A method for producing silicon nitride

Abstract

The application provides a preparation method of silicon nitride, which comprises the following steps: mixing silicon powder and silicon nitride powder, loading the uniformly mixed silicon powder and silicon nitride powder into a nitriding furnace, in a first stage, the temperature in the nitriding furnace is increased from room temperature to 800 DEG C at a rate of 3-5 DEG C / min, and the nitrogen flow rate is 30-50 L / min; in a second stage, the temperature in the nitriding furnace is increased from 800 DEG C to 1150 DEG C at a rate of 0.5-1 DEG C / min, then kept for 3-10 h, then decreased to 800 DEG C at a rate of 0.5-3 DEG C / min, and kept for 1-3 h, in the process, the nitrogen flow rate is 0.1-1 L / min, and the pressure in the nitriding furnace is 50-80 KPa; the second stage is repeated for 2-3 times; the temperature in the furnace is rapidly increased to 1300 DEG C, and the silicon nitride powder is obtained by natural cooling. The silicon nitride powder prepared by the preparation method of the silicon nitride has high quality and low energy consumption.

Description

TECHNICAL FIELD

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

[0002] Silicon nitride ceramics are widely used in aerospace, automobile engine parts, wind power, petroleum, high-end equipment and other fields due to their excellent physical properties such as high thermal conductivity, high bending strength, high fracture toughness, high temperature resistance, wear resistance and corrosion resistance. Silicon nitride powder, as the key raw material for preparing silicon nitride ceramics, is a key factor affecting the performance of silicon nitride ceramics.

[0003] There are various methods for preparing silicon nitride powder, among which the silicon powder direct nitriding method is to heat the metal silicon powder in a nitrogen atmosphere in an electric furnace to cause a nitriding reaction to obtain silicon nitride. This method is simple and direct, and is widely used in the industry to synthesize alpha silicon nitride powder.

[0004] The main evaluation indicators of silicon nitride powder quality are alpha phase content, metal impurity content, oxygen content and particle size distribution uniformity. The higher the alpha phase content (≥94%), the lower the metal impurity content and oxygen content, and the more uniform the particle size distribution, the higher the quality of the silicon nitride powder.

[0005] The existing silicon powder direct nitriding method for producing silicon nitride generally involves adding silicon powder and a diluent into a reaction furnace, maintaining a certain temperature for a period of time in a nitrogen atmosphere, for example, 1100-1400℃ for 50-120h, to cause a nitriding reaction of the silicon powder and obtain silicon nitride.

[0006] The existing silicon powder direct nitriding method for producing silicon nitride has the following disadvantages: Since the nitriding reaction of silicon powder is a strong exothermic reaction, the particle size of the silicon powder used to produce silicon nitride according to the above method cannot be too small, because too small particle size of the silicon powder will cause the local temperature in the reaction furnace to rise above the melting point of silicon, resulting in molten silicon and affecting the quality of the product. Therefore, the particle size of the silicon powder used to produce silicon nitride powder is usually above 1μm. However, when the particle size of the silicon powder as a raw material is large, the particle size distribution uniformity of the product silicon nitride powder is wide, the reaction time required is long, and the energy consumption is high. SUMMARY

[0007] Therefore, the present application proposes a preparation method of silicon nitride, which can use smaller particle size silicon powder to produce silicon nitride, improve the quality of silicon nitride powder and reduce energy consumption.

[0008] The technical solution of the present application is as follows:

[0009] A preparation method of silicon nitride, comprising the following steps:

[0010] The silicon powder is mixed with silicon nitride powder; wherein the silicon powder is prepared by refining and grading 5N silicon material, and the particle size satisfies: D50 is 0.1-0.3 μm, and D90 is 0.5-0.9 μm;

[0011] Charging and synthesis reaction; the uniformly mixed silicon powder and silicon nitride powder are loaded into a nitriding furnace, and the temperature in the nitriding furnace is controlled in the following manner, and the nitrogen flow into the nitriding furnace is controlled in the following manner:

[0012] In the first stage, the temperature in the nitriding furnace is raised from room temperature to 800℃ at a rate of 3-5℃ / min, and the nitrogen flow is 30-50L / min;

[0013] In the second stage, the temperature in the nitriding furnace is raised from 800℃ to 1150℃ at a rate of 0.5-1℃ / min, and then is kept for 3-10h, and then is lowered to 800℃ at a rate of 0.5-3℃ / min, and then is kept for 1-3h, in this process, the nitrogen flow is 0.1-1L / min, and the pressure in the nitriding furnace is 50-80KPa;

[0014] The second stage is repeated for 2-3 times;

[0015] The temperature in the furnace is quickly raised to 1300℃, and then is naturally cooled to obtain silicon nitride powder.

[0016] Further, in the step of mixing the silicon powder with the silicon nitride powder, the silicon nitride powder satisfies: the purity is above 99.9%, the α phase is above 93% by mass, D50 is 0.5-1 μm, and D90 is 1-1.5 μm.

[0017] Further, in the step of mixing the silicon powder with the silicon nitride powder, the silicon powder is 70-90% by mass, and the rest is silicon nitride powder.

[0018] Further, in the step of charging and synthesis reaction, before the first stage, it further includes heating and performing at least one gas replacement in the furnace; wherein the gas replacement is to vacuumize the nitriding furnace, and then to fill nitrogen into the nitriding furnace.

[0019] Further, the step of heating and performing at least one gas replacement includes:

[0020] After the furnace door of the nitriding furnace is closed, the first gas replacement is performed when the temperature in the nitriding furnace is at room temperature;

[0021] After the temperature in the nitriding furnace is raised to 200-250℃, the second gas replacement is performed;

[0022] After the temperature in the nitriding furnace is raised to 600-800℃, the third gas replacement is performed.

[0023] Further, in the step of loading the mixed silicon powder and silicon nitride powder into the nitriding furnace, the powder loading amount in the nitriding furnace is 10-15 g / 100 cm 2 .

[0024] The working principle and beneficial effects of the present application are as follows:

[0025] The silicon nitride preparation method provided by the present application can use silicon powder with a particle size meeting D50 of 0.1-0.3 μm and D90 of 0.5-0.9 μm as a raw material to prepare silicon nitride powder, because the particle size of the silicon powder as the raw material is small and the particle size distribution range is narrow, the particle size distribution of the silicon powder as the product is uniform, and when the particle size of the silicon powder as the raw material is small, the nitriding reaction is more sufficient, the impurity content in the silicon nitride powder is reduced, and finally the silicon nitride powder as the product has high quality; at the same time, the small particle size of the silicon powder can shorten the nitriding reaction time of the silicon powder and reduce the energy consumption required for producing silicon nitride. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0027] The present embodiment provides a silicon nitride preparation method, comprising the following steps:

[0028] S1, mixing silicon powder and silicon nitride powder; wherein the silicon powder is prepared by refining and grading 5N silicon material, and the particle size meets D50 of 0.1-0.3 μm and D90 of 0.5-0.9 μm;

[0029] S2, loading and synthesis reaction; loading the mixed silicon powder and silicon nitride powder into the nitriding furnace, and controlling the temperature in the nitriding furnace and the nitrogen flow rate into the nitriding furnace as follows:

[0030] In the first stage, the temperature in the nitriding furnace is raised from room temperature to 800℃ at a rate of 3-5℃ / min, and the nitrogen flow rate is 30-50 L / min;

[0031] In the second stage, the temperature in the nitriding furnace is increased from 800°C to 1150°C at a rate of 0.5-1°C / min, and then kept for 3-10h, and then decreased to 800°C at a rate of 0.5-3°C / min, and then kept for 1-3h, in which process, the nitrogen flow rate is 0.1-1L / min, and the pressure in the nitriding furnace is 50-80KPa;

[0032] The second stage is repeated for 2-3 times;

[0033] The temperature in the furnace is quickly increased to 1300°C, and then naturally decreased to obtain the silicon nitride powder.

[0034] In the preparation method of the silicon oxide in the embodiment, the temperature and the nitrogen flow rate provided in step S2 are adopted, in which step, the silicon powder starts the nitriding reaction to generate silicon nitride by increasing the temperature to 1150°C, and then the temperature in the nitriding furnace is decreased to 800°C, at which time, the nitriding reaction of the silicon powder can be maintained by the heat release of the nitriding reaction, while avoiding the temperature in the nitriding furnace being too high to avoid the increase of the content of β-phase silicon nitride powder in the product, and in this way, the energy consumption can be reduced due to the lower maintained reaction temperature.

[0035] In step S1, the silicon oxide powder used satisfies the purity of 99.9% or above, the α-phase is 93% or above by mass, the D50 is 0.5-1μm, and the D90 is 1-1.5μm.

[0036] By adopting the silicon oxide powder satisfying the above particle size as the diluent, the particle size of the silicon nitride powder as the product can be ensured to be relatively uniform due to the narrow particle size distribution.

[0037] In the embodiment, in the step of mixing the silicon powder and the silicon nitride powder, the silicon powder is 70-90% by mass, and the rest is the silicon nitride powder.

[0038] By mixing the silicon powder and the silicon nitride powder in the above ratio, the silicon powder can be better nitrided, if the content of the silicon nitride powder is too high, the nitriding reaction of the silicon powder is difficult to maintain when the temperature in the nitriding furnace is decreased to 800°C, and if the content of the silicon nitride powder is too low, the nitriding reaction of the silicon powder can be too violent to cause the local temperature to exceed the melting point of silicon, resulting in the flow of silicon and affecting the quality of the product.

[0039] In the embodiment, in the step of charging and synthesis reaction, before the first stage, at least one gas replacement in the furnace is further included, in which the gas replacement is to vacuumize the nitriding furnace, and then fill nitrogen into the nitriding furnace.

[0040] In the embodiment, the step of increasing the temperature and performing at least one gas replacement includes:

[0041] After closing the furnace door of the nitriding furnace, the first gas replacement is performed when the temperature in the nitriding furnace is room temperature;

[0042] After the temperature in the nitriding furnace is raised to 200-250℃, the second gas replacement is performed;

[0043] After the temperature in the nitriding furnace is raised to 600-800℃, the third gas replacement is performed.

[0044] In this embodiment, by performing the gas replacement in the above manner, the moisture and impurities in the furnace can be sufficiently discharged, and the quality of the silicon nitride powder as the product can be improved.

[0045] In this embodiment, in the step of loading the uniformly mixed silicon powder and silicon nitride powder into the nitriding furnace, the powder loading amount in the nitriding furnace is 10-15 g / 100 cm 2 .

[0046] Embodiment One:

[0047] S1, refine and grade the 5N silicon material to obtain silicon powder with smaller particle size and narrower particle size distribution, and the particle size of the silicon powder satisfies: D50 is 0.1 μm, and D90 is 0.5 μm;

[0048] S2, uniformly mix the silicon powder obtained in step S1 with silicon nitride powder; wherein, according to the mass percentage, the silicon powder is 70%, and the silicon nitride powder is 30%; and the silicon nitride powder satisfies: the purity is above 99.9%, the α phase is 93.5% (by mass), D50 is 0.5 μm, and D90 is 1 μm;

[0049] S3, load the silicon powder and silicon nitride powder mixed in step S2 into the nitriding furnace; wherein, when the mixed silicon powder and silicon nitride powder are laid into the nitriding furnace, the powder loading amount of each plate is controlled to be 10 g / 100 cm 2 ;

[0050] S4, close the furnace door, and perform the first gas replacement when the air in the furnace is at room temperature; raise the temperature of the gas in the furnace, and perform the second gas replacement when the gas in the furnace reaches 200-250℃; continue to raise the temperature of the gas in the furnace, and perform the third gas replacement when the gas in the furnace reaches 600-800℃, and wait for the gas in the furnace to naturally cool to room temperature; wherein, the gas replacement is performed in the following manner: vacuumize the nitriding furnace, and then fill nitrogen into the nitriding furnace;

[0051] S5, control the temperature in the nitriding furnace and the nitrogen flow rate into the nitriding furnace in the following manner:

[0052] In the first stage, the temperature in the nitriding furnace is raised from room temperature to 800℃ at a rate of 3℃ / min, and in this process, the nitrogen flow rate is 30 L / min;

[0053] In the second stage, the temperature in the nitriding furnace is raised from 800℃ to 1150℃ at a rate of 0.5℃ / min, and then kept for 3h, and then decreased to 800℃ at a rate of 0.5℃ / min, and then kept for 1h; during the process, the nitrogen flow is 0.1L / min, and the pressure in the nitriding furnace is 50-80KPa, wherein, when the pressure in the nitriding furnace exceeds 80KPa, the pressure in the nitriding furnace is vacuumed to 50KPa;

[0054] The second stage is repeated for 2 times;

[0055] The temperature in the nitriding furnace is rapidly raised to 1300℃, and then naturally cooled down;

[0056] S6, the nitrided silicon powder prepared in step S5 is refined to the required particle size.

[0057] It is detected that the content of α phase in the nitrided silicon crystal phase prepared by the above process is 95.5% (by mass), the content of free Si is 0, and the total power consumption for producing 160kg of nitrided silicon powder is 1300KWh.

[0058] The preparation method of the nitrided silicon in the embodiment is provided by adopting the powder laying amount in step S3 and the powder laying amount in step S5.

[0059] Example Two

[0060] The embodiment provides a preparation method of nitrided silicon, comprising the following steps:

[0061] S1, refining and grading 5N grade silicon material to obtain silicon powder with smaller particle size and narrower particle size distribution, and the particle size of the silicon powder meets: D50 is 0.2μm, and D90 is 0.7μm;

[0062] S2, uniformly mixing the silicon powder obtained in step S1 with nitrided silicon powder; wherein, according to mass percentage, the silicon powder is 85%, and the nitrided silicon powder is 15%; and the nitrided silicon powder meets: the purity is above 99.9%, the α phase is 93.5% (by mass), D50 is 0.7μm, and D90 is 1.2μm;

[0063] S3, loading the silicon powder and the nitrided silicon powder mixed in step S2 into a nitriding furnace; wherein, when the mixed silicon powder and the nitrided silicon powder are laid into the nitriding furnace, the powder laying amount of each plate is controlled to be 12g / 100cm 2 ;

[0064] S4, close the furnace door, when the air in the furnace is at room temperature, carry out the first gas replacement; heat the gas in the furnace, when the gas in the furnace reaches 200-250℃, carry out the second gas replacement; continue to heat the gas in the furnace, when the gas in the furnace reaches 600-800℃, carry out the third gas replacement, and wait for the gas in the furnace to naturally cool to room temperature; wherein, the way of gas replacement is: vacuumize the nitriding furnace, and then fill nitrogen into the nitriding furnace;

[0065] S5, control the temperature in the nitriding furnace and the flow of nitrogen into the nitriding furnace in the following way:

[0066] In the first stage, the temperature in the nitriding furnace is raised from room temperature to 800℃ at a rate of 4℃ / min, and in this process, the nitrogen flow is 40L / min;

[0067] In the second stage, the temperature in the nitriding furnace is raised from 800℃ to 1150℃ at a rate of 0.8℃ / min, then kept for 7h, and then decreased to 800℃ at a rate of 2℃ / min, and then kept for 2h; in this process, the nitrogen flow is 0.6L / min, and the pressure in the nitriding furnace is 50-80KPa, wherein, when the pressure in the nitriding furnace exceeds 80KPa, the pressure in the nitriding furnace is vacuumized to 50KPa;

[0068] Repeat the second stage for 2 times;

[0069] Rapidly raise the temperature in the nitriding furnace to 1300℃, and then naturally cool it;

[0070] S6, refine the silicon nitride powder prepared in step S5 to the required particle size.

[0071] It is detected that the content of α phase in the silicon nitride crystal phase prepared by the above process is 95.2% (by mass), the content of free Si is 0, and the total power consumption for producing 160kg of silicon nitride powder is 1200KWh.

[0072] Example Three

[0073] The present embodiment provides a preparation method of silicon nitride, comprising the following steps:

[0074] S1, refine and grade 5N grade silicon material to obtain silicon powder with smaller particle size and narrower particle size distribution, and the particle size of the silicon powder meets: D50 is 0.3μm, and D90 is 0.9μm;

[0075] S2, mix the silicon powder obtained in step S1 with silicon nitride powder uniformly; wherein, the silicon powder is 90% and the silicon nitride powder is 10% by mass percentage; and the silicon nitride powder meets: the purity is above 99.9%, the α phase is 93.5% (by mass), D50 is 1μm, and D90 is 1.5μm;

[0076] S3, the silicon powder and silicon nitride powder mixed in step S2 are loaded into a nitriding furnace; wherein, when the mixed silicon powder and silicon nitride powder are laid into the nitriding furnace, the powder laying amount of each plate is controlled to be 15g / 100cm 2 ;

[0077] S4, the furnace door is closed, and the first gas replacement is performed when the air in the furnace is at room temperature; the air in the furnace is heated, and the second gas replacement is performed when the air in the furnace reaches 200-250°C; the air in the furnace is continuously heated, and the third gas replacement is performed when the air in the furnace reaches 600-800°C, and the air in the furnace is naturally cooled to room temperature; wherein, the gas replacement is performed by vacuumizing the nitriding furnace and then filling nitrogen into the nitriding furnace;

[0078] S5, the temperature in the nitriding furnace is controlled as follows, and the nitrogen flow into the nitriding furnace is controlled as follows:

[0079] In the first stage, the temperature in the nitriding furnace is raised from room temperature to 800°C at a rate of 5°C / min, and in this process, the nitrogen flow is 50L / min;

[0080] In the second stage, the temperature in the nitriding furnace is raised from 800°C to 1150°C at a rate of 0.8°C / min, and then kept for 7h, and then lowered to 800°C at a rate of 2°C / min, and then kept for 2h; in this process, the nitrogen flow is 0.6L / min, and the pressure in the nitriding furnace is 50-80KPa, wherein, when the pressure in the nitriding furnace exceeds 80KPa, the pressure in the nitriding furnace is vacuumized to 50KPa;

[0081] The second stage is repeated twice;

[0082] The temperature in the nitriding furnace is rapidly raised to 1300°C, and then naturally cooled;

[0083] S6, the silicon nitride powder prepared in step S5 is refined to the required particle size.

[0084] It is detected that, by using the above process, the content of α phase in the silicon nitride crystal phase is 94.8% (by mass), the free Si content is 0, and the total power consumption for producing 160kg of silicon nitride powder is 1160KWh.

[0085] Comparative Example One

[0086] Compared with Example One, the other steps are the same, and the difference is that, in step S1, after the 5N grade silicon material is refined, it is not classified by particle size, but directly used for mixing and nitriding production.

[0087] It is detected that, in the obtained silicon nitride powder, the content of α phase is 91.5% (by mass), and the free silicon is 0.2%.

[0088] Comparative Example Two

[0089] The other steps are the same as in Example One, except that step S4 is not performed.

[0090] After the nitriding, the α phase content of the silicon nitride powder obtained is 93.4% (by mass), the free silicon is 0.2%, and there is 0.1% of Si2N2O.

[0091] Comparative Example Three

[0092] The other steps are the same as in Example One, except that in step S5, the temperature in the nitriding furnace is controlled in the following manner, and the nitrogen flow rate into the nitriding furnace is as follows:

[0093] In the first stage, the temperature in the nitriding furnace is raised from room temperature to 800°C at a rate of 3°C / min, and the nitrogen flow rate is 30 L / min;

[0094] In the second stage, the temperature in the nitriding furnace is raised from 800°C to 1150°C at a rate of 1°C / min, and then raised to 1300°C at a rate of 0.5°C / min, and held at 1300°C for 15-20 hours; during this process, the nitrogen flow rate is 1 L / min;

[0095] In the third stage, the temperature is rapidly raised to 1420°C, and then naturally cooled to room temperature.

[0096] After testing, the α phase content of the silicon nitride product prepared in this manner is 93.3% (by mass), the free silicon is 0.2%, and the total power consumption for producing 160 kg of silicon nitride powder is 1843 KWh.

[0097] The above is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for producing silicon nitride, characterized by, The method comprises the following steps: mixing silicon powder and silicon nitride powder; wherein the silicon powder is prepared by refining and grading 5N silicon material, and the particle size satisfies D50 of 0.1-0.3 μm and D90 of 0.5-0.9 μm; loading and synthesis reaction; the uniformly mixed silicon powder and silicon nitride powder are loaded into a nitriding furnace, and the temperature in the nitriding furnace is controlled and the nitrogen flow into the nitriding furnace is controlled in the following manner: in the first stage, the temperature in the nitriding furnace is raised from room temperature to 800 ℃ at a rate of 3-5 ℃ / min, and the nitrogen flow is 30-50 L / min; in the second stage, the temperature in the nitriding furnace is raised from 800 ℃ to 1150 ℃ at a rate of 0.5-1 ℃ / min, and then is kept for 3-10 h, and then is lowered to 800 ℃ at a rate of 0.5-3 ℃ / min, and then is kept for 1-3 h, in the process, the nitrogen flow is 0.1-1 L / min, and the pressure in the nitriding furnace is 50-80 KPa; the second stage is repeated for 2-3 times; the temperature in the furnace is quickly raised to 1300 ℃, and then is naturally cooled to obtain silicon nitride powder.

2. The method of producing silicon nitride according to claim 1, wherein In the step of mixing silicon powder and silicon nitride powder, the silicon nitride powder satisfies the following conditions: purity of 99.9% or above, α phase of 93% or above by mass, D50 of 0.5-1 μm, and D90 of 1-1.5 μm.

3. The method of producing silicon nitride according to claim 2, wherein In the step of mixing silicon powder and silicon nitride powder, the silicon powder is 70-90% by mass, and the rest is silicon nitride powder.

4. The method of claim 1, wherein the silicon nitride is prepared by a method comprising: In the step of loading and synthesis reaction, before the first stage, the step further comprises raising the temperature and performing at least one gas replacement in the furnace; wherein the gas replacement is vacuumizing the nitriding furnace, and then filling nitrogen into the nitriding furnace.

5. The method of producing silicon nitride according to claim 4, wherein The step of raising the temperature and performing at least one gas replacement comprises: after closing the door of the nitriding furnace, the first gas replacement is performed when the temperature in the nitriding furnace is at room temperature; the second gas replacement is performed when the temperature in the nitriding furnace is raised to 200-250 ℃; the third gas replacement is performed when the temperature in the nitriding furnace is raised to 600-800 ℃.

6. The method of claim 1, wherein the silicon nitride is prepared by a method comprising: forming a mixture of silicon and nitrogen; and heating the mixture to a temperature of 1000°C to 1500°C in a vacuum or an inert gas atmosphere. In the step of charging the mixed silicon powder and silicon nitride powder into the nitriding furnace, the powder charging amount in the nitriding furnace is 10-15 g / 100 cm 2 .