Silicon nitride coating used in silicon carbide reaction sintering furnace

Abstract

The invention discloses a silicon nitride coating used in a silicon carbide reaction sintering furnace, and belongs to the technical field of protective coatings. The silicon nitride coating provided by the invention does not contain boron elements, so that the introduction of the boron elements is fundamentally avoided, the content of boron impurities in a silicon carbide ceramic product sintered by adopting the silicon nitride coating sintering furnace is low, the problem that the content of the boron elements exceeds the standard due to sintering of the product is controlled, and the purity of the product is greatly improved. The silicon nitride coating is good in leveling property and stable in chemical property, the obtained coating is stable in structure, not prone to reacting with various chemical substances in the reaction sintering process of silicon carbide, not prone to cracking at the high temperature to cause damage to a protective layer of a sintering furnace, and excellent in protective performance; according to the vacuum sintering furnace adopting the coating for protection, silicon in the sintering process of silicon carbide ceramic cannot enter a graphite piece and a heating body in the furnace, and the graphite piece in the furnace cannot expand, crack and deform, so that a product is easily separated from the graphite piece after being sintered, and the product percent of pass is greatly increased.

Description

Technical Field

[0001] The invention relates to the technical field of protective coatings, in particular to a silicon nitride coating used in a silicon carbide reaction sintering furnace. Background Art

[0002] Vacuum sintering furnaces play a core role in the manufacturing of silicon carbide (SiC) ceramic products. Through the coordination of vacuum environment and high-temperature process, they can achieve high purity, high density and complex structure forming of materials.

[0003] The inner wall of the vacuum sintering furnace, the graphite support in the furnace and the surface of the graphite heating element are usually sprayed with a protective coating. The protective coating can prevent silicon in the molten or gaseous state from penetrating into the furnace graphite parts and heating body during the reaction sintering of silicon carbide, causing the risk of explosion of the graphite parts and heating elements in the furnace. Therefore, the performance of the protective coating in the sintering furnace is particularly important.

[0004] In the prior art, the protective coating sprayed in the reaction sintering furnace is a boron nitride coating. Boron nitride has good chemical inertness and corrosion resistance, and can effectively prevent silicon from penetrating into the graphite parts and the heating body during the silicon carbide reaction. However, its defect is that the boron element in boron nitride is an impurity for existing silicon carbide products and will penetrate into the silicon carbide products, affecting the purity of the sintered products. In addition, since the leveling properties of the boron nitride coating are average, the main reason is that the surface of the boron nitride nanosheets has strong inertness and sparse leveling properties. Therefore, the boron nitride coating is prone to uneven spraying and is prone to cracking when heated, resulting in damage to the protective layer. During the reaction sintering of silicon carbide ceramics, silicon will enter the graphite parts and heating elements in the furnace, causing the graphite parts to expand, crack and deform. Silicon, graphite parts and sintered products will stick together, or cause bumps and potholes on the surface of the product. After sintering is completed, it is difficult to separate the product from the graphite parts, and forced separation will cause the product to break or crack. If the boron nitride is sprayed excessively and the silicon carbide product is placed directly on the boron nitride coating, the boron content of the product will be too high after sintering.

[0005] Therefore, there is an urgent need to solve the above problems, and a protective coating is needed that can protect the sintering furnace without affecting the purity of the silicon carbide product. Summary of the Invention

[0006] In order to solve the above problems, the present invention provides a silicon nitride coating for use in a silicon carbide reactive sintering furnace.

[0007] The present invention is achieved through the following technical solutions:

[0008] A silicon nitride coating for use in a silicon carbide reactive sintering furnace, comprising, by mass percentage, 30%-40% silicon nitride micropowder, 9%-11% carbon black, 4.5%-5.5% graphene, 0.95%-1.5% polyvinyl pyrrolidone, 0.4%-0.6% polyethylene glycol, and 45%-55% alcohol;

[0009] The preparation method of the silicon nitride coating is as follows: the raw materials are ball-milled and mixed according to a ratio for 1-2 hours, the slurry is poured out for standby use, the furnace body is heated to 200-300°C and then naturally cooled to 35-45°C for spraying, and the spraying thickness is controlled at 0.3-0.8mm. After spraying, the furnace body is heated to 90-120°C and dried. After drying, a sintering furnace with a silicon nitride coating is obtained.

[0010] Preferably, the silicon nitride coating comprises, by mass percentage, 35% silicon nitride powder, 10% carbon black, 5% graphene, 1% polyvinyl pyrrolidone, 0.5% polyethylene glycol, and 48.5% alcohol.

[0011] Preferably, the preparation method of the silicon nitride coating is as follows: the raw materials are ball-milled and mixed according to the ratio for 1 hour, the slurry is poured out for standby use, the furnace body is heated to 250°C and then naturally cooled to 40°C for spraying, the spraying thickness is controlled at 0.5mm, and after spraying, the furnace body is heated to 100°C for drying.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] The present invention provides a silicon nitride coating that does not contain boron, fundamentally eliminating the introduction of boron. The boron impurity content in silicon carbide ceramic products sintered in a silicon nitride coating sintering furnace is low, and the problem of excessive boron content in the product due to sintering is controlled, thereby greatly improving the purity of the product.

[0014] The silicon nitride coating of the present invention has good leveling properties, is sprayed evenly, has stable chemical properties, and the obtained coating structure is stable. It is not easy to react with various chemical substances in the process of reactive sintering of silicon carbide. It is not easy to crack at high temperatures to cause damage to the protective layer of the sintering furnace, and has excellent protective performance. In a vacuum sintering furnace protected by the coating of the present invention, silicon in the process of sintering silicon carbide ceramics will not enter the graphite parts and heating elements in the furnace, and will not cause the graphite parts in the furnace to expand, crack, and deform. Therefore, the product is easy to separate from the graphite parts and easy to clean after sintering, and the product qualification rate is greatly improved. DETAILED DESCRIPTION

[0015] The present invention will be further described below in conjunction with the embodiments:

[0016] A silicon nitride coating for use in a silicon carbide reactive sintering furnace, comprising, by mass percentage, 30%-40% silicon nitride micropowder, 9%-11% carbon black, 4.5%-5.5% graphene, 0.95%-1.5% polyvinyl pyrrolidone, 0.4%-0.6% polyethylene glycol, and 45%-55% alcohol;

[0017] The preparation method of the silicon nitride coating is as follows: the raw materials are ball-milled and mixed according to a ratio for 1-2 hours, the slurry is poured out for standby use, the furnace body is heated to 200-300°C and then naturally cooled to 35-45°C for spraying, and the spraying thickness is controlled at 0.3-0.8mm. After spraying, the furnace body is heated to 90-120°C and dried. After drying, a sintering furnace with a silicon nitride coating is obtained.

[0018] Preferably, the silicon nitride coating comprises, by mass percentage, 35% silicon nitride powder, 10% carbon black, 5% graphene, 1% polyvinyl pyrrolidone, 0.5% polyethylene glycol, and 48.5% alcohol.

[0019] Preferably, the preparation method of the silicon nitride coating is as follows: the raw materials are ball-milled and mixed according to the ratio for 1 hour, the slurry is poured out for standby use, the furnace body is heated to 250°C and then naturally cooled to 40°C for spraying, the spraying thickness is controlled at 0.5mm, and after spraying, the furnace body is heated to 100°C for drying.

[0020] Example 1

[0021] Configuration of silicon nitride coating: The mass percentage of each component is as follows: silicon nitride powder 35%, carbon black 10%, graphene 5%, polyvinyl pyrrolidone 1%, polyethylene glycol 0.5%, and alcohol 48.5%.

[0022] The raw materials are ball-milled and mixed according to the ratio for 1 hour, and the slurry is poured out for use. The furnace body is heated to 250°C and then naturally cooled to 40°C for spraying. The spraying range is the inner wall of the furnace body, the graphite part bracket and the surface of the graphite heating part. The spraying thickness is controlled at 0.5mm. After spraying, the furnace body is heated to 100°C and dried. After drying, a sintering furnace with a silicon nitride coating is obtained.

[0023] The silicon carbide ceramic was placed in a sintering furnace with a silicon nitride coating and sintered at a temperature of 1580-1730°C for 24 hours. Under the protection of inert gas, the product was naturally cooled for 50 hours to obtain a silicon carbide ceramic product. The silicon carbide ceramic product was subjected to elemental detection and analysis. The test results are shown in Table 1.

[0024] Table 1: Elemental analysis data of the silicon carbide ceramic product obtained in Example 1

[0025]

[0026] Example 2

[0027] Configuration of silicon nitride coating: The mass percentage of each component is as follows: silicon nitride powder 38%, carbon black 10%, graphene 5%, polyvinyl pyrrolidone 1%, polyethylene glycol 0.5%, and alcohol 45.5%.

[0028] The raw materials are ball-milled and mixed according to the ratio for 1 hour, and the slurry is poured out for use. After the furnace body is heated to 300°C, it is naturally cooled to 45°C for spraying. The spraying range is the inner wall of the furnace body, the graphite part bracket and the surface of the graphite heating part. The spraying thickness is controlled at 0.6mm. After spraying, the furnace body is heated to 110°C for drying. After drying, a sintering furnace with a silicon nitride coating is obtained.

[0029] The silicon carbide ceramic was placed in a sintering furnace with a silicon nitride coating and sintered at a temperature of 1580-1730°C for 24 hours. Under the protection of inert gas, it was naturally cooled for 55 hours to obtain a silicon carbide ceramic product. The silicon carbide ceramic product was subjected to elemental detection and analysis. The test results are shown in Table 2.

[0030] Table 2: Elemental analysis data of the silicon carbide ceramic product obtained in Example 2

[0031]

[0032]

[0033] Comparative Example

[0034] The silicon carbide ceramic products produced by the existing technology using a boron nitride coating sintering furnace were tested and analyzed, and the analysis data are shown in Table 3.

[0035] Table 3: Test data of silicon carbide products produced using a boron nitride coating sintering furnace

[0036]

[0037]

[0038] From the data in Tables 1, 2, and 3, it can be concluded that the boron content in the silicon carbide ceramics sintered in the vacuum sintering furnace protected by the silicon nitride coating of the present invention is much lower than the boron content of 1038 mg / kg in the product of the comparative example. Therefore, the silicon carbide products sintered in the sintering furnace protected by the coating of the present invention contain less boron impurities and are of high purity.

[0039] The reaction principle of the present invention is as follows: silicon nitride has stable chemical properties and is not easy to react with various chemical substances in the process of reactive sintering of silicon carbide. Silicon nitride does not react with silicon and can effectively protect the furnace body; silicon nitride will react with carbon to generate silicon carbide and nitrogen, so the addition of carbon black can react with part of the silicon nitride to form silicon carbide, which can effectively protect the graphite parts and heating elements in the furnace from reacting with silicon nitride; graphene is an enhanced coating structure, which makes the silicon nitride coating less likely to peel off and can better protect the graphite parts and heating elements in the furnace; polyvinyl pyrrolidone is a suspending agent that can prevent the powder from precipitating in the solvent, polyethylene glycol is a dispersant that can better disperse the powder in the solvent, and alcohol is a solvent.

[0040] In summary, the present invention provides a silicon nitride coating that does not contain boron, fundamentally eliminating the introduction of boron. The boron impurity content in the silicon carbide ceramic product sintered in a silicon nitride coating sintering furnace is low, and the problem of excessive boron content in the product caused by sintering is controlled, thereby greatly improving the purity of the product.

[0041] The silicon nitride coating of the present invention has good leveling properties, is sprayed evenly, has stable chemical properties, and the obtained coating structure is stable. It is not easy to react with various chemical substances in the process of reactive sintering of silicon carbide. It is not easy to crack at high temperatures to cause damage to the protective layer of the sintering furnace, and has excellent protective performance. In a vacuum sintering furnace protected by the coating of the present invention, silicon in the process of sintering silicon carbide ceramics will not enter the graphite parts and heating elements in the furnace, and will not cause the graphite parts in the furnace to expand, crack, and deform. Therefore, the product is easy to separate from the graphite parts and easy to clean after sintering, and the product qualification rate is greatly improved.

[0042] In summary, the above is only a preferred embodiment of the present invention and is not intended to limit the scope of implementation of the present invention. All equivalent changes and modifications of the shape, structure, characteristics and spirit described in the scope of the claims of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A silicon nitride coating for use in a silicon carbide reactive sintering furnace, characterized in that: In terms of mass percentage, its composition is: silicon nitride powder 30%-40%, carbon black 9%-11%, graphene 4.5%-5.5%, polyvinyl pyrrolidone 0.95%-1.5%, polyethylene glycol 0.4%-0.6%, and alcohol 45%-55%; The preparation method of the silicon nitride coating is as follows: the raw materials are ball-milled and mixed according to a ratio for 1-2 hours, the slurry is poured out for standby use, the furnace body is heated to 200-300°C and then naturally cooled to 35-45°C for spraying, and the spraying thickness is controlled at 0.3-0.8mm. After spraying, the furnace body is heated to 90-120°C and dried. After drying, a sintering furnace with a silicon nitride coating is obtained.

2. The silicon nitride coating for use in a silicon carbide reactive sintering furnace according to claim 1, characterized in that: Measured in percentage by mass, the silicon nitride coating comprises the following components: 35% silicon nitride powder, 10% carbon black, 5% graphene, 1% polyvinyl pyrrolidone, 0.5% polyethylene glycol, and 48.5% alcohol.

3. The silicon nitride coating for use in a silicon carbide reactive sintering furnace according to claim 1, characterized in that: The preparation method of the silicon nitride coating is as follows: the raw materials are ball-milled and mixed according to the ratio for 1 hour, the slurry is poured out for standby use, the furnace body is heated to 250°C and then naturally cooled to 40°C for spraying, the spraying thickness is controlled at 0.5mm, and after spraying, the furnace body is heated to 100°C for drying.

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