Silicon carbide ceramic material with complex shape, preparation method and application thereof

Abstract

This invention belongs to the field of ceramic material preparation technology, and relates to a method for preparing complex-shaped silicon carbide ceramic materials using gel casting combined with pressureless sintering. The raw materials for this silicon carbide ceramic material consist of the following components by weight: 90-110 parts W0.5 silicon carbide micropowder (pressureless silicon carbide micropowder); 1-5 parts W1.5 boron carbide; 0.4-1.0 parts tetramethylammonium hydroxide; 8-12 parts of monomers A and B; 0.1-0.5 parts methylenebisacrylamide; 0.04-0.1 parts ammonium persulfate; 0.01-0.1 parts tetramethylethylenediamine; and 35-45 parts deionized water. This invention uses untreated silicon carbide powder, which is directly used for gel casting. The overall process is simple and easy to operate. Combined with pressureless sintering, it can prepare various complex-shaped, high-density silicon carbide ceramic parts.

Description

Technical Field

[0001] This invention belongs to the field of ceramic material preparation technology, and relates to a method for preparing complex-shaped silicon carbide ceramic materials by gel casting combined with pressureless sintering. Background Technology

[0002] Pressureless silicon carbide, as a structural ceramic material, is not affected by residual silicon between internal particles compared to reactive silicon carbide. It has advantages in physical and chemical properties such as strength, wear resistance, high temperature resistance, and corrosion resistance, making it widely used in chemical, metallurgical, mining, aerospace and military industries.

[0003] Gel injection molding utilizes polymer monomer polymerization to transform liquid slurry into solid green bodies. Combined with corresponding ceramic sintering processes, it can produce irregularly shaped parts that cannot be obtained by conventional pressure molding. Furthermore, it has the advantages of simple process equipment requirements, low organic matter addition, high density and strength of the green body, and large product wall thickness for other irregular product forming processes, such as injection molding, slip casting, and hot pressing. In addition to silicon carbide, it can be applied to other ceramic materials, such as alumina, zirconium oxide, and silicon nitride.

[0004] Gel casting requires a slurry with low viscosity (less than 1000 mPa·s), good dispersibility, controllable curing, and high solid content, thus placing certain requirements on raw material dosage and process control. Chinese patent application No. 102875150B discloses a method for preparing silicon carbide ceramic impellers through gel casting and pressureless sintering. The raw material is pretreated powder; specifically, silicon carbide powder, carbon black powder, and boron carbide powder or boron powder are added to a deionized water medium, using glycerol as a dispersant. The mixture is then ball-milled, vibrated-milled, or stirred-milled. The slurry is then vacuum-dried, crushed, sieved, or spray-dried to obtain a uniformly mixed powder. The initiator and catalyst in the slurry are simultaneously added and stirred during vacuum degassing, which may lead to "bursting polymerization" and premature curing. Chinese patent application No. 114988880B discloses a method for preparing silicon carbide ceramics by gel casting molding and pressureless sintering. Modified silicon carbide powder is used as raw material, and an anti-gelling agent is added to the slurry to prolong the polymerization time. However, if vacuuming is not performed before casting, air bubbles are easily introduced.

[0005] The aforementioned pretreatment and modification are all aimed at increasing the mass ratio of silicon carbide in the slurry, i.e., the solid content, to match the solid content and dispersibility of this process. In addition, they are also to avoid excessive shrinkage leading to drying cracks. Therefore, they are essential pretreatment processes. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a silicon carbide ceramic material with complex shape, its preparation method and its application.

[0007] To solve the above-mentioned technical problems, the present invention provides a silicon carbide ceramic material (silicon carbide ceramic parts) that can be used for complex shapes. The raw materials of the silicon carbide ceramic material are composed of the following components in parts by weight: 90-110 parts of W0.5 silicon carbide micro powder (silicon carbide unpressurized micro powder); 1-5 parts of W1.5 boron carbide; 0.4-1.0 parts of tetramethylammonium hydroxide; 8-12 parts of monomer A and monomer B; 0.1-0.5 parts of methylenebisacrylamide; 0.04-0.1 parts of ammonium persulfate; 0.01-0.1 parts of tetramethylethylenediamine; and 35-45 parts of deionized water.

[0008] Nymethylenebisacrylamide was used as a crosslinking agent, ammonium persulfate as an initiator, and tetramethylethylenediamine as a catalyst.

[0009] As an improvement of the present invention for use in silicon carbide ceramic materials with complex shapes: monomer A is acrylamide, monomer B is hydroxyethyl methacrylate, and the mass ratio of monomer A to B is 5-8:2-6.

[0010] The present invention also provides a method for preparing the above-mentioned silicon carbide ceramic material with complex shapes, comprising the following steps:

[0011] 1) Pre-mixed solution preparation:

[0012] Monomer A and N-methylbisacrylamide were added to deionized water and mixed to dissolve, yielding pre-treatment solution I; tetramethylammonium hydroxide and ammonium persulfate were added to deionized water and mixed to dissolve, yielding pre-treatment solution II; tetramethylethylenediamine was added to monomer B and mixed, yielding pre-treatment solution III.

[0013] 2) Slurry mixing and defoaming:

[0014] At room temperature, (60±5)% of pre-prepared solution II is added to pre-prepared solution I, followed by the addition of W0.5 silicon carbide micro powder (silicon carbide pressureless micro powder) and W1.5 boron carbide. The mixture is mechanically stirred for 1–5 h to disperse it (to obtain a dispersed mixture). Then, the remaining pre-prepared solution II is added and stirred for 1–5 min. Next, pre-prepared solution III is added and stirred for 1–10 min. Finally, vacuum stirring is performed for 2–10 min to achieve degassing (vacuum degassing) and obtain silicon carbide slurry.

[0015] Step 2) can be performed using a vacuum mixer;

[0016] 3) Green body forming:

[0017] The silicon carbide slurry obtained in step 2) is injected into the mold for slurry casting and molding. It is then heated and cured in an oven. After the curing is completed, the mold is removed, and the resulting blank (with a sponge at the bottom) is naturally cooled to room temperature and left at room temperature for a period of time. Then it is placed in the oven for segmented heating and drying.

[0018] Note: The mold can be set according to actual needs to obtain parts with complex shapes;

[0019] 4) Degreasing of the raw clay body:

[0020] After machining the material obtained in step 3) into the required shape, place it in a degumming furnace, or place the material obtained in step 3) directly into a degumming furnace and degrease it under inert gas protection (i.e., flowing nitrogen or argon gas, etc., is passed through the degumming furnace) by heating to 800-900℃ and holding for 1-3 hours.

[0021] 5) Sintering:

[0022] The material obtained in step 4) is heated to 2100-2200℃ and held for 1-3 hours for pressureless sintering to obtain silicon carbide ceramic blanks.

[0023] As an improvement to the preparation method of silicon carbide ceramic materials with complex shapes according to the present invention: the mass ratio of deionized water used in pre-prepared solution I to deionized water used in pre-prepared solution II is 8.8-9.2:0.8-1.2.

[0024] As a further improvement to the method of preparing silicon carbide ceramic materials with complex shapes according to the present invention: in step 3):

[0025] The heating and curing temperature is 40–80°C, and the time is 0.5–1.5 hours;

[0026] After cooling to room temperature, leave at room temperature for 6–24 hours.

[0027] Segmented heating and drying: raise the temperature to 60±5℃ and hold for 4 to 12 hours, then raise the temperature to 80±5℃ and hold for 4 to 12 hours, then raise the temperature to 120±5℃ and hold for 4 to 12 hours.

[0028] As a further improvement to the method of preparing silicon carbide ceramic materials with complex shapes according to the present invention:

[0029] The heating rate in step 3) of segmented heating and drying is 1-5℃ / min;

[0030] The heating rate in step 4) is 1–5 °C / min;

[0031] The heating rate in step 5) is 2 to 10 °C / min.

[0032] As a further improvement to the method of preparing silicon carbide ceramic materials with complex shapes according to the present invention: the stirring rate in step 2) is 200-400 r / min.

[0033] This invention relates to a method for preparing complex-shaped silicon carbide ceramic materials using gel casting combined with pressureless sintering. Addressing the problem of increased viscosity due to slurry reaction during vacuum degassing, this invention provides a simple, highly operable, and pressureless silicon carbide preparation method that requires no raw material modification. This invention uses untreated silicon carbide powder directly for gel casting, resulting in a simple and highly operable process. Combined with pressureless sintering, it can prepare various complex-shaped, high-density silicon carbide ceramic parts.

[0034] This invention has the following technical advantages:

[0035] 1. This invention uses two monomers, namely, hydroxyethyl methacrylate to partially replace acrylamide, which reduces the amount of toxic acrylamide while ensuring the stability of the green body forming and sintering, and at the same time extends the gel time of the slurry before casting to avoid premature curing, thereby successfully completing the two steps of stirring vacuum (degassing) + slurry casting.

[0036] 2. This invention does not require modification or pretreatment of silicon carbide raw material powder. The raw materials and processes are simple, saving costs. It is highly operable and suitable for small-batch production.

[0037] 3. By using gel casting molding combined with pressureless sintering, the green body of this invention has uniform drying shrinkage, is not prone to cracking, has low porosity, and can produce irregularly shaped silicon carbide ceramic products with high density and good appearance.

[0038] Using the method of this invention, silicon carbide ceramic products with high density, high strength and complex shape can be prepared. Since silicon carbide material has corrosion resistance, this invention can be applied to the preparation of complex-shaped components such as impellers that require corrosion resistance. Attached Figure Description

[0039] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0040] Figure 1 A silicon carbide ceramic impeller component prepared using the material of the present invention;

[0041] Figure 2 The images show silicon carbide ceramic irregular shapes prepared using the materials of this invention (the left and right images represent the front and back sides, respectively). Detailed Implementation

[0042] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0043] W0.5 and W1.5 represent different particle size designations. W0.5 has a particle size of 0–0.5 μm, while W1.5 has a particle size of 0.5–1.5 μm. This is common knowledge in the industry.

[0044] Example 1: A method for producing silicon carbide ceramic materials with complex shapes, comprising the following steps:

[0045] S1: Weigh out by weight the following components: 90 parts W0.5 silicon carbide micro powder (unpressurized silicon carbide micro powder); 1 part W1.5 boron carbide; 1.0 part tetramethylammonium hydroxide; 5.6 parts acrylamide; 2.4 parts hydroxyethyl methacrylate; 0.5 parts methylenebisacrylamide; 0.1 part ammonium persulfate; 0.01 part tetramethylethylenediamine; and 35 parts deionized water.

[0046] S2: Add acrylamide and methylenebisacrylamide to deionized water, mix and dissolve to obtain pre-treatment solution I. Add tetramethylammonium hydroxide and ammonium persulfate to deionized water, mix and dissolve to obtain pre-treatment solution II. The mass ratio of deionized water used in pre-treatment solution I to deionized water used in pre-treatment solution II is 9:1. Add tetramethylethylenediamine to hydroxyethyl methacrylate and mix to obtain pre-treatment solution III.

[0047] S3: At room temperature, take 60% of pre-prepared liquid II and add it to pre-prepared liquid I. Then add silicon carbide micro powder and boron carbide. Stir mechanically for 1 hour at a speed of 200 r / min to obtain a dispersed mixture. Then add the remaining pre-prepared liquid II and stir for 1 min. Then add pre-prepared liquid III and stir for 1 min. Finally, switch to vacuum stirring for 3 min to achieve vacuum degassing and obtain silicon carbide slurry.

[0048] This step can be performed using a vacuum mixer;

[0049] S4: Inject the silicon carbide slurry into the mold for slurry casting and molding. Heat it in the oven to 80°C for curing (about 0.5 hours). After curing, demold the blank, place a sponge at the bottom of the blank, let it cool naturally to room temperature and leave it at room temperature for 24 hours. Then, put the blank (along with the sponge) back into the oven and heat it in stages to 60°C, 80°C and 120°C for 12 hours each to dry.

[0050] S5: The material obtained after drying in step S4 is machined into the required shape and then placed in a degumming furnace, or directly placed in a degumming furnace and degreased at 800°C for 1 hour under flowing nitrogen (i.e., under nitrogen protection) at a heating rate of 1°C / min.

[0051] S6: After degreasing, heat to 2100℃ at a heating rate of 2℃ / min and hold for 1 hour to obtain a dense silicon carbide blank through pressureless sintering.

[0052] Example 2: A method for producing silicon carbide ceramic materials with complex shapes, comprising the following steps:

[0053] S1: Weigh out the following by weight: 100 parts W0.5 silicon carbide micro powder (unpressurized silicon carbide micro powder); 3 parts W1.5 boron carbide; 0.7 parts tetramethylammonium hydroxide; 6 parts acrylamide; 4 parts hydroxyethyl methacrylate; 0.25 parts methylenebisacrylamide; 0.04 parts ammonium persulfate; 0.055 parts tetramethylethylenediamine; and 40 parts deionized water.

[0054] S2: Add acrylamide and methylenebisacrylamide to deionized water, mix and dissolve to obtain pre-treatment solution I. Add tetramethylammonium hydroxide and ammonium persulfate to deionized water, mix and dissolve to obtain pre-treatment solution II. The mass ratio of deionized water used in pre-treatment solution I to deionized water used in pre-treatment solution II is 9:1. Add tetramethylethylenediamine to hydroxyethyl methacrylate and mix to obtain pre-treatment solution III.

[0055] S3: At room temperature, take 60% of pre-prepared liquid II and add it to pre-prepared liquid I. Then add silicon carbide micro powder and boron carbide. Stir mechanically at 300 r / min for 2.5 h to obtain a dispersed mixture. Then add the remaining pre-prepared liquid II and stir for 2 min. Then add pre-prepared solution III and stir for 2 min. Finally, switch to vacuum stirring for 6.5 min to achieve vacuum degassing and obtain silicon carbide slurry.

[0056] This step can be performed using a vacuum mixer;

[0057] S4: Inject silicon carbide slurry into the mold for slurry casting and molding. Heat to 60°C in the oven for curing (about 1.0 hour). After curing, demold the blank, place a sponge at the bottom of the blank, let it cool naturally to room temperature and leave it at room temperature for 15 hours. Then, put the blank (along with the sponge) back into the oven and heat it in stages to 60°C, 80°C and 120°C for 8 hours to dry.

[0058] S5: The material obtained after drying in step S4 is machined into the required shape and then placed in a degumming furnace, or directly placed in a degumming furnace and degreased at 850°C for 1 hour under flowing nitrogen (i.e., under nitrogen protection) at a heating rate of 3°C / min.

[0059] S6: After degreasing, heat to 2150℃ at a heating rate of 6℃ / min and hold for 2 hours to obtain a dense silicon carbide blank through pressureless sintering.

[0060] Example 3: A method for producing silicon carbide ceramic materials with complex shapes, comprising the following steps:

[0061] S1: Weigh out by weight the following components: 110 parts W0.5 silicon carbide micro powder (unpressurized silicon carbide micro powder); 5 parts W1.5 boron carbide; 0.4 parts tetramethylammonium hydroxide; 6 parts acrylamide; 6 parts hydroxyethyl methacrylate; 0.5 parts methylenebisacrylamide; 0.07 parts ammonium persulfate; 0.1 parts tetramethylethylenediamine; and 45 parts deionized water.

[0062] S2: Add acrylamide and methylenebisacrylamide to deionized water, mix and dissolve to obtain pre-treatment solution I. Add tetramethylammonium hydroxide and ammonium persulfate to deionized water, mix and dissolve to obtain pre-treatment solution II. The mass ratio of deionized water used in pre-treatment solution I to deionized water used in pre-treatment solution II is 9:1. Add tetramethylethylenediamine to hydroxyethyl methacrylate and mix to obtain pre-treatment solution III.

[0063] S3: At room temperature, take 60% of pre-prepared liquid II and add it to pre-prepared liquid I. Then add silicon carbide micro powder and boron carbide. Stir mechanically for 5 hours at 400 r / min to obtain a dispersed mixture. Then add the remaining pre-prepared liquid II and stir for 3 minutes. Then add pre-prepared liquid III and stir for 3 minutes. Finally, switch to vacuum stirring for 10 minutes to achieve vacuum degassing and obtain silicon carbide slurry.

[0064] This step can be performed using a vacuum mixer;

[0065] S4: Inject the silicon carbide slurry into the mold for slurry casting and molding. Heat it in the oven to 40°C for curing (about 1.5 hours). After curing, demold the blank, place a sponge at the bottom of the blank, let it cool naturally to room temperature and leave it at room temperature for 6 hours. Then put the blank (along with the sponge) back into the oven and heat it in stages to 60°C, 80°C and 120°C for 4 hours to dry.

[0066] S5: The material obtained after drying in step S4 is machined into the required shape and then placed in a degumming furnace, or directly placed in a degumming furnace and degreased at 900°C for 2 hours under flowing nitrogen (i.e., under nitrogen protection) at a heating rate of 5°C / min.

[0067] S6: After degreasing, heat to 2200℃ at a heating rate of 10℃ / min and hold for 3 hours to obtain a dense silicon carbide blank through pressureless sintering.

[0068] The test data and results of the silicon carbide ceramics prepared in Examples 1-3 above are shown in Table 1.

[0069] Table 1 Test Data

[0070]

[0071] Comparative Example 1: The "6 parts acrylamide; 4 parts hydroxyethyl methacrylate" in Example 2 was changed to "4 parts acrylamide; 6 parts hydroxyethyl methacrylate", that is, the amount of hydroxyethyl methacrylate was higher than that of acrylamide, while the total amount of both remained unchanged, and the rest was the same as in Example 2.

[0072] The test data and results are shown in Table 1 above.

[0073] Comparative Example 2: The "6 parts acrylamide; 4 parts hydroxyethyl methacrylate" in Example 2 was changed to "10 parts acrylamide; 0 parts hydroxyethyl methacrylate", that is, the total amount of both remained unchanged, and the rest was the same as in Example 2.

[0074] The test data and results are shown in Table 1 above.

[0075] Comparative Example 3: Steps S2 and S3 of Example 2 are omitted and replaced with the following: The components weighed in step S1 are mixed. The powder agglomerates and cannot be made into a slurry, therefore subsequent steps cannot be performed.

[0076] Comparative Example 4: Step S3 of Example 2 is modified as follows:

[0077] S3: At room temperature, pre-prepared liquid I, pre-prepared liquid II, pre-prepared solution III, silicon carbide micro powder, and boron carbide are mixed and mechanically stirred for 2.6 hours, then vacuum stirred for 6.5 minutes to achieve vacuum degassing and obtain silicon carbide slurry; the rest is the same as in Example 2.

[0078] The test data and results are shown in Table 1 above.

[0079] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing silicon carbide ceramic materials with complex shapes, characterized in that: The raw materials for silicon carbide ceramic materials consist of the following components in parts by weight: 90-110 parts of W0.5 silicon carbide micro powder; 1-5 parts of W1.5 boron carbide; 0.4-1.0 parts of tetramethylammonium hydroxide; 8-12 parts of monomer A and monomer B combined; 0.1-0.5 parts of methylenebisacrylamide; 0.04-0.1 parts of ammonium persulfate; 0.01-0.1 parts of tetramethylethylenediamine; and 35-45 parts of deionized water. Monomer A is acrylamide, and monomer B is hydroxyethyl methacrylate. The mass ratio of monomer A to B is 5-8:2-6. Includes the following steps: 1) Pre-mixed solution preparation: Monomer A and N-methylbisacrylamide were added to deionized water and mixed to dissolve, yielding pre-treatment solution I; tetramethylammonium hydroxide and ammonium persulfate were added to deionized water and mixed to dissolve, yielding pre-treatment solution II; tetramethylethylenediamine was added to monomer B and mixed, yielding pre-treatment solution III. 2) Slurry mixing and defoaming: At room temperature, take (60±5)% of pre-prepared solution II and add it to pre-prepared solution I. Then add W0.5 silicon carbide pressureless micro powder and W1.5 boron carbide and stir for 1-5 hours to disperse. Then add the remaining pre-prepared solution II and stir for 1-5 minutes. Then add pre-prepared solution III and stir for 1-10 minutes. Then switch to vacuum stirring for 2-10 minutes to achieve degassing and obtain silicon carbide slurry. 3) Green body forming: The silicon carbide slurry obtained in step 2) is injected into the mold for slurry casting and molding. It is then heated and cured in an oven. After the heating and curing is completed, the mold is removed, and the resulting green blank is naturally cooled to room temperature and placed at room temperature. Then it is placed in the oven for segmented heating and drying. 4) Degreasing of the raw clay body: After machining the material obtained in step 3) into the desired shape, place it in a degumming furnace, or place the material obtained in step 3) directly into a degumming furnace and degrease it by heating it to 800-900℃ and holding it for 1-3 hours under inert gas protection. 5) Sintering: The material obtained in step 4) is heated to 2100-2200℃ and held for 1-3 hours for pressureless sintering to obtain silicon carbide ceramic blanks.

2. The method for preparing silicon carbide ceramic materials with complex shapes according to claim 1, characterized in that: The mass ratio of deionized water used in pretreatment solution I to deionized water used in pretreatment solution II is 8.8–9.2:0.8–1.

2.

3. The method for preparing silicon carbide ceramic materials with complex shapes according to claim 1 or 2, characterized in that: In step 3): The heating and curing temperature is 40–80°C, and the time is 0.5–1.5 hours; After cooling to room temperature, leave at room temperature for 6–24 hours. Segmented heating and drying: raise the temperature to 60±5℃ and hold for 4 to 12 hours, then raise the temperature to 80±5℃ and hold for 4 to 12 hours, then raise the temperature to 120±5℃ and hold for 4 to 12 hours.

4. The method for preparing silicon carbide ceramic materials with complex shapes according to claim 3, characterized in that: The heating rate in step 4) is 1–5 °C / min; The heating rate in step 5) is 2 to 10 °C / min.

5. The method for preparing silicon carbide ceramic materials with complex shapes according to claim 4, characterized in that: The stirring rate in step 2) is 200-400 r / min.

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