PREPARATION METHOD FOR ALUMINUM ELECTROLYSIS METAL ANODE

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of International Application No. PCT/CN 2024/094665, filed on May 22, 2024, which claims priority to Chinese Patent Application No. 202310873392.1, filed on Jul. 17, 2023, the entire contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure generally relates to the technical field of powder metallurgy and powder engineering, and in particular to an integrated preparation method for aluminum electrolysis metal anode shell and electric connection.

BACKGROUND

Carbon-free aluminum electrolysis technology based on an inert anode can reduce carbon consumption and eliminate emission of greenhouse gases and toxic gases during an electrolysis process. The technology is currently a key area of focus in an international aluminum industry. Fe-Ni series alloys can withstand a harsh and complex corrosive environment of electrolysis in cryolite molten salt at temperatures above 700° C., and have good electrical conductivity, thermal shock resistance, and mechanical strength, making the Fe-Ni series alloys an important class of inert anode materials. Currently, manufacturing large-sized, complex-shaped inert anodes and establishing stable electrical connections between the inert anodes and metal inner cores have been key factors for determining whether metal inert anodes can achieve industrial application.

Therefore, it is necessary to provide an integrated preparation method for aluminum electrolysis metal anode shell and electric connection to obtain an anode product with both high strength and high precision through a process with simple operation and short flow.

SUMMARY

To solve the above technical problems existing in the background, the present disclosure aims to provide an integrated preparation method for a complex-structure metal inert anode and electric connection of the complex-structure metal inert anode. The method achieves near-net-shape forming of a metal anode shell with a special-shaped structure through rheological pressing, which features a rapid process and high forming precision. Meanwhile, densification of the metal anode shell and the electric connection is completed simultaneously through one-step sintering, without requiring a separate electric connection process. The method is suitable for mass manufacturing of inert anodes for aluminum electrolysis that have complex geometric shapes, high performance, and high precision. To achieve the above objective, the present disclosure provides the following technical solutions.

One or more embodiments of the present disclosure provide an integrated preparation method for aluminum electrolysis metal anode shell and electric connection. The method includes: mixing a metal shell powder with a thermoplastic binder to obtain a semisolid hot mixture; crushing the semisolid hot mixture to obtain metal shell feedstock granules; preheating a mold to a temperature 20-50° C. higher than a softening point temperature of the thermoplastic binder, filling preheated metal shell feedstock granules into the mold, applying pressure and heating to a temperature 5-50° C. higher than the softening point temperature of the thermoplastic binder, and performing a rheological pressing to obtain a metal shell green body; filling an alloy inner core powder into a core part of the metal shell green body to obtain an inert anode green body with an alloy inner core; and sintering the inert anode green body with the alloy inner core to obtain an integrated inert anode for aluminum electrolysis metal anode shell and electric connection. The metal shell powder, in mass percentage, has a composition as follows: 10-60% of Ni, 5-30% of M, and a balance of Fe, wherein M is selected from at least one of Cu, Co, Cr, Mn, Al, Ag, Zn, Ti, Sn, W, Mo, Zr, or Nb. A particle size of the metal shell feedstock granules is within a range of −10 mesh to +200 mesh. The metal shell feedstock granules are preheated to 60-80° C., and the mold is preheated to 60-100° C. A pressure of 20-60 MPa is applied along a shell pressing direction, and a temperature is increased to 120-170° C., and the rheological pressing is performed for 10-40 min to obtain the metal shell green body. The sintering is performed in a protective atmosphere, and a process of the sintering includes: first increasing a temperature to 400-600° C., holding for 8-12 h, then further increasing the temperature to K1, then decreasing the temperature to K2, holding for 4-6 h, and cooling to a room temperature, wherein K1-K2≥50° C., K1 is 1300-1400° C., and K2 is 1150-1350° C.

Compared with the prior art, the present disclosure has the following advantages:

• • (1) The integrated preparation method for aluminum electrolysis metal anode shell and electric connection provided by the present disclosure achieves near-net-shape forming of a metal anode shell with the special-shaped structure through a rheological pressing manner, which solves problems of complex forming process, poor forming precision, and low strength of a formed green body for large-size aluminum electrolysis metal anodes.
  • (2) The integrated preparation method for aluminum electrolysis metal anode shell and electric connection provided by the present disclosure adopts a two-step sintering manner to simultaneously complete densification of the metal anode shell and the electric connection, which solves problems of low bonding strength of an electric connection part of a conductive rod and anode cracking caused by secondary processing.
  • (3) The integrated preparation method for aluminum electrolysis metal anode shell and electric connection provided by the present disclosure has a simple operation process and a short flow, which can obtain anode with high strength and high precision. The method solves a contradiction that preparation of an anode with a complex shape is difficult to simultaneously achieve near-net-shape forming and mass short-flow manufacturing.

BRIEF DESCRIPTION OF THE DRAWINGS

To more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings used in the embodiments are briefly introduced below. It should be understood that the following drawings only show some embodiments of the present disclosure and therefore should not be considered as limiting the scope of the present disclosure.

FIG. 1 is a flowchart illustrating an exemplary process of an integrated preparation method for aluminum electrolysis metal anode shell and electric connection according to some embodiments of the present disclosure;

FIG. 2 is a schematic diagram illustrating a mold structure according to some embodiments of the present disclosure;

FIG. 3 is a schematic diagram illustrating an anode structure according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

To facilitate understanding of the present disclosure, a more comprehensive and detailed description of the present disclosure is provided below in conjunction with the accompanying drawings and preferred embodiments. It should be noted that the described embodiments are merely a part of the embodiments of the present disclosure, and not all embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present disclosure.

Chinese Patent Application (Publication No. CN113172222A) discloses a preparation method for aluminum electrolysis metal-ceramic inert anode based on a gel casting process, which can achieve rapid near-net-shape forming of the metal-ceramic inert anode, but the method has limited forming capability for large-sized anodes. Chinese Patent Application (Publication No. CN113337849A) describes a 3D printing preparation method for a complex-structured metal-ceramic inert anode, which can achieve near-net-shape forming of a T-shaped structure anode through additive manufacturing, but the manufacturing process is long, and electrical connection of a special-shaped structure is not considered. Chinese Patent Application (Publication No. CN108396335A) discloses a connection structure and a preparation method for a metal-ceramic-based inert anode and a conductive rod, where the connection structure consists of the metal-ceramic-based inert anode, an intermediate alloy ingot, and a metal conductive rod, but this process is complex and long. Chinese Patent Application (Publication No. CN101851767A) describes a ceramic-based anode and a preparation and assembly method thereof, where a filler is added between the ceramic-based anode and a metal conductive rod to connect and form a structure, but the method is not easy for connecting the special-shaped structures.

To avoid the above problems, the present disclosure achieves near-net-shape forming of a metal anode shell with the special-shaped structure through a rheological pressing manner, and a two-step sintering manner can simultaneously complete densification of the metal anode shell and electric connection. The method is simple to operate and has a short flow, and the obtained anode has high strength and high precision.

FIG. 1 is a flowchart illustrating an exemplary process of an integrated preparation method for aluminum electrolysis metal anode shell and electric connection according to some embodiments of the present disclosure.

In some embodiments, as shown in FIG. 1, a process 100 includes steps 110 to 150.

Step 110, mixing a metal shell powder with a thermoplastic binder to obtain a semisolid hot mixture.

The metal shell powder refers to a metal powder used for preparing an aluminum electrolysis inert metal anode shell.

In some embodiments, the metal shell powder, in mass percentage, has a composition as follows: 10-60% of Ni, 5-30% of M, and a balance of Fe. M is selected from at least one of Cu, Co, Cr, Mn, Al, Ag, Zn, Ti, Sn, W, Mo, Zr, or Nb.

It can be understood that a function of Ni is to provide basic corrosion resistance and a stable austenite structure, and a proportion of Ni needs to be maintained within a certain range. If a proportion of Ni is too high, it will lead to cost escalation, potential brittleness, and poor thermal compatibility. If the proportion of Ni is too low, it will result in poor corrosion resistance, structural instability, and short service life. A function of M is to finely adjust properties (e.g., conductivity, strengthening, oxidation resistance), and a proportion of M needs to be maintained within a certain range. If the proportion of M is too high, it will from a harmful brittle phase, impair toughness, and cause processing difficulties. If the proportion of M is too low, an adjustment effect will be not significant, and properties will be mediocre. A function of Fe is to provide basic strength and balance physical properties, and a proportion of Fe is determined by the proportion of Ni and the proportion of M.

In some embodiments, the metal shell powder, in mass percentage, has a composition as follows: 5-50% of Ni, 10-40% of M, and the balance of Fe.

In some embodiments, the metal shell powder, in mass percentage, has a composition as follows: 18-45% of Ni, 2-38% of M, and the balance of Fe.

In some embodiments, the metal shell powder, in mass percentage, has a composition as follows: 15-70% of Ni, 1-20% of M, and the balance of Fe.

In some embodiments, a particle size of the metal shell powder is within a range of 0.05-1 μm; the metal shell powder is obtained by pulverizing and classifying the metal powder. The pulverizing is performed by nano grinding using a turbine nano sand mill, and working parameters for the nano grinding include a rotational speed of 580-1500 rpm and a flow rate of 50-500 L/H. The classifying is performed using a jet air classifier, and working parameters for the classifying include a feed rate of 50-100 kg/h, a working pressure of 1.5-20 MPa, and an air pressure of a cyclone collector of 1.5-20 kPa.

In some embodiments, the particle size of the metal shell powder needs to be maintained within a certain range. If the particle size of the metal shell powder is too large, interface wettability and mixing uniformity between the metal shell powder and the thermoplastic binder decrease; if the particle size of the metal shell powder is too small, a specific surface area of the metal shell powder is too large, agglomeration is prone to occur, thereby reducing mixing uniformity between the metal shell powder and the thermoplastic binder.

In some embodiments, the particle size of the metal shell powder is within a range of 0.05-1 μm. In some embodiments, the particle size of the metal shell powder is within a range of 0.5-0.8 μm. It can be understood that the particle size of the metal shell powder may be 0.05 μm, 0.08 μm, 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, and any value within a range formed by any two of the above values.

The metal powder refers to fine particles of metal or alloy having a certain particle size distribution. For example, the metal powder may include Ni, M, and Fe. M is selected from at least one of Cu, Co, Cr, Mn, Al, Ag, Zn, Ti, Sn, W, Mo, Zr, or Nb.

In some embodiments, the pulverizing is performed in the turbine nano sand mill. During the pulverizing, particles of different particle sizes may be obtained by adjusting the rotational speed and the flow rate.

The turbine nano sand mill refers to a device used for grinding the metal powder. The turbine nano sand mill drives grinding media (e.g., zirconia beads) through a high-speed rotating turbine to generate strong shear, impact, and friction forces, which can obtain metal powder particles with a particle size of 0.05-1 μm. In some embodiments, during the nano grinding, a filling ratio of the zirconia beads is within a range of 60-70%.

The nano grinding refers to a processing process of pulverizing the metal powder to a certain particle size. For example, a process of grinding metal powder using the turbine nano sand mill to achieve a particle size of 0.05-1 μm for the metal powder.

In some embodiments, the metal powder may be placed into the turbine nano sand mill, the grinding media (e.g., the zirconia beads) may be added, and the working parameters of the turbine nano sand mill may be set as: a rotational speed of 580-1500 rpm and a flow rate of 50-500 L/H, so as to perform nano grinding on the metal powder.

In some embodiments, the classifying is performed in the jet air classifier. During the classifying, separation of particles with the different particle sizes may be achieved by adjusting the feed rate, the working pressure, and the air pressure of the cyclone collector.

The jet air classifier refers to a device for separating and sorting the power particles with different particle sizes obtained after the nano grinding. For example, the jet air classifier may be used to classify metal powder after the nano grinding, ensuring that the obtained metal shell powder has a particle size controlled within a range of 0.05-1 μm to meet raw material uniformity requirements of a subsequent rheological pressing process.

The classifying refers to a process of separating powder particles into different specifications or grades according to physical characteristics of the powder particles, such as the particle size, shape, or density. For example, the jet air classifier is used to process ground metal powder, and metal shell powder with an average particle size of 0.4 μm and a concentrated particle size distribution is obtained after the classifying.

In some embodiments, the powder particles with the different particle sizes obtained after the grinding may be placed into the jet air classifier, and working parameters of the jet air classifier may be set as follows: a feed rate of 50-100 kg/h, a working pressure of 1.5-20 MPa, and an air pressure of a cyclone collector of 1.5-20 kPa, so as to classify the powder particles with the different particle sizes obtained after the grinding.

In some embodiments of the present disclosure, metal shell powder with uniform particle size and a narrow distribution range may be obtained through the aforementioned crushing and classifying steps.

The thermoplastic binder refers to an additive that imparts viscosity, fluidity, and strength to the metal powder particles. The thermoplastic binder has characteristics such as softening or melting upon heating and re-solidifying upon cooling.

In some embodiments, the thermoplastic binder includes a filler binder, a backbone binder, a surfactant, and a plasticizer. In some embodiments, the thermoplastic binder, in volume percentage, has a composition as follows: 70-85 vol % of a filler binder, 10-20 vol % of a backbone binder, 2-5 vol % of a surfactant, and 0.5-2 vol % of a plasticizer; and the filler binder has a melt index greater than or equal to 80 g/min, and the backbone binder has a melt index greater than or equal to 35 g/min.

In some embodiments, the thermoplastic binder, in volume percentage, has a composition as follows: 60-94.5 vol % of a filler binder, 5-30 vol % of a backbone binder, 1-10 vol % of a surfactant, and 0.5-5 vol % of a plasticizer.

The filler binder refers to an additive that provides fluidity and filling lubrication for the semisolid hot mixture. A proportion of the filler binder needs to be maintained within a certain range. If the proportion of the filler binder is too large (e.g., exceeding 85 vol %), a viscosity of a system becomes too low, which may cause the material to easily leak from gaps of the mold during the subsequent rheological pressing process, resulting in pressure relief and powder-binder separation, thereby reducing a density and worsening dimensional accuracy of a metal shell green body obtained by the subsequent rheological pressing. In addition, insufficient skeleton support during a subsequent debinding stage may increase a risk of deformation or collapse of the metal shell green body. Conversely, if the proportion of the filler binder is too small (e.g., below 70 vol %), fluidity of the system is significantly insufficient, the material may have difficulty fully filling a cavity of the mold, and defects such as underfill or unfilled corners may easily form. Simultaneously, uneven powder coating may lead to low densification and poor strength of the metal shell green body, and cracks may easily form after debinding due to a loose structure.

In some embodiments, a volume percentage of the filler binder may be within a range of 70-85 vol %. In some embodiments, the volume percentage of the filler binder may be within a range of 71-83 vol %. In some embodiments, the volume percentage of the filler binder may be within a range of 75-82 vol %. In some embodiments, the volume percentage of the filler binder may be within a range of 76-80 vol %.

In some embodiments, the filler binder is selected from at least one of paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, polyethylene glycol, polyoxymethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate, or methyl cellulose.

In some embodiments, the filler binder is selected from at least one of carnauba wax, polyoxymethylene, or polyethylene glycol.

In some embodiments, the filler binder is polyoxymethylene.

In some embodiments of the present disclosure, by selecting an appropriate type and proportion of the filler binder, fluidity and forming stability of metal shell feedstock granules are optimized, and interface wettability with the metal shell powder is improved.

A melt index of the filler binder needs to be maintained within a certain range. If the melt index of the filler binder is too low, fluidity of the filler binder at a rheological temperature is insufficient to achieve complete filling of a complex cavity and particle rearrangement, which will seriously affect forming accuracy and uniformity of the metal shell green body.

In some embodiments, the melt index of the filler binder is greater than or equal to 80 g/min. In some embodiments, the melt index of the filler binder is greater than or equal to 82 g/min. In some embodiments, the melt index of the filler binder is greater than or equal to 83 g/min. In some embodiments, the melt index of the filler binder is greater than or equal to 85 g/min. In some embodiments, the melt index of the filler binder is greater than or equal to 89 g/min. In some embodiments, the melt index of the filler binder is greater than or equal to 92 g/min.

A backbone binder refers to an additive that provides skeleton strength for the semisolid hot mixture. A proportion of the backbone binder needs to be maintained within a certain range. If the proportion of the backbone binder is too high (e.g., exceeding 20 vol %), a dominant flow effect of the filler binder may be hindered, overall fluidity of a mixture may be reduced, a debinding process may be prolonged, and a final sintered product may be contaminated due to polymer residue; if the proportion of the backbone binder is too low (e.g., below 10 vol %), the metal shell green body may lack sufficient skeleton support during a middle stage of the debinding, and deformation, softening, or even collapse may easily occur.

In some embodiments, a volume percentage of the backbone binder may be within a range of 10-20 vol %. In some embodiments, the volume percentage of the backbone binder may be within a range of 11-24 vol %. In some embodiments, the volume percentage of the backbone binder may be within a range of 12-23 vol %. In some embodiments, the volume percentage of the backbone binder may be within a range of 15-20 vol %.

In some embodiments, the backbone binder is selected from at least one of polypropylene, high-density polyethylene, low-density polyethylene, polystyrene, or polymethyl methacrylate.

The high-density polyethylene refers to polyethylene with a density of 0.94-0.97 g/cm³.

The low-density polyethylene refers to polyethylene with a density of 0.91-0.93 g/cm³.

A melt index of the backbone binder needs to be maintained within a certain range. If the melt index of the backbone binder is too low, the backbone binder may not match fluidity of the filler binder, hindering homogeneous flow of the mixture, and increasing internal stress during the debinding process due to poor molecular chain mobility, thereby increasing a risk of cracking of the metal shell green body.

In some embodiments, the melt index of the backbone binder is greater than or equal to 35 g/min. In some embodiments, the melt index of the backbone binder is greater than or equal to 38 g/min. In some embodiments, the melt index of the backbone binder is greater than or equal to 40 g/min. In some embodiments, the melt index of the backbone binder is greater than or equal to 42 g/min. In some embodiments, the melt index of the backbone binder is greater than or equal to 48 g/min.

The surfactant refers to an additive used to improve interfacial compatibility and wettability between the metal powder and the thermoplastic binder. A proportion of the surfactant needs to be maintained within a certain range. If the proportion of the surfactant is too high (e.g., higher than 5 vol %), too many small-molecule substances are introduced, which reduces thermal stability of the system and may cause mixing foaming or component segregation. If the proportion of the surfactant is too low (e.g., lower than 2 vol %), the wettability between the metal powder and the thermoplastic binder is poor, which easily leads to agglomeration of the metal powder and uneven dispersion, thereby affecting uniformity and compactness of the metal shell green body.

In some embodiments, a volume percentage of the surfactant may be within a range of 2-5 vol %. In some embodiments, the volume percentage of the surfactant may be within a range of 2.5-4.5 vol %. In some embodiments, the volume percentage of the surfactant may be within a range of 3-3.5 vol %.

In some embodiments, the surfactant is selected from at least one of stearic acid, zinc stearate, glycerol, castor oil, or peanut oil.

The plasticizer refers to an additive used to enhance plasticity and formability of the semisolid hot mixture, and integrity of the metal shell green body after the demolding. A proportion of the plasticizer needs to be maintained within a certain range. If the plasticizer is excessive (e.g., higher than 2 vol %), subsequently generated metal shell feedstock granules are excessively softened, causing insufficient strength and easy deformation of the metal shell green body, and migration of the plasticizer may lead to uneven composition. If the plasticizer is insufficient (e.g., lower than 0.5 vol %), brittleness of the subsequently generated metal shell feedstock granules increases, elastic recovery during the rheological pressing is significant, and microcracks are easily initiated during the demolding.

In some embodiments, the plasticizer is selected from at least one of dibutyl phthalate, dioctyl phthalate, isodecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythritol tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 4,4′-methylenebis(2,6-di-tert-butylphenol), or n-octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

In some embodiments of the present disclosure, by using a thermoplastic binder with strong adaptability, performance of a product obtained after the rheological pressing and sintering of a material for powder metallurgy rheological pressing can be optimized. The thermoplastic binder and the metal powder have a good interfacial wettability characteristic. When a volume fraction of the metal powder is relatively high while a content of the thermoplastic binder is relatively low, the metal shell green body obtained by the subsequent rheological pressing can still maintain good strength. Based on this, a content of the thermoplastic binder in the rheological pressing process can be further reduced compared to a traditional injection molding process, which is beneficial for improving dimensional accuracy of manufactured components.

In the present disclosure, a volume fraction of the metal shell powder needs to be maintained within a certain range. If the volume fraction of the metal shell powder is too low and the volume fraction of the thermoplastic binder is too high, viscosity of a preheated metal shell feedstock granules is too low, and the metal shell feedstock granules easily continuously flow out in a fitting gap between a punch and a female die due to a shear-thinning effect, thereby causing pressure release and separation between local metal shell powder and the thermoplastic binder, and further reducing forming density and surface quality of the metal shell green body obtained by the subsequent rheological pressing. If the volume fraction of the metal shell powder is too high and the volume fraction of the thermoplastic binder is too low, fluidity of the preheated metal shell feedstock granules may be lost, the metal shell green body may not be densely formed, and cracking and deformation may be initiated during subsequent debinding and sintering, ultimately resulting in a defective product with a loose structure and poor performance.

In some embodiments, in the semisolid hot mixture, the volume fraction of the metal shell powder is within a range of 60%-80%. In some embodiments, in the semisolid hot mixture, the volume fraction of the metal shell powder is within a range of 60%-70%. In some embodiments, in the semisolid hot mixture, the volume fraction of the metal shell powder is within a range of 62%-70%. In some embodiments, in the semisolid hot mixture, the volume fraction of the metal shell powder is within a range of 63%-67%.

In some embodiments of the present disclosure, by reasonably controlling a content of the metal shell powder, incomplete debinding problems caused by an excessively high proportion of the binder are avoided, compactness of the metal shell green body is improved, pore defects in the metal anode shell after the sintering are reduced, and mechanical strength of the metal anode shell is enhanced.

In some embodiments, the metal shell powder and the thermoplastic binder may be placed into a mixing machine for mixing to obtain the semisolid hot mixture.

In some embodiments, a temperature for the mixing (or referred to as a mixing temperature) is within a range of 120-200° C., and a time for the mixing (or referred to as a mixing time) is within a range of 30-60 min.

In some embodiments, the mixing is performed in a roller-type medium-temperature internal mixer.

The temperature for the mixing refers to a temperature set when mixing to obtain the semisolid hot mixture.

In some embodiments, the temperature for the mixing needs to be controlled within a certain range. If the temperature for the mixing is too low (e.g., lower than 120° C.), the thermoplastic binder cannot be sufficiently softened and melted, making the thermoplastic binder difficult to form uniform interfacial wettability with the metal shell powder, resulting in uneven mixing of the metal shell powder and the thermoplastic binder, poor dispersion of the material, and subsequently poor formability of the metal shell feedstock granules. During rheological pressing, secondary distribution of the powder and rearrangement of the particles cannot be achieved, and the metal shell green body is prone to problems such as uneven density and surface defects. If the temperature for the mixing is too high (e.g., higher than 200° C.), the thermoplastic binder undergoes thermal decomposition, volatilization, or aging, damaging bonding performance of the thermoplastic binder, causing the powder-binder separation. After the crushing, qualified metal shell feedstock granules are difficult to form, and, during a subsequent forming process, problems such as material loss and pressure release are prone to occur.

In some embodiments, the temperature for the mixing is within a range of 120-200° C. In some embodiments, the temperature for the mixing is within a range of 150-180° C. Understandably, the temperature for the mixing may be 120° C., 140° C., 150° C., 160° C., 180° C., 200° C., or any value within a range formed by any two of the above values.

A time for the mixing refers to a working time of the mixing machine set when mixing to obtain the semisolid hot mixture.

In some embodiments, the time for the mixing needs to be controlled within a certain range. If the time for the mixing is too short (e.g., shorter than 30 min), the metal shell powder and the thermoplastic binder cannot sufficiently contact and fuse, causing the metal shell green body to be prone to uneven density and surface defects. After the sintering, porosity of the metal anode shell increases, and mechanical strength and corrosion resistance of the metal anode shell decrease. If the time for the mixing is too long (e.g., exceeding 60 min), it not only oxidizes the metal powder, affecting final conductivity and stability of the electrical connection of the anode, but also increases production energy consumption and cost, and decreases production efficiency.

In some embodiments, the time for the mixing is within a range of 30-60 min. In some embodiments, the time for the mixing may be within a range of 40-50 min. Understandably, the time for the mixing may be 30 min, 35 min, 40 min, 45 min, 50 min, 60 min, or any value within a range formed by any two of the above values.

Step 120, crushing the semisolid hot mixture to obtain the metal shell feedstock granules.

The metal shell feedstock granules refer to a material that is directly used for the rheological pressing to obtain the metal shell green body.

A particle size of the metal shell feedstock granules needs to be controlled within a certain range. If the particle size of the metal shell feedstock granules is too large (e.g., larger than −10 mesh), fluidity of the granules deteriorates, making uniform distribution of the granules during mold filling difficult and preventing the granules from fully filling fine structures of a special-shaped mold, thereby causing local uneven density and surface unevenness of the metal shell green body. If the particle size of the metal shell feedstock granules is too small (e.g., smaller than +200 mesh), specific surface area of the granules increases, easily causing agglomeration, which leads to accumulation blockage and poor filling when filling the mold, triggering pressure release and the local powder-binder separation.

In some embodiments, the particle size of the metal shell feedstock granules is within a range of −10 mesh to +200 mesh. The particle size of the metal shell feedstock granules is controlled within the range, and a filling performance is optimal. In some embodiments, the particle size of the metal shell feedstock granules is within a range of −20 mesh to +180 mesh. It can be understood that the particle size of the metal shell feedstock granules may be −20 mesh, −10 mesh, 20 mesh, 70 mesh, 100 mesh, 150 mesh, or any value within a range formed by any two of the above values.

In some embodiments, the semisolid hot mixture may be placed into a crusher for crushing to obtain the metal shell feedstock granules.

In some embodiments, a heating temperature during the crushing is within a range of 60-150° C., and a screw rotational speed is within a range of 400-600 r/min. In some embodiments, the crusher may be a screw extrusion hot-cut pelletizer.

The heating temperature refers to a temperature of the crusher set when crushing the semisolid hot mixture to obtain the metal shell feedstock granules.

In some embodiments, the heating temperature during the crushing needs to be controlled within a certain range. If the heating temperature is excessively low (e.g., lower than 60° C.), the thermoplastic binder is prone to cooling and hardening, resulting in increased brittleness of the semisolid hot mixture. During the crushing, metal shell feedstock granules having a uniform particle size are difficult to form, and large agglomerates or an excessive amount of fine powder are likely to occur, thereby affecting uniformity of subsequent filling of a mold 200. If the heating temperature is too high (e.g., above 150° C.), the thermoplastic binder may become overly softened and sticky, causing the material to agglomerate and block inside a screw, preventing effective crushing. Simultaneously, the thermoplastic binder may undergo thermal decomposition, damaging a bonding performance of the thermoplastic binder, thereby worsening formability of the subsequent metal shell feedstock granules.

In some embodiments, the heating temperature during the crushing is within a range of 60-150° C. In some embodiments, the heating temperature during the crushing may be within a range of 80-120° C. It can be understood that the heating temperature during the crushing may be 60° C., 80° C., 100° C., 120° C., 140° C., 150° C., or any value within a range formed by any two of the above values.

The screw rotational speed refers to a rotational speed of the screw of the crusher set when crushing the semisolid hot mixture to obtain the metal shell feedstock granules.

In some embodiments, the screw rotational speed during the crushing needs to be controlled within a certain range. If the screw rotational speed is too low (e.g., below 400 r/min), a crushing force is insufficient, and the semisolid hot mixture cannot be fully sheared and crushed, forming particles with an overly large particle size (exceeding −10 mesh). Simultaneously, an overly low rotational speed causes the production efficiency to decrease, and the material stays in the device for too long, easily causing excessive adhesion. If the screw rotational speed is too high (e.g., above 600 r/min), a shearing force is excessive, and the material is over-crushed (smaller than +200 mesh). Furthermore, an overly high rotational speed intensifies device wear, increases energy consumption, and may cause local overheating of the material, inducing aging and degradation of the binder, thereby affecting a debinding effect of a subsequent sintering process and strength of the metal shell green body.

In some embodiments of the present disclosure, by coordinating and adapting process parameters during the crushing, problems such as the powder-binder separation, particle agglomeration, or binder aging can be avoided, thereby improving a forming quality of the metal shell green body.

Step 130, preheating the mold to a temperature 20-50° C. higher than a softening point temperature of the thermoplastic binder, filling preheated metal shell feedstock granules into the mold, applying pressure and heating to a temperature 5-50° C. higher than the softening point temperature of the thermoplastic binder, and performing the rheological pressing to obtain the metal shell green body.

FIG. 2 is a schematic structural diagram illustrating a mold 200 according to some embodiments of the present disclosure.

The mold 200 refers to equipment for forming the metal shell green body.

In some embodiments, the mold 200 is a modular heatable mold. The mold 200 includes a modular female die A 210, a modular female die B 220, an upper punch 230, a lower punch 240, a core rod 250, and a heating jacket 260.

The modular heatable mold refers to a mold that adopts a modular structural design and integrates a heating system, and is used for forming the metal shell green body.

The modular female die A 210 refers to a component configured to fix other components, disposed at an upper portion of a structure of the mold 200, and disposed opposite to the modular female die B 220 and configured to cooperate with the modular female die B 220. The modular female die A 210 is connected to the modular female die B 220 through fitting surfaces (e.g., parting surfaces), so as to form a closed cavity for forming an external shape of the metal shell green body.

The modular female die B 220 refers to a component configured to fix other components, disposed at a lower part of the mold 200, and disposed opposite to the modular female die A 210 and configured to cooperate with the modular female die A 210. The modular female die B 220 may be connected to the modular female die A 210 by the fitting surfaces (e.g., the parting surfaces) to form the closed cavity for forming the external shape of the metal shell green body.

The upper punch 230 (also referred to as a base 230) refers to a component for applying a pressing pressure to the metal shell feedstock granules from above. The upper punch 230 cooperates with the lower punch 240 to achieve pressing and forming of the metal shell green body. The upper punch 230 is located directly above a cavity formed by the modular female die A 210 and the modular female die B 220. In some embodiments, the upper punch 230 may move downward during a pressing process to tightly insert into a material bin 280.

The lower punch 240 refers to a fixed or movable component for supporting the metal shell feedstock granules and participating in applying the pressing pressure. The lower punch 240 cooperates with the upper punch 230 to achieve the pressing and forming of the metal shell green body. The lower punch 240 is located directly below the cavity formed by the modular female die A 210 and the modular female die B 220. The lower punch 240 typically bears a weight of the metal shell feedstock granules in the cavity and provides lower support or moves upward during the pressing process. In some embodiments, the lower punch 240 may move upward during the pressing process (forming opposed pressure with the upper punch 230) or maintain a pressure-bearing state. During the demolding, the lower punch 240 may push a formed metal shell green body out of the cavity by moving upward.

The core rod 250 refers to a rod-shaped component that functions for positioning and support inside the metal shell green body. In some embodiments, the core rod 250 may penetrate a central portion of the cavity formed by the modular female die A 210 and the modular female die B 220 along a cavity axis direction, with two ends of the core rod 250 respectively connected to the upper punch 230 (or the base 230) and the lower punch 240.

The heating jacket 260 refers to a component for heating the mold 200. In some embodiments, the heating jacket 260 may wrap around and cover an outer side of the cavity formed by the modular female die A 210 and the modular female die B 220.

A base platform 270 refers to a component supporting the base 230, located between the base 230 and the modular female die A 210. In some embodiments, the base 230 may be fixedly connected to the base platform 270 via limit bolts 290. In some embodiments, a center of the base platform 270 has a through hole for the core rod 250 to pass through.

The material bin 280 refers to a space for temporarily storing the preheated metal shell feedstock granules. The material bin 280 is an annular region enclosed by a lower end surface of the upper punch 230, an outer surface of the core rod 250, and inner walls of the modular female die A 210 and the modular female die B 220.

In some embodiments of the present disclosure, a modular female die design allows the mold 200 to be parted and disassembled, which is suitable for forming and demolding of a metal anode shell having a complex external shape, an internal cavity, or an asymmetric structure. Simultaneously, through an opposed pressing design of the upper punch 230 and the lower punch 240, uniform axial pressing can be achieved, and, in cooperation with positioning and support provided by the core rod 250, uniform density distribution and reduced defects of the metal shell green body are ensured.

The preheating refers to a process of preheating the mold 200 and/or the metal shell feedstock granules to a set temperature range before filling or pressing. For example, the modular heatable mold 200 is preheated as a whole to 60° C.

In some embodiments, the metal shell feedstock granules are preheated to within a range of 60-80° C., and simultaneously the mold 200 is preheated to within a range of 60-100° C.

The softening point temperature of the thermoplastic binder refers to a temperature range at which the thermoplastic binder transforms from a solid to a flowable semisolid state.

The rheological pressing refers to a process in which the metal shell feedstock granules are injected into the mold 200 under an applied pressure.

In some embodiments, the metal shell feedstock granules may be pressurized to be within a range of 20-60 MPa along a shell pressing direction and raised to a temperature of 120-170° C., and the rheological pressing is performed for 10-40 min to obtain the metal shell green body.

In some embodiments, a temperature to which the metal shell feedstock granules are raised needs to be maintained within a certain range. If the temperature to which the metal shell feedstock granules are raised is excessively low (e.g., lower than 120° C.), the thermoplastic binder is insufficiently softened and has insufficient flowability, making secondary redistribution and particle rearrangement of metal shell powder difficult, thereby resulting in incomplete filling of the metal shell green body and increased porosity, and causing dimensional accuracy and densification after the sintering to be difficult to meet requirements. If the temperature to which the metal shell feedstock granules are raised is excessively high (e.g., higher than 170° C.), viscosity of the thermoplastic binder is excessively low, and the thermoplastic binder is prone to flowing out through fitting gaps of the mold 200, causing pressure release and the powder-binder separation, and premature decomposition of the thermoplastic binder may occur, thereby resulting in reduced strength and increased surface roughness of the metal shell green body, and even difficulty in the demolding.

In some embodiments, the temperature to which the metal shell feedstock granules are raised may be within a range of 120-170° C. In some embodiments, the temperature to which the metal shell feedstock granules are raised may also be within a range of 130-160° C. Understandably, the temperature to which the metal shell feedstock granules are raised may be 120° C., 130° C., 140° C., 150° C., 160° C., 170° C., or any value within a range formed by any two of the above values.

Rheological pressing for 10 to 40 min refers to maintaining a temperature of 120-170° C. for 10 to 40 min after the metal shell feedstock granules are softened.

In some embodiments, a duration of the rheological pressing needs to be maintained within a certain range. If the duration of the rheological pressing is too short (e.g., less than 10 min), the flow of the thermoplastic binder and a powder rearrangement process are insufficient, pores inside the metal shell green body are not effectively closed, densification is insufficient, and a relatively large count of the pores may remain after the sintering, thereby affecting conductivity and interfacial bonding strength of the anode. If the duration of the rheological pressing is too long (e.g., greater than 40 min), excessive migration or local thermal decomposition of the thermoplastic binder may occur, causing deformation of the metal shell green body or degradation of the thermoplastic binder, thereby reducing strength of the metal shell green body and dimensional stability after sintering.

In some embodiments, the duration of the rheological pressing may be within a range of 10 to 40 min. In some embodiments, the duration of the rheological pressing may also be within a range of 20 to 30 min. Understandably, the duration of the rheological pressing may be 10 min, 20 min, 30 min, 40 min, or any value within a range formed by any two of the above values.

The shell pressing direction refers to a direction in which the upper punch 230 and the lower punch 240 apply pressure to the metal shell feedstock granules along an axis of the mold 200 during the rheological pressing process.

In some embodiments, a pressure applied along the shell pressing direction needs to be maintained within a certain range. If the pressure applied along the shell pressing direction is too low (e.g., lower than 20 MPa), incomplete filling at the complex cavities or fine structural areas is likely to occur, resulting in large forming dimensional deviation and decreased near-net-shape accuracy. If the pressure applied along the shell pressing direction is too high (e.g., higher than 60 MPa), the thermoplastic binder is easily squeezed out from gaps of a mold cavity, causing the local powder-binder separation, leading to uneven density distribution and decreased surface quality of the metal shell green body.

In some embodiments, the pressure applied along the shell pressing direction may be within a range of 20-60 MPa. In some embodiments, the pressure applied along the shell pressing direction may also be within a range of 30-50 MPa. Understandably, the pressure applied along the shell pressing direction may be 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, or any value within a range formed by any two of the above values.

The metal shell green body refers to an integral green body formed by the rheological pressing process, having a specific geometric shape and an internal cavity.

In some embodiments, the mold 200 is first installed, and the core rod 250 is placed to secure the base 230 and the base platform 270. The lower punch 240 is installed, and the preheated metal shell feedstock granules are filled into the material bin 280. The modular female die A 210 and the modular female die B 220 are then connected. Pressure is applied, and the metal shell feedstock granules are raised to a temperature 5-50° C. higher than the softening point of the thermoplastic binder. The metal shell feedstock granules are maintained at this temperature for a period of time to enable secondary distribution and particle rearrangement of the metal shell feedstock granules, thereby achieving filling of the mold 200. Heating is stopped, after cooling, the pressure is released. The base 230 and the core rod 250 are removed, thereby obtaining the metal shell green body having a hollow core part.

When the metal shell feedstock granules are heated to a temperature 5-50° C. higher than the softening point temperature of the thermoplastic binder, under certain pressure and capillary forces, the thermoplastic binder undergoes slow viscous migration. The thermoplastic binder drives secondary distribution or particle rearrangement of the metal shell powder in the material, gradually reducing porosity. Finally, a high-uniformity and high-density precision part green body is obtained, thereby achieving a densification process.

Step 140, filling an alloy inner core powder into the core part of the metal shell green body to obtain an inert anode green body with an alloy inner core.

FIG. 3 is a schematic diagram illustrating an anode structure according to some embodiments of the present disclosure. In FIGS. 3, 310 is the metal anode shell; 320 is the alloy inner core.

The core part refers to a spatial region where a pre-reserved internal cavity is located after the metal shell green body is formed by the rheological pressing. A shape and dimensions of the core part are determined by the core rod 250 in the mold 200.

The alloy inner core powder refers to a metal or alloy powder used to fill the cavity of the core part of the metal shell green body and form a metallurgical bond with the metal anode shell, after melting and solidifying during a sintering process. In some embodiments, the alloy inner core powder may be a Cu-20Ni-10Ti alloy powder, a Cu-20Ni-10Ag alloy powder, a Cu-30Ni-20Co alloy powder, or the like.

The alloy inner core refers to a molten and solidified metal body formed by filling the alloy inner core powder into the core part of the metal shell green body and then sintering.

The inert anode green body refers to a composite green body with the alloy inner core obtained after the rheological pressing.

In some embodiments, after obtaining the metal shell green body, the core rod 250 may be pulled out from the metal shell green body. The alloy inner core powder is poured into the core part using a funnel, a powder feeder, or the like to obtain the inert anode green body with the alloy inner core.

Step 150, sintering the inert anode green body with the alloy inner core to obtain an integrated inert anode for aluminum electrolysis metal anode shell and electric connection.

The sintering refers to a process in which the inert anode green body with the alloy inner core is subjected to a stepwise temperature control process, such that an alloy of the alloy inner core undergoes melting and solidification and forms a dense bond with the metal anode shell, thereby ultimately achieving electrical connection between the alloy inner core and the metal anode shell.

In some embodiments, the sintering is performed in a protective atmosphere. A process of the sintering includes: first heating to H, where H is 400-600° C., holding for a first holding duration of 8-12 h; continuing heating to K1; then cooling to K2; holding for a second holding duration of 4-6 h; and cooling to a room temperature, where K1-K2≥50° C., K1 is 1300-1400° C., and K2 is 1150-1350° C.

In some embodiments, K1-K2 is within a range of 100-150° C.

In the sintering process according to some embodiments of the present disclosure, flowing argon gas is first introduced, heating is performed to a debinding temperature for the debinding, and heating is then continued to a melting temperature K1 of the alloy inner core powder to melt the alloy inner core powder. At this stage, the metal anode shell is not yet fully densified by the sintering, and favorable solid-liquid interface wettability is achieved by virtue of gravity of the molten alloy and capillary action between the molten alloy and pores on a surface of the metal anode shell material. Subsequently, the temperature is reduced to K2 to solidify the core part, followed by further holding to eliminate residual pores and defects at interfaces, thereby obtaining a dense metal anode shell and a stable electrical connection. Finally, the temperature is reduced to a sintering temperature of the metal anode shell and then cooled to the room temperature.

In some embodiments, during the sintering process, H needs to be maintained within a certain range. If a temperature H is too low (e.g., less than 400° C.), the thermoplastic binder is not completely decomposed, and residual carbon leads to reduced densification and deteriorated conductivity of the finally obtained inert anode for aluminum electrolysis, and may form brittle carbides at the interface. If the temperature H is too high (e.g., higher than 600° C.), surface sintering of the metal powder occurs prematurely, blocking volatile channels of the thermoplastic binder and causing swelling or cracking of the metal anode shell. Simultaneously, excessive holding increases the energy consumption and may cause abnormal grain growth.

In some embodiments, H may be within a range of 400-600° C. In some embodiments, H may be within a range of 450°-550° C. Understandably, H may be 400° C., 420° C., 450° C., 480° C., 500° C., 520° C., 550° C., 580° C., 600° C., or any value within a range formed by any two of the above values.

In some embodiments, the first holding duration needs to be maintained within a certain range. After the cooling, if the first holding duration is too short (e.g., less than 8 h), the debinding is incomplete, and a residual thermoplastic binder causes blistering or cracking of a product during subsequent high-temperature sintering. If the first holding duration is too long (e.g., greater than 12 h), excessive grain growth occurs in the metal anode shell and the alloy inner core, and brittle phases at an interface between the alloy inner core and the metal anode shell are thickened, thereby reducing toughness and thermal shock resistance of the finally obtained inert anode for aluminum electrolysis.

In some embodiments, during the sintering process, the first holding duration may be within a range of 8-12 h. In some embodiments, during the sintering process, the first holding duration may be within a range of 9-11 h. Understandably, during the sintering process, the first holding duration may be 8 h, 9.5 h, 10 h, 10.3 h, 11.2 h, or any value within a range formed by any two of the above values.

In some embodiments, K1 also needs to be maintained within a certain range. If K1 is too low (e.g., lower than 1300° C.), the alloy inner core powder is not sufficiently melted, resulting in insufficient fluidity, and difficulty in wetting pores of the metal anode shell through capillary action, thereby leading to low interfacial bonding strength of the inert anode green body with the alloy inner core. If K1 is too high (e.g., higher than 1400° C.), the molten alloy inner core formed by melting of the alloy inner core powder may excessively penetrate into pores of the metal anode shell, blocking gas discharge channels, and increasing a risk of brittle phases caused by interdiffusion of elements contained in the alloy inner core and the metal anode shell.

In some embodiments, K1 may be within a range of 1300-1400° C. In some embodiments, K1 may be within a range of 1330-1380° C. It may be understood that K1 may be 1300° C., 1320° C., 1330° C., 1350° C., 1370° C., 1395° C., or any value within a range formed by any two of the above values.

In some embodiments, K2 needs to be maintained within a certain range. If a temperature K2 of the cooling is too low (e.g., lower than 1150° C.), the alloy inner core solidifies too quickly, diffusion is insufficient, metallurgical bonding at an interface between the alloy inner core and the metal anode shell is weak, and the alloy inner core is prone to separate from the metal anode shell under thermal stress. If the temperature K2 of the cooling is too high (e.g., higher than 1350° C.), the temperature K2 is close to or higher than a melting point of some components in the metal anode shell, which may cause deformation or local melting of the metal anode shell, damaging structural integrity.

In some embodiments, K2 may be within a range of 1150-1350° C. In some embodiments, the temperature K2 of the cooling may be within a range of 1200-1300° C. It may be understood that the temperature K2 of the cooling may be 1150° C., 1200° C., 1250° C., 1300° C., 1350° C., or any value within a range formed by any two of the above values.

In some embodiments, a temperature difference K1-K2 needs to be maintained within a certain range. If the temperature difference K 1-K2 is too small (e.g., less than 50° C.), a diffusion driving force at an interface between an alloy inner core and the metal anode shell is insufficient, resulting in difficulty in achieving sufficient pore closure of the metal anode shell and high-strength interfacial bonding.

In some embodiments, K1-K2≥50° C. In some embodiments, K1-K2≥60° C. In some embodiments, K1-K2≥78° C. In some embodiments, K1-K2≥90° C. In some embodiments, K1-K2≥100° C.

In some embodiments, the second holding duration needs to be maintained within a certain range. After the cooling, if the second holding duration is too short (e.g., less than 4 h), the interfacial diffusion and pore elimination are insufficient, resulting in an increased residual porosity of the finally obtained inert anode for aluminum electrolysis. If the second holding duration is too long (e.g., greater than 6 h), the excessive grain growth occurs in the metal anode shell and the alloy inner core, and the brittle phases at the interface between the alloy inner core and the metal anode shell are thickened, thereby reducing the toughness and the thermal shock resistance of the finally obtained inert anode for aluminum electrolysis.

In some embodiments, during the sintering, the second holding duration may be within a range of 4-6 h. In some embodiments, during the sintering, the second holding duration may be within a range of 4.5-5.5 h. It may be understood that, during the sintering, the second holding duration may be 4 h, 4.5 h, 5 h, 5.5 h, 6 h, or any value within a range formed by any two of the above values.

In some embodiments, a resistance heating atmosphere sintering furnace or other means may be used for programmed temperature control and heating. In some embodiments, a temperature control system of a sintering furnace may be used to monitor a temperature inside the furnace in real time, and a heating power may be adjusted to stabilize the temperature within a set temperature range to achieve the holding. In some embodiments, the heating power may be cut off or reduced, and the temperature may be gradually decreased by relying on heat dissipation of a furnace body, and a cooling rate may be monitored and adjusted via the temperature control system of the sintering furnace.

In some embodiments, the temperature control system of the sintering furnace may be set or natural cooling may be used to cool a furnace temperature at a set rate.

In some embodiments, a process of the cooling includes: first decreasing the temperature to 400-500° C. at a cooling rate of less than 5° C./min, and then performing furnace cooling to the room temperature.

In some embodiments of the present disclosure, programmed cooling reduces thermal stress of the inert anode green body, prevents cracking and deformation of the metal anode shell, and ensures dimensional accuracy.

The protective atmosphere refers to an inert or reducing gas introduced into a furnace chamber during the high-temperature sintering to isolate oxygen and other active gases. In some embodiments, the protective atmosphere is argon gas.

In some embodiments of the present disclosure, cooling in the protective atmosphere achieves anti-oxidation protection for the metal anode shell and the alloy inner core, preventing degradation of material properties.

The metal anode shell refers to an external structural component of the inert anode obtained after the rheological pressing and the sintering and usable in an aluminum electrolysis process.

The integrated inert anode for aluminum electrolysis and electric connection refers to an anode structure in which the alloy inner core and the metal anode shell are electrically connected after the rheological pressing and the sintering. The alloy inner core and the metal anode shell form a dense interface through the metallurgical bonding, resulting in a bilayer integrated structure of “alloy inner core-metal anode shell” that avoids contact loosening and interfacial corrosion encountered in traditional mechanical connections. The bilayer integrated structure of “alloy inner core-metal anode shell” reduces contact resistance and prevents contact loosening and arc loss associated with the traditional mechanical connections. The structure has uniform current distribution, strong thermal shock resistance, and good capability for near-net-shape forming of complex geometries, thereby providing reliable support for efficient and long-life operation of the inert anodes for aluminum electrolysis.

In some embodiments of the present disclosure, the preparation method provided in the present disclosure includes preheating the metal shell feedstock granules and directly placing the metal shell feedstock granules into the mold cavity, heating the mold cavity to a temperature above the softening point temperature of the thermoplastic binder, and, by virtue of high interfacial wettability characteristics between the thermoplastic binder and the metal shell powder, enabling the thermoplastic binder to flow under the capillary force and drive secondary distribution and particle rearrangement of the metal shell powder in the metal shell feedstock granules, thereby achieving stable filling of complex-shaped fine structures and obtaining a metal shell green body with the special-shaped structure. Then, the alloy inner core powder for forming the electric connection is filled into the metal shell green body with the special-shaped structure, and the integrated sintering and the forming are performed to obtain the inert anode for aluminum electrolysis.

The following describes in detail preferred embodiments of the present disclosure with reference to the accompanying drawings, so that advantages and features of the present disclosure may be more easily understood by those skilled in the art, and a protection scope of the present disclosure may be more clearly and explicitly defined.

Example 1 Integrated Preparation Method for Aluminum Electrolysis Fe—Ni—Cu Alloy Anode Shell and Electric Connection

Step S1, using nano grinding and air classification technology to obtain Fe powder with an average particle size of 0.4 μm, Ni powder with an average particle size of 0.4 μm, and Cu powder with an average particle size of 0.1 μm. Working parameters of a turbine nano sand mill included a rotational speed of 800 rpm, a flow rate of 60 L/H, and a filling ratio of zirconia beads of 60%; working parameters of a jet air classifier included a feed rate of 60 kg/h, a working pressure of 10 MPa, and an air pressure of the cyclone collector of 15 kPa.

Step S2, adding 4 kg of the Fe powder, 5 kg of the Ni powder, and 10 kg of the Cu powder to a thermoplastic binder with a volume fraction of 30%, and fully mixing to obtain a semisolid hot mixture. The thermoplastic binder included polyethylene glycol, polymethyl methacrylate, glycerol, and dioctyl phthalate. By volume ratio, polyethylene glycol: polymethyl methacrylate: glycerol: dioctyl phthalate=75%: 20%: 3%: 2%. A mixing temperature was 150° C., and a mixing time was 45 min.

Step S3, filling a mold with the metal shell feedstock granules from Step S1, and forming a metal shell green body by a rheological pressing manner. This step specifically included the following sub-steps:

• • Sub-step A 1, preheating the mold to 60° C.; and preheating the metal shell feedstock granules to 80° C.
  • Sub-step A2, assembling the mold, placing a core rod to fix a base and a base platform; installing a lower punch; filling a material bin with the preheated metal shell feedstock granules; and connecting a modular female die A with a modular female die B.
  • Sub-step A 3, applying pressure to 60 MPa along a shell pressing direction, continuously heating the mold to 160° C., and maintaining the temperature for 40 min after the metal shell feedstock granules were soften.
  • Sub-step A4, stopping heating, after cooling, releasing the pressure and removing the base and the core rod.
  • Step S4, filling an inner cavity, from which the core rod is removed, with 4 kg of gas-atomized Cu-20Ni-10Ti alloy powder having an average particle size of 50 μm, reinserting the core rod and pressing with a pressure of 10 MPa to obtain an inert anode green body with an alloy inner core.
  • Step S5, placing the inert anode green body with the alloy inner core from Step S4 in an atmosphere sintering furnace to complete debinding, sintering, and connection of the alloy inner core. This step specifically included the following sub-steps:
  • Sub-step B1, introducing flowing argon gas; heating to 500° C. at a rate of 8° C./min; and holding for 10 h.
  • Sub-step B2, continuing heating to 1300° C. at a rate of 5° C./min.
  • Sub-step B3, cooling to 1150° C. at a rate of 3° C./min; and holding for 4 h.
  • Sub-step B4, continuously introducing the argon gas, first cooling to 400° C. at 5° C./min, then performing furnace cooling to room temperature.

The finally obtained inert anode has an external dimensional accuracy lower than ±2.0 mm/100 mm, a porosity of the sintered metal anode shell less than 5%, and a shear strength at a connection interface of 126 MPa.

Example 2 Integrated Preparation Method for Aluminum Electrolysis Fe—Ni—Cr Alloy Anode Shell and Electric Connection

Step S1, processing a gas-atomized Fe-50Ni-5Cr alloy powder to an average particle size of 0.4 μm by nano grinding and an air classifying technology. Working parameters of a turbine nano sand mill included a rotational speed of 800 rpm, a flow rate of 60 L/H, and a filling ratio of zirconia beads of 60%; working parameters of a jet air classifier included a feed rate of 60 kg/h, a working pressure of 10 MPa, and an air pressure of a cyclone collector of 15 KPa.

Step S2, adding 10 kg of the Fe-50Ni-5Cr alloy powder to a thermoplastic binder with a volume fraction of 40%, and mixing thoroughly to obtain a semisolid hot mixture. The thermoplastic binder included polyethylene glycol, polymethyl methacrylate, glycerol, and dioctyl phthalate. By volume ratio, polyethylene glycol: polymethyl methacrylate: glycerol: dioctyl phthalate=75%: 20%: 3%: 2%. A mixing temperature was 150° C., and a mixing time was 45 min.

Step S3, filling a mold with the metal shell feedstock granules from Step S1, and forming a metal shell green body by a rheological pressing manner. This step specifically included the following sub-steps:

• • Sub-step A1, preheating the mold to 60° C.; and preheating the metal shell feedstock granules to 80° C.
  • Sub-step A2, assembling the mold, placing a core rod to fix a base and a base platform; installing a lower punch, filling a material bin with the preheated metal shell feedstock granules; and connecting a modular female die A with a modular female die B.
  • Sub-step A3, applying pressure to 60 MPa along a shell pressing direction, and continuously heating the mold to 160° C.; and maintaining the temperature for 40 min after the metal shell feedstock granules were soften.
  • Sub-step A4, stopping heating, after cooling, releasing the pressure and removing the base and the core rod.
  • Step S4, filling an inner cavity, from which the core rod is removed, with 4 kg of gas-atomized Cu-20Ni-10Ag alloy powder having an average particle size of 50 μm, reinserting the core rod and pressing with a pressure of 10 MPa to obtain an inert anode green body with an alloy inner core.
  • Step S5, placing the inert anode green body with the alloy inner core from Step S4 in an atmosphere sintering furnace to complete debinding, sintering, and connection of the alloy inner core. This step specifically included the following sub-steps:
  • Sub-step B1, introducing flowing argon gas, heating to 500° C. at a rate of 8° C./min, and holding for 10 h.
  • Sub-step B2, continuing heating to 1300° C. at a rate of 5° C./min.
  • Sub-step B3, cooling to 1150° C. at a rate of 3° C./min, and holding for 4 h.
  • Sub-step B4, continuously introducing the argon gas, first cooling to 400° C. at 5° C./min, then performing furnace cooling to room temperature.

The finally obtained inert anode has an external dimensional accuracy lower than ±2.0 mm/100 mm, a porosity of the sintered metal anode shell less than 5%, and a shear strength at a connection interface of 103 MPa.

Example 3 Integrated Preparation Method for Aluminum Electrolysis Fe—Ni—W—Mo Alloy Anode Shell and Electric Connection

Step S1, obtaining Fe powder, Ni powder, W powder, and Mo powder each having an average particle size of 5 μm by nano grinding and an air classifying technology. working parameters of a turbine nano sand mill included a rotational speed of 800 rpm, a flow rate of 60 L/H, and a filling ratio of zirconia beads of 60%; working parameters of a jet air classifier included a feed rate of 60 kg/h, a working pressure of 10 MPa, and an air pressure of a cyclone collector of 15 KPa.

Step S2, adding 4 kg of the Fe powder, 3 kg of the Ni powder, 1.5 kg of the W powder, and 1.5 kg of the Mo powder to a thermoplastic binder with a volume fraction of 40%, and mixing thoroughly to obtain a semisolid hot mixture. The thermoplastic binder included polyethylene glycol, polymethyl methacrylate, glycerol, and dioctyl phthalate. By volume ratio, polyethylene glycol: polymethyl methacrylate: glycerol: dioctyl phthalate=75%: 20%: 3%: 2%. A mixing temperature was 150° C., and a mixing time was 45 min.

Step S3, filling a mold with the metal shell feedstock granules from Step S1, and forming a metal shell green body by a rheological pressing manner. This step specifically included the following sub-steps:

• • Sub-step A 1, preheating the mold to 60° C.; and preheating the metal shell feedstock granules to 80° C.
  • Sub-step A2, assembling the mold, placing a core rod to fix a base and a base platform; installing a lower punch, filling a material bin with the preheated metal shell feedstock granules; and connecting a modular female die A with a modular female die B.
  • Sub-step A 3, applying pressure to 40 MPa along a shell pressing direction, and continuously heating the mold to 150° C., and maintaining the temperature for 40 min after the metal shell feedstock granules were soften.
  • Sub-step A4, stopping heating, after cooling, releasing the pressure and removing the base and the core rod.
  • Step S4, filling an inner cavity, from which the core rod is removed, with 4 kg of gas-atomized Cu-30Ni-20Co alloy powder having an average particle size of 50 μm, reinserting the core rod and pressing with a pressure of 10 MPa to obtain an inert anode green body with an alloy inner core.
  • Step S5, placing the inert anode green body with the alloy inner core from Step S4 in an atmosphere sintering furnace to complete debinding, sintering, and connection of the alloy inner core. This step specifically included the following sub-steps:
  • Sub-step B1, introducing flowing argon gas, heating to 500° C. at a rate of 8° C./min, and holding for 10 h.
  • Sub-step B2, continuing heating to 1400° C. at a rate of 5° C./min.
  • Sub-step B3, cooling to 1300° C. at a rate of 3° C./min and holding for 4 h.
  • Sub-step B4, continuously introducing the argon gas, first cooling to 400° C. at 5° C./min, then performing furnace cooling to room temperature.

The finally obtained inert anode has an external dimensional accuracy lower than ±2.0 mm/100 mm, a porosity of the sintered metal anode shell less than 5%, and a shear strength at a connection interface of 137 MPa.

Comparative Example 1

Other conditions were the same as those in Example 1, except that a content of the thermoplastic binder in step S2 was 50%. Because an excessively high content of the thermoplastic binder cannot be completely removed during a sintering process, severe cracking occurs in a metal anode shell after sintering.

Comparative Example 2

Other conditions were the same as those in Example 1, except that the sintering in step S5 included directly heating to 1400° C., holding for 4 h, and then cooling to room temperature. As a result, an alloy inner core separates from a metal anode shell due to solidification shrinkage.

From Examples 1-3, it can be seen that the process 100 can make an external dimensional accuracy of the final obtained inert anode less than ±2.0 mm/100 mm, a porosity of the metal anode shell after the sintering less than 5%, and the shear strength at the connection interface relatively high (all not less than 103 MPa).

By comparing Example 1 with Comparative Example 1, it can be seen that an excessively high content of the thermoplastic binder leads to a significant reduction in quality of the obtained metal anode shell, indicating that the content of the thermoplastic binder needs to be strictly controlled within a suitable range (e.g., 20-40%). Otherwise, densification of the metal anode shell cannot be achieved.

By comparing Example 1 with Comparative Example 2, it can be seen that if the two-step sintering manner is not adopted, but rather a manner of directly heating to 1400° C., holding, and then cooling is used, solidification shrinkage of the alloy inner core does not match shrinkage of the metal anode shell, causing the alloy inner core to separate from the metal anode shell. This indicates that adopting the two-step sintering manner of the present disclosure is crucial for interfacial metallurgical bonding.

When operations performed according to steps described in embodiments of the present disclosure, unless otherwise specified, an order of the steps is adjustable, the steps are omissible, and other steps may also be included during the operations. Some features, structures, or characteristics in one or more embodiments of the present disclosure may be appropriately combined. In some embodiments, numbers describing compositions and property quantities are used. It should be understood that such numbers used in the description of embodiments are modified by modifiers “approximately,” “about,” or “substantially” in some examples. Unless otherwise stated, “approximately,” “about,” or “substantially” indicates that the stated number allows a variation of ±20%. Accordingly, in some embodiments, numerical parameters used in the specification and claims are approximate values, and the approximate values may vary according to characteristics required by individual embodiments. Although numerical ranges and parameters used to confirm the breadth of scope in some embodiments of the present disclosure are approximate values, in specific embodiments, setting of such numerical values should be as precise as possible within a feasible range. Embodiments in the present disclosure are for illustration and description only and are not intended to limit the scope of application of the present disclosure. For those skilled in the art, any equivalent structure or equivalent process transformation made by using the content of the present disclosure and the accompanying drawings, or directly or indirectly applied in other related technical fields, is equally included within the scope of the present disclosure.