Electrophoresis codeposition-in-situ thermal conversion short-process preparation method of multi-element doped Co-Mn spinel coating

Abstract

The invention relates to an electrophoresis codeposition-in-situ thermal conversion short-process preparation method of a multi-element doped Co-Mn spinel protective coating. According to the method, spinel precursor powder does not need to be prefabricated, commercial Co3O4, Mn3O4, a rare earth oxide R2O3 (R is Y, Ce or La) and a doped oxide XxOy (X is Cu, Ni or Fe) are directly dispersed in an organic mixed solvent in proportion to form a stable suspension, and after electrophoresis codeposition, the stable (Co, Mn, R, X) 3O4 spinel coating is formed in situ through three-stage heat treatment of impurity removal, conversion and structure homogenization. Compared with a traditional sol-gel method for synthesizing a precursor and then performing electrophoresis, the method has the advantages that the process is remarkably simplified, the period is shortened, the cost is reduced, thermal mismatch caused by Cr volatilization and Fe phase precipitation is effectively inhibited, and the compactness and high-temperature stability of the coating are improved. The method has the advantages of being short in process, low in equipment requirement, high in doping flexibility and the like, and is suitable for interface anti-oxidation protection of an SOFC metal connector and surface protection of other high-temperature electrochemical system metal parts.

Description

Technical Field

[0001] This invention relates to the field of high-temperature functional coatings and metal interface anti-oxidation protection technology, specifically to a multi-component doped spinel oxide coating suitable for metal components in high-temperature electrochemical systems such as solid oxide fuel cells (SOFC) and solid oxide electrolyzers (SOEC), and its short-process preparation method, belonging to the category of advanced energy materials and surface engineering technology. Background Technology

[0002] Solid oxide fuel cells (SOFCs) are high-temperature electrochemical energy systems characterized by high energy efficiency, strong fuel adaptability, and low emissions, and are widely used in distributed energy supply and waste heat utilization. The metal interconnect, serving as the structure and current channel between the anode and cathode, plays a crucial role in airtightness, conductivity, and stack stability, and is often made of high-chromium ferritic stainless steel. However, this type of material is prone to forming a Cr2O3 film and Cr volatilization and migration at 600℃-800℃, leading to cathode poisoning, increased resistance, and consequently affecting SOFC performance and lifespan. Therefore, a functional coating with both conductivity and oxidation resistance needs to be introduced onto the interconnect surface. Spinel (Co, Mn)3O4 is considered a preferred material due to its structural stability, good conductivity, and ability to effectively shield Cr diffusion. Furthermore, doping with rare earth elements (Y, Ce, La) and transition metals (Cu, Ni, Fe) can improve the coating's microstructure and interfacial properties. Current preparation methods mostly rely on pre-synthesized powders, which are complex and lack flexibility, making it difficult to meet the needs of engineering applications. There is an urgent need to develop a high-performance spinel coating preparation method with a simple process and strong stability to improve the long-term service reliability of SOFC connectors under high-temperature electrochemical conditions. Summary of the Invention

[0003] This application aims to address the problems of cumbersome processes, lengthy procedures, poor coating density, and insufficient doping uniformity in the preparation of Co-Mn spinel coatings in existing technologies. To this end, a short-process preparation method is proposed, using oxide powder as a precursor, directly electrophoretically co-depositing and then constructing a dense, compositionally tunable multi-component doped (Co,Mn,R)3O4 or (Co,Mn,R,X)3O4 spinel coating in situ through heat treatment. Here, R is one or more of Y, Ce, or La, and X is one or more of Cu, Ni, or Fe.

[0004] The method of the present invention includes the following steps:

[0005] 1. Mix Co3O4 and Mn3O4 according to a set molar ratio, add an appropriate amount of rare earth oxide R2O3 (R is Y, Ce or La), and introduce a mixed solvent system composed of ethanol and acetylacetone, supplemented with surfactants and dispersants to obtain a uniform and stable precursor suspension.

[0006] 2. A clean metal substrate with surface pretreatment is used as the cathode, and a Pt or inert electrode is used as the anode. The substrate is placed in the aforementioned suspension, and a set voltage is applied to perform electrophoretic co-deposition to obtain a multi-element oxide composite precursor coating.

[0007] 3. The obtained coating is subjected to staged heat treatment to achieve in-situ transformation of the precursor layer into a stable multi-component doped spinel (Co,Mn,R)3O4 phase.

[0008] According to embodiments of this application, transition metal oxide X may also be added to the precursor suspension. x O y (X is Cu, Ni, or Fe), forming a (Co,Mn,R,X)3O4 structure, wherein the transition metal oxide X x O y The particle size range is 300nm-500nm, so as to achieve synergistic doping to control crystal structure, charge migration and interface bonding characteristics.

[0009] According to embodiments of this application, the volume ratio of ethanol to acetylacetone in the mixed solvent is 1:1; the dispersant is iodine (concentration 0.3g / L-0.5g / L), and the surfactant is sodium dodecyl sulfate (concentration 0.03g / L-0.05g / L); ultrasonic dispersion for 30min-60min is performed to improve dispersibility and stability. The precursor powder has a particle size of 300nm-500nm, effectively ensuring the stability of the electrophoretic suspension.

[0010] According to embodiments of this application, the molar ratio of Co3O4 to Mn3O4 is 2:1 or 1:1, the solid concentration in the precursor suspension is 20g / L-30g / L, the amount of rare earth oxide R2O3 added is 0.3g / L-0.5g / L, and the particle size range of the rare earth oxide R2O3 is 300nm-500nm to ensure its stable distribution in the electrophoretic suspension.

[0011] According to the embodiments of this application, the electrophoretic deposition parameters are: voltage of 40V-60V and deposition time of 20s-60s, which are suitable for ferritic stainless steel substrates such as SUS430, AISI 441, and Crofer 22APU. The substrate needs to be polished and ultrasonically cleaned.

[0012] According to embodiments of this application, the heat treatment process is divided into three stages: a pretreatment stage (500℃-600℃, 2h-3h) to remove organic residues and densify; a phase transformation stage (800℃, 3-6h) to form the spinel main phase; and a homogenization stage (850℃-900℃, 3h-6h) to promote uniform diffusion of dopant. The heating rate is 1℃ / min-5℃ / min, and the cooling rate is <10℃ / min to ensure the uniformity of the coating's microstructure and properties.

[0013] Unlike the traditional sol-gel method, which requires pre-synthesizing spinel powder and undergoing multiple processing steps before electrophoretic deposition, the method of this invention directly uses commercially available or laboratory-prepared oxide raw materials. By optimizing the suspension formulation and electrodeposition parameters, it achieves one-step electrophoretic deposition and in-situ thermal conversion without the need for pre-prepared spinel precursors. This significantly simplifies the overall process, shortens the preparation cycle, and reduces production costs (e.g., ...). Figure 1 (See process comparison shown). This method fully leverages the dual advantages of the dispersibility of oxide particles in organic solvents and synergistic thermal treatment conversion, avoiding the complex steps of preparation, aging, drying, calcination, and ball milling in the traditional sol-gel route, thus reducing equipment dependence and time costs.

[0014] The short-process strategy proposed in this invention has comprehensive technical advantages such as simple preparation process, low equipment requirements, and high doping flexibility. Laboratory comparisons have verified that this method has a high success rate of repeated deposition, good operational stability, and significantly improves preparation efficiency and consistency. It is particularly suitable for the surface oxidation protection requirements of metal components in solid oxide fuel cell (SOFC) metal interconnects and other high-temperature electrochemical systems. Attached Figure Description

[0015] Figure 1 This diagram illustrates a comparison between the traditional gel-assisted electrophoretic coating preparation process and the short-process preparation process described in this application.

[0016] Figure 2 The surface SEM morphology of the Y-doped Co-Mn spinel coating prepared in Example 1 of this application is shown.

[0017] Figure 3 XRD phase analysis of the Y-doped Co-Mn spinel coating prepared in Example 1 of this application.

[0018] Figure 4 The areal resistivity (ASR) test results of the multi-doped Co-Mn spinel coatings prepared in Examples 1 and 5 of this application at different temperatures.

[0019] Figure 5 The surface SEM morphology of the Y-doped Co-Mn spinel coating prepared in Example 2 of this application is shown below. Figure 5 (a) shows the region where Fe oxides precipitate. Figure 5 (b) shows the coating cracking phenomenon.

[0020] Figure 6 The surface SEM morphology of the Cu and Y multi-doped Co-Mn spinel coating prepared in Example 5 of this application is shown. Detailed Implementation

[0021] Embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0022] This application provides a short-process method for preparing multi-doped (Co,Mn,R,)3O4 or (Co,Mn,R,X)3O4 (hereinafter referred to as Co-Mn spinel or multi-doped spinel) spinel coatings, the method comprising:

[0023] S10: Mix Co3O4 and Mn3O4 according to the set molar ratio, then add an appropriate amount of rare earth oxide R2O3, where R is one or more of Y, Ce or La, and add it to a mixed solvent composed of ethanol and acetylacetone, supplemented with surfactant and dispersant, to obtain a uniform and stable precursor suspension.

[0024] According to embodiments of this application, the volume ratio of ethanol to acetylacetone in the mixed solvent is 1:1. This allows for better dispersion of the raw materials and suppresses agglomeration.

[0025] According to embodiments of this application, one of the following conditions is met: the dispersant is iodine (I2); the surfactant is sodium dodecyl sulfonate (SDDS). This disperses the raw materials, prevents agglomeration, and ensures a uniform and stable suspension.

[0026] According to an embodiment of this application, one of the following conditions is met: in the precursor suspension, the concentration of iodine is 0.3 g / L-0.5 g / L; and the concentration of sodium dodecyl sulfonate is 0.03 g / L-0.05 g / L. Therefore, within the above concentration range, the dispersibility and stability of the raw material particles in the solution can be enhanced.

[0027] According to an embodiment of this application, the uniform and stable precursor suspension is obtained by ultrasonic dispersion for 30-60 minutes. This ultrasonic treatment enhances the dispersibility and stability of the raw material particles in the solution and inhibits agglomeration.

[0028] According to embodiments of this application, the rare earth oxide R2O3 includes one or more of Y2O3, Ce2O3, or La2O3; as an example, this application uses Y2O3. Transition metal oxide X xO y A class of oxide precursors including transition metal elements such as Cu, Ni, and Fe, including but not limited to CuO, NiO, and Fe2O3; as an example, this application uses CuO. Thus, these two types of oxides can undergo solid-state reactions with cobalt and manganese oxides to form a stable multi-component doped (Co,Mn,R,X)3O4 spinel structure, ensuring uniform doping and lattice integration during electrophoretic co-deposition and thermal conversion.

[0029] According to embodiments of this application, the molar ratio of Co3O4 to Mn3O4 is 2:1 or 1:1, and the solid concentration in the precursor suspension is 20 g / L-30 g / L. Therefore, within the above range, the ratio of Co and Mn elements can be controlled more precisely, and the resulting spinel coating exhibits optimal performance.

[0030] According to embodiments of this application, the amount of rare earth oxide R2O3 added is 0.3 g / L-0.5 g / L. Therefore, a suitable amount of rare earth oxide can be added to achieve multi-element synergistic doping with transition metal oxides, further improving their crystal structure stability, charge transfer efficiency, and interfacial bonding performance.

[0031] According to embodiments of this application, the particle size range of the rare earth oxides and transition metal oxides is 300nm-500nm. This particle size range is advantageous for better doping of the multi-component oxides. Unlike the sol-gel method, which requires complex sol preparation, drying, calcination, and ball milling of the precursor, resulting in a long process, high cost, and susceptibility of gel drying and crack control to humidity effects, this method directly adds Co-Mn oxides, rare earth oxides, and transition metal oxide particles in a dry powder state to an organic solution to form a suspension for electrophoresis. Ultrasonic assistance is then used to achieve uniform doping, significantly reducing pre-treatment chemical steps, shortening the manufacturing cycle, lowering costs, and improving coating quality.

[0032] According to embodiments of this application, Co3O4 and Mn3O4, rare earth oxides, transition metal oxides, dispersants, and surfactants are dispersed in an organic solvent to obtain a suspension. Specifically, the organic solvent is a mixture of ethanol and acetylacetone (volume ratio 1:1, solids concentration 20 g / L-30 g / L). Therefore, the organic solvent in the above ratio exhibits good dispersibility, and the deposited coating quality is excellent.

[0033] As a specific example, Co3O4, Mn3O4 and Y2O3 were added to a mixed organic solvent of ethanol and acetylacetone in a volume ratio of 1:1, and then I2 and sodium dodecyl sulfonate (SDDS) were added. The mixture was then dispersed by sonication for 30 min to 60 min to form a uniform and stable suspension with a solid mass fraction of 20% to 30%.

[0034] S20: A clean substrate is placed in the precursor suspension as a cathode, and a Pt or inert electrode is used as an anode. Electrophoretic co-deposition is performed under a set voltage and electric field to form a multi-element oxide composite precursor coating.

[0035] There are no particular restrictions on the method used to obtain a clean substrate in this step, as long as the substrate surface is free of impurities and oxide films. In some embodiments, the substrate can be sanded and then ultrasonically cleaned with deionized water to obtain a clean substrate.

[0036] According to embodiments of this application, the clean substrate comprises ferritic stainless steel. In some embodiments, the clean ferritic stainless steel substrate includes one of SUS430, AISI 441, AISI 430, and Crofer 22APU. As an example, this application uses SUS430 as the substrate. Thus, the substrate is widely available, low in cost, has good conductivity, and good processability.

[0037] As an example, the substrate was polished sequentially using 240-grit, 400-grit, and 800-grit sandpaper. After polishing, the substrate was ultrasonically cleaned with deionized water to obtain a clean substrate.

[0038] It is understood that there are no particular restrictions on the anode material for electrophoretic co-deposition; it can be Pt or an inert electrode. As an example, this application uses Pt as the anode.

[0039] According to embodiments of this application, the thickness of the deposited coating is 20μm-50μm, specifically 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, and 50μm. Therefore, a suitable coating thickness exhibits good Cr inhibition performance, electrical conductivity, and excellent high-temperature oxidation resistance. A coating that is too thin results in poor Cr inhibition and Fe precipitation from the substrate; a coating that is too thick leads to agglomeration of oxide particles on the coating surface, poor adhesion to the substrate, and a risk of peeling and cracking.

[0040] According to embodiments of this application, the electrophoretic co-deposition employs a DC electric field, and the DC voltage for electrophoretic co-deposition is 40V-60V, specifically 40V, 45V, 50V, 55V, and 60V. Therefore, within the aforementioned deposition voltage range, efficient deposition can be achieved, ensuring rapid directional migration of the raw material to the cathode. If the deposition voltage is too low, it will lead to uneven deposition, slow raw material migration, and low deposition efficiency. If the deposition voltage is too high, it will result in an excessively thick coating, deposit accumulation, and poor adhesion to the substrate.

[0041] According to embodiments of this application, the electrophoretic co-deposition time is 20s-60s, specifically 20s, 25s, 30s, 35s, 40s, 45s, 50s, 55s, and 60s. Therefore, within the above deposition time, the raw material can fully cover the substrate while ensuring a coating of appropriate thickness. If the deposition time is too long, the coating thickness will exceed the requirements, making it prone to cracking or peeling. If the deposition time is too short, the coating will not completely cover the substrate, and may also result in insufficient Cr inhibition capability.

[0042] As a specific example, a clean substrate is used as the cathode, and double platinum sheets are used as the double anodes. The substrate is placed in a suspension and a direct current is applied. At a deposition voltage of 40V-60V and a deposition time of 20s-60s, a multi-element oxide composite precursor coating is obtained.

[0043] S30: The multi-component doped oxide composite precursor coating is subjected to staged heat treatment to transform the multi-component oxide composite precursor layer in situ into a multi-component doped (Co,Mn,R)3O4 spinel coating.

[0044] According to embodiments of this application, the heat treatment is divided into three stages. In the pretreatment stage, holding at 500℃-600℃ for 2-3 hours removes organic solvents, providing initial conditions for the spinel coating and reducing its porosity. In the phase transformation stage, holding at 800℃ for 3-6 hours promotes the formation of the (Co,Mn,R,X)3O4 spinel phase and controls grain growth, improving the coating's density and adhesion to the substrate. In the homogenization stage, holding at 850℃-900℃ for 3-6 hours allows dopant elements to diffuse fully in the crystal lattice, improving the coating's compositional uniformity. Therefore, this staged heat treatment can improve the coating's density, interfacial adhesion, high-temperature oxidation resistance, and Cr migration inhibition ability. Appropriate heat treatment temperature and holding time can promote the full growth of the spinel phase and avoid excessively large grains, spinel phase decomposition, and secondary phase precipitation, which would reduce coating performance.

[0045] According to embodiments of this application, the heating rate of the heat treatment is 1℃ / min-5℃ / min, and the cooling rate is <10℃ / min. Choosing a suitable heating rate can avoid excessive thermal stress within the coating, maintaining its integrity; it also helps to form a uniform and dense coating structure. If the heating rate is too fast, it can easily cause the coating to crack or peel off, and it is also not conducive to the uniform distribution of elements in the coating. If the heating rate is too slow, grains are prone to grow, and the heating cycle is long. If the cooling rate is too fast, it can easily lead to coating cracking.

[0046] Therefore, the (Co,Mn,R)3O4 or (Co,Mn,R,X)3O4 spinel coating obtained by the above preparation method can reduce the growth rate of Cr2O3 and improve the Cr-blocking performance; on the other hand, it can also improve the coating density, reduce cracks and pores, and improve the coating's oxidation resistance and conductivity.

[0047] The embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0048] Example 1: A SUS430 stainless steel substrate (20mm×15mm×2mm) was polished sequentially with 240-grit, 400-grit, and 800-grit sandpaper, and then ultrasonically cleaned with deionized water to obtain a clean substrate.

[0049] Take 6.0 g Co3O4, 2.85 g Mn3O4, and 0.15 g Y2O3 powder, and add them to a mixed organic solvent consisting of 150 mL ethanol and 150 mL acetylacetone in a 1:1 volume ratio to prepare a sedimentation solution with a total volume of 300 mL. Add 0.15 g I2 and 0.033 g SDDS, and disperse by ultrasonication for 30 min to form a uniform and stable suspension.

[0050] The treated clean substrate was used as the cathode, and two platinum sheets (20mm × 20mm × 0.2mm) were used as the anodes, with a 10mm gap between the cathode and anode, arranged parallel to each other in the suspension. A Y-doped Co-Mn composite precursor coating was obtained by deposition at a DC voltage of 60V for 30s.

[0051] The coated sample was then placed in a muffle furnace and subjected to staged heat treatment at 500℃ for 2 hours, 800℃ for 3 hours, and 850℃ for 3 hours, with a heating rate of 1℃ / min. Finally, a Y-doped (Co,Mn)3O4 spinel coating with good bonding with the substrate and excellent Cr-blocking and electrical properties was obtained.

[0052] like Figure 2 The image shown is a SEM image of the coating surface. Figure 3 This is an XRD phase diagram. (Example:) Figure 4 As shown, the surface resistivity (ASR) measured at 800℃ is 1.31 mΩ·cm. 2 It is significantly superior to the bare SUS430 matrix, with a Cr content of 0.168%, indicating good Cr barrier and conductivity properties.

[0053] Example 2: Same as Example 1, except that the electrophoretic deposition voltage is 40V.

[0054] like Figure 5 As shown, the coating is relatively thin, and some Fe elements precipitate out (e.g. Figure 5(a) As shown by the red dashed line, the surface is uneven. The coefficient of thermal expansion of SUS430 is 10.4-11.3×10⁻⁶. 6 / K, the coefficient of thermal expansion of the coating of the present invention is 10.0-11.8×10- 6 / K, with good matching, can effectively reduce thermal stress. If Fe2O3 or Fe3O4 secondary phases are formed, their coefficient of thermal expansion is as high as 12.5-13.5×10- 6 / K, severe mismatch, easily leads to coating blistering, cracking, or even peeling (see...) Figure 5 (b) As indicated by the arrow. Therefore, by optimizing heat treatment and composition matching, the risk of Fe precipitation can be significantly reduced and thermal stability improved.

[0055] Example 3: Same as Example 1, except that the electrophoretic deposition time is 20s.

[0056] Shorter deposition time resulted in a thinner coating, increased Fe precipitation, and a Cr content of 0.572% on the coating surface. The ASR measured at 800℃ was 69.91 mΩ·cm. 2 The performance has decreased significantly.

[0057] Example 4: Same as Example 1, except that the staged heat treatment is cancelled and the temperature is directly kept at 850℃ for 3 hours.

[0058] Due to the lack of preliminary impurity removal and sufficient phase induction treatment, pores appeared on the coating surface, and the Cr content measured by EDS was 2.026%, indicating a significant decrease in Cr blocking performance and electrical conductivity.

[0059] Example 5: Same as Example 1, except that 0.3g CuO is added in addition to Co3O4, Mn3O4 and Y2O3 to prepare a Cu and Y multi-doped Co-Mn spinel coating.

[0060] like Figure 4 As shown, the ASR measured at 800℃ is 2.396 mΩ·cm. 2 It is still significantly superior to the SUS430 bare matrix. Figure 6 The coating surface appears relatively smooth, and the Cr content measured by EDS is 0.162%, indicating good Cr inhibition capability.

[0061] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0062] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0063] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A short-process method for preparing a multi-doped Co-Mn spinel coating, characterized in that, The following steps are involved: Solid oxide raw materials are mixed according to a set molar ratio and added to a mixed solvent composed of ethanol and acetylacetone. Surfactants and dispersants are added to prepare a uniform and stable precursor suspension. The solid oxides include Co3O4, Mn3O4 and rare earth oxide R2O3, wherein R is one or more of Y, Ce or La. The particle size of the solid oxides ranges from 300 nm to 500 nm, and the concentration is 20 g / L to 30 g / L to ensure their stable distribution in the electrophoretic suspension. A clean substrate is placed in the precursor suspension as a cathode, and a platinum or inert electrode is used as an anode. Electrophoretic co-deposition is performed under a set voltage and electric field to form a multi-component oxide composite precursor layer. The multi-component oxide composite precursor layer is subjected to staged heat treatment to transform it in situ into a multi-component doped (Co,Mn,R)3O4 spinel coating.

2. The method according to claim 1, characterized in that, The precursor suspension also includes transition metal oxide X. x O y Where X is one or more of Cu, Ni, or Fe, the composition of the obtained spinel coating is (Co,Mn,R,X)3O4, and the transition metal oxide X x O y The particle size range is 300nm-500nm.

3. The method according to claim 1, characterized in that, The volume ratio of ethanol to acetylacetone in the mixed solvent is 1:

1.

4. The method according to claim 1, characterized in that, One of the following conditions must be met: The dispersant is iodine; The surfactant is sodium dodecyl sulfonate.

5. The method according to claim 4, characterized in that: In the precursor suspension, the concentration of iodine is 0.3 g / L to 0.5 g / L; The concentration of the sodium dodecyl sulfonate is 0.03 g / L to 0.05 g / L.

6. The method according to claim 1, characterized in that, The uniform and stable precursor suspension was obtained by ultrasonic dispersion for 30-60 minutes.

7. The method according to claim 1, characterized in that, The clean substrate includes ferritic stainless steel; Preferably, the ferritic stainless steel is one of SUS430, AISI 441, AISI 430 or Crofer 22APU, and the surface of the ferritic stainless steel is treated with sandpaper polishing and ultrasonic cleaning.

8. The method according to claim 1, characterized in that, The electrophoretic co-deposition uses a DC electric field with a DC voltage of 40V-60V and a deposition time range of 20s-60s.

9. The method according to claim 1, characterized in that, One of the following conditions must be met: The molar ratio of Co3O4 to Mn3O4 is 2:1 or 1:1, and the mass fraction of solids in the precursor suspension is 20%-30%. The amount of rare earth oxide R2O3 added is 0.3g / L-0.5g / L.

10. The method according to claim 1, characterized in that, The phased heat treatment process includes: Pretreatment stage: Keep in air at 500℃-600℃ for 2h-3h to remove impurities and residues and prepare for phase change; Phase transformation stage: Sintering in air at 800℃ for 3-6 hours to complete the in-situ transformation of the spinel phase; Homogenization stage: Hold at 850℃-900℃ for 3h-6h to promote the full diffusion of dopants in the crystal lattice and improve the uniformity of coating composition; The heating rate of the heat treatment is 1℃ / min-5℃ / min, and the cooling rate is <10℃ / min, in order to obtain a uniform, dense, and strongly bonded multi-element doped spinel coating.

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