Silicon nitride ceramic for precision bearing and preparation method

Abstract

The invention relates to the technical field of silicon nitride, and discloses silicon nitride ceramic for a precision bearing and a preparation method, the silicon nitride ceramic comprises 100 parts by weight of silicon nitride powder, 0.5-2 parts by weight of carbon nanotubes, 2-6 parts by weight of a cationic dispersant and the like; the negative ions on the surface of the silicon nitride and the quaternary ammonium salt positive ions at one end of the positive ion dispersing agent form electrostatic interaction, so that the dispersing agent is modified on the surfaces of silicon nitride particles, agglomeration of the silicon nitride particles can be inhibited, the dispersity of the particles is improved, and the compactness and the mechanical property of the ceramic are improved. A carbazole structure at the other end of the cationic dispersant is a planar large pi conjugated structure, and forms pi-pi interaction with the surface of the carbon nanotube, so that silicon nitride and the carbon nanotube are tightly combined, the carbon nanotube is uniformly dispersed in a silicon nitride matrix, and the silicon nitride ceramic has bending strength, fracture toughness and the like; the method can be better applied to high-strength and high-toughness precision bearing materials.

Description

Technical Field

[0001] This invention relates to the field of silicon nitride technology, specifically to a silicon nitride ceramic for precision bearings and its preparation method. Background Technology

[0002] Silicon nitride is a high-performance ceramic material with excellent lubricity, wear resistance, high-temperature resistance, and oxidation resistance, making it widely used in grinding balls, turbine blades, and sealing rings. However, silicon nitride is brittle and lacks toughness, leading to cracking and breakage during long-term use, which hinders its practical application in high-performance precision bearings.

[0003] Currently, zirconium dioxide, carbon nanotubes, and boron nitride nanoparticles can be used to improve the fracture toughness of silicon nitride. Among these, carbon nanotubes have a large specific surface area, good wear resistance, high mechanical strength, and high toughness, and have important applications in ceramics, plastics, and other fields. Chinese patent CN111517806B discloses silicon nitride ceramics prepared using silicon nitride (Si3N4) as the main phase and carbon nanotubes as the second phase, which exhibit good toughness. However, the silicon nitride ceramics in this patent do not possess good flexural strength, hardness, or other mechanical strength properties. Summary of the Invention

[0004] (i) In view of the shortcomings of the prior art, the present invention provides a silicon nitride ceramic for precision bearings and a preparation method thereof, which solves the problems of poor strength and toughness of silicon nitride ceramics.

[0005] (II) In order to solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a silicon nitride ceramic, comprising 100 parts by weight of silicon nitride powder, 0.5-2 parts by weight of carbon nanotubes, 2-6 parts by weight of cationic dispersant, and 7-10 parts by weight of sintering aid.

[0006] The preparation method of silicon nitride ceramics is as follows: silicon nitride is added to water, stirred and dispersed, ammonia water is added dropwise, and stirring is continued. Silicon nitride hydrolyzes in water to generate Si-OH, Si-NH2 and other groups. In the alkaline system of ammonia water, these groups react with hydroxide ions (OH groups). - Combined, forming Si-O -1 Si-NH -1Anions were added; then cationic dispersants and ethanol were added, and the mixture was stirred to disperse and modify the particles. The quaternary ammonium salt cations at one end of the cationic dispersant formed electrostatic interactions with the anions of silicon nitride, thereby modifying the surface of the silicon nitride particles with the dispersant. Through the steric hindrance effect of long carbon chains and aromatic heterocycles, the aggregation of silicon nitride particles could be inhibited, and the dispersibility of the particles could be improved. Carbon nanotubes were added and stirred to mix. The planar large π-conjugated carbazole structure at the other end of the cationic dispersant formed π-π interactions with the surface of the carbon nanotubes. After filtration, the filter cake was washed with ethanol, and then added to a ball mill jar with sintering aids and ethanol for ball milling. After ball milling, the slurry was filtered, the filter cake was dried and poured into a mold, and then cold isostatically pressed in a cold isostatic press. Finally, it was placed in a sintering furnace for sintering and cooling to obtain silicon nitride ceramics.

[0007] Furthermore, the sintering aid is any one or more of magnesium oxide, cerium dioxide, and yttrium oxide.

[0008] Furthermore, the stirring and dispersion time is 2-3 hours.

[0009] Furthermore, continue stirring for 20-40 minutes.

[0010] Furthermore, the dispersion modification time is 2-5 hours.

[0011] Furthermore, the mixing time is 1-3 hours.

[0012] Furthermore, ammonia water is added dropwise to adjust the pH of the solution to 8-10, with the ammonia water having a mass fraction of 22-28%.

[0013] Furthermore, the ball milling time is 18-36 hours, and the ball milling speed is 200-500 r / min.

[0014] Furthermore, the pressure during cold isostatic pressing is 200-250 MPa, and the time is 2-4 minutes.

[0015] Furthermore, nitrogen gas is introduced into the sintering furnace during sintering. The pressure inside the sintering furnace is 20-30 MPa, the heating rate is 5-10℃ / min, the temperature is raised to 1600-1800℃, and the temperature is held for 1-1.5 hours.

[0016] Further, the preparation method of the cationic dispersant is as follows: Add solvent, 370-466 parts by weight of 9-(bromoalkyl)-9H-carbazole, and an ethanol solution containing 100 parts by weight of trimethylamine to a flask. Heat to 40-60℃, stir the reaction for 18-24 hours, heat to evaporate until a precipitate forms, then cool and crystallize in an ice-water bath. Filter, wash the filter cake with petroleum ether, and dry to obtain the cationic dispersant. The preparation reaction formula is: .

[0017] Furthermore, the solvent is tetrahydrofuran or acetonitrile.

[0018] Furthermore, silicon nitride ceramics are used in precision bearings.

[0019] (III) The beneficial technical effects of adopting the above technical solution are as follows: Silicon nitride hydrolyzes in water to generate Si-OH, Si-NH2 and other groups. In the alkaline system of ammonia water, these groups react with hydroxide ions (OH groups). - Combined, forming Si-O -1 Si-NH -1 The anions form an electrostatic interaction with the quaternary ammonium salt cations at one end of the cationic dispersant, thereby modifying the dispersant onto the surface of silicon nitride particles. Through the steric hindrance effect of long carbon chains and aromatic heterocycles, the aggregation of silicon nitride particles can be suppressed, the dispersibility of particles can be improved, and the internal porosity of silicon nitride ceramics can be reduced, thereby improving the density and mechanical properties of ceramics.

[0020] The carbazole structure at the other end of the cationic dispersant of the present invention is a planar large π-conjugated structure, which can form π-π interactions with the surface of carbon nanotubes. Thus, through the dispersant, silicon nitride and carbon nanotubes are tightly bonded together, and the bonding force and interfacial properties between the two are improved. This allows the carbon nanotubes to be uniformly dispersed in the silicon nitride matrix, which plays a good role in toughening and reinforcing the ceramic. This gives the silicon nitride ceramics good bending strength, fracture toughness and Vickers hardness, and can be better applied to high-strength, high-toughness and high-performance precision bearing materials. Detailed Implementation

[0021] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments.

[0022] 9-(12-bromododecyl)-9H-carbazole (structural formula: [structural formula would be inserted here]) was prepared according to the method described in the journal article Dyes and Pigments 112 (2015) 154-161, "Synthesis and properties of a new class of aggregation-induced enhanced emission compounds: Intense blue light emitting triphenylethylene derivatives". ) and 9-(6-bromohexyl)-9H-carbazole (structural formula is ).

[0023] Example 1: A method for preparing silicon nitride ceramics: (1) Add 350 mL of acetonitrile, 23.3 g of 9-(12-bromododecyl)-9H-carbazole and 25 mL of ethanol solution containing 5 g of trimethylamine to a flask, heat to 50 °C, stir and react for 18 h, heat to evaporate until the precipitate is formed, then cool and crystallize in an ice-water bath, filter, wash the filter cake with petroleum ether, dry, and obtain a cationic dispersant.

[0024] (2) Add 1 kg of silicon nitride powder to 2 L of water, stir and disperse for 2 h, add 28% ammonia water to adjust the pH of the solution to 10, continue stirring for 20 min, then add 20 g of cationic dispersant and 150 mL of ethanol, stir and disperse for 2 h, add 5 g of carbon nanotubes, stir and mix for 1 h, filter and wash the filter cake with ethanol, add 45 g of magnesium oxide, 35 g of cerium dioxide and 1.5 L of ethanol to a ball mill jar and ball mill for 24 h at a speed of 400 r / min. After ball milling, filter the slurry, dry the filter cake and pour it into a mold, cold isostatically press it for 4 min at a pressure of 200 MPa, and finally place it in a sintering furnace, introduce nitrogen gas, control the pressure inside the furnace to 25 MPa, heat to 1750 °C at a heating rate of 5 °C / min, hold for sintering for 1 h, cool, and obtain silicon nitride ceramic.

[0025] Example 2, a method for preparing silicon nitride ceramics: (1) Add 600 mL of tetrahydrofuran, 37 g of 9-(6-bromohexyl)-9H-carbazole and 50 mL of ethanol solution containing 10 g of trimethylamine to a flask, heat to 40 °C, stir and react for 24 h, heat to evaporate until the precipitate is formed, then cool and crystallize in an ice-water bath, filter, wash the filter cake with petroleum ether, dry, and obtain a cationic dispersant.

[0026] (2) Add 1 kg of silicon nitride powder to 2 L of water, stir and disperse for 2 h, add 28% ammonia water to adjust the pH of the solution to 9, continue stirring for 40 min, then add 30 g of cationic dispersant and 200 mL of ethanol, stir and disperse for 3 h, add 10 g of carbon nanotubes, stir and mix for 2 h, filter and wash the filter cake with ethanol, add 60 g of magnesium oxide, 40 g of cerium dioxide and 1.2 L of ethanol to a ball mill jar and ball mill for 36 h at a speed of 200 r / min. After ball milling, filter the slurry, dry the filter cake and pour it into a mold, cold isostatically press it for 4 min at a pressure of 200 MPa, and finally place it in a sintering furnace, introduce nitrogen gas, control the pressure inside the furnace to 20 MPa, heat to 1800 °C at a heating rate of 10 °C / min, hold for sintering for 1 h, cool, and obtain silicon nitride ceramic.

[0027] Example 3, a method for preparing silicon nitride ceramics: (1) Add 700 mL of acetonitrile, 44.7 g of 9-(12-bromododecyl)-9H-carbazole and 50 mL of ethanol solution containing 10 g of trimethylamine to a flask, heat to 60 °C, stir and react for 18 h, heat to evaporate until the precipitate is formed, then cool and crystallize in an ice-water bath, filter, wash the filter cake with petroleum ether, dry, and obtain a cationic dispersant.

[0028] (2) Add 1 kg of silicon nitride powder to 2.5 L of water, stir and disperse for 3 h, add 22% ammonia water to adjust the pH of the solution to 8, continue stirring for 40 min, then add 45 g of cationic dispersant and 300 mL of ethanol, stir and disperse for 5 h, add 15 g of carbon nanotubes, stir and mix for 3 h, filter and wash the filter cake with ethanol, add 40 g of magnesium oxide, 30 g of yttrium oxide and 1.2 L of ethanol into a ball mill jar and ball mill for 36 h at a speed of 200 r / min. After ball milling, filter the slurry, dry the filter cake and pour it into a mold, cold isostatically press it for 2 min at a pressure of 250 MPa, and finally place it in a sintering furnace, introduce nitrogen gas, control the pressure inside the furnace to 30 MPa, heat to 1600 °C at a heating rate of 5 °C / min, hold for sintering for 1.5 h, cool, and obtain silicon nitride ceramic.

[0029] Example 4, a method for preparing silicon nitride ceramics: (1) The cationic dispersant was prepared according to the method of Example 3.

[0030] (2) Add 1 kg of silicon nitride powder to 2.5 L of water, stir and disperse for 3 h, add 28% ammonia water to adjust the pH of the solution to 9, continue stirring for 30 min, then add 60 g of cationic dispersant and 400 mL of ethanol, stir and disperse for 5 h, add 20 g of carbon nanotubes, stir and mix for 2 h, filter and wash the filter cake with ethanol, add 50 g of magnesium oxide, 35 g of yttrium oxide and 1.4 L of ethanol into a ball mill jar and ball mill for 18 h at a speed of 500 r / min. After ball milling, filter the slurry, dry the filter cake and pour it into a mold, cold isostatically press it for 3 min at a pressure of 250 MPa, and finally place it in a sintering furnace, introduce nitrogen gas, control the pressure inside the furnace to 20 MPa, heat to 1700 °C at a heating rate of 5 °C / min, hold for sintering for 1 h, cool, and obtain silicon nitride ceramic.

[0031] Comparative Example 1 differs from Example 1 in that no cationic dispersant is added: (1) Add 1 kg of silicon nitride powder to 2 L of water, stir and disperse for 2 h, add 28% ammonia water to adjust the pH of the solution to 10, continue stirring for 20 min, add 150 mL of ethanol, stir for 2 h, add 5 g of carbon nanotubes, stir and mix for 1 h, filter and wash the filter cake with ethanol, add 45 g of magnesium oxide, 35 g of cerium dioxide and 1.5 L of ethanol to a ball mill jar and ball mill for 24 h at a speed of 400 r / min. After ball milling, filter the slurry, dry the filter cake and pour it into a mold, cold isostatically press it for 4 min at a pressure of 200 MPa, and finally place it in a sintering furnace, introduce nitrogen gas, control the pressure inside the furnace to 25 MPa, heat to 1750℃ at a heating rate of 5℃ / min, hold for sintering for 1 h, cool, and obtain silicon nitride ceramic.

[0032] Comparative Example 2 differs from Example 1 in that 9-(12-bromododecyl)-9H-carbazole is used instead of the cationic dispersant. (1) Add 1 kg of silicon nitride powder to 2 L of water, stir and disperse for 2 h, add 28% ammonia water to adjust the pH of the solution to 10, continue stirring for 20 min, then add 20 g of 9-(12-bromododecyl)-9H-carbazole and 150 mL of ethanol, stir and disperse for 2 h, add 5 g of carbon nanotubes, stir and mix for 1 h, filter and wash the filter cake with ethanol, add 45 g of magnesium oxide, 35 g of cerium dioxide and 1.5 L of ethanol into a ball mill jar and ball mill for 24 h at a speed of 400 r / min. After ball milling, filter the slurry, dry the filter cake and pour it into a mold, cold isostatically press for 4 min at a pressure of 200 MPa, and finally place it in a sintering furnace, introduce nitrogen gas, control the pressure inside the furnace to 25 MPa, heat to 1750 °C at a heating rate of 5 °C / min, hold for sintering for 1 h, cool, and obtain silicon nitride ceramic.

[0033] Comparative Example 3 differs from Example 1 in that it uses hexadecyltrimethylammonium bromide instead of a cationic dispersant. (1) Add 1 kg of silicon nitride powder to 2 L of water, stir and disperse for 2 h, add 28% ammonia water to adjust the pH of the solution to 10, continue stirring for 20 min, then add 20 g of hexadecyltrimethylammonium bromide and 150 mL of ethanol, stir and disperse for 2 h, add 5 g of carbon nanotubes, stir and mix for 1 h, filter and wash the filter cake with ethanol, add 45 g of magnesium oxide, 35 g of cerium dioxide and 1.5 L of ethanol into a ball mill jar and ball mill for 24 h at a speed of 400 r / min. After ball milling, filter the slurry, dry the filter cake and pour it into a mold, cold isostatically press it for 4 min at a pressure of 200 MPa, and finally place it in a sintering furnace, introduce nitrogen gas, control the pressure inside the furnace to 25 MPa, heat to 1750 °C at a heating rate of 5 °C / min, hold for sintering for 1 h, cool, and obtain silicon nitride ceramic.

[0034] Comparative Example 4 differs from Example 1 in that benzyltrimethylammonium bromide is used instead of the cationic dispersant. (1) Add 1 kg of silicon nitride powder to 2 L of water, stir and disperse for 2 h, add 28% ammonia water to adjust the pH of the solution to 10, continue stirring for 20 min, then add 20 g of benzyltrimethylammonium bromide and 150 mL of ethanol, stir and disperse for 2 h, add 5 g of carbon nanotubes, stir and mix for 1 h, filter and wash the filter cake with ethanol, add 45 g of magnesium oxide, 35 g of cerium dioxide and 1.5 L of ethanol into a ball mill jar and ball mill for 24 h at a speed of 400 r / min. After ball milling, filter the slurry, dry the filter cake and pour it into a mold, cold isostatically press it for 4 min at a pressure of 200 MPa, and finally place it in a sintering furnace, introduce nitrogen gas, control the pressure inside the furnace to 25 MPa, heat to 1750 °C at a heating rate of 5 °C / min, hold for sintering for 1 h, cool, and obtain silicon nitride ceramic.

[0035] The flexural strength and fracture toughness shall be tested according to the method specified in GB / T 44547-2024. The Vickers hardness shall be tested according to the method specified in GB / T 16534-2009.

[0036]

[0037] As shown in Table 1, the flexural strength, fracture toughness, and Vickers hardness of the silicon nitride ceramics in Examples 1-4 are significantly higher than those in Comparative Example 1. This is mainly due to the addition of a cationic dispersant. The quaternary ammonium salt cation at one end of the dispersant can form an electrostatic interaction with the anions on the surface of silicon nitride powder. By modifying the surface of silicon nitride particles with the dispersant, the steric hindrance effect of the long carbon chain and aromatic heterocycles can inhibit the aggregation of silicon nitride particles, improve the dispersibility of particles, reduce the internal porosity of silicon nitride ceramics, and improve the density and mechanical properties of ceramics. Furthermore, the carbazole structure at the other end of the cationic dispersant is a planar large π-conjugated structure, which can form π-π interactions with the surface of carbon nanotubes. Thus, the dispersant tightly binds silicon nitride and carbon nanotubes, improving the bonding force and interfacial properties between them. This allows the carbon nanotubes to be uniformly dispersed in the silicon nitride matrix, playing a good role in toughening and reinforcing the ceramics and significantly improving the flexural strength, fracture toughness, Vickers hardness, and mechanical properties of silicon nitride ceramics.

[0038] The 9-(12-bromododecyl)-9H-carbazole in Comparative Example 2 does not contain quaternary ammonium salt cations and cannot form electrostatic interactions with the hydroxyl anions on the surface of silicon nitride powder, thus it cannot act as a dispersant. The flexural strength, fracture toughness, and Vickers hardness of the silicon nitride ceramic are significantly lower than those in Example 1.

[0039] Comparative Example 3 uses conventional hexadecyltrimethylammonium bromide as a silicon nitride dispersant. Since it does not contain carbazole large π-conjugated structure, it cannot form π-π interaction with the surface of carbon nanotubes and cannot tightly bind silicon nitride to carbon nanotubes. As a result, the carbon nanotubes are poorly dispersed in the silicon nitride matrix, and the flexural strength, fracture toughness, and Vickers hardness of the silicon nitride ceramic are lower than those of Example 1.

[0040] Comparative Example 4 contains benzyltrimethylammonium bromide, which does not contain long carbon chains and is not effective in inhibiting the aggregation of silicon nitride particles. Furthermore, the π-π interaction force between the benzyltrimethylammonium bromide benzene ring and carbon nanotubes is lower than that of the large π conjugated structure of carbazole. This results in lower interaction forces between carbon nanotubes and silicon nitride, as well as lower carbon nanotube dispersion compared to Example 1, leading to lower flexural strength, fracture toughness, and Vickers hardness of the silicon nitride ceramic.

[0041] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A silicon nitride ceramic for precision bearings, characterized in that, The raw materials for the silicon nitride ceramic include 100 parts by weight of silicon nitride powder, 0.5-2 parts by weight of carbon nanotubes, 2-6 parts by weight of cationic dispersant, and 7-10 parts by weight of sintering aid. The structural formula of the cationic dispersant is as follows: , where a is any integer from 6 to 12.

2. The silicon nitride ceramic for precision bearings according to claim 1, characterized in that, The sintering aid is any one or more of magnesium oxide, cerium dioxide, and yttrium oxide.

3. The silicon nitride ceramic for precision bearings according to claim 1, characterized in that, The cationic dispersant is prepared as follows: a solvent, 370-466 parts by weight of 9-(bromoalkyl)-9H-carbazole, and an ethanol solution containing 100 parts by weight of trimethylamine are added to a flask. The mixture is heated to 40-60°C and stirred for 18-24 hours. The mixture is heated to evaporate until a precipitate is formed. The precipitate is then cooled and crystallized in an ice-water bath. The mixture is filtered, the filter cake is washed with petroleum ether, and then dried to obtain the cationic dispersant.

4. The silicon nitride ceramic for precision bearings according to claim 3, characterized in that, The solvent is tetrahydrofuran or acetonitrile.

5. The silicon nitride ceramic for precision bearings according to claim 3, characterized in that, The structural formula of the 9-(bromoalkyl)-9H-carbazole is: , where a is any integer from 6 to 12.

6. A method for preparing silicon nitride ceramic for precision bearings as described in any one of claims 1-5, characterized in that, The preparation method is as follows: silicon nitride is added to water, stirred and dispersed, ammonia is added dropwise, stirring is continued, then cationic dispersant and ethanol are added, stirred and dispersed for modification, carbon nanotubes are added, stirred and mixed, the filter cake is washed with ethanol after filtration, and then added to a ball mill jar with sintering aid and ethanol for ball milling. After ball milling, the slurry is filtered, the filter cake is dried and poured into a mold, and then cold isostatically pressed in a cold isostatic press. Finally, it is placed in a sintering furnace for sintering and cooling to obtain silicon nitride ceramics for precision bearings.

7. The method for preparing silicon nitride ceramic for precision bearings according to claim 6, characterized in that, The stirring and dispersion time is 2-3 hours; the stirring time is 20-40 minutes; the dispersion and modification time is 2-5 hours; and the stirring and mixing time is 1-3 hours.

8. The method for preparing silicon nitride ceramic for precision bearings according to claim 7, characterized in that, The pH of the solution is adjusted to 8-10 by adding ammonia water, and the mass fraction of the ammonia water is 22-28%; the ball milling time is 18-36 hours and the ball milling speed is 200-500 r / min.

9. The method for preparing silicon nitride ceramic for precision bearings according to claim 8, characterized in that, The pressure during cold isostatic pressing is 200-250 MPa, and the time is 2-4 min. During sintering, nitrogen gas is introduced into the sintering furnace, the pressure inside the sintering furnace is 20-30 MPa, the heating rate is 5-10℃ / min, the temperature is raised to 1600-1800℃, and the temperature is held for 1-1.5 h.

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