048] 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 1-2h; the second atmosphere is one of hydrogen, nitrogen or helium, the second temperature is 900-1000°C, and the time is 2-4h.

[0049] It should be noted that the core innovation of this process is the staged annealing treatment. The first stage is a medium-temperature annealing in a reducing atmosphere, which promotes a solid-phase reaction between the magnesium oxide shell and the silicon steel surface silicon oxide to form a magnesium silicate interface layer. The magnesium silicate layer generated by this reaction has excellent thermal expansion matching. At the same time, the reducing atmosphere effectively inhibits the oxidation of the matrix iron. The second stage is carried out in a pure hydrogen atmosphere. The high-temperature annealing is carried out in a pure hydrogen atmosphere. By increasing the reaction temperature, the core-shell structure is fully densified. The unreacted magnesium oxide forms a continuous network structure at the grain boundaries, significantly improving the anti-permeability performance of the coating.

[0050] In the first stage, at 700-800°C in a reducing atmosphere, magnesium oxide undergoes a solid-phase reaction with the silicon oxide matrix to form a magnesium silicate layer. This spinel structure has a thermal expansion coefficient that matches that of steel. In the second stage, at 900-1000°C in a pure hydrogen atmosphere, unreacted magnesium oxide recrystallizes, forming a continuous network structure that fills the pores. Simultaneously, the remaining silicon dioxide cores react with magnesium oxide to form more magnesium silicate layers, increasing the coating density to over 95%.

[0051] S6: spraying the nanosol on the product of S5, drying, and performing annealing and cross-linking in a third atmosphere and a third temperature.

[0052] In the present invention, in S6, the nanosol is selected from one of nano alumina sol, nano titania sol and nano zirconia 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 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 1-3 h.

[0053] 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 of the nanoparticles allows them to spontaneously fill the micron-sized pores under the action of capillary forces. During the drying process, the sol transforms into a gel state, achieving initial fixation. The final annealing stage achieves permanent pore closure through a spinelization reaction. The alumina reacts with residual magnesium oxide at 800°C to form magnesium-aluminum spinel. This spinel phase has excellent thermal stability and mechanical strength, and its volume expansion effect further compresses the pore space.

[0054] The sprayed alumina sol penetrates into micron-sized 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-aluminum spinel, whose volume expansion effect further compresses the pore space and reduces the porosity of the coating. The melting point of this spinel phase is as high as 2135°C, which significantly improves the high-temperature resistance of the coating. At the same time, the pinning effect of the nanoparticles increases the hardness of the coating by approximately 30%. The entire process is a multi-scale synergy of molecular-level modification, interface reaction regulation and nano-enhancement, ultimately obtaining a composite coating system with high bonding strength and low porosity.

[0055] Example 1

[0056] First, dried silica nanospheres were dispersed in ethanol and sonicated. 3-Aminopropyltriethoxysilane was then added and stirred at 60°C to introduce amino groups. After centrifugation to remove unreacted 3-aminopropyltriethoxysilane, the silica nanospheres were dried at 60°C and used. The amino groups electrostatically adsorbed magnesium ions, promoting uniform coating.

[0057] Next, the magnesium oxide shell 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 at a speed of 280 rpm. After the reaction is complete, the core-shell particles are collected by centrifugation at a speed of 8000 rpm. Finally, the core-shell particles are calcined at 500°C for 3 hours at a heating rate of 3°C / min to convert magnesium hydroxide into magnesium oxide.

[0058] The silicon steel was first ultrasonically cleaned in an alkaline cleaning solution consisting of a mixture of 5% sodium hydroxide and 0.1% sodium dodecylbenzenesulfonate to remove grease. The ultrasonic cleaning lasted for 10 minutes. The steel was then activated by pickling in hydrochloric acid for 3 minutes, and finally washed with water until the conductivity dropped below 5μS / cm. Pre-oxidation was performed in a nitrogen and oxygen mixture with a nitrogen to oxygen volume ratio of 19:1 to form a uniform silica oxide layer on the surface of the silicon steel. The steel was then heated at 600°C for 30 minutes at a heating rate of 10°C / min.

[0059] The prepared core-shell structure coating liquid was applied to the pretreated silicon steel surface by a roller coater, with the wet film thickness controlled to be 90 μm. After coating, the coating was dried at 80°C for 10 minutes to remove moisture.

[0060] The first stage annealing treatment is carried out in a mixed atmosphere of hydrogen and nitrogen at 750°C for 1.5 hours to form an interfacial magnesium silicate layer. The temperature is then raised to 950°C in a hydrogen atmosphere for a second stage annealing for 3 hours to completely react the core-shell structure to form nano-magnesium silicate grains and reduce porosity.

[0061] Nano-alumina sol was selected as the filling material for the intermediate filling layer. The nano-alumina sol was sprayed onto the core-shell coating to a thickness of 25 μm, penetrating into the gaps. The coating was then dried at 80°C for 30 minutes and annealed for a third time at 800°C in a nitrogen and hydrogen mixture for 2 hours. This allowed the aluminum oxide and magnesium oxide to react to form a spinel phase, filling the pores and enhancing interfacial bonding.

[0062] Example 2

[0063] First, dried silica nanospheres were dispersed in ethanol and sonicated. 3-Aminopropyltriethoxysilane was then added and stirred at 60°C to introduce amino groups. After centrifugation to remove unreacted 3-aminopropyltriethoxysilane, the silica nanospheres were dried at 60°C and used. The amino groups electrostatically adsorbed magnesium ions, promoting uniform coating.

[0064] Next, the magnesium oxide shell 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 at a speed of 280 rpm. After the reaction is complete, the core-shell particles are collected by centrifugation at a speed of 8000 rpm. Finally, the core-shell particles are calcined at 500°C for 3 hours at a heating rate of 3°C / min to convert magnesium hydroxide into magnesium oxide.

[0065] The silicon steel was first ultrasonically cleaned in an alkaline cleaning solution consisting of a mixture of 5% sodium hydroxide and 0.1% sodium dodecylbenzenesulfonate to remove grease. The ultrasonic cleaning lasted for 10 minutes. The steel was then activated by pickling in hydrochloric acid for 3 minutes, and finally washed with water until the conductivity dropped below 5μS / cm. Pre-oxidation was performed in a nitrogen and oxygen mixture with a nitrogen to oxygen volume ratio of 19:1 to form a uniform silica oxide layer on the surface of the steel. The steel was then heated at 550°C for 30 minutes at a heating rate of 10°C / min.

[0066] The prepared core-shell structure coating liquid was applied to the pretreated silicon steel surface by a roller coater, with the wet film thickness controlled to be 90 μm. After coating, the coating was dried at 80°C for 10 minutes to remove moisture.

[0067] The first stage annealing treatment is carried out in a mixed atmosphere of hydrogen and nitrogen at 750°C for 1.5 hours to form an interfacial magnesium silicate layer. The temperature is then raised to 950°C in a hydrogen atmosphere for a second stage annealing for 3 hours to completely react the core-shell structure to form nano-magnesium silicate grains and reduce porosity.

[0068] Nano-alumina sol was selected as the filling material for the intermediate filling layer. The nano-alumina sol was sprayed onto the core-shell coating to a thickness of 25 μm, penetrating into the gaps. The coating was then dried at 80°C for 30 minutes and annealed for a third time at 800°C in a nitrogen and hydrogen atmosphere for 2 hours. This promoted the reaction between the aluminum oxide and magnesium oxide to form a spinel phase, filling the pores and enhancing interfacial bonding.

[0069] Example 3

[0070] First, dried silica nanospheres were dispersed in ethanol and sonicated. 3-Aminopropyltriethoxysilane was then added and stirred at 60°C to introduce amino groups. After centrifugation to remove unreacted 3-aminopropyltriethoxysilane, the silica nanospheres were dried at 60°C and used. The amino groups electrostatically adsorbed magnesium ions, promoting uniform coating.

[0071] Next, the magnesium oxide shell 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 at a speed of 280 rpm. After the reaction is complete, the core-shell particles are collected by centrifugation at a speed of 8000 rpm. Finally, the core-shell particles are calcined at 500°C for 3 hours at a heating rate of 3°C / min to convert magnesium hydroxide into magnesium oxide.

[0072] The silicon steel was first ultrasonically cleaned in an alkaline cleaning solution consisting of a mixture of 5% sodium hydroxide and 0.1% sodium dodecylbenzenesulfonate to remove grease. The ultrasonic cleaning lasted for 10 minutes. The steel was then activated by pickling in hydrochloric acid for 3 minutes, and finally washed with water until the conductivity dropped below 5μS / cm. Pre-oxidation was performed in a nitrogen and oxygen mixture with a nitrogen to oxygen volume ratio of 19:1 to form a uniform silica oxide layer on the surface of the steel. The steel was then heated to 650°C for 30 minutes at a heating rate of 10°C / min.

[0073] The prepared core-shell structure coating liquid was applied to the pretreated silicon steel surface by a roller coater, with the wet film thickness controlled to be 90 μm. After coating, the coating was dried at 80°C for 10 minutes to remove moisture.

[0074] The first stage annealing treatment is carried out in a mixed atmosphere of hydrogen and nitrogen at 750°C for 1.5 hours to form an interfacial magnesium silicate layer. The temperature is then raised to 950°C in a hydrogen atmosphere for a second stage annealing for 3 hours to completely react the core-shell structure to form nano-magnesium silicate grains and reduce porosity.

[0075] Nano-alumina sol was selected as the filling material for the intermediate filling layer. The nano-alumina sol was sprayed onto the core-shell coating to a thickness of 25 μm, penetrating into the gaps. The coating was then dried at 80°C for 30 minutes and annealed for a third time at 800°C in a nitrogen and hydrogen mixture for 2 hours. This allowed the aluminum oxide and magnesium oxide to react to form a spinel phase, filling the pores and enhancing interfacial bonding.

[0076] Example 4

[0077] First, dried silica nanospheres were dispersed in ethanol and sonicated. 3-Aminopropyltriethoxysilane was then added and stirred at 60°C to introduce amino groups. After centrifugation to remove unreacted 3-aminopropyltriethoxysilane, the silica nanospheres were dried at 60°C and used. The amino groups electrostatically adsorbed magnesium ions, promoting uniform coating.

[0078] Next, the magnesium oxide shell 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 at a speed of 280 rpm. After the reaction is complete, the core-shell particles are collected by centrifugation at a speed of 8000 rpm. Finally, the core-shell particles are calcined at 500°C for 3 hours at a heating rate of 3°C / min to convert magnesium hydroxide into magnesium oxide.

[0079] The silicon steel was first ultrasonically cleaned in an alkaline cleaning solution consisting of a mixture of 5% sodium hydroxide and 0.1% sodium dodecylbenzenesulfonate to remove grease. The ultrasonic cleaning lasted for 10 minutes. The steel was then activated by pickling in hydrochloric acid for 3 minutes, and finally washed with water until the conductivity dropped below 5μS / cm. Pre-oxidation was performed in a nitrogen and oxygen mixture with a nitrogen to oxygen volume ratio of 19:1 to form a uniform silica oxide layer on the surface of the silicon steel. The steel was then heated at 600°C for 30 minutes at a heating rate of 10°C / min.

[0080] The prepared core-shell structure coating liquid was applied to the pretreated silicon steel surface by a roller coater, with the wet film thickness controlled to be 90 μm. After coating, the coating was dried at 80°C for 10 minutes to remove moisture.

[0081] The first stage annealing treatment was carried out in a mixed atmosphere of hydrogen and nitrogen at 700°C for 1.5 hours to form an interfacial magnesium silicate layer. The second stage annealing was then carried out in a hydrogen atmosphere at 950°C for 3 hours to completely react the core-shell structure to form nano-magnesium silicate grains and reduce porosity.

[0082] Nano-alumina sol was selected as the filling material for the intermediate filling layer. The nano-alumina sol was sprayed onto the core-shell coating to a thickness of 25 μm, penetrating into the gaps. The coating was then dried at 80°C for 30 minutes and annealed for a third time at 800°C in a nitrogen and hydrogen mixture for 2 hours. This allowed the aluminum oxide and magnesium oxide to react to form a spinel phase, filling the pores and enhancing interfacial bonding.

[0083] Example 5

[0084] First, dried silica nanospheres were dispersed in ethanol and sonicated. 3-Aminopropyltriethoxysilane was then added and stirred at 60°C to introduce amino groups. After centrifugation to remove unreacted 3-aminopropyltriethoxysilane, the silica nanospheres were dried at 60°C and used. The amino groups electrostatically adsorbed magnesium ions, promoting uniform coating.

[0085] Next, the magnesium oxide shell 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 at a speed of 280 rpm. After the reaction is complete, the core-shell particles are collected by centrifugation at a speed of 8000 rpm. Finally, the core-shell particles are calcined at 500°C for 3 hours at a heating rate of 3°C / min to convert magnesium hydroxide into magnesium oxide.

[0086] The silicon steel was first ultrasonically cleaned in an alkaline cleaning solution consisting of a mixture of 5% sodium hydroxide and 0.1% sodium dodecylbenzenesulfonate to remove grease. The ultrasonic cleaning lasted for 10 minutes. The steel was then activated by pickling in hydrochloric acid for 3 minutes, and finally washed with water until the conductivity dropped below 5μS / cm. Pre-oxidation was performed in a nitrogen and oxygen mixture with a nitrogen to oxygen volume ratio of 19:1 to form a uniform silica oxide layer on the surface of the silicon steel. The steel was then heated at 600°C for 30 minutes at a heating rate of 10°C / min.

[0087] The prepared core-shell structure coating liquid was applied to the pretreated silicon steel surface by a roller coater, with the wet film thickness controlled to be 90 μm. After coating, the coating was dried at 80°C for 10 minutes to remove moisture.

[0088] The first stage annealing treatment was carried out in a mixed atmosphere of hydrogen and nitrogen at 800°C for 1.5 hours to form an interfacial magnesium silicate layer. The second stage annealing was then carried out in a hydrogen atmosphere at 950°C for 3 hours to completely react the core-shell structure to form nano-magnesium silicate grains and reduce porosity.

[0089] Nano-alumina sol was selected as the filling material for the intermediate filling layer. The nano-alumina sol was sprayed onto the core-shell coating to a thickness of 25 μm, penetrating into the gaps. The coating was then dried at 80°C for 30 minutes and annealed for a third time at 800°C in a nitrogen and hydrogen mixture for 2 hours. This allowed the aluminum oxide and magnesium oxide to react to form a spinel phase, filling the pores and enhancing interfacial bonding.

[0090] Example 6

[0091] First, dried silica nanospheres were dispersed in ethanol and sonicated. 3-Aminopropyltriethoxysilane was then added and stirred at 60°C to introduce amino groups. After centrifugation to remove unreacted 3-aminopropyltriethoxysilane, the silica nanospheres were dried at 60°C and used. The amino groups electrostatically adsorbed magnesium ions, promoting uniform coating.

[0092] Next, the magnesium oxide shell 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 at a speed of 280 rpm. After the reaction is complete, the core-shell particles are collected by centrifugation at a speed of 8000 rpm. Finally, the core-shell particles are calcined at 500°C for 3 hours at a heating rate of 3°C / min to convert magnesium hydroxide into magnesium oxide.

[0093] The silicon steel was first ultrasonically cleaned in an alkaline cleaning solution consisting of a mixture of 5% sodium hydroxide and 0.1% sodium dodecylbenzenesulfonate to remove grease. The ultrasonic cleaning lasted for 10 minutes. The steel was then activated by pickling in hydrochloric acid for 3 minutes, and finally washed with water until the conductivity dropped below 5μS / cm. Pre-oxidation was performed in a nitrogen and oxygen mixture with a nitrogen to oxygen volume ratio of 19:1 to form a uniform silica oxide layer on the surface of the steel. The steel was then heated at 550°C for 30 minutes at a heating rate of 10°C / min.

[0094] The prepared core-shell structure coating liquid was applied to the pretreated silicon steel surface by a roller coater, with the wet film thickness controlled to be 90 μm. After coating, the coating was dried at 80°C for 10 minutes to remove moisture.

[0095] The first stage annealing treatment is carried out in a mixed atmosphere of hydrogen and nitrogen at 650°C for 1.5 hours to form an interfacial magnesium silicate layer. The temperature is then raised to 950°C in a hydrogen atmosphere for a second stage annealing for 3 hours to completely react the core-shell structure to form nano-magnesium silicate grains and reduce porosity.

[0096] Nano-alumina sol was selected as the filling material for the intermediate filling layer. The nano-alumina sol was sprayed onto the core-shell coating to a thickness of 25 μm, penetrating into the gaps. The coating was then dried at 80°C for 30 minutes and annealed for a third time at 800°C in a nitrogen and hydrogen mixture for 2 hours. This allowed the aluminum oxide and magnesium oxide to react to form a spinel phase, filling the pores and enhancing interfacial bonding.

[0097] Experiment 1

[0098] Silicon steel was coated according to the six coating processes of Examples 1 to 6. The coated silicon steel was placed in a muffle furnace for high-temperature heating. When heated to 800°C, the temperature was maintained for 20 minutes. The silicon steel was then taken out and placed in 25°C water for quenching. This process was repeated 50 and 100 times, respectively. The coating shedding area was detected, and the shedding area percentage was calculated (the entire shedding area / the silicon steel coating area). See Table 1 for details.

[0099] Table 1

[0100]

[0101] As can be seen from Table 1, during the surface treatment of silicon steel, the selection of a 600°C pre-oxidation temperature in the S3 stage is essentially achieved by precisely controlling the diffusion dynamics of the three elements iron, silicon, and oxygen. When the temperature rises to 600°C, the silicon atoms in the silicon steel preferentially diffuse outward in an 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 causes the diffusion rate of silicon and the oxidation rate of iron to reach a dynamic equilibrium, ultimately forming a Fe-Si-O gradient transition layer. The special feature of this transition layer is the coherent connection between silicon oxygen tetrahedrons and iron oxygen octahedrons 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 interfacial stress is absorbed by progressive lattice distortion during the thermal shock process.

[0102] When the system enters the S5 stage and is annealed at 750℃, the SiO2 in the transition layer reacts with the MgO in the coating in a solid phase reaction. At this temperature, the diffusion activation energy of magnesium ions is significantly reduced, making Able to penetrate oxygen vacancy defects in SiO2 network and The tetrahedron undergoes charge compensation reaction. replace In the network site, forming The excess positive charge is compensated by the electrons of the oxygen vacancies to achieve electrical neutrality. This process reconstructs the interface chemical environment at the atomic scale and generates magnesium silicate with a spinel structure. Key and The synergistic effect of the bonds forms a three-dimensional cross-linked network, which releases stress through dislocation slip and grain boundary migration. At this time, the chemical bond type at the interface changes from van der Waals force to covalent-ionic mixed bond, and the binding energy increases.

[0103] The Fe-Si-O layer formed by pre-oxidation at 600℃ acts as a "buffer", and its amorphous / nanocrystalline composite structure dissipates thermal mechanical stress through viscoelastic deformation; while the Fe-Si-O layer formed by annealing at 750℃ The layer acts as a "chemical anchor," forming an interdiffusion zone approximately 5 nm wide at the interface. The concentrations of Fe, Mg, Si, and O in this region are distributed in an exponential gradient. Edge and corner sharing of the metal-oxygen polyhedrons creates a continuous electron cloud, resulting in an overlap of the electronic density of states near the Fermi level and significantly improving interfacial electronic conductivity. This effectively inhibits crack nucleation and propagation during thermal shock, ultimately maintaining strong bonding strength even after thermal shock cycles.

[0104] Experiment 2

[0105] The coating process of Example 1 was used as a control group. The calcination temperature of S2 and the annealing temperature of S6 in the coating process of the control group were changed respectively, and silicon steel was coated to obtain several experimental groups. The products obtained from the experimental group and the control group were placed in a dilatometer, sealed and connected to a mercury intrusion instrument. The dilatometer was evacuated to remove gas on the sample surface and in the pores, and filled with mercury at a low pressure of 0.1pai to determine the sample skeleton volume V. s , gradually pressurize to 33000psi, corresponding to pore size 3nm-360μm, pressurize in stages according to ASTM standards, record the mercury intrusion volume at each pressure point, the instrument automatically accumulates the mercury intrusion volume, and generates the pore size distribution curve and total pore volume V p , , where V p is the volume of mercury accumulated in the mercury intrusion instrument (i.e., the total open pore volume), V t The geometric volume of the sample (or the actual volume calibrated by the dilatometer mercury exclusion method) is shown in Table 2.

[0106] Table 2

[0107]

[0108] Table 2 shows that during the 500°C calcination process 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 of magnesium hydroxide was converted into magnesium oxide and water and entered a rapid stage. At this time, the dehydration rate and the grain growth rate reached a dynamic equilibrium. Through the gradual temperature increase strategy, the (200) crystal plane of the MgO grains grew preferentially during the calcination process, forming an interlaced nanofiber network structure. The special feature of this structure is that the diameter of a single MgO fiber is about 20-30nm, and the fibers form a three-dimensional continuous skeleton by bridging the grain boundaries, and its pore size is limited to the range of 100-500nm. At the same time, the precise control of the calcination temperature avoids the sudden change of grain boundary mobility caused by local overheating, so that the residual stress inside the shell (calculated by XRD half-height width analysis is about 120MPa) is always lower than the yield strength of MgO (about 300MPa), thereby ensuring the integrity of the shell structure and reducing the initial porosity from more than 15% in the traditional process to 8-12%.

[0109] After entering the S6 stage and annealing at 800℃, the filling and reaction mechanism of the nano-alumina sol further optimizes the pore structure. At this temperature, the boehmite in the sol ( ) is formed during dehydration At the same time, its surface hydroxyl groups undergo an interfacial reaction with residual MgO. Specifically, aluminum ions diffuse into the MgO lattice through oxygen vacancies, triggering a spinelization reaction: 1 mol of magnesium oxide reacts with 1 mol of aluminum oxide to form 1 mol of magnesium-aluminum spinel, a process accompanied by a 5.8% volume expansion. This expansion effect manifests itself microscopically as the mechanical squeezing of the newly formed spinel relative to the pore space—after the original 100nm pores are filled with the expanding material, the pore diameter shrinks to less than 20nm, forming a closed pore structure in three dimensions. More importantly, the formation of the spinel phase is not uniformly distributed, but rather preferentially nucleates in dislocation cores at the MgO grain boundaries (TEM observations show that the spinel phase density at grain boundaries is over three times higher than within the grain). This selective growth effectively blocks the grain boundary diffusion channels, further compressing the porosity to below 5%.

[0110] The three-dimensional framework formed by the nanoscale spinel phase (30-50nm) not only increases the material's density but also significantly improves fracture toughness through multiple toughening mechanisms. Micromechanical analysis reveals that when a crack propagates into the spinel phase, lattice distortion and branching occur at the crack tip. Specifically, the spinel grains absorb approximately 35% of the fracture energy through a stress-induced phase transformation (tetragonal to cubic). Simultaneously, the residual stress field (approximately 200 MPa) between the nanograins deflects the crack path, with an average deflection angle of 22.5°, forcing crack propagation to overcome an additional energy barrier of 2.4×10³ J / m². This multi-scale synergistic toughening effect increases the material's fracture toughness (B) compared to conventional processes, equivalent to an increase in the critical crack length under the same load. Furthermore, the high-temperature stability of the spinel framework (melting point of 2135°C) ensures the coating's pore structure maintains long-term stability even during subsequent thermal cycling.

[0111] The above description is based on the ideal embodiment of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the content of the specification and must be determined according to the scope of the claims.

Claims

1. A process for coating a steel plate surface with magnesium oxide, comprising the following steps: S1: mixing silica nanospheres with an ethanol solution, ultrasonically treating the solution, adding a substance containing an amino functional group, and centrifuging and washing the solution to obtain silica nanospheres containing an amino functional group; S2: mixing silica 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 surface-oxidized silicon steel; S4: coating the core-shell structure coating on the surface of 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 nanosol on the product of S5, drying, and annealing and cross-linking in a third atmosphere and a third temperature; In S2, the dispersant is selected from a mixed solution of ethanol and water, a mixture of polyethylene glycol and water, or a mixed solution of polyacrylate and water, with a mixing volume ratio of 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; In S3, the pre-oxidation is specifically to place the activated silicon steel in a mixed gas of nitrogen and oxygen, raise the temperature to 550-650°C at a rate of 8-12°C / min, and keep the temperature for 25-35 minutes; In S5, the first atmosphere is one of a mixture of hydrogen and nitrogen, a mixture of argon and nitrogen, and a mixture of hydrogen and helium, the first temperature is 700-800°C, and the time is 1-2h; the second atmosphere is one of hydrogen, nitrogen or helium, the second temperature is 900-1000°C, and the time is 2-4h; in S6, the nanosol is selected from one of nano alumina sol, nano titania sol and nano zirconia sol; in S6, the third atmosphere is one of a mixture of nitrogen and hydrogen, a mixture of nitrogen and argon, or a mixture of nitrogen and helium, the third temperature is 780-820°C, and the time is 1-3h.

2. The magnesium oxide coating process for steel plate surface according to claim 1, characterized in that: In S1, the substance containing an amino functional group is 3-aminopropyltriethoxysilane.

3. The 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 dodecylbenzenesulfonate 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 to place the cleaned silicon steel in a solution of hydrogen chloride solution, nitric acid or hydrofluoric acid for 2-4 minutes to activate its surface.

4. 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 minutes.

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

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