Method for preparing inert anode

Abstract

A method for preparing an inert anode, comprising the following steps: providing a cermet mixed powder, the cermet mixed powder comprising a ceramic powder, a metal powder, and a binder, a material of the ceramic powder comprising NiFe₂O₄; pressing the cermet mixed powder into a green body; subjecting the green body to a degreasing treatment and a sintering treatment to obtain a preform; disposing an aluminum oxide powder on a surface of the preform intended to be in contact with an electrolyte liquid and disposing a mixed powder of aluminum oxide and carbon powder on a surface of the preform intended to be in contact with a conductive rod, and then roasting the preform in an aerobic atmosphere to obtain the inert anode. In the method, an integrally formed inert anode preform is prepared and then an inert anode having a gradient structure with different metal phase contents is formed by means of oxidation and reduction, so that the inert anode has good consistency.

Description

A method for preparing an inert anode Cross-reference to related applications

[0001] This application claims priority to Chinese patent application No. 202410555733.5, filed on May 7, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to the aluminum industry, and more particularly to the field of aluminum electrolysis. Background Technology

[0003] Currently, inert anode materials used in the alumina-crystal molten salt electrolysis process are mainly divided into three categories: metal alloys, ceramics, and cermets. Among them, cermets are the most promising candidates because they combine the high conductivity of metal alloys with the corrosion resistance of ceramics. However, cermets also have some drawbacks. When the metal phase content in a cermet is high, the resistance of the cermet inert anode to electrolyte melt corrosion decreases. Conversely, when the metal phase content is low, the conductivity and thermal shock resistance of the cermet inert anode decrease, and the connection between the cermet inert anode and the metal conductor increases. Specifically, during the electrolysis reaction, when the metal phase content in the cermet inert anode is high, the preferential oxidation and selective dissolution of the metal phase are more pronounced, making the surface of the cermet inert anode porous. This allows the electrolyte to penetrate into the interior of the cermet inert anode, accelerating the corrosion of the ceramic phase and causing swelling, damage, and contamination of the molten aluminum. The cermet inert anode and the metal conductor rod need to have good mechanical and electrical connections. However, the difference in electrical conductivity and thermal expansion coefficient between the low-metallic cermet inert anode and the metal conductor rod can lead to thermal stress, which in turn can cause cracks and reduce the service life of the cermet inert anode.

[0004] Therefore, for inert anodes using cermet materials, the metal phase content in the cermet material should be lower in the electrolytic reaction surface that contacts the electrolyte melt to improve the corrosion resistance of the inert anode, while the metal phase content in the cermet material in the area connected to the metal guide rod needs to be higher to facilitate the effective connection between the inert anode and the metal guide rod.

[0005] To achieve a lower metal phase content in the region of the cermet inert anode that contacts the electrolyte melt, and a higher metal phase content in the region connected to the metal conductor, researchers can improve the overall performance of cermet inert anodes through structural design or the development of gradient materials. However, the gradient distribution of the metal phase in cermet materials inevitably affects the material's consistency and further impacts the overall performance of the cermet inert anode. Currently, how to fabricate cermet inert anodes with such gradient metal phase content while maintaining the consistency of the cermet inert anode remains a technical challenge. Summary of the Invention

[0006] By utilizing one or more embodiments of the present disclosure, the technical problem of maintaining consistency in cermet inert anodes with gradient distribution of metal phase content is solved.

[0007] According to some embodiments of this disclosure, the method for preparing an inert anode includes the following steps: providing a metal-ceramic mixed powder, the metal-ceramic mixed powder comprising ceramic powder, metal powder, and a binder, wherein the ceramic powder comprises NiFe2O4; pressing the metal-ceramic mixed powder into an inert anode green blank; subjecting the inert anode green blank to degreasing and sintering treatment to obtain an inert anode preform; after setting alumina powder on the surface of the inert anode preform to be in contact with the electrolyte and setting a mixed powder of alumina and carbon powder on the surface to be in contact with the conductive rod, calcining the inert anode preform in an oxygen atmosphere to obtain the inert anode. Attached Figure Description

[0008] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0009] To more clearly illustrate the technical solutions in the embodiments or related technologies of this disclosure, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0010] Figure 1 shows a front cross-sectional view of an inert anode prepared according to a method for preparing an inert anode according to some embodiments of the present disclosure;

[0011] Figure 2 shows a side cross-sectional view of an inert anode prepared according to a method for preparing an inert anode according to some embodiments of the present disclosure;

[0012] Figure 3 shows a top cross-sectional view of an inert anode prepared according to a method for preparing an inert anode according to some embodiments of the present disclosure;

[0013] Figure 4 shows a schematic diagram of the structure of a mold used in a method for preparing an inert anode according to some embodiments of the present disclosure;

[0014] Figure 5 shows a flowchart of a method for preparing an inert anode according to some embodiments of the present disclosure;

[0015] Figure 6 shows a flowchart of the metal-ceramic mixed powder provided in Figure 5;

[0016] Figure 7 shows a flowchart of pressing the metal-ceramic mixed powder into an inert anode green body as shown in Figure 5;

[0017] Figure 8 shows another flowchart of pressing the metal-ceramic mixed powder into an inert anode green body, as shown in Figure 5; and,

[0018] Figure 9 shows a flowchart of the sintering process in Figure 5. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0020] Unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. In the event of any conflict, this specification shall prevail.

[0021] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this disclosure are available on the market or can be prepared by existing methods.

[0022] In related technologies, there is a technical problem that it is difficult to maintain the consistency of metal-ceramic inert anodes with gradient distribution of metal phase content.

[0023] The method for preparing an inert anode according to some embodiments of this disclosure aims to solve the above-mentioned technical problems, and the general approach is as follows:

[0024] Figure 5 shows a flowchart of a method for preparing an inert anode according to some embodiments of the present disclosure. Referring to Figure 5, a method for preparing an inert anode according to some embodiments of the present disclosure includes the following steps:

[0025] S1: Provides metal-ceramic hybrid powder, which includes ceramic powder, metal powder and binder, and the ceramic powder material includes NiFe2O4;

[0026] S2: Press the metal-ceramic mixed powder into an inert anode green body;

[0027] S3: The inert anode green blank is degreased and sintered to obtain the inert anode preform;

[0028] S4: After placing alumina powder on the surface of the inert anode preform that is to be in contact with the electrolyte and a mixture of alumina and carbon powder on the surface that is to be in contact with the conductive rod, the inert anode preform is calcined in an oxygen atmosphere to obtain an inert anode.

[0029] As is easily understood, the inert anode preform has the same shape as the inert anode. During use, a portion of the inert anode's surface will contact the electrolyte, applying voltage to it and causing electrolysis. A portion of the surface not in contact with the electrolyte will contact the conductive rod, which will apply the voltage to the inert anode. The surface of the inert anode preform intended to contact the electrolyte corresponds to the surface of the inert anode that will contact the electrolyte. The surface of the inert anode preform intended to contact the conductive rod corresponds to the surface of the inert anode that will contact the conductive rod.

[0030] During the calcination process, the surface of the inert anode preform that is to come into contact with the electrolyte is covered with alumina powder. Since there is a small amount of oxygen in the alumina powder, this oxygen will react with the metal phase in the inert anode preform to generate oxides, thereby reducing the content of the metal phase and increasing the content of the ceramic phase.

[0031] During the calcination process, the surface of the inert anode preform that is to contact the conductive rod is coated with a mixture of alumina and carbon powder. Under calcination conditions, the carbon powder directly reduces the ceramic phase in the inert anode preform, or it is oxidized to carbon monoxide and then reduces the ceramic phase. After deoxidation, the ceramic phase transforms into a metallic phase, thereby reducing the ceramic phase content and increasing the metallic phase content.

[0032] Therefore, this disclosure involves setting alumina powder on the surface of the inert anode preform that is to be in contact with the electrolyte, and setting a mixed powder of alumina and carbon powder on the surface that is to be in contact with the conductive rod, followed by calcination. This results in the inert anode forming a first metal-ceramic layer (which can also be considered a corrosion-resistant layer) with a low metal phase content and a high ceramic phase content in the part in contact with the electrolyte, and a third metal-ceramic layer (which can also be considered a conductive layer) with a high metal phase content and a low ceramic phase content in the part in contact with the conductive rod. Furthermore, there is a second metal-ceramic layer with the same phase composition as the inert anode preform between the first metal-ceramic layer (corrosion-resistant layer) and the third metal-ceramic layer (conductive layer), forming a gradient structure with different metal phase contents.

[0033] The inert anode preform disclosed herein is integrally formed, and a corrosion-resistant layer and a conductive layer can be formed subsequently through oxidation and reduction. Since the corrosion-resistant layer is formed by oxidizing the inert anode preform with alumina powder on the surface, the metal phase content of the corrosion-resistant layer gradually increases from the outside to the inside. Since the conductive layer is formed by reducing the inert anode preform with a mixture of alumina and carbon powder on the surface, the metal phase content of the conductive layer gradually decreases from the outside to the inside. This allows for the formation of a gradient structure with different metal phase contents inside the inert anode. Furthermore, because the metal phase content changes gradually, the consistency of the inert anode is better.

[0034]

[0035] In some embodiments of this disclosure, the ceramic powder material further includes at least one of NiO, TiN, and ZrB2; and / or,

[0036] The metal powder is made of at least one of Cu, Ni, Fe, Co, and Cr; and / or,

[0037] The metal-ceramic composite powder also includes additives, including at least one selected from MnO2, ZrO2, Y2O3, CeO2, and Nd2O5; and / or,

[0038] The adhesive includes at least one of polyvinyl alcohol, polyvinyl butyral resin, and liquid paraffin.

[0039] It is easy to understand that when the ceramic powder material includes NiO, NiO may exist in the form of NiFe2O4-10NiO.

[0040] It is easy to understand that the beneficial effect of including at least one of NiO, TiN, and ZrB2 in the ceramic powder material is that at least one of these ceramic materials will form a secondary ceramic phase different from the main ceramic phase during sintering. It is also easy to understand that the main ceramic phase is NiFe2O4. The formation of the secondary ceramic phase will help to densify the structure of the inert anode preform, thereby ensuring that the final inert anode also has a densified structure, thus increasing the strength, conductivity, thermal shock resistance, and corrosion resistance of the inert anode.

[0041] It is easy to understand that in the presence of additives, the additives will work synergistically with the sub-ceramic to further increase the densification of the final inert anode.

[0042] In some embodiments of this disclosure, the metal powder accounts for 5% to 30% of the mass of the metal-ceramic mixture; and / or,

[0043] In metal-ceramic composite powders, the ceramic powder accounts for 65%–90% of the mass; and / or,

[0044] In metal-ceramic mixed powders, the additives account for 0-3% of the total mass.

[0045] In some embodiments of this disclosure, the metal-ceramic hybrid powder includes:

[0046] The first powder, by mass percentage, comprises 3% to 5% metal powder, 92% to 94% ceramic powder, and 0% to 3% additives;

[0047] The second powder, by weight percentage, comprises 5%–30% metal powder, 65%–90% ceramic powder, and 0%–3% additives; and,

[0048] The third powder, by weight percentage, comprises 30%–45% metal powder, 55%–65% ceramic powder, and 0%–3% additives.

[0049] The first metal-ceramic layer is formed from a first powder, the second metal-ceramic layer is formed from a second powder, and the third metal-ceramic layer is formed from a third powder.

[0050] It should be noted that in most cases, inert anode green bodies can be formed by pressing a uniformly composed metal-ceramic mixture powder. However, when there are high requirements for the thickness and lifespan of the inert anode, the diffusion depth of oxygen, carbon atoms, and carbon monoxide molecules during oxidation and reduction is limited, insufficient to reduce or increase the content of the metallic phase at a thicker scale. Therefore, in such cases, it is necessary to prepare a first powder, a second powder, and a third powder with gradient distributions of metal and ceramic powder content to form the first, second, and third metal-ceramic layers, respectively. The thickness of the first, second, and third metal-ceramic layers can be directly controlled by the mold.

[0051] Figure 6 illustrates a flowchart of the metal-ceramic mixed powder provided in Figure 5. In some embodiments of this application, referring to Figure 6, the method for preparing an inert anode may include the following steps:

[0052] S11: The raw material powder is obtained by mixing ceramic powder, metal powder, additives and binder, wherein the particle size of ceramic powder, metal powder and additives is 25μm~75μm;

[0053] S12: Wet ball milling of raw material powder to obtain slurry;

[0054] S13: The slurry is processed by spray drying to obtain a metal-ceramic mixed powder.

[0055] It is easy to understand that the first powder, the second powder, and the third powder can all be prepared through steps S11 to S13.

[0056] In some embodiments of this disclosure, the inert anode has a cup-shaped structure. Please refer to Figures 1, 2, and 3. Figure 1 shows a front cross-sectional view of the inert anode prepared according to the preparation method of the inert anode according to some embodiments of this disclosure. Figure 2 shows a side cross-sectional view of the inert anode prepared according to the preparation method of the inert anode according to some embodiments of this disclosure. Figure 3 shows a top cross-sectional view of the inert anode prepared according to the preparation method of the inert anode according to some embodiments of this disclosure. The outer surface of the inert anode is a first metal-ceramic layer 11, the inner surface of the inert anode is a third metal-ceramic layer 13, and a second metal-ceramic layer 12 is disposed between the first metal-ceramic layer 11 and the third metal-ceramic layer 13.

[0057] It is easy to understand that the inert anode with the cup-shaped structure described above can be formed by preparing the first powder, the second powder, and the third powder. At the same time, a corrosion-resistant layer with low metal phase content and high ceramic phase content can be formed on the outer surface of the first metal-ceramic layer 11 by oxidation to contact the electrolyte. On the inner surface of the third metal-ceramic layer 13, a conductive layer with high metal phase content and low ceramic phase content can be formed by reduction to contact the conductive rod.

[0058] In some embodiments of this disclosure, please refer to FIG4, which shows a schematic diagram of the structure of a mold used in the preparation method of an inert anode according to some embodiments of this disclosure. The cup-shaped inert anode described above can be prepared by the mold shown in FIG4. The mold includes a mold shell 22, a top cover 21, a columnar mold core 23, a cylindrical first thin plate 24, and a cylindrical second thin plate 25, wherein the diameters of the columnar mold core 23, the cylindrical first thin plate 24, and the cylindrical second thin plate 25 increase sequentially. The mold shell 22 and the mold core 23 enclose a cup-shaped internal space. The first thin plate 24 and the second thin plate 25 are detachably disposed within the internal space, and the first thin plate 24 is disposed around the mold core 23, and the second thin plate 25 is disposed around the first thin plate 24.

[0059] Figure 7 illustrates a flowchart of pressing the metal-ceramic mixed powder into an inert anode green body as shown in Figure 5. In some embodiments of this application, as shown in Figure 7, the inert anode can have a cup-shaped structure. The method for preparing the inert anode, including pressing the metal-ceramic mixed powder into an inert anode green body, may include the following steps:

[0060] S21: Disassemble the first thin plate 24 and the second thin plate 25 in the mold;

[0061] S22: Under continuous vibration, the metal-ceramic mixture powder is filled into the internal space; and,

[0062] S23: Press the top cover 21 onto the metal-ceramic mixture powder, add the mold into the cold isostatic press, and press to obtain an inert anode green body.

[0063] Then, the inert anode green blank can be prepared into an inert anode through the aforementioned steps S3 and S4.

[0064] Figure 8 illustrates a flowchart of another method for pressing the metal-ceramic mixture powder into an inert anode green body, as shown in Figure 5. In other embodiments of this disclosure, referring to Figure 8, the inert anode can have a cup-shaped structure, comprising a first metal-ceramic layer, a second metal-ceramic layer, and a third metal-ceramic layer. During aluminum electrolysis using the inert anode, the first metal-ceramic layer is in contact with the electrolyte, the third metal-ceramic layer is in contact with the conductive rod, and the second metal-ceramic layer is disposed between the first and third metal-ceramic layers. Therefore, in the method for preparing the inert anode, pressing the metal-ceramic mixture powder into an inert anode green body may include the following steps:

[0065] S21': Under continuous vibration, the third powder is filled into the gap between the first thin plate 24 and the mold core 23, the second powder is filled into the gap between the second thin plate 25 and the first thin plate 24, and the first powder is filled into the gap between the mold shell 22 and the second thin plate 25.

[0066] S22': Extract the first thin plate 24 and the second thin plate 25, and ensure as much as possible that the first powder and the second powder, and the second powder and the third powder, do not mix with each other;

[0067] S23': A third powder is laid on the upper surface of the mold core 23 to form a third powder layer. Then a second powder is laid on the upper surface of the third powder layer to form a second powder layer. Then a first powder is laid on the upper surface of the second powder layer to form a first powder layer.

[0068] S24': Press the top cover 21 onto the first powder layer, add the mold into the cold isostatic press, and press to obtain an inert anode green body; wherein, the first metal-ceramic layer is formed by the first powder, the second metal-ceramic layer is formed by the second powder, and the third metal-ceramic layer is formed by the third powder.

[0069] Then, the inert anode green blank can be prepared into an inert anode through the aforementioned steps S3 and S4.

[0070] In some embodiments of this disclosure, the particle size of the metal-ceramic mixed powder is no greater than 830 μm.

[0071] In some embodiments of this disclosure, the degreasing treatment temperature is 600°C to 800°C; and / or,

[0072] The degreasing process is carried out in an inert atmosphere.

[0073] As an example, the degreasing temperature can be 600℃, 650℃, 700℃, 750℃, or 800℃.

[0074] Figure 9 shows a flowchart of the sintering process in Figure 5. In some embodiments of this disclosure, referring to Figure 9, the sintering process includes the following steps:

[0075] S31: The degreased inert anode green blank is treated at 1200℃~1400℃ in a predetermined atmosphere for 4h~6h, wherein the oxygen concentration of the predetermined atmosphere is 100ppm~5000ppm.

[0076] In some embodiments of this disclosure, the calcination temperature is 900°C to 1200°C; and / or,

[0077] The roasting time is 0.5h to 2h.

[0078] As an example, the roasting temperature can be 900℃, 1000℃, 11000℃, or 1200℃.

[0079] As an example, the roasting duration can be 0.5h, 1h, 1.5h, or 2h.

[0080] In some embodiments of this disclosure, the particle size of the alumina powder is between 1 μm and 1000 μm; and / or,

[0081] In alumina powder, the mass ratio of powder with a particle size of less than 48 μm is more than 20%.

[0082] In some embodiments of this disclosure, the mass ratio of carbon powder in the mixed powder of alumina and carbon powder is 1% to 2%.

[0083] The present disclosure is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the disclosure. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0084] Example 1

[0085] This embodiment discloses a method for preparing an inert anode. First, the mold used for preparing the inert anode disclosed in this embodiment is shown in Figure 4. Figure 4 shows a schematic diagram of the structure of the mold used in the method for preparing the inert anode according to some embodiments of this disclosure. The mold includes a mold shell 22, a top cover 21, a columnar mold core 23, a cylindrical first thin plate 24, and a cylindrical second thin plate 25. The diameters of the columnar mold core 23, the cylindrical first thin plate 24, and the cylindrical second thin plate 25 increase sequentially. The mold shell 22 and the mold core 23 enclose a cup-shaped internal space. The first thin plate 24 and the second thin plate 25 are detachably disposed within the internal space, with the first thin plate 24 surrounding the mold core 23 and the second thin plate 25 surrounding the first thin plate 24.

[0086] Subsequently, the metal-ceramic mixed powder disclosed in this embodiment, based on the mass percentage of the metal-ceramic mixed powder, comprises 20% metal powder, 75% NiFe2O4-10NiO, 3% ZrB2, and 2% polyvinyl alcohol. The metal powder comprises Ni, Fe, Cu, and Co, and the molar ratio of Ni atoms, Fe atoms, Cu atoms, and Co atoms is 45:30:22:3. The particle size of the metal-ceramic mixed powder is no greater than 830 μm.

[0087] The preparation method of an inert anode includes the following steps:

[0088] Disassemble the first thin plate 24 and the second thin plate 25 from the mold;

[0089] Under continuous vibration, the metal-ceramic mixture powder is filled into the internal space;

[0090] The top cover 21 is pressed onto the metal-ceramic mixture powder, and the mold is added into a cold isostatic press to press a cup-shaped inert anode green body.

[0091] The inert anode green blank is degreased and sintered to obtain a cup-shaped inert anode preform;

[0092] The space enclosed by the inner surface of the inert anode preform is completely filled with a mixture of alumina powder and graphite powder. Then, the inert anode preform is completely embedded in the alumina powder and calcined in an air atmosphere to obtain the inert anode.

[0093] The degreasing process is carried out at a temperature of 600℃ in a nitrogen atmosphere.

[0094] The sintering temperature was 1300℃, the sintering duration was 4 hours, and the sintering was carried out in an atmosphere with an oxygen concentration of 500 ppm.

[0095] The roasting temperature was 1200℃ and the roasting duration was 0.5h.

[0096] The particle size of alumina powder is between 1μm and 1000μm. In alumina powder, the mass ratio of powder with a particle size of less than 48μm is 22%. In the mixed powder of alumina and carbon powder, the mass ratio of carbon powder is 1.5%.

[0097] The obtained inert anode has a cup-shaped structure. Please refer to Figures 1, 2, and 3. Figure 1 shows a front cross-sectional view of the inert anode prepared according to the preparation method of some embodiments of the present disclosure. Figure 2 shows a side cross-sectional view of the inert anode prepared according to the preparation method of some embodiments of the present disclosure. Figure 3 shows a top cross-sectional view of the inert anode prepared according to the preparation method of some embodiments of the present disclosure. The outer surface of the inert anode is a corrosion-resistant layer, the inner surface of the inert anode is a conductive layer, and the second metal-ceramic layer 12 is disposed between the corrosion-resistant layer and the conductive layer.

[0098] The inert anode prepared in this embodiment has a smooth surface and no cracks in its cross-section. SEM-EDS analysis of the cross-sectional sample of the inert anode revealed a metallic phase content of 4.6 wt.% in the corrosion-resistant layer, 23 wt.% in the second cermet layer 12, and 78 wt.% in the conductive layer. This demonstrates that this embodiment achieves a gradient structure with varying metallic phase contents through oxidation and reduction. The inert anode exhibits excellent corrosion resistance, thermal shock resistance, and electrical connection with the guide rod, without cracking, with an average corrosion rate of 1.15 cm / a and an electrical conductivity of 62 S / cm. -1 The current carrying capacity of the conductor connection is >25A / cm. 2 .

[0099] Example 2

[0100] This embodiment discloses a method for preparing an inert anode. First, the mold used for preparing the inert anode disclosed in this embodiment is shown in Figure 4. Figure 4 shows a schematic diagram of the structure of the mold used in the method for preparing the inert anode according to some embodiments of this disclosure. The mold includes a mold shell 22, a top cover 21, a columnar mold core 23, a cylindrical first thin plate 24, and a cylindrical second thin plate 25. The diameters of the columnar mold core 23, the cylindrical first thin plate 24, and the cylindrical second thin plate 25 increase sequentially. A cup-shaped internal space is enclosed between the mold shell 22 and the mold core 23. The first thin plate 24 and the second thin plate 25 are detachably disposed within the internal space, with the first thin plate 24 surrounding the mold core 23 and the second thin plate 25 surrounding the first thin plate 24.

[0101] Subsequently, the metal-ceramic mixed powder disclosed in this embodiment, based on the mass percentage of the metal-ceramic mixed powder, comprises 10% metal powder, 70% NiFe2O4-10NiO, 15% TiN, 3% ZrB2, and 2% polyvinyl alcohol. The metal powder comprises Ni, Fe, and Cu, and the molar ratio of Ni atoms, Fe atoms, and Cu atoms is 45:30:25. The particle size of the metal-ceramic mixed powder is no greater than 830 μm.

[0102] The preparation method of an inert anode includes the following steps:

[0103] Disassemble the first thin plate 24 and the second thin plate 25 from the mold;

[0104] Under continuous vibration, the metal-ceramic mixture powder is filled into the internal space;

[0105] The top cover 21 is pressed onto the metal-ceramic mixture powder, and the mold is added into a cold isostatic press to press a cup-shaped inert anode green blank.

[0106] The inert anode green blank is degreased and sintered to obtain a cup-shaped inert anode preform;

[0107] The space enclosed by the inner surface of the inert anode preform is completely filled with a mixture of alumina powder and graphite powder. Then, the inert anode preform is completely embedded in the alumina powder and calcined in an air atmosphere to obtain the inert anode.

[0108] The degreasing process is carried out at a temperature of 600℃ in a nitrogen atmosphere.

[0109] The sintering temperature was 1300℃, the sintering duration was 4h, and the sintering was carried out in an atmosphere with an oxygen concentration of 1000ppm.

[0110] The roasting temperature was 1200℃ and the roasting duration was 0.5h.

[0111] The particle size of alumina powder is between 1μm and 1000μm. In alumina powder, the mass ratio of powder with a particle size of less than 48μm is 22%. In the mixed powder of alumina and carbon powder, the mass ratio of carbon powder is 1.5%.

[0112] The obtained inert anode has a cup-shaped structure. Please refer to Figures 1, 2, and 3. Figure 1 shows a front cross-sectional view of the inert anode prepared according to the preparation method of some embodiments of the present disclosure. Figure 2 shows a side cross-sectional view of the inert anode prepared according to the preparation method of some embodiments of the present disclosure. Figure 3 shows a top cross-sectional view of the inert anode prepared according to the preparation method of some embodiments of the present disclosure. The outer surface of the inert anode is a corrosion-resistant layer, the inner surface of the inert anode is a conductive layer, and the second metal-ceramic layer 12 is disposed between the corrosion-resistant layer and the conductive layer.

[0113] The inert anode prepared in this embodiment has a smooth surface and no cracks in its cross-section. SEM-EDS analysis of the cross-sectional sample of the inert anode revealed a metallic phase content of 4.6 wt.% in the corrosion-resistant layer, 15 wt.% in the second cermet layer, and 80 wt.% in the conductive layer. This demonstrates that this embodiment achieves a gradient structure with varying metallic phase contents through oxidation and reduction. The inert anode exhibits excellent corrosion resistance, thermal shock resistance, and electrical connection with the guide rod, without cracking, with an average corrosion rate of 1.12 cm / a and an electrical conductivity of 58 S / cm. -1 The current carrying capacity of the conductor connection is >25A / cm. 2 .

[0114] Example 3

[0115] This embodiment discloses a method for preparing an inert anode. First, the mold used for preparing the inert anode disclosed in this embodiment is shown in Figure 4. Figure 4 shows a schematic diagram of the structure of the mold used in the method for preparing an inert anode according to some embodiments of this disclosure. The mold includes a mold shell 22, a top cover 21, a columnar mold core 23, a cylindrical first thin plate 24, and a cylindrical second thin plate 25. The diameters of the columnar mold core 23, the cylindrical first thin plate 24, and the cylindrical second thin plate 25 increase sequentially. The mold shell 22 and the mold core 23 enclose a cup-shaped internal space. The first thin plate 24 and the second thin plate 25 are detachably disposed within the internal space, with the first thin plate 24 surrounding the mold core 23 and the second thin plate 25 surrounding the first thin plate 24.

[0116] Subsequently, the metal-ceramic hybrid powder disclosed in this embodiment includes:

[0117] The first powder, by mass percentage, comprises 4% first metal powder, 82% NiFe2O4-10NiO, 12% TiN and 2% polyvinyl alcohol.

[0118] The second powder, by mass percentage, comprises 5% second metal powder, 75% NiFe2O4-10NiO, 12% TiN, 3% ZrB2, 3% Nd2O5 and 2% polyvinyl alcohol.

[0119] The third powder, by mass percentage, comprises 30% third metal powder, 65% NiFe2O4-10NiO, 3% CeO2, and 2% polyvinyl alcohol.

[0120] The first metal powder comprises Ni, Fe, Cu, and Cr, with a molar ratio of Ni, Fe, Cu, and Cr atoms of 45:35:10:15. The second metal powder comprises Cu, Ni, and Fe, with a molar ratio of Cu, Ni, and Fe atoms of 65:20:15. The third metal powder comprises Cu, Ni, and Fe, with a molar ratio of Cu, Ni, and Fe atoms of 50:30:20. The particle size of all three powders is no greater than 830 μm.

[0121] The preparation method of an inert anode includes the following steps:

[0122] Under continuous vibration, the third powder is filled into the gap between the first thin plate 24 and the mold core 23, the second powder is filled into the gap between the second thin plate 25 and the first thin plate 24, and the first powder is filled into the gap between the mold shell 22 and the second thin plate 25.

[0123] Remove the first thin plate 24 and the second thin plate 25, and ensure as much as possible that the first powder and the second powder, and the second powder and the third powder, do not mix with each other;

[0124] A third powder is laid on the upper surface of the mold core 23 to form a third powder layer. Then, a second powder is laid on the upper surface of the third powder layer to form a second powder layer. Then, a first powder is laid on the upper surface of the second powder layer to form a first powder layer.

[0125] The top cover 21 is pressed onto the first powder layer, and the mold is added into the cold isostatic press to press and obtain an inert anode green blank.

[0126] The inert anode green blank is degreased and sintered to obtain a cup-shaped inert anode preform;

[0127] The space enclosed by the inner surface of the inert anode preform is completely filled with a mixture of alumina powder and graphite powder. Then, the inert anode preform is completely embedded in the alumina powder and calcined in an air atmosphere to obtain the inert anode.

[0128] The degreasing process is carried out at a temperature of 600℃ in a nitrogen atmosphere.

[0129] The sintering temperature was 1300℃, the sintering duration was 4h, and the sintering was carried out in an atmosphere with an oxygen concentration of 1000ppm.

[0130] The roasting temperature was 1200℃ and the roasting duration was 0.5h.

[0131] The particle size of alumina powder is between 1μm and 1000μm. In alumina powder, the mass ratio of powder with a particle size of less than 48μm is 22%. In the mixed powder of alumina and carbon powder, the mass ratio of carbon powder is 1.5%.

[0132] The obtained inert anode has a cup-shaped structure. Please refer to Figures 1, 2, and 3. Figure 1 shows a front cross-sectional view of the inert anode prepared according to the preparation method of some embodiments of the present disclosure. Figure 2 shows a side cross-sectional view of the inert anode prepared according to the preparation method of some embodiments of the present disclosure. Figure 3 shows a top cross-sectional view of the inert anode prepared according to the preparation method of some embodiments of the present disclosure. The outer surface of the inert anode is a first metal-ceramic layer 11, the inner surface of the inert anode is a third metal-ceramic layer 13, and a second metal-ceramic layer 12 is disposed between the first metal-ceramic layer 11 and the third metal-ceramic layer 13. The outer surface of the first metal-ceramic layer 11 is a corrosion-resistant layer, and the inner surface of the third metal-ceramic layer 13 is a conductive layer.

[0133] The inert anode prepared in this embodiment has a smooth surface and no cracks in its cross-section. The inert anode exhibits good corrosion resistance, thermal shock resistance, and electrical connection with the guide rod, without cracking. The average corrosion rate is 1.2 cm / a, and the electrical conductivity is 63 S / cm. - 1 The current carrying capacity of the conductor connection is >25A / cm. 2 .

[0134] The method for preparing an inert anode according to some embodiments of this disclosure has the following advantages compared with related technologies:

[0135] According to some embodiments of the present disclosure, the method for preparing an inert anode involves preparing an integrally formed inert anode preform and then forming an inert anode with a gradient structure having different metal phase contents through oxidation and reduction, thereby achieving high consistency of the inert anode.

[0136] Various embodiments of this disclosure may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this disclosure; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0137] In this disclosure, unless otherwise stated, directional terms such as “upper” and “lower” specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this disclosure, the terms “comprising,” “including,” etc., mean “including, but not limited to,” etc. Moreover, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase “comprising…” does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this document, relational terms such as “first” and “second” are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, “and / or” describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. For associations involving three or more related objects described using "and / or", it indicates that any one of the three related objects can exist alone, or at least two of them can exist simultaneously. For example, for A, and / or B, and / or C, it can mean that any one of A, B, and C exists alone, or any two of them exist simultaneously, or all three of them exist simultaneously. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one", "at least one of the following", or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or multiple.

[0138] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an inert anode, comprising: A metal-ceramic hybrid powder is provided, the metal-ceramic hybrid powder comprising ceramic powder, metal powder and binder, wherein the ceramic powder is composed of NiFe2O4. The metal-ceramic mixture powder is pressed into an inert anode green body; The inert anode green blank is subjected to degreasing and sintering treatment to obtain an inert anode preform; After alumina powder is applied to the surface of the inert anode preform that is to be in contact with the electrolyte, and a mixture of alumina and carbon powder is applied to the surface that is to be in contact with the conductive rod, the inert anode preform is calcined in an oxygen atmosphere to obtain the inert anode.

2. The method for preparing the inert anode according to claim 1, wherein, The ceramic powder material further includes at least one of NiO, TiN, and ZrB2; and / or, The metal powder is made of at least one of Cu, Ni, Fe, Co, and Cr; and / or, The metal-ceramic mixed powder further includes additives, which include at least one selected from MnO2, ZrO2, Y2O3, CeO2, and Nd2O5; and / or, The adhesive includes at least one of polyvinyl alcohol, polyvinyl butyral resin, and liquid paraffin.

3. The method for preparing the inert anode according to claim 2, wherein, In the aforementioned metal-ceramic composite powder, the metal powder accounts for 5% to 30% by mass; and / or, In the aforementioned metal-ceramic composite powder, the ceramic powder accounts for 65% to 90% of the total mass; and / or, In the metal-ceramic mixed powder, the additive accounts for 0-3% of the total mass.

4. The method for preparing an inert anode according to claim 2, wherein, The metal-ceramic mixed powder includes: The first powder, by mass percentage, comprises 3% to 5% metal powder, 92% to 94% ceramic powder, and 0% to 3% additives; The second powder, by weight percentage, comprises 5%–30% metal powder, 65%–90% ceramic powder, and 0%–3% additives; and, The third powder, by mass percentage, comprises 30% to 45% metal powder, 55% to 65% ceramic powder, and 0% to 3% additives; The inert anode comprises a first metal-ceramic layer, a second metal-ceramic layer, and a third metal-ceramic layer. During aluminum electrolysis at the inert anode, the first metal-ceramic layer is in contact with the electrolyte, the third metal-ceramic layer is in contact with the conductive rod, and the second metal-ceramic layer is disposed between the first metal-ceramic layer and the third metal-ceramic layer. The first metal-ceramic layer is formed from the first powder, the second metal-ceramic layer is formed from the second powder, and the third metal-ceramic layer is formed from the third powder.

5. The method for preparing an inert anode according to any one of claims 1 to 4, wherein, The particle size of the metal-ceramic mixed powder is no greater than 830 μm.

6. The method for preparing an inert anode according to claim 5, wherein, The degreasing treatment is performed at a temperature of 600℃~800℃; and / or, The degreasing process is carried out in an inert atmosphere.

7. The method for preparing an inert anode according to claim 5, wherein, The sintering process includes the following steps: The degreased inert anode green blank is treated at 1200℃~1400℃ in a predetermined atmosphere for 4h~6h, wherein the oxygen concentration of the predetermined atmosphere is 100ppm~5000ppm.

8. The method for preparing an inert anode according to claim 5, wherein, The calcination temperature is 900℃~1200℃; and / or, The roasting time is 0.5h to 2h.

9. The method for preparing an inert anode according to claim 5, wherein, The alumina powder has a particle size between 1 μm and 1000 μm; and / or, In the alumina powder, the mass ratio of powder with a particle size of less than 48 μm is more than 20%.

10. The method for preparing an inert anode according to claim 5, wherein, In the mixture of alumina and carbon powder, the mass ratio of carbon powder is 1% to 2%.