A core-shell structure powder preparation system and a core-shell structure powder based on hydrogen / nitrogen plasma jet transient heat treatment and atmosphere regulation and a preparation method thereof

Abstract

The application discloses a core-shell structure powder preparation system and a core-shell structure powder based on hydrogen / nitrogen plasma jet transient heat treatment and atmosphere regulation and a preparation method thereof, and belongs to the technical field of material preparation and surface modification. The application solves the problem that a heterogeneous coating layer on the surface of a powder material is difficult to realize complete, uniform, thickness-controllable and firm interface bonding. In the application, metal droplets or metal vapor are injected into a receiving unit, oxide particles or metal droplets formed by the metal vapor react in a controllable reaction chamber, a surface layer is formed on the surface, is stabilized through a buffer zone, is quenched by a high-speed quenching and collecting unit, and core-shell structure powder is collected, when the metal vapor is used, the core is an oxide, and the shell layer is a metal element; when the metal droplet is used, the core is a metal element, and the shell layer is a nitride. The application realizes rapid surface reaction, maintains the original structure of the core phase, forms metallurgical bonding or strong chemical bonding between the shell layer and the core, and the coating of the shell layer is complete and uniform.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation and surface modification technology, specifically relating to a core-shell structure powder preparation system and a core-shell structure powder and its preparation method based on hydrogen / nitrogen plasma jet transient heat treatment and atmosphere control. Background Technology

[0002] Core-shell composite materials, with their unique "core-shell" component design, can cleverly integrate the advantages of both core and shell materials, achieving synergistic performance enhancement and demonstrating enormous application potential in high-tech fields such as catalysis, electronic devices, aerospace, and biomedicine. Therefore, developing efficient and controllable core-shell structure powder preparation technology has become one of the research hotspots in materials science.

[0003] Core-shell composite materials, due to their unique "core-shell" component design, can integrate the advantages of both core and shell materials, achieving synergistic enhancement of mechanical, electrical, thermal, or chemical properties. This demonstrates enormous application potential in high-tech fields such as catalysis, electronic devices, aerospace, and biomedicine. Therefore, developing efficient and controllable core-shell structure powder preparation technologies has become one of the research hotspots in materials science.

[0004] Currently, the mainstream preparation technologies for core-shell composite materials are mainly divided into two categories: post-processing coating and in-situ synthesis, but each has obvious limitations. Post-processing coating methods include chemical vapor deposition (CVD), physical vapor deposition (PVD), sol-gel methods, and mechanical ball milling. Although these methods can obtain coated powders of a certain quality, the process is complex, the equipment is expensive, the deposition rate is low, and the coating layer and the powder core are mostly physically attached or have a weak chemical bond, resulting in insufficient interfacial strength, making them prone to peeling off during subsequent intensive processing or use. While the sol-gel method can achieve component control at the molecular level, its reaction process involves complex hydrolysis and condensation of organic precursors, requiring subsequent high-temperature heat treatment to remove organic matter. This process is not only energy-intensive but also leads to severe atomic interdiffusion at the core-shell interface, destroying the expected core-shell structure. Mechanical ball milling is simple and easy to operate, but the powder composite achieved through mechanical collision is highly random, often resulting in uneven coating thickness and incomplete coverage. Furthermore, the ball milling process inevitably introduces impurities from ball wear, severely impacting the purity and performance of the final product. The second type of in-situ synthesis method, such as reaction synthesis during gas atomization or thermochemical treatments like nitriding and carburizing of pre-prepared powders, has the advantage of generating the shell in situ through chemical reactions, resulting in strong interfacial bonding. However, these methods require extremely stringent control of reaction kinetics. In gas atomization reaction synthesis, the cooling rate of the molten metal droplets is extremely high, and the surface reaction window is extremely short, typically resulting in only a very thin and compositionally limited surface modification layer, making it difficult to obtain a complete shell with independently controllable thickness and composition. Traditional nitriding and carburizing of solid powders require prolonged high-temperature treatment (several hours to tens of hours) to obtain a diffusion layer of a certain thickness. This is disastrous for micron or nanoscale powders with high specific surface area, as it can lead to severe sintering and agglomeration of particles, coarsening of grains, loss of powder fluidity, sharp drop in specific surface area, or even complete hardening and loss of powder properties.

[0005] Furthermore, some high-energy beam technologies originally used for coating preparation, such as atmospheric plasma spraying (APS), while efficiently utilizing high-temperature plasma jets to process materials, essentially involve completely melting the powder and then impacting it at high speed onto the substrate to form a coating. If this technology is directly used to process discrete powder particles, the particles will completely melt during flight, ultimately leading to particle adhesion or the formation of solid spheres, failing to retain any core structure. Therefore, it is unsuitable for preparing core-shell structured powders.

[0006] Therefore, existing technologies struggle to achieve complete, uniform, thickness-controllable, and firmly bonded heterogeneous coating structures on powder material surfaces, especially at the nanometer to micrometer scale. Summary of the Invention

[0007] To overcome the aforementioned problems in the prior art, this invention provides a core-shell structure powder preparation system and a core-shell structure powder based on hydrogen / nitrogen plasma jet transient heat treatment and atmosphere control, as well as a method for preparing the same.

[0008] The technical solution of the present invention is as follows: One objective of this invention is to provide a core-shell structure powder preparation system, the system comprising: Receiving unit: Receives metal droplets or metal vapor; The plasma atmosphere reactor area includes a plasma generator: producing a stable, high-energy-density directional plasma jet; a gas supply and switching unit: providing the working gas for the plasma; a controllable reaction chamber: a chamber that encloses the plasma jet and powder flow, maintaining a specific background atmosphere; a buffer zone: to prevent droplets from being deformed by the gas after the reaction in the controllable reaction chamber, a buffer zone is set up to allow the reacted particles to continue falling for a period of time to restore their spherical shape; and an ultra-high-speed quenching and collection unit: rapidly cooling the particles passing through the buffer zone, fixing the shell structure, and collecting them under an inert atmosphere to obtain core-shell structured powder.

[0009] The second objective of this invention is to provide a method for preparing core-shell structured powders based on hydrogen / nitrogen plasma jet transient heat treatment and atmosphere control using the above-mentioned system. This preparation method includes: S1. Material input: Inject the metal droplets generated by the gas atomization process or the metal vapor generated by the non-gas atomization process into the receiving unit. S2. Plasma processing: The plasma working gas is provided by the gas supply and switching unit, and the plasma generator provides the plasma jet. In the controllable reaction chamber, the oxide particles or metal droplets formed by metal vapor in the working gas plasma jet region remain and undergo reduction or nitriding reactions. A surface layer is formed on the surface of the oxide particles or metal droplets, and a preliminary core-shell structure powder is obtained. S3. Quenching, Shaping and Collection: After the initial core-shell structure powder is stabilized for a short time in the buffer zone, it enters the ultra-high speed quenching and collection unit for quenching, so that the surface layer is solidified into a complete shell layer. The core-shell structure powder is then collected in an inert atmosphere. The plasma working gas is a mixture of hydrogen and argon, a mixture of nitrogen and argon, or nitrogen. The working gas plasma jet region consists of the plasma working gas and the plasma jet.

[0010] Further specifying, the non-atomization processes in S1 include, but are not limited to, spray pyrolysis and gas-phase synthesis.

[0011] Further specifying, the metal droplets in S1 are Ti, Al, Zr, etc.

[0012] Further specifying, the metal droplet size in S1 is 10-100 μm.

[0013] Further specifying, the metal droplet size in S1 is 10-30 μm.

[0014] Further defining the process of metal vapor forming oxide particles in S2, the controllable reaction chamber is divided into an oxidation zone and a reduction zone. First, the gas supply and switching unit provides a mixed gas composed of argon and oxygen. In the oxidation zone, the metal vapor is oxidized to generate oxide particles in the presence of the mixed gas. Then, the oxide particles enter the reduction zone to undergo a reduction reaction.

[0015] Further specifying, when metal vapor generated by a non-atomization process is used in S1, the plasma working gas in S2 is a mixture of hydrogen and argon, the working gas plasma jet region is a hydrogen plasma jet region, the residence time is 5-20 milliseconds, and the nitriding reaction is carried out. The power of the plasma generator is 30-60 kW. In S3, a high-speed cold argon gas curtain is used for quenching, with a cooling rate ≥1000 ℃ / s, so as to quickly shape the surface layer. The core of the core-shell structure powder is an oxide, and the shell is a metallic element.

[0016] Furthermore, hydrogen accounts for 20%-40% of the total volume of the mixture, and argon accounts for 60%-80% of the total volume of the mixture.

[0017] Further specifying, when the metal droplets generated by the gas atomization process are used in S1, the plasma working gas in S2 is a mixture of nitrogen and argon or nitrogen, the working gas plasma jet region is a nitrogen plasma jet region, the residence time is 20-200 milliseconds, the power of plasma generator 2 is 30-80 kW, and high-speed cold argon gas curtain is used for quenching in S3, with a cooling rate ≥1000 ℃ / s, so as to quickly shape the surface layer. The core of the core-shell structure powder is a metallic element, and the shell is a nitride.

[0018] Furthermore, the mixture is specified to contain 20%-40% hydrogen and 60%-80% argon.

[0019] Further specifying, the oxide in S2 is a transition metal oxide that can be reduced to its corresponding metallic element under a reducing atmosphere.

[0020] To be further specified, the oxide is titanium dioxide.

[0021] The third objective of this invention is to provide a core-shell structured powder obtained by the above preparation method.

[0022] The beneficial effects of this invention are as follows: (1) The present invention utilizes directional plasma jet to perform transient high-temperature treatment on oxide particles or metal droplets in flight, and generates a uniform heterogeneous coating layer on the surface of oxide particles or metal droplets by precisely controlling the treatment atmosphere, thereby preparing composite powders with different core-shell structures.

[0023] (2) The core of the core-shell structure powder preparation system provided by the present invention is a plasma atmosphere modification module that can operate independently. The system can receive materials of different forms, such as metal vapor or metal droplets, and modify them in a controllable reaction chamber.

[0024] (3) This invention can prepare core-shell structured powders in two aspects. First aspect: preparing composite powders with a metal elemental shell encapsulating an oxide ceramic core. Utilizing the highly active [H] generated by hydrogen plasma, the reducing properties of the hydrogen plasma jet are used to rapidly and selectively reduce the surface of the prepared oxide particles at transient high temperatures, thereby forming a metal elemental coating layer on the surface of the oxide ceramic powder. Second aspect: preparing composite powders with a nitride shell encapsulating a metal core. During the metal powder atomization process, surface nitriding is performed simultaneously to obtain a core-shell powder with nitride encapsulating metal. The key to this method is utilizing the highly active [N] generated in the nitrogen plasma jet region to rapidly nitrid the surface of a high-temperature metal droplet in flight to generate a nitride shell layer.

[0025] (4) This invention utilizes the ultra-high energy density and non-equilibrium characteristics of plasma jets to achieve rapid surface reactions that cannot be performed by conventional heat treatment methods, such as the instantaneous deep reduction of oxides. Moreover, the method of this invention has extremely fast processing speed and high efficiency: a single oxide particle or metal droplet can complete the reaction in milliseconds, and the system can continuously feed and discharge materials.

[0026] (5) The energy of the present invention is highly concentrated on the surface of the core-shell structure particles, resulting in low overall heat input to the particles. This maximizes the preservation of the original structure of the core phase and avoids sintering and grain coarsening.

[0027] (6) The shell of this invention is uniform and the interface bonding is strong: the shell is generated by high-temperature in-situ reaction and forms a metallurgical bond or strong chemical bond with the core, and the shell completely and uniformly covers the core. In addition, this invention is highly flexible and controllable: by adjusting parameters such as the power of the plasma generator, the composition of the plasma working gas, and the residence time, the composition and thickness of the shell and the core can be precisely controlled. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the core-shell structure powder preparation system of the present invention; Figure 2 XRD patterns of the shell and core of the core-shell powder prepared in Example 1; Figure 3 XRD patterns of the shell and core of the core-shell powder prepared in Example 2; Figure 4 (a) is a scanning electron microscope image of the core-shell powder obtained in Example 2; Figure 4 (b) is a scanning electron microscope image of pure Ti powder obtained by gas atomization powdering in Example 2; Figure 4 (c) is a scanning electron microscope image of a single particle of the core-shell powder obtained in Example 2; Figure 4 (d)-(e) are Figure 4 (c) EDS results for a single particle; Figure 5 A cross-sectional TEM image of the core-shell powder prepared in Example 2; Figure 6 XRD patterns of the shell and core of the core-shell powder prepared in Example 3; Figure 7 XRD patterns of the shell and core of the core-shell powder prepared in Example 4; The components include: 1. Receiving unit; 2. Plasma generator; 3. Gas supply and switching unit; 4. Controllable reaction chamber; 5. Buffer zone; 6. Ultra-high speed quenching and collection unit; and 7. Plasma atmosphere reactor. Detailed Implementation

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0030] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0031] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0032] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0033] Example 1 Preparation of titanium dioxide core-shell powder coated with metallic titanium In this embodiment, core-shell powder is prepared by hydrogen plasma reduction of oxide (titanium dioxide) powder prepared by non-atomization method, wherein titanium dioxide powder is prepared in situ by precursor oxidation method. The specific method in this embodiment is as follows: (i) Using high-purity titanium tetrachloride (TiCl4, liquid purity ≥99.9%, 30g) as the titanium source, it is vaporized at 50℃. High-purity argon (Ar) with a flow rate of 8 L / min is used as the carrier gas to continuously and stably carry and inject the vaporized TiCl4 into the core-shell structure powder preparation system. (II) Plasma jet process (this stage includes the synthesis of titanium dioxide powder and the final core-shell structure powder): (1) After entering the system, high-purity titanium tetrachloride vapor is received by receiving unit 1; (2) Oxidation synthesis of titanium dioxide powder: Argon and oxygen mixture (Ar:O2=4:1, volume ratio) is introduced into the controllable reaction chamber 4 by the gas supply and switching unit 3. TiCl4 vapor enters the controllable reaction chamber 4 through the receiving unit 1. The chamber height is 0.5m. The oxidation zone is set from the top of the controllable reaction chamber 4 to 0.4m from the top. The reduction zone is set from 0.4m from the top of the controllable reaction chamber 4 to the bottom. In the oxidation zone, TiCl4 vapor undergoes instantaneous oxidation reaction under the conditions of argon and oxygen mixture and radio frequency power of 60 kW, generating highly active and highly dispersed titanium dioxide particles with a particle size of 30-60nm in situ. (3) Hydrogen plasma reduction treatment: When the generated titanium dioxide particles enter the reduction zone during flight, the gas supply and switching unit 3 changes the gas type and injects a mixture of hydrogen and argon (H2:Ar=3:7, volume ratio, H2 flow rate 15 L / min, Ar flow rate 35 L / min) into the controllable reaction chamber 4 as the plasma working gas. At the same time, the generator 2 emits a plasma jet. After the gas and jet enter the controllable reaction chamber 4, a hydrogen plasma jet zone is formed in the reduction zone (which is essentially a hydrogen plasma jet). The plasma power is 50 kW. The titanium dioxide particles stay in the reduction zone for 10 milliseconds. Their surface undergoes an instantaneous reduction reaction with highly active hydrogen atoms [H], forming a metallic titanium surface layer on the surface of the titanium dioxide particles, forming a preliminary core-shell structure powder. Because the heat input is limited and the reduction time is extremely short, the titanium dioxide particles are still in the oxide state. (4) Quenching and Shaping and Collection: The initial core-shell structure powder enters the buffer zone 5. This area is set up to prevent the products after the reaction in the controllable reaction chamber 4 from being deformed by the gas. The initial core-shell structure powder continues to fall in the buffer zone 5 to restore the spherical shape. After being briefly stabilized in the buffer zone 5, it enters the ultra-high speed quenching and collection unit 6 and is quenched by high-speed cold argon gas (20℃, flow rate 50 L / min) (cooling rate ≥1000 ℃ / s). The surface layer is solidified into a complete shell layer through rapid cooling and collected under argon protection to obtain titanium dioxide core-shell powder with a particle size of 44-52nm. Among them, the core particle size is 36-48nm and the shell thickness is 2-4nm.

[0034] The phase composition of the titanium dioxide core-shell powder obtained in this embodiment was analyzed by grazing incidence X-ray diffraction using a Cu Kα X-ray source with a fixed incident angle of 0.5° and a scanning range of 20°–100°. The results are as follows: Figure 2 As shown, the shell pattern is consistent with the standard peak position of α-titanium, indicating that the powder shell phase is metallic titanium.

[0035] To determine the phase composition of the powder core, a cross-sectional depth polishing method was used to remove the outer shell of the powder surface, ensuring that the X-rays detected by XRD primarily interacted with the core material. X-ray diffraction analysis (Cu Kα rays, scanning range 20°–100°) was then performed on the deeply polished cross-section. The results are as follows: Figure 2 As shown, the core spectrum is quite consistent with the diffraction peaks of titanium dioxide.

[0036] XRD analysis of the core and shell confirmed that the shell is metallic titanium and the core is titanium dioxide. The two have distinctly different phases, indicating that a core-shell composite powder with titanium dioxide as the core and metallic titanium as the complete shell has indeed been successfully prepared.

[0037] Nanoindentation testing was performed on the titanium-coated titanium dioxide core-shell powder of this embodiment. The method was as follows: First, the powder sample was embedded and polished. Then, a test area was prepared on the cross-section of a selected individual particle using focused ion beam technology. The test was conducted in an in-situ nanomechanical testing system coupled with a scanning electron microscope, using a Berkovich diamond indenter and a continuous stiffness measurement method.

[0038] Table 1 shows the nanoindentation gradient test results of the core-shell structure powder in this embodiment. As shown in Table 1, the particles maintain a stable low hardness plateau of 4.8-5.1 GPa within a depth of approximately 3 nm from the surface (corresponding to the titanium shell), and then the hardness rapidly increases to 16.2 GPa within an extremely narrow range of 2 nm (corresponding to the titanium dioxide core). The nanoindentation results prove that the powder in this embodiment does indeed form a core-shell structure with a distinct interface.

[0039] Table 1. Nanoindentation gradient test of titanium dioxide core-shell powder in Example 1.

[0040] Example 2 Preparation of titanium nitride-coated titanium core-shell powder This embodiment prepares core-shell powder by plasma nitriding during conventional gas atomization powder preparation; The specific method in this embodiment is as follows: Plasma jet technology: (1) Gas atomization powder making: High-purity titanium ingots (purity ≥99.7%) are smelted in a vacuum consumable electrode arc furnace. The vacuum degree in the furnace is evacuated to ≤5.0 Pa. Under the smelting current of 25-38 kA and the voltage of 28-40 V, the high-purity titanium ingots are melted into liquid by electric arc. The temperature of the molten pool is maintained above 1700℃. The smelting continues until the consumable electrode is completely melted, forming a liquid titanium molten pool with uniform composition. The titanium liquid is atomized into droplets with an average particle size of 10-30μm by high-pressure argon gas (pressure 4.0 MPa, gas flow rate 60 L / min); (2) Receiving unit 1 receives the high-temperature titanium droplets generated by the gas atomization process; (3) Nitrogen plasma nitriding treatment: Pure nitrogen gas (N2, flow rate 25 L / min) is introduced into the controllable reaction chamber 4 by the gas supply and switching unit 3 as the plasma working gas. At the same time, the generator 2 emits a plasma jet (plasma power of 45 kW). After the gas and jet enter the controllable reaction chamber 4, a nitrogen plasma jet region is formed (in essence, a nitrogen plasma jet). The atomized titanium droplet group enters the controllable reaction chamber 4 from the receiver and passes through the nitrogen plasma jet region in 80 milliseconds. This time is actually the residence time of the atomized titanium droplet group in the nitrogen plasma jet region. The surface of the atomized titanium droplet group undergoes an instantaneous nitriding reaction in the nitrogen plasma jet region, generating a nitride layer. However, the interior of the droplet remains in a molten metal state due to the limitation of reaction kinetics, thus obtaining a preliminary core-shell structure powder. (4) Quenching, Shaping and Collection: The initial core-shell structure powder enters the buffer zone 5. This area is set up to prevent the products after the reaction in the controllable reaction chamber 4 from being deformed by the gas. The initial core-shell structure powder continues to fall in the buffer zone 5 to restore the spherical shape. After being briefly stabilized in the buffer zone 5, it enters the ultra-high speed quenching and collection unit 6. It is cooled and solidified in an argon protective environment (argon flow rate 40 L / min) at a cooling rate ≥1000 ℃ / s and collected to obtain titanium nitride coated titanium core-shell powder with a particle size of 25.1-30.2 μm. Among them, the core particle size is 24.9-29.9 μm and the shell thickness is 70-100 nm.

[0041] Phase analysis of the titanium nitride-coated titanium core-shell powder obtained in this embodiment was performed using grazing incidence X-ray diffraction, and the results are as follows: Figure 3 As shown, the shell pattern matches the standard peak positions of titanium nitride. To determine the phase of the powder core, a cross-sectional depth polishing method was used to remove the shell layer on the powder surface, allowing the X-rays detected by XRD to primarily interact with the core material. X-ray diffraction analysis was performed on the deeply polished cross-section, and the results are as follows. Figure 3 As shown, the spectrum of the core material is largely consistent with the diffraction peaks of α-titanium.

[0042] XRD analysis of the core and shell confirmed that the shell is titanium nitride, while the core remains metallic titanium. The two phases are distinctly different, indicating that a core-shell powder coated with titanium nitride was successfully prepared using gas atomization and nitriding processes.

[0043] The final powder SEN image obtained in this embodiment is as follows: Figure 4 As shown in (a), Figure 4 (b) is pure Ti powder prepared by ordinary gas atomization method. In contrast, it can be seen that the powder obtained in Example 2 has a coating on its surface. Figure 4 (c) represents a single powder particle obtained in the final embodiment. Figure 4 (d)-(e) are the EDS results of (c). The uniform presence of Ti and N elements on the powder surface indicates that the powder particles are uniformly coated with TiN.

[0044] Figure 5 The image shows a cross-sectional TEM image of the core-shell powder prepared in this embodiment. The interface between the TiN and α-Ti phases is clearly visible. No cracks, pores, or obvious amorphous voids were observed at the interface, indicating a strong interfacial bond. A transition region of approximately 2-5 nm exists between the two phases. The presence of this transition region suggests that the titanium nitride-coated titanium core-shell powder can reduce the interfacial energy through its own structural relaxation, thereby forming a thermodynamically stable bond.

[0045] Table 2 shows the nanoindentation gradient test results of the powder in this embodiment. As shown in Table 2, the particles maintain a stable high hardness plateau of 29.4-29.8 GPa (corresponding to the titanium nitride shell) within a depth of 80 nm from the surface, and then the hardness drops sharply to 2.8 GPa (corresponding to the metallic titanium core) within a range of about 20 nm. The nanoindentation results prove that the powder in this embodiment does indeed form a core-shell structure with a uniform shell and a clear interface.

[0046] Table 2. Nanoindentation gradient test of titanium nitride-coated titanium core-shell powder in Example 2

[0047] Example 3 The preparation of aluminum nitride coated aluminum core-shell powder in this embodiment differs from that in Example 2 in the following ways: (2) the high-purity titanium ingot is replaced with a high-purity aluminum ingot with a purity ≥99.8%, a pressure of 3.5 MPa, and a gas flow rate of 55 L / min; (3) the plasma power is 40kW, the plasma working gas is a mixture of nitrogen and argon, wherein N2:Ar=4:1 (volume ratio), N2 flow rate is 20L / min, Ar flow rate is 5 L / min, and the residence time of the atomized aluminum droplet group is 100 milliseconds; (4) the argon flow rate is 35 L / min, and the remaining process operations and parameter settings are the same as in Example 2. Finally, aluminum nitride coated aluminum core-shell powder with a particle size of 25.1-30.2μm is obtained, wherein the core particle size is 25-30μm and the shell thickness is 30-60nm.

[0048] Phase analysis of the aluminum nitride-coated aluminum core-shell powder obtained in this embodiment was performed using grazing incidence X-ray diffraction, and the results are as follows: Figure 6 As shown, the shell pattern matches the standard peak positions of aluminum nitride. To determine the phase of the powder core, a cross-sectional depth polishing method was used to remove the shell layer on the powder surface, allowing the X-rays detected by XRD to primarily interact with the core material. X-ray diffraction analysis was performed on the deeply polished cross-section, and the results are as follows. Figure 6 As shown, the core material spectrum matches the diffraction peaks of Al.

[0049] XRD analysis of the core and shell confirmed that the shell is aluminum nitride, while the core remains metallic aluminum. The two phases are distinctly different, indicating that the aluminum nitride-coated aluminum core-shell powder was successfully prepared using a gas atomization and nitriding process.

[0050] Example 4 This embodiment prepares zirconium nitride-coated zirconium core-shell powder, which differs from Example 2 in that: (1) high-purity zirconium ingots (purity ≥99.7%) are induction melted in a high-purity argon atmosphere at a melting current of 25-38 kA and a voltage of 28-40 V, and the zirconium material is heated to 720-800℃ to melt until it is completely melted, forming a liquid pool with uniform composition, and argon gas is continuously introduced throughout the process to prevent oxidation and gas absorption; (2) high-purity titanium ingots are replaced with high-purity zirconium ingots with a purity ≥99.5%, a pressure of 4.5 MPa, and a gas flow rate of 65 L / min; (3) the plasma power is 55 kW, the nitrogen flow rate is 30 L / min, and the residence time of the atomized zirconium droplet group is 50 ms; (4) the argon flow rate is 45 L / min, the remaining process operations and parameter settings are the same as in Example 2, and finally zirconium nitride coated zirconium core-shell powder with a particle size of 25.1-30.2 μm is obtained, wherein the core particle size is 24.9-30 μm and the shell thickness is 40-70 nm.

[0051] Phase analysis of the zirconium nitride-coated zirconium core-shell powder obtained in this embodiment was performed using grazing incidence X-ray diffraction, and the results are as follows: Figure 7 As shown, the shell pattern matches the standard peak positions of zirconium nitride. To determine the phase of the powder core, a cross-sectional depth polishing method was used to remove the shell layer on the powder surface, allowing the X-rays detected by XRD to primarily interact with the core material. X-ray diffraction analysis was performed on the deeply polished cross-section, and the results are as follows. Figure 7 As shown, the core material spectrum matches the diffraction peaks of α-zirconium.

[0052] XRD analysis of the core and shell confirmed that the shell is zirconium nitride, while the core remains α-zirconium. The two phases are distinctly different, indicating that a zirconium nitride-coated zirconium core-shell powder was successfully prepared using a gas atomization and nitriding process.

[0053] Comparative Example 1 (Conventional step-by-step heat treatment reduction method) The purpose of this comparative example is to illustrate that if the conventional method of first preparing oxide powder and then performing solid-state heat treatment reduction is used, it is impossible to obtain titanium dioxide powder with a clear core-shell structure as described in Example 1 of this invention.

[0054] The specific method for this comparison is as follows: Take 30g of titanium dioxide powder with an average particle size of 60nm, and mix it with 5g of metallic titanium powder with an average particle size of 5μm in an argon-protected glove box for 2h to achieve physical mixing and coating. Then, place the mixed powder in an alumina crucible in a tube furnace, and heat it to 800℃ at a rate of 10℃ / min under a hydrogen-argon mixed gas (hydrogen:argon volume ratio 3:7), and hold it at this temperature for 120 minutes for heat treatment reduction. After that, cool it to room temperature with the furnace to obtain powder with a particle size of 1-10μm.

[0055] Nanoindentation gradient tests were performed on the powder obtained in this comparative example using a single particle cross-section, and the results are shown in Table 3. The microhardness of the particles started at 8.5 GPa at the surface and showed a continuous and gradual upward trend within a test depth of 30 nm, eventually reaching 15.8 GPa. No hardness plateau or steep hardness jumps characteristic of a clear interface between the metal shell and the oxide core were observed throughout the entire test depth. These results indicate that the traditional high-temperature, long-term heat treatment process is essentially a bulk diffusion-controlled reaction, leading to the deep reduction of the titanium dioxide core into a series of low-valence titanium oxides with moderate hardness (such as Ti4O7), which mix with the incompletely reacted titanium powder on the surface, ultimately forming a mixture with continuously and gradually changing composition and mechanical properties, rather than a distinct core-shell structure.

[0056] Table 3 Comparative Example 1: Nanoscale Indentation Gradient Test

[0057] Comparative Example 2 (Solid Powder Surface Nitriding Method) The purpose of this comparative example is to illustrate that if a stepwise process of first preparing solid metal powder and then performing surface nitriding is adopted, it is impossible to obtain core-shell powder with a uniform and complete nitride shell as described in Examples 2-4 of this invention.

[0058] The specific method for this comparison is as follows: High-purity titanium ingots (purity ≥99.7%) were melted in a vacuum consumable electrode arc furnace. The vacuum level inside the furnace was evacuated to ≤5.0 Pa. Under a melting current of 25-38 kA and a voltage of 28-40 V, the high-purity titanium ingots were melted into a liquid state by an electric arc. The temperature of the molten pool was maintained above 1700℃. Melting continued until the consumable electrode was completely melted, forming a liquid titanium pool with uniform composition. The titanium liquid was atomized into droplets with an average particle size of 20 μm by high-pressure argon gas (pressure 4.0 MPa, gas flow rate 60 L / min). The droplets were then completely cooled into a solid state. The solid titanium powder was placed in a separate plasma-enhanced chemical vapor deposition device. Under a mixed atmosphere of nitrogen and argon (volume ratio 1:1), the powder bed was heated to 550℃ and subjected to plasma nitriding treatment at this temperature for 60 min. Afterward, it was cooled in a vacuum environment to obtain powder with a particle size of 15-40 μm.

[0059] Nanoindentation gradient tests were performed on the powder obtained in this comparative example using a single particle cross-section, and the results are shown in Table 4. The microhardness of the particle surface was 15.5 GPa, and then the hardness value decreased rapidly and continuously within a depth range extending 1500 nm inwards, until it stabilized at 2.8 GPa (pure metallic titanium). This hardness curve did not exhibit a high-hardness plateau region with significant thickness and stable hardness value. This indicates that the nitriding treatment of solid metal powder is limited by the bulk diffusion rate of nitrogen atoms. The reaction can form a diffusion layer of a certain depth but with decreasing concentration, and its hardness transitions continuously from the surface to the interior. It is impossible to form a titanium nitride (TiN) shell with uniform and controllable thickness and a clear interface as described in this invention.

[0060] Table 4 Comparative Example 2: Nanometer Indentation Gradient Test

[0061] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A core-shell structure powder preparation system, characterized in that, The system includes: Receiving unit (1) and plasma atmosphere reactor area (7); The plasma atmosphere reactor area (7) includes a plasma generator (2), a gas supply and switching unit (3), a controllable reaction chamber (4), a buffer zone (5), and an ultra-high speed quenching and collection unit (6).

2. A method for preparing core-shell structured powder based on hydrogen / nitrogen plasma jet transient heat treatment and atmosphere control using the system described in claim 1, characterized in that, The method includes: S1, Material input: Inject the metal droplets generated by the gas atomization process or the metal vapor generated by the non-gas atomization process into the receiving unit (1). S2, Plasma treatment: The plasma working gas is provided by the gas supply and switching unit (3), and the plasma generator (2) provides the plasma jet. In the controllable reaction chamber (4), the oxide particles or metal droplets formed by metal vapor in the working gas plasma jet zone remain and undergo reduction or nitriding reactions. A surface layer is formed on the surface of the oxide particles or metal droplets to obtain the initial core-shell structure powder. S3, Quenching and Shaping and Collection: After the initial core-shell structure powder is stabilized for a short time in the buffer zone (5), it enters the ultra-high speed quenching and collection unit (6) for quenching, so that the surface layer is solidified into a complete shell layer, and the core-shell structure powder is obtained by collection in an inert atmosphere. The plasma working gas is a mixture of hydrogen and argon, a mixture of nitrogen and argon, or nitrogen. The working gas plasma jet region consists of the plasma working gas and the plasma jet.

3. The method according to claim 2, characterized in that, The metal droplets in S1 are Ti, Al, or Zr.

4. The method according to claim 2, characterized in that, The metal droplets in S1 have a diameter of 10-100 μm.

5. The method according to claim 2, characterized in that, The oxides in S2 are transition metal oxides that are reduced to their corresponding metallic elements under a reducing atmosphere.

6. The method according to claim 2, characterized in that, Further, when metal vapor generated by non-atomization process is used in S1, the plasma working gas in S2 is a mixture of hydrogen and argon, the working gas plasma jet region is a hydrogen plasma jet region, the residence time is 5-20 milliseconds, and a nitriding reaction is carried out. The power of the plasma generator (2) is 30-60 kW. In S3, a high-speed cold argon gas curtain is used for quenching, the cooling rate is ≥1000 ℃ / s, and the core of the core-shell structure powder is an oxide, while the shell is a metallic element.

7. The method according to claim 6, characterized in that, Hydrogen accounts for 20%-40% of the total volume of the mixture, and argon accounts for 60%-80% of the total volume of the mixture.

8. The method according to claim 2, characterized in that, When the metal droplets generated by the gas atomization process are used in S1, the plasma working gas in S2 is a mixture of nitrogen and argon or nitrogen, the working gas plasma jet region is a nitrogen plasma jet region, the residence time is 20-200 milliseconds, the power of the plasma generator (2) is 30-80 kW, the quenching cooling rate in S3 is ≥1000 ℃ / s, the core of the core-shell structure powder is a metallic element, and the shell is a nitride.

9. The method according to claim 8, characterized in that, In the gas mixture, hydrogen accounts for 20%-40% of the total volume, and argon accounts for 60%-80% of the total volume.

10. A core-shell structured powder based on hydrogen / nitrogen plasma jet transient heat treatment and atmosphere control, obtained by the preparation method according to any one of claims 2-9.

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