A high-entropy spinel-phase ceramic inert anode material for carbon-free aluminum electrolysis, preparation method and application

Abstract

The present invention provides a high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis, a preparation method, and an application thereof. Using divalent metal hydroxides and trivalent metal hydroxides as raw materials, a high-entropy spinel phase is synthesized in situ by cold sintering, thereby obtaining a high-entropy spinel phase ceramic inert anode material. The present invention utilizes the delayed diffusion effect of the high-entropy spinel phase to enhance the corrosion resistance of the ceramic inert anode material, and utilizes the structural characteristics and multi-element hybridization effect of the high-entropy spinel phase to enhance the electrical conductivity of the material. At the same time, the strengthening effect of the high-entropy spinel phase and the advantages of the cold sintering process are utilized to synergistically enhance the strength of the material, thereby significantly enhancing the electrical conductivity, strength, and corrosion resistance of the prepared high-entropy spinel phase ceramic inert anode material.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum electrolysis, and particularly relates to a high-entropy spinel-phase ceramic inert anode material for carbon-free aluminum electrolysis, a preparation method and an application thereof. Background Art

[0002] The consumption of aluminum is mainly concentrated in industries such as construction, transportation, electricity, consumer goods and packaging. Traditional industries are still the main consumption scenarios of aluminum, and the incremental consumption mainly comes from photovoltaic and new energy vehicles. However, due to the high energy consumption and high carbon emissions in the production process of aluminum, the sustainable development of the aluminum electrolysis industry has been greatly restricted.

[0003] Therefore, accelerating the development of carbon-free aluminum electrolysis technology based on inert anodes is crucial for the sustainable development of the aluminum industry. The carbon-free aluminum electrolysis cell technology uses anode materials that do not participate in the reaction and does not produce CO2, which is of great significance for reducing carbon emissions. The key to developing carbon-free aluminum electrolysis technology based on inert anodes lies in finding suitable anode materials. Since the anode working environment is extremely harsh, the anode must simultaneously have characteristics such as high electrical conductivity, high strength, and corrosion resistance.

[0004] Currently, three types of materials have been studied as inert anode materials for molten salt electrolysis: oxide ceramics, alloys, and cermets. Although oxide ceramics have excellent resistance to electrolyte dissolution corrosion and new ecological oxygen erosion, they have low electrical conductivity, high brittleness, and are difficult to connect with metal conductors. Alloy anodes have high strength, are suitable for large-sized special-shaped equipment, are easy to connect with metal conductors, and have good electrical conductivity. However, since the corrosion resistance of alloy anodes in cryolite molten salt is inferior to that of ceramic materials, they cannot be used for a long time. Cermets improve the electrical conductivity of the anode by adding metal phases to the ceramic matrix, but at the same time, they will reduce the anti-molten salt corrosion performance of the anode, thereby affecting the service life of the anode and the quality of molten aluminum. Therefore, finding new ceramic inert anode materials with high electrical conductivity, high strength, and corrosion resistance is the key to promoting the development of carbon-free aluminum electrolysis. Summary of the Invention

[0005] Aiming at the defect that existing ceramic inert anode materials are difficult to simultaneously take into account electrical conductivity, strength, and corrosion resistance, the present invention provides a high-entropy spinel-phase ceramic inert anode material for carbon-free aluminum electrolysis and a preparation method thereof. The hysteresis diffusion effect of the high-entropy spinel phase is used to improve the corrosion resistance of the ceramic inert anode material, and the structural characteristics and multi-element hybridization effect of the high-entropy spinel phase are used to improve the electrical conductivity of the material. At the same time, the strengthening effect of the high-entropy spinel phase and the advantages of the cold sintering process are used to synergistically improve the strength of the material, so that the prepared high-entropy spinel-phase ceramic inert anode material for carbon-free aluminum electrolysis has been greatly improved in terms of electrical conductivity, strength, and corrosion resistance.

[0006] The present invention realizes the above technical objectives through the following technical means.

[0007] A preparation method of a high-entropy spinel-phase ceramic inert anode material for carbon-free aluminum electrolysis, comprising the following steps:

[0008] S1: Weigh divalent metal hydroxides and trivalent metal hydroxides, and obtain a ceramic-phase precursor powder after mixing and grinding; the types of metal elements in the ceramic-phase precursor powder are not less than 4; all metal hydroxides in the ceramic-phase precursor powder are prepared in an equimolar ratio;

[0009] S2: Add a fluid assistant to the ceramic-phase precursor powder, and obtain a fully wetted mixed powder after grinding;

[0010] S3: Cold sinter the mixed powder to obtain a high-entropy spinel-phase ceramic inert anode material for carbon-free aluminum electrolysis.

[0011] Further, the divalent metal hydroxides include one or more of Ni(OH)2, Co(OH)2, Mg(OH)2, Cu(OH)2, Zn(OH)2, Mn(OH)2, Fe(OH)2, and the trivalent metal hydroxides include one or more of Fe(OH)3, Al(OH)3, Cr(OH)3, Co(OH)3.

[0012] Further, the fluid assistant is prepared in an equimolar ratio from soluble salt solutions of all metal ions in divalent metal hydroxides and trivalent metal hydroxides.

[0013] Further, in the fluid assistant, with all metal salts as solutes, the concentration of this fluid assistant is 0.5 - 4 mol / L, and the addition amount of the fluid assistant is 1 - 10% of the total mass of the ceramic-phase powder.

[0014] Further, during the cold sintering treatment, the set pressure value is 100 - 500 MPa, the temperature value is 150 - 500 °C, and the sintering time is 0.5 - 4 h.

[0015] Further, in step S1, a planetary ball mill is used for grinding, and the grinding time is 2 h; in step S2, a planetary ball mill is used for grinding, and the grinding time is 1 h.

[0016] A high-entropy spinel-phase ceramic inert anode material for carbon-free aluminum electrolysis prepared by the preparation method described in any one of the above.

[0017] Further, the high-entropy spinel-phase ceramic inert anode material for carbon-free aluminum electrolysis is a ceramic phase with a general formula of M3O4, where M is composed of four or more metal ions in an equimolar ratio, and the metal ions are selected from Ni, Co, Mg, Cu, Zn, Mn, Fe, Al, Cr.

[0018] Application of the above-mentioned high-entropy spinel-phase ceramic inert anode material for carbon-free aluminum electrolysis in aluminum electrolysis.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. Due to the uniform distribution of each element, the high-entropy spinel phase in the present invention has a highly uniform organizational structure, which can not only form a dense oxide layer, but also, inside the material, due to the existence of a large number of lattice defects and impurity atoms, as well as the synergistic effect between multiple elements, all pose certain obstacles to the movement of atoms, making the diffusion and phase change speeds very slow, and it is not prone to structural changes such as grain coarsening and recrystallization at high temperatures. Therefore, the corrosion resistance of the material is greatly improved.

[0021] 2. The atomic radii and chemical bonds of different elements vary greatly, and the environment and occupancy around each atom are different, which results in greater lattice distortion and defects inside the lattice than traditional spinels. Therefore, compared with traditional metal phases and spinel phases, it has higher hardness and better wear resistance, making the anode material prepared from the high-entropy spinel phase more durable and wear-resistant, and capable of maintaining stable performance for a longer time. At the same time, the large difference in atomic radii and chemical bonds, as well as the interaction and hybridization effects between various metal elements, also make its electronic structure more complex, containing more energy levels and electron states. These energy levels and electron states can participate in electron transport within a wider energy range, thereby increasing the electron mobility and conductivity. Therefore, this high-entropy spinel can be used alone as an aluminum electrolysis anode without additional addition of a metal phase.

[0022] 3. The present invention is sintered at low temperature, and the binding energy becomes smaller, which can make it easier to form chemical bonds and physical connections between powder particles, thereby effectively enhancing the structural strength and hardness of the material. During the cold sintering process, secondary crystallization may also occur, that is, parts where the original powder particles are difficult to combine properly will rearrange and combine to form a denser structure under the application of appropriate pressure, further improving the mechanical properties. Cold sintering often can obtain nanoscale grain boundaries, and the grain boundaries have higher local stress, diffusion activity, and dislocation density, thereby making the material have higher toughness and strength at the microscopic scale.

[0023] 4. The present invention can greatly simplify the preparation process of the inert anode by in-situ synthesizing the high-entropy spinel inert anode through cold sintering, improve the electrochemical performance and thermal stability of the inert anode, greatly reduce the energy consumption and cost of inert anode production, improve the production efficiency of the anode, reduce carbon emissions during anode production, increase the service life of the anode and the quality of molten aluminum, and is conducive to the popularization of inert anodes and carbon-free aluminum electrolysis technology. Description of the Drawings

[0024] Figure 1XRD pattern of the carbon-free high-entropy spinel-phase ceramic inert anode material prepared in Example 1 of the present invention;

[0025] Figure 2 Electrochemical test pattern of the carbon-free high-entropy spinel-phase ceramic inert anode material prepared in Example 1 of the present invention;

[0026] Figure 3 XRD pattern of the carbon-free high-entropy spinel-phase ceramic inert anode material prepared in Example 2 of the present invention;

[0027] Figure 4 Electrochemical test pattern of the carbon-free high-entropy spinel-phase ceramic inert anode material prepared in Example 2 of the present invention;

[0028] Figure 5 XRD pattern of the carbon-free high-entropy spinel-phase ceramic inert anode material prepared in Example 3 of the present invention;

[0029] Figure 6 Electrochemical test pattern of the carbon-free high-entropy spinel-phase ceramic inert anode material prepared in Example 3 of the present invention. Detailed implementation manners

[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0031] Example 1

[0032] The preparation method of the carbon-free high-entropy spinel-phase ceramic inert anode material described in this example is as follows:

[0033] S1: Prepare divalent metal hydroxides Ni(OH)2, Co(OH)2 and trivalent metal hydroxides Fe(OH)3, Al(OH)3 according to a molar ratio of 1:1:1:1, and ball mill for 2 h with a planetary ball mill to obtain 50 g of ceramic phase precursor powder.

[0034] S2: Weigh and prepare Ni(NO3)2, Fe(NO3)3, Co(NO3)2 and Al(NO3)3 into a fluid aid according to a molar ratio of 1:1:1:1. Using Ni(NO3)2, Fe(NO3)3, Co(NO3)2 and Al(NO3)3 as solutes, the concentration of this fluid aid is 4 mol / L. Then add 5 g of the fluid aid to the ceramic phase precursor powder and continue to ball mill for 1 h to obtain a fully wetted mixed powder.

[0035] S3: Load the mixed powder into a cold sintering mold, set the temperature at 500 °C and the pressure at 100 MPa, and form a high-entropy spinel phase through 1 h of cold sintering. After cooling and pressure relief, a high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis is obtained.

[0036] Figure 1 This is the XRD pattern of the high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis prepared in this example. It can be seen from the figure that Ni(OH)2, Co(OH)2, Fe(OH)3, and Al(OH)3 are in-situ synthesized into 0.75 Ni 0.75 Co 0.75 Fe 0.75 Al

[0037] Perform a 100 A electrolysis experiment on the above high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis in a KF-NaF-AlF3-Al2O3 electrolyte system, with CR = 1.4 and an anode current density of 0.9 A / cm 2 , and the electrolysis voltage is 3.3 V. The test results are as Figure 2 shown: The operating voltage of the electrolytic cell remains stable during long-term operation at 820 °C, indicating that the electrolyte system has good electrical conductivity and thermal stability. After operating for 300 min, the electrolysis voltage drops to 3.12 V, indicating that the energy consumption during electrolysis is small and the electrolysis efficiency is high. The impurity content in the molten aluminum is detected to be less than 0.3%, indicating that this inert anode material can effectively prevent the generation and accumulation of impurities and has high chemical stability and corrosion resistance.

[0038] Example 2

[0039] The preparation method of the high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis described in this example is as follows:

[0040] S1: Prepare divalent metal hydroxides Ni(OH)2, Cu(OH)2, Mg(OH)2 and trivalent metal hydroxides Fe(OH)3, Cr(OH)3 according to a molar ratio of 1:1:1:1:1, and ball mill for 2 h with a planetary ball mill to obtain 50 g of ceramic phase precursor powder.

[0041] S2: Weigh Ni(CH3COO)2, Cu(CH3COO)2, Mg(CH3COO)2, Fe(CH3COO)2, and Cr(CH3COO)2 according to a molar ratio of 1:1:1:1:1 and prepare them into a fluid assistant. Using Ni(CH3COO)2, Cu(CH3COO)2, Mg(CH3COO)2, Fe(CH3COO)2, and Cr(CH3COO)2 as solutes, the concentration of this fluid assistant is 4 mol / L. Then, add 2.5 g of the fluid assistant to the ceramic phase precursor powder and continue ball milling for 1 h to obtain a well-wetted mixed powder.

[0042] S3: Load the mixed powder into a cold sintering mold, set the temperature to 350 °C, and the pressure to 300 MPa. Through 2 h of cold sintering, a high-entropy spinel phase is formed. After cooling and depressurizing, a high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis is obtained.

[0043] Figure 3 This is the XRD pattern of the high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis prepared in this example. It can be seen from the figure that Ni(OH)2, Cu(OH)2, Mg(OH)2, Fe(OH)3, and Cr(OH)3 are in-situ synthesized into

[0044] Ni 0.6 Cu 0.6 Mg 0.6 Fe 0.6 Cr 0.6 O4 high-entropy spinel phase.

[0045] Perform a 100 A electrolysis experiment on the above high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis in a KF-NaF-AlF3-Al2O3 electrolyte system. CR = 1.35, the anode current density is 1 A / cm 2 , the electrolysis voltage is 3.6 V, and the test results are as Figure 4 shown: The long-term operating voltage of the electrolytic cell remains stable at 860 °C, indicating that the electrolyte system has good electrical conductivity and thermal stability. After operating for 280 min, the electrolysis voltage drops to 3.4 V, indicating that the energy consumption during electrolysis is small and the electrolysis efficiency is high. The impurity content in the molten aluminum is detected to be less than 0.25%, indicating that this inert anode material can effectively prevent the generation and accumulation of impurities and has high chemical stability and corrosion resistance.

[0046] Example 3

[0047] The preparation method of the high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis described in this example is as follows:

[0048] S1: Prepare nickel hydroxide Ni(OH)₂, manganese hydroxide Mn(OH)₂, zinc hydroxide Zn(OH)₂, cobalt hydroxide Co(OH)₂ and iron hydroxide Fe(OH)₃, chromium hydroxide Cr(OH)₃ in a molar ratio of 1:1:1:1:1:1, and ball mill for 2 h with a planetary ball mill to obtain 50 g of ceramic phase precursor powder.

[0049] S2: Weigh and prepare a fluid aid by using nickel nitrate Ni(NO₃)₂, manganese nitrate Mn(NO₃)₂, zinc nitrate Zn(NO₃)₂, iron nitrate Fe(NO₃)₃, cobalt nitrate Co(NO₃)₂ and chromium nitrate Cr(NO₃)₃ in a molar ratio of 1:1:1:1:1:1. Using Ni(NO₃)₂, Mn(NO₃)₂, Zn(NO₃)₂, Fe(NO₃)₃, Co(NO₃)₂ and Cr(NO₃)₃ as solutes, the concentration of this fluid aid is 4 mol / L. Then add 1 g of the fluid aid to the ceramic phase precursor powder and continue ball milling for 1 h to obtain a fully wetted mixed powder.

[0050] S3: Load the mixed powder into a cold sintering mold, set the temperature at 150 °C and the pressure at 500 MPa, and form a high-entropy spinel phase through 4 h of cold sintering. After cooling and pressure relief, a high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis is obtained.

[0051] Figure 5 XRD pattern of the high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis prepared in this example. It can be seen from the figure that Ni(OH)₂, Mn(OH)₂, Zn(OH)₂, Co(OH)₂, Fe(OH)₃, Cr(OH)₃ are in-situ synthesized into 0.5 Ni 0. 5Zn 0.5 Fe 0.5 Co 0.5 Cr 0.5 O₄ high-entropy spinel phase.

[0052] Perform a 100 A electrolysis experiment on the above-mentioned high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis in a KF-NaF-AlF₃-Al₂O₃ electrolyte system, CR = 1.45, anode current density 1 A / cm 2 , the electrolysis voltage is 3.5 V, and the test results are as Figure 6 shown: The long-term operating voltage of the electrolytic cell remains stable at 830 °C, indicating that the electrolyte system has good electrical conductivity and thermal stability. After operating for 300 min, the electrolysis voltage drops to 3.17 V, indicating that the energy consumption during electrolysis is small and the electrolysis efficiency is high. The impurity content in the molten aluminum is detected to be less than 0.3%, indicating that this inert anode material can effectively prevent the generation and accumulation of impurities and has high chemical stability and corrosion resistance.

[0053] The embodiments described above are the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Without departing from the essence of the present invention, any obvious improvements, substitutions or modifications that those skilled in the art can make all fall within the protection scope of the present invention.

Claims

1. A preparation method of a high-entropy spinel-phase ceramic inert anode material for carbon-free aluminum electrolysis, characterized in that, It includes the following steps: S1: Weigh divalent metal hydroxides and trivalent metal hydroxides, and obtain a ceramic phase precursor powder after mixing and grinding; the types of metal elements in the ceramic phase precursor powder are not less than 4; all metal hydroxides in the ceramic phase precursor powder are prepared in equimolar ratio; the divalent metal hydroxides include one or more of Ni(OH)2, Co(OH)2, Mg(OH)2, Cu(OH)2, Zn(OH)2, Mn(OH)2, Fe(OH)2, and the trivalent metal hydroxides include one or more of Fe(OH)3, Al(OH)3, Cr(OH)3, Co(OH)3; S2: Add a fluid aid to the ceramic phase precursor powder and grind to obtain a fully wetted mixed powder; the fluid aid is prepared in equimolar ratio from soluble salt solutions of all metal ions in divalent metal hydroxides and trivalent metal hydroxides; in the fluid aid, with all metal salts as solutes, the concentration of this fluid aid is 0.5 - 4 mol / L, and the addition amount of the fluid aid is 1 - 10% of the total mass of the ceramic phase powder; S3: Cold sinter the mixed powder at 150 - 500 °C to obtain a high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis; during the cold sintering treatment, the set pressure value is 100 - 500 MPa, and the sintering time is 0.5 - 4 h.

2. The preparation method according to claim 1, wherein In step S1, a planetary ball mill is used for grinding, and the grinding time is 2 h; in step S2, a planetary ball mill is used for grinding, and the grinding time is 1 h.

3. A high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis prepared by the preparation method according to any one of the above claims 1 - 2.

4. The inert anode material of high-entropy spinel phase ceramic for carbon-free aluminum electrolysis according to claim 3, characterized in that, The high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis is a ceramic phase with the general formula M3O4, where M is composed of four or more metal ions in equimolar ratio, and the metal ions are selected from Ni, Co, Mg, Cu, Zn, Mn, Fe, Al, Cr.

5. Application of the high-entropy spinel phase ceramic inert anode material for carbon-free aluminum electrolysis according to claim 3 in aluminum electrolysis.

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