CN114621014B - High-strength high-thermal-conductivity silicon nitride ceramic material and preparation method thereof - Google Patents

High-strength high-thermal-conductivity silicon nitride ceramic material and preparation method thereof Download PDF

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CN114621014B
CN114621014B CN202210232862.1A CN202210232862A CN114621014B CN 114621014 B CN114621014 B CN 114621014B CN 202210232862 A CN202210232862 A CN 202210232862A CN 114621014 B CN114621014 B CN 114621014B
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曾宇平
李世帅
姚冬旭
夏咏锋
梁汉琴
尹金伟
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Shanghai Institute of Ceramics of CAS
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Abstract

The invention discloses a high-grade steel wire ropeA silicon nitride ceramic material with high strength and high thermal conductivity and a preparation method thereof. The raw materials of the high-strength high-thermal-conductivity silicon nitride ceramic material comprise Si powder and a sintering aid; the sintering aid is formed by rare earth coprecipitated starch (RE) x Eu y ) 2 O 3 And alkaline earth metal oxide composition, (RExEuy) 2 O 3 RE in (2) is one of Y, yb and Tm, the value range of x is 88-98 mol%, and the value range of Y is 2-12 mol%; the alkaline earth metal oxide is at least one of MgO, caO, srO and BaO; the molar ratio of the rare earth coprecipitated starch to the alkaline earth metal oxide is 0.5:9.5-9.5:0.5; all of Si powder is converted into Si 3 N 4 And the sintering aid accounts for 5-10mol% of the high-strength high-thermal-conductivity silicon nitride ceramic material.

Description

High-strength high-thermal-conductivity silicon nitride ceramic material and preparation method thereof
Technical Field
The invention relates to a high-strength high-thermal-conductivity silicon nitride ceramic material and a preparation method thereof, belonging to the field of inorganic nonmetallic materials.
Background
Today, human society faces energy shortage and environmental pollution problems. In order to save energy and reduce environmental pollution, energy is currently being turned from fossil fuel energy to electric energy. The power electronic device can improve the use efficiency of electric energy and has been widely applied to industries such as industrial robots, new energy automobiles, high-speed railways and the like. In order to maximize the power conversion efficiency, power electronic devices are being developed toward miniaturization, high voltage, high current, and high power density, which also accelerates the progress of substitution of Si by third generation semiconductors such as SiC, gaN, etc. However, the high power density causes larger thermal stress in the power device, which is unfavorable for long-term use of the device. Therefore, it is particularly important to study how the power device dissipates heat. Since the ceramic substrate has excellent insulation properties, a ceramic material having both good thermal conductivity and mechanical properties is an ideal material for high-power electronic devices. Aluminum nitride (AlN) ceramic substrates are currently in relatively wide use. Although AlN has good heat conduction performance, but has poor mechanical properties, and is easy to hydrolyze in a humid environment, so that the AlN is not suitable for power electronic devices with high power density.
Silicon nitride is a high temperature structural ceramic with excellent insulation, thermal conductivity, thermal shock resistance and mechanical properties. There are calculations showing that beta-Si 3 N 4 The theoretical thermal conductivity of (C) is as high as 320W/(mK). beta-Si 3 N 4 The long rod-shaped structure is formed, and the long rod-shaped structure is mutually overlapped, so that the bending strength of the material is improved. Considering mechanical properties and thermal conductivity comprehensively, silicon nitride is a material which is very potential to be used as a heat dissipation substrate of a next-generation high-power electronic device.
The preparation of high thermal conductivity dense silicon nitride has two main technical routes. One is to make high-purity Gao-Si 3 N 4 Mixing silicon nitride powder with sintering aid, and directly sintering at high temperature; the second method is to mix high-purity Si powder with low oxygen content and sintering aid for nitriding, and then sintering at high temperature. The first technical route is unfavorable for commercialization of high-thermal-conductivity silicon nitride substrates due to the high cost of high-purity silicon nitride powder. Currently, researchers agree that the most significant cause of the decrease in thermal conductivity of silicon nitride ceramics is that the presence of lattice oxygen creates silicon vacancies and thus phonon scattering, while the content and distribution of the grain boundary phase has less influence on thermal conductivity. The Si powder has lower oxygen content, and can effectively inhibit the generation of lattice oxygen, thereby improving the heat conductivity. The second technical route has the following advantages compared with the first technical route: (1) the price is low, and the commercialization is convenient; (2) a near net size sintering process; (3) the thermal conductivity of the sample is high. Therefore, the sintering after nitriding of Si powder (SRBSN) is an ideal way for preparing the high-thermal-conductivity silicon nitride ceramic.
Si powder nitriding although Si with higher thermal conductivity can be obtained 3 N 4 Ceramic, butIs that the nitriding process is very slow, resulting in an extended overall preparation cycle. So far, scientific researchers have conducted a lot of experiments on promoting the nitridation of Si powder and screened out some sintering aids (Fe powder, zrO 2 ，Ce 2 O 3 ，Eu 2 O 3 Etc.). Fe and ZrO 2 Although the nitriding of Si powder can be obviously promoted, feSi can be respectively contained in the sample after the sintering is completed 2 And ZrN intergranular phase occurs. FeSi (FeSi) 2 The method is unfavorable for improving the heat conductivity, and the density of the sample is reduced to damage the heat conductivity due to easy volatilization at high temperature; zrN exists in the intergranular phase in a granular state, so that the mechanical property of a sample is damaged, the conductivity of the ZrN is better, and if the ZrN in the intergranular phase is excessive, si 3 N 4 The breakdown voltage of the substrate is greatly reduced, and the substrate is not suitable for heat dissipation of high-power electronic devices. With Ce 2 O 3 Although dense Si can be obtained as an auxiliary agent 3 N 4 Ceramics, but the samples prepared therefrom have a lower thermal conductivity. How to promote nitridation of Si powder without compromising the mechanical properties and thermal conductivity of the post-sintered sample is a current problem.
Disclosure of Invention
The technical purpose of the invention is to provide a brand new Si with high strength and high thermal conductivity 3 N 4 Ceramic and method for producing the same, the silicon nitride ceramic being co-precipitated with rare earth starch (RE) x Eu y ) 2 O 3 And alkaline earth metal oxide is used as sintering auxiliary agent to promote nitridation of Si powder, and can adjust composition and viscosity of liquid phase in post sintering to influence development of microscopic morphology, thereby improving thermal conductivity.
In one aspect, the present invention provides a high strength, high thermal conductivity silicon nitride ceramic material. The raw materials of the high-strength high-thermal-conductivity silicon nitride ceramic material comprise Si powder and a sintering aid; the sintering aid is formed by rare earth coprecipitated starch (RE) x Eu y ) 2 O 3 And alkaline earth metal oxide composition, (RExEuy) 2 O 3 RE in (2) is one of Y, yb and Tm, the value range of x is 88-98 mol%, and the value range of Y is 2-12 mol%; the alkaline earthThe metal oxide is at least one of MgO, caO, srO and BaO; the molar ratio of the rare earth coprecipitated starch to the alkaline earth metal oxide is 0.5:9.5-9.5:0.5; all of Si powder is converted into Si 3 N 4 The sintering aid accounts for 5 to 10mol percent of the high-strength high-thermal-conductivity silicon nitride ceramic material.
In the present invention, use is made of (RExEuy) 2 O 3 And (RE is one of Y, yb and Tm) is a rare earth sintering aid, so that the nitridation of Si powder can be promoted, and the thermal conductivity of a post-sintered sample can not be damaged. Eu atoms in the rare earth sintering aid can promote the nitriding process of Si powder, and the nitriding period is greatly shortened. Eu (Eu) 2 O 3 Can be combined with SiO 2 At a lower temperature to generate a liquid phase, thereby removing SiO on the surface of Si powder 2 Is beneficial to the nitridation process. Tm (Tm) 3+ 、Yb 3+ And Y 3+ The glass can participate in the liquid phase during the post sintering process to modify the liquid phase glass network, so as to promote the diffusion of Si and N in the liquid phase; in addition, tm of small ion radius 3+ 、Yb 3+ And Y 3+ The total oxygen-attaching capacity of the liquid phase after the back sintering is stronger, and phonon scattering caused by oxygen entering into silicon nitride lattice forming defects can be effectively prevented. Compared with the mechanical mixing of two rare earth sintering aids, the rare earth sintering aid obtained by adopting the coprecipitation method effectively avoids the difference in sample performance caused by uneven rare earth distribution generated by the mechanical mixing method.
Preferably, the Si powder is fully converted into Si 3 N 4 The sintering aid accounts for 6 to 8mol percent of the high-strength high-thermal-conductivity silicon nitride ceramic material.
Preferably, the rare earth co-precipitated starch (RE x Eu y ) 2 O 3 The value of x is 92-96 mol%, and the value of y is 4-8 mol%.
Preferably, the molar ratio of the rare earth co-precipitated starch to the alkaline earth metal oxide is 1:6-6:1.
Preferably, the thermal conductivity of the silicon nitride ceramic material is 64.14-110.3W/(m.K), and the flexural strength is 476.4-820.0MPa.
In a second aspect, the invention provides a method for preparing a high-strength high-thermal-conductivity silicon nitride ceramic material. Comprising the following steps:
weighing Si powder and sintering aid according to the raw material composition of the silicon nitride ceramic material, and mixing the Si powder and the sintering aid to obtain mixed powder;
after the obtained mixed powder is pressed and molded, nitriding treatment is firstly carried out at 1200-1450 ℃, and then post-sintering treatment is carried out at 1850-1900 ℃ to obtain the high-strength high-thermal conductivity silicon nitride ceramic material.
Preferably, the pressing forming mode is dry pressing forming or/and isostatic pressing treatment, and preferably dry pressing forming is performed before isostatic pressing treatment; the pressure of the dry press molding is 0.5-5 MPa, and the pressure of the isostatic pressing treatment is 100-300 MPa.
Preferably, the nitriding atmosphere is nitrogen or a mixed atmosphere of nitrogen and hydrogen; the nitriding treatment time is 1-8 h.
Preferably, the post-sintering treatment mode is air pressure sintering, hot pressing sintering, hot isostatic pressing sintering, spark plasma sintering, vibration pressure sintering or pressureless sintering; the time of the post-sintering treatment is more than or equal to 2 hours; preferably, the atmosphere of the air pressure sintering is nitrogen, and the pressure of the nitrogen is more than or equal to 1MPa. The high nitrogen pressure at high temperature can inhibit the decomposition of silicon nitride (above 1780 ℃), improve sintering activity, promote the diffusion of N in liquid phase during sintering, and facilitate densification and grain growth.
Preferably, the temperature rising rate of the nitriding treatment is 0.1-10 ℃/min; the temperature rising rate of the post-sintering treatment is 1-15 ℃/min.
Preferably, after the post sintering is completed, cooling to 800-1200 ℃ at a cooling rate of less than or equal to 20 ℃/min, and then cooling to room temperature along with the furnace.
The beneficial effects are that:
the invention uses the coprecipitation method of rare earth to obtain coprecipitated starch (RE) x Eu y ) 2 O 3 Is a rare earth sintering aid. Wherein the element Eu can promote the nitriding process of Si, reduce the viscosity of liquid phase in the post-sintering process, facilitate the diffusion of Si and N, promote the growth and development of crystal grains, thereby effectively promotingThermal conductivity of silicon nitride ceramics. In some technical schemes, the bending strength of the obtained silicon nitride ceramic material can reach 776.8MPa, the thermal conductivity can reach 110.3W/(m.K), compared with Y 2 O 3 Compared with a rare earth auxiliary sample, the thermal conductivity is improved by 16.5%, the bending strength is improved by 7.1%, and the application of the silicon nitride ceramic in high-power density electronic components can be satisfied.
Drawings
FIG. 1 is a thermogravimetric plot of a Si powder nitriding process using different sintering aids.
FIG. 2 is a graph of the microscopic topography of different silicon nitride ceramic samples after surface polishing.
Detailed Description
The invention is further illustrated by the following embodiments, which are to be understood as merely illustrative of the invention and not limiting thereof. Unless otherwise specified, each percentage refers to a mass percent.
The invention selects the rare earth coprecipitated starch (RE) x Eu y ) 2 O 3 The silicon nitride ceramic material with high strength, high toughness and high thermal conductivity is prepared from rare earth sintering auxiliary agents. The raw materials of the high-strength high-toughness high-thermal conductivity silicon nitride ceramic material comprise high-purity low-oxygen-content Si powder and sintering aids. In some embodiments, the Si powder has a purity of 99.99% (calculated as metal) and an oxygen content of 0.46wt.%. The sintering aid is formed by rare earth coprecipitation of starch (RExEuy) 2 O 3 (RE is one of Y, yb and Tm) and alkaline earth metal oxide. The total content of sintering aid (in the silicon nitride ceramic material) is 5 to 10mol.%, preferably 6 to 8mol.%. Too little sintering aid addition can not effectively remove SiO on the surface of Si powder 2 The nitriding process of Si powder is promoted, and the liquid phase formed in the post-sintering process is less in quantity, higher in viscosity and unfavorable for densification of the sample; too much sintering aid increases the content of intergranular phases of low thermal conductivity in the sample, which is detrimental to the enhancement of thermal conductivity.
The rare earth co-precipitated starch may be (Tm x Eu y ) 2 O 3 、(Yb x Eu y ) 2 O 3 And (Y) x Eu y ) 2 O 3 One of them. Alkaline earth metal oxides include, but are not limited to MgO, caO, srO, baO and the like. Taking MgO as an example, eu in rare earth sintering aid 2 O 3 Can promote nitridation of Si powder because Eu 2 O 3 MgO and SiO 2 Can form Eu-Si-Mg-O-N liquid phase at lower temperature, and SiO is arranged on the surface of Si powder 2 Is favorable for Si powder to be exposed in N 2 In the atmosphere, promoting nitridation of Si powder; RE (RE) 2 O、Eu 2 O 3 Can be combined with SiO during MgO post-sintering 2 The reaction at low temperature produces a low eutectic liquid phase, oxygen in the liquid phase is hindered from entering the silicon nitride lattice by the presence of RE and Eu, and the dissolution-precipitation process of grain growth and development and the Oswald ripening process are also carried out in the liquid phase. The full development of the grains and the smaller oxygen content in the crystal lattice can effectively improve the thermal conductivity of the silicon nitride ceramic.
The rare earth coprecipitated starch (Tm x Eu y ) 2 O 3 、(Yb x Eu y ) 2 O 3 And (Y) x Eu y ) 2 O 3 Wherein x is 88 to 98mol.%, y is 2 to 12mol.%, preferably x is 2 to 6mol.% and y is 94 to 98mol.%. If x, y is outside the above range, it may cause difficulty in densification of the material.
The sintering aid system of the invention is alkaline earth metal oxide- (RE) X Eu Y ) 2 O 3 The invention introduces two rare earth elements by rare earth coprecipitation, which can ensure that the two rare earth elements are uniformly mixed into the powder. Eu element in the rare earth sintering aid plays a role in promoting nitridation in the silicon nitride stage of Si powder, and participates in a liquid phase together with RE element in the post-sintering process, so that the glass transition temperature and viscosity of the liquid phase are reduced, and densification of a sample is promoted. Other sintering aid systems are mechanically mixed when the multi-element rare earth elements are introduced, and the multi-element rare earth elements cannot be ensured to exist at a certain position (poor mixing uniformity) in the material at the same time. Compared with oxygen directly using REChemical compound and Eu 2 O 3 As the rare earth sintering aid, the invention adopts (RExEuy) 2 O 3 The rare earth co-precipitated starch has the advantage of being capable of uniformly dispersing two rare earths in a material system, which has great contribution to synchronously ensuring high strength and high thermal conductivity of the silicon nitride ceramic material.
(RExEuy) 2 O 3 The preparation of rare earth co-precipitated starch is not the point of creation of the present invention. As an example, (RExEuy) 2 O 3 The preparation process of the rare earth coprecipitation starch body comprises the steps of dissolving europium nitrate and yttrium nitrate in deionized water according to a certain proportion, adding ammonia water to adjust the pH value to be 12 while stirring after the europium nitrate and yttrium nitrate are completely dissolved, and standing for more than 12 hours. The precipitate was washed twice with deionized water and dried. And then sintering in a muffle furnace, and grinding the obtained sintered body to obtain the coprecipitated starch body.
The following exemplifies a method for preparing the silicon nitride ceramic material provided by the present invention.
Weighing Si powder, mgO and (RE) x Eu y ) 2 O 3 And (3) uniformly mixing the powder to obtain mixed powder. During mixing, a polytetrafluoroethylene ball milling tank is used, and alcohol and silicon nitride balls are used as ball milling media. The slurry after ball milling was dried in an oven and the powder was sieved using a 60 mesh nylon screen. Wherein the particle diameter of Si powder is 4.35 μm (D50), the oxygen content is 0.46wt%, the Fe content is 0.0005wt%, the Al content is 0.0002wt%, and the Ca content is 0.0008wt%; mgO has a particle size of 10nm to 5 mu m; (RE) x Eu y ) 2 O 3 The particle size of (3.1 μm).
In an alternative embodiment, the Si powder and the selected sintering aid (RE x Eu y ) 2 O 3 And MgO in a proportion of 93mol% to 2mol% to 5mol%.
As a detailed example of the preparation of a mixed powder, it includes: mixing Si powder and sintering aid, ball milling, stoving and sieving to obtain homogeneously mixed powder. The ball milling tank is a plastic ball milling tank made of polytetrafluoroethylene, the grinding medium is an alcohol solvent, and the powder is: the alcohol ratio can be (1:1) - (3:1); during ball milling, silicon nitride grinding balls and powder are adopted: the alcohol ratio can be (1:1) - (5:1), the mechanical mixing is carried out by adopting a planetary ball milling mode, and the ball milling is carried out for 3-5 hours at the speed of 250-300 r/min. The drying temperature can be 50-80 ℃, and the drying time can be 8-24 h. The mesh number of the sieving can be 60-200 meshes. In some technical schemes, the mixing mode is ball milling mixing, a polytetrafluoroethylene ball milling tank is adopted, and absolute ethyl alcohol and Si are adopted 3 N 4 Ball milling is carried out on a star ball mill for 4 hours at the rotating speed of 300 rpm; drying the slurry in an oven at 70 ℃; and finally, sieving with a 60-mesh nylon sieve to obtain uniformly mixed powder.
And pressing and molding the uniformly mixed powder to obtain a preliminary green body. The press forming may comprise dry press forming and/or isostatic pressing, preferably sequentially. And taking a certain amount of powder, performing dry pressing molding in a grinding tool, and performing isostatic pressing treatment. As an example, the molding pressure of the dry press was 2MPa, the pressure of the isostatic pressing treatment was 250MPa, and the dwell time was 3min. In a preferred embodiment, the isostatic pressing is a cold isostatic pressing.
The blank is nitrided at 1200-1450 deg.c, preferably 1200-1410 deg.c. Wherein, the nitriding treatment time can be 4-8 hours. Preferably, the nitriding treatment is carried out for 4 hours. In some technical schemes, the nitriding atmosphere is N 2 (95 vol%) and H 2 (5 vol%); the atmosphere pressure of the nitriding treatment is normal pressure. As an example, the nitriding procedure may be to first keep the temperature at 1350 ℃ for 2 hours, then keep the temperature at 1380 ℃ for 2 hours, and finally keep the temperature at 1400 ℃ for 4 hours.
And (3) performing post-sintering treatment on the sample subjected to nitriding treatment at 1850-1900 ℃. The post-sintering treatment mode comprises, but is not limited to, pressureless sintering, hot-press sintering, air-pressure sintering, spark plasma sintering, hot isostatic pressing sintering and oscillating pressure sintering. The post-sintering treatment time may be 4 hours or more. The post-sintering treatment is preferably air pressure sintering. Atmosphere of air pressure sintering is N 2 An atmosphere. The pressure of the post-sintering atmosphere is more than or equal to 1MPa and can be 1-10 MPa. The process conditions for one gas pressure sintering may include: by N 2 Is a sintering atmosphere, and is heated at a rate of 5-15 ℃/min under the condition of air pressure of 1-10 MPaRaising the temperature to 1850-1900 ℃ and preserving the temperature for more than 4 hours. High N 2 The pressure ensures that the silicon nitride ceramic does not decompose at high temperatures (1780 ℃). The silicon nitride has higher sintering activity above 1780 ℃, which is beneficial to the occurrence of silicon nitride phase transformation and the growth and development of crystal grains. The heating rate is preferably 10 ℃/min, the sintering temperature is preferably 1850 ℃ to 1900 ℃, and the heat preservation time is preferably 4h. By way of example, the temperature increase rate of the nitriding treatment is 5 ℃/min (to 1200 ℃), 1 ℃/min (to 1350 ℃), 1 ℃/min (to 1380 ℃), 0 ℃/min (to 1400 ℃).
According to the sintering mechanism of the silicon nitride ceramic and related literature reports, it is known that increasing the sintering temperature, prolonging the heat preservation time and reducing the cooling rate can improve the heat conductivity of the silicon nitride ceramic. The invention is obviously not limited to the temperature stage, the heat preservation stage and the cooling rate stage of the air pressure sintering; also, the present invention is not limited to gas pressure sintering, and can achieve the desired effect by using a wide range of hot press sintering, hot isostatic pressing sintering, pressureless sintering, spark plasma sintering, and the like.
After the sintering treatment is finished, the silicon nitride ceramic with high strength and high thermal conductivity is obtained after cooling to room temperature. Further preferably, after the sintering process is completed, the material is cooled to 1200 ℃ at a cooling rate of 10 ℃/min and then cooled to room temperature with a furnace.
It should be noted that although the above description of the preparation process of the silicon nitride ceramic material is given by taking MgO as an example, other alkaline earth metal oxides such as BaO, caO, and the like are also applicable to the above preparation process.
The density of the samples was measured using the Archimedes method.
The microscopic morphology of the sample was observed by scanning electron microscopy (Magellan 400, FEI, USA).
The degree of nitridation (nitriding rate) is calculated according to formula (1):
Figure BDA0003539190490000061
in formula (1), DN is the nitriding rate of the sample; m is m Front part Is the mass before nitriding; m is m Rear part (S) Is the quality after nitriding; m is m Si Is Si atomic mass; m is m N Is N atomic mass.
The thermal diffusivity is obtained by: processing the sample into
Figure BDA0003539190490000074
The thermal diffusivity (. Alpha.) was measured by laser flash (LFA 467 Hyper flash,NETZSCH Instruments Co.Ltd, selb, germany). Calculated according to formula (2): />
Figure BDA0003539190490000071
In the formula (2), α is the thermal diffusivity (mm) 2 ·s- 1 ) The method comprises the steps of carrying out a first treatment on the surface of the h is the sample thickness (mm); t is t 1/2 Is half the heating time, i.e. the time(s) required for the temperature of the back side of the sample to rise to half the maximum temperature. The same sample was measured for three thermal diffusivities and finally averaged three times.
The thermal conductivity is calculated by the formula (3):
Figure BDA0003539190490000072
wherein ρ is the density of the sample in g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the Cp is the heat capacity of the silicon nitride ceramic, and the value changes with the change of the material composition and the microstructure, but the change range is very small, and 0.68 J.g- 1 ·K- 1 The method comprises the steps of carrying out a first treatment on the surface of the Alpha is the thermal diffusivity in cm 2 S, measured using NETZSCH LFA 467.
The flexural strength is obtained by: the samples were processed into 3X 4X 36mm strips and the flexural strength was measured by the three-point bending method on a universal mechanical tester (Model 5566, instron Co., high Wycombe, UK). The specific parameters tested were as follows: the span is 30mm, and the loading rate is 0.5 mm.min- 1 At least 6 samples were measured for each sample and their average was taken while calculating the standard deviation. Flexural strength was calculated according to equation (4):
Figure BDA0003539190490000073
in the formula (4), sigma SN Is Si (Si) 3 N 4 Sample three-point flexural strength (MPa); p is the maximum load (N); l is span (mm); h is the strip height (mm); b is the test strip width (mm). The bending strength of the obtained silicon nitride ceramic is 476-821MPa.
In the invention, a thermogravimetric analyzer (NETZSCH STA 449F 3) is adopted to measure the mass change of the sample in the heating process. The heating rate selected by the thermogravimetric analysis is 10 ℃/min, and the atmosphere adopted in the heating process is N 2 The atmosphere pressure is normal pressure.
The invention selects (RE) x Eu y ) 2 O 3 As rare earth sintering aid, the silicon nitride ceramic material with high strength, high toughness and high thermal conductivity is prepared. First, the presence of Eu element can greatly promote the nitriding process of Si powder because Eu 2 O 3 MgO and SiO 2 Can form Eu-Si-Mg-O-N liquid phase at lower temperature, and SiO is arranged on the surface of Si powder 2 Is favorable for Si powder to be exposed in N 2 In the atmosphere, promoting nitridation of Si powder; RE (RE) 2 O 3 、Eu 2 O 3 Can be combined with SiO during MgO post-sintering 2 Reaction to form liquid phase, RE 2 O 3 +Eu 2 O 3 +MgO+SiO 2 As the viscosity of the Eu-containing liquid phase is lower than that of the RE-containing liquid phase at high temperature, the lower liquid phase viscosity is beneficial to the dissolution-precipitation and the Oswald ripening process and promotes the alpha-Si 3 N 4 To beta-Si 3 N 4 And can promote the growth and development of grains into grains of large size. The large-size crystal grains are beneficial to improving the thermal conductivity of the sample.
The present invention will be further illustrated by the following examples. It is also to be understood that the following examples are given solely for the purpose of illustration and are not to be construed as limitations upon the scope of the invention, since numerous insubstantial modifications and variations will now occur to those skilled in the art in light of the foregoing disclosure. The specific process parameters and the like described below are also merely examples of suitable ranges, i.e., one skilled in the art can make a suitable selection from the description herein and are not intended to be limited to the specific values described below.
Example 1
With 5mol% MgO and 2mol% (Y) 0.98 Eu 0.02 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 2
With 5mol% MgO and 2mol% (Y) 0.96 Eu 0.04 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
The surface morphology of the silicon nitride ceramic obtained in this embodiment is shown in fig. 2 (b), which shows a bimodal morphology in which large grains are distributed in small grains, the size of the large grains is more than 10 μm, the inter-crystal phase content is less, the number of small-size grains is less, and the promotion of thermal conductivity is facilitated.
Example 3
With 5mol% MgO and 2mol% (Y) 0.94 Eu 0.06 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 4
With 5mol% MgO and 2mol% (Y) 0.92 Eu 0.08 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 5
With 5mol% MgO and 2mol% (Y) 0.90 Eu 0.10 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powderA body. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 6
With 5mol% MgO and 2mol% (Y) 0.88 Eu 0.12 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 7
With 5mol% MgO and 2mol% (Tm) 0.98 Eu 0.02 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, and the post-sintering adopts a pneumatic sintering methodThe temperature rising rate is 10 ℃/min, N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 8
With 5mol% MgO and 2mol% (Tm) 0.96 Eu 0.04 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 9
With 5mol% MgO and 2mol% (Tm) 0.94 Eu 0.06 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 10
With 5mol% MgO and 2mol% (Tm) 0.92 Eu 0.08 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 11
With 5mol% MgO and 2mol% (Tm) 0.90 Eu 0.10 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 12
With 5mol% MgO and 2mol% (Tm) 0.88 Eu 0.12 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucibleIn the crucible, in N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 13
With 5mol% MgO and 2mol% (Yb) 0.98 Eu 0.02 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 14
With 5mol% MgO and 2mol% (Yb) 0.96 Eu 0.04 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling at a cooling rate of 10 ℃ per minuteCooled to 1200 ℃ and then cooled to room temperature with the furnace.
Example 15
With 5mol% MgO and 2mol% (Yb) 0.94 Eu 0.06 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 16
With 5mol% MgO and 2mol% (Yb) 0.92 Eu 0.08 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 17
With 5mol% MgO and 2mol% (Yb) 0.90 Eu 0.10 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) Si powder passageBall milling and mixing, drying and sieving to obtain uniformly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Example 18
With 5mol% MgO and 2mol% (Yb) 0.88 Eu 0.12 ) 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Comparative example 1
With 5mol% MgO and 2mol% Y 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃ and post-sinteringThe junction adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
The surface morphology of the silicon nitride ceramic obtained in this comparative example is shown in fig. 2 (a), which shows a bimodal morphology in which large grains are distributed in small grains.
Comparative example 2
With 5mol% MgO and 2mol% Tm 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Comparative example 3
With 5mol% MgO and 2mol% Yb 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Comparative example 4
In 5mol% MgO, 1.92mol% Y 2 O 3 And 0.08mol% Eu 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 1200 ℃ at a cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
The surface morphology of the silicon nitride ceramic obtained in this comparative example is shown in fig. 2 (c). The silicon nitride crystal grain structure is different from the silicon nitride crystal grain structure in (b) in that the crystal grain size is larger, the inter-crystal phase content is less, the large-size silicon nitride crystal grain in (c) is less, the crystal grain growth is incomplete, and the small-size crystal grain and the inter-crystal phase content are more. In addition, a small number of air holes are formed in the appearance (c), so that the improvement of heat conductivity is not facilitated. The silicon nitride ceramics obtained at this time have a high strength but a low thermal conductivity.
Comparative example 5
With 5mol% MgO, 2mol% Eu 2 O 3 As sintering aid, with 93mol% (complete conversion to Si according to the completion of Si powder nitriding) 3 N 4 Calculated) of Si powder is mixed by ball milling, dried and sieved to obtain evenly mixed powder. The powder was shaped by dry pressing at a pressure of 2MPa and then cold isostatic pressed at a pressure of 250 MPa. Placing the obtained biscuit in BN crucible, and adding N 2 (95 vol%) and H 2 (5 vol%) was nitrided at 1400℃for 4h in a mixed gas atmosphere. Then the sample after nitriding is subjected to post-sintering treatment at 1900 ℃, the post-sintering adopts a pneumatic sintering mode, the heating rate is 10 ℃/min, and N 2 The pressure is 1MPa, and the heat preservation time is 4 hours. After the post-sintering is completed, cooling to 12 at a cooling rate of 10 ℃/min00℃and then cooled to room temperature with the oven.
The surface morphology of the silicon nitride ceramic obtained in the comparative example is shown in (d) of fig. 2, the grain size in the sample is not completely developed, the number of intermediate phases is small, and the number of holes is large, which is not beneficial to the improvement of the mechanical property and the thermal conductivity of the sample.
Table 1 shows the performance parameters of the silicon nitride ceramic materials prepared in examples 1-18 and comparative examples 1-5 of the present invention:
Figure BDA0003539190490000151
as can be seen from table 1, the present invention was achieved by using (RE x Eu y ) 2 O 3 And MgO as sintering aid, and adopting the air pressure sintering mode to obtain Si with high strength, high toughness and high thermal conductivity 3 N 4 And (3) ceramics. Comparing comparative example 1 with example 2, it was found that (Y 0.96 Eu 0.04 ) 2 O 3 Substitute Y 2 O 3 When the rare earth sintering aid is used, the nitriding rate of the sample in the embodiment 2 is obviously improved, the heat conductivity is obviously improved, and the mechanical property is also improved. Comparing comparative example 2 with examples 7 to 11, it was found that the use (Tm 0.98 Eu 0.02 ) 2 O 3 、(Tm 0.96 Eu 0.04 ) 2 O 3 、(Tm 0.94 Eu 0.06 ) 2 O 3 、(Tm 0.92 Eu 0.08 ) 2 O 3 、(Tm 0.90 Eu 0.10 ) 2 O 3 Substitution of Tm 2 O 3 When the rare earth sintering aid is used, the nitriding rate of the samples in examples 7-11 is obviously improved; comparing comparative example 3 with examples 14 to 16, it was found that the use of (Yb 0.96 Eu 0.04 ) 2 O 3 、(Yb 0.94 Eu 0.06 ) 2 O 3 、(Yb 0.92 Eu 0.08 ) 2 O 3 Replacement of Yb 2 O 3 As a thin filmThe samples of examples 14-16 have significantly improved nitriding rates when the soil sintering aid is applied.
As can be seen from fig. 1, a number of (Y 0.96 Eu 0.04 ) 2 O 3 Sample of rare earth sintering aid Y 2 O 3 Compared with a sample of the rare earth sintering aid, the initial nitriding temperature of Si powder is obviously reduced.
Finally, what is necessary here is: the above embodiments are only for further detailed description of the present invention and should not be construed as limiting the scope of the present invention, and some insubstantial modifications and adaptations of the present invention based on the foregoing are within the scope of the present invention.

Claims (10)

1. The preparation method of the high-strength high-thermal-conductivity silicon nitride ceramic material is characterized in that the raw materials of the high-strength high-thermal-conductivity silicon nitride ceramic material comprise Si powder and sintering aids; the sintering aid is formed by rare earth coprecipitated starch (RE) x Eu y ) 2 O 3 And alkaline earth metal oxide composition, (RExEuy) 2 O 3 RE in (2) is one of Y, yb and Tm, the value range of x is 88-98 mol%, and the value range of Y is 2-12 mol%; the alkaline earth metal oxide is at least one of MgO, caO, srO and BaO; the molar ratio of the rare earth coprecipitated starch to the alkaline earth metal oxide is 0.5:9.5-9.5:0.5; all of Si powder is converted into Si 3 N 4 The sintering aid accounts for 5-10mol% of the high-strength high-thermal-conductivity silicon nitride ceramic material;
the preparation method comprises the following steps:
weighing Si powder and sintering aid according to the raw material composition of the silicon nitride ceramic material, and mixing the Si powder and the sintering aid to obtain mixed powder;
after the obtained mixed powder is pressed and molded, firstly nitriding treatment is carried out at 1200-1450 ℃, and then post-sintering treatment is carried out at 1850-1900 ℃ to obtain the high-strength high-thermal-conductivity silicon nitride ceramic material; the post-sintering treatment is air pressure sintering, the air pressure sintering atmosphere is nitrogen, the nitrogen pressure is more than or equal to 1MPa, and the time of the post-sintering treatment is more than or equal to 2 hours.
2. The method according to claim 1, wherein the Si powder is completely converted into Si 3 N 4 And the sintering aid accounts for 6-8 mol% of the high-strength high-thermal-conductivity silicon nitride ceramic material.
3. The method according to claim 1, wherein the rare earth co-precipitated starch (RE x Eu y ) 2 O 3 The value of x is 92-96 mol%, and the value of y is 4-8 mol%.
4. The preparation method of claim 1, wherein the molar ratio of the rare earth co-precipitated starch to the alkaline earth metal oxide is 1:6-6:1.
5. The method according to claim 1, wherein the silicon nitride ceramic material has a thermal conductivity of 91.211 to 110.30W/(m-K) and a flexural strength of 671.727 to 785.362MPa.
6. The method according to claim 1, wherein the press forming is dry press forming or/and isostatic pressing.
7. The preparation method according to claim 1, wherein the pressing and forming mode is dry pressing and then isostatic pressing; the pressure of the dry press molding is 0.5-5 MPa, and the pressure of the isostatic pressing treatment is 100-300 MPa.
8. The method according to claim 1, wherein the nitriding atmosphere is nitrogen or a mixed atmosphere of nitrogen and hydrogen; the nitriding treatment time is 1-8 hours.
9. The method according to claim 1, wherein the nitriding treatment has a temperature rise rate of 0.1 to 10 ℃/min; the temperature rising rate of the post-sintering treatment is 1-15 ℃/min.
10. The method according to any one of claims 1 to 9, wherein after the post-sintering is completed, the mixture is cooled to 800 to 1200 ℃ at a cooling rate of 20 ℃/min or less and then cooled to room temperature with a furnace.
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