Recrystallized silicon carbide product and preparation method thereof

Abstract

According to the preparation method of the recrystallized silicon carbide product, one-time forming is adopted, an obtained blank does not need to be sintered, a thermosetting binder is cured through gradient heating, the strength of the blank is sharply improved, a base body is obtained, then an impregnation formula and process are designed according to the structure of the base body, and the recrystallized silicon carbide product is obtained through multiple times of impregnation. Compared with the prior art, the method has the advantages that fine particles can be fully filled into holes of a base body, fine air holes are formed after sintering, accordingly, the porosity is reduced, and the obtained silicon carbide component has the high density of 3.0 g / cm < 3 > or above and the high strength of 150 MPa to 300 MPa and can meet the use requirements of high-temperature sintering crucibles and furnace tubes.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and in particular to a recrystallized silicon carbide product and a preparation method thereof. Background Art

[0002] The working environment of high-temperature sintered crucibles and furnace tubes is relatively harsh. In order to ensure stable and reliable operation, silicon carbide ceramics with excellent high temperature resistance, thermal shock resistance, high density, high strength, and chemical stability are generally used as preparation materials. The manufacturing process of silicon carbide ceramics usually adopts sintering methods such as atmospheric pressure sintering, reaction sintering, hot pressing sintering, impregnation and recrystallization. In order to meet the requirements of high-temperature sintered crucibles and furnace tubes, reaction sintering, liquid phase sintering and other methods are generally used in the preparation to obtain silicon carbide with higher density, thermal shock resistance and purity.

[0003] Recrystallized silicon carbide (R-SiC) has high purity and heat shock resistance, and has a wide range of operating temperatures and extreme operating environments. It can meet the use environment of high-temperature sintering crucibles and furnace tubes, but R-SiC sintering usually cannot achieve a sufficiently high density. Recrystallization is a process in which small particles evaporate and condense under the protection of an atmosphere at a temperature higher than 2100°C and a certain pressure, and a sintered body is formed by particle symbiosis at the contact point of large particles. The evaporation of small particles will cause a certain number of pores. Therefore, this sintering method will cause silicon carbide ceramics to have a higher porosity. Even if the particle grading of the raw material powder is controlled, its density is difficult to be higher than 2.6g / cm 3 , cannot meet the high density and high strength requirements of silicon carbide crucible, thus affecting its service life or even making it unusable.

[0004] In the prior art, there are studies that increase the density to 2.7 g / cm3 or even higher by using higher temperatures (about 2500°C) or very long sintering times (tens of hours) during the sintering of recrystallized silicon carbide. Although this increases the density of silicon carbide, it is often accompanied by significant grain growth, resulting in a decrease in the mechanical properties of the final silicon carbide product.

[0005] Therefore, the density of recrystallized silicon carbide is difficult to break through the bottleneck of 2.6g / cm3, which has become a long-term problem in the silicon carbide field. Summary of the invention

[0006] The purpose of the present invention is to provide a recrystallized silicon carbide product and a preparation method thereof in view of the deficiencies in the prior art, which improves the strength of the green body through one-time molding combined with multiple impregnations and one-time sintering, and ultimately improves the density and strength of the silicon carbide product.

[0007] According to a first aspect of the present invention, there is provided a method for preparing a recrystallized silicon carbide product, comprising the following steps:

[0008] S1, dissolving a first dispersant and a first binder in deionized water, adding a first silicon carbide powder and a second silicon carbide powder, mixing and ball milling to form a first slurry, then drying, grinding, sieving and dry pressing the first slurry to obtain a green body of a silicon carbide product; wherein the average particle size D1 of the first silicon carbide powder is greater than the average particle size D2 of the second silicon carbide powder;

[0009] S2, curing the green body obtained in step S1 by gradient temperature increase until the binder is completely cured, and then naturally cooling to room temperature to obtain a substrate of the silicon carbide product;

[0010] S3, determining the total volume of the third silicon carbide powder and the fourth silicon carbide powder according to the volume V1 and the porosity B1 of the matrix obtained in step S2, and determining the average particle size D3 of the third silicon carbide powder according to the pore size a1 of the matrix, wherein the average particle size D3 of the third silicon carbide powder is greater than the average particle size D4 of the fourth silicon carbide powder;

[0011] S4, dissolving the second dispersant and the second binder in deionized water, adding the third silicon carbide powder and the fourth silicon carbide powder, mixing and ball milling to form a second slurry, and immersing the substrate obtained in step S2 in the second slurry under vacuum conditions until the second slurry is completely immersed in the substrate, and then drying at room temperature. After the water is dried, the immersion and drying process is repeated until the porosity B2 of the treated substrate is ≤5%;

[0012] S5, placing the substrate processed in step S4 in an inert atmosphere for recrystallization and sintering, keeping the temperature and then naturally cooling to room temperature to obtain the desired recrystallized silicon carbide product.

[0013] As an optional implementation, the average particle size relationship between the first silicon carbide powder and the second silicon carbide powder is: D2<0.8D1.

[0014] As an optional implementation, the average particle size D1 of the first silicon carbide powder is 15 μm to 95 μm.

[0015] As an optional embodiment, the mass ratio of the first silicon carbide powder to the second silicon carbide powder is (1-10):1.

[0016] As an optional implementation, the process of curing the green body obtained in step S1 by gradient heating is as follows:

[0017] The first green body is placed in a furnace, and in an air atmosphere, the temperature is raised to 180° C. to 200° C. at a rate of 1 to 5° C. / min for curing, wherein the temperature is maintained for 10 to 30 minutes every time the temperature is raised by 30° C.

[0018] As an optional embodiment, the total volume of the third silicon carbide powder and the fourth silicon carbide powder is determined according to the volume V1 and the porosity B1 of the matrix obtained in step S2, and the average particle size D3 of the third silicon carbide powder is determined according to the pore size a1 of the matrix as follows:

[0019] The average particle size of the third silicon carbide powder is D3≤a1, and the total powder volume of the third silicon carbide powder and the fourth silicon carbide powder is V1*B1.

[0020] As an optional implementation, the average particle size relationship between the third silicon carbide powder and the fourth silicon carbide powder is: D4<0.8D3.

[0021] As an optional implementation, the mass ratio of the third silicon carbide powder to the fourth silicon carbide powder is (1-10):1.

[0022] As an optional embodiment, the solid content p1 of the first slurry is in the range of 50% to 80%, and the solid content p2 of the second slurry is in the range of 25% to 60%.

[0023] As an optional implementation, in step S4, the number of times of dipping and drying n≥(lnB2-lnB1) / ln(1-p2).

[0024] As an optional embodiment, in step S5, the conditions for recrystallization sintering are as follows:

[0025] The sintering temperature is 2100℃~2300℃, and the holding time is 2~5h; wherein, the temperature rises from 0℃~200℃ at a heating rate of 3~5℃ / min, from 200℃~500℃ at a heating rate of 0.5~1℃ / min, from 500℃~1600℃ at a heating rate of 1.5~2℃ / min, and from 1600℃ to the final temperature at a heating rate of 1~1.5℃ / min.

[0026] As an optional embodiment, the first dispersant is polyvinyl pyrrolidone or tetramethylammonium hydroxide, accounting for 1% to 5% of the total mass of the first silicon carbide powder and the second silicon carbide powder;

[0027] The first binder is one of phenolic resin and epoxy resin or a mixture of the two, accounting for 3% to 10% of the total mass of the first silicon carbide powder and the second silicon carbide powder.

[0028] As an optional embodiment, the second dispersant is polyvinyl pyrrolidone or tetramethyl ammonium hydroxide, accounting for 1% to 3% of the total mass of the third silicon carbide powder and the fourth silicon carbide powder;

[0029] The second binder is one of phenolic resin and epoxy resin or a mixture of the two, accounting for 3% to 10% of the total mass of the third silicon carbide powder and the fourth silicon carbide powder.

[0030] According to a second aspect of the present invention, there is provided a high-density recrystallized silicon carbide component prepared by the above method.

[0031] As an optional embodiment, the density of the high-density recrystallized silicon carbide component can reach 3.0 g / cm 3 The above has a porosity of 1% to 7% and an average pore size of 3 μm to 10 μm.

[0032] It can be seen from the above technical solutions of the present invention that the preparation method of the recrystallized silicon carbide product proposed by the present invention adopts one-time molding, and the obtained green body does not need to be sintered, but the thermosetting binder is cured by gradient temperature increase, so that the strength of the green body is sharply improved to obtain a matrix, and then the impregnation formula and process are designed according to the structure of the matrix. Through multiple impregnations, finer particles can be fully filled into the pores of the matrix, and finer pores are formed after sintering, thereby reducing the porosity. The obtained silicon carbide product has a high density, and the density can reach 3.0g / cm 3 The above, as well as the high strength of 150MPa to 300MPa, can meet the use requirements of high-temperature sintering crucibles and furnace tubes.

[0033] The preparation method of the present invention improves the strength of the green body by combining multiple impregnations and one-time sintering, thereby improving the density and strength of the finished product and having the advantages of simple operation, short process flow, low energy consumption and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a SEM picture of the silicon carbide member according to Example 1 of the present invention. DETAILED DESCRIPTION

[0035] In order to better understand the technical content of the present invention, specific embodiments are given and described as follows in conjunction with the accompanying drawings.

[0036] Various aspects of the present invention are described in this disclosure with reference to the accompanying drawings, in which many illustrative embodiments are shown. The embodiments of the present disclosure are not necessarily intended to include all aspects of the present invention. It should be understood that the various concepts and embodiments introduced above, as well as those described in more detail below, can be implemented in any of many ways.

[0037] The present invention provides a method for preparing a recrystallized silicon carbide product, which adopts a one-time molding method combined with multiple pressure impregnation and one-time sintering to obtain a density of 3.0g / cm 3 The above recrystallized silicon carbide products.

[0038] In an exemplary embodiment of the present invention, a method for preparing a recrystallized silicon carbide product is provided, comprising:

[0039] Firstly, the percentage of each component in the raw material formula and the molding pressure are designed to ensure the pore size and strength of the green body. The green body is prepared by dry pressing, injection molding and other methods, and the matrix is ​​obtained by heating, drying and curing.

[0040] Secondly, the solid content of the impregnation slurry and the percentage of each component are designed according to the pore size and strength of the matrix. After the designed components are made into slurry, the matrix is ​​cyclically vacuum-pressure impregnated-dried in the slurry, and then recrystallized and sintered once at high temperature under inert gas to obtain a density of 3.0g / cm 3 The above recrystallized silicon carbide products.

[0041] As an optional example, the average particle size relationship between the first silicon carbide powder and the second silicon carbide powder is: D2<0.8D1.

[0042] In a preferred embodiment, the average particle size D1 of the first silicon carbide powder is 15 μm to 95 μm, and the average particle size D2 of the second silicon carbide powder is 5 μm to 75 μm.

[0043] As an optional example, the mass ratio of the first silicon carbide powder to the second silicon carbide powder is (1-10):1.

[0044] As an optional example, the process of performing gradient temperature curing on the green body obtained in step S1 is as follows:

[0045] The first green body is placed in a furnace, and in an air atmosphere, the temperature is raised to 180°C to 200°C at a rate of 1 to 5°C / min for curing, wherein the temperature is kept at 30°C for 10 to 30 minutes each time the temperature is raised by 10 to 30 minutes.

[0046] As an optional example, the total volume of the third silicon carbide powder and the fourth silicon carbide powder is determined according to the volume V1 and the porosity B1 of the matrix obtained in step S2, and the principle of determining the average particle size D3 of the third silicon carbide powder according to the pore size a1 of the matrix is ​​as follows:

[0047] The average particle size of the third silicon carbide powder is D3≤a1, and the total powder volume of the third silicon carbide powder and the fourth silicon carbide powder is V1*B1.

[0048] Furthermore, the total mass of the third silicon carbide powder and the fourth silicon carbide powder is 3.2*V1*ρ1, where 3.2 is the density of silicon carbide, g / cm 3 .

[0049] As an optional example, the average particle size relationship between the third silicon carbide powder and the fourth silicon carbide powder is: D4<0.8D3.

[0050] In a preferred embodiment, the average particle size D3 of the third silicon carbide powder is 10 μm to 50 μm, and the average particle size D4 of the fourth silicon carbide powder is 0.5 μm to 40 μm.

[0051] As an optional example, the mass ratio of the third silicon carbide powder to the fourth silicon carbide powder is (1-10):1.

[0052] As an optional example, the solid content p1 of the first slurry ranges from 50% to 80%. It is understandable that there is no specific limitation on the solid content of p1, and it only needs to be able to be stirred evenly and conveniently.

[0053] As an optional example, the solid content p2 of the second slurry is in the range of 25% to 60%.

[0054] As an optional example, in step S4, the number of times of dipping and drying n≥(lnB2-lnB1) / ln(1-p2).

[0055] As an optional example, in step S5, the conditions for recrystallization sintering are as follows:

[0056] The sintering temperature is 2100℃~2300℃, and the holding time is 2-5h; wherein, the temperature rises from 0℃~200℃ at a heating rate of 3~5℃ / min, from 200℃~500℃ at a heating rate of 0.5~1℃ / min, from 500℃~1600℃ at a heating rate of 1.5~2℃ / min, and from 1600℃ to the final temperature at a heating rate of 1~1.5℃ / min.

[0057] As an optional example, the first dispersant is polyvinyl pyrrolidone or tetramethyl ammonium hydroxide, accounting for 1% to 5% of the total mass of the first silicon carbide powder and the second silicon carbide powder;

[0058] The first binder is one of phenolic resin and epoxy resin or a mixture of the two, accounting for 3% to 10% of the total mass of the first silicon carbide powder and the second silicon carbide powder.

[0059] As an optional example, the second dispersant is polyvinyl pyrrolidone or tetramethyl ammonium hydroxide, accounting for 1% to 3% of the total mass of the third silicon carbide powder and the fourth silicon carbide powder;

[0060] The second binder is one of phenolic resin and epoxy resin or a mixture of the two, accounting for 3% to 10% of the total mass of the third silicon carbide powder and the fourth silicon carbide powder.

[0061] In a typical example, a method for preparing a recrystallized silicon carbide product is provided, comprising the following specific steps:

[0062] Step 1: Design of one-step molding formula

[0063] The raw materials are composed of silicon carbide coarse powder, fine powder, dispersant, binder and other organic substances, wherein the average particle size of silicon carbide coarse powder D1 is 15μm to 95μm, the average particle size of silicon carbide fine powder D2 is less than 0.8D1, and the mass ratio of silicon carbide coarse powder to silicon carbide fine powder is (1 to 10):1; the dispersant is polyvinyl pyrrolidone or tetramethylammonium hydroxide, accounting for 1% to 5% of the total mass of silicon carbide coarse powder and silicon carbide fine powder; the binder is a thermosetting binder, preferably one or a mixture of phenolic resin and epoxy resin, accounting for 3% to 10% of the total mass of silicon carbide coarse powder and silicon carbide fine powder.

[0064] Step 2: Preparation of green body

[0065] Using the raw materials determined in step 1, the dispersant and the binder are dissolved in a mixed solution of deionized water, and then silicon carbide coarse powder and silicon carbide fine powder are added, and the mixture is ball-milled for 12 to 24 hours to form a uniform first slurry;

[0066] The first slurry is dried at 50°C to 80°C for 4 to 8 hours, and the obtained solid is ground into dry powder. After passing through a 100-mesh sieve, the dry powder is placed in a mold and dry-pressed at a pressure of 10 to 100 MPa to obtain a green body.

[0067] Step 3: Heating and curing to obtain a matrix

[0068] The green body prepared in step 2 is placed in a furnace, and in an air atmosphere, the temperature is raised to 180°C to 200°C at a rate of 1 to 5°C / min for curing. After each 30°C increase in temperature, the green body is kept warm for 10 to 30 minutes to cure the thermosetting adhesive and increase the strength sharply. Afterwards, the green body is naturally cooled to room temperature to obtain a matrix.

[0069] Step 4: Design of dipping formula

[0070] The impregnation formula is designed according to the volume V1, pores B1 and pore size a1 of the substrate prepared in step 2. In the impregnation slurry formula, the average particle size D3 of the silicon carbide coarse powder is ≤ a1, the average particle size D4 of the silicon carbide fine powder is < 0.8D3, the total volume of the silicon carbide coarse powder and the silicon carbide fine powder is V1*B1, and the mass ratio of the silicon carbide coarse powder to the silicon carbide fine powder is (1-10):1; the dispersant is polyvinyl pyrrolidone or tetramethylammonium hydroxide, accounting for 1% to 3% of the total mass of the powder; the binder is one of phenolic resin and epoxy resin or a mixture of the two, accounting for 3% to 10% of the total mass of the powder.

[0071] Step 5: Impregnation of the substrate

[0072] Using the raw materials determined in step 4, dissolving the dispersant and the binder in a mixed solution of deionized water, then adding coarse silicon carbide powder and fine silicon carbide powder, mixing and ball milling for 12-24 hours to form a uniform slurry, the solid content of the slurry is 25%≤p2≤60%;

[0073] The substrate is immersed in the slurry for 1 to 10 minutes. During the process, vacuum is required to ensure that the slurry completely enters the substrate. The impregnated substrate is dried at 50°C to 70°C for 4 to 6 hours. After the moisture is dried, the impregnation-drying cycle is repeated. The number of impregnation-drying times n ≥ (lnB2-lnB1) / ln(1-p2) is used to ensure that the porosity B2 of the substrate after the cyclic impregnation-drying is ≤5%.

[0074] Step 6: Recrystallization sintering

[0075] The substrate treated in step 5 is placed in an inert atmosphere and then sintered at a high temperature to obtain a recrystallized silicon carbide product. The sintering temperature is 2100°C to 2300°C, and the holding time is 2 to 5 hours. The heating range is 0°C to 200°C at a heating rate of 3 to 5°C / min, 200°C to 500°C at a heating rate of 0.5 to 1°C / min, 500°C to 1600°C at a heating rate of 1.5 to 2°C / min, and from 1600°C to the final temperature at a heating rate of 1 to 1.5°C / min.

[0076] In another exemplary embodiment of the present invention, a recrystallized silicon carbide product prepared by the above method is also provided, wherein the density of the silicon carbide product is 3.0 g / cm 3 More than 3.03 to 3.12 g / cm 3 ; The porosity is 1% to 7%, preferably 2% to 7%; the average pore size is 3μm to 10μm, preferably 5μm to 7μm; the strength is 150 to 300MPa, preferably 250 to 300MPa.

[0077] The obtained silicon carbide products have high density, high purity and high temperature resistance. The corresponding silicon carbide materials can meet the material requirements of high temperature sintering crucibles and furnace tubes, and also have great application potential in the links that require purity and temperature resistance in semiconductor preparation.

[0078] For better understanding, the present invention is further described below in conjunction with several specific examples, but the preparation process is not limited thereto, and the content of the present invention is not limited thereto.

[0079] Unless otherwise specified, the materials in the examples were prepared according to existing methods or directly purchased from the market.

[0080] Example 1

[0081] (1) 50 μm silicon carbide coarse powder and 30 μm silicon carbide fine powder (the mass ratio of the two is 10:1), the dry powder is mixed in a ball mill for 2 hours and set aside, 3% of the total powder mass of polyvinyl pyrrolidone and 10% of the total powder mass of phenolic resin are added to deionized water and stirred evenly, and then the mixed silicon carbide powder is added and ball-milled for 12 hours and stirred evenly to obtain a slurry with a solid content of 80%. The slurry is dried at 50°C for 6 hours, then ground into powder, passed through a 100-mesh sieve, and pressed into shape using a 50 mm diameter circular mold at a pressure of 10 MPa.

[0082] (2) The molded sample is transferred to a constant temperature box and the temperature is gradually increased from 30°C to 180°C to solidify the phenolic resin. The temperature is increased by 30°C each time and kept at this temperature for 20 minutes. After the resin undergoes cross-linking and curing reaction, the strength increases sharply to obtain a matrix. At this time, the strength can be impregnated without sintering.

[0083] (3) The diameter of the substrate is D = 50 mm and the thickness is H = 6 mm; the porosity is B1 = 62%, the median pore size is a1 is 20 μm, the volume of the raw material powder required for impregnation is V = 3.14D*D*B1*H / 4 in theory, the particle size of the coarse silicon carbide powder is smaller than a1 (20 μm), the particle size of the coarse silicon carbide powder is 15 μm, the particle size of the fine powder is 10 μm, the mass ratio of the coarse powder to the fine powder is 10:1, and the powder is mixed in a ball mill for 2 hours before use;

[0084] Add 3% of polyvinyl pyrrolidone and 10% of phenolic resin to deionized water and stir evenly, then add the mixed silicon carbide powder and ball mill for 12 hours to stir evenly, and the solid content p2 of the slurry is 50%.

[0085] (4) placing the substrate in the slurry prepared in step (3) and vacuum impregnating for 10 min, drying at 50° C. for 6 h, and continuing the vacuum impregnation-drying process until the porosity B2 of the green body A is 5%, and the number of impregnations n ≥ (lnB2-lnB1) / ln(1-p2), where n=4, is calculated, and four impregnation-drying processes are performed;

[0086] Subsequently, a recrystallization sintering is carried out to obtain high-density recrystallized silicon carbide ceramics. The sintering temperature is 2100°C, and the heating range is 0°C-200°C at a heating rate of 3°C / min, 200°C-500°C at a heating rate of 1°C / min, 500°C-1600°C at a heating rate of 2°C / min, and 1600°C to 2100°C at a heating rate of 1°C / min. After keeping warm for 3 hours, it is cooled to room temperature to obtain a silicon carbide component.

[0087] like Figure 1 As shown in the SEM image of the silicon carbide product, it can be seen that the component has very few pores and has high density.

[0088] The porosity and average pore size of the component were tested by mercury intrusion method, and the strength of the component was tested by three-point bending method. The porosity of the silicon carbide component was 2%, the average pore size was 5μm, and the density was 3.12g / cm 3 , strength 300MPa.

[0089] Example 2

[0090] (1) 40 μm silicon carbide coarse powder and 30 μm silicon carbide fine powder (the ratio of the two is 5:1), the dry powder is mixed in a ball mill for 2 hours and set aside, 3% of the total powder mass of polyvinyl pyrrolidone and 5% of the total powder mass of phenolic resin are added to deionized water and stirred evenly, and then the mixed silicon carbide powder is added and ball-milled for 12 hours and stirred evenly to obtain a slurry with a solid content of 80%. The slurry is dried at 50°C for 6 hours, then ground into powder, passed through a 100-mesh sieve, and pressed into shape using a 50 mm diameter circular mold at a pressure of 10 MPa.

[0091] (2) The molded sample is transferred to a constant temperature box and the temperature is gradually increased from 30°C to 180°C to solidify the phenolic resin. The temperature is increased by 30°C each time and kept at this temperature for 20 minutes. After the resin undergoes cross-linking and curing reaction, the strength increases sharply to obtain a matrix. At this time, the strength can be impregnated without sintering.

[0092] (3) The substrate diameter D = 50 mm and the thickness H = 6 mm; the porosity B1 = 55%, the median pore size a1 is 18 μm, and the theoretical volume of raw powder required for impregnation is V = 3.14D*D*B1*H / 4. The raw powder larger than the theoretical volume is used to prepare the slurry. The particle size of the coarse silicon carbide powder is smaller than a1. The particle size of the coarse silicon carbide powder is 12 μm and the fine powder is 7 μm. The mass ratio of the coarse and fine powders is 5:1. The powder is mixed in a ball mill for 2 hours and then set aside;

[0093] Add 3% of polyvinyl pyrrolidone and 5% of phenolic resin to deionized water and stir evenly, then add the mixed silicon carbide powder and ball mill for 12 hours to stir evenly, and the solid content p2 of the slurry is 50%.

[0094] (4) placing the substrate in the slurry prepared in step (3) and vacuum impregnating for 10 min, drying at 50° C. for 6 h, and continuing the vacuum impregnation-drying process until the porosity B2 of the green body A is 5%, and the number of impregnations n ≥ (lnB2-lnB1) / ln(1-p2), where n=4, is calculated, and four impregnation-drying processes are performed;

[0095] Subsequently, a recrystallization sintering is carried out to obtain high-density recrystallized silicon carbide ceramics. The sintering temperature is 2100°C, and the heating range is 0°C-200°C at a heating rate of 3°C / min, 200°C-500°C at a heating rate of 1°C / min, 500°C-1600°C at a heating rate of 2°C / min, and 1600°C to 2100°C at a heating rate of 1°C / min. After keeping warm for 3 hours, it is cooled to room temperature to obtain a silicon carbide component.

[0096] The porosity and average pore size of the component were tested by mercury intrusion method, and the strength of the component was tested by three-point bending method. The porosity of the silicon carbide component was 6%, the average pore size was 7μm, and the density was 3.03g / cm 3 , strength 250MPa.

[0097] Example 3

[0098] (1) 28 μm silicon carbide coarse powder and 20 μm silicon carbide fine powder (the ratio of the two is 1:1), the dry powder is mixed in a ball mill for 2 hours and set aside, 3% of the total powder mass of polyvinyl pyrrolidone and 1% of the total powder mass of phenolic resin are added to deionized water and stirred evenly, and then the mixed silicon carbide powder is added and ball-milled for 12 hours and stirred evenly to obtain a slurry with a solid content of 80%. The slurry is dried at 50°C for 6 hours, then ground into powder, passed through a 100-mesh sieve, and pressed into shape using a 50 mm diameter circular mold at a pressure of 20 MPa.

[0099] (2) The molded sample is transferred to a constant temperature box and the temperature is gradually increased from 30°C to 180°C to solidify the phenolic resin. The temperature is increased by 30°C each time and kept at this temperature for 20 minutes. After the resin undergoes cross-linking and curing reaction, the strength increases sharply to obtain a matrix. At this time, the strength can be impregnated without sintering.

[0100] (3) The substrate diameter D = 50 mm and the thickness H = 6 mm; the porosity B1 = 32%, the median pore size a1 is 13 μm, and the volume of raw powder required for impregnation is V = 3.14D*D*B1*H / 4 in theory. The raw powder larger than the theoretical volume is used to prepare the slurry. The particle size of the coarse silicon carbide powder is smaller than a1. The particle size of the coarse silicon carbide powder is 10 μm and the fine powder is 4 μm. The mass ratio of the coarse and fine powders is 1:1. The powder is mixed in a ball mill for 2 hours and then set aside;

[0101] Add 3% of polyvinyl pyrrolidone and 5% of phenolic resin to deionized water and stir evenly, then add the mixed silicon carbide powder and ball mill for 12 hours to stir evenly, and the solid content p2 of the slurry is 50%.

[0102] (4) placing the substrate in the slurry prepared in step (3) and vacuum impregnating for 10 min, drying at 50° C. for 6 h, and continuing the vacuum impregnation-drying process until the porosity B2 of the green body A is 5%, the number of impregnations n ≥ (lnB2-lnB1) / ln(1-p2), and n=3, after four impregnation-drying;

[0103] Subsequently, a recrystallization sintering is carried out to obtain high-density recrystallized silicon carbide ceramics. The sintering temperature is 2100°C, and the heating range is 0°C-200°C at a heating rate of 3°C / min, 200°C-500°C at a heating rate of 1°C / min, 500°C-1600°C at a heating rate of 2°C / min, and 1600°C to 2100°C at a heating rate of 1°C / min. After keeping warm for 3 hours, it is cooled to room temperature to obtain a silicon carbide component.

[0104] The porosity and average pore size of the component were tested by mercury intrusion method, and the strength of the component was tested by three-point bending method. The porosity of the silicon carbide component was 7%, the average pore size was 6μm, and the density was 3.1g / cm 3 , strength 270MPa.

[0105] Therefore, the method of the present invention can improve the density and strength of silicon carbide components, and the density of the prepared recrystallized silicon carbide product can reach 3.0g / cm 3 Above, the porosity can reach below 7%, the pore size is 3 to 10 μm, and the strength can reach up to 300 MPa.

[0106] Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. A person with ordinary knowledge in the technical field to which the present invention belongs may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the definition of the claims.

Claims

1. A method for preparing a recrystallized silicon carbide product, characterized in that: The following steps are involved: S1, dissolving a first dispersant and a first binder in deionized water, adding a first silicon carbide powder and a second silicon carbide powder, mixing and ball milling to form a first slurry, then drying, grinding, sieving and dry pressing the first slurry to obtain a green body of a silicon carbide product; wherein the average particle size D1 of the first silicon carbide powder is greater than the average particle size D2 of the second silicon carbide powder; S2, curing the green body obtained in step S1 by gradient temperature increase until the binder is completely cured, and then naturally cooling to room temperature to obtain a substrate of the silicon carbide product; S3, determining the total volume of the third silicon carbide powder and the fourth silicon carbide powder according to the volume V1 and the porosity B1 of the matrix obtained in step S2, and determining the average particle size D3 of the third silicon carbide powder according to the pore size a1 of the matrix, wherein the average particle size D3 of the third silicon carbide powder is greater than the average particle size D4 of the fourth silicon carbide powder; S4, dissolving the second dispersant and the second binder in deionized water, adding the third silicon carbide powder and the fourth silicon carbide powder, mixing and ball milling to form a second slurry, and immersing the substrate obtained in step S2 in the second slurry under vacuum conditions until the second slurry is completely immersed in the substrate, and then drying at room temperature. After the water is dried, the immersion and drying process is repeated until the porosity B2 of the treated substrate is ≤5%; S5, placing the substrate processed in step S4 in an inert atmosphere for recrystallization and sintering, keeping the temperature and then naturally cooling to room temperature to obtain the desired recrystallized silicon carbide product.

2. The method for preparing a recrystallized silicon carbide product according to claim 1, characterized in that: The average particle size relationship between the first silicon carbide powder and the second silicon carbide powder is: D2<0.8D1.

3. The method for preparing a recrystallized silicon carbide product according to claim 1, characterized in that: The average particle size D1 of the first silicon carbide powder is 15 μm to 95 μm.

4. The method for preparing a recrystallized silicon carbide product according to claim 1, characterized in that: The mass ratio of the first silicon carbide powder to the second silicon carbide powder is (1-10):

1.

5. The method for preparing a recrystallized silicon carbide product according to claim 1, characterized in that: The process of curing the green body obtained in step S1 by gradient heating is as follows: The green body is placed in a furnace, and in an air atmosphere, the temperature is raised to 180°C to 200°C at a rate of 1 to 5°C / min for curing, wherein the temperature is kept at 30°C for 10 to 30 minutes each time the temperature is raised by 10 to 30 minutes.

6. The method for preparing a recrystallized silicon carbide product according to claim 1, characterized in that: The principles for determining the total volume of the third silicon carbide powder and the fourth silicon carbide powder according to the volume V1 and porosity B1 of the matrix obtained in step S2, and determining the average particle size D3 of the third silicon carbide powder according to the pore size a1 of the matrix are as follows: The average particle size of the third silicon carbide powder is D3≤a1, and the total powder volume of the third silicon carbide powder and the fourth silicon carbide powder is V1*B1.

7. The method for preparing a recrystallized silicon carbide product according to claim 1, characterized in that: The relationship between the average particle sizes of the third silicon carbide powder and the fourth silicon carbide powder is: D4<0.8D3.

8. The method for preparing a recrystallized silicon carbide product according to claim 1, characterized in that: The mass ratio of the third silicon carbide powder to the fourth silicon carbide powder is (1-10):

1.

9. The method for preparing a recrystallized silicon carbide product according to claim 1, characterized in that: The solid content p2 of the second slurry is in the range of 25% to 60%.

10. The method for preparing a recrystallized silicon carbide product according to claim 1, characterized in that: In the step S4, the number of times of immersion and drying n≥(lnB2-lnB1) / ln(1-p2).

11. The method for preparing a recrystallized silicon carbide product according to claim 1, characterized in that: In step S5, the conditions for recrystallization sintering are as follows: The sintering temperature is 2100℃~2300℃, and the holding time is 2~5h; wherein, the temperature rises from 0℃~200℃ at a heating rate of 3~5℃ / min, from 200℃~500℃ at a heating rate of 0.5~1℃ / min, from 500℃~1600℃ at a heating rate of 1.5~2℃ / min, and from 1600℃ to the final temperature at a heating rate of 1~1.5℃ / min.

12. The method for preparing a recrystallized silicon carbide product according to claim 1, characterized in that: The first dispersant is polyvinyl pyrrolidone or tetramethyl ammonium hydroxide, accounting for 1% to 5% of the total mass of the first silicon carbide powder and the second silicon carbide powder; The first binder is one of phenolic resin and epoxy resin or a mixture of the two, accounting for 3% to 10% of the total mass of the first silicon carbide powder and the second silicon carbide powder.

13. The method for preparing a recrystallized silicon carbide product according to claim 1, characterized in that: The second dispersant is polyvinyl pyrrolidone or tetramethyl ammonium hydroxide, accounting for 1% to 3% of the total mass of the third silicon carbide powder and the fourth silicon carbide powder; The second binder is one of phenolic resin and epoxy resin or a mixture of the two, accounting for 3% to 10% of the total mass of the third silicon carbide powder and the fourth silicon carbide powder.

14. A recrystallized silicon carbide product prepared by the method according to any one of claims 1 to 13.

15. The recrystallized silicon carbide product according to claim 14, characterized in that The density of the recrystallized silicon carbide product can reach 3.0g / cm 3 The above has a porosity of 1% to 7% and an average pore size of 3 μm to 10 μm.

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