Method for welding ceramic inert anode based on nickel ferrite and metal conductive block of aluminium electrolyser

Abstract

FIELD: welding.SUBSTANCE: invention can be used for welding a ceramic inert anode based on nickel ferrite and a metal conductive block of an aluminium electrolyser. A ceramic inert anode based on nickel ferrite and a metal conductive block is produced and processed to form the surfaces to be joined. Producing a transition metal alloy foil and attaching the surfaces to be joined of a ceramic inert anode and a metallic conductive block, respectively, to two surfaces of the transition metal alloy foil to form a prefabricated connecting body. Vacuum diffusion welding is performed on a prefabricated connecting body at a diffusion temperature of 950 to 1200 °C, heating speeds from 10 to 30 °C / min, thermal insulation time from 2 to 20 min, pressure from 5 to 30 MPa and cooling rate from 4 to 8 °C / min.EFFECT: improved efficiency.6 cl, 3 dwg, 3 ex

Description

[0001] This application claims priority to Chinese Patent Application No. 202310298466.3, filed on March 24, 2023, the entire contents of which are incorporated herein by reference.TECHNICAL FIELD

[0002] The invention relates to the field of aluminum electrolysis and, in particular, to an aluminum electrolyzer. LEVEL OF TECHNOLOGY

[0003] The existing Hall-Herout aluminum electrolysis cell uses sacrificial carbon anodes, which consumes large quantities of high-quality carbon materials and emits large amounts of greenhouse gases such as CO2 and carcinogenic fluorocarbons. During aluminum electrolysis, constant replenishment of anode paste or replacement of the anode carbon blocks is required, leading to unstable electrolysis performance and increased labor intensity.

[0004] Inert anodes and related electrolytic processes have become the object of close attention and research in the international aluminum and materials industry, because inert anodes and related electrolytic processes can solve the above-mentioned problems and reduce the production cost of aluminum ingots by nearly 30%. The use of inert anodes in the aluminum electrolysis process has the following advantages: (1) the electrodes are almost not consumed during electrolysis, and no additional carbon recycling facility is required, thus reducing production costs; (2) the electrodes are not consumed, the distance between the electrodes is stably and easily adjusted, the number of anode replacements is less, and the labor intensity is reduced.; (3) Higher current density at the anode can be used to increase the productivity of the electrolytic cell; (4) The product of anode production is oxygen, which can avoid environmental pollution; oxygen can also be used as a by-product, and it is estimated that the amount of oxygen recovered can be increased. accounts for 3% of the cost of the original aluminum product. This series of advantages of inert anodes makes the development of suitable inert anodes an important part of improving traditional aluminum production methods. Inert anodes should have the following properties: corrosion resistance to the action of electrolytes in the aluminum electrolysis environment, i.e. low solubility in electrolytes; resistance to oxygen penetration; good electrical conductivity (specific resistance of inert anode ≤ specific resistance of carbon anode); high mechanical strength, high thermal stability.Impact-resistant and non-brittle; excellent manufacturing properties and ease of connection to metallic conductors; and readily available and inexpensive raw materials. According to modern research, ceramic alloy materials possess superior electrical conductivity and processability compared to metallic materials, as well as good resistance to corrosion by molten salts. Therefore, ceramic alloy materials are the most promising inert anode materials that can replace carbon anodes.

[0005] To operate an inert anode, an electric current must be supplied through a metal conductive block. However, there are significant differences in the physical and chemical properties of ceramic alloy materials and the metal conductive block.Therefore, the following difficulties arise when welding ceramic alloy materials and a metal conductive block: (1) the different crystal structures of the ceramic alloy materials and the metal conductive block result in different melting temperatures; (2) the high bond energy of ceramic crystals makes the diffusion of components extremely difficult; (3) the thermal expansion coefficients of the ceramic alloy materials and the metal conductive block are very different, which leads to significant thermal stress in the joints and easy cracking of the ceramic alloy materials; (4) brittle areas are formed between the surfaces to be joined, which reduces the performance characteristics of the ceramics. Therefore, it is difficult to achieve a connection between the ceramic alloy materials and the metal conductive block using conventional welding methods. SUMMARY OF THE INVENTION

[0006] The technical problem of difficulty in connecting an inert anode to a metal conductive block is solved by using one or more embodiments of the invention.

[0007] In an embodiment of the invention, a method for joining a ceramic inert anode based on nickel ferrite and a metal conductive block is proposed. The method for joining a ceramic inert anode based on nickel ferrite and a metal conductive block includes the following steps: obtaining a ceramic inert anode based on nickel ferrite and a metal conductive block and processing the surfaces of the ceramic inert anode based on nickel ferrite and the metal conductive block to form surfaces to be joined; obtaining a transition alloy foil and attaching the surfaces to be joined of the ceramic inert anode based on nickel ferrite and the metal conductive block, respectively, to two surfaces of the transition alloy foil to form a prefabricated connection body; and performing vacuum diffusion welding of the prefabricated connection body. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the invention or related technologies, a brief introduction to the accompanying drawings required for describing the embodiments or related technologies will be provided below. Obviously, for those with ordinary knowledge in this field, other accompanying drawings can be derived from these accompanying drawings without any creative efforts.

[0010] Fig. 1 is a basic structural diagram of a prefabricated connecting element according to Example 1 of the disclosure;

[0011] Fig. 2 is a basic structural diagram of a prefabricated connecting element according to Example 2 of the disclosure; and

[0012] Fig. 3 is a basic structural diagram of a prefabricated connecting element according to Example 3 of the disclosure. DESCRIPTION OF EMBODIMENTS

[0013] In order to make the objectives, technical solutions, and advantages of the embodiments of the invention more clear, the technical solutions in the embodiments of the invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the invention. It is obvious that the described embodiments are only a part of the disclosure embodiments, and not all embodiments. Based on the embodiments given in the description, all other embodiments obtained by those skilled in the art without any creative efforts fall within the scope of protection provided in the description.

[0014] Unless otherwise defined, the terms used herein shall be understood to have the same meanings as commonly used in the art. Thus, unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this description belongs. In case of conflict, the description given in this description shall prevail.

[0015] Unless otherwise specified, various raw materials, reagents, tools and devices used in the description can be purchased on the market or obtained by existing methods.

[0016] At present, there is a technical problem in the field of aluminum electrolysis that it is difficult to connect the inert anode with the metal conductive block.

[0017] The technical solution provided by the embodiments of the invention is to solve the above technical problems, and the general idea is as follows.

[0018] In an embodiment of the invention, a method for connecting a ceramic inert anode based on nickel ferrite and a metal conductive block is proposed. As shown in Figs. 1-3, the method for connecting a ceramic inert anode 1 based on nickel ferrite and a metal conductive block 3 includes the following steps:

[0019] Step 1: obtaining a ceramic inert anode 1 based on nickel ferrite and a metal conductive block 3, and processing the surfaces of the ceramic inert anode 1 based on nickel ferrite and the metal conductive block 3 to form surfaces to be connected;

[0020] Step 2: providing a transition alloy foil 2 and attaching the surfaces to be joined of the ceramic inert anode 1 based on nickel ferrite and the metal conductive block 2, respectively, to the two surfaces of the transition alloy foil 2 to form a prefabricated connecting member; and,

[0021] Step 3: Perform vacuum diffusion welding on the assembled connection body.

[0022] Those skilled in the art will appreciate that vacuum diffusion welding can be performed in a vacuum diffusion furnace. The melting point of the transition alloy foil 2 is lower than the melting point of the metallic conductive block 3 and the ceramic inert anode 1 based on nickel ferrite, which is a general condition for vacuum diffusion welding. Foil 2 made of a transition alloy with a lower melting point is selected as the intermediate layer. When heated to the melting point, the intermediate layer melts and instantly forms a liquid film between the surfaces being joined. During the thermal insulation process, as the low-melting-point components of the intermediate layer diffuse toward the metallic conductive block 3 and the ceramic inert anode 1 based on nickel ferrite, the thickness of the liquid film decreases until it disappears.After a certain period of thermal insulation, the compounds near the surfaces being joined are homogenized. As a liquid film forms and the components of the liquid film diffuse, transition alloy foil 2 is bonded between the surfaces being joined.

[0024] The concentration gradient between the liquid film and the joining surfaces can be increased by using transition alloy foil 2, which promotes the diffusion of components and accelerates the disappearance of diffusion voids. Transition alloy foil 2 can relieve residual stress caused by the different thermal expansion coefficients of ceramics and metals, control the reaction at the solidification boundary, inhibit or modify the reaction products at the solidification boundary, and improve the joint quality. Transition alloy foil 2 can be a combination of an adhesive alloy material and a reactive alloy material. With suitable compositions, transition alloy foil 2 can reduce the temperature, time, and pressure of vacuum diffusion bonding and improve the performance of the joint.An adhesive alloy material that does not react with the ceramic but can diffuse with the ceramic component is selected to form the diffusion layer. The reactive alloy material can react with the ceramic to form a reaction product, and the ceramic and metal are firmly bonded through the reaction product.

[0025] In this description, transition alloy foil 2 is used as a welding medium, and a vacuum diffusion welding method is adopted to join the nickel ferrite-based ceramic inert anode 1 and the metal conductive block 3 by means of instantaneous liquid film diffusion. Under the working conditions of vacuum diffusion welding, transition alloy foil 2 instantly forms a liquid film between the surfaces to be joined. As the components of the liquid film diffuse into the nickel ferrite-based ceramic inert anode 1 and the metal conductive block 3, and the components of the nickel ferrite-based ceramic inert anode 1 and the metal conductive block 3 diffuse into the liquid film, the thickness of the liquid film decreases and disappears, and finally, a joint of metallurgical quality is formed. The bonding seam formed in this way is uniform and dense, without cavities and cracks, and has a bond strength of ≥ 150 MPa.

[0026] Furthermore, according to the invention, the joining speed is fast and the efficiency is high. The diffusion joint between the ceramic inert anode 1 based on nickel ferrite and the metal conductive block 3 can be completed in only 20 minutes. The joining precision is high, and the material deformation is small. The joining method according to the invention can be used to join the ceramic inert anode 1 based on nickel ferrite of various shapes and structures, and can also be used to join the ceramic inert anode 1 based on nickel ferrite with a large-sized planar structure. That is, the joining method in the disclosure provides a wide range of applicability. The operations of the joining method described in the description are simple. The resulting joint has high strength, high corrosion resistance, and good electrical conductivity.The resulting connection, under the conditions of aluminum electrolysis, will not crack or fall off after long-term use.

[0027] In some embodiments, the average arithmetic deviation of the surface profile of the surfaces to be joined is 0.6×10-4 cm~2.5×10-4 cm.

[0028] Surface roughness can have a significant impact on diffusion welding. Low surface roughness can ensure tighter bonding between parts under temperature and pressure, as well as a higher degree of diffusion and more reliable welding quality.

[0029] In some embodiments, treating the surfaces of a ceramic inert anode based on nickel ferrite and a metal conductive block to form bondable surfaces includes:

[0030] Step S11: cleaning the surfaces of the ceramic inert anode 1 based on nickel ferrite and the metal conductive block 3; and

[0031] Step S12: Polish the cleaned surfaces with 120#, 220#, 500#, 1000#, 1500#, 2000#, and 2500# sandpapers in sequence.

[0032] The purpose of polishing the cleaned surfaces with sandpaper is to control the arithmetic mean deviation of the surface profile of the joined surfaces, which is 0.6×10-4cm~2.5×10-4cm.

[0033] In some embodiments, the materials of the transition alloy foil 2 include a Fe-Ni alloy.

[0034] In some embodiments, the transition alloy foil 2 materials further include at least one of B, Si, V and Co.

[0035] In some embodiments, the transition alloy foil 2 includes, in percentage by weight:

[0036] B 0.01%~2%,

[0037] Si 0.05~5%,

[0038] V 0.01%~2%,

[0039] Co 0.1~5%,

[0040] The rest is Fe-Ni alloy.

[0041] In some embodiments, the thickness of the transition alloy foil 2 is from 5 μm to 500 μm.

[0042] In some embodiments, vacuum diffusion welding has:

[0043] diffusion temperature from 950°C to 1200°C; and / or

[0044] heating speed from 10°C / min to 30°C / min; and / or

[0045] thermal insulation time from 2 to 20 minutes; and / or,

[0046] pressure from 5 MPa to 30 MPa; and / or,

[0047] cooling speed from 4°C / min to 8°C / min.

[0048] The higher the temperature, the greater the diffusion coefficient and the higher the diffusion rate. Therefore, the lower the pressure, the greater the pressure required to ensure intimate contact between the surfaces being joined. However, excessively high temperatures can easily cause the metal conductive block 3 to melt or soften, thereby not only affecting the composition and surface condition of the materials but also influencing the phase change of the intermediate layer. Therefore, the diffusion temperature is selected to be 0.6 Tm~0.8 Tm and is generally in the range of 950-1200°C. Tm is the melting point of the metal conductive block.

[0049] The greater the applied pressure, the larger the area of ​​intimate contact between the surfaces being joined, thereby contributing to a contact surface with good performance. At the same time, the cavities formed at the joint junction by the ceramic material of the nickel ferrite-based ceramic inert anode 1 can be effectively filled to prevent the formation of diffusion voids. However, excessive pressure will cause macroscopic plastic deformation of the metal conductive block 3, and therefore the diffusion pressure is 5-30 MPa.

[0050] The depth of the diffusion layer is proportional to the square root of the diffusion time. The strength, ductility, elongation, and impact toughness of the joint increase to a certain point and then generally remain stable. Excessive exposure to high temperatures and high pressures will not further improve the joint quality.

[0051] After the joint is formed by vacuum diffusion bonding using a liquid film flash, a higher cooling rate will cause greater internal stress in the joint due to the large difference in the thermal expansion coefficients between the ceramic material of the nickel ferrite-based ceramic inert anode 1 and the metal material of the metal conductive block 3, which in turn leads to the occurrence of microcracks. Therefore, after thermal insulation is completed, the cooling rate should be controlled. When the joint is cooled at a cooling rate of 4°C / min to 8°C / min, the internal stress in the joint can be effectively reduced, thereby ensuring the performance of the joint.

[0052] A special vacuum diffusion bonding method is a generally accepted technical means in this field. In some embodiments, the special vacuum diffusion bonding method comprises the following.

[0053] The prefabricated connecting element, consisting of a NiFe2O4-based ceramic inert anode, a transition alloy foil 2, and a metal conductive block 3, is placed in a vacuum diffusion furnace. The mechanical pump and the root pump are turned on respectively to effectively remove air from the vacuum diffusion furnace. When the vacuum degree in the vacuum diffusion furnace reaches 10-3 Pa, high-purity argon or high-purity nitrogen is supplied into the vacuum diffusion furnace to make the pressure in the vacuum diffusion furnace reach 0.1-0.9 Pa. The vacuum diffusion furnace is heated in it at a heating rate of 10°C / min-30°C / min to a temperature of 950°C-1200°C, and a pressure of 5-30 MPa is supplied to the vacuum diffusion furnace using high-purity argon or high-purity nitrate.Under the above conditions, the vacuum diffusion furnace is then thermally insulated for 2 min to 20 min, and then the temperature in the vacuum diffusion furnace is cooled to 400°C at a rate of 4°C / min to 8°C / min, and then cooled to room temperature.

[0054] In some embodiments, the ceramic inert anode 1 based on nickel ferrite is a ceramic inert anode NiFe2O4-X or a metal-ceramic inert anode NiFe2O4-XY, which is obtained by sintering.

[0055] In some embodiments, in the NiFe2O4-X ceramic inert anode or the NiFe2O4-XY ceramic inert anode, X is a composite ceramic phase including at least one of ZnO, CuO, Cr2O3, MgO, Y2O3 and tin.

[0056] Y is a composite metallic phase including at least one of Cu, Ni, Fe, Co, Cr, Al, Mn and rare earth elements.

[0057] X is a composite ceramic phase, which can improve the sintering or sealing performance of the inert anode.

[0058] Y is a composite metal phase, which can improve the corrosion resistance of inert anode.

[0059] The disclosure is further described below in conjunction with specific embodiments. It should be understood that these examples are used for illustrative purposes only and are not intended to limit the scope of the disclosure. The experimental methods described in the following examples, without specifying specific conditions, are generally carried out in accordance with Chinese national standards. If relevant Chinese national standards do not exist, general international standards, customary conditions, or conditions recommended by the manufacturer should be used as a guide.

[0060] Example 1

[0061] The prepared NiO, Fe2O3, ZnO, Cu, and Fe powders are pressed into an inert anode ceramic mass by isostatic pressing at a pressure of 130 MPa, and then the inert anode ceramic mass is sintered at a temperature of 1000°C in a nitrogen atmosphere to obtain a nickel ferrite ceramic inert anode 1. The oxygen content in the nitrogen atmosphere is controlled so that it does not exceed 200 ppm. Then, the metal conductive block 3 is precision machined so that the size of the metal conductive block 3 meets the connection requirements.

[0062] The foreign objects adhering to the surfaces to be joined are removed with compressed air, and then the surfaces to be joined are successively polished with 120#, 220#, 500#, 1000#, 1500#, 2000#, and 2500# sandpaper and wiped again with alcohol to ensure that the surfaces to be joined of the ceramic inert anode 1 based on nickel ferrite and the metal conductive block 3 are clean and tidy. The average arithmetic deviation of the profile of the surfaces to be joined is 1.5×10-4 cm.

[0063] As shown in Fig. 1, the size of one end of the ceramic inert anode 1 based on nickel ferrite is smaller than the other end of the ceramic inert anode 1 based on nickel ferrite. The end contour of the processed metal conductive block 3 completely corresponds to the end contour of the ceramic inert anode 1 based on nickel ferrite. The transition alloy foil 2 is attached to the connecting surfaces of the ceramic inert anode 1 based on NiFe2O4 and the metal conductive block 3, forming a prefabricated connecting element. The composition of the transition alloy foil 2 in a mass ratio includes Ni 30%, Cr 6%, B 1%, Si 1%, Co 0.5%, V 0.5%, the rest is Fe. The transition alloy foil 2 has a thickness of 20 μm. A prefabricated connecting element consisting of a ceramic inert anode based on NiFe2O6, a foil 2 made of a transition alloy and a metal conductive block 3 is placed in a vacuum diffusion furnace.The mechanical pump and root pump are turned on respectively to effectively remove air from the vacuum diffusion furnace. When the vacuum degree in the vacuum diffusion furnace reaches 10-3 Pa, high-purity argon or high-purity nitrogen is supplied to the furnace to bring the pressure in the vacuum diffusion furnace to 0.3 Pa. The vacuum diffusion furnace is heated at a heating rate of 12°C / min to a temperature of 1020°C, and a pressure of 6 MPa is applied to the vacuum diffusion furnace using high-purity argon or high-purity nitrogen. Under these conditions, the vacuum diffusion furnace is then thermally insulated for 5 min, and then cooled to 400°C at a rate of 6°C / min, and then cooled to room temperature.A ceramic inert anode 1 based on nickel ferrite, formed by sintering, and a metal conductive block 3 of a predetermined length are reconnected by threaded connection or welding to complete the inert anode assembly. This inert anode can operate stably for long periods under electrolysis conditions of 800°C and a current density of 10 A / cm2.

[0064] Example 2

[0065] The prepared NiO, Fe2O3, MgO, Cu, Fe, and Ni powders are pressed into a ceramic anode blank by isostatic pressing at a pressure of 130 MPa. The ceramic anode blank is then sintered at a temperature of 1000°C in a nitrogen atmosphere to obtain a ceramic-based nickel ferrite inert anode 1. The oxygen content in the nitrogen atmosphere is controlled at no more than 200 ppm. Then, the metal conductive block 3 is precision machined so that the size of the metal conductive block 3 meets the connection requirements.Foreign objects adhering to the surfaces to be joined are removed with compressed air, and then the surfaces to be joined are successively polished with 120#, 220#, 500#, 1000#, 1500#, 2000#, and 2500# sandpaper and then wiped again with alcohol to ensure that the surfaces to be joined of the ceramic inert anode 1 based on nickel ferrite and the metal conductive block 3 are clean and neat. The average arithmetic deviation of the profile of the surfaces to be joined is 1.2×10-4 cm.

[0066] As shown in Fig. 2, the end face of the ceramic inert anode 1 based on nickel ferrite has a groove, and the end face contour of the processed metal conductive block 3 completely matches the contour of the groove. The transition alloy foil 2 is attached to the connecting surfaces of the ceramic inert anode 1 based on NiFe2O4 and the metal conductive block 3, forming a prefabricated connecting element. The composition of the transition alloy foil 2 by weight includes Ni 26%, Cr 8%, B 1.2%, Si 1.5%, Co 1.0%, V 0.8%, the rest is Fe. The transition alloy foil 2 has a thickness of 30 μm. A prefabricated connecting element consisting of a ceramic inert anode based on NiFe2O6, a transition alloy foil 2, and a metal conductive block 3 is placed in a vacuum diffusion furnace. A mechanical pump and a root pump are activated, respectively, to effectively remove air from the vacuum diffusion furnace.When the vacuum degree in the vacuum diffusion furnace reaches 10-3 Pa, high-purity argon or high-purity nitrogen is poured into the vacuum diffusion furnace to bring the pressure in the vacuum diffusion furnace to 0.3 Pa. The vacuum diffusion furnace is heated at a heating rate of 10°C / min to a temperature of 1050°C, and a pressure of 8 MPa is applied to the vacuum diffusion furnace using high-purity argon or high-purity nitrogen. Under these conditions, the vacuum diffusion furnace is then thermally insulated for 10 min, and then the temperature in the vacuum diffusion furnace is cooled to 400°C at a heating rate of 6°C / min, and then cooled to room temperature. The ceramic inert anode 1 based on nickel ferrite formed by sintering and the metal conductive block 3 of a certain length are reconnected by a threaded connection or welding to complete the connection of the inert anode into a single whole.This inert anode can work stably for a long time under the conditions of electrolysis temperature of 850°C and current density of 10A / cm. 2 .

[0067] Example 3

[0068] The prepared NiO, Fe2O3, Y2O3, Fe, Ni, and Co powders are pressed into a ceramic anode blank by isostatic pressing at a pressure of 130 MPa, and then the ceramic anode blank is sintered at a temperature of 1000°C in a nitrogen atmosphere to obtain a nickel ferrite-ceramic inert anode 1 based on nitrogen, the oxygen content of which in the atmosphere is controlled at no more than 200 ppm. Then, the metal conductive block 3 is precision machined so that the size of the metal conductive block 3 meets the requirements for the connection.Foreign objects adhering to the surfaces to be joined are removed with compressed air, and then the surfaces to be joined are successively polished with 120#, 220#, 500#, 1000#, 1500#, 2000#, and 2500# sandpaper and then wiped again with alcohol to ensure that the surfaces to be joined of the ceramic inert anode 1 based on nickel ferrite and the metal conductive block 3 are clean and neat. The average arithmetic deviation of the profile of the surfaces to be joined is 1.8×10-4 cm.

[0069] As shown in Fig. 1, the size of one end of the ceramic inert anode 1 based on nickel ferrite is equal to the size of the other end of the ceramic inert anode 1 based on nickel ferrite. The end contour of the processed metal conductive block 3 completely corresponds to the end contour of the ceramic inert anode 1 based on nickel ferrite. The transition alloy foil 2 is attached to the connecting surfaces of the ceramic inert anode based on NiFe2O4 and the metal conductive block 3, forming a prefabricated connecting body. The composition of the transition alloy foil 2 in a mass ratio includes Ni 20%, Cr 10%, B 1.5%, Si 2%, Co 0.5%, V 0.5%, the rest is Fe. The transition alloy foil 2 has a thickness of 50 μm. A prefabricated connecting element consisting of a ceramic inert anode based on NiFe2O6, a foil 2 made of a transition alloy and a metal conductive block 3 is placed in a vacuum diffusion furnace.The mechanical pump and root pump are turned on respectively to effectively remove air from the vacuum diffusion furnace. When the vacuum degree in the vacuum diffusion furnace reaches 10-3 Pa, high-purity argon or high-purity nitrogen is poured into the vacuum diffusion furnace to bring the pressure in the vacuum diffusion furnace to 0.5 Pa. The vacuum diffusion furnace is heated at a heating rate of 12°C / min to a temperature of 1100°C, and a pressure of 10 MPa is applied to the vacuum diffusion furnace using high-purity argon or high-purity nitrogen. Under these conditions, the vacuum diffusion furnace is then thermally insulated for 15 min, and then the temperature in the vacuum diffusion furnace is cooled to 400°C at a rate of 6°C / min, and then cooled to room temperature.A ceramic inert anode 1 based on nickel ferrite, formed by sintering, and a metal conductive block 3 of a predetermined length are reconnected by threaded connection or welding to complete the inert anode assembly. This inert anode can operate stably for long periods under electrolysis conditions of 800°C and a current density of 10 A / cm. 2 .

[0070] Various embodiments of the disclosure may exist in the form of a range; it should be understood that the description in the form of a range is intended only for convenience and simplicity and should not be understood as an strict limitation on the scope of the disclosure. Therefore, it should be considered that all possible sub-ranges, as well as individual values ​​within such a range, are specifically indicated in the described range. For example, the description of a range from 1 to 6 should be considered to include specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, and from 3 to 6, as well as a single number within the stated range, such as 1, 2, 3, 4, 5, and 6, which applies regardless of the range. Furthermore, whenever a numerical range is indicated herein, it is meant to include any specified number (fractional or integer) within the stated range.

[0071] In the description, unless otherwise specified, the directional words used, such as "upper" and "lower," refer specifically to the directions of the drawings in the accompanying drawings. Furthermore, in the description in the specification of the disclosure, the terms "include," "comprise," and the like mean "including, but not limited to." Moreover, the terms "include," "substantive," or any other variations thereof are intended to mean a non-exclusive inclusion, so that a process, method, article, or device that includes a list of elements includes not only these elements, but also other elements not explicitly listed, or also includes elements inherent to such a process, method, article, or device. Without further limitation, elements defined by the phrase "including..." do not exclude the presence of other identical elements in a process, method, article, or device that includes these elements.In this specification, relational terms such as "first" and "second" are used simply to distinguish one object or operation from another object or operation, but do not necessarily require or imply any actual relationship or order between these objects or operations. In the specification, "and / or" describes the relationship between associated objects, indicating that there may be three relationships. For example, A and / or B may relate to: A alone, both A and B, and B only. For an association relationship of more than three related objects, described by "and / or," this indicates that any of the three related objects can exist separately, or at least two of the three related objects can exist simultaneously. For example, for A, and / or B, and / or C, this may indicate that any of A, B, and C exist separately, or any two of A, B, and C exist simultaneously, or three of A, B, and C exist simultaneously.As used herein, "at least one" means one or more, and "a plurality" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of those elements, including individual elements or any combination of elements in the plural. For example, "at least one of a, b, or c" or "at least one of a, b, and c" may mean: a, b, c, a~b (i.e., a and b), a~c, b~c, or a~b- c, where a, b, and c may be singular or plural.

[0072] The above descriptions are merely specific embodiments of the disclosure to enable those skilled in the art to understand or implement the disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principle defined herein may be applied in practice to other embodiments without departing from the spirit or scope of the disclosure. Therefore, the disclosure should not be limited to the embodiments shown herein, but should be accorded the broadest possible scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for welding a ceramic inert anode based on nickel ferrite and a metal conductive block of an aluminum electrolyzer, comprising: obtaining a ceramic inert anode based on nickel ferrite and a metal conductive block and processing the surfaces of the ceramic inert anode based on nickel ferrite and a metal conductive block to form the surfaces to be joined; providing a transition metal alloy foil and attaching the surfaces to be joined of a ceramic inert nickel ferrite anode and a metallic conductive block, respectively, to two surfaces of the transition metal alloy foil to form a prefabricated connecting body; and Carrying out vacuum diffusion welding on a prefabricated connecting body; where the transition metal alloy foil contains, in wt. %: B: 0.01-2, Si: 0.05-5, V: 0.01-2, Co: 0.1-5, Ni: 20-30, Fe the rest, In this case, vacuum diffusion welding is performed at a diffusion temperature of 950 to 1200°C, a heating rate of 10 to 30°C / min, a thermal insulation time of 2 to 20 min, a pressure of 5 to 30 MPa and a cooling rate of 4 to 8°C / min.

2. The method according to paragraph 1, in which the average arithmetic deviation of the surface profile of the surfaces to be joined is from 0.6×10 -4 up to 2.5×10 -4 cm.

3. The method according to paragraph 2, in which the treatment of the surfaces of the ceramic inert anode based on nickel ferrite and the metal conductive block to form the surfaces to be joined includes: cleaning the surfaces of the ceramic inert anode based on nickel ferrite and the metal conductive block; and sequential polishing of cleaned surfaces using sandpaper of the following grades: 120, 220, 500, 1000, 1500, 2000 and 2500.

4. The method according to claim 1, wherein the thickness of the transition metal alloy foil is from 5 to 500 μm.

5. The method according to claim 1, wherein the ceramic inert anode based on nickel ferrite is a ceramic inert anode NiFe2O4-X or a metal-ceramic inert anode NiFe2O4-XY obtained by sintering.

6. The method according to claim 5, wherein the ceramic inert anode is NiFe2O4-X or the metal-ceramic inert anode is NiFe2O4-XY, where X is a composite ceramic phase containing at least one of ZnO, CuO, Cr2O3, MgO, Y2O3 and tin, and Y is a composite metallic phase containing at least one of Cu, Ni, Fe, Co, Cr, Al, Mn and rare earth elements.

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