Electrolytic aluminum prebaked anode high-temperature-resistant antioxidant composite coating material

Abstract

The invention discloses a high-temperature-resistant antioxidant composite coating material for an electrolytic aluminum prebaked anode and a preparation method, and aims to solve the problem that an existing coating is easy to oxidize and crack. The material formula comprises a main aggregate phase (45%-55%), a composite binder (30%-40%), a functional additive (3%-8%), a stable reinforced phase (2%-5%) and a solvent film-forming phase (8%-12%), the binder is compounded by sodium / potash water glass (1: 0.5-1.5) and water-soluble phenolic resin; the functional additive contains a rare earth catalyst (Y2O3 and ZrO2) and a crystal form control agent (Na2SiF6 and NH4Cl), and the rare earth catalyst and the crystal form control agent synergistically inhibit anodic oxidation; the stable reinforced phase adopts an MgO whisker or Al2O3 short fiber reinforced coating structure; a solvent system takes deionized water as a main body, and polyvinyl butyral is added to relieve internal stress. The preparation process comprises the following steps: carrying out surface modification on the main aggregate by using the silane coupling agent, mixing all the components in stages, carrying out high-pressure spraying, and then carrying out normal-temperature drying, medium-temperature crosslinking and sintering and curing at 300-500 DEG C. Industrial application verifies that the service life of the anode can be prolonged by 1-2 days, and remarkable economic benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of auxiliary materials for electrolytic aluminum production, and in particular to a high-temperature resistant and oxidation-resistant composite coating material for prebaked anodes and a preparation method thereof. Background Art

[0002] In the aluminum electrolysis industry, prebaked anodes are core consumable materials, and their performance directly affects the production cost, energy efficiency, and carbon emission level of electrolytic aluminum. As the world's largest producer of electrolytic aluminum, my country's output accounted for 59.3% of the world's total by July 2023. However, the actual consumption of prebaked anodes is significantly higher than the theoretical value (theoretical consumption is 333kg / t-Al, and the actual consumption is 400-500kg / t-Al). Among them, the additional loss caused by oxidation reactions (chemical consumption and Boudol reaction with air, CO2, etc.) accounts for a large proportion. This oxidation not only increases the cost of raw materials, but also leads to large amounts of CO and CO2 emissions, which is contrary to the "dual carbon" goal. At the same time, the carbon slag produced will deteriorate the electrolyte environment, causing problems such as decreased current efficiency, side leakage, and even furnace leakage, seriously affecting the stable operation of the electrolytic cell and the quality of raw aluminum.

[0003] At present, the main means to improve the oxidation resistance of prebaked anodes is surface coating. Traditional methods such as the sol-gel method have defects such as severe drying shrinkage, low coating strength, complicated preparation process and high cost, which are difficult to meet the needs of large-scale industrial production. Among the existing patented technologies, some schemes use nano-scale alumina or complex components (such as ceramic-based continuous phase, alkaline earth metal catalytic phase, etc.). Although they can improve the oxidation resistance to a certain extent, they have problems such as high sintering temperature (such as pre-sintering above 500°C), complex composition leading to electrolyte contamination (introduction of impurities such as fluoride and alkaline salts), and high cost of nanomaterials. For example, coatings with water-soluble resins as binders rely on high-temperature sintering to form a dense structure, and the top area is often insufficiently sintered due to insufficient temperature; although coatings based on nano-solvent binding phases can be cured at room temperature, the raw material cost is high and the mixing uniformity is poor, and agglomeration is prone to occur, affecting the stability of coating performance.

[0004] In addition, with the promotion of large-scale electrolytic cells (such as those above 500kA), the anode needs to withstand higher current intensities and temperature loads, which places higher demands on the high-temperature resistance, adhesion strength, and chemical stability of the coating. Existing coatings are prone to cracking and peeling during long-term service due to problems such as crystal transformation and thermal expansion mismatch, resulting in antioxidant failure. Therefore, the development of a composite coating material that is both high-temperature resistant and has high adhesion, low cost, and environmentally friendly to achieve efficient protection of prebaked anodes and reduce oxidation losses and carbon emissions has become a technical challenge that needs to be urgently addressed in the current electrolytic aluminum industry. Summary of the Invention

[0005] This invention aims to provide a high-temperature, oxidation-resistant composite coating material for prebaked aluminum electrolytic anodes and its preparation method. This approach addresses the problems of existing prebaked anodes, such as escalating costs and persistently high carbon emissions due to oxidation losses, as well as coating cracking and flaking. By achieving breakthroughs in high-temperature resistance, adhesion, cost control, and environmental friendliness, this coating significantly improves the economic and environmental performance of electrolytic aluminum production.

[0006] To achieve this goal, the composite coating material provided by the present invention comprises the following components, by weight: 45%-55% main aggregate phase, 30%-40% composite binder, 3%-8% functional additives, 2%-5% stabilizing and reinforcing phase, and 8%-12% solvent and film-forming phase. These components work synergistically to form a dense, high-temperature, oxidation-resistant coating that effectively isolates the prebaked anode from oxidizing media such as air.

[0007] Nano-α-Al2O3 (particle size 50-100nm) accounts for 50%-60% of the main aggregate phase. Its highly active surface allows for close bonding with the binder, enhancing the coating's mechanical strength. Silicon carbide micropowder (particle size 1-5μm) accounts for 20%-30%, leveraging its high thermal conductivity and wear resistance to further enhance the coating's thermal shock resistance. Spodumene powder, comprising 10%-20%, effectively reduces shrinkage and deformation during heating, preventing cracks, thanks to its low coefficient of thermal expansion.

[0008] The composite binder consists of a mixture of sodium and potassium water glass (mass ratio 1:0.5-1.5, modulus 2.5-3.2) and water-soluble phenolic resin, with the latter comprising 20%-30% of the total weight of the composite binder. The addition of sodium and potassium water glass optimizes the coating's curing speed and bond strength, while the water-soluble phenolic resin forms a three-dimensional network structure through cross-linking, significantly improving the coating's high-temperature resistance and adhesion.

[0009] In terms of functional additives, the rare earth composite catalyst (yttrium oxide 0.5%-2.5%, zirconium oxide 0.5%-2%) inhibits the reaction between the anode carbon block and oxidizing gases by reducing the activation energy of the oxidation reaction. The crystal form control agent (sodium fluorosilicate 1%-2%, ammonium chloride 1%-2.5%) regulates the crystal form transformation of the main aggregate phase during sintering, promoting the formation of a stable and dense crystal structure and improving the chemical stability of the coating.

[0010] The stable reinforcement phase uses magnesium oxide whiskers or aluminum oxide short fibers with a particle size range of 1-5μm and a volume density of 2.5-3.0g / cm 3 , evenly dispersed in the coating, building a physical reinforcement skeleton, effectively blocking the expansion path of cracks, and improving the coating's impact resistance and spalling resistance.

[0011] Deionized water accounts for 60%-80% of the solvent and film-forming phase (by weight), serving as a dispersion medium to ensure uniform mixing of all components. Polyvinyl butyral, which accounts for 20%-40% (by weight) of the solvent and film-forming phase, forms a flexible interface layer during film formation, alleviating internal stress caused by the difference in thermal expansion coefficients between the coating and the anode carbon block and enhancing interfacial bonding.

[0012] The present invention also provides a method for preparing the aforementioned composite coating material, achieving performance optimization through four key processes: surface modification of the primary aggregate, preparation of the composite binder, staged mixing, and coating and curing. The primary aggregate surface is modified using a silane coupling agent (γ-aminopropyltriethoxysilane, at a dosage of 1%-2% of the total aggregate mass) at 80-100°C for 2-3 hours. This transforms the surface properties of the nano-α-Al2O3 and silicon carbide micropowder from hydrophilic to lipophilic, enhancing compatibility with the binder.

[0013] During the preparation of the composite adhesive, sodium water glass (modulus 3.0) and potassium water glass (modulus 2.8) are mixed in a specific proportion, and water-soluble phenolic resin (solid content 60%-70%) is added. The mixture is stirred at a low speed at 50-60°C to form a composite adhesive system that combines the fast-setting properties of water glass with the high-temperature resistance of phenolic resin, avoiding the performance shortcomings of a single adhesive.

[0014] The phased mixing process precisely controls the order of addition and mixing parameters, initially dispersing the main aggregate at high speed to ensure uniform particle distribution. Functional additives are then added sequentially to achieve precise dispersion of the catalytic and crystal-form-controlling components. Finally, the solvent and film-forming phase are added to adjust the system viscosity and ensure the coating's workability. This process effectively avoids the agglomeration of nanomaterials, allowing the components to form a multi-level composite structure at the nanometer to micrometer scale.

[0015] The coating and curing process utilizes high-pressure spraying (0.3-0.5 MPa) to form a uniform coating with a thickness of 0.3-0.5 mm. Curing proceeds through three stages: room-temperature drying, intermediate-temperature crosslinking, and high-temperature sintering. Room-temperature drying promotes solvent evaporation, forming a preliminary structure; intermediate-temperature crosslinking induces a polycondensation reaction between the phenolic resin and water glass; and high-temperature sintering (300-500°C) promotes grain growth and interfacial fusion of the main aggregate phase, forming a compact, sealed coating. This curing profile effectively overcomes the drawbacks of traditional coatings, which suffer from insufficient high-temperature sintering or excessive energy consumption.

[0016] The present invention has the following significant beneficial effects:

[0017] 1. Excellent antioxidant and high temperature resistance: Nano-α-Al2O3 and silicon carbide powder in the main aggregate phase form a mullite-silicon carbide composite structure after sintering. Combined with the inhibitory effect of rare earth catalyst on oxidation reaction, the coating can still effectively block O2 and other gases in a high temperature environment of 800-1000℃.

[0018] 2. Excellent interfacial bonding and thermal shock resistance: The main aggregate modified with a silane coupling agent forms a chemical bond with the composite binder. Combined with the bridging effect of the stabilizing reinforcing phase, the coating achieves adhesion of 5-8 MPa to the anode carbon block, a 3-5 MPa improvement over traditional coatings. The addition of spodumene and magnesium oxide whiskers improves the thermal expansion coefficient of the coating and its compatibility with the anode. After 50 cycles of thermal shock at 100-800°C, the coating remains crack-free and shows no peeling, fully meeting the long-term, high-temperature service requirements of large electrolytic cells.

[0019] 3. Environmentally friendly, low-energy consumption, and excellent process adaptability: The preparation process does not require the introduction of fluorides, alkaline salts, or other substances that could contaminate the electrolyte. Deionized water and environmentally friendly polyvinyl butyral are used as the solvent and film-forming phase, eliminating VOC emissions. The high-pressure spraying process is suitable for industrial production lines, with a curing temperature 100-200°C lower than traditional nanocoatings, reducing energy consumption by 25%, and achieving a coating thickness uniformity error of ≤5%, successfully resolving the industry challenge of insufficient sintering in the top region.

[0020] 4. Significant Cost Advantages and Long-Lasting Protection: The primary aggregate phase utilizes industrial-grade nano-α-Al₂O₃ and silicon carbide micropowder, resulting in a 40% reduction in cost compared to pure nanocoatings. The combined proportion of stabilizing reinforcement phases and functional additives is ≤10%, eliminating the cost increases associated with complex compositions. Industrial applications have proven that the coating can extend anode life by 1-2 days over its service life, resulting in significant overall economic benefits.

[0021] In summary, the present invention has successfully broken through the performance bottleneck of existing prebaked anode coatings through innovative component design and process optimization, and achieved synergistic improvements in oxidation resistance, high temperature resistance, adhesion strength, environmental protection and energy saving, providing core technical support for the green and low-carbon development of the electrolytic aluminum industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention provides a flow chart of the method for preparing the high-temperature resistant and anti-oxidation composite coating material for the electrolytic aluminum prebaked anode. DETAILED DESCRIPTION

[0023] The following will be combined with specific implementation cases to clearly and completely elaborate on the technical solutions of the present invention. It should be understood that the embodiments described herein are only partial implementations of the technical solutions of the present invention and are not all possible implementation forms. Based on the exemplary embodiments disclosed in the present invention, all equivalent technical solutions obtained by ordinary technicians in this field through reasonable transformation, simple combination or conventional improvement without the need for creative work should be included in the scope of protection of the present invention.

[0024] Example

[0025] Preparation of 100kg of high-temperature resistant and anti-oxidation composite coating material for prebaked anodes of electrolytic aluminum:

[0026] Main aggregate phase: 50 kg, accounting for 50% of the total coating material mass. Nano-α-Al2O3 (particle size 50-100 nm) accounts for 55% of the main aggregate phase, or 27.5 kg; silicon carbide powder (particle size 1-5 μm) accounts for 25% of the main aggregate phase, or 12.5 kg; and spodumene powder accounts for 20% of the main aggregate phase, or 10 kg.

[0027] Composite binder: 35% of the total coating material mass, totaling 35 kg. Mix sodium silicate (modulus 3.0) and potassium silicate (modulus 2.8) in a 1:1 mass ratio. Add water-soluble phenolic resin (solids content 65%). The water-soluble phenolic resin accounts for 25% of the total composite binder mass, or 8.75 kg.

[0028] Functional additives: 5% of the total coating material mass, totaling 5 kg, including 1.5 kg of rare earth composite catalyst (1.5% yttrium oxide, 1.5% zirconium oxide) and 2.5 kg of crystal form control agent (1.25% sodium fluorosilicate, 1.25% ammonium chloride).

[0029] Stable reinforcement phase: 3% of the total mass of the coating material, a total of 3kg. It uses magnesium oxide whiskers with a particle size range of 1-5μm and a volume density of 2.5-3.0g / cm 3 .

[0030] Solvent and film-forming phase: 7% of the total mass of the coating material, a total of 7 kg. Deionized water accounts for 70% of the mass of the solvent and film-forming phase, or 4.9 kg; polyvinyl butyral accounts for 30% of the mass of the solvent and film-forming phase, or 2.1 kg.

[0031] The method for preparing the composite coating material in this embodiment includes the following steps:

[0032] Surface modification of the main aggregate: Use a silane coupling agent (γ-aminopropyltriethoxysilane, the amount is 1.5% of the total mass of the aggregate) and treat it at 90°C for 2.5 hours to change the surface of nano-α-Al2O3 and silicon carbide powder from hydrophilic to lipophilic, thereby enhancing the compatibility with the binder.

[0033] Preparation of composite adhesive: Sodium water glass and potassium water glass are mixed in proportion, water-soluble phenolic resin is added, and stirred at low speed at 55°C to form a composite adhesive system with both the fast-setting characteristics of water glass and the high-temperature resistance of phenolic resin.

[0034] Mix in stages: first disperse the main aggregate at high speed to ensure uniform distribution of particles, then add functional additives in sequence to achieve precise dispersion of catalytic and crystal form control components, and finally add solvent and film-forming phase to adjust the system viscosity and ensure the application performance of the coating.

[0035] Coating and curing: High-pressure spraying (0.4 MPa) is used to form a uniform coating with a thickness of 0.4 mm. Curing is carried out in three stages: room temperature drying, medium temperature cross-linking, and high temperature sintering. Room temperature drying promotes solvent volatilization, forming a preliminary structure; medium temperature cross-linking causes condensation reaction between phenolic resin and water glass; high temperature sintering (400°C) promotes grain growth of the main aggregate phase and interface fusion, forming a compact sealing layer.

[0036] This embodiment has been successfully applied to a certain electrolytic aluminum plant. The anode life is extended by an average of 1.5 days, the carbon slag per ton of aluminum is reduced by about 25 kg, and the cracking and peeling of the coating is significantly reduced, effectively improving the economic efficiency and environmental protection level of electrolytic aluminum production.

[0037] Comparative Example

[0038] Preparation of 100kg of high-temperature resistant and anti-oxidation composite coating material for prebaked anodes of electrolytic aluminum:

[0039] Main aggregate: 45 kg, or 45% of the total coating material mass. Nano-α-Al₂O₃ (particle size 50-100 nm) accounts for 60% of the main aggregate, or 27 kg; silicon carbide powder (particle size 1-5 μm) accounts for 20% of the main aggregate, or 9 kg; and spodumene powder accounts for 20% of the main aggregate, or 9 kg.

[0040] Composite binder: 40 kg, accounting for 40% of the total coating material mass. Mix sodium silicate (modulus 2.5) and potassium silicate (modulus 3.2) in a mass ratio of 1:1.5. Add water-soluble phenolic resin (solids content 60%). The water-soluble phenolic resin accounts for 20% of the total composite binder mass, or 8 kg.

[0041] Functional additives: 3% of the total coating material mass, totaling 3 kg, including 1 kg of rare earth composite catalyst (0.5% yttrium oxide, 0.5% zirconium oxide) and 2 kg of crystal form control agent (1% sodium fluorosilicate, 1% ammonium chloride).

[0042] Stable reinforcement phase: 2% of the total mass of the coating material, a total of 2kg. It uses alumina short fibers with a particle size range of 1μm and a volume density of 2.5g / cm 3 .

[0043] Solvent and film-forming phase: 12% of the total coating material mass, totaling 12 kg. Deionized water accounts for 80% of the mass of the solvent and film-forming phase, or 9.6 kg; polyvinyl butyral accounts for 20% of the mass of the solvent and film-forming phase, or 2.4 kg.

[0044] The preparation method of the composite coating material in this comparative example comprises the following steps:

[0045] Surface modification of the main aggregate: Use a silane coupling agent (γ-aminopropyltriethoxysilane, the amount is 1.5% of the total mass of the aggregate) and treat it at 90°C for 2.5 hours to change the surface of nano-α-Al2O3 and silicon carbide powder from hydrophilic to lipophilic, thereby enhancing the compatibility with the binder.

[0046] Preparation of composite adhesive: Sodium water glass and potassium water glass are mixed in proportion, water-soluble phenolic resin is added, and stirred at low speed at 55°C to form a composite adhesive system with both the fast-setting characteristics of water glass and the high-temperature resistance of phenolic resin.

[0047] Mix in stages: first disperse the main aggregate at high speed to ensure uniform distribution of particles, then add functional additives in sequence to achieve precise dispersion of catalytic and crystal form control components, and finally add solvent and film-forming phase to adjust the system viscosity and ensure the application performance of the coating.

[0048] Coating and curing: High-pressure spraying (0.4 MPa) is used to form a uniform coating with a thickness of 0.4 mm. Curing is carried out in three stages: room temperature drying, medium temperature cross-linking, and high temperature sintering. Room temperature drying promotes solvent volatilization, forming a preliminary structure; medium temperature cross-linking causes condensation reaction between phenolic resin and water glass; high temperature sintering (400°C) promotes grain growth of the main aggregate phase and interface fusion, forming a compact sealing layer.

[0049] After this comparative example was applied to a certain electrolytic aluminum plant, the anode life was extended by an average of 1 day, the carbon slag per ton of aluminum was reduced by about 18 kg, and the cracking and peeling of the coating was less frequent, which to a certain extent improved the economy and environmental protection level of electrolytic aluminum production.

[0050] In summary, the present invention provides a high-temperature resistant and antioxidant composite coating material for electrolytic aluminum prebaked anodes and a preparation method thereof through innovative component design and process optimization. The composite coating material is composed of a main aggregate phase, a composite binder, functional additives, a stabilizing and reinforcing phase, and a solvent and a film-forming phase in a specific proportion. The components work together to construct a dense high-temperature resistant and antioxidant coating, which effectively isolates the prebaked anode from the oxidizing medium. The preparation method achieves breakthroughs in high-temperature resistance, adhesion, cost control, and environmental friendliness of the coating through four key processes: surface modification of the main aggregate, preparation of the composite binder, staged mixing, and coating and curing. The anode life is extended by 1-2 days, and the overall economic benefits are significant.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, any reasonable transformation, simple combination or conventional improvement based on the technical solution disclosed in the present invention, without departing from the concept of the present invention, should be regarded as an equivalent technical solution of the present invention and should be included in the scope of protection of the present invention.

Claims

1. A high temperature resistant and anti-oxidation composite coating material for electrolytic aluminum prebaked anode, characterized in that: Calculated by mass percentage, it includes: main aggregate phase 45%-55%, composite binder 30%-40%, functional additive 3%-8%, stable reinforcement phase 2%-5%, solvent and film-forming phase 8%-12%.

2. The composite coating material according to claim 1, characterized in that: The main aggregate phase comprises the following components (based on the total mass of the main aggregate phase): 50%-60% of nano-α-Al2O3, 20%-30% of silicon carbide powder, and 10%-20% of spodumene powder.

3. The composite coating material according to claim 1, characterized in that The composite binder is a composition of a mixture of sodium water glass and potassium water glass (mass ratio 1:0.5-1.5, modulus 2.5-3.2) and water-soluble phenolic resin, wherein the water-soluble phenolic resin accounts for 20%-30% of the total mass of the composite binder.

4. The composite coating material according to claim 1, characterized in that: The functional additives include: rare earth composite catalyst: yttrium oxide 0.5%-2.5%, zirconium oxide 0.5%-2%; crystal form control agent: sodium fluorosilicate 1%-2%, ammonium chloride 1%-2.5%; the above components are all calculated based on the total mass of the coating material.

5. The composite coating material according to claim 1, characterized in that: The stable reinforcement phase is magnesium oxide whiskers or aluminum oxide short fibers with a particle size range of 1-5 μm and a volume density of 2.5-3.0 g / cm 3 .

6. The composite coating material according to claim 1, characterized in that: The solvent and the film-forming phase include 60%-80% of deionized water (accounting for the mass of the solvent and the film-forming phase) and 20%-40% of polyvinyl butyral (accounting for the mass of the solvent and the film-forming phase).

7. The method for preparing a composite coating material according to any one of claims 1 to 6, characterized in that: The main aggregate surface modification treatment is to mix nano α-Al2O3 powder (particle size 50-100nm) and silicon carbide powder (particle size 1-5μm) according to the ratio of claim 2, add silane coupling agent (γ-aminopropyltriethoxysilane, the amount is 1%-2% of the total mass of the aggregate), stir and modify at 80-100°C for 2-3 hours, and then dry for use.

8. The method for preparing a composite coating material according to any one of claims 1 to 6, characterized in that: Preparation of the composite adhesive: Sodium water glass (modulus 3.0) and potassium water glass (modulus 2.8) are uniformly mixed according to the ratio of claim 3, and a water-soluble phenolic resin (solid content 60%-70%) is added. The mixture is stirred at a low speed (200-300 rpm) at 50-60° C. for 30 minutes to form a uniform adhesive matrix.

9. The method for preparing a composite coating material according to any one of claims 1 to 8, characterized in that: The modified main aggregate, the functional additive according to claim 4, and the stabilizing reinforcing phase according to claim 5 are added to the binder matrix in the following order in a staged mixing process: first, the main aggregate is added and dispersed in a high-speed mixer (1500-2000 rpm) for 10-15 minutes; the rare earth composite catalyst and the crystal form control agent are added in sequence and stirring is continued for 5-8 minutes; finally, the solvent and the film-forming phase are added, the solid content of the system is adjusted to 60%-70%, and the mixture is stirred evenly at a low speed.

10. The method for preparing a composite coating material according to any one of claims 1 to 9, characterized in that: The coating and curing process uses high-pressure spraying equipment (spraying pressure 0.3-0.5MPa) to evenly spray the coating on the surface of the prebaked anode (coating thickness 0.3-0.5mm), and then proceeds in sequence: room temperature drying (25±5℃, humidity ≤60%) for 24 hours; medium temperature crosslinking (80-120℃, insulation for 2 hours); high temperature sintering (300-500℃, heating rate 5℃ / min, insulation for 3 hours); finally forming a dense, high-temperature resistant and antioxidant coating.

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