A high thermal conductivity silicon carbide ceramic and preparation method thereof

Abstract

The invention discloses a silicon carbide ceramic and a preparation method thereof. The granulation process is effectively avoided by adjusting the particle size of silicon carbide powder and the particle size of graphite powder. The powder has good fluidity and can be directly dry pressed or isostatically pressed after being mixed with a solvent binder. In addition, the thermal conductivity of the silicon carbide ceramic is greatly improved by combining the steps of vacuum vibration and dry pressing and isostatic pressing.

Description

Technical Field

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

[0002] Silicon carbide (SiC) ceramics have the advantages of high melting point, high hardness, good chemical stability, wear resistance, high strength, etc., and are widely used in mechanical seals and bearings, aerospace and other fields. At the same time, silicon carbide (SiC) materials have the advantages of small neutron absorption cross section, good high-temperature mechanical properties, and high thermal conductivity. It is a very promising structural material in nuclear energy systems. With the rapid development of industries such as integrated circuits and heat exchangers, and the increasing requirements for high thermal conductivity, excellent thermal shock resistance and corrosion resistance of semiconductor manufacturing equipment components in recent years, the demand for high thermal conductivity silicon carbide ceramics has increased dramatically. Silicon carbide is a covalent bond compound. At room temperature, its heat conduction is mainly carried out through the transmission and scattering of lattice vibrations (phonons). Summary of the invention

[0003] The inventors found in experiments that the theoretical room temperature thermal conductivity of silicon carbide single crystal is as high as 490 W·m -1 ·K -1 The room temperature thermal conductivity of silicon carbide ceramics reported in the literature is 30-170 W·m -1 ·K -1 , which is far lower than the theoretical room temperature thermal conductivity of silicon carbide single crystal. This is mainly due to the phonon scattering caused by the presence of sintering aids, grain boundaries, solid solutions, lattice oxygen, pores, etc. in silicon carbide ceramics, resulting in lower thermal conductivity, which greatly affects the application scope and prospects of silicon carbide ceramics.

[0004] In order to overcome the problems of the prior art, the present invention provides a method for preparing high thermal conductivity silicon carbide ceramics, comprising the following steps:

[0005] S1. SiC powder and graphite powder are used as raw materials, mixed with a solvent and a binder to obtain a composite powder;

[0006] S2, molding: placing the obtained composite powder into a mold to mold and obtain a ceramic blank;

[0007] S3, high-temperature degreasing the obtained ceramic blank to obtain a degreased blank;

[0008] S4, siliconizing reaction sintering: the degreased green blank is subjected to siliconizing sintering treatment at high temperature to obtain silicon carbide ceramics.

[0009] The composite powder obtained in step S1 is a composite powder with good fluidity.

[0010] The composite powder obtained by step S1 of the present invention does not require a granulation step and can be directly subjected to a molding operation.

[0011] According to a specific embodiment of the present invention, in step S1, the particle size of the silicon carbide powder is 50-300 μm, preferably 80-200 μm, and more preferably 80-150 μm; the particle size of the graphite powder is 10-600 μm, preferably 10-100 μm. The graphite powder is porous conductive graphite powder.

[0012] In the present invention, by adjusting the particle size of silicon carbide powder and the particle size of graphite powder within the above range, the granulation process is effectively avoided, so that the obtained composite powder can be directly formed, thereby helping to improve the thermal conductivity of silicon carbide ceramic products.

[0013] According to a specific embodiment of the present invention, in step S1, the content of silicon carbide powder is 0-100wt%, and the content of porous conductive graphite powder is 10-100wt%. Preferably, the content of silicon carbide powder is 50-90wt%, and the content of graphite powder is 10-50wt%. The percentage of the content of silicon carbide powder and graphite powder is calculated based on the sum of the content of silicon carbide powder and the content of graphite powder being 100%.

[0014] According to a specific embodiment of the present invention, in step S1, the solvent is one or more of water, ethanol, p-toluenesulfonic acid, dilute sulfuric acid, hydrochloric acid, phosphoric acid, boric acid, oxalic acid, maleic anhydride, citric acid, malic acid, benzenesulfonic acid, and phenolsulfonic acid; preferably benzenesulfonic acid or phenolsulfonic acid; more preferably p-toluenesulfonic acid.

[0015] According to a specific embodiment of the present invention, in step S1, the binder is one or more of polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polymethyl methacrylate (PMMA), polyvinyl pyrrolidone (PVP), epoxy resin, furan resin, and phenolic resin.

[0016] According to a specific embodiment of the present invention, in step S1, the amount of the binder added is 0.5wt%-2wt% of the composite powder.

[0017] According to a specific embodiment of the present invention, in step S1, the added amount of the solvent accounts for 20wt%-70wt% of the binder.

[0018] According to a specific embodiment of the present invention, in step S2, the forming method is dry pressing and / or isostatic pressing, preferably dry pressing first and then isostatic pressing.

[0019] According to a specific embodiment of the present invention, in step S2, the pressure of dry pressing is 15-100 MPa, and the pressure of isostatic pressing is 150-210 MPa.

[0020] According to a specific embodiment of the present invention, step S2 further includes: performing air extraction on the powder during molding, and / or performing low-frequency vibration on the powder. Preferably, performing air extraction on the powder during molding and performing low-frequency vibration on the powder.

[0021] In the present invention, by exhausting the powder and / or performing low-frequency vibration in the molding step, the thermal conductivity of the silicon carbide ceramic product is improved. Further preferably, when the exhaust treatment and low-frequency vibration are performed simultaneously, the thermal conductivity is higher.

[0022] According to a specific embodiment of the present invention, the vacuum degree of the exhaust is 1-1100 Pa, preferably 1000 Pa; the low-frequency vibration frequency is 15-50 Hz, preferably 30 Hz.

[0023] According to a specific embodiment of the present invention, in step S3, the degreasing temperature is not higher than 1200° C., preferably 900-1100° C.; and the degreasing time is 12-48 hours.

[0024] According to a specific embodiment of the present invention, in step S3, the porosity of the defatted green billet is 10%-60%, preferably 10-30%; the pore size distribution is 0.01-20 μm, preferably 1-20 μm.

[0025] According to a specific embodiment of the present invention, in step S4, the temperature of siliconizing reaction sintering is 1450-1750° C., and the time is 60-120 minutes.

[0026] The second object of the present invention is to provide a silicon carbide ceramic prepared by the above preparation method, wherein the thermal conductivity of the silicon carbide ceramic is 180-200 W·m -1 ·K -1 .

[0027] According to a specific embodiment of the present invention, the density of silicon carbide ceramic is 2.95-3.10 g·cm -3 , flexural strength 220-400MPa, elastic modulus 300-450GPa, toughness 2.0-4.2MPam 1 / 2 .

[0028] Beneficial effects:

[0029] Compared with the prior art, the advantages of the present invention are as follows: in the present invention, the granulation process is effectively avoided by adjusting the particle size of silicon carbide powder and the particle size of graphite powder, the powder has good fluidity, and can be directly dry pressed or isostatically pressed after mixing with a solvent binder. In addition, combined with vacuum vibration and dry pressing and isostatic pressing and other operations, these factors can synergistically improve the thermal conductivity of silicon carbide ceramics to a great extent. DETAILED DESCRIPTION

[0030] The following further exemplifies the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are only examples in a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values ​​​​exemplified below.

[0031] Example 1

[0032] (1) Preparation of powder raw materials: Silicon carbide powder with a D50 of 150 μm and porous conductive graphite powder with a D50 of 10 μm are mixed with solvent water for 30 seconds, and mixed evenly, and then 1 wt% of phenolic resin is added and mixed for 60 seconds to obtain a composite powder with good fluidity, wherein the content of silicon carbide powder is 90 wt%, the content of porous conductive C powder is 10 wt%, and the amount of solvent added is 50 wt% of the resin content;

[0033] (2) Molding: The obtained composite powder is placed in a mold for dry pressing at a molding pressure of 40 MPa, followed by isostatic pressing at a molding pressure of 200 MPa, an exhaust vacuum degree of 1000 Pa, and a vibration frequency of 30 Hz;

[0034] (3) Degreasing: The obtained ceramic blank was subjected to high-temperature degreasing at a temperature of 1200°C for 12 hours. The obtained sample had a porosity of 12% and an average pore size of 1 μm.

[0035] (4) Siliconization reaction sintering: The material was siliconized at 1600°C for 1 hour to obtain a high-strength and high-thermal-conductivity silicon carbide ceramic material. The physical properties are shown in Table 1:

[0036] Example 2

[0037] (1) Preparation of powder raw materials: Silicon carbide powder with a D50 of 120 μm and porous conductive graphite powder with a D50 of 100 μm are mixed with a solvent of p-toluenesulfonic acid for 30 seconds, and the mixture is uniformly mixed. Then, 1 wt% of furan resin is added and mixed for 60 seconds to obtain a composite powder with good fluidity, wherein the content of silicon carbide powder is 60 wt%, the content of porous conductive C powder is 40 wt%, and the amount of solvent added is 50 wt% of the resin content;

[0038] (2) Molding: The obtained composite powder is placed in a mold for dry pressing, the molding pressure is 100 MPa, and the vacuum degree is 1000 Pa;

[0039] (3) Degreasing: The obtained ceramic blank is subjected to high-temperature degreasing at a temperature of 1200°C for 24 hours; the obtained sample has a porosity of 20% and an average pore size of 5 μm;

[0040] (4) Siliconization reaction sintering: The material is siliconized at 1750°C for 1 hour to obtain a high-strength and high-thermal-conductivity silicon carbide ceramic material. Its physical properties are shown in Table 1:

[0041] Example 3

[0042] (1) Preparation of powder raw materials: Silicon carbide powder with a D50 of 80 μm is mixed with solvent p-toluenesulfonic acid and mixed evenly for 30 seconds, and then 2 wt% of phenolic resin is added and mixed for 120 seconds to obtain a composite powder with good fluidity. The amount of solvent added is 50 wt% of the resin content;

[0043] (2) Molding: The obtained composite powder is placed in a mold for dry pressing at a molding pressure of 40 MPa, followed by isostatic pressing at a molding pressure of 150 MPa; the vibration frequency is 30 Hz;

[0044] (3) Degreasing: The obtained ceramic blank was subjected to high-temperature degreasing at a temperature of 1200°C for 48 hours. The obtained sample had a porosity of 30% and an average pore size of 10 μm.

[0045] (4) Siliconization reaction sintering: The material is siliconized at 1550°C for 2 hours to obtain a high-strength and high-thermal-conductivity silicon carbide ceramic material. The physical properties are shown in Table 1:

[0046] Comparative Example 1

[0047] Other conditions are the same as those in Example 1, except that the particle size D50 of the silicon carbide powder is 5 um, and the particle size D50 of the porous conductive graphite powder is 1 um.

[0048] Comparative Example 2

[0049] The other conditions are the same as those in Example 1, except that during the molding process, the powder is not subjected to vacuuming and low-frequency vibration treatment.

[0050] Comparative Example 3

[0051] The other conditions were the same as those in Comparative Example 1, except that granulation was performed before molding.

[0052] Table 1

[0053]

[0054] It can be seen from the data in Table 1 that, by analyzing Examples 1-3 and Comparative Examples 1-3, it can be found that the use of SiC powder and graphite powder of a specific particle size of the present application, combined with a vacuum treatment and / or a low-frequency vibration step, can improve the thermal conductivity of the ceramic material; in addition, by analyzing Comparative Example 3, it can be seen that the technical solution of the present application can overcome the defect of low thermal conductivity caused by the presence of grain boundaries in the prior art of using powders with lower particle sizes combined with granulation.

[0055] This specific embodiment is only an explanation of the present application, and it is not a limitation of the present application. Through the above description, relevant staff can make various changes and modifications without deviating from the technical idea of ​​the present application. The technical scope of the present application is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for preparing silicon carbide ceramics, characterized in that: The following steps are involved: S1. Using silicon carbide powder and graphite powder as raw materials, mixing with solvent and binder to obtain composite powder; In step S1, the particle size of the silicon carbide powder is 80-200 μm; the particle size of the graphite powder is 10-100 μm; S2, molding: placing the obtained composite powder into a mold to mold and obtain a ceramic blank; In the step S2, the forming method is dry pressing and / or isostatic pressing; Step S2 also includes: performing vacuum treatment on the powder and performing low-frequency vibration on the powder during molding; The low-frequency vibration frequency is 15-50Hz; S3, degreasing the obtained ceramic blank to obtain a degreased blank; S4, siliconization reaction sintering: the degreased green blank is subjected to siliconization sintering treatment to obtain the silicon carbide ceramic; the thermal conductivity of the silicon carbide ceramic is 180-200 W·m -1 ·K -1 ; Wherein, the content of the silicon carbide powder is 50-90wt%, and the content of the graphite powder is 10-50wt%; The amount of the binder added is 0.5wt%-2wt% of the total amount of the silicon carbide powder and the graphite powder, and the binder is one or more of polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyvinyl pyrrolidone, epoxy resin, furan resin, and phenolic resin; The added amount of the solvent accounts for 20wt%-70wt% of the binder, and the solvent is one or more of water, ethanol, p-toluenesulfonic acid, dilute sulfuric acid, hydrochloric acid, phosphoric acid, boric acid, oxalic acid, maleic anhydride, citric acid, malic acid, benzenesulfonic acid, and phenolsulfonic acid.

2. The preparation method according to claim 1, characterized in that: In the step S2, the forming method is to first perform dry pressing and then perform isostatic pressing.

3. The preparation method according to claim 1, characterized in that: The vacuum degree of the air extraction is 1-1100 Pa; the low-frequency vibration frequency is 30 Hz.

4. The preparation method according to claim 3, characterized in that: The vacuum degree of the exhaust is 1000 Pa.

5. The preparation method according to claim 1, characterized in that: In the step S3, the porosity of the defatted blank is 10%-60% and the pore size distribution is 0.01-20 μm.

6. The preparation method according to claim 1, characterized in that: In the step S3, the porosity of the defatted blank is 10-30% and the pore size distribution is 1-20 μm.

7. The preparation method according to claim 1, characterized in that: In the step S4, the temperature of the siliconizing reaction sintering is 1450-1750° C. and the time is 60-120 minutes.

8. Silicon carbide ceramics prepared according to the preparation method according to any one of claims 1 to 7.

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