Carbon electrode fireproof anti-oxidation coating material, and preparation and application method thereof

Abstract

This invention discloses a refractory and anti-oxidation coating for carbon electrodes and its preparation and application methods. The coating is a homogeneous and stable aqueous suspension, comprising, by weight: 28-35 parts potassium silicate, 12-18 parts sodium silicate, 18-25 parts α-alumina micro powder, 10-15 parts boron carbide micro powder, 6-10 parts nano-silicon powder, 4-7 parts cryolite micro powder, 1-3 parts magnesium fluoride micro powder, 3-5 parts mullite whiskers, 1.5-3 parts rare earth composite oxide, and silane coupling agent KH560. 0.3~0.8 parts, sodium polycarboxylate dispersant 0.6~1.2 parts, deionized water 8~15 parts; rare earth composite oxide is composed of La2O3 and CeO2 in a mass ratio of 1:1. The coating has a solid content of 68~75%, pH value of 8.8~9.5, viscosity of 35~50s, particle size D90≤4.5μm, porosity≤8%, and storage stability≥90d. Through the synergistic effect of rare earth-silane dual modification, mullite whisker reinforcement and low-temperature activation of nano-silicon powder, the coating achieves a high-temperature adhesion strength ≥2.2MPa, thermal shock resistance ≥25 cycles, and can be sintered at low temperature with excellent construction performance. It is suitable for various high-temperature working conditions such as electrolytic aluminum and ferroalloy smelting.

Description

Technical Field

[0001] This invention relates to the field of refractory and anti-oxidation coatings, and in particular to a carbon electrode refractory and anti-oxidation coating and its preparation and application methods. Background Technology

[0002] Carbon electrodes, such as prebaked anodes for electrolytic aluminum and graphite electrodes for ferroalloy smelting, face severe oxidation and burn-off problems when used in high-temperature metallurgical environments. Electrode surface oxidation not only reduces conductivity and increases energy consumption but also shortens electrode lifespan, increases replacement frequency, and affects production continuity.

[0003] To address the aforementioned problems, various electrode anti-oxidation coatings are currently available in the technology. For example, anti-oxidation coatings prepared using water glass as a binder and adding ceramic fillers such as alumina and boron carbide can form a protective layer on the electrode surface, blocking oxygen penetration. However, existing coatings still have the following shortcomings: Insufficient high-temperature bonding strength: In high-temperature environments above 900℃, the coating is prone to cracking and peeling, resulting in a decrease in protective effect.

[0004] Poor thermal shock resistance: Under frequent start-stop or rapid cooling and heating conditions, the coating cracks due to the mismatch of thermal expansion coefficients.

[0005] Poor low-temperature sintering performance: Some coatings require high-temperature sintering to form a dense coating, but the electrodes cannot withstand excessively high-temperature pretreatment before use.

[0006] Poor storage stability: Water-based coatings are prone to settling and stratification, affecting the consistency of construction and coating quality.

[0007] Therefore, a carbon electrode refractory and anti-oxidation coating and its preparation and application methods are proposed to solve the above problems. Summary of the Invention

[0008] This invention overcomes the shortcomings of the prior art and provides a carbon electrode refractory and anti-oxidation coating, its preparation method and application, to solve the technical problems of insufficient high-temperature bonding strength, poor thermal shock resistance, poor low-temperature sintering performance and poor storage stability of the coating in the prior art.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a carbon electrode refractory and anti-oxidation coating, wherein the coating is a homogeneous stable aqueous suspension, comprising the following raw materials by weight: Potassium silicate 28-35 parts, sodium silicate 12-18 parts, α-alumina micro powder 18-25 parts, boron carbide micro powder 10-15 parts, nano-silicon powder 6-10 parts, cryolite micro powder 4-7 parts, magnesium fluoride micro powder 1-3 parts, mullite whiskers 3-5 parts, rare earth composite oxide 1.5-3 parts, silane coupling agent KH560 0.3-0.8 parts, sodium polycarboxylate dispersant 0.6-1.2 parts, deionized water 8-15 parts; The rare earth composite oxide is composed of La2O3 and CeO2 in a mass ratio of 1:1. The coating has a solid content of 68-75%, a pH value of 8.8-9.5, a viscosity of 35-50 s at 25°C using a Forecast cup 4, a particle size D90 ≤ 4.5 μm, a porosity ≤ 8%, and a storage stability ≥ 90 days.

[0010] In a preferred embodiment of the present invention, the parameters of each raw material are as follows: Potassium silicate glass: modulus 3.2~3.5, Baumé degree 42~45°Be, SiO2 / K2O=3.2~3.5, water-insoluble matter ≤0.1%; Sodium silicate: modulus 2.9~3.2, Baumé degree 39~42°Be, SiO2 / Na2O = 2.9~3.2, water-insoluble matter ≤0.1%; α-Alumina micro powder: particle size 2~5μm, purity ≥99.8%, refractoriness ≥2050℃, Mohs hardness 9.0, specific surface area 5~8m² / g; Boron carbide micro powder: particle size 0.8~2μm, purity ≥99.2%, Mohs hardness 9.3, high temperature oxidation resistance temperature ≥1200℃; Nano-silicon powder: amorphous SiO2, particle size 60~90nm, specific surface area 65~80m² / g, activity ≥98.5%, surface hydroxyl content ≥5%; Cryolite micro powder: purity ≥98.5%, fluorine content ≥53%, particle size 3~6μm; Magnesium fluoride micro powder: purity ≥98%, fluorine resistance temperature ≥1100℃, particle size 1~3μm; Mullite whiskers: 3Al2O3・2SiO2, aspect ratio 15~20:1, diameter 0.6~1μm, length 9~20μm, tensile strength ≥3GPa; Rare earth composite oxides: particle size 1~2μm, purity ≥99.5%, total rare earth oxide content ≥99%; Silane coupling agent KH560: purity ≥98%, water-dispersible, epoxy group content ≥12%; Sodium polycarboxylate dispersant: molecular weight 9000~12000, solid content 40%, water-based anionic, dispersion efficiency ≥95%; Deionized water: conductivity ≤5μS / cm, pH value 7.0~7.5, free of impurity ions such as calcium, magnesium, and iron.

[0011] In a preferred embodiment of the present invention, the weight ratio of each raw material satisfies the following relationship: The mass ratio of potassium silicate to sodium silicate is 2.0~2.8:1; Ceramic phase: The mass ratio of binder is 1.1~1.3:1, wherein the ceramic phase is the sum of α-alumina micro powder and boron carbide micro powder, and the binder is the sum of potassium silicate and sodium silicate; The mass ratio of nano-silicon powder to ceramic phase is 1:3.5 to 1:4.5; The mass ratio of cryolite micro powder to magnesium fluoride micro powder is 2.5~4:1.

[0012] Another technical solution adopted in this invention is: a method for preparing a carbon electrode refractory and anti-oxidation coating, used to prepare the coating described above, comprising the following steps: S1. Preparation of rare earth-silane dual-modified water glass adhesive: Add 28-35 parts of potassium silicate and 12-18 parts of sodium silicate to the reactor, turn on the reflux condenser, stir at 350-450 r / min, heat to 45-50℃ and keep the temperature constant. Add 1.5 to 3 parts of rare earth composite oxide in 4 portions, with an interval of 8 to 9 minutes between each addition. After the addition is complete, keep warm and stir for 25 to 30 minutes. Then add 0.3 to 0.8 parts of silane coupling agent KH560 and continue to keep warm and stir for 15 to 20 minutes. Cool to 20~30℃ to obtain a double-modified water glass adhesive; S2. Preparation of ceramic phase pre-dispersion slurry: Add 18-25 parts of α-alumina micro powder, 10-15 parts of boron carbide micro powder, 4-7 parts of cryolite micro powder, 1-3 parts of magnesium fluoride micro powder, and 3-5 parts of mullite whiskers to a high-speed disperser, add 2 / 3 of the total deionized water and 0.6-1.2 parts of sodium polycarboxylate dispersant, disperse at 1600-2000 r / min for 70-90 min, and control the system temperature at 25-35℃ to obtain a pre-dispersed slurry; S3. Preparation of nano-silicon powder activated suspension: Add 6-10 parts of nano-silicon powder to the remaining 1 / 3 of deionized water, place in an ice-water bath, and intermittently sonicate at 350-500W power and 22-25kHz frequency for 25-30 minutes, pausing for 1 minute after 3 minutes of sonication, and control the system temperature ≤25℃ to obtain an activated suspension. S4. Coating composite emulsification and interfacial coupling: Add the double-modified water glass adhesive from step S1 to the pre-dispersed slurry from step S2, and stir at 800~900 r / min for 25~30 min to obtain a mixed slurry; The activated suspension from step S3 is added dropwise to the mixed slurry. After the addition is complete, the speed is adjusted to 900~1000 r / min, and stirring is continued for 45~60 min to obtain the initial coating. S5, Two-stage grinding and constant temperature curing: The initial coating was subjected to horizontal sand milling and nano sand milling in sequence until the particle size D90≤4.5μm; The ground coating was stirred and matured at 25±2℃ and 60~80r / min for 15~18h, and then filtered to obtain the finished coating.

[0013] Another technical solution adopted in this invention is: a method for applying a carbon electrode refractory and anti-oxidation coating, used for the application of the above-mentioned coating, comprising the following steps: Substrate pretreatment: The surface of the carbon electrode or steel claw is sandblasted to control the surface roughness Ra to 4~15μm, and the spraying is completed within 2 hours after treatment; High-pressure airless spraying: The coating is applied using a high-pressure airless sprayer with a working pressure of 15~20MPa and a nozzle diameter of 0.9~1.4mm. The coating is continuously stirred during the spraying process, and the coating thickness is 0.25~0.8mm. The coating can be applied in one or multiple coats. Curing and sintering: After spraying, room temperature curing and stepped temperature pre-sintering are carried out in sequence. The stepped temperature pre-sintering is as follows: the temperature is raised from room temperature to 80°C and held for 1.0~1.5h, then raised to 120~200°C and held for 2.0~3.0h, and then naturally cooled to room temperature.

[0014] In a preferred embodiment of the present invention, in the substrate pretreatment, the sandblasting medium is quartz sand or brown corundum, the sandblasting pressure is 0.4~0.7MPa, the sandblasting distance is 15~22cm, and the sandblasting angle is 45~60°.

[0015] In a preferred embodiment of the present invention, it is applied to the integrated protection of prebaked anode carbon electrodes and steel claws in electrolytic aluminum production; In the high-pressure airless spraying process, the spraying thickness is 0.35~0.5mm, the nozzle diameter is 0.9~1.2mm, and the working pressure is 15~20MPa.

[0016] In a preferred embodiment of the present invention, it is applied to the protection of graphite electrodes in ferroalloy, yellow phosphorus, or calcium carbide smelting processes. In the high-pressure airless spraying, the spraying thickness is 0.45~0.6mm, the nozzle diameter is 1.0~1.2mm, and the working pressure is 18~20MPa. In the stepped heating pre-sintering, the maximum heating temperature is 180~200℃.

[0017] In a preferred embodiment of the present invention, it is applied to the refractory and anti-oxidation treatment of carbon linings in industrial furnaces and kilns; In the high-pressure airless spraying, the spraying thickness is 0.5~0.8mm, the nozzle diameter is 1.2~1.4mm, the working pressure is 16~19MPa, and the spraying is carried out in two stages. In the stepped heating pre-sintering, the maximum heating temperature is 160~180℃.

[0018] In a preferred embodiment of the present invention, it is applied to the protection of high-temperature conductive carbon components in metallurgy; In the high-pressure airless spraying, the spraying thickness is 0.35~0.4mm, the nozzle diameter is 0.9~1.0mm, and the working pressure is 15~18MPa. In the stepped heating pre-sintering, the maximum heating temperature is 120~150℃.

[0019] This invention addresses the shortcomings of the prior art and has the following beneficial effects: (1) Excellent high-temperature bonding strength: By modifying water glass with rare earth composite oxide (La2O3 / CeO2) and silane coupling agent KH560, the structural stability of the adhesive at high temperature is significantly improved, so that the coating still maintains a bonding strength of ≥2.2MPa at 900℃, effectively preventing the coating from peeling off.

[0020] (2) Good thermal shock resistance: The introduction of mullite whiskers forms a three-dimensional network reinforcement structure. Combined with the composite ceramic phase of α-alumina and boron carbide, the thermal expansion coefficient of the coating matches that of the carbon substrate. The thermal shock resistance of rapid cooling from 900℃ to room temperature is ≥25 times, which meets the requirements of frequent start-stop conditions.

[0021] (3) Excellent low-temperature pre-sintering performance: After activation, the nano-silicon powder has high surface activity and can promote coating densification at a low temperature of 120~200℃. It does not require high-temperature sintering and is compatible with the pretreatment process before use of the electrode.

[0022] (4) Stable storage and construction performance: The coating is a homogeneous stable aqueous suspension with a storage stability of ≥90 days. It is applied by high-pressure airless spraying, resulting in good coating uniformity and controllable thickness, making it suitable for large-scale industrial applications.

[0023] (5) Multi-scenario applicability: By finely adjusting process parameters such as spraying thickness and curing temperature, it can be applied to various high-temperature working conditions such as electrolytic aluminum, ferroalloy smelting, and industrial furnaces, without changing the coating formula, and has a wide range of industrial applicability. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0026] Example 1 This embodiment provides a carbon electrode fire-resistant and anti-oxidation coating, the raw material composition and weight parts of which are as follows: Potassium silicate: 32 parts Sodium silicate: 15 parts α-Alumina micro powder: 22 parts Boron carbide micro powder: 12 parts Nano-silicon powder: 8 parts Cryolite micro powder: 5 parts Magnesium fluoride micro powder: 2 parts Mullite whiskers: 4 parts Rare earth composite oxides ( : =1:1): 2 portions Silane coupling agent KH560: 0.5 parts Sodium polycarboxylate dispersant: 0.9 parts Deionized water: 12 parts The specific parameters of each raw material are as follows: Potassium silicate glass: Modulus 3.4, Baume degree 43°Be. / =3.4, water-insoluble matter 0.05%; Sodium silicate: Modulus 3.0, Baume degree 40°Be, / =3.0, water-insoluble matter 0.06%; α-Alumina micro powder: particle size 3μm, purity 99.9%, refractoriness 2060℃, Mohs hardness 9.0, specific surface area 6.5m² / g; Boron carbide micro powder: particle size 1.2μm, purity 99.5%, Mohs hardness 9.3, high temperature oxidation resistance temperature 1250℃; Nano-silicon powder: amorphous It has a particle size of 75 nm, a specific surface area of ​​72 m² / g, an activity of 99.0%, and a surface hydroxyl content of 5.5%. Cryolite micro powder: purity 99.0%, fluorine content 54%, particle size 4μm; Magnesium fluoride micro powder: purity 98.5%, fluoride resistance temperature 1150℃, particle size 2μm; Mullite whiskers: The aspect ratio is 18:1, the diameter is 0.8μm, the length is 15μm, and the tensile strength is 3.2GPa. Rare earth composite oxides: particle size 1.5μm, purity 99.6%, total rare earth oxide content 99.2%; Silane coupling agent KH560: purity 98.5%, water-dispersible, epoxy group content 12.5%; Sodium polycarboxylate dispersant: molecular weight 10000, solid content 40%, water-based anionic type, dispersion efficiency 96%; Deionized water: conductivity 3 μS / cm, pH 7.2.

[0027] The preparation method is as follows: S1. Preparation of rare earth-silane dual-modified water glass adhesive: Add 32 parts of potassium silicate and 15 parts of sodium silicate to the reactor, turn on reflux, stir at 400 r / min, heat to 48℃ and keep the temperature constant; add 2 parts of rare earth composite oxide in 4 portions, 8 min apart each time, and keep the temperature and stir for 28 min after the addition is complete, then add 0.5 parts of silane coupling agent KH560, and continue to keep the temperature and stir for 18 min; cool to 25℃ to obtain the double-modified silicate adhesive.

[0028] S2. Preparation of ceramic phase pre-dispersion slurry: 22 parts of α-alumina micro powder, 12 parts of boron carbide micro powder, 5 parts of cryolite micro powder, 2 parts of magnesium fluoride micro powder, and 4 parts of mullite whiskers were added to a high-speed disperser, along with 8 parts of deionized water (2 / 3 of the total deionized water volume) and 0.9 parts of sodium polycarboxylate dispersant. The mixture was dispersed at 1800 r / min for 80 min, with the system temperature controlled at 30℃, to obtain a pre-dispersed slurry.

[0029] S3. Preparation of nano-silicon powder activated suspension: Add 8 parts of nano-silicon powder to the remaining 4 parts of deionized water, place in an ice-water bath, and intermittently sonicate at 400W power and 24kHz frequency for 28 minutes (sonicating for 3 minutes and pausing for 1 minute), controlling the system temperature to ≤25℃ to obtain an activated suspension.

[0030] S4. Coating composite emulsification and interfacial coupling: Add the double-modified water glass adhesive from step S1 to the pre-dispersed slurry from step S2, and stir at 850 r / min for 28 min to obtain a mixed slurry; add the activated suspension from step S3 dropwise to the mixed slurry, and after the dropwise addition is complete, adjust the speed to 950 r / min and continue stirring for 50 min to obtain the initial coating.

[0031] S5, Two-stage grinding and constant temperature curing: The initial coating was subjected to horizontal sand milling (1.1 mm zirconia beads, 1250 r / min, 32 min) and nano sand milling (0.4 mm zirconia beads, 1450 r / min, 22 min) until the particle size D90=4.2 μm. The ground coating was stirred and matured at 25℃ and 70 r / min for 16 h, and then filtered through a 200 mesh nylon filter to obtain the finished coating.

[0032] The performance test results of the coating prepared in this embodiment are shown in Table 1 below.

[0033] Coating performance test results Table 1 Examples 2-5 The difference between Examples 2-5 and Example 1 lies in the different raw material ratios, as shown in Table 2. The preparation methods are the same as in Example 1. The specific parameters of the raw materials used in each example are the same as in Example 1.

[0034] The performance test results of the coatings prepared in each embodiment are shown in Table 3.

[0035] Example 2-5 Raw material ratios (parts by weight) Table 2 Example 2-5 Coating Performance Test Results Table 3 Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that no rare earth composite oxide and silane coupling agent KH560 were added, i.e., no dual modification treatment was performed. Other raw materials and preparation methods were the same as in Example 1. The specific parameters of the raw materials used were the same as in Example 1.

[0036] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that mullite whiskers were not added. Other raw materials and preparation methods are the same as in Example 1. The specific parameters of the raw materials used are the same as in Example 1.

[0037] The performance test results of the coatings prepared in Comparative Examples 1-2 are shown in Table 4 below.

[0038] Comparative Example 1-2 Coating Performance Test Results Table 4 Application Example 1: Integrated protection of prebaked anode carbon electrode and steel claw in electrolytic aluminum production The coating prepared in Example 1 is applied according to the following steps: Substrate pretreatment: The carbon electrode was sandblasted with 0.8mm quartz sand at a pressure of 0.5MPa, a distance of 18cm, and an angle of 50°, achieving a surface roughness of Ra8μm. The steel claw was treated with the same parameters, achieving a surface roughness of Ra5μm. Spraying was completed within 2 hours after treatment.

[0039] High-pressure airless spraying: A high-pressure airless sprayer with a working pressure of 18MPa and a nozzle diameter of 1.0mm was used. The paint was continuously stirred at 60r / min, and stirred at 180r / min for 9 minutes before spraying. The coating thickness was 0.4mm on the side surface of the carbon electrode, 0.28mm on the surface of the steel claw, and 0.42mm at the joint. The coating was completed in a single spray.

[0040] Curing and sintering: Let stand at room temperature (25℃, relative humidity 50%) for 4 hours; then heat in a hot air circulating drying oven in stages: room temperature → 80℃ (heating rate 5℃ / min), hold for 1.2 hours; 80℃ → 160℃ (heating rate 3℃ / min), hold for 2.2 hours; then cool naturally (cooling rate ≤2℃ / min).

[0041] Application Example 2: Protection of Graphite Electrodes in Ferroalloy Smelting The coating prepared in Example 1 is applied according to the following steps: Substrate pretreatment: 1.0mm brown fused alumina sandblasting, pressure 0.6MPa, distance 20cm, surface roughness Ra10μm.

[0042] High-pressure airless spraying: Working pressure 19MPa, nozzle diameter 1.1mm, coating thickness 0.5mm, single-pass molding.

[0043] Curing and sintering: Curing at room temperature for 5 hours, then pre-sintering at 190℃ in stages for 2.8 hours, followed by natural cooling.

[0044] Application Example 3: Refractory and Oxidation-Proofing Treatment of Carbon Linings for Industrial Furnaces and Kilns The coating prepared in Example 1 is applied according to the following steps: Substrate pretreatment: After grinding the loose layer with an angle grinder, it was sandblasted with 0.55MPa quartz sand, resulting in a surface roughness of Ra12μm.

[0045] High-pressure airless spraying: The working pressure is 18MPa, the nozzle diameter is 1.3mm, and the coating is applied in two coats. The first coat is 0.38mm thick, and the second coat is applied after curing at room temperature for 2.5 hours. The total thickness is 0.65mm.

[0046] Curing and sintering: Curing at room temperature for 6 hours, then pre-sintering at 170℃ in stages for 2.5 hours, followed by natural cooling.

[0047] Application Example 4: Protection of High-Temperature Conductive Carbon Components in Metallurgy The coating prepared in Example 1 is applied according to the following steps: Substrate pretreatment: 0.45MPa quartz sand blasting, distance 16cm, surface roughness Ra7μm.

[0048] High-pressure airless spraying: Working pressure 16MPa, nozzle diameter 0.95mm, coating thickness 0.38mm, single-pass molding.

[0049] Curing and sintering: Curing at room temperature for 3.5 hours, then pre-sintering at 135℃ in stages for 2.0 hours, followed by natural cooling.

[0050] The performance test results of the coatings after sintering in Application Examples 1-4 are shown in Table 5 below.

[0051] Coating performance test results Table 5 Note: The thermal shock resistance test conditions are to rapidly cool from the operating temperature to room temperature, repeat the process until the coating cracks, and record the number of times.

[0052] Performance Comparison The coatings prepared in Example 1 and Comparative Examples 1-2 were subjected to performance tests, and the results are shown in Table 6 below.

[0053] Performance comparison results of Example 1 and Comparative Examples 1-2 Table 6 Test results show that Example 1 is significantly superior to Comparative Examples 1-2 in terms of high-temperature bond strength, thermal shock resistance, density, and storage stability. Specifically, Comparative Example 1, lacking rare-earth-silane dual modification, exhibited significantly reduced high-temperature bond strength and storage stability; Comparative Example 2, without the addition of mullite whiskers, showed reduced thermal shock resistance and room-temperature bond strength. These comparisons demonstrate the synergistic effect of rare-earth-silane dual modification and the introduction of mullite whiskers.

[0054] Through rare earth composite oxides ( and Double modification of potassium silicate and sodium silicate with silane coupling agent KH560 at a mass ratio of 1:1 significantly improved the high-temperature structural stability of the adhesive. A comparison between Example 1 and Comparative Example 1 showed that the double modification increased the bonding strength at 900℃ from 1.2MPa to 2.5MPa, an increase of more than 100%. At the same time, by introducing mullite whiskers (length-to-diameter ratio 15~20:1) to form a three-dimensional network reinforcement structure, combined with the composite ceramic phase of α-alumina and boron carbide, the thermal expansion coefficient of the coating was well matched with the carbon substrate. A comparison between Example 1 and Comparative Example 2 showed that the addition of mullite whiskers increased the thermal shock resistance (rapid cooling from 900℃ to room temperature) from 15 cycles to 28 cycles, an increase of more than 85%.

[0055] Furthermore, using ultrasonically activated nano-silicon powder (particle size 60~90nm, activity ≥98.5%), the coating densification can be promoted under low temperature conditions of 120~200℃. Application Examples 1-4 show that the coating porosity is controlled at 7.0~7.5%, which is fully compatible with the low temperature pretreatment process of the electrode. By using sodium polycarboxylate dispersant in combination with a two-stage grinding process, the coating forms a homogeneous and stable aqueous suspension with a solid content of 68~75%, a particle size D90≤4.5μm, and a storage stability ≥90d, meeting the requirements of industrial spraying construction. Application Examples 1-4 further verify that the coating can achieve excellent protective effects under different high temperature conditions of 800~1200℃ (including integrated protection of electrolytic aluminum prebaked anode and steel claw, protection of graphite electrodes in ferroalloy smelting, protection of carbon linings in industrial furnaces and kilns, and protection of high temperature conductive carbon components in metallurgy) by finely adjusting the spraying thickness and curing temperature. The high temperature bonding strength is maintained above 2.1MPa, and the thermal shock resistance reaches more than 26 cycles.

[0056] In summary, this invention, through component screening and ratio optimization, combined with synergistic technologies such as rare earth-silane dual modification, mullite whisker reinforcement, and low-temperature activation of nano-silicon powder, effectively solves the technical problems of insufficient high-temperature adhesion strength, poor thermal shock resistance, poor low-temperature sintering performance, and poor storage stability of coatings in the prior art. It has achieved significant synergistic effects and has outstanding substantive features and significant progress.

[0057] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These are all equivalent modifications and improvements made to the above embodiments based on the essential technology of the present invention, and all of these fall within the protection scope of the present invention.

Claims

1. A refractory and anti-oxidation coating for carbon electrodes, characterized in that, The coating is a homogeneous, stable aqueous suspension, comprising the following raw materials by weight: Potassium silicate 28-35 parts, sodium silicate 12-18 parts, α-alumina micro powder 18-25 parts, boron carbide micro powder 10-15 parts, nano-silicon powder 6-10 parts, cryolite micro powder 4-7 parts, magnesium fluoride micro powder 1-3 parts, mullite whiskers 3-5 parts, rare earth composite oxide 1.5-3 parts, silane coupling agent KH560 0.3-0.8 parts, sodium polycarboxylate dispersant 0.6-1.2 parts, deionized water 8-15 parts; The rare earth composite oxide is composed of La2O3 and CeO2 in a mass ratio of 1:

1. The coating has a solid content of 68-75%, a pH value of 8.8-9.5, a viscosity of 35-50 s at 25°C using a Forecast cup 4, a particle size D90 ≤ 4.5 μm, a porosity ≤ 8%, and a storage stability ≥ 90 days.

2. The refractory and anti-oxidation coating for carbon electrodes according to claim 1, characterized in that: The parameters for each raw material are as follows: Potassium silicate glass: modulus 3.2~3.5, Baumé degree 42~45°Be, SiO2 / K2O=3.2~3.5, water-insoluble matter ≤0.1%; Sodium silicate: modulus 2.9~3.2, Baumé degree 39~42°Be, SiO2 / Na2O = 2.9~3.2, water-insoluble matter ≤0.1%; α-Alumina micro powder: particle size 2~5μm, purity ≥99.8%, refractoriness ≥2050℃, Mohs hardness 9.0, specific surface area 5~8m² / g; Boron carbide micro powder: particle size 0.8~2μm, purity ≥99.2%, Mohs hardness 9.3, high temperature oxidation resistance temperature ≥1200℃; Nano-silicon powder: amorphous SiO2, particle size 60~90nm, specific surface area 65~80m² / g, activity ≥98.5%, surface hydroxyl content ≥5%; Cryolite micro powder: purity ≥98.5%, fluorine content ≥53%, particle size 3~6μm; Magnesium fluoride micro powder: purity ≥98%, fluorine resistance temperature ≥1100℃, particle size 1~3μm; Mullite whiskers: 3Al2O3・2SiO2, aspect ratio 15~20:1, diameter 0.6~1μm, length 9~20μm, tensile strength ≥3GPa; Rare earth composite oxides: particle size 1~2μm, purity ≥99.5%, total rare earth oxide content ≥99%; Silane coupling agent KH560: purity ≥98%, water-dispersible, epoxy group content ≥12%; Sodium polycarboxylate dispersant: molecular weight 9000~12000, solid content 40%, water-based anionic, dispersion efficiency ≥95%; Deionized water: conductivity ≤5μS / cm, pH value 7.0~7.5, free of impurity ions such as calcium, magnesium, and iron.

3. The refractory and anti-oxidation coating for carbon electrodes according to claim 2, characterized in that: The weight ratio of each raw material satisfies the following relationship: The mass ratio of potassium silicate to sodium silicate is 2.0~2.8:1; Ceramic phase: The mass ratio of binder is 1.1~1.3:1, wherein the ceramic phase is the sum of α-alumina micro powder and boron carbide micro powder, and the binder is the sum of potassium silicate and sodium silicate; The mass ratio of nano-silicon powder to ceramic phase is 1:3.5 to 1:4.5; The mass ratio of cryolite micro powder to magnesium fluoride micro powder is 2.5~4:

1.

4. A method for preparing a refractory and anti-oxidation coating for carbon electrodes, characterized in that: The preparation of the coating according to any one of claims 1-3 includes the following steps: S1. Preparation of rare earth-silane dual-modified water glass adhesive: Add 28-35 parts of potassium silicate and 12-18 parts of sodium silicate to the reactor, turn on the reflux condenser, stir at 350-450 r / min, heat to 45-50℃ and keep the temperature constant. Add 1.5 to 3 parts of rare earth composite oxide in 4 portions, with an interval of 8 to 9 minutes between each addition. After the addition is complete, keep warm and stir for 25 to 30 minutes. Then add 0.3 to 0.8 parts of silane coupling agent KH560 and continue to keep warm and stir for 15 to 20 minutes. Cool to 20~30℃ to obtain a double-modified water glass adhesive; S2. Preparation of ceramic phase pre-dispersion slurry: Add 18-25 parts of α-alumina micro powder, 10-15 parts of boron carbide micro powder, 4-7 parts of cryolite micro powder, 1-3 parts of magnesium fluoride micro powder, and 3-5 parts of mullite whiskers to a high-speed disperser, add 2 / 3 of the total deionized water and 0.6-1.2 parts of sodium polycarboxylate dispersant, disperse at 1600-2000 r / min for 70-90 min, and control the system temperature at 25-35℃ to obtain a pre-dispersed slurry; S3. Preparation of nano-silicon powder activated suspension: Add 6-10 parts of nano-silicon powder to the remaining 1 / 3 of deionized water, place in an ice-water bath, and intermittently sonicate at 350-500W power and 22-25kHz frequency for 25-30 minutes, pausing for 1 minute after 3 minutes of sonication, and control the system temperature ≤25℃ to obtain an activated suspension. S4. Coating composite emulsification and interfacial coupling: Add the double-modified water glass adhesive from step S1 to the pre-dispersed slurry from step S2, and stir at 800~900 r / min for 25~30 min to obtain a mixed slurry; The activated suspension from step S3 is added dropwise to the mixed slurry. After the addition is complete, the speed is adjusted to 900~1000 r / min, and stirring is continued for 45~60 min to obtain the initial coating. S5, Two-stage grinding and constant temperature curing: The initial coating was subjected to horizontal sand milling and nano sand milling in sequence until the particle size D90≤4.5μm; The ground coating was stirred and matured at 25±2℃ and 60~80r / min for 15~18h, and then filtered to obtain the finished coating.

5. A method for applying a refractory and anti-oxidation coating for carbon electrodes, characterized in that: The application of the coating as described in any one of claims 1 to 4 comprises the following steps: Substrate pretreatment: The surface of the carbon electrode or steel claw is sandblasted to control the surface roughness Ra to 4~15μm, and the spraying is completed within 2 hours after treatment; High-pressure airless spraying: The coating is applied using a high-pressure airless sprayer with a working pressure of 15~20MPa and a nozzle diameter of 0.9~1.4mm. The coating is continuously stirred during the spraying process, and the coating thickness is 0.25~0.8mm. The coating can be applied in one or multiple coats. Curing and sintering: After spraying, room temperature curing and stepped temperature pre-sintering are carried out in sequence. The stepped temperature pre-sintering is as follows: the temperature is raised from room temperature to 80°C and held for 1.0~1.5h, then raised to 120~200°C and held for 2.0~3.0h, and then naturally cooled to room temperature.

6. The application method of the carbon electrode refractory and anti-oxidation coating according to claim 5, characterized in that: In the substrate pretreatment, the blasting medium is quartz sand or brown corundum, the blasting pressure is 0.4~0.7MPa, the blasting distance is 15~22cm, and the blasting angle is 45~60°.

7. The application method of the carbon electrode refractory and anti-oxidation coating according to claim 5, characterized in that: Application: Integrated protection of prebaked anode carbon electrodes and steel claws in electrolytic aluminum production; In the high-pressure airless spraying process, the spraying thickness is 0.35~0.5mm, the nozzle diameter is 0.9~1.2mm, and the working pressure is 15~20MPa.

8. The application method of the carbon electrode refractory and anti-oxidation coating according to claim 5, characterized in that: Applications include the protection of graphite electrodes in ferroalloy, yellow phosphorus, or calcium carbide smelting processes. In the high-pressure airless spraying, the spraying thickness is 0.45~0.6mm, the nozzle diameter is 1.0~1.2mm, and the working pressure is 18~20MPa. In the stepped heating pre-sintering, the maximum heating temperature is 180~200℃.

9. The application method of the carbon electrode refractory and anti-oxidation coating according to claim 5, characterized in that: Applications include refractory and anti-oxidation treatment of carbon linings in industrial furnaces and kilns; In the high-pressure airless spraying, the spraying thickness is 0.5~0.8mm, the nozzle diameter is 1.2~1.4mm, the working pressure is 16~19MPa, and the spraying is carried out in two stages. In the stepped heating pre-sintering, the maximum heating temperature is 160~180℃.

10. The carbon electrode refractory and anti-oxidation coating according to claim 1, its preparation method, and its application, characterized in that: Applications include protection of high-temperature conductive carbon components in metallurgy. In the high-pressure airless spraying, the spraying thickness is 0.35~0.4mm, the nozzle diameter is 0.9~1.0mm, and the working pressure is 15~18MPa. In the stepped heating pre-sintering, the maximum heating temperature is 120~150℃.

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