NiFe2O4-based metal ceramic inert anode and preparation method thereof

Abstract

The invention relates to a NiFe2O4-based metal ceramic inert anode and a preparation method thereof.The preparation method comprises the steps that NiFe2O4 powder and metal M powder are mixed and subjected to ball milling treatment, and M-NiFe2O4 mixed powder is obtained; adding a binding agent, mixing, carrying out compression molding, and sintering to obtain an M-NiFe2O4 porous ceramic preform; and copper powder is placed on the periphery of the M-NiFe2O4 porous ceramic preform, the temperature is increased, molten copper is subjected to pressureless infiltration, and the NiFe2O4-based metal ceramic inert anode is obtained after cooling. The metal M powder and the NiFe2O4 powder are mixed to prepare the porous ceramic preform, so that the interface wettability of NiFe2O4 and copper can be improved, an alloy fusion process is omitted, pressureless infiltration of molten copper is promoted, a three-dimensional continuous network structure is formed, the cost is saved, the energy consumption is reduced, and the porous ceramic preform has corrosion resistance, high-temperature conductivity and thermal shock resistance under the condition of low copper content.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of cermet material preparation, and relates to a cermet inert anode, in particular to a NiFe2O4-based cermet inert anode and a preparation method thereof. BACKGROUND

[0002] The current industrial aluminum electrolysis process has long relied on carbon anodes. This traditional method not only consumes a large amount of high-quality carbon materials, but also produces a large amount of greenhouse gas CO2 and carcinogenic fluorocarbons, causing serious environmental pollution. Compared with carbon anodes, inert anodes, as a kind of non-consumable or trace-consumable anode material, produce only oxygen gas in the aluminum electrolysis process, which avoids the emission of CO2 and fluorocarbons from the root; at the same time, since the anode does not need to be replaced frequently, the heat balance of the electrolytic cell is more stable, and the consumption of manpower and material resources in the anode replacement process is saved.

[0003] At present, the selection of inert anode materials mainly focuses on three types of materials, namely metal alloy anode, oxide ceramic anode and cermet anode. Among them, the NiFe2O4-based cermet inert anode is a good inert anode material for replacing carbon anodes, because it has the corrosion resistance and thermal stability of the NiFe2O4 ceramic phase and the electrical conductivity and thermal shock resistance of the metal phase. In order to ensure that the NiFe2O4-based cermet inert anode has sufficient high-temperature electrical conductivity, a relatively high metal phase content is usually required. CN1772961A discloses a metal-based composite material inert anode for aluminum electrolysis and a preparation method thereof. The ceramic phase of the metal-based composite material inert anode for aluminum electrolysis includes nickel ferrite, aluminum oxide and rare earth oxides, the metal phase is composed of iron, nickel, cobalt, chromium, titanium, copper or their alloys, and the metal phase accounts for more than 50wt% of the inert anode, which has good electrical conductivity. CN102732769A discloses a nickel ferrite-copper cermet inert anode material and a preparation process thereof. The ceramic phase of the nickel ferrite-copper cermet inert anode material is nickel ferrite or nickel ferrite-based composite ceramic, accounting for 60wt% to 85wt% of the total mass, and the metal phase is composed of metallic copper and cuprous oxide, accounting for 15wt% to 40wt% of the total mass, which has good electrical conductivity and thermal shock resistance.

[0004] However, in the aluminum electrolysis process, the metal phase will preferentially corrode and dissolve, resulting in that the corrosion resistance of the NiFe2O4-based cermet inert anode cannot meet the requirements of the aluminum electrolysis process, and also reduces the purity of the product aluminum, which seriously restricts the industrial application of the inert anode.

[0005] Therefore, developing a low-cost, low-energy-consumption method for preparing NiFe2O4-based cermet inert anodes and promoting the penetration of molten copper into the NiFe2O4 ceramic to enable it to possess resistance to molten salt corrosion, high-temperature conductivity, and thermal shock resistance under low copper content conditions is an urgent problem to be solved in the field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a NiFe2O4-based cermet inert anode and its preparation method. The preparation method provided by the present invention, on the one hand, improves the interfacial wettability between NiFe2O4 and copper by introducing metallic M, promoting the pressureless capillary infiltration of molten copper into the internal pores of the M-NiFe2O4 porous ceramic preform and forming a three-dimensional continuous network structure. This allows the preform to possess resistance to molten salt corrosion, high-temperature conductivity, and thermal shock resistance even with low copper content. On the other hand, by mixing metallic M powder with NiFe2O4 powder to prepare the M-NiFe2O4 porous ceramic preform, the alloy fusion process between metallic M and copper can be omitted, and the pressureless infiltration process of copper does not require a complex external pressurization or vacuum system. This not only simplifies operation and reduces process requirements but also saves production costs and reduces energy consumption.

[0007] To achieve this objective, the present invention employs the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a NiFe2O4-based cermet inert anode, the method comprising the following steps:

[0009] (1) Mix NiFe2O4 powder and metal M powder and ball mill them to obtain M-NiFe2O4 mixed powder.

[0010] (2) The binder is mixed with the M-NiFe2O4 mixed powder, and after molding, it is sintered to obtain M-NiFe2O4 porous ceramic preform.

[0011] (3) Copper powder is placed around the M-NiFe2O4 porous ceramic preform, the temperature is increased, and the molten copper is pressurelessly melted into the pores of the M-NiFe2O4 porous ceramic preform by capillary action. After cooling, a NiFe2O4-based metal ceramic inert anode is obtained.

[0012] The preparation method provided by this invention, on the one hand, improves the interfacial wettability between NiFe2O4 and copper by introducing metal M, promoting the pressureless infiltration of molten copper into the internal pores of the M-NiFe2O4 porous ceramic preform by capillary action and forming a three-dimensional continuous network structure, so that it has the properties of molten salt corrosion resistance, high-temperature conductivity and thermal shock resistance even with low copper content; on the other hand, by mixing metal M powder with NiFe2O4 powder to prepare the M-NiFe2O4 porous ceramic preform, the alloy fusion process of metal M and copper can be omitted, and the pressureless infiltration process of copper does not require a complex external pressure or vacuum system. It is not only simple to operate and has low process requirements, but also saves production costs and reduces energy consumption.

[0013] Preferably, the material of the metal M powder in step (1) includes any one or at least two combinations of Zr, Cr, Mn, Y, Ce or Yb. Typical but non-limiting combinations include combinations of Zr and Cr, Mn and Y, Ce and Yb, Zr, Cr and Mn, Y, Ce and Yb, Zr, Cr, Mn and Y, Mn, Y, Ce and Yb, Zr, Cr, Mn, Y and Ce, Cr, Mn, Y, Ce and Yb, and Zr, Cr, Mn, Y, Ce and Yb.

[0014] Preferably, the mass ratio of NiFe2O4 powder to metal M powder in step (1) is (80~98):(2~20).

[0015] For example, the total weight of the NiFe2O4 powder and the metal M powder is 100 parts, the NiFe2O4 powder is 80 to 98 parts by weight, for example, 80, 82, 85, 88, 90, 92, 95, or 98 parts by weight; the metal M powder is 2 to 20 parts by weight, for example, 2, 5, 8, 10, 12, 15, 18, or 20 parts by weight.

[0016] This invention controls the mass ratio of NiFe2O4 powder to metal M powder to be (80~98):(2~20). If too little metal M powder is added, its effect on improving the interfacial wettability between NiFe2O4 and copper is not obvious, which affects the pressureless infiltration of molten copper into the interior of the M-NiFe2O4 porous ceramic preform, thereby affecting its resistance to molten salt corrosion, high-temperature conductivity and thermal shock resistance. If too much metal M powder is added, it will lead to an increase in temperature during sintering or pressureless infiltration, which will not only increase the risk of ceramic phase decomposition and reduce the flexural strength of the cermet, but also increase production costs and energy consumption.

[0017] Preferably, the NiFe2O4 powder in step (1) includes a first NiFe2O4 powder and a second NiFe2O4 powder. The average particle size of the first NiFe2O4 powder is 40μm to 80μm, for example, it can be 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm or 80μm, etc.; the average particle size of the second NiFe2O4 powder is 5μm to 30μm, for example, it can be 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 25μm or 30μm, etc.

[0018] This invention utilizes two NiFe2O4 powders with different particle sizes in combination. During the subsequent preparation of porous ceramic preforms, the coarse particles can construct continuous pore channels, ensuring high porosity and good connectivity. This helps reduce the penetration resistance of copper powder and promotes pressureless melting and infiltration of copper powder. Meanwhile, the fine particles can fill the pores constructed by the coarse particles, achieving pore classification, increasing specific surface area, and avoiding stress concentration caused by large pores in a single coarse particle size. This reduces internal cracks and delamination in the porous ceramic preform, improving its structural integrity and thermal shock resistance.

[0019] Preferably, the average particle size of the metal M powder in step (1) is 5μm to 100μm, for example, it can be 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm or 100μm, etc.

[0020] Preferably, the ball milling process in step (1) includes wet ball milling, and the ball milling medium includes water.

[0021] Preferably, the ratio of the total mass of the NiFe2O4 powder and the metal M powder to the mass of the water is 1:(3~5), for example, it can be 1:3, 1:3.5, 1:4, 1:4.5 or 1:5, etc.

[0022] Preferably, the ratio of the total mass of the NiFe2O4 powder and the metal M powder to the mass of the grinding balls used in the ball mill is 1:(1~3), for example, it can be 1:1, 1:1.5, 1:2, 1:2.5 or 1:3, etc.

[0023] Preferably, the ball milling speed is 200 rpm to 500 rpm, for example, it can be 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm.

[0024] Preferably, the ball milling treatment time is 12h to 36h, for example, it can be 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h or 36h.

[0025] Preferably, the ball milling process in step (1) further includes filtration and drying to obtain the M-NiFe2O4 mixed powder.

[0026] Preferably, the drying temperature is 60℃~120℃, for example, it can be 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, etc.

[0027] Preferably, the drying time is 12h to 36h, for example, it can be 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h or 36h.

[0028] Preferably, the mass of the binder in step (2) is 1wt% to 5wt% of the M-NiFe2O4 mixed powder, for example, it can be 1wt%, 2wt%, 3wt%, 4wt% or 5wt% etc.

[0029] This invention involves adding 1wt% to 5wt% of a binder (based on the mass of M-NiFe2O4 mixed powder) during the preparation of porous ceramic preforms. The binder's functional groups react with the hydroxyl groups on the surface of the NiFe2O4 powder, firmly binding the loose M-NiFe2O4 mixed powder, preventing the collapse of the ceramic green body after molding, and improving the flexural strength of the porous ceramic preform. If too little binder is added, a firm bond between the M-NiFe2O4 mixed powders cannot be achieved, potentially leading to collapse or low flexural strength of the ceramic green body after molding. If too much binder is added, it will fill the pores between the M-NiFe2O4 mixed powders, reducing the porosity or pore connectivity of the ceramic green body, affecting the subsequent pressureless melting and infiltration process of copper powder. Furthermore, excess binder cannot be completely decomposed during the subsequent sintering preparation of the porous ceramic preform, and its residual impurities will affect the sintering of the ceramic green body, reducing the thermal shock resistance and molten salt corrosion resistance of the porous ceramic preform.

[0030] Preferably, the binder in step (2) includes any one or a combination of at least two of PVA, PVB, starch or dextrin. Typical but non-limiting combinations include combinations of PVA and PVB, PVA and starch, starch and dextrin, PVA, PVB and starch, PVB, starch and dextrin, and PVA, PVB, starch and dextrin.

[0031] Preferably, the compression molding pressure in step (2) is 10MPa~180MPa, for example, it can be 10MPa, 20MPa, 30MPa, 40MPa, 50MPa, 80MPa, 100MPa, 120MPa, 140MPa, 160MPa or 180MPa, etc.

[0032] The pressure for compression molding in this invention is controlled to be between 10 MPa and 180 MPa. If the pressure is too low, the porous ceramic preform structure will be unstable, resulting in insufficient copper powder infiltration without pressure. If the pressure is too high, the porosity of the porous ceramic preform will be too low or the pores will be blocked, resulting in high resistance, incomplete infiltration, or inability to infiltrate the copper powder into the porous ceramic preform without pressure. Both too low and too high pressure will affect the flexural strength, high-temperature conductivity, and molten salt corrosion resistance of the NiFe2O4-based cermet inert anode.

[0033] Preferably, the molding time in step (2) is 3 min to 10 min, for example, it can be 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min.

[0034] Preferably, the atmosphere gas for the sintering process in step (2) includes any one or a combination of at least two of argon, nitrogen, helium or air. Typical but non-limiting combinations include combinations of argon and nitrogen, helium and air, argon, nitrogen and helium, nitrogen, helium and air, and argon, nitrogen, helium and air.

[0035] Preferably, the sintering process in step (2) includes a first sintering process and a second sintering process performed sequentially.

[0036] Preferably, the temperature of the first sintering treatment is 350℃~600℃, for example, it can be 350℃, 400℃, 450℃, 500℃, 550℃ or 600℃.

[0037] Preferably, the first sintering treatment time is 2h to 6h, for example, it can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h.

[0038] Preferably, the heating rate of the first sintering treatment is 1℃ / min to 3℃ / min, for example, it can be 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min or 3℃ / min, etc.

[0039] Preferably, the temperature of the second sintering treatment is 1200℃~1600℃, for example, it can be 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, 1500℃, 1550℃ or 1600℃, etc.

[0040] Preferably, the second sintering treatment time is 2h to 20h, for example, it can be 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h or 20h.

[0041] Preferably, the heating rate of the second sintering treatment is 1℃ / min to 5℃ / min, for example, it can be 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min or 5℃ / min, etc.

[0042] The first sintering treatment of the present invention is a binder removal stage, which can remove the added binder; the second sintering treatment is a sintering process used to prepare porous ceramic preforms.

[0043] Preferably, the mass of the copper powder in step (3) is 10wt% to 20wt% of the M-NiFe2O4 mixed powder, for example, it can be 10wt%, 12wt%, 14wt%, 15wt%, 16wt%, 18wt% or 20wt%.

[0044] Preferably, the atmosphere for pressureless melting infiltration in step (3) is argon and / or nitrogen.

[0045] Preferably, the pressureless melting temperature in step (3) is 1100℃~1350℃, for example, it can be 1100℃, 1150℃, 1200℃, 1250℃, 1300℃ or 1350℃, etc.

[0046] Preferably, the pressureless melting time in step (3) is 1 min to 30 min, for example, it can be 1 min, 5 min, 10 min, 15 min, 20 min, 25 min or 30 min.

[0047] Preferably, the heating rate of the pressureless melting infiltration in step (3) is 1℃ / min to 20℃ / min, for example, it can be 1℃ / min, 2℃ / min, 5℃ / min, 8℃ / min, 10℃ / min, 12℃ / min, 15℃ / min, 18℃ / min or 20℃ / min, etc.

[0048] Preferably, the preparation method includes the following steps:

[0049] (1) Mix NiFe2O4 powder, metal M powder, water and grinding balls, and then perform ball milling, filtration and drying to obtain M-NiFe2O4 mixed powder.

[0050] The material of the metal M powder includes any one or a combination of at least two of Zr, Cr, Mn, Y, Ce or Yb.

[0051] The mass ratio of the NiFe2O4 powder to the metal M powder is (80~98):(2~20).

[0052] The NiFe2O4 powder includes a first NiFe2O4 powder and a second NiFe2O4 powder. The average particle size of the first NiFe2O4 powder is 40μm to 80μm, and the average particle size of the second NiFe2O4 powder is 5μm to 30μm.

[0053] The average particle size of the metal M powder is 5μm~100μm.

[0054] The ratio of the total mass of the NiFe2O4 powder and the metal M powder to the mass of the water is 1:(3~5).

[0055] The ratio of the total mass of the NiFe2O4 powder and the metal M powder to the mass of the grinding balls used in the ball mill is 1:(1~3).

[0056] The ball milling process is performed at a speed of 200 rpm to 500 rpm for 12 h to 36 h.

[0057] The drying temperature is 60℃~120℃, and the drying time is 12h~36h.

[0058] (2) The binder is mixed with the M-NiFe2O4 mixed powder, and after molding, it is sintered to obtain M-NiFe2O4 porous ceramic preform.

[0059] The mass of the binder is 1wt% to 5wt% of the M-NiFe2O4 mixed powder, and the binder includes any one or a combination of at least two of PVA, PVB, starch or dextrin.

[0060] The compression molding pressure is 10MPa~180MPa, and the compression molding time is 3min~10min.

[0061] The atmosphere gas for the sintering process includes any one or a combination of at least two of argon, nitrogen, helium, or air.

[0062] The sintering process includes a first sintering process and a second sintering process performed sequentially.

[0063] The temperature of the first sintering treatment is 350℃~600℃, the time of the first sintering treatment is 2h~6h, and the heating rate of the first sintering treatment is 1℃ / min~3℃ / min.

[0064] The temperature of the second sintering treatment is 1200℃~1600℃, the time of the second sintering treatment is 2h~20h, and the heating rate of the second sintering treatment is 1℃ / min~5℃ / min.

[0065] (3) Copper powder is placed around the M-NiFe2O4 porous ceramic preform, the temperature is increased, and the molten copper is pressurelessly melted into the pores of the M-NiFe2O4 porous ceramic preform by capillary action. After cooling, a NiFe2O4-based metal ceramic inert anode is obtained.

[0066] The mass of the copper powder is 10wt% to 20wt% of the M-NiFe2O4 mixed powder.

[0067] The pressureless melting atmosphere is argon and / or nitrogen, the pressureless melting temperature is 1100℃~1350℃, the pressureless melting time is 1min~30min, and the pressureless melting heating rate is 1℃ / min~20℃ / min.

[0068] In a second aspect, the present invention provides a NiFe2O4-based cermet inert anode, wherein the NiFe2O4-based cermet inert anode is obtained by the preparation method described in the first aspect.

[0069] The NiFe2O4-based cermet inert anode comprises a ceramic phase and a metallic phase.

[0070] The ceramic phase includes NiFe2O4.

[0071] The metallic phase includes copper and metal M.

[0072] Preferably, the mass fraction of the ceramic phase is 70wt% to 90wt%, for example, it can be 70wt%, 75wt%, 80wt%, 85wt% or 90wt%.

[0073] Preferably, the mass fraction of the metallic phase is 10wt% to 30wt%, for example, it can be 10wt%, 15wt%, 20wt%, 25wt% or 30wt%.

[0074] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0075] Compared with the prior art, the present invention has the following beneficial effects:

[0076] The preparation method provided by this invention, on the one hand, improves the interfacial wettability between NiFe2O4 and copper by introducing metal M, promoting the pressureless infiltration of molten copper into the internal pores of the M-NiFe2O4 porous ceramic preform by capillary action and forming a three-dimensional continuous network structure, so that it has the properties of molten salt corrosion resistance, high-temperature conductivity and thermal shock resistance even with low copper content; on the other hand, by mixing metal M powder with NiFe2O4 powder to prepare the M-NiFe2O4 porous ceramic preform, the alloy fusion process of metal M and copper can be omitted, and the pressureless infiltration process of copper does not require a complex external pressure or vacuum system. It is not only simple to operate and has low process requirements, but also saves production costs and reduces energy consumption. Attached Figure Description

[0077] Figure 1 This is a cross-sectional SEM image of the Cu@Zr-NiFe2O4 cermet inert anode obtained in Example 1 of this invention. Detailed Implementation

[0078] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0079] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0080] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0081] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0082] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0083] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0084] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0085] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0086] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0087] Example 1

[0088] This embodiment provides a method for preparing a NiFe2O4-based cermet inert anode, the method comprising the following steps:

[0089] (1) Mix 95 parts by weight of NiFe2O4 powder, 5 parts by weight of Zr powder, 300 parts by weight of water and 200 parts by weight of grinding balls, and perform ball milling treatment. The ball milling speed is 300 rpm and the ball milling time is 24 h. After filtration, dry in a vacuum oven at 100℃ for 24 h to obtain Zr-NiFe2O4 mixed powder.

[0090] The average particle size of the first NiFe2O4 powder is 80 μm, the average particle size of the second NiFe2O4 powder is 30 μm, and the average particle size of the Zr powder is 80 μm.

[0091] (2) Mix 3 parts by weight of PVA2488 with the Zr-NiFe2O4 mixed powder obtained in step (1) evenly, and hold under pressure of 10MPa for 5min; then perform the first sintering treatment and the second sintering treatment in argon atmosphere to obtain Zr-NiFe2O4 porous ceramic preform.

[0092] The first sintering treatment involves heating to 500°C at a heating rate of 2°C / min and holding at that temperature for 3 hours; the second sintering treatment involves heating to 1300°C at a heating rate of 3°C / min from the temperature of 500°C in the first sintering treatment and holding at that temperature for 8 hours.

[0093] (3) Place 15 parts by weight of Cu powder around the Zr-NiFe2O4 porous ceramic preform, and heat it to 1250°C in an argon atmosphere at a heating rate of 5°C / min and hold it for 30 min, so that the molten Cu can be pressurelessly melted into the pores of the Zr-NiFe2O4 porous ceramic preform under capillary action. After cooling, Cu@Zr-NiFe2O4 cermet inert anode is obtained.

[0094] The Cu@Zr-NiFe2O4 cermet inert anode comprises a ceramic phase and a metallic phase; the ceramic phase comprises NiFe2O4 with a mass fraction of 83 wt%; the metallic phase comprises Cu and Zr with a total mass fraction of 17 wt%.

[0095] Figure 1 This is a cross-sectional SEM image of the Cu@Zr-NiFe2O4 cermet inert anode obtained in this embodiment. Figure 1It is known that copper penetrates into the internal pores of the M-NiFe2O4 porous ceramic preform and forms a three-dimensional continuous network structure, enabling the Cu@Zr-NiFe2O4 cermet inert anode to possess molten salt corrosion resistance, high-temperature conductivity, and thermal shock resistance even with low copper content.

[0096] Example 2

[0097] This embodiment provides a method for preparing a NiFe2O4-based cermet inert anode, the method comprising the following steps:

[0098] (1) Mix 98 parts by weight of NiFe2O4 powder, 2 parts by weight of Mn powder, 500 parts by weight of water and 100 parts by weight of grinding balls, and perform ball milling treatment. The ball milling speed is 200 rpm and the ball milling time is 36 h. After filtration, dry in a vacuum oven at 60℃ for 36 h to obtain Mn-NiFe2O4 mixed powder.

[0099] The average particle size of the first NiFe2O4 powder is 40 μm, the average particle size of the second NiFe2O4 powder is 5 μm, and the average particle size of the Mn powder is 40 μm.

[0100] (2) Mix 5 parts by weight of starch with the Mn-NiFe2O4 mixed powder obtained in step (1) and hold it under pressure of 50 MPa for 10 min; then perform the first sintering treatment and the second sintering treatment in a helium atmosphere to obtain the Mn-NiFe2O4 porous ceramic preform.

[0101] The first sintering treatment involves heating to 350°C at a heating rate of 1°C / min and holding at that temperature for 6 hours; the second sintering treatment involves heating to 1200°C at a heating rate of 1°C / min and holding at that temperature for 20 hours, while maintaining the temperature of 350°C as in the first sintering treatment.

[0102] (3) Place 20 parts by weight of Cu powder around the Mn-NiFe2O4 porous ceramic preform, and heat it to 1100℃ in a nitrogen atmosphere at a heating rate of 1℃ / min and hold it for 15min, so that the molten Cu can be pressurelessly melted into the pores of the Mn-NiFe2O4 porous ceramic preform under capillary action. After cooling, Cu@Mn-NiFe2O4 metal ceramic inert anode is obtained.

[0103] The Cu@Mn-NiFe2O4 cermet inert anode comprises a ceramic phase and a metallic phase; the ceramic phase comprises NiFe2O4 with a mass fraction of 82 wt%; the metallic phase comprises Cu and Mn with a total mass fraction of 18 wt%.

[0104] Example 3

[0105] This embodiment provides a method for preparing a NiFe2O4-based cermet inert anode, the method comprising the following steps:

[0106] (1) Mix 80 parts by weight of NiFe2O4 powder, 20 parts by weight of Ce powder, 400 parts by weight of water and 300 parts by weight of grinding balls, and perform ball milling treatment. The ball milling speed is 500 rpm and the ball milling time is 12 h. After filtration, dry in a vacuum oven at 120℃ for 12 h to obtain Ce-NiFe2O4 mixed powder.

[0107] The average particle size of the first NiFe2O4 powder is 60 μm, the average particle size of the second NiFe2O4 powder is 10 μm, and the average particle size of the Mn powder is 60 μm.

[0108] (2) Mix 1 part by weight of dextrin with the Ce-NiFe2O4 mixed powder obtained in step (1) and hold it under pressure of 100 MPa for 3 min; then perform the first sintering treatment and the second sintering treatment in a nitrogen atmosphere to obtain Ce-NiFe2O4 porous ceramic preform.

[0109] The first sintering treatment involves heating to 600℃ at a heating rate of 2℃ / min and holding at that temperature for 2 hours; the second sintering treatment involves heating to 1600℃ at a heating rate of 3℃ / min from the temperature of 600℃ in the first sintering treatment and holding at that temperature for 2 hours.

[0110] (3) Place 10 parts by weight of Cu powder around Ce-NiFe2O4 porous ceramic preform, and heat it to 1350℃ in a nitrogen atmosphere at a heating rate of 20℃ / min and hold it for 5min, so that the molten Cu can be pressurelessly melted into the pores of Ce-NiFe2O4 porous ceramic preform under capillary action. After cooling, Cu@Ce-NiFe2O4 metal ceramic inert anode is obtained.

[0111] The Cu@Ce-NiFe2O4 cermet inert anode comprises a ceramic phase and a metallic phase; the ceramic phase comprises NiFe2O4 with a mass fraction of 73 wt%; the metallic phase comprises Cu and Ce with a total mass fraction of 27 wt%.

[0112] Example 4

[0113] This embodiment provides a method for preparing a NiFe2O4-based cermet inert anode. Except for replacing the NiFe2O4 powder with 99 parts by weight and the Zr powder with 1 part by weight in step (1), all other steps are the same as in Example 1.

[0114] Example 5

[0115] This embodiment provides a method for preparing a NiFe2O4-based cermet inert anode. Except for replacing the NiFe2O4 powder with 70 parts by weight and the Zr powder with 30 parts by weight in step (1), all other steps are the same as in Example 1.

[0116] Example 6

[0117] This embodiment provides a method for preparing a NiFe2O4-based cermet inert anode. Except for step (1), where the average particle size of the NiFe2O4 powder is 30 μm, all other steps are the same as in Example 1.

[0118] Example 7

[0119] This embodiment provides a method for preparing a NiFe2O4-based cermet inert anode. Except for step (1), in which the average particle size of the NiFe2O4 powder is 80 μm, all other steps are the same as in Example 1.

[0120] Example 8

[0121] This embodiment provides a method for preparing a NiFe2O4-based cermet inert anode. Except for replacing PVA2488 in step (2) with 10 parts by weight, the method is the same as in Example 1.

[0122] Example 9

[0123] This embodiment provides a method for preparing a NiFe2O4-based cermet inert anode. Except for the pressure of 5MPa in step (2) of molding, all other steps are the same as in Example 1.

[0124] Example 10

[0125] This embodiment provides a method for preparing a NiFe2O4-based cermet inert anode. Except for the molding pressure of 200MPa in step (2), all other steps are the same as in Example 1.

[0126] Comparative Example 1

[0127] This comparative example provides a method for preparing a NiFe2O4-based cermet inert anode, which is the same as in Example 1 except that Zr powder is not added in step (1).

[0128] Comparative Example 2

[0129] This comparative example provides a method for preparing a NiFe2O4-based cermet inert anode. Except for step (1) where Zr powder is not added and step (3) where 5 parts by weight of Zr powder and 15 parts by weight of Cu powder are placed around the NiFe2O4 porous ceramic preform, all other steps are the same as in Example 1.

[0130] The apparent porosity, flexural strength, flexural strength after 10 air cooling cycles at 960℃ (thermal shock resistance), high-temperature conductivity at 960℃ (high-temperature conductivity), and annual corrosion thickness (molten salt corrosion resistance) of the Cu@M-NiFe2O4 cermet inert anodes obtained in Examples 1 to 10 and Comparative Examples 1 to 2 are shown in Table 1.

[0131]

[0132] As can be seen from Table 1, the NiFe2O4-based cermet inert anodes obtained in Examples 1-3 have high apparent porosity and flexural strength, and exhibit excellent thermal shock resistance, high-temperature conductivity and molten salt corrosion resistance.

[0133] Compared to Example 1, in Examples 4 and 5, the mass ratio of NiFe2O4 powder to metal M powder is (80~98):(2~20). If too little metal M powder is added, its effect on improving the interfacial wettability between NiFe2O4 and copper is not obvious, which affects the pressureless infiltration of molten copper into the interior of the M-NiFe2O4 porous ceramic preform, thereby affecting its resistance to molten salt corrosion, high-temperature conductivity and thermal shock resistance. If too much metal M powder is added, it will lead to an increase in temperature during sintering or pressureless infiltration, which will not only increase the risk of ceramic phase decomposition and reduce the flexural strength of the cermet, but also increase production costs and energy consumption.

[0134] Compared to Example 1, Examples 6 and 7 use only one type of NiFe2O4 powder with a single particle size. This makes it impossible to achieve high porosity and good connectivity by constructing continuous pore channels from coarse particles. Instead, fine particles fill the pores constructed by coarse particles to achieve pore gradation, thereby increasing the penetration resistance of copper powder and affecting the pressureless melting and infiltration of copper powder. Furthermore, it cannot effectively avoid stress concentration caused by large pores of a single particle size, which affects the structural integrity and thermal shock resistance of the porous ceramic preform and the cermet inert anode.

[0135] Compared to Example 1, in Example 8, due to the excessive addition of binder, on the one hand, it fills the pores between the M-NiFe2O4 mixed powders, resulting in a decrease in the porosity or pore connectivity of the ceramic green body, which affects the subsequent pressureless melting and infiltration process of copper powder. On the other hand, the excessive binder cannot be completely decomposed during the subsequent sintering preparation of porous ceramic preforms, and its residual impurities will affect the sintering of the ceramic green body, reducing the thermal shock resistance and molten salt corrosion resistance of the porous ceramic preforms.

[0136] Compared to Example 1, the molding pressure in Examples 9 and 10 is outside the range of 10 MPa to 180 MPa. If the pressure is too low, the porous ceramic preform structure will be unstable, resulting in insufficient copper powder infiltration without pressure. If the pressure is too high, the porosity of the porous ceramic preform will be too low or the pores will be blocked, resulting in high resistance, incomplete infiltration, or inability to infiltrate the copper powder into the porous ceramic preform without pressure. Both too low and too high pressure will affect the flexural strength, high-temperature conductivity, and molten salt corrosion resistance of the NiFe2O4-based cermet inert anode.

[0137] Compared to Example 1, Comparative Example 1, due to the absence of Zr powder, cannot improve the interfacial wettability between NiFe2O4 and copper. In Comparative Example 2, the Zr powder is not mixed with NiFe2O4 powder to form a porous ceramic preform, but is added together with Cu powder, and not in alloy form. Therefore, its effect on improving the interfacial wettability between NiFe2O4 and copper is not significant. Consequently, it affects the infiltration of molten copper into the internal pores of the NiFe2O4 porous ceramic preform by capillary action to form a three-dimensional continuous network structure, thus affecting the molten salt corrosion resistance, high-temperature conductivity, and thermal shock resistance of the NiFe2O4-based cermet inert anode.

[0138] In summary, the preparation method provided by this invention, on the one hand, improves the interfacial wettability between NiFe2O4 and copper by introducing metallic M, promoting the pressureless infiltration of molten copper into the internal pores of the M-NiFe2O4 porous ceramic preform through capillary action and forming a three-dimensional continuous network structure, thus enabling it to possess resistance to molten salt corrosion, high-temperature conductivity, and thermal shock resistance even with low copper content; on the other hand, by mixing metallic M powder with NiFe2O4 powder to prepare the M-NiFe2O4 porous ceramic preform, the alloy fusion process between metallic M and copper can be omitted, and the pressureless infiltration process of copper does not require a complex external pressure or vacuum system. This not only simplifies operation and reduces process requirements, but also saves production costs and reduces energy consumption.

[0139] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a NiFe2O4-based cermet inert anode, characterized in that, The preparation method includes the following steps: (1) Mix NiFe2O4 powder and metal M powder and ball mill them to obtain M-NiFe2O4 mixed powder; (2) The binder is mixed with the M-NiFe2O4 mixed powder, and after molding, it is sintered to obtain M-NiFe2O4 porous ceramic preform; (3) Copper powder is placed around the M-NiFe2O4 porous ceramic preform, the temperature is increased, and the molten copper is pressurelessly melted into the pores of the M-NiFe2O4 porous ceramic preform by capillary action. After cooling, a NiFe2O4-based metal ceramic inert anode is obtained.

2. The preparation method according to claim 1, characterized in that, The metal M powder in step (1) is made of any one or a combination of at least two of Zr, Cr, Mn, Y, Ce or Yb; Preferably, the mass ratio of NiFe2O4 powder to metal M powder in step (1) is (80~98):(2~20); Preferably, the NiFe2O4 powder in step (1) includes a first NiFe2O4 powder and a second NiFe2O4 powder, wherein the average particle size of the first NiFe2O4 powder is 40μm~80μm and the average particle size of the second NiFe2O4 powder is 5μm~30μm; Preferably, the average particle size of the metal M powder in step (1) is 5 μm to 100 μm.

3. The preparation method according to claim 1 or 2, characterized in that, The ball milling method described in step (1) includes wet ball milling, and the ball milling medium includes water; Preferably, the ratio of the total mass of the NiFe2O4 powder and the metal M powder to the mass of the water is 1:(3~5); Preferably, the ratio of the total mass of the NiFe2O4 powder and the metal M powder to the mass of the grinding balls used in the ball mill is 1:(1~3); Preferably, the ball milling speed is 200 rpm to 500 rpm; Preferably, the ball milling process takes 12 to 36 hours.

4. The preparation method according to any one of claims 1 to 3, characterized in that, Step (1) after ball milling also includes filtration and drying to obtain the M-NiFe2O4 mixed powder; Preferably, the drying temperature is 60℃~120℃; Preferably, the drying time is 12h to 36h.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The mass of the binder in step (2) is 1 wt% to 5 wt% of the M-NiFe2O4 mixed powder; Preferably, the binder in step (2) includes any one or a combination of at least two of PVA, PVB, starch or dextrin; Preferably, the compression molding pressure in step (2) is 10MPa~180MPa; Preferably, the molding time in step (2) is 3 min to 10 min.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The atmosphere gas for the sintering process in step (2) includes any one or a combination of at least two of argon, nitrogen, helium, or air; Preferably, the sintering process in step (2) includes a first sintering process and a second sintering process performed sequentially; Preferably, the temperature of the first sintering treatment is 350℃~600℃; Preferably, the first sintering treatment time is 2h~6h; Preferably, the heating rate of the first sintering treatment is 1℃ / min to 3℃ / min; Preferably, the temperature of the second sintering treatment is 1200℃~1600℃; Preferably, the second sintering treatment time is 2h~20h; Preferably, the heating rate of the second sintering treatment is 1℃ / min to 5℃ / min.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The mass of the copper powder in step (3) is 10wt%~20wt% of the M-NiFe2O4 mixed powder; Preferably, the atmosphere for pressureless melting infiltration in step (3) is argon and / or nitrogen; Preferably, the pressureless melting temperature in step (3) is 1100℃~1350℃; Preferably, the pressureless melting and infiltration time in step (3) is 1 min to 30 min; Preferably, the heating rate of the pressureless melting infiltration in step (3) is 1℃ / min to 20℃ / min.

8. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mix NiFe2O4 powder, metal M powder, water and grinding balls, and then perform ball milling, filtration and drying to obtain M-NiFe2O4 mixed powder; The material of the metal M powder includes any one or a combination of at least two of Zr, Cr, Mn, Y, Ce or Yb; The mass ratio of the NiFe2O4 powder to the metal M powder is (80~98):(2~20); The NiFe2O4 powder includes a first NiFe2O4 powder and a second NiFe2O4 powder. The average particle size of the first NiFe2O4 powder is 40μm~80μm, and the average particle size of the second NiFe2O4 powder is 5μm~30μm. The average particle size of the metal M powder is 5μm~100μm; The ratio of the total mass of the NiFe2O4 powder and the metal M powder to the mass of the water is 1:(3~5); The ratio of the total mass of the NiFe2O4 powder and the metal M powder to the mass of the grinding balls used in the ball mill is 1:(1~3); The ball milling process is performed at a speed of 200 rpm to 500 rpm for 12 h to 36 h. The drying temperature is 60℃~120℃, and the drying time is 12h~36h; (2) The binder is mixed with the M-NiFe2O4 mixed powder, and after molding, it is sintered to obtain M-NiFe2O4 porous ceramic preform; The mass of the binder is 1wt% to 5wt% of the M-NiFe2O4 mixed powder, and the binder includes any one or a combination of at least two of PVA, PVB, starch or dextrin. The compression molding pressure is 10MPa~180MPa, and the compression molding time is 3min~10min; The atmosphere gas for the sintering process includes any one or a combination of at least two of argon, nitrogen, helium, or air. The sintering process includes a first sintering process and a second sintering process performed sequentially. The temperature of the first sintering treatment is 350℃~600℃, the time of the first sintering treatment is 2h~6h, and the heating rate of the first sintering treatment is 1℃ / min~3℃ / min. The temperature of the second sintering treatment is 1200℃~1600℃, the time of the second sintering treatment is 2h~20h, and the heating rate of the second sintering treatment is 1℃ / min~5℃ / min; (3) Place copper powder around the M-NiFe2O4 porous ceramic preform, raise the temperature, and the molten copper will penetrate into the pores of the M-NiFe2O4 porous ceramic preform without pressure by capillary action. After cooling, a NiFe2O4-based metal ceramic inert anode is obtained. The mass of the copper powder is 10wt%~20wt% of the M-NiFe2O4 mixed powder; The pressureless melting atmosphere is argon and / or nitrogen, the pressureless melting temperature is 1100℃~1350℃, the pressureless melting time is 1min~30min, and the pressureless melting heating rate is 1℃ / min~20℃ / min.

9. A NiFe2O4-based cermet inert anode, characterized in that, The NiFe2O4-based cermet inert anode is obtained by the preparation method according to any one of claims 1 to 8; The NiFe2O4-based metal-ceramic inert anode comprises a ceramic phase and a metal phase; The ceramic phase includes NiFe2O4; The metallic phase includes copper and metal M.

10. The NiFe2O4-based cermet inert anode according to claim 9, characterized in that, The ceramic phase has a mass fraction of 70 wt% to 90 wt% by mass. Preferably, the mass fraction of the metallic phase is 10wt% to 30wt%.

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