Method for preparing nickel-ferrite-based eutectic ceramic inert anode material

Abstract

Disclosed in the present invention is a method for preparing a nickel-ferrite-based eutectic ceramic inert anode material. In the method disclosed herein, a eutectic ceramic preparation technique is utilized, a nickel-ferrite-based ceramic pre-sintered body is melted, and then, by controlling the processes of cooling and curing and optimizing the microstructure of a ceramic, a eutectic ceramic inert anode with good performance is prepared. The method of the present invention improves the overall performance, including the conductivity, thermal shock resistance, molten salt corrosion resistance, etc., of the ceramic inert anode, and is simple in terms of preparation process and convenient for industrialization and large-scale production.

Description

A method for preparing nickel ferrite-based eutectic ceramic inert anode material

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application with application number 202311818746.9 filed with the Patent Office of China on December 27, 2023, entitled "A Method for Preparing Nickel Ferrite-Based Eutectic Ceramic Inert Anode Material", the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present invention relates to aluminum electrolytic processing related technologies, and in particular to a method for preparing a nickel ferrite-based eutectic ceramic inert anode material. Background Art

[0004] Nickel ferrite ceramics have become a hot topic in the aluminum electrolytic industry in recent decades due to their excellent electrical conductivity and resistance to high-temperature molten salt corrosion. This is primarily due to the fact that these ceramic inert anodes can reduce carbon emissions during the aluminum electrolysis process.

[0005] In order to achieve a balance between density, mechanical properties, electrical conductivity and resistance to high-temperature molten salt corrosion, nickel ferrite-based ceramic inert anodes often add different oxide components to improve conductivity, thermal shock resistance and corrosion resistance, forming a large class of ceramic anode materials.

[0006] Tests and studies under actual production conditions have shown, through high-temperature molten salt corrosion experiments, that this type of ceramic inert anode undergoes preferential corrosion at the grain boundaries during electrolysis, causing micropores to appear on the surface of the ceramic inert anode, providing a penetration channel for the high-temperature molten salt electrolyte, and the ceramic inert anode is further corroded electrochemically and chemically.

[0007] To improve the corrosion resistance, thermal shock resistance, and electrical conductivity of ceramic anodes, existing technologies have proposed numerous methods and measures for increasing ceramic density and sintering. However, these improvements have been limited. Furthermore, conventional ceramic production processes are extremely difficult to produce large ceramic anodes, making industrialized manufacturing of such anodes extremely challenging. The associated molding and firing processes are complex, and the technical challenges faced in using ceramic anodes for industrialized carbon reduction in the electrolytic aluminum industry remain significant.

[0008] Summary of the Invention

[0009] In view of the defects or shortcomings of the prior art, the present invention provides a method for preparing a nickel ferrite-based eutectic ceramic inert anode material.

[0010] To this end, the preparation method of the nickel ferrite-based eutectic ceramic inert anode material provided by the present invention comprises:

[0011] Step 1: Prepare a pre-sintered body:

[0012] A mixed powder of NiFe2O4-based spinel powder and nickel green stone powder is mixed with a binder and granulated into 10-30 mesh pellets; the pellets are then pressed under a pressure of 100-200 MPa to obtain a green body; and the green body is pre-sintered at 1100-1300°C for 2-5 hours in an inert gas atmosphere to obtain a pre-sintered body.

[0013] Calculated based on 100% by mass, the mass percentage of the NiFe2O4-based spinel is 80wt% to 90wt%, and the mass percentage of the nickel green stone is 10wt% to 20wt%; the binder is selected from one or a mixture of two or more of polyvinyl alcohol and polyethylene glycol, and the mass of the binder accounts for 0.5wt% to 2wt% of the mass of the mixed powder;

[0014] Step 2: Pre-sintered body melting and cooling solidification:

[0015] The pre-sintered body is heated and melted in an inert gas atmosphere to be molten; the molten material is then cooled and solidified at a cooling rate of 1-100° C. / min, or the molten material is cast and then cooled and solidified at a cooling rate of 1-100° C. / min to obtain a ceramic solidified body;

[0016] Step 3, heat treatment:

[0017] The ceramic solid body obtained in step 2 is treated at a temperature of 1250-1400°C for 2-6 hours to adjust the microstructure and eliminate stress; then cooled to room temperature at a cooling rate of 1-50°C / min to obtain a nickel ferrite-based eutectic ceramic inert anode material.

[0018] An optional solution is that the NiFe2O4-based spinel composition is: NiFe2O4 accounts for 20wt% to 80wt%; ZnFe2O4 accounts for 0wt% to 20wt%; CuFe2O4 accounts for 0wt% to 20wt%; CoFe2O4 accounts for 0wt% to 20wt%; MnFe2O4 accounts for 0wt% to 20wt%; and does not include the endpoint value 0.

[0019] An optional solution is that the nickel green stone composition is: NiO accounts for 20wt% to 80wt%; CaO accounts for 0wt% to 20wt%; CeO2 accounts for 0wt% to 20wt%; ZrO2 accounts for 0wt% to 20wt%; Al2O3 accounts for 0wt% to 20wt%; V2O5 accounts for 0wt% to 20wt%; and does not include the endpoint value 0.

[0020] Alternatively, the nickel chlorite may be replaced by NiO.

[0021] Preferably, the particle size of the mixed powder is less than 100 mesh.

[0022] An optional solution is to ball-mill a mixture of NiFe2O4-based spinel powder, nickel green stone powder, a dispersant and water for 12-24 hours to prepare a ceramic slurry; then, the ceramic slurry is dried and ground to obtain a mixed powder;

[0023] The dispersant is selected from one or a mixture of two or more of ethanol, ethylene glycol and glycerol, and the mass of the dispersant accounts for 1wt%-5wt% of the total mass of the NiFe2O4-based spinel powder and the nickel green stone powder;

[0024] The mass of the water is 3-5 times the total mass of the NiFe2O4-based spinel powder and the nickel green stone powder.

[0025] Alternatively, in step 2, the pre-sintered body is melted in an inert gas atmosphere at a temperature of 1650-1850° C. for 1-2 hours to make the pre-sintered body into a molten state.

[0026] An optional solution is that the melting in step 2 is carried out by any one or a combination of arc melting, discharge plasma melting, laser suspension zone melting, optical floating zone melting, electron beam zone melting, high-frequency electromagnetic induction zone melting and energized Joule heat melting.

[0027] Furthermore, the nickel ferrite-based eutectic ceramic inert anode material prepared by the present invention has a density of 99%-100%; a thermal shock resistance of 95%-120%; a mechanical property of 70-110 MPa; a high-temperature corrosion resistance of 5-50 microns; and a conductivity of 8-30 S / cm.

[0028] The present invention utilizes eutectic ceramic preparation technology to obtain dense nickel ferrite-based eutectic ceramic materials, which greatly reduces the corrosion of traditional ceramic grain boundaries. By increasing the density of the material, the electrical conductivity, mechanical properties and corrosion resistance of the material are improved. At the same time, through ceramic melting and casting, the traditional ceramic preparation process is simplified, achieving a generational improvement in the performance of ceramic anode materials and a transformation in the preparation process.

[0029] This invention significantly increases the density of nickel ferrite-based ceramic materials, eliminates grain boundary defects present in traditional sintering processes, and improves the overall performance of the ceramic material, including corrosion resistance, conductivity, and mechanical properties. The preparation process of this invention facilitates molding, has a simple process flow, facilitates control of ceramic shape and size, and is easily industrialized and engineered. DETAILED DESCRIPTION

[0030] Unless otherwise specified, the scientific and technical terms used herein are understood according to the knowledge of ordinary technicians in the relevant fields.

[0031] The present invention pre-sinters the nickel ferrite-based eutectic ceramic inert anode material, directly melts it at a high temperature (the melting temperature can be determined according to the composition and properties of the material so that the pre-sintered body can be heated and melted within a reasonable time), and then cools and solidifies it, or cools and solidifies it after casting. In a specific scheme, the nickel ferrite-based eutectic ceramic with excellent performance can be obtained by controlling the ceramic chemical composition, melting temperature and melting atmosphere, as well as the cooling rate and post-solidification heat treatment.

[0032] It should be noted that the temperatures and amounts of materials used herein are approximate values ​​and are for illustrative purposes. Although methods and materials similar to or equivalent to the methods and materials described herein can be used for the implementation of the present disclosure, some suitable methods and raw materials are described below. In addition, the raw materials, amounts, and embodiments are merely exemplary and are not intended to be limiting. In a specific embodiment, those skilled in the art can optimize the raw materials, amounts of materials, and operating parameters involved in the method according to the disclosure of the present invention using conventional experimental time periods to achieve the purpose of the present invention.

[0033] The raw materials used in the following examples are all commercially available products, and the components of the materials are of analytical grade.

[0034] The composition of the NiFe2O4-based spinel used in the following examples is as follows: NiFe2O4 accounts for 79.6wt%; ZnFe2O4 accounts for 5.8%; CuFe2O4 accounts for 2.6wt%; CoFe2O4 accounts for 0.9wt%; MnFe2O4 accounts for 10.4wt%;

[0035] The composition of the nickel green stone used is: NiO accounts for 78.3wt%; CaO accounts for 11.5wt%; CeO2 accounts for 0.8wt%; ZrO2 accounts for 1.1wt%; Al2O3 accounts for 6.7%; V2O5 accounts for 1.4wt%.

[0036] The performance testing methods of the materials described in this article are:

[0037] Density: Measured by the Archimedes drainage method, it is the ratio of actual density to theoretical density.

[0038] Thermal shock resistance: The material is placed in a high-temperature furnace at 960°C for 10 minutes and then taken out and cooled to room temperature in air. This completes a thermal shock. The material after thermal shock is then subjected to a bending strength test. The ratio of the strength after thermal shock to the strength before thermal shock is the strength residual rate (representing thermal shock resistance). The greater the strength residual rate, the better the thermal shock resistance of the material.

[0039] Mechanical properties: Mechanical properties are expressed by flexural strength. The flexural strength test shall refer to GB / T4741-1999.

[0040] High-temperature corrosion resistance: NiFe2O4 eutectic ceramic inert anode materials sintered at different temperatures were subjected to a high-temperature molten salt static corrosion test. The inert anode materials were placed in a high-purity graphite crucible filled with sufficient electrolyte. The electrolyte composition was 90% industrial cryolite (molecular ratio of 2.2), 5% CaF2 and 5% Al2O3 (mass ratio); the inert anode materials were etched at a constant temperature of 960°C for 8 hours, then taken out and allowed to cool; the etched inert anode materials were heated in a water bath with a 30% by mass concentration of AlCl3 solution to dissolve and remove the residue on the material surface, and then the material surface was rinsed with clean water; the etched material surface was subjected to SEM and EDS elemental analysis. The thickness of the corrosion layer of the material was measured under a microscope to represent the material's high-temperature corrosion resistance.

[0041] Conductivity: The current flowing through the sample per unit area and per unit length is measured at a constant voltage at 960°C, and the conductivity of the sample is calculated according to Ohm's law.

[0042] Based on the above detection method, the density of the material prepared by the present invention is 99%-100%; the thermal shock resistance is 95%-120%; the mechanical properties are 70-110MPa; the high temperature corrosion resistance is 5-50 microns; and the electrical conductivity is 8-30S / cm.

[0043] Example 1:

[0044] 1) Preparing a pre-sintered body: ball-milling a mixture of 85 wt% NiFe2O4-based spinel powder, 15 wt% nelsonite powder, ethanol (5 wt% of the total mass of the NiFe2O4-based spinel powder and nelsonite powder), and water (4 times the total mass of the NiFe2O4-based spinel powder and nelsonite powder) for 14 hours to prepare a ceramic slurry having a particle size of less than 200 mesh; drying the ceramic slurry at 150±10°C and then grinding it to obtain a mixed powder having a particle size of less than 100 mesh; adding 1.5 wt% of polyvinyl alcohol (PVA) as a binder based on the mass of the mixed powder; and granulating the granules into 10-30 mesh granules. The granulated granules are pressed under a pressure of 150 MPa to obtain a green compact; and then pre-sintering the slurry at 1200±100°C in a nitrogen protective atmosphere for 4 hours to obtain a pre-sintered body;

[0045] 2) Melting and cooling of the pre-sintered body: The pre-sintered body is melted in a spark plasma sintering (SPS) device under argon protective gas at a temperature of 1650-1850°C for 2 hours to obtain a molten material, and then the molten material is cooled and solidified at a cooling rate of 80±5°C / min to obtain a ceramic solidified body;

[0046] 3) Crystallization Heat Treatment: The obtained ceramic solid body was crystallized and annealed in a muffle furnace at a temperature of 1250-1400°C for 6 hours to adjust the microstructure and eliminate stress, and then cooled to room temperature at a cooling rate of 30±5°C / min to obtain a nickel ferrite-based eutectic ceramic inert anode material.

[0047] After testing, the material prepared in this embodiment has a density of 99.8%, a conductivity of 25S / cm, mechanical properties of flexural strength of 89MPa, thermal shock resistance of 1st residual strength ratio of 102%, and high temperature corrosion resistance of 15 microns.

[0048] Example 2:

[0049] This embodiment differs from Example 1 in that the raw materials used are 80 wt% NiFe2O4-based spinel powder, 20 wt% nickel green stone powder, propylene glycol (accounting for 1 wt% of the total mass of NiFe2O4-based spinel powder and nickel green stone powder) and water (5 times the total mass of NiFe2O4-based spinel powder and nickel green stone powder).

[0050] After testing, the material prepared in this embodiment has a density of 99.3% and a conductivity of 23S / cm. The mechanical properties are as follows: bending strength of 91 MPa; thermal shock resistance: 1st residual strength ratio of 98%; and high temperature corrosion resistance of 17 microns.

[0051] Example 3:

[0052] This embodiment differs from Example 1 in that the raw materials used are 90 wt% NiFe2O4-based spinel powder, 10 wt% nickel oxide, propylene glycol (accounting for 4 wt% of the total mass of NiFe2O4-based spinel powder and nickel green stone powder) and water (3 times the total mass of NiFe2O4-based spinel powder and nickel green stone powder).

[0053] After testing, the material prepared in this embodiment has a density of 99.5%, a conductivity of 28S / cm, mechanical properties of 107 MPa bending strength, thermal shock resistance of 117% and high temperature corrosion resistance of 5 microns.

[0054] The molten material obtained in the above embodiment can also be cast in an anode mold and then cooled under the same conditions, and the properties of the obtained material will not change.

Claims

1. A preparation method of a nickel ferrite-based eutectic ceramic inert anode material, characterized in that the method Comprising: Step 1, preparing a pre-sintered body: Mix the mixed powder of NiFe₂O₄-based spinel powder and pyrochlore powder with a binder, granulate to make granular materials with a particle size of 10 - 30 mesh; then press the granular materials under a pressure of 100 - 200 MPa to obtain a green body; then pre-sinter the green body in an inert gas atmosphere at 1100 - 1300 °C for 2 - 5 hours to obtain a pre-sintered body; Calculated based on 100% by mass percentage, the mass percentage of the NiFe₂O₄-based spinel is 80 wt% - 90 wt%, and the mass percentage of pyrochlore is 10 wt% - 20 wt%; the binder is selected from one or a mixture of two or more of polyvinyl alcohol and polyethylene glycol, and the mass of the binder accounts for 0.5 wt% - 2 wt% of the mass of the mixed powder; Step 2, melting and cooling solidification of the pre-sintered body: Heat and melt the pre-sintered body in an inert gas atmosphere to make the pre-sintered body in a molten state; then cool and solidify the molten material at a cooling rate of 1 - 100 °C / min, or, after casting the molten material, cool and solidify it at a cooling rate of 1 - 100 °C / min to obtain a ceramic solidified body; Step 3, heat treatment: Treat the ceramic solidified body obtained in Step 2 at a temperature of 1250 - 1400 °C for 2 - 6 hours, and then cool it to room temperature at a temperature reduction rate of 1 - 50 °C / min to obtain a nickel ferrite-based eutectic ceramic inert anode material.

2. The preparation method of the nickel ferrite-based eutectic ceramic inert anode material according to claim 1, characterized in that, The composition of the NiFe₂O₄-based spinel is: NiFe₂O₄ accounts for 20 wt% - 80 wt%; ZnFe₂O₄ accounts for 0 wt% - 20 wt%; CuFe₂O₄ accounts for 0 wt% - 20 wt%; CoFe₂O₄ accounts for 0 wt% - 20 wt%; MnFe₂O₄ accounts for 0 wt% - 20 wt%; the endpoint value 0 is not included.

3. The preparation method of the nickel ferrite-based eutectic ceramic inert anode material according to claim 1, characterized in that, The composition of the pyrochlore is: NiO accounts for 20 wt% - 80 wt%; CaO accounts for 0 wt% - 20 wt%; CeO₂ accounts for 0 wt% - 20 wt%; ZrO₂ accounts for 0 wt% - 20 wt%; Al₂O₃ accounts for 0 wt% - 20 wt%; V₂O₅ accounts for 0 wt% - 20 wt%; the endpoint value 0 is not included.

4. The preparation method of the nickel ferrite-based eutectic ceramic inert anode material according to claim 1, characterized in that, Replace the pyrochlore with NiO.

5. The preparation method of the nickel ferrite-based eutectic ceramic inert anode material according to claim 1, characterized in that, The particle size of the mixed powder is less than 100 mesh.

6. The preparation method of the nickel ferrite-based eutectic ceramic inert anode material according to claim 1, characterized in that, Ball mill the mixture of NiFe₂O₄-based spinel powder, pyrochlore powder, dispersant and water for 12 - 24 hours to obtain a ceramic slurry; then dry and grind the ceramic slurry to obtain a mixed powder; The dispersant is selected from one or a mixture of two or more of ethanol, ethylene glycol and glycerol, and the mass of the dispersant accounts for 1 wt% - 5 wt% of the total mass of the NiFe₂O₄-based spinel powder and pyrochlore powder; The mass of the water is 3 - 5 times the total mass of the NiFe₂O₄-based spinel powder and pyrochlore powder.

7. The preparation method of the nickel ferrite-based eutectic ceramic inert anode material according to claim 1, wherein In Step 2, melt the pre-sintered body in an inert gas atmosphere at a temperature of 1650 - 1850 °C for 1 - 2 hours to make the pre-sintered body in a molten state.

8. The preparation method of the nickel ferrite-based eutectic ceramic inert anode material according to claim 1, characterized in that, The melting in Step 2 is carried out by any one or a combination of the following methods: arc melting, spark plasma melting, laser levitation zone melting, optical floating zone melting, electron beam zone melting, high-frequency electromagnetic induction zone melting, and Joule heating by energization.

9. The preparation method of the nickel ferrite-based eutectic ceramic inert anode material according to claim 1, characterized in that, The density of the nickel ferrite-based eutectic ceramic inert anode material is 99%-100%; the thermal shock resistance is 95%-120%; the mechanical properties are 70-110 MPa; the high-temperature corrosion resistance is 5-50 microns; the conductivity is 8-30 S / cm.