Micro-nano structure ceramic coating and its application in zircon sand boiling chlorination method reaction furnace

Abstract

The present application relates to the technical field of ceramic coating, especially to a micro-nano structure ceramic coating and its application on the reaction furnace of zircon sand boiling chlorination method, aiming at solving the problems of weak bonding force between the existing protective coating and the substrate, poor thermal shock resistance and easy failure in long-term high-temperature chlorine environment; the present application constructs a nano-wire reinforced micro-nano structure transition layer on the surface of porous corundum brick substrate in situ, and sequentially constructs a lanthanum phosphate bonding layer and a yttrium stabilized zirconium oxide barrier layer on the transition layer; the design utilizes the mechanical anchoring effect of micro-nano structure and the strong chemical bonding ability of lanthanum phosphate to realize the firm combination of the coating and the substrate; the dense characteristics of the zirconium oxide layer provide ultimate protection; the method significantly improves the overall anti-peeling ability and long-term corrosion resistance of the coating system.

Description

Technical Field

[0001] This invention relates to the field of ceramic coating technology, and in particular to a micro-nano structured ceramic coating and its application in a zircon sand fluidized bed chlorination reactor. Background Technology

[0002] The zircon sand fluidized bed chlorination reactor is the core equipment for producing zirconium tetrachloride. Its furnace lining must withstand high temperatures during operation and is constantly exposed to a highly corrosive atmosphere containing high concentrations of chlorine, carbon monoxide, and various volatile metal chlorides. Failure of the lining material directly leads to production interruptions, high maintenance costs, and safety risks.

[0003] Currently, the main methods to improve the service life of reactor linings are to use high-performance refractory bricks, such as corundum bricks or silicon carbide bricks, or to apply a protective coating to the brick surface. However, corundum bricks have poor thermal shock resistance and are prone to cracking due to sudden temperature changes; the protective film on the surface of silicon carbide bricks may fail under specific oxygen partial pressures; at the same time, the ceramic coatings prepared on the surface of refractory bricks by thermal spraying, sol-gel method, or chemical vapor deposition method are mostly physically attached or simply mechanically interlocked with the refractory brick substrate. Due to the difference in thermal expansion coefficients between the coating material and the substrate material, huge thermal stress will be generated at the interface during the thermal cycle of the reactor, which can easily lead to cracks and peeling of the coating. Once the coating fails, the corrosive medium will directly erode the substrate, accelerating the overall destruction.

[0004] Therefore, the core problem facing existing technologies is: how to construct a ceramic protective coating on the surface of a refractory brick matrix that has high bonding strength, can withstand severe thermal shock, and can effectively block the penetration of high-temperature chlorine gas for a long time; this requires the coating to not only be dense and stable, but also to form a strong and tough interface bond with the matrix that can buffer stress. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a micro / nano-structured ceramic coating and its application in a zircon sand fluidized bed chlorination reactor. It aims to solve the problems of weak adhesion between existing protective coatings and the substrate, poor thermal shock resistance, and easy failure in long-term high-temperature chlorine environments. This invention constructs a nanowire-reinforced micro / nano-structured transition layer in situ on the surface of a porous corundum brick substrate, and then sequentially constructs a lanthanum phosphate bonding layer and a yttrium-stabilized zirconium oxide barrier layer on this transition layer. This design utilizes the mechanical anchoring effect of the micro / nano structure and the strong chemical bonding ability of lanthanum phosphate to achieve a firm bond between the coating and the substrate; the dense properties of the zirconium oxide layer provide ultimate protection; this method significantly improves the overall anti-stripping ability and long-term corrosion resistance of the coating system.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: The application of a micro / nano-structured ceramic coating on a zircon sand fluidized bed chlorination reactor includes the following steps: Step S1: Mixing and Layering: Mix plate-shaped corundum, activated alumina powder, clay, elemental silicon and thermosetting phenolic resin to obtain the base material; mix activated alumina powder, nano carbon black, nano silica powder and encapsulation dopant material, then add polyethylene glycol and ethanol to adjust the solid content, transfer to a ball mill jar for ball milling, and sieve to obtain the transition layer slurry; Place the mold horizontally, pour in the transition layer slurry, let it stand at room temperature for 15 minutes, then add the base material until the mold is full, vibrate, let it stand for 1 hour, and the layered material distribution is completed to obtain the blank. Step S2: Pressing and primary sintering: Demold the brick blank from the mold, press it statically for 5 minutes under a pressure of 200 MPa, dry it at room temperature for 24 hours, dry it at 110℃ for 12 hours, and then transfer it to the sintering furnace. Under argon protection, heat it from room temperature to 800℃ at 5℃ / min and hold it for 1 hour, then heat it to 1400℃ at 8℃ / min and hold it for 3 hours, then heat it to 1750℃ at 5℃ / min and hold it for 2 hours, and then cool it to room temperature to obtain the primary sintered brick blank. Step S3: Coating and Secondary Sintering: The primary sintered brick blank is ultrasonically washed in ethanol for 10 min, dried, and then the transition layer of the primary sintered brick blank is immersed in lanthanum phosphate sol for 60 s. It is then dried at 120℃ for 1 h. Yttrium-stabilized zirconia sol is then coated on the transition layer and dried at 100℃ for 40 min. The coating of yttrium-stabilized zirconia sol is repeated 3 times. The blank is then left to stand at 80℃ for 12 h, and then transferred to a sintering furnace. The temperature is increased to 400℃ at 2℃ / min and held for 1 h, then increased to 1050℃ at 3℃ / min and held for 2 h, and then increased to 1250℃ at 5℃ / min and held for 3 h. The blank is then cooled to room temperature, thereby forming a micro-nano structured ceramic coating on the surface of the brick blank, and corundum bricks for zircon sand fluidized bed chlorination reactors are obtained.

[0007] Furthermore, in step S1: during the preparation of the base material: by mass fraction: 15-18% activated alumina powder, 6% clay, 4% elemental silicon and 4% thermosetting phenolic resin, with the remainder being tabular corundum, which is divided into 3.0-1.0mm, 0.1-1mm and <0.3mm specifications, with a weight ratio of 4:3:3; In the preparation of the transition layer slurry: the weight ratio of activated alumina powder, nano carbon black, nano silica powder, and encapsulated dopant material is 5.5:1:1.5:0.5-0.6, the amount of polyethylene glycol added is 5% of the total mass, and the solid content is adjusted to 70% by the amount of ethanol added; The mold dimensions are 240mm×120mm×70mm, and the thickness of its transition layer slurry is 2.5mm.

[0008] The encapsulated doped material is prepared through the following steps: Step A1: Mix chromium powder, aluminum powder and graphite powder and add them to a ball mill jar with a ball-to-powder ratio of 10:1 and a rotation speed of 200 rpm. Under argon conditions, ball mill for 12 hours, pass through a 100-mesh sieve, and transfer to a crucible. Perform microwave sintering in a 2.45 GHz multimode microwave sintering furnace at a sintering temperature of 1250℃ and a holding time of 30 min. Grind again, sieve, and obtain MAX phase powder. Furthermore, in step A1, the molar ratio of chromium powder, aluminum powder, and graphite powder is 2 mol: 1.1 mol: 1 mol, wherein the chromium powder has a purity ≥ 99.5% and a particle size ≤ 45 μm, the aluminum powder has a purity ≥ 99.8% and a particle size ≤ 45 μm, and the graphite powder has a purity ≥ 99.5% and a particle size ≤ 75 μm.

[0009] Step A2: Mix aluminum isopropoxide and ethanol, stir for 30 min at 300 rpm and 60°C, then add deionized water, heat to 80°C, continue stirring for 30 min, then add nitric acid solution to adjust the pH to 3.5, continue heating to 90°C, and stir for 2 h to obtain aluminum sol; mix nickel nitrate hexahydrate and deionized water, then add MAX phase powder and ultrasonically disperse for 30 min, then add aluminum sol, stir for 2 h at 300 rpm and 60°C, rotary evaporate, dry, grind, and sieve to obtain the coated doped material; Furthermore, in step A2: during the preparation of aluminum sol: the ratio of aluminum isopropoxide to ethanol is 20.4-21g:20mL:25mL, and the mass fraction of nitric acid solution is 30%; during the preparation of the encapsulated doped material: the ratio of nickel nitrate, deionized water, MAX phase powder and aluminum sol is 9.5-10g:3.5g:30mL:8g.

[0010] The lanthanum phosphate sol was prepared by the following steps: Lanthanum nitrate solution and phosphoric acid solution were mixed and stirred for 20 min at a stirring rate of 300 rpm and a temperature of 5℃. Citric acid was then added and stirring was continued for 10 min. Ammonia solution was then added to adjust the pH to 3.5. Ethylene glycol was then added, the temperature was raised to 80℃, and stirring was carried out for 5 min. The mixture was then allowed to stand for 24 h to obtain lanthanum phosphate sol. Furthermore, in the preparation process of the lanthanum phosphate sol, the ratio of lanthanum nitrate solution, phosphoric acid solution, citric acid and ethylene glycol is 15mL:15mL:5.7g:3.5g, wherein the molar concentration of lanthanum nitrate solution is 1mol / L and the molar concentration of phosphoric acid solution is 1mol / L.

[0011] The yttrium-stabilized zirconium oxide sol is prepared by the following steps: Zirconium oxychloride, yttrium nitrate and ethanol were mixed and stirred at 300 rpm at room temperature for 30 min. Then acetylacetone was added, the temperature was raised to 60 °C and stirred for 1 h. Then ethanol solution was added and stirred for 2 h. After standing for 72 h, yttrium-stabilized zirconium oxide sol was obtained. Furthermore, in the preparation process of the yttrium-stabilized zirconium oxide sol, the ratio of zirconium oxychloride, yttrium nitrate, ethanol, acetylacetone and ethanol solution is 8.05g:1.55g:40mL:3g:1mL, and the volume fraction of the ethanol solution is 50%.

[0012] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention discloses a micro / nano structured ceramic coating and its application in a zircon sand fluidized bed chlorination reactor; it aims to solve the problems of weak bonding between existing protective coatings and the substrate, poor thermal shock resistance, and easy failure in long-term high-temperature chlorine environments; this invention constructs a nanowire-reinforced micro / nano structured transition layer in situ on the surface of a porous corundum brick substrate, and sequentially constructs a lanthanum phosphate bonding layer and a yttrium-stabilized zirconium oxide barrier layer on this transition layer; this design utilizes the mechanical anchoring effect of the micro / nano structure and the strong chemical bonding ability of lanthanum phosphate to achieve a firm bond between the coating and the substrate; the dense properties of the zirconium oxide layer provide ultimate protection; this method significantly improves the overall anti-stripping ability and long-term corrosion resistance of the coating system.

[0013] This invention employs a catalytic growth-in-situ conversion method, using a three-dimensional nanowire network for reinforcement, to solve the problem of insufficient substrate surface toughness and inability to provide a stable anchoring foundation for subsequent coatings. In the transition layer construction stage, a nickel-containing catalyst-encapsulated dopant material is introduced together with nano-carbon black and nano-silica. During argon-protected sintering, firstly, in the range of 800-1400 degrees Celsius, metallic nickel nanoparticles catalyze the growth of interconnected primary carbon nanotube networks from nano-carbon black. Subsequently, in the high-temperature range of 1400-1750 degrees Celsius, a carbothermic reduction reaction (SiO2 + 3C → SiC + 2CO) occurs. Carbon nanotubes are consumed as a carbon source and transformed in situ into silicon carbide nanowires. These SiC nanowires, with diameters of 50-100 nanometers and lengths of several micrometers, overlap and intertwine within the transition layer to form a continuous three-dimensional network structure. This network has two core functions: first, it acts as a micro-skeleton with micro-nano structures, significantly improving the fracture toughness and crack resistance of the transition layer; second, it creates a unique surface micro-nano morphology, with abundant nanoscale pores and a huge specific surface area, providing ample penetration space and physical anchoring points for the sol-gel precursor of the subsequent coating, achieving a physically interlocked transition from the substrate to the coating.

[0014] This invention uses lanthanum phosphate sol as the base layer and solves the key interface problems of low bonding strength and thermal stress mismatch between the coating and the heterogeneous substrate through interfacial chemical bonding and stress buffering. Lanthanum phosphate sol is coated on a micro / nano structure transition layer as a bonding layer. During the secondary sintering process, lanthanum phosphate crystallizes into a monazite-type structure. Its key mechanism lies in interfacial chemistry: the phosphate groups on the surface of lanthanum phosphate undergo condensation reactions with the exposed hydroxyl groups or dangling bonds on the silicon carbide nanowires on the transition layer surface and the alumina substrate, forming strong PO-Si and PO-Al covalent bonds. This chemical bonding strength is much higher than van der Waals forces or mechanical interlocking, enabling the coating to bond with the substrate. Simultaneously, the monazite-type lanthanum phosphate has a low layered shear modulus. Under thermal stress, it can dissipate energy through micro-slippage between grains, acting as a stress buffer layer. This effectively alleviates the shear stress caused by the difference in thermal expansion coefficients between the upper zirconium oxide layer and the lower substrate, maintaining good overall anti-stripping ability.

[0015] This invention uses yttrium-stabilized zirconium oxide as a top layer, which acts as a dense barrier. Combined with interfacial diffusion mechanisms, it solves the problem that the coating system needs to simultaneously possess extremely high density to resist the penetration of corrosive media and to firmly bond with the underlying layer to maintain integrity. The top layer uses yttrium-stabilized zirconium oxide sol, which forms a cubic phase structure after high-temperature treatment. The doping of yttrium ions effectively suppresses the phase transformation of zirconium oxide, ensuring phase stability at high temperatures. The main function of this layer is to provide a dense physicochemical barrier: its grains are fine and tightly packed, with extremely low porosity, effectively blocking the penetration and diffusion of chlorine molecules and metal chloride vapors. In the secondary sintering process, when the temperature is raised to 1250℃ and held, the surface layer of yttrium-doped zirconium oxide not only becomes sufficiently dense, but also undergoes cation interdiffusion at the interface with the underlying lanthanum phosphate bonding layer. That is, yttrium and zirconium diffuse into the shallow surface of the lanthanum phosphate layer, and lanthanum diffuses into the shallow surface of the yttrium-doped zirconium oxide layer. This interdiffusion forms a gradient interface region with continuously changing composition and structure, rather than a sharp physical interface. This gradient interface can further smooth the distribution of thermal stress and bond the ceramics together at the atomic scale, achieving a strong and tough metallurgical-like bond from the lanthanum phosphate bonding layer to the yttrium-doped zirconium oxide barrier layer, avoiding interlayer delamination.

[0016] In summary, this invention achieves synergistic effects among its layers through a gradient structural design: a micro / nano structure transition layer, a lanthanum phosphate bonding layer, and a yttrium-stabilized zirconia surface layer. The micro / nano structure provides robust underlying support and mechanical interlocking for the entire coating system; the lanthanum phosphate layer enables strong interfacial chemical bonding and stress management; and the yttrium-stabilized zirconia layer ensures protective performance. These three elements are integrated into a cohesive whole through the fabrication process, ultimately resulting in a coating with excellent interfacial bonding strength, superior thermal shock fatigue resistance, and long-term stable high-temperature chlorine corrosion resistance, thereby significantly extending the service life of the zircon sand fluidized bed chlorination reactor lining. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0018] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0019] Furthermore, in the following preparation examples, embodiments, and comparative examples: the activated alumina powder used was α-Al2O3 with a purity ≥99% and a size of 0.5-1μm; the clay had an Al2O3 content ≥40% and a particle size ≤325 mesh; the elemental silicon had a purity ≥98% and a particle size ≤200 mesh; the thermosetting phenolic resin was liquid, model PF-2231, with a fixed carbon mass fraction greater than 36%; the nano carbon black was model N220 with a fixed carbon mass fraction of 99.5%; and the nano silica powder had a purity ≥99.5% and a particle size of 20-30nm.

[0020] Preparation Example 1: The doped material was prepared by the following steps: Step A1: Mix chromium powder, aluminum powder and graphite powder and add them to a ball mill jar with a ball-to-powder ratio of 10:1 and a rotation speed of 200 rpm. Under argon conditions, ball mill for 12 hours, pass through a 100-mesh sieve, and transfer to a crucible. Perform microwave sintering in a 2.45 GHz multimode microwave sintering furnace at a sintering temperature of 1250℃ and a holding time of 30 min. Grind again, sieve, and obtain MAX phase powder. Furthermore, in step A1, the molar ratio of chromium powder, aluminum powder, and graphite powder is 2 mol: 1.1 mol: 1 mol, wherein the chromium powder has a purity ≥ 99.5% and a particle size ≤ 45 μm, the aluminum powder has a purity ≥ 99.8% and a particle size ≤ 45 μm, and the graphite powder has a purity ≥ 99.5% and a particle size ≤ 75 μm.

[0021] Step A2: Mix aluminum isopropoxide and ethanol, stir for 30 min at 300 rpm and 60°C, then add deionized water, heat to 80°C, continue stirring for 30 min, then add nitric acid solution to adjust the pH to 3.5, continue heating to 90°C, and stir for 2 h to obtain aluminum sol; mix nickel nitrate hexahydrate and deionized water, then add MAX phase powder and ultrasonically disperse for 30 min, then add aluminum sol, stir for 2 h at 300 rpm and 60°C, rotary evaporate, dry, grind, and sieve to obtain the coated doped material; Furthermore, in step A2: during the preparation of aluminum sol: the ratio of aluminum isopropoxide to ethanol is 20.4g:20mL:25mL, and the mass fraction of nitric acid solution is 30%; during the preparation of the encapsulated doped material: the ratio of nickel nitrate, deionized water, MAX phase powder and aluminum sol is 9.5g:3.5g:30mL:8g.

[0022] Preparation Example 2: Compared with Preparation Example 1, in step A2 of Preparation Example 2, the ratio of aluminum isopropoxide to ethanol in the aluminum sol preparation process is adjusted to 21g:20mL:25mL, the mass fraction of nitric acid solution is 30%, and the other steps are the same.

[0023] Preparation Example 3: Compared with Preparation Example 1, in step A2 of the preparation process of the coating doped material, the ratio of nickel nitrate, deionized water, MAX phase powder and aluminum sol is 10g:3.5g:30mL:8g, and the other steps are the same.

[0024] Preparation Example 4: Compared with Preparation Example 1, in step A2 of the preparation process of the coating doped material, the ratio of nickel nitrate, deionized water, MAX phase powder and aluminum sol is 4g:3.5g:30mL:8g, and the other steps are the same.

[0025] Preparation Example 5: Lanthanum phosphate sol was prepared by the following steps: Lanthanum nitrate solution and phosphoric acid solution were mixed and stirred for 20 min at a stirring rate of 300 rpm and a temperature of 5℃. Citric acid was then added and stirring was continued for 10 min. Ammonia solution was then added to adjust the pH to 3.5. Ethylene glycol was then added, the temperature was raised to 80℃, and stirring was carried out for 5 min. The mixture was then allowed to stand for 24 h to obtain lanthanum phosphate sol. Furthermore, in the preparation process of the lanthanum phosphate sol, the ratio of lanthanum nitrate solution, phosphoric acid solution, citric acid and ethylene glycol is 15mL:15mL:5.7g:3.5g, wherein the molar concentration of lanthanum nitrate solution is 1mol / L and the molar concentration of phosphoric acid solution is 1mol / L.

[0026] Yttrium-stabilized zirconia sol is prepared by the following steps: Zirconium oxychloride, yttrium nitrate and ethanol were mixed and stirred at 300 rpm at room temperature for 30 min. Then acetylacetone was added, the temperature was raised to 60 °C and stirred for 1 h. Then ethanol solution was added and stirred for 2 h. After standing for 72 h, yttrium-stabilized zirconium oxide sol was obtained. Furthermore, in the preparation process of the yttrium-stabilized zirconium oxide sol, the ratio of zirconium oxychloride, yttrium nitrate, ethanol, acetylacetone and ethanol solution is 8.05g:1.55g:40mL:3g:1mL, and the volume fraction of the ethanol solution is 50%.

[0027] Preparation Example 6: Compared with Preparation Example 5, in the preparation process of the lanthanum phosphate sol, the ratio of lanthanum nitrate solution, phosphoric acid solution, citric acid and ethylene glycol was adjusted to 15 mL: 15 mL: 2 g: 3.5 g, and the other steps were the same.

[0028] Preparation Example 7: Compared with Preparation Example 5, in the preparation process of the yttrium-stabilized zirconium oxide sol, the ratio of zirconium oxychloride, yttrium nitrate, ethanol, acetylacetone and ethanol solution was adjusted to 8.05g:0.5g:40mL:3g:1mL, and the other steps were the same.

[0029] Example 1: Application of a micro / nano structured ceramic coating in a zircon sand fluidized bed chlorination reactor, comprising the following steps: Step S1: Mixing and Layering: Mix plate-shaped corundum, activated alumina powder, clay, elemental silicon and thermosetting phenolic resin to obtain the base material; mix activated alumina powder, nano carbon black, nano silica powder and the doping material of Example 1, then add polyethylene glycol and ethanol to adjust the solid content, transfer to a ball mill jar for ball milling, and sieve to obtain the transition layer slurry; Place the mold horizontally, pour in the transition layer slurry, let it stand at room temperature for 15 minutes, then add the base material until the mold is full, vibrate, let it stand for 1 hour, and the layered material distribution is completed to obtain the blank. Step S2: Pressing and primary sintering: Demold the brick blank from the mold, press it statically for 5 minutes under a pressure of 200 MPa, dry it at room temperature for 24 hours, dry it at 110℃ for 12 hours, and then transfer it to the sintering furnace. Under argon protection, heat it from room temperature to 800℃ at 5℃ / min and hold it for 1 hour, then heat it to 1400℃ at 8℃ / min and hold it for 3 hours, then heat it to 1750℃ at 5℃ / min and hold it for 2 hours, and then cool it to room temperature to obtain the primary sintered brick blank. Step S3: Coating and Secondary Sintering: The first-sintered brick blank was ultrasonically washed in ethanol for 10 min, dried, and then the transition layer of the first-sintered brick blank was immersed in the lanthanum phosphate sol of Example 5 for 60 s. It was dried at 120°C for 1 h, and then coated with the yttrium-stabilized zirconia sol of Example 5 and dried at 100°C for 40 min. The coating with the yttrium-stabilized zirconia sol of Example 5 was repeated 3 times. It was left to stand at 80°C for 12 h, and then transferred to a sintering furnace. The temperature was increased to 400°C at 2°C / min and held for 1 h, then increased to 1050°C at 3°C / min and held for 2 h, and then increased to 1250°C at 5°C / min and held for 3 h. It was then cooled to room temperature, thereby forming a micro-nano structured ceramic coating on the surface of the brick blank, and corundum bricks for zircon sand fluidized bed chlorination reactors were obtained.

[0030] Furthermore, in step S1: during the preparation of the base material: by mass fraction: 15-18% activated alumina powder, 6% clay, 4% elemental silicon and 4% thermosetting phenolic resin, with the remainder being tabular corundum, which is divided into 3.0-1.0mm, 0.1-1mm and <0.3mm specifications, with a weight ratio of 4:3:3; In the preparation of the transition layer slurry: the weight ratio of activated alumina powder, nano carbon black, nano silica powder, and encapsulated dopant material is 5.5:1:1.5:0.5; the amount of polyethylene glycol added is 5% of the total mass; and the solid content is adjusted to 70% by the amount of ethanol added. The mold dimensions are 240mm×120mm×70mm, and the thickness of its transition layer slurry is 2.5mm.

[0031] Example 2: Compared with Example 1, Example 2 changed the coating doping material to the one prepared in Example 2, while the other steps were the same.

[0032] Example 3: Compared with Example 1, Example 3 changed the coating doping material to the one prepared in Example 3, while the other steps were the same.

[0033] Example 4: In Example 4, the coating doped material was adjusted to be the same as that obtained in Preparation Example 4, while the other steps were the same.

[0034] Example 5: Compared with Example 1, the lanthanum phosphate sol and yttrium-stabilized zirconium oxide sol in Example 5 were adjusted to those obtained in Preparation Example 6, while the other steps were the same.

[0035] Example 6: Compared with Example 1, the lanthanum phosphate sol and yttrium stabilized zirconium oxide sol in Example 6 were adjusted to those obtained in Preparation Example 7, while the other steps were the same.

[0036] Example 7: Compared with Example 1, in step S1, the basic material preparation process is adjusted by mass fraction to: 18% activated alumina powder, 6% clay, 4% elemental silicon and 4% thermosetting phenolic resin, with the balance being tabular corundum. Other steps are the same.

[0037] Example 8: Compared with Example 1, in step S1, the basic material preparation process is adjusted by mass fraction to: 8% activated alumina powder, 6% clay, 4% elemental silicon and 4% thermosetting phenolic resin, with the balance being tabular corundum. Other steps are the same.

[0038] Example 9: Compared with Example 1, in step S1, the weight ratio of activated alumina powder, nano carbon black, nano silica powder and encapsulated dopant material in the preparation of transition layer slurry is adjusted to 5.5:1:1.5:0.6, and the other steps are the same.

[0039] Comparative Example 1: Compared with Example 1, in Comparative Example 1, the number of times the yttrium-stabilized zirconia sol was repeatedly coated in step S3 was reduced to 1, while the other steps remained the same.

[0040] Comparative Example 2: Compared with Example 1, Comparative Example 2 omits the first and second sintering steps in step S2 and directly performs coating followed by sintering, while the other steps are the same.

[0041] Comparative Example 3: Compared with Example 1, the coating doping material in Comparative Example 3 was replaced with the same mass of active alumina powder, while the other steps were the same.

[0042] The corundum bricks with micro / nano structured ceramic coatings on the surface of the zircon sand fluidized bed chlorination reactors obtained in Examples 1-9 and Comparative Examples 1-2 were used for performance testing: Chlorine corrosion resistance test: Referring to the principle of refractory material corrosion resistance test, the sample was placed in a tube furnace and a mixed gas of Cl2:CO:N2=1:1:8 (volume ratio) was introduced. The total gas flow rate was 200mL / min. The sample was exposed at a constant temperature of 900℃ for 100h, cooled, and its mass loss rate was measured. Thermal shock resistance test: According to GB / T 30873-2014, the sample was kept at 1100℃ for 30 min and then cooled in flowing water at 25℃ for 3 min. The number of cycles in which through-cracks appeared was observed and recorded. According to the above thermal shock test, after 0 thermal shock cycles, its resistance to chlorine corrosion was tested and recorded as the chlorine corrosion mass loss rate after thermal shock. High-speed particle erosion resistance test: Referring to the sandblasting abrasion test of ASTM G76, the sandblasting abrasion test machine was used. The alumina abrasive was 80 mesh, the nozzle diameter was 1.5 mm, the spray angle was 90°, the spray pressure was 0.4 MPa, the spray distance was 50 mm, and the abrasive flow rate was 300 g / min. The abrasion depth and maximum diameter after 5 min of erosion were measured and recorded.

[0043] The test results are shown in the table below: Table 1 Test Results The test results shown in the table indicate that the examples and comparative examples are compared as follows: Example 1: Using the encapsulated doped material from Example 1, the lanthanum phosphate sol and yttrium-stabilized zirconium oxide sol from Example 5, and the standard base material ratio and transition layer ratio, this scheme achieves synergy between the micro / nano structure transition layer and the double coating, resulting in a lower chlorine corrosion mass loss rate, a higher number of thermal shock cycles, excellent corrosion resistance after thermal shock, and good erosion resistance. Its performance stems from the synergistic effect of the sufficient growth of silicon carbide nanowires, the strong chemical bonding of the lanthanum phosphate bottom layer, and the dense barrier of the yttrium-stabilized zirconium oxide surface layer.

[0044] Example 2: Compared with Example 1, the coating doping material was adjusted to Preparation Example 2; due to the slight increase in the alumina content in the aluminum sol, the coating layer thickness was increased, and the protective effect on the MAX phase powder was slightly enhanced, but the improvement on catalytic efficiency and interfacial bonding was limited; its various properties were basically the same as those in Example 1, which shows that the slight change in the amount of aluminum sol has no significant impact on the overall performance and can be appropriately adjusted.

[0045] Example 3: Compared to Example 1, the coating doping material was adjusted to prepare Example 3. Due to the increased nickel nitrate content, more carbon nanotubes were generated during sintering, which were then transformed into a denser silicon carbide nanowire network. This network enhanced the mechanical anchoring and stress buffering effect of the subsequent coating. At the same time, the silicon carbide nanowires themselves also improved the corrosion resistance of the transition layer. Therefore, its various properties were better than those of Example 1. This further illustrates that by appropriately adjusting the nickel catalyst content and combining it with the synergistic catalytic mechanism of MAX phase powder, the performance of the micro / nano structure reinforcement layer can be improved.

[0046] Example 4: Compared to Example 1, the coating doping material was adjusted to prepare Example 4. Due to the significant reduction in nickel catalyst content, the number of catalytically generated carbon nanotubes and subsequently converted silicon carbide nanowires was significantly reduced, resulting in insufficient density and network integrity of the micro / nanostructure reinforcement layer. This led to a weakened mechanical anchoring effect on the subsequent coating, a decrease in interfacial bonding strength, and a reduction in the toughness of the transition layer. Therefore, its performance was inferior to that of Example 1, further illustrating the rationality and superiority of the catalyst content ratio used in Example 1.

[0047] Example 5: Compared to Example 1, the lanthanum phosphate sol was adjusted to prepare Example 6; the amount of citric acid as a complexing agent was reduced, which led to a decrease in the stability and particle size control of the lanthanum phosphate sol, a decrease in the uniformity of crystallization of the coating after sintering, and a decrease in the chemical bonding efficiency with the substrate; this further illustrates the rationality of the amount of citric acid used in the lanthanum phosphate sol formulation used in Example 1.

[0048] Example 6: Compared to Example 1, the yttrium-stabilized zirconia sol was adjusted to prepare Example 7; insufficient yttrium doping caused zirconia to be unable to be completely stabilized into a cubic phase after sintering, and a partial phase transition from tetragonal to monoclinic phase occurred. The volume effect accompanying the phase transition caused microcracks to be generated inside the coating, reducing its compactness. Therefore, its performance was inferior to that of Example 1; this further illustrates the necessity and superiority of the yttrium doping amount in the yttrium-stabilized zirconia sol used in Example 1.

[0049] Example 7: Compared to Example 1, the content of active alumina powder in the base material was adjusted to 18%. The increase in active alumina powder slightly improved the sintering density of the matrix and provided more active sites for bonding with the transition layer, but had little effect on the transition layer itself. This shows that fluctuations in the base material ratio within a certain range have a limited impact on the final coating performance.

[0050] Example 8: Compared to Example 1, the content of active alumina powder in the base material was adjusted to 8%; insufficient active alumina powder led to a decrease in the density of the matrix during sintering, an increase in porosity, and a decrease in the interfacial bonding strength with the transition layer, resulting in performance inferior to Example 1: This further illustrates the rationality of the base material ratio used in Example 1.

[0051] Example 9: Compared to Example 1, the ratio of the coating dopant material in the transition layer slurry was adjusted from 0.5 to 0.6. The increase in coating dopant material increased the content of catalyst and MAX phase powder in the transition layer, resulting in a denser silicon carbide nanowire network and a better micro-nano structure reinforcement effect. Therefore, its performance was superior to that of Example 1. This further illustrates that appropriately increasing the amount of coating dopant material, combined with the mechanism of nickel-catalyzed growth of carbon nanotubes and in-situ conversion into silicon carbide nanowires, can improve the reinforcement effect of the micro-nano structure layer.

[0052] Comparative Example 1: Compared to Example 1, the number of coatings of yttrium-stabilized zirconium oxide sol was reduced from 3 to 1. Due to the significant reduction in surface layer thickness, the coating lacked density and integrity, and had penetrating micropore defects, which could not effectively block chlorine gas penetration. Therefore, its performance was significantly inferior to that of Example 1. This further illustrates the necessity of the multi-layer coating process used in Example 1 for ensuring coating integrity and protective performance.

[0053] Comparative Example 2: Compared to Example 1, the step-by-step sintering process of primary and secondary sintering was eliminated. The coating was directly applied to the unsintered brick blank and then sintered once. Since the brick blank directly entered the coating sintering stage without primary sintering, the shrinkage of the brick blank during sintering was asynchronous with that of the coating, resulting in huge interfacial shear stress, which led to severe cracking and peeling of the coating. At the same time, the silicon carbide nanowire generation reaction in the transition layer interfered with the matrix densification reaction, resulting in incomplete formation of the micro-nano structure. Therefore, its performance was significantly inferior to that of Example 1. This further illustrates the key role of the step-by-step sintering process used in Example 1 in ensuring the integrity of the coating and the interfacial bonding.

[0054] Comparative Example 3: Compared to Example 1, the coating doping material was replaced with the same mass of activated alumina powder. Due to the complete elimination of the MAX phase powder and nickel catalyst, silicon carbide nanowire micro / nano structures could not be generated in the transition layer. It consisted only of activated alumina powder, nano carbon black, and nano silica. After sintering, it formed a loose and porous alumina-silicon carbide mixed layer, lacking three-dimensional interlocking network reinforcement. This resulted in extremely weak mechanical anchoring effect on subsequent coatings and a significant decrease in interfacial bonding strength. Therefore, its performance was the worst among all samples. This further illustrates the core role and irreplaceable nature of the coating doping material and its catalytic generation mechanism for micro / nano structures used in Example 1 in achieving a high-performance coating system.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. The application of a micro / nano-structured ceramic coating in a zircon sand fluidized bed chlorination reactor, characterized in that: Includes the following steps: Step S1: Mixing and Layering: Mix plate-shaped corundum, activated alumina powder, clay, elemental silicon and thermosetting phenolic resin to obtain the base material; mix activated alumina powder, nano carbon black, nano silica powder and encapsulation dopant material, then add polyethylene glycol and ethanol to adjust the solid content, transfer to a ball mill jar for ball milling, and sieve to obtain the transition layer slurry; Place the mold horizontally, pour in the transition layer slurry, let it stand at room temperature for 15 minutes, then add the base material until the mold is full, vibrate, let it stand for 1 hour, and the layered material distribution is completed to obtain the brick blank. Step S2: Pressing and primary sintering: Demold the brick blank from the mold, press it statically for 5 minutes under a pressure of 200 MPa, dry it at room temperature for 24 hours, dry it at 110℃ for 12 hours, and then transfer it to the sintering furnace. Under argon protection, heat it from room temperature to 800℃ at 5℃ / min and hold it for 1 hour, then heat it to 1400℃ at 8℃ / min and hold it for 3 hours, then heat it to 1750℃ at 5℃ / min and hold it for 2 hours, and then cool it to room temperature to obtain the primary sintered brick blank. Step S3: Coating and Secondary Sintering: The primary sintered brick blank is ultrasonically washed in ethanol for 10 min, dried, and then the transition layer of the primary sintered brick blank is immersed in lanthanum phosphate sol for 60 s. It is then dried at 120℃ for 1 h. Yttrium-stabilized zirconia sol is then coated on the transition layer and dried at 100℃ for 40 min. The coating of yttrium-stabilized zirconia sol is repeated 3 times. The blank is then left to stand at 80℃ for 12 h, and then transferred to a sintering furnace. The temperature is increased to 400℃ at 2℃ / min and held for 1 h, then increased to 1050℃ at 3℃ / min and held for 2 h, and then increased to 1250℃ at 5℃ / min and held for 3 h. The blank is then cooled to room temperature, thereby forming a micro-nano structured ceramic coating on the surface of the brick blank, and corundum bricks for zircon sand fluidized bed chlorination reactors are obtained.

2. The application of the micro / nano structured ceramic coating according to claim 1 in a zircon sand fluidized bed chlorination reactor, characterized in that: In step S1: During the preparation of the base material: by mass fraction: 15-18% activated alumina powder, 6% clay, 4% elemental silicon, and 4% thermosetting phenolic resin, with the remainder being tabular corundum, which is divided into 3.0-1.0mm, 0.1-1mm, and <0.3mm specifications, with a weight ratio of 4:3:3; During the preparation of the transition layer slurry: the weight ratio of activated alumina powder, nano carbon black, nano silica powder, and encapsulated dopant material is 5.5:1:1.5:0.5-0.6, the amount of polyethylene glycol added is 5% of the total mass, and the solid content is adjusted to 70% by the amount of ethanol added; the thickness of the transition layer slurry is 2.5mm.

3. The application of the micro / nano structured ceramic coating according to claim 1 in a zircon sand fluidized bed chlorination reactor, characterized in that: The encapsulated doped material is prepared through the following steps: Step A1: Mix chromium powder, aluminum powder and graphite powder and add them to a ball mill jar with a ball-to-powder ratio of 10:1 and a rotation speed of 200 rpm. Under argon conditions, ball mill for 12 hours, pass through a 100-mesh sieve, and transfer to a crucible. Perform microwave sintering in a 2.45 GHz multimode microwave sintering furnace at a sintering temperature of 1250℃ and a holding time of 30 min. Grind again, sieve, and obtain MAX phase powder. Step A2: Mix aluminum isopropoxide and ethanol, stir for 30 min at 300 rpm and 60°C, then add deionized water, heat to 80°C, continue stirring for 30 min, then add nitric acid solution to adjust the pH to 3.5, continue heating to 90°C, and stir for 2 h to obtain aluminum sol; mix nickel nitrate hexahydrate and deionized water, then add MAX phase powder and ultrasonically disperse for 30 min, then add aluminum sol, stir for 2 h at 300 rpm and 60°C, rotary evaporate, dry, grind, and sieve to obtain the coated doped material.

4. The application of the micro / nano structured ceramic coating according to claim 3 in a zircon sand fluidized bed chlorination reactor, characterized in that: In step A1, the molar ratio of chromium powder, aluminum powder and graphite powder is 2 mol: 1.1 mol: 1 mol, wherein the purity of chromium powder is ≥99.5% and the particle size is ≤45 μm, the purity of aluminum powder is ≥99.8% and the particle size is ≤45 μm, and the graphite powder is ≥99.5% and the particle size is ≤75 μm.

5. The application of the micro / nano structured ceramic coating according to claim 3 in a zircon sand fluidized bed chlorination reactor, characterized in that: In step A2: During the preparation of aluminum sol: the ratio of aluminum isopropoxide to ethanol is 20.4-21g:20mL:25mL, and the mass fraction of nitric acid solution is 30%; During the preparation of the coating doped material: the ratio of nickel nitrate, deionized water, MAX phase powder and aluminum sol is 9.5-10g:3.5g:30mL:8g.

6. The application of the micro / nano structured ceramic coating according to claim 1 in a zircon sand fluidized bed chlorination reactor, characterized in that: The lanthanum phosphate sol was prepared by the following steps: Lanthanum nitrate solution and phosphoric acid solution were mixed and stirred for 20 min at a stirring rate of 300 rpm and a temperature of 5℃. Citric acid was then added and stirring was continued for 10 min. Ammonia solution was then added to adjust the pH to 3.

5. Ethylene glycol was then added, the temperature was raised to 80℃, and stirring was carried out for 5 min. The mixture was then allowed to stand for 24 h to obtain lanthanum phosphate sol. In the preparation of the lanthanum phosphate sol, the ratio of lanthanum nitrate solution, phosphoric acid solution, citric acid and ethylene glycol is 15 mL:15 mL:5.7 g:3.5 g, wherein the molar concentration of lanthanum nitrate solution is 1 mol / L and the molar concentration of phosphoric acid solution is 1 mol / L.

7. The application of the micro / nano structured ceramic coating according to claim 1 in a zircon sand fluidized bed chlorination reactor, characterized in that: The yttrium-stabilized zirconium oxide sol is prepared by the following steps: Zirconium oxychloride, yttrium nitrate and ethanol were mixed and stirred at 300 rpm at room temperature for 30 min. Then acetylacetone was added, the temperature was raised to 60 °C and stirred for 1 h. Then ethanol solution was added and stirred for 2 h. After standing for 72 h, yttrium-stabilized zirconium oxide sol was obtained. In the preparation of the yttrium-stabilized zirconium oxide sol, the ratio of zirconium oxychloride, yttrium nitrate, ethanol, acetylacetone and ethanol solution is 8.05g:1.55g:40mL:3g:1mL, and the volume fraction of the ethanol solution is 50%.

8. The micro / nano structured ceramic coating used in any of the applications described in claims 1-7, characterized in that: The micro-nano structure ceramic coating is a surface coating for corundum bricks used in a zircon sand boiling chlorination reactor. It is formed by constructing a nano-wire-reinforced micro-nano structure transition layer in situ on the surface of the corundum brick substrate through a layered material distribution process, and then sequentially constructing a lanthanum phosphate binding layer and a yttrium-stabilized zirconium oxide barrier layer on this transition layer, thereby forming a micro-nano structure ceramic coating.

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