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, and particularly relates to an oxidation-resistant coating for anodes of aluminum electrolytic cells and a preparation method thereof. The oxidation-resistant coating for anodes of aluminum electrolytic cells comprises 20-70 parts of fillers, 20-40 parts of a binder and 20-40 parts of a solvent; the fillers contain treated aluminum ash; in the fillers, the weight ratio of Al2O3 and SiO2 is 1.0-2.0:1; and the treatment process of the treated aluminum ash is as follows: aluminum ash is stirred and reacted at 1000-1400 DEG C for 2h, and then cooled to obtain the treated aluminum ash. The coating is a low-temperature quasi-melting anode oxidation-resistant coating, which realizes the melting of components in the coating at a lower temperature, on the one hand increases the bonding strength of the coating and the pre-baked anode, and on the other hand endows the coating with self-healing performance, so that the coating can heal the cracking and pores caused by thermal stress, or mismatching of thermal expansion coefficients, or impurity volatilization in the oxidation process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrolytic aluminum, in particular to an oxidation-resistant coating for anodes of aluminum electrolysis cells and a preparation method thereof. BACKGROUND

[0002] In the process of aluminum electrolysis production, the carbon anode is in a high-temperature oxidation atmosphere of 450 DEG C to 950 DEG C and a fluorine-containing corrosive atmosphere, which will cause degranulation, block dropping and oxidation combustion, which is also the main reason for the increase of carbon material consumption.

[0003] The excessive consumption of carbon anode mainly includes secondary consumption caused by Boudouard reaction, selective oxidation of anode material and mechanical loss. In the process of aluminum electrolysis production, anode gas penetrates into the internal pores of the anode to cause Boudouard reaction, resulting in secondary consumption; the difference in oxidation between the binder asphalt and the aggregate petroleum coke causes part of the aggregate to fall off and form carbon residue; the huge pressure and flow rate impact force generated during the movement of anode gas bubbles to the edge causes the anode to drop slag. The carbon residue not only shortens the service life of the anode, but also causes the voltage drop to rise, generates a hot cell, increases the power consumption of aluminum electrolysis, and also increases the labor intensity of workers.

[0004] Coating method is an effective method to improve the oxidation resistance of carbon materials and carbon materials, and its main mechanism is that high-melting-point oxidation-resistant materials are sprayed onto the surface of carbon materials to form a coating, and sintering or melting products are generated on the surface of carbon materials to cut off the contact path of carbon materials with air. The carbon anode in the aluminum electrolysis cell starts to oxidize above 500 DEG C, therefore, an efficient protective coating needs to form a dense structure at 500 DEG C to prevent air erosion.

[0005] The prior art CN108315765A discloses a kind of aluminum ash slag is utilized to prepare aluminum electrolysis anode anti-oxidation coating, and aluminum ash is treated by adopting alkali solution-dewatering process, and the treated aluminum ash is used as coating binder and filler, and an oxidation-resistant coating is prepared by cooperating with organic auxiliary agent, but the method has low nitrogen removal efficiency, needs to go through alkali solution-water immersion-cooling-filtration-dewatering process, a large amount of ammonia gas will be released during the treatment process, and the process flow is long, and the operability is poor.

[0006] Prior art CN 110577758 B provides a method for preparing an anti-oxidation coating for a carbon anode used in electrolytic aluminum by comprehensive utilization of aluminum ash. The raw materials include, by weight, aluminum ash, a strong base, aluminum powder, a boron compound, an organic adhesion promoter, and water. The specific preparation method comprises: adding the aluminum ash to water and keeping it warm under stirring; collecting the generated ammonia gas, cooling the liquid material, filtering it, and transferring the filtrate to an evaporation device for evaporation to recover the soluble chloride salts therein, while collecting the distilled water generated during the evaporation process; adding a strong base to the filtrate to obtain an alkaline solution; adding the filter residue obtained by filtration and aluminum powder, stirring, and partially dissolving the solution with alkali to obtain a binder and filler for a carbon anode coating for electrolytic aluminum; and finally, adding the boron compound and the organic adhesion promoter to the binder and mixing them evenly. However, on the one hand, this invention uses dissolved alkali as a binder and organic matter as a bonding aid. After the organic bonding aid evaporates at high temperature, the viscosity of the coating decreases, and the viscosity of the melt of the strong alkali is very low, which cannot keep the coating bonded to the carbon anode surface for a long time; on the other hand, this invention adopts a wet process for aluminum ash treatment, and a large amount of ammonia with a pungent odor will be generated during the treatment process, which poses a huge threat to the environment and the health of the operators. Summary of the Invention

[0007] 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.

[0008] In order to achieve the above object, the technical solution of the present invention is as follows:

[0009] An anti-oxidation coating for an aluminum electrolytic cell anode, comprising, by weight, 20-70 parts of a filler, 20-40 parts of a binder, and 20-40 parts of a solvent;

[0010] The filler contains treated aluminum ash;

[0011] In the filler, the weight ratio of Al2O3 to SiO2 is 1.0-2.0;

[0012] The processing process of treating aluminum ash is as follows: stirring the aluminum ash at 1000-1400° C. for 2 hours, and then cooling to obtain the aluminum ash.

[0013] 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.

[0014] The present invention adopts a high-temperature denitrification process to remove nitrogen from aluminum ash and convert aluminum nitride into aluminum oxide. It has the advantages of high denitrification efficiency, short process and good denitrification effect, and avoids the occurrence of ammonia during the wet treatment process. The treated aluminum ash is returned to the electrolytic cell as filler for reuse, thereby reducing the disposal cost of the aluminum ash.

[0015] In contrast, alkali dissolution-dehydration treatment of aluminum ash will produce a large amount of toxic ammonia. The alkali dissolution treatment efficiency is low, the process flow is long, and the conversion rate of aluminum in the aluminum ash to Al2O3 is low.

[0016] In one preferred embodiment, the aluminum ash is black-gray aluminum ash obtained by extracting metallic aluminum through a roasting method.

[0017] In one preferred embodiment, the black-gray aluminum ash obtained after the extraction of metallic aluminum contains 20wt%-60wt% of aluminum element.

[0018] Aluminum ash is divided into white aluminum ash and black aluminum ash. White aluminum ash contains more aluminum. Manufacturers use the ash roasting method to roast out the metallic aluminum in the aluminum ash, and the remaining product is black aluminum ash, which is very difficult to process. The present invention uses black aluminum ash as a raw material to process and solve this problem.

[0019] In one preferred embodiment, the filler further includes alumina and silicon powder.

[0020] The addition amounts of alumina, treated aluminum ash and silicon powder are controlled so that the weight ratio of Al2O3 to SiO2 in the composition is 1.0-2.0.

[0021] In one preferred embodiment, the filler includes 10-40 parts of processed aluminum ash and 5-40 parts of silicon powder.

[0022] In one preferred embodiment, the treated aluminum ash includes 70-80 parts of aluminum oxide, 5-20 parts of aluminum nitride, 1-5 parts of aluminum fluoride, 0-1 part of calcium oxide, 0-1 part of silicon dioxide, 0-1 part of magnesium oxide, 0-1 part of potassium oxide, 0-1 part of sodium oxide and 0-1 part of iron oxide.

[0023] In one preferred embodiment, the filler accounts for 50 to 70 wt % of the total coating.

[0024] The Al2O3 in the filler is solid at high temperatures and plays a toughening role. The proportion of fillers within this range ensures the toughness of the coating. Below this range, the m(Al2O3) in the coating is low, the coating toughness is poor at high temperatures, and it is easy to fall off on the anode surface. If it is too high, the binder content in the coating is low, and it is easy to crack at room temperature. At the same time, the binder contains high molecular chain SiO2, and the filler content is high, resulting in a low m(SiO2) content in the coating, which ultimately leads to low coating viscosity.

[0025] At the same time, when the filler is less than 50wt%, the high-temperature phase of the coating is small and cannot cover the surface of the carbon block. When the filler is higher than 70wt%, the binder in the coating is too little and it is easy to crack at high temperature, and the coating loses its protective effect.

[0026] In one preferred embodiment, the treated aluminum ash accounts for 5 to 40 wt% of the total coating by mass.

[0027] Aluminum ash contains fluorine, a small amount of which helps lower the liquidus temperature in the coating. The volatile temperature of carbon is around 500°C, and the earlier formation of the liquidus can heal pores in the coating and protect the anode. However, when the aluminum ash content is too high, the liquidus temperature drops significantly, causing the coating to lose viscosity at 960°C, the operating conditions of the electrolytic cell. This reduces the viscosity between the coating and the substrate, leading to detachment from the carbon anode surface.

[0028] In one preferred embodiment, the binder includes 1-5 parts of quartz sand, 0.1-2 parts of potassium hydroxide and 0.1-2 parts of sodium hydroxide.

[0029] In one preferred embodiment, the preparation process of the binder includes:

[0030] Add quartz sand, sodium hydroxide and potassium hydroxide into an autoclave, and react for 1-6 hours at 150-2000° C., 0.4-0.8 MPa, 10-50 rpm and in the presence of water vapor to prepare a binder.

[0031] If the pressure and temperature are too low and the time is too short, less SiO2 is dissolved, there is less binder, 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 binder, the coating melting point is low, and the fluidity is strong at high temperature, which reduces the protective performance of the coating.

[0032] SiO2 is a solid, but it can be dissolved in alkali. After dissolving in alkali, under the catalytic action of alkali metals, SiO2 connects into high-molecular SiO2 chains, acting as a binder in the coating. In comparison, if simply mixed at room temperature, the solubility of SiO2 in alkaline solution is very low. The coating obtained by directly mixing alkali + SiO2 has no viscosity and will naturally fall off when sprayed onto the anode surface at room temperature.

[0033] In a preferred embodiment, the solvent is water, ethanol or methanol, preferably water.

[0034] In one preferred embodiment, the crystal form of aluminum oxide in the filler is α-aluminum oxide.

[0035] Alpha-alumina is the final crystal form of alumina and is often used as a ceramic raw material. It has strong oxidation resistance and will not cause the coating to crack due to thermal stress caused by crystal phase transition at high temperatures. If other crystal forms of alumina are used, crystal phase transition will occur at high temperatures. During this transition, the thermal expansion coefficient changes, causing thermal stress in the coating and ultimately cracking.

[0036] In one preferred embodiment, the particle size of the silicon powder D90 is ≤ 2 μm, and the particle size of the aluminum ash D90 is ≤ 5 μm.

[0037] The powder material has a smaller particle size and can better protect the coating. When the particle size is too coarse, the coating's antioxidant performance is poor.

[0038] The particle size of the coating affects the protective effect of the coating. If the particle size is too large, the gaps between the coating particles are large, making it difficult for the liquid phase to fill the gaps, and the air will eventually oxidize the substrate. If the particle size is too small, there will be too many surface hydroxyl groups between the alumina powder and the silica powder, resulting in high viscosity, easy agglomeration, and difficulty in spraying.

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

[0040] Aluminum ash and solvent are processed and ball-milled to obtain inorganic filler; then solvent and binder are added and dispersed at a rotation speed of 500-1000 rpm to obtain 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 0.3 to 0.5 mm, 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 0.3-0.5 mm, dried naturally for 24-48 hours, and then reacted at 800-1100° C. for 5-12 hours before use, which can reduce and extend the anode cycle by two days.

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

[0044] (1) The present invention uses a pyrotechnic roasting method to treat aluminum ash, and treats the nitrides in the aluminum ash into nitrogen oxides for emission, thereby achieving harmless treatment of the nitrides. The process is short, safe, environmentally friendly, efficient, and has a good nitrogen removal effect. Nitrogen elements volatilize in the form of nitrogen oxides at high temperatures, which can avoid the disadvantage of generating ammonia during the wet treatment of aluminum ash.

[0045] (2) Using aluminum ash as a source of alumina reduces the accumulation of aluminum ash and the damage it causes to the environment. At the same time, it rationally utilizes the aluminum resources in the aluminum ash and explores a new path for the resource utilization of aluminum ash.

[0046] (3) In view of the shortcomings of previous ceramic coatings, such as high sintering temperature, insufficient density of the coating surface, pores, easy air ingress, and loose bonding with the carbon anode, the coating of the present invention is a low-temperature quasi-melting anode anti-oxidation coating, which achieves melting of the components in the coating at a lower temperature. On the one hand, it increases the bonding strength between the coating and the prebaked anode, and on the other hand, it gives the coating self-healing properties, so that the coating can heal cracks and pores caused by thermal stress, mismatch of thermal expansion coefficient, or volatilization of impurities during the oxidation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is the oxidation result of the sample in Example 1.

[0048] Figure 2 This is the oxidation result of the sample in Comparative Example 1.

[0049] Figure 3 This is the oxidation result of the sample in Comparative Example 2.

[0050] Figure 4 This is the oxidation result of the sample in Comparative Example 3.

[0051] Figure 5 This is the low-temperature oxidation micromorphology of the coating in Example 1. DETAILED DESCRIPTION

[0052] 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.

[0053] Example 1

[0054] The specific implementation steps of the embodiment are as follows:

[0055] (1) Secondary aluminum ash from a certain place in Henan Province was selected, and its composition is as follows:

[0056] Table 1 Composition of secondary aluminum ash

[0057] Al Si O Na F Ca Mg K Fe N 40.68％ 2.22％ 38.53％ 2.72％ 4.12％ 2.69％ 1.55％ 0.54％ 0.37％ 7.72％

[0058] The aluminum ash was added to a 1200°C aluminum melting furnace and stirred for 2 hours. After cooling, the denitrified aluminum ash was obtained. The composition is as follows:

[0059] Table 2 Composition of denitrified aluminum ash

[0060] Al Si O Na F Ca Mg K Fe N 43.10％ 2.36％ 46.11％ 2.63％ 4.27％ 2.65％ 1.54％ 0.40％ 0.38％ 0.29％

[0061] (2) By mass, 20 parts of denitrified aluminum ash, 10 parts of silicon powder, and 10 parts of water were added to a ball mill for wet grinding to obtain an inorganic filler. At this time, the Al2O3:SiO2 ratio of the filler was 1.5:1.

[0062] (3) Add 2 parts by mass of quartz sand, 0.5 parts by mass of sodium hydroxide, 0.5 parts by mass of potassium hydroxide, and 2 parts by mass of water into an autoclave, and react at 160° C., 0.6 MPa, 20 rpm, and a steam atmosphere for 2 h to prepare a liquid binder;

[0063] (4) Add the filler and liquid binder in steps (3) and (4) into a high-speed disperser and disperse at a speed of 800 rpm for 0.5 h to obtain coating 1.

[0064] (5) The addition of 10 parts of silicon micropowder in step (3) was changed to adding 8 parts of silicon micropowder and 15 parts of silicon micropowder, respectively. At this time, the Al2O3:SiO2 ratio in the filler was 2:1 and 1:1, respectively, to obtain coating 2 and coating 3, respectively.

[0065] (6) The prepared coating 1-3 was sprayed onto the surface of a 6×4×2 cm carbon anode with a thickness of 0.3 to 0.5 mm. After drying at room temperature for 24 hours, it was placed in a muffle furnace and reacted at 950°C for 10 hours. After oxidation of coating 1, the sample was as follows: Figure 1 The results of the samples after oxidation of coating 2 and coating 3 are similar to those of Figure 1Similarly, the carbon anodization results are shown in Table 1. The low temperature oxidation micromorphology of the coating was analyzed, and the results were as follows Figure 5 As shown in the figure, at a low temperature of 350°C, the coating is mainly composed of dense solid particles. At 400°C, the low-melting-point components in the coating, such as silicates, begin to deform, and the deformed solid particles can fill the pores between the solid particles. At 450°C, the low-melting-point components approach their melting point, and the solid particles are completely deformed. At 500°C, the low-melting-point phase of the coating completely melts into a liquid phase, forming a smooth coating structure with dense cracks and pores. It can be seen that the coating can complete the melting process before carbon anodization (before 500°C), forming a dense structure and preventing air erosion.

[0066] Comparative Example 1

[0067] Example 1 was repeated, except that 4.5 parts of silicon powder were added instead of 10 parts in step (3) of Example 1. The ratio of Al2O3 to SiO2 in the filler was ≈ 3:1. The other raw materials, processes and operating steps were the same as those in Example 1. Figure 2 , the carbon anodization results are shown in Table 1.

[0068] Comparative Example 2

[0069] Repeat Example 1, except that 32 parts of silicon dioxide are added instead of 10 parts of silicon powder in step (3) of Example 1. At this time, the ratio of Al2O3 to SiO2 in the filler is 1:2. After oxidation, the sample is as follows: Figure 3 , other raw materials, processes and operating steps are the same as in Example 1. The carbon anodization results are shown in Table 1.

[0070] As can be seen from Example 1 and Comparative Examples 1-2, the optimal effect is achieved when the ratio of m(Al2O3):m(SiO2) = 1-2:1. When the ratio of m(Al2O3):m(SiO2) is greater than 2:1, the m(Al2O3) ratio is too high, resulting in reduced coating fluidity and cracks that are difficult to heal. When the ratio of m(Al2O3):m(SiO2) is less than 1:1, the m(Al2O3) ratio is too low, resulting in excessive coating fluidity and causing the coating to flow on the anode surface, exposing the carbon anode substrate.

[0071] Comparative Example 3

[0072] (1) By mass, 20 parts of aluminum oxide, 10 parts of silicon powder, and 10 parts of water were added to a ball mill and wet-ground to obtain an inorganic filler. At this time, the ratio of Al2O3 to SiO2 in the filler was 1.5:1.

[0073] (2) Add 2 parts by mass of quartz sand, 0.5 parts by mass of sodium hydroxide, 0.5 parts by mass of potassium hydroxide, and 2 parts by mass of water into an autoclave, and react at 160° C., 0.6 MPa, 20 rpm, and a steam atmosphere for 2 h to prepare a liquid binder;

[0074] (3) Add the filler and liquid binder in steps (1) and 2) into a high-speed disperser and disperse at a speed of 800 rpm for 0.5 h to obtain a coating.

[0075] (4) The prepared coating was sprayed onto the surface of a 6×4×2 cm carbon anode, dried at room temperature for 24 h, and then placed in a muffle furnace and reacted at 950°C for 10 h. After oxidation, the sample was Figure 4 , the carbon anodization results are shown in Table 1.

[0076] The examples show that high-temperature treatment of aluminum ash effectively reduces its nitrogen content. Comparison of Example 1 and Comparative Example 3 shows that the protective effect of a coating using aluminum ash after nitrogen removal as a filler is consistent with that of a coating using pure alumina as a filler. Therefore, it is feasible to use aluminum ash as a filler to produce carbon anode anti-oxidation coatings.

[0077] Example 2

[0078] The specific implementation steps of the embodiment are as follows:

[0079] (1) Secondary aluminum ash from a certain place in Henan Province was selected, and its composition is as follows:

[0080] Table 3 Composition of secondary aluminum ash

[0081] Al Si O Na F Ca Mg K Fe N 40.68％ 2.22％ 38.53％ 2.72％ 4.12％ 2.69％ 1.55％ 0.54％ 0.37％ 7.72％

[0082] The aluminum ash was added to a 1200°C aluminum melting furnace and stirred for 2 hours. After cooling, the denitrified aluminum ash was obtained. The composition is as follows:

[0083] Table 4 Composition of denitrified aluminum ash

[0084] Al Si O Na F Ca Mg K Fe N 43.10％ 2.36％ 46.11％ 2.63％ 4.27％ 2.65％ 1.54％ 0.40％ 0.38％ 0.29％

[0085] (2) By mass, 20 parts of denitrified aluminum ash, 10 parts of silicon powder, and 10 parts of water were added to a ball mill for wet grinding to obtain an inorganic filler. At this time, the Al2O3:SiO2 ratio of the filler was 1.5:1.

[0086] (3) Add 2 parts by mass of quartz sand, 0.5 parts by mass of sodium hydroxide, 0.5 parts by mass of potassium hydroxide, and 2 parts by mass of water into an autoclave, and react at 180°C, 0.8 MPa, 20 rpm, and steam atmosphere for 2 hours to prepare a liquid binder;

[0087] (4) Add the filler and liquid binder in steps (2) and (3) into a high-speed disperser and disperse at a speed of 800 rpm for 0.5 h to obtain a coating.

[0088] (5) The prepared coating was sprayed onto the surface of a 6×4×2 cm carbon anode, dried at room temperature for 24 h, and then placed in a muffle furnace and reacted at 950°C for 10 h. The carbon anode oxidation results are shown in Table 1.

[0089] Comparative Example 4

[0090] Example 2 was repeated, except that in Example 1 step (4), the reaction was carried out at 140°C, 0.4 MPa, 20 rpm, steam atmosphere for 2 h instead of 160°C, 0.6 MPa, 20 rpm, steam atmosphere for 2 h, and other raw materials, processes and operating procedures were the same as in Example 2. The carbon anode oxidation results are shown in Table 1.

[0091] Comparative Example 5

[0092] Example 2 was repeated, except that in Example 1 step (4), the reaction was carried out at 200°C, 0.9 MPa, 20 rpm, steam atmosphere for 2 h instead of 160°C, 0.6 MPa, 20 rpm, steam atmosphere for 2 h, and other raw materials, processes and operating procedures were the same as in Example 2. The carbon anode oxidation results are shown in Table 1.

[0093] Comparative Example 6

[0094] Example 2 was repeated, except that in Example 1 step (1) was omitted, and 20 parts of secondary aluminum ash from a certain place in Henan, 10 parts of silica powder and 10 parts of water were directly added to a ball mill for wet grinding to obtain an inorganic filler. Other raw materials, processes and operating procedures were the same as in Example 2. The carbon anode oxidation results are shown in Table 1.

[0095] Comparative Example 7

[0096] Example 2 was repeated, except that in Example 1 step (3) was omitted, and 2 parts of quartz sand, 0.5 parts of sodium hydroxide, 0.5 parts of potassium hydroxide and 2 parts of water were directly mixed with the filler of step (2) and then dispersed. Other raw materials, processes and operating procedures were the same as in Example 2. The carbon anode oxidation results are shown in Table 1.

[0097] Comparative Example 8

[0098] Example 2 was repeated, except that in Example 1 steps (1) and (2) were omitted, and 20 parts of secondary aluminum ash from a certain place in Henan, 10 parts of silica powder and 10 parts of water were directly added to a ball mill for wet grinding to obtain an inorganic filler, which was then directly mixed with 2 parts of quartz sand, 0.5 parts of sodium hydroxide, 0.5 parts of potassium hydroxide and 2 parts of water and then dispersed. Other raw materials, processes and operating procedures were the same as in Example 2. The carbon anode oxidation results are shown in Table 1.

[0099] Comparative Example 9

[0100] Example 2 was repeated, except that step (1) of Example 1 was modified to use secondary aluminum ash from Henan, which was subjected to alkali dissolution and dehydration, and then mixed with 10 parts of silica powder and 10 parts of water in a ball mill to obtain the inorganic filler. The steps of alkali dissolution and dehydration were as follows: 40 parts of secondary aluminum ash from Henan were weighed, and the aluminum and alumina contents in the aluminum ash were analyzed; the aluminum ash was added to an open container, and sufficient water was added to hydrolyze aluminum nitride, and ammonia gas generated in the hydrolysis process was collected. The salt solution was subjected to pressure filtration treatment, and the filtrate was returned to the salt recovery system and used as a raw material for preparing the aluminum liquid refining agent; according to the aluminum and alumina contents in the ash, sufficient alkali was added to the residue to dissolve the aluminum and alumina in the residue; the alkali solution was subjected to pressure filtration treatment, and the iron oxide and silicon oxide residue was sent to a storage yard, and the filtrate was evaporated to prepare sodium metaaluminate; 20 parts of sodium metaaluminate dry substance were mixed with 10 parts of silica powder and 10 parts of water in a ball mill to obtain the inorganic filler.

[0101] The other raw materials, processes and operation steps were the same as in Example 2. The results of the carbon anode oxidation are shown in Table 1.

[0102] Comparative Example 10

[0103] Example 2 was repeated, except that 20 parts of denitrified aluminum ash and 10 parts of silica powder were added in step (2) of Example 1, and 10 parts of denitrified aluminum ash and 5 parts of silica powder were added instead, and the other raw materials, processes and operation steps were the same as in Example 2. The results of the carbon anode oxidation are shown in Table 1.

[0104] Comparative Example 11

[0105] Example 2 was repeated, except that 20 parts of denitrified aluminum ash and 10 parts of silica powder were added in step (2) of Example 1, and 60 parts of denitrified aluminum ash and 30 parts of silica powder were added instead, and the other raw materials, processes and operation steps were the same as in Example 2. The results of the carbon anode oxidation are shown in Table 5.

[0106] Table 5: Results of graphite oxidation in different examples and comparative examples

[0107] Example Graphite mass / g Coating mass after drying / g Mass after oxidation / g Quality loss Example 1 82.12 85.88 79.66 7.24wt% Comparative Example 1 84.26 88.05 74.05 15.89wt% Comparative Example 2 82.43 86.12 71.57 16.89wt% Comparative Example 3 82.15 86.45 80.18 7.25wt% Example 2 84.33 90.52 84.08 7.11wt% Comparative Example 4 83.12 89.74 81.89 8.54wt% Comparative Example 5 83.45 88.97 80.77 9.21wt% Comparative Example 6 82.43 86.39 72.38 16.22wt% Comparative Example 7 81.56 85.99 72.89 15.23wt% Comparative Example 8 81.74 86.58 71.43 17.49wt% Comparative Example 9 80.26 85.63 85.60 19.89wt% Comparative Example 10 79.85 84.88 78.36 7.68wt% Comparative Example 11 80.41 85.23 78.13 8.33wt%

[0108] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An anti-oxidation coating for aluminum electrolytic cell anode, characterized in that: The coating comprises, by weight, 20-70 parts of a filler, 20-40 parts of a binder, and 20-40 parts of a solvent; the filler contains treated aluminum ash and silicon powder; the weight ratio of Al2O3 to SiO2 in the filler is 1.0-2.0:1; the treatment process of the treated aluminum ash is as follows: stirring the aluminum ash at 1000-1400°C for 2 hours, and cooling the aluminum ash; the treated aluminum ash accounts for 5-40wt% of the total coating; The binder comprises 1-5 parts of quartz sand, 0.1-2 parts of potassium hydroxide and 0.1-2 parts of sodium hydroxide; The preparation process of the binder comprises: adding quartz sand, sodium hydroxide and potassium hydroxide into an autoclave, reacting for 1-6 hours at 160-180° C., 0.6-0.8 MPa, 10-50 rpm and in the presence of water vapor to prepare the binder; The crystal form of the aluminum oxide in the filler is α-type aluminum oxide.

2. The anti-oxidation coating for aluminum electrolysis cell anode according to claim 1, characterized in that: The aluminum ash is black-gray aluminum ash obtained by extracting metallic aluminum through a roasting method.

3. The anti-oxidation coating for aluminum electrolysis cell anode according to claim 1, characterized in that: The filler comprises 10-40 parts of processed aluminum ash and 5-40 parts of silicon micropowder.

4. The anti-oxidation coating for aluminum electrolysis cell anode according to claim 1, characterized in that: The treated aluminum ash includes 70-80 parts of aluminum oxide, 5-20 parts of aluminum nitride, 1-5 parts of aluminum fluoride, 0-1 part of calcium oxide, 0-1 part of silicon dioxide, 0-1 part of magnesium oxide, 0-1 part of potassium oxide, 0-1 part of sodium oxide and 0-1 part of iron oxide.

5. The anti-oxidation coating for aluminum electrolysis cell anode according to claim 1, characterized in that: The filler accounts for 50-70 wt% of the total coating.

6. The method for preparing an anti-oxidation coating for an aluminum electrolysis cell anode according to any one of claims 1 to 5, characterized in that: include: The treated aluminum ash, silicon powder and solvent are ball-milled to obtain an inorganic filler; then a solvent and a binder are added and dispersed at a rotation speed of 500-1000 rpm to obtain the anti-oxidation coating for the aluminum electrolytic cell anode.

7. 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 anodes according to any one of claims 1 to 5 onto the surface of a carbon anode with a thickness of 0.3 to 0.5 mm, drying the coating naturally for 24 to 48 hours, and reacting the coating at 800 to 1100° C. for 5 to 12 hours.

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