Heat-preservation anti-oxidation coating for anode carbon block and preparation method of heat-preservation anti-oxidation coating

Abstract

The invention relates to the technical field of aluminum electrolysis anode covering and anode carbon block coatings, and discloses a preparation method of a heat-preservation anti-oxidation coating for an anode carbon block. The heat-preservation anti-oxidation coating for the anode carbon block is composed of an anode anti-oxidation coating and a sintering covering material. The anode anti-oxidation coating is prepared from mixed aluminum oxide, ytterbium oxide, strontium oxide, plant ash, potassium sodium lithium feldspar and limestone according to the proportion through the processes of crushing and sieving, mixed pulping, acid-base adjustment, standing and aging, spraying and drying in the shade, low-temperature sintering, high-temperature activation and the like, and the anode anti-oxidation capacity can be provided for an anode. And the sintering covering material is prepared by mixing aluminum fluoride into high-aluminum refractory mortar, coating the outer layer of the anode anti-oxidation coating with the high-aluminum refractory mortar, condensing and hardening, and sintering at high temperature generated by working of an electrolytic cell, and can provide good thermal insulation performance on the premise of not influencing the working of the anode.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum electrolysis anode covering and anode carbon block coatings, and in particular to a heat-insulating and anti-oxidation coating for an anode carbon block and a preparation method thereof. Background Art

[0002] Carbon anode production is one of the important processes in modern aluminum electrolysis and is also the core component of aluminum electrolytic cells. The extra consumption of carbon anodes directly affects economic and technical indicators such as energy consumption per ton of aluminum, anode carbon consumption, and electrolytic aluminum purity. In addition, extra anode consumption will also cause damage to electrolytic equipment, reduce cell life, shorten overhaul cycles, increase greenhouse gas CO2 emissions, and carry fluoride to pollute the environment. As aluminum electrolytic cells have increasingly stringent requirements on carbon anode quality, reducing the extra consumption of carbon anodes as much as possible is an important guarantee for the normal production of large-scale electrolytic cells and achieving advanced technical and economic indicators. It is also a key issue that must be solved by various aluminum electrolytic plants to strengthen current and increase production capacity. Therefore, how to improve the antioxidant properties of aluminum electrolytic anodes has become crucial.

[0003] In response to the needs of the above-mentioned aluminum electrolysis industry, a large number of technologies for anode carbon block protective coatings have emerged, but the existing technologies have obvious defects. For example, Guangxi University's 2012 patent CN1584125A uses alumina-based materials to isolate oxygen from traditional coating technology, but requires high-temperature sintering (above 1400°C), and has problems such as high energy consumption and brittle coating and easy cracking; Chalco Zhengzhou Institute's 2024 patent CN119287452A improves conductivity by adding metals such as Cu, but it is easy to introduce impurities to pollute the electrolyte; Ningxia Weihang's patent CN119286288A uses low-temperature sintering (400-800°C) plus secondary coating technology, which has a relatively simple process but high cost; Yunnan Aluminum Co., Ltd.'s patent CN116904047B relies on magnetic separation of powdered material to remove impurities (iron content <0.002%), and the low raw material utilization rate is not conducive to environmental protection and cost reduction. Therefore, in response to the pain points of existing technologies, coatings with outstanding comprehensive capabilities that combine the advantages of high strength, good effect, low cost, simple process, and environmental friendliness have become the industry's demand direction. Summary of the invention

[0004] In order to solve the above problems, the present invention provides an anode carbon block coating with heat preservation and anti-oxidation properties and a preparation process thereof. The coating has the advantages of high density, not easy to fall off, low sintering temperature, low production energy consumption, good conductivity, not easy to introduce impurities to pollute the electrolyte, simple process, environmentally friendly raw materials, easy to obtain, and low production cost.

[0005] The technical solution of the present invention is: a method for preparing a thermal insulation and anti-oxidation coating for an anode carbon block is:

[0006] (1) 0.5% ytterbium oxide, 0.3% strontium oxide, 3% wood ash, 10% potassium sodium lithium feldspar, and 5% limestone are crushed and sieved respectively, and then slurried with 200% deionized water by weight. An appropriate amount of NaOH solution is added to adjust the pH to above 11, and then aged for 0.5 hours. After aging, HCl solution is used to neutralize the pH to 7, and the crushed and sieved mixed alumina is added and stirred to mix well. The weight percentage is 81.2%. The obtained slurry is sprayed on the electrode surface and dried in the shade at room temperature for 1-2 hours. The treated electrode is sintered at low temperature, cooled to room temperature, and activated for 12 hours (about 960°C) using the high temperature generated by the normal operation of the electrolytic cell. This is the preparation method of the anode anti-oxidation coating.

[0007] (2) High-alumina refractory mud and aluminum fluoride are mixed evenly in a weight ratio of (90-99): (1-10), and a proper amount of deionized water is added as a dispersion medium to prepare a slurry, which is evenly coated on the surface of the anode anti-oxidation coating. After solidification, the sintering is carried out at a high temperature generated by the normal operation of the electrolytic cell for 12 hours. This is the preparation method of the sintered covering material.

[0008] Wherein, the weight percentage of the mixed alumina in (1) is 20-40% α-alumina and 60-80% γ-alumina.

[0009] Among them, the mesh sizes of the mixed alumina, ytterbium oxide, strontium oxide, wood ash, potassium sodium lithium feldspar and limestone crushed and sieved in (1) are 800 mesh, 1200 mesh, 600 mesh, 500 mesh, 500 mesh and 500 mesh respectively.

[0010] Wherein, the concentration of the NaOH solution in (1) is 5 mol / L, and the concentration of the HCl solution is 5 mol / L.

[0011] Wherein, the low-temperature sintering temperature in (1) is 300-600°C, the heating rate is 5-10°C / min, and the holding time is greater than 3h.

[0012] Among them, (1) during medium and high temperature activation, the heating rate of the anode carbon block is 5-10°C / min; (2) during medium and high temperature sintering, the heating rate of the anode carbon block is 5-10°C / min.

[0013] The spraying method of the anodic anti-oxidation coating in (1) is multiple spraying and shade drying, the number of times should be greater than or equal to 3 times, and the spraying thickness is 0.1-0.3mm; the thickness of the sintered covering material in (2) is 10-15mm.

[0014] The slurry in (1) is sprayed using a sprayer, and the particle size of the spray is 10-30 μm.

[0015] The anode carbon block obtained by the preparation method is used in electrolytic aluminum with thermal insulation and anti-oxidation coating.

[0016] The technical effect of the present invention is as follows: the anodic anti-oxidation coating of the present invention uses mixed alumina as the main skeleton, the α-alumina in the mixed alumina has high stability, strong corrosion resistance, and good mechanical properties to ensure the integrity of the structure, and the γ-alumina has good ionic conductivity to ensure the conductivity of the coating layer; ytterbium oxide as a grain boundary strengthener can inhibit the abnormal growth of alumina grains to form a Y-Al-O solid solution to improve thermal shock resistance, and reacts with SiO2 at high temperature to form a YSiO7 glass phase to fill the pores; strontium oxide is used as a sintering aid to reduce the eutectic temperature, Sr 2 + Ionic radius and Al 3 + large difference, resulting in lattice distortion, promoting material migration in the liquid phase sintering stage; wood ash is a low-cost industrial residue waste, which can achieve waste recycling and conform to the concept of green chemistry. It is a natural silicate mineral (containing K2O8-12%, SiO250-60%), providing K + The conductivity of the ion-enhanced coating contains CaO to promote carbonate decomposition (react with CO2 to form a CaCO3 buffer layer), and the organic carbon residue forms a nanocarbon skeleton (pyrolysis below 500°C) to provide strength for the main body; potassium-sodium-lithium feldspar forms a continuous glassy sealing layer at high temperature to improve the compactness of the main body; the CaO produced when the limestone is heated and decomposed reacts with SiO2 to form CaSiO3, which is also part of the main structure. The purpose of crushing and screening in the process is to reduce the particle size as much as possible while controlling the cost at a low level, to prevent the pipeline from being blocked during spraying, and to avoid the formation of stress concentration points during sintering; the purpose of adjusting the acid and alkali is to promote the hydrolysis of SrO to form Sr(OH)2 colloid during aging, to form a three-dimensional flocculation network to improve the uniformity and stability of the main body; in order to inhibit the formation of hard agglomerates, it is necessary to initially sinter at a low temperature to initially obtain a three-dimensional network skeleton, and then use the high temperature generated by the normal operation of the electrolytic cell for 12 hours to promote the reconstruction of the crystal phase, form a continuous glass phase network, and promote structural densification. The coating formed by low-temperature sintering and high-temperature activation has high density and is not easy to fall off; the low sintering temperature means low production energy consumption, and the high-temperature activation generated by the normal operation of the electrolytic cell saves time and energy; the frame with alumina as the main body has good electrical conductivity and is not easy to introduce impurities to pollute the electrolyte; the production process is simple, the raw materials are easy to obtain and the total price is low, and the use of industrial residue waste wood ash is also conducive to environmental protection.

[0017] The sintered covering material is prepared by mixing aluminum fluoride into high-aluminum refractory mud and coating it on the outer layer of the anode anti-oxidation coating to solidify and harden, and then sintering it at high temperature generated by the operation of the electrolytic cell. It is distributed on the upper layer of the carbon anode that does not contact the electrolyte, and on the surface of the steel claw above the carbon anode. The difference from the traditional thermal insulation coating is that aluminum fluoride is mixed into the high-aluminum refractory mud, and after sintering, it forms a stable Al2O3-AlF3 solid solution with the anode anti-oxidation coating layer, which reduces chemical erosion at the interface, enhances its adhesion, and is not prone to aging and shedding while keeping the heat. DETAILED DESCRIPTION

[0018] To better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be understood by those skilled in the art that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0019] Example 1

[0020] 0.5% ytterbium oxide, 0.3% strontium oxide, 3% plant ash, 10% potassium sodium lithium feldspar, and 5% limestone are crushed and sieved respectively, and the mesh numbers of the crushed and sieved are 1200 mesh, 600 mesh, 500 mesh, 500 mesh, and 500 mesh respectively. 200% deionized water is added to make pulp, and a proper amount of 3mol / L_NaOH solution is added to adjust the pH to above 11, and then it is left to stand for 0.5h. After aging, a 3mol / L_HCl solution is used to neutralize the pH to 7, and the mixed alumina with a mesh number of 800 mesh after crushing and sieving is added and stirred and mixed, and the weight percentage is 81.2%. The components of the mixed alumina are 20% by weight of α-alumina and 80% of γ-alumina. The obtained slurry was sprayed on the surface of anode carbon blocks with a size of 400×400×1100mm in the laboratory and dried in the shade at room temperature for 2 hours. The spraying was repeated 3 times using a sprayer and dried in the shade. The particle size of the spray was controlled between 10-15μm and the thickness of the spray was 0.1mm. The treated electrode was sintered at 500℃ with a heating rate of 5℃ / min.

[0021] The high-alumina refractory mud and aluminum fluoride were mixed evenly in a weight ratio of 90:10, and a proper amount of deionized water was added as a dispersion medium to prepare a slurry, which was evenly coated on the upper surface of the anode carbon block with an area of ​​400×1100mm after the above treatment, with a thickness of 10mm. After coagulation and hardening, the high temperature (about 960℃) generated by the normal operation of the electrolytic cell was used to activate the anode anti-oxidation coating and sinter the sintering covering material for 12 hours, and the heating rate was 5℃ / min.

[0022] Example 2

[0023] The thermal insulation and anti-oxidation coating for the anode carbon block was prepared in the manner of Example 1, except that the ratio of α-alumina to γ-alumina was 40 g:60 g.

[0024] Example 3

[0025] The anodic anti-oxidation coating was prepared in the same manner as in Example 2, except that the thickness of the anodic anti-oxidation coating layer was 0.3 mm.

[0026] Example 4

[0027] The anode anti-oxidation coating was prepared in the manner of Example 2, except that the ratio of high-alumina refractory clay to aluminum fluoride was 99 g:1 g.

[0028] Example 5

[0029] The anode anti-oxidation coating was prepared in the same manner as in Example 4, except that the thickness of the sintered covering material was 15 mm.

[0030] The preparation parameters of Examples 1-5 are shown in Table 1: Preparation parameters of Examples 1-5.

[0031] Table 1: Preparation parameters of Examples 1-5

[0032]

[0033]

[0034] Comparative Example 1

[0035] An anode carbon block with a size of 400×400×1100 mm for laboratory use without any treatment was used as experimental control example 1.

[0036] Comparative Example 2

[0037] The anode carbon block coating is prepared using the carbon anode coating preparation method provided by CN1584125A. The specific preparation steps are as follows:

[0038] 40g of 15% aluminum hydroxide sol by mass, 40g of α-alumina with a particle size of less than 165μm through a 100 mesh sieve, 10g of α-alumina with a particle size of less than 10μm through a 2000 mesh sieve, 0.5g of AlF3 powder with a particle size of less than 74μm through a 200 mesh sieve, 0.5g of Li2CO3 powder with a particle size of less than 74μm through a 200 mesh sieve, 0.5g of boron nitride powder with a particle size of less than 74μm through a 200 mesh sieve, 1g of boron oxide powder with a particle size of less than 165μm through a 100 mesh sieve, and 5g of a polyvinyl alcohol solution with a mass percentage concentration of 20% are mixed evenly to prepare a coating slurry. The obtained slurry is coated on the surface of an anode carbon block with a specification of 400×400×1100mm for laboratory use, with a thickness of 0.1mm, left for 10 hours, and dried naturally. As experimental control example 2.

[0039] Comparative Example 3

[0040] The anodic anti-oxidation coating was prepared in the same manner as in Example 2, except that aluminum fluoride was not added to the formulation.

[0041] The resistivity at both ends of the center point of the anode carbon block with an area of ​​400×400mm at both ends in Example 1-5 and Control Example 1-3 was measured to evaluate the conductivity of the coating layer. The anode carbon block was directly exposed to the air, and an adjustable DC regulated power supply was used to apply a voltage of 50V and a current of 5A to both ends of the untreated anode carbon block and the treated anode carbon blocks in Example 1-11 and Control Example 1-2 to simulate the overload operation of the anode carbon block. After 10 minutes, the power was turned off, and after cooling to room temperature, the coating layer at both ends was polished off to measure the resistivity at both ends of the anode carbon block in each case. Three experiments were conducted in parallel for each type of anode carbon block, and the results were taken as the average of the three experiments. The final results are shown in Table 2: Resistivity of anode carbon blocks.

[0042] Table 2: Resistivity of anode carbon blocks

[0043]

[0044] Oxidation of the anode carbon block will change its internal structure, resulting in a change in resistivity. The higher the degree of oxidation, the greater the resistivity of the anode carbon block. Comparing the resistivity of Examples 1-5 and Comparative Examples 1-3, it can be seen that the thermal insulation and anti-oxidation coating prepared by the preparation method of this patent can significantly reduce the degree of oxidation of the anode carbon block, and the effect is significantly better than that of traditional anti-oxidation coatings.

[0045] The aging degree of the coating is evaluated with the help of a polarizing microscope. Under a polarizing microscope, cracks and shedding caused by aging of the coating surface will produce abnormal birefringence due to structural damage. If the birefringence phenomenon is obvious and the interference color changes strongly, it means that the cracks or peeling have a great influence on the optical properties of the coating surface, and the intensity may be low, and the aging phenomenon is more likely to deepen further. The detached coating layer is collected and weighed to evaluate the degree of contamination of the electrolyte by the detachment of the coating. Three experiments were conducted in parallel for each type of anode carbon block, and the results were taken as the average of the three experiments. The results are shown in Table 3: Coating aging evaluation.

[0046] Table 3: Coating aging evaluation

[0047]

[0048] The strength of the anode protective layer itself and the strength of its bonding with the anode carbon block are closely related to the aging rate of the anode protective layer. The coating prepared by this patented method is more stable and resistant to aging than traditional coatings. Less peeling and peeling can also reduce the impact on production, and less dust is generated due to high temperature and high current during operation. At the same time, due to the high adhesion, high strength, and high oxidation resistance of the coating, the anode anti-oxidation coating can also provide protection for the steel claws above the carbon anode.

[0049] The time required for the side coated with the sintered covering material to cool naturally from 500°C to 300°C after the power is turned off in the above experiment is measured using a thermocouple thermometer to evaluate the thermal insulation capacity of the coating. The longer the time required, the better the thermal insulation capacity of the material. Three experiments were conducted in parallel for each type of anode carbon block, and the results were taken as the average of the three experiments. The results are shown in Table 4: Time required for the anode carbon block to cool from 500°C to 300°C.

[0050] Table 4: Time required for anode carbon block to cool from 500℃ to 300℃

[0051]

[0052] It can be seen from Table 4 that the low-temperature sintered covering material layer can significantly improve the thermal insulation capacity of the anode carbon block.

[0053] From Tables 1-4, the present invention can significantly enhance the anti-oxidation and heat preservation capabilities of the anode carbon block and reduce the working power consumption of the electrode; the high density and high mechanical strength allow the coating to have a longer service life and reduce the pollution to the electrolyte.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a thermal insulation and anti-oxidation coating for an anode carbon block, characterized in that: The preparation method is: (1) Grind and sieve 0.5% ytterbium oxide, 0.3% strontium oxide, 3% wood ash, 10% potassium sodium lithium feldspar, and 5% limestone in weight percentage, add 200% deionized water to make pulp, add appropriate amount of NaOH solution to adjust the pH to above 11, and then let it stand for 0.5h. After aging, use HCl solution to neutralize the pH to 7, add the crushed and sieved mixed alumina, stir and mix, the weight percentage is 81.2%. Spray the obtained slurry on the surface of the electrode and dry it in the shade at room temperature for 1-2h. Sinter the treated electrode at low temperature, cool to room temperature, and activate it at the high temperature generated by the normal operation of the electrolytic cell for 12h (about 960°C). This is the preparation method of the anode antioxidant coating; (2) High-alumina refractory mud and aluminum fluoride are mixed evenly in a weight ratio of (90-99): (1-10), and a proper amount of deionized water is added as a dispersion medium to prepare a slurry, which is evenly coated on the surface of the anode anti-oxidation coating. After solidification, the sintering is carried out at a high temperature generated by the normal operation of the electrolytic cell for 12 hours. This is the preparation method of the sintered covering material.

2. The method for preparing the thermal insulation and anti-oxidation coating for anode carbon blocks according to claim 1, characterized in that: The weight percentage of the mixed alumina in (1) is 20-40% α-alumina and 60-80% γ-alumina.

3. The method for preparing the thermal insulation and anti-oxidation coating for anode carbon blocks according to claim 1, characterized in that: The mesh sizes of the mixed alumina, ytterbium oxide, strontium oxide, wood ash, potassium sodium lithium feldspar and limestone crushed and sieved in (1) are 800 mesh, 1200 mesh, 600 mesh, 500 mesh, 500 mesh and 500 mesh respectively.

4. The method for preparing the thermal insulation and anti-oxidation coating for anode carbon blocks according to claim 1, characterized in that: The concentration of the NaOH solution in (1) is 5 mol / L, and the concentration of the HCl solution is 5 mol / L.

5. The method for preparing the thermal insulation and anti-oxidation coating for anode carbon blocks according to claim 1, characterized in that: The low-temperature sintering temperature in (1) is 300-600°C, the heating rate is 5-10°C / min, and the heat preservation time is greater than 3h.

6. The method for preparing the thermal insulation and anti-oxidation coating for anode carbon blocks according to claim 1, characterized in that: During the (1) medium-high temperature activation, the heating rate of the anode carbon block is 5-10°C / min; during the (2) medium-high temperature sintering, the heating rate of the anode carbon block is 5-10°C / min.

7. The method for preparing the thermal insulation and anti-oxidation coating for anode carbon blocks according to claim 1, characterized in that: The spraying method of the anode anti-oxidation coating in (1) is multiple spraying and shade drying, the number of times should be greater than or equal to 3 times, and the spraying thickness is 0.1-0.3mm; the thickness of the sintered covering material in (2) is 10-15mm.

8. The method for preparing the thermal insulation and anti-oxidation coating for anode carbon blocks according to claim 1, characterized in that: The slurry in (1) is sprayed using a sprayer, and the particle size of the spray is 10-30 μm.

9. Application of thermal insulation and anti-oxidation coating for anode carbon block obtained by the preparation method according to any one of claims 1 to 8 in electrolytic aluminum.

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