Silicon nitride ceramic and method for producing the same

Abstract

The application relates to the technical field of ceramics, and discloses a silicon nitride ceramic and a preparation method thereof. The raw materials of the silicon nitride ceramic include, in terms of the measurement quantity, 72-80 parts of silicon nitride, 4-12 parts of a sintering aid, 5-10 parts of a binder, 3-8 parts of a lubricant and 0.1-1.5 parts of a dispersing agent. The binder is acrylic acid and polyvinyl alcohol, and the mass ratio of the acrylic acid to the polyvinyl alcohol is 1:0.4-0.5. The binder of the raw materials of the silicon nitride ceramic is acrylic acid and polyvinyl alcohol. The polyvinyl alcohol and the acrylic acid in the binder can be combined in a specific ratio to control the particle size interval of the powder particles after spray granulation, can significantly improve the loose bulk density of the green body, and can significantly improve the strength of the silicon nitride ceramic.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramics, in particular to a silicon nitride ceramic and a preparation method thereof. BACKGROUND

[0002] The silicon nitride ceramic has excellent properties such as high strength, high hardness, high thermal shock resistance, high wear resistance, high toughness, corrosion resistance, and is widely used in core technical fields such as mechanical engineering, aerospace, national defense and military industry, and semiconductor. The method for applying silicon nitride ceramic to semiconductor devices in the prior art is mainly to form a layer of silicon nitride film on the surface of the semiconductor device by using a mask method, such as the manufacturing method of a silicon nitride film and a semiconductor device disclosed in CN110120343B. Due to the harsh process conditions for semiconductor preparation, the parts of semiconductor manufacturing equipment also need to meet higher performance indicators, and the performance of conventional substrates cannot meet the use requirements. Therefore, the technical personnel in the field propose to make silicon nitride ceramic into the required parts of semiconductor manufacturing equipment, but at present, when silicon nitride is made into large parts, the shape of the parts is simple and the related performance indicators are low. Therefore, the process conditions of the silicon nitride ceramic need to be further optimized to realize the development and application of silicon nitride ceramic samples with high strength, low dielectric, low thermal expansion coefficient, and complex shape.

[0003] At present, silicon nitride is mainly made into parts by ball milling silicon nitride, sintering agent, binder, dispersant and lubricant and other raw materials to form slurry, then the slurry is made into powder particles, then the powder particles are pressed into green body, and then the green body is sintered to form a silicon nitride ceramic part. The method for making powder particles mainly includes vacuum ball milling, rotary vibration screen and double-cone mixer method, and spray granulation method. The spray granulation method is a commonly used granulation method, such as the preparation method of a silicon nitride ceramic granulated powder disclosed in CN113999019B. The method points out that polyvinyl alcohol has high viscosity as a binder, and then the deformation ability of polyvinyl alcohol is increased by using polyethylene glycol, so that the shrinkage of liquid droplets during spray drying is larger, and the powder particles are more densely packed, and higher packaging density can be obtained. However, the present application found through further research that the combination of polyvinyl alcohol and polyethylene glycol has a large difference in the particle size interval of the powder particles when applied, and the particle size interval in a specific range can significantly improve the loose bulk density of the silicon nitride ceramic, thereby improving the performance of the silicon nitride ceramic. Therefore, selecting a suitable binder is of great significance to improve the performance of the silicon nitride ceramic. SUMMARY

[0004] This invention addresses the problem of significant particle size variations when using polyvinyl alcohol and polyethylene glycol as binders in existing silicon nitride ceramics. It provides a silicon nitride ceramic and its preparation method. The binder in this silicon nitride ceramic raw material uses acrylic acid and polyvinyl alcohol. The combination of polyvinyl alcohol and acrylic acid in this binder, at a specific ratio, can control the particle size range of the powder after spray granulation, significantly improving the loose packing density of the green body, thereby significantly increasing the strength of the silicon nitride ceramic.

[0005] The specific technical solution of this invention is as follows:

[0006] A silicon nitride ceramic, comprising, by weight, the following raw materials:

[0007] 75-80 parts of silicon nitride

[0008] 5-12 parts of sintering aid

[0009] 5-10 parts of adhesive,

[0010] 3-8 parts lubricant

[0011] Dispersant 0.1–1.5 parts;

[0012] The adhesive is acrylic acid and polyvinyl alcohol, with a mass ratio of acrylic acid to polyvinyl alcohol of 1:0.4 to 0.5.

[0013] This invention provides a silicon nitride ceramic, the raw materials of which include silicon nitride, sintering aid, binder, lubricant, and dispersant. The binder uses a specific ratio of acrylic acid and polyvinyl alcohol. Existing technology indicates that when polyvinyl alcohol is used as a binder, the powder particles produced after spray drying of the slurry can shrink rapidly, quickly forming spherical particles, thereby increasing the bulk density of the green body. However, this invention finds that when polyvinyl alcohol is used as a binder, the rapid shrinkage of the spray-dried powder particles leads to a greater difference in particle size distribution. Through experiments, this invention has found that a larger difference in particle size distribution is not necessarily better; rather, a better bulk density is obtained within a specific range. Therefore, to address the above problem, this invention further optimizes the polyvinyl alcohol binder. Testing revealed that when acrylic acid and polyvinyl alcohol are used as binders at a mass ratio of 1:0.4–0.5, the optimal particle size range is achieved, and within this range, the bulk density of the green body is significantly improved.

[0014] Preferably, the sintering aid is alumina and yttrium oxide.

[0015] Preferably, the alumina is present in a mass fraction of 2 to 5 parts, and the yttrium oxide is present in a mass fraction of 3 to 7 parts.

[0016] Preferably, the alumina has a particle size of 0.5–0.9 μm, and the yttrium oxide has a particle size of 0.8–1.2 μm.

[0017] The sintering aids of this invention use alumina and yttrium oxide. Silicon nitride ceramics are mainly densified through a liquid phase during sintering. Therefore, during pressureless sintering, the sintering aids alumina and yttrium oxide react with the silicon oxide on the surface of silicon nitride particles to generate a liquid phase. Under capillary action, the silicon nitride particles rotate and rearrange to form a denser packing state. The liquid phase also fills more pores, thereby significantly reducing the porosity of silicon nitride ceramics, significantly increasing the density, significantly increasing the bending strength, and significantly reducing the dielectric loss.

[0018] Preferably, the lubricant includes one or more of stearic acid, lauric acid, and fatty acids; the dispersant is polyacrylamide.

[0019] The dispersant chosen in this invention is polyacrylamide. While polyethylene glycol is a commonly used dispersant, existing technologies indicate that the combined use of polyethylene glycol and polyvinyl alcohol can accelerate the shrinkage of polyvinyl alcohol. Therefore, selecting a suitable dispersant is crucial. This invention, after screening, found that the combined use of polyacrylamide and a binder can further reduce the particle size distribution differences in the powder, thereby further improving the bulk density of the green body. Simultaneously, ammonium polyacrylamide can act as an anti-hydration agent for silicon nitride powder. Silicon nitride powder undergoes hydrolysis upon contact with water, and the resulting agglomeration is severe. Ammonium polyacrylamide can form an isolation layer between the silicon nitride powder and the aqueous medium, and its addition can inhibit the hydrolysis reaction during high-speed ball milling.

[0020] A method for preparing the above-mentioned silicon nitride ceramic includes the following steps: ball milling silicon nitride, sintering aid, binder, surfactant, dispersant and water to form a slurry; spray granulating the slurry to form a powder; cold isostatic pressing the powder into a mold to form a green body; and rough machining, degreasing and sintering the green body to form silicon nitride ceramic.

[0021] Preferably, the powder has a moisture content of 0.3-0.8% and a bulk density of 0.95-0.97 g / cm³. 3 .

[0022] Preferably, the cold isostatic pressing pressure is 120–160 MPa, the time is 1–5 min, and the density of the green body is 2.0–2.1 g / cm³. 3 .

[0023] Preferably, the degreasing temperature is 450–550°C, and the degreasing time is 5–8 hours.

[0024] Preferably, the sintering temperature is 1750–1780°C.

[0025] This invention also provides a method for preparing the aforementioned silicon nitride ceramics. The method includes six steps: ball milling to prepare slurry, spray drying to prepare powder particles, cold isostatic pressing to prepare green body, rough machining of green body to prepare rough machined parts, degreasing of rough machined parts to prepare degreased crude products, and sintering of degreased crude products to prepare silicon nitride ceramics. This method is simple, can be mass-produced, and the silicon nitride ceramic parts produced have the characteristics of high strength, low dielectric constant, and low coefficient of thermal expansion.

[0026] Compared with the prior art, this application has the following technical effects:

[0027] (1) The binder of the present invention uses a specific ratio of acrylic acid and polyvinyl alcohol. Using the binder, the particle size range of the powder produced by spray drying can be optimized, and the loose density of the green body is significantly improved within this particle size range.

[0028] (2) When the dispersant polyacrylamide of the present invention is used in combination with the binder, it can further reduce the grading difference of the particle size range of the powder and further improve the loose density of the green body.

[0029] (3) The preparation method of the present invention includes six steps: ball milling to make slurry, spray drying to make powder, cold isostatic pressing to make green body, rough processing of green body to make rough processed parts, degreasing of rough processed parts to make degreased crude product, and sintering of degreased crude product to make silicon nitride ceramic. The method is simple and can be mass-produced. The silicon nitride ceramic parts produced have the characteristics of high strength, low dielectric and low coefficient of thermal expansion. Attached Figure Description

[0030] Figure 1 SEM images of spray-dried powder particles prepared using the methods of Examples 1 to 3.

[0031] Figure 2 SEM images of silicon nitride ceramics prepared in Examples 1 to 3.

[0032] Figure 3 This is a schematic diagram of the silicon nitride ceramic parts manufactured in Examples 1 to 3. Detailed Implementation

[0033] The present invention will be further described below with reference to embodiments.

[0034] Example 1:

[0035] A method for preparing silicon nitride ceramics includes the following steps:

[0036] Step 1: Add 76 parts by weight of silicon nitride powder, 8 parts by weight of sintering aid (3 parts by weight of alumina powder and 5 parts by weight of yttrium oxide powder), 1 part by weight of dispersant (ammonium polyacrylate) and 60 parts by weight of deionized water into a ball mill and ball mill for 6 hours until the powder is evenly dispersed. Then add 10 parts by weight of binder (acrylic acid and polyvinyl alcohol in a mass ratio of 7:3) and 5 parts by weight of lubricant (fatty acid) and continue ball milling for 1 hour to make a slurry.

[0037] Step 2: The slurry is injected into a spray granulation device for spray granulation to produce powder. The inlet temperature of the spray granulation device is 190℃, the outlet temperature is 90℃, the moisture content of the powder is 0.5%, and the loose density is 0.966 g / cm³. 3 ;

[0038] Step 3: Load the powder into the molding die, and then use 140 MPa pressure for cold isostatic pressing for 1-5 minutes to form a green body with a density of 2.07 g / cm³. 3 ;

[0039] Step 4: Grind and rough-machine the shape of the raw part to produce a rough-machined part;

[0040] Step 5: Place the rough-machined parts in a degreasing furnace at 500℃ for 3 hours. After the heat treatment is completed, allow them to cool naturally to room temperature to produce the degreased crude product.

[0041] Step Six: Place the degreased crude product in the graphite mold of the vacuum sintering furnace, use embedded powder to embed and compact the degreased crude product, then slowly heat the sintering furnace to 1760℃ and hold for 3 hours, with nitrogen gas flowing through the furnace to maintain a slightly positive pressure inside the furnace. After the holding period, cool with the furnace to room temperature to produce silicon nitride ceramics. Then, finely process and clean the silicon nitride ceramics to produce silicon nitride ceramic parts.

[0042] Example 2:

[0043] A method for preparing silicon nitride ceramics includes the following steps:

[0044] Step 1: Add 76 parts by weight of silicon nitride powder, 8 parts by weight of sintering aid (3 parts by weight of alumina powder and 5 parts by weight of yttrium oxide powder), 1 part by weight of dispersant (ammonium polyacrylate) and 60 parts by weight of deionized water into a ball mill and ball mill for 6 hours until the powder is evenly dispersed. Then add 10 parts by weight of binder (acrylic acid and polyvinyl alcohol in a mass ratio of 1:0.4) and 5 parts by weight of lubricant (fatty acid) and continue ball milling for 1 hour to make a slurry.

[0045] Step 2: The slurry is injected into a spray granulation device for spray granulation to produce powder. The inlet temperature of the spray granulation device is 190℃, the outlet temperature is 90℃, the moisture content of the powder is 0.5%, and the loose density is 0.958 g / cm³. 3

[0046] Step 3: Load the powder into the molding die, and then use 140 MPa pressure for cold isostatic pressing for 1-5 minutes to form a green body with a density of 2.06 g / cm³. 3 ;

[0047] Step 4: Grind and rough-machine the shape of the raw part to produce a rough-machined part;

[0048] Step 5: Place the rough-machined parts in a degreasing furnace at 500℃ for 3 hours. After the heat treatment is completed, allow them to cool naturally to room temperature to produce the degreased crude product.

[0049] Step Six: Place the degreased crude product in the graphite mold of the vacuum sintering furnace, use embedded powder to embed and compact the degreased crude product, then slowly heat the sintering furnace to 1760℃ and hold for 3 hours, with nitrogen gas flowing through the furnace to maintain a slightly positive pressure inside the furnace. After the holding period, cool with the furnace to room temperature to produce silicon nitride ceramics. Then, finely process and clean the silicon nitride ceramics to produce silicon nitride ceramic parts.

[0050] Example 3:

[0051] A method for preparing silicon nitride ceramics includes the following steps:

[0052] Step 1: Add 76 parts by weight of silicon nitride powder, 8 parts by weight of sintering aid (3 parts by weight of alumina powder and 5 parts by weight of yttrium oxide powder), 1 part by weight of dispersant (ammonium polyacrylate) and 60 parts by weight of deionized water into a ball mill and ball mill for 6 hours until the powder is evenly dispersed. Then add 10 parts by weight of binder (acrylic acid and polyvinyl alcohol in a mass ratio of 1:0.5) and 5 parts by weight of lubricant (fatty acid) and continue ball milling for 1 hour to make a slurry.

[0053] Step 2: The slurry is injected into a spray granulation device for spray granulation to produce powder. The inlet temperature of the spray granulation device is 190℃, the outlet temperature is 90℃, the moisture content of the powder is 0.6%, and the loose density is 0.954 g / cm³. 3

[0054] Step 3: Load the powder into the molding die, and then use 140 MPa pressure for cold isostatic pressing for 1-5 minutes to form a green body with a density of 2.05 g / cm³. 3 ;

[0055] Step 4: Grind and rough-machine the shape of the raw part to produce a rough-machined part;

[0056] Step 5: Place the rough-machined parts in a degreasing furnace at 500℃ for 3 hours. After the heat treatment is completed, allow them to cool naturally to room temperature to produce the degreased crude product.

[0057] Step Six: Place the degreased crude product in the graphite mold of the vacuum sintering furnace, use embedded powder to embed and compact the degreased crude product, then slowly heat the sintering furnace to 1760℃ and hold for 3 hours, with nitrogen gas flowing through the furnace to maintain a slightly positive pressure inside the furnace. After the holding period, cool with the furnace to room temperature to produce silicon nitride ceramics. Then, finely process and clean the silicon nitride ceramics to produce silicon nitride ceramic parts.

[0058] Example 4:

[0059] A method for preparing silicon nitride ceramics includes the following steps:

[0060] Step 1: Add 72 parts by weight of silicon nitride powder, 12 parts by weight of sintering aid (3 parts by weight of alumina powder and 5 parts by weight of yttrium oxide powder), 1 part by weight of dispersant (ammonium polyacrylate) and 60 parts by weight of deionized water into a ball mill and ball mill for 6 hours until the powder is evenly dispersed. Then add 10 parts by weight of binder (acrylic acid and polyvinyl alcohol in a mass ratio of 7:3) and 5 parts by weight of lubricant (stearic acid) and continue ball milling for 1 hour to make a slurry.

[0061] Step 2: The slurry is injected into a spray granulation device for spray granulation to produce powder. The inlet temperature of the spray granulation device is 190℃, the outlet temperature is 90℃, the moisture content of the powder is 0.3%, and the loose density is 0.96 g / cm³. 3 ;

[0062] Step 3: Load the powder into the molding die, and then use 120 MPa pressure for cold isostatic pressing for 1-5 minutes to form a green body with a density of 1.98 g / cm³. 3 ;

[0063] Step 4: Grind and rough-machine the shape of the raw part to produce a rough-machined part;

[0064] Step 5: Place the rough-machined parts in a degreasing furnace at 500℃ for 3 hours. After the heat treatment is completed, allow them to cool naturally to room temperature to produce the degreased crude product.

[0065] Step Six: Place the degreased crude product in the graphite mold of the vacuum sintering furnace, use embedded powder to embed and compact the degreased crude product, then slowly heat the sintering furnace to 1750℃ and hold for 3 hours, with nitrogen gas flowing through the furnace to maintain a slightly positive pressure inside the furnace. After the holding period, cool with the furnace to room temperature to produce silicon nitride ceramics. Then, finely process and clean the silicon nitride ceramics to produce silicon nitride ceramic parts.

[0066] Example 5:

[0067] A method for preparing silicon nitride ceramics includes the following steps:

[0068] Step 1: Add 80 parts by weight of silicon nitride powder, 3 parts by weight of sintering aid (1.5 parts by weight of alumina powder and 2.5 parts by weight of yttrium oxide powder), 1 part by weight of dispersant (ammonium polyacrylate), and 60 parts by weight of deionized water into a ball mill. Ball mill for 6 hours until the powder is evenly dispersed. Then add 10 parts by weight of binder (acrylic acid and polyvinyl alcohol in a mass ratio of 7:3) and 5 parts by weight of lubricant (lauric acid) and continue ball milling for 1 hour to make a slurry.

[0069] Step 2: The slurry is injected into a spray granulation device for spray granulation to produce powder. The inlet temperature of the spray granulation device is 190℃, the outlet temperature is 90℃, the moisture content of the powder is 0.7%, and the bulk density is 0.96 g / cm³. 3 ;

[0070] Step 3: Load the powder into the molding die, then use 160 MPa pressure for cold isostatic pressing for 1-5 minutes to form a green body with a density of 2.0 g / cm³. 3 ;

[0071] Step 4: Grind and rough-machine the shape of the raw part to produce a rough-machined part;

[0072] Step 5: Place the rough-machined parts in a degreasing furnace at 500℃ for 3 hours. After the heat treatment is completed, allow them to cool naturally to room temperature to produce the degreased crude product.

[0073] Step Six: Place the degreased crude product in the graphite mold of the vacuum sintering furnace, embed and compact the degreased crude product with embedded powder, then slowly heat the sintering furnace to 1780℃ and hold for 3 hours. Nitrogen gas is circulated in the furnace to maintain a slightly positive pressure. After the holding period, the furnace is cooled to room temperature to produce silicon nitride ceramics. The silicon nitride ceramics are then finely processed and cleaned to produce silicon nitride ceramic parts.

[0074] Comparative Example 1:

[0075] Compared to Example 1, Comparative Example 1 uses 10 parts of polyvinyl alcohol as the adhesive, and includes the following steps:

[0076] Step 1: Add 76 parts by weight of silicon nitride powder, 8 parts by weight of sintering aid (3 parts by weight of alumina powder and 5 parts by weight of yttrium oxide powder), 1 part by weight of dispersant (ammonium polyacrylate) and 60 parts by weight of deionized water into a ball mill and ball mill for 6 hours until the powder is evenly dispersed. Then add 10 parts by weight of binder (polyvinyl alcohol) and 5 parts by weight of lubricant (fatty acid) and continue ball milling for 1 hour to make a slurry.

[0077] Step 2: The slurry is injected into a spray granulation device for spray granulation to produce powder. The inlet temperature of the spray granulation device is 190℃, the outlet temperature is 90℃, the moisture content of the powder is 0.5%, and the loose density is 0.915 g / cm³. 3 ;

[0078] Step 3: Load the powder into the molding die, and then use 140 MPa pressure for cold isostatic pressing for 1-5 minutes to form a green body with a density of 1.91 g / cm³. 3 ;

[0079] Step 4: Grind and rough-machine the shape of the raw part to produce a rough-machined part;

[0080] Step 5: Place the rough-machined parts in a degreasing furnace at 500℃ for 3 hours. After the heat treatment is completed, allow them to cool naturally to room temperature to produce the degreased crude product.

[0081] Step Six: Place the degreased crude product in the graphite mold of the vacuum sintering furnace, use embedded powder to embed and compact the degreased crude product, then slowly heat the sintering furnace to 1760℃ and hold for 3 hours, with nitrogen gas flowing through the furnace to maintain a slightly positive pressure inside the furnace. After the holding period, cool with the furnace to room temperature to produce silicon nitride ceramics. Then, finely process and clean the silicon nitride ceramics to produce silicon nitride ceramic parts.

[0082] Comparative Example 2:

[0083] Compared to Example 1, Comparative Example 2 uses 10 parts of acrylic acid as the adhesive, and includes the following steps:

[0084] Step 1: Add 76 parts by weight of silicon nitride powder, 8 parts by weight of sintering aid (3 parts by weight of alumina powder and 5 parts by weight of yttrium oxide powder), 1 part by weight of dispersant (ammonium polyacrylate) and 60 parts by weight of deionized water into a ball mill and ball mill for 6 hours until the powder is evenly dispersed. Then add 10 parts by weight of binder (acrylic acid) and 5 parts by weight of lubricant (fatty acid) and continue ball milling for 1 hour to make a slurry.

[0085] Step 2: The slurry is injected into a spray granulation device for spray granulation to produce powder. The inlet temperature of the spray granulation device is 190℃, the outlet temperature is 90℃, the moisture content of the powder is 0.6%, and the loose density is 0.921 g / cm³. 3 ;

[0086] Step 3: Load the powder into the molding die, and then use 140 MPa pressure for cold isostatic pressing for 1-5 minutes to form a green body with a density of 1.93 g / cm³. 3 ;

[0087] Step 4: Grind and rough-machine the shape of the raw part to produce a rough-machined part;

[0088] Step 5: Place the rough-machined parts in a degreasing furnace at 500℃ for 3 hours. After the heat treatment is completed, allow them to cool naturally to room temperature to produce the degreased crude product.

[0089] Step Six: Place the degreased crude product in the graphite mold of the vacuum sintering furnace, use embedded powder to embed and compact the degreased crude product, then slowly heat the sintering furnace to 1760℃ and hold for 3 hours, with nitrogen gas flowing through the furnace to maintain a slightly positive pressure inside the furnace. After the holding period, cool with the furnace to room temperature to produce silicon nitride ceramics. Then, finely process and clean the silicon nitride ceramics to produce silicon nitride ceramic parts.

[0090] Comparative Example 3:

[0091] Compared to Example 1, the ratio of acrylic acid to polyvinyl alcohol in the adhesive of Comparative Example 3 is 1:1, and includes the following steps:

[0092] Step 1: Add 76 parts by weight of silicon nitride powder, 8 parts by weight of sintering aid (3 parts by weight of alumina powder and 5 parts by weight of yttrium oxide powder), 1 part by weight of dispersant (ammonium polyacrylate) and 60 parts by weight of deionized water into a ball mill and ball mill for 6 hours until the powder is evenly dispersed. Then add 10 parts by weight of binder (acrylic acid and polyvinyl alcohol in a 1:1 mass ratio) and 5 parts by weight of lubricant (fatty acid) and continue ball milling for 1 hour to make a slurry.

[0093] Step 2: The slurry is injected into a spray granulation device for spray granulation to produce powder. The inlet temperature of the spray granulation device is 190℃, the outlet temperature is 90℃, the moisture content of the powder is 0.5%, and the loose density is 0.937 g / cm³. 3 ;

[0094] Step 3: Load the powder into the molding die, and then use 140 MPa pressure for cold isostatic pressing for 1-5 minutes to form a green body with a density of 2.01 g / cm³. 3 ;

[0095] Step 4: Grind and rough-machine the shape of the raw part to produce a rough-machined part;

[0096] Step 5: Place the rough-machined parts in a degreasing furnace at 500℃ for 3 hours. After the heat treatment is completed, allow them to cool naturally to room temperature to produce the degreased crude product.

[0097] Step Six: Place the degreased crude product in the graphite mold of the vacuum sintering furnace, use embedded powder to embed and compact the degreased crude product, then slowly heat the sintering furnace to 1760℃ and hold for 3 hours, with nitrogen gas flowing through the furnace to maintain a slightly positive pressure inside the furnace. After the holding period, cool with the furnace to room temperature to produce silicon nitride ceramics. Then, finely process and clean the silicon nitride ceramics to produce silicon nitride ceramic parts.

[0098] Comparative Example 4:

[0099] Compared to Example 1, in Comparative Example 4, the ratio of acrylic acid to polyvinyl alcohol in the adhesive was 1:0.1, and the process included the following steps:

[0100] Step 1: Add 76 parts by weight of silicon nitride powder, 8 parts by weight of sintering aid (3 parts by weight of alumina powder and 5 parts by weight of yttrium oxide powder), 1 part by weight of dispersant (ammonium polyacrylate) and 60 parts by weight of deionized water into a ball mill and ball mill for 6 hours until the powder is evenly dispersed. Then add 10 parts by weight of binder (acrylic acid and polyvinyl alcohol in a mass ratio of 1:0.1) and 5 parts by weight of lubricant (fatty acid) and continue ball milling for 1 hour to make a slurry.

[0101] Step 2: The slurry is injected into a spray granulation device for spray granulation to produce powder. The inlet temperature of the spray granulation device is 190℃, the outlet temperature is 90℃, the moisture content of the powder is 0.5%, and the loose density is 0.936 g / cm³. 3 ;

[0102] Step 3: Load the powder into the molding die, then use 140 MPa pressure for cold isostatic pressing for 1-5 minutes to form a green body with a density of 2.02 g / cm³. 3 ;

[0103] Step 4: Grind and rough-machine the shape of the raw part to produce a rough-machined part;

[0104] Step 5: Place the rough-machined parts in a degreasing furnace at 500℃ for 3 hours. After the heat treatment is completed, allow them to cool naturally to room temperature to produce the degreased crude product.

[0105] Step Six: Place the degreased crude product in the graphite mold of the vacuum sintering furnace, use embedded powder to embed and compact the degreased crude product, then slowly heat the sintering furnace to 1760℃ and hold for 3 hours, with nitrogen gas flowing through the furnace to maintain a slightly positive pressure inside the furnace. After the holding period, cool with the furnace to room temperature to produce silicon nitride ceramics. Then, finely process and clean the silicon nitride ceramics to produce silicon nitride ceramic parts.

[0106] Comparative Example 5:

[0107] Compared to Example 1, the dispersant in Comparative Example 5 is polyethylene glycol, and the process includes the following steps:

[0108] Step 1: Add 76 parts by weight of silicon nitride powder, 8 parts by weight of sintering aid (3 parts by weight of alumina powder and 5 parts by weight of yttrium oxide powder), 1 part by weight of dispersant (polyethylene glycol), and 60 parts by weight of deionized water into a ball mill. Ball mill for 6 hours until the powder is evenly dispersed. Then add 10 parts by weight of binder (acrylic acid and polyvinyl alcohol in a mass ratio of 7:3) and 5 parts by weight of lubricant (fatty acid) and continue ball milling for 1 hour to make a slurry.

[0109] Step 2: The slurry is injected into a spray granulation device for spray granulation to produce powder. The inlet temperature of the spray granulation device is 190℃, the outlet temperature is 90℃, the moisture content of the powder is 0.6%, and the loose density is 0.929 g / cm³. 3 ;

[0110] Step 3: Load the powder into the molding die, then use 140 MPa pressure for cold isostatic pressing for 1-5 minutes to form a green body with a density of 2.0 g / cm³. 3 ;

[0111] Step 4: Grind and rough-machine the shape of the raw part to produce a rough-machined part;

[0112] Step 5: Place the rough-machined parts in a degreasing furnace at 500℃ for 3 hours. After the heat treatment is completed, allow them to cool naturally to room temperature to produce the degreased crude product.

[0113] Step Six: Place the degreased crude product in the graphite mold of the vacuum sintering furnace, use embedded powder to embed and compact the degreased crude product, then slowly heat the sintering furnace to 1760℃ and hold for 3 hours, with nitrogen gas flowing through the furnace to maintain a slightly positive pressure inside the furnace. After the holding period, cool with the furnace to room temperature to produce silicon nitride ceramics. Then, finely process and clean the silicon nitride ceramics to produce silicon nitride ceramic parts.

[0114] Comparative Example 6:

[0115] Compared with Example 1, the degreased crude product in Comparative Example 7 was not buried with powder, and all other conditions were the same as in Example 1.

[0116] Detection Example 1:

[0117] The properties of the silicon nitride ceramics prepared in Examples 1 to 5 and Comparative Examples 1 to 6 were tested, including: density, flexural strength, coefficient of thermal expansion, dielectric constant, and dielectric loss.

[0118] The density of the sample was accurately determined using the Archimedes displacement method.

[0119] The flexural strength was determined on a universal testing machine using the three-point bending method according to GB / T 6569-1986 standard;

[0120] The coefficient of thermal expansion was determined using a thermal expansion meter according to the standard GB / T 16535-2008.

[0121] The dielectric constant and dielectric loss were tested according to JIS C2141 standard using the Q instrument method at a test frequency of 13.56MHz.

[0122] Test results are shown in Table 1.

[0123] Table 1 Properties of silicon nitride ceramics

[0124]

[0125] As shown in Table 1, the densities of the silicon nitride ceramics prepared in Examples 1 to 3 are 3.17–3.19 g / cm³. 3 Its bending strength can reach 750 MPa, and its coefficient of thermal expansion can reach 2.78 × 10⁻⁶. -6 At ℃, the dielectric constant can reach 9.17, and the dielectric loss can reach 5.19 × 10⁻⁶. -3 The above results show that the silicon nitride ceramic prepared by the present invention has the advantages of high strength, low dielectric loss and low coefficient of thermal expansion.

[0126] Examples 4 and 5 show silicon nitride ceramics prepared with different raw material ratios. The results indicate that the raw material ratio has a significant impact on the performance of silicon nitride ceramics. Therefore, the raw material ratio can be adjusted according to the required performance.

[0127] Comparative Example 1 is a silicon nitride ceramic made using only polyvinyl alcohol as a binder. Compared with Example 1, Comparative Example 1 has lower strength, but higher coefficient of thermal expansion, dielectric constant, and dielectric loss. Comparative Example 2 is a silicon nitride ceramic made using only acrylic acid as a binder. Compared with Example 1, Comparative Example 2 has lower strength, but higher coefficient of thermal expansion, dielectric constant, and dielectric loss. Comparative Examples 3 and 4 adjusted the ratio of acrylic acid and polyvinyl alcohol, respectively. Analysis of the results of Comparative Examples 3 and 4 revealed that silicon nitride ceramics made with acrylic acid and polyvinyl alcohol in a ratio outside a specific range had lower strength than Example 1, and significantly higher coefficient of thermal expansion, dielectric constant, and dielectric loss. These results show that silicon nitride ceramics made with acrylic acid and polyvinyl alcohol as binders in a specific ratio have high strength, low dielectric constant, and low coefficient of thermal expansion.

[0128] In Comparative Example 5, polyethylene glycol was used as the dispersant. The results showed that the performance of silicon nitride ceramics prepared with polyethylene glycol as the dispersant was worse than that of Example 1. This indicates that the combination of polyacrylamide and binder can optimize particle size distribution, inhibit hydrolysis of powder, and improve the performance of silicon nitride ceramics.

[0129] In Comparative Example 6, no embedding powder was used for embedding, which prevented the sample from forming porcelain.

[0130] Detection Example 2:

[0131] The particle size range and green bulk density of the powders obtained in Example 1 and Comparative Examples 1 to 5 were tested. The particle size and particle size range of the powder were tested by a laser particle size analyzer, and the bulk density of the granulated powder was tested by a bulk density meter. The test results are shown in Table 2.

[0132] Table 2. Particle size distribution of spray granulation in Examples 1 and Comparative Examples 1 to 5

[0133]

[0134]

[0135] As shown in Table 2, the results of Example 1 and Comparative Examples 1 to 5 demonstrate that different binders have a significant impact on the particle size distribution range of the spray-dried powder. Different binder selections and proportions result in different particle size ranges. Furthermore, the results of bulk density and particle size range show that a more uniform or varied particle size distribution is not necessarily better; rather, the optimal bulk density is achieved within a specific particle size range. In addition to meeting basic physical performance requirements, granulated powder must also meet particle size distribution requirements. Granulated powder with excellent particle size distribution has a higher bulk density, resulting in densely packed green particles, fewer pores after sintering, and a higher degree of product densification. This invention characterizes particle size distribution as a percentage of the particle size distribution in each example.

[0136] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing silicon nitride ceramics, characterized in that, Includes the following steps: 72-80 parts of silicon nitride, 4-12 parts of sintering aid, 5-10 parts of binder, 3-8 parts of lubricant, 0.1-1.5 parts of dispersant, and water are ball-milled to form a slurry. The slurry is then spray-granulated to form a powder. The powder is then placed in a mold and cold isostatically pressed to form a green body. The green body is then rough-processed, degreased, and sintered to produce silicon nitride ceramics. The binder is acrylic acid and polyvinyl alcohol, with a mass ratio of acrylic acid to polyvinyl alcohol of 1:0.4-0.

5.

2. The preparation method according to claim 1, characterized in that, The sintering aid is aluminum oxide and yttrium oxide.

3. The preparation method according to claim 2, characterized in that, The alumina is present in 2 to 5 parts by mass, and the yttrium oxide is present in 3 to 7 parts by mass.

4. The preparation method according to claim 2 or 3, characterized in that, The alumina has a particle size of 0.5~0.9μm, and the yttrium oxide has a particle size of 0.8~1.2μm.

5. The preparation method according to claim 1, characterized in that, The lubricant includes one or more of stearic acid, lauric acid, and fatty acids; the dispersant is polyacrylamide; and the binder is acrylic acid and polyvinyl alcohol.

6. The preparation method according to claim 1, characterized in that, The powder has a moisture content of 0.3-0.8% and a bulk density of 0.95-0.97 g / cm³. 3 .

7. The preparation method according to claim 1, characterized in that, The cold isostatic pressing is performed at a pressure of 120-160 MPa for 1-5 minutes, and the density of the green body is 2.0-2.1 g / cm³. 3 .

8. The preparation method according to claim 1, characterized in that, The degreasing temperature is 450~550 ℃, and the degreasing time is 5~8 h.

9. The preparation method according to claim 1, characterized in that, The sintering temperature is 1750~1780 ℃.

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