A low-viscosity silicon carbide ceramic slurry, a preparation method and application thereof

Abstract

The application relates to the technical field of ceramic materials, in particular to a low-viscosity silicon carbide ceramic slurry as well as a preparation method and application thereof. The silicon carbide ceramic slurry comprises modified alpha-SiC powder and a dispersant, wherein the dispersant comprises tetramethylammonium hydroxide or a combination of tetramethylammonium hydroxide and octadecylamine polyoxyethylene ether. The powder modified by Al(NO3)3 and sodium humate has better hydrophilicity, and the zeta potential on the surface is negative; the sodium humate is adsorbed on the surface of the alpha-SiC powder to form steric hindrance to prevent the powder from gathering and depositing; the tetramethylammonium hydroxide is ionized in water to generate OH ‑ A strong alkaline environment is provided for the solution, the Zeta negative potential on the surface is improved, and the agglomeration of the alpha-SiC powder is prevented. When the octadecylamine polyoxyethylene ether is added, the octadecylamine polyoxyethylene ether is also adsorbed on the surface of the alpha-SiC powder to form steric hindrance and prevent the powder from gathering and depositing, so that the silicon carbide ceramic slurry with high solid content, low viscosity and stable performance can be obtained.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, specifically to a low-viscosity silicon carbide ceramic slurry, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Silicon carbide ceramics are novel high-temperature resistant ceramics with extremely strong covalent bonds, and have been widely used in high-tech fields in recent years. They can be used as linings for high-temperature furnaces, rocket combustion chambers, radar radomes, precision bearings, ceramic engines, nozzles, high-temperature gas turbine rotors, fuel units, heat exchange components, and nuclear reactor materials, among others.

[0004] Obtaining highly reliable silicon carbide materials is inseparable from their molding process. The molding processes for silicon carbide ceramic materials are mainly divided into two types: wet molding and dry molding. Dry molding includes dry pressing and isostatic pressing. Wet molding includes plastic forming and colloidal molding. Colloidal molding mainly includes slip casting, tape casting, and novel colloidal molding methods.

[0005] Slip casting is a near-net-shape forming technology. Its forming process is relatively simple, easy to control, highly efficient, and low-cost. It produces uniform silicon carbide ceramic blanks and can form geometrically complex, large-sized, porous tubular supports, as well as thin-walled blanks. The slip casting process for silicon carbide ceramics involves injecting a suitable amount of well-dispersed, water-soluble ceramic powder organic suspension into a plaster mold. The capillary force of the small pores within the plaster mold removes excess water from the slurry, causing it to solidify and adhere to the inner wall of the mold. After a certain period of drying and shrinkage, the formed blank gradually separates from the plaster mold, and is then removed from the mold.

[0006] The success of slip casting hinges on the preparation of the slurry, which requires high solids content (volume solids ≥ 50%), low viscosity (≤ 1 Pa·s), good fluidity, stability, uniformity, low thixotropy, and good permeability. Low viscosity facilitates smooth slip casting, while high solids content ensures a dense and high-strength green body. However, there is a trade-off between high solids content and low viscosity; high solids content can lead to agglomeration and sedimentation of the powder. Therefore, how to prepare a silicon carbide ceramic slurry with high solids content, low viscosity, and stable performance has become an urgent problem to be solved in the production of silicon carbide ceramic components. Summary of the Invention

[0007] To overcome the above problems, the present invention provides a low-viscosity silicon carbide ceramic slurry, its preparation method and application.

[0008] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a low-viscosity silicon carbide ceramic slurry, the components of which include: modified α-SiC powder and a dispersant, wherein the dispersant is tetramethylammonium hydroxide.

[0010] A second aspect of the present invention provides a method for preparing the silicon carbide ceramic slurry described in the first aspect, comprising:

[0011] A mixed dispersion was obtained by mixing tetramethylammonium hydroxide and deionized water.

[0012] Modified α-SiC powder was added to the mixed dispersion in batches and stirred to obtain silicon carbide ceramic slurry.

[0013] The beneficial effects of this invention are as follows:

[0014] (1) To improve the dispersion stability of α-SiC powder in water, it was first modified with Al(NO3)3 and sodium humate. The α-SiC powder modified with Al(NO3)3 had better hydrophilicity, and the Zeta potential of the modified α-SiC powder surface was negative. Sodium humate formed hydrogen bonds or van der Waals forces with the surface of α-SiC powder, thus adsorbing onto the surface of α-SiC particles and forming steric hindrance to prevent powder aggregation and precipitation. The modified α-SiC powder was dispersed in a mixed dispersion. Tetramethylammonium hydroxide ionizes in water. The generated OH - Providing a strongly alkaline environment to the solution significantly increases the negative charge on the surface of the modified α-SiC powder, reduces the surface zeta potential, and prevents the agglomeration of the α-SiC powder. When the dispersant includes octadecylamine polyoxyethylene ether, the hydroxyl groups in the octadecylamine polyoxyethylene ether molecules form hydrogen bonds or van der Waals forces with the surface of the α-SiC powder, thereby adsorbing onto the surface of the α-SiC particles and forming steric hindrance to prevent powder aggregation and precipitation. Therefore, this invention can obtain a silicon carbide ceramic slurry with high solids content, low viscosity, and stable performance.

[0015] (2) The silicon carbide ceramic slurry prepared by the present invention has a viscosity of 0.1123 Pa·s to 0.5633 Pa·s at a solid content of 50 vol.% and a settling height of 2 mm to 5 mm after standing for 24 hours. It has good stability and meets the requirements of high solid content and low viscosity. Attached Figure Description

[0016] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0017] Figure 1 The viscosity test results are for the silicon carbide ceramic slurries prepared in Examples 2-4;

[0018] Figure 2 The viscosity test results are for the silicon carbide ceramic slurries prepared in Examples 5-8. Detailed Implementation

[0019] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0020] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0021] A first typical embodiment of the present invention provides a low-viscosity silicon carbide ceramic slurry, the components of which include: modified α-SiC powder and a dispersant, wherein the dispersant is tetramethylammonium hydroxide.

[0022] In one or more embodiments, the mass ratio of modified α-SiC powder to tetramethylammonium hydroxide is 100:1.5 to 2.5.

[0023] In one or more embodiments, the dispersant further includes octadecylamine polyoxyethylene ether.

[0024] Preferably, the mass ratio of modified α-SiC powder to tetramethylammonium hydroxide and octadecylamine polyoxyethylene ether is 100:1.5-2.5:0.3-1.0, and more preferably 100:2:0.3-1.0.

[0025] In one or more embodiments, the method for preparing modified α-SiC powder includes: placing α-SiC powder and aluminum salt in deionized water, heating and stirring, then adding sodium humate (C9H8Na2O4), continuing to stir, and finally collecting the solid as modified α-SiC powder.

[0026] Preferably, the particle size of the α-SiC powder is 0.5 to 5 μm, and more preferably 2.5 μm.

[0027] Preferably, the aluminum salt comprises Al(NO3)3.

[0028] More preferably, the mass ratio of α-SiC powder to Al(NO3)3 is 1:0.003 to 0.007.

[0029] Preferably, the mass ratio of deionized water to α-SiC powder is 2:0.5 to 1.2, and more preferably 2:1.

[0030] Preferably, the heating and stirring temperature is 60-80℃, the heating and stirring time is 2.5-4.5h, and the stirring rate is 400r / min-600r / min.

[0031] Preferably, the mass ratio of α-SiC powder to sodium humate is 1:0.004 to 0.009, and more preferably 1:0.008.

[0032] Preferably, the stirring time is 2.5 to 4.5 hours.

[0033] Preferably, the method for collecting the solids includes centrifugation to remove the supernatant and then obtaining aluminum salt-modified α-SiC powder.

[0034] More preferably, the centrifugation rate is 3500–4500 r / min, and the centrifugation time is 5–15 min.

[0035] Preferably, the modified α-SiC powder is obtained by collecting and drying the solid and then passing it through an 80-100 mesh sieve.

[0036] A second aspect of the present invention provides a method for preparing the silicon carbide ceramic slurry described in the first aspect, comprising:

[0037] A mixed dispersion was obtained by mixing tetramethylammonium hydroxide and deionized water.

[0038] Modified α-SiC powder was added to the mixed dispersion in batches and stirred to obtain silicon carbide ceramic slurry.

[0039] In one or more embodiments, a mixed dispersion is obtained by mixing tetramethylammonium hydroxide, octadecylamine polyoxyethylene ether, and deionized water.

[0040] In one or more embodiments, tetramethylammonium hydroxide and deionized water are stirred and mixed to obtain a mixed dispersion. The stirring rate is 400 r / min to 600 r / min, and the stirring time is 10 min to 20 min.

[0041] In one or more embodiments, during the process of obtaining silicon carbide ceramic slurry by stirring, the stirring rate is 400 r / min to 600 r / min, and the stirring time is 16 h to 24 h.

[0042] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0043] Example 1

[0044] Preparation of modified α-SiC powder:

[0045] 100g of 99.5% pure α-SiC powder with a particle size of 2.5μm and 0.5g of 99.5% pure Al(NO3)3 powder were dispersed in 200mL of deionized water. The entire system was placed in a water bath at 70℃ and stirred at a rate of 500r / min for 3h. Then, 0.8g of sodium humate was added to the reaction system, and stirring was continued for another 3h. The stirred α-SiC suspension was centrifuged at 4500r / min for 10min to separate the supernatant. The solid was collected, dried in a forced-air drying oven at 70℃, and passed through an 80-100 mesh sieve to obtain the modified α-SiC powder.

[0046] Example 2

[0047] Add 0.96g of a 25% aqueous solution of tetramethylammonium hydroxide (0.24g of tetramethylammonium hydroxide and 0.72mL of water) and 4.04mL of deionized water to a beaker, stir evenly with a mechanical stirrer at a speed of 500r / min for 15min to obtain a mixed dispersion.

[0048] The modified α-SiC powder prepared in Example 1 was added to the above mixed dispersion in batches of 8g, 4g, 1g, 1g, and 1g, with the remaining 1g powder added in 10 separate batches. Simultaneously, the magnetic stirrer speed was adjusted to 200-400 rpm and continuously operated according to the viscosity until all the modified α-SiC was added to the beaker to form a slurry. The slurry was then stirred for 20 hours to obtain a silicon carbide ceramic slurry with a solid content of 50 vol.%.

[0049] Formula for calculating solid content:

[0050]

[0051] Example 3

[0052] Add 1.28g of a 25% aqueous solution of tetramethylammonium hydroxide (0.32g of tetramethylammonium hydroxide and 0.96mL of water) and 3.72mL of deionized water to a beaker, and stir evenly with a mechanical stirrer at a speed of 500r / min for 15min to obtain a mixed dispersion.

[0053] The modified α-SiC powder prepared in Example 1 was added to the above mixed dispersion in batches of 8g, 4g, 1g, 1g, and 1g, with the remaining 1g powder added in 10 separate batches. Simultaneously, the magnetic stirrer speed was adjusted to 200-400 rpm and continuously operated according to the viscosity until all the modified α-SiC was added to the beaker to form a slurry. The slurry was then stirred for 20 hours to obtain a silicon carbide ceramic slurry with a solid content of 50 vol.%.

[0054] Example 4

[0055] Add 1.6g of 25% tetramethylammonium hydroxide aqueous solution (0.4g of tetramethylammonium hydroxide and 1.2mL of water) and 3.4mL of deionized water to a beaker, stir evenly with a mechanical stirrer at a speed of 500r / min for 15min to obtain a mixed dispersion.

[0056] The modified α-SiC powder prepared in Example 1 was added to the above mixed dispersion in batches of 8g, 4g, 1g, 1g, and 1g, with the remaining 1g powder added in 10 separate batches. Simultaneously, the magnetic stirrer speed was adjusted to 200-400 rpm and continuously operated according to the viscosity until all the modified α-SiC was added to the beaker to form a slurry. The slurry was then stirred for 20 hours to obtain a silicon carbide ceramic slurry with a solid content of 50 vol.%.

[0057] The viscosity test results of the silicon carbide ceramic slurries prepared in Examples 2-4 are as follows: Figure 1 As shown.

[0058] from Figure 1 As can be seen, under different amounts of tetramethylammonium hydroxide, the viscosity of silicon carbide ceramic slurry with a solid content of 50 vol.% decreases with increasing shear rate. When the amount of tetramethylammonium hydroxide added is 2.0 wt.%, the slurry viscosity is the lowest and the silicon carbide particle dispersion effect is the best.

[0059] Example 5

[0060] Add 1.28g of a 25% aqueous solution of tetramethylammonium hydroxide (0.32g of tetramethylammonium hydroxide and 0.96mL of water), 0.048g of octadecylamine polyoxyethylene ether, and 3.72mL of deionized water to a beaker, stir evenly with a mechanical stirrer at a speed of 500r / min for 15min to obtain a mixed dispersion.

[0061] The modified α-SiC powder prepared in Example 1 was added to the above mixed dispersion in batches of 8g, 4g, 1g, 1g, and 1g, with the remaining 1g powder added in 10 separate batches. Simultaneously, the magnetic stirrer speed was adjusted to 200-400 rpm and continuously operated according to the viscosity until all the modified α-SiC was added to the beaker to form a slurry. The slurry was then stirred for 20 hours to obtain a silicon carbide ceramic slurry with a solid content of 50 vol.%.

[0062] Example 6

[0063] Add 1.28g of a 25% aqueous solution of tetramethylammonium hydroxide (0.32g of tetramethylammonium hydroxide and 0.96mL of water), 0.09g of octadecylamine polyoxyethylene ether, and 3.72mL of deionized water to a beaker, stir evenly with a mechanical stirrer at a speed of 500r / min for 15min to obtain a mixed dispersion.

[0064] The modified α-SiC powder prepared in Example 1 was added to the above mixed dispersion in batches of 8g, 4g, 1g, 1g, and 1g, with the remaining 1g powder added in 10 separate batches. Simultaneously, the magnetic stirrer speed was adjusted to 200-400 rpm and continuously operated according to the viscosity until all the modified α-SiC was added to the beaker to form a slurry. The slurry was then stirred for 20 hours to obtain a silicon carbide ceramic slurry with a solid content of 50 vol.%.

[0065] Example 7

[0066] Add 1.28g of a 25% aqueous solution of tetramethylammonium hydroxide (0.32g of tetramethylammonium hydroxide and 0.96mL of water), 0.112g of octadecylamine polyoxyethylene ether, and 3.72mL of deionized water to a beaker, stir evenly with a mechanical stirrer at a speed of 500r / min for 15min to obtain a mixed dispersion.

[0067] The modified α-SiC powder prepared in Example 1 was added to the above mixed dispersion in batches of 8g, 4g, 1g, 1g, and 1g, with the remaining 1g powder added in 10 separate batches. Simultaneously, the magnetic stirrer speed was adjusted to 200-400 rpm and continuously operated according to the viscosity until all the modified α-SiC was added to the beaker to form a slurry. The slurry was then stirred for 20 hours to obtain a silicon carbide ceramic slurry with a solid content of 50 vol.%.

[0068] Example 8

[0069] Add 1.28g of 25% tetramethylammonium hydroxide aqueous solution (0.32g of tetramethylammonium hydroxide and 0.96mL of water), 0.16g of octadecylamine polyoxyethylene ether, and 3.72mL of deionized water to a beaker, stir evenly with a mechanical stirrer at a speed of 500r / min for 15min to obtain a mixed dispersion.

[0070] The modified α-SiC powder prepared in Example 1 was added to the above mixed dispersion in batches of 8g, 4g, 1g, 1g, and 1g, with the remaining 1g powder added in 10 separate batches. Simultaneously, the magnetic stirrer speed was adjusted to 200-400 rpm and continuously operated according to the viscosity until all the modified α-SiC was added to the beaker to form a slurry. The slurry was then stirred for 20 hours to obtain a silicon carbide ceramic slurry with a solid content of 50 vol.%.

[0071] The viscosity test results of the silicon carbide ceramic slurries prepared in Examples 5-8 are as follows: Figure 2 As shown.

[0072] from Figure 2 As can be seen, when the amount of tetramethylammonium hydroxide added is 2.0 wt.%, the viscosity of silicon carbide slurry with a solid content of 50 vol.% decreases with increasing shear rate under different amounts of octadecylamine polyoxyethylene ether added. When the amount of octadecylamine polyoxyethylene ether added is 0.7 wt.%, the relative viscosity of the slurry is the lowest, and the dispersion effect of silicon carbide particles in the slurry is the best.

[0073] Comparative Example 1

[0074] When the amount of tetramethylammonium hydroxide added is 0 wt.%, the maximum solid content of the ceramic slurry formed by the modified silicon carbide powder does not exceed 43 vol.%, which cannot meet the standard of 50 vol.% solid content.

[0075] Comparative Example 2

[0076] Replace with a different solvent.

[0077] Tetramethylammonium hydroxide cannot be replaced by solvents such as ethanol, methyl ethyl ketone, n-butanol, toluene, or ethyl acetate. This is because tetramethylammonium hydroxide hydrolyzes in the slurry to produce hydroxyl groups, providing a strongly alkaline environment. Another hydrolysis product adsorbs onto the surface of silicon carbide particles, increasing the thickness of the double electron layer, which reduces the zeta potential of the silicon carbide particles and improves the dispersibility of the slurry. The hydroxyl groups in octadecylamine polyoxyethylene ether adsorb onto the surface of silicon carbide particles through hydrogen bonding or van der Waals forces, forming an adsorption layer that provides steric hindrance. It can be replaced by other substances that can adsorb onto the powder surface, but the effect on the slurry will differ.

[0078] Comparative Example 3

[0079] When the dispersant is only tetramethylammonium hydroxide, without modification of silicon carbide, unmodified silicon carbide powder can form a silicon carbide ceramic slurry with a solid content of 50 vol.% under the dispersion effect of 2 wt.% tetramethylammonium hydroxide. However, the viscosity of the slurry is 0.8428 Pa·s, which is much higher than that of the slurry prepared with modified silicon carbide. At the same time, the stability is 7.231, which is higher than the 5.882 of the slurry prepared with modified silicon carbide. This indicates that the modification of Al(NO3)3 and sodium humate can effectively improve the dispersibility and stability of silicon carbide ceramic slurry.

[0080] The composition, viscosity, and stability test results of the silicon carbide ceramic slurries prepared in Examples 2-8 are shown in Table 1.

[0081] Table 1. Composition, viscosity, and stability test results of silicon carbide ceramic slurry.

[0082]

[0083]

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-viscosity silicon carbide ceramic slurry, characterized in that, The components of the silicon carbide ceramic slurry include: modified α-SiC powder and a dispersant, wherein the dispersant is tetramethylammonium hydroxide and octadecylamine polyoxyethylene ether; The method for preparing the modified α-SiC powder includes: placing α-SiC powder and aluminum salt in deionized water, heating and stirring, then adding sodium humate, continuing to stir, and finally collecting the solid, which is the modified α-SiC powder. The mass ratio of modified α-SiC powder to tetramethylammonium hydroxide and octadecylamine polyoxyethylene ether is 100:2:0.5~0.

7.

2. The silicon carbide ceramic slurry as described in claim 1, characterized in that, The particle size of the α-SiC powder is 0.5~5 μm; Alternatively, the aluminum salt may include Al(NO3)3; Alternatively, the mass ratio of deionized water to α-SiC powder is 2:0.5~1.

2.

3. The silicon carbide ceramic slurry as described in claim 2, characterized in that, The particle size of the α-SiC powder is 2.5 μm; Alternatively, the mass ratio of α-SiC powder to Al(NO3)3 is 1:0.003~0.007; Alternatively, the mass ratio of deionized water to α-SiC powder is 2:

1.

4. The silicon carbide ceramic slurry as described in claim 3, characterized in that, The heating and stirring temperature is 60~80 ℃, the heating and stirring time is 2.5~4.5 h, and the stirring rate is 400 r / min~600 r / min; Alternatively, the mass ratio of α-SiC powder to sodium humate is 1:0.004~0.009; Alternatively, continue stirring for 2.5 to 4.5 hours; Alternatively, methods for collecting solids include centrifugation to remove the supernatant and then obtaining aluminum salt-modified α-SiC powder; Alternatively, the solid can be collected, dried, and passed through an 80-100 mesh sieve to obtain modified α-SiC powder.

5. The silicon carbide ceramic slurry as described in claim 4, characterized in that, The mass ratio of α-SiC powder to sodium humate is 1:0.008; Alternatively, the centrifugation rate is 3500 ~ 4500 r / min, and the centrifugation time is 5 ~ 15 min.

6. The method for preparing silicon carbide ceramic slurry according to any one of claims 1 to 5, characterized in that, include: A mixed dispersion was obtained by mixing tetramethylammonium hydroxide, octadecylamine polyoxyethylene ether and deionized water. Modified α-SiC powder was added to the mixed dispersion in batches and stirred to obtain silicon carbide ceramic slurry.

7. The preparation method according to claim 6, characterized in that, Tetramethylammonium hydroxide and deionized water were stirred and mixed to obtain a mixed dispersion. The stirring rate was 400 r / min to 600 r / min and the stirring time was 10 min to 20 min. Alternatively, during the process of obtaining silicon carbide ceramic slurry by stirring, the stirring rate is 400 r / min to 600 r / min, and the stirring time is 16 h to 24 h.

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