Silicon carbide sheet based on salivation method and preparation method thereof
Preparing silicon carbide thin plates by salivation method solves the mechanical strength and dielectric constant problems of silicon carbide heat dissipation substrates in high-frequency applications, realizes the comprehensive performance of high-strength and low dielectric constants, and expands its application in high-frequency equipment.
Patent Information
- Application Number
- CN202510564240.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-30
- Publication Date
- 2025-07-11
AI Technical Summary
Silicon carbide heat dissipation substrates have problems of poor mechanical strength and high dielectric constant in high frequency applications, resulting in deterioration of signal integrity and exceeding the standard of electromagnetic interference, limiting its large-scale application in 5G communications and new energy vehicle motor controllers.
Silicon carbide thin plates were prepared by salivation method. By mixing the original silicon carbide powder and liquid polycarbide into a slurry, casting and molding, thermal crosslinking and pyrolysis treatment were performed, combined with thermal isostatic densification, a silicon carbide thin plate containing polycarbide converted silicon carbide and original silicon carbide particles was prepared.
The bending strength and thermal conductivity of the silicon carbide thin plate are improved, while the high-frequency dielectric constant is reduced, and its application prospects in high-tech fields are broadened.
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Figure CN120289188A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of silicon carbide materials, and particularly relates to a silicon carbide thin plate based on the tape casting method and a preparation method thereof. Background Art
[0002] As one of the core materials of the third-generation semiconductors, silicon carbide (SiC) is regarded as an ideal heat dissipation substrate carrier for high-frequency and high-power power electronic devices due to its high thermal conductivity (theoretical value up to 490 W·m-1·K-1), high breakdown field strength (3 MV / cm - 5 MV / cm), and high temperature resistance (>300 °C). However, its relatively high dielectric constant significantly conflicts with the stringent electromagnetic compatibility (EMC) requirements in high-frequency application scenarios, resulting in problems such as signal integrity degradation, sharp increase in parasitic parameters, and excessive electromagnetic interference (EMI) in devices under high-frequency (>100 kHz) operating conditions, becoming a key bottleneck restricting its large-scale application in fields such as 5G communication and new energy vehicle motor controllers. Summary of the Invention
[0003] Aiming at the above problems, the purpose of the present invention is to provide a silicon carbide thin plate based on the tape casting method and a preparation method thereof to solve the problems of poor mechanical strength and high high-frequency dielectric constant of the silicon carbide heat dissipation substrate.
[0004] The preparation method of a silicon carbide thin plate based on the tape casting method described in the present invention includes the following steps:
[0005] (1) Prepare a mixed slurry by mixing raw silicon carbide powder A, raw silicon carbide powder B, and liquid polycarbosilane.
[0006] (2) Obtain a silicon carbide thin plate preform after tape casting the mixed slurry.
[0007] (3) Perform thermal cross-linking treatment on the silicon carbide thin plate preform to obtain a silicon carbide thin plate cross-linked body.
[0008] (4) Perform pyrolysis treatment on the silicon carbide thin plate cross-linked body to obtain an un-densified silicon carbide thin plate.
[0009] (5) Perform densification treatment on the un-densified silicon carbide thin plate to obtain the silicon carbide thin plate.
[0010] In the mixed slurry in step (1), the mass fraction of raw silicon carbide powder A is 20% - 60%, the particle size is 1 μm - 50 μm, the mass fraction of raw silicon carbide powder B is 10% - 55%, the particle size is 500 nm - 50 μm, the mass fraction of liquid polycarbosilane is 6.5% - 20%, the yield of pyrolysis conversion to silicon carbide is 81% - 89%, and the curing temperature is 130 °C - 180 °C.
[0011] In step (2), the mixed slurry is tape-cast at 30°C to 70°C, and after casting, a film with a thickness of 100 μm to 400 μm is obtained, which is the silicon carbide thin plate preform;
[0012] The thermal cross-linking treatment in step (3) means maintaining the temperature at 180°C to 220°C for 4 hours to 6 hours;
[0013] The pyrolysis treatment in step (4) means heating to 850°C to 1200°C at a rate of 8°C / min to 12°C / min in an argon atmosphere of 0.2 MPa to 0.4 MPa and maintaining the temperature for 1 hour to 2 hours;
[0014] The densification treatment in step (5) means performing hot isostatic pressing at 1200°C to 1400°C and 80 MPa to 100 MPa for 1 hour to 2 hours.
[0015] The above-mentioned silicon carbide thin plate prepared from the slurry composed of liquid polycarbosilane and silicon carbide particles by tape-casting method, in terms of volume percentage, the silicon carbide thin plate contains 5% to 15% of polycarbosilane converted silicon carbide and 70% to 80% of original silicon carbide particles by mass fraction, and the rest is polycarbosilane that has not been completely pyrolyzed; the particle size of the original silicon carbide particles is 500 nm to 50 μm.
[0016] The intrinsic properties of the thin plate can be adjusted, the density is 70% to 90%, the thermal conductivity is 90 W / m·K to 128 W / m·K, the flexural strength is 193 MPa to 280 MPa, the average value of the dielectric constant in the range of 0.5 GHz to 18 GHz is 9.13 to 13.94, and the average value of the dielectric constant in the range of 26.5 GHz to 40 GHz is 17.79 to 31.00.
[0017] Compared with existing materials and technologies, the present invention has the following advantages and beneficial effects:
[0018] The present invention uses liquid vinyl polycarbosilane as a precursor to prepare SiC thin plates, which have excellent compressive strength, good thermal conductivity and high-frequency dielectric properties. In addition to being used as a high-frequency heat dissipation substrate, the SiC thin plates of the present invention effectively broaden the broad application prospects of silicon carbide ceramics in high-tech fields. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 It is a diagram of the silicon carbide thin plate of the present invention; wherein: (a) is a schematic diagram of the preparation process of the silicon carbide thin plate preform, and (b) is a physical diagram of the silicon carbide thin plate of Example 1.
[0020] Figure 2Graph showing the relationship between the viscosity and temperature of the mixed slurry used to prepare the single-layer silicon carbide sheet in Example 1; where: (a) shows the rheological properties at different temperatures, and (b) shows the rheological properties at 60 °C.
[0021] Figure 3 Diagram explaining the phase structures of pure polycarbosilane converted silicon carbide and original silicon carbide in Example 1; where: (a) is the X-ray diffraction pattern of polycarbosilane pyrolyzed into silicon carbide (PCS) and original silicon carbide; (b) is the transmission image of polycarbosilane pyrolyzed into silicon carbide.
[0022] Figure 4 Diagram explaining the thermal analysis of pure polycarbosilane and slurry in Example 1; where: (a) is the thermogravimetric analysis curve of polycarbosilane; (b) is the thermogravimetric analysis curve of the slurry for preparing a single-layer silicon carbide single sheet.
[0023] Figure 5 Scanning electron micrograph of the surface of the silicon carbide thin plate in Example 1.
[0024] Figure 6 Performance diagram of the silicon carbide thin plate in Example 1; where: (a) is the bending curve diagram; (b) and (c) are the fracture morphology diagrams.
[0025] Figure 7 Dielectric constant curve diagram of the silicon carbide thin plate at 0.5 GHz to 18 GHz in Example 1.
[0026] Figure 8 Dielectric constant curve diagram of the silicon carbide thin plate at 26.5 GHz to 40 GHz in Example 1.
[0027] Figure 9 Scanning electron micrograph of the silicon carbide thin plate in Example 2; where: (a) is the scanning electron micrograph of the cross-section of the thin plate; (b) is the scanning electron micrograph of the surface of the thin plate.
[0028] Figure 10 Scanning electron micrograph of the silicon carbide thin plate in Example 3; where: (a) is the scanning electron micrograph of the cross-section of the thin plate; (b) is the scanning electron micrograph of the surface of the thin plate.
[0029] Figure 11 Bending curve diagram of the silicon carbide thin plate in Example 3.
[0030] Figure 12 Dielectric constant curve diagram of the silicon carbide thin plate at 0.5 GHz to 18 GHz in Example 3.
[0031] Figure 13 Dielectric constant curve diagram of the silicon carbide thin plate at 26.5 GHz to 40 GHz in Example 3.
[0032] Figure 14 Scanning electron micrograph of the silicon carbide thin sheet in Example 4; wherein: (a) is the scanning electron micrograph of the cross-section of the thin sheet; (b) is the scanning electron micrograph of the surface of the thin sheet.
[0033] Figure 15 Bending curve of the silicon carbide thin sheet in Example 4.
[0034] Figure 16 Dielectric constant curve of the silicon carbide thin sheet at 0.5 GHz to 18 GHz in Example 4.
[0035] Figure 17 Dielectric constant curve of the silicon carbide thin sheet at 26.5 GHz to 40 GHz in Example 4.
[0036] Figure 18 Scanning electron micrograph of the surface of the silicon carbide thin wafer in Comparative Example 1.
[0037] Figure 19 Scanning electron micrograph of the surface of the silicon carbide bulk in Comparative Example 2. Detailed implementation mode
[0038] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments and the drawings. It should be noted that the embodiments described in the present invention are only used for further explanation and illustration, rather than limiting its application scope. Based on the present invention, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present invention.
[0039] The thermal conductivity is tested by the laser transient method, the dielectric constant is tested by the waveguide method of the vector network analyzer, and the mechanical properties are tested by the mechanical testing machine.
[0040] Example 1
[0041] (1) Prepare a mixed slurry from the raw silicon carbide powder A, the raw silicon carbide powder B, and the liquid polycarbosilane; in the mixed slurry, the mass fraction of the raw silicon carbide powder A is 40%, the purity is 99.99%, and the particle size is 20 μm, the mass fraction of the silicon carbide powder B is 40%, the purity is 99.99%, and the particle size is 500 nm, and the mass fraction of the liquid polycarbosilane is 20%.
[0042] The prepared slurry exhibits shear thinning effect, that is, the viscosity drops sharply after the shear rate reaches the critical value. This phenomenon indicates that the rheological characteristics of the slurry are suitable for the tape casting process of layered materials, as shown in Figure 2 (a) and Figure 2 (b).
[0043] (2) The green body layer with a thickness of about 100 μm was prepared by casting the mixed slurry in step (1) at 60 °C. The preparation process is as Figure 1 (a) shown; after cooling at room temperature, the obtained green body layer was cut into a pre-treated layer material with a size of 10 cm × 5 cm, namely a silicon carbide thin plate preform, as Figure 1 (b) shown.
[0044] (3) The silicon carbide thin plate preform was subjected to a thermal cross-linking treatment at 200 °C for 4 hours to obtain a silicon carbide thin plate cross-linked body containing silicon carbide particles.
[0045] (4) The silicon carbide thin plate cross-linked body was heated to 1000 °C at a rate of 10 °C / min in an argon atmosphere of 0.4 MPa and held for 1 hour for pyrolysis treatment to obtain an un-densified silicon carbide thin plate.
[0046] (5) The un-densified silicon carbide thin plate was densified by hot isostatic pressing (HIP) at 1400 °C and 100 MPa for 1 hour to obtain a densified silicon carbide thin plate.
[0047] The above-mentioned silicon carbide thin plate prepared from the slurry composed of liquid polycarbosilane and raw silicon carbide particles by the casting method contains 10% volume fraction of polycarbosilane converted silicon carbide and 80% of raw silicon carbide particles. The particle size of the raw silicon carbide particles is 20 μm and 500 nm.
[0048] The raw silicon carbide particles in the silicon carbide thin plate exhibit characteristic diffraction peaks of the 6H-SiC phase, indicating that it belongs to the thermodynamically stable α-SiC at high temperature; while the silicon carbide converted by the pyrolysis of polycarbosilane shows characteristic peaks of the 3C-SiC phase, which is confirmed as β-SiC, as Figure 3 (a) shown; Figure 3 (b) shows clear lattice fringes of silicon carbide grains with good crystallinity. Amorphous SiCxOy phases are interspersed between the grains. The silicon carbide grains do not exhibit a specific shape or orientation and are uniformly distributed in the matrix. From Figure 3 (b) The selected area electron diffraction (SAED) pattern in the upper left corner, three obvious diffraction rings can be identified, corresponding to the (111), (220), and (311) diffraction rings of the silicon carbide grains respectively. Among them, the (111) diffraction ring is significantly broadened, indicating incomplete crystallization of the silicon carbide microcrystals. Although a large amount of free carbon is contained in the polycarbosilane and the atomic ratio of carbon to silicon is 1.5:1, the crystallinity of the free carbon is poor and no corresponding diffraction ring is observed.
[0049] During the heating process, pure polycarbosilane undergoes pyrolysis, resulting in a mass loss of about 20%. The temperature at which the mass loss is most significant is about 460 °C, indicating a significant reduction in carbon and oxygen elements in the matrix. In contrast, due to the low content of polycarbosilane in the slurry, its mass loss is only about 4%, asFigure 4 (a) and Figure 4 (b) as shown. The density data of pure polycarbosilane and the slurry in the initial state and after high-temperature sintering are listed in Table 1. According to the thermogravimetric analysis data and density values, the theoretical shrinkage rate of pure polycarbosilane after sintering is calculated to be 66%, which makes it prone to cracking during the sintering process under atmospheric pressure. In contrast, the theoretical shrinkage rate of the slurry is 30%.
[0050] Figure 5 The microstructure of the silicon carbide thin plate after densification treatment (sintering) at 1400 °C under 100 MPa pressure is shown (the lower left inset is the macroscopic physical image of the silicon carbide thin plate). Due to the thin thickness of the thin plate, it experiences a plane stress state during the sintering process, allowing free shrinkage along the thickness direction. Finally, silicon carbide particles are evenly distributed in the continuous matrix, and the resulting final product is dense and without obvious defects. Figure 5 The upper right inset is the backscattered electron (BSE) image of this area, and no obvious cracks are observed even at the micron scale. The bright areas in the image correspond to the nano-scale original silicon carbide particles in the slurry, and the dark areas represent the silicon carbide formed by the high-temperature pyrolysis of polycarbosilane. Their chemical compositions are listed in Table 2. The incomplete pyrolysis at high temperature results in a large amount of carbon and oxygen elements remaining in the matrix.
[0051] Table 1 Density and shrinkage rate of pure polycarbosilane and slurry before and after pyrolysis
[0052]
[0053] Table 2 Elemental compositions of polycarbosilane, the pyrolyzed slurry (containing silicon carbide formed by the high-temperature pyrolysis of polycarbosilane), and the original silicon carbide particles
[0054]
[0055] The bending strength of the silicon carbide thin plate prepared in this example is calculated to be 280 MPa, the relative density is 90%, the thermal conductivity is 128 W / m·K, the average value of the dielectric constant in the range of 0.5 GHz to 18 GHz is 13.94, and the average value of the dielectric constant in the range of 26.5 GHz to 40 GHz is 31.00, as Figure 7 and Figure 8 shown. Different from conventional silicon carbide ceramics, the widely existing nano-scale structures in the thin plate effectively prevent the propagation of cracks, enabling the thin plate to withstand further loading without fracture. The absence of significant plastic deformation before fracture is a typical characteristic of ceramic materials. Ceramics usually exhibit high stiffness but low toughness, as Figure 6 (a) shown. The fracture surface shows a mixture of transgranular and intergranular fracture modes, manifested as cleavage steps and rough textures, as Figure 6 (b) and Figure 6 (c) shown.
[0056] Example 2
[0057] (1) Prepare a mixed slurry from the original silicon carbide powder A, the original silicon carbide powder B, and liquid polycarbosilane; in the mixed slurry, the mass fraction of the original silicon carbide powder A is 60%, the purity is 99.99%, and the particle size is 1 μm, the mass fraction of the original silicon carbide powder B is 17%, the purity is 99.99%, and the particle size is 50 μm, and the mass fraction of the liquid polycarbosilane is 18%.
[0058] (2) Prepare a green sheet about 200 μm thick by casting the mixed slurry in step (1) at 65 °C, and the preparation process is as shown in Figure 1 (a); after cooling at room temperature, cut the obtained green sheet layer into a pre-treatment layer material with a size of 10 cm × 5 cm, that is, a silicon carbide thin sheet preform.
[0059] (3) Perform a thermal cross-linking treatment on the silicon carbide thin sheet preform at 180 °C for 5 hours to obtain a cross-linked silicon carbide thin sheet containing silicon carbide particles.
[0060] (4) Heat-treat the cross-linked silicon carbide thin sheet in an argon atmosphere at 0.35 MPa, heat it to 1200 °C at a rate of 10 °C / min, and hold for 1 hour to obtain an un-densified silicon carbide thin sheet.
[0061] (5) Perform a hot isostatic pressing (HIP) densification treatment on the un-densified silicon carbide thin sheet at 1300 °C and 90 MPa for 1.5 hours to obtain a densified silicon carbide thin sheet. The cross-sectional scanning electron micrograph of this silicon carbide thin sheet is as shown in Figure 9 (a), and the scanning electron micrograph of the thin sheet surface is as shown in Figure 9 (b).
[0062] The above silicon carbide thin sheet prepared from the slurry composed of liquid polycarbosilane and original silicon carbide particles by the casting method contains 8% of polycarbosilane-converted silicon carbide and 77% of original silicon carbide particles by mass fraction. The particle sizes of the original silicon carbide particles are 1 μm and 50 μm. The bending strength of the silicon carbide thin sheet is calculated to be 265 MPa, the density is 85%, the thermal conductivity is 120 W / m·K, and the average value of the dielectric constant in the range of 0.5 GHz to 18 GHz is 12.71, and the average value of the dielectric constant in the range of 26.5 GHz to 40 GHz is 28.03.
[0063] Example 3
[0064] (1) Prepare a mixed slurry by mixing raw silicon carbide powder A, raw silicon carbide powder B, and liquid polycarbosilane. In the mixed slurry, the mass fraction of raw silicon carbide powder A is 20%, the purity is 99.99%, and the particle size is 50 μm; the mass fraction of raw silicon carbide powder B is 55%, the purity is 99.99%, and the particle size is 10 μm; the mass fraction of liquid polycarbosilane is 6.5%.
[0065] (2) Cast and form the mixed slurry in step (1) at 65 °C to prepare a green sheet about 200 μm thick. The preparation process is as shown in Figure 1 (a). After cooling at room temperature, cut the obtained green sheet into a pre-treatment layer material with a size of 10 cm × 5 cm, that is, a silicon carbide sheet preform.
[0066] (3) Perform a thermal cross-linking treatment on the silicon carbide sheet preform at 180 °C for 5 hours to obtain a cross-linked silicon carbide sheet containing silicon carbide particles.
[0067] (4) Heat-treat the cross-linked silicon carbide sheet in an argon atmosphere at 0.3 MPa, heat it to 1100 °C at a rate of 12 °C / min, and hold for 1 hour to obtain an un-densified silicon carbide sheet.
[0068] (5) Perform a hot isostatic pressing (HIP) densification treatment on the un-densified silicon carbide sheet at 1300 °C and 85 MPa for 1 hour to obtain a densified silicon carbide sheet. The cross-sectional scanning electron micrograph of this silicon carbide sheet is as shown in Figure 10 (a), and the scanning electron micrograph of the sheet surface is as shown in Figure 10 (b).
[0069] The above-mentioned silicon carbide sheet prepared from a slurry composed of liquid polycarbosilane and silicon carbide particles by the casting method contains 5% of polycarbosilane-converted silicon carbide and 75% of raw silicon carbide particles by mass fraction. The particle sizes of the raw silicon carbide particles are 10 μm and 50 μm. The bending strength of the silicon carbide sheet is calculated to be 226 MPa, as shown in Figure 11 ; the density is 80%, the thermal conductivity is 115 W / m·K, the average dielectric constant in the range of 0.5 GHz to 18 GHz is 10.97, and the average dielectric constant in the range of 26.5 GHz to 40 GHz is 22.25, as shown in Figure 12 and Figure 13 .
[0070] Example 4
[0071] (1) Prepare a mixed slurry by mixing raw silicon carbide powder A, raw silicon carbide powder B, and liquid polycarbosilane; in the mixed slurry, the mass fraction of raw silicon carbide powder A is 60%, the purity is 99.99%, and the particle size is 10 μm; the mass fraction of raw silicon carbide powder B is 10%, the purity is 99.99%, and the particle size is 50 μm; the mass fraction of liquid polycarbosilane is 7.5%.
[0072] (2) Prepare a green sheet about 400 μm thick by tape casting the mixed slurry in step (1) at 30 °C, and the preparation process is as Figure 1 (a) shown; after cooling at room temperature, cut the obtained green sheet layer into a pre-treatment layer material with dimensions of 10 cm × 5 cm, that is, a silicon carbide thin sheet preform.
[0073] (3) Perform a thermal cross-linking treatment on the silicon carbide thin sheet preform at 220 °C for 6 hours to obtain a cross-linked silicon carbide thin sheet containing silicon carbide particles.
[0074] (4) Heat the cross-linked silicon carbide thin sheet in an argon atmosphere at 0.2 MPa, raise the temperature to 850 °C at a rate of 8 °C / min, and hold for 1 hour for pyrolysis treatment to obtain an un-densified silicon carbide thin sheet.
[0075] (5) Subject the un-densified silicon carbide thin sheet to hot isostatic pressing (HIP) densification treatment at 1200 °C and 80 MPa for 1 hour to obtain a densified silicon carbide thin sheet. The cross-sectional scanning electron micrograph of this silicon carbide thin sheet is as Figure 14 (a) shown, and the scanning electron micrograph of the thin sheet surface is as Figure 14 (b) shown.
[0076] The above-mentioned silicon carbide thin sheet prepared from a slurry composed of liquid polycarbosilane and raw silicon carbide particles by tape casting method contains 6% of polycarbosilane converted silicon carbide and 70% of raw silicon carbide particles by mass fraction. The particle sizes of the raw silicon carbide particles are 10 μm and 50 μm.
[0077] The bending strength of the silicon carbide thin sheet prepared in this example is calculated to be 193 MPa, as Figure 15 shown; the density is 70%, the thermal conductivity is 90 W / m·K, the average value of the dielectric constant in the range of 0.5 GHz to 18 GHz is 9.13, and the average value of the dielectric constant in the range of 26.5 GHz to 40 GHz is 17.79, as Figure 16 and Figure 17 shown.
[0078] Comparative Example 1
[0079] The main differences between Comparative Example 1 and Examples 1-4 are as follows: The method for preparing the silicon carbide thin plate is not the tape casting method. Instead, the prepared mixed slurry is directly used for stacking into a plate, and there is no hot isostatic pressing densification treatment in step (5), which is specifically as follows:
[0080] (1) Prepare a mixed slurry from raw silicon carbide powder A, raw silicon carbide powder B, and liquid polycarbosilane; in the mixed slurry, the mass fraction of raw silicon carbide powder A is 40%, the purity is 99.99%, and the particle size is 20 μm; the mass fraction of raw silicon carbide powder B is 40%, the purity is 99.99%, and the particle size is 500 nm; the mass fraction of liquid polycarbosilane is 20%.
[0081] (2) Prepare a green body layer about 1 mm thick by naturally stacking the mixed slurry in step (1) at 60°C; after cooling at room temperature, cut the obtained green body layer into a pre-treatment layer material with a size of 10 cm × 5 cm, namely a silicon carbide thin plate preform.
[0082] (3) Perform a thermal cross-linking treatment on the silicon carbide thin plate preform at 200°C for 4 hours to obtain a silicon carbide thin plate cross-linked body containing silicon carbide particles.
[0083] (4) Heat the silicon carbide thin plate cross-linked body in an argon atmosphere at 0.1 MPa, raise the temperature to 1400°C at a rate of 10°C / min, and hold for 1 hour for pyrolysis treatment to obtain an undensified silicon carbide thin plate.
[0084] (5) There is no densification treatment step.
[0085] The above-mentioned silicon carbide thin plate prepared based on the natural stacking of the slurry composed of liquid polycarbosilane and raw silicon carbide particles contains 10% of polycarbosilane converted silicon carbide and 80% of raw silicon carbide particles by mass fraction, and the particle sizes of the raw silicon carbide particles are 20 μm and 500 nm.
[0086] The calculated flexural strength of the undensified silicon carbide thin plate prepared in this comparative example is 50 MPa, and the density is 45%. Figure 18 The microscopic structure of the surface of the silicon carbide thin plate after pyrolysis in an argon atmosphere is shown (the lower left inset is a physical picture). The particles are irregular in shape, and there are large voids between the particles. Since significant shrinkage occurs when polycarbosilane is converted to silicon carbide at high temperature and there is no densification treatment, the overall shrinkage rate of the thin plate is inconsistent with the shrinkage rate of polycarbosilane, resulting in insufficient overall shrinkage of the sample and a low density.
[0087] Comparative Example 2
[0088] The main differences between Comparative Example 2 and Examples 1-4 are as follows: The method for preparing the silicon carbide thin plate is not the tape casting method. Instead, the prepared mixed slurry is directly used to prepare a block, and then cut into thin plates, which is specifically as follows:
[0089] (1) Prepare a mixed slurry from the original silicon carbide powder A, the original silicon carbide powder B, and liquid polycarbosilane; in the mixed slurry, the mass fraction of the original silicon carbide powder A is 40%, the purity is 99.99%, and the particle size is 20 μm, the mass fraction of the original silicon carbide powder B is 40%, the purity is 99.99%, and the particle size is 500 nm, and the mass fraction of the liquid polycarbosilane is 20%.
[0090] (2) Naturally stack the mixed slurry in step (1) into a block at 60 °C, i.e., a silicon carbide block preform with dimensions of 2.2 mm × 2.2 mm × 4.5 mm.
[0091] (3) Perform a thermal cross-linking treatment on the silicon carbide block preform at 200 °C for 4 hours to obtain a silicon carbide block cross-linked body containing silicon carbide particles.
[0092] (4) Heat the silicon carbide block cross-linked body in an argon atmosphere at 0.4 MPa, raise the temperature to 1000 °C at a rate of 10 °C / min, and hold for 1 hour for pyrolysis treatment to obtain an un-densified silicon carbide block.
[0093] (5) Subject the un-densified silicon carbide block to hot isostatic pressing (HIP) densification treatment at 1400 °C and 100 MPa for 1 hour to obtain a densified silicon carbide block.
[0094] The above slurry composed of liquid polycarbosilane and original silicon carbide particles is used to prepare a silicon carbide block based on the natural stacking of the slurry, and then the block is sliced to obtain a silicon carbide thin plate. The thin plate contains 10% of polycarbosilane-converted silicon carbide and 80% of original silicon carbide particles by mass fraction, and the particle sizes of the original silicon carbide particles are 20 μm and 500 nm.
[0095] The bending strength of the silicon carbide thin plate prepared in this comparative example is calculated to be 80 MPa, and the density is 55%. Figure 19 Shows the microstructure of the cross-section of the silicon carbide block after densification treatment at 1400 °C under 100 MPa pressure (the lower left inset is a physical image of the silicon carbide block). The hot isostatic pressing (HIP) technology provides thermal stress during the high-temperature process, resulting in a significant increase in shrinkage. However, due to uneven stress distribution, a large number of cracks appear in the sample.
[0096] Matters not covered by this invention are well-known technologies.
[0097] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims
1. A method for preparing a silicon carbide thin plate based on the drooling method, characterized in that, It includes the following contents: (1) Prepare a mixed slurry from raw silicon carbide powder A, raw silicon carbide powder B, and liquid polycarbosilane; (2) Obtain a silicon carbide thin plate preform after tape casting the mixed slurry; (3) Perform thermal cross-linking treatment on the silicon carbide thin plate preform to obtain a silicon carbide thin plate cross-linked body; (4) Perform pyrolysis treatment on the silicon carbide thin plate cross-linked body to obtain an un-densified silicon carbide thin plate; (5) Perform densification treatment on the un-densified silicon carbide thin plate to obtain the silicon carbide thin plate.
2. The preparation method of a silicon carbide thin sheet based on the drooling method according to claim 1, characterized in that In the mixed slurry in step (1), the mass fraction of raw silicon carbide powder A is 20% - 60%, the particle size is 1μm - 50μm, the mass fraction of raw silicon carbide powder B is 10% - 55%, the particle size is 500nm - 50μm, the mass fraction of liquid polycarbosilane is 6.5% - 20%, the yield of pyrolysis conversion to silicon carbide is 81% - 89%, and the curing temperature is 130°C - 180°C.
3. A method for preparing a silicon carbide thin plate based on the drooling method according to claim 1, characterized in that, In step (2), the mixed slurry is tape cast at 30°C - 70°C, and after forming, a film with a thickness of 100μm - 400μm is obtained, which is the silicon carbide thin plate preform.
4. The preparation method of a silicon carbide thin plate based on the casting method according to claim 1, characterized in that, The thermal cross-linking treatment in step (3) means keeping at 180°C - 220°C for 4 hours - 6 hours.
5. The preparation method of a silicon carbide thin plate based on the casting method according to claim 1, wherein The pyrolysis treatment in step (4) means heating to 850°C - 1200°C at a rate of 8°C / min - 12°C / min in an argon atmosphere of 0.2MPa - 0.4MPa and keeping for 1 hour - 2 hours.
6. The preparation method of a silicon carbide thin plate based on the casting method according to claim 1, characterized in that, The densification treatment in step (5) means performing hot isostatic pressing treatment at 1200°C - 1400°C and 80MPa - 100MPa for 1 hour - 2 hours.
7. The silicon carbide thin plate prepared by the method according to any one of claims 1 to 6, characterized in that, The density of the silicon carbide thin plate is 70% - 90%, the thermal conductivity is 90W / m·K - 128W / m·K, the flexural strength is 193MPa - 280MPa, the average value of the dielectric constant in the range of 0.5GHz - 18GHz is 9.13 - 13.94, and the average value of the dielectric constant in the range of 26.5GHz - 40GHz is 17.79 - 31.
00.
8. The silicon carbide thin plate prepared by the method according to any one of claims 1 to 6, characterized in that, By volume percentage, the silicon carbide thin plate contains 5% - 15% of silicon carbide converted from liquid polycarbosilane and 70% - 80% of raw silicon carbide particles, and the rest is polycarbosilane that has not been completely pyrolyzed; the particle size of the raw silicon carbide particles is 500nm - 50μm.