Boric acid zol crystals and methods of making and boron nitride materials prepared by pyrolysis of boric acid zol precursors

Abstract

The present application is borazyl crystal and preparation method and boron nitride material prepared by pyrolysis of borazyl precursor. Single crystal particle size of not less than 1mm and single crystal agglomerate particle size of not less than 1cm can be prepared. Two kinds of crystals are named as crystal ZB and crystal AB respectively, chemical formula is [C4H 11 N 10 ][B5O6(OH)4] and [C2H5N4][C2N4H4B5O6(OH)4] respectively, which has clear chemical properties: molecular weight of ZB is 417.31, belongs to monoclinic system, space group Ia, cell parameters are Z=4; molecular weight of AB is 387.27, belongs to triclinic system, space group P-1, cell parameters are Z=2. In view of these borazyl crystals can be directly converted into hexagonal boron nitride by high temperature pyrolysis under inert atmosphere, combined with high solubility, good melting characteristics and viscous property when solution is concentrated, they are suitable for preparing various types of hexagonal boron nitride material as precursor material, which is efficient and suitable for large-scale production.

Description

Technical field:

[0001] The present invention relates to the technical field of growth of synthetic crystals and pyrolysis preparation of precursors of boron nitride ceramics, and in particular to a boric acid azole crystal and a preparation method, as well as a boron nitride material prepared by pyrolysis of a boric acid azole precursor. Various types of boron nitride materials are prepared by pyrolysis of boric acid azole. Background technology:

[0002] Hexagonal boron nitride (h-BN), with its unique physical and chemical properties, has demonstrated broad and profound application potential in materials science, not only as a high-temperature lubricant, ceramic reinforcement, and electronic packaging material, but also as a key precursor in the field of two-dimensional materials. However, the synthesis of high-quality h-BN depends heavily on the selection and pretreatment of the precursor, which requires high pyrolysis efficiency and extremely low impurity content, while also ensuring process operability, controllability, and environmental friendliness.

[0003] Although many borates have been explored as precursors for the preparation of h-BN, each material has obvious limitations, which seriously restricts the large-scale industrial production of h-BN and the further expansion of its application fields. The following is an in-depth analysis of several typical precursors and the challenges they face: (1) Ammonia borane complex: As one of the first h-BN precursors studied, the thermal decomposition of ammonia borane can indeed effectively generate h-BN. However, its violent decomposition at high temperatures, accompanied by the release of a large amount of hydrogen, not only greatly increases the safety risks during operation, but also puts more stringent requirements on production equipment, increases production costs and safety management difficulties. In addition, the synthesis path of ammonia borane is complex and requires strict control of conditions to avoid the potential dangers brought by the by-product hydrogen, further exacerbating the production difficulty and cost burden. (2) Melamine·2-boric acid adduct: Although the formation of this phase is relatively easy, it is quite difficult to obtain high-purity and high-crystallinity crystals. Its extremely low solubility in conventional solvents limits its application potential in the thermal decomposition synthesis of multi-morphological and multi-structural h-BN. After pyrolysis, a single porous boron nitride fiber material is mainly formed, which poses a significant obstacle to the development of other types of boron nitride materials. (3) Guanidine borate salts: The synthesis of guanidine borate also faces the problem of complexity, which is mainly reflected in the uncontrollable defects in the crystal growth process, often resulting in a powder product mixed with multiple guanidine borate phases, which brings new challenges to phase purification. In addition, it is difficult to grow guanidine borate crystals into large-sized single crystals, and most guanidine borate crystal phases have low solubility in many common solvents, which greatly limits its application as a precursor in the preparation strategy of diversified pyrolytic boron nitride. (4) Boric acid imidazole salts: Although the structure of imidazole borate is conducive to the formation of h-BN, its synthesis route is lengthy and costly, and it is easy to produce carbon pollution during the pyrolysis process, which affects the purity of the final product.

[0004] In summary, the existing precursor generally has problems such as complex synthesis, great pyrolysis safety hazard, low solubility and many impurities in pyrolysis products. Therefore, the development of a new type of hexagonal boron nitride precursor crystal phase needs to have the characteristics of simple synthesis, controllable pyrolysis process, excellent solubility and high purity of pyrolysis products, which is of great strategic significance for overcoming the shortcomings of the existing precursor and promoting the wide application and development of h-BN in solution-based preparation technology. Future research should focus on exploring new precursor materials, optimizing the synthesis path, improving the pyrolysis efficiency and product purity, and paying attention to environmental friendliness and the reduction of production cost, so as to comprehensively promote the progress and industrial upgrading of h-BN material science. SUMMARY

[0005] The purpose of the present application is to provide a boronic acid azole crystal and a preparation method and a boron nitride material prepared by pyrolysis of a boronic acid azole precursor.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0007] In a first aspect, the present application provides a boronic acid azole crystal, denoted as boronic acid azole crystal ZB, the chemical formula of the boronic acid azole crystal is [C4H 11 N 10 ][B 5 O6(OH)4], the molecular weight is 417.31, it belongs to monoclinic system, the space group is Ia, the cell edge length is the cell edge angle is α=90°, β=90.7880(10)°, γ=90°, Z=4, and the cell volume is

[0008] In a second aspect, the present application provides a boronic acid azole crystal, denoted as boronic acid azole crystal AB, the chemical formula of the boronic acid azole crystal is [C2H5N4][C2N4H4B5O6(OH)4], the molecular weight is 387.27, it belongs to triclinic system, the space group is P-1, the cell edge length is the cell edge angle is α=92.699(2)°, β=98.516(2)°, γ=107.985(2)°, Z=2, and the cell volume is

[0009] The two kinds of boronic acid azole crystals are prepared by using 3-amino-1,2,4-triazole or 3,5-diamino-1,2,4-triazole as the nitrogen source and using the supersaturated solution growth method for the nitrogen source and the boron-containing compound.

[0010] In the raw material of the boronic acid azole crystal, the molar ratio of nitrogen atoms to boron atoms in the nitrogen source and the boron-containing compound is 2-5.

[0011] In the present invention, the boric acid azole crystals or agglomerated particles formed by single crystals can be referred to as boric acid azole particles. The preparation method of the boric acid azole particles is to adopt a supersaturated solution growth method of a nitrogen source and a boron-containing compound, comprising the following steps:

[0012] (1) dissolving the mixture of the nitrogen source and the boron-containing compound in a solvent at a target dissolution temperature at one time, and stirring until the reaction is complete to obtain a light yellow clear and transparent solution;

[0013] Wherein, the nitrogen source is 3-amino-1,2,4-triazole or 3,5-diamino-1,2,4-triazole, and the molar ratio of nitrogen atoms to boron atoms in the nitrogen source and the boron-containing compound is 2 to 5;

[0014] wherein the solvent is capable of dissolving the nitrogen source and the boron-containing compound at a target dissolution temperature;

[0015] wherein the ratio of the total mass (in grams) of the nitrogen source and the boron-containing compound to the volume (in milliliters) of the solvent is in the range of 0.5-2;

[0016] (2) setting a cooling target temperature, cooling the solution obtained in step (1) to the cooling target temperature at a cooling rate range of 0.1°C / min-10°C / min, wherein the solution reaches a supersaturated state during the cooling process, and performing constant temperature static growth at the cooling target temperature until single crystal particles or agglomerated particles formed by single crystal particles grow at the bottom of the solution in the container and the side wall of the container, namely, boric acid azole particles;

[0017] Alternatively, a target evaporation temperature is set, the solution obtained in step (1) is transferred to a container with an opening for circulation, and the solution is heated to the target evaporation temperature. The solvent is slowly evaporated during the heating process. As the solvent continues to evaporate, the solution reaches a supersaturated state. The solution is allowed to stand at a constant temperature and grow at the target evaporation temperature. The solvent is kept in a volatile state during the standing process until single crystal particles or agglomerated particles formed by single crystal particles grow at the bottom of the solution and the side walls of the container, namely, boric acid azole particles.

[0018] Wherein, the cooling target temperature is lower than the dissolving target temperature.

[0019] The preparation method of the present invention is to perform constant temperature static growth at a cooling target temperature, during which the container containing the solution is kept sealed and does not cause any solvent to volatilize.

[0020] The average size of the single crystal particles grown by the preparation method of the present invention exceeds 1 mm, and the agglomerated particles formed by the single crystal particles are not less than 1 cm;

[0021] If the preparation method of the present invention is to perform constant temperature static growth at the target evaporation temperature, the size of the single crystal particles is not less than 1 mm, and the agglomerated particles formed by the single crystal particles are also not less than 1 cm.

[0022] The boron-containing compound in step (1) of the present invention is at least one of boric acid, boron trioxide or sodium borate (borax);

[0023] The solvent in step (1) of the present invention is at least one of water, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC) or ethylene glycol methyl ether.

[0024] Boric acid azolate crystal materials are used to prepare boron nitride materials.

[0025] In a third aspect, the present invention provides a boron nitride material obtained using the above-mentioned boric acid azole crystals or the boric acid azole particles obtained by the preparation method as a raw material.

[0026] The boric acid azole crystals described above or the boric acid azole particles obtained by the preparation method are used as raw materials, and the boron nitride material is obtained by pyrolysis in a high-temperature direct nitrogen environment. The purpose is to use the pyrolysis process of the boric acid azole material to prepare hexagonal boron nitride, thereby realizing the use of the boric acid azole crystals or particles.

[0027] The obtained boric acid azole crystals or boric acid azole particles of the present invention have the following characteristics:

[0028] Boric acid azole crystals have the characteristic of melting into a fluid melt in the temperature range of 150-250°C;

[0029] The solution of oxazole borate has the characteristic of transforming into a viscous and fluid liquid state as the solvent evaporates within the temperature range of 90-250°C.

[0030] A typical feature of the present invention is that the boron nitride material prepared by utilizing the above two features is boron nitride foam or boron nitride fiber.

[0031] In terms of synthesizing boron nitride, the present invention utilizes the obtained boric acid azole crystals or boric acid azole particles to dissolve in a solvent within a temperature range of 25-150° C. to form a boric acid azole solution with the boric acid azole particles as a solute and a concentration ranging from 1 wt.% to 15 wt.%;

[0032] The solvent is at least one of water, formic acid, acetic acid, methanol, ethanol, isopropanol, DMAC, diethanolamine, triethanolamine, propylene glycol, ethylene glycol, ethylene glycol methyl ether, dimethyl sulfoxide, or tert-butanol;

[0033] Next, a high molecular weight polymer is added to the boric acid azole solution for mixing and dissolving to form a mixed liquid;

[0034] wherein the mass ratio of the mass of the high molecular weight polymer (in grams) to the mass of the mixed liquid (in grams) is in the range of 1 wt.% to 15 wt.%;

[0035] Wherein, the high molecular polymer is at least one of polyvinyl alcohol, polyethylene oxide, polyethylene imine, polyvinyl pyrrolidone, polyacrylonitrile, polycaprolactone, polyether sulfone, polyimide, chitosan, polyether ether ketone or cellulose;

[0036] Finally, the mixed liquid is spun at a temperature range of 25-80°C to form a continuous fiber precursor. The precursor is then pyrolyzed in a nitrogen atmosphere containing ammonia at a temperature range of 800-1600°C for 1-4 hours to obtain a continuous fiber material of boron nitride.

[0037] The nitrogen environment with ammonia is a mixed gas environment of ammonia + nitrogen with an ammonia volume content ranging from 10 vol.% to 100 vol.%.

[0038] Compared with previous boron nitride precursor materials or crystal types, the present invention has the following advantages:

[0039] The synthesis of the precursor ammonia borane complex faces numerous challenges, particularly solvent selection and solubility. In traditional methods, sodium borohydride readily hydrolyzes in aqueous solvents, necessitating the use of non-aqueous solvents such as dioxane, tetrahydrofuran, or acetone. However, the solubility of both sodium borohydride and the resulting ammonia borane in these solvents is low, resulting in mixed product precipitation, difficult separation, and low yields. This severely impacts the efficiency and economics of subsequent pyrolysis to prepare boron nitride.

[0040] In contrast, the boric acid azole crystals (ZB and AB) proposed in the present invention have significant advantages. They are obtained by growing single crystal particles of not less than 1 mm in size by a simple saturated solution method in a conventional aqueous solvent. This process has mild reaction conditions and a high crystal yield. More importantly, the solubility of these crystals in aqueous solvents is extremely high, effectively avoiding the precipitation of by-products, thereby ensuring the high purity and high yield of the crystals. This characteristic makes the synthesis strategy of the present invention not only efficient, but also economically significant, and very suitable for large-scale production.

[0041] Furthermore, the traditional pyrolysis of ammonia borane complexes to produce boron nitride is accompanied by the release of large amounts of hydrogen, which increases production safety risks. However, the precursor pyrolysis process of the present invention is relatively mild, and the main byproducts are carbon dioxide, nitrogen, and water, all of which are safe substances, significantly improving production safety and the feasibility of mass production.

[0042] Compared to melamine-2-boric acid adducts, although they can also be used to prepare porous boron nitride fibers, their solubility is relatively low, limiting their application in various boron nitride precursor forms. The ZB and AB crystals of the present invention, on the other hand, have extremely high solvent solubility, with a solubility of nearly 10 g in water at room temperature and up to 200 g at 80-95°C, which is 20 times that of melamine-2-boric acid adducts. Their solubility in ethylene glycol, triethanolamine, diethanolamine, or propylene glycol solvents under standard conditions can reach 5-10 g, their solubility in methanol and ethanol solvents under standard conditions is no less than 4 g, their solubility in DMAC solvent is no less than 3 g, and their solubility in ethylene glycol monomethyl ether solvent is no less than 1 g; these solubilities are far higher than those of conventional boron nitride precursor crystal materials. This high solubility gives the crystals of the present invention a significant advantage in preparing various types of boron nitride precursors such as micro-nano fibers, foams, low-porosity fibers and spherical particles, further broadening their scope of application.

[0043] Compared to guanidine borate salts, the crystalline material of the present invention has higher solubility in a variety of common solvents, which makes it have a wider range of application options. Furthermore, the crystal preparation process of the present invention is simple and high-purity, avoiding the mixed crystal phase problem that may occur during the growth of guanidine borate crystals, thereby improving the controllability of the morphology and structure of pyrolytic boron nitride.

[0044] Finally, it is worth noting that in the prior art, due to the relatively low nitrogen content in imidazole or methylimidazole, the grown imidazole borate tends to have a high carbon content. This results in the boron nitride obtained after pyrolysis typically containing a high carbon content, requiring further purification. However, the crystalline material of the present invention has a high nitrogen content, and almost no carbon impurities remain during the pyrolysis process, which is conducive to the pyrolysis synthesis of high-purity hexagonal boron nitride materials.

[0045] The boric acid azole crystals (ZB and AB) proposed in the present invention have high solubility, high purity and mild synthesis and pyrolysis processes, which significantly optimize the preparation of boron nitride precursors, improve production efficiency, safety and application range, and are particularly suitable for large-scale production of high-purity hexagonal boron nitride materials. Description of the drawings:

[0046] In order to more clearly introduce the technical solutions and product types of the present invention, the drawings required for the description of the embodiments are briefly elaborated and explained below. It should be emphasized that these illustrations are only some embodiments of the present invention. For ordinary technicians in this field, without paying creative work, these are likely to extend and multiply to other similar and related illustrations. In the case of similar and similar illustrations as new creative embodiments, it is regarded as infringement of the present invention.

[0047] Figure 1 1 is a macroscopic photograph of crystal ZB and crystal AB grown in Example 1 and Example 2;

[0048] Figure 2 The XRD patterns of the ground powder of the crystal ZB of Example 1 and the XRD patterns simulated by single crystal diffraction are compared;

[0049] Figure 3 Schematic diagram of the anion and cation parts and their combination of the asymmetric minimum unit of crystal ZB of Example 1;

[0050] Figure 4 The XRD patterns of the boron nitride products obtained from the crystalline ZB of Example 1 at different pyrolysis temperatures;

[0051] Figure 5 The actual photograph of the crystal ZB after direct pyrolysis in Example 1 is compared with the actual photograph of the crystal ZB before pyrolysis;

[0052] Figure 6 The XRD patterns of the ground powder of crystal AB in Example 2 and the XRD patterns simulated by single crystal diffraction are compared;

[0053] Figure 7 Schematic diagram of the anion and cation parts and their combination of the asymmetric minimum unit of crystal AB of Example 2;

[0054] Figure 8 The XRD patterns of the boron nitride products obtained from the crystal AB of Example 2 at different pyrolysis temperatures;

[0055] Figure 9 The following are the comparison of the photos of the crystal ZB before and after pyrolysis in Example 2;

[0056] Figure 10 This is a SEM photograph of a boron nitride nanofiber product obtained by pyrolysis of a continuous fiber precursor prepared using crystalline ZB as a raw material in Example 3;

[0057] Figure 11 This is a SEM photograph of a boron nitride nanofiber product obtained by pyrolysis of a continuous fiber precursor prepared using crystal AB as a raw material in Example 4;

[0058] Figure 12 The boron nitride foam product is obtained by pyrolysis using crystalline AB particles as a precursor in Example 5;

[0059] Figure 13 This is an optical electron microscope photograph of the fiber precursor of Example 9. Specific implementation:

[0060] In order to facilitate understanding by those skilled in the art, the present invention is further described below in conjunction with examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some improvements and adjustments made by those skilled in the art to the present invention based on the contents of the present invention still fall within the scope of protection of the present invention.

[0061] Unless otherwise defined, the professional terms used in the present invention have the same meanings as those commonly understood by those skilled in the art. The raw materials, reagents, instruments, equipment and some loss materials used in the present invention can be purchased from the market or prepared by existing technologies and methods.

[0062] Example 1:

[0063] (1) The preparation method of azole borate single crystal ZB particles is as follows:

[0064] (a) Add 99.1 g of 3,5-diamino-1,2,4-triazole (C2H5N5, 1 mol) and 61.8 g of boric acid (H3BO3, 1 mol) to 180 mL of deionized water. Stir in an oil bath at 95°C for 1 h until completely dissolved. Continue stirring and heating for 2 hours to obtain a clear, transparent solution.

[0065] (b) The transparent solution obtained above was cooled to 45°C at a cooling rate of 5°C / min and kept warm overnight. The solution reached a supersaturated state during the cooling process. The solution was then allowed to grow at a constant temperature at the target temperature. After 25 hours, the precipitated crystals were taken out and dried in air to obtain single crystal particles ZB. Figure 1 The actual photo of the crystal on the left side of the picture can clearly show that the single crystal particles have agglomerated to form an agglomerated particle assembled with 1mm single crystal as the unit. The size of this agglomerated particle exceeds 1 cm.

[0066] (2) Characterization, single crystal diffraction and analytical analysis of boric acid azole single crystal ZB are as follows:

[0067] The single crystal ZB particles are ground into super powder and the powder XRD pattern is tested (see Figure 2 Select a single crystal particle of ZB and perform single crystal diffraction analysis on a single crystal diffractometer, and use the diffraction data to simulate the XRD pattern line of the single crystal (see Figure 2 The analysis shows that the two lines are almost completely overlapped, indicating that the single crystal diffraction data can completely resolve the structure of the single crystal. The single crystal diffraction data was analyzed on the OLEX2 software system and the crystal chemical formula was [C4H 11 N 10][B5O6(OH)4], with a molecular weight of 417.31, belongs to the monoclinic system, the space group is Ia, and the unit cell parameters are: the unit cell edge lengths are The angles between the unit cell edges are α = 90°, β = 90.7880(10)°, γ = 90°; Z = 4; the unit cell volume is like Figure 3 The figure shows the smallest asymmetric unit in the unit cell drawn by simulation after crystal ZB analysis. This asymmetric unit consists of anion clusters [B5O6(OH)4] - and cationic clusters [C4H 11 N 10 ] + The combination is formed in the form of hydrogen bonds, where [C4H 11 N 10 ] + It is composed of two asymmetric monomers 3,5-diamino-1,2,4-triazole (C2H5N5) molecules and [C2N5H6] + Composition, these two monomers and anionic clusters [B5O6(OH)4] - The crystal chemical formula is [C4H 11 N 10 ][B5O6(OH)4] crystal phase.

[0068] (3) Preparation of Boron Nitride Materials by Pyrolysis of Crystalline ZB Particles:

[0069] The obtained agglomerated blocks of crystalline ZB particles were directly placed in a tubular furnace with a nitrogen flow rate of 100 mL / min, and the temperature was raised to 800-1500°C at a rate of 5°C / min. After keeping the temperature for 4 hours, hexagonal boron nitride material was obtained. Figure 4 As shown in the XRD pattern: Crystal ZB can be pyrolyzed to obtain boron nitride phase at 800℃, but from the analysis of XRD characteristics, it is believed that the boron nitride pyrolyzed at this temperature stage should belong to staggered boron nitride, but with high purity, and no boron oxide or boric acid impurity phase is detected; with the increase of pyrolysis temperature to 1100 and 1500℃, the crystallinity of the obtained boron nitride crystal phase is significantly improved, and still maintains extremely high purity characteristics. The impurities of the obtained boron nitride are relatively few, such as Figure 5 The actual photo of the obtained boron nitride shows the ultra-white body color feature, which illustrates the typical body color feature of obvious few or no carbon impurities. Compared with the agglomerated block of crystalline ZB particles, the boron nitride after the final pyrolysis also presents a block structure feature, and a bulk material of boron nitride is obtained. This boron nitride belongs to the hexagonal crystal system.

[0070] Example 2:

[0071] (1) The preparation method of azole borate single crystal AB particles is as follows:

[0072] (a) 84.1 g of 3-amino-1,2,4-triazole (C2H4N4) and 61.8 g of boric acid (H3BO3) were added into 75 mL of deionized water. After complete dissolution at 95 °C oil bath stirring for 1 h, the stirring and temperature were kept unchanged for 4 h after the reaction, and a clear transparent solution was obtained;

[0073] (b) The transparent solution obtained above was cooled to 45 °C at a cooling rate of 5 °C / min and kept overnight. The solution reached supersaturation during the cooling process, and the crystals were precipitated at the target temperature. The crystals were taken out after 36 h, and after air-drying, single crystal particles AB were obtained. Please see the actual photo of the crystal on the right side of Figure 1 . The picture clearly shows that the single crystal particles have been agglomerated to form an agglomerated particle with a single crystal of 1 mm as a unit. The size of the agglomerated particle exceeds 1 cm.

[0074] (2) The single crystal AB was characterized, and the single crystal diffraction and analysis are as follows:

[0075] The single crystal AB particles were ground into super powder, and the powder XRD pattern was tested (see the diffraction pattern line at the top of Figure 6 ); a single crystal particle of AB was selected for single crystal diffraction analysis on a single crystal diffractometer, and the XRD pattern line of the single crystal was simulated using the diffraction data (see the diffraction pattern line at the bottom of Figure 6 ). The analysis shows that the two pattern lines are almost completely coincident, indicating that the single crystal diffraction data can completely analyze the structure of the single crystal. After the single crystal diffraction data were analyzed on the OLEX2 software system, it was obtained that the chemical formula of the crystal is [C2H5N4][C2N4H4B5O6(OH)4], the molecular weight is 387.27, it belongs to the triclinic system, the space group is P-1, the cell edge parameters are the cell edge angle parameters are α = 92.699 (2) °, β = 98.516 (2) °, γ = 107.985 (2) °; Z = 2; the cell volume is As shown in Figure 7 , the smallest asymmetric unit in the cell after simulation of the analyzed crystal AB is shown. The asymmetric unit is composed of anionic cluster [C2N4H4B5O6(OH)4] - and cationic cluster [C4H5N4] + combined in the form of hydrogen bonds, wherein [C2N4H4B5O6(OH)4] -A BN coordination covalent bond is formed in the ion cluster. The formation of this BN bond is a coordination bond formed by the breaking of the N=C double bond on the 3-amino-1,2,4-triazole (C2H4N4) molecule and the bonding with B on [B5O6(OH)4]. Therefore, the two monomers and the anion cluster are bonded by hydrogen bonds to form a crystal phase with the crystal chemical formula [C2H5N4][C2N4H4B5O6(OH)4].

[0076] (3) Preparation of Boron Nitride Material by Pyrolysis of Crystalline AB:

[0077] The obtained agglomerated block of crystal AB particles is directly placed in a tubular furnace with a nitrogen flow rate of 100 mL / min, and the temperature is raised to 800-1500°C at a rate of 5°C / min. After keeping the temperature for 4 hours, the hexagonal boron nitride material is obtained. Figure 8 As shown in the XRD pattern: crystal AB can be pyrolyzed to obtain boron nitride phase at 800℃, but from the analysis of XRD characteristics, it is believed that the boron nitride pyrolyzed at this temperature stage should belong to staggered boron nitride, but with high purity, and no boron oxide or boric acid impurity phase is detected; with the increase of pyrolysis temperature to 1100 and 1500℃, the crystallinity of the obtained boron nitride crystal phase is significantly improved, and still maintains extremely high purity characteristics. The impurities of the obtained boron nitride are relatively few, as shown in the attached figure. Figure 9 The actual photo of the obtained boron nitride shows the ultra-white body color feature, which illustrates the typical body color feature of obvious few or no carbon impurities. Compared with the agglomerated block of crystal AB particles, the boron nitride after the final pyrolysis also presents a block structure feature, and a bulk material of boron nitride is obtained. This boron nitride belongs to the hexagonal crystal system.

[0078] Example 3:

[0079] Preparation of continuous fiber precursor using crystalline ZB material and preparation of continuous boron nitride fiber by pyrolysis:

[0080] (1) 2 g of ZB crystals were dissolved in a mixed solution of 2 g of polyvinyl alcohol and 25 mL of formic acid. After reacting in an oil bath at 95 °C for 1 hour, the mixture was cooled naturally to room temperature to obtain a viscous spinnable solution, which was a mixed liquid.

[0081] (2) electrospinning the obtained viscous spinnable solution at a spinning voltage of 18 kV and a spinning equipment cavity temperature of 35° C. to obtain a continuous fiber precursor;

[0082] (3) The fiber precursor was placed in a tube furnace, and ammonia gas was introduced at a flow rate of 100 mL / min, a heating rate of 2 °C / min, and the temperature was kept at 1100 °C for 4 h to obtain the following Figure 10 The boron nitride nanofiber product shown.

[0083] Example 4:

[0084] After replacing the ZB crystals in Example 3 with AB crystals, the other preparation and pyrolysis processes remain unchanged, and the following can be obtained: Figure 11 The boron nitride nanofiber product shown.

[0085] Example 5:

[0086] Continuous boron nitride fibers similar to those in the examples can also be obtained by replacing the polyvinyl alcohol in example 3 or example 4 with polyethylene oxide, polyvinyl pyrrolidone, polyacrylonitrile, polycaprolactone, polyethersulfone, polyimide, chitosan, polyetheretherketone or cellulose.

[0087] Example 6:

[0088] After the AB crystals are ground into fine powder, they are formed into compacted blocks by molding or pressure molds. The temperature is directly increased to 330°C at a heating rate of 10°C / min under a nitrogen flow of 200 ml / min and kept warm for 1.5 hours. Then, the temperature is continued to be increased at a heating rate of 5°C / min to a target temperature of 1100°C while maintaining the nitrogen flow rate unchanged. The temperature is kept warm for 4 hours. Then, the temperature is continued to be increased to 1500°C and kept warm for 4 hours in nitrogen to obtain the following: Figure 12 The boron nitride foam product shown in the figure is a crystalline boron nitride foam. This embodiment fully utilizes the characteristic of AB crystals that a fluid melt forms upon melting as the temperature rises. Due to the rapid temperature rise from 200°C to 330°C, the sample quickly passes through the melting point and partially decomposes. These two processes occur simultaneously, causing the cracking atmosphere to bubble the viscous melt, resulting in the final pyrolyzed boron nitride exhibiting a foamy structure.

[0089] Example 7:

[0090] By replacing the nitrogen in Example 56 with a mixture of nitrogen and ammonia and replacing crystal AB with crystal ZB, while keeping other factors unchanged, a similar boron nitride foam product can be obtained. The principle is the same as that of Example 6.

[0091] Example 8:

[0092] Dissolve 10 g of crystalline AB particles in 30 ml of water, and heat the resulting aqueous solution in an oven at 190 degrees to evaporate the water. After 1 hour, the substance in the oven bubbles to form a foam precursor. The foam precursor is subjected to the same pyrolysis process as in Example 6 or Example 7 to obtain a boron nitride foam material.

[0093] Example 9:

[0094] Dissolve 170g of crystalline AB particles in a 100ml container in an oil bath at 95℃ or above, and stir for at least 4 hours. As the water evaporates, a viscous aqueous solution is formed. The viscous aqueous solution is spun under a centrifugal turntable at 200℃ to form a fibrous precursor, such as Figure 13 After pyrolysis at 1100°C in nitrogen, fibrous boron nitride material can still be obtained.

[0095] Example 10:

[0096] Crystalline AB particles or their ground powder can be thrown out in a centrifugal spinning disk heated to about 180°C to form a fibrous precursor. This fibrous precursor has the properties of crystalline AB, that is, after pyrolysis at 1100°C-1500°C in a high-temperature nitrogen environment, it remains boron nitride and maintains the fiber morphology.

[0097] Examples 11 to 25

[0098] The amounts of 3,5-diamino-1,2,4-triazole and boric acid in Example 1 were changed to the amounts in the following examples, and the amount changes after boric acid was replaced by boron trioxide or borax were shown in the following table:

[0099]

[0100]

[0101] The remaining steps remained unchanged, and the physical phases of the grown precipitate crystals obtained in Examples 14, 15, 19, 20, 24, and 25 were all of the same crystal type as in Example 1. The physical phases of the grown precipitate crystals obtained in the other Examples were essentially the same as in Example 1, with a small amount of precipitated miscellaneous components such as boric acid or sodium borate. This was due to the presence of excessive boric acid groups in the growth solution environment and the relatively high solubility of the nitrogen source, which resulted in a gradual and increasingly significant deviation from the 1:2.5 balance of components consumed in the solution by the growing ZB crystals, and an increasingly significant excess of boric acid. Ultimately, after the supersaturation of boric acid in the supersaturated solution was pre-reached, boric acid crystals gradually grew in the later stages of the ZB crystal growth process. Therefore, trace amounts of boric acid crystal phases were detected, but the ZB crystal component still dominated.

[0102] Example 26

[0103] The amounts of 3-amino-1,2,4-triazole and boric acid in Example 2 were changed to the amounts in the following examples, and the amount changes after boric acid was replaced by boron trioxide or borax were shown in the following table:

[0104]

[0105]

[0106] The remaining steps remained unchanged, and the phases of the grown precipitate crystals obtained in Examples 29, 30, 31, 34, 35, 36, 39, 40, and 41 were all the same crystal type as in Example 2. The phases of the grown precipitate crystals obtained in Examples 27, 33, and 38 were essentially the same as in Example 2, but the particles of the grown crystals were significantly smaller. In Examples 32, 37, and 42, impurities precipitated in the latter stages of the crystal growth process, most of which were the same AB crystal phase as in Example 2, with larger particles. However, a trace amount of precipitated impurities, namely 3-amino-1,2,4-triazole phase, existed, and the particles were smaller.

[0107] Example 43

[0108] The clear solution in Example 2 was transferred to an open beaker and allowed to stand at 50° C. for more than 48 hours. After the solution slowly evaporated, as the solvent continued to evaporate, the solution reached a supersaturated state, and crystals precipitated and grew on the bottom and side walls of the beaker, obtaining a crystalline substance similar to that in Example 2.

[0109] Utilizing the methods and techniques of the present invention, indirectly or directly adopting the technical routes and basic principles of the present invention to synthesize the corresponding boron nitride product types, and utilizing the prepared hexagonal boron nitride products to apply the technologies and means in other related fields, have the same protection scope as the present invention.

[0110] Without departing from the basic principles, basic raw materials and basic routes of the present invention, any non-inventive technology and process that replaces, simplifies, replaces, modifies, improves, modifies and adds experimental steps and raw materials to synthesize hexagonal boron nitride products similar to those produced by the present invention, including hexagonal boron nitride fibers, hexagonal boron nitride micro-nano spherical particles or powders, hexagonal boron nitride single crystal sheets and hexagonal boron nitride nanosheets, etc., shall be deemed to infringe upon the present invention.

[0111] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A boric acid azole crystal, which is a boric acid azole crystal ZB, characterized in that: The chemical formula of the boric acid azole crystal is [C4H 11 N 10 ][B5O6(OH)4], with a molecular weight of 417.31, belongs to the monoclinic system, the space group is Ia, and the unit cell parameters are: the unit cell edge lengths are The angles between the unit cell edges are α = 90°, β = 90.7880(10)°, and γ = 90°; the unit cell volume is 2. A boric acid azole crystal, which is a boric acid azole crystal AB, characterized in that: The chemical formula of the boric acid azole crystal is [C2H5N4][C2N4H4B5O6(OH)4], the molecular weight is 387.27, it belongs to the triclinic system, the space group is P-1, and the unit cell parameters are: the unit cell edge lengths are The angles between the unit cell edges are α = 92.699(2)°, β = 98.516(2)°, and γ = 107.985(2); the unit cell volume is 3. The boric acid azole crystal according to claim 1 or 2, characterized in that The boric acid azole crystal uses 3-amino-1,2,4-triazole or 3,5-diamino-1,2,4-triazole as a nitrogen source, and the nitrogen source and the boron-containing compound are prepared by a supersaturated solution growth method.

4. The boric acid azole crystal according to claim 3, characterized in that The molar ratio of nitrogen atoms to boron atoms in the nitrogen source and the boron-containing compound is 2-5.

5. A method for preparing boric acid azole particles, characterized in that: The preparation method comprises the following steps: (1) dissolving the mixture of the nitrogen source and the boron-containing compound in a solvent at a target dissolution temperature at one time, and stirring until the reaction is complete to obtain a light yellow, clear, transparent solution; The nitrogen source is 3-amino-1,2,4-triazole or 3,5-diamino-1,2,4-triazole, and the molar ratio of nitrogen atoms to boron atoms in the nitrogen source and the boron-containing compound is 2 to 5; the solvent is capable of dissolving the nitrogen source and the boron-containing compound at a target dissolution temperature; wherein the ratio of the total mass (in grams) of the nitrogen source and the boron-containing compound to the volume (in milliliters) of the solvent is in the range of 0.5-2; (2) setting a cooling target temperature, cooling the solution obtained in step (1) to the cooling target temperature at a cooling rate range of 0.1°C / min-10°C / min, wherein the solution reaches a supersaturated state during the cooling process, and performing constant temperature static growth at the cooling target temperature until single crystal particles or agglomerated particles formed by single crystal particles grow at the bottom of the solution in the container and the side wall of the container, namely, boric acid azole particles; Alternatively, a target evaporation temperature is set, the solution obtained in step (1) is transferred to a container with an opening for circulation, and the solution is heated to the target evaporation temperature. The solvent is slowly evaporated during the heating process. As the solvent continues to evaporate, the solution reaches a supersaturated state. The solution is allowed to stand at a constant temperature and grow at the target evaporation temperature. The solvent is kept in a volatile state during the standing process until single crystal particles or agglomerated particles formed by single crystal particles grow at the bottom of the solution and the side walls of the container, namely, boric acid azole particles. The cooling target temperature is lower than the dissolving target temperature.

6. The preparation method according to claim 5, characterized in that When performing constant temperature static growth at the target cooling temperature, the container containing the solution is kept sealed and no solvent is volatilized, the average size of the grown single crystal particles exceeds 1 mm, and the agglomerated particles formed by the single crystal particles are not less than 1 cm; The constant temperature static growth is carried out at the evaporation target temperature, the size of the single crystal particles is not less than 1 mm, and the agglomerated particles formed by the single crystal particles are not less than 1 cm.

7. The preparation method according to claim 5, characterized in that The boron-containing compound is at least one of boric acid, boron trioxide or sodium borate; The solvent in step (1) is at least one of water, N,N-dimethylformamide, N,N-dimethylacetamide or ethylene glycol methyl ether.

8. A boron nitride material, characterized in that: The boron nitride material is obtained using the boric acid azole crystals according to any one of claims 1 to 4 or the boric acid azole particles obtained by the preparation method according to any one of claims 5 to 7 as raw materials.

9. The boron nitride material according to claim 8, characterized in that The oxadiazole borate crystals according to any one of claims 1 to 4 or the oxadiazole borate particles obtained by the preparation method according to any one of claims 5 to 7 are dissolved in a solvent at a temperature range of 25-150° C. to form an oxadiazole borate solution having a concentration of 1 wt.% to 15 wt.% with the oxadiazole borate particles as a solute; The solvent is at least one of water, formic acid, acetic acid, methanol, ethanol, isopropanol, DMAC, diethanolamine, triethanolamine, or propylene glycol, ethylene glycol, ethylene glycol methyl ether, dimethyl sulfoxide or tert-butanol; Add high molecular weight polymer to the boric acid azole solution and mix and dissolve to form a mixed liquid. The mass ratio of the mass of the high molecular weight polymer (in grams) to the mass of the mixed liquid (in grams) is in the range of 1 wt.% to 15 wt.%; The mixed liquid is spun at a temperature range of 25-80°C to form a continuous fiber precursor, and the precursor is pyrolyzed in a nitrogen environment containing ammonia at a temperature range of 800-1600°C for 1-4 hours to obtain a continuous fiber material of boron nitride; The nitrogen environment with ammonia is a mixed gas environment of ammonia + nitrogen with an ammonia volume content ranging from 10 vol.% to 100 vol.%; Alternatively, the hexagonal boron nitride material is obtained by directly pyrolyzing the boric acid azole crystals according to any one of claims 1 to 4 or the boric acid azole particles obtained by the preparation method according to any one of claims 5 to 7 under a nitrogen inert environment.

10. The boron nitride material according to claim 9, characterized in that The high molecular polymer is at least one of polyvinyl alcohol, polyethylene oxide, polyethylene imine, polyvinyl pyrrolidone, polyacrylonitrile, polycaprolactone, polyether sulfone, polyimide, chitosan, polyether ether ketone or cellulose; The boron nitride material is boron nitride foam or boron nitride fiber; Boric acid azole crystals have the characteristic of melting into a fluid melt in the temperature range of 150-250°C; The solution of oxazole borate has the characteristic of transforming into a viscous and fluid liquid state as the solvent evaporates within the temperature range of 90-250°C.

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