Method for producing boron nitride nanotubes

Abstract

This application discloses a method for preparing boron nitride nanotubes, comprising placing reactants, including a boron source and a metal sulfide, into a reactor; introducing an inert gas into the reactor and controlling the reactor heating to raise the reactants to the growth temperature under an inert atmosphere, and continuously reacting to generate a low-melting-point precursor during the heating process; introducing ammonia into the reactor to maintain the growth temperature, allowing the low-melting-point precursor to continuously react and grow boron nitride nanotubes; and introducing an inert gas into the reactor and stopping the reactor heating to cool the boron nitride nanotubes to room temperature under an inert atmosphere. The preparation method of this application uses metal sulfide and a boron source as reactants, heating the reactants under an inert atmosphere. During the heating process, sulfur activates boron to generate a low-melting-point precursor. Based on the low-melting-point precursor, a large number of boron nitride nanotubes can be grown at a lower temperature, which contributes to the efficient and low-cost preparation of boron nitride nanotubes.

Description

Technical Field

[0001] This application belongs to the field of nanotube materials technology, specifically relating to a method for preparing boron nitride nanotubes. Background Technology

[0002] BNNTs exhibit excellent physicochemical properties such as oxidation resistance, chemical stability, high thermal conductivity, piezoelectricity, and outstanding mechanical properties. Furthermore, as wide-bandgap insulators, they are unaffected by nanotube diameter and chirality, thus having broad application value in fields such as electronic packaging materials, metal matrix composites, aerospace, and electronic sensors.

[0003] Existing methods for preparing boron nitride nanotubes (BNNTs) mainly include laser ablation, thermal plasma, arc discharge, and chemical vapor deposition (CVD). The first three methods require high-temperature and high-pressure growth conditions, leading to high costs. Furthermore, the combination of boron and nitrogen during the preparation process is unpredictable, resulting in a violent reaction and uncontrollable structure of the boron nitride nanotubes. In contrast, CVD offers good process control, low cost, and provides high-quality boron nitride nanotubes, making it more suitable for industrial manufacturing. Currently, BOCVD is the most efficient method for preparing BNNTs using CVD. Its mechanism involves the reaction of boron with metal oxides to generate boron oxide vapor and metal vapor, which are then used to prepare boron nitride nanotubes after the addition of ammonia. However, this method requires a relatively high growth temperature that cannot be further reduced, hindering the low-cost and efficient preparation of boron nitride nanotubes. Summary of the Invention

[0004] The purpose of this application is to provide a method for preparing boron nitride nanotubes, in order to solve the problem that the growth temperature of boron nitride nanotubes prepared by the existing BOCVD method is too high and cannot be further reduced.

[0005] To achieve the above objectives, the technical solution adopted in this application is:

[0006] A method for preparing boron nitride nanotubes is provided, comprising:

[0007] The reactants are placed into the reactor, and the reactants include a boron source and a metal sulfide;

[0008] An inert gas is introduced into the reactor and the reactor is heated to raise the temperature of the reaction raw materials to the growth temperature under an inert atmosphere, and the reaction continues to generate a low-melting-point precursor during the heating process.

[0009] Ammonia gas is introduced into the reactor to maintain the growth temperature, so that the low-melting-point precursor can continuously react and grow boron nitride nanotubes.

[0010] An inert gas is introduced into the reactor and the reactor is controlled to stop heating, so that the boron nitride nanotubes are cooled to room temperature under an inert atmosphere.

[0011] In one or more embodiments, the metal sulfide includes one or more combinations of lithium sulfide, ferrous sulfide, magnesium sulfide, and nickel sulfide, and the lower limit of the growth temperature range is 800–1000°C.

[0012] In one or more embodiments, the molar ratio of the metal sulfide to the boron source is 1:(1 to 3).

[0013] In one or more embodiments, the metal sulfide is lithium sulfide, and the growth temperature is greater than or equal to 900°C.

[0014] In one or more embodiments, the metal sulfide is ferrous sulfide, and the growth temperature is greater than or equal to 950°C.

[0015] In one or more embodiments, the metal sulfide is magnesium sulfide or nickel sulfide, and the growth temperature is greater than or equal to 1000°C.

[0016] In one or more embodiments, the reaction raw materials further include a sulfur source, the molar ratio of the metal sulfide, the boron source and the sulfur source is 1:2:(0.5-3), and the lower limit of the growth temperature range is 800-950°C.

[0017] In one or more embodiments, the metal sulfide is lithium sulfide, and the growth temperature is greater than or equal to 800°C.

[0018] In one or more embodiments, the metal sulfide is ferrous sulfide, and the growth temperature is greater than or equal to 900°C.

[0019] In one or more embodiments, the metal sulfide is magnesium sulfide or nickel sulfide, and the growth temperature is greater than or equal to 950°C.

[0020] In one or more embodiments, in the step of introducing an inert gas into the reactor and controlling the reactor to heat it so that the reactants are heated to the growth temperature under an inert atmosphere and continue to react to generate a low-melting-point precursor during the heating process, the flow rate of the inert gas is 20 to 100 sccm, and the heating is specifically a uniform heating rate of 10 to 30 °C / min.

[0021] In one or more embodiments, in the step of introducing ammonia gas into the reactor and maintaining the growth temperature so that the low-melting-point precursor can continuously react and grow boron nitride nanotubes, the flow rate of the ammonia gas is 20-100 sccm, and the growth time of the boron nitride nanotubes is 60-180 min.

[0022] The advantages of this application, which differ from existing technologies, are:

[0023] The preparation method of this application uses metal sulfide and boron source as reaction raw materials. The reaction raw materials are heated under an inert atmosphere. During the heating process, sulfur activates boron to generate a low-melting-point precursor: metal-BS system. Based on the low-melting-point precursor, a large number of boron nitride nanotubes can be grown at a relatively low temperature of 800-1000℃, which helps to prepare boron nitride nanotubes efficiently and at low cost. 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 description of the embodiments or the prior art 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 without creative effort.

[0025] Figure 1 This is a schematic flowchart of one embodiment of the method for preparing boron nitride nanotubes according to this application;

[0026] Figure 2 This is the FTIR spectrum of the boron nitride nanotubes prepared in Example 13 of this application;

[0027] Figure 3 This is a scanning electron microscope image of the boron nitride nanotubes prepared in Example 13 of this application;

[0028] Figure 4 This is a scanning electron microscope image of the tip of the boron nitride nanotube prepared in Example 13 of this application;

[0029] Figure 5 These are scanning electron microscope (SEM) images of boron nitride nanotubes prepared in Examples 1 to 3 and Comparative Example 1 of this application;

[0030] Figure 6 These are scanning electron microscope images of boron nitride nanotubes prepared in Examples 4 to 6 and Comparative Example 2 of this application;

[0031] Figure 7 These are scanning electron microscope images of boron nitride nanotubes prepared in Examples 7 to 9 and Comparative Example 3 of this application;

[0032] Figure 8These are scanning electron microscope (SEM) images of boron nitride nanotubes prepared in Examples 10 to 12 and Comparative Example 4 of this application;

[0033] Figure 9 These are scanning electron microscope images of boron nitride nanotubes prepared in Examples 13 to 15 and Comparative Example 5 of this application;

[0034] Figure 10 These are scanning electron microscope (SEM) images of boron nitride nanotubes prepared in Examples 16 to 18 and Comparative Example 6 of this application;

[0035] Figure 11 These are scanning electron microscope images of boron nitride nanotubes prepared in Examples 19 to 21 and Comparative Example 7 of this application;

[0036] Figure 12 These are scanning electron microscope images of boron nitride nanotubes prepared in Examples 22 to 24 and Comparative Example 8 of this application;

[0037] Figure 13 These are the XPS spectra of the low-melting-point precursors prepared in Examples 1, 4, 7, and 10 of this application;

[0038] Figure 14 This is a Raman spectrum analysis of the boron nitride nanotubes prepared in the embodiments of this application;

[0039] Figure 15 This is the XRD pattern of the product of Example 5 of this application;

[0040] Figure 16 This is the FTIR spectrum of the product of Example 5 of this application;

[0041] Figure 17 This is a scanning electron microscope image of the product at 800°C in Example 5 of this application. Detailed Implementation

[0042] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0043] Boron nitride nanotubes (BNNTs) are hexagonal nanotubes composed of boron and nitrogen atoms, with a structure similar to carbon nanotubes. BNNTs possess high thermal conductivity and mechanical strength similar to carbon nanotubes, with a Young's modulus of ~1.2 TPa. Unlike carbon nanotubes, BNNTs are insulators with a band gap of 5.5 to 6.0 eV. More importantly, BNNTs exhibit high oxidation resistance in air up to 800°C and in inert atmospheres up to 2800°C.

[0044] Therefore, BNNTs have very broad application prospects in microelectromechanical systems (MEMS), biomedicine (targeted drug delivery and neutron capture therapy, etc.), cathodoluminescence, and solid-state neutron detectors. In addition, BNNTs can also serve as a very useful nanofiller, improving the thermal conductivity of fiber and polymer films. Furthermore, they have potential applications in spintronic devices and various nanoscale and microscale electronics.

[0045] The main methods for synthesizing boron nuclei (BNNTs) include arc discharge, laser heating, induction thermal plasma, chemical vapor deposition (CVD), ball milling, and annealing. The first three methods require high-temperature, high-pressure growth conditions (up to 5000°C / 1.4 MPa), which significantly increases production costs and leads to unpredictable boron and nitrogen combination, resulting in poor product purity. In contrast, the CVD method offers good process control, low cost, and provides high-quality BNNTs, making it more suitable for industrial manufacturing.

[0046] Currently, BOCVD is a highly efficient method for CVD preparation of boron nitride nanotubes. Its mechanism involves the reaction of boron with metal oxides to generate boron oxide vapor and metal vapor, which are then used to prepare boron nitride nanotubes after the addition of ammonia. However, this method requires a relatively high growth temperature, which cannot be further reduced, hindering the low-cost and efficient preparation of boron nitride nanotubes.

[0047] To address the aforementioned issues, the applicant has developed a novel method for preparing boron nitride nanotubes (BNNTs). This method is based on an activation reaction between sulfur and boron, whereby high-melting-point boron is activated by sulfur to obtain a low-melting-point precursor. BNNTs are then grown using this low-melting-point precursor, effectively reducing the growth temperature of BNNTs and thus significantly lowering the growth cost. This enables the low-cost and efficient preparation of BNNTs.

[0048] Specifically, please refer to Figure 1 , Figure 1 This is a schematic flowchart of one embodiment of the method for preparing boron nitride nanotubes according to this application.

[0049] like Figure 1 As shown, the preparation method includes:

[0050] S100. Place the reaction raw materials into the reactor.

[0051] In one embodiment, the reaction raw materials may consist of a boron source and a metal sulfide.

[0052] The boron source can be boron powder, or other materials containing boron such as boron oxide or sodium tetraborate, or a combination of multiple materials containing boron, all of which can achieve the effect of this embodiment.

[0053] Metal sulfides can be one or more combinations of lithium sulfide, ferrous sulfide, magnesium sulfide, and nickel sulfide.

[0054] The molar ratio of metal sulfide to boron source can be 1:(1-3); preferably, the molar ratio of metal sulfide to boron source can be 1:2.

[0055] In another embodiment, the reaction raw materials may also include a sulfur source.

[0056] The sulfur source can be sulfur powder or other sulfur-containing materials.

[0057] The molar ratio of metal sulfide, boron source and sulfur source can be 1:2:(0.5-3); preferably, the molar ratio of metal sulfide, boron source and sulfur source can be 1:2:1.

[0058] S200: Inert gas is introduced into the reactor and the reactor is heated to raise the temperature of the reactants to the growth temperature under an inert atmosphere, and the reaction continues to generate low-melting-point precursors during the heating process.

[0059] In one embodiment, the flow rate of the inert gas can be 20 to 100 sccm, and the inert gas can be argon; preferably, the inert gas can be argon at a flow rate of 50 sccm.

[0060] In one embodiment, when the reactants consist of a boron source and a metal sulfide, the reactants are heated under an inert atmosphere. Based on the activation effect of S on B, B and MeS can continue to react during the heating process to generate a low-melting-point Me-BS system, i.e., a low-melting-point precursor. The melting point of this low-melting-point precursor is lower than that of boron, thereby enabling the subsequent growth of BNNTs at a lower temperature.

[0061] In another embodiment, when the reactants consist of a boron source, a metal sulfide, and a sulfur source, the addition of the sulfur source can further enhance the activation effect of sulfur on boron, thereby accelerating the reaction to generate a low-melting-point Me-BS system.

[0062] In one embodiment, in order to ensure a stable and continuous reaction of S and B, the temperature can be increased at a constant rate of 10 to 30 °C / min; preferably, the temperature can be increased at a constant rate of 20 °C / min.

[0063] S300. Ammonia gas is introduced into the reactor to maintain the growth temperature, so that the low-melting-point precursor can continue to react and grow boron nitride nanotubes.

[0064] After the low-melting-point precursor is generated by the reaction, ammonia gas can be introduced and the growth temperature can be maintained, thereby allowing the precursor to react and generate boron nitride nanotubes.

[0065] Since low-melting-point precursors have lower melting points, the growth temperature can be lower than that of conventional BOCVD methods.

[0066] In one embodiment, when the metal sulfide is one or more combinations of lithium sulfide, ferrous sulfide, magnesium sulfide, and nickel sulfide, the growth temperature can be less than or equal to 1000°C and greater than or equal to 800°C.

[0067] Of course, higher growth temperatures can also be used to prepare boron nitride nanotubes, but higher growth temperatures are not conducive to reducing the preparation cost of boron nitride nanotubes. That is, the lower limit of the growth temperature range can be 800-1000℃, thereby significantly reducing the preparation cost.

[0068] Specifically, the lower limit of the growth temperature can vary depending on the choice of metal sulfide and whether the reaction raw materials include a sulfur source.

[0069] For example, when the reaction raw materials consist of a boron source and a metal sulfide, the metal sulfide is lithium sulfide, and the growth temperature can be greater than or equal to 900°C; the metal sulfide is ferrous sulfide, and the growth temperature is greater than or equal to 950°C; the metal sulfide is magnesium sulfide or nickel sulfide, and the growth temperature is greater than or equal to 1000°C.

[0070] When the reaction raw materials consist of a boron source, a metal sulfide, and a sulfur source, the metal sulfide is lithium sulfide, with a growth temperature greater than or equal to 800℃; the metal sulfide is ferrous sulfide, with a growth temperature greater than or equal to 900℃; the metal sulfide is magnesium sulfide or nickel sulfide, with a growth temperature greater than or equal to 950℃.

[0071] Understandably, the addition of a sulfur source to the reaction feedstock can further promote the activation reaction of S on B, forming a low-melting-point Me-BS system, which in turn helps to grow boron nitride nanotubes at a lower growth temperature.

[0072] S400: Inert gas is introduced into the reactor and the reactor is stopped from heating, so that the boron nitride nanotubes are cooled to room temperature under an inert atmosphere.

[0073] The effects of the technical solution of this application will be further explained in detail below with reference to specific embodiments.

[0074] Example 1:

[0075] A boron nitride nanotube was prepared by the following method:

[0076] Lithium sulfide and boron powder are mixed and placed in a boron nitride boat, which is then placed in the center of a tube furnace for heating. The molar ratio of lithium sulfide to boron powder is 1:2.

[0077] Argon gas of 50 sccm is introduced into the tube furnace, and the heating of the tube furnace is controlled so that the center of the tube furnace is heated at a uniform rate of 20℃ / min until the center of the tube furnace reaches 900℃, and the reaction yields a low melting point precursor.

[0078] Stop introducing argon into the tubular furnace, simultaneously introduce 50 sccm of ammonia into the tubular furnace, and control the center of the tubular furnace to maintain 900℃ to continuously grow boron nitride nanotubes.

[0079] After 120 minutes of growth, the ammonia gas was stopped, and 50 sccm of argon gas was simultaneously introduced into the tube furnace. The tube furnace was then stopped heating, allowing the boron nitride nanotubes to cool naturally to room temperature under an inert atmosphere, thus obtaining boron nitride nanotubes.

[0080] Example 2:

[0081] A boron nitride nanotube was prepared by the following method:

[0082] Lithium sulfide and boron powder are mixed and placed in a boron nitride boat. The boron nitride boat is placed in the center of a tube furnace for heating. The molar ratio of lithium sulfide to boron powder is 1:1.

[0083] Argon gas of 20 sccm is introduced into the tubular furnace, and the heating of the tubular furnace is controlled so that the center of the tubular furnace is heated at a uniform rate of 10℃ / min until the center of the tubular furnace reaches 1000℃, and the reaction yields a low melting point precursor.

[0084] Stop introducing argon into the tubular furnace, simultaneously introduce 20 sccm of ammonia into the tubular furnace, and control the center of the tubular furnace to maintain 1000℃ to continuously grow boron nitride nanotubes.

[0085] After 180 minutes of growth, the ammonia gas was stopped, and 20 sccm of argon gas was simultaneously introduced into the tube furnace. The tube furnace was then stopped heating, allowing the boron nitride nanotubes to cool naturally to room temperature under an inert atmosphere, thus obtaining boron nitride nanotubes.

[0086] Example 3:

[0087] A boron nitride nanotube was prepared by the following method:

[0088] Lithium sulfide and boron powder are mixed and placed in a boron nitride boat, which is then placed in the center of a tube furnace for heating. The molar ratio of lithium sulfide to boron powder is 1:3.

[0089] Argon gas of 100 sccm is introduced into the tube furnace, and the heating of the tube furnace is controlled so that the center of the tube furnace is heated at a uniform rate of 30℃ / min until the center of the tube furnace reaches 1100℃, and the reaction yields a low melting point precursor.

[0090] Stop introducing argon into the tubular furnace, simultaneously introduce 100 sccm of ammonia into the tubular furnace, and control the center of the tubular furnace to maintain 1100℃ to continuously grow boron nitride nanotubes.

[0091] After 60 minutes of growth, the ammonia gas was stopped, and 100 sccm of argon gas was simultaneously introduced into the tube furnace. The tube furnace was then stopped heating, allowing the boron nitride nanotubes to cool naturally to room temperature under an inert atmosphere, thus obtaining boron nitride nanotubes.

[0092] Example 4:

[0093] A boron nitride nanotube was prepared using the same method as in Example 1, except that:

[0094] In Example 4, ferrous sulfide was used instead of lithium sulfide in Example 1.

[0095] The growth temperature in Example 4 was 950°C.

[0096] Example 5:

[0097] A boron nitride nanotube was prepared using the same method as in Example 2, except that in Example 5, ferrous sulfide was used instead of lithium sulfide in Example 2.

[0098] The growth temperature in Example 5 was 1050℃.

[0099] Example 6:

[0100] A boron nitride nanotube was prepared using the same method as in Example 3, except that:

[0101] In Example 6, ferrous sulfide was used instead of lithium sulfide in Example 3.

[0102] The growth temperature in Example 6 was 1150°C.

[0103] Example 7:

[0104] A boron nitride nanotube was prepared using the same method as in Example 1, except that:

[0105] In Example 7, magnesium sulfide was used instead of lithium sulfide in Example 1;

[0106] The growth temperature in Example 7 was 1000℃.

[0107] Example 8:

[0108] A boron nitride nanotube was prepared using the same method as in Example 2, except that:

[0109] In Example 8, magnesium sulfide was used instead of lithium sulfide in Example 2.

[0110] The growth temperature in Example 8 was 1100℃.

[0111] Example 9:

[0112] A boron nitride nanotube was prepared using the same method as in Example 3, except that:

[0113] In Example 9, magnesium sulfide was used instead of lithium sulfide in Example 3.

[0114] The growth temperature in Example 9 was 1200℃.

[0115] Example 10:

[0116] A boron nitride nanotube was prepared using the same method as in Example 1, except that:

[0117] In Example 10, nickel sulfide was used instead of lithium sulfide in Example 1.

[0118] The growth temperature in Example 10 was 1000℃.

[0119] Example 11:

[0120] A boron nitride nanotube was prepared using the same method as in Example 2, except that:

[0121] In Example 11, nickel sulfide was used instead of lithium sulfide in Example 2.

[0122] The growth temperature in Example 11 was 1100℃.

[0123] Example 12:

[0124] A boron nitride nanotube was prepared using the same method as in Example 3, except that:

[0125] In Example 12, nickel sulfide was used instead of lithium sulfide in Example 3.

[0126] The growth temperature in Example 12 was 1200℃.

[0127] Example 13:

[0128] A boron nitride nanotube was prepared by the following method:

[0129] Lithium sulfide, boron powder, and sulfur powder are mixed and placed in a boron nitride boat. The boron nitride boat is placed in the center of a tube furnace for heating. The molar ratio of lithium sulfide to boron powder is 1:2:1.

[0130] 50 sccm of argon gas was introduced into the tubular furnace, and the heating of the tubular furnace was controlled so that the center of the tubular furnace was heated at a uniform rate of 20℃ / min until the center of the tubular furnace reached 800℃.

[0131] Stop introducing argon into the tubular furnace, simultaneously introduce 50 sccm of ammonia into the tubular furnace, and control the center of the tubular furnace to maintain 800℃ to continuously grow boron nitride nanotubes.

[0132] After 120 minutes of growth, the ammonia gas was stopped, and 50 sccm of argon gas was simultaneously introduced into the tube furnace. The tube furnace was then stopped heating, allowing the boron nitride nanotubes to cool naturally to room temperature under an inert atmosphere, thus obtaining boron nitride nanotubes.

[0133] Example 14:

[0134] A boron nitride nanotube was prepared by the following method:

[0135] Lithium sulfide, boron powder, and sulfur powder are mixed and placed in a boron nitride boat. The boron nitride boat is placed in the center of a tube furnace for heating. The molar ratio of lithium sulfide, boron powder, and sulfur powder is 1:2:0.5.

[0136] Introduce 20 sccm of argon gas into the tubular furnace and control the heating of the tubular furnace so that the center of the tubular furnace heats up at a uniform rate of 10℃ / min until the center of the tubular furnace reaches 900℃.

[0137] Stop introducing argon into the tubular furnace, simultaneously introduce 20 sccm of ammonia into the tubular furnace, and control the center of the tubular furnace to maintain 900℃ to continuously grow boron nitride nanotubes.

[0138] After 180 minutes of growth, the ammonia gas was stopped, and 20 sccm of argon gas was simultaneously introduced into the tube furnace. The tube furnace was then stopped heating, allowing the boron nitride nanotubes to cool naturally to room temperature under an inert atmosphere, thus obtaining boron nitride nanotubes.

[0139] Example 15:

[0140] A boron nitride nanotube was prepared by the following method:

[0141] Lithium sulfide, boron powder, and sulfur powder are mixed and placed in a boron nitride boat. The boron nitride boat is placed in the center of a tube furnace for heating. The molar ratio of lithium sulfide, boron powder, and sulfur powder is 1:2:3.

[0142] 100 sccm of argon gas was introduced into the tubular furnace, and the heating of the tubular furnace was controlled so that the center of the tubular furnace was heated at a uniform rate of 30℃ / min until the center of the tubular furnace reached 1000℃.

[0143] Stop introducing argon into the tubular furnace, simultaneously introduce 100 sccm of ammonia into the tubular furnace, and control the center of the tubular furnace to maintain 1000℃ to continuously grow boron nitride nanotubes.

[0144] After 60 minutes of growth, the ammonia gas was stopped, and 100 sccm of argon gas was simultaneously introduced into the tube furnace. The tube furnace was then stopped heating, allowing the boron nitride nanotubes to cool naturally to room temperature under an inert atmosphere, thus obtaining boron nitride nanotubes.

[0145] Example 16:

[0146] A boron nitride nanotube was prepared using the same method as in Example 13, except that:

[0147] In Example 16, ferrous sulfide was used instead of lithium sulfide in Example 1.

[0148] The growth temperature in Example 16 was 900°C.

[0149] Example 17:

[0150] A boron nitride nanotube was prepared using the same method as in Example 14, except that ferrous sulfide was used instead of lithium sulfide in Example 14 as the raw material in Example 17.

[0151] The growth temperature in Example 17 was 1000°C.

[0152] Example 18:

[0153] A boron nitride nanotube was prepared using the same method as in Example 15, except that:

[0154] In Example 18, ferrous sulfide was used instead of lithium sulfide in Example 15.

[0155] The growth temperature in Example 18 was 1100°C.

[0156] Example 19:

[0157] A boron nitride nanotube was prepared using the same method as in Example 13, except that:

[0158] In Example 19, magnesium sulfide was used instead of lithium sulfide in Example 1.

[0159] The growth temperature in Example 19 was 950°C.

[0160] Example 20:

[0161] A boron nitride nanotube was prepared using the same method as in Example 14, except that:

[0162] In Example 20, magnesium sulfide was used instead of lithium sulfide in Example 14;

[0163] The growth temperature for Example 20 was 1050°C.

[0164] Example 21:

[0165] A boron nitride nanotube was prepared using the same method as in Example 15, except that:

[0166] In Example 21, magnesium sulfide was used instead of lithium sulfide in Example 15.

[0167] The growth temperature for Example 21 was 1150°C.

[0168] Example 22:

[0169] A boron nitride nanotube was prepared using the same method as in Example 13, except that:

[0170] In Example 22, nickel sulfide was used instead of lithium sulfide in Example 13.

[0171] The growth temperature for Example 22 was 950°C.

[0172] Example 23:

[0173] A boron nitride nanotube was prepared using the same method as in Example 14, except that:

[0174] In Example 23, nickel sulfide was used instead of lithium sulfide in Example 14.

[0175] The growth temperature for Example 23 was 1050°C.

[0176] Example 24:

[0177] A boron nitride nanotube was prepared using the same method as in Example 15, except that:

[0178] In Example 24, nickel sulfide was used instead of lithium sulfide in Example 15.

[0179] The growth temperature for Example 24 was 1150°C.

[0180] Comparative Example 1:

[0181] A boron nitride nanotube was prepared using the same method as in Example 1, except that the growth temperature of Comparative Example 1 was 800°C.

[0182] Comparative Example 2:

[0183] A boron nitride nanotube was prepared using the same method as in Example 4, except that the growth temperature of Comparative Example 2 was 850°C.

[0184] Comparative Example 3:

[0185] A boron nitride nanotube was prepared using the same method as in Example 7, except that the growth temperature of Comparative Example 3 was 900°C.

[0186] Comparative Example 4:

[0187] A boron nitride nanotube was prepared using the same method as in Example 10, except that the growth temperature of Comparative Example 3 was 900°C.

[0188] Comparative Example 5:

[0189] A boron nitride nanotube was prepared using the same method as in Example 13, except that the growth temperature of Comparative Example 1 was 800°C.

[0190] Comparative Example 2:

[0191] A boron nitride nanotube was prepared using the same method as in Example 4, except that the growth temperature of Comparative Example 2 was 850°C.

[0192] Comparative Example 3:

[0193] A boron nitride nanotube was prepared using the same method as in Example 7, except that the growth temperature of Comparative Example 3 was 900°C.

[0194] Comparative Example 4:

[0195] A boron nitride nanotube was prepared using the same method as in Example 10, except that the growth temperature of Comparative Example 4 was 900°C.

[0196] Comparative Example 5:

[0197] A boron nitride nanotube was prepared using the same method as in Example 13, except that the growth temperature of Comparative Example 5 was 700°C.

[0198] Comparative Example 6:

[0199] A boron nitride nanotube was prepared using the same method as in Example 16, except that the growth temperature of Comparative Example 6 was 900°C.

[0200] Comparative Example 7:

[0201] A boron nitride nanotube was prepared using the same method as in Example 19, except that the growth temperature of Comparative Example 7 was 850°C.

[0202] Comparative Example 8:

[0203] A boron nitride nanotube was prepared using the same method as in Example 22, except that the growth temperature of Comparative Example 8 was 850°C.

[0204] The reaction materials and growth temperatures corresponding to the above embodiments are shown in the table below:

[0205] Group reaction raw materials Growth temperature Comparative Example 1 Lithium sulfide:boron powder = 1:2 800℃ Example 1 Lithium sulfide:boron powder = 1:2 900℃ Example 2 Lithium sulfide:boron powder = 1:1 1000℃ Example 3 Lithium sulfide:boron powder = 1:3 1100℃ Comparative Example 2 Ferrous sulfide:boron powder = 1:2 850℃ Example 4 Ferrous sulfide:boron powder = 1:2 950℃ Example 5 Ferrous sulfide:boron powder = 1:1 1050℃ Example 6 Ferrous sulfide:boron powder = 1:3 1150℃ Comparative Example 3 Magnesium sulfide:boron powder = 1:2 900℃ Example 7 Magnesium sulfide:boron powder = 1:2 1000℃ Example 8 Magnesium sulfide:boron powder = 1:1 1100℃ Example 9 Magnesium sulfide:boron powder = 1:3 1200℃ Comparative Example 4 Nickel sulfide: boron powder = 1:2 900℃ Example 10 Nickel sulfide: boron powder = 1:2 1000℃ Example 11 Nickel sulfide: boron powder = 1:1 1100℃ Example 12 Nickel sulfide:boron powder = 1:3 1200℃ Comparative Example 5 Lithium sulfide:boron powder:sulfur powder = 1:2:1 700℃ Example 13 Lithium sulfide:boron powder:sulfur powder = 1:2:1 800℃ Example 14 Lithium sulfide:boron powder:sulfur powder = 1:2:0.5 900℃ Example 15 Lithium sulfide:boron powder:sulfur powder = 1:2:3 1000℃ Comparative Example 6 Ferrous sulfide:boron powder:sulfur powder = 1:2:1 800℃ Example 16 Ferrous sulfide:boron powder:sulfur powder = 1:2:1 900℃ Example 17 Ferrous sulfide:boron powder:sulfur powder = 1:2:0.5 1000℃ Example 18 Ferrous sulfide:boron powder:sulfur powder = 1:2:3 1100℃ Comparative Example 7 Magnesium sulfide:boron powder:sulfur powder = 1:2:1 850℃ Example 19 Magnesium sulfide:boron powder:sulfur powder = 1:2:1 950℃ Example 20 Magnesium sulfide:boron powder:sulfur powder = 1:2:0.5 1050℃ Example 21 Magnesium sulfide:boron powder:sulfur powder = 1:2:3 1150℃ Comparative Example 8 Nickel sulfide:boron powder:sulfur powder = 1:2:1 850℃ Example 22 Nickel sulfide:boron powder:sulfur powder = 1:2:1 950℃ Example 23 Nickel sulfide:boron powder:sulfur powder = 1:2:0.5 1050℃ Example 24 Nickel sulfide:boron powder:sulfur powder = 1:2:3 1150℃

[0206] Example of effect 1:

[0207] Scanning electron microscopy and Fourier transform infrared spectroscopy were performed on the boron nitride nanotubes prepared in Example 13 to obtain... Figure 2 and Figure 3 .

[0208] Please see Figure 2 , Figure 2 This is the FTIR spectrum of the boron nitride nanotubes prepared in Example 13 of this application. Figure 2 As shown, the FTIR spectrum is displayed at 1520 cm⁻¹. -1 1365cm -1 and 806cm -1 Three absorption zones were identified nearby. 806cm -1 The absorption peak at 1365 cm⁻¹ is due to the BNb bending vibration parallel to the c-axis. -1 The absorption peak at 1520 cm⁻¹ is a characteristic of BN tensile vibration perpendicular to the c-axis. -1 The absorption peak at that point belongs to the vibration of the BN framework along the tangential direction of the nanotube, and is only observed in high-purity, high-crystallinity BNNT.

[0209] Please see Figure 3 , Figure 3 This is a scanning electron microscope (SEM) image of the boron nitride nanotubes prepared in Example 13 of this application. Figure 3 As shown, the boron nitride nanotubes prepared in Example 13 have a hollow tubular structure.

[0210] As can be seen from the above, Example 13 prepared high-purity boron nitride nanotubes.

[0211] In addition, scanning electron microscopy analysis was performed on the ends of the boron nitride nanotubes prepared in Example 13, and the results were obtained. Figure 4 .

[0212] Please see Figure 4 , Figure 4 This is a scanning electron microscope (SEM) image of the tip of the boron nitride nanotube prepared in Example 13 of this application. Figure 4As shown, sulfur was present at the ends of the boron nitride nanotubes prepared in Example 13, proving that sulfur exists in the nanotube precursor material and plays a role in the growth of boron nitride nanotubes.

[0213] Example 2:

[0214] (1) The boron nitride nanotubes prepared in Examples 1 to 3 and Comparative Example 1 were characterized and analyzed to obtain... Figure 5 .

[0215] Please see Figure 5 , Figure 5 These are scanning electron microscope (SEM) images of the boron nitride nanotubes prepared in Examples 1 to 3 and Comparative Example 1 of this application. Figure 5 As shown, Example 1, grown at a growth temperature of 900°C, produced a large number of boron nitride nanotubes, while Examples 2 and 3, grown at growth temperatures of 1000°C and 1100°C, produced even more high-quality boron nitride nanotubes. Comparative Example 1, grown at a growth temperature of 800°C, struggled to grow boron nitride nanotubes.

[0216] As can be seen from the above, when the reaction raw materials are lithium sulfide and boron powder, a large number of boron nitride nanotubes can be grown at a relatively low temperature of 900℃. However, at a growth temperature as low as 800℃, the growth of boron nitride nanotubes cannot be achieved due to the low temperature.

[0217] (2) The boron nitride nanotubes prepared in Examples 4 to 6 and Comparative Example 2 were characterized and analyzed to obtain... Figure 6 .

[0218] Please see Figure 6 , Figure 6 These are scanning electron microscope (SEM) images of the boron nitride nanotubes prepared in Examples 4 to 6 and Comparative Example 2 of this application. Figure 6 As shown, Example 4, with a growth temperature of 950°C, produced a large number of boron nitride nanotubes, while Examples 5 and 6, with growth temperatures of 1050°C and 1150°C, produced even more high-quality boron nitride nanotubes. Comparative Example 2, with a growth temperature of 850°C, struggled to grow boron nitride nanotubes.

[0219] As can be seen from the above, when the reaction raw materials are ferrous sulfide and boron powder, a large number of boron nitride nanotubes can be grown at a relatively low temperature of 950℃. However, at a growth temperature as low as 850℃, the growth of boron nitride nanotubes cannot be achieved due to the excessively low temperature.

[0220] (3) The boron nitride nanotubes prepared in Examples 7 to 9 and Comparative Example 3 were characterized and analyzed to obtain... Figure 7 .

[0221] Please see Figure 7 , Figure 7These are scanning electron microscope (SEM) images of the boron nitride nanotubes prepared in Examples 7 to 9 and Comparative Example 3 of this application. Figure 7 As shown, Example 7, grown at a growth temperature of 1000°C, produced a large number of boron nitride nanotubes, while Examples 8 and 9, grown at growth temperatures of 1100°C and 1200°C, produced even more high-quality boron nitride nanotubes. Comparative Example 3, grown at a growth temperature of 900°C, struggled to produce boron nitride nanotubes.

[0222] As can be seen from the above, when the reaction raw materials are magnesium sulfide and boron powder, a large number of boron nitride nanotubes can be grown at a relatively low temperature of 1000℃, but boron nitride nanotubes cannot be grown at a growth temperature as low as 900℃ due to the low temperature.

[0223] (4) The boron nitride nanotubes prepared in Examples 10 to 12 and Comparative Example 4 were characterized and analyzed to obtain... Figure 8 .

[0224] Please see Figure 8 , Figure 8 These are scanning electron microscope (SEM) images of boron nitride nanotubes prepared in Examples 10 to 12 and Comparative Example 4 of this application. Figure 8 As shown, Example 10, grown at a growth temperature of 1000°C, produced a large number of boron nitride nanotubes, while Examples 11 and 12, grown at 1100°C and 1200°C, produced even more high-quality boron nitride nanotubes. Comparative Example 4, grown at a growth temperature of 900°C, struggled to produce boron nitride nanotubes.

[0225] As can be seen from the above, when the reaction raw materials are nickel sulfide and boron powder, a large number of boron nitride nanotubes can be grown at a relatively low temperature of 1000℃, but boron nitride nanotubes cannot be grown at a growth temperature as low as 900℃ due to the low temperature.

[0226] (5) The boron nitride nanotubes prepared in Examples 13 to 15 and Comparative Example 5 were characterized and analyzed to obtain... Figure 9 .

[0227] Please see Figure 9 , Figure 9 These are scanning electron microscope (SEM) images of boron nitride nanotubes prepared in Examples 13 to 15 and Comparative Example 5 of this application. Figure 9 As shown, Example 13, grown at a growth temperature of 800°C, produced a large number of boron nitride nanotubes, while Examples 14 and 15, grown at 900°C and 1000°C respectively, produced even more high-quality boron nitride nanotubes. Comparative Example 5, grown at a growth temperature of 700°C, failed to produce boron nitride nanotubes.

[0228] As can be seen from the above, when the reaction raw materials are lithium sulfide, boron powder and sulfur powder, a large number of boron nitride nanotubes can be grown at a relatively low temperature of 800℃, but boron nitride nanotubes cannot be grown at a growth temperature as low as 700℃ due to the low temperature.

[0229] (6) The boron nitride nanotubes prepared in Examples 16 to 18 and Comparative Example 6 were characterized and analyzed to obtain... Figure 10 .

[0230] Please see Figure 10 , Figure 10 These are scanning electron microscope (SEM) images of the boron nitride nanotubes prepared in Examples 16 to 18 and Comparative Example 6 of this application. Figure 10 As shown, Example 16, grown at a growth temperature of 900°C, produced a large number of boron nitride nanotubes, while Examples 17 and 18, grown at 1000°C and 1100°C respectively, produced even more high-quality boron nitride nanotubes. Comparative Example 6, grown at 800°C, failed to produce boron nitride nanotubes.

[0231] As can be seen from the above, when the reaction raw materials are ferrous sulfide, boron powder and sulfur powder, a large number of boron nitride nanotubes can be grown at a relatively low temperature of 900℃. However, at a growth temperature as low as 800℃, the growth of boron nitride nanotubes cannot be achieved due to the low temperature.

[0232] (7) The boron nitride nanotubes prepared in Examples 19 to 21 and Comparative Example 7 were characterized and analyzed to obtain... Figure 11 .

[0233] Please see Figure 11 , Figure 11 These are scanning electron microscope (SEM) images of the boron nitride nanotubes prepared in Examples 19 to 21 and Comparative Example 7 of this application. Figure 11 As shown, Example 19, grown at a growth temperature of 950°C, produced a large number of boron nitride nanotubes, while Examples 20 and 21, grown at growth temperatures of 1050°C and 1150°C, produced even more high-quality boron nitride nanotubes. Comparative Example 7, grown at a growth temperature of 850°C, struggled to grow boron nitride nanotubes.

[0234] As can be seen from the above, when the reaction raw materials are magnesium sulfide, boron powder and sulfur powder, a large number of boron nitride nanotubes can be grown at a relatively low temperature of 950℃. However, at a growth temperature as low as 850℃, the growth of boron nitride nanotubes cannot be achieved due to the low temperature.

[0235] (8) The boron nitride nanotubes prepared in Examples 22 to 24 and Comparative Example 8 were characterized and analyzed to obtain... Figure 12 .

[0236] Please see Figure 12 , Figure 12These are scanning electron microscope (SEM) images of the boron nitride nanotubes prepared in Examples 22 to 24 and Comparative Example 8 of this application. Figure 12 As shown, Example 22, grown at a growth temperature of 950°C, produced a large number of boron nitride nanotubes, while Examples 23 and 24, grown at growth temperatures of 1050°C and 1150°C, produced even more high-quality boron nitride nanotubes. Comparative Example 8, grown at a growth temperature of 850°C, struggled to grow boron nitride nanotubes.

[0237] As can be seen from the above, when the reaction raw materials are nickel sulfide, boron powder and sulfur powder, a large number of boron nitride nanotubes can be grown at a relatively low temperature of 950℃. However, at a growth temperature as low as 850℃, the growth of boron nitride nanotubes cannot be achieved due to the low temperature.

[0238] Based on the above experiments, it can be seen that using metal sulfides and boron powder as raw materials can achieve the mass growth of boron nitride nanotubes at a lower temperature; at the same time, adding sulfur powder to the raw materials can further reduce the growth temperature, and can achieve the mass growth of boron nitride nanotubes at an even lower temperature.

[0239] Example of effect 3:

[0240] To demonstrate that the metal sulfide and boron powder reacted during argon heating to generate a low-melting-point precursor, X-ray photoelectron spectroscopy analysis was performed on the low-melting-point precursors prepared in Examples 1, 4, 7, and 10, yielding... Figure 13 .

[0241] Please see Figure 13 , Figure 13 These are the XPS spectra of the low-melting-point precursors prepared in Examples 1, 4, 7, and 10 of this application. Figure 13 As shown, the low-melting-point precursors prepared in Examples 1, 4, 7, and 10 all include metal-sulfur bonds, metal-boron bonds, and boron-sulfur bonds. Therefore, it can be seen that the reaction raw materials of this application were used to prepare a low-melting-point metal-BS system during the heating process under an inert atmosphere.

[0242] Example of effect 4:

[0243] Raman spectroscopy analysis was performed on the boron nitride nanotubes prepared in Examples 1 to 24 of this application to obtain... Figure 13 .

[0244] Please see Figure 14 , Figure 14 This is the Raman spectrum analysis of the boron nitride nanotubes prepared in the embodiments of this application. Figure 14 As shown, the Raman spectra of the boron nitride nanotubes prepared in Examples 1 to 24 of this application all show a value at 1368 cm⁻¹. -1 There is a strong absorption band at this point, which is related to the E2g in-plane vibration mode of h-BN.

[0245] As can be seen from the above, the high-purity boron nitride nanotubes prepared in Examples 1 to 24 of this application are all high-purity boron nitride nanotubes.

[0246] Example 5:

[0247] To demonstrate the activation effect of sulfur on boron during the heating process of the reaction raw materials in this application, an experiment was designed using sulfur powder and boron powder as raw materials; the specific experimental contents are as follows:

[0248] Sulfur powder and boron powder were mixed in a 1:1 molar ratio and added to a boron nitride boat. The boron nitride boat was placed in the center of a tube furnace for heating. Argon gas at 50 sccm was introduced into the tube furnace, and the heating was controlled to maintain a uniform temperature rise of 20℃ / min at the center of the furnace. The temperature was raised to 800℃, 900℃, and 1000℃ respectively. The product was analyzed by XRD diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Figures 15 to 17 .

[0249] Please see Figure 15 , Figure 15 This is the XRD pattern of the product of Example 5 of this application. For example... Figure 15 As shown, B2S3 appeared in the products at 800℃, 900℃, and 1000℃, indicating that sulfur can react with boron powder and can activate boron.

[0250] Please see Figure 16 , Figure 16 This is the FTIR spectrum of the product of Example 5 of this application. For example... Figure 16 As shown, the FTIR spectra of the products at 800℃, 900℃, and 1000℃ are displayed at 990 cm⁻¹. -1 and 772cm -1 Two absorption regions were obtained nearby, one at 990cm. -1 The peak belongs to the six-membered ring vibration mode, 772 cm⁻¹ -1 The peak belongs to the vibration mode of the B3(0) group, which proves that B2S3 is present in the product, indicating that sulfur can activate boron.

[0251] Please see Figure 17 , Figure 17 This is a scanning electron microscope (SEM) image of the product at 800°C in Example 5 of this application. Figure 17 As shown, the product at 800℃ contains B and S elements, proving that it is a BS compound, indicating that sulfur can activate boron.

[0252] In summary, the experiments show that the preparation method of this application, by activating high-melting-point boron through the reaction of sulfur and boron, can achieve the mass growth of boron nitride nanotubes at a relatively low temperature of 800-1000℃.

[0253] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0254] 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 preparing boron nitride nanotubes, characterized in that, include: The reactants are placed in the reactor, and the reactants include a boron source and a metal sulfide; An inert gas is introduced into the reactor and the reactor is heated to raise the temperature of the reaction raw materials to the growth temperature under an inert atmosphere, and the reaction continues to generate a low-melting-point precursor during the heating process. Ammonia gas is introduced into the reactor to maintain the growth temperature, so that the low-melting-point precursor can continuously react and grow boron nitride nanotubes. An inert gas is introduced into the reactor and the reactor is controlled to stop heating, so that the boron nitride nanotubes are cooled to room temperature under an inert atmosphere.

2. The preparation method according to claim 1, characterized in that, The metal sulfide includes one or more combinations of lithium sulfide, ferrous sulfide, magnesium sulfide, and nickel sulfide, and the lower limit of the growth temperature range is 800~1000℃.

3. The preparation method according to claim 2, characterized in that, The molar ratio of the metal sulfide to the boron source is 1:(1~3).

4. The preparation method according to claim 2, characterized in that, The metal sulfide is lithium sulfide, and the growth temperature is greater than or equal to 900°C.

5. The preparation method according to claim 2, characterized in that, The metal sulfide is ferrous sulfide, and the growth temperature is greater than or equal to 950°C.

6. The preparation method according to claim 2, characterized in that, The metal sulfide is magnesium sulfide or nickel sulfide, and the growth temperature is greater than or equal to 1000°C.

7. The preparation method according to claim 2, characterized in that, The reaction raw materials also include sulfur powder, and the molar ratio of the metal sulfide, the boron source and the sulfur powder is 1:2:(0.5~3). The lower limit of the growth temperature range is 800~950℃.

8. The preparation method according to claim 7, characterized in that, The metal sulfide is lithium sulfide, and the growth temperature is greater than or equal to 800°C.

9. The preparation method according to claim 7, characterized in that, The metal sulfide is ferrous sulfide, and the growth temperature is greater than or equal to 900°C.

10. The preparation method according to claim 7, characterized in that, The metal sulfide is magnesium sulfide or nickel sulfide, and the growth temperature is greater than or equal to 950°C.

11. The preparation method according to claim 1, characterized in that, In the step of introducing inert gas into the reactor and controlling the reactor to heat it so that the reaction raw materials are heated to the growth temperature under an inert atmosphere and continuously react to generate a low-melting-point precursor during the heating process, the flow rate of the inert gas is 20~100 sccm, and the heating is specifically a uniform heating rate of 10~30℃ / min.

12. The preparation method according to claim 1, characterized in that, In the step of introducing ammonia gas into the reactor and maintaining the growth temperature so that the low-melting-point precursor can continuously react and grow boron nitride nanotubes, the flow rate of the ammonia gas is 20~100 sccm, and the growth time of the boron nitride nanotubes is 60~180 min.

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