A reaction-sintered silicon carbide special ceramic material with fine silicon distribution and its preparation method

Abstract

This invention provides a reaction-sintered silicon carbide special ceramic material with fine silicon distribution and its preparation method, belonging to the field of special ceramic product manufacturing technology. This application constructs a porous carbon layer on the surface of silicon carbide micropowder to obtain a titanium-doped bifunctional polymer dispersant. At low temperatures, this improves the dispersion and slurry rheology of high-solids-content coarse and fine silicon carbide and silicon carbide with a surface-coated carbon layer. At high temperatures, a titanium-containing inorganic phase is formed at the interface between the carbon layer and silicon carbide to regulate the wetting and reaction of molten silicon. Combined with multi-level particle gradation and vacuum segmented sintering, the proportion of small pores is increased, and carbon sources and titanium-containing components are enriched near the micropores, allowing molten silicon to preferentially penetrate and generate new silicon carbide, reducing the size of the free silicon phase and decreasing its connectivity. This results in a reaction-sintered silicon carbide special ceramic material with a fine silicon phase distribution, suitable for manufacturing special ceramic products such as ceramic valve plates and ceramic cylinder valve plates, which have stringent requirements for wear resistance, corrosion resistance, and sealing performance.

Description

Technical Field

[0001] This invention belongs to the field of special ceramic product manufacturing technology, and relates to a reaction-sintered silicon carbide special ceramic material with fine silicon distribution and its preparation method. Background Technology

[0002] Reaction-bonded silicon carbide, due to its excellent mechanical properties, high thermal conductivity, wear resistance, and corrosion resistance, has been widely used in the manufacture of special ceramic products such as ceramic valves and ceramic cylinder valve plates, as well as in aerospace, semiconductor equipment, mechanical seals, and armor protection. This process typically involves mixing silicon carbide particles, a carbon source, and a binder to prepare a porous green body. Then, at high temperature, molten silicon is infiltrated into the green body through capillary force, reacting with the carbon source to generate new silicon carbide, thereby binding the original silicon carbide particles into a dense body. However, existing technologies still face certain challenges in achieving high density and uniform microstructure.

[0003] To ensure complete reaction, a fine carbon source with high reactivity (such as nano-sized carbon black) is usually added. However, carbon black has a large specific surface area and high oil absorption value, and its direct introduction into the slurry often leads to a sharp increase in slurry viscosity. This not only makes it difficult to prepare slurries with high solid content, but also easily causes agglomeration. To improve rheological properties, it is often necessary to reduce the solid content or increase the liquid medium, but this will lead to a decrease in green density and an increase in porosity, which in turn affects the molding quality and density of components such as ceramic valve plates.

[0004] Secondly, due to the inhomogeneity of the internal pore structure of the green body, molten silicon tends to accumulate in larger pores during the infiltration process. After the reaction, these areas often retain large-sized free silicon particles. Since silicon has a much lower hardness and strength than silicon carbide and is brittle, the presence of large-sized free silicon particles may disrupt the continuity of the material's microstructure, thereby affecting the bending strength, wear resistance, and sealing reliability of ceramic valves and cylinder valve plates under harsh operating conditions. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a reaction-sintered silicon carbide special ceramic material with a fine silicon distribution and its preparation method. This application constructs a porous carbon layer on the surface of silicon carbide micropowder, concentrating the carbon source on the surface and forming silicon-infiltrating channels. A titanium-doped bifunctional polymer dispersant is prepared using polyacrylic acid, titanium lactate, and polyethylene glycol monomethyl ether. This dispersant improves the dispersion and slurry rheology of high-solids-content coarse and fine silicon carbide and silicon carbide with a surface-coated carbon layer at low temperatures. At high temperatures, a titanium-containing inorganic phase is formed at the interface between the carbon layer and silicon carbide to regulate the wetting and reaction of molten silicon. Combined with multi-level particle gradation and vacuum segmented sintering, the green body is predominantly composed of small pores, with carbon source and titanium-containing components enriched near the micropores. Molten silicon preferentially infiltrates into these areas and generates new silicon carbide, while the remaining silicon tends to have narrow gaps. This synergistic effect helps reduce the size of the free silicon phase and decrease its connectivity, resulting in a reaction-sintered silicon carbide special ceramic material with a fine silicon phase distribution.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a reaction-sintered silicon carbide special ceramic material with fine silicon distribution, the method comprising:

[0008] S1: Disperse silicon carbide micro powder in a mixed solvent to obtain a suspension. Add resorcinol, formaldehyde solution and polyethylene glycol to the suspension in sequence to obtain a mixed reaction solution. Add ammonia water to adjust the pH to obtain reaction solution A. Stir the reaction in a water bath, centrifuge and dry to obtain a pre-product. Place the pre-product under a nitrogen atmosphere and pre-carbonize it to obtain silicon carbide with a carbon layer on the surface.

[0009] S2: Polyacrylic acid is dispersed in deionized water to obtain a dispersion. Titanium lactate is added to obtain reaction solution B. After stirring and complexing, polyethylene glycol monomethyl ether is added to obtain reaction solution C. Stirring is continued to obtain reaction solution D. After cooling, the pH is adjusted with ammonia water. The titanium-doped bifunctional polymer dispersant is obtained by adjusting the solvent content.

[0010] S3: Add titanium-doped bifunctional polymer dispersant to deionized water, add silicon carbide with a carbon coating to obtain dispersion E, stir evenly, adjust pH with tetramethylammonium hydroxide aqueous solution and ultrasonically disperse to obtain a mixed liquid, add coarse silicon carbide and fine silicon carbide particles, ball mill and mix, and then vacuum defoam to obtain slurry.

[0011] S4: The slurry is injected into the mold, and after demolding and drying, a green body is obtained. Elemental silicon is laid on the surface of the green body to obtain a mixed sintering material. The mixed sintering material is placed in a vacuum sintering furnace for reaction sintering: the temperature is raised to the first temperature at the first heating rate and held, then raised to the second temperature and held, then raised to the third temperature at the second heating rate and held, and after cooling, a reaction sintered silicon carbide special ceramic material with fine silicon distribution is obtained.

[0012] As a preferred technical solution of the present invention, in step S1, the particle size of the silicon carbide micro powder is 0.5-0.8 μm.

[0013] In some optional embodiments, the mass ratio of ethanol to deionized water in the mixed solvent is 1:(1-1.5), for example, it can be 1:1.00, 1:1.05, 1:1.10, 1:1.15, 1:1.20, 1:1.25, 1:1.30, 1:1.35, 1:1.40, 1:1.45 or 1:1.50, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0014] In some optional embodiments, the mass-to-volume ratio of the silicon carbide micropowder to the mixed solvent is 1 g:(4-6) mL, for example, it can be 1 g:4.0 mL, 1 g:4.2 mL, 1 g:4.4 mL, 1 g:4.6 mL, 1 g:4.8 mL, 1 g:5.0 mL, 1 g:5.2 mL, 1 g:5.4 mL, 1 g:5.6 mL, 1 g:5.8 mL or 1 g:6.0 mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0015] In some optional embodiments, the concentration of the formaldehyde solution is 37-40 wt.%, for example, it can be 37.0 wt.%, 37.3 wt.%, 37.6 wt.%, 37.9 wt.%, 38.2 wt.%, 38.5 wt.%, 38.8 wt.%, 39.1 wt.%, 39.4 wt.%, 39.7 wt.%, or 40.0 wt.%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0016] In some optional embodiments, the molar ratio of formaldehyde to resorcinol is (1.8-2.2):1, for example, it can be 1.80:1, 1.84:1, 1.88:1, 1.92:1, 1.96:1, 2.00:1, 2.04:1, 2.08:1, 2.12:1, 2.16:1 or 2.20:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0017] In some optional embodiments, the total mass ratio of resorcinol and formaldehyde to silicon carbide micropowder is (0.08-0.15):1, for example, it can be 0.080:1, 0.087:1, 0.094:1, 0.101:1, 0.108:1, 0.115:1, 0.122:1, 0.129:1, 0.136:1, 0.143:1 or 0.150:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0018] In some optional embodiments, the total mass ratio of resorcinol and formaldehyde to polyethylene glycol is 1:(0.1-0.2), for example, it can be 1:0.10, 1:0.11, 1:0.12, 1:0.13, 1:0.14, 1:0.15, 1:0.16, 1:0.17, 1:0.18, 1:0.19 or 1:0.20, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0019] In some optional embodiments, the concentration of the ammonia water is 25-28 wt.%, for example, it can be 25.0 wt.%, 25.3 wt.%, 25.6 wt.%, 25.9 wt.%, 26.2 wt.%, 26.5 wt.%, 26.8 wt.%, 27.1 wt.%, 27.4 wt.%, 27.7 wt.%, or 28.0 wt.%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0020] In some alternative embodiments, the mixed reaction solution is adjusted to pH 8-9 by adding ammonia water dropwise to obtain reaction solution A. For example, the pH can be adjusted to 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9 or 9.0, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] In some optional embodiments, the temperature of the reaction solution A in the water bath is 50-80°C, for example, it can be 50°C, 53°C, 56°C, 59°C, 62°C, 65°C, 68°C, 71°C, 74°C, 77°C or 80°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0022] In some optional embodiments, the reaction time of the reaction solution A in a water bath is 4-6 hours, for example, it can be 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5.0 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours or 6.0 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0023] In some optional embodiments, the pre-carbonization temperature of the preproduct is 650-750°C, for example, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C or 750°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0024] In some optional embodiments, the pre-carbonization treatment time of the preproduct is 1-2 hours, for example, it can be 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours or 2.0 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0025] As a preferred technical solution of the present invention, in step S2, the molecular weight of the polyacrylic acid is 3000-5000.

[0026] In some alternative embodiments, the mass ratio of the polyacrylic acid to deionized water is 1:(5-10), for example, it can be 1:5.0, 1:5.5, 1:6.0, 1:6.5, 1:7.0, 1:7.5, 1:8.0, 1:8.5, 1:9.0, 1:9.5 or 1:10.0, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0027] In some optional embodiments, the mass ratio of polyacrylic acid to titanium lactate is (4.5-5.5):1, for example, it can be 4.5:1, 4.6:1, 4.7:1, 4.8:1, 4.9:1, 5.0:1, 5.1:1, 5.2:1, 5.3:1, 5.4:1 or 5.5:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0028] In some optional embodiments, the stirring and complexing temperature of the reaction solution B is 40-60°C, for example, it can be 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0029] In some optional embodiments, the stirring and complexation time of the reaction solution B is 1-2 hours, for example, it can be 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours or 2.0 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0030] The molecular weight of the polyethylene glycol monomethyl ether is 1000-5000.

[0031] In some optional embodiments, the mass ratio of polyethylene glycol monomethyl ether to polyacrylic acid is (0.8-1.2):1, for example, it can be 0.80:1, 0.84:1, 0.88:1, 0.92:1, 0.96:1, 1.00:1, 1.04:1, 1.08:1, 1.12:1, 1.16:1 or 1.20:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0032] In some optional embodiments, the stirring time of the reaction solution C is 1-2 hours, for example, 1.0 hours, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours, 1.9 hours or 2.0 hours, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0033] In some alternative embodiments, the pH of the reaction solution D is adjusted to 7.5-8.5 with ammonia, for example, to 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4 or 8.5, but not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0034] In some optional embodiments, the solid content of the titanium-doped bifunctional polymer dispersant is 30-40%, for example, it can be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39% or 40%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0035] As a preferred technical solution of the present invention, in step S3, after the dispersion E is stirred evenly, the pH is adjusted to 7-8.5 using a tetramethylammonium hydroxide aqueous solution. For example, the pH can be adjusted to 7.00, 7.15, 7.30, 7.45, 7.60, 7.75, 7.90, 8.05, 8.20, 8.35 or 8.50, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] In some optional embodiments, the concentration of the tetramethylammonium hydroxide aqueous solution is 10-25 wt.%, for example, it can be 10.0 wt.%, 11.5 wt.%, 13.0 wt.%, 14.5 wt.%, 16.0 wt.%, 17.5 wt.%, 19.0 wt.%, 20.5 wt.%, 22.0 wt.%, 23.5 wt.%, or 25.0 wt.%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0037] In some optional embodiments, the ultrasonic dispersion time of the dispersion E after pH adjustment is 10-20 min, for example, it can be 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min or 20 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0038] The coarse silicon carbide particles have a particle size of 45-60 μm.

[0039] The particle size of the fine silicon carbide is 2-5 μm.

[0040] In some optional embodiments, the ball milling mixing time is 6-10 hours, for example, 6.0 hours, 6.4 hours, 6.8 hours, 7.2 hours, 7.6 hours, 8.0 hours, 8.4 hours, 8.8 hours, 9.2 hours, 9.6 hours, or 10.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0041] In some optional embodiments, the mass ratio of the coarse silicon carbide particles, fine silicon carbide particles, and silicon carbide with a carbon coating is (65-70):(15-20):(10-20), for example, (65.0, 65.5, 66.0, 66.5, 67.0, 67.5, 68.0, 68.5, 69.0, 69.5, or 70.0):(15.0, 15.5, 16.0, 16.5, 17.0, 17.5, 18.0, 18.5, 19.0, 19.5, or 20.0):(10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20), but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0042] In some optional embodiments, the mass ratio of the titanium-doped bifunctional polymer dispersant to the total mass of coarse silicon carbide, fine silicon carbide, and silicon carbide with a carbon coating is (0.008-0.015):1, for example, it can be 0.0080:1, 0.0087:1, 0.0094:1, 0.0101:1, 0.0108:1, 0.0115:1, 0.0122:1, 0.0129:1, 0.0136:1, 0.0143:1, or 0.0150:1, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0043] In some optional embodiments, the total mass ratio of the coarse silicon carbide, fine silicon carbide, and silicon carbide with a carbon coating to deionized water is (4.5-5.5):1, for example, it can be 4.5:1, 4.6:1, 4.7:1, 4.8:1, 4.9:1, 5.0:1, 5.1:1, 5.2:1, 5.3:1, 5.4:1, or 5.5:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0044] As a preferred technical solution of the present invention, in step S4, the pressure of grouting is 0.1-0.3 MPa, for example, it can be 0.10 MPa, 0.12 MPa, 0.14 MPa, 0.16 MPa, 0.18 MPa, 0.20 MPa, 0.22 MPa, 0.24 MPa, 0.26 MPa, 0.28 MPa or 0.30 MPa, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] In some optional embodiments, the mass ratio of elemental silicon to green blank is (0.3-0.5):1, for example, it can be 0.30:1, 0.32:1, 0.34:1, 0.36:1, 0.38:1, 0.40:1, 0.42:1, 0.44:1, 0.46:1, 0.48:1 or 0.50:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0046] In some alternative embodiments, the first heating rate is 2-5 °C / min, for example, it can be 2.0 °C / min, 2.3 °C / min, 2.6 °C / min, 2.9 °C / min, 3.2 °C / min, 3.5 °C / min, 3.8 °C / min, 4.1 °C / min, 4.4 °C / min, 4.7 °C / min or 5.0 °C / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0047] In some alternative embodiments, the first temperature is 600-650°C, for example, it can be 600°C, 605°C, 610°C, 615°C, 620°C, 625°C, 630°C, 635°C, 640°C, 645°C or 650°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0048] In some optional embodiments, the holding time at the first temperature is 30-60 min, for example, it can be 30 min, 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min, 57 min or 60 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0049] In some alternative embodiments, the second temperature is 1420-1425°C, for example, it can be 1420.0°C, 1420.5°C, 1421.0°C, 1421.5°C, 1422.0°C, 1422.5°C, 1423.0°C, 1423.5°C, 1424.0°C, 1424.5°C or 1425.0°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0050] In some optional embodiments, the holding time at the second temperature is 15-30 min, for example, it can be 15.0 min, 16.5 min, 18.0 min, 19.5 min, 21.0 min, 22.5 min, 24.0 min, 25.5 min, 27.0 min, 28.5 min or 30.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0051] In some alternative embodiments, the second heating rate is 2-3 °C / min, for example, it can be 2.0 °C / min, 2.1 °C / min, 2.2 °C / min, 2.3 °C / min, 2.4 °C / min, 2.5 °C / min, 2.6 °C / min, 2.7 °C / min, 2.8 °C / min, 2.9 °C / min or 3.0 °C / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0052] In some optional embodiments, the third temperature is 1550-1600°C, for example, it can be 1550°C, 1555°C, 1560°C, 1565°C, 1570°C, 1575°C, 1580°C, 1585°C, 1590°C, 1595°C or 1600°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0053] In some optional embodiments, the holding time at the third temperature is 30-60 min, for example, it can be 30 min, 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min, 57 min or 60 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0054] Secondly, the present invention provides a reaction-sintered silicon carbide special ceramic material with fine silicon distribution prepared by the preparation method described above.

[0055] This application selects coarse-grained silicon carbide, fine-grained silicon carbide, and silicon carbide with a carbon coating as green aggregates, and introduces titanium-doped bifunctional polymer dispersants. Through slip casting and segmented reaction sintering, reaction sintered silicon carbide special ceramic materials with fine silicon distribution are prepared.

[0056] In this application, resorcinol and formaldehyde undergo hydroxymethylation and polycondensation reactions under alkaline conditions and at 50-80°C to generate a three-dimensionally cross-linked resorcinol-formaldehyde resin. Polyethylene glycol (PEG) dissolves in the initial reaction solution, forming a homogeneous system with the PEG-formaldehyde resin. As the polycondensation reaction proceeds, the molecular weight and cross-linking density of the PEG-formaldehyde resin increase, and its thermodynamic compatibility with PEG gradually decreases. This leads to phase separation of PEG segments, forming PEG-rich nano- to submicron-sized microdomains within the continuous phase of the PEG-formaldehyde resin. The characteristic size of these PEG microdomains is primarily controlled by the PEG molecular weight and the cross-linking rate of the PEG-formaldehyde resin: PEG with a molecular weight of 2000-10000 typically forms phase-separated microdomains under reaction conditions at 50-80°C. Polyethylene glycol (PEG) does not primarily function as a covalent crosslinking unit in resorcinol-formaldehyde resin; its molecular chains are physically trapped within the resorcinol-formaldehyde resin matrix after the resin undergoes polycondensation. During the subsequent pre-carbonization stage at 650-750℃ under nitrogen atmosphere, the resorcinol-formaldehyde resin matrix carbonizes into an amorphous carbon framework, while PEG thermally decomposes at 250-450℃ and escapes as gaseous products, leaving nanoscale or submicron-scale pores at the original PEG micro-region locations, forming a porous carbon layer with a specific pore structure. By adjusting the PEG molecular weight and dosage, the pore size and total pore volume can be controlled, optimizing the density of silicon-infiltrating channels and the reaction interface area within the carbon layer.

[0057] This application utilizes the reaction of polyacrylic acid and titanium lactate. The carboxyl groups on the polyacrylic acid molecular chain coordinate with the titanium element in the titanium lactate, forming a polyacrylic acid-titanium lactate complex structure. This allows the titanium element to be dispersed in the aqueous phase in an organically coordinated form. By controlling the addition rate of titanium lactate and the pH adjustment rate, the risk of local hydrolysis and precipitation of titanium species is reduced. Subsequently, polyethylene glycol monomethyl ether is added. The polyethylene glycol segments form a composite system with the polyacrylic acid segments through hydrogen bonding and chain entanglement. This results in a polymer that retains the hydrophilicity and charge of polyacrylic acid while also possessing the wetting ability of polyethylene glycol for particle surfaces and weakly polar interfaces. Within a suitable pH range, the carboxyl groups of polyacrylic acid exist in ionic form, giving the titanium-doped bifunctional polymer dispersant anionic properties, combining water solubility and adsorption capacity for inorganic particle surfaces. The titanium element in the titanium lactate binds to the polymer chain through coordination with the carboxyl groups of the polyacrylic acid segments, moving and adsorbing along with the polymer chain. In the low-temperature stage, the titanium-doped bifunctional polymer dispersant is mainly used in the slurry to disperse silicon carbide and silicon carbide with a carbon coating, reduce the viscosity of the slurry, and limit the agglomeration of fine particles. In the high-temperature stage, the titanium-containing inorganic substances released by the decomposition of titanium lactate will remain in the area near the surface of silicon carbide with a carbon coating, forming a titanium-containing inorganic phase near the interface between the carbon layer and silicon carbide. These titanium-containing inorganic phases may change the local interface composition and interfacial energy state, thereby affecting the spreading behavior of molten silicon at the local interface and the silicon carbide formation reaction rate, thus affecting the spreading and consumption mode of molten silicon at these interfaces.

[0058] First, a titanium-doped bifunctional polymer dispersant is mixed with silicon carbide coated with a carbon layer, and the pH is adjusted to 7-8.5. Under stirring and ultrasonication, the titanium-doped bifunctional polymer dispersant preferentially forms an adsorption layer on the porous carbon layer with a large specific surface area, maintaining a relatively stable dispersion in the aqueous phase. Subsequently, when fine silicon carbide particles are added, the remaining dispersant in the solution is further adsorbed onto the surface of the fine particles, thereby jointly improving the dispersion state of the fine particles. Ball milling is then used to uniformly mix and rearrange the coarse particles, fine particles, and silicon carbide coated with a carbon layer. The coarse silicon carbide particles mainly serve to build the framework, while the fine silicon carbide particles fill the gaps between the coarse particles, and the silicon carbide coated with a carbon layer further penetrates into the smaller pore areas between the fine particles, forming a multi-level particle-filled structure. Under the action of the titanium-doped bifunctional polymer dispersant, the slurry retains its injectable rheological properties even at a high solids content. With this configuration of particle size distribution and addition sequence, silicon carbide with a carbon coating layer on the surface and the associated titanium-doped bifunctional polymer dispersant component are more easily distributed in smaller pores and high specific surface area regions, while the proportion of large pores between coarse particles is controlled to a certain extent, so that the green body forms a pore structure dominated by small pores, and carbon sources and titanium-containing interface components are introduced near the small pore region.

[0059] The green body is subjected to programmed temperature rise under vacuum conditions. In the initial temperature stage of 600-650℃, the titanium-doped bifunctional polymer dispersant, polyethylene glycol, and incompletely carbonized residual organic matter decompose, volatilize, or further carbonize. Titanium lactate decomposes to release titanium, transforming into corresponding titanium-containing inorganic substances. These inorganic substances tend to remain near the carbon layer and silicon carbide particle surface due to their initial adsorption behavior. By controlling the heating rate and holding time in this stage, it is beneficial to control the gas generation rate during the organic matter decomposition and expulsion stage, reducing the risk of green body cracking caused by rapid gas release. When the temperature is raised to near the silicon melting point and held for a short time, the elemental silicon coated on the green body surface begins to melt and penetrate into the green body pores. In the region in contact with the porous carbon layer and titanium-containing inorganic phase, it gradually reacts with carbon to generate new silicon carbide and establishes percolation and venting channels. When the temperature is further increased to 1550-1600℃ and held, molten silicon continues to penetrate into the green body, reacting more fully with the porous carbon layer. New silicon carbide grows on the surface of the existing silicon carbide particles and near the pores. Titanium-containing inorganic materials at the interface between the carbon layer and silicon carbide may regulate the local interface composition and wetting state, affecting the spreading pattern and residence time of molten silicon at these interfaces, increasing the likelihood of reaction in the carbon-rich and titanium-containing microporous region. Because the pore structure of the green body becomes finer after being filled with multi-level particles, and the carbon source is concentrated in the porous carbon layer on the particle surface, unreacted silicon is more easily distributed in the narrow region between the new silicon carbide and the original silicon carbide particles. Its spatial size is limited, making it difficult to form a large-scale continuous silicon phase.

[0060] This application employs a synergistic enhancement mechanism. By forming a porous carbon layer on the surface of silicon carbide micropowder, the reactive carbon source is brought close to the silicon carbide interface, providing a pore structure. A titanium-doped bifunctional polymer dispersant is used to link titanium elements to the silicon carbide interface, influencing the penetration and reaction of molten silicon near the particles at high temperatures. Furthermore, the multi-level gradation of coarse and fine particles with the carbon-coated silicon carbide, along with high-solids-content slurry casting, increases the green compact density and the proportion of small pores. This is further enhanced by segmented sintering to control the binder removal and silicon infiltration processes. This synergistic effect helps reduce the size and connectivity of the free silicon phase during reaction sintering, contributing to the acquisition of silicon carbide-based materials with a finer silicon phase distribution.

[0061] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0062] This application constructs a porous carbon layer coating structure dominated by amorphous carbon by in-situ generating resorcinol-formaldehyde resin on the surface of silicon carbide micropowder and pre-carbonizing it with polyethylene glycol. This concentrates the reactive carbon source on and near the surface of the fine silicon carbide particles, forming channels that facilitate the penetration and reaction of molten silicon along shorter paths at the particle scale. This structure is suitable for special ceramic products such as ceramic valve plates and cylinder valve plates, where stringent requirements for microstructure uniformity are necessary.

[0063] This application prepares a titanium-doped bifunctional polymer dispersant with hydrophilicity, chargeability, and particle wetting ability by coordinating polyacrylic acid with titanium lactate and introducing polyethylene glycol monomethyl ether. At low temperature, it is used to disperse silicon carbide and silicon carbide with a carbon coating, reduce slurry viscosity, and inhibit agglomeration. At high temperature, the titanium-containing inorganic phase released by its decomposition is distributed near the interface between the carbon layer and silicon carbide, which regulates the wetting of molten silicon and the reaction consumption process, and is conducive to the formation of a uniform and dense microstructure at the ceramic valve plate connection interface.

[0064] This application first utilizes a titanium-doped bifunctional polymer dispersant to disperse silicon carbide with a carbon-coated surface layer, coarse silicon carbide particles, and fine silicon carbide particles, obtaining a slurry with good rheological properties at a high solids content. After ball milling, the coarse silicon carbide particles form the framework, the fine particles fill the interstitial pores, and the silicon carbide with the carbon-coated layer further penetrates into even smaller pores, forming a multi-level particle-filled structure. This results in the carbon source and its associated titanium-containing components being mainly distributed in smaller pores and high specific surface area regions, giving the green body a predominantly small-pore pore structure.

[0065] This application utilizes segmented vacuum heating to gradually decompose and remove organic materials such as titanium-doped bifunctional polymer dispersants and polyethylene glycol. Titanium lactate is transformed into titanium-containing inorganic matter distributed near the interface between the carbon layer and silicon carbide. Furthermore, moderate venting reduces the risk of green body cracking. Subsequently, molten silicon penetrates the pores of the porous carbon layer, reacting more readily with carbon in the titanium-containing interface region to form new silicon carbide. Due to the low porosity and high proportion of small pores in the green body, and the concentration of the carbon source on the particle surface, the remaining silicon is largely confined to the narrow region between the newly formed silicon carbide and the original silicon carbide, helping to reduce the possibility of large-scale continuous silicon phase formation.

[0066] This application exhibits a synergistic enhancement effect: the porous carbon layer brings the carbon source closer to the silicon carbide interface and provides channels; the titanium-doped bifunctional polymer dispersant concentrates the titanium-containing components at the interface, regulating the penetration and reaction of molten silicon; and multi-level particle gradation and high-solids-content slurry casting combined with segmented sintering improve density and optimize pore structure. This synergistic effect helps reduce the size of the free silicon phase and decrease its connectivity, contributing to the production of silicon carbide-based materials with a finer silicon phase distribution. This makes them suitable for manufacturing special ceramic products such as ceramic valves and ceramic cylinder valve plates, which require stringent wear resistance, corrosion resistance, and sealing performance. Detailed Implementation

[0067] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The embodiments described herein are specific implementations of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limiting the implementation of the present invention or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include technical solutions that employ any obvious substitutions and modifications made to the embodiments described herein.

[0068] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone further purification or processing.

[0069] Example 1

[0070] This embodiment provides a reaction-sintered silicon carbide special ceramic material with fine silicon distribution and its preparation method. The preparation method of the reaction-sintered silicon carbide special ceramic material with fine silicon distribution specifically includes the following steps:

[0071] S1: Silicon carbide micro powder was dispersed in a mixed solvent to obtain a suspension, wherein the mass ratio of ethanol to deionized water in the mixed solvent was 1:1.4, and the mass-volume ratio of silicon carbide micro powder to the mixed solvent was 1g:5.5mL. Resorcinol, a 39wt.% formaldehyde solution, and polyethylene glycol were added sequentially to the suspension to obtain a mixed reaction solution, wherein the molar ratio of formaldehyde to resorcinol was 2.1:1, the mass ratio of the total mass of resorcinol and formaldehyde to the mass of silicon carbide micro powder was 0.12:1, and the mass ratio of the total mass of resorcinol and formaldehyde to the mass of polyethylene glycol was 1:0.18. Ammonia water with a concentration of 27wt.% was added dropwise to adjust the pH to 8.5 to obtain reaction solution A. The reaction was stirred in a water bath at 75℃ for 5.5h, centrifuged, and dried to obtain a preproduct. The preproduct was placed under a nitrogen atmosphere and pre-carbonized at 720℃ for 1.8h to obtain silicon carbide with a carbon-coated surface.

[0072] S2: Polyacrylic acid with a molecular weight of 3000-5000 is dispersed in deionized water to obtain a dispersion, wherein the mass ratio of polyacrylic acid to deionized water is 1:9. Titanium lactate is added to obtain reaction solution B, wherein the mass ratio of polyacrylic acid to titanium lactate is 5.2:1. After stirring and complexing at 55℃ for 1.8h, polyethylene glycol monomethyl ether with a molecular weight of 1000-5000 is added to obtain reaction solution C, wherein the mass ratio of polyethylene glycol monomethyl ether to polyacrylic acid is 1.1:1. Stirring is continued for 1.7h to obtain reaction solution D. After cooling, the pH is adjusted to 8.2 with ammonia water with a concentration of 27wt.%. The solid content of titanium-doped bifunctional polymer dispersant with a solid content of 38% is obtained by adjusting the solvent content.

[0073] S3: Add titanium-doped bifunctional polymer dispersant to deionized water, add silicon carbide with a carbon coating to obtain dispersion E, stir evenly, adjust pH to 8.0 with 22wt.% tetramethylammonium hydroxide aqueous solution and ultrasonically disperse for 18 min to obtain a mixture, add coarse silicon carbide particles with a particle size of 45-60μm and fine silicon carbide particles with a particle size of 2-5μm, ball mill and mix for 9 h, and then vacuum defoam to obtain a slurry; wherein the mass ratio of coarse silicon carbide, fine silicon carbide and silicon carbide with a carbon coating is 68:18:14, the total mass ratio of titanium-doped bifunctional polymer dispersant to coarse silicon carbide, fine silicon carbide and silicon carbide with a carbon coating is 0.012:1, and the total mass ratio of coarse silicon carbide, fine silicon carbide and silicon carbide with a carbon coating to deionized water is 5.2:1;

[0074] S4: The slurry is injected into the mold and formed under a pressure of 0.25 MPa. After demolding, it is dried to obtain a green body. Elemental silicon is laid on the surface of the green body to obtain a mixed sintering material, wherein the mass ratio of elemental silicon to green body is 0.45:1. The mixed sintering material is placed in a vacuum sintering furnace for reaction sintering: the temperature is raised to the first temperature of 640℃ at a first heating rate of 4℃ / min and held for 50 min, then raised to the second temperature of 1424℃ and held for 25 min, and raised to the third temperature of 1580℃ at a second heating rate of 2.8℃ / min and held for 55 min. After cooling, a reaction sintered silicon carbide special ceramic material with fine silicon distribution is obtained.

[0075] Example 2

[0076] This embodiment provides a reaction-sintered silicon carbide special ceramic material with fine silicon distribution and its preparation method. The preparation method of the reaction-sintered silicon carbide special ceramic material with fine silicon distribution specifically includes the following steps:

[0077] S1: Silicon carbide micro powder is dispersed in a mixed solvent to obtain a suspension, wherein the mass ratio of ethanol to deionized water in the mixed solvent is 1:1, and the mass-volume ratio of silicon carbide micro powder to the mixed solvent is 1g:4mL. Resorcinol, a 37wt.% formaldehyde solution, and polyethylene glycol are added sequentially to the suspension to obtain a mixed reaction solution, wherein the molar ratio of formaldehyde to resorcinol is 1.8:1, the total mass ratio of resorcinol and formaldehyde to silicon carbide micro powder is 0.08:1, and the total mass ratio of resorcinol and formaldehyde to polyethylene glycol is 1:0.1. Ammonia water with a concentration of 25wt.% is added dropwise to adjust the pH to 8 to obtain reaction solution A. The reaction is stirred in a water bath at 50℃ for 4h, centrifuged, and dried to obtain a preproduct. The preproduct is placed under a nitrogen atmosphere and pre-carbonized at 650℃ for 1h to obtain silicon carbide with a carbon-coated surface.

[0078] S2: Polyacrylic acid with a molecular weight of 3000-5000 is dispersed in deionized water to obtain a dispersion, wherein the mass ratio of polyacrylic acid to deionized water is 1:5. Titanium lactate is added to obtain reaction solution B, wherein the mass ratio of polyacrylic acid to titanium lactate is 4.5:1. After stirring and complexing at 40°C for 1 hour, polyethylene glycol monomethyl ether with a molecular weight of 1000-5000 is added to obtain reaction solution C, wherein the mass ratio of polyethylene glycol monomethyl ether to polyacrylic acid is 0.8:1. Stirring is continued for 1 hour to obtain reaction solution D. After cooling, the pH is adjusted to 7.5 with ammonia water with a concentration of 28wt.%. The solid content of titanium-doped bifunctional polymer dispersant with a solid content of 30% is obtained by adjusting the solvent content.

[0079] S3: Add titanium-doped bifunctional polymer dispersant to deionized water, add silicon carbide with a carbon coating to obtain dispersion E, stir evenly, adjust pH to 7 with 10wt.% tetramethylammonium hydroxide aqueous solution and ultrasonically disperse for 10 min to obtain a mixture, add coarse silicon carbide particles with a particle size of 45-60μm and fine silicon carbide particles with a particle size of 2-5μm, ball mill and mix for 6 h, and then vacuum defoam to obtain a slurry; wherein the mass ratio of coarse silicon carbide, fine silicon carbide and silicon carbide with a carbon coating is 65:15:20, the total mass ratio of titanium-doped bifunctional polymer dispersant to coarse silicon carbide, fine silicon carbide and silicon carbide with a carbon coating is 0.008:1, and the total mass ratio of coarse silicon carbide, fine silicon carbide and silicon carbide with a carbon coating to deionized water is 4.5:1;

[0080] S4: The slurry is injected into the mold and formed under a pressure of 0.1 MPa. After demolding, it is dried to obtain a green body. Elemental silicon is laid on the surface of the green body to obtain a mixed sintering material, wherein the mass ratio of elemental silicon to green body is 0.3:1. The mixed sintering material is placed in a vacuum sintering furnace for reaction sintering: the temperature is raised to the first temperature of 600℃ at a first heating rate of 2℃ / min and held for 30 min, then raised to the second temperature of 1420℃ and held for 15 min, and raised to the third temperature of 1550℃ at a second heating rate of 2℃ / min and held for 30 min. After cooling, a reaction sintered silicon carbide special ceramic material with fine silicon distribution is obtained.

[0081] Example 3

[0082] This embodiment provides a reaction-sintered silicon carbide special ceramic material with fine silicon distribution and its preparation method. The preparation method of the reaction-sintered silicon carbide special ceramic material with fine silicon distribution specifically includes the following steps:

[0083] S1: Silicon carbide micropowder was dispersed in a mixed solvent to obtain a suspension, wherein the mass ratio of ethanol to deionized water in the mixed solvent was 1:1.1, and the mass-volume ratio of silicon carbide micropowder to the mixed solvent was 1g:4.5mL. Resorcinol, a 38wt.% formaldehyde solution, and polyethylene glycol were added sequentially to the suspension to obtain a mixed reaction solution, wherein the molar ratio of formaldehyde to resorcinol was 1.9:1, the mass ratio of the total mass of resorcinol and formaldehyde to the mass of silicon carbide micropowder was 0.1:1, and the mass ratio of the total mass of resorcinol and formaldehyde to the mass of polyethylene glycol was 1:0.12. Ammonia water with a concentration of 26wt.% was added dropwise to adjust the pH to 8.2 to obtain reaction solution A. The reaction was stirred in a water bath at 60℃ for 4.5h, centrifuged, and dried to obtain a preproduct. The preproduct was placed under a nitrogen atmosphere and pre-carbonized at 680℃ for 1.2h to obtain silicon carbide with a carbon-coated surface.

[0084] S2: Polyacrylic acid with a molecular weight of 3000-5000 is dispersed in deionized water to obtain a dispersion, wherein the mass ratio of polyacrylic acid to deionized water is 1:6. Titanium lactate is added to obtain reaction solution B, wherein the mass ratio of polyacrylic acid to titanium lactate is 4.8:1. After stirring and complexing at 45°C for 1.2 h, polyethylene glycol monomethyl ether with a molecular weight of 1000-5000 is added to obtain reaction solution C, wherein the mass ratio of polyethylene glycol monomethyl ether to polyacrylic acid is 0.9:1. Stirring is continued for 1.3 h to obtain reaction solution D. After cooling, the pH is adjusted to 7.8 with ammonia water with a concentration of 25 wt.%. The solid content of titanium-doped bifunctional polymer dispersant is obtained by adjusting the solvent content.

[0085] S3: Add titanium-doped bifunctional polymer dispersant to deionized water, add silicon carbide with a carbon coating to obtain dispersion E, stir evenly, adjust pH to 7.5 with 15wt.% tetramethylammonium hydroxide aqueous solution and ultrasonically disperse for 12 min to obtain a mixture, add coarse silicon carbide particles with a particle size of 45-60μm and fine silicon carbide particles with a particle size of 2-5μm, ball mill and mix for 7 h, and then vacuum defoam to obtain a slurry; wherein the mass ratio of coarse silicon carbide, fine silicon carbide and silicon carbide with a carbon coating is 70:20:10, the total mass ratio of titanium-doped bifunctional polymer dispersant to coarse silicon carbide, fine silicon carbide and silicon carbide with a carbon coating is 0.01:1, and the total mass ratio of coarse silicon carbide, fine silicon carbide and silicon carbide with a carbon coating to deionized water is 4.8:1;

[0086] S4: The slurry is injected into the mold and formed under a pressure of 0.15 MPa. After demolding, it is dried to obtain a green body. Elemental silicon is laid on the surface of the green body to obtain a mixed sintering material, wherein the mass ratio of elemental silicon to green body is 0.35:1. The mixed sintering material is placed in a vacuum sintering furnace for reaction sintering: the temperature is raised to the first temperature of 610℃ at a first heating rate of 3℃ / min and held for 40 min, then raised to the second temperature of 1421℃ and held for 20 min, and raised to the third temperature of 1560℃ at a second heating rate of 2.2℃ / min and held for 40 min. After cooling, a reaction sintered silicon carbide special ceramic material with fine silicon distribution is obtained.

[0087] Example 4

[0088] This embodiment provides a reaction-sintered silicon carbide special ceramic material with fine silicon distribution and its preparation method. The preparation method of the reaction-sintered silicon carbide special ceramic material with fine silicon distribution specifically includes the following steps:

[0089] S1: Silicon carbide micro powder is dispersed in a mixed solvent to obtain a suspension, wherein the mass ratio of ethanol to deionized water in the mixed solvent is 1:1.5, and the mass-volume ratio of silicon carbide micro powder to the mixed solvent is 1g:6mL. Resorcinol, a 40wt.% formaldehyde solution, and polyethylene glycol are added sequentially to the suspension to obtain a mixed reaction solution, wherein the molar ratio of formaldehyde to resorcinol is 2.2:1, the total mass ratio of resorcinol and formaldehyde to silicon carbide micro powder is 0.15:1, and the total mass ratio of resorcinol and formaldehyde to polyethylene glycol is 1:0.2. Ammonia water with a concentration of 28wt.% is added dropwise to adjust the pH to 9 to obtain reaction solution A. The reaction is stirred in a water bath at 80℃ for 6h, centrifuged, and dried to obtain a preproduct. The preproduct is placed under a nitrogen atmosphere and pre-carbonized at 750℃ for 2h to obtain silicon carbide with a carbon-coated surface.

[0090] S2: Polyacrylic acid with a molecular weight of 3000-5000 is dispersed in deionized water to obtain a dispersion, wherein the mass ratio of polyacrylic acid to deionized water is 1:10. Titanium lactate is added to obtain reaction solution B, wherein the mass ratio of polyacrylic acid to titanium lactate is 5.5:1. After stirring and complexing at 60°C for 2 hours, polyethylene glycol monomethyl ether with a molecular weight of 1000-5000 is added to obtain reaction solution C, wherein the mass ratio of polyethylene glycol monomethyl ether to polyacrylic acid is 1.2:1. Stirring is continued for 2 hours to obtain reaction solution D. After cooling, the pH is adjusted to 8.5 with ammonia water with a concentration of 26wt.%. The solid content of titanium-doped bifunctional polymer dispersant with a solid content of 40% is obtained by adjusting the solvent content.

[0091] S3: Add titanium-doped bifunctional polymer dispersant to deionized water, add silicon carbide with a carbon coating to obtain dispersion E, stir evenly, adjust pH to 8.5 with 25wt.% tetramethylammonium hydroxide aqueous solution and ultrasonically disperse for 20 min to obtain a mixture, add coarse silicon carbide particles with a particle size of 45-60μm and fine silicon carbide particles with a particle size of 2-5μm, ball mill and mix for 10 h, and then vacuum defoam to obtain a slurry; wherein the mass ratio of coarse silicon carbide, fine silicon carbide and silicon carbide with a carbon coating is 66:17:17, the total mass ratio of titanium-doped bifunctional polymer dispersant to coarse silicon carbide, fine silicon carbide and silicon carbide with a carbon coating is 0.015:1, and the total mass ratio of coarse silicon carbide, fine silicon carbide and silicon carbide with a carbon coating to deionized water is 5.5:1;

[0092] S4: The slurry is injected into the mold and formed under a pressure of 0.3 MPa. After demolding, it is dried to obtain a green body. Elemental silicon is laid on the surface of the green body to obtain a mixed sintering material, wherein the mass ratio of elemental silicon to green body is 0.5:1. The mixed sintering material is placed in a vacuum sintering furnace for reaction sintering: the temperature is raised to the first temperature of 650℃ at a first heating rate of 5℃ / min and held for 60min, then raised to the second temperature of 1425℃ and held for 30min, and raised to the third temperature of 1600℃ at a second heating rate of 3℃ / min and held for 60min. After cooling, a reaction sintered silicon carbide special ceramic material with fine silicon distribution is obtained.

[0093] Comparative Example 1

[0094] This comparative example provides a reaction-sintered silicon carbide special ceramic material with fine silicon distribution. The difference from Example 1 is that steps S1 and S3 are omitted, and silicon carbide micro powder and carbon black are directly added. Other operation steps and process parameters are exactly the same as in Example 1.

[0095] Comparative Example 2

[0096] This comparative example provides a reaction-sintered silicon carbide special ceramic material with fine silicon distribution. The difference from Example 1 is that polyethylene glycol is not added in S1, while the other operating steps and process parameters are exactly the same as in Example 1.

[0097] Comparative Example 3

[0098] This comparative example provides a reaction-sintered silicon carbide special ceramic material with fine silicon distribution. The difference from Example 1 is that polyacrylic acid is used instead of titanium-doped bifunctional polymer dispersant in S3. Other operating steps and process parameters are exactly the same as in Example 1.

[0099] Comparative Example 4

[0100] This comparative example provides a reaction-sintered silicon carbide special ceramic material with fine silicon distribution. The difference from Example 1 is that carbon black is used to replace the silicon carbide with a carbon coating in S3. Other operating steps and process parameters are exactly the same as in Example 1.

[0101] The performance of the reaction-sintered silicon carbide special ceramic materials with fine silicon distribution in Examples 1-4 and Comparative Examples 1-4 was tested, and the specific process is as follows:

[0102] The bulk density of the sample was tested according to GB / T 2997-2015;

[0103] According to GB / T 6569-2006, the bending strength, high temperature (1400℃, inert atmosphere) bending strength and thermal shock cycle (heating to 1000℃ and holding for 3 hours followed by extreme air cooling is one cycle, and the cycle is repeated 20 times) of the test sample were tested.

[0104] The fracture toughness of the test samples was determined according to GB / T 23806-2009;

[0105] The test results are shown in Table 1.

[0106] Table 1. Performance test results of reaction-sintered silicon carbide special ceramic materials with fine silicon distribution in Examples 1-4 and Comparative Examples 1-4.

[0107] <![CDATA[Apparent density (g / cm 3 ).]]> Bending strength (MPa) High-temperature flexural strength (MPa) <![CDATA[Fracture toughness (MPa·m 1 / 2 ).]]> Bending strength (MPa) after thermal shock cycling Example 1 3.05 385 263 4.82 340 Example 2 2.98 358 235 4.35 316 Example 3 3.02 371 259 4.58 324 Example 4 3.06 378 254 4.68 331 Comparative Example 1 2.82 305 170 3.53 225 Comparative Example 2 2.88 330 205 3.84 260 Comparative Example 3 2.95 345 220 4.25 280 Comparative Example 4 2.79 295 165 3.46 215

[0108] As can be seen from the test results of Example 1 and Comparative Example 1 in Table 1, omitting steps S1 and directly adding silicon carbide micro powder and carbon black in S3 results in the lack of the coating relationship and relatively stable interface between the carbon source and silicon carbide micro powder. The carbon source is more likely to agglomerate and locally enrich during the slurry and sintering process. During the silicon infiltration stage, there may be insufficient carbon in some areas and excessive carbon in others. The densification process is disturbed, and the residual pores and coarse free silicon phases increase, resulting in a decrease in bulk density and flexural strength. At the same time, the stress concentration around the coarse silicon phases and pores is aggravated, and the high-temperature flexural strength and fracture toughness are reduced. Cracks are more likely to initiate and propagate in these areas during thermal shock cycling, resulting in a decrease in flexural strength after thermal shock cycling.

[0109] As can be seen from the test results of Example 1 and Comparative Example 2 in Table 1, without the addition of polyethylene glycol in S1, the carbon layer lacks the pore structure formed by the thermal decomposition of polyethylene glycol. The resorcinol-formaldehyde derived carbon layer is relatively denser, and the penetration and diffusion path of molten silicon on the particle surface is limited. The contact and reaction between the local carbon layer and molten silicon are restricted. In some areas, there may be a state of coexistence between residual carbon layer and free silicon phase, which leads to the deterioration of the overall densification degree and interface bonding, and a decrease in bulk density and flexural strength. Insufficient density and uneven local reaction at high temperature reduce the high-temperature flexural strength. Under thermal shock cycling, these interfaces are more likely to form and propagate cracks. After thermal shock, both flexural strength and fracture toughness decrease.

[0110] As can be seen from the test results of Example 1 and Comparative Example 3 in Table 1, although using polyacrylic acid to replace the titanium-doped bifunctional polymer dispersant can provide a certain dispersion and viscosity reduction effect in the slurry stage, and the change in bulk density is not significant, the lack of titanium-containing inorganic components at the interface between the carbon layer and silicon carbide weakens the regulation effect on the local spreading behavior and reaction position of molten silicon in the silicon infiltration stage. Molten silicon is more likely to form relatively coarse free silicon phases or continuous silicon channels locally, resulting in a decrease in bending strength, fracture toughness, high-temperature bending strength and bending strength after thermal shock cycling.

[0111] As can be seen from the test results of Example 1 and Comparative Example 4 in Table 1, the use of carbon black to replace the surface-coated silicon carbide in S3 disrupts the multi-level filling structure of "coarse-grained silicon carbide-fine-grained silicon carbide". The small and medium pores that were originally filled by the surface-coated silicon carbide are replaced by carbon black, resulting in a decrease in bulk density and an increase in macropores and irregular pores, leading to a decrease in bulk density and flexural strength. Carbon black is more likely to be locally enriched during sintering and silicon infiltration, increasing the possibility of the formation of carbon-rich areas and silicon-rich areas, producing coarse free silicon phases and weak interfaces, resulting in a decrease in high-temperature flexural strength and fracture toughness. During thermal shock cycling, cracks tend to propagate along these macropores and coarse silicon phases, and the flexural strength decreases after thermal shock.

[0112] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a reaction-sintered silicon carbide special ceramic material with fine silicon distribution, characterized in that, The preparation method includes: S1: Disperse silicon carbide micro powder in a mixed solvent to obtain a suspension. Add resorcinol, formaldehyde solution and polyethylene glycol to the suspension in sequence to obtain a mixed reaction solution. Add ammonia water to adjust the pH to obtain reaction solution A. Stir the reaction in a water bath, centrifuge and dry to obtain a pre-product. Place the pre-product under a nitrogen atmosphere and pre-carbonize it to obtain silicon carbide with a carbon layer on the surface. S2: Polyacrylic acid is dispersed in deionized water to obtain a dispersion. Titanium lactate is added to obtain reaction solution B. After stirring and complexing, polyethylene glycol monomethyl ether is added to obtain reaction solution C. Stirring is continued to obtain reaction solution D. After cooling, the pH is adjusted with ammonia water. The titanium-doped bifunctional polymer dispersant is obtained by adjusting the solvent content. S3: Add titanium-doped bifunctional polymer dispersant to deionized water, add silicon carbide with a carbon coating to obtain dispersion E, stir evenly, adjust pH with tetramethylammonium hydroxide aqueous solution and ultrasonically disperse to obtain a mixed liquid, add coarse silicon carbide and fine silicon carbide particles, ball mill and mix, and then vacuum defoam to obtain slurry. S4: The slurry is injected into the mold, and after demolding and drying, a green body is obtained. Elemental silicon is laid on the surface of the green body to obtain a mixed sintering material. The mixed sintering material is placed in a vacuum sintering furnace for reaction sintering: the temperature is raised to the first temperature at the first heating rate and held, then raised to the second temperature and held, then raised to the third temperature at the second heating rate and held, and after cooling, a reaction sintered silicon carbide special ceramic material with fine silicon distribution is obtained.

2. The method for preparing a reaction-sintered silicon carbide special ceramic material with fine silicon distribution according to claim 1, characterized in that, In S1: The silicon carbide micro powder has a particle size of 0.5-0.8 μm; The mass ratio of ethanol to deionized water in the mixed solvent is 1:(1-1.5); The mass-to-volume ratio of the silicon carbide micro powder to the mixed solvent is 1 g:(4-6) mL.

3. The method for preparing a reaction-sintered silicon carbide special ceramic material with fine silicon distribution according to claim 1, characterized in that, In S1: The molar ratio of formaldehyde to resorcinol is (1.8-2.2):1; The total mass ratio of resorcinol and formaldehyde to silicon carbide micro powder is (0.08-0.15):1; The total mass ratio of resorcinol and formaldehyde to polyethylene glycol is 1:(0.1-0.2).

4. The method for preparing a reaction-sintered silicon carbide special ceramic material with fine silicon distribution according to claim 1, characterized in that, In S1: The pre-carbonization treatment temperature of the pre-product is 650-750℃; The pre-carbonization treatment time of the preproduct is 1-2 hours.

5. The method for preparing a reaction-sintered silicon carbide special ceramic material with fine silicon distribution according to claim 1, characterized in that, In S2: The mass ratio of the polyacrylic acid to deionized water is 1:(5-10); The mass ratio of polyacrylic acid to titanium lactate is (4.5-5.5):

1.

6. The method for preparing a reaction-sintered silicon carbide special ceramic material with fine silicon distribution according to claim 1, characterized in that, In S2: The mass ratio of polyethylene glycol monomethyl ether to polyacrylic acid is (0.8-1.2):

1.

7. The method for preparing a reaction-sintered silicon carbide special ceramic material with fine silicon distribution according to claim 1, characterized in that, In S3: The coarse silicon carbide particles have a particle size of 45-60 μm; The particle size of the fine silicon carbide is 2-5 μm.

8. The method for preparing a reaction-sintered silicon carbide special ceramic material with fine silicon distribution according to claim 1, characterized in that, In S3: The mass ratio of the coarse silicon carbide particles, the fine silicon carbide particles, and the silicon carbide with a carbon coating on the surface is (65-70):(15-20):(10-20); The mass ratio of the titanium-doped bifunctional polymer dispersant to the total mass of coarse silicon carbide, fine silicon carbide, and silicon carbide with a surface carbon coating is (0.008-0.015):

1. The total mass ratio of the coarse silicon carbide, fine silicon carbide, and silicon carbide coated with a carbon layer to the deionized water is (4.5-5.5):

1.

9. The method for preparing a reaction-sintered silicon carbide special ceramic material with fine silicon distribution according to claim 1, characterized in that, In S4: The pressure for grouting is 0.1-0.3 MPa; The mass ratio of elemental silicon to green blank is (0.3-0.5):1; The first temperature is 600-650℃; The second temperature is 1420-1425℃; The third temperature is 1550-1600℃.

10. A reaction-sintered silicon carbide special ceramic material with fine silicon distribution prepared by the preparation method according to any one of claims 1-9.