Crack self-repairing acid-resistant spray paint and method of use thereof

Abstract

The present application belongs to the technical field of unshaped refractory material, and discloses a kind of crack self-repairing acid-resistant spray coating and its using method.The crack self-repairing acid-resistant spray coating of the present application includes the following mass percentage of raw materials: 35~50% of coke-vitreous stone aggregate, 20~30% of high alumina bauxite powder, 6~10% of active alumina micro powder, 1~4% of quartz powder, 2~5% of kyanite powder, 2~4% of crack self-repairing microcapsule, 0.08~0.2% of plasticizer, 0.1~0.4% of curing agent, 0.1~0.5% of surface modifier, and 9~13% of ammonium type silica sol.The crack self-repairing acid-resistant spray coating of the present application has the characteristics of easy construction, high strength, good high-temperature volume stability, self-repairing after crack, excellent acid corrosion resistance, etc., and is especially suitable for hot blast furnace dome position.

Description

Technical Field

[0001] This invention belongs to the technical field of monolithic refractory materials, specifically relating to a self-healing acid-resistant spray coating for cracks and its application method. Background Technology

[0002] With the rapid development of blast furnace ironmaking technology, high blast temperature and high oxygen content can accelerate the reaction and improve ironmaking efficiency. Blast furnace production places increasingly higher demands on the temperature of hot blast stoves. Currently, most hot blast stoves in my country use a top-fired structure with a blower temperature range of 1250~1300℃. However, the temperature in the combustion chamber area at the dome of the hot blast stove can reach over 1350℃. During the operation of the hot blast stove, a large amount of NOx is generated at the dome. When NOx gas combines with condensate on the low-temperature surface inside the furnace shell, it forms an acidic nitrate solution, causing intergranular stress corrosion on the furnace shell. This damages the furnace shell due to nitrate corrosion, and in severe cases, can lead to the shutdown of the hot blast stove. Therefore, the furnace shell at the dome of the hot blast stove is first coated with an acid-resistant coating to prevent intergranular stress corrosion and thus prevent corrosion by acidic substances. Then, an acid-resistant coating is sprayed as an insulation layer to prevent heat transfer to the furnace shell and avoid excessive temperature causing deformation of the furnace shell, thereby affecting the service life of the hot blast stove.

[0003] Due to its structural characteristics, the dome of a hot blast stove is not suitable for cast-in-place construction. Currently, spraying is the most common method of application. Spray coatings include cement-bonded, water glass-bonded, and sol-gel-bonded coatings. However, regardless of the bonding method, the dome's hemispherical shape makes it susceptible to shrinkage cracks and spalling under the influence of internal material stress, its own weight, and other factors, making the furnace shell vulnerable to acid and high-temperature erosion. Therefore, the performance of acid-resistant spray coatings is particularly crucial, requiring them to simultaneously possess characteristics such as ease of application, high strength, crack resistance, good acid corrosion resistance, and good high-temperature volume stability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a self-healing acid-resistant spray coating for cracks, which has the characteristics of easy construction, high strength, good high temperature volume stability, self-repair after cracks are generated, and excellent acid corrosion resistance. It is particularly suitable for the top of the hot blast stove arch.

[0005] To address the technical problem presented in this invention, a self-healing acid-resistant spray coating for cracks is provided, comprising the following raw materials in weight percentages: 35-50% coke aggregate, 20-30% high-alumina bauxite powder, 6-10% activated alumina micro powder, 1-4% quartz powder, 2-5% kyanite powder, 2-4% self-healing microcapsules for cracks, 0.08-0.2% plasticizer, 0.1-0.4% curing agent, 0.1-0.5% surface modifier, and 9-13% ammonium silica sol.

[0006] In the above scheme, the Al2O3 content of the charred gemstone aggregate is ≥45wt%, and the Fe2O3 content is ≤1wt%.

[0007] In the above scheme, the coked gemstone aggregate is composed of the following three grades of particles in the following mass percentages: particles with a diameter of 5-3mm account for 20-30%, particles with a diameter of 3-1mm account for 40-50%, and particles with a diameter of 1-0.074mm account for 30-40%.

[0008] In the above scheme, the Al2O3 content of the high-alumina bauxite powder is ≥88wt%, and the Fe2O3 content is ≤1wt%.

[0009] In the above scheme, the particle size of the high-alumina bauxite powder is ≤0.074mm.

[0010] In the above scheme, the Al2O3 content of the activated alumina micro powder is ≥99.5wt%, and the median particle size D is... 50 ≤2μm.

[0011] In the above scheme, the activated alumina micro powder is microcrystalline phase-transformed alumina micro powder with an α-Al2O3 phase content ≥95% and a primary crystal size of 0.4~0.5μm.

[0012] In the above scheme, the SiO2 content of the quartz powder is ≥99wt%, and the Fe2O3 content is ≤0.02wt%.

[0013] In the above scheme, the particle size of the quartz powder is ≤0.074mm.

[0014] In the above scheme, the kyanite powder has an Al2O3 content ≥ 60wt% and an Fe2O3 content ≤ 1.2wt%.

[0015] In the above scheme, the particle size of the kyanite powder is 0.074~0.15mm.

[0016] In the above scheme, the wall material of the self-healing crack microcapsule is alumina, and the core material is WSi2 and TiB2.

[0017] In the above scheme, the preparation method of the self-healing crack microcapsule is as follows: 1) The mixed powder of WSi2 and TiB2 was washed alternately with acid and water and then dried in an inert atmosphere to obtain the modified mixed powder; 2) After uniformly mixing the modified powder and aluminum sol, freeze spray drying is performed to obtain aluminum sol-coated composite particles; 3) The aluminum sol-coated composite particles were calcined in an inert atmosphere and cooled to obtain self-healing crack microcapsules.

[0018] Furthermore, the particle size of WSi2 is ≤44μm, and the particle size of TiB2 is ≤44μm.

[0019] Furthermore, the mass ratio of WSi2 to TiB2 is 1:1 to 1:2.

[0020] Furthermore, the alternating washing is performed 1 to 10 times, each time including acid washing and water washing.

[0021] Furthermore, the washing acid is a dilute hydrochloric acid solution with a mass fraction of 5-15%.

[0022] Furthermore, the washing process involves immersing the mixed powder in a dilute hydrochloric acid solution, stirring and washing thoroughly for 3-5 minutes, filtering, then immersing it in water again, stirring and washing thoroughly for 5-8 minutes, and filtering; repeating this process 1-10 times until the washed water is neutral.

[0023] Furthermore, the inert atmosphere is either nitrogen or argon.

[0024] Further, in step 1), the drying temperature is 50~150℃ and the time is 5~10h.

[0025] Furthermore, the solid content of the aluminum sol is ≥20%.

[0026] Furthermore, the mass ratio of the modified mixed powder to the aluminum sol is 1.5:1 to 1.2:1.

[0027] Furthermore, the freezing temperature of the freeze spray drying is -20 to -40°C, and the total time from the start of cooling to the end of sublimation drying is 15 to 20 hours.

[0028] Furthermore, the roasting adopts a three-stage heating system: the first stage is to raise the temperature to 100~120℃ and hold for 9~13 hours; the second stage is to raise the temperature to 140~160℃ and hold for 10~14 hours; the third stage is to raise the temperature to 500~600℃ and hold for 20~25 hours.

[0029] Furthermore, the heating rate in the first stage is 5~8℃ / min, the heating rate in the second stage is 10~15℃ / min, and the heating rate in the third stage is 5~7℃ / min.

[0030] In the above scheme, the diameter of the self-healing crack microcapsule is 200~400μm.

[0031] In the above scheme, the plasticizer is one or both of carboxymethyl cellulose and hydroxypropyl starch.

[0032] In the above scheme, the curing agent is active magnesium oxide with an MgO content ≥90wt% and a particle size ≤45μm.

[0033] In the above scheme, the surface modifier is an aminosilane coupling agent, specifically one or more of γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and γ-aminopropyltrimethoxysilane.

[0034] In the above scheme, the ammonium silica sol has a silica content of 30-40 wt%, an ammonium ion content of 0.05-0.2 wt%, and a pH value of 7-9.

[0035] This invention also provides a method for using a self-healing acid-resistant spray coating for cracks, comprising the following steps: S1. Mix coke aggregate, high-alumina bauxite powder, activated alumina micro powder, quartz powder, kyanite powder, crack self-healing microcapsules, plasticizer, curing agent and surface modifier into a uniform aggregate. S2. Add a portion of ammonium silica sol to the uniform aggregate, mix evenly, and then feed it into the spraying machine. Add the remaining ammonium silica sol at the outlet of the spraying machine to achieve a material state suitable for spraying. S3. Apply a semi-dry spraying method to the top of the hot air furnace. After the application is completed, allow it to cure naturally, then heat it up and bake it until it reaches the service temperature.

[0036] In the above scheme, 60-70% of the total amount of ammonium silica sol is added before the uniform aggregate is fed into the spraying machine.

[0037] In the above scheme, the natural maintenance time is 24~72 hours.

[0038] In the above scheme, the baking includes multiple heating stages performed sequentially: the first stage, heating to 110~150℃ and holding for 24~48h; the second stage, heating to 300~400℃ and holding for 48~72h; the third stage, heating to 550~650℃ and holding for 24~48h.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention uses calcined bauxite as aggregate and high-alumina bauxite powder and kyanite powder as matrix, utilizing the synergistic effect of the three: bauxite is rich in corundum and mullite precursors, which react with the active SiO2 in calcined bauxite and kyanite at high temperature to generate secondary mullite, enhancing the matrix bonding force. This "in-situ mullitization" process can fill pores and increase density, thereby improving the thermal shock resistance and erosion resistance of the castable; in addition, the stable skeleton structure provided by calcined bauxite is conducive to the directional growth of mullite crystals, forming a needle-like interwoven network, which significantly improves the high-temperature flexural strength and anti-stripping performance of the material.

[0040] 2) This invention achieves self-repair of cracks by incorporating self-healing microcapsules. The self-healing microcapsules have a double-layer structure: an inner layer of WSi2 and TiB2 mixed powder, and an outer layer of nano-alumina film. When added to the spray coating, the nano-alumina on the outside of the microcapsules reacts with SiO2 and other substances in the surrounding material to form a shell-like bond. When cracks appear in the spray coating, under the stress of crack propagation, the shell breaks open, exposing the internal self-healing agents WSi2 and TiB2. These two substances can react with oxygen at a relatively low temperature (800℃) to generate TiO2, SiO2, and B2O3. All three products can effectively fill the cracks, and no gas is generated during the oxidation reaction, preventing further crack propagation. The SiO2 generated by the reaction is an excellent crack filler. It can fill the cracks in the material to form a dense SiO2 oxide layer, while also preventing the further diffusion of acidic gases. The B2O3 generated by the reaction is a sintering accelerator, which promotes the reaction of Al2O3 and SiO2 in the matrix to form mullite whiskers, effectively improving the mechanical properties of the coating. The TiO2 generated by the reaction has strong adhesion to the alumina in the material, which can form a strong interfacial bond, thus ensuring the strength recovery of the coating after self-healing.

[0041] 3) This invention uses ammonium ion-stabilized silica sol as a binder. Silica sol and fused silica have good wettability and coating properties. During the drying and heating process, silica sol forms a continuous gel film at the aggregate-matrix interface, reducing microcracks caused by thermal expansion mismatch. At high temperature, SiO2 in silica sol reacts with Al2O3 in activated alumina micropowder to generate mullite (3Al2O3·2SiO2), forming a needle-like interwoven structure, which significantly enhances the toughness and bonding strength of the matrix. Furthermore, the generated mullite phase further "welds" the interface, improving the overall structural stability. Detailed Implementation

[0042] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0043] In the following examples, the coke alumina aggregate used has an Al2O3 content of 45-50 wt% and an Fe2O3 content of ≤1 wt%; the high-alumina bauxite powder has an Al2O3 content of ≥88 wt%, an Fe2O3 content of ≤1 wt%, and a particle size of ≤0.074 mm; the activated alumina micro powder has an Al2O3 content of ≥99.5 wt% and a median particle size D. 50The particle size is ≤2μm. It is a microcrystalline phase-transformed alumina powder with an α-Al2O3 phase content ≥95% and a primary crystal size of 0.4~0.5μm; the quartz powder has a SiO2 content ≥99wt%, an Fe2O3 content ≤0.02wt%, and a particle size ≤0.074mm; the kyanite powder has an Al2O3 content 60~65wt%, an Fe2O3 content ≤1.2wt%, and a particle size of 0.074~0.15mm; the WSi2 has a particle size ≤44μm, and the TiB2 has a particle size ≤44μm; the alumina sol has a solid content of 20~30%; the active magnesium oxide has an MgO content ≥90wt% and a particle size ≤45μm; the ammonium silica sol has a silica content of 30±1wt%, an ammonium ion content of 0.16±0.01wt%, and a pH value of 7.2~7.5.

[0044] Example 1 A self-healing acid-resistant spray coating for cracks, the composition of which is as follows by mass percentage: The composition includes: 36 wt% coke aggregate, 30 wt% high-alumina bauxite powder, 10 wt% activated alumina micro powder, 4 wt% quartz powder, 5 wt% kyanite powder, 5 wt% self-healing microcapsules, 0.1 wt% carboxymethyl cellulose, 0.4 wt% activated magnesium oxide, 0.5 wt% surface modifier (γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, γ-aminopropyltrimethoxysilane in a mass ratio of 1:1:1), and 9 wt% ammonium silica sol.

[0045] The coke aggregate is composed of the following three grades of particles by mass percentage: 30% of particles with a diameter of 5-3mm, 40% of particles with a diameter of 3-1mm, and 30% of particles with a diameter of 1-0.074mm.

[0046] The crack self-healing microcapsules have a diameter of 240 μm and are prepared by the following method: 1) The mixed powder of WSi2 and TiB2 in a mass ratio of 1:1.2 was washed alternately with a 7% (w / w) dilute hydrochloric acid solution and deionized water. The specific washing process was as follows: the mixed powder was immersed in the dilute hydrochloric acid solution and thoroughly stirred and washed for 3-5 minutes, then filtered. It was then immersed in deionized water and thoroughly stirred and washed for 5-8 minutes, and then filtered. This process was repeated 1-10 times until the washing water was neutral. After washing, it was dried in nitrogen at 70°C for 7 hours to obtain the modified mixed powder. 2) The modified mixed powder and aluminum sol were mixed evenly at a mass ratio of 1.3:1 and then subjected to freeze spray drying at a freezing temperature of -28℃. The total time from the start of cooling to the end of sublimation drying was 18h, resulting in aluminum sol-coated composite particles. 3) The aluminum sol-coated composite particles were calcined in nitrogen. The specific calcination process was as follows: in the first stage, the temperature was increased from room temperature to 110℃ at a rate of 6℃ / min and held for 12h; in the second stage, the temperature was increased to 150℃ at a rate of 12℃ / min and held for 13h; in the third stage, the temperature was increased to 550℃ at a rate of 6℃ / min and held for 20h; after calcination, the particles were cooled to obtain self-healing crack microcapsules.

[0047] According to the above formula, coke aggregate, high-alumina bauxite powder, activated alumina micro powder, quartz powder, kyanite powder, crack self-healing microcapsules, plasticizer, curing agent and surface modifier are mixed into a uniform aggregate; 62% of the total amount of ammonium silica sol is added to the uniform aggregate, and after mixing evenly, it is fed into the spraying machine. The remaining ammonium silica sol is added at the outlet of the spraying machine to achieve a material state suitable for spraying; the top part of the hot air furnace is sprayed using a semi-dry spraying method. After the construction is completed, it is naturally cured for 36 hours, and then baked at 110℃ for 30 hours → 350℃, 60 hours → 600℃ for 30 hours, and finally heated to the service temperature.

[0048] Example 2 An acid-resistant spray coating containing self-healing crack microcapsules, the composition of which is as follows by mass percentage: The composition includes: 47wt% coke aggregate, 25wt% high-alumina bauxite powder, 7wt% activated alumina micro powder, 3wt% quartz powder, 3wt% kyanite powder, 4wt% self-healing microcapsules for cracks, 0.2wt% plasticizer (carboxymethyl cellulose and hydroxypropyl starch in a mass ratio of 3:1), 0.4wt% activated magnesium oxide, 0.4wt% surface modifier (N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane), and 10wt% ammonium silica sol.

[0049] The coke aggregate is composed of the following three grades of particles by mass percentage: particles with a diameter of 5-3mm account for 22%, particles with a diameter of 3-1mm account for 48%, and particles with a diameter of 1-0.074mm account for 30%.

[0050] The crack self-healing microcapsules have a diameter of 200 μm and are prepared by the following method: 1) The mixed powder of WSi2 and TiB2 in a mass ratio of 1:1 was washed alternately with a 5% (w / w) dilute hydrochloric acid solution and deionized water. The specific washing process was as follows: the mixed powder was immersed in the dilute hydrochloric acid solution and thoroughly stirred and washed for 3-5 minutes, then filtered. It was then immersed in deionized water and thoroughly stirred and washed for 5-8 minutes, and then filtered. This process was repeated 1-10 times until the washing water was neutral. After washing, it was placed in nitrogen and dried at 80°C for 6 hours to obtain the modified mixed powder. 2) The modified mixed powder and aluminum sol were mixed evenly at a mass ratio of 1.5:1 and then subjected to freeze spray drying at a freezing temperature of -25℃. The total time from the start of cooling to the end of sublimation drying was 15h, resulting in aluminum sol-coated composite particles. 3) The aluminum sol-coated composite particles were calcined in nitrogen. The specific calcination process was as follows: in the first stage, the temperature was increased from room temperature to 105℃ at a rate of 5℃ / min and held for 10h; in the second stage, the temperature was increased to 140℃ at a rate of 11℃ / min and held for 10h; in the third stage, the temperature was increased to 500℃ at a rate of 5℃ / min and held for 20h; after calcination, the particles were cooled to obtain self-healing crack microcapsules.

[0051] According to the above formula, coke aggregate, high-alumina bauxite powder, activated alumina micro powder, quartz powder, kyanite powder, crack self-healing microcapsules, plasticizer, curing agent and surface modifier are mixed into a uniform aggregate. 65% of the total amount of ammonium silica sol is added to the uniform aggregate, and after mixing evenly, it is fed into a spraying machine. The remaining ammonium silica sol is added at the outlet of the spraying machine to achieve a material state suitable for spraying. The top part of the hot air furnace is sprayed using a semi-dry spraying method. After the construction is completed, it is naturally cured for 48 hours, and then baked at 110℃ for 35 hours → 350℃, 60 hours → 600℃ for 35 hours. Finally, the temperature is raised to the service temperature.

[0052] Example 3 An acid-resistant spray coating containing self-healing crack microcapsules, the composition of which is as follows by mass percentage: The composition includes: 50wt% coke aggregate, 23wt% high-alumina bauxite powder, 6wt% activated alumina micro powder, 3wt% quartz powder, 2wt% kyanite powder, 2wt% self-healing microcapsules, 0.1wt% hydroxypropyl starch, 0.4wt% activated magnesium oxide, 0.5wt% surface modifier (γ-aminopropyltrimethoxysilane), and 13wt% ammonium silica sol.

[0053] The coke aggregate is composed of the following three grades of particles by mass percentage: particles with a diameter of 5-3mm account for 20%, particles with a diameter of 3-1mm account for 46%, and particles with a diameter of 1-0.074mm account for 34%.

[0054] The crack self-healing microcapsules have a diameter of 300 μm and are prepared by the following method: 1) The mixed powder of WSi2 and TiB2 in a mass ratio of 1:1.5 was washed alternately with a 9% (w / w) dilute hydrochloric acid solution and deionized water. The specific washing process was as follows: the mixed powder was immersed in the dilute hydrochloric acid solution and thoroughly stirred and washed for 3-5 minutes, then filtered. It was then immersed in deionized water and thoroughly stirred and washed for 5-8 minutes, and then filtered. This process was repeated 1-10 times until the washing water was neutral. After washing, it was placed in nitrogen and dried at 100°C for 5 hours to obtain the modified mixed powder. 2) The modified mixed powder and aluminum sol were mixed evenly at a mass ratio of 1.4:1 and then subjected to freeze spray drying at a freezing temperature of -30℃. The total time from the start of cooling to the end of sublimation drying was 17h, resulting in aluminum sol-coated composite particles. 3) The aluminum sol-coated composite particles were calcined in nitrogen. The specific calcination process was as follows: in the first stage, the temperature was increased from room temperature to 120℃ at a rate of 7℃ / min and held for 10h; in the second stage, the temperature was increased to 150℃ at a rate of 13℃ / min and held for 11h; in the third stage, the temperature was increased to 550℃ at a rate of 7℃ / min and held for 22h; after calcination, the particles were cooled to obtain crack self-healing microcapsules.

[0055] According to the above formula, coke aggregate, high-alumina bauxite powder, activated alumina micro powder, quartz powder, kyanite powder, crack self-healing microcapsules, plasticizer, curing agent and surface modifier are mixed into a uniform aggregate. 68% of the total amount of ammonium silica sol is added to the uniform aggregate, and after mixing evenly, it is fed into a spraying machine. The remaining ammonium silica sol is added at the nozzle of the spraying machine to achieve a material state suitable for spraying. The top part of the hot air furnace is sprayed using a semi-dry spraying method. After the construction is completed, it is naturally cured for 40 hours, and then baked at 110℃ for 48 hours → 350℃ for 48 hours → 600℃ for 30 hours. Finally, the temperature is raised to the service temperature.

[0056] Example 4 An acid-resistant spray coating containing self-healing crack microcapsules, the composition of which is as follows by mass percentage: The composition includes: 38 wt% coke aggregate, 28 wt% high-alumina bauxite powder, 10 wt% activated alumina micro powder, 3 wt% quartz powder, 4 wt% kyanite powder, 3 wt% self-healing microcapsules for cracks, 0.2 wt% plasticizer (carboxymethyl cellulose and hydroxypropyl starch in a 1:1 mass ratio), 0.3 wt% activated magnesium oxide, 0.5 wt% surface modifier (γ-aminopropyltriethoxysilane and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane in a 1:1 mass ratio), and 13 wt% ammonium silica sol.

[0057] The coke aggregate is composed of the following three grades of particles by mass percentage: particles with a diameter of 5-3mm account for 26%, particles with a diameter of 3-1mm account for 42%, and particles with a diameter of 1-0.074mm account for 32%.

[0058] The crack self-healing microcapsules have a diameter of 350 μm and are prepared by the following method: 1) The mixed powder of WSi2 and TiB2 in a mass ratio of 1:1.8 was washed alternately with a 10% (w / w) dilute hydrochloric acid solution and deionized water. The specific washing process was as follows: the mixed powder was immersed in the dilute hydrochloric acid solution and thoroughly stirred and washed for 3-5 minutes, then filtered. It was then immersed in deionized water and thoroughly stirred and washed for 5-8 minutes, and then filtered. This process was repeated 1-10 times until the washing water was neutral. After washing, it was placed in nitrogen and dried at 120℃ for 9 hours to obtain the modified mixed powder. 2) The modified mixed powder and aluminum sol were mixed evenly at a mass ratio of 1.2:1 and then subjected to freeze spray drying at a freezing temperature of -35℃. The total time from the start of cooling to the end of sublimation drying was 20h, resulting in aluminum sol-coated composite particles. 3) The aluminum sol-coated composite particles were calcined in nitrogen. The specific calcination process was as follows: in the first stage, the temperature was increased from room temperature to 110℃ at a rate of 6℃ / min and held for 13h; in the second stage, the temperature was increased to 160℃ at a rate of 10℃ / min and held for 10h; in the third stage, the temperature was increased to 600℃ at a rate of 6℃ / min and held for 25h; after calcination, the particles were cooled to obtain self-healing crack microcapsules.

[0059] According to the above formula, coke aggregate, high-alumina bauxite powder, activated alumina micro powder, quartz powder, kyanite powder, crack self-healing microcapsules, plasticizer, curing agent and surface modifier are mixed into a uniform aggregate. 69% of the total amount of ammonium silica sol is added to the uniform aggregate, and after mixing evenly, it is fed into a spraying machine. The remaining ammonium silica sol is added at the outlet of the spraying machine to achieve a material state suitable for spraying. The top part of the hot air furnace is sprayed using a semi-dry spraying method. After the construction is completed, it is naturally cured for 72 hours, and then baked at 110℃ for 24 hours → 350℃, 50 hours → 600℃ for 30 hours. Finally, the temperature is raised to the service temperature.

[0060] Example 5 An acid-resistant spray coating containing self-healing crack microcapsules, the composition of which is as follows by mass percentage: The composition includes: 42 wt% coke aggregate, 26 wt% high-alumina bauxite powder, 8 wt% activated alumina micro powder, 2 wt% quartz powder, 5 wt% kyanite powder, 4 wt% self-healing microcapsules for cracks, 0.1 wt% plasticizer (carboxymethyl cellulose and hydroxypropyl starch in a mass ratio of 2:1), 0.4 wt% activated magnesium oxide, 0.5 wt% surface modifier (γ-aminopropyltriethoxysilane and γ-aminopropyltrimethoxysilane in a mass ratio of 1:1), and 12 wt% ammonium silica sol.

[0061] The coke aggregate is composed of the following three grades of particles by mass percentage: particles with a diameter of 5-3mm account for 25%, particles with a diameter of 3-1mm account for 43%, and particles with a diameter of 1-0.074mm account for 32%.

[0062] The crack self-healing microcapsules have a diameter of 380 μm and are prepared by the following method: 1) The mixed powder of WSi2 and TiB2 in a mass ratio of 1:2 was washed alternately with a 13% (w / w) dilute hydrochloric acid solution and deionized water. The specific washing process was as follows: the mixed powder was immersed in the dilute hydrochloric acid solution and thoroughly stirred and washed for 3-5 minutes, then filtered. It was then immersed in deionized water and thoroughly stirred and washed for 5-8 minutes, and then filtered. This process was repeated 1-10 times until the washing water was neutral. After washing, it was placed in nitrogen and dried at 150°C for 10 hours to obtain the modified mixed powder. 2) The modified mixed powder and aluminum sol were mixed evenly at a mass ratio of 1.5:1 and then subjected to freeze spray drying at a freezing temperature of -25℃. The total time from the start of cooling to the end of sublimation drying was 15h, resulting in aluminum sol-coated composite particles. 3) The aluminum sol-coated composite particles were calcined in nitrogen. The specific calcination process was as follows: in the first stage, the temperature was increased from room temperature to 105℃ at a rate of 5℃ / min and held for 10h; in the second stage, the temperature was increased to 140℃ at a rate of 11℃ / min and held for 10h; in the third stage, the temperature was increased to 500℃ at a rate of 5℃ / min and held for 20h; after calcination, the particles were cooled to obtain self-healing crack microcapsules.

[0063] According to the above formula, coke aggregate, high-alumina bauxite powder, activated alumina micro powder, quartz powder, kyanite powder, crack self-healing microcapsules, plasticizer, curing agent and surface modifier are mixed into a uniform aggregate; 70% of the total amount of ammonium silica sol is added to the uniform aggregate, mixed evenly and then fed into the spraying machine. The remaining ammonium silica sol is added at the outlet of the spraying machine to achieve a material state suitable for spraying; the top part of the hot air furnace is sprayed using a semi-dry spraying method. After the construction is completed, it is naturally cured for 48 hours, and then baked at 110℃, 48h→350℃, 50h→600℃, 30h, and finally heated to the service temperature.

[0064] Example 6 An acid-resistant spray coating containing self-healing crack microcapsules, the composition of which is as follows by mass percentage: The composition includes: 47wt% coke aggregate, 27wt% high-alumina bauxite powder, 9wt% activated alumina micro powder, 1wt% quartz powder, 2wt% kyanite powder, 2wt% self-healing microcapsules for cracks, 0.2wt% plasticizer (carboxymethyl cellulose and hydroxypropyl starch in a mass ratio of 1:2), 0.4wt% activated magnesium oxide, 0.4wt% surface modifier (N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane and γ-aminopropyltrimethoxysilane in a mass ratio of 1:1), and 11wt% ammonium silica sol.

[0065] The coke aggregate is composed of the following three grades of particles by mass percentage: particles with a diameter of 5-3mm account for 23%, particles with a diameter of 3-1mm account for 42%, and particles with a diameter of 1-0.074mm account for 35%.

[0066] The crack self-healing microcapsules have a diameter of 400 μm and are prepared by the following method: 1) The mixed powder of WSi2 and TiB2 in a mass ratio of 1:1 was washed alternately with a 5% (w / w) dilute hydrochloric acid solution and deionized water. The specific washing process was as follows: the mixed powder was immersed in the dilute hydrochloric acid solution and thoroughly stirred and washed for 3-5 minutes, then filtered. It was then immersed in deionized water and thoroughly stirred and washed for 5-8 minutes, and then filtered. This process was repeated 1-10 times until the washing water was neutral. After washing, it was placed in nitrogen and dried at 150°C for 8 hours to obtain the modified mixed powder. 2) The modified mixed powder and aluminum sol were mixed evenly at a mass ratio of 1.2:1 and then subjected to freeze spray drying at a freezing temperature of -40℃. The total time from the start of cooling to the end of sublimation drying was 20h, resulting in aluminum sol-coated composite particles. 3) The aluminum sol-coated composite particles were calcined in nitrogen. The specific calcination process was as follows: in the first stage, the temperature was increased from room temperature to 120℃ at a rate of 5℃ / min and held for 13h; in the second stage, the temperature was increased to 160℃ at a rate of 15℃ / min and held for 14h; in the third stage, the temperature was increased to 600℃ at a rate of 7℃ / min and held for 25h; after calcination, the particles were cooled to obtain crack self-healing microcapsules.

[0067] According to the above formula, coke aggregate, high-alumina bauxite powder, activated alumina micro powder, quartz powder, kyanite powder, crack self-healing microcapsules, plasticizer, curing agent and surface modifier are mixed into a uniform aggregate; 62% of the total amount of ammonium silica sol is added to the uniform aggregate, and after mixing evenly, it is fed into the spraying machine. The remaining ammonium silica sol is added at the outlet of the spraying machine to achieve a material state suitable for spraying; the top part of the hot air furnace is sprayed using a semi-dry spraying method. After the construction is completed, it is naturally cured for 50 hours, and then baked at 110℃ for 40 hours → 350℃, 60 hours → 600℃ for 35 hours, and finally heated to the service temperature.

[0068] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that: no self-healing microcapsules were added, the self-healing microcapsules were reduced to 0 wt%, the coke aggregate was increased to 40 wt%, and the high-alumina bauxite powder was increased to 31 wt%.

[0069] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the self-healing microcapsules of crack were replaced with a mixed powder of WSi2 and TiB2, in which the mass ratio of WSi2 to TiB2 was 1:1.2.

[0070] The performance tests for all examples and comparative examples were conducted according to the following standards: bulk density of the samples was tested according to GB / T2997-2015; flexural strength at room temperature and residual strength after thermal shock were tested according to GB / T3001-2017; flexural strength after immersion in nitric acid solution was tested according to DL / T901; linear change rate of the samples was tested according to GB / T5988-2022; and thermal shock of the samples was tested according to GB / T 30873-2014. The results are shown in Table 1.

[0071] Table 1 Product Performance Indicators

[0072] The above examples and comparative examples show that without the addition of crack self-healing capsules, the performance indicators of the castable are poor in all aspects. Adding a mixture of WSi2 and TiB2 powder alone improves the performance indicators, while adding crack self-healing microcapsules significantly improves the performance indicators, especially the strength retention rate after thermal shock, which reflects the crack healing status. Under alternating hot and cold cycles, refractory castables are prone to cracking and even fracture due to internal thermal stress. Crack self-healing microcapsules can aid in crack healing; therefore, the residual strength after thermal shock reflects the degree of crack healing.

[0073] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A self-healing acid-resistant spray coating for cracks, characterized in that, The raw materials include the following components by weight percentage: 35-50% coke aggregate, 20-30% high-alumina bauxite powder, 6-10% activated alumina micro powder, 1-4% quartz powder, 2-5% kyanite powder, 2-4% self-healing crack microcapsules, 0.08-0.2% plasticizer, 0.1-0.4% curing agent, 0.1-0.5% surface modifier, and 9-13% ammonium silica sol; the wall material of the self-healing crack microcapsules is alumina, and the core material is WSi2 and TiB2.

2. The self-healing acid-resistant spray coating for cracks according to claim 1, characterized in that, The method for preparing the self-healing crack microcapsules includes the following steps: 1) The mixed powder of WSi2 and TiB2 was washed alternately with acid and water and then dried in an inert atmosphere to obtain the modified mixed powder; 2) After uniformly mixing the modified powder and aluminum sol, freeze spray drying is performed to obtain aluminum sol-coated composite particles; 3) The aluminum sol-coated composite particles were calcined in an inert atmosphere and cooled to obtain self-healing crack microcapsules.

3. The self-healing acid-resistant spray coating for cracks according to claim 2, characterized in that, The particle size of WSi2 is ≤44μm, and the particle size of TiB2 is ≤44μm; the solid content of the aluminum sol is ≥20%; the mass ratio of WSi2 to TiB2 is 1:1 to 1:

2. The mass ratio of the modified mixed powder to the aluminum sol is 1.5:1 to 1.2:1; the freezing temperature of the freeze spray drying is -20 to -40°C, and the total time from the start of cooling to the end of sublimation drying is 15 to 20 hours.

4. The self-healing acid-resistant spray coating for cracks according to claim 2, characterized in that, The roasting process employs a three-stage heating regime: the first stage involves heating to 100-120℃ and holding for 9-13 hours; the second stage involves heating to 140-160℃ and holding for 10-14 hours; and the third stage involves heating to 500-600℃ and holding for 20-25 hours. The heating rate in the first stage is 5-8℃ / min, the heating rate in the second stage is 10-15℃ / min, and the heating rate in the third stage is 5-7℃ / min.

5. The self-healing acid-resistant spray coating for cracks according to claim 2, characterized in that, The washing acid is a dilute hydrochloric acid solution with a mass fraction of 5-15%. The washing process involves immersing the mixed powder in the acid, stirring and washing for 3-5 minutes, filtering, then immersing it in water, stirring and washing for 5-8 minutes, and filtering. This process is repeated 1-10 times until the water used for washing is neutral.

6. The self-healing acid-resistant spray coating for cracks according to claim 1, characterized in that, The diameter of the self-healing crack microcapsules is 200-400 μm; the charred alumina aggregate is composed of the following three grades of particles by mass percentage: 20-30% particles with a diameter of 5-3 mm, 40-50% particles with a diameter of 3-1 mm, and 30-40% particles with a diameter of 1-0.074 mm; the particle size of the high-alumina bauxite powder is ≤0.074 mm; the median particle size D of the activated alumina micropowder is... 50 The particle size of the quartz powder is ≤2μm; the particle size of the kyanite powder is ≤0.074mm; the particle size of the kyanite powder is 0.074~0.15mm.

7. The self-healing acid-resistant spray coating for cracks according to claim 1, characterized in that, The coke aggregate has an Al2O3 content ≥ 45wt% and an Fe2O3 content ≤ 1wt%; the high-alumina bauxite powder has an Al2O3 content ≥ 88wt% and an Fe2O3 content ≤ 1wt%; the activated alumina micropowder is microcrystalline phase-transformed alumina micropowder with an Al2O3 content ≥ 99.5wt%, an α-Al2O3 phase content ≥ 95%, and a primary crystal size of 0.4~0.5μm; the quartz powder has a SiO2 content ≥ 99wt% and an Fe2O3 content ≤ 0.02wt%; and the kyanite powder has an Al2O3 content ≥ 60wt% and an Fe2O3 content ≤ 1.2wt%.

8. The self-healing acid-resistant spray coating for cracks according to claim 1, characterized in that, The plasticizer is one or both of carboxymethyl cellulose and hydroxypropyl starch; the curing agent is active magnesium oxide with an MgO content ≥90wt% and a particle size ≤45μm; the surface modifier is an aminosilane coupling agent, specifically one or more of γ-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and γ-aminopropyltrimethoxysilane; the ammonium silica sol has a silica content of 30~40wt%, an ammonium ion content of 0.05~0.2wt%, and a pH value of 7~9.

9. A method of using a self-healing acid-resistant spray coating for cracks as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Mix coke aggregate, high-alumina bauxite powder, activated alumina micro powder, quartz powder, kyanite powder, crack self-healing microcapsules, plasticizer, curing agent and surface modifier into a uniform aggregate. S2. Add a portion of ammonium silica sol to the uniform aggregate, mix evenly, and then feed it into the spraying machine. Add the remaining ammonium silica sol at the outlet of the spraying machine to achieve a material state suitable for spraying. S3. Apply a semi-dry spraying method to the top of the hot air furnace. After the application is completed, allow it to cure naturally, then heat it up and bake it until it reaches the service temperature.

10. The method of using the self-healing acid-resistant spray coating for cracks according to claim 9, characterized in that, Before the uniform aggregate is fed into the spraying machine, 60-70% of the total amount of ammonium silica sol is added; the natural curing time is 24-72 hours; the baking includes multiple heating stages performed sequentially: the first stage, heating to 110-150℃ and holding for 24-48 hours; the second stage, heating to 300-400℃ and holding for 48-72 hours; the third stage, heating to 550-650℃ and holding for 24-48 hours.

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