A high-fill-ratio and high-thermal-conductivity spherical powder and its preparation method

Abstract

The present invention provides a high-fill-ratio and high-thermal-conductivity spherical powder and a preparation method thereof, belonging to the technical field of high-thermal-conductivity spherical powders; the preparation method includes steps of preparing a magnesium oxide slurry, preparing a magnesium salt solution, spray granulation and calcination; the step of preparing the magnesium oxide slurry is to mix light magnesium oxide powder, dead-burned magnesium oxide powder, deionized water, nano-aluminum oxide, carbon nanotubes and an additive 1, and perform vacuum stirring to obtain the magnesium oxide slurry; the additive 1 is composed of a PVA solution, magnesium stearate, glycerol and γ-methacryloxypropyltrimethoxysilane; the high-fill-ratio and high-thermal-conductivity spherical powder prepared by the present invention has a controllable particle size of 1-100 μm, high sphericity, good mechanical strength, and stable temperature resistance and chemical resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of high thermal conductivity spherical powders, and particularly relates to a high filling rate and high thermal conductivity spherical powder and a preparation method thereof. Background Art

[0002] With the rapid development of modern technology, many industries have put forward more stringent requirements for material properties, and high filling rate and high thermal conductivity spherical powders have emerged as the times require, playing an irreplaceable important role in many key fields; in the fields of electronic devices, energy storage, and aerospace, efficient heat dissipation is always a key factor to ensure the stable operation of equipment.

[0003] For a long time, alumina thermal conductivity powders, boron nitride thermal conductivity powders, etc. have been widely used, but generally have the following problems:

[0004] First, the morphology of the thermal conductivity powder is irregular, resulting in insufficient packing density of the powder in the substrate, and the filling amount is usually less than 50wt%, which limits the formation of the thermal conductivity path; second, the hydrophilicity and hydrophobicity of the surface of the thermal conductivity powder do not match the substrate, and the interfacial bonding force is poor, resulting in an increase in the interfacial thermal resistance; third, the brittleness of the thermal conductivity powder is high, it is easy to crack under thermal cycling, and the mechanical strength is low, thus reducing the long-term stability performance.

[0005] Magnesium oxide has a high thermal conductivity, and its thermal conductivity coefficient is better than that of alumina, and it can transfer heat more quickly and effectively. Moreover, the raw materials for preparing magnesium oxide powder are widely available, and the preparation process is relatively simple, and it has greater potential for large-scale popularization and application.

[0006] The existing technologies for the preparation method of magnesium oxide thermal conductivity powder usually adopt the sol-gel method, hydrothermal method, precipitation method and traditional spray drying method;

[0007] The sol-gel method forms a sol through the hydrolysis of the precursor, and then obtains spherical powder through gelation and calcination, but it is difficult to control the uniformity of the particle size and the yield is low; the hydrothermal method synthesizes spherical particles in a high-temperature and high-pressure aqueous solution, which has high requirements for equipment, a long reaction time, and it is difficult to achieve wide-range control of the particle size; the precipitation method generates a precipitate by reacting magnesium nitrate and other salts with an alkaline solution, and then obtains magnesium oxide through calcination, and then the product is easy to agglomerate, with low sphericity, and the filler is limited by the single particle size; the traditional spray drying method sprays and dries the precursor solution and then calcines it, and the obtained powder has a rough surface, insufficient sphericity, and low filling rate, and it is difficult to achieve a dense structure.

[0008] Therefore, providing a magnesium oxide thermal conductivity powder with a dense and smooth surface, high sphericity and filling rate, excellent thermal conductivity performance, controllable particle size in the range of 1-100μm, high mechanical strength, and stable temperature resistance and chemical resistance is a technical problem that the existing technology urgently needs to solve. Summary of the Invention

[0009] In order to solve the technical problems existing in the prior art, the present invention provides a high-fill-rate and high-thermal-conductivity spherical powder and a preparation method thereof, with a controllable particle size of 1-100 μm, high sphericity, good mechanical strength, and stable temperature resistance and chemical resistance.

[0010] In view of the above technical problems, the present invention adopts the following technical solutions:

[0011] A preparation method of a high-fill-rate and high-thermal-conductivity spherical powder includes steps of preparing a magnesium oxide slurry, preparing a magnesium salt solution, spray granulation, and calcination. The specific operations are as follows:

[0012] 1. Preparation of magnesium oxide slurry

[0013] Mix light magnesium oxide powder, dead-burned magnesium oxide powder, deionized water, nano-aluminum oxide, carbon nanotubes, and additive 1, put them into a vacuum stirring tank, stir at a speed of 760-830 r / min at 78-82 °C for 5.8-6.5 hours, and control the vacuum degree to be -0.09~-0.05 MPa to obtain a magnesium oxide slurry;

[0014] The light magnesium oxide powder has a purity of 98.0-99.0% and a particle size of 0.1-1 μm;

[0015] The dead-burned magnesium oxide powder has a purity of 96.5-97.0% and a particle size of 5-10 μm;

[0016] The nano-aluminum oxide has a particle size of 1-100 nm;

[0017] The carbon nanotubes have a particle size of 1-50 nm;

[0018] The mass ratio of the light magnesium oxide powder, dead-burned magnesium oxide powder, deionized water, nano-aluminum oxide, and carbon nanotubes is 10-28:20-25:50-60:1.5-3.0:0.5-2.0;

[0019] The addition amount of additive 1 in the magnesium oxide slurry is 1.0-3.0 wt%;

[0020] Additive 1 is composed of a PVA solution, magnesium stearate, glycerol, and γ-methacryloyloxypropyltrimethoxysilane, and the mass ratio of the PVA solution, magnesium stearate, glycerol, and γ-methacryloyloxypropyltrimethoxysilane is 0.6-1.0:0.4-0.6:0.3-0.7:0.2-0.4.

[0021] 2. Preparation of magnesium salt solution

[0022] Mix deionized water, magnesium chloride, magnesium sulfate, magnesium nitrate and Additive II, stir at a speed of 290 - 310 r / min for 27 - 35 minutes, then place it in a sealed tank and keep it warm in an oven at 98 - 105 °C for 11 - 13 hours to obtain a magnesium salt solution with a viscosity of 50 - 80 mPa·S;

[0023] The mass ratio of the deionized water, magnesium chloride, magnesium sulfate, and magnesium nitrate is 20 - 70:20 - 40:5 - 25:5 - 15;

[0024] The addition amount of Additive II in the magnesium salt solution is 3.0 - 5.0 wt%;

[0025] The Additive II is composed of OP emulsifier, polyvinylpyrrolidone, and oxalic acid, and the mass ratio of the OP emulsifier, polyvinylpyrrolidone, and oxalic acid is 4.8 - 5.2:0.1:1.3 - 1.7.

[0026] 3. Spray granulation

[0027] Mix the magnesium oxide slurry and the magnesium salt solution, stir at room temperature at a speed of 780 - 820 r / min for 0.8 - 1.3 hours to obtain a slurry to be spray - granulated; perform spray granulation on the slurry to be spray - granulated, control the inlet temperature at 195 - 205 °C, the outlet temperature at 85 - 95 °C, the nozzle aperture at 0.4 - 0.6 mm, and the centrifugal speed at 14000 - 16000 r / min to obtain spherical powder;

[0028] The mass ratio of the magnesium oxide slurry and the magnesium salt solution is 1:1.0 - 1.4.

[0029] 4. Calcination

[0030] Calcine the spherical magnesium oxide powder in a nitrogen atmosphere, heat it up at a rate of 4.5 - 5.5 °C / min to 1350 - 1450 °C, and keep it warm for 1.8 - 2.3 h to obtain a spherical powder with high filling rate and high thermal conductivity.

[0031] A spherical powder with high filling rate and high thermal conductivity is prepared by the aforementioned preparation method.

[0032] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0033] 1. The magnesium oxide slurry of the present invention, under the action of nano-aluminum oxide and carbon nanotubes, obtains a toughening effect inside the spherical magnesium oxide, improving the toughness and thermal shock resistance of the spherical magnesium oxide. For additives I such as magnesium stearate, glycerol, and γ-methacryloxypropyltrimethoxysilane, their organic functional groups react with the surface of the magnesium oxide powder to form stable chemical bonds. These chemical bonds not only enhance the strength of the magnesium oxide powder but also, under the action of the silyl groups, make the magnesium oxide powder have a certain hydrophobicity, causing the surface of the spherical magnesium oxide to be in a mirror state, enhancing the interfacial bonding force between the powder and the substrate, and improving the overall thermal conductivity. In the magnesium salt solution, under the action of additives II such as oxalic acid, a certain proportion of nano-magnesium salt particles are formed in the magnesium salt solution, and the magnesium salt solution has a certain viscosity under the action of the OP emulsifier. In the preparation method of the spherical powder, when the magnesium oxide slurry is mixed with the magnesium salt solution, the nano-magnesium salt particles fill the gaps on the surface of the magnesium oxide powder, and the magnesium salt solution with a certain viscosity coats the surface of the magnesium oxide, forming a dense and smooth surface. After spray granulation and firing, magnesium oxide powder with a mirror state, high sphericity, high filling amount, and high thermal conductivity is formed.

[0034] 2. The high filling rate and high thermal conductivity spherical powder of the present invention has a particle size of 1 - 100 μm.

[0035] 3. The high filling rate and high thermal conductivity spherical powder of the present invention has a sphericity > 98%, a filling rate reaching 76 - 85%, a thermal conductivity of 37 - 50 W / (m·K), and a compressive strength of 41.5 - 50.6 MPa.

[0036] 4. The high filling rate and high thermal conductivity spherical powder of the present invention, when heat-treated at 1300 °C for 20 h in an air atmosphere, has a compressive strength of 39.4 - 48.4 MPa; when immersed in a 15 wt% hydrochloric acid solution with 3 times the mass for 48 h, the mass loss rate is 0.42 - 0.58%. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 FIG. 15 shows the SEM image of the high filling rate and high thermal conductivity spherical powder prepared in Example 2 at 1400 times magnification;

[0038] Figure 2 FIG. 19 shows the SEM image of the high filling rate and high thermal conductivity spherical powder prepared in Example 2 at 300 times magnification;

[0039] Figure 3 FIG. 23 shows the SEM image of the high filling rate and high thermal conductivity spherical powder prepared in the comparative example at 1700 times magnification. DETAILED DESCRIPTION OF THE INVENTION

[0040] In order to understand the technical features, objectives, and effects of the present invention more clearly, the specific embodiments of the present invention are described below.

[0041] Example 1

[0042] 1. Preparation of magnesium oxide slurry

[0043] Mix light magnesium oxide powder, dead-burned magnesium oxide powder, deionized water, nano-aluminum oxide, carbon nanotubes and additive 1, put them into a vacuum stirring tank, stir at a speed of 760 r / min at 78 °C for 6.5 hours, and control the vacuum degree to be -0.09 MPa to obtain magnesium oxide slurry;

[0044] The light magnesium oxide powder has a purity of 98.0% and a particle size of 0.1 um;

[0045] The dead-burned magnesium oxide powder has a purity of 96.5% and a particle size of 5 um;

[0046] The nano-aluminum oxide has a particle size of 100 nm;

[0047] The carbon nanotubes have a particle size of 1 nm;

[0048] The mass ratio of the light magnesium oxide powder, dead-burned magnesium oxide powder, deionized water, nano-aluminum oxide, and carbon nanotubes is 10:20:50:1.5:0.5;

[0049] The addition amount of additive 1 in the magnesium oxide slurry is 1.0 wt%;

[0050] Additive 1 is composed of PVA solution, magnesium stearate, glycerol, and γ-methacryloxypropyltrimethoxysilane, and the mass ratio of the PVA solution, magnesium stearate, glycerol, and γ-methacryloxypropyltrimethoxysilane is 0.6:0.4:0.3:0.2.

[0051] 2. Preparation of magnesium salt solution

[0052] Mix deionized water, magnesium chloride, magnesium sulfate, magnesium nitrate and additive 2, stir at a speed of 290 r / min for 35 minutes, then place it in a sealed tank and keep it warm in an oven at 98 °C for 13 hours to obtain a magnesium salt solution with a viscosity of 50 mPa·S;

[0053] The mass ratio of the deionized water, magnesium chloride, magnesium sulfate, and magnesium nitrate is 20:20:5:5;

[0054] The addition amount of additive 2 in the magnesium salt solution is 3.0 wt%;

[0055] Additive 2 is composed of OP emulsifier, polyvinylpyrrolidone, and oxalic acid, and the mass ratio of the OP emulsifier, polyvinylpyrrolidone, and oxalic acid is 4.8:0.1:1.3.

[0056] 3. Spray granulation

[0057] Mix the magnesia slurry and the magnesium salt solution, and stir at a speed of 780 r / min at room temperature for 1.3 hours to obtain the slurry to be spray-dried; perform spray granulation on the slurry to be spray-dried, control the inlet temperature at 195 °C, the outlet temperature at 85 °C, the nozzle aperture at 0.4 mm, and the centrifugal rotation speed at 14,000 r / min to obtain spherical powder;

[0058] The mass ratio of the magnesia slurry to the magnesium salt solution is 1:1.0.

[0059] 4. Calcination

[0060] Calcine the spherical magnesia powder in a nitrogen atmosphere, heat it up to 1350 °C at a rate of 4.5 °C / min, and keep it warm for 1.8 h to obtain high-fill high-thermal-conductivity spherical powder.

[0061] The high-fill high-thermal-conductivity spherical powder prepared by the method of Example 1 has a sphericity of 98.3%, a fill rate of 76%, a thermal conductivity of 37 W / (m·K), and a compressive strength of 41.5 MPa; in an air atmosphere, after heat preservation treatment at 1300 °C for 20 h, the compressive strength is 39.4 MPa; when immersed in 3 times the mass of 15 wt% hydrochloric acid solution for 48 h, the mass loss rate is 0.58%.

[0062] Example 2

[0063] 1. Preparation of magnesia slurry

[0064] Mix light magnesia powder, dead-burned magnesia powder, deionized water, nano-aluminum oxide, carbon nanotubes and additive 1, put them into a vacuum stirring tank, stir at a speed of 800 r / min at 80 °C for 6.0 hours, and control the vacuum degree at -0.07 MPa to obtain magnesia slurry;

[0065] The light magnesia powder has a purity of 99.0% and a particle size of 0.5 μm;

[0066] The dead-burned magnesia powder has a purity of 97.0% and a particle size of 8 μm;

[0067] The particle size of the nano-aluminum oxide is 40 nm;

[0068] The particle size of the carbon nanotubes is 20 nm;

[0069] The mass ratio of the light magnesia powder, dead-burned magnesia powder, deionized water, nano-aluminum oxide, and carbon nanotubes is 20:22:54:2.2:1.5;

[0070] The addition amount of additive 1 in the magnesia slurry is 2.0 wt%;

[0071] The first admixture consists of a PVA solution, magnesium stearate, glycerol, and γ-methacryloxypropyltrimethoxysilane. The mass ratio of the PVA solution, magnesium stearate, glycerol, and γ-methacryloxypropyltrimethoxysilane is 0.8:0.5:0.5:0.3.

[0072] 2. Preparation of magnesium salt solution

[0073] Mix deionized water, magnesium chloride, magnesium sulfate, magnesium nitrate, and the second admixture, stir at a speed of 300 r / min for 30 minutes, then place it in a sealed tank and keep it warm in an oven at 100 °C for 12 hours to obtain a magnesium salt solution with a viscosity of 60 mPa·S;

[0074] The mass ratio of the deionized water, magnesium chloride, magnesium sulfate, and magnesium nitrate is 50:30:16:10;

[0075] The addition amount of the second admixture in the magnesium salt solution is 4.0 wt%;

[0076] The second admixture consists of an OP emulsifier, polyvinylpyrrolidone, and oxalic acid. The mass ratio of the OP emulsifier, polyvinylpyrrolidone, and oxalic acid is 5:0.1:1.5.

[0077] 3. Spray granulation

[0078] Mix the magnesium oxide slurry and the magnesium salt solution, stir at room temperature at a speed of 800 r / min for 1.0 hour to obtain a slurry to be spray granulated; perform spray granulation on the slurry to be spray granulated, control the inlet temperature at 200 °C, the outlet temperature at 90 °C, the nozzle aperture at 0.5 mm, and the centrifugal rotation speed at 15000 r / min to obtain spherical powder;

[0079] The mass ratio of the magnesium oxide slurry and the magnesium salt solution is 1:1.2.

[0080] 4. Calcination

[0081] Calcine the spherical magnesium oxide powder in a nitrogen atmosphere, heat it up to 1400 °C at a rate of 5.0 °C / min, and keep it warm for 2.0 h to obtain a spherical powder with high filling rate and high thermal conductivity.

[0082] The spherical powder with high filling rate and high thermal conductivity prepared by the method of Example 2 has a sphericity of 99.6%, a filling rate of 85%, a thermal conductivity of 50 W / (m·K), and a compressive strength of 50.6 MPa; in an air atmosphere, after heat preservation treatment at 1300 °C for 20 h, the compressive strength is 48.4 MPa; when immersed in a 15 wt% hydrochloric acid solution with 3 times the mass for 48 h, the mass loss rate is 0.42%.

[0083] Example 3

[0084] 1. Preparation of magnesium oxide slurry

[0085] Mix light magnesium oxide powder, dead-burned magnesium oxide powder, deionized water, nano-aluminum oxide, carbon nanotubes and additive one, put them into a vacuum stirring tank, stir at a speed of 830 r / min at 82 °C for 5.8 hours, and control the vacuum degree to -0.05 MPa to obtain magnesium oxide slurry;

[0086] The light magnesium oxide powder has a purity of 98.5% and a particle size of 1 μm;

[0087] The dead-burned magnesium oxide powder has a purity of 96.8% and a particle size of 10 μm;

[0088] The particle size of the nano-aluminum oxide is 1 nm;

[0089] The particle size of the carbon nanotubes is 50 nm;

[0090] The mass ratio of the light magnesium oxide powder, dead-burned magnesium oxide powder, deionized water, nano-aluminum oxide, and carbon nanotubes is 28:25:60:3.0:2.0;

[0091] The addition amount of additive one in the magnesium oxide slurry is 3.0 wt%;

[0092] Additive one is composed of PVA solution, magnesium stearate, glycerol, and γ-methacryloxypropyltrimethoxysilane, and the mass ratio of the PVA solution, magnesium stearate, glycerol, and γ-methacryloxypropyltrimethoxysilane is 1.0:0.6:0.7:0.4.

[0093] 2. Preparation of magnesium salt solution

[0094] Mix deionized water, magnesium chloride, magnesium sulfate, magnesium nitrate and additive two, stir at a speed of 310 r / min for 27 minutes, then place it in a sealed tank and keep it warm in an oven at 105 °C for 11 hours to obtain a magnesium salt solution with a viscosity of 80 mPa·S;

[0095] The mass ratio of the deionized water, magnesium chloride, magnesium sulfate, and magnesium nitrate is 70:40:25:15;

[0096] The addition amount of additive two in the magnesium salt solution is 5.0 wt%;

[0097] Additive two is composed of OP emulsifier, polyvinylpyrrolidone, and oxalic acid, and the mass ratio of the OP emulsifier, polyvinylpyrrolidone, and oxalic acid is 5.2:0.1:1.7.

[0098] 3. Spray granulation

[0099] Mix the magnesia slurry and the magnesium salt solution, and stir at a normal temperature of 820 r / min for 0.8 hours to obtain the slurry to be spray-dried. Spray granulate the slurry to be spray-dried, control the inlet temperature at 205 °C, the outlet temperature at 95 °C, the nozzle aperture at 0.6 mm, and the centrifugal rotation speed at 16,000 r / min to obtain spherical powder;

[0100] The mass ratio of the magnesia slurry to the magnesium salt solution is 1:1.4.

[0101] 4. Calcination

[0102] Calcine the spherical magnesia powder in a nitrogen atmosphere, heat it up to 1450 °C at a rate of 5.5 °C / min, and keep it warm for 2.3 h to obtain high-fill high-thermal-conductivity spherical powder.

[0103] The high-fill high-thermal-conductivity spherical powder prepared by the method of Example 3 has a sphericity of 99.2%, a fill rate of 80%, a thermal conductivity of 45 W / (m·K), and a compressive strength of 47.3 MPa; in an air atmosphere, after heat preservation treatment at 1300 °C for 20 h, the compressive strength is 45.1 MPa; when soaked in 3 times the mass of 15 wt% hydrochloric acid solution for 48 h, the mass loss rate is 0.46%.

[0104] Comparative Example

[0105] Based on Example 2, make the following changes:

[0106] 1. In the step of preparing the magnesia slurry, replace the carbon nanotube component with an equal amount of light magnesia powder, and replace the additive I with an equal amount of dead-burned magnesia powder; the light magnesia powder has a purity of 99.0% and a particle size of 0.5 μm; the dead-burned magnesia powder has a purity of 97.0% and a particle size of 8 μm; keep the rest of the operations unchanged;

[0107] 2. In the step of preparing the magnesium salt, replace the additive II with an equal amount of deionized water, and keep the rest of the operations unchanged;

[0108] 3. The spray granulation step and the calcination step are exactly the same as those in Example 2.

[0109] The product obtained in the comparative example has a sphericity of 82.5%, a fill rate of 64%, a thermal conductivity of 30 W / (m·K), and a compressive strength of 35.2 MPa; in an air atmosphere, after heat preservation treatment at 1300 °C for 20 h, the compressive strength is 28.3 MPa; when soaked in 3 times the mass of 15 wt% hydrochloric acid solution for 48 h, the mass loss rate is 2.4%.

[0110] Unless otherwise specified, the ratios described in the present invention are all mass ratios, and the percentages are all mass percentages.

[0111] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features; any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of high-fill-ratio and high-thermal-conductivity spherical powder, characterized in that It includes steps of preparing magnesium oxide slurry, preparing magnesium salt solution, spray granulation and calcination; In the step of preparing magnesium oxide slurry, light magnesium oxide powder, dead-burned magnesium oxide powder, deionized water, nano-aluminum oxide, carbon nanotubes and additive 1 are mixed and subjected to vacuum stirring to obtain magnesium oxide slurry; Additive 1 is composed of PVA solution, magnesium stearate, glycerol and γ-methacryloxypropyltrimethoxysilane; In the step of preparing magnesium salt solution, deionized water, magnesium chloride, magnesium sulfate, magnesium nitrate and additive 2 are mixed, stirred evenly and placed in a sealed tank, and kept warm at 98 - 105 °C to obtain a magnesium salt solution with a viscosity of 50 - 80 mPa·S; Additive 2 is composed of OP emulsifier, polyvinylpyrrolidone and oxalic acid; In the spray granulation step, magnesium oxide slurry and magnesium salt solution are mixed and stirred at a normal temperature at a speed of 780 - 820 r / min for 0.8 - 1.3 hours to obtain a slurry to be sprayed; the slurry to be sprayed is subjected to spray granulation, controlling the inlet temperature at 195 - 205 °C, the outlet temperature at 85 - 95 °C, the nozzle aperture at 0.4 - 0.6 mm, and the centrifugal rotation speed at 14000 - 16000 r / min to obtain spherical powder; In the calcination step, the spherical magnesium oxide powder is calcined in a nitrogen atmosphere, heated at a rate of 4.5 - 5.5 °C / min to 1350 - 1450 °C, and kept warm for 1.8 - 2.3 h to obtain a spherical powder with high filling rate and high thermal conductivity.

2. The preparation method of a spherical powder with high filling rate and high thermal conductivity according to claim 1, characterized in that, In the step of preparing magnesium oxide slurry, for the vacuum stirring, the stirring temperature is 78 - 82 °C, the stirring speed is 760 - 830 r / min, the stirring time is 5.8 - 6.5 hours, and the vacuum degree is -0.09~-0.05 MPa.

3. The preparation method of a spherical powder with high filling rate and high thermal conductivity according to claim 1, characterized in that, In the step of preparing magnesium oxide slurry, for the light magnesium oxide powder, the purity is 98.0 - 99.0%, and the particle size is 0.1 - 1 um; For the dead-burned magnesium oxide powder, the purity is 96.5 - 97.0%, and the particle size is 5 - 10 um; The particle size of the nano-aluminum oxide is 1 - 100 nm; The particle size of the carbon nanotubes is 1 - 50 nm; The mass ratio of the light magnesium oxide powder, dead-burned magnesium oxide powder, deionized water, nano-aluminum oxide, and carbon nanotubes is 10 - 28:20 - 25:50 - 60:1.5 - 3.0:0.5 - 2.0; The addition amount of additive 1 in the magnesium oxide slurry is 1.0 - 3.0 wt%.

4. The preparation method of a spherical powder with high filling rate and high thermal conductivity according to claim 1, characterized in that, In additive 1, the mass ratio of the PVA solution, magnesium stearate, glycerol, and γ-methacryloxypropyltrimethoxysilane is 0.6 - 1.0:0.4 - 0.6:0.3 - 0.7:0.2 - 0.

4.

5. The preparation method of a spherical powder with high filling rate and high thermal conductivity according to claim 1, characterized in that, In the step of preparing the magnesium salt, the mass ratio of the deionized water, magnesium chloride, magnesium sulfate, and magnesium nitrate is 20-70:20-40:5-25:5-15; The addition amount of the additive II in the magnesium salt solution is 3.0-5.0 wt%.

6. The preparation method of a high-fill-ratio and high-thermal-conductivity spherical powder according to claim 1, wherein In the additive II, the mass ratio of the OP emulsifier, polyvinylpyrrolidone, and oxalic acid is 4.8-5.2:0.1:1.3-1.

7.

7. The preparation method of a high-fill-ratio and high-thermal-conductivity spherical powder according to claim 1, wherein In the spray granulation step, the mass ratio of the magnesium oxide slurry and the magnesium salt solution is 1:1.0-1.

4.

8. A high-fill-ratio and high-thermal-conductivity spherical powder is prepared by using the preparation method according to any one of claims 1-7.

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