Preparation method for coating silicon nitride ceramic powder through molten salt decomposition

Abstract

The invention discloses a preparation method of molten salt decomposition coated silicon nitride ceramic powder, which comprises the following steps: mixing a nitrate or acetate sintering aid containing crystal water, heating, and removing the crystal water; the method comprises the following steps: dissolving a nitrate or acetate sintering aid without crystal water in absolute ethyl alcohol, adding silicon nitride powder, ball-milling until the mixture is uniformly mixed, then drying through rotary evaporation, and crushing and sieving the mixture to obtain silicon nitride powder uniformly mixed with nitrate or acetate; calcining the obtained mixed powder again to remove nitrate or acetate ions in the mixed powder, converting the sintering aid into an oxide to coat the surfaces of the silicon nitride powder particles, and then sieving again. The method has the beneficial effects that the mixing problem is solved, the microstructure and performance are optimized, the liquid phase uniformity is improved, and the mechanical strength is improved.

Description

Technical Field

[0001] The present invention relates to the field of silicon nitride ceramics, and particularly to a preparation method of molten salt decomposition-coated silicon nitride ceramic powder. Background Art

[0002] Silicon nitride is a widely used ceramic. It has excellent flexural strength and fracture toughness, making it a highly regarded key material in extreme environments. Moreover, its excellent thermal conductivity enables large-scale applications in the semiconductor field. The mechanical properties of silicon nitride ceramics mainly depend on whether the grain size distribution is uniform. Uniformly distributed grains can withstand greater shear stress, while abnormally grown grains are more prone to fracture. When using the traditional ball milling method to mix silicon nitride powder and sintering aids, due to the differences in the properties of silicon nitride particles and sintering aid particles, the uniformity of powder mixing is limited, and it is difficult to form a uniform liquid phase during the sintering process, thus unable to obtain uniformly distributed grains. Summary of the Invention

[0003] In order to overcome the disadvantages and deficiencies existing in the prior art, the purpose of the present invention is to provide a preparation method of molten salt decomposition-coated silicon nitride ceramic powder.

[0004] The purpose of the present invention is achieved through the following technical solutions: A preparation method of molten salt decomposition-coated silicon nitride ceramic powder, comprising the following steps:

[0005] S1. Mix a nitrate or acetate sintering aid containing crystal water and heat it to remove the crystal water;

[0006] S2. Dissolve the nitrate or acetate sintering aid after removing crystal water in absolute ethanol, add silicon nitride powder and ball mill until uniformly mixed, then dry by rotary evaporation, and then crush and screen the mixture to obtain silicon nitride powder uniformly mixed with nitrate or acetate;

[0007] S3. Calcinate the mixed powder obtained in S2 again to remove the nitrate or acetate ions therein, and convert the sintering aid into an oxide to uniformly coat the surface of the silicon nitride powder particles, and then screen again.

[0008] Further, specifically in S1, prepare a nitrate or acetate sintering aid containing crystal water, mix it in a beaker and place the beaker in a muffle furnace, calcine at 200 - 300 °C for 30 min to remove the crystal water contained therein.

[0009] Further, in S1, the nitrate or acetate sintering aid includes nitrates and acetates of various metal oxides or rare earth oxides.

[0010] Further, in the step S2, the dosage of the nitrate or acetate sintering aid is 0 - 20 parts, and the dosage of the silicon nitride powder is 80 - 100 parts.

[0011] Further, in the step S2, the following steps are specifically further included:

[0012] S21, Dissolution: Dissolve the nitrate or acetate sintering aid after removing the crystal water in anhydrous ethanol according to the proportion;

[0013] S22, Ball milling: Mix the solution after dissolution in S21 with the silicon nitride powder, add grinding balls and make up anhydrous ethanol, and ball mill at a rotation speed of 200 - 350 rpm for 3 - 6 h;

[0014] S23, Drying and sieving: Dry the powder in S22 through a rotary evaporator and sieve it through a 50 - 150 mesh sieve to obtain a uniform and highly dispersive silicon nitride ceramic powder.

[0015] Further, in the step S3, the mixed powder is placed in a muffle furnace for calcination, the calcination temperature of the muffle furnace is 400 - 550 °C, and the calcination holding time is 0.5 - 2 h.

[0016] Further, the surface of the prepared silicon nitride powder particles is uniformly coated with the sintering aid after oxidation of the nitrate or acetate, including yttrium oxide, magnesium oxide, aluminum oxide and gadolinium oxide.

[0017] Further, the forming methods after the powder is prepared include dry pressing - cold isostatic pressing, photocuring forming and 3DP forming.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. Solve the mixing problem: Solve the problem that it is difficult to mix the silicon nitride ceramic powder and the sintering aid evenly in the traditional ball milling process. Through steps such as first removing the crystal water, then dissolving, ball milling, drying, and calcining, the sintering aid can be evenly coated on the surface of the silicon nitride powder particles;

[0020] 2. Optimize the microstructure and properties

[0021] 2.1. Improve the liquid phase uniformity: Improve the uniformity of the liquid phase during sintering, enable the silicon nitride ceramic to form a more uniform liquid phase during the sintering process, and create conditions for obtaining uniformly distributed grains;

[0022] 2.2. Refine the grains: Promote the silicon nitride ceramic to obtain a more uniform microstructure, ensure the uniformity of the grain size, avoid the appearance of abnormally grown grains, and improve the overall quality of the material;

[0023] 2.3. Improve mechanical strength: Significantly improve the mechanical strength of silicon nitride ceramics. The flexural strength can reach 800 MPa. The flexural strengths of the silicon nitride ceramics prepared in each embodiment of the present invention are relatively high. For example, the flexural strength of Example 1 is 833 MPa, and that of Example 4 is 875 MPa, etc.;

[0024] 3. Enrich the selection of forming methods: The forming methods after preparing the powder are diverse, including dry pressing - cold isostatic pressing, photocuring forming, 3DP forming, etc., and are not limited to the listed methods, providing multiple options for subsequent processing to meet different production requirements. Detailed implementation

[0025] For the convenience of understanding by those skilled in the art, the present invention will be further described below in conjunction with embodiments. The content mentioned in the implementation manner does not limit the present invention.

[0026] A preparation method of molten salt decomposition - coated silicon nitride ceramic powder includes the following steps:

[0027] S1. Mix nitrate or acetate sintering aids containing crystal water and heat to remove the crystal water; in this embodiment, specifically: prepare nitrate or acetate sintering aids containing crystal water, mix them in a beaker and place the beaker in a muffle furnace, calcine at 200 - 300 °C for 30 min to remove the crystal water contained therein;

[0028] The nitrate or acetate sintering aids include nitrates and acetates of various metal oxides or rare earth oxides.

[0029] S2. Dissolve the nitrate or acetate sintering aids after removing crystal water in absolute ethanol, add silicon nitride powder and ball - mill until evenly mixed, then dry by rotary evaporation, and then crush and screen the mixture to obtain silicon nitride powder evenly mixed with nitrate or acetate;

[0030] In this embodiment, the dosage of the nitrate or acetate sintering aids is 0 - 20 parts, and the dosage of the silicon nitride powder is 80 - 100 parts; specifically:

[0031] S21. Dissolution: Dissolve the nitrate or acetate sintering aids after removing crystal water in absolute ethanol according to the proportion;

[0032] S22. Ball - milling: Mix the solution after dissolution in S21 with silicon nitride powder, add grinding balls and make up absolute ethanol, and ball - mill at a rotation speed of 200 - 350 rpm for 3 - 6 h;

[0033] S23. Drying and screening: Dry the powder in S22 by a rotary evaporator and screen through a 50 - 150 - mesh sieve to obtain silicon nitride ceramic powder with high uniformity and dispersibility.

[0034] S3. Calcinate the mixed powder obtained in S2 again to remove nitrate or acetate ions therein, and convert the sintering aid into an oxide to uniformly coat the surface of silicon nitride powder particles, and then screen again.

[0035] In this embodiment, in step S3, the mixed powder is calcined in a muffle furnace. The calcination temperature of the muffle furnace is 400 - 550 °C, and the calcination holding time is 0.5 - 2 h.

[0036] S4. Shape the coated silicon nitride ceramic powder and perform high-temperature sintering to obtain a high-performance silicon nitride ceramic device.

[0037] The surface of the prepared silicon nitride powder particles is uniformly coated with a sintering aid after oxidation of nitrate or acetate, including but not limited to yttrium oxide, magnesium oxide, aluminum oxide, gadolinium oxide, etc.

[0038] The shaping methods after the powder is prepared include dry pressing - cold isostatic pressing, stereolithography, and 3DP. In the present invention, only the above several shaping methods are listed, but it is not limited to the above methods, and various shaping methods can be used for subsequent processing. The flexural strength of the silicon nitride ceramic produced after the shaped silicon nitride powder is prepared is higher, reaching more than 800 MPa.

[0039] The silicon nitride powder prepared by the present invention for stereolithography can greatly improve the curing depth compared with the traditional method of incorporating a sintering aid.

[0040] The present invention also includes the following embodiments

[0041] Example 1

[0042] Step 1: By mass fraction, first weigh silicon nitride powder, magnesium nitrate hexahydrate, and yttrium nitrate hexahydrate in a ratio of 82:8:10; pour magnesium nitrate hexahydrate and yttrium nitrate hexahydrate into a beaker, then place it in a muffle furnace and raise the temperature to 200 °C for 1 hour to remove the crystal water contained therein. Then add absolute ethanol and ultrasonicate and stir until the solid is completely dissolved to form a salt solution.

[0043] Step 2: Take the silicon nitride powder weighed in Step 1 and the salt solution and pour them into a polytetrafluoroethylene ball mill jar, add an appropriate amount of silicon nitride grinding balls and make up absolute ethanol, and ball mill at a speed of 350 rpm for 4 h to obtain a uniformly mixed suspension; then perform rotary evaporation drying through a rotary evaporator, and screen the dried powder through a 100-mesh sieve to obtain a powder with uniform particles and high dispersibility.

[0044] Step 3: Re-place the mixed powder prepared in Step 2 into a muffle furnace, heat it up to 500 °C and hold for 2 h to completely remove the crystal water and nitrate ions therein. The generated products are discharged in the form of gas, leaving only the oxidized magnesium oxide and yttrium oxide uniformly coated on the surface of silicon nitride particles. Finally, sieve it again through a 100-mesh sieve to obtain a powder with uniform particles and high dispersibility.

[0045] Step 4: Use the powder prepared in Step 3 to prepare a green body by dry pressing - cold isostatic pressing, and sinter the green body by gas pressure sintering. Under a nitrogen pressure of 1 MPa, the temperature is 1850 °C and hold for 4 h to finally obtain a dense silicon nitride ceramic.

[0046] The density of the silicon nitride ceramic obtained in this example is 98.82%, the flexural strength is 833 MPa, the fracture toughness is 7.2 MPa·m1 / 2, and the thermal conductivity is 72 W·m-1·K-1.

[0047] Example 2

[0048] Step 1: By mass fraction, first weigh silicon nitride powder, magnesium acetate tetrahydrate, and yttrium acetate hexahydrate in a ratio of 82.5:6.8:10.7. Pour magnesium acetate tetrahydrate and yttrium acetate hexahydrate into a beaker, then place it in a muffle furnace, heat it up to 200 °C and hold for 1 h to remove part of the crystal water contained therein. Subsequently, add anhydrous ethanol and ultrasonicate and stir until the solid is completely dissolved to form a salt solution.

[0049] Step 2: Take the silicon nitride powder weighed in Step 1 and the salt solution and pour them into a polytetrafluoroethylene ball milling tank. Add an appropriate amount of silicon nitride grinding balls and make up anhydrous ethanol, and ball mill at a speed of 400 rpm for 3 h to obtain a uniformly mixed suspension. Then carry out rotary evaporation drying through a rotary evaporator, and sieve the dried powder through a 100-mesh sieve to obtain a powder with uniform particles and high dispersibility.

[0050] Step 3: Re-place the mixed powder prepared in Step 2 into a muffle furnace, heat it up to 450 °C and hold for 2 h to completely remove the crystal water and acetate ions therein. The generated products are discharged in the form of gas, leaving only the oxidized magnesium oxide and yttrium oxide uniformly coated on the surface of silicon nitride particles. Finally, sieve it again through a 200-mesh sieve to obtain a powder with uniform particles and high dispersibility.

[0051] Step 4: Use the powder prepared in Step 3 to prepare a green body by dry pressing - cold isostatic pressing, and sinter the green body by gas pressure sintering. Under a nitrogen pressure of 1 MPa, the temperature is 1850 °C and hold for 8 h to finally obtain a dense silicon nitride ceramic.

[0052] The density of the silicon nitride ceramic prepared in this example is 99.23%, the flexural strength is 811 MPa, the fracture toughness is 6.9 MPa·m1 / 2, and the thermal conductivity is 101 W·m-1·K-1.

[0053] Example 3

[0054] Step 1: By mass fraction, first weigh silicon nitride powder, magnesium nitrate hexahydrate, and yttrium acetate hexahydrate in a ratio of 81.5:8:10.5; pour magnesium nitrate hexahydrate and yttrium acetate hexahydrate into a beaker, then place it in a muffle furnace, heat it to 200 °C and keep it warm for 1 hour to remove part of the crystal water contained therein. Subsequently, add absolute ethanol and ultrasonicate and stir until the solid is completely dissolved to form a salt solution.

[0055] Step 2: Take the silicon nitride powder weighed in Step 1 and the salt solution and pour them into a polytetrafluoroethylene ball milling tank. Add an appropriate amount of silicon nitride grinding balls and make up absolute ethanol, and ball mill at a speed of 300 rpm for 6 h to obtain a uniformly mixed suspension; then perform rotary evaporation drying through a rotary evaporator, and pass the dried powder through a 300-mesh sieve to obtain a powder with uniform particles and high dispersibility.

[0056] Step 3: Place the mixed powder prepared in Step 2 in the muffle furnace again, heat it to 450 °C and keep it warm for 2 h to completely remove the crystal water, nitrate ions, and acetate ions contained therein. The generated products are discharged in the form of gas, and only the oxidized magnesium oxide and yttrium oxide are left uniformly coated on the surface of the silicon nitride particles; finally, pass through a 300-mesh sieve again to obtain a powder with uniform particles and high dispersibility.

[0057] Step 4: Use the powder prepared in Step 3 to prepare a green body by dry pressing-cold isostatic pressing, and sinter the green body by atmosphere sintering. Under a nitrogen pressure of 1 MPa, the temperature is 1850 °C and keep it warm for 8 h to finally obtain a dense silicon nitride ceramic.

[0058] The density of the silicon nitride ceramic prepared in this example is 99.6%, the flexural strength is 815 MPa, the fracture toughness is 7.1 MPa·m1 / 2, and the thermal conductivity is 98 W·m-1·K-1.

[0059] Example 4

[0060] Step 1: By mass fraction, first weigh silicon nitride powder, aluminum nitrate nonahydrate, and yttrium acetate hexahydrate in a ratio of 83:6.6:10.4; pour aluminum nitrate nonahydrate and yttrium acetate hexahydrate into a beaker, then place it in a muffle furnace, heat it to 200 °C and keep it warm for 1 hour to remove part of the crystal water contained therein. Subsequently, add absolute ethanol and ultrasonicate and stir until the solid is completely dissolved to form a salt solution.

[0061] Step 2: Take the silicon nitride powder weighed in Step 1 and pour it into a polytetrafluoroethylene ball milling tank together with the salt solution. Add an appropriate amount of silicon nitride grinding balls and make up anhydrous ethanol. Ball mill at a speed of 350 rpm for 4 h to obtain a uniformly mixed suspension; then perform rotary evaporation drying through a rotary evaporator. Sieve the dried powder through a 100-mesh sieve to obtain a powder with uniform particles and high dispersibility.

[0062] Step 3: Place the mixed powder prepared in Step 2 into a muffle furnace again. Heat it to 500 °C and hold for 2 h to completely remove the crystal water, nitrate ions, and acetate ions therein. The generated products are discharged in the form of gas, and only the oxidized alumina and yttrium oxide are left uniformly coated on the surface of the silicon nitride particles; finally, sieve through a 200-mesh sieve again to obtain a powder with uniform particles and high dispersibility.

[0063] Step 4: Mix the powder prepared in Step 3 with a photocurable resin to prepare a silicon nitride ceramic slurry with a solid content of 55 vol%. Test the curing performance of the slurry with a photocurable printer, print a green body, and then use air pressure sintering to fire the green body after debinding. Under a nitrogen pressure of 1 MPa, the temperature is 1850 °C and hold for 4 h to finally obtain a dense silicon nitride ceramic.

[0064] The density of the silicon nitride ceramic obtained in this example is 99.23%, the flexural strength is 875 MPa, the fracture toughness is 7.6 MPa·m1 / 2, and the thermal conductivity is 66 W·m-1·K-1.

[0065] Example 5

[0066] Step 1: By mass fraction, first weigh silicon nitride powder, magnesium acetate tetrahydrate, and gadolinium acetate hexahydrate in a ratio of 84:7:9; pour magnesium acetate tetrahydrate and gadolinium acetate hexahydrate into a beaker, and then place it in a muffle furnace. Heat to 200 °C and hold for 1 hour to remove part of the crystal water contained therein. Then add anhydrous ethanol and ultrasonicate and stir until the solid is completely dissolved to form a salt solution.

[0067] Step 2: Take the silicon nitride powder weighed in Step 1 and pour it into a polytetrafluoroethylene ball milling tank together with the salt solution. Add an appropriate amount of silicon nitride grinding balls and make up anhydrous ethanol. Ball mill at a speed of 350 rpm for 4 h to obtain a uniformly mixed suspension; then perform rotary evaporation drying through a rotary evaporator. Sieve the dried powder through a 100-mesh sieve to obtain a powder with uniform particles and high dispersibility.

[0068] Step 3: Place the mixed powder prepared in Step 2 into a muffle furnace again. Heat it to 500 °C and hold for 2 h to completely remove the crystal water and acetate ions therein. The generated products are discharged in the form of gas, and only the oxidized magnesium oxide and gadolinium oxide are left uniformly coated on the surface of the silicon nitride particles; finally, sieve through a 200-mesh sieve again to obtain a powder with uniform particles and high dispersibility.

[0069] Step 4: The powder prepared in Step 3 is used to prepare a green body by dry pressing - cold isostatic pressing, and the green body is sintered by gas pressure sintering. Under a nitrogen pressure of 1 Mpa, the temperature is 1850 °C and it is kept warm for 8 h, and finally a dense silicon nitride ceramic is obtained.

[0070] The density of the silicon nitride ceramic obtained in this example is 99.51%, the flexural strength is 822 MPa, the fracture toughness is 6.7 MPa·m1 / 2, and the thermal conductivity is 100 W·m-1·K-1.

[0071] For the silicon nitride powder after molten salt decomposition coating prepared by the present invention, the sintering aid is evenly coated on the surface of the silicon nitride powder, and a liquid phase can be formed more evenly during the liquid phase sintering stage, ensuring uniform grain size and improving the strength of the silicon nitride ceramic.

[0072] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention can also be implemented in other ways. Any obvious replacement without departing from the concept of the present invention is within the protection scope of the present invention.

Claims

1. A preparation method of molten salt decomposition-coated silicon nitride ceramic powder, characterized in that: It includes the following steps: S1. Mix nitrate or acetate sintering aids containing crystal water and heat them to remove the crystal water; S2. Dissolve the nitrate or acetate sintering aids after removing the crystal water in absolute ethanol, add silicon nitride powder and ball mill until evenly mixed, then dry by rotary evaporation, and then crush and screen the mixture to obtain silicon nitride powder evenly mixed with nitrate or acetate; S3. Calcinate the mixed powder obtained in S2 again to remove nitrate or acetate ions therein, and convert the sintering aid into an oxide to coat the surface of silicon nitride powder particles, and then screen again.

2. The preparation method of the molten salt decomposition-coated silicon nitride ceramic powder according to claim 1, wherein, Specifically in S1, prepare nitrate or acetate sintering aids containing crystal water, mix them in a beaker and place the beaker in a muffle furnace, calcine at 200 - 300 °C for 30 min to remove the crystal water contained therein.

3. The preparation method of the molten salt decomposition-coated silicon nitride ceramic powder according to claim 1, wherein, In S1, the nitrate or acetate sintering aids include nitrates or acetates of metal oxides or rare earth oxides.

4. The preparation method of the molten salt decomposition-coated silicon nitride ceramic powder according to claim 1, characterized in that, In S2, the dosage of the nitrate or acetate sintering aid is 0 - 20 parts, and the dosage of the silicon nitride powder is 80 - 100 parts.

5. The preparation method of the molten salt decomposition-coated silicon nitride ceramic powder according to claim 1, wherein Specifically in S2, it further includes the following steps: S21. Dissolution: Dissolve the nitrate or acetate sintering aids after removing the crystal water in absolute ethanol according to the proportion; S22. Ball milling: Mix the solution after dissolution in S21 with silicon nitride powder, add grinding balls and make up absolute ethanol, and ball mill at a rotation speed of 200 - 350 rpm for 3 - 6 h; S23. Drying and screening: Dry the powder in S22 by a rotary evaporator and screen it through a 50 - 150 mesh sieve to obtain silicon nitride ceramic powder with uniform and high dispersibility.

6. The preparation method of the molten salt decomposition-coated silicon nitride ceramic powder according to claim 1, wherein, In step S3, the mixed powder is placed in a muffle furnace for calcination, the calcination temperature of the muffle furnace is 400 - 550 °C, and the calcination holding time is 0.5 - 2 h.

7. The preparation method of the molten salt decomposition-coated silicon nitride ceramic powder according to claim 1, characterized in that, The surface of the prepared silicon nitride powder particles is evenly coated with a sintering aid after oxidation of nitrate or acetate, including yttrium oxide, magnesium oxide, aluminum oxide and gadolinium oxide.

8. The preparation method of the molten salt decomposition-coated silicon nitride ceramic powder according to claim 1, wherein, The forming methods after preparing the powder include dry pressing - cold isostatic pressing, stereolithography and 3DP forming.