Silicon nitride ceramic and preparation method and application thereof

Abstract

The invention discloses silicon nitride ceramic as well as a preparation method and application thereof, and belongs to the technical field of silicon nitride ceramic. The preparation method of the silicon nitride ceramic comprises the following steps: heating a formed silicon nitride biscuit to 180-250 DEG C in vacuum under the condition that the oxygen content does not exceed 100 ppm, and preserving heat; the temperature is continuously increased to 450-600 DEG C, and heat preservation is conducted; nitrogen is introduced until the pressure is 0.9-1.5 MPa, the temperature is increased to 1000-1200 DEG C, and heat preservation is conducted; raising the pressure and the temperature to 1.0-2.0 MPa and 1350-1450 DEG C, and keeping the temperature; raising the temperature to 1450-1550 DEG C, and keeping the temperature; raising the pressure and the temperature to 2-3 MPa and 1650-1750 DEG C, and keeping the temperature; raising the pressure and the temperature to 3-5 MPa and 1750-1900 DEG C, and keeping the temperature; and cooling. The method is simple, easy to operate, short in period and low in cost, and the high-density, high-thermal-conductivity and high-strength silicon nitride ceramic can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon nitride ceramics, and in particular to a silicon nitride ceramic and a preparation method and application thereof. Background Art

[0002] Currently, silicon nitride ceramics are typically produced by sintering a preformed silicon nitride blank. The sintering process is typically conventional gas pressure sintering or hot pressing, performed at a preset target sintering temperature. The resulting silicon nitride ceramics typically have less than ideal density. Furthermore, existing sintering processes typically separate the sintering and debinding processes, with debinding performed first and then placed back into the sintering furnace for sintering. This results in a lengthy production cycle and high costs.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The object of the present invention is to provide a silicon nitride ceramic and a preparation method and application thereof, so as to solve or improve the above-mentioned technical problems.

[0005] The present invention can be achieved like this:

[0006] In a first aspect, the present invention provides a method for preparing a silicon nitride ceramic, comprising the following steps:

[0007] The formed silicon nitride blank is subjected to the following degreasing and sintering steps in sequence:

[0008] Degreasing stage: under vacuum conditions with oxygen content not exceeding 100ppm, heat to 180℃~250℃, keep warm for 60min~180min; continue to heat to 450℃~600℃, keep warm for 60min~180min;

[0009] Sintering stage: nitrogen is introduced to a pressure of 0.9MPa~1.5MPa, and the temperature is raised to 1000℃~1200℃ at the same time, and kept warm for 30min~90min; the pressure and temperature are continued to be raised to 1.0MPa~2.0MPa and 1350℃~1450℃, and kept warm for 30min~90min; the temperature is continued to be raised to 1450℃~1550℃, and kept warm for 160min~240min; the pressure and temperature are continued to be raised to 2MPa~3MPa and 1650℃~1750℃, and kept warm for 60min~180min; the pressure and temperature are continued to be raised to 3MPa~5MPa and 1750℃~1900℃, and kept warm for 240min~480min; then the temperature is lowered.

[0010] In an optional embodiment, the heating rate in the degreasing stage is 0.2° C. / min to 0.8° C. / min.

[0011] In an optional embodiment, the heating rate in the sintering stage is 3° C. / min to 6° C. / min.

[0012] In an optional embodiment, the cooling includes a first cooling stage, a second cooling stage, and a third cooling stage;

[0013] Among them, the first cooling stage is to cool to 1400℃~1600℃ and keep it warm for 60min~120min;

[0014] The second cooling stage is to cool to 1000℃~1400℃ and keep it at that temperature for 60min~120min;

[0015] The third cooling stage is to cool to 600°C ~ 1000°C and keep warm for 60min ~ 120min.

[0016] In an optional embodiment, the cooling rate in the cooling stage is 2°C / min to 7°C / min.

[0017] In an optional embodiment, the raw materials for preparing the silicon nitride blank include silicon nitride and a sintering aid;

[0018] The mass of the sintering aid is 6wt% to 12wt% of the silicon nitride.

[0019] In an alternative embodiment, the sintering aid includes at least one of yttria, magnesia, and zirconia.

[0020] In an optional embodiment, the raw materials for preparing the silicon nitride blank further include an organic solvent, a dispersant, a binder and a plasticizer;

[0021] Wherein, the amount of the organic solvent is 60wt% to 90wt% of the silicon nitride;

[0022] The amount of the dispersant is 1 wt% to 5 wt% of the silicon nitride;

[0023] The amount of the binder is 5wt% to 15wt% of the silicon nitride;

[0024] The amount of the plasticizer used is 3wt% to 10wt% of the silicon nitride.

[0025] In an alternative embodiment, the organic solvent comprises at least one of ethanol, toluene and ethyl acetate;

[0026] and / or, the dispersant comprises at least one of polyacrylic acid, polyvinyl pyrrolidone and ammonium polyacrylate;

[0027] and / or, the binder comprises at least one of polyvinyl butyral and polyvinyl alcohol;

[0028] And / or, the plasticizer includes at least one of nitrocellulose and polyethylene glycol.

[0029] In a second aspect, the present invention provides a silicon nitride ceramic, which is prepared by the preparation method of any one of the aforementioned embodiments.

[0030] In an optional embodiment, the silicon nitride ceramic has at least one of the following characteristics:

[0031] Feature 1: The density of silicon nitride ceramics is not less than 3.15g / cm 3 ;

[0032] Feature 2: The flexural strength of silicon nitride ceramics is not less than 805MPa;

[0033] Feature 3: The thermal conductivity of silicon nitride ceramics is not less than 110W / (m·K).

[0034] In a third aspect, the present invention provides a structural component, wherein the raw materials for preparing the structural component include the silicon nitride ceramic of the aforementioned embodiment.

[0035] The beneficial effects of the present invention include:

[0036] The preparation method of silicon nitride ceramics provided by the present invention realizes degreasing of the silicon nitride blank in the degreasing stage and densification of the material in the sintering stage, wherein the process of "continuing to increase the pressure and temperature to 2MPa-3MPa and 1650°C-1750°C, and keeping the temperature for 60min-180min" can promote the formation of closed pores in the material through grain boundary migration, etc., thereby improving the density; the process of "continuing to increase the pressure and temperature to 3MPa-5MPa and 1750°C-1850°C, and keeping the temperature for 240min-480min" can promote grain growth and fill closed pores; at the same time, based on the high temperature in the previous stage that has prompted the material to form closed pores, excessive grain growth in this stage can be effectively prevented.

[0037] The above preparation method is simple and easy to operate. Degreasing and densification are performed in the same equipment, without removing the green body during the process. Furthermore, the method has a short cycle time and low cost, and can produce silicon nitride ceramics with high density, high thermal conductivity, and high strength. The resulting silicon nitride ceramics are suitable for the manufacture of structural components such as electronic substrates. DETAILED DESCRIPTION

[0038] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0039] The silicon nitride ceramic provided by the present invention and its preparation method and application are described in detail below.

[0040] The present invention provides a method for preparing silicon nitride ceramics, comprising the following steps: sequentially degreasing and sintering a formed silicon nitride blank:

[0041] Degreasing stage: under vacuum conditions with oxygen content not exceeding 100ppm, heat to 180℃~250℃, keep warm for 60min~180min; continue to heat to 450℃~600℃, keep warm for 60min~180min;

[0042] Sintering stage: nitrogen is introduced to a pressure of 0.9MPa~1.5MPa, and the temperature is raised to 1000℃~1200℃ at the same time, and kept warm for 30min~90min; the pressure and temperature are continued to be raised to 1.0MPa~2.0MPa and 1350℃~1450℃, and kept warm for 30min~90min; the temperature is continued to be raised to 1450℃~1550℃, and kept warm for 160min~240min; the pressure and temperature are continued to be raised to 2MPa~3MPa and 1650℃~1750℃, and kept warm for 60min~180min; the pressure and temperature are continued to be raised to 3MPa~5MPa and 1750℃~1900℃, and kept warm for 240min~480min; then the temperature is lowered.

[0043] The entire sintering process is always carried out in a sintering device (such as a sintering furnace), and the silicon nitride blank is not taken out during the process.

[0044] In some optional embodiments, the degreasing stage can be initially heated to 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, 235°C, 240°C, 245°C, or 250°C, or other temperatures within the range of 180°C to 250°C. The heated temperature can be maintained for 60 minutes, 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes, 120 minutes, 130 minutes, 140 minutes, 150 minutes, 160 minutes, 170 minutes, or 180 minutes, or other temperatures within the range of 60 minutes to 180 minutes. This process gradually decomposes the residual organic solvent in the silicon nitride blank. The temperature can be further increased to 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, or 600°C, or other values within the range of 450°C to 600°C. The temperature can be maintained at this increased temperature for 60 minutes, 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes, 120 minutes, 130 minutes, 140 minutes, 150 minutes, 160 minutes, 170 minutes, or 180 minutes, or other values within the range of 60 minutes to 180 minutes. This process completely decomposes the residual organic solvent in the silicon nitride blank.

[0045] For example, the heating rate in the degreasing stage can be 0.2°C / min to 0.8°C / min, such as 0.2°C / min, 0.25°C / min, 0.3°C / min, 0.35°C / min, 0.4°C / min, 0.45°C / min, 0.5°C / min, 0.55°C / min, 0.6°C / min, 0.65°C / min, 0.7°C / min, 0.75°C / min, or 0.8°C / min, or other values within the range of 0.2°C / min to 0.8°C / min. If the heating rate in the degreasing stage is lower than 0.2°C / min, it is not conducive to the timely removal of decomposition products, and carbonization may result, which may remain in the green body. If the heating rate in the degreasing stage is higher than 0.8°C / min, cracks or even splitting of the green body may occur.

[0046] Continuing from the above, the degreasing of the silicon nitride blank is completed through the degreasing stage. This stage is carried out under vacuum conditions, which is conducive to the rapid discharge of decomposition products of substances such as organic solvents to prevent them from remaining inside the material after carbonization.

[0047] In some optional embodiments, the pressure increase during the sintering stage is achieved by adjusting the amount of nitrogen gas introduced. The introduction of nitrogen gas is used to provide pressure on the one hand, and to prevent the decomposition of silicon nitride on the other hand.

[0048] At the beginning of the sintering stage, nitrogen is introduced into the sintering apparatus to raise the pressure to 0.9 MPa, 0.95 MPa, 1.0 MPa, 1.05 MPa, 1.1 MPa, 1.15 MPa, 1.2 MPa, 1.25 MPa, 1.3 MPa, 1.35 MPa, 1.4 MPa, 1.45 MPa, or 1.5 MPa, or other values within the range of 0.9 MPa to 1.5 MPa. Simultaneously, the temperature is raised to 1000°C, 1050°C, 1100°C, 1150°C, or 1200°C, or other values within the range of 1000°C to 1200°C. The above pressure and temperature conditions are maintained for 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, or 90 minutes, or other values within the range of 30 minutes to 90 minutes. Under the above temperature and pressure conditions, on the one hand, the sintering aid begins to produce a liquid phase, and on the other hand, it can promote the rearrangement of material particles and improve its densification. In addition, it also helps to reduce the final sintering temperature of the material.

[0049] Subsequently, the pressure can be increased to 1.0 MPa, 1.2 MPa, 1.5 MPa, 1.8 MPa, or 2.0 MPa, or other values within the range of 1.0 MPa to 2.0 MPa. Simultaneously, the temperature can be increased to 1350°C, 1380°C, 1400°C, 1420°C, or 1450°C, or other values within the range of 1350°C to 1450°C. Under the above pressure and temperature conditions, the temperature can be maintained for 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, or 90 minutes, or other values within the range of 30 minutes to 90 minutes. Subsequently, the temperature can be increased to 1450°C, 1480°C, 1500°C, 1520°C, or 1550°C, or other values within the range of 1450°C to 1550°C. At this temperature, the temperature can be kept warm for 160 minutes, 170 minutes, 180 minutes, 190 minutes, 200 minutes, 210 minutes, 220 minutes, 230 minutes or 240 minutes, etc., or other values within the range of 160 minutes to 240 minutes.

[0050] The above process is the phase transition temperature stage. Specifically, the holding time of this stage can be adjusted according to the actual required β-phase silicon nitride content. Continuing to increase the pressure in this stage can promote the phase transition.

[0051] Subsequently, the pressure can be increased to 2.0 MPa, 2.2 MPa, 2.5 MPa, 2.8 MPa, or 3.0 MPa, or other values within the range of 2.0 MPa to 3.0 MPa. Simultaneously, the temperature can be increased to 1650°C, 1680°C, 1700°C, 1720°C, or 1750°C, or other values within the range of 1650°C to 1750°C. Under these pressure and temperature conditions, the sintering can be maintained for 60 min, 80 min, 100 min, 120 min, 140 min, 160 min, or 180 min, or other values within the range of 60 min to 180 min. This process can promote the formation of closed pores in the material through grain boundary migration and other processes, thereby improving density. If the pressure during this process is lower than 2.0 MPa, densification of the sintered sample is not conducive; if the pressure during this process is higher than 3.0 MPa, production costs are not saved. If the temperature during the process is lower than 1650°C, it is not conducive to the growth of β-phase grains; if the temperature during the process is higher than 1750°C, it may cause abnormal growth of grains and reduce their mechanical properties.

[0052] Subsequently, the pressure can be increased to 3.0 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, or 5.0 MPa, or other values within the range of 3 MPa to 5 MPa. Simultaneously, the temperature can be increased to 1750°C, 1780°C, 1800°C, 1820°C, 1850°C, 1880°C, or 1900°C, or other values within the range of 1750°C to 1900°C. Under the aforementioned pressure and temperature conditions, the temperature can be maintained for 240 min, 260 min, 280 min, 300 min, 320 min, 340 min, 360 min, 380 min, 400 min, 420 min, 440 min, 460 min, or 480 min, or other values within the range of 240 min to 480 min. The above process primarily promotes grain growth and fills closed pores. Furthermore, since the high temperature in the previous stage has already caused the material to form closed pores, it effectively prevents excessive grain growth in this stage. If the pressure during this process is lower than 3.0 MPa, it is not conducive to densification of the sintered sample; if the pressure during this process is higher than 5.0 MPa, it is not conducive to reducing production costs. If the temperature during this process is lower than 1750°C, it is not conducive to the growth of β-phase grains; if the temperature during this process is higher than 1850°C, it may lead to abnormal grain growth and reduce its mechanical properties.

[0053] For example, the heating rate during the sintering stage can be 3°C / min to 6°C / min, such as 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min, or 6°C / min, or other values within the range of 3°C / min to 6°C / min. If the heating rate during the sintering stage is lower than 3°C / min, it is not conducive to saving production costs. If the heating rate during the sintering stage is higher than 6°C / min, it may cause cracks or even splitting of the sample.

[0054] Continuing from the above, the material is densified through the second sintering stage.

[0055] In some optional embodiments, cooling includes a first cooling stage, a second cooling stage, and a third cooling stage.

[0056] The temperature in the first cooling stage can be lowered to 1400° C. to 1600° C., such as 1400° C., 1450° C., 1500° C., 1550° C., or 1600° C., or other values within the range of 1400° C. to 1600° C. The temperature can be kept at the lowered temperature for 60 to 120 minutes, such as 60, 70, 80, 90, 100, 110, or 120 minutes, or other values within the range of 60 to 120 minutes.

[0057] The temperature in the second cooling stage can be lowered to 1000° C. to 1400° C., such as 1000° C., 1050° C., 1100° C., 1150° C., 1200° C., 1250° C., 1300° C., 1350° C., or 1400° C., or other values within the range of 1000° C. to 1400° C. The temperature is then maintained at the lowered temperature for 60 to 120 minutes, such as 60, 70, 80, 90, 100, 110, or 120 minutes, or other values within the range of 60 to 120 minutes.

[0058] The temperature in the third cooling stage can be lowered to 600° C. to 1000° C., such as 600° C., 650° C., 700° C., 750° C., 800° C., 850° C., 900° C., 950° C., or 1000° C., or other values within the range of 600° C. to 1000° C. The temperature is then maintained at the lowered temperature for 60 to 120 minutes, such as 60, 70, 80, 90, 100, 110, or 120 minutes, or other values within the range of 60 to 120 minutes.

[0059] In some optional embodiments, the cooling rate during the cooling stage can be 2°C / min to 7°C / min, such as 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min, or 7°C / min, or other values within the range of 2°C / min to 7°C / min. If the heating rate during the cooling stage is lower than 2°C / min, it is not conducive to saving production costs; if the heating rate during the cooling stage is higher than 7°C / min, it is not conducive to eliminating thermal stress.

[0060] As mentioned above, the residual stress inside the material can be fully released by cooling.

[0061] In some optional embodiments, the raw materials for preparing the silicon nitride green body include silicon nitride and a sintering aid.

[0062] The mass of the sintering aid can be 6 wt% to 12 wt% of the silicon nitride, such as 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, or 12 wt%, or can be other values within the range of 6 wt% to 12 wt%. The sintering aid can illustratively include at least one of yttrium oxide, magnesium oxide, and zirconium oxide.

[0063] The raw materials for preparing the silicon nitride blank may also include an organic solvent, a dispersant, a binder and a plasticizer;

[0064] Among them, the amount of organic solvent used can be 60wt% to 90wt% of silicon nitride, such as 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt% or 90wt%, etc., or it can be other values within the range of 60wt% to 90wt%.

[0065] The amount of the dispersant used can be 1 wt% to 5 wt% of silicon nitride, such as 1 wt%, 2 wt%, 3 wt%, 4 wt% or 5 wt%, or other values within the range of 1 wt% to 5 wt%.

[0066] The amount of the binder may be 5 wt% to 15 wt% of silicon nitride, such as 5 wt%, 8 wt%, 10 wt%, 12 wt% or 15 wt%, or other values within the range of 5 wt% to 15 wt%.

[0067] The amount of plasticizer used can be 3wt% to 10wt% of silicon nitride, such as 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%, etc., or other values within the range of 3wt% to 10wt%.

[0068] In some optional embodiments, the organic solvent may illustratively but not limitatively include at least one of ethanol, toluene and ethyl acetate.

[0069] The dispersant may illustratively but not limitatively include at least one of polyacrylic acid, polyvinyl pyrrolidone, and ammonium polyacrylate.

[0070] The binder may illustratively but not limitatively include at least one of polyvinyl butyral and polyvinyl alcohol.

[0071] The plasticizer may illustratively but not limitatively include at least one of nitrocellulose and polyethylene glycol.

[0072] Correspondingly, the present invention also provides a silicon nitride ceramic, which is prepared by the above preparation method.

[0073] In some optional embodiments, the density of silicon nitride ceramic is not less than 3.15 g / cm 3 , such as 3.18g / cm 3 ~3.22g / cm 3 .

[0074] In some optional embodiments, the flexural strength of the silicon nitride ceramic is not less than 805 MPa, such as 809 MPa to 857 MPa.

[0075] In some optional embodiments, the thermal conductivity of the silicon nitride ceramic is not less than 110 W / (m·K), such as 113 W / (m·K) to 128 W / (m·K).

[0076] In addition, the present invention also provides a structural component, wherein the raw materials for preparing the structural component include the above-mentioned silicon nitride ceramic. For example, the above-mentioned structural component can be an electronic substrate, etc.

[0077] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0078] Example 1

[0079] This embodiment provides a silicon nitride ceramic, the preparation method of which is as follows:

[0080] S1: Degreasing stage.

[0081] The formed silicon nitride blank was placed in a sintering furnace, and heated to 220°C at a heating rate of 0.5°C / min under vacuum conditions with an oxygen content not exceeding 100 ppm, and kept warm for 120 minutes; the temperature was further raised to 550°C and kept warm for 120 minutes.

[0082] The silicon nitride blank is formed by tape-casting slurry formed from the prepared raw materials, and its thickness is 0.5 mm. The prepared slurry includes silicon nitride powder, a sintering aid, an organic solvent, a binder, a dispersant, and a plasticizer. The sintering aids are Y2O3 and MgO, with the amount of Y2O3 being 5wt% of the silicon nitride powder and the amount of MgO being 5wt% of the silicon nitride powder. The organic solvent is ethanol and toluene (mass ratio is 1:1), and its amount is 80wt% of the silicon nitride powder; the binder is polyvinyl alcohol, and its amount is 8wt% of the silicon nitride powder; the dispersant is polyvinyl pyrrolidone, and its amount is 3wt% of the silicon nitride powder; the plasticizer is polyethylene glycol, and its amount is 4wt% of the silicon nitride powder.

[0083] S2: Sintering stage.

[0084] Nitrogen was introduced to a pressure of 0.9 MPa, and the temperature was raised to 1000°C at a heating rate of 5°C / min, and kept warm for 30 minutes; the pressure and temperature were continued to be raised to 1.5 MPa and 1400°C, and kept warm for 30 minutes; the temperature was continued to be raised to 1500°C, and kept warm for 160 minutes; the pressure and temperature were continued to be raised to 2 MPa and 1700°C, and kept warm for 60 minutes; the pressure and temperature were continued to be raised to 3 MPa and 1800°C, and kept warm for 360 minutes.

[0085] S3: Cooling stage.

[0086] The temperature was lowered to 1500°C at a cooling rate of 5°C / min and kept at this temperature for 120 minutes; the temperature was then lowered to 1200°C and kept at this temperature for 120 minutes; the temperature was then lowered to 800°C and kept at this temperature for 120 minutes.

[0087] Example 2

[0088] The only difference between this embodiment and embodiment 1 is that the "continue to increase the pressure and temperature to 2 MPa and 1700°C, and keep warm for 60 minutes; continue to increase the pressure and temperature to 3 MPa and 1800°C, and keep warm for 360 minutes" in the sintering stage is adjusted to "continue to increase the pressure and temperature to 2 MPa and 1750°C, and keep warm for 60 minutes; continue to increase the pressure and temperature to 3 MPa and 1850°C, and keep warm for 360 minutes".

[0089] Example 3

[0090] The only difference between this embodiment and embodiment 1 is that the sintering aids are Y2O3 and MgO, the amount of Y2O3 is 3wt% of the silicon nitride powder, and the amount of MgO is 6wt% of the silicon nitride powder.

[0091] Example 4

[0092] The only difference between this embodiment and embodiment 3 is that the "continue to increase the pressure and temperature to 2 MPa and 1700°C, and keep warm for 60 minutes; continue to increase the pressure and temperature to 3 MPa and 1800°C, and keep warm for 360 minutes" in the sintering stage is adjusted to "continue to increase the pressure and temperature to 2 MPa and 1750°C, and keep warm for 60 minutes; continue to increase the pressure and temperature to 3 MPa and 1850°C, and keep warm for 360 minutes".

[0093] Example 5

[0094] The only difference between this embodiment and embodiment 1 is that the sintering aids are Y2O3 and MgO, the amount of Y2O3 is 3wt% of the silicon nitride powder, and the amount of MgO is 9wt% of the silicon nitride powder.

[0095] Example 6

[0096] The only difference between this embodiment and embodiment 5 is that the "continue to increase the pressure and temperature to 2 MPa and 1700°C, and keep warm for 60 minutes; continue to increase the pressure and temperature to 3 MPa and 1800°C, and keep warm for 360 minutes" in the sintering stage is adjusted to "continue to increase the pressure and temperature to 2 MPa and 1750°C, and keep warm for 60 minutes; continue to increase the pressure and temperature to 3 MPa and 1850°C, and keep warm for 360 minutes".

[0097] Example 7

[0098] This embodiment provides a silicon nitride ceramic, the preparation method of which is as follows:

[0099] S1: Degreasing stage.

[0100] The formed silicon nitride blank was placed in a sintering furnace, and heated to 180°C at a heating rate of 0.2°C / min under vacuum conditions with an oxygen content not exceeding 100 ppm, and kept warm for 180 minutes; the temperature was further raised to 450°C and kept warm for 180 minutes.

[0101] The silicon nitride blank is formed by tape-casting slurry formed from the prepared raw materials and has a thickness of 0.5 mm. The prepared slurry includes silicon nitride powder, a sintering aid, an organic solvent, a binder, a dispersant, and a plasticizer. The sintering aids are Y2O3 and ZrO2, with the amount of Y2O3 accounting for 5wt% of the silicon nitride powder and the amount of ZrO2 accounting for 5wt% of the silicon nitride powder. The organic solvent is ethyl acetate, which is used in an amount of 60wt% of the silicon nitride powder; the binder is polyvinyl butyral, which is used in an amount of 5wt% of the silicon nitride powder; the dispersant is polyacrylic acid, which is used in an amount of 1wt% of the silicon nitride powder; and the plasticizer is nitrocellulose, which is used in an amount of 3wt% of the silicon nitride powder.

[0102] S2: sintering stage.

[0103] Nitrogen was introduced to a pressure of 0.9 MPa, and the temperature was raised to 1100°C at a heating rate of 3°C / min, and kept warm for 90 minutes; the pressure and temperature were continued to be raised to 1 MPa and 1350°C, and kept warm for 90 minutes; the temperature was continued to be raised to 1450°C, and kept warm for 240 minutes; the pressure and temperature were continued to be raised to 2.5 MPa and 1650°C, and kept warm for 180 minutes; the pressure and temperature were continued to be raised to 4 MPa and 1900°C, and kept warm for 480 minutes.

[0104] S3: Cooling stage.

[0105] The temperature was lowered to 1400°C at a cooling rate of 2°C / min and kept at this temperature for 100 minutes; the temperature was then lowered to 1000°C and kept at this temperature for 100 minutes; the temperature was then lowered to 600°C and kept at this temperature for 100 minutes.

[0106] Example 8

[0107] This embodiment provides a silicon nitride ceramic, the preparation method of which is as follows:

[0108] S1: Degreasing stage.

[0109] The formed silicon nitride blank was placed in a sintering furnace, and heated to 250°C at a heating rate of 0.8°C / min under vacuum conditions with an oxygen content not exceeding 100 ppm, and kept warm for 60 minutes; the temperature was further raised to 600°C and kept warm for 60 minutes.

[0110] The silicon nitride blank is formed by tape-casting slurry formed from the prepared raw materials and has a thickness of 0.5 mm. The prepared slurry includes silicon nitride powder, a sintering aid, an organic solvent, a binder, a dispersant, and a plasticizer. The sintering aids are Y2O3 and ZrO2, with the amount of Y2O3 accounting for 3wt% of the silicon nitride powder and the amount of ZrO2 accounting for 3wt% of the silicon nitride powder. The organic solvent is ethanol, which is used in an amount of 90wt% of the silicon nitride powder; the binder is polyvinyl alcohol, which is used in an amount of 15wt% of the silicon nitride powder; the dispersant is polyacrylic acid, which is used in an amount of 5wt% of the silicon nitride powder; and the plasticizer is polyethylene glycol, which is used in an amount of 10wt% of the silicon nitride powder.

[0111] S2: Sintering stage.

[0112] Nitrogen was introduced to a pressure of 1.5 MPa, and the temperature was raised to 1200°C at a heating rate of 6°C / min, and kept warm for 60 min; the pressure and temperature were continued to be raised to 2 MPa and 1450°C, and kept warm for 60 min; the temperature was continued to be raised to 1550°C, and kept warm for 200 min; the pressure and temperature were continued to be raised to 3 MPa and 1750°C, and kept warm for 120 min; the pressure and temperature were continued to be raised to 5 MPa and 1750°C, and kept warm for 240 min.

[0113] S3: Cooling stage.

[0114] The temperature was lowered to 1600°C at a cooling rate of 7°C / min and kept at this temperature for 90 minutes; the temperature was then lowered to 1400°C and kept at this temperature for 60 minutes; the temperature was then lowered to 1000°C and kept at this temperature for 60 minutes.

[0115] Comparative Example 1

[0116] The difference between this comparative example and Example 1 is that during the sintering stage, “continue to increase the pressure and temperature to 2 MPa and 1700°C, and keep warm for 60 minutes; continue to increase the pressure and temperature to 3 MPa and 1800°C, and keep warm for 360 minutes” is replaced by only “continue to increase the pressure and temperature to 2 MPa and 1750°C, and keep warm for 2 hours”.

[0117] Comparative Example 2

[0118] The difference between this comparative example and Example 2 is that during the sintering stage, "continue to increase the pressure and temperature to 2 MPa and 1750°C, and keep warm for 60 minutes; continue to increase the pressure and temperature to 3 MPa and 1850°C, and keep warm for 360 minutes" is replaced by only "continue to increase the pressure and temperature to 2 MPa and 1800°C, and keep warm for 2 hours".

[0119] Comparative Example 3

[0120] The difference between this comparative example and Example 3 is that during the sintering stage, “continue to increase the pressure and temperature to 2 MPa and 1700°C, and keep warm for 60 minutes; continue to increase the pressure and temperature to 3 MPa and 1800°C, and keep warm for 360 minutes” is replaced by only “continue to increase the pressure and temperature to 2 MPa and 1750°C, and keep warm for 2 hours”.

[0121] Comparative Example 4

[0122] The difference between this comparative example and Example 4 is that during the sintering stage, “continue to increase the pressure and temperature to 2 MPa and 1750°C, and keep warm for 60 minutes; continue to increase the pressure and temperature to 3 MPa and 1850°C, and keep warm for 360 minutes” is replaced by only “continue to increase the pressure and temperature to 2 MPa and 1800°C, and keep warm for 2 hours”.

[0123] Comparative Example 5

[0124] The difference between this comparative example and Example 5 is that during the sintering stage, “continue to increase the pressure and temperature to 2 MPa and 1700°C, and keep warm for 60 minutes; continue to increase the pressure and temperature to 3 MPa and 1800°C, and keep warm for 360 minutes” is replaced by only “continue to increase the pressure and temperature to 2 MPa and 1750°C, and keep warm for 2 hours”.

[0125] Comparative Example 6

[0126] The difference between this comparative example and Example 6 is that during the sintering stage, “continue to increase the pressure and temperature to 2 MPa and 1750°C, and keep warm for 60 minutes; continue to increase the pressure and temperature to 3 MPa and 1850°C, and keep warm for 360 minutes” is replaced by only “continue to increase the pressure and temperature to 2 MPa and 1800°C, and keep warm for 2 hours”.

[0127] Test example

[0128] The silicon nitride ceramics obtained in Examples 1 to 8 and Comparative Examples 1 to 6 were subjected to performance tests, and the results are shown in Table 1, wherein the density was tested in accordance with GB / T2413, the flexural strength was tested in accordance with GB / T6569, and the thermal conductivity was tested in accordance with GB / T32064.

[0129] Table 1 Performance test results

[0130] <![CDATA[Density, g / cm 3 > Flexural strength, MPa Thermal conductivity, W / (m·K) Example 1 3.18 827 118 Example 2 3.20 840 123 Example 3 3.19 832 119 Example 4 3.20 849 125 Example 5 3.19 841 121 Example 6 3.22 857 128 Example 7 3.18 809 113 Example 8 3.21 817 125 Comparative Example 1 2.89 669 85 Comparative Example 2 2.94 675 89 Comparative Example 3 2.90 688 88 Comparative Example 4 2.98 697 89 Comparative Example 5 3.01 704 96 Comparative Example 6 3.09 710 99

[0131] It can be seen from Table 1 that the methods provided by Examples 1 to 8 of the present invention can prepare silicon nitride ceramics with good density, flexural strength and thermal conductivity.

[0132] Moreover, from the comparison of Example 1 with Comparative Example 1, Example 2 with Comparative Example 2, Example 3 with Comparative Example 3, Example 4 with Comparative Example 4, Example 5 with Comparative Example 5, and Example 6 with Comparative Example 6 in Table 1, it can be seen that when the staged sintering and pressure-temperature coupling sintering method is adopted, the density, thermal conductivity, bending strength and other properties of the silicon nitride ceramic substrate prepared therefrom are superior to those of the method using only single-stage temperature and pressure sintering.

[0133] In summary, the preparation method of silicon nitride ceramics provided by the present invention is simple, easy to operate, has a short cycle, and is low in cost. Degreasing and densification are always carried out in the same equipment, and there is no need to take out the blank in the middle. That is, degreasing and sintering are carried out in a unified process flow. In addition, the present invention improves the sintering effect by setting a reasonable sintering process pressure and temperature, and synchronous coupling; in addition, the final stage of sintering adopts a segmented sintering method to improve the sintering densification and improve the sintering effect. This method can obtain silicon nitride ceramics with high density, high thermal conductivity and high strength, which are suitable for the manufacture of structural parts such as electronic substrates.

[0134] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing silicon nitride ceramics, characterized in that: The following steps are involved: The formed silicon nitride blank is subjected to the following degreasing and sintering steps in sequence: Degreasing stage: under vacuum conditions with oxygen content not exceeding 100ppm, heat to 180℃~250℃, keep warm for 60min~180min; continue to heat to 450℃~600℃, keep warm for 60min~180min; Sintering stage: nitrogen is introduced to a pressure of 0.9MPa~1.5MPa, and the temperature is raised to 1000℃~1200℃ at the same time, and kept warm for 30min~90min; the pressure and temperature are continued to be raised to 1.0MPa~2.0MPa and 1350℃~1450℃, and kept warm for 30min~90min; the temperature is continued to be raised to 1450℃~1550℃, and kept warm for 160min~240min; the pressure and temperature are continued to be raised to 2MPa~3MPa and 1650℃~1750℃, and kept warm for 60min~180min; the pressure and temperature are continued to be raised to 3MPa~5MPa and 1750℃~1900℃, and kept warm for 240min~480min; then the temperature is lowered.

2. The preparation method according to claim 1, characterized in that The heating rate in the degreasing stage is 0.2℃ / min~0.8℃ / min.

3. The preparation method according to claim 1, characterized in that The heating rate in the sintering stage is 3°C / min to 6°C / min.

4. The preparation method according to any one of claims 1 to 3, characterized in that The cooling process includes the first cooling stage, the second cooling stage and the third cooling stage; Among them, the first cooling stage is to cool to 1400℃~1600℃ and keep it warm for 60min~120min; The second cooling stage is to cool to 1000℃~1400℃ and keep it at that temperature for 60min~120min; The third cooling stage is to cool to 600°C ~ 1000°C and keep warm for 60min ~ 120min.

5. The preparation method according to claim 4, characterized in that The cooling rate in the cooling stage is 2°C / min to 7°C / min.

6. The preparation method according to claim 1, characterized in that The raw materials for preparing the silicon nitride blank include silicon nitride and a sintering aid; Wherein, the mass of the sintering aid is 6wt% to 12wt% of the silicon nitride; And / or, the sintering aid includes at least one of yttrium oxide, magnesium oxide and zirconium oxide.

7. The preparation method according to claim 6, characterized in that The raw materials for preparing the silicon nitride blank also include an organic solvent, a dispersant, a binder and a plasticizer; Wherein, the amount of the organic solvent is 60wt% to 90wt% of the silicon nitride; The amount of the dispersant is 1 wt% to 5 wt% of the silicon nitride; The amount of the binder is 5wt% to 15wt% of the silicon nitride; The amount of the plasticizer is 3wt% to 10wt% of the silicon nitride; Preferably, the organic solvent comprises at least one of ethanol, toluene and ethyl acetate; and / or, the dispersant comprises at least one of polyacrylic acid, polyvinyl pyrrolidone and ammonium polyacrylate; and / or, the binder comprises at least one of polyvinyl butyral and polyvinyl alcohol; And / or, the plasticizer includes at least one of nitrocellulose and polyethylene glycol.

8. A silicon nitride ceramic, characterized in that: The silicon nitride ceramic is prepared by the preparation method according to any one of claims 1 to 7.

9. The silicon nitride ceramic according to claim 8, characterized in that The silicon nitride ceramic has at least one of the following characteristics: Feature 1: The density of the silicon nitride ceramic is not less than 3.15 g / cm 3 ; Feature 2: The flexural strength of the silicon nitride ceramic is not less than 805 MPa; Feature 3: The thermal conductivity of the silicon nitride ceramic is not less than 110 W / (m·K).

10. A structural member, characterized in that: The raw material for preparing the structural component includes the silicon nitride ceramic according to claim 8 or 9.