Method and device for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron

Abstract

The application discloses a method and device for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron, and relates to the technical field of nano-metal powder and metal oxide powder preparation, and comprises the following steps: taking pure iron as raw material, and directly sublimating the pure iron to generate gaseous iron atoms by electromagnetic induction and electromagnetic suspension non-contact heating to 1050-1150 DEG C under super vacuum condition; controlling the reaction atmosphere at the top outlet of the vacuum furnace, and feeding pure oxygen to generate nano-iron trioxide, and feeding argon or nitrogen to generate nano-pure iron powder; collecting through the magnetic force grading system at the outlet of the vacuum fan, and separating by the magnetic moment difference between iron and iron trioxide, and protecting the pure iron powder collecting bin from oxidation by nitrogen protection; and the application realizes the efficient synchronous preparation of high-purity and narrow-distribution nano-pure iron powder and iron trioxide powder by the super vacuum low-temperature non-melting sublimation, electromagnetic suspension non-contact heating and nitrogen-protection magnetic force grading collection technology of pure iron.

Description

Technical Field

[0001] This invention relates to the field of nano-metal powder and metal oxide powder preparation technology, specifically to a method and apparatus for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron. Background Technology

[0002] Nano-iron powder and nano-ferric oxide, as important functional nanomaterials, have extremely broad application prospects in fields such as magnetohydrodynamics, catalysis, adsorption, lithium-ion battery cathode materials, powder metallurgy, biomedicine, and environmental remediation. Currently, traditional preparation methods for nano-iron powder and nano-ferric oxide mainly include high-temperature melt atomization, gas-phase reduction, chemical precipitation, and mechanical ball milling.

[0003] However, the high-temperature melt atomization method requires heating iron to above 1538℃ to melt it, then atomizing it into droplets through high-pressure gas and condensing it into powder. This method is extremely energy-intensive, and the high-temperature molten iron readily reacts with refractory materials such as crucibles and furnace walls, introducing a large number of impurities, resulting in low product purity and a wide particle size distribution, making it difficult to obtain uniform nano-sized particles. The gas-phase reduction method typically uses iron halides or carbonyl compounds as precursors, preparing nano-iron powder through hydrogen reduction at high temperatures. This method not only has high raw material costs and high toxicity, but also easily introduces impurities such as carbon and oxygen during the reduction process, making it difficult to guarantee product purity and posing safety hazards. The chemical precipitation method involves adding a precipitant to an iron salt solution to generate ferric hydroxide or ferrous hydroxide precipitate, followed by filtration, washing, drying, and calcination to obtain nano-ferric oxide or nano-iron powder. This method has a complex process, cumbersome post-processing, and inevitably introduces a large number of anionic impurities during preparation, requiring multiple washings and generating a large amount of wastewater, placing significant environmental pressure on the process. Mechanical ball milling uses a high-energy ball mill to grind coarse iron powder into nano-sized particles. This method has low production efficiency, high energy consumption, and easily introduces impurities from the grinding media and air during the grinding process. At the same time, the powder is prone to agglomeration and uneven particle size distribution.

[0004] Furthermore, vacuum sublimation is an effective method for preparing high-purity nanoparticles. Its principle utilizes the characteristic that a substance's melting point decreases and its sublimation rate accelerates under high vacuum conditions, allowing the raw material to directly sublimate from a solid to a gaseous state, and then condense and nucleate in the gas phase to form nanoparticles. This method offers advantages such as high product purity, narrow particle size distribution, and good dispersibility. However, existing vacuum sublimation technologies mainly target low-melting-point metals such as zinc, cadmium, and magnesium. Research on vacuum sublimation technology for high-melting-point metals like iron is limited, and effective coupling between electromagnetic levitation non-contact heating and atmosphere-controlled magnetic classification collection has not yet been achieved. This results in problems such as slow sublimation rates, insufficient controllability of powder purity and particle size, and low collection efficiency, making large-scale industrial production difficult. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron, so as to solve the problems of high energy consumption, easy introduction of wall materials and chemical impurities, low purity, difficulty in producing two products in one machine, and easy oxidation during the collection of nano-pure iron powder.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] According to the first aspect of this disclosure, a method for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron is proposed, comprising the following steps:

[0008] S1. Using pure iron as raw material, under ultra-vacuum conditions, pure iron is heated to 1050-1150℃ by electromagnetic induction heating and electromagnetic levitation non-contact heating, so that pure iron directly sublimates to generate gaseous iron atoms.

[0009] S2. Control the reaction atmosphere at the top outlet of the vacuum furnace: when pure oxygen is introduced, gaseous iron atoms react with oxygen to generate nano-sized ferric oxide; when argon or nitrogen inert atmosphere is introduced, nano-sized pure iron powder is directly generated.

[0010] S3. The iron powder is collected by a magnetic classification and collection system installed at the outlet of the vacuum fan. The magnetic classification and collection system includes an adjustable magnetic field, an oxygen flow curtain, an iron oxide powder chamber, and a pure iron powder collection chamber with nitrogen protection.

[0011] When pure oxygen is introduced, gaseous iron atoms are attracted by an adjustable magnetic field and pass through the oxygen flow curtain. After being oxidized into ferric oxide, their magnetic moment is significantly weakened, and they fall into the iron oxide powder silo under the action of gravity.

[0012] When an inert atmosphere is introduced, the gaseous iron atoms, maintaining their strong magnetism, are attracted by an adjustable magnetic field and enter a pure iron powder collection chamber protected by nitrogen to complete the collection.

[0013] Furthermore, the heating temperature of the pure iron is 1100°C, which is lower than the melting point of iron, 1538°C.

[0014] Furthermore, the vacuum level of the ultra-vacuum condition is better than 1×10⁻⁶. -3 Pa.

[0015] Furthermore, the magnetic field strength of the adjustable magnetic field is 0.1 to 0.5 T.

[0016] Furthermore, the pure iron powder collection chamber with nitrogen protection maintains a slightly positive pressure high-purity nitrogen atmosphere of 0.01 to 0.05 MPa.

[0017] According to the first aspect of this disclosure, an apparatus for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron is also provided, comprising a vacuum sublimation furnace, a vacuum system, an electromagnetic heating levitation system, an atmosphere control system, and a magnetic classification and collection system with nitrogen protection; the vacuum sublimation furnace is provided with a top outlet; the electromagnetic heating levitation system is disposed inside the vacuum sublimation furnace and includes an electromagnetic induction heating coil and an electromagnetic levitation coil, used to achieve non-contact heating and stable levitation of pure iron raw materials; the atmosphere control system is connected to the top outlet of the vacuum sublimation furnace and includes a pure oxygen inlet, an argon inlet, and a nitrogen inlet, each inlet being independently controllable; the magnetic classification and collection system with nitrogen protection is connected to the top outlet of the vacuum sublimation furnace through a vacuum fan and includes an adjustable electromagnet or permanent magnet, an oxygen flow curtain, an iron oxide powder chamber, and a pure iron powder collection chamber; the pure iron powder collection chamber is a sealed structure and is provided with a nitrogen inlet and an exhaust outlet to form a nitrogen protective atmosphere.

[0018] Furthermore, the electromagnetic induction heating coil and the electromagnetic levitation coil work together to keep the pure iron raw material in a suspended state inside the furnace and prevent it from contacting any furnace wall material.

[0019] Furthermore, the adjustable electromagnet is positioned between the vacuum fan outlet and the oxygen flow curtain to attract gaseous iron atoms toward the oxygen flow curtain.

[0020] The built-in electromagnet of the electromagnetic adsorption hopper generates an adjustable magnetic field of 0.1 to 0.5T, and high-purity nitrogen is continuously introduced into the hopper as a protective atmosphere.

[0021] Furthermore, the iron oxide powder chamber is located directly below the oxygen flow curtain, and the pure iron powder collection chamber is located below the adsorption area of ​​the adjustable electromagnet or permanent magnet.

[0022] Furthermore, the vacuum system of the vacuum sublimation furnace achieves a vacuum level better than 1×10⁻⁶. -3 Pa, the electromagnetic heating suspension system heats pure iron to 1100℃ and keeps it suspended, and the atmosphere control system independently controls the introduction and switching of pure oxygen, argon or nitrogen through a mass flow meter.

[0023] Compared with existing technologies, the method and apparatus for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron provided by this invention uses ultra-vacuum low-temperature non-melting sublimation technology of pure iron to control the heating temperature at 1050-1150℃, which is far below the melting point of iron; and adopts a non-contact heating method coupled with electromagnetic induction and electromagnetic levitation to achieve the pure iron raw material to be suspended throughout the process without contacting any furnace wall material, thus eliminating wall material contamination; and nano-pure iron powder and nano-ferric oxide powder can be prepared separately or simultaneously in the same set of equipment by simply switching atmospheres, which greatly reduces equipment investment and production costs; the magnetic classification and collection system with nitrogen micro-positive pressure protection used to achieve efficient separation by utilizing the difference in magnetic moments between iron and ferric oxide, and at the same time solves the problem of easy oxidation of nano-pure iron powder during collection, effectively realizing continuous industrial production and significantly improving the preparation efficiency and quality of nano-iron-based powders. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0025] Figure 1 Flowchart of a method for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron;

[0026] Figure 2 A block diagram of the apparatus for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] As attached Figure 1 As shown,

[0029] Example 1:

[0030] This embodiment provides a specific implementation method for preparing nano-pure iron powder based on the method of the present invention, and the steps are as follows:

[0031] Raw material preparation: Select pure iron blocks with a purity of 99.995% as raw materials, process them into cylinders with a diameter of about 20mm and a height of about 30mm, clean the surface with anhydrous ethanol to remove oil and impurities, and dry them for later use.

[0032] Equipment inspection and preparation: Check the sealing performance of the vacuum sublimation furnace to ensure that there are no leaks in any sealing parts; check the operating status of the vacuum system, electromagnetic heating levitation system, atmosphere control system and magnetic classification and collection system to ensure that each piece of equipment is working properly; introduce high-purity nitrogen into the pure iron powder collection chamber to replace the air in the chamber, and then adjust the nitrogen flow rate to maintain a slight positive pressure of 0.02MPa in the chamber.

[0033] Charging and Vacuuming: Open the furnace door of the vacuum sublimation furnace, place the prepared pure iron block in the center of the electromagnetic levitation coil, close and lock the furnace door. Start the vacuum system, first turn on the mechanical pump for coarse evacuation of the furnace. When the vacuum level inside the furnace reaches below 10 Pa, turn on the molecular pump for fine evacuation until the vacuum level inside the furnace reaches 5 × 10 Pa. -4 Pa.

[0034] Heating and Suspension: The electromagnetic heating and levitation system is activated, and the power of the electromagnetic induction heating coil and the electromagnetic levitation coil is gradually increased. By adjusting the current of the electromagnetic levitation coil, the pure iron block is stably suspended in the center of the heating zone; by adjusting the power of the electromagnetic induction heating coil, the temperature of the pure iron block is slowly raised to 1100℃ and maintained at this constant temperature. During the heating process, the vacuum level inside the furnace is monitored in real time to ensure that the vacuum level is always better than 1×10⁻⁶. -3 Pa.

[0035] Atmosphere Control and Collection: Open the high-purity nitrogen inlet valve of the atmosphere control system, adjust the mass flow controller to make the nitrogen flow rate 5 L / min, and introduce it into the vacuum sublimation furnace from the top outlet. Start the vacuum fan and adjust the pumping speed to stabilize the vacuum level inside the furnace at 5 × 10⁻⁶. -4 Pa. The magnetic field strength of the adjustable electromagnet is adjusted to 0.3T. At this time, the pure iron block continues to sublimate in an ultra-vacuum environment at 1100℃. The generated gaseous iron atoms move upward with the nitrogen flow. After reaching the top outlet, they are captured and adsorbed by the adjustable magnetic field and then fall into the pure iron powder collection chamber.

[0036] Shutdown and Discharge: After 2 hours of reaction, gradually reduce the power of the electromagnetic heating suspension system and stop heating. Continue to purge with nitrogen and maintain the vacuum system until the furnace temperature drops to room temperature. Then, shut down the vacuum system and vacuum fan, and close the nitrogen inlet valve. Open the outlet of the pure iron powder collection chamber to collect the prepared nano-pure iron powder.

[0037] Testing showed that the nano-pure iron powder prepared in this embodiment had a purity of 99.992%, an average particle size of 45 nm, a particle size distribution range of 20–80 nm, a specific surface area of ​​35.6 m² / g, and an oxygen content of less than 0.05%, indicating excellent product performance.

[0038] Example 2:

[0039] This embodiment provides a specific implementation method for preparing nano-ferric oxide powder based on the method of the present invention, and the steps are as follows:

[0040] Raw material preparation: Similar to Example 1, pure iron blocks with a purity of 99.995% were selected as raw materials, and were cleaned and dried for later use.

[0041] Equipment Inspection and Preparation: Check the operating status of each system to ensure the equipment is working properly. Introduce a small amount of high-purity nitrogen into the iron oxide powder silo to replace the air inside.

[0042] Charging and Vacuuming: Same as in Example 1, place the pure iron block in the center of the electromagnetic levitation coil, close the furnace door, start the vacuum system, and evacuate the furnace to a vacuum level of 5×10⁻⁶. -4 Pa.

[0043] Heating and levitation: Similar to Example 1, the electromagnetic heating levitation system is activated to heat the pure iron block to 1100°C and maintain stable levitation.

[0044] Atmosphere Control and Collection: Open the high-purity oxygen inlet valve of the atmosphere control system, adjust the mass flow controller to make the oxygen flow rate 3L / min, and introduce it into the vacuum sublimation furnace from the top outlet. Simultaneously, open the oxygen curtain and adjust the oxygen flow rate to 2L / min. Start the vacuum fan and adjust the pumping speed to stabilize the vacuum level inside the furnace at 5×10⁻⁶. -4 Pa. The magnetic field strength of the adjustable electromagnet is adjusted to 0.3T. At this time, the gaseous iron atoms generated by the sublimation of the pure iron block move upward with the oxygen flow. Under the attraction of the adjustable magnetic field, they pass through the oxygen flow curtain and react with pure oxygen to generate nano-ferric oxide particles. Because the magnetic moment of ferric oxide weakens, it cannot be captured by the magnetic field and falls into the iron oxide powder silo under the action of gravity.

[0045] Shutdown and Discharge: After 2 hours of reaction, gradually reduce the power of the electromagnetic heating suspension system and stop heating. Close the oxygen inlet valve and oxygen curtain, and introduce high-purity nitrogen to replace the oxygen in the furnace. Continue to maintain the vacuum system until the furnace temperature drops to room temperature. Then, shut down the vacuum system and vacuum fan, open the discharge port of the iron oxide powder silo, and collect the prepared nano-iron oxide powder.

[0046] Testing revealed that the nano-ferric oxide powder prepared in this embodiment had a purity of 99.98%, an average particle size of 60 nm, a particle size distribution range of 30–100 nm, a specific surface area of ​​28.3 m² / g, a crystal form of α-Fe₂O₃, and good magnetic properties.

[0047] Example 3:

[0048] This embodiment provides a specific implementation method for simultaneously preparing nano-pure iron powder and nano-ferric oxide powder based on the method of the present invention, and the steps are as follows:

[0049] Raw material preparation and equipment inspection: Same as in Example 1.

[0050] Charging and Vacuuming: Same as in Example 1, place the pure iron block in the center of the electromagnetic levitation coil, close the furnace door, start the vacuum system, and evacuate the furnace to a vacuum level of 5×10⁻⁶. -4 Pa.

[0051] Heating and levitation: Similar to Example 1, the electromagnetic heating levitation system is activated to heat the pure iron block to 1100°C and maintain stable levitation.

[0052] Atmosphere Control and Synchronous Collection: Simultaneously open the high-purity nitrogen and high-purity oxygen inlet valves of the atmosphere control system. Adjust the mass flow controller to achieve a nitrogen flow rate of 3 L / min and an oxygen flow rate of 2 L / min, introducing the nitrogen into the vacuum sublimation furnace from the top outlet. Open the oxygen curtain and adjust the oxygen flow rate to 2 L / min. Start the vacuum fan and adjust the pumping speed to stabilize the vacuum level inside the furnace at 5 × 10⁻⁶. -4 Pa. The magnetic field strength of the adjustable electromagnet is adjusted to 0.3T. At this time, some gaseous iron atoms are captured by the magnetic field in the nitrogen atmosphere and fall into the pure iron powder collection chamber; other gaseous iron atoms pass through the oxygen flow curtain and are oxidized into ferric oxide, falling into the iron oxide powder chamber. By adjusting the flow ratio of nitrogen and oxygen, the output ratio of the two products can be controlled.

[0053] Shutdown and discharge: After the reaction has been going on for 2 hours, heating is stopped, nitrogen is introduced to replace the gas in the furnace, and after the furnace temperature drops to room temperature, the products are collected from the pure iron powder collection bin and the iron oxide powder collection bin respectively.

[0054] Testing showed that the performance indicators of the nano-pure iron powder and nano-ferric oxide powder prepared in this embodiment were basically consistent with those in Embodiment 1 and Embodiment 2, and the yield ratio of the two products was approximately 3:2.

[0055] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron, characterized in that, Includes the following steps: S1. Using pure iron as raw material, under ultra-vacuum conditions, pure iron is heated to 1050-1150℃ by electromagnetic induction heating and electromagnetic levitation non-contact heating, so that pure iron directly sublimates to generate gaseous iron atoms. S2. Control the reaction atmosphere at the top outlet of the vacuum furnace: when pure oxygen is introduced, gaseous iron atoms react with oxygen to generate nano-sized ferric oxide; when argon or nitrogen inert atmosphere is introduced, nano-sized pure iron powder is directly generated. S3. The iron powder is collected by a magnetic classification and collection system installed at the outlet of the vacuum fan. The magnetic classification and collection system includes an adjustable magnetic field, an oxygen flow curtain, an iron oxide powder chamber, and a pure iron powder collection chamber with nitrogen protection. When pure oxygen is introduced, gaseous iron atoms are attracted by an adjustable magnetic field and pass through the oxygen flow curtain. After being oxidized into ferric oxide, their magnetic moment is significantly weakened, and they fall into the iron oxide powder silo under the action of gravity. When an inert atmosphere is introduced, the gaseous iron atoms, maintaining their strong magnetism, are attracted by an adjustable magnetic field and enter a pure iron powder collection chamber protected by nitrogen to complete the collection.

2. The method for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron according to claim 1, characterized in that, The heating temperature of the pure iron is 1100℃, which is lower than the melting point of iron, 1538℃.

3. The method for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron according to claim 1, characterized in that, The vacuum level under the ultra-high vacuum condition is better than 1×10⁻⁶. -3 Pa.

4. The method for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron according to claim 1, characterized in that, The magnetic field strength of the adjustable magnetic field is 0.1 to 0.5 T.

5. The method for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron according to claim 1, characterized in that, The pure iron powder collection chamber with nitrogen protection maintains a slightly positive pressure high-purity nitrogen atmosphere of 0.01 to 0.05 MPa.

6. An apparatus for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron, used to implement the method described in any one of claims 1-5, characterized in that, The system includes a vacuum sublimation furnace, a vacuum system, an electromagnetic heating and levitation system, an atmosphere control system, and a magnetic classification and collection system with nitrogen protection. The vacuum sublimation furnace has a top outlet. The electromagnetic heating and levitation system is located inside the vacuum sublimation furnace and includes an electromagnetic induction heating coil and an electromagnetic levitation coil to achieve non-contact heating and stable levitation of pure iron raw materials. The atmosphere control system is connected to the top outlet of the vacuum sublimation furnace and includes a pure oxygen inlet, an argon inlet, and a nitrogen inlet, each of which is independently controllable. The magnetic classification and collection system with nitrogen protection is connected to the top outlet of the vacuum sublimation furnace through a vacuum fan and includes an adjustable electromagnet or permanent magnet, an oxygen flow curtain, an iron oxide powder silo, and a pure iron powder collection silo. The pure iron powder collection silo is a sealed structure with a nitrogen inlet and an exhaust outlet to form a nitrogen protective atmosphere.

7. The apparatus for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron according to claim 6, characterized in that, The electromagnetic induction heating coil and the electromagnetic levitation coil work together to keep the pure iron raw material in a suspended state inside the furnace and prevent it from contacting any furnace wall material.

8. The apparatus for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron according to claim 6, characterized in that, The adjustable electromagnet is positioned between the vacuum fan outlet and the oxygen flow curtain to attract gaseous iron atoms toward the oxygen flow curtain. The built-in electromagnet of the electromagnetic adsorption hopper generates an adjustable magnetic field of 0.1 to 0.5T, and high-purity nitrogen is continuously introduced into the hopper as a protective atmosphere.

9. The apparatus for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron according to claim 6, characterized in that, The iron oxide powder chamber is located directly below the oxygen flow curtain, and the pure iron powder collection chamber is located below the adsorption area of ​​the adjustable electromagnet or permanent magnet.

10. The apparatus for preparing nano-iron powder and iron oxide powder by vacuum low-temperature sublimation of pure iron according to claim 6, characterized in that, The vacuum system of the vacuum sublimation furnace ensures a vacuum level inside the furnace that is better than 1×10⁻⁶. -3 Pa, the electromagnetic heating suspension system heats pure iron to 1100℃ and keeps it suspended, and the atmosphere control system independently controls the introduction and switching of pure oxygen, argon or nitrogen through a mass flow meter.

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