Hexagonal boron nitride platelets, methods of making and using the same

Abstract

The application provides a hexagonal boron nitride flake, a preparation method and application thereof. The hexagonal boron nitride flake has a D50 of 1-4 microns, a specific surface area of 12-20 m 2 / g, and a thermal conductivity of 0.9-1.1 W·m ‑1 ·K ‑1 The hexagonal boron nitride flake has the characteristics of small D50, large specific surface area and high thermal conductivity, so that the heat-conducting insulating material has excellent heat-conducting performance.

Description

Technical Field

[0001] This invention belongs to the field of hexagonal boron nitride lamellar crystal preparation, specifically relating to a hexagonal boron nitride lamellar crystal, its preparation method, and its application. Background Technology

[0002] Hexagonal boron nitride is an important fine chemical product with properties such as high bandgap, high-temperature oxidation resistance, high corrosion resistance, high chemical stability, low coefficient of thermal expansion, low dielectric constant, and thermal shock resistance. Due to these numerous excellent properties, hexagonal boron nitride is widely used in insulating materials, high-temperature resistant materials, catalysts, ceramic composite additives, and high-temperature resistant electronic components.

[0003] Hexagonal boron nitride (BN) readily forms plate-like crystals due to its graphite-like layered structure. Currently, most commercially available BN plate-like products have a D50 (diameter of diameter) of 8 μm or larger. BN plate-like products with a D50 of 1–4 μm are expensive and unsuitable for industrial mass production. Compared to large-particle-size BN, small-particle-size BN exhibits a larger specific surface area and higher filler content. The smaller particle size and thinner plate-like structure result in excellent intrinsic thermal conductivity in thermal conductivity applications, creating good thermal pathways, reducing interfacial thermal resistance, and improving thermal performance. In lubrication applications, small-particle-size BN exhibits a lower coefficient of friction and higher friction performance. Furthermore, small-particle-size BN shows great application potential in ceramics, cosmetics, and electronics.

[0004] Methods suitable for large-scale synthesis of small-particle-size boron nitride include ball milling and ultrasonic stripping. However, during ball milling, the impact of the milling balls not only causes crystal breakage, resulting in crystal defects and irregular morphology, but also leads to agglomeration caused by a rapid increase in temperature, resulting in a loss of thermal conductivity. Ultrasonic stripping, on the other hand, has lower efficiency and a higher loss rate.

[0005] Small-particle-size hexagonal boron nitride flakes exhibit superior performance; therefore, it is necessary to provide a new method for preparing small-particle-size hexagonal boron nitride flakes. Summary of the Invention

[0006] This invention provides a hexagonal boron nitride sheet crystal, which has the characteristics of small D50, large specific surface area and high thermal conductivity.

[0007] The present invention also provides a method for preparing the above-mentioned hexagonal boron nitride wafers and their applications.

[0008] The first aspect of this invention provides a hexagonal boron nitride lamellar crystal, wherein the hexagonal boron nitride lamellar crystal has a D50 of 1-4 μm and a specific surface area of ​​12-20 m². 2 / g, thermal conductivity 0.9~1.1W·m -1 ·K -1 .

[0009] The hexagonal boron nitride wafers described above contain boron nitride content of not less than 99.0% and water-soluble boron content of not more than 0.3%.

[0010] The hexagonal boron nitride lamellar crystals described above are prepared by the following method:

[0011] The first hexagonal boron nitride flakes with a D50 of 6-10 μm are calcined in an air or oxygen atmosphere at a temperature of 700-1000℃ for 1-8 hours to obtain the second hexagonal boron nitride flakes with a particle size reduction rate of not less than 40%.

[0012] The second hexagonal boron nitride wafer was acid-washed using an acid-washing solution containing H2O. + The concentration of the pickling solution is 0.1–5 mol / L, the temperature of the pickling solution is 40–90 °C, the pickling time is 0.5–5 h, and the filtered solution yields boron nitride flakes with a D50 of 1–4 μm.

[0013] The third hexagonal boron nitride crystal was washed with deionized water at a temperature of 40–90°C for 0.5–6 hours. After filtration and drying, hexagonal boron nitride crystals were obtained.

[0014] A second aspect of the present invention provides a method for preparing the above-mentioned hexagonal boron nitride lamellar crystals, comprising the following steps:

[0015] The first hexagonal boron nitride flakes with a D50 of 6-10 μm are calcined in an air or oxygen atmosphere at a temperature of 700-1000℃ for 1-8 hours to obtain the second hexagonal boron nitride flakes with a particle size reduction rate of not less than 40%.

[0016] The second hexagonal boron nitride wafer was acid-washed using an acid-washing solution containing H2O. + The concentration of the pickling solution is 0.1–5 mol / L, the temperature of the pickling solution is 40–90 °C, the pickling time is 0.5–5 h, and the filtered solution yields boron nitride flakes with a D50 of 1–4 μm.

[0017] The third hexagonal boron nitride crystal was washed with deionized water at a temperature of 40–90°C for 0.5–6 hours. After filtration and drying, hexagonal boron nitride crystals were obtained.

[0018] The hexagonal boron nitride lamellar crystals have a D50 of 1–4 μm and a specific surface area of ​​12–20 m². 2 / g, thermal conductivity 0.9~1.1W·m -1 .K -1 .

[0019] In the method described above, the pickling solution includes at least one of hydrochloric acid, sulfuric acid, and nitric acid.

[0020] As described above, the boron nitride content in the hexagonal boron nitride wafer is not less than 99.0%, and the water-soluble boron content is not more than 0.3%.

[0021] As described above, the particle size reduction rate of the hexagonal boron nitride flakes is not less than 50%.

[0022] The total boron nitride loss rate in the hexagonal boron nitride is no higher than 15% as described above.

[0023] As described above, the calcination treatment is carried out in a crucible, and based on a 500 mL crucible, the mass of the first hexagonal boron nitride is 50–150 g.

[0024] The third aspect of the present invention provides the application of the above-mentioned hexagonal boron nitride flakes in thermally conductive and insulating materials. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a scanning electron microscope image of the first hexagonal boron nitride wafer used in Embodiment 1 of the present invention;

[0027] Figure 2 This is a scanning electron microscope image of the hexagonal boron nitride wafers prepared in Example 1 of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0029] Patent literature on hexagonal boron nitride includes patent CN113753866B, which discloses a method for preparing hexagonal boron nitride nanocrystals and their solid-phase preparation. The method includes: reacting melamine with boric acid by stirring, then cooling and co-crystallizing or evaporating water and drying to obtain a boric acid-melamine precursor; laying the boric acid-melamine precursor in a reaction bed with a thickness not exceeding 2 cm and heat-treating it under air conditions to obtain hexagonal boron nitride solid; repeatedly centrifuging and washing the hexagonal boron nitride solid with ethanol and deionized water, followed by membrane filtration, or dispersing the hexagonal boron nitride solid in deionized water and dialysis and membrane filtration to obtain a hexagonal boron nitride nanocrystal dispersion; and freeze-drying the hexagonal boron nitride nanocrystal dispersion to obtain hexagonal boron nitride nanocrystal powder. Patent CN114466818A provides a hexagonal boron nitride powder with a purity of over 98% and a specific surface area of ​​less than 2.0 m². 2 / g. Patent CN115028892A discloses a three-dimensional structure modified boron nitride, its preparation method and application. The boron nitride nanosheets provide rapid phonon conduction, improve the thermal conductivity of the material, and the three-dimensional structure prevents the agglomeration of nanocomposite materials.

[0030] Non-patent literature on hexagonal boron nitride (hBN) includes several notable studies. Sun Changhong et al., in their article "Synthesis and Application Status of Hexagonal Boron Nitride Microcrystals," reviewed the synthesis methods, functional modifications, ceramic product preparation methods, and main applications of hBN. Zhang Zhenhao et al., in their article "Research Progress on the Application of Hexagonal Boron Nitride in Insulating and Thermally Conductive Polymer Composites," introduced the research progress of hexagonal boron nitride as a high thermal conductivity and high insulation inorganic filler in polymers, and discussed the development direction of boron nitride in insulating and thermally conductive composite materials. Ma Xiaotong, in her paper "Exfoliation of Boron Nitride and its Application in Polymer Composites," used surfactants ethyl cellulose (EC) and cationic ethyl cellulose (CEC) to assist in the exfoliation of hexagonal boron nitride (h-BN) to prepare boron nitride nanosheets BN / EC and BN / CEC, respectively. Boron nitride / acrylic-alkyd composites (WAAR / BN) and boron nitride / epoxy composites (WEP / BN) were constructed using waterborne acrylic-alkyd and waterborne epoxy as matrices, respectively. Zhang Wangxi et al., in their paper "Research Progress of Hexagonal Boron Nitride Nanomaterials," focused on hexagonal boron nitride nanotubes, summarizing the preparation methods, properties, and main application areas of boron nitride nanomaterials. Cui Ruxin et al., in their paper "Preparation of Hexagonal Boron Nitride Nanosheets," reviewed recent advanced exfoliation techniques and preparation methods for hexagonal boron nitride nanosheets, analyzed and compared the technical characteristics and shortcomings of different methods, and synthesized recent research progress to derive a clean and efficient method for the exfoliation and preparation of hexagonal boron nitride nanosheets, proposing a feasible scheme for large-scale industrial preparation. Gao Rui, in his paper titled "Preparation and Performance Study of Hexagonal Boron Nitride Materials," conducted research on boron nitride nanosheets, surface modification of boron nitride nanosheets, and boron nitride nanotubes.

[0031] The first aspect of this invention provides a hexagonal boron nitride lamellar crystal, wherein the hexagonal boron nitride lamellar crystal has a D50 of 1-4 μm and a specific surface area of ​​12-20 m². 2 / g, thermal conductivity 0.9~1.1W·m -1 ·K -1 .

[0032] D50 refers to the particle size corresponding to a cumulative particle size distribution percentage of 50% for hexagonal boron nitride flakes. It can reflect the particle size distribution of hexagonal boron nitride flakes and can be obtained by particle size analyzer.

[0033] Specific surface area refers to the total area per unit mass of material, i.e., area / volume, and the unit is m². 2 / g. Generally speaking, the finer the dust particles, the larger the specific surface area. Specific surface area can be measured by the BET method.

[0034] Thermal conductivity refers to the ability of an object to conduct heat, and its unit is W·m. -1 ·K-1 The higher the thermal conductivity value, the greater the material's ability to transfer heat. Thermal conductivity can be measured using a thermal conductivity meter.

[0035] In one specific embodiment, the hexagonal boron nitride wafers provided by the present invention have a boron nitride content of not less than 99.0% and a water-soluble boron content of not more than 0.3%, thus exhibiting high purity.

[0036] The boron nitride content in hexagonal boron nitride wafers can be calculated according to Equation 1.

[0037]

[0038] Where C is the concentration of sodium hydroxide, in mol / L;

[0039] V1 is the volume of sodium hydroxide consumed, in mL;

[0040] V2 is the volume of sodium hydroxide consumed in the blank test, in mL;

[0041] m is the mass of the experiment, in grams (g).

[0042] 0.02481 refers to the mass of boron nitride, expressed in grams, equivalent to 1.00 ml of a standard sodium hydroxide titration solution with c(NaOH) = 1.000 mol / L.

[0043] 0.7127 refers to the coefficient used to convert the percentage of free boron oxide to the percentage of boron nitride.

[0044] Water-soluble boron refers to the content of soluble boric acid compounds in hexagonal boron nitride crystals, mainly B2O3.

[0045] The content of water-soluble boron in hexagonal boron nitride wafers can be calculated according to Equation 2.

[0046]

[0047] Where C is the concentration of sodium hydroxide, in mol / L;

[0048] V1 is the volume of sodium hydroxide consumed, in mL;

[0049] V2 is the volume of sodium hydroxide consumed in the blank test, in ml;

[0050] m is the mass of the experiment, in grams (g).

[0051] 0.03481 refers to the mass of boron trioxide, expressed in grams, equivalent to 1.00 ml of a standard sodium hydroxide titration solution with c(NaOH) = 1.000 mol / L.

[0052] In one specific embodiment, the hexagonal boron nitride lamellar crystals are prepared by the following method:

[0053] The first hexagonal boron nitride flakes with a D50 of 6-10 μm are calcined in an air or oxygen atmosphere at a temperature of 700-1000℃ for 1-8 hours to obtain the second hexagonal boron nitride flakes with a particle size reduction rate of not less than 40%.

[0054] The second hexagonal boron nitride wafer was acid-washed using an acid-washing solution containing H2O. + The concentration of the pickling solution is 0.1–5 mol / L, the temperature of the pickling solution is 40–90 °C, the pickling time is 0.5–5 h, and the filtered solution yields boron nitride flakes with a D50 of 1–4 μm.

[0055] The third hexagonal boron nitride crystal was washed with deionized water at a temperature of 40–90°C for 0.5–6 hours. After filtration and drying, hexagonal boron nitride crystals were obtained.

[0056] A second aspect of this invention provides a method for preparing hexagonal boron nitride lamellar crystals, comprising the following steps:

[0057] The first hexagonal boron nitride flakes with a D50 of 6-10 μm are calcined in an air or oxygen atmosphere at a temperature of 700-1000℃ for 1-8 hours to obtain the second hexagonal boron nitride flakes with a particle size reduction rate of not less than 40%.

[0058] The second hexagonal boron nitride wafer was acid-washed using an acid-washing solution containing H2O. + The concentration of the pickling solution is 0.1–5 mol / L, the temperature of the pickling solution is 40–90 °C, the pickling time is 0.5–5 h, and the filtered solution yields boron nitride flakes with a D50 of 1–4 μm.

[0059] The third hexagonal boron nitride crystal was washed with deionized water at a temperature of 40–90°C for 0.5–6 hours. After filtration and drying, hexagonal boron nitride crystals were obtained.

[0060] The hexagonal boron nitride lamellar crystals have a D50 of 1–4 μm and a specific surface area of ​​12–20 m². 2 / g, thermal conductivity 0.9~1.1W·m -1 ·K -1 .

[0061] In one specific embodiment, the method for preparing hexagonal boron nitride lamellar crystals includes the following steps:

[0062] Step 1: Calcining the first hexagonal boron nitride flakes with a D50 of 6-10 μm is carried out in an air or oxygen atmosphere at a temperature of 700-1000℃ for 1-8 hours to obtain the second hexagonal boron nitride flakes with a particle size reduction rate of not less than 40%.

[0063] The hexagonal boron nitride lamellar crystals of this invention are obtained from first hexagonal boron nitride lamellar crystals with a D50 of 6-10 μm through calcination and subsequent processing. Calcination helps to partially oxidize the surface of the hexagonal boron nitride lamellar crystals, generating boron oxide. The bond length of the oxygen-boron bond is shorter than that of the nitrogen-boron bond, which helps to reduce the particle size of the hexagonal boron nitride. Simultaneously, calcination causes oxidative decomposition of some crystal defects and incomplete areas, resulting in a more regular crystal morphology and improved crystallinity of the boron nitride lamellar crystals.

[0064] In one specific embodiment, the calcination temperature is 700–1000℃. When the calcination temperature is below 700℃, the temperature is too low, and the calcination efficiency is low; when the calcination temperature is above 1000℃, the temperature is too high, the loss of boron nitride is relatively large, and the cost increases. The temperature can be adjusted within the range of 700–1000℃ according to the particle size of the raw material and the required product specifications.

[0065] Furthermore, the calcination temperature is 800–900℃, specifically within the range of 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, or any combination thereof. Within this range, a faster calcination rate can be achieved, while product loss is minimized, resulting in the highest overall efficiency.

[0066] The present invention does not impose too many restrictions on the container used for calcination. In one specific embodiment, the calcination is carried out in a crucible. Based on a 500 mL crucible, the mass of the first hexagonal boron nitride is 50-150 g.

[0067] Furthermore, based on a 500 mL crucible, the mass of the first hexagonal boron nitride is 50 g.

[0068] Step 2: Pickling the second hexagonal boron nitride wafer with a pickling solution, wherein the pickling solution contains H... + The concentration of the pickling solution is 0.1–5 mol / L, the temperature of the pickling solution is 40–90 °C, the pickling time is 0.5–5 h, and the filtered solution yields boron nitride flakes with a D50 of 1–4 μm.

[0069] Pickling can remove the oxide layer on the surface of the second hexagonal boron nitride wafer after calcination, thereby improving product purity and further reducing the particle size of hexagonal boron nitride.

[0070] In one specific embodiment, the pickling solution includes at least one of hydrochloric acid, sulfuric acid, or nitric acid.

[0071] Step 3: Wash the third hexagonal boron nitride crystal with deionized water at a temperature of 40-90°C for 0.5-6 hours. After filtration and drying, the hexagonal boron nitride crystal is obtained.

[0072] It is understandable that after pickling, there will be pickling solution residue on the third hexagonal boron nitride wafer. The residual pickling solution can be removed by washing with water.

[0073] During the pickling and washing processes, a small amount of hexagonal boron nitride will also be lost. Compared with the first hexagonal boron nitride wafer, the particle size reduction rate of the hexagonal boron nitride wafer is not less than 50%, and the loss rate of hexagonal boron nitride is not higher than 15%.

[0074] The hexagonal boron nitride flakes prepared by the above method have a boron nitride content of not less than 99.0% and a water-soluble boron content of not more than 0.3%, indicating high purity.

[0075] The third aspect of the present invention provides the application of the above-mentioned hexagonal boron nitride flakes in thermally conductive and insulating materials.

[0076] The hexagonal boron nitride flakes of the present invention have the characteristics of small D50, large specific surface area, high thermal conductivity and high purity. When used in thermally conductive insulating materials, they can give the thermally conductive insulating materials excellent thermal conductivity.

[0077] The solution provided by the present invention will be further described below with reference to specific embodiments.

[0078] Example 1

[0079] The method for preparing hexagonal boron nitride lamellar crystals in this embodiment includes the following steps:

[0080] Step 1: Weigh 50.00g of hexagonal boron nitride lamellar crystals with D50 = 8.56μm (i.e., the first hexagonal boron nitride lamellar crystals), loosely pack them into a 500mL crucible, then place the crucible containing the boron nitride lamellar crystals in a muffle furnace, calcine at 800℃ in an air atmosphere for 6 hours, and obtain the second hexagonal boron nitride lamellar crystals after cooling to room temperature.

[0081] Step 2: Place the second hexagonal boron nitride crystal sheet in a 500mL beaker, add 250mL of 1mol / L hydrochloric acid, and heat to 60℃ while stirring, maintaining this temperature for 2 hours. After acid washing, remove the acid solution by suction filtration using a vacuum flask, and remove the filter cake to obtain the third hexagonal boron nitride crystal sheet.

[0082] Step 3: Place the third hexagonal boron nitride crystal sheet in a beaker, add 250 mL of deionized water, and heat to 60°C while stirring, maintaining this temperature for 1 hour. Filter the washed sample, and continue washing the filter cake with water until the filtrate pH is neutral (pH = 7). Dry the neutralized filter cake in an oven at 90-110°C. The resulting sample is a hexagonal boron nitride crystal sheet.

[0083] Scanning electron microscope images of the first hexagonal boron nitride lamellar crystal and the hexagonal boron nitride lamellar crystal prepared in Example 1 are shown below. Figure 1 and Figure 2 As shown in the figure, it can be seen that by calcining at high temperature in an air atmosphere, large-particle-size boron nitride flakes can be prepared into small-particle-size boron nitride flakes. Compared with the samples before calcination, the particle size distribution of the treated samples is more uniform, and the flake edges are basically without obvious sharp corners and the morphology is more regular.

[0084] Example 2

[0085] The preparation method of hexagonal boron nitride flakes in this embodiment is basically the same as that in Example 1, except that the calcination temperature is 900℃ and the calcination time is 2h.

[0086] Example 3

[0087] The preparation method of hexagonal boron nitride flakes in this embodiment is basically the same as that in Example 1, except that the calcination temperature is 800℃ and the calcination time is 4h.

[0088] Example 4

[0089] The preparation method of the hexagonal boron nitride wafer in this embodiment is basically the same as that in Example 1, except that the D50 of the first hexagonal boron nitride wafer is 6.23 μm.

[0090] Comparative Example 1

[0091] This comparative example uses the first hexagonal boron nitride wafer from Example 1 as the comparative example.

[0092] Comparative Example 2

[0093] The preparation method of the hexagonal boron nitride lamellar crystals in this comparative example is basically the same as that in Example 1, except that the calcination treatment in step 1 is replaced by ball milling treatment. The specific method of ball milling treatment is as follows:

[0094] Dissolve 0.1g of carboxymethyl cellulose dispersant in 200mL of deionized water, then add it to the ball mill jar of a ball mill, add 50g of first hexagonal boron nitride flakes with D50=8.56μm, add 100g of grinding beads, and grind at 1000rpm for 3h.

[0095] Comparative Example 3

[0096] The preparation method of hexagonal boron nitride lamellar crystals in this comparative example is basically the same as that in Example 1, except that the calcination treatment in step 1 is replaced by air jet milling treatment. The specific method of air jet milling treatment is as follows:

[0097] Set the feed pressure to 0.4 MPa, add 50 g of first hexagonal boron nitride flakes with D50 = 8.56 μm to the air jet mill, turn on the equipment switch, and process the flakes through the air jet mill.

[0098] Comparative Example 4

[0099] The preparation method of the hexagonal boron nitride lamellar crystals in this comparative example is basically the same as that in Example 1, except that the calcination treatment in step 1 is replaced by liquid-phase ultrasonic exfoliation. The specific method of liquid-phase ultrasonic exfoliation is as follows:

[0100] Set the ultrasonic frequency to 100 kHz, add 50 g of the first hexagonal boron nitride sheet with D50 = 8.56 μm to a beaker, add 200 mL of deionized water, add 0.1 g of H2O2 to assist ultrasonic exfoliation, turn on the device, and perform ultrasonic exfoliation for 30 minutes.

[0101] Test case

[0102] The D50, specific surface area, boron nitride content, and water-soluble boron content of the hexagonal boron nitride lamellar crystals in Examples 1-4 and Comparative Examples 1-4 were determined using the following methods. The results are shown in Table 1.

[0103] The method for testing boron nitride content is as follows: Weigh 0.07-0.08 g (accurate to 0.1 mg) of pre-dried sample and place it in a pyrolytic graphite crucible or nickel crucible. Add 3 g of potassium hydroxide or sodium hydroxide and heat in an electric furnace until the mixture becomes a transparent solution. Rotate the crucible to ensure complete melting. After slightly cooling, dissolve the melt in a beaker with warm water. Add 0.4 mL of mixed indicator and neutralize with 6 mol / L hydrochloric acid until the solution turns red. Boil the solution for 5 minutes, cool rapidly, and neutralize excess acid with 0.1 mol / L sodium hydroxide until the solution changes from red to dark red, which is the titration starting point. Add 7 g of mannitol, then add 0.1 mL of mixed indicator and immediately titrate with 0.1 mol / L sodium hydroxide solution until the endpoint is gray. The color change sequence is red-dark red-green-gray. Perform a blank test simultaneously. Calculate the boron nitride content according to Equation 1.

[0104] The method for testing the content of water-soluble boron is as follows: Weigh 0.5-1g of pre-dried sample, accurate to 0.1mg, place it in a 250mL Erlenmeyer flask, add a little water to mix, and add 5ml of 0.1mol / L sulfuric acid solution. Add water to a total volume of 50 mL, assemble the reflux cooler, and connect the cooling water. Maintain a gentle boil for 1 hour, then stop heating. After slightly cooling, rinse the cooler and connections with water. While still hot, filter using a G3 glass funnel. Wash the filter residue 7-9 times with warm water. Transfer the filtrate and washings to a 500 mL Erlenmeyer flask. Add 0.4 mL of mixed indicator, adjust the solution to green with 0.1 mol / L sodium hydroxide solution, then adjust to red with 1+4 hydrochloric acid solution, adding an excess of 0.1 mL. Heat to boiling for 2-3 minutes, then rapidly cool. Add another 0.1 mL of mixed indicator, and immediately neutralize the excess acid with 0.1 mol / L sodium hydroxide solution until the solution changes from red to dark red. This is the titration starting point. Add 4 g of mannitol, and titrate with 0.1 mol / L sodium hydroxide solution until the solution just turns gray, which is the endpoint. The indicator color change sequence is red-dark red-gray-green-gray. Perform a blank titration simultaneously. Calculate the water-soluble boron content according to Equation 2.

[0105] The method for testing thermal conductivity is as follows: 30g of boron nitride powder is added to 70g of vinyl silicone oil and stirred thoroughly for 30 minutes to obtain a uniform slurry. After standing to remove bubbles, the resulting thermally conductive composite material is baked in an oven at 110℃ for 30 minutes. After cooling, the thermal conductivity of the composite material is tested in a thermal conductivity meter.

[0106]

[0107] As can be seen from Table 1, compared with Comparative Example 1, the hexagonal boron nitride flakes prepared in Examples 1 to 4 all showed a reduction in particle size of more than 50%; higher purity, all greater than 99.0%; and improved thermal conductivity.

[0108] Compared with Comparative Example 2 (ball milling to synthesize small particle size), Comparative Example 3 (air jet milling to synthesize small particle size), and Comparative Example 4 (ultrasonic liquid phase exfoliation to synthesize small particle size), the products of Examples 1 to 4 have a greater reduction in particle size, higher product purity, better thermal conductivity, and lower total loss rate of boron nitride, proving that the preparation method of the present invention has significant advantages.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hexagonal boron nitride platelet, characterized by, The D50 of the hexagonal boron nitride platelet is 1-4 μm, the specific surface area is 12-20 m 2 / g, and the thermal conductivity is 0.9-1.1 W m -1 K -1 ; The hexagonal boron nitride platelets are prepared by the following method: The first hexagonal boron nitride platelets with a D50 of 6-10 μm are subjected to calcination treatment, the calcination treatment is carried out in an air or oxygen atmosphere, the calcination temperature is 700-1000 ℃, and the calcination time is 1-8 h, to obtain second hexagonal boron nitride platelets with a particle size reduction rate of not less than 40%; The second hexagonal boron nitride platelets are subjected to acid washing using an acid washing solution, the concentration of H+ in the acid washing solution is 0.1-5 mol / L, the temperature of the acid washing solution is 40-90 ℃, the acid washing time is 0.5-5 h, and filtration is performed to obtain third hexagonal boron nitride platelets with a D50 of 1-4 μm; The third hexagonal boron nitride platelets are subjected to water washing using deionized water, the temperature of the deionized water is 40-90 ℃, the water washing time is 0.5-6 h, and filtration and drying are performed to obtain hexagonal boron nitride platelets.

2. The hexagonal boron nitride platelets of claim 1, wherein, The content of boron nitride in the hexagonal boron nitride platelets is not less than 99.0%, and the content of water-soluble boron is not higher than 0.3%.

3. A method of producing hexagonal boron nitride platelets, characterized by, The method comprises the following steps: The first hexagonal boron nitride platelets with a D50 of 6-10 μm are subjected to calcination treatment, the calcination treatment is carried out in an air or oxygen atmosphere, the calcination temperature is 700-1000 ℃, and the calcination time is 1-8 h, to obtain second hexagonal boron nitride platelets with a particle size reduction rate of not less than 40%; The second hexagonal boron nitride platelets are subjected to acid washing using an acid washing solution having a concentration of 0.1-5 mol / L of H + , a temperature of 40-90 DEG C, and an acid washing time of 0.5-5 h, and then filtered to obtain third hexagonal boron nitride platelets having a D50 of 1-4 μm. The third hexagonal boron nitride platelets are subjected to water washing using deionized water, the temperature of the deionized water is 40-90 ℃, the water washing time is 0.5-6 h, and filtration and drying are performed to obtain hexagonal boron nitride platelets; The D50 of the hexagonal boron nitride platelet is 1-4 μm, the specific surface area is 12-20 m 2 / g, and the thermal conductivity is 0.9-1.1 W m -1 K -1 .

4. The method of claim 3, wherein, The acid washing solution comprises at least one of hydrochloric acid, sulfuric acid, and nitric acid.

5. The method according to claim 3 or 4, characterized in that, The content of boron nitride in the hexagonal boron nitride platelets is not less than 99.0%, and the content of water-soluble boron is not higher than 0.3%.

6. The method according to claim 3 or 4, characterized in that, The particle size reduction rate of the hexagonal boron nitride platelets is not less than 50%.

7. The method according to claim 3 or 4, characterized in that, The total boron nitride loss rate in the hexagonal boron nitride is not higher than 15%.

8. The method according to any one of claims 3 to 7, characterized in that, The calcination treatment is carried out in a crucible, and based on a 500 mL crucible, the mass of the first hexagonal boron nitride is 50-150 g.

9. Use of the hexagonal boron nitride platelets according to any one of claims 1-2 or the hexagonal boron nitride platelets prepared by the method according to any one of claims 3-8 in a heat-conducting insulating material.

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