CN113353898A - Microwave molten salt method for preparing hexagonal boron nitride - Google Patents
Microwave molten salt method for preparing hexagonal boron nitride Download PDFInfo
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- CN113353898A CN113353898A CN202110365222.3A CN202110365222A CN113353898A CN 113353898 A CN113353898 A CN 113353898A CN 202110365222 A CN202110365222 A CN 202110365222A CN 113353898 A CN113353898 A CN 113353898A
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- C01B21/00—Nitrogen; Compounds thereof
- C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
- C01B21/064—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with boron
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Abstract
The invention discloses a method for preparing hexagonal boron nitride by a microwave molten salt method. The method comprises the following specific steps: using borax, boric acid or boron oxide as a boron source, urea or melamine as a nitrogen source, using sodium chloride-potassium chloride as a molten salt system, using silicon carbide as a microwave absorbent, uniformly mixing the boron source, the nitrogen source and molten salt, then placing the mixture into a small crucible, then covering the small crucible, then embedding the small crucible into a large crucible filled with the silicon carbide, placing the large crucible into a microwave oven, heating for a certain time, taking out the large crucible, cooling, washing a product with deionized water, performing vacuum filtration, and drying to obtain hexagonal boron nitride powder. The invention has the characteristics of short production period, simple process and the like, does not use organic solvent, does not need inert gas protection, has low production cost and does not pollute the environment.
Description
Technical Field
The invention belongs to the field of preparation of inorganic nonmetal powder, and particularly relates to a method for preparing hexagonal boron nitride by a microwave molten salt method.
Background
Hexagonal boron nitride has a similar interlayer structure and lattice parameters to graphite, and is also called white graphite, and each layer is formed by arranging nitrogen atoms and boron atoms alternately into a hexagonal ring network. The heat-resistant lubricating grease has the advantages of good heat resistance, high corrosion resistance, low thermal expansion coefficient, high thermal conductivity, excellent lubricating property, high chemical stability and the like. The boron nitride can be used for manufacturing high-grade refractory materials, high-temperature-resistant lubricants and high-temperature coatings, and also is a raw material for synthesizing cubic boron nitride, and is widely applied to the fields of energy, electronics, aerospace machinery, optical device manufacturing, polymer heat conduction materials, solid lubricating materials, energy storage materials and the like. The method for preparing hexagonal boron nitride mainly comprises a high-temperature method, a solvothermal synthesis method, a hydrothermal synthesis method, a self-propagating combustion method and the like. The equipment used for preparing hexagonal boron nitride by the high-temperature method is generally a tubular furnace, and ammonia gas or inert gas is required for protection, so that the production equipment is limited to a certain extent. The organic solvent used for preparing hexagonal boron nitride by the solvothermal synthesis method is generally toxic solvent such as acetone, toluene and the like, so that the production cost is increased on one hand, and the environment is polluted on the other hand. The hexagonal boron nitride prepared by the hydrothermal synthesis method can use substances with high toxicity, such as sodium borohydride, boron trichloride and the like, and the hexagonal boron nitride is not suitable for industrial production because the hexagonal boron nitride is processed by a subsequent process after synthesis. The self-propagating combustion method generally uses elemental boron as a reaction raw material, and although the method has the advantages of simple processing, low energy consumption, quick reaction and the like, the industrial production of the elemental boron is limited by the expensive price of the elemental boron.
The invention provides a microwave molten salt method for preparing hexagonal boron nitride, which takes a cheap boron source and a nitrogen source as reaction raw materials, reduces the cost and is beneficial to mass production; in addition, ammonia gas, nitrogen gas and other atmospheres are not required to be introduced in the reaction, so that the pollution of the reaction to the environment is reduced; the sodium chloride-potassium chloride is used as a molten salt system, the hexagonal boron nitride can be prepared at normal pressure and low temperature by using the molten salt system with low melting point, and meanwhile, the melt obtained after sintering is insulated from oxygen in the processes of heat preservation and temperature reduction, so that the oxidation of products at high temperature is prevented; the product obtained by washing with deionized water can recover molten salt to the maximum extent, and simultaneously reduce the impurity content in the boron nitride product.
Disclosure of Invention
The invention aims to provide a method for preparing hexagonal boron nitride by a microwave molten salt method, which comprises the following steps: firstly, mixing a boron source and a nitrogen source according to a molar ratio of 1: (5-12), uniformly mixing the molten salt and the nitrogen source in a molar ratio of (0-8) to 1; placing the small crucible filled with the materials into a large crucible filled with silicon carbide, and heating for 30-80 min by microwave; and after the reaction is finished, adding deionized water to remove impurities after the reaction is cooled, and drying for 8-12 h at the temperature of 60-100 ℃ after vacuum filtration to obtain hexagonal boron nitride powder.
The invention has the advantages of preparing the hexagonal boron nitride powder: (1) the method has the advantages that the boron source and the nitrogen source with low cost and low toxicity are used as raw materials, the sodium chloride-potassium chloride is used as a molten salt system, the used reagent is low in price, and the generated byproducts are few and are easy to remove; (2) in the preparation process, no organic solvent or atmosphere is used, and the product does not need acid washing, so that the production safety is improved; (3) the preparation method is simple, has small technical difficulty and is suitable for large-scale production.
The invention is further described with reference to the following examples, which are not intended to limit the scope of the invention.
Best mode for carrying out the invention
Respectively weighing 1.68g of borax, 4.01g of urea, 11.69g of sodium chloride and 14.91g of potassium chloride, uniformly mixing the materials, and putting the mixture into a small crucible; and (3) putting the small crucible filled with the materials into a large crucible filled with silicon carbide, heating for 60min by using microwaves, cooling after the reaction is finished, adding deionized water to remove impurities, and drying for 10h at 90 ℃ after vacuum filtration to obtain the hexagonal boron nitride powder.
Drawings
Figure 1 is an XRD spectrum of a hexagonal boron nitride sample. The obtained sample is proved to be hexagonal boron nitride by conforming to the spectrogram of standard card PDF # 34-0421. Furthermore, no diffraction peaks characteristic of other impurities were present, indicating that no other crystalline impurities were present in the sample.
FIG. 2 shows that the hexagonal boron nitride sample is 500-4000 cm-1FTIR spectra in the wavelength range. Located at 780cm-1And 1370cm-1The absorption peaks at the left and right wavelengths respectively correspond to out-of-plane bending vibration of the B-N-B bond and in-plane stretching vibration of the B-N bond. At 3410cm-1The nearby absorption peak is due to the presence of O-H bonds after partial hydrolysis of the sample surface. FTIR spectraNo absorption peaks for other impurities were observed, indicating a very high product purity.
Claims (3)
1. The microwave molten salt method for preparing hexagonal boron nitride is characterized by comprising the following steps: uniformly mixing a boron source, a nitrogen source and a molten salt system according to a certain proportion, and filling the mixture into a large crucible filled with silicon carbide; and (3) heating the crucible in a microwave oven for a period of time, cooling the crucible, adding deionized water, washing and drying to obtain the hexagonal boron nitride.
2. The method for preparing hexagonal boron nitride according to claim 1, wherein the boron source is one of anhydrous borax, boric acid or boron oxide, and the nitrogen source is one of melamine or urea.
3. The microwave molten salt method for preparing hexagonal boron nitride according to claim 1, wherein the molar ratio of the boron source to the nitrogen source is 1:5 to 1: 12.
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| CN202110365222.3A CN113353898A (en) | 2021-04-06 | 2021-04-06 | Microwave molten salt method for preparing hexagonal boron nitride |
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| CN202110365222.3A CN113353898A (en) | 2021-04-06 | 2021-04-06 | Microwave molten salt method for preparing hexagonal boron nitride |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114083853A (en) * | 2021-11-12 | 2022-02-25 | 江苏冠之星管道***有限公司 | Light power cable reinforced protective sleeve and preparation method thereof |
| CN114132904A (en) * | 2021-12-06 | 2022-03-04 | 湖南大学 | High oil absorption whitening hexagonal boron nitride porous microspheres for cosmetics |
-
2021
- 2021-04-06 CN CN202110365222.3A patent/CN113353898A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114083853A (en) * | 2021-11-12 | 2022-02-25 | 江苏冠之星管道***有限公司 | Light power cable reinforced protective sleeve and preparation method thereof |
| CN114132904A (en) * | 2021-12-06 | 2022-03-04 | 湖南大学 | High oil absorption whitening hexagonal boron nitride porous microspheres for cosmetics |
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