A high-strength silicon carbide ceramic and its preparation method

Abstract

This invention belongs to the field of silicon carbide ceramic preparation, specifically relating to a high-strength silicon carbide ceramic and its preparation method. The preparation method of the high-strength silicon carbide ceramic of this invention includes the following steps: the main raw material is composed of the following components in the following proportions: 80-95 wt% submicron α-silicon carbide powder, 1-7 wt% alumina, 1-8 wt% yttrium oxide, 1-3 wt% polyethylene glycol, and 1-2 wt% polyvinyl alcohol; the main raw material is ball-milled and dispersed with deionized water to prepare a water-based slurry; the water-based slurry is spray-granulated to prepare ceramic granulated powder; the ceramic granulated powder is hot-pressed and sintered to obtain the high-strength silicon carbide ceramic.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide ceramic preparation, specifically relating to a high-strength silicon carbide ceramic and its preparation method. Background Technology

[0002] Dry gas sealing is a novel shaft end sealing technology that utilizes gas for sealing. It is a non-contact seal with extremely wide applications. The dynamic ring of a dry gas seal operates in a high-pressure environment for extended periods, placing extremely high demands on the material's strength, toughness, corrosion resistance, and coefficient of friction. Silicon carbide ceramic, a commonly used special ceramic material in industry, possesses excellent properties such as high strength, high hardness, high temperature resistance, chemical corrosion resistance, wear resistance, and thermal shock resistance, thus finding applications in many fields including petroleum, chemical, machinery, electronics, and aerospace. While silicon carbide ceramic materials have stable chemical properties, their poor toughness and brittleness limit their application in dry gas seal dynamic rings. Improving the mechanical properties of silicon carbide ceramic sealing materials through methods such as modified sintering techniques represents a future development direction in this field. Industrially, silicon carbide ceramic sealing materials are mainly prepared through reaction sintering and pressureless sintering. The former involves a chemical reaction between carbon and silicon sources at high temperatures to generate silicon carbide, resulting in lower density and excess silicon residue. The latter, pressureless sintering, involves sintering silicon carbide powder into a dense material at high temperatures under normal pressure. Due to the higher difficulty of sintering, sintering aids are needed to promote mass transfer during the sintering process. Both sintering techniques result in silicon carbide ceramic sealing materials with low strength, limiting their application in dry gas sealing.

[0003] With the continuous development of sintering technology, the sintering technology of silicon carbide ceramics has evolved from reaction sintering and pressureless sintering to hot pressing sintering. Hot pressing sintering involves heating a silicon carbide powder green body while simultaneously applying external pressure along the axial direction through mechanical action. This provides additional driving force for the entire sintering process, enabling the green body to rapidly densify and achieving simultaneous sintering and forming. Because the external pressure provides additional sintering driving force, hot pressing sintering significantly reduces the temperature, time, and amount of sintering aids required for densification of silicon carbide materials compared to pressureless sintering. Simultaneously, the overall mechanical properties of silicon carbide ceramics are significantly improved. Therefore, hot pressing sintering is an efficient method for preparing high-performance silicon carbide ceramic materials, possessing significant research significance and engineering value for the development of silicon carbide ceramic materials.

[0004] Currently, there are reports on the preparation of high-strength and high-toughness silicon carbide ceramic materials by hot pressing sintering. CN202011027381.4 discloses a high-toughness hot-pressed sintered silicon carbide sealing ring and its preparation method. The main raw materials used are silicon carbide, polyvinyl alcohol, maltose, bamboo charcoal powder, chromium powder, alumina, barium carbonate, talc powder, wollastonite, and bentonite. The cost of silicon carbide ceramics is reduced mainly by introducing mineral components, resulting in a final strength of only 550 MPa. CN202011027381.4 also discloses a silicon carbide ceramic material and its preparation method. Boron carbide is introduced in liquid phase as a sintering aid, and hot pressing sintering is used to prepare a high-purity, high-thermal-conductivity silicon carbide ceramic material with a density of 99.59% and a thermal conductivity of 165.6 W / (m·K). This process requires high pressure, reaching 80 MPa. CN201810164824.0 discloses a method for preparing a high-density, high-purity silicon carbide substrate material. Using β-silicon carbide and α-silicon carbide as raw materials, without adding sintering aids, high-purity silicon carbide ceramics with a relative density of 98% are prepared by hot pressing sintering. However, no related mechanical properties have been reported. CN201710917024.7 discloses a high thermal conductivity liquid-phase sintered silicon carbide ceramic and its preparation method. Using silicon carbide powder as raw material and cerium oxide, yttrium oxide, and erbium oxide as sintering aids, high thermal conductivity liquid-phase sintered silicon carbide ceramics are prepared by hot pressing sintering. Its thermal conductivity is 150 W / (m·K), but no flexural strength related properties have been reported.

[0005] The invention CN113511899A, "Preparation Method and Application of Wear-Resistant Silicon Carbide Ceramics," employs pressureless sintering. Pressureless sintering is carried out under argon protection at a sintering temperature of 1650–1700℃. After holding at this temperature for 2.5–3.5 hours, the temperature is slowly lowered to 1350–1450℃, and then cooled to obtain the final product. The raw materials involved are as follows: by mass, 95–99 parts of α-SiC micro powder and 0.4–1 parts of sintering aid are added to 100–105 parts of deionized water and mixed evenly. Then, 2.5–4 parts of dispersant, 0.3–0.8 parts of forming agent, and 0.1–0.9 parts of binder are added and mixed evenly to obtain a grinding mixture. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a high-strength silicon carbide ceramic that can improve the room temperature strength of silicon carbide ceramics and its preparation method.

[0007] To solve the above-mentioned technical problems, the present invention provides a method for preparing high-strength silicon carbide ceramics, comprising the following steps:

[0008] 1) Main raw materials for equipment:

[0009] The main raw material is composed of the following components: 80-95 wt% submicron α-silicon carbide powder, 1-7 wt% alumina, 1-8 wt% yttrium oxide, 1-3 wt% polyethylene glycol, and 1-2 wt% polyvinyl alcohol.

[0010] Note: Submicron α-silicon carbide powder is used as the matrix, alumina and yttrium oxide are mixed as sintering aids, polyethylene glycol is used as a dispersant, and polyvinyl alcohol is used as a binder;

[0011] 2) Slurry preparation:

[0012] The main raw material and deionized water are ball-milled and dispersed according to a weight ratio of 1:1 to 1.5 to obtain a water-based slurry.

[0013] 3) Spray granulation:

[0014] The water-based slurry obtained in step 2) is spray-granulated to prepare ceramic granulated powder (spherical ceramic granulated powder);

[0015] 4) Hot pressing and sintering:

[0016] The ceramic granules obtained in step 3) are hot-pressed and sintered to obtain high-strength silicon carbide ceramics.

[0017] As an improvement to the preparation method of the high-strength silicon carbide ceramic of the present invention: the spray granulation in step 3) is as follows: the water-based slurry feed rate is 40-60 mL / min, the hot air inlet temperature is 250-300℃, the outlet temperature is 70-90℃, and the centrifugal atomizer speed is 40-70 Hz.

[0018] As a further improvement to the preparation method of the high-strength silicon carbide ceramic of the present invention: the hot pressing sintering in step 4) is as follows: the temperature is raised to the holding temperature at a heating rate of 10-20℃ / min, and then held at the holding temperature for 60±5min; the holding temperature is 1900-2000℃ (preferably 1950-2000℃), the applied initial external pressure is 10-20MPa, and the external pressure during the holding stage is 30-40MPa.

[0019] As a further improvement to the preparation method of the high-strength silicon carbide ceramic of the present invention, in step 4):

[0020] The ceramic granulated powder (spherical ceramic granulated powder) obtained in step 3) is loaded into the graphite mold of the hot pressing sintering furnace for hot pressing sintering.

[0021] After the heat preservation is completed, the product is cooled and demolded to obtain high-strength silicon carbide ceramic.

[0022] As a further improvement to the preparation method of the high-strength silicon carbide ceramic of the present invention:

[0023] In step 3), the preferred slurry feed rate is 40 mL / min, the hot air inlet temperature is 280℃, the outlet temperature is 86℃, and the centrifugal atomizer frequency is 48 Hz.

[0024] In step 4), the preferred heating rate is 10℃ / min, the holding temperature range is 1950℃, the initial external pressure is 10MPa, and the external pressure during the holding stage is 30MPa.

[0025] The present invention also provides high-strength silicon carbide ceramics prepared using any of the above methods.

[0026] This invention relates to a method for preparing silicon carbide ceramic materials that combines hot pressing sintering with a yttrium aluminum garnet sintering aid system. The method involves filling a graphite mold with spherical granulated powder, placing it in a hot pressing sintering furnace, and applying external pressure through mechanical action during the heating and holding process. After sintering, the material is demolded and processed to obtain the desired silicon carbide ceramic material.

[0027] This invention relates to the successful preparation of a high-strength silicon carbide ceramic material using a hot-pressing sintering method combined with a yttrium aluminum garnet (YAG) sintering aid system. YAG, generated from the high-temperature reaction of alumina and yttrium oxide, is used as a sintering aid. Under high-temperature conditions, YAG forms a eutectic liquid phase, transforming the mass transfer mechanism of the ceramic powder from simple diffusion to viscous flow, thus promoting the sintering of silicon carbide ceramics. Simultaneously, the application of external pressure during sintering provides additional sintering driving force, reducing the difficulty of the silicon carbide ceramic sintering process and resulting in a high-density silicon carbide ceramic material with superior mechanical properties. This material has high practical value in special ceramic applications such as dry gas sealing. Attached Figure Description

[0028] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0029] Figure 1 These are SEM images of the cross-section of silicon carbide ceramic prepared in Example 1; the left image is magnified at 5kx, and the right image is magnified at 10kx.

[0030] Figure 2 These are SEM images of the cross-section of silicon carbide ceramic prepared in Example 2; the left image is magnified at 5kx, and the right image is magnified at 10kx.

[0031] Figure 3 These are SEM images of the cross-section of silicon carbide ceramic prepared in Comparative Example 1; the left image is magnified at 5k times, and the right image is magnified at 10k times. Detailed Implementation

[0032] 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:

[0033] The average particle size of submicron α-silicon carbide powder is about 0.5 μm; both alumina and yttrium oxide are required to pass through a 325-mesh sieve.

[0034] Example 1: A method for preparing high-strength silicon carbide ceramics, comprising the following steps:

[0035] 1) Main raw materials for equipment:

[0036] The main raw material (powder raw material) is composed of the following components in the following proportions: 87wt% submicron α-silicon carbide powder, 5wt% alumina, 5wt% yttrium oxide, 2wt% polyethylene glycol, and 1wt% polyvinyl alcohol.

[0037] 2) Slurry preparation:

[0038] The weighed main raw material (powder raw material) is added into a ball mill barrel, and 1.5 times the weight of deionized water is added to stir, ball mill and disperse to prepare a water-based slurry.

[0039] 3) Spray granulation:

[0040] Spherical ceramic granules were prepared by spray granulation of water-based slurry.

[0041] The parameters of the spray granulation tower are: hot air inlet temperature 280℃, outlet temperature 86℃, centrifugal atomizer frequency 48Hz. After the temperature of the granulation tower reaches the facility parameters, the feed pump is turned on and the water-based slurry is introduced into the granulation tower at a flow rate of 40mL / min, and finally ceramic granulated powder with uniform particle size (particle size is about 20 to 50μm) is obtained.

[0042] 4) Hot pressing and sintering:

[0043] Ceramic granulation powder is added to a graphite mold in a hot-press sintering furnace, and pressure is applied mechanically, increasing the pressure from 10 MPa to 30 MPa as the heating process proceeds.

[0044] That is, the temperature is increased to the holding temperature at a heating rate of 10℃ / min, and then held at the holding temperature for 60min; the holding temperature is 1950℃, the initial external pressure is 10MPa, and the external pressure during the holding stage is 30MPa.

[0045] After the heat preservation is completed, it is cooled along with the furnace.

[0046] 5) After sintering and cooling, the silicon carbide ceramic is demolded to obtain a high-strength silicon carbide ceramic, named S-1. In this formula, the sintering aid, composed of alumina and yttrium oxide, accounts for 10 wt% of the raw material powder.

[0047] Then, according to actual needs, through precision processing, high-density silicon carbide ceramic products of various sizes can be obtained.

[0048] The cross-sectional SEM image of the high-strength silicon carbide ceramic S-1 obtained in Example 1 is shown below. Figure 1 As shown, the silicon carbide ceramic obtained by hot pressing sintering has a tight grain bond, and no visible defects or voids were found between the grains. The relevant mechanical properties were tested using standard methods, and are shown in Table 1. Its flexural strength is 702 MPa. Note: The flexural strength was tested according to the three-point flexural strength test method in the national standard GB / T 6569-2006 "Flexural Strength of Fine Ceramics".

[0049] Example 2: A method for preparing high-strength silicon carbide ceramics:

[0050] The main raw material has been changed to consist of the following components: 92wt% submicron α-silicon carbide powder, 2.5wt% alumina, 2.5wt% yttrium oxide, 2wt% polyethylene glycol, and 1wt% polyvinyl alcohol.

[0051] The rest is the same as in Example 1.

[0052] The resulting high-strength silicon carbide ceramic was named S-2. Compared to Example 1, the sintering aid composed of alumina and yttrium oxide in Example 2 accounted for 5 wt% of the raw material powder.

[0053] The cross-sectional SEM image of the obtained high-strength silicon carbide ceramic S-2 is as follows: Figure 2 As shown, the bonding between silicon carbide ceramic grains is also very tight, with no visible defects or voids. However, compared to S-1, S-2 has a significantly smaller grain size. This indicates that when the sintering aid content is higher, the sintering aid forms more eutectic liquid phase, accelerating the mass transfer process and resulting in a higher grain growth rate, thus yielding larger grains. The relevant mechanical properties are shown in Table 1. Its flexural strength is 646 MPa, which is somewhat lower than that of Example 1, but still maintains a relatively high level.

[0054] Example 3: A method for preparing high-strength silicon carbide ceramics.

[0055] The main raw material has been changed to consist of the following components: 95wt% submicron α-silicon carbide powder, 1wt% alumina, 1wt% yttrium oxide, 2wt% polyethylene glycol, and 1wt% polyvinyl alcohol.

[0056] The rest is the same as in Example 1.

[0057] The resulting high-strength silicon carbide ceramic was named S-3. Compared to Example 1, the sintering aid composed of alumina and yttrium oxide in Example 3 accounted for 2 wt% of the raw material powder.

[0058] Compared with Examples 1 and 2, the high-strength silicon carbide ceramic S-3 showed certain defects and voids, and its mechanical properties were significantly reduced. Its bending strength was 587 MPa, indicating that too little sintering aid would seriously affect the performance.

[0059] Example 4: A method for preparing high-strength silicon carbide ceramics.

[0060] The main raw material has been changed to consist of the following components: 80wt% submicron α-silicon carbide powder, 7wt% alumina, 8wt% yttrium oxide, 3wt% polyethylene glycol, and 2wt% polyvinyl alcohol.

[0061] The rest is the same as in Example 1.

[0062] The resulting high-strength silicon carbide ceramic was named S-4. Compared to Example 1, the sintering aid composed of alumina and yttrium oxide in Example 4 accounted for 15 wt% of the raw material powder.

[0063] Compared to Example 1, the internal grain composition of the high-strength silicon carbide ceramic S-4 is more compact, but its bulk density and strength have decreased to a certain extent. The flexural strength is 686 MPa, indicating that although adding too much sintering aid to the raw materials can promote the sintering process, its low density and strength, and its large presence in the ceramic matrix, will affect the mechanical properties of the ceramic.

[0064] Example 5: A method for preparing high-strength silicon carbide ceramics.

[0065] The hot pressing sintering in step 4) is changed to: heating to the holding temperature at a heating rate of 20℃ / min, and then holding at the holding temperature for 60min; the holding temperature is 2000℃, the initial external pressure is 20MPa, and the external pressure during the holding stage is 40MPa.

[0066] The rest is the same as in Example 1.

[0067] The resulting high-strength silicon carbide ceramic was named S-5. Compared to Example 1, Example 5 improved the heating rate, the holding temperature for ceramic hot pressing sintering, and the applied pressure.

[0068] Compared to Example 1, the overall structure of the high-strength silicon carbide ceramic S-5 remains largely unchanged, and its flexural strength is 713 MPa, with little variation. This indicates that the sintering pressure conditions in Example 1 have achieved a relatively good sintering effect.

[0069] Example 6: A method for preparing high-strength silicon carbide ceramics.

[0070] The hot pressing sintering in step 4) is changed to: heating to the holding temperature at a heating rate of 10℃ / min, and then holding at the holding temperature for 60min; the holding temperature is 1900℃, the initial external pressure is 10MPa, and the external pressure during the holding stage is 30MPa.

[0071] The rest is the same as in Example 1.

[0072] The resulting high-strength silicon carbide ceramic was named S-6. The main difference between Example 1 and Example 6 is that the hot-pressing sintering temperature of the ceramic is 1900℃.

[0073] Compared to Example 1, the density of the high-strength silicon carbide ceramic S-6 decreased slightly, and its flexural strength was 611 MPa, showing a slight decrease. This indicates that under the same sintering conditions, a holding temperature of 1900°C is not sufficient to completely sinter the ceramic into a dense state.

[0074] Comparative Example 1: A method for preparing silicon carbide ceramics by hot pressing sintering without adding sintering aids:

[0075] Compared to Example 1, the composition of the main raw material (powder raw material) was changed to: 98wt% submicron α-silicon carbide micro powder, 1wt% polyethylene glycol, and 1wt% polyvinyl alcohol.

[0076] The rest is the same as in Example 1.

[0077] The resulting silicon carbide ceramic was named S-7. The main difference between Comparative Example 1 and Example 1 is that no sintering aid was added.

[0078] The silicon carbide ceramic S-7 exhibits very poor density and large grain size, indicating that under the same sintering conditions, sintering aids, in addition to promoting sintering, also inhibit grain growth. Furthermore, significant voids are present between the grains, indicating that the silicon carbide material has not achieved densification. This suggests that without sintering aids, higher holding temperatures and more stringent sintering conditions are required. Additionally, the flexural strength of S-7 is only 297 MPa, showing a significant decrease in mechanical properties, largely due to the lack of densification during sintering.

[0079] Comparative Example 2: Compared to Example 1, the initial external pressure was changed from 10 MPa to 30 MPa, meaning that the external pressure was 30 MPa regardless of whether it was the heating or heat preservation stage. Everything else was the same as in Example 1.

[0080] The resulting silicon carbide ceramic was named S8. Mechanical property tests revealed that the density of silicon carbide ceramic S8 was slightly lower than that of Example 1, with a density of 3.17 g / cm³. 2Furthermore, the mechanical strength also decreases. On the one hand, in the early stages of sintering, due to the low temperature and small sintering driving force, applying relatively large external pressure from the beginning can damage the internal structure of the preform, causing internal defects and resulting in a decrease in density and mechanical properties. This invention, through a gradual pressurization method, also avoids the hot-pressing sintering furnace operating under high pressure for extended periods, thus reducing the overall operating pressure of the hot-pressing sintering furnace.

[0081] Table 1 Mechanical properties of silicon carbide ceramic samples obtained from each embodiment and comparative example.

[0082]

[0083] Note: The above sample is a strip-shaped sample with dimensions of 3*4*40mm.

[0084] 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 high-strength silicon carbide ceramic, characterized in that... Includes the following steps: 1) Main raw materials for equipment: The main raw material consists of the following components in the following proportions: 87 wt% submicron α-silicon carbide powder, 5 wt% alumina, 5 wt% yttrium oxide, 2 wt% polyethylene glycol, and 1 wt% polyvinyl alcohol. 2) Slurry preparation: The main raw material and deionized water are ball-milled and dispersed to prepare a water-based slurry by a weight ratio of 1:1 to 1.

5. 3) Spray granulation: The water-based slurry obtained in step 2) is spray-granulated to prepare ceramic granulated powder. The spray granulation process is as follows: slurry feed rate 40 mL / min, hot air inlet temperature 280 ℃, outlet temperature 86 ℃, and centrifugal atomizer frequency 48 Hz. 4) Hot pressing and sintering: The ceramic granulated powder obtained in step 3) is hot-pressed and sintered to obtain high-strength silicon carbide ceramics. The hot pressing sintering process is as follows: the heating rate is 10 ℃ / min, the holding temperature is 1950 ℃, the applied initial external pressure is 10 MPa, and the external pressure during the holding stage is 30 MPa.

2. The method for preparing high-strength silicon carbide ceramics according to claim 1, characterized in that... In step 4): The ceramic granulated powder obtained in step 3) is loaded into the graphite mold of the hot pressing sintering furnace for hot pressing sintering. After the heat preservation is completed, the product is cooled and demolded to obtain high-strength silicon carbide ceramic.

3. High-strength silicon carbide ceramics prepared by any one of claims 1 to 2.

Images