Ultra-thick silicon carbide product and preparation method thereof

Abstract

The present application relates to the technical field of silicon carbide processing, and specifically discloses a super-thick silicon carbide product and its preparation method. The silicon carbide product includes the following raw materials in parts by weight: 25-40 parts of modified silicon carbide, 5-10 parts of zirconium oxide, 1-3 parts of silicon boride, 0.5-2 parts of molybdenum carbide, 3-6 parts of additives, and 9-15 parts of water; wherein the modified silicon carbide is prepared by modifying silicon carbide with a mullite composite; its preparation method is as follows: the modified silicon carbide, zirconium oxide, silicon boride, molybdenum carbide, additives, and water are uniformly mixed to obtain a slurry; the slurry is vacuum-treated, injected into a mold and sealed, heated, kept warm, and cooled to obtain a blank; the blank is sintered and cooled to obtain a silicon carbide product. The super-thick silicon carbide product of the present application has the advantages of reducing sintering cracking and improving strength through the synergistic effect between the raw materials.

Description

Technical Field

[0001] The present application relates to the technical field of silicon carbide processing, and in particular to an ultra-thick silicon carbide product and a preparation method thereof. Background Art

[0002] Silicon carbide is an inorganic material produced by smelting quartz sand, petroleum coke, sawdust, and other raw materials at high temperatures in an electric resistance furnace. Also known as moissanite, silicon carbide is the most widely used and economical non-oxide high-tech refractory raw material, including carbon, nitrogen, and boron. It is also known as diamond grit or refractory sand. Due to its stable chemical properties, high thermal conductivity, and low thermal expansion coefficient, silicon carbide is widely used in glass, ceramics, stone, refractories, cast iron, and non-ferrous metals.

[0003] At present, the thickness of general silicon carbide products is about 50mm. If the thickness of the silicon carbide products is thicker, it is difficult to control during sintering and it is easy to crack during the sintering process, thus affecting the strength of the silicon carbide products. Summary of the Invention

[0004] In order to reduce sintering cracking and improve the strength of silicon carbide products, the present application provides an ultra-thick silicon carbide product and a preparation method thereof.

[0005] In a first aspect, the present application provides an ultra-thick silicon carbide product, which adopts the following technical solution:

[0006] An ultra-thick silicon carbide product comprises the following raw materials in parts by weight: 25-40 parts of modified silicon carbide, 5-10 parts of zirconium oxide, 1-3 parts of silicon boride, 0.5-2 parts of molybdenum carbide, 3-6 parts of an auxiliary agent, and 9-15 parts of water; wherein the modified silicon carbide is obtained by modifying silicon carbide with a mullite composite.

[0007] By adopting the above technical solution, the ultra-thick silicon carbide product of the present application improves the bulk density, hardness, radial compressive strength and bending strength of the silicon carbide product through the synergistic effect between the raw materials, reduces the cracking phenomenon caused by the sintering process, and improves the fracture toughness. Among them, the bulk density is 3.10-3.19g / cm 3 , Vickers hardness is 21.3-22.8GPa, fracture toughness is 2.7-4.5MPa·m 1 / 2 , radial compressive strength is 562-598MPa, and bending strength is 447-480MPa.

[0008] Modified silicon carbide is made by modifying silicon carbide with a mullite composite. The crystal structure of mullite is orthorhombic, with needle-shaped or columnar crystals arranged in chains. These needle-shaped or columnar crystals intersperse with each other to form an interlaced and strong network structure, thus giving mullite the advantages of high hardness, high strength, good thermal stability and good corrosion resistance. The mullite composite further increases the hardness of mullite. Modifying silicon carbide can form a close bond between the network structure of mullite and silicon carbide, thereby increasing the strength of silicon carbide products, improving the thermal stability of silicon carbide products, and reducing cracking of silicon carbide products during sintering.

[0009] Zirconia offers the advantages of high hardness, high corrosion resistance, high-temperature stability, and high strength. Silicon boride exhibits excellent stability and corrosion resistance at high temperatures. Molybdenum carbide offers corrosion resistance, high-temperature resistance, high strength, and excellent thermal conductivity. Adding zirconium oxide, silicon boride, and molybdenum carbide to the raw materials of silicon carbide products can further improve their strength and reduce cracking during sintering.

[0010] Preferably, the modified silicon carbide is prepared by the following method: uniformly mixing the mullite composite and silicon carbide, heating and melting, adding dextrin, stirring, extruding and granulating, and cooling to obtain the modified silicon carbide.

[0011] Furthermore, the modified silicon carbide is prepared by the following method: mixing the mullite composite and silicon carbide uniformly, heating and melting them at a temperature of 1350-1400° C., adding dextrin, stirring for 1-3 hours, extruding and granulating, and cooling to obtain the modified silicon carbide;

[0012] The weight ratio of silicon carbide to dextrin is 1:(0.1-0.2).

[0013] By adopting the above technical solution and utilizing the above preparation method to prepare modified silicon carbide, the mullite composite and silicon carbide can be better compounded, which helps to improve the strength of silicon carbide products.

[0014] Preferably, the weight ratio of the silicon carbide and mullite composite is 1:(0.5-0.8).

[0015] If the amount of mullite compound added is too small, it won't effectively modify silicon carbide and improve the strength of silicon carbide products. If the amount of mullite compound added is too large, the thermal expansion coefficients of silicon carbide and mullite differ significantly during sintering, and excessive mullite content can cause more severe cracking. By adopting the above technical solution, when the amount of mullite compound added is within the above range, it is more conducive to improving the strength of silicon carbide products and reducing cracking during sintering.

[0016] Preferably, the mullite composite is prepared by the following method: crushing mullite and sieving to obtain mullite powder; uniformly mixing mullite powder, cobalt powder, titanium powder and nickel powder, ball milling, vacuum hot pressing sintering, heat preservation, extrusion granulation and cooling to obtain the mullite composite.

[0017] Furthermore, the mullite composite is prepared by the following method: crushing mullite and passing it through a 120-mesh sieve to obtain mullite powder; mixing the mullite powder, cobalt powder, titanium powder, and nickel powder evenly, ball milling at a speed of 200-300 r / min for 4-6 hours, sintering at 20 MPa and 1300-1500°C, keeping warm for 20-40 minutes, extruding and granulating, and cooling to obtain the mullite composite.

[0018] By adopting the above technical solution and using the above preparation method to prepare the mullite composite, the cobalt powder can maintain a high strength even at high temperatures; the titanium powder can not only improve the sintering performance of silicon carbide products, but also hinder the propagation rate of cracks and increase the strength of silicon carbide products; the nickel powder has good high-temperature resistance; by mixing mullite powder, cobalt powder, titanium powder and nickel powder and applying them to silicon carbide products, the strength of the silicon carbide products can be further improved and the cracking phenomenon during sintering can be reduced.

[0019] Preferably, the weight ratio of the mullite, cobalt powder, titanium powder and nickel powder is 1:(0.4-0.6):(0.4-0.6):(0.4-0.6).

[0020] Too little cobalt, titanium, or nickel powder can lead to poor results and ineffective strength enhancement of silicon carbide products. Excessive amounts can increase brittleness and easily cause cracking in silicon carbide products. By adopting the above technical solution, when the amounts of cobalt, titanium, and nickel powder added are within the above ranges, the strength of silicon carbide products can be improved while reducing cracking during sintering.

[0021] Preferably, the auxiliary agent is a mixture of a dispersant, a sintering aid and a binder.

[0022] Preferably, the weight ratio of the dispersant, sintering aid and binder is 1:1:1.

[0023] By adopting the above technical solution, dispersants, sintering aids and binders are also added to the raw materials of silicon carbide products, which can help to disperse the raw materials more evenly, facilitate the function of each raw material, improve the strength of silicon carbide, and reduce cracking during sintering.

[0024] In a second aspect, the present application provides a method for preparing an ultra-thick silicon carbide product, which adopts the following technical solution:

[0025] A method for preparing an ultra-thick silicon carbide product comprises the following steps:

[0026] S1: uniformly mixing modified silicon carbide, zirconium oxide, silicon boride, molybdenum carbide, additives, and water to obtain a slurry;

[0027] S2: vacuum-treating the slurry, injecting it into a mold, sealing it, heating it, keeping it warm, and cooling it to obtain a green body;

[0028] S3: Sintering the green blank and cooling it to obtain a silicon carbide product.

[0029] Furthermore, a method for preparing an ultra-thick silicon carbide product comprises the following steps:

[0030] S1: uniformly mixing modified silicon carbide, zirconium oxide, silicon boride, molybdenum carbide, additives, and water to obtain a slurry;

[0031] S2: Treat the slurry under a vacuum of 20-40 kPa for 15-18 minutes, inject it into a mold, seal it, heat it to 70-90°C, keep it warm for 3-4 hours, and cool it to obtain a green body;

[0032] S3: The green body is first heated to 1000°C at a rate of 1.5°C / min, and then continued to be heated to 1600°C at a rate of 1°C / min, sintered at a constant temperature for 3-5 hours, and cooled to obtain a silicon carbide product.

[0033] By adopting the above technical solution, the raw materials are first mixed evenly, vacuum treated, injected into a mold, heated, kept warm, and cooled to obtain a blank, which is then sintered to obtain a silicon carbide product. This facilitates the raw materials to play their role, improves the strength of the silicon carbide product, and reduces cracking during sintering.

[0034] Preferably, the silicon carbide product is further subjected to oxidation treatment.

[0035] Furthermore, the silicon carbide product is further subjected to the following oxidation treatment: the silicon carbide product is subjected to oxidation treatment, the oxidation temperature is set to 1000-1400°C, the temperature is increased at a rate of 10°C / min, the temperature is kept for 1-3 hours, and the silicon carbide product is cooled to obtain the treated silicon carbide product.

[0036] By adopting the above technical solution, the silicon carbide products are oxidized to effectively remove surface defects and cracks of the silicon carbide products, and an oxide layer can be formed on the surface of the silicon carbide products to repair surface defects and cracks, and even generate residual stress, thereby improving the strength of the silicon carbide products.

[0037] In summary, this application includes at least one of the following beneficial technical effects:

[0038] 1. Since the modified silicon carbide used in this application is a mullite composite modified silicon carbide, the mullite is arranged in a chain of needle-shaped or columnar crystals, which interweave with each other to form an interlaced and strong network structure, making it have the advantages of high hardness, high strength, good thermal stability, and good corrosion resistance. The mullite composite further increases the hardness of the mullite. Modifying the silicon carbide can improve the strength of the silicon carbide product and reduce the cracking of the silicon carbide product during sintering, and can make the volume density reach 3.19g / cm 3 , Vickers hardness reaches 22.8GPa, fracture toughness reaches 4.5MPa·m 1 / 2 , radial compressive strength reaches 598MPa and bending strength reaches 480MPa.

[0039] 2. In this application, the preferred mullite composite is a mixture of mullite, cobalt powder, titanium powder, and nickel powder. Cobalt powder can maintain high strength even at high temperatures; titanium powder can not only improve the sintering performance of silicon carbide products, but also hinder the propagation rate of cracks, thereby increasing the strength of silicon carbide products; nickel powder has good high temperature resistance; by mixing mullite powder, cobalt powder, titanium powder, and nickel powder and applying them to silicon carbide products, the strength of silicon carbide products can be further improved and the phenomenon of cracking during sintering can be reduced. DETAILED DESCRIPTION

[0040] The following is a further detailed description of this application in conjunction with the specific content.

[0041] raw material

[0042] All raw materials in this application can be obtained commercially.

[0043] The dextrin is β-cyclodextrin; the average particle size of the cobalt powder is 50 nm; the average particle size of the titanium powder is 40 nm; the average particle size of the nickel powder is 50 nm; the dispersant is polyethylene glycol with a molecular weight of 697; the sintering aid is aluminum oxide; and the binder is sodium hydroxymethyl cellulose.

[0044] Preparation Example

[0045] Preparation Example 1

[0046] A mullite composite is prepared by the following method:

[0047] 2 kg of mullite was crushed and passed through a 120-mesh sieve to obtain mullite powder; the mullite powder, 0.8 kg of cobalt powder, 0.8 kg of titanium powder, and 0.8 kg of nickel powder were evenly mixed, ball-milled at a speed of 250 r / min for 5 hours, sintered at 20 MPa and 1400°C, kept warm for 30 minutes, extruded into granules, and cooled to obtain a mullite composite.

[0048] Preparation Example 2

[0049] A mullite composite is provided, which differs from Preparation Example 1 in that the amount of cobalt powder added is different. In Preparation Example 2, the amount of cobalt powder added is 1 kg.

[0050] Preparation Example 3

[0051] A mullite composite is provided, which differs from Preparation Example 1 in that the amount of cobalt powder added is different. In Preparation Example 3, the amount of cobalt powder added is 1.2 kg.

[0052] Preparation Example 4

[0053] A mullite composite is provided, which differs from Preparation Example 2 in that the amount of titanium powder added is different. In Preparation Example 3, the amount of cobalt powder added is 1 kg.

[0054] Preparation Example 5

[0055] A mullite composite is provided, which differs from Preparation Example 1 in that the amount of titanium powder added is different. In Preparation Example 5, the amount of cobalt powder added is 1.2 kg.

[0056] Preparation Example 6

[0057] A mullite composite is provided, which differs from Preparation Example 4 in that the amount of nickel powder added is different. In Preparation Example 6, the amount of cobalt powder added is 1 kg.

[0058] Preparation Example 7

[0059] A mullite composite is different from Preparation Example 4 in that the amount of nickel powder added is different. In Preparation Example 7, the amount of cobalt powder added is 1.2 kg.

[0060] Preparation Example 8

[0061] A modified silicon carbide is prepared by the following method:

[0062] 1 kg of the mullite composite prepared in Preparation Example 1 and 2 kg of silicon carbide were mixed evenly, heated to melt at 1370° C., 0.3 kg of dextrin was added, stirred for 2 h, extruded into granules, and cooled to obtain modified silicon carbide.

[0063] Preparation Example 9

[0064] A modified silicon carbide is different from Preparation Example 8 in that the amount of the mullite compound added is different. The amount of the mullite compound added in Preparation Example 9 is 1.3 kg.

[0065] Preparation Example 10

[0066] A modified silicon carbide is different from Preparation Example 8 in that the amount of the mullite compound added is different. The amount of the mullite compound added in Preparation Example 9 is 1.6 kg.

[0067] Preparation Examples 11-17

[0068] A modified silicon carbide is different from Preparation Example 9 in that the mullite composite has a different source and is prepared using Preparation Examples 2-7, respectively.

[0069] Example

[0070] Example 1

[0071] An ultra-thick silicon carbide product, the raw material ratio of which is shown in Table 1.

[0072] A method for preparing an ultra-thick silicon carbide product comprises the following steps: S1: uniformly mixing the modified silicon carbide, zirconium oxide, silicon boride, molybdenum carbide, an additive, and water prepared in Preparation Example 8 to obtain a slurry;

[0073] S2: The slurry was treated under a vacuum of 30 kPa for 16 minutes, injected into a mold, sealed, heated to 80°C, kept warm for 3.5 hours, and cooled to obtain a green body;

[0074] S3: The green body is first heated to 1000°C at a rate of 1.5°C / min, and then further heated to 1600°C at a rate of 1°C / min, sintered at a constant temperature for 4 hours, and cooled to obtain a silicon carbide product.

[0075] Table 1 Raw materials of silicon carbide products in different embodiments

[0076]

[0077] Examples 6-14

[0078] An ultra-thick silicon carbide product is different from Example 4 in that the modified silicon carbide has different sources. Examples 6-14 are prepared using Preparation Examples 9-17, respectively.

[0079] Example 15

[0080] An ultra-thick silicon carbide product, which differs from Example 12 in that the silicon carbide product is further subjected to the following oxidation treatment: the silicon carbide product is oxidized, the oxidation temperature is set to 1200°C, the temperature is increased at a rate of 10°C / min, the temperature is kept for 2 hours, and the treated silicon carbide product is obtained.

[0081] Comparative Example

[0082] Comparative Example 1

[0083] An ultra-thick silicon carbide product, which differs from Example 1 in that the modified silicon carbide is replaced by silicon carbide in equal amounts.

[0084] Comparative Example 2

[0085] An ultra-thick silicon carbide product, which differs from Example 1 in that the mullite composite in the modified silicon carbide is replaced by mullite in equal amounts.

[0086] Comparative Example 3

[0087] An ultra-thick silicon carbide product is different from Example 1 in that the cobalt powder and titanium powder in the mullite composite are replaced by nickel powder in equal amounts.

[0088] Comparative Example 4

[0089] An ultra-thick silicon carbide product is different from Example 1 in that the cobalt powder and nickel powder in the mullite composite are replaced by titanium powder in equal amounts.

[0090] Comparative Example 5

[0091] An ultra-thick silicon carbide product is different from Example 1 in that titanium powder and nickel powder in the mullite composite are replaced by cobalt powder in equal amounts.

[0092] Comparative Example 6

[0093] An ultra-thick silicon carbide product, which differs from Example 1 in that the cobalt powder in the mullite composite is replaced by titanium powder in equal amounts.

[0094] Performance testing

[0095] The following performance tests were performed on the ultra-thick silicon carbide products in Examples 1-15 and Comparative Examples 1-6:

[0096] Bulk density: The bulk density of silicon carbide products was measured in accordance with GB / T25995-2010 “Test method for density and apparent porosity of fine ceramics”. The test results are shown in Table 2.

[0097] Vickers hardness: The Vickers hardness of silicon carbide products was measured in accordance with GB / T16534-2009 “Test method for room temperature hardness of fine ceramics”. The test results are shown in Table 2.

[0098] Fracture toughness: The fracture toughness of silicon carbide products was measured in accordance with JIS R1607-1995 "Test method for fracture strength of fine ceramics". The test results are shown in Table 2.

[0099] Radial compressive strength: The room temperature compressive strength of silicon carbide products was measured in accordance with JB / T8133.10-2013 "Test methods for physical and chemical properties of electric carbon products Part 3: Rockwell hardness". The test results are shown in Table 2.

[0100] Bending strength: The bending strength of silicon carbide products was measured in accordance with GB / T14390-2008 “Test method for high-temperature flexural strength of fine ceramics”. The test results are shown in Table 2.

[0101] Table 2 Test results

[0102]

[0103]

[0104] As can be seen from Table 2, the ultra-thick silicon carbide products of the present application have improved the bulk density, hardness, radial compressive strength and bending strength of the silicon carbide products through the synergistic effect between the raw materials, and also reduced the cracking phenomenon caused by the sintering process and improved the fracture toughness. Among them, the bulk density is 3.10-3.19 g / cm 3 , Vickers hardness is 21.3-22.8GPa, fracture toughness is 2.7-4.5MPa·m 1 / 2 , radial compressive strength is 562-598MPa, and bending strength is 447-480MPa.

[0105] Combining Example 1 with Comparative Examples 1-6, it can be seen that the bulk density of the silicon carbide product in Example 1 is 3.10 g / cm 3 , Vickers hardness is 21.3GPa, fracture toughness is 2.7MPa·m 1 / 2 The radial compressive strength is 562 MPa and the bending strength is 447 MPa, which are better than those of comparative examples 1-6, indicating that the modified silicon carbide is prepared by modifying silicon carbide with a mullite composite, and the mullite composite is more suitable for mullite, cobalt powder, titanium powder, and nickel powder, which can reduce cracking during sintering and improve the strength of silicon carbide products.

[0106] Combining Examples 1-5, it can be seen that the bulk density of the silicon carbide product in Example 4 is 3.13 g / cm 3 , Vickers hardness is 22.0GPa, fracture toughness is 3.4MPa·m 1 / 2 The radial compressive strength is 576 MPa and the bending strength is 460 MPa, which are better than those of other embodiments, indicating that the addition amount of the silicon carbide product in Example 4 is more appropriate, which can reduce cracking during sintering and improve the strength of the silicon carbide product.

[0107] Combining Examples 4 and 6-14, it can be seen that the bulk density of the silicon carbide product in Example 13 is 3.17 g / cm 3 , Vickers hardness is 22.5GPa, fracture toughness is 4.3MPa·m 1 / 2The radial compressive strength is 587 MPa and the bending strength is 477 MPa, which are better than those of other embodiments, indicating that the modified silicon carbide prepared by Preparation Example 16 is more suitable, which can not only reduce cracking during sintering, but also improve the strength of silicon carbide products.

[0108] Combining Example 13 and Example 15, it can be seen that the bulk density of the silicon carbide product in Example 15 is 3.19 g / cm 3 , Vickers hardness is 22.8GPa, fracture toughness is 4.5MPa·m 1 / 2 The radial compressive strength is 595 MPa and the bending strength is 480 MPa, which are better than those in Example 13, indicating that the oxidation treatment of silicon carbide products is more appropriate, which further improves the strength of silicon carbide products.

[0109] The above-mentioned specific implementation examples are all preferred embodiments of the present application and are not intended to limit the scope of protection of the present application. Therefore, any equivalent changes made based on the structure, shape, and principle of the present application should be included in the scope of protection of the present application.

Claims

1. An ultra-thick silicon carbide product, characterized in that: The method comprises the following raw materials in parts by weight: 25-40 parts of modified silicon carbide, 5-10 parts of zirconium oxide, 1-3 parts of silicon boride, 0.5-2 parts of molybdenum carbide, 3-6 parts of an auxiliary agent, and 9-15 parts of water; wherein the modified silicon carbide is prepared by modifying silicon carbide with a mullite composite; The modified silicon carbide is prepared by the following method: mixing the mullite composite and silicon carbide uniformly, heating and melting, adding dextrin, stirring, extruding and granulating, and cooling to obtain the modified silicon carbide; The weight ratio of the silicon carbide and mullite composite is 1: (0.5-0.8); The mullite composite is prepared by the following method: crushing mullite and sieving to obtain mullite powder; uniformly mixing the mullite powder, cobalt powder, titanium powder and nickel powder, ball milling, sintering by vacuum hot pressing, heat preservation, extrusion granulation and cooling to obtain the mullite composite; The weight ratio of the mullite, cobalt powder, titanium powder and nickel powder is 1: (0.4-0.6): (0.4-0.6): (0.4-0.6); The method for preparing the ultra-thick silicon carbide product comprises the following steps: S1: uniformly mixing modified silicon carbide, zirconium oxide, silicon boride, molybdenum carbide, additives, and water to obtain a slurry; S2: vacuum-treating the slurry, injecting it into a mold, sealing it, heating it, keeping it warm, and cooling it to obtain a green body; S3: Sintering the green blank and cooling it to obtain a silicon carbide product.

2. The ultra-thick silicon carbide product according to claim 1, characterized in that: The auxiliary agent is a mixture of a dispersant, a sintering auxiliary agent and a binder.

3. The ultra-thick silicon carbide product according to claim 2, characterized in that: The weight ratio of the dispersant, sintering aid and binder is 1:1:

1.

4. The ultra-thick silicon carbide product according to claim 1, characterized in that: The silicon carbide product is further subjected to an oxidation treatment.

Images