Antioxidant coating for anodes of aluminum electrolytic cells and method for preparing same

Abstract

The present application relates to the technical field of electrolytic aluminum, in particular to an oxidation-resistant coating for anode of aluminum electrolysis cell and a preparation method thereof. The oxidation-resistant coating for anode of aluminum electrolysis cell comprises 30-55 parts of inorganic filler, 1-15 parts of sintering aid, 5-10 parts of binder and 1-25 parts of solvent; the inorganic filler contains fly ash; the weight ratio of Al2O3 and SiO2 in the inorganic filler is 1.0-2.0. After activation, a high-viscosity alkali metal silicate solution is generated in the inorganic filler, the melting point of the silicate is relatively low, and the ion state alkali metal silicate can fill the pores between the powders to prevent the coating from cracking. At the same time, the air is not reserved with a penetration channel to block the air invasion. The shortcomings of high sintering temperature of the previous ceramic coating, insufficiently dense coating surface, pores and easy falling are overcome, and the amount of binder is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytic aluminum, and in particular to an anti-oxidation coating for an anode of an aluminum electrolytic cell and a preparation method thereof. Background Art

[0002] The carbon anode, the "heart" of the aluminum electrolytic cell, is primarily composed of pitch, petroleum coke, coke, and residual anode. Its function is to input direct current into the cell during the electrolysis process, participating in the electrochemical reaction in the high-temperature molten salt. During the aluminum electrolysis process, the carbon anode is exposed to a high-temperature oxidizing atmosphere of 450°C to 950°C and a corrosive fluorine-containing atmosphere. Its quality affects the normal operation of the electrolytic cell and various production technical indicators, and is closely related to the production cost of primary aluminum.

[0003] During the aluminum electrolysis process, anode gas penetrates the anode's internal pores, causing a Boudall reaction and secondary consumption. The difference in oxidizability between the binder pitch and the aggregate petroleum coke causes some aggregate to fall off, forming carbon slag. The immense pressure and velocity impact generated by the anode bubbles migrating toward the edges causes anode slag to fall off. This carbon slag not only shortens the anode's service life but also increases voltage drop, creates heat sinks, and increases electricity consumption during aluminum electrolysis. Removing the carbon slag also increases worker labor. Therefore, improving the quality of anode carbon blocks is crucial, both for economic reasons and to reduce worker labor.

[0004] There are two main ways to improve the quality of anode carbon blocks in industry: one is to improve the quality of carbon anodes by using high-quality low-sulfur petroleum coke as raw material. Low-sulfur petroleum coke can not only reduce the slagging of anode carbon blocks, but also improve anode efficiency. However, with the development of the aluminum electrolysis industry, the demand for high-quality petroleum coke continues to grow, resulting in a reduction in high-quality petroleum coke reserves worldwide. Therefore, this method greatly increases the cost of carbon anodes. Another method is to spray high-temperature anti-oxidation coatings on carbon anodes. Carbon materials begin to oxidize above 500°C. Nanopowder materials are sprayed onto the anode surface to form a dense glass phase or ceramic phase below 500°C, isolating the carbon anode from high-temperature gases and reducing excessive consumption of carbon anodes.

[0005] Prior art CN102424730A discloses an anti-oxidation coating for electrolytic aluminum anode carbon blocks and a preparation method thereof. The coating comprises the following components: borax or boric acid, kaolin, industrial phosphoric acid, industrial aluminum sulfate, and water. However, the industrial phosphoric acid in the coating will dehydrate upon heating, causing the coating to crack. Aluminum sulfate will decompose to release sulfur-containing gas at approximately 770°C, causing harm to the environment.

[0006] The prior art CN104005056A discloses a method for preparing an electrolytic aluminum carbon anode protective coating, which uses calcium aluminate cement as a binder, waste electrolyte from aluminum electrolysis production as aggregate, and sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, sodium lignin sulfonate, calcium lignin sulfonate, etc. as admixtures. However, the coating has a complex composition, and the admixtures used contain carbon-containing organic matter, which is easily volatilized at high temperatures and causes the coating to crack.

[0007] Prior art CN 113563056B proposes a coating material for high-temperature oxidation protection of carbon anodes, comprising the following components: 35-55wt% inorganic binder, 30-60wt% composite ceramic filler, 1-10wt% catalyst, 0-1wt% sintering agent, and 1-10wt% toughening agent. This coating material exhibits excellent toughness, strong bonding, and strong thermal shock resistance. It is also easy to construct, cures at room temperature, densifies at low temperatures, is non-toxic and environmentally friendly, and is durable and effective. It can significantly reduce high-temperature oxidation and burnout of carbon anodes, extending the anode's service life. However, this coating relies on low-temperature sintering of the coating components to form a ceramic structure that resists oxidation by air. The micro-liquid phase in the coating makes it difficult to fill the ceramic pores, resulting in a loose structure. The reserved ceramic pores provide a channel for air oxidation, which can easily cause partial oxidation of the anode substrate.

[0008] Fly ash is a solid waste emitted during the combustion process in coal-fired power plant boilers. It consists of fine particles captured in the flue gas duct after pulverized coal or coal slurry is burned at high temperatures in the furnace. The inorganic minerals in the raw materials undergo a series of physical and chemical changes, including ignition, conversion, melting, and cooling. Its primary components are SiO2 and Al2O3, accounting for 60-90% of the total, with smaller amounts of Fe2O3, CaO, MgO, K2O, and Na2O also present. The comprehensive utilization of fly ash has evolved through three stages: primarily storage, then a combination of storage and utilization, and finally primarily utilization. Although the annual utilization rate of fly ash has reached over 70%, the accumulated stockpile volume remains substantial, exceeding 2.5 billion tons and growing annually, resulting in significant environmental impacts. At present, the utilization of fly ash is mainly concentrated in building products, construction projects, road projects, etc. However, due to the high content of impurities in fly ash and the difficulty of pretreatment, the utilization rate still needs to be further increased. Summary of the Invention

[0009] The purpose of the present invention is to provide an anti-oxidation coating for aluminum electrolytic cell anodes to increase the service life of aluminum electrolytic anode carbon blocks.

[0010] In order to achieve the above object, the technical solution of the present invention is as follows:

[0011] An anti-oxidation coating for aluminum electrolytic cell anodes, comprising, by weight: 30-55 parts of an inorganic filler, 1-15 parts of a sintering aid, 5-10 parts of a binder, and 1-25 parts of a solvent;

[0012] The inorganic filler contains fly ash;

[0013] In the inorganic filler, the weight ratio of Al2O3 to SiO2 is 1.0-2.0.

[0014] The main components of antioxidant coatings for aluminum electrolytic cell anodes are Al2O3 and SiO2. The weight ratio of Al2O3 to SiO2 determines the coating's antioxidant properties. SiO2 determines the coating's fluidity. At high temperatures, SiO2 forms a highly viscous liquid phase. When cracks or bubbles appear in the coating, the flowing liquid can heal them, preventing the coating from cracking. When m(SiO2) is low, cracks in the coating are difficult to heal. Al2O3 forms a solid phase at high temperatures, determining the coating's toughness. If m(Al2O3) is too low, the coating easily flows freely on the anode surface, exposing the inner carbon anode. The coating has the best protective effect when the weight ratio of Al2O3 and SiO2 is 1.0-2.0. When the weight ratio of Al2O3 and SiO2 is greater than 2, m(Al2O3) is too large, the fluidity of the coating decreases, and cracks in the coating are difficult to heal. When the weight ratio of Al2O3 and SiO2 is less than 1, m(Al2O3) is too small, the fluidity of the coating is too large, and it flows on the anode surface, exposing the carbon anode substrate.

[0015] The present invention utilizes the characteristics of high aluminum and high silicon in fly ash, uses fly ash as a filler, and prepares a new type of antioxidant coating for aluminum electrolytic cell anodes. On the one hand, it reduces the fly ash inventory and provides a new idea for the rational use of this solid waste; on the other hand, it can effectively reduce the excessive consumption of carbon anodes, reduce the slagging of anode carbon blocks, extend the service life of aluminum electrolysis anode carbon blocks, and reduce the labor intensity of workers.

[0016] In a preferred embodiment, the inorganic filler is an activated inorganic filler.

[0017] The reasons for activation are as follows:

[0018] 1. The activation components are fly ash and alkali metal. Before activation, the two components are not sticky and cannot adhere to the coating surface, and will also crack. After activation, the two components can adhere to the coating surface;

[0019] 2. The principle of activation is that the silica in fly ash dissolves under alkaline conditions to generate high-viscosity alkali metal silicates such as sodium silicate and potassium silicate (inorganic polymer materials). The solubility of silica is related to the activation temperature and pressure. The higher the activation temperature and the greater the pressure, the higher the solubility of silica.

[0020] 3. During the activation process, the silica powder dissolves and turns into ions in the solution. The two are completely dissolved and mixed. After the inorganic filler is air-dried, no pores will be left, forming a dense surface structure.

[0021] In one preferred embodiment, the activation step of the inorganic filler comprises:

[0022] S1. Wet-grinding the inorganic filler to obtain a slurry;

[0023] S2. Activate the slurry for 1.5-5 hours at a pressure of not less than 0.6 MPa, a temperature of not less than 160° C., and a stirring rate of 15-80 rpm to obtain an activated inorganic filler.

[0024] The activation principle is as follows:

[0025] 1. Activation: The first step, wet grinding, produces a slurry to reduce the particle size of the powder. Reduced particle size increases the specific surface area, allowing for faster and more complete dissolution in alkaline solutions. Without wet grinding, the powder will have a larger particle size, dissolve more slowly, or even not dissolve at all.

[0026] 2. Activation is to dissolve silica and increase its activity. Undissolved silica is a powder and has no viscosity. The prepared coating is very easy to crack at room temperature.

[0027] If the activation pressure and temperature are too low, the activation time is too short, the dissolved SiO2 is less, the fluidity is low, the coating viscosity is low, and the protective performance is poor; if the temperature is too high, the pressure is too high, the time is too long, there is too much SiO2, the melting point of the coating is low, and the fluidity is strong at high temperature, which reduces the protective performance of the coating.

[0028] In one preferred embodiment, in step S2, the slurry is activated at an activation pressure of 0.6-0.8 MPa and an activation temperature greater than 160-180°C.

[0029] In one preferred embodiment, the fly ash includes 30-70 parts of Al2O3, 10-30 parts of quartz sand, 0-12 parts of calcium oxide, 0-2 parts of magnesium oxide and 0-10 parts of volatile matter.

[0030] In one preferred embodiment, the inorganic filler further includes one or both of alumina and quartz sand.

[0031] The system of the present invention can only include alumina and quartz sand. Other materials such as silicon dioxide powder have high water absorption, are easy to dry, and cannot be sprayed.

[0032] By adding alumina and quartz sand, the amount of alumina, fly ash and quartz sand added in the system is controlled so that the weight ratio of Al2O3 and SiO2 in the composition is 1.0-2.0.

[0033] In one preferred embodiment, the inorganic filler includes 30-60 parts of fly ash and 2-20 parts of aluminum oxide.

[0034] In one preferred embodiment, the inorganic filler includes 30-60 parts of fly ash and 2-20 parts of quartz sand.

[0035] In one preferred embodiment, the sintering aid is potassium chloride.

[0036] There are two reasons for adding potassium chloride: 1. Potassium feldspar formed by potassium reacting with SiO2 and Al2O3 at high temperature has high viscosity, which bonds the coating to the surface of the carbon anode; 2. Potassium chloride has a low melting point and can melt at a lower temperature to fill the pores and cracks in the middle of the solid coating and protect the carbon anode substrate. The temperature of KF is too high and cannot fill the pores and cracks between the coatings in time at low temperatures, which will lead to increased mass loss of the carbon anode.

[0037] In one preferred embodiment, the binder is sodium silicate.

[0038] In one preferred embodiment, the solvent is one or more of water, ethanol, methanol, and ethylene glycol monobutyl ether, preferably water, which has higher safety.

[0039] The present invention also claims a method for preparing the anti-oxidation coating for aluminum electrolytic cell anode, comprising:

[0040] A solvent is added to the activated inorganic filler to disperse it; and then a sintering aid and a binder are added to prepare the anti-oxidation coating for the anode of the aluminum electrolytic cell.

[0041] The invention discloses an anti-oxidation coating for an aluminum electrolytic cell anode. The preparation method thereof comprises the following steps: spraying the anti-oxidation coating for an aluminum electrolytic cell anode onto the surface of a carbon anode with a thickness controlled at 0.2 to 0.8 μm, naturally drying the coating for 24 to 48 hours, and reacting the coating at 800 to 1100° C. for 5 to 12 hours.

[0042] The coating material of the present invention only needs to be sprayed on the surface of the carbon anode with a thickness controlled at 0.2-0.8 μm, dried naturally for 24-48 hours, and then reacted at 800-1100° C. for 5-12 hours before use, which can extend the anode cycle by two days.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] (1) The activated inorganic filler of the present application generates a high-viscosity alkali metal silicate solution, and the melting point of the silicate is low, which can be melted into a liquid phase at high temperature. The ionic alkali metal silicate can fill the pores between the powders, preventing the coating from cracking. At the same time, it does not reserve a channel for air penetration, preventing air from invading. It overcomes the shortcomings of high sintering temperature of the previous ceramic coating, insufficiently dense coating surface, and easy peeling, while reducing the cost of the coating. The activated alkali metal silicate is a silicate structure with silicon-oxygen tetrahedral backbone. After the formation of this structure, part of the silicon-oxygen tetrahedral is replaced by aluminum oxide to form an aluminum silicate structure. The high-temperature molten aluminum silicate has higher viscosity and forms a dense structure similar to the surface glaze of ceramic, preventing air erosion of the carbon anode.

[0045] (2) The present application adds a sintering aid to reduce the sintering temperature of the filler, so that the filler is sintered at a temperature of 500-600℃ to form a dense ceramic structure, and the anode oxidation rate can be effectively reduced at a temperature above 600℃.

[0046] (3) The present application uses activated fly ash as a coating raw material, which is a new way to reasonably utilize fly ash and reduce solid waste accumulation. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is the oxidation result of the sample of Example 1;

[0048] Figure 2 is the oxidation result of the sample of Comparative Example 1;

[0049] Figure 3 is the oxidation result of the sample of Comparative Example 2;

[0050] Figure 4 is the oxidation result of the sample of Example 2;

[0051] Figure 5 is the oxidation result of the sample of Comparative Example 3;

[0052] Figure 6 is the oxidation result of the sample of Example 3;

[0053] Figure 7 is the micro-morphology of the coating of Example 3;

[0054] Figure 8 is the XRD phase result of the coating of Example 3. DETAILED DESCRIPTION

[0055] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] Example 1

[0057] The specific implementation steps of this embodiment are as follows:

[0058] (1) Fly ash from a certain place in Inner Mongolia was selected, and its composition is as follows:

[0059] Al2O3 <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> CaO MgO Loss on ignition 44.74％ 31.91％ 4.17％ 9.77％ 0.58％ 6.19％

[0060] (2) Wet-grind 30 parts fly ash, 20 parts alumina, and 20 parts water in a sand mill for 5-12 hours, until the Al2O3:SiO2 ratio in the filler is approximately 2:1.

[0061] (3) The wet-milled slurry was added to an autoclave and activated at 0.6 MPa, 160°C, and a stirring rate of 50 rpm for 3 h;

[0062] (4) The filler in step (3) was added to a high-speed disperser, and 10 parts of sodium silicate and 5 parts of potassium chloride were added to the disperser and dispersed at a speed of 200 rpm for 1 to 2 hours to obtain coating 1.

[0063] (5) The addition of 20 parts of aluminum oxide in step (2) was changed to adding 10 parts of aluminum oxide and 5 parts of aluminum oxide. At this time, the Al2O3:SiO2 in the filler was 1.5:1 and 1:1 respectively. The other steps, raw materials and processes were the same as above, and coating 2 and coating 3 were prepared respectively.

[0064] (6) The prepared coating 1-3 was sprayed onto the surface of a 6×6×1 cm carbon anode with a film thickness of 0.4 to 0.6 μm. After drying at room temperature for 48 hours, it was placed in a muffle furnace and reacted at 950°C for 10 hours. After oxidation, the samples were all as shown in FIG. Figure 1 The carbon anodization results of coating 2 are shown in Table 1. The carbon anodization results of coatings 1 and 3 are close to those of coating 2.

[0065] Comparative Example 1

[0066] Fly ash from a certain place in Inner Mongolia was selected, and 14 parts of quartz sand powder were added instead of 20 parts of alumina in step (2) of Example 1. At this time, the Al2O3:SiO2 ratio in the filler was 0.5:1. The other steps, raw materials and processes were the same as those in Example 1. Figure 2 , the carbon anodization results are shown in Table 1.

[0067] Comparative Example 2

[0068] Fly ash from a certain place in Inner Mongolia was selected, and the addition of 20 parts of alumina in step (1) of Example 1 was changed to adding 16 parts of alumina powder. At this time, the Al2O3:SiO2 in the filler was ≈3:1. The other steps, raw materials and processes were the same as those in Example 1. Figure 3 , the carbon anodization results are shown in Table 1.

[0069] Comparing Example 1 with Comparative Examples 1-2, the best protection effect was achieved by using the Al2O3:SiO2≈1-2:1 ratio in Example 1.

[0070] Example 2

[0071] The specific implementation steps of this embodiment are as follows:

[0072] (1) Fly ash from a certain place in Inner Mongolia was selected, and its composition is as follows:

[0073] <![CDATA[Al2O3]]> <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> CaO MgO Loss on ignition 44.74％ 31.91％ 4.17％ 9.77％ 0.58％ 6.19％

[0074] (2) Wet-grind 30 parts fly ash, 10 parts alumina, and 20 parts water in a sand mill for 5-12 hours, until the Al2O3:SiO2 ratio in the filler is 1.5:1.

[0075] (3) The wet-milled slurry was added to an autoclave and activated at 0.8 MPa, 180°C, and a stirring rate of 50 rpm for 3 h;

[0076] (4) The filler in step (3) was added to a high-speed disperser, and 10 parts of sodium silicate and 5 parts of potassium chloride were added to the disperser and dispersed at a speed of 200 rpm for 1 to 2 hours to obtain coating 4.

[0077] (5) The prepared coating 4 was sprayed onto the surface of a 6×6×1 cm carbon anode to a film thickness of 0.4 to 0.6 μm. After drying at room temperature for 48 hours, it was placed in a muffle furnace and reacted at 950°C for 10 hours. After oxidation, the sample was as follows: Figure 4 , the carbon anodization results are shown in Table 1.

[0078] Comparing coating 2 and coating 4, increasing the activation temperature to 180°C and the pressure to 0.8 MPa has no effect on the protective performance of the coating.

[0079] Comparative Example 3

[0080] Example 2 was repeated, except that the pressure in step (3) of Example 2 was changed to 0.3 MPa and the temperature was changed to 130°C. The other steps, raw materials and processes were the same as those of Example 2. Figure 5 , the carbon anodization results are shown in Table 1.

[0081] Comparative Example 4

[0082] Example 2 was repeated except that the pressure in step (3) of Example 2 was changed to 0.9 MPa and the temperature was changed to 190° C. The other steps, raw materials, and processes were the same as Example 2. The carbon anodization results are shown in Table 1.

[0083] Comparing Examples 1, 2 and Comparative Examples 3-4, when the activation pressure is lower than 0.6 MPa and the activation temperature is lower than 160°C, the protective performance of the coating will be reduced. When the activation pressure is higher than 0.8 MPa and the activation temperature is higher than 180°C, the protective performance of the coating will be reduced. The optimal activation conditions are activation pressure of 0.6-0.8 MPa, activation temperature greater than 160-180°C, and activation treatment for 2 hours at a stirring rate of 50 rpm.

[0084] Example 3

[0085] Fly ash from a place in Heilongjiang was selected, and its composition is as follows:

[0086] <![CDATA[Al2O3]]> <![CDATA[SiO2]]> <![CDATA[Fe2O3]]> CaO MgO Loss on ignition 20.70％ 61.15％ 4.75％ 3.60％ 0.86％ 4.60％

[0087] (1) Wet-grind 20 parts fly ash, 25 parts alumina, and 20 parts water in a sand mill for 5-12 hours until the Al2O3:SiO2 ratio in the filler is 1.5:1.

[0088] (2) adding the wet-milled slurry into an autoclave and subjecting it to activation treatment for 2 to 5 hours at 0.6 MPa, 170°C, and a stirring rate of 50 rpm;

[0089] (3) The filler in step (3) is added to a high-speed disperser, and 10 parts of sodium silicate and 5 parts of potassium chloride are added to the disperser and dispersed at a speed of 200 rpm for 1 to 2 hours.

[0090] (4) The prepared coating was sprayed onto the surface of a 6×6×1 cm carbon anode, dried at room temperature for 48 h, and then placed in a muffle furnace and reacted at 950°C for 10 h. After oxidation, the sample was Figure 6 The carbon anodization results are shown in Table 1. The coating micromorphology is as follows Figure 7 , XRD results are as follows Figure 8 .

[0091] Comparing Examples 2 and 3, it was found that fly ash from different regions did not affect the coating's antioxidant properties. Instead, the primary factor influencing antioxidant performance was the mass ratio of Al2O3 to SiO2, with the best antioxidant effect achieved when the Al2O3:SiO2 ratio was 1.0-2.0:1. Furthermore, the activation conditions during the coating preparation process significantly impacted antioxidant performance. After wet grinding, the coating filler entered the autoclave, and the activation pressure exceeded 0.6 MPa, no longer affecting the coating's antioxidant properties.

[0092] Comparative Example 2 and Example 3 can be found that the different origin of different enterprises of fly ash, can be used for the preparation of antioxidant coating, therefore, the method for processing fly ash has universal usability.

[0093] Comparative Example 5

[0094] Example 3 is repeated, the only difference is that the addition of 5 parts of potassium chloride in step (3) of Example 3 is replaced by the addition of 5 parts of potassium fluoride, and the carbon anode oxidation results are shown in Table 1.

[0095] Comparative Example 6

[0096] Example 3 is repeated, the only difference is that the addition of 5 parts of potassium chloride in step (3) of Example 3 is replaced by the addition of 5 parts of sodium chloride, and the carbon anode oxidation results are shown in Table 1.

[0097] Comparative Example 3 and Comparative Example 5, because the melting point of chloride is lower than that of potassium fluoride, therefore, the air hole in the liquid phase sealing coating can be formed at a lower temperature, avoiding the entry of air, thus the protection effect is strong.

[0098] Comparative Example 3 and Comparative Example 6, because the potassium ion into the coating can form a higher viscosity of potassium feldspar, increase the binding force of the coating and the carbon anode, thus the protection effect is good.

[0099] Example 4

[0100] Select a fly ash from a certain place in Heilongjiang, its composition is as follows:

[0101] <![CDATA[Al2O3]]> SiO2 <![CDATA[Fe2O3]]> CaO MgO Loss on ignition 60.70％ 20.15％ 4.75％ 3.60％ 0.86％ 4.60％

[0102] (1) 20 parts of fly ash, 4 parts of quartz sand, 20 parts of water by mass were put into a sand mill and wet ground for 5-12h, at this time the Al2O3: SiO2 in the filler was about 1.5:1;

[0103] (2) The slurry after wet grinding was added to an autoclave and activated under the conditions of 0.6 MPa, 170℃ and stirring rate of 50 revolutions / minute for 2-5h;

[0104] (3) The filler in step (3) was added to a high-speed disperser, 10 parts of sodium silicate and 5 parts of potassium chloride were added to the disperser and dispersed at a speed of 200 revolutions / minute for 1-2h.

[0105] (4) The prepared coating was sprayed onto the surface of a carbon anode of 6x6x1cm, dried at room temperature for 48h and then put into a muffle furnace, reacted at 950℃ for 10h, and the carbon anode oxidation results are shown in Table 1.

[0106] Comparative Example 7

[0107] Example 4 was repeated, except that steps (1) and (2) of Example 4 were replaced by not adding the activated inorganic material. Instead, 20 parts of fly ash, 4 parts of quartz sand, and 20 parts of water were directly added to a high-speed disperser and mixed with 10 parts of sodium silicate and 5 parts of potassium chloride. The other raw materials, processes, and steps were the same as those of Example 4. The resulting coating was sprayed onto the surface of a 6×6×1 cm carbon anode, dried at room temperature for 48 hours, and then placed in a muffle furnace and reacted at 950°C for 10 hours. The carbon anode oxidation results are shown in Table 1.

[0108] Comparative Example 8

[0109] Example 4 was repeated, except that the slurry obtained after wet grinding in step (1) of Example 4 was directly added to a high-speed disperser and mixed with 10 parts of sodium silicate and 5 parts of potassium chloride. The other raw materials, processes, and steps were the same as those of Example 4. The resulting coating was sprayed onto the surface of a 6 × 6 × 1 cm carbon anode, dried at room temperature for 48 h, and then placed in a muffle furnace for reaction at 950°C for 10 h. The carbon anode oxidation results are shown in Table 1.

[0110] Comparative Example 9

[0111] Example 4 was repeated, except that 20 parts fly ash, 4 parts quartz sand, and 20 parts water from Example 4 were simply stirred and mixed before being added to an autoclave. The mixture was activated at 0.6 MPa, 170°C, and a stirring rate of 50 rpm for 2-5 hours. Other raw materials, processes, and steps were the same as in Example 4. The resulting coating was sprayed onto the surface of a 6×6×1 cm carbon anode, dried at room temperature for 48 hours, and then placed in a muffle furnace for reaction at 950°C for 10 hours. The carbon anode oxidation results are shown in Table 1.

[0112] Comparing Example 4 with Comparative Example 7, the unactivated fly ash added to the coating in Comparative Example 7 resulted in a lower sodium silicate content and low viscosity, preventing effective adhesion to the carbon anode surface. Furthermore, the high melting points of alumina and silica reduced the liquid phase content of the coating, ultimately leading to coating failure and the greatest weight loss of the carbon anode.

[0113] Comparing Example 4 and Comparative Example 8, in Comparative Example 8, an inorganic filler that has only been wet-ground is added to the coating. Although the particle size of the inorganic filler is appropriate, since it has not been activated at high temperature, the silica dissolves and increases its activity, and the undissolved silica is a powder and has no viscosity. The prepared coating is extremely easy to crack at room temperature.

[0114] Comparing Example 4 with Comparative Example 9, in Comparative Example 9, inorganic fillers that were directly activated at high temperature without wet grinding were added to the coating. Although the particle size of the inorganic filler was not suitable, the dissolution rate was slow, or it was basically insoluble, resulting in coating failure.

[0115] Table 1 Graphite oxidation results obtained in different examples and comparative examples

[0116]

[0117]

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An anti-oxidation coating for aluminum electrolytic cell anode, characterized in that: include: 30-55 parts of inorganic filler, 1-15 parts of sintering aid, 5-10 parts of binder and 1-25 parts of solvent; The inorganic filler contains fly ash; In the inorganic filler, the weight ratio of Al2O3 to SiO2 is 1.0-2.0; The inorganic filler is an activated inorganic filler; The activation step of the inorganic filler comprises: S1. Wet-grinding the inorganic filler to obtain a slurry; S2, activating the slurry at a pressure of 0.6-0.8 MPa, a temperature of 160-180° C., and a stirring rate of 15-80 rpm for 1.5-5 h to obtain an activated inorganic filler; The inorganic filler further comprises one or two of alumina and quartz sand; The sintering aid is potassium chloride; The binder is sodium silicate.

2. The anti-oxidation coating for aluminum electrolysis cell anode according to claim 1, characterized in that: The fly ash comprises 30-70 parts of Al2O3, 10-30 parts of quartz sand, 0-12 parts of calcium oxide, 0-2 parts of magnesium oxide and 0-10 parts of volatile matter.

3. The anti-oxidation coating for aluminum electrolysis cell anode according to claim 1 or 2, characterized in that: The solvent is one or more of water, ethanol, methanol, and ethylene glycol monobutyl ether.

4. The method for preparing an anti-oxidation coating for an aluminum electrolysis cell anode according to any one of claims 1 to 3, characterized in that: include: Adding a solvent to the activated inorganic filler to disperse it; Then, a sintering aid and a binder are added to prepare the anti-oxidation coating for the anode of the aluminum electrolytic cell.

5. An anti-oxidation coating for an aluminum electrolytic cell anode, characterized in that: The preparation method comprises the following steps: spraying the anti-oxidation coating for aluminum electrolytic cell anode according to any one of claims 1 to 3 onto the surface of the carbon anode with a thickness controlled at 0.2 to 0.8 μm, drying naturally for 24 to 48 hours, and reacting at 800 to 1100° C. for 5 to 12 hours to obtain the product.

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