Low-oxygen-content silicon nitride powder and preparation method thereof, and silicon nitride ceramic and application thereof

Abstract

The invention provides low-oxygen-content silicon nitride powder and a preparation method thereof as well as silicon nitride ceramic and application thereof, and relates to the field of heat conduction materials. The preparation method of the low-oxygen-content silicon nitride powder comprises the following steps: mixing silicon nitride powder and magnesium powder, and reducing to obtain reduced powder; and sequentially carrying out acid washing and neutral washing on the reduced powder to obtain the low-oxygen-content silicon nitride powder. According to the method, SiO2 on the surface of Si3N4 is reduced by adopting magnesium powder, then the reduced powder is subjected to acid pickling to remove MgO in the reduced powder, and finally the reduced powder is washed to be neutral, so that the purpose of reducing the oxygen content of the Si3N4 powder is achieved. Furthermore, the low-oxygen-content silicon nitride powder is mixed with a sintering aid and then sintered, so that the silicon nitride ceramic with high thermal conductivity can be prepared.

Description

Technical Field

[0001] The present invention belongs to the field of thermal conductive materials, and particularly relates to a silicon nitride powder with low oxygen content, a preparation method thereof, a silicon nitride ceramic, and applications thereof. Background Art

[0002] As a key encapsulation material for power semiconductor devices, the ceramic substrate is responsible for both dissipating the heat inside the device to the outside and providing effective mechanical support for the device. The performance of the ceramic substrate determines the working efficiency and service life of the power semiconductor device. Currently, the ceramic substrate material widely used is mainly alumina (Al2O3), whose thermal conductivity is about 20 - 30 W / m·K, flexural strength is about 400 MPa, and fracture toughness is about 3 MPa·m 1 / 2 , and its various performances are difficult to meet the usage requirements of power semiconductor devices, so it is necessary to develop ceramic substrate materials with more excellent performances. To solve the above technical problems, silicon nitride (Si3N4) is used instead of alumina in the prior art. Si3N4 has the advantages of high strength (800 - 1000 MPa), high toughness (6 - 8 MPa·m 1 / 2 ) and high thermal conductivity performance (80 - 120 W / m·K). Therefore, Si3N4 is regarded as an ideal material for preparing ceramic substrates.

[0003] However, since the surface of Si3N4 powder in the prior art will spontaneously oxidize to form a SiO2 film, the oxygen content of Si3N4 powder is higher than 1.5 wt.%. These oxygen impurities will penetrate into the Si3N4 lattice during the sintering process, resulting in phonon scattering, so that the thermal conductivity of Si3N4 ceramic is usually 50 - 60 W / m·K, having the defect of relatively low thermal conductivity. Summary of the Invention

[0004] The purpose of the present invention is to provide a silicon nitride powder with low oxygen content, a preparation method thereof, a silicon nitride ceramic, and applications thereof. The silicon nitride powder with low oxygen content provided by the present invention has a lower oxygen content, and the silicon nitride ceramic prepared by using the silicon nitride powder with low oxygen content of the present invention has a higher thermal conductivity.

[0005] To achieve the purpose of the present invention, the present invention provides the following technical solutions:

[0006] A preparation method of a silicon nitride powder with low oxygen content, comprising the following steps:

[0007] Mix silicon nitride powder and magnesium powder and carry out reduction to obtain a reduced powder;

[0008] Perform pickling and neutral washing on the reduced powder in sequence to obtain the silicon nitride powder with low oxygen content.

[0009] Preferably, the mass ratio of the silicon nitride powder to the magnesium powder is 100:0.5 - 5.

[0010] Preferably, the particle size of the magnesium powder is 0.5 - 1 μm, and the purity > 99.9%; the particle size of the silicon nitride powder is 2 - 0.5 μm.

[0011] Preferably, the reagent for pickling includes one or more of hydrochloric acid, sulfuric acid, and nitric acid; the reagent for neutral washing includes water and / or ethanol.

[0012] Preferably, the temperature for reduction is 600 - 800 °C, and the time is 3 - 5 h.

[0013] The present invention also provides silicon nitride powder with a low oxygen content prepared by the preparation method described in the above technical solution, and the oxygen content is 1.22 - 1.48 wt%.

[0014] The present invention also provides a silicon nitride ceramic, which is prepared by sintering after mixing silicon nitride powder with a low oxygen content and a sintering aid; the silicon nitride powder with a low oxygen content is the silicon nitride powder with a low oxygen content described in the above technical solution; the mass ratio of the silicon nitride powder with a low oxygen content to the sintering aid is 89 - 97:3 - 11.

[0015] Preferably, the sintering aid includes one or more of Y2O3, MgSiN2, YF3, YH2, and MgF2.

[0016] Preferably, the temperature for sintering is 1700 - 1900 °C, and the time is 3 - 12 h.

[0017] The present invention also provides the application of the silicon nitride ceramic described in the above technical solution in power semiconductor devices.

[0018] The present invention provides a method for preparing silicon nitride powder with a low oxygen content, including the following steps: mixing silicon nitride powder and magnesium powder, performing reduction to obtain reduced powder; sequentially pickling and neutrally washing the reduced powder to obtain the silicon nitride powder with a low oxygen content. The present invention reduces SiO2 on the surface of Si3N4 by using magnesium powder for reduction, and then removes MgO in the reduced powder by sequentially pickling and neutrally washing the reduced powder, so as to achieve the purpose of reducing the oxygen content of Si3N4 powder. From the results of the examples of the present invention, it can be seen that the oxygen content in the silicon nitride powder with a low oxygen content is reduced by 5 - 21%, and the thermal conductivity of the silicon nitride ceramic prepared using the silicon nitride powder with a low oxygen content is 90 - 110 W / m·K. In addition, the present invention uses magnesium powder to reduce silicon nitride, the reduction temperature is 600 - 800 °C, and the time is 3 - 5 h, which has the advantages of low energy consumption and high efficiency. Detailed Embodiments

[0019] The present invention provides a method for preparing silicon nitride powder with a low oxygen content, including the following steps:

[0020] Mix silicon nitride powder and magnesium powder, and perform reduction to obtain reduced powder;

[0021] Perform pickling and neutral washing on the reduced powder in sequence to obtain the silicon nitride powder with low oxygen content.

[0022] In the present invention, without special instructions, all preparation raw materials are preferably commercially available products.

[0023] In the present invention, silicon nitride powder and magnesium powder are mixed and reduced to obtain reduced powder. In the present invention, the particle size of the silicon nitride powder is preferably 0.5 - 3 μm, more preferably 0.5 - 2 μm; the purity of the silicon nitride powder is preferably > 99%. In the present invention, the silicon nitride powder preferably includes α - Si3N4 and β - Si3N4, and the content of α - Si3N4 in the silicon nitride powder is preferably > 90 wt.%, more preferably 95 wt.%. In the present invention, the oxygen content of the silicon nitride powder is preferably 1.56 - 2 wt.%. In the present invention, the particle size of the magnesium powder is preferably 0.5 - 1 μm; the purity of the magnesium powder is preferably > 99.9%. In the present invention, the mass ratio of the silicon nitride powder to the magnesium powder is preferably 100:0.5 - 5, more preferably 100:0.83 - 4.17, further preferably 100:1.6 - 3.3, and most preferably 100:2.5.

[0024] In the present invention, silicon nitride powder and magnesium powder are mixed. In the present invention, the mixing is preferably ball - milling mixing, and the ball - milling medium for the ball - milling mixing is preferably silicon nitride grinding balls. In the present invention, the rotation speed of the ball - milling mixing is preferably 100 - 300 r / min, more preferably 200 r / min; the time is preferably 1 - 6 h, more preferably 3 h. In the present invention, the ball - milling mixing is preferably carried out in an inert gas atmosphere, and the inert gas is preferably N2 and / or Ar. After ball - milling and mixing the silicon nitride powder and magnesium powder in the present invention, it is preferred to sequentially dry and screen the obtained mixed powder to obtain the powder to be reduced. In the present invention, the drying is preferably vacuum drying; the aperture of the sieve for screening is preferably 100 - 200 mesh.

[0025] In the present invention, the powder to be reduced is reduced to obtain reduced powder. In the present invention, the reduction is preferably carried out in a sintering furnace, and the sintering furnace is preferably one of a hot - pressing sintering furnace, a gas - pressure sintering furnace, an atmospheric - pressure protective - atmosphere sintering furnace, a microwave - heating sintering furnace, and a tube furnace. In the present invention, the reduction temperature is preferably 550 - 800 °C, more preferably 650 °C; the time is preferably 3 - 5 h, more preferably 5 h. In the present invention, the reduction is preferably carried out in a flowing inert gas atmosphere, and the inert gas is preferably one of argon, nitrogen, and helium, more preferably argon; in the present invention, during the reduction process, magnesium powder can reduce SiO2 on the surface of Si3N4 to generate MgO, and the reaction equation is as shown in Equation I:

[0026] SiO2(s) + Mg(g) → 2MgO(s) + Si(s), Equation I.

[0027] After obtaining the reduced powder, the present invention sequentially subjects the reduced powder to pickling and neutral washing to obtain the silicon nitride powder with low oxygen content. In the present invention, the reagent for pickling preferably includes one or more of hydrochloric acid, sulfuric acid, and nitric acid, more preferably hydrochloric acid. In the present invention, the concentration of the hydrochloric acid is preferably 0.5 - 2 mol / L, more preferably 1 mol / L. In the present invention, the reagent for neutral washing preferably includes one or more of water and ethanol, more preferably water, and further preferably deionized water.

[0028] In the present invention, the pickling method is preferably to immerse the reduced powder in the pickling reagent. In the present invention, the pickling temperature is preferably 40 - 60 °C, more preferably 55 °C, and the time is preferably 2 - 8 h, more preferably 5 h. In the present invention, the neutral washing method is preferably suction filtration washing. The present invention reduces the oxygen content in the silicon nitride powder by pickling the reduced powder to dissolve MgO in the reduced powder. Taking hydrochloric acid as an example, the chemical equation during the pickling process is shown in Equation II:

[0029] 3MgO(s) + HCl(l) → MgCl2(s) + H2O(l), Equation II.

[0030] After the neutral washing in the present invention, it is preferably to vacuum dry the washed powder. In the present invention, the drying temperature is preferably 50 - 80 °C, more preferably 60 °C, and the time is preferably 8 - 24 h, more preferably 12 h.

[0031] In the present invention, the oxygen content of the silicon nitride powder with low oxygen content is preferably 1.22 - 1.48 wt%, more preferably 1.28 - 1.38 wt%, and further preferably 1.34 wt%, 1.35 wt%, 1.36 wt%, or 1.37 wt%.

[0032] The present invention also provides a silicon nitride ceramic, which is prepared by mixing silicon nitride powder with a low oxygen content and a sintering aid and then sintering; the silicon nitride powder with a low oxygen content is the silicon nitride powder with a low oxygen content in the above technical solution; the mass ratio of the silicon nitride powder with a low oxygen content to the sintering aid is 89-97:3-11. In the present invention, the sintering aid preferably includes one or more of Y2O3, MgSiN2, YF3, YH2 and MgF2, more preferably MgSiN2 and Y2O3, and the mass ratio of MgSiN2 to Y2O3 is preferably 3-5:2-4, more preferably 3:2. In the present invention, the particle size of the sintering aid is preferably <3 μm, more preferably 0.5-2 μm; the purity of the sintering aid is preferably >99%.

[0033] In the present invention, the mass ratio of the silicon nitride powder with a low oxygen content to the sintering aid is 89-97:3-11, preferably 94:6.

[0034] The present invention mixes the silicon nitride powder with a low oxygen content and the sintering aid. In the present invention, the mixing method is preferably the same as the above mixing method, which will not be elaborated here. After mixing the silicon nitride powder with a low oxygen content and the sintering aid, the obtained mixed powder is preferably dried and sieved in sequence to obtain the powder to be sintered. In the present invention, the drying is preferably vacuum drying; the aperture of the sieve for sieving is preferably 100-200 meshes.

[0035] The present invention preferably presses the powder to be sintered to obtain a green body to be sintered. In the present invention, the pressing preferably includes first pressing and second pressing in sequence. In the present invention, the pressure of the first pressing is preferably 10-30 MPa, more preferably 20 MPa; the pressure of the second pressing is preferably 150-250 MPa, more preferably 200 MPa. The present invention has no special limitation on the pressing time, and conventional time limitations can be adopted.

[0036] The present invention sinters the green body to be sintered to obtain a silicon nitride ceramic. In the present invention, the sintering temperature is preferably 1750-1900 °C, more preferably 1850 °C; the pressure is preferably 0.5-2 MPa, more preferably 1 MPa; the time is preferably 3-12 h, more preferably 6 h. In the present invention, the sintering is preferably carried out in an inert atmosphere, and the inert atmosphere is preferably one of argon, nitrogen and helium, more preferably nitrogen.

[0037] In the present invention, the lattice oxygen content in the silicon nitride ceramic is preferably 0.041-0.069 wt.%, more preferably 0.045-0.059 wt.%, still more preferably 0.051-0.058 wt.%, and even more preferably 0.054 wt.%, 0.055 wt.% or 0.057 wt.%. In the present invention, the flexural strength of the silicon nitride ceramic is preferably 881.3-935.8 MPa, more preferably 885.6-930.6 MPa, still more preferably 896.7-925.2 MPa, and specifically preferably 897.3 MPa, 898.8 MPa or 902.1 MPa; the fracture toughness of the silicon nitride ceramic is preferably 7.6-8.8 MPa·m 1 / 2 and more preferably 7.7-8.5 MPa·m 1 / 2 and still more preferably 7.9-8.4 MPa·m 1 / 2 and most preferably 8.2-8.3 MPa·m 1 / 2 ; the thermal conductivity of the silicon nitride ceramic is preferably 89.1-113.4 W / m·K, more preferably 92.3-109.4 W / m·K, still more preferably 93.2-100.5 W / m·K, and specifically preferably 95.5 W / m·K, 96.3 W / m·K or 96.8 W / m·K.

[0038] The present invention also provides an application of the silicon nitride ceramic described in the above technical solution in a power semiconductor device.

[0039] To further illustrate the present invention, the low-oxygen-content silicon nitride powder and the silicon nitride ceramic provided by the present invention are described in detail below with reference to embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0040] The parameters of the preparation raw materials used in the following examples and comparative examples of the present invention are as follows:

[0041] Si3N4 powder: particle size is 0.7 μm, purity > 99 wt.%, the content of α-Si3N4 is 93 wt.%, and the oxygen content is 1.56 wt.%;

[0042] Mg powder: particle size is 0.5 μm, purity > 99.9 wt.%;

[0043] Sintering aid: particle size is 0.5 μm.

[0044] Example 1

[0045] Weigh 60 g of Si3N4 powder and 1.5 g of Mg powder and pour them into the ball milling tank, which is a ball milling tank that can be filled with inert gas. Then add the ball milling medium (silicon nitride grinding balls), and ball mill and mix at 200 r / min for 3 h. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced; load the above powder to be reduced into a crucible, put it into a tube furnace and reduce it under an Ar atmosphere at 650 °C for 5 h to obtain the reduced powder;

[0046] Pour the above reduced powder into 250 mL of 1 mol / L hydrochloric acid, and pickle it at 50 °C for 5 h. Then wash the pickled reduced powder with deionized water until it is neutral, and vacuum dry the washed reduced powder at 60 °C for 12 h to obtain the silicon nitride powder with low oxygen content;

[0047] Weigh 50 g of the above silicon nitride powder with low oxygen content and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2) and pour them into the ball milling tank. Then add the ball milling medium (silicon nitride grinding balls), and ball mill and mix at 200 r / min for 3 h. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered; weigh 30 g of the above powder to be sintered and place it in a stainless steel mold Use a bench top press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further compact the green body (200 MPa) to obtain the green body to be sintered; put the above green body to be sintered into a gas pressure sintering furnace and sinter it under an N2 atmosphere at 1 MPa and 1850 °C for 6 h, and then obtain the silicon nitride ceramic after cooling with the furnace.

[0048] Example 2

[0049] Weigh 60 g of Si3N4 powder and 0.5 g of Mg powder and pour them into the ball milling tank, which is a ball milling tank that can be filled with inert gas. Then add the ball milling medium (silicon nitride grinding balls), and ball mill and mix at 200 r / min for 3 h. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced; load the above powder to be reduced into a crucible, put it into a tube furnace and reduce it under an Ar atmosphere at 650 °C for 5 h to obtain the reduced powder;

[0050] Pour the above reduced powder into 250 mL of 1 mol / L hydrochloric acid, and pickle it at 50 °C for 5 h. Then wash the pickled reduced powder with deionized water until it is neutral, and dry the washed reduced powder at 60 °C for 12 h to obtain the silicon nitride powder with low oxygen content;

[0051] Weigh 50 g of the above-mentioned silicon nitride powder with low oxygen content and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2), pour them into a ball milling tank, then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered; Weigh 30 g of the above-mentioned powder to be sintered and place it in a stainless steel mold Use a bench-top tablet press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further densify the green body (200 MPa) to obtain a green body to be sintered; Place the above-mentioned green body to be sintered in a gas pressure sintering furnace and sinter it for 6 h under the conditions of N2 atmosphere, 1 MPa, and 1850 °C. After cooling with the furnace, the silicon nitride ceramic is obtained.

[0052] Example 3

[0053] Weigh 60 g of Si3N4 powder and 1 g of Mg powder and pour them into a ball milling tank. The ball milling tank is a ball milling tank that can be filled with inert gas. Then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced; Load the above-mentioned powder to be reduced into a crucible and place it in a tube furnace to be reduced for 5 h under the conditions of Ar atmosphere and 650 °C to obtain the reduced powder;

[0054] Pour the above-mentioned reduced powder into 250 mL of 1 mol / L hydrochloric acid, pickle it for 5 h under the condition of 50 °C, then wash the pickled reduced powder with deionized water until it is neutral, and vacuum dry the washed reduced powder at 60 °C for 12 h to obtain the silicon nitride powder with low oxygen content;

[0055] Weigh 50 g of the above-mentioned silicon nitride powder with low oxygen content and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2), pour them into a ball milling tank, then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered; Weigh 30 g of the above-mentioned powder to be sintered and place it in a stainless steel mold Use a bench-top tablet press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further densify the green body (200 MPa) to obtain a green body to be sintered; Place the above-mentioned green body to be sintered in a gas pressure sintering furnace and sinter it for 6 h under the conditions of N2 atmosphere, 1 MPa, and 1850 °C. After cooling with the furnace, the silicon nitride ceramic is obtained.

[0056] Example 4

[0057] Weigh 60 g of Si3N4 powder and 2 g of Mg powder and pour them into a ball milling jar, which is a ball milling jar that can be filled with inert gas. Then add ball milling media (silicon nitride grinding balls) and ball mill and mix for 3 h at 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced; load the above powder to be reduced into a crucible, place it in a tube furnace and reduce it for 5 h under Ar atmosphere and at 650 °C to obtain the reduced powder;

[0058] Pour the above reduced powder into 250 mL of 1 mol / L hydrochloric acid, pickle it for 5 h at 50 °C, then wash the pickled reduced powder with deionized water until neutral, and vacuum dry the washed reduced powder for 12 h at 60 °C to obtain silicon nitride powder with low oxygen content;

[0059] Weigh 50 g of the above silicon nitride powder with low oxygen content and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2) and pour them into a ball milling jar. Then add ball milling media (silicon nitride grinding balls) and ball mill and mix for 3 h at 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered; weigh 30 g of the above powder to be sintered and place it in a stainless steel mold Use a bench top press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further densify the green body (200 MPa) to obtain the green body to be sintered; place the above green body to be sintered in a gas pressure sintering furnace and sinter it for 6 h under N2 atmosphere, 1 MPa and 1850 °C, and then obtain the silicon nitride ceramic after cooling with the furnace.

[0060] Example 5

[0061] Weigh 60 g of Si3N4 powder and 2.5 g of Mg powder and pour them into a ball milling jar, which is a ball milling jar that can be filled with inert gas. Then add ball milling media (silicon nitride grinding balls) and ball mill and mix for 3 h at 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced; load the above powder to be reduced into a crucible, place it in a tube furnace and reduce it for 5 h under Ar atmosphere and at 650 °C to obtain the reduced powder;

[0062] Pour the above reduced powder into 250 mL of 1 mol / L hydrochloric acid, pickle it for 5 h at 50 °C, then wash the pickled reduced powder with deionized water until neutral, and vacuum dry the washed reduced powder for 12 h at 60 °C to obtain silicon nitride powder with low oxygen content;

[0063] Weigh 50 g of the above-mentioned silicon nitride powder with low oxygen content and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2), pour them into a ball mill jar, then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered. Weigh 30 g of the above-mentioned powder to be sintered and place it in a stainless steel mold Use a bench-top tablet press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further densify the green body (200 MPa) to obtain a green body to be sintered. Put the above-mentioned green body to be sintered into a gas pressure sintering furnace and sinter it for 6 h under the conditions of N2 atmosphere, 1 MPa, and 1850 °C. After cooling with the furnace, the silicon nitride ceramic is obtained.

[0064] Example 6

[0065] Weigh 60 g of Si3N4 powder and 1.5 g of Mg powder and pour them into a ball mill jar which is a ball mill jar that can be filled with inert gas. Then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced. Load the above-mentioned powder to be reduced into a crucible, put it into a tube furnace and reduce it for 5 h under the conditions of Ar atmosphere and 675 °C to obtain the reduced powder;

[0066] Pour the above-mentioned reduced powder into 250 mL of 1 mol / L hydrochloric acid, pickle it for 5 h under the condition of 50 °C, then wash the pickled reduced powder with deionized water until it is neutral, and vacuum dry the washed reduced powder for 12 h under the condition of 60 °C to obtain the silicon nitride powder with low oxygen content;

[0067] Weigh 50 g of the above-mentioned silicon nitride powder with low oxygen content and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2), pour them into a ball mill jar, then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered. Weigh 30 g of the above-mentioned powder to be sintered and place it in a stainless steel mold Use a bench-top tablet press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further densify the green body (200 MPa) to obtain a green body to be sintered. Put the above-mentioned green body to be sintered into a gas pressure sintering furnace and sinter it for 6 h under the conditions of N2 atmosphere, 1 MPa, and 1850 °C. After cooling with the furnace, the silicon nitride ceramic is obtained.

[0068] Example 7

[0069] Weigh 60 g of Si3N4 powder and 1.5 g of Mg powder and pour them into a ball milling jar, which is a ball milling jar that can be filled with inert gas. Then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h at 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced; load the above powder to be reduced into a crucible, place it in a tubular furnace, and reduce it for 5 h under an Ar atmosphere at 700 °C to obtain the reduced powder;

[0070] Pour the above reduced powder into 250 mL of 1 mol / L hydrochloric acid, and perform acid washing for 5 h at 50 °C. Then wash the acid-washed reduced powder with deionized water until it is neutral, and vacuum dry the washed reduced powder for 12 h at 60 °C to obtain silicon nitride powder with a low oxygen content;

[0071] Weigh 50 g of the above silicon nitride powder with a low oxygen content and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2) and pour them into a ball milling jar. Then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h at 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered; weigh 30 g of the above powder to be sintered and place it in a stainless steel mold Use a bench top press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further densify the green body (200 MPa) to obtain the green body to be sintered; place the above green body to be sintered in a gas pressure sintering furnace, and sinter it for 6 h under an N2 atmosphere at 1 MPa and 1850 °C. After cooling with the furnace, the silicon nitride ceramic is obtained.

[0072] Example 8

[0073] Weigh 60 g of Si3N4 powder and 1.5 g of Mg powder and pour them into a ball milling jar, which is a ball milling jar that can be filled with inert gas. Then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h at 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced; load the above powder to be reduced into a crucible, place it in a tubular furnace, and reduce it for 5 h under an Ar atmosphere at 725 °C to obtain the reduced powder;

[0074] Pour the above reduced powder into 250 mL of 1 mol / L hydrochloric acid, and perform acid washing for 5 h at 50 °C. Then wash the acid-washed reduced powder with deionized water until it is neutral, and vacuum dry the washed reduced powder for 12 h at 60 °C to obtain silicon nitride powder with a low oxygen content;

[0075] Weigh 50 g of the above silicon nitride powder with low oxygen content and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2), pour them into a ball milling tank, then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered. Weigh 30 g of the above powder to be sintered and place it in a stainless steel mold Use a bench-top tablet press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further densify the green body (200 MPa) to obtain the green body to be sintered. Put the above green body to be sintered into a gas pressure sintering furnace and sinter it for 6 h under the conditions of N2 atmosphere, 1 MPa, and 1850 °C. After cooling with the furnace, the silicon nitride ceramic is obtained.

[0076] Example 9

[0077] Weigh 60 g of Si3N4 powder and 1.5 g of Mg powder and pour them into a ball milling tank. The ball milling tank is a ball milling tank that can be filled with inert gas. Then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced. Load the above powder to be reduced into a crucible and place it in a tubular furnace to be reduced for 5 h under the conditions of Ar atmosphere and 750 °C to obtain the reduced powder;

[0078] Pour the above reduced powder into 250 mL of 1 mol / L hydrochloric acid, pickle it for 5 h under the condition of 50 °C, then wash the pickled reduced powder with deionized water until it is neutral, and vacuum dry the washed reduced powder for 12 h under the condition of 60 °C to obtain the silicon nitride powder with low oxygen content;

[0079] Weigh 50 g of the above silicon nitride powder with low oxygen content and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2), pour them into a ball milling tank, then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered. Weigh 30 g of the above powder to be sintered and place it in a stainless steel mold Use a bench-top tablet press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further densify the green body (200 MPa) to obtain the green body to be sintered. Put the above green body to be sintered into a gas pressure sintering furnace and sinter it for 6 h under the conditions of N2 atmosphere, 1 MPa, and 1850 °C. After cooling with the furnace, the silicon nitride ceramic is obtained.

[0080] Comparative Example 1

[0081] Weigh 60 g of Si3N4 powder and pour it into the ball milling tank, which is a ball milling tank that can be filled with inert gas. Then add the ball milling medium (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced; Load the above-mentioned powder to be reduced into a crucible, put it into a tube furnace and reduce it for 5 h under the conditions of Ar atmosphere and 650 °C to obtain the powder to be used;

[0082] Pour the above-mentioned powder to be used into 250 mL of 1 mol / L hydrochloric acid, and carry out acid washing for 5 h under the condition of 50 °C. Then wash the acid-washed reduced powder with deionized water until it is neutral, and vacuum dry the washed reduced powder for 12 h under the condition of 60 °C to obtain the silicon nitride powder to be used;

[0083] Weigh 50 g of the above-mentioned silicon nitride powder and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2) and pour them into the ball milling tank. Then add the ball milling medium (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered; Weigh 30 g of the above-mentioned powder to be sintered and place it in a stainless steel mold Use a bench top press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further densify the green body (200 MPa) to obtain the green body to be sintered; Put the above-mentioned green body to be sintered into a gas pressure sintering furnace and sinter it for 6 h under the conditions of N2 atmosphere, 1 MPa, and 1850 °C. After cooling with the furnace, the silicon nitride ceramic is obtained.

[0084] Comparative Example 2

[0085] Weigh 60 g of Si3N4 powder and pour it into the ball milling tank, which is a ball milling tank that can be filled with inert gas. Then add the ball milling medium (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced; Load the above-mentioned powder to be reduced into a crucible, put it into a tube furnace and reduce it for 5 h under the conditions of Ar atmosphere and 675 °C to obtain the powder to be used;

[0086] Pour the above-mentioned powder to be used into 250 mL of 1 mol / L hydrochloric acid, and carry out acid washing for 5 h under the condition of 50 °C. Then wash the acid-washed reduced powder with deionized water until it is neutral, and vacuum dry the washed reduced powder for 12 h under the condition of 60 °C to obtain the silicon nitride powder to be used;

[0087] Weigh 50 g of the above-mentioned silicon nitride powder to be used and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2), pour them into a ball milling tank, then add ball milling media (silicon nitride grinding balls), and ball mill and mix them at 200 r / min for 3 h. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered. Weigh 30 g of the above-mentioned powder to be sintered and place it in a stainless-steel mold Use a bench-top press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further densify the green body (200 MPa) to obtain a green body to be sintered. Place the above green body to be sintered in a gas-pressure sintering furnace and sinter it for 6 h under the conditions of N2 atmosphere, 1 MPa, and 1850 °C. After cooling with the furnace, the silicon nitride ceramic is obtained.

[0088] Comparative Example 3

[0089] Weigh 60 g of Si3N4 powder and 1.5 g of Mg powder and pour them into a ball milling tank, which is a ball milling tank that can be filled with inert gas. Then add ball milling media (silicon nitride grinding balls), and ball mill and mix them at 200 r / min for 3 h. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced. Load the above powder to be reduced into a crucible and place it in a tubular furnace to be reduced at 700 °C under Ar atmosphere for 5 h to obtain the powder to be used

[0090] Pour the above powder to be used into 250 mL of 1 mol / L hydrochloric acid, carry out acid washing at 50 °C for 5 h, then wash the acid-washed reduced powder with deionized water until it is neutral, and vacuum dry the washed reduced powder at 60 °C for 12 h to obtain the silicon nitride powder to be used

[0091] Weigh 50 g of the above-mentioned silicon nitride powder to be used and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2), pour them into a ball milling tank, then add ball milling media (silicon nitride grinding balls), and ball mill and mix them at 200 r / min for 3 h. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered. Weigh 30 g of the above-mentioned powder to be sintered and place it in a stainless-steel mold Use a bench-top press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further densify the green body (200 MPa) to obtain a green body to be sintered. Place the above green body to be sintered in a gas-pressure sintering furnace and sinter it for 6 h under the conditions of N2 atmosphere, 1 MPa, and 1850 °C. After cooling with the furnace, the silicon nitride ceramic is obtained.

[0092] Comparative Example 4

[0093] Weigh 60 g of Si3N4 powder and pour it into a ball milling jar, which is a ball milling jar that can be filled with inert gas. Then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced; Load the above powder to be reduced into a crucible, put it into a tubular furnace and reduce it for 5 h under the conditions of Ar atmosphere and 725 °C to obtain the powder for use;

[0094] Pour the above powder for use into 250 mL of 1 mol / L hydrochloric acid, and carry out acid washing for 5 h under the condition of 50 °C. Then wash the reduced powder after acid washing with deionized water until it is neutral, and vacuum dry the washed reduced powder for 12 h under the condition of 60 °C to obtain the silicon nitride powder for use;

[0095] Weigh 50 g of the above silicon nitride powder for use and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2), pour them into a ball milling jar, then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered; Weigh 30 g of the above powder to be sintered and place it in a stainless steel mold Use a bench top press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further compact the green body (200 MPa) to obtain the green body to be sintered; Put the above green body to be sintered into a gas pressure sintering furnace, and sinter it for 6 h under the conditions of N2 atmosphere, 1 MPa and 1850 °C. After cooling with the furnace, the silicon nitride ceramic is obtained.

[0096] Comparative Example 5

[0097] Weigh 60 g of Si3N4 powder and pour it into a ball milling jar, which is a ball milling jar that can be filled with inert gas. Then add ball milling media (silicon nitride grinding balls), and ball mill and mix for 3 h under the condition of 200 r / min. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be reduced; Load the above powder to be reduced into a crucible, put it into a tubular furnace and reduce it for 5 h under the conditions of Ar atmosphere and 750 °C to obtain the powder for use;

[0098] Pour the above powder for use into 250 mL of 1 mol / L hydrochloric acid, and carry out acid washing for 5 h under the condition of 50 °C. Then wash the reduced powder after acid washing with deionized water until it is neutral, and vacuum dry the washed reduced powder for 12 h under the condition of 60 °C to obtain the silicon nitride powder for use;

[0099] Weigh 50 g of the above-mentioned silicon nitride powder to be used and 2.5 g of sintering aids (1.5 g of Y2O3 and 1 g of MgSiN2), pour them into a ball milling jar, then add ball milling media (silicon nitride grinding balls), and ball mill and mix them at 200 r / min for 3 h. Vacuum dry the mixed powder, and then sieve it through a 100-mesh sieve to obtain the powder to be sintered. Weigh 30 g of the above-mentioned powder to be sintered and place it in a stainless steel mold Use a bench top press to pre-press the powder to be sintered (20 MPa), and then use a cold isostatic press to further densify the green body (200 MPa) to obtain the green body to be sintered. Place the above-mentioned green body to be sintered into a gas pressure sintering furnace, and sinter it under the conditions of N2 atmosphere, 1 MPa, and 1850 °C for 6 h. After cooling with the furnace, the silicon nitride ceramic is obtained.

[0100] Test examples

[0101] Test the density, thermal diffusivity, fracture toughness, flexural strength, lattice oxygen content of the silicon nitride ceramics prepared in Examples 1-9 and Comparative Examples 1-5, and the oxygen content of the prepared silicon nitride powders (low-oxygen-content silicon nitride powders in Examples 1-9 and silicon nitride powders to be used in Comparative Examples 1-5). The specific test methods are as follows:

[0102] Use the Archimedes drainage method to test the density of the above-mentioned silicon nitride ceramics; use a laser thermal diffusivity meter to test the thermal diffusivity of the silicon nitride ceramics, and the specimen size is The thermal conductivity of the silicon nitride ceramic is calculated by the following formula: k = C p ×ρ×α; where ρ is the density, α is the thermal diffusivity, and C p is the specific heat capacity. The specific heat capacity in the above formula can be regarded as a constant, taking 0.68 J / (g·K).

[0103] Use the single-edge notched beam method to test the fracture toughness of the above-mentioned silicon nitride ceramics, and the specimen size is 3 mm × 6 mm × 36 mm;

[0104] Use a universal testing machine to test the flexural strength of the above-mentioned silicon nitride ceramics, and the specimen size is 3 mm × 4 mm × 36 mm;

[0105] Test method for oxygen content of silicon nitride powder: Take 1 g of the silicon nitride powder to be tested and use an oxygen, nitrogen, and hydrogen analyzer to test the oxygen content;

[0106] Test method for lattice oxygen content in silicon nitride ceramics: Weigh 1 g of silicon nitride ceramics and add 50 mL of methanol, then ball mill for 10 min at 200 r / min using tungsten carbide, and then sieve through a 500-mesh sieve and dry at 60 °C for 12 h. Take the dried silicon nitride ceramic powder and soak it in an HF solution (HF concentration is 60 wt.%) heated in a water bath at 60 °C for 3 h, and then place it in an H2SO4 solution (H2SO4 concentration is 50 wt.%) heated in a water bath at 120 °C for 12 h. Then wash it 3 times with deionized water, dry at 110 °C for 12 h, sieve through a 100-mesh sieve, and finally use an oxygen, nitrogen, and hydrogen analyzer to test the oxygen content in the silicon nitride ceramics.

[0107] Table 1 Performance test results of the silicon nitride ceramics and silicon nitride powders described in Examples 1 - 9 and Comparative Examples 1 - 5

[0108]

[0109] Note: In Table 1, the oxygen content of the silicon nitride powders in Examples 1 - 9 is the oxygen content of the low-oxygen-content silicon nitride powders after magnesiothermic reduction, and the oxygen content of the silicon nitride powders in Comparative Examples 1 - 5 is the oxygen content of the silicon nitride powders to be used; the lattice oxygen content of the silicon nitride ceramics is the lattice oxygen content of the silicon nitride ceramics prepared by pressureless sintering.

[0110] It can be seen from the results in Table 1 that by comparing Example 1 and Comparative Example 1, Example 6 and Comparative Example 2, Example 7 and Comparative Example 3, Example 8 and Comparative Example 4, and Example 9 and Comparative Example 5, using the same process, adding Mg as a reducing agent, and using the magnesiothermic reduction reaction of Mg with SiO2 on the surface of silicon nitride to reduce the oxygen element in SiO2 to MgO, and then using acid washing to dissolve MgO can reduce the oxygen content of the silicon nitride powder; it can be seen from the results in Table 1 that using the low-oxygen-content silicon nitride powder described in the present invention is beneficial to preparing silicon nitride ceramics with more excellent thermal conductivity.

[0111] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all of them. People can also obtain other embodiments without creative efforts based on these embodiments, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A preparation method of silicon nitride powder with low oxygen content, comprising the following steps: Mix silicon nitride powder and magnesium powder, and perform reduction to obtain reduced powder; Perform pickling and neutral washing on the reduced powder in sequence to obtain the silicon nitride powder with low oxygen content.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the silicon nitride powder to the magnesium powder is 100:0.5 - 5.

3. The preparation method according to claim 1 or 2, characterized in that, The particle size of the magnesium powder is 0.5 - 1 μm, and the purity > 99.9%; the particle size of the silicon nitride powder is 2 - 0.5 μm.

4. The preparation method according to claim 1, characterized in that, The reagent for pickling includes one or more of hydrochloric acid, sulfuric acid, and nitric acid; the reagent for neutral washing includes water and / or ethanol.

5. The preparation method according to claim 1, characterized in that, The temperature of the reduction is 600 - 800 °C, and the time is 3 - 5 h.

6. The silicon nitride powder with low oxygen content prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The oxygen content is 1.22 - 1.48 wt%.

7. A silicon nitride ceramic is prepared by mixing silicon nitride powder with low oxygen content and a sintering aid and then performing sintering; the silicon nitride powder with low oxygen content is the silicon nitride powder with low oxygen content as described in claim 6; the mass ratio of the silicon nitride powder with low oxygen content to the sintering aid is 89 - 97:3 - 11.

8. The silicon nitride ceramic according to claim 7, characterized in that, The sintering aid includes one or more of Y2O3, MgSiN2, YF3, YH2, and MgF2.

9. The silicon nitride ceramic according to claim 7, characterized in that, The temperature of the sintering is 1700 - 1900 °C, and the time is 3 - 12 h.

10. The application of the silicon nitride ceramic as described in any one of claims 7 - 9 in a power semiconductor device.

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