High-thermal-conductivity silicon carbide ceramic material and preparation method thereof

Abstract

The invention belongs to the field of ceramic material production, and relates to a high-thermal-conductivity silicon carbide ceramic material and a preparation method thereof. The preparation method comprises the following steps: mixing silicon carbide powder, cane sugar, boric acid, a dispersing agent and water to prepare slurry; on the basis that the total mass of the silicon carbide powder, the carbon element obtained after cane sugar is debonded, the boron element in the boric acid and the dispersing agent is 100 wt.%, the adding amount of the carbon element obtained after cane sugar is debonded is 1.0 wt.%-2.5 wt.%, and the adding amount of the boron element in the boric acid is 0.1 wt.%-0.3 wt.%; drying, sieving, forming and debonding the slurry to obtain a ceramic body; and sintering the ceramic green body at normal pressure to obtain the high-thermal-conductivity silicon carbide ceramic material. The water-soluble sucrose and boric acid are added as sintering aids to be mixed with the silicon carbide powder, so that the uniform dispersity of the sintering aids is improved, and finally, the use amount of the sintering aids is effectively reduced while the sintering densification of the ceramic is ensured, thereby reducing the adverse effect of a second phase and internal impurities on the thermal conductivity of the silicon carbide ceramic as much as possible.

Description

Technical Field

[0001] The present invention belongs to the field of ceramic material production, and particularly relates to a high thermal conductivity silicon carbide ceramic material and a preparation method thereof. Background Art

[0002] Since silicon carbide has extremely strong covalent bonds, it has the advantages of high strength, high hardness, good chemical stability, excellent corrosion resistance and wear resistance, and low thermal expansion coefficient, and is widely used in many fields including microelectronics, mechanical seals, aerospace, energy, and military. Among them, the excellent thermal conductivity of silicon carbide ceramics is utilized in heating components, heat exchangers, substrates, etc.

[0003] The intrinsic thermal conductivity of pure single crystal silicon carbide at room temperature is 490 W / (m·K). However, due to the random grain orientation, lattice defects of grains, grain boundary structure, pores, and the second phase at grain boundaries in polycrystalline silicon carbide, its thermal conductivity is much lower than the intrinsic thermal conductivity. The type of sintering aid affects the thermal conductivity of polycrystalline silicon carbide. Watari et al. added 2 wt.% BeO as a sintering aid and prepared silicon carbide ceramics with a thermal conductivity as high as 270 W / (m·K) by hot pressing sintering, which is the silicon carbide ceramic with the highest thermal conductivity so far. However, due to the extremely strong toxicity of powders of Be and its compounds, it cannot meet the requirements of environmental protection. Therefore, researchers have been looking for environmentally friendly sintering aids.

[0004] Compared with liquid-phase sintered silicon carbide ceramics, solid-phase sintered silicon carbide ceramics have a cleaner grain boundary structure, which is beneficial to obtaining excellent high-temperature stability and corrosion resistance. Moreover, the atmospheric pressure sintering process is simple, the cost is low, large-size and complex-shaped ceramics can be formed, and it is easy for industrial production. Munro et al. used α-silicon carbide powder as raw material, and the thermal conductivity of the atmospheric pressure solid-phase sintered silicon carbide ceramics obtained by adding 0.4% B and 0.5% C is 114 W / (m·K). Malik and Kim et al. added 0.7 wt.% B4C and 2.5 wt.% C as sintering aids, and obtained silicon carbide ceramics with a relative density greater than 98% by atmospheric pressure sintering, and the thermal conductivity can reach 154 W / (m·K).

[0005] However, since the B and C sintering aids added to atmospheric pressure solid-phase sintered silicon carbide ceramics are usually in solid form, agglomeration is likely to occur between particles, so the sintering aids are not evenly dispersed enough, and a slightly excessive amount of sintering aids needs to be added to promote ceramic sintering. This also leads to local excess of sintering aids and forms more second phases at the grain boundaries of silicon carbide ceramics that are not conducive to improving the thermal conductivity.

[0006] Therefore, there is an urgent need for a new method that can highly uniformly disperse sintering aids and can prepare high thermal conductivity silicon carbide ceramic materials by adding only a very small amount of sintering aids. Summary of the Invention

[0007] In order to overcome the deficiencies of the existing preparation methods of silicon carbide ceramic materials, the present invention provides a preparation method of high-thermal-conductivity silicon carbide ceramics. Compared with the sintering aids required under existing conventional conditions, sucrose and boric acid, which are both easily soluble in water, are added in the present invention as sintering aids and mixed with silicon carbide powder, improving the uniform dispersion of the sintering aids. The carbon generated after the debinding of sucrose can remove the silica on the surface of silicon carbide particles during the sintering process, increasing the surface energy of silicon carbide particles and improving the sintering performance. At the same time, it can also reduce boron oxide generated after the debinding of boric acid to boron carbide or boron, and the boron solid dissolved in the silicon carbide lattice can further increase the sintering activity of the silicon carbide powder. Finally, while ensuring the densification of the ceramic sintering, the amount of the sintering aid is effectively reduced, thereby minimizing the adverse effects of the second phase and internal impurities on the thermal conductivity of the silicon carbide ceramic as much as possible.

[0008] In a first aspect, the present invention provides a preparation method of a high-thermal-conductivity silicon carbide ceramic material. The preparation method includes the following steps:

[0009] Step (1): Mix silicon carbide powder, sucrose, boric acid, a dispersant and water to prepare a slurry; based on the total mass of the silicon carbide powder, the carbon element after the debinding of sucrose, the boron element in boric acid and the dispersant being 100 wt.%, the addition amount of the carbon element after the debinding of sucrose is 1.0 wt.% to 2.5 wt.%, and the addition amount of the boron element in boric acid is 0.1 wt.% to 0.3 wt.%.

[0010] Step (2): Subject the slurry obtained in step (1) to drying, sieving, forming and debinding to obtain a ceramic green body;

[0011] Step (3): Subject the ceramic green body obtained in step (2) to atmospheric pressure sintering to obtain a high-thermal-conductivity silicon carbide ceramic material.

[0012] Preferably, the drying is vacuum rotary evaporation drying; preferably, the temperature of the vacuum rotary evaporation drying is 50 to 80 °C, the vacuum degree is 1 to 5 kPa, and the rotation speed is 50 to 200 revolutions per minute.

[0013] Preferably, in step (2), the forming methods are dry pressing forming and isostatic pressing forming; preferably, the pressure of the dry pressing forming is 30 to 80 MPa, and the time is 0.5 to 2 minutes; the pressure of the isostatic pressing forming is 150 to 300 MPa, and the time is 2 to 5 minutes.

[0014] Preferably, in step (2), the debinding atmosphere is vacuum, the vacuum degree is 0 to 20 Pa, the debinding temperature is 500 to 1000 °C, and the debinding time is 30 to 90 minutes.

[0015] Preferably, in step (3), the sintering atmosphere is an argon atmosphere, the sintering temperature is 2100-2200 °C, and the holding time is 30-120 minutes; preferably, the ceramic green body is annealed after normal pressure sintering; more preferably, the annealing temperature is 1650-2050 °C, the annealing time is 2-12 h, and the annealing atmosphere is an argon atmosphere.

[0016] Preferably, the silicon carbide powder is α-silicon carbide; the average particle size of the α-silicon carbide powder is 0.1-1 μm; the purities of the silicon carbide powder, sucrose, and boric acid are all > 99%.

[0017] Preferably, the dispersant is tetramethylammonium hydroxide; preferably, the addition amount of the dispersant is 0.3 wt.% - 1 wt.%; more preferably, the addition amount of water is such that the solid content of the slurry is 40 wt.% - 60 wt.%.

[0018] In a second aspect, the present invention provides a high thermal conductivity silicon carbide ceramic material. The high thermal conductivity silicon carbide ceramic material is obtained according to the preparation method described in any one of the above.

[0019] Preferably, the high thermal conductivity silicon carbide ceramic material mainly consists of silicon carbide and carbon particles present inside or in the gaps of silicon carbide grains, where no more than 10 carbon particles are distributed per 100 square micrometers of the high thermal conductivity silicon carbide ceramic material, and the average diameter of the carbon particles does not exceed 1 μm.

[0020] Preferably, the relative density of the high thermal conductivity silicon carbide ceramic material is above 97%, the thermal diffusivity at room temperature is above 80 mm 2 / s, and the thermal conductivity is above 165 W / (m·K).

[0021] Advantages of the present invention:

[0022] The present invention relates to a high thermal conductivity silicon carbide ceramic material and a preparation method thereof. By using a soluble carbon source and a boron source as sintering aids and adopting a vacuum rotary evaporation drying method for drying the slurry, the uniform dispersion of the sintering aids can be effectively improved, and the preparation of a high thermal conductivity silicon carbide ceramic can be achieved with only a very small amount of sintering aids. The prepared silicon carbide ceramic has high purity, contains fewer and more uniform boron elements and carbon particles, and tries to avoid the formation of a second phase at the grain boundaries, which can effectively reduce the phonon scattering problem caused by impurity elements, thereby improving the thermal conductivity. Description of the drawings

[0023] Figure 1 SEM image of the surface of the high thermal conductivity silicon carbide ceramic prepared in Example 1 of the present invention after alkali corrosion; Figure 2 SEM image of the fracture morphology of the high thermal conductivity silicon carbide ceramic prepared in Example 1 of the present invention; Figure 3 SEM image of the surface of the high - thermal - conductivity silicon carbide ceramic prepared in Example 2 of the present invention after alkali corrosion; Figure 4 SEM image of the fracture morphology of the high - thermal - conductivity silicon carbide ceramic prepared in Example 2 of the present invention; Figure 5 Flow chart for the preparation of the present invention; Figure 6 Surface photos of the debound material block obtained by conventional drying using fructose as the carbon source. Among them, (a) top surface, (b) side surface, (c) bottom surface. Detailed implementation manners

[0024] The present invention will be further described below in conjunction with the accompanying drawings and the following implementation manners. It should be understood that the accompanying drawings and the following implementation manners are only used to illustrate the present invention, rather than limiting the present invention.

[0025] The present invention provides a method for preparing a high - thermal - conductivity silicon carbide ceramic, which is prepared by mixing silicon carbide powder, sucrose, boric acid, a dispersant and water, followed by drying, forming and sintering at atmospheric pressure. The following combines Figure 5 Exemplarily illustrate the method for preparing the high - thermal - conductivity silicon carbide ceramic of the present invention.

[0026] Mix silicon carbide powder, sucrose, boric acid, a dispersant and water to prepare a slurry. The addition order of each raw material is not limited. Each raw material can be directly mixed. It is also possible to dissolve sucrose and boric acid in water and then mix with silicon carbide powder and a dispersant.

[0027] The silicon carbide powder is α - silicon carbide. For example, the average particle size of the α - silicon carbide powder is 0.1 - 1 μm.

[0028] The purities of silicon carbide powder, sucrose and boric acid are all > 99%.

[0029] Among them, based on the total mass of 100 wt.% of silicon carbide powder, the carbon element after debinding of sucrose, the boron element in boric acid and the dispersant, the addition amount of the carbon element after debinding of sucrose is 1.0 wt.% - 2.5 wt.%. The carbon element content after debinding of sucrose is obtained according to the residual carbon rate of sucrose at the corresponding debinding temperature (which can be calculated from the thermogravimetric curve).

[0030] The carbon element addition amount of the present invention is an optimized addition amount obtained through exploration under the premise of atmospheric pressure sintering, which can densify the ceramic. The higher the sucrose addition amount, the more impurities in the ceramic and the lower the thermal conductivity. However, if the sucrose addition amount is too low, it will lead to too low density of the ceramic, which will also affect the improvement of the thermal conductivity. Therefore, it is necessary to explore the minimum sucrose dosage (or carbon element addition amount) required to densify the ceramic. Please note that the sintering driving force of atmospheric pressure sintering mainly comes from the reduction of the grain boundary energy and the increase of the surface energy of silicon carbide by the sintering aid. In addition to the sintering aid, the sintering driving force of hot press sintering also comes partly from the pressure applied during the sintering process. The magnitude of the sintering pressure affects the magnitude of the sintering driving force and also affects the addition amount of the sintering aid required (higher pressure is helpful for the densification of the ceramic).

[0031] Among them, based on the total mass of silicon carbide powder, carbon element after debinding of sucrose, boron element in boric acid, and dispersant being 100 wt.%, the addition amount of boron element in boric acid is 0.1 wt.% - 0.3 wt.%. The boron element content in boric acid is determined by the theoretical boron content

[0032] The boron element addition amount of the present invention is an optimized addition amount obtained through exploration under the premise of atmospheric pressure sintering, which can densify the ceramic. The higher the boric acid addition amount, the more impurities in the ceramic and the lower the thermal conductivity. However, if the boric acid addition amount is too low, it will lead to too low density of the ceramic, which will also affect the improvement of the thermal conductivity. Therefore, it is necessary to explore the minimum boric acid dosage (or boron element addition amount) required to densify the ceramic.

[0033] In some embodiments, after dissolving boric acid and sucrose in water to obtain a solution, ammonia water is added to adjust the pH to 12, and then it is mixed with silicon carbide and a dispersant to obtain a slurry.

[0034] The obtained slurry is dried, sieved, formed, and debound to obtain a ceramic green body.

[0035] Both sucrose and boric acid are dissolved in the slurry. If the slurry is dried in a conventional manner, due to long-term static placement, the water on the surface of the slurry is continuously dried and evaporated, the slurry settles, and the sucrose and boric acid molecules dissolved in the slurry will diffuse and concentrate towards the surface of the slurry, thus destroying the uniform dispersion state of the sintering aid and silicon carbide powder after mixing. The hard block formed after drying will also cause difficulties in subsequent grinding. That is to say, conventional drying (such as drying in a blast drying oven) will cause a certain degree of settlement and stratification of the slurry during long-term static placement, the water on the surface of the slurry is continuously dried and evaporated, and the small molecules dissolved in the slurry will diffuse and concentrate towards the surface of the slurry, thus destroying the mixed and uniform state after ball milling, affecting the thermal conductivity of the prepared ceramic (the dried slurry becomes a yellowish-brown hard block, and yellowish-brown is the color of silicon carbide powder. If it is not ground and sieved and directly debound, it can be found that there is a layer of black substance on the surface of the yellowish-brown hard block. The black substance is carbon produced by the cracking of fructose, and its covering on the surface proves that small molecules diffuse and concentrate during drying, as Figure 6 shown), and the drying time often takes several hours or even longer, and the drying efficiency is lower.

[0036] It is preferred to use vacuum rotary evaporation to dry the slurry. Vacuum rotary evaporation drying adopts a dynamic drying method, evacuating the slurry while rotating and heating, which can realize the continuous mixing of the sintering aid and silicon carbide powder during the drying process, avoid the diffusion and concentration of the sintering aid molecules dissolved in water, and what is obtained after drying is a relatively soft powder block, which is easy to grind and break. The temperature of vacuum rotary evaporation drying needs to be higher than the boiling point of water corresponding to this vacuum degree. Within a certain range, the higher the drying temperature and rotation speed, and the lower the vacuum degree, the shorter the required drying time. Moreover, the drying time required for vacuum rotary evaporation drying is shorter, which can be shortened to within 1 hour, and the drying efficiency is higher. At present, there are very few reports on the use of vacuum rotary evaporation drying in the preparation of silicon carbide ceramics. This is because most of the sintering aids used in the preparation of silicon carbide ceramics are added in solid rather than liquid form, so the sintering aid will not diffuse to the surface of the slurry during the drying process. However, the sintering aids (carbon source and boron source) used in the present invention are added in liquid form, so vacuum rotary evaporation drying rather than conventional drying method needs to be used for drying, which is determined by the state (solid or liquid) of the sintering aid.

[0037] In some embodiments, the drying method is vacuum rotary evaporation drying, the drying temperature is 50-80 °C, the vacuum degree is 1-5 kPa, and the rotation speed is 50-200 revolutions per minute.

[0038] The debinding atmosphere can be vacuum, the vacuum degree is 0-20 Pa, the debinding temperature is 500-1000 °C, and the debinding time is 30-90 minutes.

[0039] The forming methods are dry pressing and isostatic pressing. The dry pressing pressure is 30 - 80 Mpa, and the time is 0.5 - 2 minutes. The isostatic pressing pressure is 150 - 300 MPa (preferably 150 - 200 Mpa), and the time is 2 - 5 minutes. First, dry pressing is carried out, and then isostatic pressing.

[0040] The obtained ceramic green body is sintered under normal pressure to obtain the high - thermal - conductivity silicon carbide ceramic material.

[0041] The sintering atmosphere is an inert atmosphere, such as argon. The sintering temperature is 2100 - 2200 °C, and the holding time is 30 - 120 minutes.

[0042] In addition to impurities, the factors affecting the thermal conductivity of ceramics also include the influence of grain size. The larger the grain size, the higher the thermal conductivity. However, for silicon carbide ceramics prepared by hot - press sintering, due to the application of pressure during sintering to inhibit grain growth, the obtained grain size is relatively small (for example, only 1.5 μm), so the improvement of thermal conductivity is inhibited. The normal - pressure sintering adopted in the present invention does not apply pressure to inhibit grain growth, and the grain size is larger (for example, about 3 μm), so a higher thermal conductivity (165 - 190 W / (m·K)) can be obtained.

[0043] The ceramic green body after normal - pressure sintering can also be annealed. The annealing temperature is 1650 - 2050 °C, the annealing time is 2 - 12 h, and the annealing atmosphere is an argon atmosphere. Annealing helps to further promote the thermal conductivity of silicon carbide ceramics. This is because during the annealing process, mass diffusion is promoted, internal defects of the ceramics are filled, lattice defects are reduced, and grain growth is promoted. These combined factors contribute to the improvement of the thermal conductivity of silicon carbide ceramics.

[0044] The silicon carbide ceramic material prepared by the above - mentioned preparation method has a thermal diffusivity of more than 80 mm 2 / s at room temperature and a thermal conductivity of more than 165 W / (m·K). The relative density of the ceramic material is more than 97%.

[0045] The sintered ceramic is mainly composed of silicon carbide and a very small amount of C particles existing inside or in the gaps of silicon carbide grains. There are no more than 10 C particles per 100 square micrometers, and the average diameter of C particles does not exceed 1 μm. Therefore, the high - thermal - conductivity silicon carbide ceramic material prepared in the present invention has a low carbon content, no more than 10 carbon particles per 100 square micrometers; the carbon particles generated by the pyrolysis of the carbon source are smaller, and the average diameter does not exceed 1 μm. The carbon particles with low content and more uniform distribution (vacuum rotary evaporation drying helps the dissolved small - molecule carbon source and boron source to be mixed uniformly with silicon carbide powder) and the larger grain size (normal - pressure sintering, for example, about 3 μm) make the silicon carbide ceramic prepared in the present invention have a higher thermal conductivity (more than 165 W / (m·K)) and excellent mechanical property indexes.

[0046] In addition, the density of the silicon carbide ceramic may be 3.1 g / cm 3 Above, the relative density may be 97% - 99%, the flexural strength may be 350 - 450 Mpa, the elastic modulus may be 350 - 410 Gpa, the Vickers hardness may be 23 - 25 Gpa, and the fracture toughness may be 2.3 - 2.9 MPa·m 1 / 2 .

[0047] In summary, the preparation method of the high - thermal - conductivity silicon carbide ceramic material of the present invention is to prepare the high - thermal - conductivity silicon carbide ceramic through mixing, drying, forming, vacuum debinding, and atmospheric - pressure sintering of silicon carbide powder, sucrose, boric acid, dispersant, and water. The present invention improves the thermal conductivity of the material by adding soluble sucrose and boric acid as sintering aids, using vacuum rotary evaporation drying to improve the dispersion uniformity of the sintering aids, and using as little sintering aid dosage as possible to prepare a dense and high - thermal - conductivity silicon carbide ceramic.

[0048] The following further lists examples to illustrate the present invention in detail. Similarly, it should be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Those skilled in the art's non - essential improvements and adjustments based on the above content of the present invention all fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are also only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description in this article, rather than being limited to the specific values in the following examples.

[0049] Example 1

[0050] (1) Preparation of slurry

[0051] Taking the total mass of silicon carbide powder, carbon element after sucrose debinding, boron element in boric acid, and dispersant as 100 wt.%, the silicon carbide content is 97.8 wt.%, the B element in boric acid is 0.1 wt.%, the addition amount of C element after sucrose debinding is 1.5 wt.%, and the addition amount of dispersant tetramethylammonium hydroxide is 0.6 wt.%. Boric acid and sucrose are dissolved in water to obtain a solution, and ammonia water is added to adjust the pH to 12. Finally, it is mixed with silicon carbide powder and dispersant to obtain a slurry with a solid content of 50 wt.%. 200 g of silicon carbide ball - milling beads are added to the slurry as the ball - milling medium, and it is ball - milled in a planetary ball - mill at a speed of 300 r / min for 4 h.

[0052] (2) Preparation of green body

[0053] The ball-milled slurry is dried by vacuum rotary evaporation using a rotary evaporator, and then ground and sieved to obtain a powder. After the powder is formed, it is debound in a debinding furnace to obtain a ceramic green body. The vacuum degree of vacuum rotary evaporation is 5 kPa, the rotation speed is 80 r / min, the drying temperature is 65 °C, and it is sieved through a 100-mesh sieve. The forming methods are dry pressing and isostatic pressing. The dry pressing pressure is 60 MPa, and the pressure is maintained for 30 s. The isostatic pressing pressure is 200 MPa, and the pressure is maintained for 2 minutes. The vacuum debinding temperature is 900 °C, the holding time is 30 minutes, and the vacuum degree is 10 Pa.

[0054] (3) Preparation of ceramics

[0055] The high-thermal-conductivity silicon carbide ceramics are obtained after sintering the ceramic green body under atmospheric pressure. The sintering temperature is 2150 °C, the holding time is 60 minutes, and the sintering atmosphere is an argon atmosphere.

[0056] The microstructure of the silicon carbide ceramics prepared in this example is as Figure 1 and Figure 2 shown. The microstructure of the silicon carbide ceramic material is dense. After sintering, the ceramic is mainly composed of silicon carbide and a very small amount of C particles present inside or in the gaps of silicon carbide grains. The content of C particles is extremely low, and only some C particles are present at the grain boundaries or between grains. Among them, there are about 7 C particles per 100 square micrometers on average, and the average diameter of C particles is about 0.73 μm.

[0057] Example 2

[0058] (1) Preparation of slurry

[0059] Taking the total mass of silicon carbide powder, carbon element after debinding of sucrose, boron element in boric acid, and dispersant as 100 wt.%, the content of silicon carbide is 98.3 wt.%, the B element in boric acid is 0.1 wt.%, the addition amount of C element after debinding of sucrose is 1 wt.%, and the addition amount of the dispersant tetramethylammonium hydroxide is 0.6 wt.%. Boric acid and sucrose are dissolved in water to obtain a solution, and then ammonia water is added to adjust the pH to 12. Finally, it is mixed with silicon carbide powder and dispersant to obtain a slurry with a solid content of 50 wt.%. 200 g of silicon carbide milling beads are added to the slurry as the milling medium, and it is milled in a planetary ball mill at a rotation speed of 300 r / min for 4 h.

[0060] (2) Preparation of green body

[0061] The ball-milled slurry is dried by vacuum rotary evaporation using a rotary evaporator, then ground and sieved to obtain a powder. After the powder is formed, it is debound in a debinding furnace to obtain a ceramic green body. The vacuum degree for vacuum rotary evaporation drying is 5 kPa, the rotation speed is 120 r / min, the drying temperature is 60 °C, and it is sieved through a 100-mesh sieve. The forming methods are dry pressing and isostatic pressing. The dry pressing pressure is 60 Mpa, and the pressure is maintained for 30 s. The isostatic pressing pressure is 200 MPa, and the pressure is maintained for 2 minutes. The vacuum debinding temperature is 900 °C, the holding time is 30 minutes, and the vacuum degree is 10 Pa.

[0062] (3) Preparation of ceramics

[0063] The ceramic green body is sintered under normal pressure and annealed to obtain a high-thermal-conductivity silicon carbide ceramic. The sintering temperature is 2150 °C, the holding time is 60 minutes, the sintering atmosphere is argon atmosphere, the annealing temperature is 1750 °C, the annealing time is 4 h, and the annealing atmosphere is argon atmosphere.

[0064] The microstructure of the silicon carbide ceramic prepared in this example is as Figure 3 and Figure 4 shown. The microstructure of the silicon carbide ceramic material is dense. After sintering, the ceramic is mainly composed of silicon carbide and a very small amount of C particles existing inside or in the gaps of silicon carbide grains. The content of C particles is extremely low, and only some C particles exist at the grain boundaries or between grains. Among them, there are about 5 C particles per 100 square micrometers on average, and the average diameter of C particles is about 0.68 μm.

[0065] Example 3

[0066] The preparation method of this example is basically the same as that of Example 1, except that in this example, the silicon carbide content is 97.1 wt.%, the addition amount of B element of boric acid is 0.3 wt.%, the addition amount of C element after sucrose debinding is 2.0 wt.%, the addition amount of dispersant tetramethylammonium hydroxide is 0.6 wt.%, the drying temperature is 60 °C, the rotation speed is 130 r / min, and other process conditions and parameters are the same as those in Example 1.

[0067] Example 4

[0068] The preparation method of this example is basically the same as that of Example 1, except that in this example, the silicon carbide content is 96.7 wt.%, the addition amount of B element of boric acid is 0.2 wt.%, the addition amount of C element after sucrose debinding is 2.5 wt.%, the addition amount of dispersant tetramethylammonium hydroxide is 0.6 wt.%, the drying temperature is 65 °C, the rotation speed is 80 r / min, and other process conditions and parameters are the same as those in Example 1.

[0069] Example 5

[0070] The preparation method of this example is basically the same as that of Example 1, except that in this example, the silicon carbide content is 97.7 wt.%, the addition amount of B element in boric acid is 0.2 wt.%, the addition amount of C element after sucrose debinding is 1.5 wt.%, the addition amount of dispersant tetramethylammonium hydroxide is 0.6 wt.%, the drying temperature is 70 °C, the rotation speed is 110 r / min, the annealing temperature is 1950 °C, and other process conditions and parameters are the same as those in Example 1.

[0071] Comparative Example 1

[0072] The preparation method of this comparative example is basically the same as that of Example 1, except that in this comparative example, the silicon carbide content is 98.3 wt.%, the B element in boric acid is 0.1 wt.%, the addition amount of C element after sucrose debinding is 1.0 wt.%, the addition amount of dispersant tetramethylammonium hydroxide is 0.6 wt.%, the drying method is drying in an oven (forced air drying) at 90 °C for 24 h, and other process conditions and parameters are the same as those in Example 1.

[0073] Comparative Example 2

[0074] The preparation method of this comparative example is basically the same as that of Example 1, except that in this example, the silicon carbide content is 97.85 wt.%, the addition amount of B element in boric acid is 0.05 wt.%, the addition amount of C element after sucrose debinding is 1.5 wt.%, the addition amount of dispersant tetramethylammonium hydroxide is 0.6 wt.%, the drying temperature is 55 °C, the rotation speed is 150 r / min, and other process conditions and parameters are the same as those in Example 1.

[0075] Comparative Example 3

[0076] The preparation method of this comparative example is basically the same as that of Example 1, except that in this comparative example, the silicon carbide content is 98.7 wt.%, the addition amount of B element in boric acid is 0.2 wt.%, the addition amount of C element after sucrose debinding is 0.5 wt.%, the addition amount of dispersant tetramethylammonium hydroxide is 0.6 wt.%, the drying temperature is 60 °C, the rotation speed is 100 r / min, and other process conditions and parameters are the same as those in Example 1.

[0077] Performance Test Method

[0078] Density: Tested according to the method specified in GBT 25995-2010.

[0079] Flexural strength: Tested according to the method specified in GBT 6569-2006.

[0080] Elastic modulus: Tested according to the method specified in GBT 10700-2006.

[0081] Vickers hardness: Tested according to the method specified in GBT 16534-2009.

[0082] Fracture toughness: Tested according to the method specified in JISR 1607-2015.

[0083] Thermal diffusivity and thermal conductivity: Tested according to the method specified in ASTM E1530.

[0084] Table 1 shows the performance parameters of the atmospheric pressure solid-phase sintered silicon carbide ceramics prepared in Examples 1-5 and Comparative Examples 1-3 of the present invention.

[0085] Table 1

[0086] From the results of Comparative Example 1, it can be seen that when the drying method is drying (forced air drying), the density of the prepared silicon carbide ceramic is lower. The Vickers hardness and thermal conductivity are affected by the density, so the thermal conductivity and Vickers hardness are also lower. This shows that vacuum rotary evaporation drying is more conducive to the uniform dispersion of the sintering aid, thereby reducing the amount of sintering aid used and promoting the densification of the ceramic. From the results of Comparative Example 2, it can be seen that since the boron element addition amount is only 0.05 wt.%, the sintering aid content is too low, and the sintering driving force generated is insufficient to promote the dense sintering of the ceramic, and the density of the prepared ceramic is also lower. Therefore, the thermal conductivity and Vickers hardness of the prepared ceramic are lower. From the results of Comparative Example 3, it can be seen that since the carbon element addition amount is only 0.5 wt.%, the amount of sintering aid used is too low, so the density of the obtained silicon carbide ceramic is too low, resulting in a lower thermal conductivity. This shows that reducing the amount of sintering aid used and the densification of the ceramic need to be considered simultaneously to further improve the thermal conductivity of the silicon carbide ceramic.

[0087] The above-described embodiments merely represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent should be subject to the appended claims, and the specification can be used to explain the content of the claims.

Claims

1. A preparation method of a high thermal conductivity silicon carbide ceramic material, characterized in that, The preparation method includes the following steps: Step (1): Mix silicon carbide powder, sucrose, boric acid, a dispersant and water to prepare a slurry; based on the total mass of silicon carbide powder, carbon element after debinding of sucrose, boron element in boric acid and the dispersant being 100 wt.%, the addition amount of carbon element after debinding of sucrose is 1.0 wt.% to 2.5 wt.%, and the addition amount of boron element in boric acid is 0.1 wt.% to 0.3 wt.%. Step (2): Subject the slurry obtained in step (1) to drying, sieving, forming and debinding to obtain a ceramic green body; Step (3): Subject the ceramic green body obtained in step (2) to atmospheric pressure sintering to obtain a high thermal conductivity silicon carbide ceramic material.

2. The preparation method according to claim 1, wherein The drying is vacuum rotary evaporation drying; preferably, the temperature of the vacuum rotary evaporation drying is 50 - 80 °C, the vacuum degree is 1 - 5 kPa, and the rotation speed is 50 - 200 revolutions per minute.

3. The preparation method according to claim 1 or 2, characterized in that, In step (2), the forming methods are dry pressing and isostatic pressing; preferably, the pressure of dry pressing is 30 - 80 MPa and the time is 0.5 - 2 minutes; the pressure of isostatic pressing is 150 - 300 MPa and the time is 2 - 5 minutes.

4. The preparation method according to any one of claims 1 to 3, characterized in that, In step (2), the debinding atmosphere is vacuum, the vacuum degree is 0 - 20 Pa, the debinding temperature is 500 - 1000 °C, and the debinding time is 30 - 90 minutes.

5. The preparation method according to any one of claims 1 to 4, characterized in that, In step (3), the sintering atmosphere is argon atmosphere, the sintering temperature is 2100 - 2200 °C, and the holding time is 30 - 120 minutes; preferably, the ceramic green body is subjected to annealing treatment after atmospheric pressure sintering; more preferably, the annealing temperature is 1650 - 2050 °C, the annealing time is 2 - 12 h, and the annealing atmosphere is argon atmosphere.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The silicon carbide powder is α-silicon carbide; the average particle size of the α-silicon carbide powder is 0.1 - 1 μm; the purities of the silicon carbide powder, sucrose and boric acid are all > 99%.

7. The preparation method according to any one of claims 1 to 6, characterized in that, The dispersant is tetramethylammonium hydroxide; preferably, the addition amount of the dispersant is 0.3 wt.% to 1 wt.%; more preferably, the addition amount of water is such that the solid content of the slurry is 40 wt.% to 60 wt.%.

8. High thermal conductivity silicon carbide ceramic material, characterized in that, The high thermal conductivity silicon carbide ceramic material is obtained according to the preparation method described in any one of claims 1 to 7.

9. The high thermal conductivity silicon carbide ceramic material according to claim 8, wherein, The high thermal conductivity silicon carbide ceramic material mainly consists of silicon carbide and carbon particles existing inside or in the gaps of silicon carbide grains, wherein no more than 10 carbon particles are distributed on every 100 square micrometers of the high thermal conductivity silicon carbide ceramic material, and the average diameter of the carbon particles does not exceed 1 μm.

10. The high thermal conductivity silicon carbide ceramic material according to claim 8 or 9, characterized in that, The relative density of the high thermal conductivity silicon carbide ceramic material is above 97%, and the thermal diffusivity at room temperature is above 80 mm 2 / s or more, and the thermal conductivity is above 165 W / (m·K).

Images