A method and device for continuously preparing core-shell structure powder by using a multi-section ceramic membrane reactor

Abstract

The application provides a method and device for continuously preparing core-shell structure powder by using a multi-section ceramic membrane reactor structure, and in an axial partition fluid system without physical isolation, in-situ synthesis of FeOOH core particles and in-situ coating of Al2O3, SiO2, TiO2 and ZrO2 oxide shells are continuously completed, the core particles are kept in the original reaction medium, and intermediate separation, drying and redispersion treatment are not needed. The application uses ceramic membrane micro-scale jet forced mixing and continuous flow equal coating to effectively solve the technical defects of powder agglomeration, uneven coating, poor batch stability and discontinuous production in the prior art, and can realize large-scale continuous preparation of single-layer, double-layer and multi-layer gradient core-shell powder. The finished powder is uniformly coated, has a compact structure and excellent high-temperature stability, and can be widely applied to high-end technical fields such as high-frequency soft magnetic composite materials, industrial catalysis, electromagnetic shielding and powder insulation modification.

Description

Technical Field

[0001] This invention relates to the field of nanopowder technology, and in particular to a method and apparatus for the continuous preparation of core-shell structured powders using a multi-stage ceramic membrane reactor. Background Technology

[0002] Core-shell composite powders, relying on the complementary properties of the core and shell materials and the synergistic effect of the interface, can achieve performance optimization such as insulation modification, anti-sintering, resistance to high-temperature crystal phase transformation, and corrosion resistance, making them one of the core research directions of functional powder materials. Among them, γ-Fe₂O₃ soft magnetic powder possesses excellent magnetic permeability and low coercivity, making it a core raw material for high-frequency electromagnetic devices and magnetorheological materials. However, pure-phase γ-Fe₂O₃ powder has inherent performance defects: high eddy current loss under high-frequency operating conditions, susceptibility to γ→α crystal phase transformation in high-temperature environments, and easy sintering and agglomeration of particles, severely restricting its application performance and long-term working stability. By coating the surface of γ-Fe₂O₃ particles with insulating ceramic shells such as Al₂O₃, SiO₂, TiO₂, and ZrO₂, these defects can be effectively compensated for, stabilizing the overall application performance of the powder.

[0003] Existing core-shell powder preparation processes mainly include liquid phase deposition, vapor phase deposition, and sol-gel methods. Each process has inherent technical drawbacks, as detailed below:

[0004] Conventional liquid phase deposition (LPD) is a segmented and intermittent production process. The overall process consists of multiple independent steps, including core powder pre-preparation, separation and washing, drying, redispersion, shell coating, and secondary separation. These steps are fragmented and production is discontinuous. Submicron-sized powders are prone to forming hard agglomerates after drying, and subsequent ultrasonic and mechanical redispersion processes cannot achieve uniform dispersion of individual particles. This ultimately leads to problems such as incomplete coating, discontinuous shells, and uneven shell thickness in the finished powder. At the same time, the spatial distribution of reaction system parameters is uneven, resulting in poor batch-to-batch consistency of the product.

[0005] Powders prepared by vapor deposition have good coating uniformity, but the equipment structure is complex, the equipment investment and operation and maintenance costs are high, the process control window is narrow, organic precursors are prone to introducing carbon impurities, and the production efficiency is low. It is only suitable for small-batch sample preparation in the laboratory and cannot achieve industrial-scale application.

[0006] The sol-gel method has mild reaction conditions, but the reaction rate is uncontrollable. The prepared shell has high porosity and poor density. After high-temperature calcination, the shell is prone to cracking. The powder has poor insulation and anti-sintering properties, and the overall performance of the finished product is low.

[0007] In summary, existing core-shell powder preparation technologies generally suffer from technical problems such as the separation of core powder synthesis and shell coating processes, severe powder agglomeration, low coating precision, poor production continuity, and insufficient product performance stability. Currently, there is no integrated continuous preparation process and dedicated supporting equipment that can simultaneously meet the industrialization needs of high-precision coating, low-cost preparation, and large-scale continuous production.

[0008] In view of this, it is necessary to improve the existing methods and apparatus for preparing core-shell structured powders to solve the above-mentioned problems. Summary of the Invention

[0009] The first objective of this invention is to disclose a method for continuously preparing core-shell structured powders using a multi-stage ceramic membrane reactor. The method employs an axially connected, partitioned structure within the same reactor to continuously complete the in-situ synthesis of core particles and the in-situ coating of the shell. The core particles remain in the primary reaction medium throughout the process, eliminating intermediate separation, drying, and redispersion operations, thus achieving integrated continuous production. Simultaneously, the ceramic membrane is used as a distributor of the reactants, adding them into the reactor in the form of microporous microjets for localized rapid mixing, avoiding large amounts of homogeneous precipitation. Furthermore, multi-point pH monitoring is employed to achieve precise pH control in specific sections.

[0010] To achieve the above objectives, this invention discloses a method for continuously preparing core-shell structured powders using a multi-stage ceramic membrane reactor, comprising the following steps:

[0011] S1: First stage of nuclear layer synthesis process: The nuclear particle precursor solution and the precipitant are injected into the upstream reaction zone of the reactor through at least one set of first ceramic membrane components in the form of microporous microjet to react and obtain nuclear particles;

[0012] S2: Second shell coating process: The fluid containing the nucleus particles flows continuously to the downstream coating area of ​​the reactor. The shell precursor solution and pH adjuster are injected into the downstream reaction area of ​​the reactor in the form of microporous microjet through at least one set of second ceramic membrane components. Selective nucleation of the shell precursor is induced in situ on the surface of the nucleus particles to obtain a core-shell structured precursor slurry.

[0013] S3: The core-shell structure precursor slurry from the reactor outlet is continuously collected and then subjected to solid-liquid separation, washing, drying and calcination. During the calcination process, the shell precursor is densified and crystallized, and the nucleus particle precursor is phase-transformed, finally yielding core-shell structure powder.

[0014] The core layer synthesis process and the shell coating process of the core-shell structured powder are continuously completed in an axially connected section without physical isolation within the same reactor.

[0015] In some embodiments, the solid content of the core-shell structure precursor slurry output by S2 is 0.5wt%-2wt%.

[0016] In some embodiments, the nuclear particle precursor solution in S1 is a mixed aqueous solution of FeCl3 and FeCl2 in a molar ratio of 2:1, and the total iron ion concentration is 0.1 mol / L-0.2 mol / L; the precipitant is a NaOH solution of 1.0 mol / L-1.5 mol / L.

[0017] In some embodiments, the shell precursor solution in S2 is at least one selected from 0.01 mol / L-0.03 mol / L AlCl3 solution, 0.04 mol / L-0.06 mol / L Na2SiO3 solution, 0.02 mol / L-0.04 mol / L TiOSO4 solution, and 0.02 mol / L-0.04 mol / L ZrOCl2 solution, and the pH adjuster is NaOH solution or HCl solution.

[0018] In some embodiments, the reaction temperature of the first core layer synthesis process is 30℃-40℃, and the fluid residence time is 12min-18min; the reaction temperature of the second shell layer coating process is 25℃-35℃, and the fluid residence time is 6min-10min.

[0019] In some embodiments, the pH value of the first core layer synthesis process is 8-10; the pH value of the second shell layer coating process is 4-10.

[0020] In some embodiments, when the shell precursor solution in S2 is at least one of 0.01 mol / L-0.03 mol / L AlCl3 solution, 0.02 mol / L-0.04 mol / L TiOSO4 solution, or 0.02 mol / L-0.04 mol / L ZrOCl2 solution, the pH value of the second shell coating process is 4-6; when the shell precursor solution in S2 is 0.04 mol / L-0.06 mol / L Na2SiO3 solution, the pH value of the second shell coating process is 8-10.

[0021] In some embodiments, the post-processing in S3 involves first centrifuging to separate the solid and liquid phases at a speed of 3500 rpm to 4500 rpm for 8 min to 12 min; then drying at a temperature of 55℃ to 65℃ for 8 h to 12 h; followed by calcination at a temperature of 600℃ to 700℃ for 25 to 35 min, simultaneously completing the integrated treatment of core particle crystal transformation, shell precursor dehydration and densification crystallization, and core-shell interface strengthening.

[0022] The second objective of this invention is to disclose a multi-stage ceramic membrane reactor for the continuous preparation of core-shell structured powders, used to implement any of the above-mentioned preparation methods. The reactor includes a continuous flow reactor body, first and second multi-stage independent ceramic membrane module groups, a zoned pH monitor, a fluid drive system, and a continuous discharge unit. The multi-stage ceramic membrane modules are arranged in series along the reactor axis, consisting of multiple independently controllable ceramic membrane elements used for reactant distribution and reaction, achieving steady-state continuous reaction. A third multi-stage ceramic membrane module group can also be added to adapt to the continuous preparation requirements of multi-layer core-shell powders.

[0023] To achieve the above objectives, the present invention discloses a multi-stage ceramic membrane reactor for the continuous preparation of core-shell structured powders. The reactor is used in the above preparation method and includes: a reactor body, a first ceramic membrane assembly and a second ceramic membrane assembly arranged sequentially along the axial direction of the reactor body, and a first pH monitor and a second pH monitor respectively arranged at the first ceramic membrane assembly and the second ceramic membrane assembly.

[0024] In some embodiments, a third ceramic membrane module and a third pH monitor are also included, located downstream of the second ceramic membrane module, to achieve multi-layer coating of the nuclei and prepare multi-layer core-shell structured powder.

[0025] In some embodiments, a continuous fluid channel with uniform axial flow is formed within the reactor body.

[0026] In some embodiments, the first ceramic membrane assembly is arranged at a first position along the axial direction of the reactor body, and includes at least one set of independently controlled first ceramic membrane elements, which are respectively connected to a nuclear particle precursor solution tank and a precipitant tank for conveying synthesis reaction raw materials; the second ceramic membrane assembly is arranged at a second position along the axial direction of the reactor body and located downstream of the first ceramic membrane assembly, and includes at least one set of independently controlled second ceramic membrane elements, which are respectively connected to a shell precursor solution tank and a pH adjuster tank for conveying coating reaction raw materials.

[0027] In some embodiments, the first ceramic membrane element and the second ceramic membrane element are tubular ceramic membranes or disc ceramic membranes.

[0028] In some embodiments, the first ceramic membrane element and the second ceramic membrane element are tubular ceramic membranes; the first ceramic membrane assembly includes at least one first ceramic membrane element, the outer side of which is divided into two isolated liquid inlet sides that are respectively connected to a nuclear particle precursor solution tank and a precipitant tank for precise delivery of synthesis reaction raw materials; the second ceramic membrane assembly includes at least one second ceramic membrane element, the outer side of which is divided into two isolated liquid inlet sides that are respectively connected to a shell precursor solution tank and a pH adjuster tank for precise delivery of coating reaction raw materials.

[0029] In some embodiments, the first ceramic membrane element and the second ceramic membrane element are disc ceramic membranes, the first ceramic membrane assembly includes at least two first ceramic membrane elements arranged longitudinally and opposite to each other along the reactor, and the second ceramic membrane assembly includes at least two second ceramic membrane elements arranged longitudinally and opposite to each other along the reactor.

[0030] In some embodiments, the first group of first ceramic film elements consists of two opposing circular ceramic films, both of which can rotate or only one of which can rotate; the second group of second ceramic film elements consists of two opposing circular ceramic films, both of which can rotate or only one of which can rotate.

[0031] In some embodiments, the first group of first ceramic membrane elements and the second group of second ceramic membrane elements can rotate synchronously or differentially.

[0032] In some embodiments, the distance between the first ceramic membrane elements in the first group is H1, and the distance between the second ceramic membrane elements in the second group is H2; both H1 and H2 are adjustable.

[0033] In some embodiments, micro-reaction channels are formed between the first group of first ceramic membrane elements and the second group of second ceramic membrane elements; the two disc ceramic membranes of the first group of first ceramic membrane elements have membrane pores only on their opposite surfaces, and the two disc ceramic membranes of the second group of second ceramic membrane elements have membrane pores only on their opposite surfaces, with the remaining surfaces being closed structures.

[0034] In some embodiments, the tubular ceramic membrane or the disc ceramic membrane is made of any one or a combination of multiple materials selected from Al2O3, ZrO2, or TiO2, and has a pore size of 0.1 μm-1 μm.

[0035] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention abandons the traditional segmented intermittent production mode and completes the core process of nuclear particle synthesis and shell coating continuously in a single device, eliminating redundant processes such as intermediate separation, drying, and redispersion, greatly shortening the preparation process, realizing large-scale continuous production, and effectively improving production efficiency; (2) The nuclear particles of the present invention are retained in the original reaction medium throughout the process, without drying and agglomeration process. Combined with the micro-jet forced mixing and uniform residence time coating mechanism, the defects of traditional processes such as incomplete coating, uneven shell thickness, and shell breakage are solved from the root, significantly improving the integrity and uniformity of powder coating; (3) The independent pH, temperature, and flow closed-loop control of each reaction zone is adopted, and the process parameters of each reaction zone are in a steady state. Controllable, the reaction and coating environment of all nuclear particles are highly uniform, the particle size, shell thickness, electrical and magnetic properties of the finished powder have minimal batch deviations, and the product consistency is significantly improved; (4) Al2O3, SiO2, TiO2 and ZrO2 can be coated with single-layer and multi-layer gradients by adjusting the precursor system and increasing the number of ceramic membrane components, which can meet the preparation needs of various inorganic core-shell powder materials and have a wide range of applications; (5) The reaction material is fed through the micropores of the ceramic membrane in the form of micro-jet, which reduces the agglomeration of reactants and allows for precise control of the feed rate; (6) The disc ceramic membrane can adjust the distance between ceramic membrane elements to form a micro-reaction channel, which solves the problem of uneven material reaction and incomplete coating in traditional reactors. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the multi-segment ceramic membrane reactor structure shown in Embodiment 6 of the present invention;

[0037] Figure 2 This is a schematic diagram of the multi-segment ceramic membrane reactor structure shown in Embodiment 7 of the present invention. Detailed Implementation

[0038] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. Any equivalent substitutions or replacements in function, method, or structure made by those skilled in the art based on these embodiments are within the scope of protection of the present invention.

[0039] Example 1

[0040] A method for continuously preparing core-shell structured powders using a multi-stage ceramic membrane reactor includes the following steps:

[0041] S1: First stage of nuclear layer synthesis process: The nuclear particle precursor solution and the precipitant are injected into the upstream reaction zone of the reactor through at least one set of first ceramic membrane components in the form of microporous microjet to react and obtain nuclear particles;

[0042] S2: Second shell coating process: The fluid containing the nucleus particles flows continuously to the downstream coating area of ​​the reactor. The shell precursor solution and pH adjuster are injected into the downstream reaction area of ​​the reactor in the form of microporous microjet through at least one set of second ceramic membrane components. Selective nucleation of the shell precursor is induced in situ on the surface of the nucleus particles to obtain a core-shell structured precursor slurry.

[0043] S3: The core-shell structure precursor slurry from the reactor outlet is continuously collected and then subjected to solid-liquid separation, washing, drying and calcination. During the calcination process, the shell precursor is densified and crystallized, and the nucleus particle precursor is phase-transformed, finally yielding core-shell structure powder.

[0044] The core layer synthesis process and the shell layer coating process of the core-shell structure powder are continuously completed in an axially connected section without physical isolation within the same reactor; the solid content of the core-shell structure precursor slurry output by S2 is 0.5wt%-2wt%.

[0045] In this invention, the precursor solution of nuclear particles in S1 is a mixed aqueous solution of FeCl3 and FeCl2 in a molar ratio of 2:1, and the total iron ion concentration is 0.1 mol / L-0.2 mol / L; the precipitant is a NaOH solution of 1.0 mol / L-1.5 mol / L.

[0046] The shell precursor solution in S2 is at least one of the following: 0.01 mol / L-0.03 mol / L AlCl3 solution, 0.04 mol / L-0.06 mol / L Na2SiO3 solution, 0.02 mol / L-0.04 mol / L TiOSO4 solution, and 0.02 mol / L-0.04 mol / L ZrOCl2 solution. The pH adjuster is a dilute NaOH solution or a dilute HCl solution.

[0047] The reaction temperature of the first stage core layer synthesis process is 30℃-40℃, and the fluid residence time is 12min-18min, generating spherical FeOOH precursor nuclei in situ; the reaction temperature of the second stage shell coating process is 25℃-35℃, and the fluid residence time is 6min-10min.

[0048] The pH value of the first core layer synthesis process is 8-10; the pH value of the second shell layer coating process is 4-10.

[0049] When the shell precursor solution in S2 is at least one of 0.01 mol / L-0.03 mol / L AlCl3 solution, 0.02 mol / L-0.04 mol / L TiOSO4 solution, or 0.02 mol / L-0.04 mol / L ZrOCl2 solution, the pH value of the second shell coating process is 4-6; when the shell precursor solution in S2 is 0.04 mol / L-0.06 mol / L Na2SiO3 solution, the pH value of the second shell coating process is 8-10.

[0050] The post-processing in S3 involves first centrifuging to separate the solid and liquid phases at a speed of 3500 rpm to 4500 rpm for 8 min to 12 min; then drying at a temperature of 55℃ to 65℃ for 8 h to 12 h; followed by calcination at a temperature of 600℃ to 700℃ for 25 to 35 min, simultaneously completing the integrated treatment of core particle crystal transformation, shell precursor dehydration and densification crystallization, and core-shell interface strengthening.

[0051] In this embodiment, a mixed aqueous solution of FeCl3 and FeCl2 is first prepared. 3+ with Fe 2+ The molar ratio was 2:1, the total iron ion concentration was 0.15 mol / L, and a 1.0 mol / L NaOH precipitant solution was prepared. In this process, the reaction temperature was controlled at 35℃, the pH value was 9±0.2, and the fluid residence time was 15 min. The solution was injected into the ceramic membrane element through microporous microjets in the first ceramic membrane module to induce precipitation through forced mixing. The mixing uniformity was far superior to that of the stirring method in the existing reactor. 3+ with Fe 2+ The mixed salt and NaOH co-precipitate to generate in-situ dispersed spherical FeOOH nuclei with an average particle size of 350 nm and a particle size uniformity deviation of ≤4%. These nuclei are then uniformly transported downstream of the reactor due to fluid inertia. The nuclei do not precipitate or settle, requiring no intermediate treatment. The specific reaction formula is as follows:

[0052] 2FeCl3+FeCl2+8NaOH=3FeOOH↓+8NaCl+H2O

[0053] Secondly, a 0.02 mol / L AlCl3 precursor solution and NaOH solution were prepared and injected into the downstream region of the reactor, i.e., the coating zone, through the second ceramic membrane module. The injection flow rate of the dilute NaOH solution was adjusted in a closed loop by an intelligent controller to stabilize the pH value of the system at 5.0 ± 0.2, the temperature at 30℃, and the fluid residence time at 8 min. Relying on the zoned pH independent control and uniform continuous flow coating mechanism, heterogeneous nucleation was initiated in situ on the surface of FeOOH nuclei, and the Al(OH)3 shell precursor was uniformly deposited. There was no homogeneous nucleation phenomenon in the system. The specific reaction formula is as follows:

[0054] AlCl3 + 3NaOH = Al(OH)3↓ + 3NaCl

[0055] The solid content of the core-shell structured powder slurry in the reactor remained stable at 1.2 wt%.

[0056] The material was continuously and steadily discharged from the reactor outlet. Solid-liquid separation was first achieved by centrifugation at 4000 rpm for 10 min, followed by washing three times with deionized water. Then, it was vacuum dried at 60℃ for 10 h, and subsequently calcined at 650℃ under a high-purity argon inert atmosphere for 30 min. Simultaneously, core-phase crystal transformation, shell densification, and core-shell interface strengthening were completed, ultimately producing γ-Fe2O3@Al2O3 monolayer core-shell powder. The following reaction occurred during calcination:

[0057] 6FeOOH = 2γ−Fe2O3 + 3H2O↑

[0058] 2Al(OH)3 = Al2O3 + 3H2O↑

[0059] It should be noted that although γ-Fe2O3 in core-shell structured powder is a metastable phase, the coating and confinement effect of the shell layer and the stress at the core-shell interface ensure that the core layer is γ-Fe2O3. Even if calcination at 600-700℃ for 25-35 minutes may transform it into α-Fe2O3, this does not affect the implementation of the nucleation and coating processes in the same reactor by distributing the ceramic membrane module in a microporous microjet manner. The technical solution claimed in this invention is not aimed at the γ-Fe2O3 or α-Fe2O3 phase, but rather at the technical solution of continuously preparing shell structured powder using a ceramic membrane device as a reactor.

[0060] Example 2

[0061] The difference compared to Example 1 is as follows:

[0062] S1: First stage of core layer synthesis: Total iron ion concentration is 0.1 mol / L, NaOH precipitant concentration is 1.5 mol / L, reaction temperature is 30℃, system pH is 10.0±0.2, fluid residence time is 18 min, and uniform spherical FeOOH core particles with an average particle size of 500 nm are generated in situ in the upstream region of the reactor.

[0063] S2: Second shell coating process: Prepare a Na2SiO3 precursor solution with a concentration of 0.06mol / L, use dilute HCl as a pH adjuster, coat at 35℃, pH value of 9.5±0.2, fluid residence time of 6min, and deposit SiO2 shell precursor in situ in the downstream area of ​​the reactor.

[0064] S3 post-processing stage: The powder was centrifuged at 3500 rpm for 12 min, vacuum dried at 65℃ for 8 h, and then vacuum calcined at 700℃ for 25 min to prepare γ-Fe2O3@SiO2 core-shell powder. The following reaction occurred during calcination:

[0065] 6FeOOH = 2γ−Fe2O3 + 3H2O↑

[0066] H₂SiO₃ = SiO₂ + H₂O↑

[0067] Example 3

[0068] The difference compared to Example 1 is as follows:

[0069] S1: First stage of core layer synthesis: Total iron ion concentration is 0.2 mol / L, NaOH precipitant concentration is 1.0 mol / L, reaction temperature is 40℃, system pH is 8.0±0.2, fluid residence time is 12 min, and uniform spherical FeOOH core particles with an average particle size of 300 nm are generated in situ in the upstream region of the reactor.

[0070] S2: Second shell coating process: Prepare a TiOSO4 precursor solution with a concentration of 0.03 mol / L, use dilute NaOH solution as pH adjuster, coating temperature is 32℃, pH value is 5.5±0.2, fluid residence time is 9 min, and deposit TiO(OH)2 shell precursor in situ in the downstream area of ​​the reactor.

[0071] S3 Post-processing stage: Vacuum calcination at 630℃ for 25 min to prepare γ-Fe2O3@TiO2 core-shell powder. The following reaction occurs during calcination:

[0072] TiOSO4+2NaOH+H2O=TiO(OH)2↓+Na2SO4;

[0073] TiO(OH)₂ = TiO₂ + H₂O↑

[0074] Example 4

[0075] The difference compared to Example 2 is as follows:

[0076] S2: Second shell coating process: Prepare a ZrOCl2 precursor solution with a concentration of 0.03mol / L, use dilute NaOH solution as pH adjuster, coating temperature is 25℃, pH value is 4.0±0.2, fluid residence time is 10min, and ZrO2 shell precursor is deposited in situ in the downstream area of ​​the reactor.

[0077] S3 Post-processing stage: Vacuum calcination at 600℃ for 35 min to prepare γ-Fe2O3@ZrO2 core-shell powder. The following reaction occurs during calcination:

[0078] ZrOCl2+2NaOH+H2O=Zr(OH)4↓+2NaCl;

[0079] Zr(OH)4 = ZrO2 + 2H2O↑

[0080] Example 5

[0081] The difference compared to Example 1 is as follows:

[0082] S2: Second shell coating process: Prepare a Na2SiO3 precursor solution with a concentration of 0.06mol / L, use dilute HCl as a pH adjuster, coat at 35℃, pH value of 9.5±0.2, fluid residence time of 6min, and deposit SiO2 shell precursor in situ in the downstream area of ​​the reactor.

[0083] A third set of ceramic membrane components and a pH monitor were added downstream of the coating area. A 0.05 mol / L Na2SiO3 precursor solution was prepared, and the pH value was adjusted to 9.0±0.2 with dilute HCl. The coating temperature was 30℃, the fluid residence time was 7 min, and a SiO2 outer layer was deposited on the outside of Al2O3 to form γ-Fe2O3@Al2O3@SiO2.

[0084] Comparative Example 1

[0085] The traditional segmented intermittent process was adopted: after the pre-prepared FeOOH powder was centrifuged, washed and dried, 10g of the dried powder was dispersed in 500mL of deionized water by high-energy ultrasonication, and AlCl3 precursor solution in the same proportion as in Example 1 was added. The pH value of the system was adjusted to 5.0 under mechanical stirring, and the coating was carried out at a constant temperature for 30min. The finished powder was prepared by post-processing process completely consistent with that in Example 1.

[0086] The following performance tests were performed on the powders prepared in Examples 1-5 and Comparative Example 1.

[0087] 1. Powder particle size and particle size distribution test: The powder was ultrasonically dispersed in an ethanol solution using a wet laser particle size analyzer. The average particle size and the coefficient of variation (CV) of the sample were tested to evaluate the uniformity of the powder particle size.

[0088] 2. Insulation performance test: The powder is pressed into standard sheet-like samples, and the volumetric insulation resistivity at room temperature is tested using a high insulation resistance tester to characterize the insulation modification effect of the powder.

[0089] 3. Specific saturation magnetization test: The hysteresis loop of the powder was tested using a vibrating sample magnetometer (VSM) under room temperature and ±10000 Oe magnetic field conditions, and the specific saturation magnetization (Ms, unit: emu / g) was obtained by fitting.

[0090] Table 1 Comparison of performance test data between Examples 1-5 and the comparative examples

[0091] Performance indicators Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Shell material <![CDATA[Al2O3]]> <![CDATA[SiO2]]> <![CDATA[TiO2]]> <![CDATA[ZrO2]]> <![CDATA[Al2O3@SiO2]]> <![CDATA[Al2O3]]> Average core diameter (nm) 350 500 300 500 350 380 Particle size variation coefficient CV (%) 3.8 4.2 3.5 4.0 3.9 12.5 Specific saturation magnetization (emu / g) 62.8 57.5 60.2 58.5 61.5 56.3 Volume resistivity (Ω·cm) <![CDATA[8.6×10 12 ]]> <![CDATA[9.2×10 12 ]]> <![CDATA[7.9×10 12 ]]> <![CDATA[9.5×10 12 ]]> <![CDATA[9.8×10 12 ]]> <![CDATA[2.3×10 11 ]]>

[0092] As can be seen from the table above, the particle size CV value of the core-shell structured powder prepared by the technical solution of the present invention is stable at 3.5%-4.2%, while the CV value of the prior art is 12.5%, indicating an extremely wide particle size distribution; in terms of electrical insulation properties, the volume resistivity of Examples 1-5 is all above 10. 12 The specific saturation magnetization of the core-shell structured powders prepared in Examples 1-5 was stable at 57.5-62.8 emu / g, with excellent magnetic properties and small fluctuations. In contrast, the magnetic properties of Comparative Example 1 were only 56.3 emu / g, with a significant decrease in magnetic properties and a significant increase in magnetic loss.

[0093] Example 6

[0094] like Figure 1 As shown, a multi-stage ceramic membrane reactor for the continuous preparation of core-shell structured powders is provided. The reactor is used to implement the preparation methods described in Examples 1-5 above. It includes: a reactor body 1, a first ceramic membrane assembly 4 and a second ceramic membrane assembly 8 arranged sequentially along the axial direction of the reactor body 1, and a first pH monitor 7 and a second pH monitor 11 respectively arranged at the first ceramic membrane assembly 4 and the second ceramic membrane assembly 8.

[0095] If necessary, a third ceramic membrane module and a third pH monitor can be added downstream of the second ceramic membrane module 8 to achieve multi-layer coating of nuclear particles and prepare multi-layer core-shell structured powder.

[0096] A continuous fluid channel with uniform axial flow is formed within the reactor body 1. In this example, the continuous fluid channel is not a physical structural component inside the reactor, but rather a continuous fluid channel formed by the continuous fluid flow in the horizontal direction below the first ceramic membrane assembly 4 and the second ceramic membrane assembly 8. The reaction occurs at this channel, and the particles do not diffuse over a large area but flow along the horizontal region.

[0097] The first ceramic membrane assembly 4 is arranged at a first position along the axial direction of the reactor body 1, and includes at least one set of independently controlled first ceramic membrane elements, which are respectively connected to the nuclear particle precursor solution tank A and the precipitant tank B, for precise delivery of synthesis reaction raw materials; the second ceramic membrane assembly 8 is arranged at a second position along the axial direction of the reactor body 1 and is located downstream of the first ceramic membrane assembly 4, and includes at least one set of independently controlled second ceramic membrane elements, which are respectively connected to the shell precursor solution tank C and the pH adjuster tank D, for precise delivery of coating reaction raw materials.

[0098] The first pH monitor 7 is embedded in the ceramic membrane element of the first ceramic membrane assembly 4, that is, the monitoring probe 71 of the first pH monitor 7 is inserted into the interior of the first ceramic membrane assembly 4; the second pH monitor 11 is embedded in the ceramic membrane element of the second ceramic membrane assembly 8, that is, the monitoring probe 111 of the second pH monitor 11 is inserted into the interior of the second ceramic membrane assembly 8.

[0099] The first ceramic membrane element 4 and the second ceramic membrane element 8 are tubular ceramic membranes. Therefore, the first pH monitor 7 and the second pH monitor 11 can both be embedded inside the tubular ceramic membranes that are connected to each other.

[0100] The first ceramic membrane assembly 4 includes at least one first ceramic membrane element. The outer side of the first ceramic membrane element is divided into two isolated liquid inlet sides, namely the first liquid inlet side 5 and the second liquid inlet side 6, which are respectively connected to the nuclear particle precursor solution tank A and the precipitant tank B for precise delivery of synthesis reaction raw materials. The second ceramic membrane assembly 8 includes at least one second ceramic membrane element. The outer side of the second ceramic membrane element is divided into two isolated liquid inlet sides, namely the third liquid inlet side 9 and the fourth liquid inlet side 10, which are respectively connected to the shell precursor solution tank C and the pH adjuster tank D for precise delivery of coating reaction raw materials.

[0101] The tubular or disc ceramic membrane is made of any one or a combination of Al2O3, ZrO2, or TiO2, and has a pore size of 0.1 μm-1 μm.

[0102] In this example, a closed inlet side is provided on the outside of the first ceramic membrane assembly 4 and the second ceramic membrane assembly 8, meaning that the first, second, third, and fourth inlet sides are all closed structures. The nuclear particle precursor solution is introduced into the first inlet side 5 and, under pressure, enters the tubular ceramic membrane in the form of a microjet along the micropores of the membrane layer. Similarly, the precipitant is introduced into the second inlet side 6 and, under pressure, enters the tubular ceramic membrane in the form of a microjet along the micropores of the membrane layer, mixing with the nuclear particle precursor solution. The mixing uniformity is higher than that of existing stirring methods. The first pH monitor 7 continuously monitors the pH value inside the tubular ceramic membrane and is linked to the precipitant tank B to achieve real-time fine-tuning of the precipitant dosage, ensuring that the inside of the tubular ceramic membrane remains in a stable reaction medium system.

[0103] Because the top of the tubular ceramic membrane in this embodiment is closed, the FeOOH nuclei generated by the reaction escape from the bottom of the tubular ceramic membrane and flow continuously downstream in the axial direction of the reactor body 1. The reactor body 1 of this invention is provided with an inlet 2 and an outlet 3. The reactor body 1 is filled with a deionized water medium system, and a booster pump is provided at the inlet 2 to make the fluid in the reactor body 1 flow at a uniform speed in the axial direction. Therefore, after the FeOOH nuclei are generated, they flow downstream with the fluid to the coating zone to carry out the coating reaction.

[0104] A second ceramic membrane module 8 is provided downstream of the reactor body 1, and the pH value of this area is adjusted differently according to the type of shell layer to be coated.

[0105] Similarly, the shell precursor solution is introduced into the third inlet side 9, and the pH adjuster is introduced into the fourth inlet side 10. The second pH monitor 11 monitors the pH value inside the second ceramic membrane module 8 in real time and is linked with the pH adjuster tank D to ensure that the pH value inside the second ceramic membrane module 8 remains stable. The second ceramic membrane module 8 delivers a precise amount of pH adjuster, independently maintaining the pH of the coating zone, without interfering with the upstream nucleation and synthesis zone, relying solely on the natural transition of the fluid axial gradient.

[0106] Because the axial flow velocity of the reactor is constant, the residence time of all core particles in the coating section is completely consistent, the concentration of the contacted shell precursor is uniform, and there is no difference in thickness between coating first and coating later; combined with the forced mixing of the membrane microjets, agglomeration and leakage of coating are completely eliminated, forming powders with various core-shell structures.

[0107] In addition, to achieve multi-layer coating, a third ceramic membrane component is added, which can deposit a second oxide precursor on the outside of the first shell to obtain a double-layer gradient coating structure.

[0108] In this embodiment, the first ceramic membrane assembly 4 and the second ceramic membrane assembly 8 are arranged in parallel along the axial direction of the reactor body 1, and the bottom openings of the first ceramic membrane assembly 4 and the second ceramic membrane assembly 8 are always located on the same horizontal line to ensure that the nuclear particles flow downstream along the axial direction rather than diffuse in all directions. That is, a continuous fluid channel with uniform axial flow is formed in the reactor body 1.

[0109] Example 7

[0110] like Figure 2 As shown, a multi-stage ceramic membrane reactor for the continuous preparation of core-shell structured powders is provided. The reactor is used to implement the preparation methods described in Examples 1-5. It includes: a reactor body 1, a first ceramic membrane assembly 12 and a second ceramic membrane assembly 13 arranged sequentially along the axial direction of the reactor body 1, and a first pH monitor 7 and a second pH monitor 11 respectively arranged at the first ceramic membrane assembly 12 and the second ceramic membrane assembly 13.

[0111] Multiple ceramic membrane modules, such as a third ceramic membrane module and a third pH monitor, a fourth ceramic membrane module and a fourth pH monitor, can be set downstream of the second ceramic membrane module 13 to achieve multi-layer coating of nuclear particles and prepare multi-layer core-shell structure powder.

[0112] A continuous fluid channel with uniform axial flow is formed inside the reactor body 1. In this embodiment, since the ceramic membrane element is a disc ceramic membrane, a micro-reaction channel is formed between two oppositely arranged disc ceramic membranes, and the first ceramic membrane assembly 12 and the second ceramic membrane assembly 13 are located on the same horizontal line. This continuous flow channel is the micro-reaction channel, and it is not an independent physical structural component set inside the reactor.

[0113] The first ceramic membrane module 12 is arranged at a first position along the axial direction of the reactor body 1, and includes at least one set of independently controlled first ceramic membrane elements (122, 124), which are respectively connected to the nuclear particle precursor solution tank A and the precipitant tank B, for precise delivery of synthesis reaction raw materials; the second ceramic membrane module 13 is arranged at a second position along the axial direction of the reactor body 1 and is located downstream of the first ceramic membrane module 12, and includes at least one set of independently controlled second ceramic membrane elements (132, 134), which are respectively connected to the shell precursor solution tank C and the pH adjuster tank D, for precise delivery of coating reaction raw materials.

[0114] The first pH monitor 7 is embedded between the ceramic membrane elements of the first ceramic membrane assembly 12, and the second pH monitor 11 is embedded between the ceramic membrane elements of the second ceramic membrane assembly 13.

[0115] The first ceramic membrane element and the second ceramic membrane element are disk ceramic membranes.

[0116] The first ceramic membrane assembly 12 includes at least two first ceramic membrane elements (122, 124) arranged longitudinally and opposite to each other along the reactor body 1, and the second ceramic membrane assembly 13 includes at least two second ceramic membrane elements (132, 134) arranged longitudinally and opposite to each other along the reactor body 1.

[0117] The first group of first ceramic membrane elements (122, 124) consists of two oppositely arranged disc ceramic membranes, both of which can rotate or only one of them can rotate while the other does not; the second group of second ceramic membrane elements (132, 134) also consists of two oppositely arranged disc ceramic membranes, both of which can rotate or only one of them can rotate.

[0118] In this embodiment, both the first group of first ceramic membrane elements (122, 124) and the second group of second ceramic membrane elements (132, 134) can rotate independently. Specifically, the first group of first ceramic membrane elements (122, 124) are driven to rotate by hollow rotating shafts (121, 123), and the second group of second ceramic membrane elements (132, 134) are driven to rotate by hollow rotating shafts (131, 133), and the ceramic membrane elements can rotate synchronously or differentially.

[0119] The distance between the first ceramic membrane elements (122, 124) in the first group is H1, and the distance between the second ceramic membrane elements (132, 134) in the second group is H2; both H1 and H2 are adjustable to form micro-reaction channels. In this embodiment, the distance between H1 and H2 is 0.5-2mm.

[0120] Specifically, in this embodiment, a ceramic membrane element is fixedly installed on a hollow rotating shaft. The hollow rotating shaft is driven by a drive structure to rotate the ceramic membrane element. The two ceramic membrane elements arranged opposite each other can rotate synchronously or at different speeds.

[0121] remove Figure 2 Besides the structure shown, the ceramic membrane elements arranged opposite each other can also be configured in other ways, such as one rotating and the other not rotating. As long as the effect of shearing fluid is formed between the ceramic membrane elements arranged opposite each other due to the rotation of the ceramic membrane elements can be achieved, it is all included in the technical solution of this invention.

[0122] In this embodiment, a dynamic ceramic membrane system can be directly selected as the reactor. Working principle: The reactor body 1 is equipped with an inlet 2 and an outlet 3. The reactor body 1 is filled with a deionized water medium system, and a booster pump is installed at the inlet 2 to ensure that the fluid inside the reactor body 1 flows uniformly along the axial direction. Therefore, after FeOOH nuclei are generated, they flow downstream with the fluid to the coating zone, where a coating reaction takes place.

[0123] Micro-reaction channels are formed between the first ceramic membrane elements (122, 124) of the first group and the second ceramic membrane elements (132, 134) of the second group; the two disc ceramic membranes of the first group have membrane pores only on their opposite surfaces, and the two disc ceramic membranes of the second group have membrane pores only on their opposite surfaces, with the other surfaces being closed structures.

[0124] Specifically, the first ceramic membrane module 12 is arranged upstream of the reactor body 1. The nuclear particle precursor solution and the precipitant are respectively distributed through the first ceramic membrane elements (122, 124). That is, the nuclear particle precursor solution is introduced into the ceramic membrane element 122 through the hollow rotating shaft 121, and the precipitant is introduced into the ceramic membrane element 124 through the hollow rotating shaft 123. Since the ceramic membrane element in this invention is a single-sided open structure, that is, the opposite side is an open structure and the back side is a closed structure, the nuclear particle precursor solution and the precipitant are mixed in the form of micro-jet through the micropores on the membrane surface, react, and are thrown outward under the action of shear force, realizing instant reaction and instant movement, without agglomeration, and can achieve uniform nuclear particles.

[0125] Similarly, in the coating zone, downstream of reactor body 1, the shell precursor solution and pH adjuster are mixed and coated via microjets through micropores on the membrane surface, achieving rapid molecular-level mixing and avoiding local concentration gradients, thus obtaining core-shell particles with uniform particle size. The core synthesis zone and the shell coating zone are axially connected in series within the same reactor without any partitions, allowing the fluid containing the core particles to flow naturally downstream, achieving continuous production. Throughout the process, a low solids content of 0.5-2 wt% is maintained to suppress homogeneous nucleation.

[0126] In this embodiment, a disc ceramic membrane is used as a feeder. The microjet diameter is on the same order of magnitude as the aperture, and the specific surface area is extremely large. Laminar flow injection avoids turbulent shearing damage to the nuclei and shell. The microsecond-level mixing time ensures that the reactants are uniformly dispersed before reaching the surface of the nuclei.

[0127] The core-shell structured powder prepared by this invention includes a core layer and at least one shell layer covering the core layer; the core layer is γ-Fe2O3 with an average particle size of 200nm-500nm and a particle size distribution variation coefficient (CV) of less than 10%; the shell layer is selected from at least one of Al2O3, SiO2, TiO2, and ZrO2, and the shell layer thickness is 10nm-50nm. The shell layer can also be a bilayer composite shell of Al2O3 and SiO2, wherein the Al2O3 layer is located between the core layer and the SiO2 layer.

[0128] This invention uses multiple ceramic membrane modules arranged in sections within the same reactor to make the core layer synthesis and shell layer coating continuous in space and time. After the nuclei are generated in situ in the front section, they flow directly into the coating area without separation. The shell layer precursors selectively nucleate and deposit in situ on the surface of the nuclei, and the entire process is continuous.

[0129] This invention uses ceramic membrane micropore dispersion feeding, which allows the shell precursor and pH adjuster to enter the main fluid in the form of micron-sized droplets, achieving extremely fast local mixing. For different shells, the deposition environment can be flexibly controlled by pH adjuster. Low solid content control can effectively reduce collision frequency and inhibit homogeneous nucleation.

[0130] This invention achieves simultaneous completion in a single calcination process, significantly shortening the calcination time. It enables core-shell particle crystal transformation, shell precursor dehydration, densification, and crystallization, resulting in high interfacial bonding strength, excellent anti-peeling properties, and significantly improved powder stability under strong acid, strong alkali, or high-temperature environments. Furthermore, this invention is not limited to a single material system and can be used to prepare various functional core-shell powders.

[0131] This invention uses a ceramic membrane system, preferably a dynamic rotating ceramic membrane system, as a reactor. Multiple sets of independently controllable ceramic membrane components are arranged, and the distance between the ceramic membrane elements in each set is adjustable to form a micro-reaction channel. This allows the reactants to come into contact with the reaction after being distributed along the micropores on the surface of the ceramic membrane, and to be thrown outward by the shear force generated by the rotation of the ceramic membrane elements, resulting in a uniform particle size effect.

[0132] In this invention, the reaction temperature of the nuclear particle synthesis process and the reaction temperature of the shell coating process can both be achieved by setting a heating device on the ceramic membrane element.

[0133] In this invention, the ceramic membrane module is no longer a "separation medium" but a "reaction dispersion medium," and the continuous flow process is naturally suitable for pipelined, modular, and scaled-up industrial applications.

[0134] The "pH monitor" described in this invention refers to an integrated device that monitors and adjusts pH values ​​in real time. This device is linked with the precipitant tank and the pH adjuster tank. According to the process settings, it monitors whether the pH values ​​of the nucleoprotein synthesis area and the coating area meet the requirements, and feeds back the real-time monitoring data to the precipitant tank and the pH adjuster tank to adjust the amount of acid or alkali added.

[0135] In this invention, "upstream" and "downstream" refer to the liquid medium that fills the multi-stage ceramic membrane reactor from the inlet to the outlet, which flows continuously due to the action of the fluid drive device, i.e., the booster pump. The liquid medium closer to the inlet along the direction of liquid flow is upstream, and the liquid medium closer to the outlet is downstream. The fluid flow rate is adjusted by adjusting the power of the booster pump.

[0136] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

[0137] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for continuous preparation of core-shell structured powder using a multi-stage ceramic membrane reactor, characterized in that, Includes the following steps: S1: First stage of nuclear layer synthesis process: The nuclear particle precursor solution and the precipitant are injected into the upstream reaction zone of the reactor through at least one set of first ceramic membrane components in the form of microporous microjet to react and obtain nuclear particles; S2: Second shell coating process: The fluid containing the nucleus particles flows continuously to the downstream coating area of ​​the reactor. The shell precursor solution and pH adjuster are injected into the downstream reaction area of ​​the reactor in the form of microporous microjet through at least one set of second ceramic membrane components. Selective nucleation of the shell precursor is induced in situ on the surface of the nucleus particles to obtain a core-shell structured precursor slurry. S3: The core-shell structure precursor slurry from the reactor outlet is continuously collected and then subjected to solid-liquid separation, washing, drying and calcination. During the calcination process, the shell precursor is densified and crystallized, and the nucleus particle precursor is phase-transformed, finally yielding core-shell structure powder. The core layer synthesis process and the shell coating process of the core-shell structured powder are continuously completed in an axially connected section without physical isolation within the same reactor.

2. The method for continuous preparation of core-shell structured powder using a multi-stage ceramic membrane reactor according to claim 1, characterized in that, The solid content of the core-shell structure precursor slurry output by S2 is 0.5wt%-2wt%.

3. The method for continuous preparation of core-shell structured powder using a multi-stage ceramic membrane reactor according to claim 1, characterized in that, The precursor solution for the nuclear particles in S1 is a mixed aqueous solution of FeCl3 and FeCl2 in a molar ratio of 2:1, and the total iron ion concentration is 0.1 mol / L-0.2 mol / L; the precipitant is a NaOH solution with a concentration of 1.0 mol / L-1.5 mol / L.

4. The method for continuous preparation of core-shell structured powder using a multi-stage ceramic membrane reactor according to claim 1, characterized in that, The shell precursor solution in S2 is at least one of the following: 0.01 mol / L-0.03 mol / L AlCl3 solution, 0.04 mol / L-0.06 mol / L Na2SiO3 solution, 0.02 mol / L-0.04 mol / L TiOSO4 solution, and 0.02 mol / L-0.04 mol / L ZrOCl2 solution. The pH adjuster is NaOH solution or HCl solution.

5. The method for continuous preparation of core-shell structured powder using a multi-stage ceramic membrane reactor according to claim 1, characterized in that, The reaction temperature of the first core layer synthesis process is 30℃-40℃, and the fluid residence time is 12min-18min; the reaction temperature of the second shell layer coating process is 25℃-35℃, and the fluid residence time is 6min-10min.

6. The method for continuous preparation of core-shell structured powder using a multi-stage ceramic membrane reactor according to claim 5, characterized in that, The pH value of the first core layer synthesis process is 8-10; the pH value of the second shell layer coating process is 4-10.

7. The method for continuous preparation of core-shell structured powder using a multi-stage ceramic membrane reactor according to claim 6, characterized in that, When the shell precursor solution in S2 is at least one of 0.01 mol / L-0.03 mol / L AlCl3 solution, 0.02 mol / L-0.04 mol / L TiOSO4 solution, or 0.02 mol / L-0.04 mol / L ZrOCl2 solution, the pH value of the second shell coating process is 4-6; when the shell precursor solution in S2 is 0.04 mol / L-0.06 mol / L Na2SiO3 solution, the pH value of the second shell coating process is 8-10.

8. The method for continuous preparation of core-shell structured powder using a multi-stage ceramic membrane reactor according to claim 1, characterized in that, The post-processing in S3 involves first centrifuging to separate the solid and liquid phases at a speed of 3500 rpm to 4500 rpm for 8 min to 12 min; then drying at a temperature of 55℃ to 65℃ for 8 h to 12 h; followed by calcination at a temperature of 600℃ to 700℃ for 25 to 35 min, simultaneously completing the integrated treatment of core particle crystal transformation, shell precursor dehydration and densification crystallization, and core-shell interface strengthening.

9. A multi-stage ceramic membrane reactor for the continuous preparation of core-shell structured powders, characterized in that, The reactor is used to implement the preparation method according to any one of claims 1-7, comprising: a reactor body, a first ceramic membrane assembly and a second ceramic membrane assembly arranged sequentially along the axial direction of the reactor body, and a first pH monitor and a second pH monitor respectively disposed at the first ceramic membrane assembly and the second ceramic membrane assembly.

10. The multi-stage ceramic membrane reactor for continuous preparation of core-shell structured powders according to claim 9, characterized in that, It also includes a third ceramic membrane module and a third pH monitor located downstream of the second ceramic membrane module, to achieve multi-layer coating of nuclear particles and prepare multi-layer core-shell structured powder.

11. The multi-stage ceramic membrane reactor for continuous preparation of core-shell structured powders according to claim 9, characterized in that, The reactor body contains a continuous fluid channel with uniform axial flow.

12. The multi-stage ceramic membrane reactor for continuous preparation of core-shell structured powders according to claim 11, characterized in that, The first ceramic membrane assembly is arranged at a first position along the axial direction of the reactor body, and includes at least one set of independently controlled first ceramic membrane elements, which are respectively connected to the nuclear particle precursor solution tank and the precipitant tank for conveying the synthesis reaction raw materials; the second ceramic membrane assembly is arranged at a second position along the axial direction of the reactor body and is located downstream of the first ceramic membrane assembly, and includes at least one set of independently controlled second ceramic membrane elements, which are respectively connected to the shell precursor solution tank and the pH adjuster tank for conveying the coating reaction raw materials.

13. The multi-stage ceramic membrane reactor for continuous preparation of core-shell structured powders according to claim 11, characterized in that, The first ceramic membrane element and the second ceramic membrane element are tubular ceramic membranes or disc ceramic membranes.

14. The multi-stage ceramic membrane reactor for continuous preparation of core-shell structured powders according to claim 13, characterized in that, The first ceramic membrane element and the second ceramic membrane element are tubular ceramic membranes; the first ceramic membrane assembly includes at least one first ceramic membrane element, the outer side of which is divided into two isolated liquid inlet sides that are respectively connected to a nuclear particle precursor solution tank and a precipitant tank for precise delivery of synthesis reaction raw materials; the second ceramic membrane assembly includes at least one second ceramic membrane element, the outer side of which is divided into two isolated liquid inlet sides that are respectively connected to a shell precursor solution tank and a pH adjuster tank for precise delivery of coating reaction raw materials.

15. The multi-stage ceramic membrane reactor for continuous preparation of core-shell structured powders according to claim 13, characterized in that, The first ceramic membrane element and the second ceramic membrane element are disc ceramic membranes. The first ceramic membrane assembly includes at least two first ceramic membrane elements arranged in opposite directions along the longitudinal direction of the reactor. The second ceramic membrane assembly includes at least two second ceramic membrane elements arranged in opposite directions along the longitudinal direction of the reactor.

16. The multi-stage ceramic membrane reactor for continuous preparation of core-shell structured powders according to claim 15, characterized in that, The first group of first ceramic membrane elements consists of two opposing circular ceramic membranes, both of which can rotate or only one of which can rotate; the second group of second ceramic membrane elements consists of two opposing circular ceramic membranes, both of which can rotate or only one of which can rotate.

17. The multi-stage ceramic membrane reactor for continuous preparation of core-shell structured powders according to claim 16, characterized in that, Both the first ceramic membrane element in the first group and the second ceramic membrane element in the second group can rotate synchronously or differentially.

18. The multi-stage ceramic membrane reactor for continuous preparation of core-shell structured powders according to claim 16, characterized in that, The distance between the first ceramic membrane elements in the first group is H1, and the distance between the second ceramic membrane elements in the second group is H2; both H1 and H2 are adjustable.

19. The multi-stage ceramic membrane reactor for continuous preparation of core-shell structured powders according to claim 18, characterized in that, Micro-reaction channels are formed between the first ceramic membrane element in the first group and the second ceramic membrane element in the second group; the two disc ceramic membranes of the first ceramic membrane element in the first group have membrane pores only on their opposite surfaces, and the two disc ceramic membranes of the second ceramic membrane element in the second group have membrane pores only on their opposite surfaces, with the other surfaces being closed structures.

20. The multi-stage ceramic membrane reactor for continuous preparation of core-shell structured powders according to claim 13, characterized in that, The tubular or disc ceramic membrane is made of any one or a combination of Al2O3, ZrO2, or TiO2, and has a pore size of 0.1 μm-1 μm.

Images