A multi-element cermet inert anode for electrolytic aluminum and a preparation method and application thereof

Abstract

The application discloses a multi-element cermet inert anode for electrolytic aluminum and a preparation method and application thereof, and belongs to the technical field of cermet composite material preparation, and the multi-element cermet inert anode comprises an oxide ceramic phase, a metal conductive phase and a rare earth modifier; the oxide ceramic phase comprises an AB2O4 type spinel oxide ceramic, the metal conductive phase comprises a Cu-Ni alloy, and the rare earth modifier comprises CeO2 or Y2O3; the preparation method comprises seven steps of preparing a ceramic phase precursor mixed powder, preparing a Cu-Ni alloy powder, mixing and granulating, preparing a green body, two-step sintering, oxidation treatment and mechanical processing. Through the synergy of the specific cermet composite design and the rare earth modification and the two-step sintering process, the bottleneck that the existing inert anode material is difficult to consider the conductivity, corrosion resistance and mechanical performance at the same time is effectively broken through.

Description

Technical Field

[0001] This invention belongs to the field of metal-ceramic composite material preparation technology, specifically relating to a multi-element metal-ceramic inert anode for electrolytic aluminum, its preparation method, and its application. Background Technology

[0002] Aluminum is the world's most consumed non-ferrous metal, with a global annual production exceeding 70 million tons. Current industrial electrolytic aluminum production generally employs the Hall-Herut process, using consumable prebaked carbon anodes. Electrolysis takes place in cryolite-alumina molten salt at approximately 1000°C. The carbon anode is consumed as a reactant; approximately 400-500 kg of carbon anodes are consumed and about 1.5 tons of CO2 are emitted for every ton of aluminum produced. Furthermore, the manufacture of carbon anodes requires large quantities of coal tar pitch, is complex and costly, and involves frequent anode replacements, severely impacting the stable operation of the electrolytic cell. Replacing the prebaked carbon anodes with inert anodes, which do not react with oxygen anions, can not only reduce CO2 emissions and generate O2 for recycling, but also reduce electrode consumption, significantly saving costs, increasing electrolytic cell capacity, and providing technical support for zero-carbon electrolytic aluminum production.

[0003] Currently, inert anodes are mainly divided into three categories: oxide ceramics, metal alloys, and metal-ceramic composites. Oxide ceramics, represented by NiFe2O4, have good corrosion resistance, but low high-temperature conductivity (<100S / cm) and insufficient mechanical strength. Metal alloys, represented by Cu-Ni-Fe alloys, have good conductivity and processability, but poor corrosion resistance, and the metal dissolves into the molten salt, severely contaminating the aluminum melt. Metal-ceramic composites combine the advantages of both and are currently the most promising direction for industrialization, but there are still significant shortcomings in the synergistic optimization of conductivity, corrosion resistance, and mechanical properties.

[0004] Patent CN1443877A discloses a metal-based inert anode based on a binary or multi-element alloy system of metals such as chromium, nickel, iron, and cobalt. While it exhibits good conductivity, the alloy components continuously dissolve into the molten salt during long-term electrolysis, causing excessive levels of impurities such as Fe and Ni in the aluminum melt, thus affecting the quality of the aluminum product. Patent CN117816964A discloses a method for preparing a metal-ceramic inert anode assembly. By connecting the guide rod to the anode blank with foamed nickel, the connection reliability is improved, but the synergistic optimization of the anode material's corrosion resistance and high conductivity is not resolved. Patent CN 117403279A discloses a rare-earth modified metal-ceramic inert anode composite material for aluminum electrolysis. By doping a high-entropy alloy with thermal shock resistance, corrosion resistance, and high conductivity into a spinel ceramic matrix instead of an ordinary alloy and adding a large amount of rare-earth metals, the conductivity of the inert anode material can be significantly improved while ensuring the annual corrosion rate required for aluminum electrolysis. However, the high production cost hinders large-scale industrial application.

[0005] Therefore, there is an urgent need in this field for a novel inert anode material and its electrolysis process that combines high electrical conductivity, low corrosion rate, high mechanical strength, and low production cost, and whose preparation process can be scaled up industrially. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a multi-metal ceramic inert anode for electrolytic aluminum, its preparation method, and its application.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A multi-element metal-ceramic inert anode for electrolytic aluminum includes an oxide ceramic phase, a metallic conductive phase, and a rare earth modifier; the oxide ceramic phase includes AB2O4 type spinel oxide ceramic, the metallic conductive phase includes Cu-Ni alloy, and the rare earth modifier includes CeO2 or Y2O3.

[0009] A further improvement of the technical solution of the present invention is that the mass ratio of the oxide ceramic phase to the metal conductive phase is 65~80:20~35, and the amount of rare earth modifier added is 0.5%~3.0% of the total mass of the oxide ceramic phase and the metal conductive phase.

[0010] A further improvement of the technical solution of the present invention is that the AB2O4 type spinel oxide ceramic is NiFe2O4; and the mass ratio of Cu to Ni in the metallic conductive phase is 1.5 to 2.5:1.

[0011] A further improvement of the technical solution of the present invention is that the average grain size of the NiFe2O4 spinel ceramic phase is 2-8 μm; the Cu-Ni alloy phase is uniformly distributed at the ceramic phase grain boundaries with connectivity ≥85%; and a composite oxide protective film is distributed on the outer surface of the multi-element metal ceramic inert anode, the protective film having a thickness of 10-50 μm and a porosity ≤2%.

[0012] A further improvement of the technical solution of the present invention is that the relative density of the multi-element metal ceramic inert anode is ≥97%, the conductivity at 900℃ is ≥800S / cm, and the corrosion rate in the cryolite molten salt system is ≤3 mm / year.

[0013] A further improvement of the technical solution of the present invention is that the multi-element metal ceramic inert anode adopts a gradient functional material structure, including a core layer, a transition layer and a surface layer, each layer having a thickness of 5 to 40 mm; the mass fraction of the oxide ceramic phase in the core layer is 15% to 25%, the mass fraction of the oxide ceramic phase in the transition layer is 45% to 55%, and the mass fraction of the oxide ceramic phase in the surface layer is ≥80%.

[0014] This invention also discloses a method for preparing a multi-metal ceramic inert anode for electrolytic aluminum, comprising the following steps:

[0015] S1. Mix NiO powder, Fe2O3 powder and rare earth oxides according to the mass ratio to obtain ceramic phase precursor mixed powder;

[0016] S2. Preparation of Cu-Ni alloy powder;

[0017] S3. Mix the ceramic phase precursor powder obtained in S1 with the Cu-Ni alloy powder obtained in S2, add an appropriate amount of molding aid, wet ball mill to mix evenly, and spray dry to granulate.

[0018] S4. Prepare green bodies from the particles obtained in S3;

[0019] S5. The green body prepared in S4 is sintered in two steps under atmosphere protection.

[0020] S6. Oxidize the sintered body;

[0021] S7. The sintered body prepared in S6 is precision machined to the target size, and the anode guide rod is installed to obtain the finished inert anode.

[0022] Further, in step S1, ball milling is used for mixing, with ZrO2 balls as the milling medium, a ball-to-material ratio of 3:1, a rotation speed of 200-300 rpm, and mixing for 8-12 h; the BET specific surface area of ​​the ceramic phase precursor powder is 8-15 m² / g.

[0023] Furthermore, in step S2, Cu-Ni alloy powder is prepared by gas atomization, and the particle size of the prepared Cu-Ni alloy powder is 10-45 μm.

[0024] Further, in step S3, the molding aid is polyvinyl alcohol, and the amount added is 1.5% to 2.5% of the total mass of the oxide ceramic phase and the metal conductive phase.

[0025] Furthermore, in step S4, a green blank is prepared by cold isostatic pressing, with an operating pressure of 200-300 MPa and a holding time of 2-5 min;

[0026] Further, the sintering process in step S5 is as follows: first, pre-fire at 900-1000℃ for 1-2 h in an air atmosphere to synthesize NiFe2O4 in situ from NiO and Fe2O3; then, sinter at 1200-1350℃ for 2-4 h in a mixed reducing atmosphere of H2 and Ar to complete densification; the sintering heating rate is 2-5℃ / min, and the cooling rate is ≤3℃ / min.

[0027] Further, in step S6, the sintered body is oxidized in an air atmosphere at 800-900°C for 1-3 h to generate a dense protective composite oxide film layer with a thickness of 10-50 μm in situ on the surface.

[0028] This invention also discloses the application of the aforementioned multi-metal ceramic inert anode for aluminum electrolysis in the aluminum electrolysis process, as detailed below:

[0029] Electrolyte system: Low-temperature, low cryolite ratio electrolyte is used, with the composition of NaF-AlF3-Al2O3 and a molecular ratio of 2.0 to 2.4. 2% to 4% CaF2 and 1% to 3% MgF2 are added to the electrolyte as additives.

[0030] Operating temperature: Electrolysis temperature is controlled at 870℃~930℃;

[0031] Current density: Anode current density is 0.6–1.2 A / cm²;

[0032] Electrode spacing: The distance between the anode and cathode is maintained at 3-5 cm, using the multi-element metal ceramic inert anode and graphitized cathode prepared in this invention;

[0033] The current efficiency of aluminum is ≥92%, and the DC power consumption per ton of aluminum is ≤12500 kWh / t;

[0034] Anode gas management: The generated O2 is collected by a sealed electrolytic cell, and the tail gas is discharged after treatment. The anode bubble separation efficiency is ≥95%.

[0035] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0036] This invention effectively overcomes the bottleneck of existing inert anode materials that struggle to balance conductivity, corrosion resistance, and mechanical properties by combining metal-ceramic composite structure design, rare earth grain boundary modification, and a two-step sintering process.

[0037] This invention utilizes a Cu-Ni alloy phase to construct a three-dimensional interconnected conductive network in a ceramic matrix. The conductivity remains ≥950 S / cm at a high temperature of 900℃, fully meeting the requirements of industrial electrolysis.

[0038] The rare earth modified components of this invention segregate and accumulate at the grain boundaries of the material, which not only enhances the corrosion resistance of the grain boundaries but also promotes the formation of a dense and stable protective film on the anode surface. The resulting anode has an annual corrosion rate of ≤3 mm in the cryolite molten salt system, which is more than 50% lower than the corrosion rate of the sample without rare earth modification. While ensuring high conductivity, it significantly reduces the dissolution of anode metal components and effectively suppresses the problem of impurity contamination of electrolytic aluminum melt.

[0039] The anode prepared by the present invention using a two-step sintering process has high density, relative density ≥97%, flexural strength ≥80MPa, and excellent overall mechanical properties, which can meet the requirements of industrial electrolysis.

[0040] The gradient functional material structure multi-element metal ceramic inert anode prepared by this invention exhibits superior thermal shock resistance and corrosion rate compared to traditional metal alloy inert anodes. It can withstand more than 20 cycles of water quenching at 300℃ without cracking or breakage. While inheriting the high conductivity advantage of metal alloy inert anodes, it effectively solves the defect of traditional metal anodes contaminating aluminum liquid. It can withstand the high temperature environment and frequent temperature changes of the electrolytic cell for a long time, maintain the integrity of the anode structure, and extend the service life of the anode.

[0041] This invention, combined with a low-temperature, low-crystal-ratio electrolysis process, reduces CO2 emissions per ton of aluminum by ≥90% compared to the traditional carbon anode process, achieving near-zero carbon emissions in the aluminum electrolysis process and possessing significant environmental value.

[0042] The raw materials used in the preparation of this invention are abundant and have wide procurement channels; the molding adopts a mature cold isostatic pressing process, and the matching two-step sintering process parameters are stable and the process is controllable. The whole preparation process is simple and easy to carry out, easy to scale up mass production, and has good economic value and industrial application prospects. Attached Figure Description

[0043] Figure 1 This is an electron microscope image of the multi-element metal-ceramic inert anode of Example 1;

[0044] Figure 2 The image shows an electron microscope image of the multi-metal ceramic inert anode of Comparative Example 1.

[0045] Figure 3 This is an electron microscope image of the multi-element metal ceramic inert anode of Comparative Example 2. Detailed Implementation

[0046] The present invention will be further described in detail below through specific embodiments. It should be understood that the described embodiments are only for explaining the present invention and do not limit the present invention. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with those documents. In the event of any conflict with any incorporated document, the content of this specification shall prevail.

[0047] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0048] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0049] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the instruments and equipment used in the following examples are all conventional laboratory instruments and equipment; unless otherwise specified, the experimental materials used in the following examples were all purchased from conventional biochemical reagent stores.

[0050] The following examples use NiO powder with a purity ≥99.5% and a particle size of 1-3 μm; Fe2O3 powder with a purity ≥99.5% and a particle size of 1-3 μm; CeO2 powder with a purity ≥99.0% and a particle size ≤12 μm; and Y2O3 powder with a purity ≥99.0% and a particle size ≤6 μm.

[0051] Example 1

[0052] The following is a method for preparing a multi-metal ceramic inert anode for electrolytic aluminum in this embodiment:

[0053] Raw material formula (parts by weight): 22.0 parts NiO powder, 47.0 parts Fe2O3 powder, 1.5 parts CeO2 powder, 29.5 parts Cu-Ni alloy powder (Cu:Ni=2:1).

[0054] Preparation steps:

[0055] S1. The above-mentioned mass fractions of NiO, Fe2O3 and CeO2 mixed powder were added to a ball mill (ZrO2 grinding balls, ball-to-material ratio 3:1) and ball-milled at 240 rpm for 10 h to obtain ceramic phase precursor mixed powder; the BET specific surface area of ​​the ceramic phase precursor mixed powder was measured to be 11.3 m² / g.

[0056] S2. The Cu-Ni alloy powder of the above mass fraction was prepared by gas atomization method, and the resulting Cu-Ni alloy powder had a particle size of 10-45 μm.

[0057] S3. Mix the ceramic phase precursor powder prepared in S1 with the Cu-Ni alloy powder prepared in S2, add 2.0 parts of polyvinyl alcohol, wet ball mill for 4 hours to mix, and spray dry and granulate at 180℃ to obtain particles with a particle size of 80-200 μm.

[0058] S4. The granules obtained in S3 are loaded into a rubber mold and held under pressure at 250 MPa for 3 minutes to obtain a green compact.

[0059] S5. Sinter the green body prepared in S4 in two steps: ① In an air atmosphere, heat to 950℃ at 3℃ / min and hold for 1.5 h; ② In a H2 / Ar mixed gas (H2 volume percentage 5%), heat to 1280℃ at 3℃ / min and hold for 3 h; cooling rate 2℃ / min.

[0060] S6. The sintered body prepared in S5 is kept at 850℃ in air atmosphere for 2 h to form a composite oxide film layer with a thickness of about 50 μm on the surface.

[0061] S7. Machining the sintered body prepared in S6 to standard dimensions, and installing the guide rod.

[0062] Finished product testing: relative density 97.8%, electrical conductivity at 900℃ 1020 S / cm, flexural strength 92 MPa, corrosion rate 2.3 mm / year. Figure 1 As shown: the average grain size of the NiFe2O4 spinel ceramic phase is 2-8 μm; the Cu-Ni alloy phase is uniformly distributed at the ceramic phase grain boundaries with a connectivity ≥85%; CeO2 is uniformly distributed at the grain boundaries.

[0063] Example 2

[0064] The following is a method for preparing a multi-metal ceramic inert anode for electrolytic aluminum in this embodiment:

[0065] Raw material formula (parts by weight): 24.6 parts NiO powder, 52.6 parts Fe2O3 powder, 2.9 parts CeO2 powder, 19.9 parts Cu-Ni alloy powder (Cu:Ni=2.5:1).

[0066] Preparation steps:

[0067] S1. The above-mentioned mass fractions of NiO, Fe2O3 and CeO2 mixed powder were added to a ball mill (ZrO2 grinding balls, ball-to-material ratio 3:1) and ball-milled at 300 rpm for 8 hours to obtain ceramic phase precursor mixed powder; the BET specific surface area of ​​the ceramic phase precursor mixed powder was measured to be 8.3 m² / g.

[0068] S2. The Cu-Ni alloy powder of the above mass fraction was prepared by gas atomization method, and the resulting Cu-Ni alloy powder had a particle size of 10-45 μm.

[0069] S3. Mix the ceramic phase precursor powder prepared in S1 with the Cu-Ni alloy powder prepared in S2, and add 2.4 parts of polyvinyl alcohol. Mix by wet ball milling for 4 hours, and then spray dry and granulate at 180℃. The particle size is 80-200 μm.

[0070] S4. The granules obtained in S3 are loaded into a rubber mold and held under pressure at 200 MPa for 5 minutes to obtain a green compact.

[0071] S5. Sinter the green body prepared in S4 in two steps: ① In an air atmosphere, heat to 900℃ at 2℃ / min and hold for 2h; ② In a H2 / Ar mixed gas (5% H2), heat to 1200℃ at 5℃ / min and hold for 4h; cooling rate 3℃ / min.

[0072] S6. The sintered body prepared in S5 is kept at 800℃ in air atmosphere for 3 hours to form a composite oxide film layer with a thickness of about 25μm on the surface.

[0073] S7. Machining the sintered body prepared in S6 to standard dimensions, and installing the guide rod.

[0074] Finished product testing: relative density 97.9%, electrical conductivity at 900℃ 1018 S / cm, flexural strength 93 MPa, corrosion rate 2.4 mm / year.

[0075] Example 3

[0076] The following is a method for preparing a multi-metal ceramic inert anode for electrolytic aluminum in this embodiment:

[0077] Raw material formula (parts by weight): 20.7 parts NiO powder, 44.3 parts Fe2O3 powder, 0.5 parts CeO2 powder, 34.5 parts Cu-Ni alloy powder (Cu:Ni=1.5:1).

[0078] Preparation steps:

[0079] S1. Add the above-mentioned mass fractions of NiO, Fe2O3 and CeO2 mixed powder to a ball mill (ZrO2 grinding balls, ball-to-material ratio 3:1) and ball mill at 200 rpm for 12 h to obtain ceramic phase precursor mixed powder; take a sample and measure the BET specific surface area of ​​the ceramic phase precursor mixed powder to be 14.8 m² / g.

[0080] S2. The Cu-Ni alloy powder of the above mass fraction was prepared by gas atomization method, and the resulting Cu-Ni alloy powder had a particle size of 10-45 μm.

[0081] S3. Mix the ceramic phase precursor powder prepared in S1 with the Cu-Ni alloy powder prepared in S2, add 1 part of polyvinyl alcohol, wet ball mill for 4 hours to mix, and spray dry and granulate at 180℃ to obtain particles with a particle size of 80-200 μm.

[0082] S4. The granules obtained in S3 are loaded into a rubber mold and held under pressure at 300 MPa for 2 minutes to obtain a green compact.

[0083] S5. Sinter the green body prepared in S4 in two steps: ① In an air atmosphere, heat to 1000℃ at 5℃ / min and hold for 1 h; ② In a H2 / Ar mixed gas (5% H2), heat to 1350℃ at 2℃ / min and hold for 2 h; cooling rate 1℃ / min.

[0084] S6. The sintered body prepared in S5 is kept at 900℃ in air atmosphere for 1 h to form a composite oxide film layer with a thickness of about 10 μm on the surface.

[0085] S7. Machining the sintered body prepared in S6 to standard dimensions, and installing the guide rod.

[0086] Finished product testing: relative density 97.7%, electrical conductivity at 900℃ 1023 S / cm, flexural strength 95 MPa, corrosion rate 2.2 mm / year.

[0087] Example 4

[0088] In Example 1, CeO2 was replaced with an equal mass of Y2O3, while the rest of the formulation and process parameters remained the same.

[0089] Finished product test results: relative density 97.5%, electrical conductivity at 900℃ 980 S / cm, flexural strength 88 MPa, corrosion rate 2.6 mm / year. The modification effect of Y2O3 is comparable to that of CeO2, and the multi-element metal ceramic inert anodes prepared by both meet the requirements for industrial applications.

[0090] Example 5

[0091] The following is a method for preparing a graded functional material structure multi-element metal-ceramic inert anode for electrolytic aluminum in this embodiment:

[0092] Raw material formula (parts by weight):

[0093] Core layer: 6.4 parts NiO powder, 13.6 parts Fe2O3 powder, 80 parts Cu-Ni alloy powder (Cu:Ni=2:1);

[0094] Transition layer: 15.9 parts NiO powder, 34.1 parts Fe2O3 powder, and 50 parts Cu-Ni alloy powder (Cu:Ni=2:1);

[0095] Surface layer: 25.0 parts NiO powder, 53.5 parts Fe2O3 powder, 1.5 parts CeO2 powder, 20.0 parts Cu-Ni alloy powder (Cu:Ni=2:1);

[0096] Preparation steps:

[0097] S1. Add the above-mentioned mass fractions of the mixed powder of each layer to a ball mill (ZrO2 grinding balls, ball-to-material ratio 3:1) and ball mill at 240 rpm for 10 h to obtain the mixed powder of ceramic phase precursor of each layer; take samples of each layer and measure the BET specific surface area of ​​the mixed powder of ceramic phase precursor to be 10.5 m² / g, 11.3 m² / g and 10.8 m² / g respectively.

[0098] S2. Cu-Ni alloy powder of the above mass fractions for each layer is prepared by gas atomization method, and the resulting Cu-Ni alloy powder has a particle size of 10-45 μm.

[0099] S3. Mix the ceramic phase precursor powders prepared in S1 with the corresponding Cu-Ni alloy powders prepared in S2. Add 2.0 parts of polyvinyl alcohol according to the ratio, and after wet ball milling for 4 hours to mix thoroughly, spray dry and granulate at 180℃ to obtain powder particles of each layer. The particle size of the obtained particles is 80-200μm.

[0100] S4. The particles obtained in S3 are loaded into the rubber mold in sequence, with the core layer being 30 mm thick, the transition layer being 10 mm thick, and the surface layer being 10 mm thick. The mold is then held under pressure at 250 MPa for 3 minutes to obtain the green body.

[0101] S5. Sinter the green body prepared in S4 in two steps: ① In an air atmosphere, heat to 950℃ at 3℃ / min and hold for 1.5 h; ② In a H2 / Ar mixed gas (5% H2), heat to 1280℃ at 3℃ / min and hold for 3 h; cooling rate 2℃ / min.

[0102] S6. The sintered body prepared in S5 is kept at 850℃ in air atmosphere for 2 h to form a composite oxide film layer with a thickness of about 50 μm on the surface.

[0103] S7. Machining the sintered body prepared in S6 to standard dimensions, and installing the guide rod.

[0104] Finished product test results: No cracking after 28 cycles of water quenching at 300℃, corrosion rate of 1.8 mm / year, and core conductivity of 1500 S / cm at 900℃.

[0105] Compared to traditional metal alloy inert anodes, the gradient functional material structure multi-metal ceramic inert anode of this invention has superior thermal shock resistance and low corrosion rate. While inheriting the high conductivity advantage of metal alloy inert anodes, it effectively solves the defect of traditional metal anodes contaminating molten aluminum.

[0106] Example 6

[0107] The difference from Example 5 lies in the different mass fractions of the raw materials in each layer, as detailed below:

[0108] Core layer: 4.8 parts NiO powder, 10.2 parts Fe2O3 powder, 85 parts Cu-Ni alloy powder (Cu:Ni=2.5:1);

[0109] Transition layer: 20.7 parts NiO powder, 44.3 parts Fe2O3 powder, and 45 parts Cu-Ni alloy powder (Cu:Ni=2.5:1);

[0110] Surface layer: 27.8 parts NiO powder, 59.3 parts Fe2O3 powder, 2.9 parts CeO2 powder, 10.0 parts Cu-Ni alloy powder (Cu:Ni=2.5:1).

[0111] Preparation step S4: The particles obtained in S3 are loaded into the rubber mold layer by layer, with the core layer being 40 mm thick, the transition layer being 20 mm thick, and the surface layer being 15 mm thick. The mold is then held under pressure at 250 MPa for 3 minutes to obtain the green body.

[0112] Finished product test results: No cracking after 28 cycles of water quenching at 300℃, corrosion rate of 1.9 mm / year, and core conductivity of 1520 S / cm at 900℃.

[0113] Example 7

[0114] The difference from Example 5 lies in the different mass fractions of the raw materials in each layer, as detailed below:

[0115] Core layer: 8.0 parts NiO powder, 17.0 parts Fe2O3 powder, 75 parts Cu-Ni alloy powder (Cu:Ni=1.5:1);

[0116] Transition layer: 14.3 parts NiO powder, 30.7 parts Fe2O3 powder, and 55 parts Cu-Ni alloy powder (Cu:Ni=1.5:1);

[0117] Surface layer: 25.3 parts NiO powder, 54.2 parts Fe2O3 powder, 0.5 parts CeO2 powder, 20.0 parts Cu-Ni alloy powder (Cu:Ni=1.5:1).

[0118] Preparation step S4: The particles obtained in S3 are loaded into the rubber mold layer by layer, with the core layer being 20 mm thick, the transition layer being 30 mm thick, and the surface layer being 20 mm thick. The mold is then held under pressure at 250 MPa for 3 minutes to obtain the green body.

[0119] Finished product test results: No cracking after 28 cycles of water quenching at 300℃, corrosion rate of 1.7 mm / year, and core conductivity of 1498 S / cm at 900℃.

[0120] Comparative Example 1

[0121] The difference from Example 1 is that CeO2 is not added.

[0122] Finished product testing results: relative density 96.1%, electrical conductivity at 900℃ 950 S / cm, flexural strength 73 MPa, corrosion rate 6.8 mm / year. The electron microscope image of the prepared anolyte is shown below. Figure 2 As shown in the figure, compared with Example 1, the anodic corrosion rate without rare earth modifier increased by about 2 times and the mechanical strength decreased by about 21%, indicating that rare earth modifier has a significant effect on improving corrosion resistance and strength.

[0123] Comparative Example 2

[0124] The difference from Example 1 is that S5 only involves one sintering step, in an H2 / Ar mixed gas (5% H2), the temperature is raised to 1280°C at 3°C / min and held for 4.5 h; the cooling rate is 2°C / min.

[0125] Finished product testing results: relative density 96.9%, electrical conductivity at 900℃ 990 S / cm, flexural strength 83 MPa, corrosion rate 4.7 mm / year. The prepared anolyte electron microscope image is shown below. Figure 3 As shown in Example 1, one-step sintering has a certain impact on the in-situ synthesis of NiFe2O4 and the overall microstructure, which in turn affects the corrosion rate of the anode. This indicates that two-step sintering has a significant effect on improving the corrosion resistance rate, strength, conductivity and overall integrity of the anode.

[0126] Application examples

[0127] Low-temperature, low cryolite ratio electrolyte (composition: NaF-AlF3-Al2O) was used. Under standard aluminum electrolysis conditions, DC electrolysis was performed using the multi-element metal ceramic inert anode prepared in Example 1 and the multi-element metal ceramic inert anode with a gradient functional material structure prepared in Example 5 as working anodes.

[0128] The electricity consumption per ton of aluminum during the electrolysis process is 12501 kWh / t and 12476 kWh / t, respectively, and the purity of the produced aluminum is 99.72% and 99.71%, respectively.

[0129] It should be noted that the above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may use the above technical content as inspiration to make changes or modifications to equivalent embodiments. However, any simple modifications, equivalent changes and modifications made to the above embodiments without departing from the technical essence of the claims of the present invention shall still fall within the scope of protection of the claims of the present invention.

Claims

1. A multi-metal ceramic inert anode for electrolytic aluminum, characterized in that: It includes an oxide ceramic phase, a metallic conductive phase, and a rare earth modifier; the oxide ceramic phase includes AB2O4 type spinel oxide ceramic, the metallic conductive phase includes Cu-Ni alloy, and the rare earth modifier includes CeO2 or Y2O3.

2. The multi-metal ceramic inert anode for electrolytic aluminum according to claim 1, characterized in that: The mass ratio of the oxide ceramic phase to the metallic conductive phase is 65~80:20~35, and the amount of rare earth modifier added is 0.5%~3.0% of the total mass of the oxide ceramic phase and the metallic conductive phase.

3. The multi-metal ceramic inert anode for electrolytic aluminum according to claim 2, characterized in that: The AB2O4 type spinel oxide ceramic is NiFe2O4; the mass ratio of Cu to Ni in the metallic conductive phase is 1.5 to 2.5:

1.

4. The multi-metal ceramic inert anode for electrolytic aluminum according to claim 3, characterized in that: The average grain size of the NiFe2O4 spinel ceramic phase is 2-8 μm; the Cu-Ni alloy phase is uniformly distributed at the ceramic phase grain boundaries with a connectivity ≥85%; the outer surface of the multi-metal ceramic inert anode is covered with a composite oxide protective film with a thickness of 10-50 μm and a porosity ≤2%.

5. A multi-metal ceramic inert anode for electrolytic aluminum according to any one of claims 1 to 4, characterized in that: The relative density of the multi-metal ceramic inert anode is ≥97%, the conductivity at 900℃ is ≥800S / cm, and the corrosion rate in the cryolite molten salt system is ≤3 mm / year.

6. The multi-metal ceramic inert anode for electrolytic aluminum according to claim 1, characterized in that: The multi-element metal ceramic inert anode adopts a gradient functional material structure, including a core layer, a transition layer and a surface layer, each layer having a thickness of 5 to 40 mm; the core layer has an oxide ceramic phase mass fraction of 15% to 25%, the transition layer has an oxide ceramic phase mass fraction of 45% to 55%, and the surface layer has an oxide ceramic phase mass fraction of ≥80%.

7. A method for preparing a multi-metal ceramic inert anode for electrolytic aluminum according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Mix NiO powder, Fe2O3 powder and rare earth oxides according to the mass ratio to obtain ceramic phase precursor mixed powder; S2. Preparation of Cu-Ni alloy powder; S3. Mix the ceramic phase precursor powder obtained in S1 with the Cu-Ni alloy powder obtained in S2, add an appropriate amount of molding aid, wet ball mill to mix evenly, and spray dry to granulate. S4. Prepare green bodies from the particles obtained in S3; S5. The green body prepared in S4 is sintered in two steps under atmosphere protection. S6. Oxidize the sintered body; S7. The sintered body prepared in S6 is precision machined to the target size, and the anode guide rod is installed to obtain the finished inert anode.

8. The method for preparing a multi-metal ceramic inert anode for electrolytic aluminum according to claim 7, characterized in that: Step S1 involves ball milling, using ZrO2 balls as the milling medium, with a ball-to-material ratio of 3:1, a rotation speed of 200–300 rpm, and mixing for 8–12 h; the BET specific surface area of ​​the ceramic phase precursor powder is 8–15 m² / g.

9. A method for preparing a multi-metal ceramic inert anode for electrolytic aluminum according to claim 7 or 8, characterized in that: In step S2, Cu-Ni alloy powder is prepared by gas atomization, and the particle size of the prepared Cu-Ni alloy powder is 10-45 μm.

10. A method for preparing a multi-metal ceramic inert anode for electrolytic aluminum according to claim 9, characterized in that: In step S3, the molding aid is polyvinyl alcohol, and the amount added is 1.5% to 2.5% of the total mass of the oxide ceramic phase and the metal conductive phase; in step S4, the green body is prepared by cold isostatic pressing, the operating pressure is 200 to 300 MPa, and the holding time is 2 to 5 min.

11. The method for preparing a multi-metal ceramic inert anode for electrolytic aluminum according to claim 7, characterized in that: The sintering process in step S5 is as follows: first, pre-fire at 900-1000℃ for 1-2 h in an air atmosphere; then sinter at 1200-1350℃ for 2-4 h in a reducing atmosphere of H2 and Ar; the sintering heating rate is 2-5℃ / min, and the cooling rate is ≤3℃ / min.

12. A method for preparing a multi-metal ceramic inert anode for electrolytic aluminum according to any one of claims 7, 8, or 11, characterized in that: In step S6, the sintered body is oxidized in an air atmosphere at 800-900°C for 1-3 hours.

13. The application of any one of the multi-metal ceramic inert anodes for electrolytic aluminum in the electrolytic aluminum process according to any one of claims 1 to 6.

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