A preparation method of block-shaped boron nitride powder and its product

Abstract

The present invention relates to a preparation method and product of a blocky boron nitride powder. The preparation method mainly uses borax, boric acid, zinc sulfate, sodium stearate, and sodium oleate as raw materials, a mixed reaction to obtain a [B-C-O-Zn-S-Na] precursor, and then the [B-C-O-Zn-S-Na] precursor is placed in a tubular furnace, a nitrogen-containing reaction gas is introduced, and the mixture is heated to 1000-1250° C. The mixture is kept warm for 2-4 hours to obtain a blocky boron nitride powder. The raw materials used in the present invention are widely available, the synthesis process is simple and convenient, the energy consumption is low, no purification is required, and the purity of the target product is as high as 98%, which helps to achieve the mass production of new blocky boron nitride materials.

Description

Technical Field

[0001] The invention relates to a preparation method of block-shaped boron nitride powder and a product thereof, belonging to the field of inorganic materials. Background Art

[0002] High-purity blocky boron nitride has a graphite-like layered structure with good insulation and dielectric properties. It can be used in high-voltage electrical insulation or as a boron source and nitrogen source material in chemical vapor deposition methods. In the prior art, borax, boric acid, etc. are generally used as boron sources, and ammonium chloride, urea, melamine, etc. are generally used as nitrogen sources. The crude product prepared using the above raw materials generally needs to be acid-washed to obtain a high-purity BN product, which is not conducive to environmental protection and low-cost preparation. In addition, the main existing technologies for preparing boron nitride are solid-phase method, liquid-phase method, gas-phase chemical reaction method and organic precursor method. These methods have high preparation costs, or some of the raw materials used are toxic. Some methods have low yields and the purity of the synthesized products is relatively low.

[0003] Currently, various hexagonal boron nitride (HBN) morphologies have been obtained using various preparation methods, including BN nanosheets, BN nanotubes, BN fibers, and BN microspheres. For example, Shi Xianbin et al. efficiently exfoliated 20-30 μm HBN in a green solvent consisting of choline chloride and phytic acid aqueous solution to produce BN nanosheets with a thickness of 3-5 nm and a diameter of 1-5 μm. The synergistic effect of the BN nanosheets prepared by this method and the dual filler of aluminum oxide, through the formation of a peapod structure, resulted in a polyvinylidene fluoride-based composite with excellent thermal conductivity. This composite can effectively reduce the surface temperature of electronic devices as a thermal interface material. Feng et al. used NH3 as a hydrogen source and N2 as a carrier gas to carry a B(OMe)3 solution into a quartz tube for reaction and collection. They then annealed the solution at high temperature in an Ar atmosphere, resulting in highly crystalline h-BN nanospheres. Boron nitride nanosheets were then camouflaged within red blood cells (CM-BNNS) by simple physical extrusion. CM-BNNS significantly prolonged blood circulation and reduced lung accumulation, with no adverse effects on all blood parameters and tissues in mice. The BN nanospheres exhibited a large contact area with cell membrane receptors, excellent biocompatibility, and water dispersibility, demonstrating high biosafety both in vitro and in vivo. Huang Qingwu et al. reacted boric acid and melamine under relatively mild conditions to form a boron nitride fiber precursor. This precursor was soluble in formic acid solution, and electrospun fibers with uniform diameters and lengths up to nearly 100 microns were prepared by high-temperature calcination. These fibers can be used as reinforcements in heat-resistant and wave-transmitting components such as missile antenna windows and radomes. Liu Bingsai and others used boric acid and magnesium chloride as reaction raw materials, sodium chloride or potassium chloride as co-solvents, mixed them in a certain proportion, annealed them at 800-1000°C to form a boron-containing precursor, and then introduced ammonia protection to anneal it at about 1100°C, collecting a one-dimensional hierarchical structure thin-walled BN micron tube with an internal tube diameter range of 0.4-2um, a tube length of 5-60um, and a tube wall thickness of 30-100nm. The tube surface is loaded with boron nitride nanosheets, which are interwoven to form boron nitride sheets with a thickness of 40-80nm. The boron nitride hierarchical structure obtained by this preparation method has important and broad application prospects in the reinforcement and toughening of ceramics and the improvement of the thermal conductivity of polymers.

[0004] It's well known that for materials of the same phase, morphology significantly influences their intrinsic physicochemical properties, and materials with different morphologies are suitable for different applications. Literature research reveals that there are few reports on blocky hexagonal boron nitride (h-BN), making it crucial to explore its preparation, intrinsic physicochemical properties, and applications. Summary of the Invention

[0005] The present invention addresses the shortcomings of the prior art by providing a method for preparing blocky boron nitride powder and its product. The present invention utilizes readily available raw materials. Borax, boric acid, zinc sulfate, sodium stearate, and sodium oleate are synthesized in a two-step process, followed by high-temperature nitriding to produce blocky boron nitride powder without purification.

[0006] The technical solution adopted by the present invention to solve the above-mentioned problems is:

[0007] A method for preparing blocky boron nitride powder is characterized by the following main steps:

[0008] (1) uniformly mixing borax, boric acid, zinc sulfate and water to obtain a mixture;

[0009] (2) Sodium stearate and sodium oleate were added to the mixture, and then reacted at 80-100°C for 4-6 hours, and rotary evaporated at 80-90°C until the sample was dry to obtain the precursor [BCO-Zn-S-Na];

[0010] (3) The [BCO-Zn-S-Na] boron-containing precursor is transferred to an alumina crucible and placed in a tube furnace. The temperature is raised to 1000-1250°C in a nitrogen atmosphere and kept at this temperature for 2-4 hours to obtain a block-shaped boron nitride powder.

[0011] According to the above scheme, the specific operation in step (1) is: heating water to 70-90° C., and then adding borax, boric acid and zinc borate in sequence to achieve mixing of the four.

[0012] According to the above scheme, in step (1), the molar ratio of borax:boric acid:zinc sulfate:water is 1:(1-3):(0.8-1.2):(40-50). Preferably, the optimal molar ratio of borax:boric acid:zinc sulfate:water is 1:2:1:45.

[0013] According to the above scheme, in step (2), the total amount of sodium stearate and sodium oleate added is 1.5-2.5% of the mass of zinc sulfate in the mixture obtained in step (1); wherein the molar ratio of sodium stearate to sodium oleate is (1-5):1. Preferably, the optimal value of the total amount of sodium stearate and sodium oleate added is 2% of the mass of zinc sulfate in the mixture, wherein the molar ratio of sodium stearate to sodium oleate is 3:1.

[0014] According to the above scheme, in step (2), the optimal reaction temperature is 90°C.

[0015] According to the above scheme, in step (3), the nitrogen-containing atmosphere is one of N2 atmosphere, NH3 atmosphere, N2 and H2 mixed atmosphere, etc.; the flow rate of the nitrogen-containing atmosphere is 50ml / min to 200ml / min, with an optimal flow rate of 100ml / min. Preferably, in step (3), the temperature is raised to an optimal temperature of 1150°C under the nitrogen-containing atmosphere, and the optimal holding time is 4 hours.

[0016] The boron nitride prepared by the method is in the shape of a block with a width of 0.5 to 3 μm, a length of 1 to 3 μm and a thickness of 0.5 to 3 μm.

[0017] The following chemical reactions may occur during the preparation of the precursors and the synthesis of blocky boron nitride by nitridation reaction involved in the present invention:

[0018] Na2B4O7·10H2O(l)+H3BO3(l)+ZnSO4(l)+C 18 H 35 O2Na(l)+C 17 H 33 CO2Na(l)→[BCO-Zn-S-Na](s)+H2O(l)(1)

[0019] [BCO-Zn-S-Na](s)+NH3(g)→BN(s)+CO2(g)+SO2(g)+[Zn-Na-O](g)+H2O(s) (2)

[0020] The possible reaction mechanism for preparing a block-shaped boron nitride powder in the present invention is as follows: a boron source from borax and boric acid reacts with zinc sulfate, and sodium stearate and sodium oleate are added simultaneously to prepare a solid [BCO-Zn-S-Na] precursor. During the nitriding process, as the temperature rises, the active N* in the nitrogen-containing gas diffuses and penetrates into the [BCO-Zn-S-Na] precursor, etching the precursor. At high temperatures, carbon and sulfur elements combine with oxygen in the precursor to form a gas that is removed. At the same time, the boron atoms exposed on the surface of the precursor come into contact with the active N* to react and generate BN, forming an initial BN outer layer. Among them, zinc sulfate, sodium stearate and sodium oleate provide zinc and sodium elements in the precursor respectively. As the temperature continues to rise, a low-melting-point alloy similar to [Zn-Na-O] is formed. Under the action of a highly active nitrogen-containing atmosphere and high temperature, due to its high saturated vapor pressure, it gradually precipitates from the precursor and is carried out with the gas. At this time, the unreacted boron atoms gradually become active B*, react with N* faster, and gradually fill the vacancies left by the volatilization of other atoms, thus finally forming a blocky boron nitride structure.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention uses easily available borax, boric acid, zinc sulfate, sodium stearate and sodium oleate as raw materials to prepare a boron-containing precursor, and conducts a nitridation reaction in a tube furnace. Except for boron nitride, all other by-products are carried away with the reaction gas and do not require purification. The prepared product is shown by XRD analysis to be free of impurity phases and has a purity of 98% or above. In addition, the boron element conversion rate reaches more than 90%, which is conducive to large-scale industrial production.

[0023] 2. The synthesis process of the present invention is simple, the equipment is simple, and a common single-temperature zone tubular furnace can be used for preparation during the nitridation process. The temperature control range is not strictly required, the repetition rate is high, the process stability is good, and it is conducive to mass production.

[0024] 3. The present invention is the first to prepare block boron nitride, which has not been reported in the literature. The width of the block boron nitride is 0.5 to 3 μm, the length is 1 to 3 μm, and the thickness is 0.5 to 3 μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the scanning electron microscope (SEM) image of BN obtained in Example 1.

[0026] Figure 2 This is the EDS graph of the BN sample obtained in Example 1.

[0027] Figure 3 is the X-ray diffraction (XRD) pattern of BN obtained in Example 1.

[0028] Figure 4 This is the infrared (FIIR) image of BN obtained in Example 1.

[0029] Figure 5 3 is a scanning electron microscope (SEM) image of BN obtained in the comparative example. DETAILED DESCRIPTION

[0030] In order to better understand the present invention, the content of the present invention is further illustrated below with reference to the embodiments, but the content of the present invention is not limited to the following embodiments.

[0031] In the following examples, the morphology of the obtained products was observed using a FEIQuanta FEG 250 scanning electron microscope (FSEM); X-ray diffraction analysis (XRD) was performed using a Rigaku D / MAX-LLIA X-ray powder diffractometer. 2θ is 10-80°; infrared spectroscopy (FTIR) tests were performed using a Thermo Nexus 470 Fourier transform infrared spectrometer (Thermo Nicolás, USA).

[0032] Example 1

[0033] A method for preparing blocky boron nitride powder comprises the following steps:

[0034] (1) Borax: boric acid: zinc sulfate: water are mixed in a molar ratio of 1:2:1:45 to obtain a mixture;

[0035] (2) Sodium stearate and sodium oleate were added to the above mixture (the total mass of sodium stearate and sodium oleate was 2% of zinc sulfate), reacted at 90°C for 5 h, and then rotary evaporated at 80°C until the sample was dry to obtain the [BCO-Zn-S-Na] precursor;

[0036] (3) Take 2.47g of [BCO-Zn-S-Na] precursor and evenly spread it in an alumina crucible, place it in a tubular furnace, and introduce ammonia gas after vacuuming. The ammonia flow rate is 200ml / min. Keep it at 1150℃ for 4h, cool it to 200℃ with the furnace, close the vent valve, and cool it naturally to room temperature to obtain the product, which is a block-shaped boron nitride powder (BN sample).

[0037] like Figure 1 As shown in FIG, the SEM spectrum of the BN sample prepared in this embodiment. Figure 1 As shown in (a), the structure is similar to a square, with a length of 1 to 2 μm, a width of 0.5 to 2 μm, and a uniform morphology. Figure 1 As shown in (b), the thickness is basically 0.5 to 2 μm.

[0038] like Figure 2 As shown in Figure 2, the EDS diagram of the BN sample prepared in this embodiment. Figure 2 From (b), we can see that this BN sample is composed of two elements: B and N. The presence of O is due to moisture absorbed by the sample surface. The calculated atomic percentages of B and N atoms in this BN sample are 48.04:47.31, which is consistent with the theoretical atomic ratio of BN. This indicates that all byproducts generated after the nitridation reaction have been removed, indicating a high purity sample free of other impurities.

[0039] like Figure 3 The XRD pattern of the BN sample prepared in this example is shown in FIG. There are four obvious main diffraction peaks in the spectrum, located at 2θ = 26.81°, 42.51°, 44.56°, 54.82°, and 76.95°, respectively, corresponding to the (002), (100), (101), (004), and (110) crystal planes of h-BN crystal (JCPDF NO. 34-0421). It can be seen that the product is free of impurity phases and has high purity.

[0040] like Figure 4As shown in the FIIR spectrum of the BN sample prepared in this embodiment, there are three obvious characteristic peaks in the spectrum, namely 795cm -1 、1390cm -1 、3440cm -1 , of which 795cm -1 、1390cm -1 The out-of-plane tensile vibration and in-plane tensile vibration peaks of BN once again prove that it is a boron nitride material; and 3440cm -1 It is the hydroxyl peak, which is caused by the water absorbed by the sample surface.

[0041] The above spectrum analysis results prove that the prepared sample is a cubic boron nitride powder without impurity phase.

[0042] Comparative Example

[0043] A method for preparing boron nitride powder comprises the following steps:

[0044] (1) Borax: boric acid: zinc sulfate: water are mixed in a molar ratio of 1:2:1:45 to obtain a mixture;

[0045] (2) The mixture was reacted directly at 90 °C for 5 h without adding sodium stearate and sodium oleate, and then rotary evaporated at 80 °C until the sample was dry to obtain the [BCO-Zn-S-Na] precursor;

[0046] (3) Take 2.47g of [BCO-Zn-S-Na] precursor and evenly spread it in an alumina crucible, place it in a tubular furnace, and after vacuuming, introduce ammonia gas at an ammonia flow rate of 200ml / min. Keep it at 1150℃ for 4h, cool it to 200℃ with the furnace, close the vent valve, and cool it naturally to room temperature to obtain the product, which is a block-shaped boron nitride powder.

[0047] The product was analyzed by XRD, FSEM and FIIR, and the purity of the product was up to 99%, and the conversion rate of boron element was over 90%. Figure 5 As shown, there is no block, severe agglomeration, fine particles, and the particle size is 60 to 150 nm.

[0048] Example 2

[0049] A method for preparing blocky boron nitride powder comprises the following steps:

[0050] (1) Borax: boric acid: zinc sulfate: water are mixed in a molar ratio of 1:2:1:45 to obtain a mixture;

[0051] (2) Sodium stearate and sodium oleate were added to the mixture (the total mass of sodium stearate and sodium oleate was 2% of zinc sulfate), and the mixture was reacted at 80°C for 5 h, and then rotary evaporated at 80°C until the sample was dry to obtain the [BCO-Zn-S-Na] precursor;

[0052] (3) Take 2.47g of [BCO-Zn-S-Na] precursor and evenly spread it in an alumina crucible, place it in a tubular furnace, and after vacuuming, introduce ammonia gas at an ammonia flow rate of 200ml / min. Keep it at 1000℃ for 3h, cool it to 200℃ with the furnace, close the vent valve, and cool it naturally to room temperature to obtain the product, which is a block-shaped boron nitride powder.

[0053] The product was analyzed by XRD, FSEM and FIIR, and the purity of the product can reach 98%, the conversion rate of boron element is more than 90%, the morphology is similar to that of a block, the morphology is uniform, the width is 1 to 3 μm, the length is 1 to 3 μm, and the thickness is 0.5 to 1 μm.

[0054] Example 3

[0055] A method for preparing blocky boron nitride powder comprises the following steps:

[0056] (1) Borax: boric acid: zinc sulfate: water are mixed in a molar ratio of 1:1:1:45 to obtain a mixture;

[0057] (2) Sodium stearate and sodium oleate were added to the mixture (the total mass of sodium stearate and sodium oleate was 2% of zinc sulfate), and the mixture was reacted at 80°C for 5 h, and then rotary evaporated at 80°C until the sample was dry to obtain the [BCO-Zn-S-Na] precursor;

[0058] (3) Take 2.47g of [BCO-Zn-S-Na] precursor and evenly spread it in an alumina crucible, place it in a tubular furnace, and after vacuuming, introduce ammonia gas at an ammonia flow rate of 100ml / min. Keep it at 1250℃ for 3h, cool it to 200℃ with the furnace, close the vent valve, and cool it naturally to room temperature to obtain the product, which is a block-shaped boron nitride powder.

[0059] The product was analyzed by XRD, FSEM and FIIR, and the purity of the product can reach 99%, the conversion rate of boron element is more than 90%, the morphology is similar to that of a block, the morphology is uniform, the length is 2 to 3 μm, the width is 1 to 3 μm, and the thickness is 0.5 to 3 μm.

[0060] Example 4

[0061] A method for preparing blocky boron nitride powder comprises the following steps:

[0062] (1) Borax: boric acid: zinc sulfate: water are mixed in a molar ratio of 1:3:1:45 to obtain a mixture;

[0063] (2) Sodium stearate and sodium oleate were added to the mixture (the total mass of sodium stearate and sodium oleate was 2% of zinc sulfate), and the mixture was reacted at 80°C for 5 h, and then rotary evaporated at 80°C until the sample was dry to obtain the [BCO-Zn-S-Na] precursor;

[0064] (3) Take 2.47g of [BCO-Zn-S-Na] precursor and evenly spread it in an alumina crucible, place it in a tubular furnace, and after vacuuming, introduce ammonia gas with a nitrogen flow rate of 100ml / min. Keep it at 1250℃ for 3h, cool it to 200℃ with the furnace, close the vent valve, and cool it naturally to room temperature to obtain the product, which is a block-shaped boron nitride powder.

[0065] The product was analyzed by XRD, FSEM and FIIR, and the purity of the product can reach 98%, the conversion rate of boron element is more than 90%, the morphology is similar to that of a block, the morphology is uniform, the width is 0.5 to 2 μm, the length is 1 to 3 μm, and the thickness is 2 to 3 μm.

[0066] The above-described embodiments are merely for illustrating the technical concept and features of the present invention. It should be noted that equivalent changes and modifications made without departing from the creative concept of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a block-shaped boron nitride material, characterized in that The main steps are as follows: (1) uniformly mixing borax, boric acid, zinc sulfate and water to obtain a mixture; (2) sodium stearate and sodium oleate were added to the mixture, and then reacted at 80-100°C for 4-6 hours, and rotary evaporated at 80-90°C until dry to obtain a boron-containing precursor [BCO-Zn-S-Na]; (3) placing the [BCO-Zn-S-Na] boron-containing precursor in a tube furnace, heating it to 1000-1250°C in a nitrogen atmosphere and keeping it at that temperature for 2-4 hours to obtain a block-shaped boron nitride material; The microscopic morphology of the block-shaped boron nitride material is block-shaped, with a width of 0.5-3 μm, a length of 1-3 μm, and a thickness of 0.5-3 μm.

2. The method for preparing the blocky boron nitride material according to claim 1, characterized in that The specific operation in step (1) is: heating water to 70-90° C., and then adding borax, boric acid and zinc sulfate in sequence to achieve mixing of the four.

3. The method for preparing the blocky boron nitride material according to claim 1, characterized in that In step (2), the total amount of sodium stearate and sodium oleate added is 1.5% to 2.5% of the mass of zinc sulfate in the mixture of step (1).

4. The method for preparing a blocky boron nitride material according to claim 1, wherein In step (2), the molar ratio of sodium stearate to sodium oleate is (1-5):

1.

5. The method for preparing a blocky boron nitride material according to claim 1, characterized in that The nitrogen-containing atmosphere in step (3) is one of N2 atmosphere, NH3 atmosphere, and a mixed atmosphere of N2 and H2.

6. The method for preparing a blocky boron nitride material according to claim 1, characterized in that In step (3), the flow rate of the nitrogen-containing atmosphere is 50 ml / min to 200 ml / min.

7. The method for preparing a blocky boron nitride material according to claim 1, characterized in that In step (1), the molar ratio of borax:boric acid:zinc sulfate is 1:(1-3):(0.8-1.2).

8. The method for preparing a blocky boron nitride material according to claim 1, characterized in that In step (1), the molar ratio of borax to water is 1:(40-50).

9. The method for preparing a blocky boron nitride material according to claim 1, characterized in that The block-shaped boron nitride material is powder.

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