Preparation method of high thermal conductivity silicon nitride ceramic material for lightning protection insulator

Abstract

The present invention discloses a preparation method of a high thermal conductivity silicon nitride ceramic material for lightning protection insulators, belonging to the technical field of silicon nitride ceramics. The method includes the following steps: preparing β-silicon nitride whiskers, modifying β-silicon nitride whiskers, preparing silicon nitride composite powder, cold isostatic pressing molding, and gas pressure sintering; the method for modifying β-silicon nitride whiskers is to disperse β-silicon nitride whiskers in a hydrolyzed and activated polyacrylamide solution, add a dehydrating agent N,N-dicyclohexylcarbodiimide, react at 50-60 °C for 2-3 h, after the reaction ends, filter and separate the product, wash with water and dry to obtain modified β-silicon nitride whiskers. The thermal conductivity of the silicon nitride ceramic prepared by the method of the present invention is 87.5-89.2 W / (m·K), the flexural strength is 837-850 MPa, the fracture toughness is 10.6-11.1 MPa·m 1 / 2 , and the density is 3.09-3.21 g / cm 3 .

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon nitride ceramics, and particularly relates to a preparation method of a high thermal conductivity silicon nitride ceramic material for lightning protection insulators. Background Art

[0002] Lightning protection insulators are key components in communication systems that combine lightning protection and insulation support functions. To prevent large currents generated by direct lightning strikes from damaging backend equipment through communication antennas, current communication antenna insulators are required to integrate lightning protection functions. During lightning strikes, a large amount of lightning energy accumulates inside the insulators, leading to heat accumulation and temperature rise. This requires lightning protection insulators to dissipate heat quickly to reduce damage to electronic components in the lightning discharge path. The materials in existing antenna insulators mainly use high-aluminum ceramics. Although high-aluminum ceramic materials have advantages such as high temperature resistance, high insulation, corrosion resistance, wear resistance, and high strength, they have poor thermal shock resistance, low thermal conductivity, and slow heat dissipation, unable to meet the usage requirements.

[0003] To solve the inherent defects of high-aluminum ceramics, in recent years, high-performance ceramic materials represented by silicon nitride (Si3N4) ceramics, with their ultra-high thermal conductivity and excellent thermal shock resistance, have become the preferred direction for the upgrade of lightning protection insulators. Existing high thermal conductivity silicon nitride ceramics are mostly prepared by hot pressing sintering. The unidirectional pressure in hot pressing sintering causes β-Si3N4 grains to grow directionally along the pressure direction, resulting in fewer grain boundaries, a low phonon scattering rate, and a higher thermal conductivity. However, this hot pressing sintering method is only suitable for the forming of simple geometric shapes and is difficult to achieve uniform pressing and forming for the complex-shaped structures of lightning protection insulators. Gas pressure sintering can sinter various shaped silicon nitride ceramics, but the grains in gas-phase sintering are randomly oriented, the phonon conduction path is blocked, and the thermal conductivity is generally low.

[0004] To solve the problem of improving the thermal conductivity of silicon nitride ceramic materials prepared by gas pressure sintering, in the prior art, β-Si3N4 whiskers are used as templates to guide the growth of grains along a specific direction, reduce the number of grain boundaries, and improve the thermal conductivity.

[0005] CN112573936A discloses a method for preparing a silicon nitride ceramic substrate, comprising the following steps: step S1, rolling α-Si3N4 powder, β-Si3N4 whiskers, h-BN powder, sintering aids and binders to prepare a sheet-like body with oriented β-Si3N4 whiskers; step S2, degreasing the sheet-like body to obtain a degreased body; step S3, gas pressure sintering the degreased body to make α-Si3N4 undergo phase change under the induction of β-Si3N4 whiskers and promote the oriented growth of β-Si3N4 grains, so as to prepare a silicon nitride ceramic substrate with oriented β-Si3N4 rod-shaped grains. The use of β-Si3N4 whiskers as seeds in this patent can promote nucleation, increase growth driving force, and also act as a template to guide the growth of grains in a specific direction, increase density, reduce lattice oxygen defects, and increase thermal conductivity. However, as a high aspect ratio material, the ball milling mixing method used in the mixing process of β-Si3N4 whiskers can easily destroy the structure of the β-Si3N4 whiskers, and the mixing uniformity is poor, making it difficult to improve thermal conductivity and increase strength. Therefore, in the raw material powder of silicon nitride ceramics, protecting the β-Si3N4 whisker structure from being destroyed, improving the uniformity of the raw material mixing, and improving the thermal conductivity of silicon nitride ceramics under gas pressure sintering are problems that need to be urgently solved in the prior art. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a method for preparing a high thermal conductivity silicon nitride ceramic material for lightning protection insulators, which improves the thermal conductivity of silicon nitride ceramics and increases the bending strength, fracture toughness and density of silicon nitride ceramics.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a high thermal conductivity silicon nitride ceramic material for a lightning protection insulator comprises the following steps: preparing β-silicon nitride whiskers, modifying the β-silicon nitride whiskers, preparing silicon nitride composite powder, cold isostatic pressing, and gas pressure sintering;

[0009] The method for preparing β-silicon nitride whiskers comprises: using silicon powder and α-Si3N4 as raw materials, and Y2O3 as an auxiliary agent, uniformly mixing the raw materials and the auxiliary agent, sintering the raw materials in a N2 atmosphere at 3-5MPa and 1700-1800°C for 1-1.5h, soaking the sintered material in a hydrofluoric acid solution for 10-15min, washing with water and drying after the soaking, and obtaining β-silicon nitride whiskers;

[0010] The mass ratio of silicon powder, α-Si3N4 and Y2O3 is 70-80:20-30:2.5-3;

[0011] The particle size of the silicon powder is 300-500nm;

[0012] The particle size of the α-Si3N4 is 500 - 800 nm;

[0013] The concentration of the hydrofluoric acid solution is 5 - 10 wt%.

[0014] The method for modifying the β-silicon nitride whiskers is to disperse the β-silicon nitride whiskers in a hydrolyzed and activated polyacrylamide solution, add the dehydrating agent N,N'-dicyclohexylcarbodiimide, react at 50 - 60 °C for 2 - 3 h, after the reaction ends, filter and separate the product, wash with water and dry to obtain the modified β-silicon nitride whiskers;

[0015] The mass ratio of the β-silicon nitride whiskers, the hydrolyzed and activated polyacrylamide solution, and N,N'-dicyclohexylcarbodiimide is 10:50 - 70:0.2 - 0.4;

[0016] The preparation method of the hydrolyzed and activated polyacrylamide solution is to dissolve polyacrylamide in water to prepare a polyacrylamide solution, dropwise add a NaOH solution to the polyacrylamide solution under stirring, stop dropping when the pH of the solution reaches 10 - 11, heat the mixed solution to 60 - 80 °C, and stir and react at a constant temperature for 1 - 2 h, and control the pH range of the solution during the reaction to be 10 - 11, and obtain the hydrolyzed and activated polyacrylamide solution after the reaction ends;

[0017] The number-average molecular weight of the polyacrylamide is 1.06 - 2.11 million;

[0018] The concentration of the polyacrylamide solution is 5 - 8 wt%.

[0019] The concentration of the NaOH solution is 20 - 30 g / L.

[0020] The method for preparing the silicon nitride composite powder is to dissolve methacrylamide in water, then add the α-Si3N4 powder, Y2O3, MgSiN2, and a dispersant, ultrasonically disperse for 10 - 15 min once to obtain a premixed solution, then add the modified β-silicon nitride whiskers to the premixed solution under stirring, and ultrasonically disperse for 20 - 30 min again, dry at 60 - 80 °C for 4 - 6 h to obtain a gel, and sinter the gel at 500 - 600 °C in a nitrogen atmosphere for 2 - 3 h to obtain the silicon nitride composite powder;

[0021] The mass ratio of water, methacrylamide, α-Si3N4 powder, Y2O3, MgSiN2, dispersant, and modified β-silicon nitride whiskers is 100:8 - 10:100 - 120:3 - 4:3 - 4:0.6 - 1:6 - 8;

[0022] The dispersant is one of sodium polyacrylate and polyvinyl alcohol;

[0023] The frequency of the first ultrasonic wave is 50 - 70 kHz;

[0024] The frequency of the second ultrasonic wave is 20 - 30 kHz.

[0025] The method of cold isostatic pressing is to press the silicon nitride composite powder at a pressure of 110 - 130 MPa for 30 - 35 min to obtain a silicon nitride ceramic blank.

[0026] The method of gas pressure sintering is to send the silicon nitride ceramic blank into a gas pressure sintering furnace and sinter it in a nitrogen atmosphere at 1800 - 1900 °C and 3 - 4 MPa to obtain a high - thermal - conductivity silicon nitride ceramic.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. In the preparation method of the high - thermal - conductivity silicon nitride ceramic of the present invention, β - silicon nitride whiskers are used as crystal seeds to provide nucleation sites, promote the transformation of α - silicon nitride to β - silicon nitride. At the same time, the added β - silicon nitride whiskers can also improve the flexural strength and fracture toughness of the silicon nitride ceramic. In the preparation steps of the β - silicon nitride whiskers, after the fired material is soaked in a hydrofluoric acid solution, single - root whiskers can be separated from the interlaced - growing whiskers, and a certain degree of etching can be generated on the whisker surface. The modification treatment of the β - silicon nitride whiskers and the firing in the preparation of the silicon nitride composite powder will not damage the etched surface of the silicon nitride whiskers. During the sintering process of preparing the silicon nitride ceramic, the etched surface can provide more nucleation sites for the β - silicon nitride whiskers as crystal seeds, promote the densification process during sintering, reduce the porosity, increase the density of the silicon nitride ceramic, and further improve the thermal conductivity and strength properties of the silicon nitride ceramic; the β - silicon nitride whiskers have a high aspect ratio and can be used as templates to guide the growth of grains along specific directions, forming a more uniform microstructure, which helps to improve the thermal conductivity, flexural strength and fracture toughness of the silicon nitride ceramic; the more uniform grain dense - growth structure can reduce the lattice oxygen defects, and the long - strip structure of the β - silicon nitride whiskers helps to form a more effective heat - conduction path, thereby increasing the thermal conductivity of the material.

[0029] 2. The preparation method of the high - thermal - conductivity silicon nitride ceramic of the present invention can improve the thermal conductivity, flexural strength, fracture toughness and density of the silicon nitride ceramic. The thermal conductivity of the high - thermal - conductivity silicon nitride ceramic prepared by the method of the present invention is 87.5 - 89.2 W / (m·K), the flexural strength is 837 - 850 MPa, the fracture toughness is 10.6 - 11.1 MPa·m 1 / 2 and the density is 3.09 - 3.21 g / cm 3 . Detailed implementation manners

[0030] To have a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention will now be described.

[0031] Example 1

[0032] A preparation method of a high thermal conductivity silicon nitride ceramic material for lightning protection insulators is as follows:

[0033] (1) Preparation of β-silicon nitride whiskers

[0034] 70 g of silicon powder, 30 g of α-Si3N4, and 2.5 g of Y2O3 are uniformly mixed, fired in an N2 atmosphere at 3 MPa and 1800 °C for 1 h, and then the fired material is immersed in a hydrofluoric acid solution for 10 min. After immersion, the product is filtered and separated, washed with water, and dried to obtain β-silicon nitride whiskers;

[0035] The particle size of the silicon powder is 300 nm;

[0036] The particle size of the α-Si3N4 is 500 nm;

[0037] The concentration of the hydrofluoric acid solution is 10 wt%.

[0038] (2) Modification of β-silicon nitride whiskers

[0039] 10 g of β-silicon nitride whiskers are dispersed in 50 g of a hydrolyzed and activated polyacrylamide solution, 0.2 g of N,N-dicyclohexylcarbodiimide is added, and the reaction is carried out at 50 °C for 3 h. After the reaction is completed, the product is filtered and separated, washed with water, and dried to obtain modified β-silicon nitride whiskers;

[0040] The preparation method of the hydrolyzed and activated polyacrylamide solution is as follows: Polyacrylamide is dissolved in water to prepare a polyacrylamide solution with a concentration of 5 wt%. While stirring, a NaOH solution with a concentration of 20 g / L is added dropwise to the polyacrylamide solution. The addition is stopped when the pH of the solution reaches 10. The mixed solution is heated to 60 °C and stirred and reacted at a constant temperature for 2 h, and the pH of the solution during the reaction is controlled to be 10. After the reaction is completed, the hydrolyzed and activated polyacrylamide solution is obtained.

[0041] (3) Preparation of silicon nitride composite powder

[0042] Dissolve 8 g of methacrylamide in 100 g of water, then add 100 g of α-Si3N4 powder, 3 g of Y2O3, 3 g of MgSiN2, and 0.6 g of sodium polyacrylate, and ultrasonically disperse for 15 min at a frequency of 50 kHz to obtain a premixed solution. Then add 6 g of modified β-silicon nitride whiskers to the premixed solution under stirring, ultrasonically disperse for 30 min at a frequency of 20 kHz, dry at 60 °C for 6 h to obtain a gel, and sinter the gel at 500 °C under a nitrogen atmosphere for 3 h to obtain a silicon nitride composite powder;

[0043] The number-average molecular weight of the polyacrylamide is 1.06 million.

[0044] (4)Cold isostatic pressing

[0045] Press the silicon nitride composite powder at a pressure of 110 MPa for 30 min to obtain a silicon nitride ceramic blank of 50×40×20 mm.

[0046] (5)Gas pressure sintering

[0047] Feed the silicon nitride ceramic blank into a gas pressure sintering furnace and sinter it under a nitrogen atmosphere at 1800 °C and 4 MPa to obtain a high thermal conductivity silicon nitride ceramic.

[0048] Example 2

[0049] A preparation method of a high thermal conductivity silicon nitride ceramic material for lightning protection insulators is as follows:

[0050] (1)Preparation of β-silicon nitride whiskers

[0051] Uniformly mix 75 g of silicon powder, 25 g of α-Si3N4, and 2.7 g of Y2O3, sinter at 1750 °C under a N2 atmosphere of 4 MPa for 1.2 h, then immerse the sintered material in a hydrofluoric acid solution for 12 min, filter and separate the product after immersion, wash with water and dry to obtain β-silicon nitride whiskers;

[0052] The particle size of the silicon powder is 400 nm;

[0053] The particle size of the α-Si3N4 is 600 nm;

[0054] The concentration of the hydrofluoric acid solution is 8 wt%.

[0055] (2)Modification of β-silicon nitride whiskers

[0056] Disperse 10 g of β-silicon nitride whiskers in 60 g of hydrolyzed and activated polyacrylamide solution, add 0.3 g of N,N-dicyclohexylcarbodiimide, react at 55 °C for 2.5 h, after the reaction, filter and separate the product, wash with water and dry to obtain modified β-silicon nitride whiskers;

[0057] The preparation method of the hydrolyzed and activated polyacrylamide solution is as follows: Dissolve polyacrylamide in water to prepare a polyacrylamide solution with a concentration of 6 wt%. While stirring, add a NaOH solution with a concentration of 25 g / L to the polyacrylamide solution. Stop adding when the pH of the solution reaches 10.5. Heat the mixed solution to 70 °C, stir and react at a constant temperature for 1.5 h, and control the pH of the solution during the reaction to be 10.5. After the reaction, a hydrolyzed and activated polyacrylamide solution is obtained;

[0058] The number-average molecular weight of the polyacrylamide is 1.54 million.

[0059] (3) Preparation of silicon nitride composite powder

[0060] Dissolve 9 g of methacrylamide in 100 g of water, then add 110 g of α-Si3N4 powder, 3.5 g of Y2O3, 3.5 g of MgSiN2, and 0.7 g of sodium polyacrylate. Ultrasonically disperse for 12 min at a frequency of 60 kHz to obtain a premixed solution. Then add 7 g of modified β-silicon nitride whiskers to the premixed solution while stirring, ultrasonically disperse for 25 min at a frequency of 25 kHz, dry at 70 °C for 5 h to obtain a gel, and sinter the gel at 550 °C in a nitrogen atmosphere for 2.5 h to obtain silicon nitride composite powder.

[0061] (4) Cold isostatic pressing

[0062] Press the silicon nitride composite powder at a pressure of 120 MPa for 32 min to obtain a silicon nitride ceramic blank with dimensions of 50×40×20 mm.

[0063] (5) Gas pressure sintering

[0064] Feed the silicon nitride ceramic blank into a gas pressure sintering furnace and sinter it at 1850 °C in a nitrogen atmosphere of 3.5 MPa to obtain a high thermal conductivity silicon nitride ceramic.

[0065] Example 3

[0066] A preparation method of a high thermal conductivity silicon nitride ceramic material for lightning protection insulators is as follows:

[0067] (1) Preparation of β-silicon nitride whiskers

[0068] Uniformly mix 80 g of silicon powder, 20 g of α-Si3N4, and 3 g of Y2O3, sinter at 1700 °C in a N2 atmosphere of 5 MPa for 1.5 h, then immerse the sintered material in a hydrofluoric acid solution for 15 min. After immersion, filter and separate the product, wash it with water and dry it to obtain β-silicon nitride whiskers;

[0069] The particle size of the silicon powder is 500 nm;

[0070] The particle size of the α-Si3N4 is 800 nm;

[0071] The concentration of the hydrofluoric acid solution is 5 wt%.

[0072] (2) Modification of β-silicon nitride whiskers

[0073] Disperse 10 g of β-silicon nitride whiskers in 70 g of hydrolyzed and activated polyacrylamide solution, add 0.4 g of N,N-dicyclohexylcarbodiimide, react at 60 °C for 2 h. After the reaction, filter and separate the product, wash it with water and dry it to obtain modified β-silicon nitride whiskers;

[0074] The preparation method of the hydrolyzed and activated polyacrylamide solution is as follows: dissolve polyacrylamide in water to prepare a polyacrylamide solution with a concentration of 8 wt%, dropwise add a NaOH solution with a concentration of 30 g / L to the polyacrylamide solution under stirring. Stop adding when the pH of the solution reaches 11, heat the mixed solution to 80 °C, and stir and react at a constant temperature for 1 h, and control the pH of the solution during the reaction to be 11. After the reaction, obtain the hydrolyzed and activated polyacrylamide solution;

[0075] The number-average molecular weight of the polyacrylamide is 2.11 million.

[0076] (3) Preparation of silicon nitride composite powder

[0077] Dissolve 10 g of methylacrylamide in 100 g of water, then add 120 g of α-Si3N4 powder, 4 g of Y2O3, 4 g of MgSiN2, and 0.8 g of polyvinyl alcohol, ultrasonically disperse for 10 min at a frequency of 70 kHz to obtain a premixed solution. Then add 8 g of modified β-silicon nitride whiskers to the premixed solution under stirring, ultrasonically disperse for 20 min at a frequency of 30 kHz, dry at 80 °C for 4 h to obtain a gel, and sinter the gel at 600 °C in a nitrogen atmosphere for 2 h to obtain silicon nitride composite powder.

[0078] (4) Cold isostatic pressing

[0079] Press the silicon nitride composite powder at a pressure of 130 MPa for 35 min to obtain a silicon nitride ceramic blank with dimensions of 50×40×20 mm.

[0080] (5) Gas pressure sintering

[0081] Put the silicon nitride ceramic blank into a gas pressure sintering furnace and sinter it at 1900 °C in a nitrogen atmosphere of 3 MPa to obtain a high thermal conductivity silicon nitride ceramic.

[0082] Comparative example 1

[0083] Comparative Example 1 adopted the preparation method of the high thermal conductivity silicon nitride ceramic described in Example 2, except that the β-silicon nitride whisker modification step was omitted, and β-silicon nitride whiskers were used to replace the modified β-silicon nitride whiskers in the step of preparing the silicon nitride composite powder, and the remaining steps were the same.

[0084] Comparative Example 2

[0085] Comparative Example 2 adopted the preparation method of the high thermal conductivity silicon nitride ceramic described in Example 2, except that the β-silicon nitride whisker modification step was omitted, and the step of preparing the silicon nitride composite powder was changed to: adding 110 g of α-Si3N4 powder, 3.5 g of Y2O3, 3.5 g of MgSiN2, 0.7 g of sodium polyacrylate, and 7 g of β-silicon nitride whiskers into 100 g of ethanol, ball milling for 8 h at a ball-to-material ratio of 6:1, filtering and separating the product, and drying to obtain the silicon nitride composite powder;

[0086] The remaining steps were the same.

[0087] Test Example 1

[0088] For the high thermal conductivity silicon nitride ceramic materials prepared by the methods of Examples 1-3 and Comparative Examples 1-2, the thermal conductivity, flexural strength, fracture toughness, and density were measured respectively. Among them, the thermal conductivity was measured by the transient plane heat source method, the flexural strength was calculated by the three-point bending method, the fracture toughness was tested by the indentation method, and the density was measured by the Archimedes drainage method.

[0089] The test results are shown in Table 1.

[0090] Table 1 Thermal conductivity, flexural strength, fracture toughness, and density of the high thermal conductivity silicon nitride ceramic materials prepared in Examples 1-3 and Comparative Examples 1-2

[0091]

[0092] As can be seen from Table 1, the thermal conductivity, flexural strength, fracture toughness, and density of the high thermal conductivity silicon nitride ceramics prepared by the methods of Examples 1-3 are higher than those of Comparative Examples 1-2, indicating that soaking the β-silicon nitride whiskers prepared by firing in a hydrofluoric acid solution, modifying the β-silicon nitride whiskers, and obtaining the silicon nitride composite powder by gel firing can improve the thermal conductivity, flexural strength, fracture toughness, and density of the prepared silicon nitride ceramics.

[0093] For the modification of β-silicon nitride whiskers, after the β-silicon nitride whiskers were soaked in the hydrofluoric acid solution, a certain amount of hydroxyl groups were introduced on the surface. The hydroxyl groups on the surface of the β-silicon nitride whiskers reacted with the activated polyacrylamide to undergo a dehydration esterification reaction, grafting the polyacrylamide onto the surface of the β-silicon nitride whiskers, introducing hydrophilic amide groups onto the surface of the whiskers, reducing the surface energy, and increasing the hydrophilicity.

[0094] This change in surface properties makes it easier for the whiskers to be surrounded by water molecules in water, reducing the intermolecular forces between particles and thus improving the dispersibility. At the same time, the polyacrylamide molecular chain is relatively long, forming a dense protective layer on the surface of the whiskers, hindering the direct contact between the whisker particles, preventing the aggregation and sedimentation of the whisker particles, and improving the stability of the whisker suspension state. In the step of preparing the silicon nitride composite powder, the β-silicon nitride whiskers can be evenly dispersed in the premixed solution to obtain a silicon nitride composite powder with uniform mixing. The silicon nitride ceramic prepared by pressing and molding the silicon nitride composite powder with uniform mixing and then sintering at high temperature has good thermal conductivity, flexural strength, fracture toughness and density.

[0095] In Comparative Example 1, the modification of the β-silicon nitride whiskers was omitted, and the β-silicon nitride whiskers were directly used to prepare the silicon nitride composite powder with other raw materials. Due to the van der Waals forces between the particles of the β-silicon nitride whiskers, the whiskers are prone to aggregation and it is difficult to maintain uniform dispersion. Moreover, the surface energy of the β-silicon nitride whiskers is relatively high, which is easy to interact with other particles, resulting in agglomeration and sedimentation, and it is impossible to form a silicon nitride composite powder with uniform mixing, thereby affecting the thermal conductivity, strength properties and density of the silicon nitride ceramic.

[0096] In Comparative Example 2, compared with Example 2, the ball milling method was used for mixing. Under the ball milling state, the β-silicon nitride whiskers were damaged, resulting in whisker fracture or fragmentation. The density of the prepared silicon nitride ceramic decreased, and the degree of order of grain production decreased, affecting the thermal conductivity, flexural strength, fracture toughness and density of the silicon nitride ceramic.

[0097] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they 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 a high thermal conductivity silicon nitride ceramic material for a lightning protection insulator, characterized in that, The method includes the following steps: preparing β-silicon nitride whiskers, modifying the β-silicon nitride whiskers, preparing silicon nitride composite powder, cold isostatic pressing molding, and gas pressure sintering; The method for modifying the β-silicon nitride whiskers is to disperse the β-silicon nitride whiskers in a hydrolyzed and activated polyacrylamide solution, add dehydrating agent N,N'-dicyclohexylcarbodiimide, react at 50-60 °C for 2-3 h. After the reaction, filter and separate the product, wash with water and dry to obtain modified β-silicon nitride whiskers; The method for preparing the silicon nitride composite powder is to dissolve methacrylamide in water, then add α-Si3N4 powder, Y2O3, MgSiN2, and a dispersant, and perform ultrasonic dispersion for 10-15 min once to obtain a premixed solution. Then add the modified β-silicon nitride whiskers to the premixed solution under stirring, and perform ultrasonic dispersion for 20-30 min again. Dry at 60-80 °C for 4-6 h to obtain a gel, and sinter the gel at 500-600 °C in a nitrogen atmosphere for 2-3 h to obtain the silicon nitride composite powder.

2. The preparation method of a highly thermally conductive silicon nitride ceramic material for a lightning protection insulator according to claim 1, wherein The method for preparing β-silicon nitride whiskers is to use silicon powder and α-Si3N4 as raw materials, and Y2O3 as an auxiliary agent. Uniformly mix the raw materials and the auxiliary agent, sinter in a N2 atmosphere at 3-5 MPa and 1700-1800 °C for 1-1.5 h. Immerse the sintered material in a hydrofluoric acid solution for 10-15 min, wash with water and dry after immersion to obtain β-silicon nitride whiskers.

3. The preparation method of a high thermal conductivity silicon nitride ceramic material for a lightning protection insulator according to claim 2, characterized in that, In the step of preparing β-silicon nitride whiskers, The mass ratio of the silicon powder, α-Si3N4, and Y2O3 is 70-80:20-30:2.5-3; The particle size of the silicon powder is 300-500 nm; The particle size of the α-Si3N4 is 500-800 nm; The concentration of the hydrofluoric acid solution is 5-10 wt%.

4. The preparation method of a high thermal conductivity silicon nitride ceramic material for a lightning protection insulator according to claim 1, characterized in that, In the step of modifying the β-silicon nitride whiskers, the mass ratio of the β-silicon nitride whiskers, the hydrolyzed and activated polyacrylamide solution, and N,N'-dicyclohexylcarbodiimide is 10:50-70:0.2-0.

4.

5. The preparation method of a high thermal conductivity silicon nitride ceramic material for lightning protection insulators according to claim 1, characterized in that, In the step of modifying the β-silicon nitride whiskers, the preparation method of the hydrolyzed and activated polyacrylamide solution is to dissolve polyacrylamide in water to prepare a polyacrylamide solution. Dropwise add NaOH solution to the polyacrylamide solution under stirring. Stop adding when the solution pH reaches 10-11. Heat the mixed solution to 60-80 °C, and stir and react at a constant temperature for 1-2 h, and control the pH range of the solution during the reaction to be 10-11. After the reaction, obtain the hydrolyzed and activated polyacrylamide solution.

6. The preparation method of a high thermal conductivity silicon nitride ceramic material for a lightning protection insulator according to claim 5, characterized in that, The number average molecular weight of the polyacrylamide is 1.06-2.11 million; The concentration of the polyacrylamide solution is 5-8 wt%; The concentration of the NaOH solution is 20-30 g / L.

7. The preparation method of a high thermal conductivity silicon nitride ceramic material for a lightning protection insulator according to claim 1, characterized in that, In the step of preparing the silicon nitride composite powder, The mass ratio of water, methacrylamide, α-Si3N4 powder, Y2O3, MgSiN2, dispersant, and modified β-silicon nitride whiskers is 100:8-10:100-120:3-4:3-4:0.6-1:6-8; The dispersant is one of sodium polyacrylate and polyvinyl alcohol.

8. The preparation method of a high thermal conductivity silicon nitride ceramic material for a lightning protection insulator according to claim 1, characterized in that, In the step of preparing the silicon nitride composite powder, The frequency of the first ultrasonic wave is 50 - 70 kHz; The frequency of the second ultrasonic wave is 20 - 30 kHz.

9. The preparation method of a high thermal conductivity silicon nitride ceramic material for a lightning protection insulator according to claim 1, characterized in that, The method of cold isostatic pressing is to press the silicon nitride composite powder at a pressure of 110 - 130 MPa for 30 - 35 min to obtain a silicon nitride ceramic blank.

10. The preparation method of a high thermal conductivity silicon nitride ceramic material for a lightning protection insulator according to claim 1, characterized in that, The method of gas pressure sintering is to send the silicon nitride ceramic blank into a gas pressure sintering furnace and sinter it at 1800 - 1900 °C under a nitrogen pressure of 3 - 4 MPa to obtain a high thermal conductivity silicon nitride ceramic.

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