CN104803362B - The preparation method of hexagonal boron nitride powder and three-dimensional boron nitride - Google Patents

Abstract

The invention belongs to Inorganic synthese technical field, the preparation method of specially a kind of hexagonal boron nitride powder and three-dimensional boron nitride.The present invention uses chemical vapour deposition technique, and using transition metal elemental powders or the compound containing transition metal is catalyst, is reacted by high temperature reduction, prepares porous metal catalyst skeleton；Chemical vapour deposition technique growth hexagonal boron nitride is recycled, obtains the hexagonal boron nitride powder with catalyst backbone and three-dimensional boron nitride；The present invention is easy to operate, equipment requirement is low, yield is high；Quick, a large amount of preparations of boron nitride powder and three-dimensional boron nitride can be realized, and obtaining three-dimensional boron nitride has space small（100 nanometers 100 microns）, density is big（It is per cubic centimeter up to 100 milligrams）The advantages that, the three-dimensional boron nitride has wide practical use with boron nitride powder in space heat conduction, catalyst carrier and sound absorption are shockproof etc..

Description

Preparation method of hexagonal boron nitride powder and three-dimensional boron nitride

technical field

The invention belongs to the technical field of inorganic synthesis, and in particular relates to a method for preparing hexagonal boron nitride powder and a three-dimensional structure.

Background technique

Nano-hexagonal boron nitride is a two-dimensional material similar to graphene, and it is also a new type of ceramic material with excellent performance and great development potential, because of its high temperature oxidation resistance, radiation resistance, high thermal conductivity, high temperature lubrication It is widely used in the fields of metallurgy, aerospace, electronics and nuclear industry due to its good properties of properties, dielectric properties and insulation properties. The hexagonal boron nitride powder material is based on a three-dimensional network structure formed by two-dimensional boron nitride nanosheets through spatial crosslinking. In addition to the properties of two-dimensional boron nitride nanosheets, three-dimensional boron nitride nanomaterials conduct heat in space, Catalyst carrier and sound absorption and shock resistance have greater advantages.

Hexagonal boron nitride can remain stable at 2500 degrees Celsius under an inert atmosphere, and can maintain good stability at 850 degrees Celsius under an oxidizing atmosphere. In comparison, three-dimensional graphene and its metal array framework will collapse, decompose, or oxidize when the temperature is higher than 600 degrees, which limits the application of three-dimensional graphene materials. Due to the above excellent properties, hexagonal boron nitride has great application prospects in the preparation of high thermal conductivity ceramic devices, high thermal conductivity special coatings, thermal conductivity and insulation polymer composite materials, high temperature resistant solid lubricants and lubricating grease additives. In 2013, the Guo Wanlin group of Nanjing University of Aeronautics and Astronautics used metal foam as a template to prepare a three-dimensional boron nitride foam with excellent properties such as low density and high thermal stability. However, the network pores of metal foam are as high as hundreds of microns, and the three-dimensional boron nitride foam prepared with this template has a low volume density, which is not conducive to its mass preparation. The present invention uses a transition metal element or a compound containing a transition metal element as a raw material. After high-temperature reduction, a porous catalyst template is prepared to replace the traditional foam metal template. The porosity of the three-dimensional boron nitride obtained by using foam metal as a catalytic skeleton is higher High; in addition, a large amount of high-quality hexagonal boron nitride powder can also be prepared.

Contents of the invention

The object of the present invention is to provide a method for preparing hexagonal boron nitride powder and three-dimensional boron nitride rapidly and in large quantities, and the obtained three-dimensional boron nitride has small voids and high density.

The preparation method of hexagonal boron nitride powder and three-dimensional boron nitride provided by the present invention uses transition metal elemental powder or a compound containing transition metal elements as a catalyst to prepare a porous metal catalyst skeleton through high-temperature reduction reaction; reuse chemical Hexagonal boron nitride is grown by vapor deposition method to obtain hexagonal boron nitride powder and three-dimensional boron nitride with catalyst skeleton; among them, hexagonal boron nitride powder refers to two-dimensional boron nitride nanosheets overlapping each other Three-dimensional network powder, the length of nanosheets is 10 nanometers to 100 microns, and the thickness is 1 nanometers to 10 microns; three-dimensional boron nitride refers to hexagonal boron nitride obtained by polymer protection before etching the catalyst with a solution, with The high-porosity three-dimensional fully connected network structure is a network interconnected by boron nitride nanobelts, with a density of 0.2 mg per cubic centimeter to 100 mg per cubic centimeter.

The concrete steps of this method are as follows;

The first step, catalyst pretreatment: the catalyst is transition metal elemental powder and/or a compound containing transition metal elements, the catalyst is placed in the reaction container, or the catalyst is filled in the macroporous metal foam template, and then placed in the reaction In the container; the reaction container is evacuated or protected by an inert atmosphere, and the temperature is raised to 500-1500 degrees Celsius at a rate of 1-100 degrees per minute to heat the container area where the catalyst is located, and a reducing atmosphere such as hydrogen is introduced, and annealed for 1 minute-10 hour, obtain the porous metal catalyst skeleton;

The second step, growing boron nitride: heat the catalyst placed in the reaction vessel to the reaction temperature (400-1200 degrees Celsius), and at the same time pass the reaction source (ie boron, nitrogen source) into the catalyst area (by heating the reaction vessel Solid boron, nitrogen source, or gaseous reaction source, or the atmosphere carrying the reaction source), the growth time is 30 seconds to 10 hours, and the growth pressure is 1 millitorr to 1 atmosphere; then at 1-100 degrees Cool down to room temperature at a rate of one minute; obtain hexagonal boron nitride powder with a catalyst skeleton;

The third step, post-processing: take out the grown hexagonal boron nitride powder with the catalyst skeleton, put it into the solution to etch the catalyst, and obtain the hexagonal boron nitride powder; or, take the grown boron nitride powder The sample is taken out, protected with a high molecular polymer, then put into a solution to etch the catalyst, and then the high molecular polymer is removed to obtain three-dimensional boron nitride.

In the present invention, the reaction container is a quartz tube, a corundum tube or other containers that can enter and exit gas.

In the present invention, the inert atmosphere is one or more mixed gases of inert gases such as nitrogen and argon; the reducing atmosphere is hydrogen or a mixed gas of hydrogen and the above-mentioned inert gases.

In the present invention, the transition metal element may be selected from but not limited to nickel, copper, cobalt, platinum, iron or rubidium. The particle size of the transition metal elemental powder is 0.1 micron-100 micron. The compound containing transition metal elements may be selected from, but not limited to, transition metal oxides, transition metal salts or hydrates thereof.

Among them, for the transition metal salt hydrate, it can be dried at 50-300 degrees Celsius or microwave heated to remove the crystallization water to obtain anhydrous transition metal salt or directly perform high-temperature reduction.

In the present invention, the reaction source may be a solid-phase boron or nitrogen source, or a gas-phase boron or nitrogen source, or a liquid-phase boron or nitrogen source, and the solid-phase boron or nitrogen source may be selected from but not limited to: Boron and nitrogen-containing compounds such as borane and ammonia; gas-phase boron and nitrogen sources include one or more mixtures of boron and nitrogen-containing gases such as diborane, boron chloride, nitrogen, and ammonia; boron and nitrogen sources can also be Boron and nitrogen sources are provided by bringing boron and nitrogen-containing liquids (such as inorganic benzene) into the reaction vessel through inert gas.

In the present invention, the porous catalyst skeleton has a three-dimensional cross-linked structure, and its pore diameter is 100 nanometers to 100 microns.

In the present invention, the diameter of the pores contained in the hexagonal boron nitride with catalyst skeleton is 100 nanometers to 100 micrometers.

In the present invention, the solution used to etch the metal catalyst skeleton can be any one of sulfuric acid, hydrochloric acid, nitric acid, ferric chloride, ferric nitrate, ammonium persulfate and Marble reagent with a concentration of 0.05-6 moles per liter. Or a solution of two or more mixtures.

In the present invention, during the aforementioned etching process, the three-dimensional boron nitride is also protected by a high molecular polymer, which includes polymethyl methacrylate, polyethylene, polystyrene or polypropylene one or a mixture of several. High-temperature calcination (100-1000 degrees Celsius) can be used to remove polymers, or organic solvents (one or more of ketones, chlorinated hydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbon reagents) can be used to dissolve.

As one of the schemes that can be implemented, the scheme may also include: filling the macroporous metal foam template with a transition metal element and/or a compound containing a transition metal element, and obtaining a three-dimensional porous metal catalyst template after high-temperature reduction.

The diameter of the pores contained in the macroporous metal foam catalyst is 500 nanometers to 500 micrometers. Macroporous metal foam mainly includes nickel foam, iron foam, copper foam or cobalt foam.

As one of the more preferred embodiments, in step (1), the high-temperature reduction reaction is carried out in a reducing atmosphere at a temperature of 100-1200 degrees Celsius, and the reducing atmosphere is mainly composed of a flow ratio of 1-500 10-1000 argon and hydrogen composition, the total flow rate of carrier gas is 1-2000 ml per minute.

As one of the more preferred embodiments, in step (2), the growth temperature is 1000 degrees Celsius, the growth time is 40 minutes, and the growth pressure is 1 atmosphere.

Compared with the prior art, the present invention has at least the following advantages: simple and convenient operation, low equipment requirements, and high yield; the present invention can realize the preparation of boron nitride powder in large quantity and high quality; at the same time, the method can realize three-dimensional boron nitride Rapid and large-scale preparation, and the obtained three-dimensional boron nitride has the advantages of small gaps (100 nanometers to 100 microns) and high density (up to 100 mg per cubic centimeter). It has wide application prospects in heat conduction, catalyst carrier, sound absorption and shock resistance.

Description of drawings

Figure 1 is a scanning electron microscope image of hexagonal boron nitride powder.

Fig. 2 is a scanning electron microscope image of hexagonal boron nitride powder.

Fig. 3 is a three-dimensional boron nitride scanning electron micrograph of nickel catalyst protected by polymethyl methacrylate and etched away.

Fig. 4 is a Raman spectrum of copper powder catalyzed growth of hexagonal boron nitride.

Fig. 5 is a scanning electron micrograph of nickel foam added with nickel powder.

detailed description

The present invention is described in detail below in conjunction with accompanying drawing:

The present invention uses transition metal elemental powder, salt or its hydrate, oxide (that is, precursor) to obtain a three-dimensional metal framework with catalytic properties through high-temperature reduction, and uses chemical vapor deposition technology to catalyze the growth of nitriding in an appropriate atmosphere. Boron, and finally etch the metal skeleton to obtain boron nitride powder or three-dimensional boron nitride. Among them, the transition metal salt hydrate is subjected to heating and drying or microwave heating to remove crystal water before high-temperature reduction to obtain anhydrous transition metal salt.

1. Preparation of hexagonal boron nitride powder

Embodiment 1, at first, the preparatory work before reaction: 0.5 gram borane ammonium complex (boron, nitrogen source), 0.5 gram nickel powder (catalyst) are packed in the same quartz tube, wherein, borane ammonia place quartz tube The front end is wrapped with a heating jacket, and the quartz tube where the nickel powder is located is placed in a tube furnace. Turn on the vacuum pump to evacuate the internal air pressure of the quartz tube to below 5× ^10-3 Torr, and then inject argon gas with a flow rate of 400 ml/min to flush the air pressure back to normal pressure, and continue to inject argon gas to exhaust the air (at this time until the end of the reaction) , the outlet valve is opened to maintain the normal pressure environment), the temperature of the tube furnace is raised to 1000 degrees Celsius at a rate of 50 degrees per minute, then the argon gas is closed, and 200 milliliters per minute of hydrogen gas is used to reduce the annealed nickel powder for 30 minutes to obtain a porous nickel skeleton.

Second, the reaction stage: after the catalyst is reduced at 1000 degrees Celsius for 30 minutes, the temperature is kept constant, and the heating mantle is heated to 100 degrees Celsius to heat the borane ammonium complex (reaction source) (brought to the nickel powder by airflow) to start To grow hexagonal boron nitride, the gas atmosphere is adjusted to a ratio of argon to hydrogen of 40 to 10 (milliliters per minute), and the growth time is 60 minutes. After the end, remove the heating jacket, turn on the tube furnace, let the quartz tube cool down to room temperature with the furnace, and obtain hexagonal boron nitride powder with a nickel skeleton.

Thirdly, sample post-treatment: Take out the grown sample and put it into 3 moles per liter of hydrochloric acid solution for etching, and suction filter to obtain boron nitride powder (as shown in Figure 1, 2).

Embodiment 2, preparation method is basically the same as embodiment 1, and difference is: adopt copper powder as catalyst, the solution of post-etching catalyst adopts the hydrochloric acid mixed solution of 1 mole per liter of iron trichloride and 0.1 mole per liter, can Obtain hexagonal boron nitride powder.

2. Preparation of three-dimensional boron nitride

Embodiment 3, preparation method is basically the same as embodiment 1, also adopts nickel powder to make catalyst. The difference is in the sample treatment part after growth: before etching the nickel skeleton with 3 moles per liter of hydrochloric acid, the sample was first immersed in anisole solution of polymethyl methacrylate (4% by mass) for 10 After a few minutes remove to dry. After etching the catalyst, three-dimensional boron nitride with a polymer protective layer can be obtained (as shown in Figure 3), and then dissolved in acetone to remove polymethyl methacrylate to obtain three-dimensional boron nitride.

Example 4, the preparation method is basically the same as that of Example 1, except that copper powder is used as the catalyst, and the post-etching catalyst solution is a mixed solution of 1 mole per liter of ferric chloride and 0.1 mole per liter of hydrochloric acid. Before etching, the sample was dipped in an anisole solution of polymethyl methacrylate (4% by mass) for 10 minutes and then taken out to dry. After etching, three-dimensional boron nitride with a polymer protective layer can be obtained, and then polymethyl methacrylate is dissolved and removed with acetone to obtain three-dimensional boron nitride. (as shown in Figure 4)

Example 5, the preparation method is basically the same as in Example 1, the difference is that nickel powder (as shown in Figure 5) is added as a catalyst in the nickel foam, and the sample processing part after the growth is also different: after etching with 3 moles per liter of hydrochloric acid Before removing the nickel skeleton, the sample was immersed in an anisole solution of polymethyl methacrylate (4% by mass) for 10 minutes and then taken out to dry. After etching the catalyst, three-dimensional boron nitride with a polymer protective layer can be obtained, and then the polymethyl methacrylate is dissolved and removed with acetone to obtain three-dimensional boron nitride.

Claims (8)

1. The preparation method of hexagonal boron nitride powder and three-dimensional boron nitride is characterized in that the specific steps are as follows: The first step, catalyst pretreatment: the catalyst is transition metal elemental powder and/or a compound containing transition metal elements, the catalyst is placed in the reaction container, or the catalyst is filled in the macroporous metal foam template, and then placed in the reaction In the container; the reaction container is evacuated or protected by an inert atmosphere, and the temperature is raised to 500-1500 degrees Celsius at a rate of 1-100 degrees Celsius per minute to heat the container area where the catalyst is located, and a reducing atmosphere is introduced, and annealed for 1 minute to 10 hours. Obtain porous metal catalyst skeleton; The second step, growing boron nitride: the catalyst placed in the reaction vessel is heated to a reaction temperature of 400-1200 degrees Celsius, and at the same time, the reaction source, namely boron and nitrogen sources, are passed into the catalyst area, and the growth time is 30 seconds to 10 hours. The pressure is 1 millitorr-1 atmospheric pressure; then cooled to room temperature at a rate of 1-100 degrees Celsius per minute; obtain hexagonal boron nitride powder with a catalyst skeleton; The third step, post-processing: take out the grown hexagonal boron nitride powder with the catalyst skeleton, put it into the solution to etch the catalyst, and obtain the hexagonal boron nitride powder; or, take the grown boron nitride powder The sample is taken out, protected with a high molecular polymer, then put into a solution to etch the catalyst, and then the high molecular polymer is removed to obtain three-dimensional boron nitride. 2. the preparation method of hexagonal boron nitride powder and three-dimensional boron nitride according to claim 1, is characterized in that, described transition metal element is selected from nickel, copper, cobalt, platinum, iron, gold, silver, rubidium ; The particle size of the transition metal elemental powder is 0.1 micron-100 micron; The compound containing transition metal elements includes transition metal oxides, transition metal salts or hydrates thereof. 3. according to the preparation method of claim 1 and 2 described hexagonal boron nitride powder and three-dimensional boron nitride, it is characterized in that, described reaction source is the boron of solid phase, liquid phase or gas phase, nitrogen source, described Solid-phase boron and nitrogen sources are selected from compounds containing boron and nitrogen; gaseous-phase boron and nitrogen sources include diborane, boron chloride, nitrogen, ammonia, and one or more mixtures of these boron- and nitrogen-containing gases; liquid phase The boron and nitrogen sources are borazine; or the boron and nitrogen sources are provided by bringing boron and nitrogen-containing liquids into the reaction vessel through an inert gas. 4. the preparation method of hexagonal boron nitride powder and three-dimensional boron nitride according to claim 3, is characterized in that, the aperture of the contained hole of described macroporous metal foam is 200 nanometers-500 micron, macroporous metal foam The material is nickel foam, iron foam, copper foam or cobalt foam. 5 . The method for preparing hexagonal boron nitride powder and three-dimensional boron nitride according to claim 1 , wherein the reaction vessel is a quartz tube, a corundum tube, a vacuum chamber or other containers that can enter and exit gas. 6. the preparation method of hexagonal boron nitride powder and three-dimensional boron nitride according to claim 1, is characterized in that, described inert atmosphere is one or more mixed gases in nitrogen, argon; Reducing atmosphere It is hydrogen or a mixed gas of hydrogen and the above-mentioned inert gases. 7. The preparation method of hexagonal boron nitride powder and three-dimensional boron nitride according to claim 1, characterized in that, the solution used to etch the metal catalyst skeleton has a concentration of 0.05-6 moles per liter Any one of sulfuric acid, hydrochloric acid, nitric acid, ferric chloride, ferric nitrate, ammonium persulfate and Marble reagent, or a mixture of two or more. 8. The preparation method of hexagonal boron nitride powder and three-dimensional boron nitride according to claim 1, characterized in that, in the etching process, the high molecular polymer used to protect three-dimensional boron nitride is Polymethyl methacrylate, polyethylene, polystyrene or polypropylene or a combination of several; the high-molecular polymers are calcined at a temperature of 100-1000 degrees Celsius, or organic solvents such as ketones, chlorinated hydrocarbons, One or more of aromatic hydrocarbons and halogenated hydrocarbon reagents are dissolved.