Carbon anode high temperature oxidation resistant coating and its preparation method and use method

Abstract

This invention relates to the field of carbon anode anti-oxidation technology, and discloses a high-temperature anti-oxidation coating for carbon anodes, its preparation method, and its application method. The high-temperature anti-oxidation coating for carbon anodes comprises the following components in the indicated weight ratios: 10-70 parts borax; 5-60 parts sodium hydroxide; 5-50 parts light magnesium oxide; and 10-50 parts hot water. Under the high temperature of the carbon anode, the boric acid generated in the coating on the carbon anode surface reacts with the light magnesium oxide to form a glossy glassy magnesium borate protective layer. This protective layer can withstand long-term exposure to temperatures up to 1000 degrees Celsius, demonstrating a significant anti-oxidation effect on electrolytic aluminum carbon anodes. This invention can withstand the corrosion of hydrogen fluoride and high-concentration carbon dioxide gas for a long time at temperatures of 1000-1200 degrees Celsius. This invention has good wettability with the anode surface at high temperatures. Within the effective temperature range, the coating is in a viscous liquid phase, exhibiting strong self-healing properties against cracks, blistering, peeling, and other phenomena that occur in the coating.

Description

Technical Field

[0001] This invention relates to the field of carbon anode anti-oxidation technology, specifically to a high-temperature anti-oxidation coating for carbon anodes, its preparation method, and its application method. Background Technology

[0002] Carbon anodes are one of the main raw materials in the electrolytic aluminum production process, playing a crucial role and often referred to as the heart of the electrolytic cell. They are also a significant component of the production cost, accounting for approximately 15% of the total aluminum production cost. Carbon anode consumption in electrolytic aluminum production consists of two main parts: first, the reasonable consumption involved in the chemical reaction. This consumption is determined by the working principle, with a theoretical consumption value of 334 kg / ton of aluminum. However, due to the influence of current efficiency and carbon purity, the actual consumption value is approximately 365 kg / ton. Second, excessive consumption. Excessive consumption refers to the total loss due to oxidation reactions between the anode surface and oxygen in the air and carbon dioxide in the cell at high temperatures, as well as selective oxidation losses. This manifests as flaking, slagging, burning, and pulverization of the anode surface. This type of consumption is considered unreasonable and excessive. Currently, the net carbon consumption in the electrolytic aluminum market is generally between 430 kg / ton and 450 kg / ton of aluminum. Excessive consumption accounts for approximately 16% to 20% of this.

[0003] Adding an anti-oxidation layer to the carbon anode can reduce excessive consumption. Currently, there are two main types of such products on the market: one is the immersion type; the other is the coating type.

[0004] The impregnation method involves first placing the carbon anode in a container, then evacuating it to remove air from the capillaries within the anode. After evacuation, an impregnation solution is injected under pressure, forcing the liquid into the capillaries on the anode surface. This process is paused for a few minutes, then the pressure is released and the impregnation solution is removed from the container, completing one impregnation cycle. This method essentially seals the capillaries on the carbon anode surface, preventing oxygen from diffusing into the carbon block. The outer film also possesses resistance to high-temperature oxidation, making this method highly effective. Currently, this method is widely used for high-temperature oxidation protection of graphite electrodes and carbon materials. Its biggest drawbacks are high equipment investment, cumbersome procedures, and low efficiency.

[0005] The coating method involves applying a prepared coating to the surface of the carbon anode using methods such as spraying or brushing, followed by drying or natural drying. This type of coating is primarily thermosetting. When the carbon anode is placed in an electrolytic cell, the ambient temperature allows it to solidify. Under certain high temperatures, the coating components sinter to form a hard outer shell, thus isolating the carbon anode surface from oxygen. The biggest advantage of this method is its simplicity and speed of application. However, its biggest drawback is poor self-healing; blistering or cracking of the coating during use is almost impossible to heal on its own. Furthermore, this method is unsuitable for porous materials like carbon. Data shows that the voids in carbon materials account for 25-30% of the total volume of the anode carbon block. Therefore, when the anode carbon block is heated, the gas in its internal capillaries expands rapidly and protrudes to the surface, causing the coating to crack and essentially losing its anti-oxidation effect. Summary of the Invention

[0006] The purpose of this invention is to solve the problems in the prior art mentioned above, and to provide a carbon anode high-temperature anti-oxidation coating and its preparation and application methods.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A carbon anode high-temperature anti-oxidation coating comprises the following components in parts by weight: 10-70 parts borax; 5-60 parts sodium hydroxide; 5-50 parts light magnesium oxide; and 10-50 parts hot water.

[0008] Further, it includes the following components in parts by weight: 35-45 parts borax; 6-30 parts sodium hydroxide; 10-25 parts light magnesium oxide; and 35-45 parts hot water.

[0009] Furthermore, the temperature of the hot water is 80-95℃.

[0010] This invention also provides the following technical solutions: A method for preparing a high-temperature anti-oxidation coating for carbon anodes, the method comprising the following steps: a. First, pour hot water into the container; b. Then slowly add light magnesium oxide and sodium hydroxide, and dissolve them completely with the help of a stirrer; c. Finally, slowly add borax until it is completely dissolved to obtain the carbon anode high-temperature anti-oxidation coating.

[0011] Furthermore, the sodium hydroxide is a solid.

[0012] Furthermore, the operating speed of the mixer is 50-300 revolutions per minute.

[0013] This invention also provides the following technical solutions: A method for using a high-temperature anti-oxidation coating for carbon anodes, the method comprising: spraying or brushing the high-temperature anti-oxidation coating onto the surface of an electrolytic aluminum carbon anode; energizing the coated carbon anode in an electrolytic cell, causing it to heat up and generate high temperature; the sodium metaborate in the coating generates boric acid under high temperature; and the boric acid reacts with light magnesium oxide to generate liquid magnesium borate.

[0014] Furthermore, the high temperature generated by the self-heating of the carbon anode is above 400°C.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention, under the high temperature of a carbon anode, generates boric acid within the coating on the carbon anode surface, which reacts with light magnesium oxide to form a glossy, glassy magnesium borate protective layer. This layer can withstand long-term exposure to temperatures up to 1000 degrees Celsius, demonstrating a significant anti-oxidation effect on electrolytic aluminum carbon anodes. This invention can also withstand long-term corrosion from hydrogen fluoride and high-concentration carbon dioxide gas at 1000-1200 degrees Celsius. Furthermore, this invention exhibits good wettability with the anode surface at high temperatures. Within the effective temperature range, the coating remains in a viscous liquid phase, exhibiting strong self-healing properties against cracks, blistering, and peeling. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0017] Figure 1 This is a schematic diagram of the anode side oxidation process after 6 days in the tank according to the present invention.

[0018] Figure 2 This is a schematic diagram showing the oxidation of the exposed portion of the product after 14 days in the tank, according to the present invention.

[0019] Figure 3 This is a schematic diagram showing the appearance of the residual electrode after 33 days in the test cell of the present invention.

[0020] Figure 4 This is a schematic diagram showing the appearance of the residual electrode after the test cell of the present invention has been extended to 35 days. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] It should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0023] Specific embodiments of the carbon anode high-temperature anti-oxidation coating of the present invention, its preparation method and application method: The carbon anode high-temperature anti-oxidation coating comprises the following components in parts by weight: 10-70 parts borax; 5-60 parts sodium hydroxide; 5-50 parts light magnesium oxide; and 10-50 parts hot water.

[0024] In some other embodiments, the carbon anode high-temperature anti-oxidation coating comprises the following components in parts by weight: 35-45 parts borax; 6-30 parts sodium hydroxide; 10-25 parts light magnesium oxide; and 35-45 parts hot water.

[0025] The selection of raw material components in this embodiment: Borax: Wengquan brand; Sodium hydroxide: Junzheng brand; Light magnesium oxide: preferably produced in Shandong region; Hot water: 80-95℃.

[0026] The preparation method of high-temperature anti-oxidation coating for carbon anodes includes the following steps: a. First, pour hot water at 80-95℃ into the container; b. Then slowly add light magnesium oxide and solid sodium hydroxide, and dissolve them completely in a stirrer at 50-300 revolutions per minute; c. Finally, slowly add borax until it is completely dissolved to obtain the carbon anode high-temperature anti-oxidation coating.

[0027] Example 1 of preparation of high-temperature anti-oxidation coating for carbon anode First, 300 kg of hot water at 90°C is added to the container; then 70 kg of light magnesium oxide and 60 kg of solid sodium hydroxide are slowly added and stirred at 200 revolutions per minute until they are completely dissolved; finally, 290 kg of borax is slowly added and the carbon anode high-temperature anti-oxidation coating is obtained after the borax is completely dissolved.

[0028] Example 2 of preparation of high-temperature anti-oxidation coating for carbon anode First, 500 kg of hot water at 90°C is added to the container; then 260 kg of light magnesium oxide and 150 kg of solid sodium hydroxide are slowly added and stirred at 200 rpm until they are completely dissolved; finally, 500 kg of borax is slowly added and stirred until the borax is completely dissolved to obtain the carbon anode high-temperature anti-oxidation coating.

[0029] Example 3 of preparation of high-temperature anti-oxidation coating for carbon anode First, 420 kg of hot water at 90°C is added to the container; then 120 kg of light magnesium oxide and 80 kg of solid sodium hydroxide are slowly added and stirred at 200 revolutions per minute until they are completely dissolved; finally, 400 kg of borax is slowly added and the carbon anode high-temperature anti-oxidation coating is obtained after the borax is completely dissolved.

[0030] Example 4 of preparation of high-temperature anti-oxidation coating for carbon anode First, 400 kg of hot water at 90°C is added to the container; then 150 kg of light magnesium oxide and 83 kg of solid sodium hydroxide are slowly added and stirred at 200 rpm until they are completely dissolved; finally, 410 kg of borax is slowly added and the carbon anode high-temperature anti-oxidation coating is obtained after the borax is completely dissolved.

[0031] Example 5 of preparation of high-temperature anti-oxidation coating for carbon anode First, 390 kg of hot water at 90°C is added to the container; then 130 kg of light magnesium oxide and 70 kg of solid sodium hydroxide are slowly added and stirred at 200 rpm until they are completely dissolved; finally, 400 kg of borax is slowly added and stirred until the borax is completely dissolved to obtain the carbon anode high-temperature anti-oxidation coating.

[0032] Example 6 of preparation of high-temperature anti-oxidation coating for carbon anode First, a certain amount of hot water at 90°C is added to the container; then, a certain amount of light magnesium oxide and a certain amount of solid sodium hydroxide are slowly added and stirred at 200 revolutions per minute until they are completely dissolved; finally, a certain amount of borax is slowly added and stirred until the borax is completely dissolved to obtain the carbon anode high-temperature anti-oxidation coating; the carbon anode high-temperature anti-oxidation coating of this embodiment is a water-soluble product, milky white, with a pH value of 11, a density of 1.34, and a stability period of 4 months (within the range of -5 to 40 degrees Celsius).

[0033] The application method of high-temperature anti-oxidation coating for carbon anodes includes: spraying or brushing the high-temperature anti-oxidation coating onto the surface of the electrolytic aluminum carbon anode; energizing the coated carbon anode in the electrolytic cell, where it generates heat and high temperature; the sodium metaborate in the coating generates boric acid under high temperature, and the boric acid reacts with light magnesium oxide to form liquid magnesium borate.

[0034] Specifically, when the carbon anode enters the electrolytic cell and is energized, it generates a high temperature of approximately 700 degrees Celsius. At this point, the boric acid generated within the coating on the carbon anode surface reacts with light magnesium oxide to form a glossy, glassy magnesium borate protective layer. This protective layer can withstand long-term exposure to temperatures up to 1000 degrees Celsius, demonstrating a significant high-temperature anti-oxidation effect on the carbon anode of electrolytic aluminum. The basic principle is as follows: Borax reacts with sodium hydroxide to produce sodium metaborate. When sodium metaborate is further heated above 400 degrees Celsius, boric acid is generated. This boric acid reacts with the light magnesium oxide in the coating layer to form liquid-phase magnesium borate. The coating can withstand the corrosion of hydrogen fluoride and high-concentration carbon dioxide gas for extended periods at temperatures of 1000-1200 degrees Celsius. The coating's effective temperature is 350-1200 degrees Celsius. It exhibits good wettability with the carbon anode surface at high temperatures. Within the effective temperature range, the coating is in a viscous liquid phase, exhibiting strong self-healing properties against cracks, blistering, and peeling.

[0035] Economic benefit analysis, taking experimental data from an aluminum plant in Sichuan as an example: 1. New electrode's external geometric dimensions: Length: 1570 x Width: 660 x Height: 640; Steel bowl depth: 115. 2. Dimensions of the residual electrode after 33 days in the comparison tank: Length 1400 x Width 500 x Height 135; 3. Dimensions of the residual electrode in the test cell after 35 days: Length 1500 x Width 645 x Height 140; 4. The temperature of the test tank is 960-970 degrees Celsius, and the electrolyte molecular ratio is 2.2-2.3. 5. Number of tanks involved in the experiment: 6; of which: 3 are test tanks and 3 are control tanks.

[0036] Economic benefit calculation: Taking a 400KVA electrolytic cell as an example: Service life of uncoated anodes: 33 days; Service life of coated anodes: 35 days; extending the service life by 2 days. Currently, the net carbon consumption per ton of aluminum in the electrolytic aluminum industry is approximately 430 kg; the average daily aluminum production of a 400KAV electrolytic cell is 2.98 tons; based on the above data, the carbon saved per electrolytic cell over two days is calculated as: daily aluminum production × extended days × net carbon consumption per ton of aluminum, i.e., 2980 kg / day × 2 days × 430 kg / ton of aluminum = 2562.8 kg, carbon saved per ton of aluminum: 2562.8 / 95.36 = 26.875 kg; carbon unit price: 7000 yuan / ton; amount saved per ton of aluminum: 26.875 kg × 7 yuan / kg = 188.125 yuan (95.36 is the monthly electrolytic aluminum production per cell); for an electrolytic aluminum enterprise with an annual production of 500,000 tons, adopting this technology could increase the enterprise's efficiency by nearly 100 million yuan annually, thus demonstrating its considerable economic benefits.

[0037] While directly improving economic efficiency, it also has the following effects: It extends the electrode switching cycle, reduces the number of electrode switching operations, and improves the stability of the electrolytic cell; The significant reduction in carbon slag content in the tank not only reduced the labor intensity of workers and improved the working environment, but also optimized the tank condition. Because there is less oxidation at the anode edge, the anode bottom area is relatively large, which increases the conductive area, reduces resistance, and helps improve electrical efficiency. It is beneficial for energy conservation and carbon reduction, reducing carbon dioxide emissions and is of great significance for improving the human ecological environment.

[0038] Workshop test results: Please see Figure 1 Oxidation of the anode side after 6 days in the tank: the edges and corners are clear, the surface is flat and hard, and no signs of oxidation are observed; Please see Figure 2 Oxidation status of exposed parts after 14 days in the tank: sharp edges and corners, hard surface, no signs of oxidation observed; Please see Figure 3 The appearance of the residual electrode after 33 days in the test cell: the edges and corners are clear, the length and width dimensions are basically intact, and it has a relatively high thickness; Please see Figure 4 The test cell cycle was extended to 35 days. The appearance of the residual electrode: the edges and contours are still clearly visible. Although the thickness has decreased, the appearance shape is still relatively clear.

[0039] The experiment was conducted in four cycles. The first two cycles were conducted in the original 33-day cycle for the residual electrode. The third cycle was extended to 35 days based on the remaining thickness of the residual electrode after the first two cycles.

[0040] This product has been tested and proven safe by users, bringing them substantial economic benefits and receiving high praise.

[0041] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0042] In this specification, the illustrative expressions of the terms used do not necessarily refer to the same embodiments or examples. Furthermore, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples, without contradiction.

[0043] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still make modifications to the technical solutions described in the foregoing embodiments without creative effort, or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-temperature anti-oxidation coating for carbon anodes, characterized in that, It is prepared from the following components in the indicated weight ratios: 10-70 parts borax; 5-60 parts sodium hydroxide; 5-50 parts light magnesium oxide; 10-50 parts hot water; wherein the hot water temperature is 80-95℃.

2. The high-temperature anti-oxidation coating for carbon anodes according to claim 1, characterized in that, It is prepared from the following components in the indicated weight ratios: 35-45 parts borax; 6-30 parts sodium hydroxide; 10-25 parts light magnesium oxide; and 35-45 parts hot water.

3. The method for preparing the high-temperature anti-oxidation coating for carbon anodes according to claim 1 or 2, characterized in that, The preparation method includes the following steps: a. First, pour hot water into the container; b. Then slowly add light magnesium oxide and sodium hydroxide, and dissolve them completely with the help of a stirrer; c. Finally, slowly add borax until it is completely dissolved to obtain the carbon anode high-temperature anti-oxidation coating.

4. The method for preparing the high-temperature anti-oxidation coating for carbon anodes according to claim 3, characterized in that, The sodium hydroxide is a solid.

5. The method for preparing the high-temperature anti-oxidation coating for carbon anodes according to claim 3, characterized in that, The mixer rotates at a speed of 50-300 revolutions per minute.

6. The method of using the carbon anode high-temperature anti-oxidation coating according to claim 1 or 2, characterized in that, The method of use includes: spraying or brushing a high-temperature anti-oxidation coating onto the surface of an electrolytic aluminum carbon anode; then energizing the coated carbon anode in an electrolytic cell, where it generates heat and produces a high temperature, thus obtaining a glassy magnesium borate protective layer.

7. The method of using the carbon anode high-temperature anti-oxidation coating according to claim 6, characterized in that, The high temperature generated by the self-heating of the carbon anode is above 400°C.

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