Silicon nitride ceramic ball and preparation method thereof

Abstract

The invention relates to the technical field of ceramic materials, in particular to a silicon nitride ceramic ball and a preparation method thereof. The preparation method comprises the following steps: S1, adding silicon powder and a nitrate solution into a ball mill, carrying out ball milling, taking out, and drying to obtain raw powder; s2, uniformly mixing the raw powder with a binder, a plasticizer and a solvent, and carrying out ball milling to obtain slurry; s3, performing spray granulation on the slurry to obtain coarse powder, fine powder and micro powder; sequentially filling a mold with the coarse powder, the fine powder and the micro powder, and performing isostatic pressing to obtain a green body; and S4, carrying out primary grinding pre-rounding and primary sintering on the green body, cooling to room temperature, then carrying out secondary grinding pre-rounding and secondary sintering, and carrying out rough grinding, accurate grinding and polishing to obtain the silicon nitride ceramic ball. The silicon nitride ceramic ball prepared by the invention has relatively high sphericity degree, excellent mechanical property and compactness.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and specifically to a silicon nitride ceramic ball and a preparation method thereof. Background Art

[0002] Silicon nitride ceramics are a kind of high-performance ceramic materials. Due to their advantages such as high hardness, good wear resistance, and strong oxidation resistance, they are widely used in fields such as machinery, electronics, and aerospace. The preparation of silicon nitride ceramic balls is an important link in the preparation of silicon nitride ceramics, and indexes such as sphericity and density uniformity directly affect the performance of silicon nitride ceramics.

[0003] Currently, the commercial production methods of silicon nitride powder mainly include direct nitridation of silicon powder, self-propagating high-temperature synthesis method, and thermal decomposition method, etc. These methods either have high preparation costs or have deficiencies in aspects such as phase composition and sintering activity of the powder. Moreover, due to the high price of silicon nitride raw powder, long processing cycle, and great difficulty, the application of silicon nitride balls is restricted. Therefore, how to prepare silicon nitride ceramic balls with high sphericity and uniform density at low cost has become an important problem faced by current technologies.

[0004] Therefore, we propose a silicon nitride ceramic ball and a preparation method thereof. Summary of the Invention

[0005] The purpose of the present invention is to provide a silicon nitride ceramic ball and a preparation method thereof to solve the problems raised in the prior art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions: A preparation method of a silicon nitride ceramic ball, comprising the following steps: Step S1: Add silicon powder and nitrate solution into a ball mill, carry out ball milling, take out, and after drying, obtain the raw powder; Step S2: Mix the raw powder, binder, plasticizer, and solvent evenly, carry out ball milling, and obtain the slurry; Step S3: Carry out spray granulation on the slurry to obtain coarse powder, fine powder, and micro powder; Fill the coarse powder, fine powder, and micro powder into a mold in sequence, and carry out isostatic pressing to form a green body; Step S4: Carry out primary grinding and pre-rounding, primary sintering on the green body, cool to room temperature, then carry out secondary grinding and pre-rounding, secondary sintering, and after rough grinding, fine grinding, and polishing, obtain the silicon nitride ceramic ball.

[0007] Further, in the step S1, the nitrate in the nitrate solution is one or more of magnesium nitrate, yttrium nitrate, and barium nitrate.

[0008] Further, in the step S1, the molar ratio of silicon powder to nitrate is 1:0.02 - 0.2.

[0009] Further, in the step S1, the process conditions for ball milling are as follows: the protective atmosphere is nitrogen, the ball-to-material ratio is 2 - 5:1, the ball milling time is 1 - 10 h, and the ball milling speed is 500 - 700 r / min.

[0010] Further, in the step S1, the process conditions for drying are as follows: the drying temperature is 75 - 85 °C, and the drying time is 4 - 6 h.

[0011] Further, in the step S2, the slurry is composed of the following components in parts by weight: 90 - 100 parts of raw powder, 1 - 10 parts of binder, 1 - 10 parts of plasticizer, and 50 - 80 parts of solvent.

[0012] Further, in the step S2, the process conditions for ball milling are as follows: the ball-to-material ratio is 2 - 5:1, the ball milling time is 5 - 48 h, and the ball milling speed is 200 - 1000 r / min.

[0013] Further, the binder is polyvinyl alcohol or polyvinyl butyral.

[0014] Further, the plasticizer is dibutyl phthalate or butyl benzyl phthalate.

[0015] Further, the solvent is one of ethanol, n-butanol, and ethyl acetate.

[0016] Further, the slurry further includes 5 - 15 parts of bentonite composite, and the specific preparation process is as follows: Step (1): Mix sodium-based bentonite, cyclohexane, and ethanol evenly, dropwise add acrylic acid, and finish dropping in 1 - 2 h. React at 70 - 80 °C for 3 - 5 h. After filtration, washing, and drying, obtain acidified sodium-based bentonite; Step (2): Mix the acidified sodium-based bentonite and lanthanum chloride solution evenly, then add aluminum chloride hexahydrate, and react for 1 - 3 h. After filtration, washing, and drying, obtain modified bentonite; Step (3): Mix the modified bentonite and deionized water evenly, add double bond-containing β-cyclodextrin, methacrylic acid, 2-hydroxyethyl acrylate, vinyltriethoxysilane, and ammonium persulfate, and react at 70 - 80 °C for 6 - 8 h. After filtration, washing, and drying, obtain bentonite composite.

[0017] Further, in the step (1), the mass ratio of sodium-based bentonite, cyclohexane, ethanol, and acrylic acid is 1:(5 - 10):(2 - 4):(0.5 - 0.8).

[0018] Further, in the step (2), the mass ratio of the acidified sodium-based bentonite and lanthanum chloride solution is 1:(20 - 25).

[0019] Further, the concentration of the lanthanum chloride solution is 0.2 mol / L.

[0020] Further, the mass of the aluminum chloride hexahydrate is 0.3 - 0.5 times the mass of the acidified sodium-based bentonite.

[0021] Further, in the step (3), the bentonite composite is composed of the following components in parts by weight: 5 - 15 parts of modified bentonite, 8 - 12 parts of double-bonded β-cyclodextrin, 3 - 6 parts of methacrylic acid, 5 - 10 parts of 2-hydroxyethyl acrylate, 2 - 4 parts of vinyltriethoxysilane, 1 - 5 parts of ammonium persulfate, and 80 - 100 parts of deionized water.

[0022] Further, the preparation method of the double-bonded β-cyclodextrin is as follows: Mix β-cyclodextrin, N-hydroxymethylacrylamide, and dilute hydrochloric acid evenly, react at 70 - 80 °C for 15 - 30 min, and obtain double-bonded β-cyclodextrin after precipitation, filtration, washing, and drying.

[0023] Further, the mass ratio of the β-cyclodextrin, N-hydroxymethylacrylamide, and dilute hydrochloric acid is 1:(1.0 - 1.2):(2 - 3).

[0024] Further, the concentration of the dilute hydrochloric acid is 1 - 3 wt%.

[0025] Further, the particle size of the coarse powder is 80 μm < coarse powder < 150 μm, the particle size of the fine powder is 40 μm < fine powder ≤ 80 μm, and the particle size of the micropowder is 0.1 μm < micropowder ≤ 40 μm.

[0026] Further, the mass ratio of the coarse powder, fine powder, and micropowder is 1:(0.1 - 0.5):(0.1 - 0.3).

[0027] Further, the process conditions for isostatic pressing are: the pressure is 100 - 200 Mpa, and the pressure holding time is 5 - 60 min.

[0028] Further, the process conditions for the first grinding and pre-rounding are: use a ball grinding machine for pre-rounding, wrap the grinding disc with polishing flannel, and the grinding time is 5 - 30 min.

[0029] Further, the process conditions for the first sintering are: the sintering temperature is 1200 - 1400 °C, and the heat preservation time is 1 - 3 h.

[0030] Further, the process conditions for the second grinding and pre-rounding are: use a cast iron grinding disc with a hardness of HB 210 - 280, and the grinding time is 5 - 30 min.

[0031] Further, the process conditions for the secondary sintering are as follows: the sintering temperature is 1600 - 1950 °C, and the heat preservation time is 2 - 10 h.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. For the silicon nitride ceramic ball and its preparation method of the present invention, by in-situ loading a sintering aid on silicon powder, it can promote the nitridation of silicon powder during the sintering process, reducing the non-uniformity and deformation of the ceramic green ball after sintering caused by uneven powder mixing; In the prior art, the granulated microspheres have a single size, a low tapped density, and large pores in the green balls pressed. In this technical solution, granulated microspheres of different sizes, namely coarse powder, fine powder, and micro powder, are prepared by spray granulation; the coarse powder, fine powder, and micro powder are mixed and filled in a certain proportion, which can improve the green density and reduce the pores in the silicon nitride green balls during the forming stage; In the prior art, the processing of silicon nitride ceramic balls is difficult, which not only increases the production cost but also affects the production efficiency. In this technical solution, the silicon nitride ceramic balls are subjected to secondary grinding and pre-rounding treatment, and the silicon nitride green balls and α-Si 3 N 4 ceramic balls with relatively low hardness are pre-round ground to correct the sphericity, reducing the subsequent processing difficulty, shortening the processing time, and improving the production efficiency; The processing of the present invention is less difficult, suitable for large-scale production, conducive to reducing the production cost, and having good economic benefits.

[0033] 2. For the silicon nitride ceramic ball and its preparation method of the present invention, taking advantage of the characteristics that acrylic acid monomer has strong acidity and also has a carbon-carbon double bond, it can quickly undergo a neutralization reaction with a large number of active hydroxyl groups between the layers of sodium-based bentonite, grafting the reactive functional group C = C onto the bentonite lamellae through chemical bonds, increasing the layer spacing between the bentonite lamellae and further improving the exfoliation degree to obtain acidified sodium-based bentonite; then, lanthanum and aluminum ions are intercalated into the bentonite by impregnation method for composite modification to obtain modified bentonite; among them, aluminum ions have the effect of promoting the sintering of silicon nitride, helping to improve the sintering rate and densification of silicon nitride ceramics, and lanthanum ions, as rare earth elements, can significantly refine the grains of silicon nitride, thereby improving the toughness and strength of the material. The synergistic effect of these two elements effectively improves the comprehensive performance of silicon nitride ceramics; Using N-methylolacrylamide as a coupling agent, the double bond is grafted onto β-cyclodextrin to obtain β-cyclodextrin containing a double bond; using modified bentonite, β-cyclodextrin containing a double bond, methacrylic acid, 2-hydroxyethyl acrylate, vinyltriethoxysilane as raw materials, and ammonium persulfate as an initiator, through a polymerization reaction, a bentonite composite is obtained, which can be used as a sintering aid to promote the sintering process of silicon nitride, improve the sintering efficiency, and contribute to improving the density, mechanical properties, and thermal stability of silicon nitride ceramics. Detailed implementation mode

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] In this embodiment, the silicon powder has a particle size of 1 - 20 μm and is sourced from Sichuan Evender New Materials Co., Ltd.; magnesium nitrate has a particle size of 1 - 5 μm; yttrium nitrate has a particle size of 1 - 5 μm; the plasticizer is dibutyl phthalate; the binder is polyvinyl butyral with the brand name Kuraray B75H; the sodium-based bentonite has a particle size of 20 μm and is sourced from Shandong Yousuo Chemical Technology Co., Ltd.

[0036] In the following examples and comparative examples, 1 part is equal to 10 g.

[0037] Example 1: A preparation method of silicon nitride ceramic balls, comprising the following processes: Step S1: Using magnesium nitrate and yttrium nitrate as nitrates, 100 parts of silicon powder, 53 mL of magnesium nitrate solution, and 136 mL of yttrium nitrate solution are added to a ball mill for ball milling (the protective atmosphere is nitrogen, the ball-to-material ratio is 2:1, the ball milling time is 10 h, and the ball milling speed is 600 r / min). After taking out and drying (the drying temperature is 80 °C and the drying time is 5 h), the raw powder is obtained; the molar ratio of silicon powder to nitrate is 1:0.1; Step S2: 100 parts of the raw powder, 2 parts of the binder, 2 parts of the plasticizer, and 70 parts of ethanol are mixed evenly and ball milled (the ball-to-material ratio is 2:1, the ball milling time is 20 h, and the ball milling speed is 500 r / min) to obtain a slurry; Step S3: The slurry is spray granulated to obtain coarse powder, fine powder, and micro powder; the coarse powder, fine powder, and micro powder are filled into a mold in a mass ratio of 1:0.3:0.1 in sequence and isostatically pressed (the pressure is 200 Mpa and the pressure holding time is 15 min) to obtain a green body; Step S4: The green body is first polished and pre-rounded using a ball grinding machine, the grinding disc is wrapped with polishing flannel, the grinding time is 30 min, and it is put into a high-temperature furnace for the first sintering (the sintering temperature is 1400 °C and the heat preservation time is 2 h). After cooling to room temperature, it is polished and pre-rounded for the second time (the grinding disc is a cast iron grinding disc with a hardness of HB 280 and the grinding time is 15 min), and the second sintering (the sintering temperature is 1800 °C and the heat preservation time is 2 h) is carried out. After rough grinding, fine grinding, and polishing, silicon nitride ceramic balls are obtained.

[0038] Example 2: A preparation method of silicon nitride ceramic balls, comprising the following processes: Step S1: Using magnesium nitrate and yttrium nitrate as nitrates, add 100 parts of silicon powder, 106 mL of magnesium nitrate solution, and 136 mL of yttrium nitrate solution into a ball mill, and carry out ball milling (the protective atmosphere is nitrogen, the ball-to-material ratio is 3:1, the ball milling time is 1 h, and the ball milling speed is 600 r / min). Take out the mixture, dry it (the drying temperature is 80 °C and the drying time is 5 h) to obtain the raw powder; the molar ratio of silicon powder to nitrate is 1:0.2; Step S2: Mix 100 parts of the raw powder, 5 parts of binder, 5 parts of plasticizer, and 70 parts of ethanol evenly, and carry out ball milling (the ball-to-material ratio is 3:1, the ball milling time is 20 h, and the ball milling speed is 500 r / min) to obtain the slurry; Step S3: Carry out spray granulation on the slurry to obtain coarse powder, fine powder, and micropowder; fill the coarse powder, fine powder, and micropowder into the mold in sequence according to the mass ratio of 1:0.2:0.2, and carry out isostatic pressing (the pressure is 150 Mpa and the pressure holding time is 30 min) to obtain the green body; Step S4: Carry out primary grinding and pre-rounding on the green body using a grinding ball machine. The grinding disc is wrapped with polishing flannelette, and the grinding time is 30 min. Then put it into a high-temperature furnace for primary sintering (the sintering temperature is 1400 °C and the heat preservation time is 2 h), cool it to room temperature, and then carry out secondary grinding and pre-rounding (the grinding disc is a cast iron grinding disc with a hardness of HB 220, and the grinding time is 20 min), secondary sintering (the sintering temperature is 1800 °C and the heat preservation time is 2 h). After rough grinding, fine grinding, and polishing, the silicon nitride ceramic ball is obtained.

[0039] Example 3: A preparation method of a silicon nitride ceramic ball, including the following processes: Step S1: Using magnesium nitrate and yttrium nitrate as nitrates, add 90 parts of silicon powder, 53 mL of magnesium nitrate solution, and 136 mL of yttrium nitrate solution into a ball mill, and carry out ball milling (the protective atmosphere is nitrogen, the ball-to-material ratio is 3:1, the ball milling time is 2 h, and the ball milling speed is 700 r / min). Take out the mixture, dry it (the drying temperature is 75 °C and the drying time is 4 h) to obtain the raw powder; the molar ratio of silicon powder to nitrate is 1:0.02; Step S2: Mix 90 parts of the raw powder, 1 part of binder, 1 part of plasticizer, and 50 parts of ethanol evenly, and carry out ball milling (the ball-to-material ratio is 3:1, the ball milling time is 5 h, and the ball milling speed is 1000 r / min) to obtain the slurry; Step S3: Carry out spray granulation on the slurry to obtain coarse powder, fine powder, and micropowder; fill the coarse powder, fine powder, and micropowder into the mold in sequence according to the mass ratio of 1:0.1:0.1, and carry out isostatic pressing (the pressure is 100 Mpa and the pressure holding time is 60 min) to obtain the green body; Step S4: The green body is pre-rounded by grinding with a ball grinding machine. The grinding disc is wrapped with polishing flannel, and the grinding time is 5 minutes. Then it is put into a high-temperature furnace for the first sintering (the sintering temperature is 1200 °C and the heat preservation time is 3 hours), cooled to room temperature, and then subjected to secondary pre-rounding by grinding (the grinding disc is a cast iron grinding disc with a hardness of HB 210 and the grinding time is 30 minutes), and secondary sintering (the sintering temperature is 1600 °C and the heat preservation time is 10 hours). After rough grinding, fine grinding and polishing, silicon nitride ceramic balls are obtained; The slurry also includes 5 parts of bentonite composite, and the specific preparation process is as follows: Step (1): Mix 5 parts of sodium-based bentonite, 25 parts of cyclohexane and 10 parts of ethanol evenly, dropwise add 2.5 parts of acrylic acid, finish dropping in 1 hour, react at 70 °C for 3 hours, and after filtration, washing and drying, obtain acidified sodium-based bentonite; Step (2): Mix 5 parts of acidified sodium-based bentonite and 100 parts of 0.2 mol / L lanthanum chloride solution evenly, then add 1.5 parts of aluminum chloride hexahydrate, react for 1 hour, and after filtration, washing and drying, obtain modified bentonite; Step (3): Mix 8 parts of β-cyclodextrin, 8 parts of N-hydroxymethylacrylamide and 16 parts of 1 wt% dilute hydrochloric acid evenly, react at 70 °C for 15 minutes, and after precipitation, filtration, washing and drying, obtain β-cyclodextrin containing double bonds; Mix 5 parts of modified bentonite and 80 parts of deionized water evenly, add 8 parts of β-cyclodextrin containing double bonds, 3 parts of methacrylic acid, 5 parts of 2-hydroxyethyl acrylate, 2 parts of vinyltriethoxysilane and 1 part of ammonium persulfate, react at 70 °C for 6 hours, and after filtration, washing and drying, obtain bentonite composite.

[0040] Example 4: A preparation method of silicon nitride ceramic balls, including the following processes: Step S1: Using magnesium nitrate and yttrium nitrate as nitrates, add 95 parts of silicon powder, 53 mL of magnesium nitrate solution and 136 mL of yttrium nitrate solution into a ball mill for ball milling (the protective atmosphere is nitrogen, the ball-to-material ratio is 4:1, the ball milling time is 3 hours, and the ball milling speed is 550 r / min). Take out and dry (the drying temperature is 80 °C and the drying time is 5 hours) to obtain the original powder; the molar ratio of silicon powder to nitrate is 1:0.08; Step S2: Mix 95 parts of the original powder, 5 parts of binder, 5 parts of plasticizer and 60 parts of ethanol evenly, and carry out ball milling (the ball-to-material ratio is 4:1, the ball milling time is 24 hours, and the ball milling speed is 600 r / min) to obtain a slurry; Step S3: Spray granulate the slurry to obtain coarse powder, fine powder and micro powder; fill the coarse powder, fine powder and micro powder into the mold in sequence according to the mass ratio of 1:0.3:0.2, and perform isostatic pressing (the pressure is 180 Mpa and the pressure holding time is 40 minutes) to obtain a green body; Step S4: The green body is pre-rounded by grinding with a ball grinding machine. The grinding disc is wrapped with polishing flannel. The grinding time is 10 min. Then it is put into a high-temperature furnace for the first sintering (the sintering temperature is 1300 °C and the heat preservation time is 2 h), cooled to room temperature, and then subjected to secondary pre-rounding by grinding (the grinding disc is a cast iron grinding disc with a hardness of HB 250 and the grinding time is 10 min), and secondary sintering (the sintering temperature is 1850 °C and the heat preservation time is 8 h) to obtain silicon nitride ceramic balls; The slurry also includes 10 parts of bentonite complex, and the specific preparation process is as follows: Step (1): 10 parts of sodium-based bentonite, 80 parts of cyclohexane and 30 parts of ethanol are mixed evenly, 7 parts of acrylic acid are added dropwise, and the dropping is completed in 1.5 h. The reaction is carried out at 75 °C for 4 h. After filtration, washing and drying, acidified sodium-based bentonite is obtained; Step (2): 10 parts of acidified sodium-based bentonite and 220 parts of 0.2 mol / L lanthanum chloride solution are mixed evenly, and then 4 parts of aluminum chloride hexahydrate are added. The reaction is carried out for 2 h. After filtration, washing and drying, modified bentonite is obtained; Step (3): 10 parts of β-cyclodextrin, 11 parts of N-hydroxymethylacrylamide and 30 parts of 2 wt% dilute hydrochloric acid are mixed evenly. The reaction is carried out at 75 °C for 20 min. After precipitation, filtration, washing and drying, double-bond-containing β-cyclodextrin is obtained; 10 parts of modified bentonite and 90 parts of deionized water are mixed evenly, and 10 parts of double-bond-containing β-cyclodextrin, 5 parts of methacrylic acid, 8 parts of 2-hydroxyethyl acrylate, 3 parts of vinyltriethoxysilane and 3 parts of ammonium persulfate are added. The reaction is carried out at 75 °C for 7 h. After filtration, washing and drying, bentonite complex is obtained.

[0041] Example 5: A preparation method of silicon nitride ceramic balls, including the following processes: Step S1: Using magnesium nitrate and yttrium nitrate as nitrates, 100 parts of silicon powder, 106 mL of magnesium nitrate solution and 136 mL of yttrium nitrate solution are added to a ball mill for ball milling (the protective atmosphere is nitrogen, the ball-to-material ratio is 5:1, the ball milling time is 1 h, and the ball milling speed is 700 r / min). After taking out and drying (the drying temperature is 85 °C and the drying time is 4 h), raw powder is obtained; the molar ratio of silicon powder to nitrate is 1:0.15; Step S2: 100 parts of raw powder, 10 parts of binder, 10 parts of plasticizer and 80 parts of ethanol are mixed evenly and subjected to ball milling (the ball-to-material ratio is 5:1, the ball milling time is 48 h, and the ball milling speed is 200 r / min) to obtain a slurry; Step S3: The slurry is spray granulated to obtain coarse powder, fine powder and micro powder; the coarse powder, fine powder and micro powder are sequentially filled into a mold and isostatically pressed (the pressure is 200 Mpa and the pressure holding time is 5 min) to obtain a green body; Step S4: The green body is polished and pre-rounded once by a ball grinding machine. The grinding disc is wrapped with polishing flannel, and the grinding time is 30 minutes. Then it is put into a high-temperature furnace for the first sintering (sintering temperature: 1400 °C, heat preservation time: 1 hour), cooled to room temperature, and then polished and pre-rounded for the second time (the grinding disc is a cast iron grinding disc with a hardness of HB 280, and the grinding time is 5 minutes), and the second sintering (sintering temperature: 1950 °C, heat preservation time: 2 hours) is carried out to obtain silicon nitride ceramic balls; The slurry also includes 15 parts of bentonite composite, and the specific preparation process is as follows: Step (1): Mix 15 parts of sodium-based bentonite, 150 parts of cyclohexane and 60 parts of ethanol evenly, dropwise add 12 parts of acrylic acid, finish dropping in 2 hours, react at 80 °C for 5 hours, and after filtration, washing and drying, obtain acidified sodium-based bentonite; Step (2): Mix 15 parts of acidified sodium-based bentonite and 375 parts of 0.2 mol / L lanthanum chloride solution evenly, then add 7.5 parts of aluminum chloride hexahydrate, react for 3 hours, and after filtration, washing and drying, obtain modified bentonite; Step (3): Mix 12 parts of β-cyclodextrin, 14.4 parts of N-hydroxymethyl acrylamide and 36 parts of 3 wt% dilute hydrochloric acid evenly, react at 80 °C for 30 minutes, and after precipitation, filtration, washing and drying, obtain double bond-containing β-cyclodextrin; Mix 15 parts of modified bentonite and 100 parts of deionized water evenly, add 12 parts of double bond-containing β-cyclodextrin, 6 parts of methacrylic acid, 10 parts of 2-hydroxyethyl acrylate, 4 parts of vinyltriethoxysilane and 5 parts of ammonium persulfate, react at 80 °C for 8 hours, and after filtration, washing and drying, obtain bentonite composite.

[0042] Comparative Example 1: A preparation method of silicon nitride ceramic balls, including the following process: Step S1: Using magnesium nitrate and yttrium nitrate as nitrates, add 100 parts of silicon powder, 106 mL of magnesium nitrate solution and 136 mL of yttrium nitrate solution into a ball mill for ball milling (the protective atmosphere is nitrogen, the ball-to-material ratio is 3:1, the ball milling time is 1 hour, and the ball milling speed is 600 r / min), take out, and after drying (drying temperature: 80 °C, drying time: 5 hours), obtain the raw powder; the molar ratio of silicon powder to nitrate is 1:0.2; Step S2: Mix 100 parts of the raw powder, 5 parts of binder, 5 parts of plasticizer and 70 parts of ethanol evenly, and carry out ball milling (ball-to-material ratio 3:1, ball milling time 20 hours, ball milling speed 500 r / min) to obtain slurry; Step S3: Spray granulate the slurry to obtain coarse powder; fill the coarse powder into a mold and isostatically press it (pressure: 150 Mpa, pressure holding time: 30 minutes) to obtain a green body; Step S4: The green body is pre-rounded by grinding once with a ball grinding machine. The grinding disc is wrapped with polishing flannel. The grinding time is 30 min. Then it is put into a high-temperature furnace for the first sintering (sintering temperature is 1400 °C, heat preservation time is 2 h), cooled to room temperature, and then pre-rounded by grinding for the second time (the grinding disc is a cast iron grinding disc with a hardness of HB 220, and the grinding time is 20 min), and the second sintering (sintering temperature is 1800 °C, heat preservation time is 2 h). After rough grinding, fine grinding, and polishing, silicon nitride ceramic balls are obtained; Compared with Example 2, in Step S3 of Comparative Example 1, the particle sizes obtained by spray granulation are all coarse powders, and other steps are the same as those in Example 2.

[0043] Comparative Example 2: A preparation method of silicon nitride ceramic balls includes the following processes: Step S1: Using magnesium nitrate and yttrium nitrate as nitrates, 100 parts of silicon powder, 106 mL of magnesium nitrate solution, and 136 mL of yttrium nitrate solution are added to a ball mill for ball milling (the protective atmosphere is nitrogen, the ball-to-material ratio is 3:1, the ball milling time is 1 h, and the ball milling speed is 600 r / min). After taking out and drying (drying temperature is 80 °C, drying time is 5 h), the raw powder is obtained; the molar ratio of silicon powder to nitrate is 1:0.2; Step S2: 100 parts of the raw powder, 5 parts of binder, 5 parts of plasticizer, and 70 parts of ethanol are mixed evenly and ball milled (ball-to-material ratio 3:1, ball milling time 20 h, ball milling speed 500 r / min) to obtain a slurry; Step S3: The slurry is spray granulated to obtain coarse powder, fine powder, and micro powder; the coarse powder, fine powder, and micro powder are filled into a mold in a mass ratio of 1:0.2:0.2 in sequence, and isostatically pressed (pressure is 150 Mpa, pressure holding time is 30 min) to obtain a green body; Step S4: The green body is pre-rounded by grinding once with a ball grinding machine. The grinding disc is wrapped with polishing flannel. The grinding time is 30 min. Then it is put into a high-temperature furnace for the first sintering (sintering temperature is 1400 °C, heat preservation time is 2 h), cooled to room temperature, and then the second sintering (sintering temperature is 1800 °C, heat preservation time is 2 h). After rough grinding, fine grinding, and polishing, silicon nitride ceramic balls are obtained; Compared with Example 2, Comparative Example 2 does not include the step of pre-rounding by grinding for the second time, and other steps are the same as those in Example 2.

[0044] Comparative Example 3: A preparation method of silicon nitride ceramic balls includes the following processes: Compared with Example 4, in Comparative Example 3, the bentonite complex is replaced with sodium-based bentonite of the same mass, and other steps are the same as those in Example 4.

[0045] Comparative Example 4: A preparation method of silicon nitride ceramic balls includes the following processes: Compared with Example 4, in Comparative Example 4, the double bond-containing β-cyclodextrin was not added, and the other steps were the same as those in Example 4.

[0046] Experiment: Take the silicon nitride ceramic balls obtained in Examples 1-5 and Comparative Examples 1-4, prepare specimens, and detect and record the test results of their properties respectively: Use a density tester and a roundness tester to test the relative density and spherical error of the specimens, and measure the fracture toughness (load 196 N) according to the indentation method proposed by Niihara.

[0047] The test results are as follows:

[0048] From the data in the above table, the following conclusions can be clearly obtained: 1. Compared with Examples 1-5, the relative density and fracture toughness of the products obtained in Comparative Examples 1 and 2 decreased, and the spherical error increased. This shows that compared with the coarse powder, the coarse powder, fine powder, and micro powder prepared by the spray granulation technology of the present invention can better improve the green density and reduce the pores of the silicon nitride green balls in the forming stage. At the same time, through the secondary pre-round grinding treatment of the present invention, the sphericity was corrected, and the subsequent processing difficulty was reduced.

[0049] 2. Compared with Examples 3-5, the relative density and fracture toughness of the products obtained in Comparative Examples 3 and 4 decreased, and the spherical error increased. This indicates that compared with sodium-based bentonite, the bentonite composite prepared by the present invention has a better strengthening effect. At the same time, the addition of double bond-containing β-cyclodextrin in the present invention can enhance the crosslinking degree of the polymer network, thereby improving the mechanical properties of the material.

[0050] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention.

Claims

1. A method for preparing a silicon nitride ceramic ball, characterized in that: The steps include: Step S1: adding silicon powder and nitrate solution into a ball mill, performing ball milling, taking out, and drying to obtain raw powder; Step S2: uniformly mixing the raw powder, the binder, the plasticizer and the solvent, and ball milling to obtain a slurry; Step S3: spray granulate the slurry to obtain coarse powder, fine powder and micro powder; fill the coarse powder, fine powder and micro powder into a mold in sequence, and isostatically press to obtain a green body; Step S4: grinding and pre-rounding the green body once, sintering once, cooling to room temperature, grinding and pre-rounding the green body twice, sintering twice, and obtaining silicon nitride ceramic balls after rough grinding, fine grinding and polishing.

2. The method for preparing a silicon nitride ceramic ball according to claim 1, characterized in that: In step S1, the nitrate in the nitrate solution is one or more of magnesium nitrate, yttrium nitrate and barium nitrate.

3. The method for preparing a silicon nitride ceramic ball according to claim 1, characterized in that: In the step S1, the molar ratio of silicon powder to nitrate is 1:0.02-0.

2.

4. The method for preparing a silicon nitride ceramic ball according to claim 1, characterized in that: In step S2, the slurry is composed of the following components in parts by weight: 90-100 parts of raw powder, 1-10 parts of binder, 1-10 parts of plasticizer, and 50-80 parts of solvent.

5. The method for preparing a silicon nitride ceramic ball according to claim 1, characterized in that: In the step S3, the particle size of the coarse powder is 80 μm<coarse powder<150 μm, the particle size of the fine powder is 40 μm<fine powder≤80 μm, and the particle size of the micro powder is 0.01 μm<micro powder≤40 μm.

6. The method for preparing a silicon nitride ceramic ball according to claim 1, characterized in that: In step S4, the process conditions for secondary grinding and pre-rounding are: the grinding wheel adopts a cast iron grinding wheel with a hardness of HB 210-280, and the grinding time is 5-30 minutes.

7. The method for preparing a silicon nitride ceramic ball according to claim 4, characterized in that: The slurry also includes 5-15 parts of bentonite composite, and the specific preparation process is as follows: Step (1): Evenly mix sodium bentonite, cyclohexane and ethanol, add acrylic acid dropwise for 1-2 hours, react at 70-80°C for 3-5 hours, filter, wash and dry to obtain acidified sodium bentonite; Step (2): Evenly mix the acidified sodium bentonite and lanthanum chloride solution, add aluminum chloride hexahydrate, react for 1-3 hours, filter, wash and dry to obtain modified bentonite; Step (3): uniformly mix the modified bentonite and deionized water, add double-bond β-cyclodextrin, methacrylic acid, hydroxyethyl acrylate, vinyl triethoxysilane and ammonium persulfate, react at 70-80° C. for 6-8 hours, filter, wash and dry to obtain a bentonite composite.

8. The method for preparing a silicon nitride ceramic ball according to claim 8, characterized in that: In step (3), the bentonite composite is composed of the following components in parts by weight: 5-15 parts of modified bentonite, 8-12 parts of double-bond β-cyclodextrin, 3-6 parts of methacrylic acid, 5-10 parts of hydroxyethyl acrylate, 2-4 parts of vinyl triethoxysilane, 1-5 parts of ammonium persulfate, and 80-100 parts of deionized water.

9. The method for preparing a silicon nitride ceramic ball according to claim 8, characterized in that: The preparation method of the double-bond-containing β-cyclodextrin is as follows: β-cyclodextrin, N-hydroxymethyl acrylamide and dilute hydrochloric acid are uniformly mixed, reacted at 70-80° C. for 15-30 minutes, and β-cyclodextrin containing double bonds is obtained after precipitation, filtration, washing and drying.

10. A silicon nitride ceramic ball prepared according to the preparation method according to any one of claims 1 to 9.

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