A method for preparing nano diamond / boron nitride composite material

Abstract

The present invention belongs to the field of porous ceramic foam materials, and relates to a method for preparing a nano-diamond / boron nitride composite material, which is used to solve the problems of complex process, high cost, poor porosity and specific surface area of ​​the material existing in the template method and chemical vapor deposition method. By organically modifying the nano-diamond, the nano-diamond can be effectively dispersed in the prepolymer to form a dense foam skeleton. The boron nitride precursor is evenly applied to the skeleton of melamine by an impregnation method, and a diamond / boron nitride precursor foam is formed by drying. After high-temperature calcination, a nano-diamond / boron nitride composite material is obtained. The nano-diamond / boron nitride composite material has high porosity and large specific surface area; it is easy to fill, and the pore size and pores can be adjusted by adjusting the content of the curing agent and the foaming agent. And because of its large specific surface area and high thermal conductivity, it can also be used in the fields of gas adsorption and catalyst carrier.

Description

Technical Field

[0001] The invention belongs to the field of porous ceramic foam materials and relates to a method for preparing a nano diamond / boron nitride composite material. Background Art

[0002] The three-dimensional network carbon foam material has good medium filling, passing and heat exchange capabilities due to its good open-pore structure and good thermal conductivity, and is suitable for thermal management systems in aerospace, shipbuilding and other fields. However, in high-temperature air environments, many high-thermal-conductivity carbon foam materials are no longer competent. Foam carbon materials are very easy to oxidize in an environment above 300°C, causing the heat conduction channel to break and destroying the three-dimensional connected foam structure. Traditional ceramic foam materials are mostly silicon carbide, aluminum nitride, mullite, etc. These ceramic foam materials have poor high-temperature stability, low thermal conductivity, and poor resistance to thermal shock. Therefore, it is very necessary to develop high-temperature-resistant and high-thermal-conductivity foam materials in an aerobic environment.

[0003] As a new type of ceramic material, hexagonal boron nitride has the characteristics of high temperature resistance, corrosion resistance, high thermal conductivity, electrical insulation, and extremely low thermal expansion coefficient. It has a wide range of applications in the fields of ceramics, metallurgy, coatings, adsorption, catalysis, etc. In a high temperature environment above 530°C, hexagonal boron nitride is the ceramic material with the highest thermal conductivity, and the thermal conductivity basically does not decrease with increasing temperature.

[0004] The template method is the most commonly used method for preparing ordered mesoporous boron nitride foam materials. Patent CN109095930A discloses a boron nitride foam material and a preparation method thereof. The material is made of melamine foam plastic as a template. After being immersed in a slurry containing boron nitride powder and a sintering aid, the material is densified by hot pressing in a closed high-pressure container, and then degreased and subjected to high-temperature heat treatment to obtain a boron nitride foam material. Patent CN114180972A discloses a method for preparing a boron nitride / carbon foam material. The modified boron nitride is added to a pre-crosslinked resin for foaming and curing, and a boron nitride / carbon foam composite material is obtained by heat treatment. The material prepared by this method has adjustable pore size and porosity, and has the characteristics of high porosity and high specific surface area. However, due to the presence of a large number of graphite microcrystals, the material belongs to a conductive material, and the material has a large number of macropores (≥50nm), so it is still subject to certain limitations in terms of adsorption and catalysis. Summary of the invention

[0005] In view of the technical problems of the template method and chemical vapor deposition method, such as complex process, high cost, poor porosity and specific surface area of ​​the material, the present invention proposes a method for preparing a nano-diamond / boron nitride composite material. The nano-diamond / BN foam composite material obtained by the method has the characteristics of high porosity, large specific surface area, adjustable pore size and porosity, low production cost, simple process, short production cycle and low energy consumption.

[0006] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for preparing a nano-diamond / boron nitride composite material, comprising the following steps:

[0008] (1) adding nanodiamonds to melamine prepolymer after organic modification to carry out a pre-crosslinking reaction to obtain a pre-crosslinked resin containing diamonds;

[0009] (2) foaming and curing the diamond-containing pre-crosslinked resin obtained in step (1) to obtain a diamond foam material;

[0010] (3) placing the diamond foam material obtained in step (2) in a nitrogen-boron solution, repeatedly pulling and drying, to obtain a diamond / boron nitride precursor foam;

[0011] (4) subjecting the diamond / boron nitride precursor foamed material obtained in step (3) to high temperature heat treatment to obtain a diamond / boron nitride composite material;

[0012] In step (3), the nitrogen-boron solution is a mixed aqueous solution of a boron source and a nitrogen source, wherein the molar ratio of the nitrogen source to the boron source is 1:(1-10); the boron source is any one of boric acid, borazine or boron oxide; the nitrogen source is any one of urea, melamine, biuret or ammonium nitrate; and the total mass of the nitrogen source and the boron source in the nitrogen-boron solution accounts for 2wt%-5.5wt% of the total mass of the mixed aqueous solution.

[0013] The organic modification method in step (1) is as follows: adjusting the pH of tris(hydroxymethyl)aminomethane to 8.5 to prepare a buffer solution, adding nano-diamond powder and dopamine hydrochloride in a mass ratio of 1:1, ultrasonically shaking for 3 h, stirring at 60°C for 24 h, filtering, and washing with anhydrous ethanol for several times to obtain an organically modified nano-diamond slurry; the nano-diamond particle size is 20-500 nm.

[0014] The preparation method of the melamine prepolymer in step (1) is as follows: melamine and formaldehyde solution are mixed in a molar ratio of 1: (1-4), the pH is adjusted to 8, the temperature is raised for reaction, ethylene glycol is added after the solution is clarified, and the reaction is continued for 20-60 minutes to obtain the melamine prepolymer; the concentration of the formaldehyde solution is 37%; and the amount of ethylene glycol added accounts for 3-12% of the mass of the prepolymer.

[0015] In the step (1), the mass ratio of the organic modified nanodiamond to the prepolymer is (0.05-0.4):1, and the mass of the prepolymer is measured by solid content.

[0016] In the step (1), a surfactant is added during the pre-crosslinking reaction. The amount of the surfactant added accounts for 4% of the mass of the prepolymer. The surfactant is at least one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfate or dodecyltrimethylammonium bromide.

[0017] The temperature of the pre-crosslinking reaction in step (1) is 80° C., and the time of the pre-crosslinking reaction is 0.5 to 2 hours.

[0018] The foaming agent used for foaming in step (2) is at least one of petroleum ether, sodium carbonate, sodium bicarbonate or n-pentane; the curing agent used for curing is at least one of formic acid or acetic acid.

[0019] The amount of the foaming agent added is 3-9% of the mass of the prepolymer; the amount of the curing agent added is 4-8% of the mass of the prepolymer; the foaming is microwave foaming, and the foaming time is 60-210s.

[0020] The high temperature heat treatment in step (4) is carried out in a nitrogen atmosphere, and the method is: heating to 1200-1600°C in nitrogen, keeping the temperature for 1-5 hours, then cooling to 550-750°C, keeping the temperature in air for 1-5 hours. The heating rate is 1-10°C / min.

[0021] The thermal conductivity of the nano-diamond / boron nitride composite material is 1.38-1.67 W / (m·K) and the volume density is 0.40-0.52 g / cm 3 .

[0022] The present invention has the following beneficial effects:

[0023] Nano diamond has high modulus, high hardness, high thermal conductivity, good insulation, unique photoelectric properties, low friction coefficient and wear characteristics, and good chemical stability, so it has many potential functional development and application spaces. The present invention prepares a three-dimensional network structure foam material after compounding diamond with hexagonal boron nitride, which can be made into a high-temperature resistant high-thermal conductivity foam material. Specifically, the present invention first organically modifies the nano diamond, and grafts some groups compatible with the polymer on the surface of the particles, which can effectively make the nano diamond evenly dispersed in the prepolymer to form a dense foam skeleton together. Microwave foaming has a fast heating rate, uniform heating without temperature gradient, and can make the foaming agent instantly reach the boiling point and bubble to form a diamond foam. The boron nitride precursor is evenly applied to the skeleton of melamine by impregnation method, and dried to form a diamond / boron nitride precursor foam; during the high-temperature treatment in nitrogen atmosphere, hexagonal boron nitride crystals are generated on the surface of the melamine skeleton. The higher the heat treatment temperature and the longer the insulation time, the better the crystallinity of the crystal material. At the same time, the presence of nano-diamonds as high thermal conductivity fillers also greatly improves the thermal conductivity of the composite material. In addition, in the high-temperature heat treatment in nitrogen, the porosity, specific surface area and pore size of the nano-diamond / boron nitride composite material can be adjusted by adjusting the heat treatment process. During the high-temperature heat treatment in nitrogen, some nano-diamond particles are graphitized, and corresponding holes appear during the low-temperature heat treatment in air.

[0024] The porosity (up to 87%) and specific surface area (up to 91.79 m 2 ). Compared with the template method and chemical vapor deposition method, it does not use expensive metal foam materials, so the cost is low; it does not use a large amount of strong acid to remove the metal foam template, so it is safe and environmentally friendly. The nanodiamond / boron nitride composite material prepared by this method is easy to fill, and the curing agent, foaming agent content, and heat treatment temperature can be adjusted by adjusting the nanodiamond content or particle size to obtain mesopores and adjust the pore size and porosity. This method for preparing nanodiamond / boron nitride composite materials has a large specific surface area and high thermal conductivity (thermal conductivity is 1.38~1.67W / (m·K), and the volume density is 0.40~0.52g / cm 3 ), can also be used in fields such as gas adsorption and catalyst carrier. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1This is the XRD spectrum of the nano-diamond / BN foam composite material prepared in Example 1 of the present invention.

[0027] Figure 2 The pore volume and pore size distribution diagram of the nano-diamond / BN foam composite materials prepared in Examples 1, 3, and 4 of the present invention.

[0028] Figure 3 This is the N2 isothermal adsorption-desorption curve of the sample in Example 1. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] The raw materials used in the present invention are purchased from the market, and the concentration of the formaldehyde solution used is 37%;

[0031] Example 1

[0032] The specific steps of the preparation method of the nano-diamond / boron nitride composite material in this embodiment are as follows:

[0033] (1) Organically modified nano-diamond powder. Hydrochloric acid was added to tris(hydroxymethylaminomethane) to adjust the pH to 8.5 to prepare a buffer solution, and 20 nm nano-diamond and dopamine hydrochloride were added in a mass ratio of 1:1. After ultrasonic vibration for 3 h, the suspension was stirred at 60°C for 24 h to obtain a suspension, which was filtered, washed with anhydrous ethanol, dried, and cooled to room temperature to obtain organically modified nano-diamond powder.

[0034] (2) Preparation of diamond foam. Melamine and formaldehyde were added in a molar ratio of 1:3, heated to 60°C, and after the solution was clarified, the pH was adjusted to 8, and then 10% of the mass of the prepolymer was added with ethylene glycol, and the reaction was continued for 1 hour to obtain a melamine prepolymer. The modified nano-diamond powder in step (1) was added to the melamine prepolymer in a mass ratio of 0.05:1, 4% sodium dodecylbenzene sulfonate, heated to 80°C and reacted for 1 hour; 6% of the mass of the prepolymer was added with n-pentane and 4% formic acid, stirred and mixed for 2 minutes, and poured into a standard mold; then placed in a microwave oven and cured at high temperature for 180 seconds to obtain a diamond foam. The amount added in this process is calculated based on the solid content of the prepolymer.

[0035] (3) Preparation of diamond / boron nitride precursor foam. Boric acid and urea are added to water in a molar ratio of 1:3 to prepare a nitrogen-boron solution; the total mass of the nitrogen source and the boron source in the solution accounts for 2 wt% of the total mass of the mixed aqueous solution. The diamond foam is immersed in the nitrogen-boron solution for multiple pull-ups and soaking, and then placed in a vacuum drying oven for 24 h to obtain a diamond / boron nitride precursor foam.

[0036] (4) Preparation of nano-diamond / boron nitride composite materials. The diamond / boron nitride precursor foam was placed in a nitrogen atmosphere furnace, heated to 1200°C at 4°C / min, kept warm for 2 h, cooled to 550°C, and kept warm in air for 5 h to obtain a crude product. The crude product was then placed in hot water for ultrasonic washing for 3 h, and then placed in a 150°C drying oven for drying for 6 h to obtain a nano-diamond / boron nitride composite material.

[0037] Example 2

[0038] The specific steps of the preparation method of the nano-diamond / boron nitride composite material in this embodiment are as follows:

[0039] (1) Organically modified nano-diamond powder. Nano-diamonds with a size of 20 nm were selected for organic modification. The specific steps and processes were the same as those of (1) the method for organically modifying nano-diamond powder in Example 1.

[0040] (2) Preparation of diamond foam. Melamine and formaldehyde were added in a molar ratio of 1:3, heated to 50°C, and after the solution was clarified, the pH was adjusted to 8, and then 10% of the mass of ethylene glycol was added to the prepolymer, and the reaction was continued for 1 hour to obtain a melamine prepolymer. The modified nano-diamond powder in step (1) was added to the melamine prepolymer in a mass ratio of 0.4:1 (the amount added was calculated based on the solid content of the prepolymer), 4% sodium dodecyl sulfate, heated to 80°C and reacted for 2 hours; 8% of the mass of the prepolymer was added with n-pentane and 4% formic acid, stirred and mixed for 2 minutes, and poured into a standard mold; then placed in a microwave oven and cured at high temperature for 2 minutes to obtain a diamond foam. The amount added in this process was calculated based on the solid content of the prepolymer.

[0041] (3) Preparation of diamond / boron nitride precursor foam. The molar ratio of boric acid to urea was changed to 1:3 to prepare a nitrogen-boron solution, in which the mass of the nitrogen source and the boron source in the solution accounted for 3 wt % of the total mass of the mixed aqueous solution. The specific steps and process were the same as those of the method for preparing the diamond / boron nitride precursor foam in Example 1 (3).

[0042] (4) Preparation of nano-diamond / boron nitride composite materials. The diamond / boron nitride precursor foam was placed in a nitrogen atmosphere furnace, heated to 1200°C at 1°C / min, kept warm for 5 h, cooled to 550°C, and kept warm in air for 5 h to obtain a crude product. The crude product was then ultrasonically washed in hot water for 3 h, and then placed in a 150°C drying oven for 6 h to obtain a nano-diamond / boron nitride composite material.

[0043] Example 3

[0044] The specific steps of the preparation method of the nano-diamond / boron nitride composite material in this embodiment are as follows:

[0045] (1) Organically modified nano-diamond powder. Nano-diamonds with a size of 20 nm were selected for organic modification. The specific steps and processes were the same as those of (1) the method for organically modifying nano-diamond powder in Example 1.

[0046] (2) Preparation of diamond foam. Melamine and formaldehyde were added in a molar ratio of 1:3, heated to 50°C, and after the solution was clarified, the pH was adjusted to 8, and then 12% of the mass of ethylene glycol was added to the prepolymer, and the reaction was continued for 1 hour to obtain a melamine prepolymer. The modified nano-diamond powder in step (1) was added to the melamine prepolymer in a mass ratio of 0.05:1 (the amount added was calculated based on the solid content of the prepolymer), 4% dodecyltrimethylammonium bromide, heated to 80°C and reacted for 2 hours; 8% of the mass of the prepolymer was added with n-pentane and 4% formic acid, stirred and mixed for 2 minutes, and poured into a standard mold; then placed in a microwave oven and cured at high temperature for 2 minutes to obtain a diamond foam. The amount added in this process was calculated based on the solid content of the prepolymer.

[0047] (3) Preparation of diamond / boron nitride precursor foam. The molar ratio of boric acid and ammonium nitrate was changed to 1:1 to prepare a nitrogen-boron solution, wherein the mass of the nitrogen source and the boron source in the solution accounted for 4 wt% of the total mass of the mixed aqueous solution. The specific steps and process were the same as those of the method for preparing the diamond / boron nitride precursor foam in Example 1 (3).

[0048] (4) Preparation of nano-diamond / boron nitride composite materials. The diamond / boron nitride precursor foam was placed in a nitrogen atmosphere furnace, heated to 1600°C at 1°C / min, kept at that temperature for 1 h, cooled to 550°C, and kept in air for 5 h to obtain a crude product. The crude product was then ultrasonically washed in hot water for 3 h, and then placed in a 150°C drying oven for 6 h to obtain a nano-diamond / boron nitride composite material.

[0049] Example 4

[0050] The specific steps of the preparation method of the nano-diamond / boron nitride composite material in this embodiment are as follows:

[0051] (1) Organically modified nano-diamond powder. 50 nm nano-diamond was selected for organic modification. The specific steps and process were the same as those of (1) organically modified nano-diamond powder in Example 1.

[0052] (2) Preparation of diamond foam. Melamine and formaldehyde were added in a molar ratio of 1:1, heated to 50°C, and after the solution was clarified, the pH was adjusted to 8, and then 12% of the mass of ethylene glycol was added to the prepolymer, and the reaction was continued for 1 hour to obtain a melamine prepolymer. The modified nano-diamond powder in step (1) was added to the melamine prepolymer in a mass ratio of 0.2:1 (the amount added was calculated based on the solid content of the prepolymer), 4% dodecyltrimethylammonium bromide, heated to 80°C and reacted for 2 hours; 8% of the mass of the prepolymer was added with n-pentane and 4% of acetic acid, stirred and mixed for 2 minutes, and poured into a standard mold; then placed in a microwave oven and cured at high temperature for 2 minutes to obtain a diamond foam. The amount added in this process was calculated based on the solid content of the prepolymer.

[0053] (3) Preparation of diamond / boron nitride precursor foam. The molar ratio of boric acid to ammonium nitrate was changed to 1:1 to prepare a nitrogen-boron solution, in which the mass of the nitrogen source and the boron source in the solution accounted for 5.5 wt% of the total mass of the mixed aqueous solution. The specific steps and process were the same as those of the method for preparing the diamond / boron nitride precursor foam in Example 1 (3).

[0054] (4) Preparation of nano-diamond / boron nitride composite materials. The diamond / boron nitride precursor foam was placed in a nitrogen atmosphere furnace, heated to 1200°C at 1°C / min, kept at this temperature for 5 h, cooled to 600°C, and kept in air for 4 h to obtain a crude product. The crude product was then ultrasonically washed in hot water for 3 h, and then placed in a 150°C drying oven for 6 h to obtain a nano-diamond / boron nitride composite material.

[0055] Example 5

[0056] The specific steps of the preparation method of the nano-diamond / boron nitride composite material in this embodiment are as follows:

[0057] (1) Organically modified nanodiamond. Nanodiamond with a size of 100 nm was selected for organic modification. The specific steps and process were the same as those of (1) organically modified nanodiamond powder in Example 1.

[0058] (2) Preparation of diamond foam. Melamine and formaldehyde were added in a molar ratio of 1:4, heated to 60 °C, and after the solution was clarified, the pH was adjusted to 8, and then 6% of the prepolymer weight of ethylene glycol was added, and the reaction was continued for 1 h to obtain melamine prepolymer. The modified nano-diamond powder in step (1) was added to the melamine prepolymer in a mass ratio of 0.2:1 (the amount added was calculated based on the solid content of the prepolymer), 4% dodecyltrimethylammonium bromide, heated to 80 °C for 1 h; 6% of the prepolymer weight of n-pentane and 6% of formic acid were added, stirred and mixed for 2 min, and poured into a standard mold; then placed in a microwave oven and cured at high temperature for 60 seconds to obtain the preparation of diamond foam. The amount added in this process was calculated based on the solid content of the prepolymer.

[0059] (3) Preparation of diamond / boron nitride precursor foam. The molar ratio of boron oxide to ammonium nitrate was changed to 1:10 to prepare a nitrogen-boron solution, in which the mass of the nitrogen source and the boron source in the solution accounted for 2 wt % of the total mass of the mixed aqueous solution. The specific steps and process were the same as those of the method for preparing the diamond / boron nitride precursor foam in Example 1 (3).

[0060] (4) Preparation of nano-diamond / boron nitride composite materials. The diamond / boron nitride precursor foam was placed in a nitrogen atmosphere furnace, heated to 1400°C at 10°C / min, kept at this temperature for 1 h, cooled to 600°C, and kept in air for 3 h to obtain a crude product. The crude product was then ultrasonically washed in hot water for 3 h, and then placed in a 150°C drying oven for 6 h to obtain a nano-diamond / boron nitride composite material.

[0061] Example 6

[0062] The specific steps of the preparation method of the nano-diamond / boron nitride composite material in this embodiment are as follows:

[0063] (1) Organically modified nanodiamond. Nanodiamond of 500 nm was selected for organic modification. The specific steps and process were the same as those of (1) organically modified nanodiamond powder in Example 1.

[0064] (2) Preparation of diamond foam. Melamine and formaldehyde were added in a molar ratio of 1:4, heated to 60°C, and after the solution was clarified, the pH was adjusted to 8, and then 8% of the mass of the prepolymer was added with ethylene glycol, and the reaction was continued for 1 h to obtain a melamine prepolymer. The modified nano-diamond powder in step (1) was added to the melamine prepolymer in a mass ratio of 0.2:1 (the amount added was calculated based on the solid content of the prepolymer), 4% dodecyltrimethylammonium bromide, and the temperature was raised to 80°C for 1 h; 13% of the mass of the prepolymer was added with n-pentane and 6% of acetic acid, stirred and mixed for 2 min, and poured into a standard mold; then placed in a microwave oven and cured at high temperature for 3 min to obtain a diamond foam. The amount added in this process was calculated based on the solid content of the prepolymer.

[0065] (3) Preparation of diamond / boron nitride precursor foam. The molar ratio of borohydrazine and biuret was changed to 1:6 to prepare a nitrogen-boron solution, in which the mass of the nitrogen source and the boron source in the solution accounted for 5.5 wt% of the total mass of the mixed aqueous solution. The specific steps and process were the same as those of the method for preparing the diamond / boron nitride precursor foam in Example 1 (3).

[0066] (4) Preparation of nano-diamond / boron nitride composite materials. The diamond / boron nitride precursor foam was placed in a nitrogen atmosphere furnace, heated to 1400°C at 5°C / min, kept warm for 1 h, cooled to 750°C, and kept warm in air for 1 h to obtain a crude product. The crude product was then ultrasonically washed in hot water for 3 h, and then placed in a 150°C drying oven for 6 h to obtain a nano-diamond / boron nitride composite material.

[0067] Example 7

[0068] The specific steps of the preparation method of the nano-diamond / boron nitride composite material in this embodiment are as follows:

[0069] (1) Organically modified nanodiamond. Nanodiamond with a size of 100 nm was selected for organic modification. The specific steps and process were the same as those of (1) organically modified nanodiamond powder in Example 1.

[0070] (2) Preparation of diamond foam. Melamine and formaldehyde were added in a molar ratio of 1:2, heated to 60°C, and after the solution was clarified, the pH was adjusted to 8, and then ethylene glycol accounting for 5% of the mass of the prepolymer was added, and the reaction was continued for 20 min to obtain a melamine prepolymer. The modified nano-diamond powder in step (1) was added to the melamine prepolymer in a mass ratio of 0.1:1 (the amount added was calculated based on the solid content of the prepolymer), 4% sodium dodecylbenzene sulfonate, heated to 80°C and reacted for 0.5 h; 9% petroleum ether and 4% acetic acid accounting for the mass of the prepolymer were added, stirred and mixed for 1 min, and poured into a standard mold; then placed in a microwave oven and cured at high temperature for 3 min to obtain a diamond foam. The amount added in this process was calculated based on the solid content of the prepolymer.

[0071] (3) Preparation of diamond / boron nitride precursor foam. The molar ratio of borohydrazine and biuret was changed to 1:6 to prepare a nitrogen-boron solution, in which the mass of the nitrogen source and the boron source in the solution accounted for 2.5 wt% of the total mass of the mixed aqueous solution. The specific steps and process were the same as those of the method for preparing the diamond / boron nitride precursor foam in Example 1 (3).

[0072] (4) Preparation of nano-diamond / boron nitride composite materials. The 77 diamond / boron nitride precursor foam was placed in a nitrogen atmosphere furnace, heated to 1300 °C at 3 °C / min, kept warm for 1 h, cooled to 650 °C, and kept warm in air for 2 h to obtain a crude product. The crude product was then placed in hot water for ultrasonic washing for 3 h, and then placed in a 150 °C drying oven for 6 h to obtain a nano-diamond / boron nitride composite material.

[0073] Example 8

[0074] The specific steps of the preparation method of the nano-diamond / boron nitride composite material in this embodiment are as follows:

[0075] (1) Organically modified nanodiamond. Nanodiamond of 200 nm was selected for organic modification. The specific steps and process were the same as those of (1) organically modified nanodiamond powder in Example 1.

[0076] (2) Preparation of diamond foam. Melamine and formaldehyde were added in a molar ratio of 1:3, heated to 60°C, and after the solution was clarified, the pH was adjusted to 8, and then 3% of the mass of the prepolymer was added with ethylene glycol, and the reaction was continued for 40 min to obtain a melamine prepolymer. The modified nano-diamond powder in step (1) was added to the melamine prepolymer in a mass ratio of 0.3:1 (the amount added was calculated based on the solid content of the prepolymer), 4% dodecyltrimethylammonium bromide, heated to 80°C and reacted for 1.5 h; 3% of the mass of the prepolymer sodium carbonate and 8% formic acid were added, stirred and mixed for 210 s, and poured into a standard mold; then placed in a microwave oven and cured at high temperature for 3 min to obtain a diamond foam. The amount added in this process was calculated based on the solid content of the prepolymer.

[0077] (3) Preparation of diamond / boron nitride precursor foam. The molar ratio of borohydrazine and biuret was changed to 1:6 to prepare a nitrogen-boron solution, in which the mass of the nitrogen source and the boron source in the solution accounted for 3.5 wt% of the total mass of the mixed aqueous solution. The specific steps and process were the same as those of the method for preparing the diamond / boron nitride precursor foam in Example 1 (3).

[0078] (4) Preparation of nano-diamond / boron nitride composite materials. The diamond / boron nitride precursor foam was placed in a nitrogen atmosphere furnace, heated to 1500°C at 6°C / min, kept at this temperature for 1 h, cooled to 700°C, and kept in air for 1 h to obtain a crude product. The crude product was then ultrasonically washed in hot water for 3 h, and then placed in a 150°C drying oven for 6 h to obtain a nano-diamond / boron nitride composite material.

[0079] Comparative Example 1

[0080] The specific steps of the preparation method of the boron nitride foam material of this comparative example are as follows:

[0081] (1) Preparation of foam. Melamine and formaldehyde were added in a molar ratio of 1:3, heated to 60°C, and after the solution was clarified, the pH was adjusted to 8. Then, 10% of the mass of the prepolymer was added in ethylene glycol, and the reaction was continued for 1 h to obtain melamine prepolymer. Then, 4% of sodium dodecylbenzene sulfonate was added, and the temperature was raised to 75°C for reaction for 1 h. Then, 13% of the mass of the prepolymer was added in n-pentane and 6% of formic acid. The mixture was stirred for 2 min and poured into a standard mold. Then, the mixture was placed in a microwave oven and cured at high temperature for 3 min to obtain a foam. The amount added in this process was calculated based on the solid content of the prepolymer.

[0082] (2) Preparation of boron nitride precursor foam. Boric acid and urea are added to water in a molar ratio of 1:3 to prepare a nitrogen-boron solution, in which the mass of the nitrogen source and the boron source in the solution accounts for 2 wt% of the total mass of the mixed aqueous solution; the foam is immersed in the nitrogen-boron solution for multiple times, and then placed in a vacuum drying oven for 24 h to obtain a boron nitride precursor foam.

[0083] (3) Preparation of boron nitride foam material. The boron nitride precursor foam was placed in a nitrogen atmosphere furnace, heated to 1200°C at 4°C / min, kept warm for 5 h, cooled to 650°C, and kept warm in air for 5 h to obtain a crude product. The crude product was then ultrasonically washed in hot water for 3 h, and then placed in a 150°C drying oven for 6 h to obtain a boron nitride foam material.

[0084] Comparative Example 2

[0085] The specific steps of the preparation method of the nano-diamond / boron nitride / carbon composite material of this comparative example are as follows:

[0086] (1) Organically modified nanodiamond. Nanodiamond with a diameter of 20 nm was selected for organic modification. The specific steps and process were the same as those of (1) organically modified nanodiamond powder in Example 1.

[0087] (2) Preparation of diamond foam. Melamine and formaldehyde were added in a molar ratio of 1:3, heated to 60°C, and after the solution was clarified, the pH was adjusted to 8, and then 10% of the mass of the prepolymer was added with ethylene glycol, and the reaction was continued for 1 hour to obtain a melamine prepolymer. The modified nano-diamond powder in step (1) was added to the melamine prepolymer in a mass ratio of 0.05:1 (the amount added was calculated based on the solid content of the prepolymer), 4% dodecyltrimethylammonium bromide, and the temperature was raised to 85°C for 1 hour; 8% of the mass of the prepolymer was added with n-pentane and 6% of acetic acid, stirred and mixed for 2 minutes, and poured into a standard mold; then placed in a microwave oven and cured at high temperature for 3 minutes to obtain a diamond foam. The amount added in this process was calculated based on the solid content of the prepolymer.

[0088] (3) Preparation of diamond / boron nitride precursor foam. The nitrogen-boron solution was prepared by changing the molar ratio of borohydrazine to biuret to 1:6. The mass of the nitrogen source and the boron source in the solution accounted for 3 wt % of the total mass of the mixed aqueous solution. The specific steps and process were the same as those of the method for preparing the diamond / boron nitride precursor foam in Example 1 (3).

[0089] (4) Preparation of nano-diamond / boron nitride composite materials. The diamond / boron nitride precursor foam was placed in a nitrogen atmosphere furnace, heated to 1200°C at 5°C / min, and kept warm for 4 h to obtain a crude product. The crude product was then ultrasonically washed in hot water for 3 h, and then placed in a 150°C drying oven for 6 h to obtain a nano-diamond / boron nitride / carbon foam composite material.

[0090] Performance Testing

[0091] Nanodiamond was added into XC-107 room temperature vulcanized rubber at 5% and cured, and the thermal conductivity was tested.

[0092] The thermal conductivity test method is to soak the prepared material in XC-107 room temperature vulcanized rubber, impregnate it to saturation through vacuum assistance, and test the thermal conductivity of the composite material after curing. The specific surface area of ​​the foam material is measured by nitrogen adsorption and desorption method, and the porosity is measured by Archimedes drainage method. The test results are shown in Table 1. The test results are shown in Table 1.

[0093] Table 1 Test data of thermal conductivity, specific surface area, porosity, etc.

[0094]

[0095] Figure 1 This is the XRD spectrum of the nano-diamond / BN foam composite material prepared in Example 1 of the present invention.

[0096] Figure 2 The pore volume and pore size distribution diagram of the nano-diamond / BN foam composite materials prepared in Examples 1, 3, and 4 of the present invention.

[0097] Figure 3 This is the N2 isothermal adsorption-desorption curve of the sample in Example 1.

[0098] from Figure 1 It can be observed that 26.3°, 41.6° and 54.7° correspond to the (002), (100) and (004) crystal planes of hBN, respectively, while 43.8° and 75.2° correspond to the (111) and (220) crystal planes of nanodiamond, respectively. No absorption peak of graphite was found, indicating that the heat-treated sample contains only nanodiamonds and hexagonal boron nitride, but no graphite crystallites. Factors such as diamond content and particle size, and heat treatment process have a significant effect on the physical properties of the composite material. As can be seen from Table 1, with the increase of nanodiamond content, the thermal conductivity and volume density of the composite material increase significantly, while the porosity and specific surface area decrease. It will also be seen from Figure 2It can be seen that the composite material has a large number of mesopores. The material made of 20 nn diamond has more mesopores with a pore size of about 20 nm, and the higher the heat treatment temperature, the more obvious it is; the material made of 50 nm diamond has more mesopores with a pore size of about 50 nm, but no more mesopores of 20 nm appear. In general, the higher the porosity, the lower the thermal conductivity. There are many factors that affect thermal conductivity, including the crystallinity of the composite material and the diamond content. The higher the nitrogen gas temperature, the higher the crystallinity of the synthetic boron nitride, and the higher the thermal conductivity. Diamond has a much higher thermal conductivity than boron nitride, and the more diamond content, the higher the thermal conductivity. When the temperature exceeds 1200 ° C, in a nitrogen atmosphere, diamond is more likely to undergo graphitization, and the higher the temperature or the longer the time, the more obvious the graphitization effect. After the graphitization, it is easy to remove carbon elements by calcining in low-temperature air, so that holes appear at the position of the diamond where the graphitization occurs. The higher the porosity, the more unfavorable it is for heat transfer. The introduction of micron-sized diamonds is mainly to adjust the size of the holes, making it easier to produce more micron-sized holes. When the temperature is higher or the time is longer, the crystallinity of the grown boron nitride microcrystals is better, the defects are fewer, and the thermal conductivity is higher.

[0099] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a nano-diamond / boron nitride composite material, characterized in that: Here are the steps: (1) adding nanodiamonds to melamine prepolymer after organic modification to perform a pre-crosslinking reaction to obtain a pre-crosslinked resin containing diamonds; (2) foaming and curing the diamond-containing pre-crosslinked resin obtained in step (1) to obtain a diamond foam material; (3) placing the diamond foam material obtained in step (2) in a nitrogen-boron solution, repeatedly pulling and drying, to obtain a diamond / boron nitride precursor foam; (4) subjecting the diamond / boron nitride precursor foamed material obtained in step (3) to high temperature heat treatment to obtain a diamond / boron nitride composite material; The organic modification method in step (1) is as follows: adjusting the pH of tris(hydroxymethyl)aminomethane to 8.5 to prepare a buffer solution, adding nano-diamond powder and dopamine hydrochloride in a mass ratio of 1:1, subjecting the solution to ultrasonic vibration for 3 h, stirring the solution under microwave ultrasonic conditions at 60 °C for 24 h, filtering the solution, and washing the solution with anhydrous ethanol for several times to obtain an organically modified nano-diamond slurry; the nano-diamond particle size is 20-500 nm; the nitrogen-boron solution in step (3) is a mixed aqueous solution of a boron source and a nitrogen source, wherein the molar ratio of the nitrogen source to the boron source is 1:(1-10); the boron source is any one of boric acid, borohydrazine or boron oxide; the nitrogen source is any one of urea, melamine, biuret or ammonium nitrate; the total mass of the nitrogen source and the boron source in the nitrogen-boron solution accounts for 2 wt%-5.5 wt% of the total mass of the mixed aqueous solution.

2. The method for preparing the nano-diamond / boron nitride composite material according to claim 1, characterized in that: The preparation method of the melamine prepolymer in step (1) is as follows: melamine and formaldehyde solution are mixed in a molar ratio of 1: (1-4), the pH is adjusted to 8, the temperature is raised for reaction, ethylene glycol is added after the solution is clarified, and the reaction is continued for 20-60 minutes to obtain the melamine prepolymer; the concentration of the formaldehyde solution is 37%; and the amount of ethylene glycol added accounts for 3-12% of the mass of the prepolymer.

3. The method for preparing the nano-diamond / boron nitride composite material according to any one of claims 1 to 2, characterized in that: In the step (1), the mass ratio of the organic modified nanodiamond to the prepolymer is (0.05-0.4):1, and the mass of the prepolymer is measured by solid content.

4. The method for preparing the nano-diamond / boron nitride composite material according to claim 3, characterized in that: In the step (1), a surfactant is added during the pre-crosslinking reaction. The amount of the surfactant added accounts for 4% of the mass of the prepolymer. The surfactant is at least one of sodium dodecylbenzene sulfonate, sodium dodecyl sulfate or dodecyltrimethylammonium bromide.

5. The method for preparing the nano-diamond / boron nitride composite material according to claim 4, characterized in that: The temperature of the pre-crosslinking reaction in step (1) is 80° C., and the time of the pre-crosslinking reaction is 0.5 to 2 hours.

6. The method for preparing the nano-diamond / boron nitride composite material according to claim 1, characterized in that: The foaming agent used for foaming in step (2) is at least one of petroleum ether, sodium carbonate, sodium bicarbonate or n-pentane; the curing agent used for curing is at least one of formic acid or acetic acid.

7. The method for preparing the nano-diamond / boron nitride composite material according to claim 6, characterized in that: In the step (2), the amount of the foaming agent added is 3-9% of the mass of the prepolymer; the amount of the curing agent added is 4-8% of the mass of the prepolymer; the foaming is microwave foaming, and the foaming time is 60-210s.

8. The method for preparing the nano-diamond / boron nitride composite material according to claim 7, characterized in that: The high temperature heat treatment in step (4) is carried out in a nitrogen atmosphere, and the method is: heating to 1200-1600°C in nitrogen, keeping the temperature for 1-5 hours, then cooling to 550-750°C, and keeping the temperature in air for 1-5 hours.

9. The nano-diamond / boron nitride composite material prepared by the method according to any one of claims 1 to 8, characterized in that: The volume density of the nanodiamond / boron nitride composite material is 0.40-0.52 g / cm 3 The obtained material was impregnated in XC-107 room temperature vulcanized rubber and impregnated to saturation by vacuum assisted impregnation. After curing, the thermal conductivity measured was 1.38~1.71W / (m·K).

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