Method for preparing high-strength and high-thermal-conductivity silicon nitride ceramic through two-step sintering

A technology of silicon nitride ceramics and high thermal conductivity, which is applied in the field of two-step sintering to prepare high-strength and high thermal-conductivity silicon nitride ceramics, can solve the problems of low content of sintering aids, high content of second phase, low thermal conductivity of ceramics, etc. The effect of reducing the content of the second phase, improving the thermal conductivity of ceramics, and simple process flow

Active Publication Date: 2021-11-12
UNIV OF SCI & TECH BEIJING
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Problems solved by technology

The content of sintering aids is low, the amount of liquid phase is small, and the purpose of densification cannot be achieved, and the oxygen fixation effect of rare earth oxides cannot be reflected; the content of sintering aids is high, and the formation of too much liquid phase will cause uneven shrinkage of the product, and the density of ceramics will increase. Low, high second phase content results in low ceramic thermal conductivity

Method used

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  • Method for preparing high-strength and high-thermal-conductivity silicon nitride ceramic through two-step sintering
  • Method for preparing high-strength and high-thermal-conductivity silicon nitride ceramic through two-step sintering
  • Method for preparing high-strength and high-thermal-conductivity silicon nitride ceramic through two-step sintering

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Experimental program
Comparison scheme
Effect test

Embodiment 1

[0027] 1. Weigh 920g of silicon nitride powder with an oxygen content of 1.0wt%, 24g of magnesium oxide and 56g of ytterbium oxide, ball mill them with a binder in absolute ethanol, and mix them uniformly to obtain a slurry;

[0028] 2. Spray granulate the above slurry to obtain a granulated powder with a particle size of 60 μm;

[0029] 3. Press the granulated material into a square plate of 100×100×2 mm, and then carry out isostatic pressing at 200 MPa for 15 minutes to obtain a green body.

[0030] 4. Degrease the green body at 600°C; then perform two-step sintering, raise the temperature to 1350°C at 5°C / min for 2 hours, accompanied by a nitrogen flow rate of 1L / min; continue to heat up to 1900°C for 5 hours, and the nitrogen pressure to 1.2 MPa;

[0031] 5. Grinding and polishing the sintered product to obtain the final silicon nitride ceramic. Its ceramic thermal conductivity is 96.4W / m·K, and its bending strength is 792Mpa.

Embodiment 2

[0033] 1. Weigh 920g of silicon nitride powder with an oxygen content of 1.0wt%, 24g of magnesium oxide and 56g of ytterbium oxide, ball mill them with a binder in absolute ethanol, and mix them uniformly to obtain a slurry;

[0034] 2. Spray granulate the above slurry to obtain a granulated powder with a particle size of 60 μm;

[0035] 3. Press the granulated material into a square plate of 100×100×2 mm, and then carry out isostatic pressing at 200 MPa for 15 minutes to obtain a green body.

[0036] 4. Degrease the green body at 600°C; then perform two-step sintering, heat at 1350°C at 5°C / min for 2 hours, accompanied by a nitrogen flow rate of 1L / min; continue to heat up to 1900°C for 10 hours, and nitrogen pressure to 1.2 MPa;

[0037] 5. Grinding and polishing the sintered product to obtain the final silicon nitride ceramic. Its ceramic thermal conductivity is 108.6W / m·K, and its bending strength is 758Mpa.

Embodiment 3

[0039] 1. Weigh 920g of silicon nitride powder with an oxygen content of 1.0wt%, 24g of magnesia and 56g of yttrium oxide, ball mill them with a binder in absolute ethanol, and mix them uniformly to obtain a slurry;

[0040] 2. Spray granulate the above slurry to obtain a granulated powder with a particle size of 80 μm;

[0041] 3. Press the granulated material into a square plate of 100×100×2mm, and then perform isostatic pressing at 200MPa for 15 minutes to obtain a green body;

[0042] 4. Degrease the green body at 600°C; then perform two-step sintering, raise the temperature to 1350°C at 5°C / min for 2 hours, accompanied by a nitrogen flow rate of 1L / min; continue to heat up to 1900°C for 5 hours, and the nitrogen pressure to 1.2 MPa;

[0043] 5. Grinding and polishing the sintered product to obtain the final silicon nitride ceramic. Its ceramic thermal conductivity is 95.2W / m·K, and its bending strength is 796Mpa.

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Abstract

The invention belongs to the field of ceramic preparation, and particularly relates to a method for preparing high-strength and high-thermal-conductivity silicon nitride ceramic through two-step sintering. The method comprises the following steps: mixing silicon nitride powder and a sintering aid with an organic solvent according to a certain ratio, granulating, pressing, degreasing, pretreating for 1-5 hours under the conditions of low temperature, normal pressure and nitrogen introduction, and sintering at a high temperature under the nitrogen pressure of 0.9-10 MPa. In the first-step pretreatment, the content of the magnesium oxide sintering aid is adjusted according to the oxygen content of the silicon nitride powder, the oxygen content of a green body is reduced before sintering by utilizing the low-temperature reaction characteristic of magnesium oxide and silicon dioxide on the surface of the silicon nitride powder, and then the second-step air pressure sintering is performed. Compared with the sintered body which is not pretreated, the silicon nitride ceramic subjected to two-step sintering has higher density, the total oxygen content and the second phase content are obviously reduced, and the silicon nitride ceramic of which the thermal conductivity is greater than 90W/m.K and the bending strength is greater than 750MPa can be prepared.

Description

technical field [0001] The invention belongs to the technical field of ceramic material preparation, and relates to a method for preparing silicon nitride ceramics with high strength and high thermal conductivity by two-step sintering. Background technique [0002] Silicon nitride ceramics have insulation, chemical corrosion resistance, excellent mechanical properties and thermal properties, and are widely used in metallurgy, machinery, aerospace and medical fields. Especially for high strength, high thermal conductivity and excellent thermal shock resistance, silicon nitride is very suitable for heat dissipation substrates of semiconductor power devices in pure electric and hybrid electric vehicles. IGBT heat dissipation modules for vehicles such as BYD and Toyota Prius have used nitrogen SiC ceramic heat sink substrate. [0003] The gas pressure sintering method of silicon nitride is to add 0.9-10MPa nitrogen pressure during the sintering process, on the one hand to inhib...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C04B35/584C04B35/64
CPCC04B35/584C04B35/64C04B2235/3224C04B2235/3225C04B2235/3227C04B2235/3206C04B2235/661C04B2235/6586C04B2235/6562C04B2235/6567C04B2235/9607C04B2235/96C04B2235/77
Inventor 秦明礼王月隆田建军吴昊阳贾宝瑞张一铭章林曲选辉
Owner UNIV OF SCI & TECH BEIJING
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