A method for producing a spherical silicon nitride powder

Abstract

The application relates to a preparation method of spherical silicon nitride powder, belonging to the technical field of ceramic powder preparation, and overcomes the defects of high preparation cost and long path of high fluidity spherical silicon nitride powder in the prior art. The preparation method of the spherical silicon nitride powder comprises the following steps: step 1, mixing a silicon source, a carbon source and water to prepare slurry; step 2, performing spray granulation on the slurry to prepare granulated powder; step 3, performing nitriding on the granulated powder; and step 4, removing carbon from the product of step 3. The application combines the synthesis of silicon nitride powder and the preparation of spherical silicon nitride, and the process flow is short and the cost is low.

Description

Technical Field

[0001] This invention belongs to the field of ceramic powder preparation technology, specifically relating to a method for preparing spherical silicon nitride powder. Background Technology

[0002] Silicon nitride ceramics are among the most promising materials for many engineering applications due to their high strength, high toughness, high thermal conductivity, and high insulation properties. With the increasing popularity of silicon nitride ceramic products, their preparation technology has also developed significantly, with different preparation techniques having different requirements for powder properties.

[0003] Selective laser sintering (SLS) is a powder-based 3D printing technology that can directly manufacture complex-shaped ceramic parts without the need for molding or post-sintering machining. The particle size of the ceramic powder directly affects the flowability and packing density of the 3D printing material. Powder with too small a particle size has poor flowability and low printing efficiency; powder with too large a particle size has high flowability but can cause uneven packing and low density. Therefore, it is necessary to select ceramic powder with an appropriate particle size based on the specific requirements of the material being prepared.

[0004] Commonly used processes for preparing silicon nitride powder include direct nitriding, silimide pyrolysis, and carbothermic reduction nitriding. Among these, carbothermic reduction nitriding has the lowest production cost and is easy to mass-produce. However, existing powder preparation processes struggle to produce highly fluid spherical silicon nitride powder. A common process for preparing spherical silicon nitride powder involves spray granulation of silicon nitride powder into spherical particles, followed by sintering. This process suffers from high cost and a long processing route. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of high cost and long path in the preparation of high-flowability spherical silicon nitride powder in the prior art, thereby providing a method for preparing spherical silicon nitride powder.

[0006] To this end, the present invention provides the following technical solution.

[0007] In a first aspect, the present invention provides a method for preparing spherical silicon nitride powder, comprising the following steps:

[0008] Step 1: Mix silicon source, carbon source and water to prepare slurry;

[0009] Step 2: Spray granulation of the slurry to obtain granulated powder;

[0010] Step 3: Nitride the granulated powder;

[0011] Step 4: Remove carbon from the product of step 3.

[0012] Furthermore, the process includes step 5, which involves crushing and dispersing the product from step 4; preferably, an air jet mill is used for crushing and dispersing. The sintered powder exhibits agglomeration, which can be broken up using an air jet mill to obtain individual spherical silicon nitride powders.

[0013] Furthermore, the slurry also includes a dispersant.

[0014] Furthermore, at least one of the following conditions must be met:

[0015] (1) Before adding the dispersant, dissolve it in an organic solvent;

[0016] Preferably, the organic solvent is miscible with water;

[0017] Preferably, the organic solvent includes one or more of methanol, ethanol, or isopropanol;

[0018] Preferably, the ratio of water to organic solvent is 1:(0.01 to 0.6).

[0019] (2) The dispersant is a silane coupling agent;

[0020] Preferably, the silane coupling agent includes one or more of vinylsilane, epoxysilane, or aminosilane;

[0021] (3) The mass ratio of the dispersant to the silicon source is (0.02~0.10):1.

[0022] Furthermore, in step 1, the carbon source includes inorganic carbon sources and organic soluble carbon sources.

[0023] Furthermore, at least one of the following conditions must be met:

[0024] (1) The inorganic carbon source includes one or more of acetylene black, carbon black or graphite;

[0025] (2) The organic soluble carbon source includes one or more of glucose, sucrose or maltose;

[0026] (3) The mass ratio of the inorganic carbon source to the organic soluble carbon source is (0.3-0.6):(1.0-5.0).

[0027] Furthermore, step 1 satisfies at least one of the following conditions:

[0028] (1) The silicon source is silicon dioxide;

[0029] (2) The particle size of the silicon source is 0.1 to 0.6 μm;

[0030] (2) The mass ratio of carbon source to silicon source is (1.3~5.6):1;

[0031] (3) The solid content of the slurry is 40-52 wt.%.

[0032] Furthermore, step 2 also includes drying the granulated powder in an oven at 100-150°C for 1-20 hours.

[0033] Furthermore, in step 3, the nitriding process includes:

[0034] The first step is to raise the temperature to 450-600℃ under vacuum conditions at a rate of 5-10℃ / min;

[0035] The second step is to raise the temperature to 1350-1550℃ at a nitrogen pressure of 70-95 kPa and a rate of 2-5℃ / min.

[0036] The third step is to maintain a constant temperature at the highest temperature reached in the second step, and keep it at a nitrogen pressure of 120–145 kPa for 1–10 hours.

[0037] Furthermore, in step 4, the carbon removal process involves removing carbon at 450–600°C for 2–8 hours.

[0038] Preferably, the carbon removal process is carried out under flowing air; more preferably, the air flow rate is 0.5 to 2 L / min.

[0039] Furthermore, step 1 includes: placing the silicon source and carbon source into a ball mill jar, dissolving the dispersant in an organic solvent and pouring it into the ball mill jar, adding water, and mixing by ball milling; preferably, mixing in the ball mill jar for 1 to 5 hours.

[0040] Furthermore, the granulated powder is placed in a graphite furnace for nitriding.

[0041] The technical solution of this invention has the following advantages:

[0042] 1. The preparation method of spherical silicon nitride powder of the present invention includes the following steps: Step 1, mixing silicon source, carbon source and water to prepare slurry; Step 2, spray granulating the slurry to obtain granulated powder; Step 3, nitriding the granulated powder; Step 4, removing carbon from the product of Step 3.

[0043] This invention involves directly spray-granulating the mixed raw materials to obtain spherical precursors, followed by nitriding and decarbonization to produce spherical silicon nitride powder. This process combines the synthesis of silicon nitride powder with the preparation of spherical silicon nitride, featuring a short process flow and low cost, and can be used for the large-scale production of spherical silicon nitride powder.

[0044] 2. The slurry of this invention also includes a dispersant. Adding a dispersant to the slurry can optimize the uniformity of the distribution of silicon and carbon sources, provide a bridge for the connection between silicon and carbon sources, facilitate the nitridation of powder, and enable the preparation of spherical silicon nitride powder with high α phase content.

[0045] 3. The carbon source of this invention includes inorganic carbon sources and organic soluble carbon sources. The method of combining organic and inorganic carbon sources is employed. Inorganic carbon sources are low-cost, while organic carbon sources can dissolve in solvents, achieving sufficient contact with the silicon source. In the first step of nitriding, vacuum sintering, the organic carbon can be carbonized, thereby fully coating the silicon dioxide, which is beneficial for nitriding during the sintering process and improves nitriding efficiency.

[0046] 4. The mass ratio of inorganic carbon source to organic soluble carbon source is (0.3~0.6):(1.0~5.0). Within this range, the carbon source is cost-effective while achieving thorough mixing with the silicon source.

[0047] 5. In step 3 of the method for preparing spherical silicon nitride powder, the nitriding process includes: First, heating to 450-600℃ at a rate of 5-10℃ / min under vacuum conditions; Second, heating to 1350-1550℃ at a rate of 2-5℃ / min under a nitrogen pressure of 70-95KPa; Third, maintaining a constant temperature at the highest temperature reached in the second step and holding at a nitrogen pressure of 120-145KPa for 1-10 hours.

[0048] Nitriding employs a three-step sintering process. The first step, vacuum sintering, promotes the carbonization of the organic carbon source. The second and third steps combine a process of micro-negative pressure and micro-positive pressure. Micro-negative pressure sintering is used during the heating stage to reduce the content of carbon monoxide gas, a byproduct, and promote nitriding on the surface of the spherical powder. Micro-positive pressure sintering during the holding stage accelerates the nitriding inside the spherical powder and increases the reaction rate. Attached Figure Description

[0049] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0050] Figure 1 This is a SEM image of the spherical precursor after spray granulation and drying in Example 1.

[0051] Figure 2 The image shows the XRD pattern of the spherical silicon nitride powder prepared in Example 1. Detailed Implementation

[0052] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0053] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0054] Example 1

[0055] This embodiment provides a method for preparing spherical silicon nitride powder, including the following steps:

[0056] (1) Take 1 kg of silica powder (particle size 0.3-0.4 μm), 0.5 kg of acetylene black and 1.5 kg of sucrose and put them into a ball mill jar; take 50 g of aminosilane, dissolve it in 200 g of ethanol and pour it into the ball mill jar, then add deionized water to make the slurry solid content 48 wt.%, mix in the ball mill jar for 5 hours to obtain the slurry.

[0057] (2) Spray granulation of the slurry to obtain granulated powder. The collected powder after granulation is dried in an oven at 130℃ for 10 hours. Figure 1 Here is a SEM image of the dried spherical precursor. Figure 1 It can be seen that this embodiment produces a spherical precursor with good sphericity.

[0058] (3) The dried granulated powder was placed in a graphite furnace and heated to 600°C at a rate of 10°C / min under vacuum. Then, it was heated to 1550°C at a rate of 2°C / min under a nitrogen pressure of 90 kPa. Finally, it was held at a nitrogen pressure of 120 kPa for 5 hours.

[0059] (4) The product of (3) is decarbonized under flowing air at a flow rate of 2L / min. The temperature is raised from room temperature to 600℃ in 3 hours and kept at that temperature for 5 hours.

[0060] (5) The product of (4) is crushed and dispersed by air jet mill to obtain spherical silicon nitride powder.

[0061] Figure 2 The XRD pattern of the spherical silicon nitride powder prepared in Example 1 is shown below. Figure 2It is known that the α phase is the main component in the spherical silicon nitride powder prepared by this invention. The α phase of the spherical silicon nitride powder prepared in this embodiment is 99.2 wt.%, and the flowability is high, reaching 75.2 s / 50 g.

[0062] Example 2

[0063] This embodiment provides a rapid preparation method for spherical silicon nitride powder, including the following steps:

[0064] (1) Take 1 kg of silica powder (particle size 0.3-0.4 μm), 0.6 kg of acetylene black, and 1.2 kg of sucrose and place them in a ball mill jar. Take 75 g of aminosilane, dissolve it in 300 g of ethanol, pour it into the ball mill jar, and then add deionized water to make the slurry solid content 48 wt.%. Mix in the ball mill jar for 5 hours to obtain the slurry.

[0065] (2) Spray granulation of the slurry to obtain granulated powder. The collected powder after granulation is dried in an oven at 130℃ for 10 hours.

[0066] (3) The dried granulated powder was placed in a graphite furnace and heated to 600°C at a rate of 10°C / min under vacuum. Then, it was heated to 1530°C at a rate of 2°C / min under a nitrogen pressure of 90 kPa. Finally, it was held at a nitrogen pressure of 120 kPa for 5 hours.

[0067] (4) The product of (3) is decarbonized under flowing air at a flow rate of 2L / min. The temperature is raised from room temperature to 600℃ in 3 hours and kept at that temperature for 5 hours.

[0068] (5) The product of (4) was crushed and dispersed by air jet milling to obtain spherical silicon nitride powder. The spherical silicon nitride powder prepared in this embodiment has an α phase of 99.3 wt.% and high flowability of 78.4 s / 50 g.

[0069] Example 3

[0070] This embodiment provides a rapid preparation method for spherical silicon nitride powder, including the following steps:

[0071] (1) Take 1 kg of silica powder (particle size 0.3-0.4 μm), 0.5 kg of carbon black, and 1.2 kg of glucose and place them in a ball mill jar. Take 60 g of vinylsilane, dissolve it in 200 g of ethanol, pour it into the ball mill jar, and then add deionized water to make the slurry solid content 48 wt.%. Mix in the ball mill jar for 5 hours to obtain the slurry.

[0072] (2) Spray granulation of the slurry to obtain granulated powder. The collected powder after granulation is dried in an oven at 130℃ for 10 hours.

[0073] (3) The dried granulated powder was placed in a graphite furnace and heated to 600°C at a rate of 10°C / min under vacuum. Then, it was heated to 1550°C at a rate of 2°C / min under a nitrogen pressure of 85 kPa. Finally, it was held at a nitrogen pressure of 130 kPa for 5 hours.

[0074] (4) The product of (3) was decarbonized under flowing air at a flow rate of 1.5 L / min. The temperature was raised from room temperature to 600 °C in 3 hours and held for 5 hours.

[0075] (5) The product of (4) is crushed and dispersed by air jet mill to obtain spherical silicon nitride powder.

[0076] The spherical silicon nitride powder prepared in this embodiment has an α phase content of 99.5 wt.% and a high flowability of 71.6 s / 50 g.

[0077] Example 4

[0078] This embodiment is basically the same as Example 1, except that aminosilane was not added, and silicon dioxide, acetylene black and sucrose were mixed and granulated directly.

[0079] The spherical silicon nitride powder obtained in this embodiment has a low α content of only 97.3 wt.% and its flowability is reduced to 81.3 s / 50 g.

[0080] Example 5

[0081] This embodiment is basically the same as that in Embodiment 1, except that the amount of aminosilane used is 120g.

[0082] The spherical silicon nitride powder obtained in this embodiment has low flowability, reduced to 89.5 s / 50 g, at which point the α content is 98.6 wt.%.

[0083] Example 6

[0084] This embodiment is basically the same as Embodiment 1, except that the second and third sintering steps do not use a sintering process that combines micro-negative pressure and micro-positive pressure, but only atmospheric pressure sintering.

[0085] The spherical silicon nitride powder prepared in this embodiment has a low α-phase content of only 98.1 wt.%, and its flowability is 78.5 s / 50 g.

[0086] Test case

[0087] The flowability of the spherical silicon nitride powders obtained in Examples 1-6 was tested according to GB / T 40934-2021. The flowability test method is as follows: take 50g of powder and measure the time required for it to flow through a standard funnel with a specified aperture. The unit usually used is s / 50g.

[0088] The test results are shown in Table 1.

[0089] Table 1 Properties of Spherical Silicon Nitride Powder

[0090]

[0091]

[0092] The present invention provides a method for preparing spherical silicon nitride powder that combines the synthesis of silicon nitride powder with the preparation of spherical silicon nitride. The process is characterized by a short flow and low cost, and can be used for the large-scale production of spherical silicon nitride powder.

[0093] Comparing Example 1 with Examples 4 and 5, it can be seen that adding a dispersant and limiting the dispersant to the mass ratio of the dispersant to the silicon source in the present invention is (0.02~0.10):1, which can further improve the α content and flowability of the spherical silicon nitride powder.

[0094] A comparison of Example 1 and Example 6 shows that the sintering process combining micro-negative pressure and micro-positive pressure of the present invention can further improve the α content and flowability of spherical silicon nitride powder.

[0095] The silicon nitride powders obtained in Examples 1-3 have high α-phase content (≥98wt.%) and high flowability (≤80s / 50g).

[0096] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing spherical silicon nitride powder, characterized in that, Includes the following steps: Step 1: Mix silicon source, carbon source and water to prepare slurry; Step 2: Spray granulation of the slurry to obtain granulated powder; Step 3: Nitride the granulated powder; Step 4: Remove carbon from the product of Step 3; The slurry also includes a dispersant, which is a silane coupling agent; The mass ratio of the dispersant to the silicon source is (0.02~0.10):1; In step 3, the nitriding process includes: The first step is to raise the temperature to 450-600℃ under vacuum conditions at a rate of 5-10℃ / min; The second step is to raise the temperature to 1350-1550℃ at a nitrogen pressure of 70-95 kPa and a rate of 2-5℃ / min. The third step is to maintain a constant temperature at the highest temperature reached in the second step, and keep it at a nitrogen pressure of 120~145 kPa for 1~10 hours.

2. The method for preparing spherical silicon nitride powder according to claim 1, characterized in that, It also includes step 5, which involves crushing and dispersing the product from step 4.

3. The method for preparing spherical silicon nitride powder according to claim 1, characterized in that, Before adding the dispersant, dissolve it in an organic solvent.

4. The method for preparing spherical silicon nitride powder according to claim 1 or 2, characterized in that, In step 1, the carbon source includes inorganic carbon sources and organic soluble carbon sources.

5. The method for preparing spherical silicon nitride powder according to claim 4, characterized in that, At least one of the following conditions must be met: (1) The inorganic carbon source includes one or more of acetylene black, carbon black, or graphite; (2) The organic soluble carbon source includes one or more of glucose, sucrose or maltose; (3) The mass ratio of the inorganic carbon source to the organic soluble carbon source is (0.3~0.6):(1.0~5.0).

6. The method for preparing spherical silicon nitride powder according to claim 1 or 2, characterized in that, Step 1 satisfies at least one of the following conditions: (1) The silicon source is silicon dioxide; (2) The particle size of the silicon source is 0.1~0.6μm; (2) The mass ratio of carbon source to silicon source is (1.3~5.6):1; (3) The solid content of the slurry is 40~52 wt.%.

7. The method for preparing spherical silicon nitride powder according to claim 1, characterized in that, Step 2 further includes drying the granulated powder in an oven at 100-150°C for 1-20 hours.

8. The method for preparing spherical silicon nitride powder according to claim 1, characterized in that, In step 4, the carbon removal process involves removing carbon at 450~600℃ for 2~8 hours.

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