A method for laser-assisted mass production of boron nitride nanotubes

Abstract

The application belongs to the technical field of nanometer material preparation, and specifically discloses a method for laser-assisted mass preparation of boron nitride nanotubes, which comprises the following steps: (1) placing a boron source into a container and erecting a metal net above the container; (2) irradiating the container with a laser under a nitrogen-containing atmosphere; and (3) after the irradiation is completed, cooling the container and collecting the product. By using the erected metal net as an activator for the reaction of the boron source with nitrogen, the reactivity of nitrogen molecules is improved, and the introduction of metal impurities in the reaction of the boron source is avoided. The process of the application is suitable for various types of boron sources and metal nets, is simple, has high yield, and can realize high-quality and macro-quantity production of boron nitride nanotubes with complete shape, high crystallinity and good mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, specifically relating to a method for laser-assisted mass production of boron nitride nanotubes. Background Technology

[0002] Boron nitride nanotubes (BNNTs) have a similar structure to carbon nanotubes. In a graphite-like layer, alternating boron and nitrogen atoms completely replace carbon atoms, with minimal change in interatomic spacing. The boron-nitrogen and carbon-carbon units have the same number of valence electrons. In the hexagonal boron nitride plane, a boron atom and a nitrogen atom undergo sp2 hybridization to form three boron-nitrogen covalent bonds, creating a graphite-like planar hexagonal network structure.

[0003] Boron nitride nanotubes, as insulating materials, possess extremely high mechanical strength, thermal conductivity, and thermal stability. Existing methods for preparing boron nitride nanotubes mostly focus on chemical vapor deposition (CVD) and ball milling. For example, Chinese patent CN101717077A discloses a technique for generating boron nitride nanotubes by mixing boron powder and metal oxides, using reducing metal particles as a catalyst, and then introducing nitrogen gas and maintaining a high temperature. However, this method suffers from drawbacks such as difficulty in controlling the diameter of the boron nitride nanotubes, poor process stability, low purity, and low efficiency.

[0004] Chinese Patent CN107758633A discloses a technique for producing boron nitride nanotubes by ball milling boron powder and a catalyst into boron powder, directly ball milling the boron powder with iron-containing ball milling beads to obtain a highly active precursor, and then reacting it in a high-temperature deposition furnace containing a nitrogen source. However, this method suffers from problems such as low quality, the presence of other boron nitride impurities, and poor crystallization performance. Therefore, there is an urgent need to provide a technical solution that can both mass-produce boron nitride nanotubes and significantly improve their quality.

[0005] US Patent No. 8679300B2 discloses a technique for preparing boron nitride nanotubes by using a laser to heat a boron source in a pressurized chamber, followed by cooling the boron vapor with a condenser to react it with a nitrogen source in the chamber. This method can yield boron nitride nanotubes with high crystallinity and few walls. However, due to the lack of a catalyst, it suffers from low preparation efficiency. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for laser-assisted mass production of boron nitride nanotubes.

[0007] To achieve the above objectives, according to one aspect of the present invention, a method for laser-assisted mass production of boron nitride nanotubes is provided, the method comprising the following steps:

[0008] (1) Place the boron source into a container and set up a metal mesh above the container;

[0009] (2) Irradiate the container with a laser in a nitrogen-containing atmosphere;

[0010] (3) After irradiation, cool the container and collect the product.

[0011] Preferably, the boron source in step (1) is at least one of boron oxide, boron powder, boric acid, hexagonal boron nitride, and ammoniaborane.

[0012] Preferably, the metal mesh in step (1) is one of stainless steel mesh, copper mesh, nickel mesh, iron mesh, zinc mesh, aluminum mesh, lead mesh, molybdenum mesh, chromium mesh, and cobalt mesh.

[0013] Preferably, the metal mesh aperture in step (1) is 1-5000 mesh.

[0014] Preferably, the distance between the metal mesh and the boron source in step (1) is 2-200 cm.

[0015] Preferably, the nitrogen-containing atmosphere in step (2) is at least one of ammonia, nitrogen, nitric oxide, and nitrogen dioxide.

[0016] Preferably, the nitrogen-containing atmosphere pressure in step (2) is 0.2MPa-5MPa.

[0017] Preferably, the effective laser power in step (2) is 200W-10kW.

[0018] According to another aspect of the present invention, boron nitride nanotubes prepared by the above method are also provided.

[0019] According to another aspect of the invention, the invention also provides the application of the above-described boron nitride nanotubes in insulating materials.

[0020] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0021] 1. The process of the present invention adds a metal mesh to the laser radiation process. The presence of the metal mesh increases the activity of nitrogen molecules, thereby increasing the reaction rate and yield of boron nitride nanotubes. On the other hand, it avoids the introduction of metal impurities into the product by directly placing metal particles in the boron source, which would lead to poor electrical insulation.

[0022] 2. This invention uses a laser beam of preferred power to bombard a boron target, which can rapidly heat the boron source to the evaporation temperature, thereby inducing the generation of boron nanoliquid required for the growth of boron nitride nanotubes. No other precursors or by-products are generated, which improves the preparation yield and ensures the purity of the product.

[0023] 3. The process of this invention is rapid, and boron nitride nanotube products can be obtained within several to tens of minutes. In addition, the sources of boron and metal mesh are widely available, which greatly saves energy consumption and process costs. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the process for preparing boron nitride nanotubes according to the present invention.

[0025] Figure 2 This is a high-magnification SEM image of the boron nitride nanotubes obtained in Example 1 of the present invention.

[0026] Figure 3 This is an SEM image of the product obtained in Comparative Example 1 without using a metal mesh. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0028] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0029] Example 1

[0030] (1) Weigh the boron powder and put it into an open container; cut a metal mesh with a 1-mesh aperture;

[0031] (2) Place the container containing boron powder into the laser equipment, set up the metal mesh, keep the height of the mesh at 2cm, and cover it with the quartz glass window;

[0032] (3) Turn on the main switch of the laser equipment, the chiller switch and the laser switch, adjust the nitrogen atmosphere pressure to a stable 0.2MPa, adjust the laser power to 200W, press the laser enable button to start laser irradiation for a certain period of time, and observe the laser processing situation in the laser equipment cavity at any time.

[0033] (4) Completely remove the residual gas from the laser equipment and wait for the temperature inside the laser equipment to drop to 50°C before recovering the product.

[0034] In this embodiment, during laser irradiation, boron is initially heated and melted within the chamber, forming macroscopic boron spheres. Upon reaching boiling point, the boron spheres begin to evaporate, generating a vertical gas plume. Once the boron vapor in the gas plume condenses into molten boron nanodroplets as the temperature decreases, nitrogen molecules from the surrounding environment permeate to the surface of the boron nanodroplets. Due to its high chemical reactivity in the liquid phase, boron can dissociate nitrogen molecules into individual atoms. These nitrogen atoms migrate on the surface under the influence of surface diffusion, assembling into hexagonal boron nitride structures. Nitrogen atoms on the outer surface of the boron droplets diffuse towards the boundary of the boron nitride, where they combine with boron atoms, causing the planar hexagonal boron nitride structure to gradually evolve into a cylindrical structure. The final SEM image of the resulting boron nitride nanotubes is shown below. Figure 1 As shown.

[0035] Example 2

[0036] This embodiment is basically similar to Embodiment 1 in terms of conditions, except that the boron source is boron oxide, the height of the metal mesh is 100cm, the aperture is 2500 mesh, the nitrogen atmosphere pressure is 1MPa, and the laser power is 3000W.

[0037] Example 3

[0038] This embodiment is basically similar to Embodiment 1 in terms of conditions, except that the boron source is boric acid, the height of the metal mesh is 200cm, the aperture is 5000 mesh, the nitrogen atmosphere pressure is 5MPa, and the laser power is 10000W.

[0039]

[0040] Comparative Example 1

[0041] The difference between Comparative Example 1 and Example 1 is that no metal mesh was used during the laser irradiation process. The SEM image of the obtained product is shown below. Figure 3 As shown, no nanotubes were formed.

[0042] As can be seen from the above embodiments and comparative examples, this solution is applicable to various types of boron sources and metal meshes, has a wide range of applications, simple process, and high output; the boron nitride nanotubes have complete shape, high crystallinity, and good mechanical properties, which can realize high-quality and large-scale production of boron nitride nanotubes.

[0043] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for laser-assisted mass production of boron nitride nanotubes, characterized in that, The method includes the following steps: (1) Place the boron source in a container and set up a metal mesh above the container; the metal mesh is one of stainless steel mesh, copper mesh, nickel mesh, iron mesh, zinc mesh, aluminum mesh, lead mesh, molybdenum mesh, chromium mesh, and cobalt mesh; the height of the metal mesh from the boron source is 2-200cm; (2) In a nitrogen-containing atmosphere, the container is irradiated with a laser; the presence of a metal mesh increases the activity of nitrogen molecules; boron is initially heated and melted by the laser in the chamber to form macroscopic boron spheres. When the boiling temperature is reached, the boron spheres begin to evaporate, generating a vertical gas plume; once the boron vapor in the gas plume condenses into molten boron nanodroplets as the temperature decreases, nitrogen molecules from the surrounding area permeate to the surface of the boron nanodroplets. Due to the high chemical reactivity in the liquid phase, boron dissociates nitrogen molecules into individual atoms. These nitrogen atoms migrate on the surface under the influence of surface diffusion and assemble into a hexagonal boron nitride structure; nitrogen atoms on the outer surface of the boron droplet diffuse toward the boundary of the boron nitride, where they combine with boron atoms, thereby causing the planar hexagonal boron nitride structure to gradually evolve into a cylindrical structure. (3) After irradiation, cool the container and collect the product.

2. The method for laser-assisted mass production of boron nitride nanotubes according to claim 1, characterized in that, The boron source mentioned in step (1) is at least one of boron oxide, boron powder, boric acid, hexagonal boron nitride, and ammoniaborane.

3. The method for laser-assisted mass production of boron nitride nanotubes according to claim 1, characterized in that, The metal mesh aperture in step (1) is 1-5000 mesh.

4. The method for laser-assisted mass production of boron nitride nanotubes according to claim 1, characterized in that, In step (2), the nitrogen-containing atmosphere is at least one of ammonia, nitrogen, nitric oxide, and nitrogen dioxide.

5. The method for laser-assisted mass production of boron nitride nanotubes according to claim 1, characterized in that, In step (2), the nitrogen-containing atmosphere pressure is 0.2MPa-5MPa.

6. The method for laser-assisted mass production of boron nitride nanotubes according to claim 1, characterized in that, In step (2), the effective power of the laser is 200W-10kW.

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