A nano-whisker reinforced silicon nitride bonded silicon carbide ceramic and its preparation method

Abstract

The present invention discloses a nano-whisker reinforced silicon nitride bonded silicon carbide ceramic and a preparation method thereof. The method comprises: mixing 55-75% by mass of silicon carbide powder, 15-35% by mass of silicon powder and 10-20% by mass of carbon black as main raw materials with a binder, a dispersant and water to obtain a ceramic slurry; pouring the ceramic slurry into a mold, allowing it to stand and dry to form a porous ceramic body; burying the porous ceramic body with silicon powder twice the mass of the porous ceramic body, heating the body to 1200-1500° C. in a flowing nitrogen atmosphere and keeping the temperature, and directly nitriding the body to obtain Si3N 4nw The present invention provides a porous ceramic preform of SiC / C; the temperature is then raised to 1600-1700°C, maintained in a vacuum of 1-30 Pa, and cooled to obtain a nanowhisker-reinforced silicon nitride-bonded silicon carbide ceramic. The present invention utilizes a simple preparation process to generate nanowhiskers in situ, thereby achieving excellent toughening of the silicon nitride-bonded silicon carbide ceramic.

Description

Technical Field

[0001] The invention relates to a nano whisker reinforced silicon nitride bonded silicon carbide ceramic and a preparation method thereof, belonging to the technical field of preparation of silicon nitride bonded silicon carbide ceramics. Background Art

[0002] Silicon nitride (Si3N4) and silicon carbide (SiC) are both compounds with extremely strong covalent bonds and similar physical and chemical properties. Silicon nitride-silicon carbide ceramic products, produced by combining the advantages of both, exhibit a range of excellent properties, including high-temperature resistance, corrosion resistance, wear resistance, erosion resistance, and oxidation resistance. As advanced refractory materials, they can normally operate at temperatures up to approximately 1500°C in various atmospheres, making them widely used in industries such as ceramics, nonferrous metallurgy, steel metallurgy, powder metallurgy, and the chemical industry.

[0003] However, traditional silicon nitride bonded silicon carbide ceramics have the common problems of excessive brittleness and low toughness. Brittle fracture is prone to occur during application, causing material damage, and their application is limited to a certain extent. At present, the main solutions to this defect include: introducing nano whiskers or fibers into silicon nitride bonded silicon carbide ceramics to toughen them, and achieving energy loss of internal stress in the ceramic material through mechanisms such as fiber breakage, fiber debonding, fiber pullout, crack bridging and crack deflection, which can improve the toughness of the bonded ceramic material. However, some of the externally added whisker reinforcements are not easy to disperse and are easily mechanically damaged during the dispersion process, resulting in defects in the bonded ceramic material, which has a certain impact on its performance. Summary of the Invention

[0004] In order to overcome the defects of the prior art, the purpose of the present invention is to provide a nanowhisker reinforced silicon nitride bonded silicon carbide ceramic and a preparation method thereof. Through the simple preparation process of the present invention, nanowhiskers can be generated in situ to achieve good toughening of silicon nitride bonded silicon carbide ceramics, which is beneficial for application.

[0005] The present invention provides a method for preparing nano-whisker reinforced silicon nitride bonded silicon carbide ceramics, comprising the following steps:

[0006] 1) By mass fraction, 55-75% silicon carbide powder, 15-35% silicon powder and 10-20% carbon black are mixed with a binder, a dispersant and water to prepare a ceramic slurry;

[0007] 2) pouring the ceramic slurry into a mold, allowing it to stand and dry to form, and then demolding to obtain a porous ceramic body;

[0008] 3) The porous ceramic body is buried with silicon powder twice the mass of the porous ceramic body, and the temperature is raised to 1200-1500°C and kept warm in a flowing nitrogen atmosphere, and Si3N is obtained by direct nitridation of the silicon powder.4nw / SiC / C porous ceramic preform; then heating to 1600-1700°C, vacuum insulation under vacuum conditions of 1-30Pa, and then cooling to obtain nano-whisker reinforced silicon nitride bonded silicon carbide ceramics.

[0009] The present invention provides a method for preparing silicon nitride-bonded silicon carbide ceramics. Si3N4 ceramic nanowhiskers are generated in situ within a porous ceramic body through direct nitridation of silicon powder. Reactive infiltration is then used to react molten silicon with carbon black to form SiC, achieving reactive sintering of the ceramic material. This method utilizes a one-step nitridation and reactive sintering process, combining direct nitridation with reactive infiltration, to produce nanowhisker-reinforced silicon nitride-bonded silicon carbide ceramics. This method improves material preparation efficiency and achieves toughening of the silicon nitride-bonded silicon carbide ceramics through a stress loss mechanism within the material caused by the in-situ generated nanowhiskers.

[0010] The first step of the method described in the embodiment of the present invention is to prepare a ceramic slurry, wherein 55-75wt% of silicon carbide powder, 15-35wt% of silicon powder and 10-20wt% of carbon black are used as main raw materials, and a binder and a dispersant are added and mixed with water to obtain the ceramic slurry.

[0011] In step 1), the purity of the silicon powder in the main raw material is greater than or equal to 90%, specifically 90-99.9%, and its particle size is 1-10 μm. In some embodiments, the purity of the silicon carbide powder is greater than 85%, specifically 85-99.9%, and its particle size is 5-40 μm. The purity of the carbon black is greater than 95%, specifically 95-99.9%, and its particle size is 1-20 μm.

[0012] In step 1), preferably, silicon carbide powder with a particle size of 5 to 40 μm, carbon black with a particle size of 1 to 20 μm, and silicon powder with a particle size of 1 to 10 μm are ball-milled, for example, for 3 hours to allow thorough mixing, to obtain a ball-milled raw material. The mass fraction of the silicon carbide powder can be 55%, 60%, 65%, 70%, or 75%, the mass fraction of the silicon powder can be 15%, 20%, 30%, or 35%, and the mass fraction of the carbon black can be 10%, 15%, 16%, or 20%, etc.

[0013] In step 1), preferably, 1-5% of the total mass of a binder and 1-5% of the total mass of a dispersant are added to the main raw material, and then 80-100% of the total mass of water is added thereto, stirred and mixed to prepare a ceramic slurry.

[0014] Preferably, in step 1), the binder is one or more of hydroxymethyl cellulose salt and hydroxyethyl cellulose, further sodium hydroxymethyl cellulose or hydroxyethyl cellulose. Moreover, the amount of the binder can be 2-5 wt% of the total mass of the main raw material.

[0015] In step 1), the dispersant is preferably one or more of ethanol, methylpentanol, polyethylene glycol, and fatty acid polyethylene glycol ester, more preferably ethanol, methylpentanol, or polyethylene glycol. The dispersant can be used in an amount of 3-5 wt % based on the total weight of the main raw material. The main powder raw material, binder, and dispersant in the embodiments of the present invention can all be conventional commercially available products. Furthermore, the water used is typically deionized water.

[0016] The second step of the method described in the embodiment of the present invention is to prepare a porous ceramic body by pouring the ceramic slurry into a mold, allowing it to stand and dry to form, and then demolding the body.

[0017] Preferably, the step 2) comprises: pouring the ceramic slurry into a mold, allowing it to stand for 7 to 9 hours (such as 8 hours, 8.5 hours), freeze-drying or forced air drying for 24 hours, and demolding to obtain a porous ceramic body.

[0018] After obtaining the porous ceramic body, the embodiment of the present invention uses silicon powder twice as much as the porous ceramic body to bury the porous ceramic body, heats up to 1200-1500°C in a flowing nitrogen atmosphere and keeps the temperature, and directly nitrides the silicon powder to obtain Si3N 4nw / SiC / C porous ceramic preform; then heating to 1600-1700°C, vacuum insulation under vacuum conditions of 1-30Pa, and then cooling to obtain nano-whisker reinforced silicon nitride bonded silicon carbide ceramics.

[0019] Burying the porous ceramic body in step 3) includes weighing an equal mass of silicon powder to the porous ceramic body, pouring the silicon powder into a graphite crucible and spreading it, placing the porous ceramic body on the spread silicon powder, and then weighing an equal mass of silicon powder and spreading it evenly on the porous ceramic body, thereby burying the porous ceramic body in the silicon powder. The purity and particle size range of the silicon powder used here can be the same as described above.

[0020] In the embodiment of the present invention, the graphite crucible can be placed in a vacuum carbon tube furnace, the air inlet valve and the exhaust valve are opened, the temperature is raised to 1250-1450°C in a flowing nitrogen atmosphere, and the temperature is kept to perform nitridation to form Si3N 4nw / SiC / C porous ceramic preform. In the embodiment of the present invention, Si3N4 ceramic nano whiskers are in-situ generated in the porous ceramic preform mainly by direct nitridation of silicon powder.

[0021] In an embodiment of the present invention, after the insulation is completed, the air inlet valve and the exhaust valve are closed, the vacuum valve and the vacuum pump are opened, and the vacuum degree in the carbon tube furnace is preferably maintained at 5-20 Pa. The temperature is raised to 1600-1700° C. and kept warm for a certain period of time. After the vacuum insulation is completed, the furnace can be naturally cooled to obtain a nano-whisker reinforced silicon nitride bonded silicon carbide ceramic material.

[0022] In step 3), the holding time under nitrogen atmosphere is 2 to 10 hours, preferably 2 to 6 hours; the holding time under vacuum is 30 to 120 minutes, preferably 30 to 60 minutes. After nitriding, the embodiment of the present invention uses reactive infiltration (vacuum reactive infiltration temperature is 1600 to 1700°C) to react molten Si with carbon black to form SiC, thereby achieving reactive sintering of the enhanced bonding ceramic material.

[0023] The present invention provides nano whisker reinforced silicon nitride bonded silicon carbide ceramics prepared by the above-mentioned preparation method, which has Si3N4 ceramic nano whiskers.

[0024] Compared with the prior art, the present invention provides a preparation technology for bonded silicon carbide ceramics with a simple process and easy-to-control process. In the preparation method described in the present invention, Si3N4 ceramic nanowhiskers are generated in situ in a porous ceramic body by direct nitridation of silicon powder, and then molten Si reacts with carbon black to generate SiC by reactive infiltration to achieve reactive sintering of the ceramic material; that is, a one-step nitridation reaction sintering method combining direct nitridation and reactive infiltration is used to prepare nanowhisker-reinforced silicon nitride bonded silicon carbide ceramic material. The present invention mainly achieves a good toughening effect on silicon nitride bonded silicon carbide ceramics through the stress loss mechanism of in-situ generated nanowhiskers inside the material, simplifies the preparation process of the ceramic material, and has high preparation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention or the core of the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings under the premise of continuous creative work.

[0026] Figure 1 Si3N prepared for the present invention 4nw / SiC / C porous ceramic preform XRD pattern;

[0027] Figure 2 Si3N prepared for the present invention 4nw SEM image of / SiC / C porous ceramic preform. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. Unless otherwise defined, all professional terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0029] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0030] Unless otherwise specified, all reagents and raw materials used in the present invention are commercially available commodities or products produced by recognized methods, and material sample testing is carried out in accordance with national standard methods.

[0031] Example 1

[0032] The nano-whisker reinforced silicon nitride bonded silicon carbide ceramic and the preparation method thereof include the following steps:

[0033] Step 1: Using 60wt% silicon carbide powder, 30wt% silicon powder and 10wt% carbon black as the main raw materials, the silicon carbide powder, silicon powder and carbon black are ball-milled for 3h to fully mix them, the ball-milled raw materials are placed in a stirring tank, 5wt% of the total weight of the main raw materials in the form of a binder and 5wt% of the total weight of the main raw materials in the form of a dispersant are added, and then 100% of the total weight of the main raw materials in the form of deionized water is added thereto, and stirring is continued for 45min to prepare a ceramic slurry;

[0034] Step 2: pour the ceramic slurry into a mold, let it stand for 8 hours, and then air dry it for 24 hours before demoulding to obtain a porous ceramic body;

[0035] Step 3: Weigh the same weight of silicon powder as the porous ceramic body and pour it into a graphite crucible and spread it out. Place the porous ceramic body on the spread silicon powder. Then weigh the same weight of silicon powder and spread it flat on the porous ceramic body so that the porous ceramic body is buried in the silicon powder. Place the graphite crucible in a vacuum carbon tube furnace, open the air inlet valve and exhaust valve, and heat it to 1250°C under a flowing nitrogen atmosphere and keep it warm for 3 hours.

[0036] Step 4: After the insulation is completed, close the air inlet valve and the exhaust valve, open the vacuum valve and the vacuum pump, maintain the vacuum degree in the carbon tube furnace at 5 Pa, heat to 1600 ° C, and keep warm for 30 minutes. After the insulation is completed, cool naturally to obtain nano-whisker reinforced silicon nitride bonded silicon carbide ceramic material.

[0037] The silicon carbide powder has a purity of 95% and a particle size of 5μm; the silicon powder has a purity of 99% and a particle size of 5μm; the carbon black has a purity of 98% and a particle size of 15μm. The binder is sodium hydroxymethyl cellulose, and the dispersant is polyethylene glycol. The resulting nanowhisker-reinforced silicon nitride-bonded silicon carbide ceramic has a flexural strength of 352MPa and a fracture toughness of 4.3MPa·m. 1 / 2 .

[0038] Example 2

[0039] The same as Example 1, the only difference is that the nitriding temperature is 1300 ° C. The bending strength of the nano whisker reinforced silicon nitride bonded silicon carbide ceramics is 346 MPa and the fracture toughness is 4.1 MPa·m 1 / 2 .

[0040] Example 3

[0041] The same as Example 1, the only difference is that the vacuum reaction infiltration temperature is 1650 ° C. The bending strength of the nano whisker reinforced silicon nitride bonded silicon carbide ceramic is 338 MPa and the fracture toughness is 4.5 MPa·m 1 / 2 .

[0042] Example 4

[0043] Step 1: Using 65wt% silicon carbide powder, 20wt% silicon powder and 15wt% carbon black as the main raw materials, the silicon carbide powder, silicon powder and carbon black are ball-milled for 3h to fully mix them, and the ball-milled raw materials are placed in a stirring tank, and a binder of 2wt% of the total weight of the main raw materials and a dispersant of 4wt% of the total weight of the main raw materials are added, and then deionized water of 80% of the total weight of the main raw materials is added thereto, and stirring is continued for 60min to prepare a ceramic slurry;

[0044] Step 2: pour the ceramic slurry into a mold, let it stand for 8 hours, and then air dry it for 24 hours before demoulding to obtain a porous ceramic body;

[0045] Step 3: Weigh the same weight of silicon powder as the porous ceramic body and pour it into a graphite crucible and spread it out. Place the porous ceramic body on the spread silicon powder. Then weigh the same weight of silicon powder and spread it flat on the porous ceramic body so that the porous ceramic body is buried in the silicon powder. Place the graphite crucible in a vacuum carbon tube furnace, open the air inlet valve and exhaust valve, and heat it to 1300°C under a flowing nitrogen atmosphere for 2 to 10 hours.

[0046] Step 4: After the insulation is completed, close the air inlet valve and the exhaust valve, open the vacuum valve and the vacuum pump, maintain the vacuum degree in the carbon tube furnace at 20Pa, heat to 1650°C, and keep warm for 60 minutes. After the insulation is completed, cool naturally to obtain nano-whisker reinforced silicon nitride bonded silicon carbide ceramic material.

[0047] The silicon carbide powder has a purity of 99% and a particle size of 40 μm; the silicon powder has a purity of 96% and a particle size of 3 μm; and the carbon black has a purity of 99% and a particle size of 20 μm. The binder is hydroxyethyl cellulose, and the dispersant is methyl amyl alcohol. The resulting nanowhisker-reinforced silicon nitride-bonded silicon carbide ceramic has a flexural strength of 348 MPa and a fracture toughness of 4.1 MPa·m. 1 / 2 .

[0048] Example 5

[0049] The same as Example 4, the only difference is that the vacuum reaction infiltration temperature is 1600 ° C. The bending strength of the nano whisker reinforced silicon nitride bonded silicon carbide ceramic is 352 MPa and the fracture toughness is 4.0 MPa·m 1 / 2 .

[0050] Example 6

[0051] The same as Example 4, the only difference is that the nitriding temperature is 1400 ° C. The bending strength of the nano whisker reinforced silicon nitride bonded silicon carbide ceramics is 343 MPa and the fracture toughness is 4.7 MPa·m 1 / 2 .

[0052] Example 7

[0053] Step 1: Using 55wt% silicon carbide powder, 30wt% silicon powder and 15wt% carbon black as the main raw materials, the silicon carbide powder, silicon powder and carbon black are ball-milled for 3h to fully mix them, the ball-milled raw materials are placed in a stirring tank, 5wt% of the total weight of the main raw materials in the form of a binder and 5wt% of the total weight of the main raw materials in the form of a dispersant are added, and then 80% of the total weight of the main raw materials in the form of deionized water is added thereto, and stirring is continued for 30min to prepare a ceramic slurry;

[0054] Step 2: pour the ceramic slurry into a mold, let it stand for 8 hours, and then air dry it for 24 hours before demoulding to obtain a porous ceramic body;

[0055] Step 3: Weigh the same weight of silicon powder as the porous ceramic body and pour it into a graphite crucible and spread it out. Place the porous ceramic body on the spread silicon powder. Then weigh the same weight of silicon powder and spread it flat on the porous ceramic body so that the porous ceramic body is buried in the silicon powder. Place the graphite crucible in a vacuum carbon tube furnace, open the air inlet valve and exhaust valve, and heat it to 1400°C under a flowing nitrogen atmosphere and keep it warm for 2 hours.

[0056] Step 4: After the insulation is completed, close the air inlet valve and the exhaust valve, open the vacuum valve and the vacuum pump, maintain the vacuum degree in the carbon tube furnace at 15Pa, heat to 1600℃, and keep warm for 60 minutes. After the insulation is completed, cool naturally to obtain nano-whisker reinforced silicon nitride bonded silicon carbide ceramic material.

[0057] The silicon carbide powder has a purity of 97% and a particle size of 20 μm. The silicon powder has a purity of 98% and a particle size of 4 μm. The carbon black has a purity of 99% and a particle size of 10 μm. The binder is hydroxyethyl cellulose and the dispersant is ethanol. The resulting nanowhisker-reinforced silicon nitride-bonded silicon carbide ceramic has a flexural strength of 372 MPa and a fracture toughness of 4.8 MPa·m. 1 / 2 .

[0058] Example 8

[0059] The same as Example 7, the only difference is that the nitriding temperature is 1350 ° C. The bending strength of the nano whisker reinforced silicon nitride bonded silicon carbide ceramics is 366 MPa and the fracture toughness is 4.5 MPa·m 1 / 2 .

[0060] Example 9

[0061] The same as Example 7, the only difference is that the vacuum reaction infiltration temperature is 1700 ° C. The bending strength of the nano whisker reinforced silicon nitride bonded silicon carbide ceramic is 378 MPa and the fracture toughness is 4.7 MPa·m 1 / 2 .

[0062] Figure 1 Before the implementation of the present invention, the Si3N prepared by direct nitridation at 1400℃ was explored. 4nw / SiC / C porous ceramic preform XRD (X-ray diffraction) diagram, analysis shows that Si is nitrided to Si3N4 and a small amount of C remains, which can be used as a carbon source for vacuum reactive infiltration.

[0063] Figure 2 Before the implementation of the present invention, the Si3N prepared by direct nitridation at 1400℃ was explored. 4nw / SiC / C porous ceramic preform SEM (scanning electron microscope) image, analysis shows that Si3N4 whiskers are generated in situ in the porous ceramic preform, and have no effect on the SiC and C grains and the pore distribution of the porous ceramic, so the subsequent vacuum reactive infiltration treatment can be carried out normally.

[0064] As can be seen from the above examples, the present invention utilizes a one-step process combining direct nitridation of silicon powder in a nitrogen atmosphere with reactive infiltration to produce a Si3N4 nanowhisker-reinforced silicon nitride-bonded silicon carbide ceramic material. This simple and easily controllable process improves material preparation efficiency. Furthermore, the in-situ generated Si3N4 nanowhisker-based material effectively toughens the silicon nitride-bonded silicon carbide ceramic material through a stress-dissipating mechanism within the material.

[0065] It should be noted that, for those skilled in the art, various improvements and modifications may be made to the present invention without departing from the principles of the present invention, and such improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection for the present invention is defined by the claims and may include other embodiments that can be imagined by those skilled in the art. If such other embodiments have structural elements similar to those described in the claims, or if they include equivalent structural elements that are not substantially different from the literal description of the claims, then such other embodiments should also be included within the scope of the claims.

Claims

1. A method for preparing nanowhisker reinforced silicon nitride bonded silicon carbide ceramics, characterized in that: The steps include: 1) By mass fraction, 55-75% of silicon carbide powder, 15-35% of silicon powder and 10-20% of carbon black are used as main raw materials, and the particle size of the silicon powder is 1-10 μm; according to the mass fraction ratio, silicon carbide powder with a particle size of 5-40 μm, carbon black with a particle size of 1-20 μm and silicon powder are ball-milled to obtain a ball-milled raw material, which is mixed with a binder, a dispersant and water to prepare a ceramic slurry; the binder is one or more of hydroxymethyl cellulose salt and hydroxyethyl cellulose; the dispersant is one or more of ethanol, methyl amyl alcohol, polyethylene glycol and fatty acid polyethylene glycol ester; 2) pouring the ceramic slurry into a mold, allowing it to stand and dry to form, and then demolding to obtain a porous ceramic body; 3) The porous ceramic body is buried with silicon powder twice the mass of the porous ceramic body, wherein the particle size of the silicon powder is 1 to 10 μm; in a flowing nitrogen atmosphere, the temperature is raised to 1200 to 1500°C and kept warm, and Si3N is obtained by direct nitridation of the silicon powder. 4nw / SiC / C porous ceramic preform; then heating to 1600-1700°C, vacuum insulation under vacuum conditions of 1-30Pa, and then cooling to obtain nano-whisker reinforced silicon nitride bonded silicon carbide ceramics.

2. The preparation method according to claim 1, characterized in that In the step 1), the purity of the silicon powder in the main raw material is greater than or equal to 90%.

3. The preparation method according to any one of claims 1 to 2, characterized in that In the step 1), 1-5% of the total mass of a binder and 1-5% of the total mass of a dispersant are added to the main raw material, and then 80-100% of the total mass of water is added thereto, and the mixture is stirred and mixed to prepare a ceramic slurry.

4. The preparation method according to any one of claims 1 to 2, characterized in that The step 2) comprises: pouring the ceramic slurry into a mold, allowing it to stand for 7 to 9 hours, freeze-drying or forced air drying for 24 hours, and demolding to obtain a porous ceramic body.

5. The preparation method according to any one of claims 1 to 2, characterized in that The step 3) of burying the porous ceramic body comprises: weighing silicon powder of the same mass as the porous ceramic body, pouring it into a graphite crucible and spreading it, placing the porous ceramic body on the spread silicon powder, and then weighing silicon powder of the same mass and spreading it evenly on the porous ceramic body to bury it in the silicon powder.

6. The preparation method according to claim 5, characterized in that In the step 3), the heat preservation time under the nitrogen atmosphere is 2 to 10 hours; the heat preservation time under vacuum is 30 to 120 minutes.

7. Nano-whisker reinforced silicon nitride bonded silicon carbide ceramic prepared by the preparation method according to any one of claims 1 to 6, comprising Si3N4 ceramic nano-whiskers.

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