CN111196730A

CN111196730A - High-thermal-conductivity silicon nitride ceramic material and preparation method thereof

Info

Publication number: CN111196730A
Application number: CN201911142254.6A
Authority: CN
Inventors: 曾宇平; 王为得; 左开慧; 夏咏锋; 姚冬旭; 尹金伟; 梁汉琴
Original assignee: Shanghai Institute of Ceramics of CAS
Current assignee: Shanghai Institute of Ceramics of CAS
Priority date: 2019-11-20
Filing date: 2019-11-20
Publication date: 2020-05-26
Anticipated expiration: 2039-11-20
Also published as: CN111196730B

Abstract

The invention relates to a silicon nitride ceramic material with high thermal conductivity and a preparation method thereof, wherein the silicon nitride ceramic material comprises α -Si₃N₄And a sintering aid; the sintering aid is metal hydride and alkaline earth metal oxide, and the total content is 2-12 mol%; the metal hydride is ZrH₂(ii) a The alkaline earth metal oxide is preferably at least one of MgO, CaO and BaO.

Description

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

Technical Field

The invention relates to a silicon nitride ceramic material with high thermal conductivity and a preparation method thereof, in particular to a silicon nitride ceramic material prepared from metal hydride ZrH₂And metal oxide as a sintering aid and producing Si with high thermal conductivity by gas pressure sintering₃N₄A method for preparing ceramic material belongs to the field of inorganic non-metallic material.

Background

With the development of electronic devices toward miniaturization, integration and high power density, heat dissipation is one of the bottlenecks in the development of electronic devices. In integrated circuits, the performance of ceramic substrates is critical to solving heat dissipation problems. Meanwhile, the ceramic substrate must have good mechanical properties to withstand the cyclic thermal stress. Silicon nitride (Si)₃N₄) Haggerty et al (J.Haggerty and A.Lightfoot Opportunities for improving the thermal conductivity of SiC and Si3N4 Ceramic through improved processing, p.475-487 in improvements of the 19th environmental Conference Composites, advanced ceramics, Materials, and Structure-A: Ceramic Engineering and scientific improvements, Volume 16, sue 4.) predict β -Si₃N₄The theoretical thermal conductivity can reach 200-320 Wm^-1K^-1This discovery has made silicon nitride ceramics a promising candidate material for heat sink substrates in high-density high-power semiconductor devices.

For ideal β -Si₃N₄For single crystals, no scattering factors such as impurities, grain boundaries and defects exist, the phonon free path is the largest, and the thermal conductivity of the single crystals is optimal. However, when silicon nitride is actually produced, addition of metal oxides such as MgO, Y is usually employed₂O₃、ZrO₂、Al₂O₃And the like as a sintering aid to obtain dense silicon nitride ceramics through liquid phase sintering, α -Si₃N₄β -Si formed by dissolution precipitation process in liquid phase₃N₄And the growth and densification of crystal grains are realized through a liquid phase, and the liquid phase is used as low heat conduction during coolingThe intergranular phase of the rate remains in the sintered body, therefore, β -Si obtained by liquid phase sintering₃N₄The ceramic consists of crystal grains and a small amount of intercrystalline phase, and phonons are scattered by various defects in the intercrystalline phase and the crystal grains, so that β -Si is used₃N₄Is much lower than the theoretical value.

At home and abroad researchers improve sintering temperature, prolong heat preservation time and other means, and promote crystal grain growth to purify crystal lattice so as to reduce crystal lattice defects and further improve the heat conductivity of silicon nitride ceramic materials, but the method has high cost and is not beneficial to popularization and application of silicon nitride₃N₄A crystal lattice. Therefore, researchers also often replace oxides with non-oxides, such as MgSiN₂Instead of MgO, YF₃、Y₂Si₄N₆C, etc. instead of Y₂O₃Using ZrSi₂Substituted for ZrO₂To regulate the liquid phase composition and reduce the oxygen content in the liquid phase to reduce β -Si₃N₄The oxygen content in the crystal lattice further improves the thermal conductivity.

Disclosure of Invention

The invention aims to provide a brand new method for preparing a silicon nitride ceramic material with high thermal conductivity, which uses metal hydride ZrH for the first time₂And alkaline earth metal oxide is used as a sintering aid, and the solid solution of oxygen into the silicon nitride crystal lattice is prevented by regulating and controlling the composition of a liquid phase, so that the defects in the silicon nitride crystal lattice are reduced, the scattering of phonons is reduced, and the thermal conductivity is further improved.

In one aspect, the invention provides a silicon nitride ceramic material, which comprises α -Si₃N₄And a sintering aid; the sintering aid is metal hydride and alkaline earth metal oxide, and the total content is 2-12 mol%; the metal hydride is ZrH₂The alkaline earth metal oxide is preferablyAt least one of MgO, CaO and BaO. Wherein a metal hydride ZrH is used₂The sintering aid is used, so that the amount of oxygen introduced by the sintering aid can be reduced, the oxygen concentration in a liquid phase is reduced, oxygen is prevented from being dissolved into a silicon nitride crystal lattice in a solid solution mode, crystal defects are reduced, and phonon scattering is reduced; in addition, a metal hydride ZrH is used₂As a sintering aid, the content of low-thermal-conductivity amorphous phase in the obtained silicon nitride ceramic is reduced, and the thermal conductivity is improved. Moreover, zirconium hydride can decompose simple substance Zr along with the temperature rise, and the essence is to utilize the simple substance Zr and SiO on the surface of the raw material powder₂Redox removal of SiO₂。

Preferably, the total content of the sintering aid is 5-10 mol%.

Preferably, the molar ratio of the metal hydride to the alkaline earth metal oxide is 1:10 to 10:1, preferably 1:5 to 5: 1.

Preferably, the thermal conductivity of the silicon nitride ceramic material is 61.25-115.18W/(m.K), the bending strength is 475-759 MPa, and the fracture toughness is 5.38-7.95 MPa.m^1/2。

In another aspect, the present invention provides a method for preparing the silicon nitride ceramic material, including:

(1) α -Si is weighed according to the raw material composition of the silicon nitride ceramic material₃N₄Mixing the powder and the sintering aid to obtain mixed powder;

(2) and pressing and molding the obtained mixed powder, performing pre-sintering treatment at 600-1600 ℃, and performing sintering treatment at 1780-1950 ℃ to obtain the silicon nitride ceramic material.

In the invention, metal hydride ZrH is selected₂And alkaline earth metal oxide as a sintering aid to prepare a high thermal conductivity silicon nitride ceramic. Wherein the metal hydride ZrH₂As an oxygen-free auxiliary agent, the introduction of oxygen can be reduced, so that the content of the low-thermal-conductivity intergranular phase in the silicon nitride sintered body is reduced, and the improvement of the thermal conductivity is facilitated. On the other hand, added metal hydride ZrH₂Can be decomposed into simple substances Zr and H in the process of pre-sintering treatment₂，H₂The existence of which can reduce the oxygen content in the hearthPressure (formula 1: ZrH)₂→Zr+H₂(g) ). Further, the simple substance Zr and SiO on the surface of the silicon nitride powder₂The reaction is carried out at a lower temperature during the presintering treatment to lead SiO₂Reduction to SiO (g) or Si to thereby form SiO₂Removal with simultaneous reaction to form ZrO₂(formula 2: Zr + SiO)₂→ZrO₂+ SiO (g); and formula 3: zr + SiO₂→ZrO₂+ Si). And, H₂As a strong reducing agent, the oxygen content is clearly reduced. Generated ZrO₂And alkaline earth metal oxides can form low oxygen eutectic phases (exemplified by MgO, ZrO) at lower temperatures₂+MgO+SiO₂+α-Si₃N₄→β-Si₃N₄+ Zr-Si-Mg-O-N (liquid phase)), the low oxygen content in the liquid phase can prevent oxygen from being dissolved into the silicon nitride crystal lattice, reduce the number of defects in the crystal lattice, reduce phonon scattering, and the generated liquid phase promotes the crystal grain growth through a dissolution-precipitation mechanism, thereby being beneficial to improving the thermal conductivity.

Preferably, the mixing mode is that after wet ball milling is carried out by adopting a vacuum ball milling tank, the mixed powder is obtained through rotary evaporation drying or vacuum drying; the ball milling atmosphere in the vacuum ball milling tank is vacuum atmosphere, inert atmosphere or nitrogen atmosphere. The mixing mode is adopted for preventing the metal hydride ZrH in the ball milling process or the drying process₂Oxidation of (2).

Preferably, the compression molding mode is dry compression molding or/and isostatic pressing treatment, and preferably the dry compression molding is firstly carried out and then the isostatic pressing treatment is carried out; the pressure of the dry pressing is 10-50 MPa, and the pressure of the isostatic pressing is 100-300 MPa. Wherein the isostatic pressing treatment may be cold isostatic pressing.

Preferably, the atmosphere of the pre-sintering treatment is a vacuum atmosphere, a nitrogen atmosphere or an inert atmosphere, and the inert atmosphere is an argon atmosphere; the time of the pre-sintering treatment is 1-8 hours.

Preferably, the sintering treatment mode is air pressure sintering, hot pressing sintering, spark plasma sintering, hot isostatic pressing sintering or pressureless sintering; the time of the sintering treatment is more than or equal to 2 hours; preferably, the atmosphere of the air pressure sintering is nitrogen, and the air pressure is more than or equal to 1 MPa. Wherein, the high nitrogen pressure during the air pressure sintering can avoid the decomposition of silicon nitride at high temperature (above 1780 ℃), improve the sintering activity and be beneficial to densification and grain growth.

Preferably, the temperature rise rate of the sintering treatment is 1-15 ℃/min.

Preferably, after the sintering treatment is completed, the mixture is cooled to 800-1200 ℃ at a cooling rate of less than or equal to 20 ℃/min (preferably to 1000 ℃) and then cooled to room temperature along with the furnace.

Has the advantages that:

in the present invention, a metal hydride ZrH is used₂As sintering aid, metal hydride ZrH₂As an oxygen-free auxiliary agent, the introduction of oxygen is reduced, the content of a glass phase in a final sintered body can be reduced, the volume fraction of the low-thermal-conductivity glass phase in the sintered body is reduced, and the improvement of the thermal conductivity is facilitated;

in the present invention, the metal hydride ZrH is added₂Can be decomposed into simple substances Zr and H in the pretreatment process₂，H₂The presence of which reduces the partial pressure of oxygen in the furnace and, in addition, the simple substances Zr and α -Si₃N₄SiO on the surface of powder₂React to form ZrO₂ZrO produced₂And the silicon nitride and the auxiliary sintering aid alkaline earth metal oxide form a eutectic liquid phase, and the sintering of the silicon nitride is promoted through a dissolution and precipitation mechanism. This reaction promotes SiO₂To block oxygen with SiO₂Form of (b) is solid-dissolved in β -Si₃N₄The medium crystal lattice reduces defects in the silicon nitride crystal lattice, thereby improving the thermal conductivity;

in the invention, the thermal conductivity of the obtained silicon nitride ceramic material is above 115.18W/(m.K), the bending strength can reach 759MPa, the fracture toughness can be improved, and can reach 7.95 MPa.m^1/2Can meet the application requirements of the silicon nitride ceramics in the field of high-density and high-power semiconductor devices.

Drawings

FIG. 1 is a cross-sectional micro-topography of the silicon nitride ceramic material prepared in example 4;

FIG. 2 is a cross-sectional micro-topography of the silicon nitride ceramic material prepared in example 5.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

In this disclosure, the first time is with a metal hydride ZrH₂And alkaline earth metal oxide as sintering aid to prepare high heat conductivity silicon nitride ceramic. Wherein the metal hydride ZrH₂As an oxygen-free auxiliary agent, Zr element can be introduced under the premise of not introducing oxygen, so that the content of the intercrystalline phase with low thermal conductivity in the silicon nitride sintered body can be reduced, and the thermal conductivity can be improved. On the other hand, added metal hydride ZrH₂Can be decomposed into simple substances Zr and H in the pretreatment process₂，H₂The presence of (b) reduces the partial pressure of oxygen within the furnace; in addition, the simple substance Zr and SiO on the surface of the silicon nitride powder₂The reaction is carried out at a lower temperature during the presintering treatment to lead SiO₂Reduction to SiO (g) or Si to thereby form SiO₂Removal with simultaneous reaction to form ZrO₂. Generated ZrO₂And the alkaline earth metal oxide can form a eutectic liquid phase with low oxygen content at a lower temperature, the low oxygen content in the liquid phase can prevent oxygen from being dissolved into a silicon nitride crystal lattice, the number of defects in the crystal lattice is reduced, phonon scattering is reduced, and the generated liquid phase promotes the growth of crystal grains through a dissolution-precipitation mechanism, so that the thermal conductivity is improved. Wherein the alkaline earth metal oxide is at least one selected from BaO, MgO, CaO, etc.

The method for producing the silicon nitride ceramic material will be described as an example when the alkaline earth metal oxide is MgO.

α -Si₃N₄And uniformly mixing the powder and the sintering aid to obtain mixed powder. Wherein the sintering aid comprises metal hydride ZrH₂And MgO. During pre-sintering treatment, ZrH₂Firstly, the decomposition is carried out to generate simple substances Zr and H₂Elemental Zr and α -Si₃N₄SiO on the surface of powder₂React to form ZrO₂ZrO produced₂Forming low viscosity liquid with MgO in subsequent temperature rise processAnd phase, to promote sintering of the silicon nitride. Metal hydride ZrH₂The molar ratio of MgO to MgO may be (1:10) to (10:1), preferably (1:5) to (5: 1). When the metal hydride ZrH₂The molar ratio of MgO to MgO is (1:5) to (5:1), the most possible ratio is α -Si₃N₄SiO on the surface of powder₂Reaction takes place and the metal hydride ZrH₂With SiO₂ZrO formed by reaction₂Forming eutectic liquid phase with MgO in subsequent temperature raising process, and promoting β -Si by dissolution and precipitation mechanism₃N₄And (4) growing crystal grains.

In an alternative embodiment, α -Si₃N₄The particle size of the powder can be 0.1-2 μm, and the oxygen content is less than 2 wt%; metal hydride ZrH₂The particle size of the particles is 0.1-20.0 μm; the particle size of the MgO powder may be 10nm to 5 μm.

In an alternative embodiment, α -Si₃N₄The proportion of the powder and the sintering aid is 88mol percent to 12mol percent to 98mol percent to 2mol percent, preferably 90mol percent to 10mol percent to 95mol percent to 5mol percent, the sum of the proportions of the components is 100 percent, the addition amount of the sintering aid is too small, and α -Si cannot be completely removed₃N₄SiO on the surface of powder₂And a sufficient amount of low viscosity liquid phase cannot be formed, the sample is difficult to densify; too much sintering aid can increase the content of low thermal conductivity grain boundary phase and affect the thermal conductivity.

In an alternative embodiment, α -Si is added₃N₄The powder and the sintering aid are ball-milled by a vacuum ball-milling tank wet method, and the atmosphere in the ball-milling tank can be vacuum or filled with Ar and N₂The obtained slurry is dried by rotary evaporation or vacuum drying, and then is sieved to obtain mixed powder, wherein the ball milling mixing method comprises the following steps of mixing α -Si₃N₄The powder and the sintering aid are mixed, and the uniformly mixed powder is obtained through the processes of ball milling, drying and sieving. Ball milling material mixing adopts a wet ball milling process in a vacuum ball milling tank, and the atmosphere in the ball milling tank can be vacuum or filled with Ar and N₂. Wet ball milling uses alcohol as a solvent, and comprises the following materials: the solvent ratio can be (1:1) - (3:1), material: the ball ratio can be (1:1) - (5:1), the ball milling revolution is 200-500 rpm, and the ball milling time is 4-20 h.Drying by rotary evaporation drying or vacuum drying, wherein the whole drying process can be carried out in vacuum, Ar or N₂And the like in a protective atmosphere. Wherein the drying temperature can be 50-120 ℃, and the drying time can be 8-24 h. The mesh number of the sieve can be 60-300 meshes.

And pressing and molding the mixed powder to obtain a blank. The press forming may include: and sequentially carrying out dry pressing and isostatic pressing. Wherein, the pressure of dry pressing molding is 10-50 MPa, and the pressure of isostatic pressing treatment is 100-300 MPa. In a preferred embodiment, the isostatic pressing is a cold isostatic pressing.

And placing the blank body in an inert atmosphere, a nitrogen atmosphere or a vacuum environment, and performing pre-sintering treatment at the temperature of 600-1600 ℃ for 1-8 hours. Wherein the temperature of the pre-sintering treatment is preferably 1000-1500 ℃, and more preferably 1000-1400 ℃. The high presintering treatment temperature can accelerate the ZrH of the metal hydride₂And α -Si₃N₄SiO on the surface of powder₂The reaction rate and the heat preservation time are preferably 2-8h, and the metal hydride ZrH can be ensured by prolonging the heat preservation time₂And α -Si₃N₄SiO on the surface of powder₂The reaction was complete. The pre-sintering treatment may be performed in a vacuum atmosphere or under Ar.

And sintering the pre-sintered body at 1780-1950 deg.c to obtain high heat conductivity silicon nitride ceramic. The time of the air pressure sintering is at least 2 hours. Wherein, the atmosphere of the pressure sintering can be nitrogen atmosphere. High nitrogen pressure ensures that the silicon nitride does not decompose above 1780 ℃. The silicon nitride has higher sintering activity at 1780 ℃ and is beneficial to the growth and development of crystal grains. The preferred pressure sintering temperature is 1850-1900 ℃ for 2-12 hours. The pressure sintering can be carried out under a pressurized inert atmosphere, and the pressurized pressure can be 1-10 MPa. As an example of the gas pressure sintering, the process conditions include: with N₂Heating to 1780-1950 ℃ at a speed of 1-15 ℃/min under the condition of 1-10 MPa of air pressure in a sintering atmosphere, and preserving the temperature for more than 2 hours. The preferable heating rate can be 3-10 ℃/min.

Preferably, after the air pressure sintering is finished, the silicon nitride ceramic is further cooled to room temperature at a specific cooling rate, and the high-thermal-conductivity silicon nitride ceramic is obtained. For example, after sintering, the mixture can be cooled to 1000-1400 ℃ (preferably 1200 ℃) at a cooling rate of 1-15 ℃/min, and then cooled to room temperature along with the furnace.

According to the sintering mechanism of silicon nitride ceramics and literature reports, the thermal conductivity can be further improved by adopting the methods of increasing the pressure and the sintering temperature, prolonging the heat preservation time and slowing down the cooling rate, and obviously, the invention is not limited to the pressure and the sintering temperature range, the heat preservation time and the cooling rate. Also, the present invention should not be limited to the gas pressure sintering, and the desired effects can be obtained by a widely used method of pressureless sintering, hot press sintering, hot isostatic pressing sintering, or thermal treatment after spark plasma sintering.

In the present invention, the bulk density of the sample is measured by the Ahimedes method; si₃N₄The thermal conductivity of the ceramic material is calculated by the following formula: k is C_pRho. α, where rho is the bulk density of the sample in g.cm^-3α is the thermal diffusivity in cm²·s^-1C, measured using Netzsch LFA 467_pThe heat capacity of the silicon nitride ceramic material is very small with the change of the composition and the microstructure, and can be regarded as a constant, and 0.68J (g.K) is adopted in the invention^-1. The thermal conductivity of the obtained silicon nitride ceramic material can be 61.25-115.18W/(m.K).

In the present invention, Si was measured by a three-point bending method using an Instron-5566 Universal Material testing machine₃N₄The bending strength of the ceramic material is 30mm in span and 0.5mm min in loading rate^-1Each data point was tested on 6 bars and then averaged.

The bending strength of the obtained silicon nitride ceramic material can be 475-759 MPa.

In the present invention, the fracture toughness was measured by a single edge notched beam method (SENB), the sample was machined to a size of 3.0 × 6.0 × 30.0mm, the notch width was about 0.25mm, the notch depth was about 3mm, and the fracture toughness of the sample was measured by a three-point bending method on a universal material testing machine. The test span was 24.0mm, the loading rate was 0.05mm/min, 6 specimens were selected for each sample and measured for mean and standard deviation.

The fracture toughness of the obtained silicon nitride ceramic material can be 5.38-7.95 MPa.m^1/2。

It should be noted that although the above-described process for preparing a silicon nitride ceramic material is described using MgO as an example, other alkaline earth metal oxides such as BaO, CaO, and the like are also applicable to the above-described process.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.

Example 1

With 0.5 mol% ZrH₂And 1.5 mol% of MgO as a sintering aid, and 98 mol% of α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 20MPa, and then carrying out cold isostatic pressing treatment under the pressure of 250 MPa; putting the obtained blank into a BN crucible, preserving heat for 4h at 300 ℃ in Ar atmosphere, heating to 600 ℃ and preserving heat for 4h for pretreatment; then sintering the pre-sintered blank at 1800 ℃ of air pressure, wherein the heating rate is 10 ℃/min, N₂The pressure is 1MPa, and the heat preservation time is 4 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material prepared in the example 1 has a thermal conductivity of 66.3W/(m.K), a three-point bending strength of 759 + -42 MPa, and a fracture toughness of 7.35 + -0.24 MPa.m^1/2。

Example 2

With 0.5 mol% ZrH₂And 1.5 mol% MgO as sintering aid, with 98mol% α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 20MPa, and then carrying out cold isostatic pressing treatment under the pressure of 250 MPa; putting the obtained blank into a BN crucible, preserving heat for 4 hours at 500 ℃ in Ar atmosphere, heating to 1000 ℃ and preserving heat for 4 hours for pretreatment; then sintering the pre-sintered blank at 1900 ℃ under the air pressure, wherein the heating rate is 10 ℃/min, N₂The pressure is 1MPa, and the heat preservation time is 4 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material prepared in example 2 has a thermal conductivity of 105.08W/(m.K), a three-point bending strength of 539 + -20 MPa, and a fracture toughness of 6.75 + -0.24 MPa.m^1/2。

Example 3

With 2.5 mol% ZrH₂And 1.5 mol% MgO as a sintering aid, with 96 mol% α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 30MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; putting the obtained blank into a BN crucible, preserving heat for 4h at 400 ℃ under vacuum, heating to 1400 ℃ and preserving heat for 6h for pretreatment; then sintering the pre-sintered blank at 1850 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N₂The pressure is 1MPa, and the heat preservation time is 4 h; after sintering, cooling to 1000 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material prepared in example 3 has a thermal conductivity of 78.90W/(m.K), a three-point bending strength of 621 + -14 MPa, and a fracture toughness of 7.72 + -0.23 MPa.m^1/2。

Example 4

With 2mol% ZrH₂And 2mol% of MgO as a sintering aid, and 96 mol% of α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 20MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; putting the obtained blank into a BN crucible, and preserving heat for 4 hours at 600 ℃ in a vacuum environmentHeating to 1300 ℃ and preserving heat for 8h for pretreatment; then sintering the pre-sintered blank at 1900 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N₂The pressure is 2MPa, and the heat preservation time is 12 h; after sintering, cooling to 1200 ℃ at the cooling rate of 5 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material prepared in example 4 has a thermal conductivity of 115.18W/(m.K), a three-point bending strength of 547 + -26 MPa, and a fracture toughness of 7.95 + -27 MPa.m^1/2. The cross-sectional micro-morphology of the silicon nitride ceramic material prepared by the embodiment is shown in fig. 1, the micro-morphology shows bimodal distribution of large grains dispersed in a small grain matrix, wherein the large grains have larger size and higher long diameter ratio, which is very beneficial to the improvement of thermal conductivity.

Example 5

With 3 mol% ZrH₂And 2mol% of MgO as a sintering aid, and 95 mol% of α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 20MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; putting the obtained blank into a BN crucible, preserving heat for 2h at 500 ℃ in a vacuum environment, heating to 1300 ℃ and preserving heat for 4h for pretreatment; then sintering the pre-sintered blank at 1900 ℃ under the air pressure, wherein the heating rate is 10 ℃/min, N₂The pressure is 1MPa, and the heat preservation time is 12 h; after sintering, cooling to 1000 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material prepared in example 5 had a thermal conductivity of 110.30W/(m.K), a three-point bending strength of 564. + -. 26MPa, and a fracture toughness of 7.72. + -. 0.15 MPa.m^1/2. The cross-section micro-topography of the silicon nitride ceramic material prepared by the embodiment is shown in fig. 2, large grains are sufficiently grown, the length can reach more than 50 microns, the combination part of the grains is cleaner, and the intercrystalline phase with low thermal conductivity is less.

Example 6

With 3 mol% ZrH₂And 2mol% of MgO as a sintering aid, and 95 mol% of α -Si₃N₄The powder is mixed by ball milling, dried and sieved to obtain the uniformUniformly mixing the powder; then dry pressing and forming under the pressure of 30MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; putting the obtained blank into a BN crucible, preserving heat for 2h at 450 ℃ under Ar, then heating to 1500 ℃ and preserving heat for 2h for pretreatment; then sintering the pre-sintered blank at 1850 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N₂The pressure is 1MPa, and the heat preservation time is 2 h; after sintering, cooling to 1200 ℃ at the cooling rate of 5 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material prepared in example 5 has a thermal conductivity of 82.21W/(m.K), a three-point bending strength of 621 + -14 MPa, and a fracture toughness of 7.66 + -0.35 MPa.m^1/2。

Example 7

With 4 mol% ZrH₂And 3 mol% of MgO as a sintering aid, and 93 mol% of α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 20MPa, and then carrying out cold isostatic pressing treatment under the pressure of 280 MPa; putting the obtained blank into a BN crucible, preserving heat for 2h at 300 ℃ under Ar, then heating to 1000 ℃ and preserving heat for 6h for pretreatment; then sintering the pre-sintered blank at 1800 ℃ of air pressure, wherein the heating rate is 10 ℃/min, N₂The pressure is 1MPa, and the heat preservation time is 4 h; after sintering, cooling to 1200 ℃ at the cooling rate of 15 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material prepared in example 7 had a thermal conductivity of 73.60W/(m.K), a three-point bending strength of 707. + -.18 MPa, and a fracture toughness of 6.66. + -. 0.09 MPa.m^1/2。

Example 8

With 5 mol% ZrH₂And 5 mol% of MgO as a sintering aid, and 90 mol% of α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 40MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; putting the obtained blank into a BN crucible, preserving heat for 2h at 400 ℃ under Ar, then heating to 1100 ℃ and preserving heat for 2h for pretreatment; then sintering the pre-sintered blank at 1900 ℃ under the air pressure, wherein the temperature rise rate is5℃/min，N₂The pressure is 3MPa, and the heat preservation time is 4 h; after sintering, cooling to 1100 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material prepared in this example 8 has a thermal conductivity of 103.23W/(m.K), a three-point bending strength of 575. + -. 46MPa, and a fracture toughness of 6.18. + -. 0.18 MPa.m^1/2。

Example 9

With 7 mol% ZrH₂And 3 mol% of MgO as a sintering aid, and 90 mol% of α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 30MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; putting the obtained blank into a BN crucible, preserving heat for 2h at 600 ℃ under Ar, then heating to 1400 ℃, preserving heat for 2h and carrying out pretreatment; then sintering the pre-sintered blank at 1850 ℃ under the air pressure, wherein the heating rate is 3 ℃/min, N₂The pressure is 1MPa, and the heat preservation time is 4 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material prepared in example 9 had a thermal conductivity of 82.56W/(m.K), a three-point bending strength of 561. + -. 40MPa, and a fracture toughness of 6.71. + -. 0.17 MPa. m^1/2。

Example 10

With 9 mol% ZrH₂And 2mol% of MgO as a sintering aid, and 89 mol% of α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 30MPa, and then carrying out cold isostatic pressing treatment under the pressure of 250 MPa; putting the obtained blank into a BN crucible, preserving heat for 2h at 500 ℃ under Ar, then heating to 1100 ℃ and preserving heat for 6h for pretreatment; then sintering the pre-sintered blank at 1950 ℃ under the pressure of 5 ℃/min with the temperature rise rate of N₂The pressure is 2MPa, and the heat preservation time is 4 h; after sintering, cooling to 1200 ℃ at the cooling rate of 15 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material obtained in this example 10 had a thermal conductivity of 107.85W/(m.K) and a three-point bending strength of475 +/-19 MPa, and fracture toughness of 5.38 +/-0.32 MPa.m^1/2。

Example 11

With 1 mol% ZrH₂And 10mol% of MgO as a sintering aid, and 89 mol% of α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 40MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; putting the obtained blank into a BN crucible, preserving heat for 2h at 500 ℃ in Ar atmosphere, heating to 1400 ℃, preserving heat for 2h, and carrying out pretreatment; then sintering the pre-sintered blank at 1800 ℃ of air pressure, wherein the heating rate is 5 ℃/min, N₂The pressure is 2MPa, and the heat preservation time is 2 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material prepared in this example 11 had a thermal conductivity of 61.25W/(m.K), a three-point bending strength of 736. + -. 24MPa, and a fracture toughness of 5.38. + -. 0.31 MPa.m^1/2。

Example 12

A silicon nitride ceramic material was prepared according to the process flow of example 5, with the only difference that: the alkaline earth metal oxide is CaO.

The silicon nitride ceramic material obtained in example 12 had a thermal conductivity of 106.2W/(mK), a three-point bending strength of 634. + -. 12MPa, and a fracture toughness of 8.01. + -. 0.13 MPa. m^1/2。

Example 13

A silicon nitride ceramic material was prepared according to the process flow of example 8, with the only difference that: the alkaline earth metal oxide is BaO.

The silicon nitride ceramic material prepared in example 13 had a thermal conductivity of 99.3W/(mK), a three-point bending strength of 602. + -. 23MPa, and a fracture toughness of 6.81. + -. 0.42 MPa. m^1/2。

Comparative example 1

With 3 mol% of ZrO₂And 2mol% of MgO as a sintering aid, and 95 mol% of α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry-pressing under 30MPa, and then under 300MPaCold isostatic pressing treatment; sintering the obtained blank at 1900 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N₂The pressure is 1MPa, and the heat preservation time is 12 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material prepared by the comparative example 1 has a thermal conductivity of 89.2W/(m.K), a three-point bending strength of 529 + -2 MPa, and a fracture toughness of 7.34 + -0.27 MPa.m^1/2。

Comparative example 2

5mol percent of MgO is taken as a sintering aid, and 95mol percent of α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 30MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; sintering the obtained blank at 1900 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N₂The pressure is 1MPa, and the heat preservation time is 12 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material obtained in the present comparative example 2 had a thermal conductivity of 56.10W/(mK), a three-point bending strength of 426. + -.22 MPa, and a fracture toughness of 4.89. + -. 0.35 MPa. m^1/2。

Comparative example 3

With 5 mol% ZrH₂As a sintering aid, with 95 mol% of α -Si₃N₄Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 30MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; preserving heat for 2h at 500 ℃ in Ar atmosphere, heating to 1300 ℃ and preserving heat for 8h for pretreatment; sintering the obtained blank at 1900 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N₂The pressure is 1MPa, and the heat preservation time is 12 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.

The silicon nitride ceramic material prepared by the present comparative example 3 had a thermal conductivity of 45.70W/(m.K), a three-point bending strength of 389. + -. 18MPa, and a fracture toughness of 5. + -. 0.18 MPa. m^1/2。

Comparative example 4

A silicon nitride ceramic material was prepared according to the process flow of example 5, with the only difference that: no sintering aid was added.

The silicon nitride ceramic material obtained in this comparative example 4 had a thermal conductivity of 30.2W/(m.K), a three-point bending strength of 203. + -. 52MPa, and a fracture toughness of 4.02. + -. 0.11 MPa.m^1/2。

Table 1 shows the raw material compositions and performance parameters of the silicon nitride ceramic materials prepared in examples 1 to 13 of the present invention and comparative examples 1 to 4:

。

comparing comparative example 1, example 3 and example 4, the same or similar processes are used for the three, and it can be found that ZrH is used₂The thermal conductivity of the materials obtained in examples 3 and 4 was significantly improved when zirconium oxide was substituted as a sintering aid.

Finally, it must be said here that: the above embodiments are only used for further detailed description of the technical solutions of the present invention, and should not be understood as limiting the scope of the present invention, and the insubstantial modifications and adaptations made by those skilled in the art according to the above descriptions of the present invention are within the scope of the present invention.

Claims

1. The silicon nitride ceramic material is characterized by comprising α -Si₃N₄And a sintering aid; the sintering aid is metal hydride and alkaline earth metal oxide, and the total content is 2-12 mol%; the metal hydride is ZrH₂(ii) a The alkaline earth metal oxide is preferably at least one of MgO, CaO and BaO.

2. The silicon nitride ceramic material of claim 1, wherein the total content of the sintering aid is 5 to 10 mol%.

3. The silicon nitride ceramic material according to claim 1 or 2, wherein the molar ratio of the metal hydride to the alkaline earth metal oxide is 1:10 to 10:1, preferably 1:5 to 5: 1.

4. The silicon nitride ceramic material according to any one of claims 1 to 3, wherein the silicon nitride ceramic material has a thermal conductivity of 61.25 to 115.18W/(m-K), a bending strength of 475 to 759MPa, and a fracture toughness of 5.38 to 7.95 MPa-m^1/2。

5. A method of preparing a silicon nitride ceramic material according to any one of claims 1 to 4, comprising:

6. The preparation method according to claim 5, wherein the mixing is performed by wet ball milling in a vacuum ball milling tank, and then rotary evaporation drying or vacuum drying is performed to obtain mixed powder; the ball milling atmosphere in the vacuum ball milling tank is vacuum atmosphere, inert atmosphere or nitrogen atmosphere.

7. The method according to claim 5 or 6, wherein the compression molding is performed by dry compression molding or/and isostatic pressing, preferably by dry compression molding followed by isostatic pressing; the pressure of the dry pressing is 10-50 MPa, and the pressure of the isostatic pressing is 100-300 MPa.

8. The production method according to any one of claims 5 to 7, wherein an atmosphere of the pre-sintering treatment is a vacuum atmosphere, a nitrogen atmosphere, or an inert atmosphere, and the inert atmosphere is an argon atmosphere; the time of the pre-sintering treatment is 1-8 hours.

9. The production method according to any one of claims 5 to 8, wherein the sintering treatment is performed by gas pressure sintering, hot press sintering, spark plasma sintering, hot isostatic pressing sintering, or pressureless sintering; the time of the sintering treatment is more than or equal to 2 hours; preferably, the atmosphere of the air pressure sintering is nitrogen, and the air pressure is more than or equal to 1 MPa.

10. The production method according to any one of claims 5 to 9, wherein a temperature rise rate of the sintering treatment is 1 to 15 ℃/min.

11. The preparation method according to any one of claims 5 to 10, wherein after the sintering treatment is completed, the mixture is cooled to 800 to 1200 ℃ at a cooling rate of 20 ℃/min or less, and then is furnace-cooled to room temperature.