Silicon nitride ceramic with high thermal conductivity and preparation method thereof

Abstract

The invention belongs to the technical field of ceramic materials, and relates to high-thermal-conductivity silicon nitride ceramic and a preparation method thereof. The invention discloses a preparation method of high-thermal-conductivity silicon nitride ceramic, which comprises the following steps: (1) uniformly mixing silicon powder and a sintering aid to obtain mixed powder, and carrying out compression molding on the mixed powder to obtain a silicon blank; the sintering aid is a rare earth metal oxide; (2) placing the silicon blank in a nitrogen-containing reducing atmosphere environment, pre-treating at 600-1180 DEG C, heating to 1350-1700 DEG C, and carrying out nitriding treatment to obtain a silicon nitride blank; and (3) placing the silicon nitride green body in an inert atmosphere, and sintering at 1800-2200 DEG C to obtain the silicon nitride ceramic. The pretreatment step is added before the nitridation reaction, so that silicon dioxide impurities wrapped on the surface of the silicon powder are effectively eliminated, and the oxygen content in a liquid phase is reduced on the basis of not reducing the total content of a sintering aid, so that a silicon nitride blank with low lattice oxygen content is more easily prepared, and the heat conductivity of the silicon nitride ceramic is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ceramic materials, and relates to high-thermal-conductivity silicon nitride ceramic and a preparation method thereof. BACKGROUND

[0002] With the development of semiconductor devices towards high frequency, integration and high power, the thermal stress in the devices increases sharply, and thermal failure becomes a key factor restricting the performance and service life of the devices. The thermal conductivity of ceramic substrates, which are core heat dissipation components of electronic packaging, directly affects the reliability and heat dissipation efficiency of the devices. At present, commonly used ceramic substrate materials mainly include aluminum oxide (Al2O3), aluminum nitride (AlN) and beryllium oxide (BeO). Among them, although the aluminum oxide substrate is low in cost and mature in process, its thermal conductivity is low (20-30 W / m·K), which is difficult to meet the heat dissipation demand of high-power devices; the thermal conductivity of the aluminum nitride substrate is high (170-200 W / m·K), but the mechanical properties are poor and the thermal shock resistance is insufficient; the beryllium oxide substrate has high thermal conductivity and excellent mechanical properties, but its toxicity limits its large-scale application.

[0003] Silicon nitride (Si3N4) is a traditional structural ceramic, which has good thermal shock resistance, excellent comprehensive mechanical properties and high theoretical thermal conductivity (320 W / (m·K)). Therefore, silicon nitride has become a popular candidate material for heat dissipation substrates of new-generation high-power devices. At present, there are mainly two methods for preparing high-thermal-conductivity silicon nitride ceramic: one is to mix high-purity α-Si3N4 powder and sintering additives and then sinter at high temperature; and the other is to form a silicon nitride ceramic blank by nitriding high-purity Si powder and then sinter at high temperature. Both methods need to introduce oxides (such as Y2O3, MgO and ZrO2) as sintering additives to obtain dense silicon nitride ceramic by liquid phase sintering. However, the low-thermal-conductivity grain boundary phase and lattice defects (dislocations, vacancies, etc.) in the Si3N4 ceramic prepared by liquid phase sintering will reduce its thermal conductivity.

[0004] Lattice oxygen is considered as one of the most important factors affecting the thermal conductivity of silicon nitride ceramics. Excessive lattice oxygen content will cause a large number of silicon vacancies in the silicon nitride grains, intensify phonon scattering, increase the mean free path, and thus reduce the thermal conductivity of silicon nitride ceramics. The content of lattice oxygen usually increases with the increase of oxygen content in the liquid phase at the grain boundary. The oxygen in the liquid phase at the grain boundary mainly comes from the silicon dioxide on the surface of silicon powder or silicon nitride powder and the added oxide sintering aid. Using high-purity silicon powder or silicon nitride powder with low oxygen content is the key to preparing high-thermal-conductivity silicon nitride ceramics. For the preparation of high-thermal-conductivity silicon nitride ceramics by nitriding-gas-pressure sintering, the use of fine silicon powder (usually 0.5-10 μm) with small particle size as raw material can improve the nitriding efficiency and sintering activity. However, the surface silicon dioxide content of the silicon powder increases after being refined, which increases the oxygen content in the liquid phase during the reaction sintering process, and thus increases the lattice oxygen content and reduces the thermal conductivity of silicon nitride ceramics.

[0005] The Chinese patent application file (publication number: CN111196728A) discloses a method for preparing silicon nitride ceramics with high thermal conductivity and excellent mechanical properties. The method uses Si3N4 powder as raw material, rare earth metal (Y) and alkaline earth metal oxide as sintering aid, mixes and presses the raw materials to obtain a green body, preheats the green body to 800-1500 ℃ for 1-8 h, and then sintered at 1780-1950 ℃. However, the use of elemental rare earth metal is active and easily oxidized, which requires an oxygen-free environment during preparation, resulting in increased process complexity and making it unsuitable for large-scale production.

[0006] The Chinese patent application file (publication number: CN108585881A) discloses a method for preparing silicon nitride ceramics. The method first deoxidizes silicon nitride powder and carbon powder in nitrogen or ammonia at 1200-1400 ℃ for 4-8 h, then mixes the obtained silicon nitride powder with a binary composite sintering aid composed of rare earth oxide and alkaline earth metal compound, presses the mixture into a green body, and finally obtains the silicon nitride ceramic material by gas pressure sintering. However, this method deoxidizes the silicon nitride powder before mixing it with the sintering aid, which can cause the deoxidized silicon nitride powder to be re-oxidized, reducing the deoxidization effect and making it difficult to significantly improve the thermal conductivity. Moreover, the process complexity is increased.

[0007] The Chinese patent application file (publication number: CN111253162A) discloses a method for preparing high-strength, high-toughness, and high-thermal-conductivity silicon nitride ceramics. The method uses silicon powder with a particle size of <0.5 μm as raw material, adds 6-12 wt% of a sintering aid composed of rare earth oxide and alkaline earth metal compound, presses the mixture into a green body, removes the binder, nitrides the green body, and finally obtains the silicon nitride ceramic material by gas pressure sintering. However, this method uses micron-sized silicon powder as raw material, which is ground into sub-micron-sized silicon powder by long-time planetary ball milling. This process can oxidize the surface of the silicon powder and introduce a large amount of silicon dioxide, increasing the lattice oxygen content in the silicon nitride green body and the ceramic, making it difficult to prepare silicon nitride ceramics with high thermal conductivity. SUMMARY

[0008] The present application aims at solving the above problems existing in the prior art, and provides a pretreatment step in a nitrogen-containing reducing atmosphere environment to remove oxygen on the surface of silicon powder and avoid the solid solution of oxygen into the crystal lattice during the nitriding reaction, thereby reducing the oxygen content in the crystal lattice and obtaining high-thermal-conductivity silicon nitride ceramic.

[0009] One object of the present application is achieved by the following technical scheme:

[0010] A preparation method of high-thermal-conductivity silicon nitride ceramic comprises:

[0011] (1) uniformly mixing silicon powder and sintering aids to obtain a mixed powder, and pressing the mixed powder to obtain a silicon blank; the sintering aids are rare earth metal oxides;

[0012] (2) placing the silicon blank in a nitrogen-containing reducing atmosphere environment, and performing pretreatment at 600-1180 DEG C, and then heating to 1350-1700 DEG C to perform nitriding treatment, thereby obtaining a silicon nitride blank;

[0013] (3) placing the silicon nitride blank in an inert atmosphere, and performing sintering at 1800-2200 DEG C to obtain silicon nitride ceramic.

[0014] Preferably, the molar ratio of the silicon powder to the sintering aids in (1) is (92.0-99.9):(8.0-0.1).

[0015] Further preferably, the molar ratio of the silicon powder to the sintering aids in (1) is (96.6-99.5):(3.4-0.5).

[0016] Preferably, the mass ratio of the silicon powder to the sintering aids in (1) is (5-30):1.

[0017] Further preferably, the mass ratio of the silicon powder to the sintering aids in (1) is (10-26):1.

[0018] Preferably, the mass ratio of the silicon powder to the sintering aids in (1) is (5-30):1.

[0019] Further preferably, the mass ratio of the silicon powder to the sintering aids in (1) is (10-26):1.

[0020] As preferred, the rare earth metal oxide in (1) comprises one or more of yttrium oxide Y2O3, scandium oxide Sc2O3, ytterbium oxide Yb2O3, lutetium oxide Lu2O3, lanthanum oxide La2O3, cerium oxide Ce2O3, praseodymium oxide Pr2O3, neodymium oxide Nd2O3, promethium oxide Pm2O3, samarium oxide Sm2O3, europium oxide Eu2O3, gadolinium oxide Gd2O3, terbium oxide Tb2O3, dysprosium oxide Dy2O3, holmium oxide Ho2O3, erbium oxide Er2O3, thulium oxide Tm2O3.

[0021] Further preferred, the rare earth metal oxide in (1) comprises two or more of yttrium oxide Y2O3, scandium oxide Sc2O3, ytterbium oxide Yb2O3, lutetium oxide Lu2O3, lanthanum oxide La2O3, cerium oxide Ce2O3, praseodymium oxide Pr2O3, neodymium oxide Nd2O3, promethium oxide Pm2O3, samarium oxide Sm2O3, europium oxide Eu2O3, gadolinium oxide Gd2O3, terbium oxide Tb2O3, dysprosium oxide Dy2O3, holmium oxide Ho2O3, erbium oxide Er2O3, thulium oxide Tm2O3.

[0022] As preferred, the sintering aid in (1) comprises a first rare earth metal oxide and a second rare earth metal oxide, and the mass ratio of the first rare earth metal oxide to the second rare earth metal oxide is 1:(1-10).

[0023] Further preferred, the mass ratio of the first rare earth metal oxide to the second rare earth metal oxide is 1:2.

[0024] Further preferred, the first rare earth metal oxide is one or more of Y2O3, La2O3; and the second rare earth metal oxide is one or more of Sc2O3, Lu2O3.

[0025] As preferred, the mixing in (1) comprises one or more of crushing, mechanical stirring, wet ball milling, jet milling, sand milling.

[0026] Further preferred, the mixing comprises: first crushing, and then one or more of wet ball milling, jet milling, sand milling.

[0027] Further preferred, the crushing comprises: adding the silicon powder and the sintering aid into a crushing device in proportion, and crushing.

[0028] Further preferred, the wet ball milling comprises: adding the silicon powder and the sintering aid into a ball milling device in proportion, adding a solvent, the ball-to-material ratio is (3-20):1, the ball milling speed is 200-1200 rpm, and the ball milling time is 1-24 h.

[0029] Further preferred, the wet ball milling is followed by drying, and the drying is vacuum drying or rotary evaporation drying.

[0030] Further preferably, the sand milling comprises: mixing the silicon powder, the sintering aid and the solvent in proportion, and then adding the mixture into a sand mill, the sand mill rotates at a speed of 1500-2500 rpm, and the sand milling lasts for 1-4 hours.

[0031] Further preferably, the jet milling comprises: adding the silicon powder and the sintering aid into a jet mill in proportion, and then crushing the particles by high pressure gas flow.

[0032] Preferably, the silicon powder has a purity of more than 99.99% and an average particle size of 0.1-10 μm.

[0033] Further preferably, the silicon powder has an average particle size of 0.1-1 μm.

[0034] Preferably, the sintering aid has a purity of more than 99.99% and an average particle size of 0.1-5 μm.

[0035] Further preferably, the sintering aid has an average particle size of 0.1-2 μm.

[0036] Preferably, the mixed powder in (1) has an average particle size of 0.1-10 μm.

[0037] Further preferably, the mixed powder in (1) has an average particle size of 0.1-5 μm.

[0038] Further preferably, the mixed powder in (1) has an average particle size of 0.1-1.2 μm.

[0039] Preferably, the pressing in (1) is dry pressing and / or cold isostatic pressing.

[0040] Further preferably, the dry pressing is performed at a pressure of 10-30 MPa.

[0041] Further preferably, the cold isostatic pressing is performed at a pressure of 100-300 MPa.

[0042] Further preferably, the pressing in (1) is dry pressing and cold isostatic pressing.

[0043] Preferably, the N-containing reducing atmosphere in (2) comprises one or both of ammonia and nitrogen,

[0044] or, a mixture of one or both of ammonia and nitrogen and one or both of hydrogen and carbon monoxide.

[0045] Further preferably, the N-containing reducing atmosphere in (2) is ammonia,

[0046] or, a mixture of nitrogen and hydrogen,

[0047] or, a mixture of nitrogen and carbon monoxide,

[0048] or a mixture of ammonia and nitrogen,

[0049] Or, one of the mixed gases of ammonia, nitrogen, hydrogen and carbon monoxide.

[0050] More preferably, the nitrogen-containing reducing atmosphere in (2) is ammonia.

[0051] More preferably, the nitrogen-containing reducing atmosphere in (2) is a mixed gas of nitrogen and hydrogen in a volume ratio of (75-95): (25-9).

[0052] More preferably, the nitrogen-containing reducing atmosphere in (2) is 95 vol% N2 / 5 vol% H2.

[0053] Preferably, the gas flow rate of the nitrogen-containing reducing atmosphere in (2) is 10 to 1000 mL / min.

[0054] More preferably, the gas flow rate of the nitrogen-containing reducing atmosphere in (2) is 50 to 200 mL / min.

[0055] Preferably, the pretreatment temperature in (2) is 700-1150° C., the first heating rate is 1-20° C. / min, and the time is 1-10 h.

[0056] More preferably, the pretreatment temperature in (2) is 800-1000° C., the first heating rate is 2-10° C. / min, and the time is 2-5 h.

[0057] Preferably, the gas used for the nitriding treatment in (2) is a mixed gas of nitrogen and hydrogen, wherein the volume ratio of nitrogen to hydrogen is (75-95): (25-5).

[0058] More preferably, the gas used for the nitriding treatment is 95 vol% N2 / 5 vol% H2.

[0059] Preferably, the nitriding treatment temperature in (2) is 1400-1550° C., the second heating rate is 1-10° C. / min, and the time is 1-10 h.

[0060] More preferably, the nitriding treatment temperature in (2) is 1420-1490° C., the second heating rate is 1-5° C. / min, and the time is 4-8 h.

[0061] More preferably, the first heating rate is greater than the second heating rate.

[0062] Preferably, the silicon nitride body in (2) has a porous structure and is mainly composed of equiaxed crystals, with the content of α-Si3N4 being 68-98% and the content of lattice oxygen being less than 0.4%.

[0063] Preferably, the silicon nitride body in (2) comprises intergranular secondary phase Y4Si2O7N2.

[0064] Preferably, the nitriding rate of the silicon nitride body in (2) is greater than 95%.

[0065] Further preferably, the nitriding rate of the silicon nitride body in (2) is greater than 97%.

[0066] Preferably, the relative density of the silicon nitride body in (2) is 65-72%.

[0067] Further preferably, the relative density of the silicon nitride body in (2) is 68-70%.

[0068] Preferably, the inert atmosphere in (3) is one or more of nitrogen, helium and argon.

[0069] Preferably, the sintering in (3) comprises one or more of gas pressure sintering, hot-press sintering, hot isostatic sintering, pressureless sintering, vacuum sintering, microwave sintering, spark plasma sintering or laser sintering.

[0070] Preferably, the sintering in (3) is gas pressure sintering.

[0071] Further preferably, the gas pressure sintering process is performed by embedding the silicon nitride body in BN powder.

[0072] Further preferably, the gas pressure sintering in (3) is performed at a temperature of 1850-2000°C, a third heating rate of 1-20°C / min, a time of 1-24h and a gas pressure of 0.1-2MPa.

[0073] Further preferably, the gas pressure sintering in (3) is performed at a temperature of 1860-1960°C, a third heating rate of 8-12°C / min, a time of 6-16h and a gas pressure of 0.6-1.2MPa.

[0074] Further preferably, the third heating rate is greater than the first heating rate, which is greater than the second heating rate.

[0075] Preferably, the volume density of the silicon nitride ceramic in (3) is 2.9-3.3g / cm 3 .

[0076] Preferably, the relative density of the silicon nitride ceramic in (3) is greater than 98%.

[0077] Preferably, the lattice oxygen content of the silicon nitride ceramic in (3) is < 0.07%.

[0078] Preferably, the proportion of β-Si3N4 in the silicon nitride ceramic in (3) is 100%.

[0079] Preferably, the thermal conductivity of the silicon nitride ceramic in (3) is > 100 W / (m·K).

[0080] Further preferably, the thermal conductivity of the silicon nitride ceramic in (3) is 120-130 W / (m·K).

[0081] The second object of the present application is achieved by the following technical solution:

[0082] A high-thermal-conductivity silicon nitride ceramic prepared by the above preparation method.

[0083] Preferably, the high-thermal-conductivity silicon nitride ceramic includes a grain boundary second phase Y2Si3O3N4.

[0084] Preferably, the bulk density of the high-thermal-conductivity silicon nitride ceramic is 2.9-3.3 g / cm 3 , and the relative density is > 98%.

[0085] Preferably, the lattice oxygen content of the high-thermal-conductivity silicon nitride ceramic is < 0.07%.

[0086] Further preferably, the lattice oxygen content of the high-thermal-conductivity silicon nitride ceramic is < 0.05%.

[0087] Preferably, the thermal conductivity of the high-thermal-conductivity silicon nitride ceramic is > 100 W / (m·K).

[0088] Further preferably, the thermal conductivity of the high-thermal-conductivity silicon nitride ceramic is > 110 W / (m·K).

[0089] Still further preferably, the thermal conductivity of the high-thermal-conductivity silicon nitride ceramic is 120-130 W / (m·K).

[0090] Preferably, the fracture toughness of the high-thermal-conductivity silicon nitride ceramic is > 8.3 MPa·m 1 / 2 .

[0091] Further preferably, the fracture toughness of the high-thermal-conductivity silicon nitride ceramic is > 8.6 MPa·m 1 / 2 .

[0092] The third object of the present application is achieved by the following technical solution:

[0093] Application of a high-thermal-conductivity silicon nitride ceramic in the fields of semiconductor devices, aerospace, and high-end manufacturing technology.

[0094] Compared with the prior art, the present application has the following beneficial effects:

[0095] 1、The present application uses silicon powder as raw material, and prepares silicon nitride blank through nitriding reaction, and then sintering into silicon nitride ceramic; the present application adds a pretreatment step before nitriding reaction, which effectively eliminates the silicon dioxide impurities wrapped on the surface of silicon powder through reduction of nitrogen-containing reducing atmosphere, reduces the oxygen content in liquid phase without reducing the total content of sintering aids, reduces the probability of oxygen solid solution into silicon nitride lattice and forming lattice oxygen defects, so that it is easier to prepare silicon nitride blank with low lattice oxygen content, and increases the glass transition temperature of sintering aids forming liquid phase in the sintering process, improves the crystallinity of grain boundary phase, thereby improving the thermal conductivity of silicon nitride ceramic.

[0096] 2、The present application forms α-Si3N4 nucleus in situ on the surface of silicon powder through nitriding, effectively improves the content of α-Si3N4 phase in the silicon nitride blank after nitriding, improves the sintering activity, and makes it easier to densify in the gas pressure sintering process; at the same time, in the subsequent sintering process, more α-Si3N4 is caused to change phase through dissolution-precipitation process to generate β-Si3N4 with higher aspect ratio and more quantity, release lattice oxygen, reduce the content of grain boundary phase, and form a continuous thermal conduction network, optimize the transmission path of phonons, reduce scattering at the grain boundary, thereby improving the thermal conductivity of the material.

[0097] 3、The temperature of the pretreatment step of the present application is 600-1180℃, while silicon powder usually starts to nitride at 1200℃ or above, and it is difficult to effectively remove oxygen at too high temperature; and ammonia usually decomposes at 800-1200℃, and at too low temperature, the reaction activity of silicon dioxide on the surface of silicon powder is low, and it is difficult for ammonia to react with it; ammonia is basically completely decomposed into nitrogen and hydrogen at 1200℃ or above, and the hydrogen content is as high as 75vol%; if the temperature continues to rise, there is a large amount of reducing hydrogen in the atmosphere, and the nitrogen content is only 25vol%, which will lead to insufficient nitriding reaction and difficult to form pure silicon nitride blank.

[0098] 4、The present application selects two kinds of rare earth metal oxides as sintering aids, compared with the traditional single rare earth metal oxide matched with alkaline earth metal oxide as sintering aids, there is no reduction reaction between the aids and ammonia, the stability of the aids is higher, and the silicon powder can be deoxidized and nitrided without reducing the total amount of sintering aids, which is beneficial to the densification and grain growth of the ceramic, thereby improving the thermal conductivity.

[0099] 5. The present invention uses silicon powder as raw material. Compared with directly using silicon nitride as raw material, high-purity silicon powder is cheaper, and the cost of preparing high thermal conductivity silicon nitride ceramics using silicon powder as raw material is lower; secondly, the silicon nitride ceramics prepared by reaction sintering using silicon powder as raw material have a lower shrinkage rate, and are easy to achieve near-net forming of complex shapes. In addition, the prepared silicon nitride ceramics have higher thermal conductivity and better comprehensive mechanical properties.

[0100] 6. After the pretreatment step is completed, the present invention directly replaces the reaction atmosphere and slowly raises the temperature to 1350-1700°C for nitriding treatment, which promotes the full nitriding reaction, reduces defects in grain boundaries and grains, makes the structure at the grain boundaries denser, the grains purer, and reduces thermal conductivity loss; and has good process continuity, further improving the nitriding effect and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Figure 1 The figure is a process flow chart for preparing high thermal conductivity silicon nitride ceramics in the present invention.

[0102] Figure 2 This is the XRD pattern of the silicon nitride body in Example 7 of the present invention.

[0103] Figure 3 This is the XRD pattern of the silicon nitride body in Comparative Example 2 of the present invention.

[0104] Figure 4 This is an SEM image of the fracture of the silicon nitride body in Example 7 of the present invention.

[0105] Figure 5 This is an SEM image of the fracture of the silicon nitride body in Comparative Example 2 of the present invention.

[0106] Figure 6 This is the XRD pattern of the silicon nitride ceramic in Example 7 of the present invention.

[0107] Figure 7 This is the XRD pattern of the silicon nitride ceramic in Comparative Example 2 of the present invention.

[0108] Figure 8 This is an SEM image of the silicon nitride ceramic in Example 7 of the present invention.

[0109] Figure 9 This is an SEM image of the silicon nitride ceramic in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0110] The technical solutions of the present invention are further described below through specific embodiments. It should be understood that the specific embodiments described herein are only used to help understand the present invention and are not used to specifically limit the present invention.

[0111] If no special description, the raw materials used in the examples of the present application are all the raw materials commonly used in the art, and the methods used in the examples are all the conventional methods in the art.

[0112] In this paper, the smaller the particle size of the silicon powder used in the preparation of silicon nitride ceramic by reaction sintering, the higher the sintering activity, but the high oxygen content on the surface of the small particle size silicon powder affects the nitriding process in the reaction sintering and the performance of the subsequent silicon nitride ceramic; the preparation method of the high thermal conductivity silicon nitride ceramic of the present application realizes the low oxygen content control of the nano-silicon powder and the sub-micron silicon powder, thereby reducing the lattice oxygen content of the silicon nitride ceramic.

[0113] In this paper, the flow chart of the preparation method of the high thermal conductivity silicon nitride ceramic of the present application is as shown in Figure 1 , which comprises:

[0114] (1) The silicon powder and the sintering aid are weighed according to the proportion and uniformly mixed to obtain a mixed powder, and the mixed powder is pressed to form a silicon blank;

[0115] The molar ratio of the silicon powder and the sintering aid is (92.0-99.9):(8.0-0.1);

[0116] The sintering aid is a rare earth metal oxide; the rare earth metal oxide includes one or more of yttrium oxide Y2O3, scandium oxide Sc2O3, ytterbium oxide Yb2O3, lutetium oxide Lu2O3, lanthanum oxide La2O3, cerium oxide Ce2O3, praseodymium oxide Pr2O3, neodymium oxide Nd2O3, promethium oxide Pm2O3, samarium oxide Sm2O3, europium oxide Eu2O3, gadolinium oxide Gd2O3, terbium oxide Tb2O3, dysprosium oxide Dy2O3, holmium oxide Ho2O3, erbium oxide Er2O3, thulium oxide Tm2O3;

[0117] The average particle size of the mixed powder is 0.1-10 μm;

[0118] The pressing forming is dry pressing and / or cold isostatic pressing forming;

[0119] The dry pressing pressure is 10-30 MPa;

[0120] The cold isostatic pressing pressure is 100-300 MPa.

[0121] (2) The silicon blank is placed in a nitrogen-containing reducing atmosphere environment, and after the pretreatment at 600-1200℃, the nitriding treatment is carried out at 1350-1700℃ to obtain a silicon nitride blank;

[0122] The nitrogen-containing reducing atmosphere is ammonia,

[0123] or a mixed gas of nitrogen and hydrogen,

[0124] or, a mixed gas of nitrogen and carbon monoxide,

[0125] or, a mixed gas of ammonia and nitrogen,

[0126] or, one of a mixed gas of ammonia, nitrogen, hydrogen and carbon monoxide;

[0127] The pretreatment includes pre-deoxidation and pre-nitridation, both of which are performed synchronously.

[0128] The pretreatment temperature is 700-1150℃, the first temperature rising rate is 1-20℃ / min, and the time is 1-10h.

[0129] The gas for the nitridation treatment is a mixed gas of nitrogen and hydrogen, wherein the volume ratio of nitrogen to hydrogen is (75-95):(25-5).

[0130] The nitridation treatment temperature is 1400-1550℃, the second temperature rising rate is 1-10℃ / min, and the time is 1-10h.

[0131] The silicon nitride blank is of a porous structure and mainly composed of equiaxed crystals.

[0132] The proportion of α-Si3N4 in the silicon nitride blank is 68-98%, and the lattice oxygen content is <0.4%.

[0133] The nitridation rate of the silicon nitride blank is >95%.

[0134] The relative density of the silicon nitride blank is 65-72%.

[0135] (3) placing the silicon nitride blank in an inert atmosphere and sintering at 1800-2200℃ to obtain a silicon nitride ceramic.

[0136] The sintering includes one or more of gas pressure sintering, hot-press sintering, hot isostatic pressing sintering, pressureless sintering, vacuum sintering, microwave sintering, discharge plasma sintering and laser sintering.

[0137] The sintering is gas pressure sintering, and the gas pressure sintering process is performed by embedding the silicon nitride blank in BN powder.

[0138] The temperature for the gas pressure sintering is 1850-2000℃, the third temperature rising rate is 1-20℃ / min, the time is 1-24h, and the gas pressure is 0.1-2MPa.

[0139] Then, the performance of the high-thermal-conductivity silicon nitride ceramic is characterized.

[0140] In this article, the bulk density of the high-thermal-conductivity silicon nitride ceramic of the present application is 2.9-3.3g / cm 3 ;

[0141] The high-thermal-conductivity silicon nitride ceramic has a relative density of > 98%;

[0142] The high-thermal-conductivity silicon nitride ceramic has a lattice oxygen content of < 0.07%;

[0143] The high-thermal-conductivity silicon nitride ceramic has a beta-Si3N4 content of 100%;

[0144] The high-thermal-conductivity silicon nitride ceramic has a thermal conductivity of > 100 W / (m·K);

[0145] The high-thermal-conductivity silicon nitride ceramic has a fracture toughness of > 8.3 MPa·m 1 / 2 .

[0146] In the present application, dry pressing is adopted without the need to add a binder and the need to remove glue and the like, and if a binder is introduced and a glue removal process is introduced, residual carbon will be left on the sample after glue removal, which is not conducive to the sintering densification of the sample and reduces the insulation performance thereof; the present application directly adopts dry pressing, and the process flow is simple and the preparation period is short.

[0147] Example 1

[0148] (1) 20.16 g of silicon powder (92.6 wt%), 0.565 g of yttrium oxide (2.6 wt%) and 1.035 g of scandium oxide (4.8 wt%) are taken as raw material powder, anhydrous ethanol is taken as solvent, and the mixture is placed in a ball mill tank for ball milling for 12 h, the ball-to-material ratio is 10:1, and after ball milling, the mixture is dried and sieved to obtain mixed powder with an average particle size of 0.8 μm, 2 g of the mixed powder (the molar ratio of silicon powder, yttrium oxide and scandium oxide is 288:1:3) is dry-pressed at 20 MPa, and then cold isostatic pressing is performed at 200 MPa to obtain a silicon blank.

[0149] (2) The silicon blank is placed in a tube furnace with flowing ammonia, and heated to 700℃ at a heating rate of 5℃ / min, and after holding for 2 h, the flowing gas atmosphere is switched to a nitrogen-hydrogen mixed gas (95vol% N2 / 5vol% H2), and nitriding is performed at a heating rate of 3℃ / min to 1450℃ for 6 h to obtain a silicon nitride blank, and the properties thereof are shown in Table 1.

[0150] (3) The obtained ceramic blank is buried in powder (BN powder) and placed in a gas pressure sintering furnace, the gas pressure is 0.9 MPa (nitrogen atmosphere), the temperature is raised to 1900℃ at a rate of 10℃ / min, and the sample is held for 12 h, and then the furnace is cooled to room temperature to obtain a silicon nitride ceramic, and the properties thereof are shown in Table 1.

[0151] Example 2

[0152] (1) The same as step (1) in Example 1;

[0153] (2) The silicon body was placed in a tube furnace with flowing ammonia gas, and heated to 800°C at a heating rate of 5°C / min. After holding for 2 h, the flowing gas was switched to a nitrogen-hydrogen mixed gas (95 vol% N2 / 5 vol% H2), and heated to 1450°C at a heating rate of 3°C / min. Nitriding was carried out for 6 h to obtain a nitrided silicon body.

[0154] (3) The same as step (3) in Example 1.

[0155] The properties of the nitrided silicon body and the nitrided silicon ceramic obtained in this example are shown in Table 1.

[0156] Example 3

[0157] (1) The same as step (1) in Example 1;

[0158] (2) The silicon body was placed in a tube furnace with flowing ammonia gas, and heated to 900°C at a heating rate of 5°C / min. After holding for 2 h, the flowing gas was switched to a nitrogen-hydrogen mixed gas (95 vol% N2 / 5 vol% H2), and heated to 1450°C at a heating rate of 3°C / min. Nitriding was carried out for 6 h to obtain a nitrided silicon body.

[0159] (3) The same as step (3) in Example 1.

[0160] The properties of the nitrided silicon body and the nitrided silicon ceramic obtained in this example are shown in Table 1.

[0161] Example 4

[0162] (1) The same as step (1) in Example 1;

[0163] (2) The silicon body was placed in a tube furnace with flowing ammonia gas, and heated to 1000°C at a heating rate of 5°C / min. After holding for 2 h, the flowing gas was switched to a nitrogen-hydrogen mixed gas (95 vol% N2 / 5 vol% H2), and heated to 1450°C at a heating rate of 3°C / min. Nitriding was carried out for 6 h to obtain a nitrided silicon body.

[0164] (3) The same as step (3) in Example 1.

[0165] The properties of the nitrided silicon body and the nitrided silicon ceramic obtained in this example are shown in Table 1.

[0166] Example 5

[0167] (1) The same as step (1) in Example 1;

[0168] (2) Place the silicon blank in a tubular furnace with flowing ammonia, heat it to 1200°C at a heating rate of 5°C / min, keep it warm for 2 hours, switch the flowing atmosphere to a nitrogen-hydrogen mixture (95 vol% N2 / 5 vol% H2), heat it to 1450°C at a heating rate of 3°C / min, and nitride it for 6 hours to obtain a silicon nitride blank.

[0169] (3) The same as step (3) in Example 1.

[0170] The properties of the silicon nitride body and silicon nitride ceramic obtained in this example are shown in Table 1.

[0171] Example 6

[0172] (1) The same as step (1) in Example 1;

[0173] (2) The silicon blank was placed in a tubular furnace with flowing ammonia gas, and the temperature was raised to 900°C at a heating rate of 5°C / min. After keeping warm for 1 hour, the flowing atmosphere was switched to a nitrogen-hydrogen mixture (95 vol% N2 / 5 vol% H2), and the temperature was raised to 1450°C at a heating rate of 3°C / min and nitrided for 6 hours to obtain a silicon nitride blank.

[0174] (3) The same as step (3) in Example 1.

[0175] The properties of the silicon nitride body and silicon nitride ceramic obtained in this example are shown in Table 1.

[0176] Example 7

[0177] (1) The same as step (1) in Example 1;

[0178] (2) The silicon blank was placed in a tubular furnace with flowing ammonia, and the temperature was raised to 900°C at a heating rate of 5°C / min. After keeping warm for 4 hours, the flowing atmosphere was switched to a nitrogen-hydrogen mixture (95 vol% N2 / 5 vol% H2), and the temperature was raised to 1450°C at a heating rate of 3°C / min and nitrided for 6 hours to obtain a silicon nitride blank.

[0179] (3) The same as step (3) in Example 1.

[0180] The properties of the silicon nitride body and silicon nitride ceramic obtained in this example are shown in Table 1.

[0181] Example 8

[0182] (1) The same as step (1) in Example 1;

[0183] (2) The silicon blank was placed in a tube furnace with flowing 95 vol% N2 / 5 vol% H2, and heated to 900°C at a heating rate of 5°C / min. After holding for 4 h, the flowing atmosphere was switched to nitrogen-hydrogen mixed gas (95 vol% N2 / 5 vol% H2), and heated to 1450°C at a heating rate of 3°C / min. Nitriding was carried out for 6 h to obtain a nitrided silicon blank.

[0184] (3) The same as step (3) in Example 1.

[0185] The properties of the nitrided silicon blank and the nitrided silicon ceramic obtained in this example are shown in Table 1.

[0186] Example 9

[0187] (1) The same as step (1) in Example 1;

[0188] (2) The silicon blank was placed in a tube furnace with flowing 75 vol% N2 / 25 vol% H2, and heated to 900°C at a heating rate of 5°C / min. After holding for 4 h, the flowing atmosphere was switched to nitrogen-hydrogen mixed gas (95 vol% N2 / 5 vol% H2), and heated to 1450°C at a heating rate of 3°C / min. Nitriding was carried out for 6 h to obtain a nitrided silicon blank.

[0189] (3) The same as step (3) in Example 1.

[0190] The properties of the nitrided silicon blank and the nitrided silicon ceramic obtained in this example are shown in Table 1.

[0191] Example 10

[0192] (1) 24.496 g of silicon powder (96.2 wt%), 0.339 g of yttrium oxide (1.3 wt%), and 0.621 g of scandium oxide (2.5 wt%) were taken as raw material powders, and anhydrous ethanol was taken as a solvent. The mixture was placed in a ball mill pot and ball-milled for 12 h at a ball-to-material ratio of 10:1. 2 g of the dried and sieved mixed powders (the molar ratio of silicon powder, yttrium oxide, and scandium oxide was 576:1:3) were dry-pressed at 20 MPa, and then cold isostatic pressed at 200 MPa to obtain a silicon blank.

[0193] (2) The same as step (2) in Example 7.

[0194] (3) The same as step (3) in Example 1.

[0195] The properties of the nitrided silicon blank and the nitrided silicon ceramic obtained in this example are shown in Table 1.

[0196] Example 11

[0197] (1) 20.16 g of silicon powder (90.0 wt%), 2.26 g of yttrium oxide as raw material powder, and anhydrous ethanol as solvent were placed in a ball mill pot, and ball milling was performed for 12 h at a ball-to-powder ratio of 10:1. After the ball milling, the mixture was dried and sieved to obtain a mixed powder having an average particle size of 0.8 μm. 2 g of the mixed powder (molar ratio of silicon powder to yttrium oxide: 288:4) was dry-pressed at 20 MPa, and then cold isostatic pressing was performed at 200 MPa to obtain a silicon compact.

[0198] (2) The same as step (2) in Example 2.

[0199] (3) The same as step (3) in Example 1.

[0200] The properties of the silicon nitride compact and the silicon nitride ceramic obtained in this example are shown in Table 1.

[0201] Example 12

[0202] (1) 20.16 g of silicon powder (91.6 wt%), 0.81 g of lanthanum oxide, and 1.03 g of scandium oxide as raw material powder, and anhydrous ethanol as solvent were placed in a ball mill pot, and ball milling was performed for 12 h at a ball-to-powder ratio of 10:1. After the ball milling, the mixture was dried and sieved to obtain a mixed powder having an average particle size of 0.4 μm. 2 g of the mixed powder (molar ratio of silicon powder to lanthanum oxide to scandium oxide: 288:1:3) was dry-pressed at 20 MPa, and then cold isostatic pressing was performed at 200 MPa to obtain a silicon compact.

[0203] (2) The silicon compact was placed in a tube furnace in which flowing ammonia gas was supplied, and the temperature was raised to 800°C at a rate of 5°C / min. After maintaining the temperature for 2 h, the flowing gas atmosphere was switched to a nitrogen-hydrogen mixed gas (95 vol% N2 / 5 vol% H2), and the temperature was raised to 1470°C at a rate of 3°C / min. Nitriding was performed for 6 h to obtain a silicon nitride compact.

[0204] (3) The same as step (3) in Example 1.

[0205] The properties of the silicon nitride compact and the silicon nitride ceramic obtained in this example are shown in Table 1.

[0206] Example 13

[0207] (1) 20.16 g of silicon powder (84.1 wt%), 0.81 g of lanthanum oxide, and 2.98 g of lutetium oxide as raw material powder, and anhydrous ethanol as solvent were placed in a ball mill pot, and ball milling was performed for 12 h at a ball-to-powder ratio of 10:1. After the ball milling, the mixture was dried and sieved to obtain a mixed powder having an average particle size of 0.8 μm. 2 g of the mixed powder (molar ratio of silicon powder to lanthanum oxide to lutetium oxide: 288:1:3) was dry-pressed at 20 MPa, and then cold isostatic pressing was performed at 200 MPa to obtain a silicon compact.

[0208] (2) The silicon blank was placed in a tubular furnace with flowing ammonia gas, and the temperature was raised to 800°C at a heating rate of 5°C / min. After keeping warm for 2 hours, the flowing atmosphere was switched to a nitrogen-hydrogen mixture (95 vol% N2 / 5 vol% H2), and the temperature was raised to 1430°C at a heating rate of 3°C / min for nitriding for 6 hours to obtain a silicon nitride blank.

[0209] (3) The same as step (3) in Example 1.

[0210] The properties of the silicon nitride body and silicon nitride ceramic obtained in this example are shown in Table 1.

[0211] Example 14

[0212] (1) 19.53 g of silicon powder (92.3 wt%), 1.13 g of yttrium oxide, and 0.5 g of magnesium oxide were used as raw material powders and anhydrous ethanol was used as solvent. The mixture was placed in a ball mill and ball milled for 12 h with a ball-to-material ratio of 10:1. After ball milling, the mixture was dried and sieved to obtain a mixed powder with an average particle size of 0.8 μm. 2 g of the mixed powder (the molar ratio of silicon powder, yttrium oxide, and magnesium oxide was 279:2:5) was dry pressed at 20 MPa and then cold isostatically pressed at 200 MPa to obtain a silicon blank.

[0213] (2) The same as step (2) in Example 2.

[0214] (3) The same as step (3) in Example 1.

[0215] The properties of the silicon nitride body and silicon nitride ceramic obtained in this comparative example are shown in Table 1.

[0216] Comparative Example 1

[0217] (1) 19.53 g of silicon powder (92.3 wt%), 1.13 g of yttrium oxide, and 0.5 g of magnesium oxide were used as raw material powders and anhydrous ethanol was used as solvent. They were placed in a ball mill and ball milled for 12 h with a ball-to-material ratio of 10:1. After ball milling, they were dried and sieved to obtain a mixed powder with an average particle size of 0.8 μm. 2 g of the mixed powder (the molar ratio of silicon powder, yttrium oxide, and magnesium oxide was 279:2:5) was dry pressed at 20 MPa and then cold isostatically pressed at 200 MPa to obtain a silicon blank.

[0218] (2) The silicon blank was placed in a tubular furnace with a flowing nitrogen-hydrogen mixture (95 vol% N2 / 5 vol% H2), and the temperature was raised to 1450°C at a heating rate of 3°C / min for nitriding for 6 hours to obtain a silicon nitride blank.

[0219] (3) The same as step (3) in Example 1.

[0220] The properties of the silicon nitride body and silicon nitride ceramic obtained in this comparative example are shown in Table 1.

[0221] Comparative Example 2

[0222] (1) The same as step (1) in Example 2.

[0223] (2) The same as step (2) in Comparative Example 1.

[0224] (3) The same as step (3) in Example 1.

[0225] The properties of the silicon nitride compact and the silicon nitride ceramic obtained in this comparative example are shown in Table 1.

[0226] Comparative Example 3

[0227] (1) The same as step (1) in Example 10.

[0228] (2) The same as step (2) in Comparative Example 1.

[0229] (3) The same as step (3) in Example 1.

[0230] The properties of the silicon nitride compact and the silicon nitride ceramic obtained in this comparative example are shown in Table 1.

[0231] Comparative Example 4

[0232] (1) Silicon powder was placed in a tube furnace with flowing ammonia gas, and heated to 800°C at a heating rate of 5°C / min, and held for 2 h to obtain pretreated silicon powder.

[0233] (2) The pretreated silicon powder, yttria, and scandia were placed in a ball mill pot as raw material powder, and anhydrous ethanol was used as solvent, and ball-milled for 12 h with a ball-to-material ratio of 10:1. After ball-milling, the mixture was dried and sieved to obtain a mixed powder with an average particle size of 0.8 μm. 2 g of the mixed powder (molar ratio of silicon powder, yttria, and scandia was 288:1:3) was dry-pressed at 20 MPa, and then cold isostatic pressed at 200 MPa to obtain a silicon compact after isostatic pressing.

[0234] (3) The same as step (2) in Comparative Example 1.

[0235] (4) The same as step (3) in Example 1.

[0236] The properties of the silicon nitride compact and the silicon nitride ceramic obtained in this comparative example are shown in Table 1.

[0237] Comparative Example 5

[0238] (1) Yttria and scandia with a molar ratio of 1:3 were placed in a tube furnace with flowing ammonia gas, and heated to 800°C at a heating rate of 5°C / min, and held for 2 h to obtain pretreated sintering aids.

[0239] (2) The silicon powder, the sintering aid after pretreatment as raw material powder, and anhydrous ethanol as solvent were placed in a ball mill pot and ball milled for 12 h with a ball-to-powder ratio of 10:1. After ball milling, the mixture was dried and sieved to obtain a mixed powder with an average particle size of 0.8 μm. 2 g of the mixed powder (molar ratio of silicon powder, yttria, scandia was 288:1:3) was dry-pressed at 20 MPa, followed by cold isostatic pressing at 200 MPa to obtain a silicon compact.

[0240] (3) The same as step (2) in Comparative Example 1.

[0241] (4) The same as step (3) in Example 1.

[0242] The properties of the silicon nitride compact and the silicon nitride ceramic obtained in this comparative example are shown in Table 1.

[0243] Comparative Example 6

[0244] (1) The same as step (1) in Example 1.

[0245] (2) The silicon compact was placed in a tube furnace with flowing hydrogen, and heated to 800°C at a heating rate of 5°C / min. After holding for 2 h, the flowing gas was switched to a nitrogen-hydrogen mixed gas (95 vol% N2 / 5 vol% H2), and heated to 1450°C at a heating rate of 3°C / min. Nitriding was carried out for 6 h to obtain a silicon nitride compact.

[0246] (3) The same as step (3) in Example 1.

[0247] The properties of the silicon nitride compact and the silicon nitride ceramic obtained in this comparative example are shown in Table 1.

[0248] Comparative Example 7

[0249] (1) The same as step (1) in Example 1.

[0250] (2) The silicon compact was placed in a tube furnace with flowing nitrogen, and heated to 800°C at a heating rate of 5°C / min. After holding for 2 h, the flowing gas was switched to a nitrogen-hydrogen mixed gas (95 vol% N2 / 5 vol% H2), and heated to 1450°C at a heating rate of 3°C / min. Nitriding was carried out for 6 h to obtain a silicon nitride compact.

[0251] (3) The same as step (3) in Example 1.

[0252] The properties of the silicon nitride compact and the silicon nitride ceramic obtained in this comparative example are shown in Table 1.

[0253] Comparative Example 8

[0254] (1) The same as step (1) in Example 12.

[0255] (2) The same as step (2) in Comparative Example 1.

[0256] (3) The same as step (3) in Example 1.

[0257] The properties of the silicon nitride blank and the silicon nitride ceramic obtained in the present comparative example are shown in Table 1.

[0258] Comparative Example 9

[0259] (1) The same as step (1) in Example 11.

[0260] (2) The same as step (2) in Comparative Example 1.

[0261] (3) The same as step (3) in Example 1.

[0262] The properties of the silicon nitride blank and the silicon nitride ceramic obtained in the present comparative example are shown in Table 1.

[0263] Table 1, Properties of silicon nitride blank and silicon nitride ceramic

[0264]

[0265] According to Table 1, the silicon nitride blank prepared in the present application has a high nitriding rate (> 95%) and a low lattice oxygen content; the silicon nitride ceramic prepared in the present application has good density and high thermal conductivity.

[0266] According to Figures 2 to 5 It can be seen that after ammonia gas deoxidization and nitriding treatment, the peak area corresponding to α-Si3N4 in the silicon nitride blank increases significantly, and the proportion increases significantly, which can reach 79.4%; and at this stage, a low proportion of intergranular secondary phase (Y4Si2O7N2, equivalent to 4Y2O3: SiO2: Si3N4) is generated; the silicon nitride blank is mainly composed of equiaxed crystals (α-Si3N4), and a large number of pores are generated.

[0267] According to Figures 6 to 9 It can be seen that after ammonia gas pre-nitriding sintering, a grain boundary secondary phase (Y2Si3O3N4, equivalent to Y2O3: Si3N4) without silicon dioxide is generated in the silicon nitride ceramic. As can be seen from the figure, the black area is the silicon nitride substrate particles, and the gray bright area is the grain boundary liquid phase. The silicon nitride ceramic sintered after ammonia gas pre-deoxidization and nitriding has large grain size, less grain boundary liquid phase, and high connectivity between grains.

[0268] In Example 10, the amount of sintering aid is reduced, and the thermal conductivity of the silicon nitride ceramic decreases slightly; in Example 11, the thermal conductivity of the silicon nitride ceramic obtained by using a single sintering aid is lower than that of the silicon nitride ceramic obtained by using two kinds of sintering aids in Example 2.

[0269] The reason for poor thermal conductivity performance in Comparative Example 1 is that: in the ammonia deoxidation nitriding process, the alkali metal oxide will react with ammonia to generate volatile magnesium or other compounds, reducing the total content of the additive, leading to difficulty in densification and grain growth during sintering, and reducing the thermal conductivity; compared with the additive system of yttrium oxide / scandium oxide, the additive system of yttrium oxide combined with magnesium oxide has lower crystallinity of the grain boundary phase of the silicon nitride ceramic prepared, more defects at the grain boundary, and lower thermal conductivity.

[0270] In Comparative Examples 2 and 3, no pretreatment is performed, and direct nitriding treatment is performed, resulting in a high lattice oxygen content of the silicon nitride blank.

[0271] In Comparative Example 6, the silicon nitride blank has a low lattice oxygen content after pretreatment in a pure hydrogen environment, but the thermal conductivity performance of the silicon nitride ceramic is reduced, because a large amount of silicon dioxide is completely eliminated in the pure hydrogen environment, the liquid phase amount is reduced during sintering, the density is reduced, and the thermal conductivity is reduced.

[0272] In Comparative Example 7, the silicon powder is pretreated in a pure nitrogen environment, and only some nitrogen can be adsorbed on the surface of the silicon powder in the pure nitrogen environment, and cannot react to form silicon nitride. Therefore, there is no obvious direct effect after treatment, and the surface of the powder does not change obviously, which is consistent with the untreated sample.

[0273] In summary, the present application prepares a silicon nitride blank by nitriding reaction with silicon powder as raw material, and then sintering into a silicon nitride ceramic; the present application increases a pretreatment step before nitriding reaction, which effectively eliminates the silicon dioxide impurities wrapped on the surface of the silicon powder by reducing the nitrogen-containing reducing atmosphere, reduces the oxygen content in the liquid phase without reducing the total content of the sintering additive, reduces the probability of oxygen solid solution into the silicon nitride lattice and forming lattice oxygen defects, thereby more easily preparing a silicon nitride blank with low lattice oxygen content, and increasing the glass transition temperature of the sintering additive to form a liquid phase during the sintering process, improving the crystallinity of the grain boundary phase, thereby improving the thermal conductivity of the silicon nitride ceramic. The present application forms α-Si3N4 nuclei in situ on the surface of the silicon powder by nitriding the surface of the silicon powder, effectively improves the content of α-Si3N4 phase in the nitrided silicon nitride blank, improves the sintering activity, and makes it easier to densify during gas pressure sintering; at the same time, more α-Si3N4 is generated through the dissolution-precipitation process during the subsequent sintering process, forming more β-Si3N4 with higher aspect ratio, releasing lattice oxygen, reducing the content of the grain boundary phase, and forming a continuous thermal conduction network, optimizing the transmission path of phonons, reducing scattering at the grain boundary, and thereby improving the thermal conductivity of the material.

[0274] Aspects, embodiments, features of the present invention are to be considered illustrative only and not restrictive in all respects. The scope of the present invention is defined solely by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art, and the embodiments are not to be considered limited to the specific embodiments set forth herein, but rather are to be given the full scope of the claims.

[0275] In the preparation method of the present invention, the order of the steps is not limited to the listed order, and for those skilled in the art, the order of the steps can be changed without creative effort, and such changes are within the protection scope of the present invention. In addition, two or more steps or actions can be performed simultaneously.

[0276] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, and it is not necessary or possible to fully describe all embodiments. Any obvious changes or variations derived from the spirit of the present invention are still within the protection scope of the present invention, and any additional limitations are contrary to the spirit of the present invention.

Claims

1. A method for preparing high thermal conductivity silicon nitride ceramics, characterized in that: The preparation method comprises: (1) uniformly mixing silicon powder and a sintering aid to obtain a mixed powder, and pressing the mixed powder to obtain a silicon blank; the sintering aid is a rare earth metal oxide; (2) placing the silicon blank in a nitrogen-containing reducing atmosphere, performing a pretreatment at 600-1180° C., and then heating the silicon blank to 1350-1700° C. for nitriding to obtain a silicon nitride blank; (3) placing the silicon nitride blank in an inert atmosphere and sintering it at 1800-2200° C. to obtain silicon nitride ceramics.

2. The method for preparing high thermal conductivity silicon nitride ceramics according to claim 1, wherein: The molar ratio of silicon powder to sintering aid in (1) is (92.0-99.9): (8.0-0.1).

3. The method for preparing high thermal conductivity silicon nitride ceramics according to claim 1, wherein: The rare earth metal oxides in (1) include one or more of yttrium oxide Y2O3, scandium oxide Sc2O3, ytterbium oxide Yb2O3, lutetium oxide Lu2O3, lanthanum oxide La2O3, cerium oxide Ce2O3, praseodymium oxide Pr2O3, neodymium oxide Nd2O3, promethium oxide Pm2O3, samarium oxide Sm2O3, europium oxide Eu2O3, gadolinium oxide Gd2O3, terbium oxide Tb2O3, dysprosium oxide Dy2O3, holmium oxide Ho2O3, erbium oxide Er2O3, and thulium oxide Tm2O3.

4. The method for preparing high thermal conductivity silicon nitride ceramics according to claim 1, wherein: The sintering aid in (1) comprises a first rare earth metal oxide and a second rare earth metal oxide, and the mass ratio of the first rare earth metal oxide to the second rare earth metal oxide is 1:(1-10).

5. The method for preparing high thermal conductivity silicon nitride ceramics according to claim 1, wherein: The average particle size of the mixed powder in (1) is 0.1 to 10 μm.

6. The method for preparing high thermal conductivity silicon nitride ceramics according to claim 1, wherein: The nitrogen-containing reducing atmosphere in (2) includes one or two of ammonia and nitrogen, or a mixed gas of one or two of ammonia and nitrogen and one or two of hydrogen and carbon monoxide.

7. The method for preparing high thermal conductivity silicon nitride ceramics according to claim 1, characterized in that: The pretreatment temperature in (2) is 700-1150° C., the first heating rate is 1-20° C. / min, and the time is 1-10 h.

8. The method for preparing high thermal conductivity silicon nitride ceramics according to claim 1, characterized in that: The gas used for the nitriding treatment in (2) is a mixed gas of nitrogen and hydrogen, wherein the volume ratio of nitrogen to hydrogen is (75-95): (25-5).

9. The method for preparing high thermal conductivity silicon nitride ceramics according to claim 1, wherein: The nitriding treatment temperature in (2) is 1400-1550° C., the second heating rate is 1-10° C. / min, and the time is 1-10 h.

10. The method for preparing high thermal conductivity silicon nitride ceramics according to claim 1, characterized in that: The silicon nitride blank in (2) is a porous structure, mainly composed of equiaxed crystals, with α-Si3N4 accounting for 68-98% and lattice oxygen content less than 0.4%.

11. The method for preparing high thermal conductivity silicon nitride ceramics according to claim 1, characterized in that: The sintering in (3) includes one or more of gas pressure sintering, hot pressing sintering, hot isostatic pressing sintering, pressureless sintering, vacuum sintering, microwave sintering, spark plasma sintering or laser sintering; the temperature of the gas pressure sintering is 1850-2000°C, the third heating rate is 1-20°C / min, the time is 1-24h, and the gas pressure is 0.1-2MPa.

12. A high thermal conductivity silicon nitride ceramic, characterized in that: The high thermal conductivity silicon nitride ceramic is prepared by the preparation method of the high thermal conductivity silicon nitride ceramic according to any one of claims 1 to 11.

13. The high thermal conductivity silicon nitride ceramic according to claim 12, characterized in that: The volume density of the high thermal conductivity silicon nitride ceramic is 2.9 to 3.3 g / cm 3 , relative density>98%.

14. The high thermal conductivity silicon nitride ceramic according to claim 12, characterized in that: The lattice oxygen content of the high thermal conductivity silicon nitride ceramic is less than 0.07%.

15. The high thermal conductivity silicon nitride ceramic according to claim 12, characterized in that: The thermal conductivity of the high thermal conductivity silicon nitride ceramic is greater than 100 W / (m·K).

16. Application of high thermal conductivity silicon nitride ceramics in the fields of semiconductor devices, aerospace and high-end manufacturing technology, characterized in that: The high thermal conductivity silicon nitride ceramic is prepared by the preparation method of the high thermal conductivity silicon nitride ceramic according to any one of claims 1 to 11, or is the high thermal conductivity silicon nitride ceramic according to any one of claims 12 to 15.

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