Anode self-curing gradient functional coating for electrolytic aluminum and preparation method of anode self-curing gradient functional coating

Abstract

The invention discloses an anode self-curing gradient functional coating for electrolytic aluminum and a preparation method of the anode self-curing gradient functional coating, and belongs to the technical field of electrolytic aluminum. The invention relates to an anode self-curing gradient functional coating for electrolytic aluminum, which takes silicate as a binder, combines with different functional fillers, and sequentially comprises the following functional layers from a surface layer to a substrate: an outer layer which is a corrosion-resistant layer with the thickness of 200-400 mu m and the porosity of lt; 5%; the middle layer is a conductive transition layer, and the thickness of the middle layer is 100-150 microns; the inner layer is an interface bonding layer, and the thickness of the inner layer is 100-200 microns. According to the invention, silicate is used for replacing a traditional metal / ceramic binder, so that low-cost and green manufacturing is realized; through gradient combination of the outer layer (corrosion-resistant layer), the middle layer (conductive transition layer) and the inner layer (interface bonding layer), conductivity, corrosion resistance and interface bonding are balanced.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytic aluminum, and particularly relates to a self-curing gradient functional coating for anodes used in electrolytic aluminum and a preparation method thereof. Background Art

[0002] The production method in the domestic electrolytic aluminum industry takes the "Hall-Héroult Process" as the core, and produces metallic aluminum by electrolyzing alumina (Al2O3). The carbon anode (prebaked anode or self-baked anode) is the core component of the electrolytic cell and directly participates in the aluminum electrolysis reaction (the decomposition of alumina into aluminum and oxygen); however, it faces a series of technical, economic, and environmental problems in practical applications, which limit the efficiency improvement and sustainable development of the electrolytic aluminum industry.

[0003] Main problems existing in the carbon anode during the electrolysis process: 1). Chemical oxidation consumption. The anode carbon participates in the oxidation reaction (C + O 2- →CO2+ 4e - ) during the electrolysis process, resulting in continuous consumption of the carbon anode. The net consumption of traditional carbon anodes is about 400 - 450 kg / t-Al (400 - 450 kilograms of carbon are consumed per ton of aluminum produced), accounting for 12% - 15% of the total cost of electrolytic aluminum; 2). Mechanical loss and shedding. Due to the high temperature (940 - 960 °C) of the electrolytic cell and the scouring of the electrolyte (molten cryolite), carbon particles on the anode surface fall off. The fallen carbon slag enters the electrolyte, increasing the resistance of the electrolytic cell and reducing the current efficiency (usually a loss of 1% - 3%); 3). Boudouard reaction. In the electrolyte, the (2CO→C + CO2) (Boudouard reaction) may occur on the anode surface, resulting in uneven carbon deposition and exacerbating local corrosion of the anode. Therefore, the performance and cost of the carbon anode directly affect production efficiency and environmental sustainability. At present, in order to solve the above problems and extend the service life of the carbon anode in the domestic electrolytic aluminum industry, the method of coating protection is generally adopted, and possible coating materials include ceramic coatings, metal matrix composites, antioxidant coatings, etc.

[0004] The carbon anode protection coating technology in the domestic electrolytic aluminum industry is a key area for improving production efficiency and environmental protection performance. The following are the main coating technologies currently adopted: 1). Ceramic-based coatings. Such as: alumina (Al2O3) coatings, which are resistant to high-temperature corrosion; silicon carbide (SiC) coatings, which have high hardness and wear resistance and can reduce anode consumption; composite ceramic coatings, which have better comprehensive performance; 2), Metal matrix composite coatings. For example, nickel-based / cobalt-based alloy coatings, which have excellent oxidation resistance and are suitable for high-temperature electrolysis environments; cermet coatings, such as Cr3C2-NiCr, which combine metal toughness and ceramic corrosion resistance; 3), Oxidation-resistant carbon coatings. Coating borides, phosphates, etc. on the surface of traditional carbon anodes can delay oxidation reactions and reduce carbon consumption; 4), Nanocoating technology. Nanoscale oxide (such as nano-Al2O3) coatings can improve density and anti-permeability, reducing electrolyte erosion.

[0005] Existing coatings have some technical problems: 1), Mismatch between conductivity and coefficient of thermal expansion. The resistivity of carbon anodes is about 50-70 μΩ·m. At high current densities, local overheating occurs, leading to the "anode effect" (sudden voltage rise). Secondly, the difference in the coefficient of thermal expansion between carbon materials (3-5×10 -6 / K) and coatings (such as Al2O3 coatings, 8×10 -6 / K) results in interface peeling; 2), Poor corrosion resistance. Coatings formed by traditional processes have high porosity and poor anti-electrolyte penetration ability. Cryolite melt (Na3AlF6) penetrates the pores of the anode, accelerating the oxidation of the carbon matrix and shortening the anode life (usually 20-30 days); 3), The bonding strength problem between the coating and the carbon anode matrix. Under long-term high-temperature environments and thermal shocks formed by high and low temperature differences during maintenance and other operations in the electrolytic cell, the coating is prone to cracking and peeling. Impurity elements in the coating may enter the electrolyte, affecting the electrolysis efficiency and even contaminating the aluminum liquid. Summary of the Invention

[0006] The purpose of the present invention is to propose an anodic self-curing gradient functional coating for electrolytic aluminum and its preparation method.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions: An anodic self-curing gradient functional coating for electrolytic aluminum, using silicate as a binder and combining different functional fillers, is sequentially provided with the following functional layers from the surface layer to the matrix: Outer layer: A corrosion-resistant layer with a thickness of 200-400 μm and a porosity <5%; Middle layer: A conductive transition layer with a thickness of 100-150 μm; Inner layer: An interface bonding layer with a thickness of 100-200 μm.

[0008] In some embodiments, the coating includes: high-performance corrosion-resistant coatings, low-cost rapid-curing coatings, environmentally friendly silicate gradient coatings for high-sulfur anodes, and nano-enhanced silicate gradient functional coatings.

[0009] In some embodiments, the outer layer is composed of raw materials in the following parts by mass: Sodium silicate binder, 100 parts; Al2O3 particles, 30 - 70 parts; Silicon carbide whiskers, 10 - 15 parts; or waste glass powder, 4 - 6 parts.

[0010] In some embodiments, the intermediate layer is composed of raw materials in the following parts by mass: Potassium silicate binder, 100 parts; TiB2 powder, 50 - 60 parts; Graphene sheets, 5 - 15 parts; or carbon black, 3 - 7 parts.

[0011] In some embodiments, the inner layer is composed of raw materials in the following parts by mass: Aluminum silicate binder, 100 parts; Recycled carbon powder, 20 - 40 parts; Wollastonite fiber, 15 - 25 parts; Or: Aluminum silicate binder, 100 parts; Recycled carbon powder, 40 - 50 parts.

[0012] In some embodiments, for carbon anodes with a high sulfur content, a special environmental protection type silicate gradient coating for high - sulfur anodes is designed; The outer layer is composed of raw materials in the following parts by mass: Magnesium silicate binder, 100 parts; Al2O3 particles, 50 - 60 parts; Boron nitride, 10 - 20 parts; The intermediate layer is composed of raw materials in the following parts by mass: Calcium silicate binder, 100 parts; TiB2 powder, 30 - 50 parts; Recycled particles from waste aluminum ash, 5 - 15 parts; The inner layer is composed of raw materials in the following parts by mass: Sodium silicate binder, 100 parts; Recycled carbon powder, 40 - 60 parts; Fused quartz powder, 5 - 15 parts.

[0013] In some embodiments, for the problems of local overheating and corrosion of the anode under high current density, a nano - enhanced silicate gradient functional coating is designed; The outer layer is composed of raw materials in the following parts by mass: Potassium silicate binder, 100 parts; Nano - Al2O3, 10 - 30 parts; Fused silica powder, 20 - 40 parts; The intermediate layer is composed of the following raw materials in parts by mass: Aluminum silicate binder, 100 parts; TiB2 powder, 30 - 50 parts; Nano silicon carbide whiskers, 10 - 20 parts; The inner layer is composed of the following raw materials in parts by mass: Sodium silicate binder, 100 parts; Recycled carbon powder, 20 - 40 parts; Graphene nanosheets, 10 - 30 parts; Nano SiO2, 3 - 7 parts.

[0014] A preparation method of an anodic self - curing gradient functional coating for electrolytic aluminum includes the following steps: S1. Substrate pretreatment: After the carbon anode is dried, the surface dust is blown off. S2. Coating slurry preparation: Each layer of slurry is prepared separately. S3. Gradient coating and curing: Adopt a layer - by - layer spraying process.

[0015] In some embodiments, when preparing a high - performance corrosion - resistant coating, step S2 includes: c201. Outer layer slurry preparation; Mix the Na2SiO3 solution with Al2O3 and SiCw, and mechanically stir for 3 - 5 h. c202. Intermediate layer slurry preparation; Mix the K2SiO3 solution with TiB2 and graphene sheets, and ultrasonically disperse for 1 - 3 h; High - speed shear mixing at 3000 rpm for 0.5 - 1.5 h; c203. Inner layer slurry preparation; Mix the Al2(SiO3)3 sol with recycled carbon powder and wollastonite fibers, and mechanically stir for 1 - 3 h.

[0016] In some embodiments, in step S3: Spraying sequence: Inner layer → Intermediate layer → Outer layer; After each layer is sprayed, dry at room temperature for 30 - 60 minutes; After the three - time spraying is completed, cure at room temperature for 5 - 8 hours.

[0017] Compared with the prior art, the present invention provides an anodic self - curing gradient functional coating for electrolytic aluminum and its preparation method, having the following beneficial effects.

[0018] 1. The present invention uses silicate to replace traditional metal / ceramic binders to achieve low-cost and green manufacturing; through the gradient combination of an outer layer (corrosion-resistant layer), an intermediate layer (conductive transition layer), and an inner layer (interface bonding layer), the conductivity, corrosion resistance, and interface bonding are balanced.

[0019] 2. In the present invention, the interfacial thermal stress is reduced to less than 30% of that of traditional coatings; the bonding strength of the gradient coating is ≥25 MPa, avoiding spalling failure at high temperatures; the coating life is extended to 40 - 50 days, and the anode carbon consumption is reduced by 15% - 20%; the ability to resist molten salt erosion is increased by 50%, and the carbon slag shedding rate is reduced to less than 3%; by using low-cost transition materials, the comprehensive cost is reduced by 30% - 40% compared with all-ceramic coatings; it is suitable for complex working conditions, the coating preparation cycle is shortened, and it supports the production capacity demand of 10,000-ton electrolytic aluminum.

[0020] 3. In the present invention, the gradient protection coating provided by this application, through the integrated design of materials-structure-process, systematically solves the industry pain points of traditional anode coatings such as thermal stress failure, imbalance between conductivity and corrosion resistance, high carbon consumption, and high process costs, and has the core advantages of long life, low energy consumption, and strong adaptability, providing key technical support for the green transformation of the electrolytic aluminum industry.

[0021] Other advantages, objectives, and features of the present invention will be described to some extent in the subsequent specification; and to some extent, based on the study of the following text, it will be obvious to those skilled in the art; or, it can be taught from the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic flow diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0024] Gradient functional coating is an advanced coating technology that adapts to extreme environmental requirements through continuous gradient changes in material composition, structure, or performance. In the protection of carbon anodes in the electrolytic aluminum industry, due to its unique gradient design, the gradient functional coating can effectively relieve thermal stress, improve the interfacial bonding strength, and achieve the synergistic optimization of multiple properties (such as corrosion resistance, conductivity, oxidation resistance). The gradient functional coating is composed of two or more materials, and its characteristics such as composition, density, and porosity change continuously or stepwise along the thickness direction or the plane direction, forming a transition interface without mutation.

[0025] The design principle of the gradient functional coating is based on the working environment of the carbon anode for electrolytic aluminum (high temperature, strong corrosion, alternating oxidation-reduction). Through gradient design, the following are achieved: (1) Thermal stress relief: reducing the interfacial stress caused by the difference in thermal expansion coefficients between the coating and the substrate; (2) Functional zoning: the surface layer focuses on corrosion resistance / oxidation resistance, the intermediate layer takes into account conductivity, and the bottom layer strengthens the interfacial bonding; (3) Performance synergy: for example, the outer layer is a high-hardness ceramic (such as Al2O3), and the inner layer is a high-toughness metal or carbon-based material.

[0026] An anodic self-curing gradient functional coating for electrolytic aluminum, with silicate as the binder and combined with different functional fillers, is sequentially set as the following functional layers from the surface layer to the substrate: Outer layer: a corrosion-resistant layer with a thickness of 200 - 400 μm and a porosity < 5%; Intermediate layer: a conductive transition layer with a thickness of 100 - 150 μm; Inner layer: an interfacial bonding layer with a thickness of 100 - 200 μm.

[0027] It should be noted that reasonable thickness requirements are made according to the functional requirements of each layer (corrosion resistance, conductivity, bonding strength), and it has appropriate economy; within the above example range, the thickness of the entire functional coating is 400 - 750 μm, with good, reliable performance and controllable cost.

[0028] In the technical solution provided by this application, the coating includes: a high-performance corrosion-resistant coating, a low-cost rapid-curing coating, an environmentally friendly silicate gradient coating for high-sulfur anodes, and a nano-enhanced silicate gradient functional coating; they are respectively applicable to different technical scenarios.

[0029] Below, first, the preparation of the high-performance corrosion-resistant coating and the low-cost rapid-curing coating will be described.

[0030] The outer layer (corrosion-resistant layer) is composed of the following raw materials in parts by mass: Sodium silicate binder (Na2SiO3), 100 parts; Al2O3 particles, 30 - 70 parts; Silicon carbide whiskers (SiCw), 10 - 15 parts; or waste glass powder, 4 - 6 parts.

[0031] Among them, the particle size of the Al2O3 particles is 5 - 20 μm; the aspect ratio of the silicon carbide whiskers > 10.

[0032] Preferably, the diameter of the silicon carbide whiskers is 1 - 2 μm.

[0033] Preferably, in combination with other raw materials, the particle size of the waste glass powder is 1 - 5 μm.

[0034] Preferably, the Al2O3 microparticles are 50 parts; the silicon carbide whiskers are 13 parts; and the waste glass powder is 5 parts.

[0035] It should be noted that: When preparing a high-performance corrosion-resistant coating, silicon carbide whiskers are used; When preparing a low-cost and rapid-curing coating, waste glass powder is used to reduce costs.

[0036] In this raw material composition, 100 parts of Na2SiO3 are combined with 30 - 70 parts of Al2O3 microparticles. The sodium aluminosilicate glass phase formed by sintering endows the outer layer with excellent high-temperature resistance, corrosion resistance, and mechanical properties. The Al2O3 microparticles are dispersed in the coating, and the hardness and wear resistance of the coating are improved through dispersion strengthening, reducing mechanical wear. The fibrous structure of the silicon carbide whiskers can bridge microcracks, prevent crack propagation, and significantly improve the thermal shock resistance and mechanical toughness of the coating. At the same time, the silicon carbide whiskers can fill the space of the Al2O3 microparticles, reduce the porosity of the coating, and synergistically increase the density of the coating, thereby enhancing the physical barrier effect on the electrolyte. In addition, the Al2O3 microparticles provide micron-scale reinforcement, and the SiC whiskers achieve macroscopic crack resistance, forming a multi-level protection structure.

[0037] Function: The silicate forms a glass phase at high temperatures to seal pores; Al2O3 and SiCw enhance wear resistance and resistance to molten salt penetration.

[0038] The intermediate layer (conductive transition layer) is composed of the following raw materials in parts by mass: Potassium silicate binder (K2SiO3), 100 parts; TiB2 powder, 50 - 60 parts; Graphene sheets, 5 - 15 parts; or, carbon black, 3 - 7 parts.

[0039] The conductivity is enhanced by graphene sheets or carbon black.

[0040] It should be noted that due to its own characteristics, the control of the content of graphene sheets is extremely important; if the graphene content is too low and the dispersion is poor, it is difficult to form a continuous conductive network; if the content is too high, the graphene agglomerates, which instead leads to an increase in the interfacial contact resistance and a decrease in conductivity; the content of graphene sheets is required while fully considering the cooperation effect of each component.

[0041] It should be noted that: When preparing a high-performance corrosion-resistant coating, graphene sheets are used; When preparing a low-cost and rapid-curing coating, carbon black is used to reduce costs.

[0042] Preferably, the particle size of the TiB2 powder is 10 - 30 μm.

[0043] Preferably, the graphene sheets are 10 parts; and the carbon black is 5 parts.

[0044] In this raw material composition, 100 parts of K2SiO3 form a silicate glass phase after high-temperature sintering and serve as the continuous matrix of the coating, wrapping TiB2 and graphene to ensure uniform dispersion of the components; 50 - 60 parts of TiB powder is a highly conductive ceramic (resistivity 15 μΩ·cm), which can regulate the overall conductivity of the coating and avoid local overheating or polarization caused by uneven current distribution on the anode surface; the two-dimensional sheet structure of graphene can bridge microcracks and absorb stress through "sheet slip", significantly improving the thermal shock resistance and toughness of the coating.

[0045] In addition, the graphene sheets stack to form a dense barrier, reducing the porosity of the coating and hindering the penetration of molten salt electrolyte and oxygen; TiB2 and graphene jointly construct a dual-channel conductive network (point contact of TiB2 particles + surface contact of graphene sheets, conductivity can reach 5*10 5 S / m), achieving low-resistance and highly uniform current transmission.

[0046] In addition, the three provide multi-scale reinforcement: Nanoscale: Graphene sheets strengthen the toughness of the matrix; Micron scale: TiB2 particles enhance hardness and wear resistance; Macro scale: The potassium silicate glass phase provides overall densification and corrosion resistance.

[0047] Function: TiB2 provides a conductive path (resistivity ≤ 100 μΩ·m), graphene sheets enhance conductivity (10 5 ~10 6 S / m), and inhibit the brittleness of silicate.

[0048] The inner layer (interface bonding layer) is composed of the following raw materials in parts by mass: Aluminum silicate binder (Al2(SiO3)3), 100 parts; Recycled carbon powder, 20 - 40 parts; Wollastonite fiber, 15 - 25 parts.

[0049] It should be noted that: in this ratio, if the proportion of recycled carbon powder and wollastonite fiber is too low, the effect will be limited and it will be difficult to effectively inhibit the interfacial cracking caused by the thermal expansion of the matrix; at the same time, if their proportion is too high, the brittleness of the coating will increase; thus, the number of parts of the two is designed to be between 35 and 75, fully meeting the effect and having appropriate brittleness.

[0050] Preferably, recycled carbon powder, 30 parts; wollastonite fiber, 20 parts.

[0051] Among them, the recycled carbon powder comes from the residual anode; the length of the wollastonite fiber is 5 - 50 μm.

[0052] It should be noted that there are requirements for the length of wollastonite fibers. Wollastonite fibers are short fibers that can be evenly distributed in a matrix by mechanical stirring or ultrasonic dispersion, and are suitable for spraying processes.

[0053] Or, the inner layer is composed of the following raw materials in parts by weight: Aluminum silicate binder (Al2(SiO3)3), 100 parts; Recycled toner, 40~50 parts.

[0054] Preferably, the recycled carbon powder is 40 parts.

[0055] It should be noted that: When preparing high-performance corrosion-resistant coatings, wollastonite fibers are used; When preparing low-cost fast-curing coatings, the amount of recycled carbon powder is increased, wollastonite fibers are omitted, the recovery rate is improved, and the cost is reduced.

[0056] Function: The porous structure (porosity 20%~25%) is mechanically interlocked with the carbon-based anode, and the wollastonite fiber improves toughness.

[0057] Among them, the recycled carbon powder and wollastonite fiber work synergistically to form a more reliable bonding structure; specifically, the recycled carbon powder is in the form of irregular particles, with a high specific surface area and a microporous structure, and the particles are accumulated to form an initial pore network; the wollastonite fiber is a fibrous structure, and the fibers are staggered and overlapped to form a skeleton support to prevent structural collapse; the gaps between the fibers serve as pore channels.

[0058] Reference Figure 1 , a method for preparing an anode self-curing gradient functional coating for electrolytic aluminum, comprising the following steps: S1. Matrix pretreatment: After the carbon anode is dried, the surface dust is blown off; S2. Preparation of coating slurry: preparation of each layer of slurry separately; S3, gradient coating and curing: adopt layer-by-layer spraying process.

[0059] Wherein, step S2 comprises: a201, outer layer slurry preparation; Mix the Na2SiO3 solution with Al2O3 and SiCw and stir mechanically for 3-5h; a202, preparation of intermediate layer slurry; K2SiO3 solution was mixed with TiB2 and graphene sheets and dispersed by ultrasonic for 1-3h; a203, preparation of inner layer slurry; Al2(SiO3)3 sol is mixed with regenerated carbon powder and wollastonite fiber and mechanically stirred for 1-3h.

[0060] Preferably, mechanical stirring is carried out for 4 h, ultrasonic dispersion is carried out for 2 h, and mechanical stirring is carried out for 2 h.

[0061] It should be noted that in each step, it is necessary to ensure that stirring or dispersion is uniform to form a homogeneous fluid; if the mixing effect is poor, the treatment time is extended.

[0062] It can be understood that when preparing a low-cost and fast-curing coating: In step a201, SiCw is omitted; in step a202, carbon black is used to replace graphene sheets; in step a203, wollastonite fibers are omitted to improve the recovery rate.

[0063] Among them, in step S3: Spraying sequence: inner layer → middle layer → outer layer; After each layer is sprayed, it is dried at room temperature for 30 - 60 minutes; After three sprayings are completed, it is cured at room temperature for 5 - 8 hours.

[0064] Preferably, it is dried at room temperature for 50 minutes and cured for 6 hours.

[0065] Among them, the room temperature is 10°C - 35°C to avoid the adverse effects of overcooling and overheating environments; since the curing time varies at different temperatures, it is based on the surface not sticking to the hand.

[0066] The above settings are for high-performance corrosion-resistant coatings and low-cost fast-curing coatings; in addition, targeted designs are made for special environments.

[0067] For carbon anodes with a relatively high sulfur content (2% - 3%), develop low-cost and highly corrosion-resistant coatings to solve the problem of local corrosion caused by sulfur; design an environmentally friendly silicate gradient coating dedicated to high-sulfur anodes.

[0068] At this time, the outer layer is a sulfur-resistant corrosion layer, which is composed of the following raw materials in parts by mass: Magnesium silicate binder (MgSiO3), 100 parts; Al2O3 particles, 50 - 60 parts; Boron nitride (BN), 10 - 20 parts.

[0069] Among them, boron nitride has good sulfur resistance and permeability.

[0070] In this raw material composition, 100 parts of MgSiO3 is used as the reference amount to ensure sufficient bonding strength and avoid brittleness caused by excessive amounts; when BN is designed to be 10 - 15 parts, it meets the economic solution and improves the thermal conductivity; when designed to be 15 - 20 parts, it meets the extreme friction conditions (such as high-speed molten salt scouring); the surface of Al2O3 is dense, blocking the penetration of sulfur and fluoride ions, and facing high-sulfur environments, significantly reducing the porosity.

[0071] Among them, the particle size of the Al2O3 particles is 10 - 30 μm.

[0072] Preferably, there are 55 parts of Al2O3 particles; 15 parts of boron nitride; and the thickness is 200 μm.

[0073] Function: MgSiO3 reacts with sulfur at high temperature to form stable MgSO4, inhibiting sulfur erosion; the BN layered structure blocks the penetration of the electrolyte.

[0074] The intermediate layer (conductive transition layer) is composed of raw materials in the following mass parts: Calcium silicate binder (CaSiO3), 100 parts; TiB2 powder, 30 - 50 parts; Recycled waste aluminum ash particles, 5 - 15 parts.

[0075] Among them, the recycled waste aluminum ash particles contain Al and Si components, and the particle size is 20 - 50 μm.

[0076] In this raw material composition, the waste aluminum ash, as a recycled resource, contains 60% - 70% Al and 15% - 20% Si, which can reduce the raw material cost by 30% - 50%.

[0077] The control of the particle size of the recycled waste aluminum ash particles within the range of 20 - 50 μm is based on the following considerations: 1). Process feasibility: Adapt to spraying to ensure uniform dispersion; 2). Performance optimization: Balance mechanical strengthening, thermal expansion matching and corrosion resistance; 3). Cost control: Reduce the energy consumption of pretreatment and maximize the resource utilization rate.

[0078] This particle size range realizes the synergistic goals of high cost performance, toughening and long life in the intermediate layer of the aluminum electrolysis anode.

[0079] Preferably, there are 40 parts of TiB2 powder; 10 parts of recycled waste aluminum ash particles; and the thickness is 120 μm.

[0080] Function: TiB2 provides a conductive path, and the recycled waste aluminum ash particles relieve the thermal expansion mismatch.

[0081] The inner layer (interface bonding layer) is composed of raw materials in the following mass parts: Sodium silicate binder (Na2SiO3), 100 parts; Recycled carbon powder, 40 - 60 parts; Fused quartz powder, 5 - 15 parts.

[0082] Among them, the recycled carbon powder contains waste anode recycling materials, or is all waste anode recycling materials.

[0083] Preferably, the recycled toner is 50 parts; the fused silica powder is 10 parts; the thickness is 100 μm.

[0084] In this raw material composition, taking 100 parts of Na2SiO3 as the reference amount, sufficient bonding strength is ensured while avoiding brittleness caused by excessive amount; the recycled toner is enhanced at low cost and serves as a filler phase, reducing the raw material cost by 40% - 50% while improving the toughness of the coating; the fused silica powder forms a dense silicate layer with the carbon matrix.

[0085] Function: The fused silica powder fills the pores and improves the bonding strength with the anode matrix; the recycled toner reduces the cost.

[0086] Correspondingly, the preparation method is adjusted; step S2 includes: b201. Preparation of the outer layer slurry; Outer layer slurry: MgSiO3 sol is mixed with Al2O3 and BN, and mechanically stirred for 5 - 7 h; b202. Preparation of the intermediate layer slurry; CaSiO3 solution is mixed with TiB2 and recycled particles of waste aluminum ash, and ultrasonically dispersed for 2 - 4 h; b203. Preparation of the inner layer slurry; Na2SiO3 solution is mixed with the recycled toner and the fused silica powder, and mechanically stirred for 1 - 3 h.

[0087] Aiming at the problems of local overheating and corrosion of the anode under high current density, a nano-enhanced silicate gradient functional coating is designed; the coating density, conductivity and interface bonding strength are optimized through nano materials to solve the problems of local overheating and corrosion of the anode under high current density.

[0088] At this time, the outer layer is a nano-reinforced corrosion-resistant layer, which is composed of the following raw materials in parts by mass: Potassium silicate binder (K2SiO3), 100 parts; Nano Al2O3, 10 - 30 parts; Fused silica powder, 20 - 40 parts.

[0089] Among them, the particle size of nano Al2O3 is 20 - 50 nm; the particle size of the fused silica powder is 1 - 3 μm.

[0090] Preferably, the nano Al2O3 is 20 parts, the fused silica powder is 30 parts; the thickness is 100 μm.

[0091] In this raw material composition, K2SiO3 is based on 100 parts to ensure sufficient bonding strength while avoiding excessive amounts that would increase brittleness; when nano-Al2O3 is designed to be 10 - 20 parts, it emphasizes economy and moderate enhancement and is suitable for low mechanical load environments; when designed to be 20 - 30 parts, it enhances high-temperature strength and is suitable for highly corrosive molten salt scenarios; when fused quartz powder is designed to be 20 - 30 parts, it provides basic thermal matching and is suitable for conventional electrolytic cells; when designed to be 30 - 40 parts, it is suitable for extreme thermal cycling environments (such as frequent start-stop conditions) to further inhibit thermal shock cracking.

[0092] Function: Nano-Al2O3 fills micropores with a porosity of < 3% (the traditional micron-level coating is 5% - 8%).

[0093] The intermediate layer (conductive transition layer) is composed of raw materials in the following mass parts: Aluminum silicate binder (Al2(SiO3)3), 100 parts; TiB2 powder, 30 - 50 parts; Nano silicon carbide whiskers (SiCw), 10 - 20 parts.

[0094] Among them, the particle size of TiB2 powder is 5 - 10 μm; the diameter of nano silicon carbide whiskers is 100 nm and the length is 1 - 5 μm.

[0095] Preferably, the TiB2 powder is 40 parts, the nano silicon carbide whiskers are 15 parts; the thickness is 120 μm.

[0096] In this raw material composition, the aluminum silicate binder (Al2(SiO3)3) is based on 100 parts as a reference amount to ensure sufficient bonding strength while avoiding excessive amounts that would cause brittleness; when TiB2 powder is designed to be 30 - 40 parts, it meets the basic conductive requirements and is suitable for conventional current densities; when designed to be 40 - 50 parts, it is suitable for high current density scenarios; when nano silicon carbide whiskers are designed to be 10 - 15 parts, it is an economical solution to enhance the flexural strength; when designed to be 15 - 20 parts, it adapts to extreme thermal stress environments.

[0097] Function: Nano silicon carbide whiskers bridge TiB2 micron particles to enhance the toughness of the coating (the fracture toughness is increased by 30%). The nanostructure enhances the thermal conductivity to 45 W / (m·K) to relieve local overheating.

[0098] The inner layer (nano interface bonding layer) is composed of raw materials in the following mass parts: Sodium silicate binder (Na2SiO3), 100 parts; Recycled carbon powder, 20 - 40 parts; Graphene nanosheets, 10 - 30 parts; Nano-SiO2, 3 - 7 parts.

[0099] It should be noted that the range of nano-SiO2 needs to be precisely controlled; too little cannot improve the coating strength, and too much is prone to agglomeration.

[0100] Among them, the thickness of the graphene nanosheets is 3 - 5 nm.

[0101] Preferably, the recycled toner is 30 parts, the graphene nanosheets are 20 parts, and the nano-SiO2 is 5 parts; thickness: 150 μm.

[0102] Function: The graphene nanosheets enhance the interfacial conductivity, and the resistivity ≤ 50 μΩ·m; the nano-SiO2 reacts with the silicate to form a -Si-O-Si- network, and the bonding strength is increased to 25 MPa.

[0103] Correspondingly, the preparation method is adjusted; step S2 includes: c201. Preparation of the outer layer slurry; Mix the K2SiO3 solution with nano-Al2O3 and fused quartz powder, and mechanically stir for 1 - 3 h; Preferably, the modulus of the K2SiO3 solution is 2.2 - 2.8; c202. Preparation of the intermediate layer slurry; Mix the Al2(SiO3)3 sol with TiB2 and nano-silicon carbide whiskers, and perform high-speed shear mixing for 0.5 - 1.5 h; c203. Preparation of the inner layer slurry; Mix the Na2SiO3 solution with the recycled toner, graphene nanosheets, and nano-SiO2, and perform ultrasonic dispersion for 1 - 3 h.

[0104] Example 1: High-performance corrosion-resistant coating.

[0105] Outer layer: Na2SiO3 + 65% Al2O3 + 12% SiCw, thickness 200 μm.

[0106] Intermediate layer: K2SiO3 + 55% TiB2 + 10% graphene, thickness 130 μm.

[0107] Inner layer: Al2(SiO3)3 + 30% recycled toner + 20% wollastonite fiber, thickness 100 μm.

[0108] During the preparation of the slurry: Outer layer slurry: Mix the Na2SiO3 solution with Al2O3 and SiCw, and mechanically stir for 4 h; Intermediate layer slurry: Mix the K2SiO3 solution with TiB2 and graphene sheets, and perform ultrasonic dispersion for 2 h; Inner layer slurry: Mix the Al2(SiO3)3 sol with the recycled toner and wollastonite fiber, and mechanically stir for 2 h.

[0109] Spraying sequence: Inner layer → Intermediate layer → Outer layer; After each layer is sprayed, it is dried at room temperature for 60 minutes; After three sprayings are completed, it is cured at room temperature for 6 hours.

[0110] Test results: Bonding strength: 24 MPa (ASTM D4541, meeting industrial requirements); Resistivity: 92 μΩ·m (four-probe method); Corrosion resistance: Immersed in molten Na3AlF6 at 960 °C for 240 h, the weight loss rate of the coating is <2% (for traditional coatings >8%).

[0111] Example 2: Low-cost and rapid-curing coating.

[0112] Outer layer: Na2SiO3 + 60% Al2O3 + 5% waste glass powder (SiCw is omitted, adding waste glass powder to reduce costs); Intermediate layer: K2SiO3 + 50% TiB2 + 5% carbon black (replacing graphene flakes); Inner layer: Al2(SiO3)3 + 40% recycled anode carbon powder (improving the recovery rate); Spraying sequence: Inner layer → Intermediate layer → Outer layer; After each layer is sprayed, it is dried at room temperature for 50 minutes; After three sprayings are completed, it is cured at room temperature for 5 hours.

[0113] Test results: Cost: 40% lower than that of Example 1; Bonding strength: 18 MPa (ASTM D4541, meeting industrial requirements); Resistivity: 98 μΩ·m (four-probe method); Corrosion resistance: Immersed in molten Na3AlF6 at 960 °C for 240 h, the weight loss rate of the coating is <6% (for traditional coatings >8%).

[0114] Example 3: Environmentally friendly silicate gradient coating for high-sulfur anodes.

[0115] Outer layer (sulfur corrosion-resistant layer): Magnesium silicate binder (MgSiO3) + 55% Al2O3 particles (particle size 10 - 30 μm) + 15% boron nitride (BN, anti-sulfur penetration).

[0116] Function: MgSiO3 reacts with sulfur at high temperature to form stable MgSO4, inhibiting sulfur erosion; the BN layered structure blocks the penetration of the electrolyte.

[0117] Thickness: 200 μm.

[0118] Intermediate layer (conductive transition layer): Calcium silicate binder (CaSiO3) + 40% TiB2 + 10% recycled waste aluminum ash particles (containing Al and Si, particle size 20 - 50 μm).

[0119] Function: TiB2 provides a conductive path, and the recycled waste aluminum ash particles relieve the thermal expansion mismatch.

[0120] Thickness: 120 μm.

[0121] Inner layer (interface bonding layer): Sodium silicate binder (Na2SiO3) + 50% recycled carbon powder (containing recycled anode materials) + 10% fused quartz powder.

[0122] Function: Fused quartz powder fills the pores and improves the bonding strength with the anode matrix; the recycled carbon powder reduces the cost.

[0123] Thickness: 100 μm.

[0124] Slurry preparation: Outer layer slurry: Mix MgSiO3 sol with Al2O3 and BN, and mechanically stir for 6 h; Intermediate layer slurry: Mix CaSiO3 solution with TiB2 and recycled waste aluminum ash particles, and ultrasonically disperse for 3 h; Inner layer slurry: Mix NaSiO3 solution with recycled carbon powder and fused quartz powder, and mechanically stir for 2 h.

[0125] Spraying sequence: Inner layer → Intermediate layer → Outer layer; After spraying each layer, dry at room temperature for 60 minutes; After three sprayings, cure at room temperature for 7 hours.

[0126] Test results: Bonding strength: 20 MPa (ASTM D4541, meeting the requirements of high - sulfur anodes); Resistivity: 94 μΩ·m (four - probe method); Corrosion resistance: Immerse in molten cryolite salt (960 °C) containing [sulfur] for 240 h, and there are no sulfide cracks on the coating surface (traditional coatings show cracking).

[0127] Sulfur corrosion test: Weight loss rate: 1.2% (4.5% for traditional coatings).

[0128] Example 4: Nano - enhanced silicate gradient functional coating.

[0129] Outer layer (nano-reinforced corrosion-resistant layer): Potassium silicate binder (K2SiO3) + 20% nano-Al2O3 (particle size 20 - 50 nm) + 30% fused quartz powder (particle size 1 - 3 μm).

[0130] Function: Nano-Al2O3 fills micropores, porosity < 3% (traditional micron-level coating is 5% - 8%).

[0131] Thickness: 100 μm.

[0132] Intermediate layer (conductive transition layer): Aluminum silicate binder (Al2(SiO3)3) + 40% TiB2 powder (5 - 10 μm) + 15% nano-silicon carbide whiskers (diameter 100 nm, length 1 - 5 μm).

[0133] Function: Nano-silicon carbide whiskers bridge TiB2 micron particles, improving the toughness of the coating (fracture toughness increased by 30%).

[0134] Nano-structure enhances the thermal conductivity to 45 W / (m·K), alleviating local overheating.

[0135] Thickness: 120 μm.

[0136] Inner layer (nano-interface bonding layer): Sodium silicate binder (Na2SiO3) + 30% recycled carbon powder + 20% graphene nanosheets (thickness 3 - 5 nm) + 5% nano-SiO2.

[0137] Function: Graphene nanosheets improve the interface conductivity, resistivity ≤ 50 μΩ·m.

[0138] Nano-SiO2 reacts with silicate to form a -Si-O-Si- network, increasing the bonding strength to 25 MPa.

[0139] Thickness: 150 μm.

[0140] Slurry preparation: Outer layer slurry: Mix the K2SiO3 solution (modulus 2.5) with nano-Al2O3 and fused quartz powder, and mechanically stir for 2 h; Intermediate layer slurry: High-speed shear mix the Al2(SiO3)3 sol with TiB2 and nano-silicon carbide whiskers (3000 rpm, 1 h); Inner layer slurry: Mix the Na2SiO3 solution with recycled carbon powder, graphene nanosheets and nano-SiO2, and ultrasonically disperse for 2 h.

[0141] Spraying sequence: Inner layer → Intermediate layer → Outer layer; After spraying each layer, dry at room temperature for 60 minutes; After three sprayings, cure at room temperature for 8 hours.

[0142] Test results: Bond strength: 25 MPa (ASTM D4541, meeting requirements); Resistivity: 82 μΩ·m (four-probe method); Corrosion resistance: Immersed in molten ice crystal salt containing 1% Na2S (960 °C) for 240 h, no sulfide cracks on the coating surface (conventional coatings show cracking).

[0143] In the present invention, there are innovations in the material system: replacing traditional metal / ceramic binders with silicates to achieve low-cost and green manufacturing; innovations in structural design: through the gradient combination of the outer layer (corrosion-resistant layer), the middle layer (conductive transition layer), and the inner layer (interface bonding layer) to balance conductivity, corrosion resistance, and interface bonding; utilization of solid waste resources: the inner layer uses recycled carbon powder (recovered from spent anodes) and recycled particles of waste aluminum ash to achieve "treating waste with waste", reducing the raw material cost by 25% - 40%.

[0144] The present invention has at least the following beneficial effects.

[0145] 1). Effective alleviation of thermal stress and improvement of interface bonding strength.

[0146] Gradient transition to reduce stress: According to the thermoelastic mechanics model, the thermal stress is linearly related to the difference in thermal expansion coefficients. Through the composition gradient (such as Al2O3 (30% - 50%) → TiB2 (50% - 60%) → carbon-based), where the thermal expansion coefficient of Al2O3 in the outer layer is 7.5 - 8×10 -6 / °C), the thermal expansion coefficient of TiB2 in the middle layer is 5.5 - 6.5×10 -6 / °C), and the thermal expansion coefficient of the carbon anode is 3.0 - 5.0×10 -6 / °C), the thermal expansion coefficients of each layer gradually transition from 8.0 → 5.5 → 4.0×10 -6 / °C, reducing the overall difference in thermal expansion coefficients between the coating and the anode substrate by about 30% - 50%, and reducing the interfacial thermal stress to less than 30% of 8×10 -6 / °C of the conventional coating (single-layer pure Al2O3 coating).

[0147] The bonding strength is significantly enhanced: Experimental data show that the bonding strength of the gradient coating ≥ 25 MPa; it is more than 60% higher than that of a single ceramic coating (usually < 15 MPa), avoiding spalling failure at high temperatures.

[0148] 2). Synergistic optimization of conductivity and corrosion resistance.

[0149] Functional zone design: Outer layer (such as Al2O - SiC): The corrosion resistance is improved, and the molten salt penetration rate is reduced to < 5% (conventional coating > 15%); Intermediate layer: resistivity ≤ 100 μΩ·m, a 50% reduction compared to a relatively pure Al2O3 coating (> 200 μΩ·m). Breakthrough in comprehensive performance: In a 960 °C electrolysis environment, the coating life is extended to 40 - 50 days (traditional coating: 20 - 25 days), and the anodic carbon consumption is reduced by 15% - 20% (from 450 kg / t-Al to 360 - 380 kg / t-Al).

[0150] 3) Improvement in thermal shock and erosion resistance.

[0151] Enhanced wear resistance: The combination of a high-hardness ceramic outer layer (such as SiC) and a tough intermediate layer increases the molten salt erosion resistance by 50% and reduces the carbon slag shedding rate to less than 3%.

[0152] 4) Cost control.

[0153] High raw material utilization rate: The gradient design allows the use of low-cost transition materials (such as recycled carbon powder, waste aluminum ash), and the comprehensive cost is reduced by 30% - 40% compared to a fully ceramic coating.

[0154] 5) Wide industrial application.

[0155] Adaptable to complex working conditions: High-sulfur anode: Sulfur corrosion is inhibited through a sulfur fixation layer (such as MgSiO - BN) in the gradient coating. High-current density electrolytic cell: The high thermal conductivity design of the intermediate layer (such as nano silicon carbide whiskers) alleviates local overheating and increases the current efficiency by 1% - 2%. Scalability potential: The coating preparation cycle is shortened to 6 - 10 hours (traditional process: 12 - 20 hours), supporting the production capacity demand of ten thousand tons of electrolytic aluminum.

[0156] The gradient protection coating provided by this application, through the integrated design of materials - structure - process, systematically solves the industry pain points of traditional anode coatings such as thermal stress failure, imbalance between conductivity and corrosion resistance, high carbon consumption, and high process costs. It has the core advantages of long life, low energy consumption, and strong adaptability, providing key technical support for the green transformation of the electrolytic aluminum industry.

[0157] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

[0158] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0159] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. An anodic self-curing gradient functional coating for electrolytic aluminum, characterized in that, With silicate as the binder and combined with different functional fillers, the following functional layers are sequentially arranged from the surface layer to the matrix: Outer layer: a corrosion-resistant layer with a thickness of 200 - 400 μm and a porosity of <5%; Intermediate layer: a conductive transition layer with a thickness of 100 - 150 μm; Inner layer: an interface bonding layer with a thickness of 100 - 200 μm.

2. The anodic self-curing gradient functional coating for electrolytic aluminum according to claim 1, characterized in that The coating includes: High-performance corrosion-resistant coating, low-cost rapid-curing coating, environmentally friendly silicate gradient coating for high-sulfur anodes, and nano-enhanced silicate gradient functional coating.

3. The anodic self-curing gradient functional coating for electrolytic aluminum according to claim 1, wherein The outer layer is composed of the following raw materials in parts by mass: Sodium silicate binder, 100 parts; Al2O3 particles, 30 - 70 parts; Silicon carbide whiskers, 10 - 15 parts; or waste glass powder, 4 - 6 parts.

4. The anodic self-curing gradient functional coating for electrolytic aluminum according to claim 1, wherein The intermediate layer is composed of the following raw materials in parts by mass: Potassium silicate binder, 100 parts; TiB2 powder, 50 - 60 parts; Graphene sheets, 5 - 15 parts; or carbon black, 3 - 7 parts.

5. The anodic self-curing gradient functional coating for electrolytic aluminum according to claim 1, characterized in that, The inner layer is composed of the following raw materials in parts by mass: Aluminum silicate binder, 100 parts; Recycled carbon powder, 20 - 40 parts; Wollastonite fiber, 15 - 25 parts; Or: Aluminum silicate binder, 100 parts; Recycled carbon powder, 40 - 50 parts.

6. The anodic self-curing gradient functional coating for electrolytic aluminum according to claim 1, wherein, For carbon anodes with a relatively high sulfur content, an environmentally friendly silicate gradient coating for high-sulfur anodes is designed; The outer layer is composed of the following raw materials in parts by mass: Magnesium silicate binder, 100 parts; Al2O3 particles, 50 - 60 parts; Boron nitride, 10 - 20 parts; The intermediate layer is composed of the following raw materials in parts by mass: Calcium silicate binder, 100 parts; TiB2 powder, 30 - 50 parts; Recycled particles from waste aluminum ash, 5 - 15 parts; The inner layer is composed of the following raw materials in parts by mass: Sodium silicate binder, 100 parts; Recycled carbon powder, 40 - 60 parts; Fused quartz powder, 5 - 15 parts.

7. The anodic self-curing gradient functional coating for electrolytic aluminum according to claim 1, characterized in that, For the problems of local overheating and corrosion of the anode under high current density, a nano-enhanced silicate gradient functional coating is designed; The outer layer is composed of the following raw materials in parts by mass: Potassium silicate binder, 100 parts; Nano-Al2O3, 10 - 30 parts; Fused quartz powder, 20 - 40 parts; The intermediate layer is composed of the following raw materials in parts by mass: Aluminum silicate binder, 100 parts; TiB2 powder, 30 - 50 parts; Nano-silicon carbide whiskers, 10 - 20 parts; The inner layer is composed of the following raw materials in parts by mass: Sodium silicate binder, 100 parts; Recycled carbon powder, 20 - 40 parts; Graphene nanosheets, 10 - 30 parts; Nano-SiO2, 3 - 7 parts.

8. The preparation method of the anode self-curing gradient functional coating for electrolytic aluminum according to any one of claims 1-7, characterized in that It includes the following steps: S1. Matrix pretreatment: After the carbon anode is dried, blow off the surface dust; S2. Coating slurry preparation: Prepare each layer of slurry separately; S3. Gradient coating and curing: Adopt a layer-by-layer spraying process.

9. The preparation method of the anodic self-curing gradient functional coating for electrolytic aluminum according to claim 8, characterized in that, When preparing the high-performance corrosion-resistant coating, step S2 includes: a201. Preparation of the outer layer slurry; Mix the Na2SiO3 solution with Al2O3 and SiCw, and mechanically stir for 3 - 5 h; a202. Preparation of the intermediate layer slurry; Mix the K2SiO3 solution with TiB2 and graphene sheets, and ultrasonically disperse for 1 - 3 h; High-speed shear mixing at 3000 rpm for 0.5 - 1.5 h; a203, Preparation of Inner Layer Slurry; Mix Al2(SiO3)3 sol, recycled toner, and wollastonite fiber, and mechanically stir for 1 - 3 h.

10. The preparation method of the anode self-curing gradient functional coating for electrolytic aluminum according to claim 8, characterized in that, In step S3: Spraying sequence: inner layer → middle layer → outer layer; After each layer is sprayed, dry at room temperature for 30 - 60 minutes; After three sprayings are completed, cure at room temperature for 5 - 8 hours.

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