Preparation method for improving performance of silicon nitride granulation powder and sintered body

Abstract

The invention discloses a preparation method for improving the performance of silicon nitride granulation powder and a sintered body, and belongs to the technical field of ceramic products. According to the preparation method, a grain composition method of a silicon nitride raw material is adopted, in the process of preparing silicon nitride spray granulation slurry, silicon nitride powder with different grain sizes D50 of 500-700 nm and D50 of 200-300 nm is adopted for the grain composition method, the silicon nitride powder is mixed with a sintering aid, then ball-milled and dispersed by a ball mill, and spray granulation is performed after glue mixing. Coarse and fine particles cooperate to bring dense accumulation, so that the surface tension distribution of the liquid drops is more uniform, apple-shaped deformation caused by local tension unbalance is reduced, and the sphericity degree of the dried liquid drops is increased from 0.6 to 0.85 or above. The existence of the fine particles reduces the micro gaps in the granulation powder and on the surface of the granulation powder, the smoothness of the surface of the spherical granulation powder is improved, and the fluidity of the granulation powder is improved due to high sphericity and high smoothness.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic products, and particularly relates to a preparation method for improving the performance of silicon nitride granulation powder and sintered body. BACKGROUND

[0002] As a structural ceramic material, silicon nitride ceramic has excellent wear resistance, corrosion resistance, high temperature resistance and good thermal shock resistance, and is widely used in high-speed, high-precision and long-life bearings in the fields of machine tool spindles, electric spindles, automobile engines, aerospace engines and wind power generation. The green density of silicon nitride ceramic balls directly affects the performance indicators of the sintered body of ceramic balls, and the most important factor affecting the performance of the green body is the morphology, bulk density, flow rate and hardness of the silicon nitride spray granulation powder. Among them, the good flowability of the granulation powder in the filling mold process is very important, which is suitable for dry pressing industrial production, so it is necessary to improve the performance of the granulation powder to improve its flowability.

[0003] For the preparation of silicon nitride ceramic granulation powder, only a few related patent documents have been published in China. In the prior art, patent CN 113999019 A discloses a preparation method of silicon nitride ceramic granulation powder, which controls the mass ratio of PVA / PEG to make the shrinkage of liquid droplets during spray drying larger, and the accumulation of powder is more compact, forming a granulation powder similar to red blood cells, thereby obtaining a higher bulk density. Patent CN 102875153 A discloses a spray drying granulation method of silicon nitride ceramic powder for mechanical seals, which uses a silicon nitride micro-powder particle size preparation slurry, but the performance of the prepared granulation powder is not mentioned. The density of the sintered body of the small sample pressed in the example is 3.188, 3.226, 3.208 g / cm 3 It can be seen that the performance of the granulation powder needs to be improved. SUMMARY

[0004] The application adopts the particle grading method of silicon nitride raw material. In the process of preparing the silicon nitride spray granulation slurry, the silicon nitride powder with different particle sizes D50=500-700nm and D50=200-300nm is used for particle grading method, mixed with sintering aids, and then ball milled and dispersed by a ball mill, mixed with glue, and then spray granulated. In the spray granulation process, the coarse and fine particles cooperatively bring about dense packing, so that the liquid drop surface tension distribution is more uniform, the "apple-shaped" deformation caused by local tension imbalance is reduced, and the sphericity of the liquid drop after drying is improved to above 0.85 from 0.6. The existence of fine particles reduces the micro voids inside and on the surface of the granulation powder, increases the smoothness of the surface of the spherical granulation powder, and the high sphericity and high smoothness increase the flowability of the granulation powder. In the drying stage of spray granulation, the water will evaporate from the inside to the surface of the liquid drop, and the colloid (such as the binder PVB, PEG) in the slurry will migrate to the surface with the water due to the concentration gradient generated by the evaporation of water. The particle grading shortens the water evaporation path by optimizing the packing structure, reduces the colloid migration driving force, and at the same time, the small particles block the colloid migration channel. The colloid can form a continuous bonding layer between the coarse and fine particles, rather than concentrating on the surface, which significantly enhances the bonding force between the particles and improves the overall hardness of the granulation powder, so that the surface of the granulation powder is not too hard and the inside is not too soft, and the defects and cracks of the green body after pressing can be greatly reduced.

[0005] The high sphericity and high bulk density help to reduce the filling voids of the initial granulation powder, lay the foundation for the high density of the green body; the granulation powder with moderate hardness is not easy to be damaged during transportation and the green body to be cracked during pressing; the granulation powder with good flowability can significantly improve the production efficiency and reduce the comprehensive cost in industrial production. At the same time, the small particle size silicon nitride powder is uniformly distributed between the large particle size silicon nitride particles after ball milling, granulation and dry pressing, and the microstructure of the sintered body after hot pressing and sintering presents a microstructure of coarse and fine grains interlaced, which solves the defects of single coarse powder "coarse grains and low density" and makes up for the shortcomings of single fine powder "insufficient toughness and fragile grain boundary", and finally improves the fracture toughness and bending strength of silicon nitride ceramics.

[0006] A preparation method for improving the performance of silicon nitride granulation powder and sintered body, characterized by the following steps: S1, the dispersing agent, anhydrous ethanol and grinding medium balls are placed in a polyurethane drum ball mill tank, and ball milling is carried out for 0.5-2h to form a first liquid.

[0007] S2, the sintering aid is placed in the first liquid in the polyurethane drum ball mill tank, and ball milling is carried out for 0.5-2h to form a second liquid.

[0008] S3, the D50=500-700nm of silicon nitride raw powder, D50=200-300nm of silicon nitride raw powder is placed in the second liquid in the polyurethane drum ball mill tank, continue ball milling 12-24h hour, form the third liquid, the solid content of slurry is 40%-60%. The purity of silicon nitride powder is above 99.9%, and the adding ratio of the two particle sizes of silicon nitride powder is 7:3.

[0009] S4, the binder sol, plasticizer, defoaming agent is added to the third slurry, and the ball milling is continued for 12-24 hours to form the alcohol-based silicon nitride slurry.

[0010] S5, the mixed slurry is sprayed and dried by using a centrifugal spray granulation tower.

[0011] S6, the granulated powder is pressed into a shape, and the forming pressure is 100-250MPa.

[0012] S7, the green body is degreased by using a vacuum degreasing furnace.

[0013] S8, the green body after degreasing is sintered by using a hot-pressing sintering furnace.

[0014] Preferably, the dispersing agent in step S1 is a PVP series dispersing agent.

[0015] Preferably, the sintering aid in step S2 includes two or three or four or five of Al2O3, MgO, Y2O3, MgSiN2, YH3 and YF3, and the D50 of the sintering aid is 0.2-1 microns.

[0016] Preferably, the binder in step S4 is one or two of PEG, PVB and phenolic resin, and the concentration of the binder is 5%-30%; the plasticizer is DOP; and the defoaming agent is silicone.

[0017] Preferably, the viscosity of the alcohol-based silicon nitride slurry in step S4 is 400-800mPa·s.

[0018] Preferably, the hot air inlet temperature of the spray dryer in step S5 is 110-180℃, the outlet temperature is 60-100℃, the speed of the atomizer is 8000-15000r / min, the feeding speed is 0.5-2.5L / min, and the pressure of the spray granulation pump is 750-950MPa.

[0019] Preferably, the degreasing temperature in step S7 is 400-650℃ / min, the heating rate is 3-10℃ / min, and the holding time is 4-8h.

[0020] Preferably, the sintering atmosphere of step S8 is nitrogen atmosphere, the sintering temperature is 1700-1850℃, the holding time is 4-8h, the heating rate is 3-10℃ / min, and the nitrogen pressure is 100-200MPa. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the specific embodiments of the present application or the prior art, the drawings required to be used in the specific embodiments or the prior art description will be briefly introduced.

[0022] Figure 1 The process flow chart of the present application is shown in the following. DETAILED DESCRIPTION

[0023] The following examples are provided to better further understand the present application, and are not limited to the best mode, and do not limit the content and protection scope of the present application. Any person under the inspiration of the present application or the combination of the present application with other prior art features, any product same or similar to the present application, falls within the protection scope of the present application. Example 1

[0024] Take dispersant PVP 1.2g, 95g of anhydrous ethanol in polyurethane ball mill tank, medium ball is silicon nitride ceramic ball, as the ball mill on the dispersion ball mill 1h, the preparation of the first liquid (ball mill speed of 100-250r / min). Take 3g of alumina, 7g of yttrium oxide, add to the first liquid, continue to ball mill 1h, to prepare the second liquid (ball mill speed of 100-250r / min). Take D50=500-700nm silicon nitride powder 70g, D50=200-300nm silicon nitride powder 30g, add to the second liquid, continue to ball mill 16h, form the third liquid, (ball mill speed of 100-250r / min). Take a certain concentration of phenolic resin sol 10g, plasticizer DOP 1.2g, silicone antifoam agent 2.2g, add to the third liquid, continue to ball mill 12h (ball mill speed of 100-250r / min) to prepare the silicon nitride slurry, the viscosity of the slurry is 430mPa·s measured by viscosity meter, the mixed slurry is sprayed and granulated by centrifugal spray granulation tower, the hot air inlet temperature of the spray dryer is: 140℃, the outlet temperature is 80℃, the speed of the atomizer is 8000r / min, the feeding speed is 1.5L / min, the spray granulation pump pressure is 800MPa. After drying, the granulation powder with uniform particle size distribution is formed after screening. The powder is pressed into a green body using an automatic dry press, the molding pressure is 150MPa, and the silicon nitride ceramic ball green body sample with a diameter of 30mm is obtained by pressing. The green body is degreased using a vacuum degreasing furnace, the degreasing temperature is 600℃ / min, the heating rate is 5℃ / min, and the holding time is 2h. Finally, the degreased green body is sintered at 1700℃ using a hot-pressing sintering furnace to obtain the sample. Example 2

[0025] Take dispersant PVP 1.2g, 95g of anhydrous ethanol in polyurethane ball mill tank, medium ball is silicon nitride ceramic ball, as the ball mill on the dispersion ball mill 1h, the preparation of the first liquid (ball mill speed of 100-250r / min). Take 3g of alumina, 7g of yttrium oxide, add to the first liquid, continue to ball mill 1h, to prepare the second liquid (ball mill speed of 100-250r / min). Take D50=500-700nm silicon nitride powder 50g, D50=200-300nm silicon nitride powder 50g, add to the second liquid, continue to ball mill 16h, form the third liquid, (ball mill speed of 100-250r / min). Take a certain concentration of phenolic resin sol 10g, plasticizer DOP 1.2g, silicone antifoam agent 2.2g, add in the third liquid, continue to ball mill 12h (ball mill speed of 100-250r / min) to prepare the silicon nitride slurry, the viscosity of the slurry is 500mPa·s measured by viscosity meter, the mixed slurry is sprayed and granulated by centrifugal spray granulation tower, the hot air inlet temperature of the spray dryer is: 140℃, the outlet temperature is 80℃, the speed of the atomizer is 8000r / min, the feeding speed is 1.5L / min, the spray granulation pump pressure is 800MPa. After drying, the granulation powder with uniform particle size distribution is formed after screening. The powder is pressed into a green body using an automatic dry press, the molding pressure is 150MPa, and the silicon nitride ceramic ball green body sample with a diameter of 30mm is obtained by pressing. The green body is degreased using a vacuum degreasing furnace, the degreasing temperature is 600℃ / min, the heating rate is 5℃ / min, and the holding time is 2h. Finally, the degreased green body is sintered at 1700℃ using a hot-pressing sintering furnace to obtain the sample.

[0026] Comparative example 3: Take dispersant PVP 1.2g, 95g of anhydrous ethanol in polyurethane ball mill tank, medium ball is silicon nitride ceramic ball, to the ball mill on the dispersion ball mill 1h, the preparation of the first liquid (ball mill speed is 100-250r / min). Take 3g of alumina, 7g of yttrium oxide, add to the first liquid, continue to ball mill 1h, to prepare the second liquid (ball mill speed is 100-250r / min). Take D50=500-700nm silicon nitride powder 100g, add to the second liquid, continue to ball mill 16h, form the third liquid, (ball mill speed is 100-250r / min). Take a certain concentration of phenolic resin sol 10g, take a certain concentration of phenolic resin sol 10g, plasticizer DOP 1.2g, silicone antifoam agent 2.2g, add in the third liquid, continue to ball mill 12h (ball mill speed is 100-250r / min) to prepare silicon nitride slurry, the viscosity of the slurry is 310mPa·s measured by viscometer, the mixed slurry is sprayed and granulated by using centrifugal spray granulation tower, the hot air inlet temperature of the spray dryer is: 140℃, the outlet temperature is 80℃, the speed of the atomizer is 8000r / min, the feeding speed is 1.5L / min, the spray granulation pump pressure is 800MPa. After drying, the granulation powder with uniform particle size distribution is formed after screening. The powder is pressed into a green body by using an automatic dry press, the molding pressure is 150MPa, and the silicon nitride ceramic ball green body sample with a diameter of 30mm is obtained by pressing. The green body is degreased by using a vacuum degreasing furnace, the degreasing temperature is 600℃ / min, the heating rate is 5℃ / min, and the holding time is 2h. Finally, the degreased green body is sintered at 1700℃ by using a hot-pressing sintering furnace to obtain a sample.

[0027] Comparative example 4: Take dispersant PVP 1.2g, 95g anhydrous ethanol in polyurethane ball mill tank, medium ball is silicon nitride ceramic ball, to the ball mill on the dispersion ball mill 1h, the first liquid is prepared (ball mill speed is 100-250r / min). Take 3g of alumina, 7g of yttrium oxide, add to the first liquid, continue to ball mill 1h, prepare the second liquid (ball mill speed is 100-250r / min). 100g of D50=200-300nm silicon nitride powder is added to the second liquid, and the third liquid is formed by continuing to ball mill for 16h (ball mill speed is 100-250r / min). A certain concentration of phenolic resin sol 10g, plasticizer DOP 1.2g, silicone antifoam agent 2.2g are added into the third liquid, and the silicon nitride slurry is prepared by continuing to ball mill for 12h (ball mill speed is 100-250r / min). The viscosity of the slurry is measured by a viscometer to be 580mPa·s. The mixed slurry is sprayed and granulated by a centrifugal spray granulation tower. The hot air inlet temperature of the spray dryer is 140℃, the outlet temperature is 80℃, the speed of the atomizer is 8000r / min, the feeding speed is 1.5L / min, and the pressure of the spray granulation pump is 800MPa. After drying, the granulated powder with uniform particle size distribution is formed. The powder is pressed and formed by an automatic dry press, and the formed pressure is 150MPa. The silicon nitride ceramic ball green body sample with a diameter of 30mm is obtained by pressing. The green body is degreased by a vacuum degreasing furnace, the degreasing temperature is 600℃ / min, the heating rate is 5℃ / min, and the holding time is 2h. Finally, the degreased green body is sintered at 1700℃ by a hot-pressing sintering furnace to obtain the sample.

[0028] Table 1 Performance parameters of silicon nitride granulated powder and sintered body in implementation and comparison examples Examples Sphericity Loose bulk density g / cm 3 ]]> Flow rate 30 g / s Green density g / cm 3 ]] Residual intact granulation powder at 50 MPa pressure Sintered body density g / cm 3 ]]> Fracture toughness MPa / m 1 / 2 ]]> Bending strength MPa Example 1 0.87 0.9456 18.32 1.93 No 3.265 6.87 950 Example 2 0.71 0.9013 20.1 1.9 No 2.243 6.56 900 Comparative Example 3 0.60 0.8212 23.12 1.82 Yes 3.182 6.31 812 Comparative Example 4 0.68 0.8325 22.34 1.84 Yes 3.204 6.35 820 As shown in Table 1, in the preparation of silicon nitride spray granulation slurry, when the addition ratio of D50=500-700nm and D50=200-300nm silicon nitride powder is 7:3, the sphericity of the prepared granulated powder is best, and the apparent density and flow rate are correspondingly improved. In order to compare the softness and hardness of the granulated powder, the green body samples are pressed at 50MPa, and the cross-sectional morphology of the green body is tested. It is found that the slurry prepared by particle grading and the granulated powder prepared by spray granulation have moderate softness and hardness. The green body density increases to 1.93g / cm 3 after pressing at 150MPa. The density of the sintered sample after sintering reaches 3.265g / cm 3 .

Claims

1. A preparation method for improving the performance of silicon nitride granulated powder and sintered body, characterized in that the steps are as follows: S1. Put dispersant, anhydrous ethanol and grinding medium balls into a polyurethane drum ball mill tank, ball mill for 0.5-2 h to form a first liquid; S2. Put sintering aids into the first liquid in the polyurethane drum ball mill tank, ball mill for 0.5-2 h to form a second liquid; S3. Put D50=500-700 nm silicon nitride raw powder and D50=200-300 nm silicon nitride raw powder into the second liquid in the polyurethane drum ball mill tank, continue to ball mill for 12-24 h to form a third liquid, and the solid content of the slurry is 40%-60%. The purity of the silicon nitride powder is above 99.9%, and the adding ratio of the two kinds of silicon nitride powder is (5-8):(2-4); S4. Add a binder sol, a plasticizer and a defoaming agent to the third slurry, continue to ball mill for 12-24 h to form an alcohol-based silicon nitride slurry; S5. Use a centrifugal spray granulation tower to spray dry the mixed slurry; S6. Press the granulated powder to form a shape, and the forming pressure is 100-250 MPa; S7. Use a vacuum glue removal furnace to remove glue from the green body; and S8. Use a hot-pressing sintering furnace to sinter the glue-removed green body. The dispersant in step S1 is a PVP series dispersant. The sintering aids in step S2 include two or three or four or five of Al2O3, MgO, Y2O3, MgSiN2, YH3 and YF3, and the D50 of the sintering aids is 0.2-1 micron. The binder in step S4 is one or two of PEG, PVB and phenolic resin, the concentration of the binder is 5%-30%, the plasticizer is DOP, and the defoaming agent is an organic silicon type. The viscosity of the alcohol-based silicon nitride slurry in step S4 is 400-800 mPa·s. The hot air inlet temperature of the spray dryer in step S5 is 110-180℃, the outlet temperature is 60-100℃, the speed of the atomizer is 8000-15000 r / min, the feeding speed is 0.5-2.5 L / min, and the pressure of the spray granulation pump is 750-950 MPa. The glue removal temperature in step S7 is 400-650℃ / min, the heating rate is 3-10℃ / min, and the holding time is 4-8 h. The sintering atmosphere in step S8 is a nitrogen atmosphere, the sintering temperature is 1700-1850℃, the holding time is 4-8 h, the heating rate is 3-10℃ / min, and the nitrogen pressure is 100-200 MPa. ​ 2. The method according to claim 1, wherein the method for improving the properties of the silicon nitride granulated powder and sintered body is characterized by: ​ 3. The method according to claim 1, wherein the method is characterized by: ​ 4. The method according to claim 1, wherein the method for improving the properties of the silicon nitride granulated powder and sintered body is characterized by: ​ 5. The method according to claim 1, wherein the method is characterized by: ​ 6. The method according to claim 1, wherein the method for improving the properties of the silicon nitride granulated powder and sintered body is characterized by. ​ 7. The method according to claim 1, wherein the method is characterized by: ​ ​ 8. The method according to claim 1, wherein the method is characterized by: ​ ​

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