A prebaked anode anti-oxidation ceramic coating for electrolytic aluminum and its preparation method

Abstract

This invention belongs to the field of coating technology and discloses a prebaked anode anti-oxidation ceramic coating for electrolytic aluminum and its preparation method. The coating comprises the following raw materials in the indicated mass percentages: ceramic aggregate 45-55%, binder 40-50%, suspending agent 0.5-5%, functional additives 0.2-5%, and water 0.5-6%. The ceramic aggregate is composed of at least two of alumina, silicon carbide, zirconium oxide, and silica powder, and contains at least alumina and silicon carbide. The binder is a mixture of sodium silicate and potassium silicate. The prebaked anode anti-oxidation ceramic coating for electrolytic aluminum of this invention is prepared by a two-step curing method. The binder interacts with the ceramic aggregate, undergoing a chemical reaction at high temperature to generate substances that improve the performance of the ceramic coating and increase its strength. The ceramic coating of this invention, after being kept at 900℃ for 72 hours, exhibits a weight loss rate of less than 1% in an oxidation experiment, demonstrating its excellent anti-oxidation properties at high temperatures.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a prebaked anode anti-oxidation ceramic coating for the electrolytic aluminum industry and its preparation method. Background Technology

[0002] my country leads the world in electrolytic aluminum production, accounting for 59.3% of global output as of July 2023. In the electrolysis process, alumina serves as the solute, and carbon anodes act as the anode, undergoing an electrochemical reaction in an aluminum electrolysis cell. Prebaked anodes, as consumable materials, account for a significant portion of the cost. Theoretically, the minimum amount of carbon anodes consumed is 333 kg / t-Al. However, due to anode losses during electrolysis, the actual electrolysis consumption of prebaked anodes is approximately 410 kg / t-Al. A large portion of this prebaked anode is consumed through chemical reactions with air and carbon dioxide during electrolysis. The oxidation of prebaked anodes not only increases the cost of electrolytic aluminum but also generates large amounts of CO and CO2, hindering the achievement of the "dual carbon" target (carbon dioxide, carbon dioxide, and carbon sequestration). Therefore, developing a cost-effective and easy-to-operate prebaked anode coating is urgently needed.

[0003] The common method for preparing prebaked anodic anti-oxidation coatings is the sol-gel method. This method suffers from severe shrinkage during drying, resulting in low coating strength. Furthermore, the preparation process is cumbersome and costly, hindering large-scale industrial production. Therefore, it is necessary to provide a novel prebaked anodic anti-oxidation ceramic-based coating and its coating method to overcome the aforementioned technical problems. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing coatings and provide a prebaked anode anti-oxidation coating, ceramic coating and preparation method for electrolytic aluminum based on slurry method. The coating is sprayed or brushed onto the surface of the prebaked anode and dried and cured at a low temperature to form a coating with good adhesion, density and high strength. During the electrolytic aluminum process, the oxidizing atmosphere is effectively prevented from contacting the prebaked anode, thereby reducing the consumption of the anode.

[0005] The technical solution adopted in this invention is:

[0006] A prebaked anode anti-oxidation ceramic coating for electrolytic aluminum, the coating comprising the following raw materials in the following mass percentages: ceramic aggregate 45-55%, binder 40-50%, suspending agent 0.5-5%, functional additives 0.2-5%, and water 0.5-6%; wherein the ceramic aggregate is composed of at least two of alumina, silicon carbide, zirconium oxide, and silicon micropowder, and contains at least alumina and silicon carbide, with a mass percentage of alumina in the ceramic aggregate being 50%-80% and a mass percentage of silicon carbide in the ceramic aggregate being 20%-40%; the binder is a mixture of sodium silicate (Na2O·nSiO2) and potassium silicate (K2O·nSiO2).

[0007] In some embodiments, the alumina is α-alumina.

[0008] In some embodiments, the silicon carbide is green silicon carbide.

[0009] In some embodiments, the modulus of the sodium silicate and potassium silicate in the binder is 2.3 to 3.4.

[0010] In some embodiments, the suspending agent is one or both of sodium bentonite and fumed silica.

[0011] In some embodiments, the functional additive is at least one of yttrium oxide, sodium hydroxide, and potassium hydroxide.

[0012] In some embodiments, the mass ratio of sodium silicate to potassium silicate in the binder is 1:(0.2-1).

[0013] A method for preparing a prebaked anode anti-oxidation ceramic coating for electrolytic aluminum includes the following steps: weighing raw materials as described above;

[0014] (1) Mix the binder with half of the ceramic aggregate evenly to obtain the first mixed slurry;

[0015] (2) The first mixed slurry is mixed evenly with the suspending agent and functional additives to obtain the second mixed slurry;

[0016] (3) Add the remaining ceramic aggregate and water to the second mixed slurry, stir evenly, and obtain the prebaked anode anti-oxidation ceramic coating for electrolytic aluminum;

[0017] (4) Apply coating to the surface of the prebaked anode;

[0018] (5) Wait for the coating to dry and cure to form a prebaked anode anti-oxidation ceramic coating for electrolytic aluminum.

[0019] Adding raw materials all at once may cause agglomeration, thus affecting the mixing effect and the quality of the ceramic coating obtained subsequently. However, the method of this invention, by adjusting the process, can obtain a uniformly mixed slurry without agglomeration, resulting in a prebaked anode anti-oxidation ceramic coating for electrolytic aluminum.

[0020] In some embodiments, the method of applying the coating includes spraying or brushing.

[0021] In some embodiments, when using the brush coating method, the sides and top of the prebaked anode can be coated first as needed. After drying, the bottom surface can be coated. The drying temperature is 45-55℃ and the drying time is 25-35 minutes. The coating is repeated 2-4 times, and the thickness of the coating is controlled to be 0.2-0.5mm.

[0022] In some embodiments, the drying and curing process is a two-step drying and curing method, comprising the following steps:

[0023] The prebaked anode coated with the paint is heated at 65℃~85℃ for 1.5-2.5 hours; then heated at 120℃~150℃ for 6.5-9.5 hours.

[0024] The beneficial effects of this invention are:

[0025] (1) In the electrolytic aluminum prebaked anode anti-oxidation ceramic coating of the present invention, the binder is water glass, the main component is silicate, which has good stability in high temperature environment, the coating has short curing time, high strength, and can be dried and cured at a low temperature without high temperature sintering, which reduces the difficulty of coating preparation.

[0026] (2) In the electrolytic aluminum prebaked anode anti-oxidation ceramic coating of the present invention, silicate binders such as water glass can interact with the ceramic aggregate used in the present invention and can undergo a chemical reaction at high temperature to generate substances that can improve the performance of the ceramic coating and further improve the coating strength.

[0027] (3) In the electrolytic aluminum prebaked anode anti-oxidation ceramic coating of the present invention, the main component of the aggregate is aluminum oxide, which can minimize the impurities added in the aluminum electrolytic cell and basically not affect the electrolysis process and the purity of the product.

[0028] (4) The electrolytic aluminum prebaked anode anti-oxidation ceramic coating of the present invention is prepared by a slurry method. The coating overcomes the problem of shrinkage that is common in conventional coatings during the drying process, and the resulting coating has high strength. The method is easy to operate, requires simple equipment, is not limited by environmental or site conditions, and the coating composition is simple and inexpensive, making it suitable for mass production and easy to industrialize. Attached Figure Description

[0029] Figure 1 This is a flowchart of the coating preparation process.

[0030] Figure 2 Fourier transform infrared spectra of the coating prepared according to Example 1 after drying and curing under different conditions.

[0031] Figure 3 This is a 100x SEM image of the surface of the coating prepared according to Example 1 after drying and curing.

[0032] Figure 4 This is a 1500x SEM image of the surface of the coating prepared according to Example 1 after drying and curing.

[0033] Figure 5 The left side is untreated, and the right side is coated with the coating prepared according to Example 1. These are photographs before and after the oxidation experiment.

[0034] Figure 6 Photos of untreated test blocks before and after the oxidation experiment.

[0035] Figure 7 Photographs of test blocks coated with the paint prepared according to Example 2 after an oxidation experiment.

[0036] Figure 8 Photographs of test blocks coated with the paint prepared according to Comparative Example 2 after oxidation experiments.

[0037] Figure 9 Photographs of test blocks coated with the paint prepared according to Comparative Example 3 after oxidation experiments.

[0038] Figure 10 Photographs of test blocks coated with the paint prepared according to Comparative Example 4 after oxidation experiments.

[0039] Figure 11 This is a 100x SEM image of the surface of the coating prepared according to Comparative Example 4 after drying and curing.

[0040] Figure 12 This is a 1500x SEM image of the surface of the coating prepared according to Comparative Example 4 after drying and curing. Detailed Implementation

[0041] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0042] The slurry method mentioned in this invention is a technique in which ceramic aggregates, binders and other materials are mixed in a certain slurry ratio to prepare a slurry, and the uniform slurry is applied evenly to the substrate surface by spraying or brushing, and the coating is obtained after drying and curing for a certain period of time.

[0043] Prebaked anodes for electrolytic aluminum, also known as carbon anodes for aluminum, are an indispensable and irreplaceable core raw material in the production of electrolytic aluminum. They possess excellent electrical conductivity and resistance to high-temperature corrosion, and are considered the heart of the electrolytic cell. Currently, conventional prebaked anodes for electrolytic aluminum can utilize the coating of this invention. This coating dries and cures at a relatively low temperature, forming a dense, high-strength coating with good adhesion. This coating effectively prevents contact between the oxidizing atmosphere and the prebaked anode during the electrolytic aluminum process, thereby reducing anode consumption.

[0044] This invention provides a prebaked anode anti-oxidation coating and ceramic coating for electrolytic aluminum based on a slurry method, and the preparation method thereof. The technical solution uses powders such as alumina and silicon carbide as ceramic aggregates, and prepares a prebaked anode anti-oxidation ceramic coating for electrolytic aluminum through a slurry process under the action of binders, suspending agents, functional additives, and water.

[0045] A prebaked anode anti-oxidation ceramic coating for electrolytic aluminum, wherein the components and their mass percentages are as follows: ceramic aggregate 45-55%, binder 40-50%, suspending agent 0.5-5%, functional additives 0.2-5%, and water 0.5-6%.

[0046] The ceramic aggregate is composed of at least two of alumina, silicon carbide, zirconium oxide, and silicon micro powder, wherein the ceramic aggregate contains at least alumina and silicon carbide.

[0047] That is, ceramic aggregates can be composed of alumina and silicon carbide, or ceramic aggregates can be composed of alumina, silicon carbide and zirconium oxide, or ceramic aggregates can be composed of alumina, silicon carbide and silicon micro powder, or ceramic aggregates can be composed of alumina, silicon carbide and zirconium oxide and silicon micro powder.

[0048] The binder is a mixture of sodium silicate and potassium silicate.

[0049] Water glass is a water-soluble silicate. It is composed of alkali metals and silicon dioxide in varying proportions. The most commonly used are sodium silicate and potassium silicate. Sodium silicate is an aqueous solution of sodium silicate, with the chemical formula Na₂O·nSiO₂. Potassium silicate is an aqueous solution of potassium silicate, with the molecular formula K₂O·nSiO₂.

[0050] In some embodiments, sodium silicate and potassium silicate can be prepared and used immediately, and the mass of the binder defined in the ceramic coating formulation of the present invention is the mass of the prepared sodium silicate and potassium silicate.

[0051] In the prebaked anode anti-oxidation coating for electrolytic aluminum of the present invention, silicate binders such as water glass can interact with the ceramic aggregate used in the present invention and undergo a chemical reaction at high temperature to generate substances that can improve the performance of the ceramic coating and further improve the coating strength. This overcomes the problem of contaminating the primary aluminum when using phosphate binders in the prior art, as well as the problem of high temperature resistance when using organic binders such as methylcellulose and resin.

[0052] Because the binder is water glass, whose main component is silicate, it has good stability at high temperatures, resulting in a short curing time, high strength, and the ability to dry and cure at lower temperatures without the need for high-temperature sintering, thus reducing the difficulty of coating preparation.

[0053] In some embodiments, the mass percentage of alumina in the ceramic aggregate is controlled between 50% and 80%.

[0054] Alumina and water glass in the aggregate can generate substances that improve the performance of ceramic coatings, further enhancing coating strength. Therefore, the proportion of alumina needs to be limited. If the proportion of alumina is below 50% or above 80%, the coating is prone to defects such as reduced mechanical properties and density. Furthermore, too low an alumina proportion will introduce excessive amounts of other elements into the electrolytic cell.

[0055] In some preferred embodiments, the alumina is α-alumina.

[0056] Alumina can be divided into two main types: α-alumina and γ-alumina. This invention preferably uses α-alumina. A coating prepared using α-alumina is applied to an anti-oxidation ceramic coating obtained from a prebaked anode of electrolytic aluminum, resulting in better overall performance.

[0057] In some preferred embodiments, the silicon carbide is green silicon carbide.

[0058] Silicon carbide is generally classified into black silicon carbide and green silicon carbide. This invention preferably utilizes green silicon carbide to prepare the coating, resulting in a ceramic coating with higher strength.

[0059] In some embodiments, the mass percentage of silicon carbide in the ceramic aggregate is controlled between 20% and 40%.

[0060] Silicon carbide can improve the hardness, toughness, and wear resistance of ceramic coatings.

[0061] In some embodiments, the ceramic aggregate has an average particle size of 1.3–18 μm.

[0062] In some embodiments, the mass ratio of sodium silicate to potassium silicate is 1:(0.2-1). This is significant because using composite silicate results in better anti-aging properties of the coating, making it easier to preserve, and also allows for faster curing during use.

[0063] In some embodiments, the modulus of the sodium silicate and potassium silicate in the binder is 2.3 to 3.4.

[0064] The modulus of sodium silicate refers to the molar ratio of SiO2 to Na2O in its composition, and this parameter has a significant impact on the performance and application of sodium silicate. The modulus of sodium silicate is typically between 1.5 and 3.5, reflecting the relative content of SiO2 and Na2O. This invention preferably uses sodium silicate and potassium silicate with a modulus of 2.3 to 3.4.

[0065] In some embodiments, the suspending agent is one or both of sodium bentonite and fumed silica.

[0066] The main function of the suspending agent is to uniformly disperse solid particles in the liquid, achieving liquid mixing and solid dispersion, and forming a stable suspension system. When coating the surface of prebaked anodes for electrolytic aluminum with the coating of this invention, ordinary brushing methods require 2-4 coats and generally take 2-5 hours, while the mixed coating can continuously maintain a stable suspension system.

[0067] In some embodiments, the functional additive is one, two, or three of yttrium oxide, sodium hydroxide, and potassium hydroxide.

[0068] The functional additives improve the stability and enhance the mechanical properties of the coating.

[0069] This invention also provides a method for preparing an anti-oxidation ceramic coating for prebaked anodes of electrolytic aluminum based on a slurry method, as described above. The coating preparation flow chart is shown below. Figure 1 .

[0070] The specific steps are as follows:

[0071] Weigh the raw materials as described in any of the above descriptions.

[0072] (1) Prepare the first mixed slurry by mixing the binder with half of the ceramic aggregate evenly to obtain the first mixed slurry.

[0073] (2) Prepare the second mixed slurry by mixing the first mixed slurry with the suspending agent and functional additives evenly to obtain the second mixed slurry.

[0074] (3) Add the remaining ceramic aggregate and water to the second mixed slurry, stir evenly, and obtain the electrolytic aluminum prebaked anode anti-oxidation ceramic coating;

[0075] (4) Apply coating to the surface of the prebaked anode;

[0076] (5) Wait for the coating to dry and cure to form a prebaked anode anti-oxidation ceramic coating for electrolytic aluminum.

[0077] In some embodiments, the adhesive is prepared fresh for immediate use, thus requiring on-the-spot preparation. Those skilled in the art can handle this based on common sense.

[0078] In some embodiments, the sodium silicate in the binder is prepared by dissolving readily soluble sodium silicate in deionized water, heating to 35-45°C, and stirring until the readily soluble sodium silicate is completely dissolved. The potassium silicate in the binder is prepared by dissolving readily soluble potassium silicate in deionized water, heating to 35-45°C, and stirring until the readily soluble potassium silicate is completely dissolved.

[0079] In some embodiments, the method of applying the coating to the surface of the test block includes spraying or brushing.

[0080] The specific operation of the brush coating method is as follows: brush the sides and top of the prebaked anode → dry at 45-55℃ for 25-35 minutes → cool to room temperature (approximately 12-18 minutes in this example) → brush the bottom surface → dry at 45-55℃ for 25-35 minutes → cool to room temperature. Repeat this process 2 to 4 times. Ensure the coating thickness is 0.2-0.5 mm.

[0081] Technical personnel in this industry can also use the spraying method as needed, and optimize and adjust the spraying parameters in the spraying method.

[0082] In step (5), the coating is dried and cured. Technicians in this industry can perform the drying and curing of the coating according to standard procedures. For example, drying and curing at room temperature for 24 hours.

[0083] In some preferred embodiments, the coating drying and curing is a two-step process. The first step involves heating the sample at 65°C-85°C for 1.5-2.5 hours, and the second step involves heating at 120°C-150°C for 6.5-9.5 hours. The first step ensures that the free water in the coating evaporates sufficiently without being too rapid, effectively preventing defects such as blistering, cracks, and pores. The second step ensures that the coating is fully dried and cured, guaranteeing that most of the -Si-OH groups are converted into high-bond-energy Si-O-Si structures.

[0084] The ceramic coating of this invention and the application scenario of the formed ceramic coating are prebaked anodes for electrolytic aluminum. In the anti-oxidation ceramic coating of the prebaked anode for electrolytic aluminum of this invention, the main component of the aggregate is alumina, which can minimize the increase of impurities in the aluminum electrolysis cell and has virtually no impact on the electrolysis process and the purity of the product.

[0085] Modern aluminum electrolysis employs the cryolite-alumina molten salt electrolysis method. Molten cryolite serves as the solvent, alumina as the solute, carbonaceous material as the anode, and molten aluminum as the cathode. A strong direct current is applied, and an electrochemical reaction (electrolysis) occurs at the electrodes within the electrolytic cell at 950℃–970℃. Therefore, the anti-oxidation ceramic coating applied to the prebaked anode used in aluminum electrolysis forms a ceramic coating that needs to withstand temperatures above 800℃ for extended periods. This invention utilizes a 900℃ holding period of 72 hours, with air as the oxidizing gas, to test and evaluate the protective and insulating effect of the ceramic coating on the prebaked anode.

[0086] The prebaked anode test block used in the examples was cut from an actual prebaked anode used in electrolytic aluminum production, and the experimental results are equivalent to those using an industrial prebaked anode used in electrolytic aluminum production.

[0087] The alumina used in the following examples is α-alumina, the silicon carbide is green silicon carbide, and the other raw materials are all commercially available products.

[0088] The following description is based on specific embodiments.

[0089] Example 1

[0090] 65 g of 3.3-mold instant-dissolving sodium silicate and 65 g of deionized water were heated to 40°C and stirred until a semi-transparent viscous liquid was formed, yielding 130 g of sodium silicate (Na₂O·nSiO₂). 40 g of 3.3-mold instant-dissolving potassium silicate and 60 g of deionized water were heated to 40°C and stirred until a semi-transparent viscous liquid was formed, yielding 100 g of potassium silicate (K₂O·nSiO₂). The prepared sodium silicate and potassium silicate were stirred for 10 minutes to obtain a binder. 70 g of alumina, 32 g of silicon carbide, 12 g of zirconium oxide, and 10 g of silica powder were added to 230 g of the prepared binder and stirred for 10 minutes to obtain the first slurry. Then, 6 g of sodium-based bentonite and 11 g of yttrium oxide were added and stirred for 10 minutes to obtain the second mixed slurry. Add 70g of alumina, 32g of silicon carbide, 12g of zirconium oxide, 10g of silicon micro powder, and 5g of deionized water, and stir for 10 minutes to obtain an electrolytic aluminum prebaked anode anti-oxidation ceramic coating.

[0091] Brush the coating onto the sides and top of the test block → dry at 50℃ for 30 minutes → cool to room temperature → coat the bottom side → dry at 50℃ for 30 minutes → cool to room temperature. Repeat this process three times to obtain a prebaked anode test block with the coating applied. The thickness of the coating is between 0.2 and 0.5 mm.

[0092] The coating is dried and cured using a two-step curing method, and the specific operation is as follows:

[0093] The first curing step involved heating the sample at 85°C for 2.5 hours, and the second curing step involved heating at 150°C for 7.5 hours. This process yielded a ceramic coating for the prebaked anode.

[0094] The first curing step ensures that the free water in the coating evaporates fully without evaporating too quickly, effectively preventing defects such as blistering, cracks, and pores. The second curing step ensures that the coating is fully dried and cured, guaranteeing that most of the -Si-OH groups are converted into high-bond-energy Si-O-Si structures.

[0095] In contrast, the prebaked anode specimens coated with paint were dried and cured at room temperature for 24 hours to obtain the ceramic coating of the prebaked anode.

[0096] Infrared spectroscopy analysis was performed on the coating obtained by drying and curing according to Example 1 and the coating obtained by drying and curing at room temperature for 24 hours. The Fourier transform infrared spectra after drying and curing under different conditions are shown below. Figure 2 As shown.

[0097] Depend on Figure 2 It can be seen that the coating cures at room temperature at 1644 cm⁻¹ -1 and 990cm -1 There are obvious sharp peaks at all locations, at 3200cm. -1 It has a broad peak. 1644cm -1 The peak at 990 cm⁻¹ is related to the H-OH bonds in free water. -1 There is a distinct peak and 3200cm -1 The broad peaks are related to the -Si-OH groups in the binder. Even after 24 hours of drying and curing at room temperature, the coating still contains a significant amount of free water and -Si-OH groups, indicating that it was not completely dried and cured at room temperature. The coating reached 1644 cm⁻¹ after the first curing step. -1 The peaks at the point of curing have basically disappeared, proving that the free water in the coating has been completely evaporated after the first curing step. The absence of obvious peaks after the second curing step proves that the -Si-OH groups in the coating have been transformed into high-bond-energy Si-O-Si structures after the second curing step, and the coating has been fully cured.

[0098] Electron microscopy analysis was performed on the ceramic coating obtained by the two-step curing method in Example 1. The results are shown in [Figure 1]. Figure 3 and Figure 4 . Figure 3 This is a 100x SEM image of the ceramic coating surface obtained by a two-step curing method using the coating prepared in Example 1. Figure 3 The ceramic coating surface is smooth and free of obvious defects. Furthermore, Figure 4 This is a 1500x SEM image of the ceramic coating surface obtained by a two-step curing method using the coating prepared in Example 1. Figure 4 This shows that the aggregate and binder are fully bonded together in the ceramic coating.

[0099] The prebaked anode specimen with an anti-oxidation ceramic coating prepared in Example 1 was weighed (M1) after drying and curing. The specimen was placed in a tube furnace and held at 900℃ for 72 hours. Heating was stopped, and the specimen was allowed to cool to room temperature before being weighed (M2). The weight loss rate was calculated as (M1-M2) / M1×100%. The weight loss rate of the specimen was 0.54%.

[0100] Weight loss rate reflects the antioxidant properties of the coating. The specimen with coating protection showed a weight loss rate of only 0.54% after being kept at 900℃ for 72 hours, demonstrating excellent antioxidant properties.

[0101] The test block (Example 1), with the left side untreated and the right side coated, was placed in a tube furnace and held at 900°C for 20 hours. Heating was then stopped, and the block was removed after cooling to room temperature. Photos of the test block before and after the oxidation experiment are shown below. Figure 5 As shown.

[0102] Figure 5 In the middle, the untreated part on the left is severely oxidized, and the height of the test block decreases by about 40%. The part on the right with the coating protection shows no obvious oxidation, indicating that the ceramic coating of the present invention has good anti-oxidation performance at high temperature.

[0103] Example 2

[0104] Sodium silicate (2.7 mold) and 80g of deionized water were heated to 40°C and stirred until a semi-transparent viscous liquid was formed, thus obtaining sodium silicate. Potassium silicate (3.3 mold) and 24g of potassium silicate (3.3 mold) were heated to 40°C and stirred until a semi-transparent viscous liquid was formed, thus obtaining potassium silicate. The sodium silicate and potassium silicate were stirred for 10 minutes to obtain a binder. 72g of alumina, 40g of silicon carbide, and 14g of zirconium oxide were added to the binder and stirred for 10 minutes to obtain the first slurry. 6g of fumed silica, 5g of sodium bentonite, 3g of sodium hydroxide, and 4g of yttrium oxide were then added and stirred for 10 minutes to obtain the second mixed slurry. 72g of alumina, 40g of silicon carbide, 14g of zirconium oxide, and 10g of deionized water were then added and stirred for 10 minutes to obtain the electrolytic aluminum prebaked anode anti-oxidation ceramic coating.

[0105] Apply coating to the sides and top of the prebaked anode test block → dry at 55℃ for 25 minutes → cool to room temperature → apply coating to the bottom surface → dry at 55℃ for 25 minutes → cool to room temperature. Repeat this process 4 times to obtain a prebaked anode test block with the coating applied. The thickness of the coating is between 0.2 and 0.5 mm.

[0106] The coating is dried and cured using a two-step curing method, and the specific operation is as follows:

[0107] The first curing step involves heating the test block at 85°C for 2 hours, and the second curing step involves heating at 150°C for 8 hours.

[0108] A ceramic coating for a prebaked anode was prepared.

[0109] The untreated test block and the coated test block (Example 2) were placed together in a tube furnace and held at 900°C for 72 hours. Heating was then stopped, and the test blocks were removed after cooling to room temperature. The weight loss of the two test blocks was compared under the same conditions. Figure 6 The untreated sample was completely oxidized, with a weight loss of 100%. Figure 7 The results showed that the test block coated with the protective coating did not exhibit obvious oxidation, with a weight loss rate of 0.64%, and the coating had no obvious defects, indicating that the coating of the present invention has good anti-oxidation properties at high temperatures.

[0110] Example 3

[0111] Sodium silicate (sodium silicate) of type 3 and 80g of deionized water were heated to 40°C and stirred until a semi-transparent viscous liquid was formed, thus obtaining sodium silicate. Potassium silicate (potassium silicate) of type 3 and 3 was heated to 40°C and stirred until a semi-transparent viscous liquid was formed, thus obtaining potassium silicate. The sodium silicate and potassium silicate were stirred for 10 minutes to obtain a binder. 110g of alumina and 27.5g of silicon carbide were added to the binder and stirred for 10 minutes to obtain the first slurry. 6g of fumed silica, 4g of sodium bentonite, and 3g of potassium hydroxide were then added and stirred for 10 minutes to obtain the second mixed slurry. 110g of alumina, 27.5g of silicon carbide, and 12g of deionized water were then added and stirred for 10 minutes to obtain the electrolytic aluminum prebaked anode anti-oxidation ceramic coating.

[0112] Apply coating to the sides and top of the prebaked anode test block → dry at 50℃ for 25 minutes → cool to room temperature → apply coating to the bottom surface → dry at 50℃ for 25 minutes → cool to room temperature. Repeat this process twice to obtain a prebaked anode test block with the coating applied. The thickness of the coating is between 0.2 and 0.5 mm.

[0113] The coating is dried and cured using a two-step curing method, and the specific operation is as follows:

[0114] The first curing step involves heating the test block at 85°C for 2 hours, and the second curing step involves heating at 150°C for 8 hours.

[0115] A ceramic coating for a prebaked anode was prepared.

[0116] The coated specimen (Example 3) was placed in a tube furnace and held at 900°C for 72 hours. Heating was then stopped, and the specimen was allowed to cool to room temperature before being removed. The weight loss was measured to be 0.88%.

[0117] Example 4

[0118] Sodium silicate (sodium silicate) was prepared by heating 62.5 g of 3.3-mold instant-dissolving sodium silicate and 62.5 g of deionized water to 40°C and stirring until a semi-transparent viscous liquid was formed. Potassium silicate (potassium silicate) was prepared by heating 50 g of 3.3-mold instant-dissolving potassium silicate and 75 g of deionized water to 40°C and stirring until a semi-transparent viscous liquid was formed. The sodium silicate and potassium silicate were stirred for 10 minutes to obtain a binder. 56.25 g of alumina, 45 g of silicon carbide, and 11.25 g of silica powder were added to the binder and stirred for 10 minutes to obtain the first slurry. 12.5 g of yttrium oxide and 10 g of sodium bentonite were then added and stirred for 10 minutes to obtain the second mixed slurry. Finally, 56.25 g of alumina, 45 g of silicon carbide, 11.25 g of silica powder, and 2.5 g of deionized water were added and stirred for 10 minutes to obtain the electrolytic aluminum prebaked anode anti-oxidation ceramic coating.

[0119] Apply coating to the sides and top of the prebaked anode sample block → dry at 55℃ for 30 minutes → cool to room temperature → apply coating to the bottom surface → dry at 55℃ for 30 minutes → cool to room temperature. Repeat this process 4 times to obtain the prebaked anode sample block with coating.

[0120] The coating is dried and cured using a two-step curing method, and the specific operation is as follows:

[0121] The first curing step involves heating the sample at 85°C for 2.5 hours, and the second curing step involves heating at 140°C for 7.5 hours.

[0122] A ceramic coating for a prebaked anode was prepared.

[0123] The coated specimen (Example 4) was placed in a tube furnace and held at 900°C for 72 hours. Heating was then stopped, and the specimen was allowed to cool to room temperature before being removed. The weight loss was measured to be 0.92%.

[0124] Comparative Example 1

[0125] Chinese patent application number 201911337979.0, entitled "A High-Temperature Antioxidant Coating for Prebaked Carbon Anode Ceramic Matrix of Electrolytic Aluminum and Its Preparation Method" (publication number CN 111039662A), describes a process where "an antioxidant coating is brushed onto a graphite rod, dried at room temperature for one day, and then placed in a muffle furnace along with graphite rods without the antioxidant coating. The furnace is first heated to 500°C and held for 1 hour, then further heated to 970°C and held for 8 hours. Heating is then stopped, the furnace is cooled to room temperature, and the graphite rods are removed. Under the same conditions, the weight loss of the graphite rods coated with the antioxidant coating and those without the antioxidant coating is compared."

[0126] The results showed that the weight loss rate of Example 1 was 2.76%, and the weight loss rate of Example 2 was 3.14%.

[0127] The prebaked anodic anti-oxidation ceramic coating and its coating method of the present invention form a ceramic coating with a weight loss rate of less than 1% in an oxidation experiment after being kept at 900°C for 72 hours, which shows that the ceramic coating of the present invention has good anti-oxidation performance at high temperatures.

[0128] Comparative Example 2

[0129] The 40% binder in the original Example 1 was replaced with water. Specifically, the binder was 78g of sodium silicate + 60g of potassium silicate (130g of sodium silicate + 100g of potassium silicate in Example 1), and the water was 97g. Other raw materials and preparation methods were the same as in Example 1.

[0130] After the obtained test blocks dried and cured, it was found that the coating had cracked. Figure 8 .

[0131] Comparative Example 3

[0132] The binder is increased by half, specifically 195g of sodium silicate + 150g of potassium silicate (in Example 1, it was 130g of sodium silicate + 100g of potassium silicate). Other raw materials and preparation methods are the same as in Example 1.

[0133] After the obtained test block was kept at 900℃ for 72 hours, it was removed, and obvious blistering was found in the coating. (See details...) Figure 9 .

[0134] This indicates that the amount of binder added should not be too low or too high. Strict control of the binder addition is necessary to prepare a defect-free, dense, antioxidant coating.

[0135] Comparative Example 4

[0136] The ceramic aggregate used was only 275g of alumina (220g of alumina + 55g of silicon carbide in Example 3), and the other raw materials and preparation methods were the same as in Example 3.

[0137] After the prebaked anode sample was kept at 900℃ for 72 hours, obvious cracks were found on the coating surface. (See details...) Figure 10 . Figure 11 In the study, a 100x SEM image of the coating surface after drying and curing showed that the coating prepared according to Comparative Example 4 had an uneven surface with obvious defects such as pores and cracks after drying and curing. Figure 12 In the SEM image of the coating surface after drying and curing, it is shown that after drying and curing, the aggregate and binder of the coating prepared according to Comparative Example 4 were not fully bonded together, and defects such as pores and cracks were more obvious.

[0138] The comparison shows that ceramic aggregates cannot be made of alumina alone. To prepare a dense, defect-free, and antioxidant coating, it is necessary to use ceramic aggregates with appropriate proportions.

[0139] The parameters of the above embodiments and comparative examples were compared, and the results are shown in Table 1.

[0140] Table 1 Weight loss rate of samples in antioxidant experiments

[0141] Mass before oxidation / g Mass after oxidation / g Weight loss rate / % Untreated test blocks 109.26 0 100％ Example 1 117.57 116.93 0.54％ Example 2 116.82 116.07 0.64％ Example 3 116.70 115.67 0.88％ Example 4 117.31 116.23 0.92％ Comparative Example 1 2.76％ Comparative Example 2 110.41 101.55 8.02％ Comparative Example 3 115.13 111.94 2.77％ Comparative Example 4 113.17 106.38 6.00％

[0142] The comparison shows that the ceramic coating prepared by the coating formula according to the present invention has a lower weight loss rate and no obvious defects after oxidation experiments. This indicates that the ceramic coating of the present invention has good high-temperature oxidation resistance.

[0143] The above is a further detailed description of the present invention and should not be considered as a limitation on the specific implementation of the present invention. For those skilled in the art, simple deductions or substitutions without departing from the concept of the present invention are all within the protection scope of the present invention.

Claims

1. A method for the production of an oxidation-resistant ceramic coating for prebaked anodes for the electrolysis of aluminium, characterised in that It comprises the following steps: (1) The raw materials are weighed according to the following mass percentage: ceramic aggregate 45-55%, binder 40-50%, suspending agent 0.5-5%, functional additive 0.2-5%, and water 0.5-6%; The ceramic aggregate is composed of at least two of alumina, silicon carbide, zirconia, and silicon powder, wherein the ceramic aggregate contains at least alumina and silicon carbide, the mass percentage of alumina in the ceramic aggregate is 50-80%, and the mass percentage of silicon carbide in the ceramic aggregate is 20-40%; the binder is a mixture of sodium water glass Na2O·nSiO2 and potassium water glass K2O·nSiO2; the modulus of sodium water glass and potassium water glass in the binder is 2.3-3.4, and the mass ratio of sodium water glass to potassium water glass in the binder is 1:(0.2-1); the functional additive is at least one of yttrium oxide, sodium hydroxide, and potassium hydroxide; (2) The binder is mixed with half of the ceramic aggregate to obtain a first mixed slurry; (3) The first mixed slurry is mixed with the suspending agent and the functional additive to obtain a second mixed slurry; (4) The remaining ceramic aggregate and water are added to the second mixed slurry, and stirred uniformly to obtain a prebaked anode anti-oxidation ceramic coating for electrolytic aluminum; (5) The coating is applied to the surface of the prebaked anode; (6) The coating is dried and solidified to form a prebaked anode anti-oxidation ceramic coating for electrolytic aluminum; The drying and solidification in step (6) comprises the following steps: the prebaked anode coated with the coating is heated at 65-85℃ for 1.5-2.5 hours, and then heated at 120-150℃ for 6.5-9.5 hours.

2. The production method according to claim 1, characterized by, The alumina is α-alumina.

3. The method of claim 1, wherein, The silicon carbide is green silicon carbide.

4. The method of claim 1, wherein, The suspending agent is one or both of sodium bentonite and fumed silica.

5. The preparation method according to claim 1, characterized in that, The method for applying the coating comprises spraying or brushing.

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