Boron nitride composite powder and preparation method thereof

Abstract

The invention provides boron nitride composite powder and a preparation method thereof, and belongs to the technical field of inorganic heat-conducting powder. The preparation method of the boron nitride composite powder comprises the following steps: preparing boron nitride slurry by taking spherical boron nitride as a raw material; preparing modified slurry from oxide, hydroxide or carbonate; mixing and stirring the boron nitride slurry and the modified slurry, and performing spray drying to obtain boron nitride precursor powder; and calcining and discharging glue, calcining in a protective gas atmosphere, and cooling to obtain the boron nitride composite powder. On the basis of keeping the characteristics of high thermal conductivity, high insulation, low density, low dielectric loss and the like of boron nitride, a core-shell structure is formed on the surface of spherical boron nitride, so that the surface inertia of boron nitride is changed, surface pores are reduced, boron nitride is endowed with better compatibility in a polymer matrix, and the thermal conductivity of boron nitride is improved. Therefore, the oil absorption value of the powder is reduced, the maximum filling rate of the powder in a polymer matrix is increased, and higher heat conduction is realized.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic thermal conductive powders, and in particular to a boron nitride composite powder and a preparation method thereof. Background Art

[0002] Boron nitride has the advantages of high thermal conductivity, high insulation, low dielectric loss, thermal stability, acid and alkali resistance, etc. It is widely used in products in the fields of mobile equipment, aerospace, low-altitude facilities, etc. However, boron nitride is not perfect. It has severe anisotropy, and the difference in thermal conductivity in different directions is nearly 10 times. In addition, because the surface of boron nitride is very inert and difficult to be compatible with the polymer matrix, although it has a high intrinsic thermal conductivity, the filling rate in the polymer matrix is ​​low, and the thermal conductivity of the final thermal conductive interface material is also low.

[0003] Some researchers have improved the filling rate of boron nitride in a polymer matrix and weakened the anisotropy of boron nitride by sintering flake boron nitride into boron nitride agglomerates. For example: China's invention application (name: "A hexagonal boron nitride material and its preparation method and application", publication number: CN117800739A, publication date: 20240402) discloses a hexagonal boron nitride material and its preparation method and application, the preparation method comprising the following steps: hydrophilic modification of the hexagonal boron nitride raw material to obtain a modified hexagonal boron nitride raw material; mixing the modified hexagonal boron nitride raw material, surfactant, polymer binder, sintering aid and dispersion medium to prepare a second slurry; spray drying the second slurry to form a spherical particle product; sintering the spherical particle product to obtain the hexagonal boron nitride material. The present invention can improve the properties of the hexagonal boron nitride material such as sphericity and size, increase the filling amount of the hexagonal boron nitride material in the thermal conductive composite material, and reduce the viscosity of the thermal conductive composite material.

[0004] Although the boron nitride agglomerate is a structure composed of many boron nitride flakes sintered together, there are still many pores on its surface, and the specific surface area and oil absorption value are still large. Therefore, a surface modification method is urgently needed to reduce the pores on the surface of the boron nitride agglomerate, so as to reduce the oil absorption value and increase the filling rate. Summary of the invention

[0005] The present invention aims to provide a boron nitride composite powder and a preparation method thereof, which forms a core-shell structure on the surface of spherical boron nitride on the basis of maintaining the high thermal conductivity, high insulation, low density, low dielectric loss and other characteristics of boron nitride, changes the surface inertness of boron nitride, reduces surface pores, and gives boron nitride better compatibility in a polymer matrix, thereby reducing the oil absorption value of the powder, increasing the maximum filling rate of the powder in the polymer matrix, and further achieving higher thermal conductivity.

[0006] The technical solution adopted by the present invention is:

[0007] A method for preparing a boron nitride composite powder comprises the following steps:

[0008] Step S1, fully mixing and stirring the spherical boron nitride and the sodium hydroxide solution, filtering and washing with pure water and anhydrous ethanol in turn, and then mixing and stirring the washed spherical boron nitride, pure water and the first dispersant according to a ratio to prepare a boron nitride slurry;

[0009] Step S2, weighing one or more of oxides, hydroxides and carbonates with the same cations according to the ratio and then ball milling, and then adding an appropriate amount of pure water, a second dispersant, a binder and a sintering aid to continue ball milling to obtain a modified slurry; wherein the amount of oxide, hydroxide or carbonate is 2-15% of the weight of spherical boron nitride; the oxide is one or more of magnesium oxide, zinc oxide, aluminum oxide, silicon oxide, titanium oxide; the hydroxide is one or more of magnesium hydroxide, zinc hydroxide, aluminum hydroxide; the carbonate is one or more of magnesium carbonate, zinc carbonate, aluminum carbonate.

[0010] Step S3, mixing and stirring the boron nitride slurry and the modified slurry, and spray drying to obtain a boron nitride precursor powder;

[0011] Step S4, calcining the boron nitride precursor powder to remove binder, then calcining in a protective gas atmosphere, and cooling to obtain a boron nitride composite powder.

[0012] Furthermore, in step S1, the molar concentration of the sodium hydroxide solution is 2-5 mol / L, and the spherical boron nitride and the sodium hydroxide solution are stirred and mixed for 3-12 hours.

[0013] Furthermore, in step S1, the weight ratio of spherical boron nitride to pure water is 1:1.5-1:6; and the amount of the first dispersant is 0.1-5% of the weight of the spherical boron nitride.

[0014] Furthermore, in step S2, the amount of the second dispersant is 0.1-5% of the total weight of the oxides, hydroxides and carbonates; the amount of the binder is 0.5-3% of the total weight of the oxides, hydroxides and carbonates; and the amount of the sintering aid is 2-3% of the total weight of the oxides, hydroxides and carbonates.

[0015] Further, in step S1, the first dispersant is one or more of anhydrous ethanol, polyacrylic acid, fatty acid modified polymer, polyethylene glycol 200, isopropanol, polypropylene glycol 400, and polycarboxylic acid sodium salt;

[0016] In the step S2, the second dispersant is one or more of anhydrous ethanol, polyacrylic acid, fatty acid modified polymer, polyethylene glycol 200, isopropanol, polypropylene glycol 400, and polycarboxylic acid sodium salt;

[0017] The adhesive is one or more of hydroxypropyl methylcellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, polyvinyl alcohol, polyanionic cellulose, and polyvinyl butyral;

[0018] The sintering aid is one or more of calcium oxide, calcium fluoride, aluminum fluoride, boron oxide, silicon dioxide, magnesium oxide, and yttrium oxide.

[0019] Further, in step S2, the oxide is one or both of an oxide with a particle size ranging from 20 to 100 nm and an oxide with a D50 particle size of 0.3 to 3 μm;

[0020] The hydroxide is one or both of a hydroxide having a particle size range of 20 to 100 nm and a hydroxide having a D50 particle size of 0.3 to 3 μm;

[0021] The carbonate is one or both of a carbonate having a particle size range of 20 to 100 nm and a carbonate having a D50 particle size of 0.3 to 3 μm.

[0022] Furthermore, in step S2, the ratio of the total weight of oxides with a particle size range of 20-100 nm, hydroxides with a particle size range of 20-100 nm and carbonates with a particle size range of 20-100 nm to the total weight of oxides with a D50 particle size of 0.3-3 μm, hydroxides with a D50 particle size of 0.3-3 μm and carbonates with a D50 particle size of 0.3-3 μm is 1:2-1:9.

[0023] Furthermore, in step S2, the mass ratio of the ball mill to the modified slurry is 2:1-5:1, and the ball milling time after adding pure water is 1-6 hours.

[0024] Furthermore, in the step S4, during calcination and debinding, the debinding temperature is 450° C. to 850° C., and the holding time is 0.5 to 4 hours.

[0025] Furthermore, in step S4, during calcination in a protective gas atmosphere, the temperature is heated from room temperature to 1000-1300° C. at a rate of 5-15° C. / min and kept warm for 1-3 hours, and then heated to 1400-1600° C. at a rate of 1-5° C. / min and kept warm for 0.5-5 hours.

[0026] Furthermore, in step S4, the protective gas is argon or nitrogen.

[0027] Based on the same inventive concept, the present invention also provides a boron nitride composite powder, which is prepared by the above-mentioned method for preparing the boron nitride composite powder, with spherical boron nitride as the core and coated to form a core-shell structure.

[0028] The beneficial effects of the present invention are:

[0029] The boron nitride composite powder and preparation method designed in the present invention maintain the high thermal conductivity, high insulation, low density, low dielectric loss and other characteristics of boron nitride, form a core-shell structure on the surface of spherical boron nitride, change the surface inertness of boron nitride, reduce surface pores, and give boron nitride better compatibility in the polymer matrix, thereby reducing the oil absorption value of the powder and increasing the maximum filling rate of the powder in the polymer matrix, thereby achieving higher thermal conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present application 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 application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 This is the microscopic morphology of spherical boron nitride powder.

[0032] Figure 2 The microscopic morphology of the boron nitride composite powder prepared in Example 1.

[0033] Figure 3 The microscopic morphology of the boron nitride composite powder prepared in Example 2.

[0034] Figure 4 The microscopic morphology of the boron nitride composite powder prepared in Example 3.

[0035] Figure 5 The microscopic morphology of the boron nitride composite powder prepared in Example 4.

[0036] Figure 6 This is the microscopic morphology of the boron nitride composite powder prepared in Example 5.

[0037] Figure 7 The microscopic morphology of the boron nitride composite powder prepared in Example 6.

[0038] Figure 8 This is the microscopic morphology of the boron nitride composite powder prepared in Example 7.

[0039] Fig. 9 This is the microscopic morphology of the boron nitride composite powder prepared in Control Example 5. DETAILED DESCRIPTION

[0040] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0041] The disclosure below provides many different embodiments or examples to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention.

[0042] The embodiments of the invention are described in detail below with reference to the accompanying drawings.

[0043] Example 1

[0044] A method for preparing a boron nitride composite powder comprises the following steps:

[0045] Step 1: fully mix 1 kg of spherical boron nitride with 5 L of 2 mol / L sodium hydroxide solution and stir for 3 h. After stirring, wash the powder with pure water and ethanol for 5 times in sequence. After drying, mix the spherical boron nitride, 2 L of pure water and 1 g of polyacrylic acid, and stir them evenly to form a boron nitride slurry.

[0046] Step 2: Take 2g of nano-alumina (particle size range is 20-100nm) and 18g of submicron alumina (D50 particle size is 0.5μm) and mix them by ball milling for 0.5h using a planetary ball mill, with 210g of ball mill (the diameter of the large-particle zirconia beads is 2.0mm, the diameter of the small-particle zirconia beads is 0.5mm, and the two are prepared in a weight ratio of 3:1);

[0047] Step 3: Add 50 mL of pure water, 0.1 g of polyacrylic acid, 0.1 g of carboxymethyl cellulose, and 0.5 g of aluminum fluoride to the mixed powder obtained in step 2, and continue to use a planetary ball mill for 1 hour to obtain a uniform modified slurry;

[0048] Step 4, mixing the boron nitride slurry prepared in step 1 and the modified slurry prepared in step 3 and stirring them thoroughly;

[0049] Step 5, spray granulating the slurry obtained in step 4 to obtain dry boron nitride precursor powder;

[0050] Step 6: Place the boron nitride precursor powder obtained in step 5 into a muffle furnace for calcination and debinding at a debinding temperature of 450° C. for 4 hours;

[0051] Step seven, the powder after calcination and debinding in step six is ​​placed in a high-temperature furnace for calcination, and nitrogen is introduced as a protective gas. The pressure is slightly greater than the atmospheric pressure. The heating method is to heat to 1000°C at 5°C / min and keep it warm for 1h, then heat to 1400°C at a rate of 2°C / min and keep it warm for 1h, and then naturally cool down to obtain boron nitride composite powder.

[0052] The obtained boron nitride composite powder was photographed with a scanning electron microscope, and then mixed with silicone oil with a viscosity of 500cp. The weight of the silicone oil was kept constant and the weight of the powder was gradually increased until the powder and the silicone oil could not be mixed. The maximum mass filling rate of the powder (the ratio of the weight of the powder to the weight of the powder-silicone oil mixed system) was calculated, and the thermal conductivity of the system when the maximum mass filling rate was reached was tested by the transient method. The results are shown in Table 1.

[0053] Example 2

[0054] A method for preparing a boron nitride composite powder comprises the following steps:

[0055] Step 1: fully mix 1 kg of spherical boron nitride with 5 L of 3 mol / L sodium hydroxide solution and stir for 6 hours. After stirring, wash the powder with pure water and ethanol for 5 times in sequence. After drying, mix the spherical boron nitride, 4 L of pure water and 2.5 g of polyacrylic acid, and stir them evenly to form a boron nitride slurry.

[0056] Step 2: 4 g of nano silicon oxide (particle size range is 20-100 nm) and 16 g of micro silicon oxide (D50 particle size is 1 μm) are mixed by ball milling in a planetary ball mill for 0.5 h; 210 g of ball mill (the diameter of large-particle zirconium oxide beads is 2.0 mm, the diameter of small-particle zirconium oxide beads is 0.5 mm, and the two are prepared in a weight ratio of 3:1);

[0057] Step 3: add 50 mL of pure water, 0.1 g of fatty acid-modified polymer, 0.1 g of carboxymethyl cellulose, and 0.5 g of yttrium oxide to the mixed powder obtained in step 2, and continue to use a planetary ball mill for 3 hours to obtain a uniform modified slurry;

[0058] Step 4, mixing the boron nitride slurry prepared in step 1 and the modified slurry prepared in step 3 and stirring them thoroughly;

[0059] Step 5, spray granulating the slurry obtained in step 4 to obtain dry boron nitride precursor powder;

[0060] Step 6: Place the boron nitride precursor powder obtained in step 5 into a muffle furnace for calcination and debinding at a debinding temperature of 600° C. for 2 hours;

[0061] Step seven, the powder after calcination and debinding in step six is ​​placed in a high-temperature furnace for calcination, and nitrogen is introduced as a protective gas. The pressure is slightly greater than the atmospheric pressure. The heating method is to heat to 1000°C at 10°C / min and keep it warm for 2h, then heat to 1500°C at a rate of 2°C / min and keep it warm for 3h, and obtain boron nitride composite powder after natural cooling.

[0062] The obtained boron nitride composite powder was photographed with a scanning electron microscope, and then mixed with silicone oil with a viscosity of 500cp. The weight of the silicone oil was kept constant and the weight of the powder was gradually increased until the powder and the silicone oil could not be mixed. The maximum mass filling rate of the powder (the ratio of the weight of the powder to the weight of the powder-silicone oil mixed system) was calculated, and the thermal conductivity of the system when the maximum mass filling rate was reached was tested by the transient method. The results are shown in Table 1.

[0063] Example 3

[0064] A method for preparing a boron nitride composite powder comprises the following steps:

[0065] Step 1: fully mix 1 kg of spherical boron nitride with 5 L of 5 mol / L sodium hydroxide solution and stir for 12 h. After stirring, wash the powder with pure water and ethanol for 5 times in sequence. After drying, mix the spherical boron nitride, 6 L of pure water and 2.5 g of polyacrylic acid and stir them evenly to form a boron nitride slurry.

[0066] Step 2: Take 45g of nano magnesium oxide (particle size range is 20-100nm) and 105g of micro magnesium oxide (D50 particle size is 3μm) and mix them by ball milling in a planetary ball mill for 0.5h; 750g of ball mill (the diameter of large-particle zirconium oxide beads is 2.0mm, the diameter of small-particle zirconium oxide beads is 0.5mm, and the two are prepared in a weight ratio of 3:1);

[0067] Step 3: add 100 mL of pure water, 7.5 g of polypropylene glycol 400, 4.5 g of a mixture of polyvinyl alcohol and polyvinyl butyral (the weight ratio of the two is 1:1), and 4.5 g of yttrium oxide to the mixed powder obtained in step 2, and continue to use a planetary ball mill for 6 hours to obtain a uniform modified slurry;

[0068] Step 4, mixing the boron nitride slurry prepared in step 1 and the modified slurry prepared in step 3 and stirring them thoroughly;

[0069] Step 5, spray granulating the slurry obtained in step 4 to obtain dry boron nitride precursor powder;

[0070] Step 6: Place the boron nitride precursor powder obtained in step 5 into a muffle furnace for calcination and debinding at a debinding temperature of 800° C. for 1 hour;

[0071] Step seven, the powder after calcination and debinding in step six is ​​placed in a high-temperature furnace for calcination, and nitrogen is introduced as a protective gas. The pressure is slightly greater than the atmospheric pressure. The heating method is to heat to 1300°C at 12°C / min and keep warm for 3h, then heat to 1600°C at a rate of 3°C / min and keep warm for 5h, and obtain boron nitride composite powder after natural cooling.

[0072] The obtained boron nitride composite powder was photographed with a scanning electron microscope, and then mixed with silicone oil with a viscosity of 500cp. The weight of the silicone oil was kept constant and the weight of the powder was gradually increased until the powder and the silicone oil could not be mixed. The maximum mass filling rate of the powder (the ratio of the weight of the powder to the weight of the powder-silicone oil mixed system) was calculated, and the thermal conductivity of the system when the maximum mass filling rate was reached was tested by the transient method. The results are shown in Table 1.

[0073] Example 4

[0074] A method for preparing a boron nitride composite powder comprises the following steps:

[0075] Step 1: fully mix 1 kg of spherical boron nitride with 5 L of 2 mol / L sodium hydroxide solution and stir for 3 h. After stirring, wash the powder with pure water and ethanol for 5 times in sequence. After drying, mix the spherical boron nitride, 2 L of pure water and 1 g of polyacrylic acid, and stir them evenly to form a boron nitride slurry.

[0076] Step 2: Take 2g of nano-alumina (particle size range is 20-100nm) and 18g of submicron aluminum hydroxide (D50 particle size is 0.5μm) and mix them by ball milling in a planetary ball mill for 0.5h; 210g of ball mill (the diameter of large-particle zirconium oxide beads is 2.0mm, the diameter of small-particle zirconium oxide beads is 0.5mm, and the two are prepared in a weight ratio of 3:1);

[0077] Step 3: Add 50 mL of pure water, 0.1 g of polyacrylic acid, 0.1 g of carboxymethyl cellulose, and 0.5 g of calcium oxide to the mixed powder obtained in step 2, and continue to use a planetary ball mill for 1 hour to obtain a uniform modified slurry;

[0078] Step 4, mixing the boron nitride slurry prepared in step 1 and the modified slurry prepared in step 3 and stirring them thoroughly;

[0079] Step 5, spray granulating the slurry obtained in step 4 to obtain dry boron nitride precursor powder;

[0080] Step 6: Place the boron nitride precursor powder obtained in step 5 into a muffle furnace for calcination and debinding at a debinding temperature of 450° C. for 4 hours;

[0081] Step seven, the powder after calcination and debinding in step six is ​​placed in a high-temperature furnace for calcination, and nitrogen is introduced as a protective gas. The pressure is slightly greater than the atmospheric pressure. The heating method is to heat to 1000°C at 5°C / min and keep it warm for 1h, then heat to 1400°C at a rate of 2°C / min and keep it warm for 1h, and then naturally cool down to obtain boron nitride composite powder.

[0082] The obtained boron nitride composite powder was photographed with a scanning electron microscope, and then mixed with silicone oil with a viscosity of 500cp. The weight of the silicone oil was kept constant and the weight of the powder was gradually increased until the powder and the silicone oil could not be mixed. The maximum mass filling rate of the powder (the ratio of the weight of the powder to the weight of the powder-silicone oil mixed system) was calculated, and the thermal conductivity of the system when the maximum mass filling rate was reached was tested by the transient method. The results are shown in Table 1.

[0083] Example 5

[0084] A method for preparing a boron nitride composite powder comprises the following steps:

[0085] Step 1: fully mix 1 kg of spherical boron nitride with 5 L of 2 mol / L sodium hydroxide solution and stir for 3 h. After stirring, wash the powder with pure water and ethanol for 5 times in sequence. After drying, mix the spherical boron nitride, 2 L of pure water and 1 g of polyacrylic acid, and stir them evenly to form a boron nitride slurry.

[0086] Step 2: 4 g of nano zinc oxide (particle size range is 20-100 nm) and 36 g of submicron zinc oxide (D50 particle size is 0.3 μm) are mixed by ball milling for 0.5 h using a planetary ball mill; 330 g of ball mill (the diameter of large-particle zirconium oxide beads is 2.0 mm, the diameter of small-particle zirconium oxide beads is 0.5 mm, and the two are prepared in a weight ratio of 3:1);

[0087] Step 3: Add 70 mL of pure water, 0.1 g of polyacrylic acid, 0.1 g of carboxymethyl cellulose, and 0.5 g of calcium oxide to the mixed powder obtained in step 2, and continue to use a planetary ball mill for 1 hour to obtain a uniform modified slurry;

[0088] Step 4, mixing the boron nitride slurry prepared in step 1 and the modified slurry prepared in step 3 and stirring them thoroughly;

[0089] Step 5, spray granulating the slurry obtained in step 4 to obtain dry boron nitride precursor powder;

[0090] Step 6: Place the boron nitride precursor powder obtained in step 5 into a muffle furnace for calcination and debinding at a debinding temperature of 450° C. for 4 hours;

[0091] Step seven, the powder after calcination and debinding in step six is ​​placed in a high-temperature furnace for calcination, and nitrogen is introduced as a protective gas. The pressure is slightly greater than the atmospheric pressure. The heating method is to heat to 1000°C at 8°C / min and keep it warm for 1h, then heat to 1450°C at a rate of 2°C / min and keep it warm for 2h, and obtain boron nitride composite powder after natural cooling.

[0092] The obtained boron nitride composite powder was photographed with a scanning electron microscope, and then mixed with silicone oil with a viscosity of 500cp. The weight of the silicone oil was kept constant and the weight of the powder was gradually increased until the powder and the silicone oil could not be mixed. The maximum mass filling rate of the powder (the ratio of the weight of the powder to the weight of the powder-silicone oil mixed system) was calculated, and the thermal conductivity of the system when the maximum mass filling rate was reached was tested by the transient method. The results are shown in Table 1.

[0093] Example 6

[0094] A method for preparing a boron nitride composite powder comprises the following steps:

[0095] Step 1: fully mix 1 kg of spherical boron nitride with 5 L of 2 mol / L sodium hydroxide solution and stir for 3 h. After stirring, wash the powder with pure water and ethanol for 5 times in sequence. After drying, mix the spherical boron nitride, 2 L of pure water and 1 g of polyacrylic acid, and stir them evenly to form a boron nitride slurry.

[0096] Step 2: 40 g of submicron zinc oxide (D50 particle size is 0.3 μm) is ball-milled for 0.5 h using a planetary ball mill; 330 g of ball mill (the diameter of the large-particle zirconium oxide beads is 2.0 mm, the diameter of the small-particle zirconium oxide beads is 0.5 mm, and the two are prepared in a weight ratio of 3:1);

[0097] Step 3: Add 70 mL of pure water, 0.1 g of polyacrylic acid, 0.1 g of carboxymethyl cellulose, and 0.5 g of calcium oxide to the mixed powder obtained in step 2, and continue to use a planetary ball mill for 1 hour to obtain a uniform modified slurry;

[0098] Step 4, mixing the boron nitride slurry prepared in step 1 and the modified slurry prepared in step 3 and stirring them thoroughly;

[0099] Step 5, spray granulating the slurry obtained in step 4 to obtain dry boron nitride precursor powder;

[0100] Step 6: Place the boron nitride precursor powder obtained in step 5 into a muffle furnace for calcination and debinding at a debinding temperature of 450° C. for 4 hours;

[0101] Step seven, the powder after calcination and debinding in step six is ​​placed in a high-temperature furnace for calcination, and nitrogen is introduced as a protective gas. The pressure is slightly greater than the atmospheric pressure. The heating method is to heat to 1000°C at 8°C / min and keep it warm for 1h, then heat to 1450°C at a rate of 2°C / min and keep it warm for 2h, and obtain boron nitride composite powder after natural cooling.

[0102] The obtained boron nitride composite powder was photographed with a scanning electron microscope, and then mixed with silicone oil with a viscosity of 500cp. The weight of the silicone oil was kept constant and the weight of the powder was gradually increased until the powder and the silicone oil could not be mixed. The maximum mass filling rate of the powder (the ratio of the weight of the powder to the weight of the powder-silicone oil mixed system) was calculated, and the thermal conductivity of the system when the maximum mass filling rate was reached was tested by the transient method. The results are shown in Table 1.

[0103] Example 7

[0104] A method for preparing a boron nitride composite powder comprises the following steps:

[0105] Step 1: fully mix 1 kg of spherical boron nitride with 5 L of 5 mol / L sodium hydroxide solution and stir for 12 h. After stirring, wash the powder with pure water and ethanol for 5 times in sequence. After drying, mix the spherical boron nitride, 6 L of pure water and 2.5 g of polyacrylic acid and stir them evenly to form a boron nitride slurry.

[0106] Step 2: Take 50g of nano magnesium oxide (particle size range is 20-100nm) and 100g of micron magnesium carbonate (D50 particle size is 3μm) and mix them by ball milling for 0.5h using a planetary ball mill; 750g of ball mill (the diameter of large-particle zirconium oxide beads is 2.0mm, the diameter of small-particle zirconium oxide beads is 0.5mm, and the two are prepared in a weight ratio of 3:1);

[0107] Step 3: add 100 mL of pure water, 7.5 g of polypropylene glycol 400, 4.5 g of a mixture of polyvinyl alcohol and polyvinyl butyral, and 4.5 g of yttrium oxide to the mixed powder obtained in step 2, and continue to use a planetary ball mill for 6 hours to obtain a uniform modified slurry;

[0108] Step 4, mixing the boron nitride slurry prepared in step 1 and the modified slurry prepared in step 3 and stirring them thoroughly;

[0109] Step 5, spray granulating the slurry obtained in step 4 to obtain dry boron nitride precursor powder;

[0110] Step 6: Place the boron nitride precursor powder obtained in step 5 into a muffle furnace for calcination and debinding at a debinding temperature of 800° C. for 1 hour;

[0111] Step seven, the powder after calcination and debinding in step six is ​​placed in a high-temperature furnace for calcination, and nitrogen is introduced as a protective gas. The pressure is slightly greater than the atmospheric pressure. The heating method is to heat to 1300°C at 12°C / min and keep warm for 3h, then heat to 1600°C at a rate of 3°C / min and keep warm for 5h, and obtain boron nitride composite powder after natural cooling.

[0112] The obtained boron nitride composite powder was photographed with a scanning electron microscope, and then mixed with silicone oil with a viscosity of 500cp. The weight of the silicone oil was kept constant and the weight of the powder was gradually increased until the powder and the silicone oil could not be mixed. The maximum mass filling rate of the powder (the ratio of the weight of the powder to the weight of the powder-silicone oil mixed system) was calculated, and the thermal conductivity of the system when the maximum mass filling rate was reached was tested by the transient method. The results are shown in Table 1.

[0113] Comparative Example 1

[0114] The spherical boron nitride raw powder used in the above embodiment was mixed with silicone oil with a viscosity of 500cp, the weight of the silicone oil was kept constant, and the weight of the powder was gradually increased until the powder and the silicone oil could not be mixed. The maximum mass filling rate of the powder (the ratio of the weight of the powder to the weight of the powder-silicone oil mixed system) was calculated, and the thermal conductivity of the system when the maximum mass filling rate was reached was tested by the transient method. The results are shown in Table 1.

[0115] Comparative Example 2

[0116] 1 kg of spherical boron nitride was mixed with 2 g of nano-alumina (particle size range of 20-100 nm) and 18 g of submicron alumina, and then mixed with silicone oil with a viscosity of 500 cp. The weight of the silicone oil was kept constant and the weight of the powder was gradually increased until the powder and silicone oil could not be mixed. The maximum mass filling rate of the powder (the ratio of the weight of the powder to the weight of the powder-silicone oil mixed system) was calculated, and the thermal conductivity of the system when the maximum mass filling rate was reached was tested by the transient method. The results are shown in Table 1.

[0117] Comparative Example 3

[0118] 1 kg of spherical boron nitride was mixed with 4 g of nano-silicon oxide (particle size range of 20-100 nm) and 16 g of micron silicon oxide (D50 particle size of 1 μm), and then mixed with silicone oil with a viscosity of 500 cp. The weight of the silicone oil was kept constant and the weight of the powder was gradually increased until the powder and silicone oil could not be mixed. The maximum mass filling rate of the powder (the ratio of the weight of the powder to the weight of the powder-silicone oil mixed system) was calculated, and the thermal conductivity of the system when the maximum mass filling rate was reached was tested by the transient method. The results are shown in Table 1.

[0119] Comparative Example 4

[0120] 1 kg of spherical boron nitride was fully mixed with 45 g of nano magnesium oxide (particle size range of 20-100 nm) and 105 g of micron magnesium oxide (D50 particle size of 3 μm), and then mixed with silicone oil with a viscosity of 500 cp. The weight of the silicone oil was kept constant and the weight of the powder was gradually increased until the powder and silicone oil could not be mixed. The maximum mass filling rate of the powder (the ratio of the weight of the powder to the weight of the powder-silicone oil mixed system) was calculated, and the thermal conductivity of the system when the maximum mass filling rate was reached was tested by the transient method. The results are shown in Table 1.

[0121] Comparative Example 5

[0122] A method for preparing a boron nitride composite powder comprises the following steps:

[0123] Step 1: fully mix 1 kg of flaky boron nitride with 5 L of 5 mol / L sodium hydroxide solution and stir for 12 h. After stirring, wash the powder with pure water and ethanol for 5 times in sequence. After drying, mix spherical boron nitride, 6 L of pure water and 2.5 g of polyacrylic acid and stir them evenly to form a boron nitride slurry.

[0124] Step 2: Take 45g of nano magnesium oxide (particle size range is 20-100nm) and 105g of micro magnesium oxide (D50 particle size is 3μm) and mix them by ball milling in a planetary ball mill for 0.5h; 750g of ball mill (the diameter of large-particle zirconium oxide beads is 2.0mm, the diameter of small-particle zirconium oxide beads is 0.5mm, and the two are prepared in a weight ratio of 3:1);

[0125] Step 3: add 100 mL of pure water, 7.5 g of polypropylene glycol 400, 4.5 g of a mixture of polyvinyl alcohol and polyvinyl butyral (the weight ratio of the two is 1:1), and 4.5 g of yttrium oxide to the mixed powder obtained in step 2, and continue to use a planetary ball mill for 6 hours to obtain a uniform modified slurry;

[0126] Step 4, mixing the boron nitride slurry prepared in step 1 and the modified slurry prepared in step 3 and stirring them thoroughly;

[0127] Step 5, spray granulating the slurry obtained in step 4 to obtain dry boron nitride precursor powder;

[0128] Step 6: Place the boron nitride precursor powder obtained in step 5 into a muffle furnace for calcination and debinding at a debinding temperature of 800° C. for 1 hour;

[0129] Step seven, the powder after calcination and debinding in step six is ​​placed in a high-temperature furnace for calcination, and nitrogen is introduced as a protective gas. The pressure is slightly greater than the atmospheric pressure. The heating method is to heat to 1300°C at 12°C / min and keep warm for 3h, then heat to 1600°C at a rate of 3°C / min and keep warm for 5h, and obtain boron nitride composite powder after natural cooling.

[0130] The obtained boron nitride composite powder was photographed with a scanning electron microscope, and then mixed with silicone oil with a viscosity of 500cp. The weight of the silicone oil was kept constant and the weight of the powder was gradually increased until the powder and the silicone oil could not be mixed. The maximum mass filling rate of the powder (the ratio of the weight of the powder to the weight of the powder-silicone oil mixed system) was calculated, and the thermal conductivity of the system when the maximum mass filling rate was reached was tested by the transient method. The results are shown in Table 1.

[0131] The microscopic morphology of spherical boron nitride powder is shown in the attached Figure 1 The microscopic morphology of the boron nitride composite powder prepared in Example 1 is shown in the attached Figure 2 The microscopic morphology of the boron nitride composite powder prepared in Example 2 is shown in the attached Figure 3 The microscopic morphology of the boron nitride composite powder prepared in Example 3 is shown in the attached Figure 4 The microscopic morphology of the boron nitride composite powder prepared in Example 4 is shown in the attached Figure 5 The microscopic morphology of the boron nitride composite powder prepared in Example 5 is shown in the attached Figure 6 The microscopic morphology of the boron nitride composite powder prepared in Example 6 is shown in the attached Figure 7 The microscopic morphology of the boron nitride composite powder prepared in Example 7 is shown in the attached Figure 8 The microscopic morphology of the boron nitride composite powder prepared in Comparative Example 5 is shown in the attached Fig. 9 From the comparison in the figure, it can be seen that after using spherical boron nitride as the raw material composite oxide, hydroxide or carbonate, the surface voids are further reduced.

[0132] Table 1 Maximum mass filling rate and thermal conductivity test results

[0133] Numbered Items Maximum mass filling rate (wt%) Thermal conductivity (W / m·K) Example 1 73 3.87 Example 2 79 4.65 Example 3 64 3.95 Example 4 74 3.73 Example 5 77 4.12 Example 6 71 3.64 Example 7 65 3.98 Comparative Example 1 50 2.47 Comparative Example 2 54 2.72 Comparative Example 3 47 2.31 Comparative Example 4 49 2.26 Comparative Example 5 41 1.4

[0134] By comparison, it is found that if spherical boron nitride is directly mixed with oxides, hydroxides or carbonates and used as thermal conductive fillers, its thermal conductivity and maximum filling rate are not significantly improved compared with the original spherical boron nitride powder. Fig. 9 As shown, due to the large difference in the liquid phase temperature points between the two, more pores are left on the surface of the composite powder, and the density decreases, which in turn leads to a lower maximum filling rate and thermal conductivity than the spherical boron nitride original powder. The preparation method of the boron nitride composite powder in this embodiment can activate the surface of the spherical boron nitride, adjust the content of oxides, hydroxides or carbonates, and select suitable oxide, hydroxide or carbonate particle sizes. After sintering, an ideal coating structure can be formed on the spherical boron nitride, thereby reducing the oil absorption value of the powder and increasing the maximum filling rate of the powder in the polymer matrix, thereby achieving higher thermal conductivity. Due to the low content of oxides, hydroxides or carbonates, the main body of the composite powder is still boron nitride, so the composite powder still retains the characteristics of high thermal conductivity, high insulation and low density of boron nitride.

Claims

1. A method for preparing a boron nitride composite powder, characterized in that: The following steps are involved: Step S1, fully mixing and stirring the spherical boron nitride and the sodium hydroxide solution, filtering and washing with pure water and anhydrous ethanol in turn, and then mixing and stirring the washed spherical boron nitride, pure water and the first dispersant according to a ratio to prepare a boron nitride slurry; Step S2, weighing one or more of oxides, hydroxides and carbonates with the same cations according to the ratio and then ball milling, and then adding an appropriate amount of pure water, a second dispersant, a binder and a sintering aid to continue ball milling to obtain a modified slurry; wherein the amount of oxide, hydroxide or carbonate is 2-15% of the weight of spherical boron nitride; the oxide is one or more of magnesium oxide, zinc oxide, aluminum oxide, silicon oxide, titanium oxide; the hydroxide is one or more of magnesium hydroxide, zinc hydroxide, aluminum hydroxide; the carbonate is one or more of magnesium carbonate, zinc carbonate, aluminum carbonate.

2. Step S3, mixing and stirring the boron nitride slurry and the modified slurry, and spray drying to obtain a boron nitride precursor powder; Step S4, calcining the boron nitride precursor powder to remove binder, then calcining in a protective gas atmosphere, and cooling to obtain a boron nitride composite powder.

3. The method for preparing the boron nitride composite powder according to claim 1, characterized in that: In the step S1, the molar concentration of the sodium hydroxide solution is 2-5 mol / L, and the spherical boron nitride and the sodium hydroxide solution are stirred and mixed for 3-12 hours.

4. The method for preparing a boron nitride composite powder according to claim 1, characterized in that: In the step S1, the weight ratio of spherical boron nitride to pure water is 1:1.5-1:6; the amount of the first dispersant is 0.1-5% of the weight of the spherical boron nitride.

5. The method for preparing the boron nitride composite powder according to claim 1, characterized in that: In step S2, the amount of the second dispersant is 0.1-5% of the total weight of the oxides, hydroxides and carbonates; the amount of the binder is 0.5-3% of the total weight of the oxides, hydroxides and carbonates; and the amount of the sintering aid is 2-3% of the total weight of the oxides, hydroxides and carbonates.

6. The method for preparing a boron nitride composite powder according to claim 1, characterized in that: In the step S1, the first dispersant is one or more of anhydrous ethanol, polyacrylic acid, fatty acid modified polymer, polyethylene glycol 200, isopropanol, polypropylene glycol 400, and polycarboxylic acid sodium salt; In the step S2, the second dispersant is one or more of anhydrous ethanol, polyacrylic acid, fatty acid modified polymer, polyethylene glycol 200, isopropanol, polypropylene glycol 400, and polycarboxylic acid sodium salt; The adhesive is one or more of hydroxypropyl methylcellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, polyvinyl alcohol, polyanionic cellulose, and polyvinyl butyral; The sintering aid is one or more of calcium oxide, calcium fluoride, aluminum fluoride, boron oxide, silicon dioxide, magnesium oxide, and yttrium oxide.

7. The method for preparing a boron nitride composite powder according to any one of claims 1 to 5, characterized in that: In step S2, the oxide is one or both of an oxide with a particle size range of 20 to 100 nm and an oxide with a D50 particle size of 0.3 to 3 μm; The hydroxide is one or both of a hydroxide having a particle size range of 20 to 100 nm and a hydroxide having a D50 particle size of 0.3 to 3 μm; The carbonate is one or both of a carbonate having a particle size range of 20 to 100 nm and a carbonate having a D50 particle size of 0.3 to 3 μm.

8. The method for preparing a boron nitride composite powder according to claim 6, characterized in that: In step S2, the ratio of the total weight of oxides with a particle size range of 20-100 nm, hydroxides with a particle size range of 20-100 nm and carbonates with a particle size range of 20-100 nm to the total weight of oxides with a D50 particle size of 0.3-3 μm, hydroxides with a D50 particle size of 0.3-3 μm and carbonates with a D50 particle size of 0.3-3 μm is 1:2-1:

9.

9. The method for preparing the boron nitride composite powder according to any one of claims 1 to 5 and 7, characterized in that: In the step S2, the mass ratio of the ball mill to the modified slurry is 2:1-5:1, and the ball milling time after adding pure water is 1-6 hours.

10. The method for preparing a boron nitride composite powder according to any one of claims 1 to 5 and 7, characterized in that: In the step S4, during calcination and debinding, the debinding temperature is 450° C. to 850° C., and the heat preservation time is 0.5 to 4 hours.

11. The method for preparing the boron nitride composite powder according to any one of claims 1 to 5 and 7, characterized in that: In the step S4, during calcination in a protective gas atmosphere, the temperature is heated from room temperature to 1000-1300° C. at a rate of 5-15° C. / min and kept at that temperature for 1-3 hours, and then heated to 1400-1600° C. at a rate of 1-5° C. / min and kept at that temperature for 0.5-5 hours.

12. The method for preparing the boron nitride composite powder according to any one of claims 1 to 5 and 7, characterized in that: In step S4, the protective gas is argon or nitrogen.

13. A boron nitride composite powder, characterized in that: The boron nitride composite powder is prepared by the preparation method of any one of claims 1 to 11, with spherical boron nitride as the core and coated to form a core-shell structure.

Images