Alpha-silicon carbide combined beta-silicon carbide sintered ceramic and preparation method thereof

Abstract

The invention provides alpha-silicon carbide combined beta-silicon carbide sintered ceramic and a preparation method thereof. The alpha-silicon carbide combined beta-silicon carbide sintered ceramic is prepared from the following raw materials in percentage by mass: 60 to 75 percent of silicon carbide particles, 5 to 14 percent of ferrosilicon chromium alloy powder, 0.2 to 1.5 percent of binder, 4 to 10 percent of carbon source, 5 to 10 percent of water, 0.2 to 2 percent of dispersing agent, 0.1 to 1 percent of water reducing agent, 0.5 to 3 percent of sintering aid and 0.5 to 2 percent of defoaming agent. The porosity of the sintered ceramic can be reduced, and the mechanical property and corrosion resistance of the sintered ceramic can be improved.

Description

Technical Field

[0001] This invention belongs to the field of sintered ceramics technology for special industrial pumps, specifically relating to an α-silicon carbide-bonded β-silicon carbide sintered ceramic and its preparation method. Background Technology

[0002] With the development of modern industry, the service environment of industrial slurry pumps has become harsher. Under the interaction of corrosion, erosion and cavitation, the service life of the metal flow parts of general industrial slurry pumps is reduced, and their performance is difficult to meet the harsh working environment.

[0003] Some industrial slurry pumps use sintered ceramic materials as the pump body flow parts. Currently, the commonly used sintered ceramic material is silicon nitride-bonded silicon carbide sintered ceramic. Silicon carbide particles, due to their high hardness and stable chemical structure, possess advantages such as good wear resistance and corrosion resistance. However, in silicon nitride-bonded silicon carbide ceramic materials, the silicon nitride (whiskers and small particles) generated by the reaction of elemental silicon with nitrogen is not densely bonded to the silicon carbide particles in the raw material, resulting in a loose and non-dense bond. Under a nitrogen atmosphere, silicon nitride gradually decomposes above 1600℃, thus limiting the maximum sintering temperature and consequently restricting the overall mechanical properties of silicon nitride-bonded silicon carbide sintered ceramic material samples. The porosity of silicon nitride-bonded silicon carbide sintered ceramic materials is usually 15-18%, and the flexural strength generally does not exceed 65 MPa. Moreover, due to the presence of silicon nitride, the degree of corrosion increases significantly under high-concentration strong alkali (40 wt%, NaOH solution) conditions. However, as a flow-through rotating part, it requires excellent mechanical properties and corrosion resistance.

[0004] Therefore, it is of great significance to provide a sintered ceramic that can reduce porosity and improve mechanical properties and corrosion resistance. Summary of the Invention

[0005] In view of this, the present invention provides an α-silicon carbide-bonded β-silicon carbide sintered ceramic and its preparation method, which can reduce the porosity of the sintered ceramic and improve its mechanical properties and corrosion resistance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an α-silicon carbide-bonded β-silicon carbide sintered ceramic, wherein the raw materials of the sintered ceramic, by mass percentage, include: 60-75% silicon carbide particles, 5-14% ferrosilicon-chromium alloy powder, 0.2-1.5% binder, 4-10% carbon source, 5-10% water, 0.2-2% dispersant, 0.1-1% water-reducing agent, 0.5-3% sintering aid, and 0.5-2% defoamer.

[0007] Preferably, the silicon carbide particles have a particle size distribution of 12-20 mesh, 20-36 mesh, 36-70 mesh, 70-100 mesh, 100-150 mesh, 150-200 mesh, and >200 mesh, with a mass ratio of (0-50):(0-25):(5-20):(5-20):(2-15):(10-20):(5-30); and the density of the silicon carbide particles is greater than 98%. It is understood that the particle size distribution of the silicon carbide particles is a normal distribution.

[0008] Preferably, in the ferrosilicon-chromium alloy powder, the mass ratio of silicon, iron and chromium is (55~75):(5~10):(5~15), the particle size of the ferrosilicon-chromium alloy powder is 10~88 μm, and the purity is ≥99.8%.

[0009] Preferably, the carbon source is composed of carbon black, graphite, and chopped carbon fibers, wherein the mass ratio of the carbon black, graphite, and chopped carbon fibers is (25~40):(35~60):(15~20), the carbon black has a particle size of 200~500 nm, the graphite has a particle size of 45 < μm, and the chopped carbon fibers have a length of 0.1~7 mm and a diameter of 5~70 μm. It is understood that the chopped carbon fibers have a fixed diameter but vary in length, with the diameter being the particle size.

[0010] Preferably, the dispersant is composed of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol, wherein the mass ratio of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol is (30~100):(20~40):(20~40), and the polyvinylpyrrolidone is at least one of polyvinylpyrrolidone K30 and polyvinylpyrrolidone K90.

[0011] Preferably, the sintering aid is composed of activated lanthanum oxide micro powder and activated zirconium oxide micro powder, wherein the mass ratio of the activated lanthanum oxide micro powder to the activated zirconium oxide micro powder is (10~30):(70~90), and the sintering aid is an amorphous phase with a particle size of 1~74μm.

[0012] Preferably, the adhesive is at least one selected from water-soluble phenolic resin, gum arabic, sodium carboxymethyl cellulose, and sodium carboxymethyl cellulose; and / or, The water-reducing agent is polyhydroxy acid; and / or, The defoamer is at least one of diethylhexanol, isooctanol, isoamyl alcohol, and diisobutylmethanol.

[0013] Secondly, the present invention also provides a method for preparing the α-silicon carbide-bonded β-silicon carbide sintered ceramic, comprising the following steps: S1. The silicon carbide particles, ferrosilicon-chromium alloy powder, carbon source and sintering aid are divided into a first group and a second group according to the particle size. The particle size of the raw materials in the first group is ≤100μm, and the particle size of the raw materials in the second group is >100μm. S2. Mix the raw materials of the first group and ball mill them to obtain the first mixture; S3. Add the raw materials of the second group to the first mixture, and then roll the mixture to obtain the second mixture. S4. Add binder, water, dispersant, water-reducing agent and defoamer to the second mixture, knead and tame the mixture to obtain a mixture; S5. Inject the mixture into the mold, cure it at room temperature, then heat it up and keep it at that temperature to dry, then demold it to obtain a ceramic blank; S6. Under a protective gas atmosphere, the ceramic green body is embedded in expanded graphite, heated to 770-830 ℃ at 3-10 ℃ / min, held for 0.5-2 h, then heated to 1470-1730 ℃ at 3-5 ℃ / min, held for 2-8 h, then cooled to 770-1030 ℃ at 3-5 ℃ / min, and then cooled to room temperature to obtain α-silicon carbide bonded β-silicon carbide sintered ceramic.

[0014] Preferably, in step S2, the ball mill rotates at a speed of 80-120 r / min for a time of 1-48 h; and / or, In step S3, the rotational speed of the roller is 10~50 r / min, and the time is 2~12 h; and / or, In step S4, the kneading speed is 50~350 r / min, and the time is 1~5 h; and / or, In step S4, the time for trapping the material is 10~48 h.

[0015] Preferably, in step S5, the curing time at room temperature is 1-2 days; and / or, In step S5, the heating and drying process involves: increasing the temperature to 50-180℃ at a rate of 3-10℃ / min and maintaining the temperature for 1-7 days; and / or, In step S6, the protective gas is at least one of argon and nitrogen. It should be noted that when the protective gas is nitrogen, when the temperature exceeds 900°C, nitrogen is no longer introduced, the vacuum pump is turned on, and the kiln is in a vacuum state, with no nitrogen present.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In this invention, the use of water-reducing agent reduces the use of water, which can reduce the porosity of sintered ceramics and improve the mechanical properties of sintered ceramics; the sintering temperature can reach 1500~1700℃, and the sintering of the material is more complete, which is conducive to improving the mechanical properties of sintered ceramics; the introduction of silicon iron chromium alloy powder can play a role in reducing silicon dioxide while ensuring the amount of β-silicon carbide generated, promoting the growth of β-silicon carbide whiskers and avoiding silicon dioxide residue; the β-silicon carbide generated by high temperature reaction combines with the unreacted metal alloy network in the raw materials, which can improve the mechanical properties of sintered ceramics; moreover, the β-silicon carbide formed by sintering is a low-temperature modified phase with a diamond structure, which can improve the wear resistance of sintered ceramics and make sintered ceramics have excellent corrosion resistance under strong alkaline conditions.

[0017] (2) In this invention, the carbon source is composed of carbon black, graphite and short carbon fibers in a mass ratio of (25~40):(35~60):(15~20). This can fill the pores of the sintered ceramic to the maximum extent while ensuring that the sintered ceramic does not crack. Moreover, the β-silicon carbide generated by the reaction adheres to the short carbon fibers and forms a skeleton structure together with the short carbon fibers, which can significantly improve the mechanical properties of the sintered ceramic.

[0018] (3) In this invention, the sintering aid is composed of active lanthanum oxide micro powder and active zirconium oxide micro powder in a mass ratio of (10~30): (70~90), which can make the sintered ceramic more compact without generating too much liquid phase, thereby improving the mechanical properties of the sintered ceramic.

[0019] (4) In this invention, the ceramic blank is embedded in expanded graphite for sintering, which can ensure that the silicon in the ceramic blank reacts completely. The residual ferrochrome alloy combines with the β-silicon carbide generated by the high-temperature reaction, which can make the sintered ceramic have metallic plasticity and improve its mechanical properties. At the same time, there is no silicon infiltration residue, which can improve the corrosion resistance of the sintered ceramic under strong alkaline conditions. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can more clearly understand the present invention.

[0021] Example 1 This embodiment provides an α-silicon carbide-bonded β-silicon carbide sintered ceramic, with a total raw material weight of 10 kg and the raw material composition as follows: The following materials were used: 3307 g of silicon carbide particles with a mesh size of 12-20; 472 g of silicon carbide particles with a mesh size of 20-36; 945 g of silicon carbide particles with a mesh size of 36-70; 473 g of silicon carbide particles with a mesh size of 70-100; 203 g of silicon carbide particles with a mesh size of 100-150; 945 g of silicon carbide particles with a mesh size of 150-200; 505 g of silicon carbide particles with a mesh size >200; 1200 g of ferrosilicon-chromium alloy powder (900 g of silicon, 120 g of iron, and 180 g of chromium); 100 g of binder (gum arabic); 700 g of purified water; 800 g of carbon source (240 g of carbon black, 416 g of graphite, and 144 g of chopped carbon fibers); and 100 g of dispersant (50 g of polyvinylpyrrolidone K30, 30 g of polyethylene glycol, and 20 g of polyvinyl alcohol). g), water-reducing agent (polyhydroxy acid) 50 g; sintering aid 100 g (active lanthanum oxide micro powder 20 g, active zirconium oxide micro powder 80 g), defoamer (diethylhexanol) 100 g; wherein, the particle size of silicon iron chromium alloy powder, carbon source and sintering aid are all ≤88μm; The preparation method of α-silicon carbide-bonded β-silicon carbide sintered ceramics includes the following steps: Step 1: Raw material mixing: Mix silicon carbide particles with a mesh size of 150-200, silicon carbide particles with a mesh size >200, ferrosilicon-chromium alloy powder, carbon source, and sintering aid. Then, ball mill the mixture at 100 r / min for 12 h. Next, add silicon carbide particles with a mesh size of 12-20, 20-36, 36-70, 70-100, and 100-150. Finally, roller mill the mixture at 30 r / min for 6 h. Then, add binder, purified water, dispersant, water-reducing agent, and defoamer. Knead the mixture using a kneader at 200 r / min for 5 h to obtain a uniformly distributed mixture. Allow the mixture to rest for 10 h. Step 2, Injection Molding: Inject the mixture into the plaster mold, let it stand for 0.5 hours, and after the mold is fully filled with the mixture, replenish the fallen liquid level and let it cure at room temperature for 2 days. Step 3, Heating and Molding: Place the shaped ceramic part into an oven, gradually increase the temperature to 150 ℃, dry for 3 days, and then demold to obtain the solidified ceramic blank. Step 4, High-Temperature Sintering: The ceramic blank is placed in a sintering furnace filled with high-purity nitrogen (nitrogen purity > 99.99%), and the sample is embedded in expanded graphite. The temperature is increased to 800±30℃ at 10℃ / min and held for 1 h. Then the temperature is increased to 1700±30℃ at 5℃ / min and held for 8 h. When the temperature exceeds 900℃, nitrogen is no longer introduced and the vacuum pump is turned on. After the heat treatment is completed, the sintering furnace is cooled to 900±30℃ at 5℃ / min, and then cooled to room temperature with the furnace to obtain the sintered ceramic part.

[0022] Example 2 This embodiment provides an α-silicon carbide-bonded β-silicon carbide sintered ceramic, with a total raw material weight of 10 kg and the raw material composition as follows: The following materials were used: 3307 g of silicon carbide particles with a mesh size of 12-20; 472 g of silicon carbide particles with a mesh size of 20-36; 945 g of silicon carbide particles with a mesh size of 36-70; 473 g of silicon carbide particles with a mesh size of 70-100; 203 g of silicon carbide particles with a mesh size of 100-150; 945 g of silicon carbide particles with a mesh size of 150-200; 505 g of silicon carbide particles with a mesh size >200; 1200 g of ferrosilicon-chromium alloy powder (900 g of silicon, 120 g of iron, and 180 g of chromium); 100 g of binder (gum arabic); 700 g of purified water; 800 g of carbon source (240 g of carbon black, 400 g of graphite, and 160 g of chopped carbon fibers); and 100 g of dispersant (50 g of polyvinylpyrrolidone K30, 30 g of polyethylene glycol, and 20 g of polyvinyl alcohol). g), water-reducing agent (polyhydroxy acid) 50 g; sintering aid 100 g (active lanthanum oxide micro powder 20 g, active zirconium oxide micro powder 80 g), defoamer (diethylhexanol) 100 g; wherein, the particle size of silicon iron chromium alloy powder, carbon source and sintering aid are all ≤88μm; The preparation method of α-silicon carbide-bonded β-silicon carbide sintered ceramics includes the following steps: Step 1: Raw material mixing: Mix silicon carbide particles with a mesh size of 150-200, silicon carbide particles with a mesh size >200, ferrosilicon-chromium alloy powder, carbon source, and sintering aid. Then, ball mill the mixture at 100 r / min for 12 h. Next, add silicon carbide particles with a mesh size of 12-20, 20-36, 36-70, 70-100, and 100-150. Finally, roller mill the mixture at 30 r / min for 6 h. Then, add binder, purified water, dispersant, water-reducing agent, and defoamer. Knead the mixture using a kneader at 200 r / min for 5 h to obtain a uniformly distributed mixture. Allow the mixture to rest for 10 h. Step 2, Injection Molding: Inject the mixture into the plaster mold, let it stand for 0.5 hours, and after the mold is fully filled with the mixture, replenish the fallen liquid level and let it cure at room temperature for 2 days. Step 3, Heating and Molding: Place the shaped ceramic part into an oven, gradually increase the temperature to 150 ℃, dry for 3 days, and then demold to obtain the solidified ceramic blank; Step 4, High-Temperature Sintering: The ceramic blank is placed in a sintering furnace filled with high-purity nitrogen (nitrogen purity > 99.99%), and the sample is embedded in expanded graphite. The temperature is increased to 800±30℃ at 10℃ / min and held for 1 h. Then the temperature is increased to 1700±30℃ at 5℃ / min and held for 8 h. When the temperature exceeds 900℃, nitrogen is no longer introduced and the vacuum pump is turned on. After the heat treatment is completed, the sintering furnace is cooled to 900±30℃ at 5℃ / min, and then cooled to room temperature with the furnace to obtain the sintered ceramic part.

[0023] Example 3 This embodiment provides an α-silicon carbide-bonded β-silicon carbide sintered ceramic, with a total raw material weight of 10 kg and the raw material composition as follows: 3507 g of silicon carbide particles with a mesh size of 12-20, 472 g of silicon carbide particles with a mesh size of 20-36, 945 g of silicon carbide particles with a mesh size of 36-70, 473 g of silicon carbide particles with a mesh size of 70-100, 203 g of silicon carbide particles with a mesh size of 100-150, 945 g of silicon carbide particles with a mesh size of 150-200, 505 g of silicon carbide particles with a mesh size >200, 1000 g of ferrosilicon-chromium alloy powder (750 g of silicon, 100 g of iron, and 150 g of chromium), 100 g of binder (gum arabic), 700 g of purified water, 800 g of carbon source (240 g of carbon black, 400 g of graphite, and 160 g of chopped carbon fiber), and 100 g of dispersant (50 g of polyvinylpyrrolidone K30, 30 g of polyethylene glycol, and 20 g of polyvinyl alcohol). g), water-reducing agent (polyhydroxy acid) 50 g; sintering aid 100 g (active lanthanum oxide micro powder 20 g, active zirconium oxide micro powder 80 g), defoamer (diethylhexanol) 100 g; wherein, the particle size of silicon iron chromium alloy powder, carbon source and sintering aid are all ≤88μm; The preparation method of α-silicon carbide-bonded β-silicon carbide sintered ceramics includes the following steps: Step 1: Raw material mixing: Mix silicon carbide particles with a mesh size of 150-200, silicon carbide particles with a mesh size >200, ferrosilicon-chromium alloy powder, carbon source, and sintering aid. Then, ball mill the mixture at 100 r / min for 12 h. Next, add silicon carbide particles with a mesh size of 12-20, 20-36, 36-70, 70-100, and 100-150. Finally, roller mill the mixture at 30 r / min for 6 h. Then, add binder, purified water, dispersant, water-reducing agent, and defoamer. Knead the mixture using a kneader at 200 r / min for 5 h to obtain a uniformly distributed mixture. Allow the mixture to rest for 10 h. Step 2, Injection Molding: Inject the mixture into the plaster mold, let it stand for 0.5 hours, and after the mold is fully filled with the mixture, replenish the fallen liquid level and let it cure at room temperature for 2 days. Step 3, Heating and Molding: Place the shaped ceramic part into an oven, gradually increase the temperature to 150 ℃, dry for 3 days, and then demold to obtain the solidified ceramic blank. Step 4, High-Temperature Sintering: The ceramic blank is placed in a sintering furnace filled with high-purity nitrogen (nitrogen purity > 99.99%), and the sample is embedded in expanded graphite. The temperature is increased to 800±30℃ at 10℃ / min and held for 1 h. Then the temperature is increased to 1700±30℃ at 5℃ / min and held for 8 h. When the temperature exceeds 900℃, nitrogen is no longer introduced and the vacuum pump is turned on. After the heat treatment is completed, the sintering furnace is cooled to 900±30℃ at 5℃ / min, and then cooled to room temperature with the furnace to obtain the sintered ceramic part.

[0024] Comparative Example 1 This comparative example provides an α-silicon carbide-bonded β-silicon carbide sintered ceramic. The raw materials and preparation method are basically the same as those in Example 1, except that the carbon source is composed of carbon black and graphite, wherein the carbon black is 400 g and the graphite is 400 g.

[0025] Comparative Example 2 This comparative example provides an α-silicon carbide-bonded β-silicon carbide sintered ceramic. The raw materials and preparation method are basically the same as those in Example 1, except that no water-reducing agent is used and the amount of pure water is 750 g.

[0026] Comparative Example 3 This comparative example provides an α-silicon carbide-bonded β-silicon carbide sintered ceramic. The raw materials and preparation method are basically the same as those in Example 1, except that silicon powder is used instead of silicon-iron-chromium alloy powder.

[0027] Comparative Example 4 This comparative example provides an α-silicon carbide-bonded β-silicon carbide sintered ceramic. The raw materials and preparation method are basically the same as those in Example 1, except that in step four, the sample is not embedded in expanded graphite.

[0028] Performance Tests and Results The sintered ceramics obtained in Examples 1-3 and Comparative Examples 1-5 were subjected to the following performance tests: 1. Porosity test: The apparent porosity of the sample was tested using an apparent porosity and volumetric density tester (model: XKQ-01, Antelier Company) in accordance with GB / T2997-2015 standard; 2. Room temperature flexural strength test: In accordance with GB / T3001-2017 standard, the room temperature flexural strength of the specimens was tested using a microcomputer-controlled fully automatic flexural strength testing machine (model: CCS600 / 20P, Antler Company). Three specimens were tested for each group of specimens. 3. Room Temperature Abrasion Resistance Test: The bottom and surface of the sample were eroded once each using a sand-containing slurry to test the sample's room temperature erosion resistance. Each group of samples was eroded twice, with an erosion angle of 30°, an erosion time of 30 min, and an erosion pressure of 0.3 MPa; the erosion medium was a mixture of 80-mesh mullite, 80-mesh quartz sand, and water (mass ratio 1:1:8). The volume loss of the sample after erosion was calculated to measure the sample's erosion resistance; the calculation formula is as follows: ; Among them, V s V1 represents the volume lost due to erosion; m1 represents the mass before erosion; m2 represents the mass after erosion; and V1 represents the volume before erosion.

[0029] 4. Corrosion resistance test: The sample was washed with water, dried, and weighed. A 40% NaOH solution was prepared in a container, placed in a water bath and heated to 100 ℃. The experiment was conducted continuously for 72 h. The sample was then removed, and the corrosion products were removed by ultrasonic vibration. After drying, the sample was weighed, the mass loss was calculated, and the surface morphology was observed.

[0030] The performance test results of each sintered ceramic are as follows: Example 1: Porosity 8.4%; flexural strength at room temperature 92.2 MPa; abrasion resistance at room temperature 0.134 cm. 3 Under strong alkaline conditions (40 wt%, NaOH solution) at 100℃, the ceramic part lost 0.002 g in weight, and there was no obvious change on the surface.

[0031] Example 2: Porosity 8.9%; flexural strength at room temperature 99.8 MPa; abrasion resistance at room temperature 0.135 cm. 3 Under strong alkaline conditions (40 wt%, NaOH solution) at 100℃, the ceramic part lost 0.008 g in weight, with no obvious changes on the surface.

[0032] Example 3: Porosity 7.5%; flexural strength at room temperature 105.3 MPa; abrasion resistance at room temperature 0.135 cm. 3 Under strong alkaline conditions (40 wt%, NaOH solution) at 100℃, the ceramic part lost 0.006 g in weight, and there was no obvious change on the surface.

[0033] Comparative Example 1: Porosity 9.1%; flexural strength at room temperature 68.3 MPa; abrasion resistance at room temperature 0.138 cm. 3 Under strong alkaline conditions (40 wt%, NaOH solution) at 100℃, the ceramic part lost 0.002 g in weight, and there was no obvious change on the surface.

[0034] Comparative Example 2: Porosity 11.8%; flexural strength at room temperature 92.2 MPa; abrasion resistance at room temperature 0.192 cm. 3 Under strong alkaline conditions (40 wt%, NaOH solution) at 100℃, the ceramic part lost 0.016 g in weight and showed slight wear on the surface.

[0035] Comparative Example 3: Porosity 8.6%; flexural strength at room temperature 50.9 MPa; abrasion resistance at room temperature 0.135 cm. 3 Under strong alkaline conditions (40 wt%, NaOH solution) at 100℃, the ceramic part lost 0.003 g in weight, and there was no obvious change on the surface.

[0036] Comparative Example 4: Porosity 9.6%; flexural strength at room temperature 71.6 MPa; abrasion resistance at room temperature 0.136 cm. 3 Under strong alkaline conditions (40 wt%, NaOH solution) at 100℃, the ceramic part lost 0.018 g in weight and showed slight wear on the surface.

[0037] As can be seen from Examples 1-3 and Comparative Examples 1-4, the use of water-reducing agents reduces water usage, which can lower the porosity of sintered ceramics and improve their mechanical properties. The β-silicon carbide generated by the reaction adheres to the chopped carbon fibers and forms a skeleton structure together with the chopped carbon fibers, which can significantly improve the mechanical properties of sintered ceramics. Embedding the ceramic green body in expanded graphite for sintering can ensure that silicon in the ceramic green body reacts completely. The residual ferrochrome alloy combines with the β-silicon carbide generated by the high-temperature reaction, which can give the sintered ceramics metallic plasticity and improve their mechanical properties. At the same time, there is no silicon infiltration residue, which can improve the corrosion resistance of sintered ceramics under strong alkaline conditions.

[0038] Unless otherwise specified, all raw materials used in this invention are existing substances that can be purchased directly from the market.

[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. 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 sintered ceramic combining α-silicon carbide and β-silicon carbide, characterized in that, The raw materials of the sintered ceramic, by mass percentage, include: 60-75% silicon carbide particles, 5-14% ferrosilicon-chromium alloy powder, 0.2-1.5% binder, 4-10% carbon source, 5-10% water, 0.2-2% dispersant, 0.1-1% water-reducing agent, 0.5-3% sintering aid, and 0.5-2% defoamer.

2. The α-silicon carbide-bonded β-silicon carbide sintered ceramic according to claim 1, characterized in that, The silicon carbide particles have a particle size distribution of 12-20 mesh, 20-36 mesh, 36-70 mesh, 70-100 mesh, 100-150 mesh, 150-200 mesh, and >200 mesh, with a mass ratio of (0-50):(0-25):(5-20):(5-20):(2-15):(10-20):(5-30); the density of the silicon carbide particles is greater than 98%.

3. The α-silicon carbide-bonded β-silicon carbide sintered ceramic according to claim 1, characterized in that, The silicon-iron-chromium alloy powder has a mass ratio of silicon, iron, and chromium of (55~75):(5~10):(5~15), a particle size of 10~88μm, and a purity of ≥99.8%.

4. The α-silicon carbide-bonded β-silicon carbide sintered ceramic according to claim 1, characterized in that, The carbon source is composed of carbon black, graphite and chopped carbon fibers, wherein the mass ratio of the carbon black, the graphite and the chopped carbon fibers is (25~40):(35~60):(15~20), the particle size of the carbon black is 200~500 nm, the particle size of the graphite is 45<μm, and the length of the chopped carbon fibers is 0.1~7 mm and the diameter is 5~70 μm.

5. The α-silicon carbide-bonded β-silicon carbide sintered ceramic according to claim 1, characterized in that, The dispersant is composed of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol, wherein the mass ratio of polyvinylpyrrolidone, polyethylene glycol, and polyvinyl alcohol is (30~100):(20~40):(20~40), and the polyvinylpyrrolidone is at least one of polyvinylpyrrolidone K30 and polyvinylpyrrolidone K90.

6. The α-silicon carbide-bonded β-silicon carbide sintered ceramic according to claim 1, characterized in that, The sintering aid is composed of activated lanthanum oxide micro powder and activated zirconium oxide micro powder, with a mass ratio of (10~30):(70~90) of activated lanthanum oxide micro powder to activated zirconium oxide micro powder. The sintering aid is an amorphous phase with a particle size of 1~74μm.

7. The α-silicon carbide-bonded β-silicon carbide sintered ceramic according to claim 1, characterized in that, The adhesive is at least one selected from water-soluble phenolic resin, gum arabic, sodium carboxymethyl cellulose, and sodium carboxymethyl cellulose; and / or, The water-reducing agent is polyhydroxy acid; and / or, The defoamer is at least one of diethylhexanol, isooctanol, isoamyl alcohol, and diisobutylmethanol.

8. The method for preparing α-silicon carbide-bonded β-silicon carbide sintered ceramics according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. The silicon carbide particles, ferrosilicon-chromium alloy powder, carbon source and sintering aid are divided into a first group and a second group according to the particle size. The particle size of the raw materials in the first group is ≤100 μm, and the particle size of the raw materials in the second group is >100 μm. S2. Mix the raw materials of the first group and ball mill them to obtain the first mixture; S3. Add the raw materials of the second group to the first mixture, and then roll the mixture to obtain the second mixture. S4. Add binder, water, dispersant, water-reducing agent and defoamer to the second mixture, knead and tame the mixture to obtain a mixture; S5. Inject the mixture into the mold, cure it at room temperature, then heat it up and keep it at that temperature to dry, then demold it to obtain a ceramic blank; S6. Under a protective gas atmosphere, the ceramic green body is embedded in expanded graphite, heated to 770-830 ℃ at 3-10 ℃ / min and held for 0.5-2 h, then heated to 1470-1730 ℃ at 3-5 ℃ / min and held for 2-8 h, then cooled to 770-1030 ℃ at 3-5 ℃ / min and then cooled to room temperature to obtain α-silicon carbide bonded β-silicon carbide sintered ceramic.

9. The method for preparing α-silicon carbide-bonded β-silicon carbide sintered ceramics according to claim 8, characterized in that, In step S2, the ball mill rotates at a speed of 80-120 r / min for a time of 1-48 h; and / or, In step S3, the rotational speed of the roller is 10~50 r / min, and the time is 2~12 h; and / or, In step S4, the kneading speed is 50~350 r / min, and the time is 1~5 h; and / or, In step S4, the time for trapping the material is 10~48 h.

10. The method for preparing α-silicon carbide-bonded β-silicon carbide sintered ceramics according to claim 8, characterized in that, In step S5, the curing time at room temperature is 1~2 days; and / or, In step S5, the heating and drying process involves: heating at a rate of 3–10 °C / min to 50–180 °C and maintaining the temperature for 1–7 days; and / or, In step S6, the protective gas is at least one of argon and nitrogen.