WO2023088019A1 - Preparation method for silicon nitride ceramic granulated powder - Google Patents

Abstract

The present invention relates to the technical field of silicon nitride ceramics, and provides a method for preparing silicon nitride ceramic granulated powder. In the present invention, a sintering aid, water, and silicon nitride raw powder are ground and mixed to obtain a first slurry; polyvinyl alcohol and polyethylene glycol are dissolved in water to obtain a colloidal solution, the mass ratio of polyvinyl alcohol to polyethylene glycol being (0.16-0.20): 1, and the total mass of polyvinyl alcohol and polyethylene glycol being 2-8% of the total mass of the sintering aid and the silicon nitride raw powder; the first slurry, the colloidal solution, and a dispersant are mixed to obtain a second slurry; the second slurry is subjected to spray granulation to obtain granulated powder, the inlet temperature of the spray granulation being 300-340°C.The method of the present invention can increase the bulk density of the silicon nitride ceramic granulated powder to more than 0.92 g/cm3.

Description

A kind of preparation method of silicon nitride ceramic granulated powder

This application claims the priority of the Chinese patent application submitted to the China Patent Office on November 19, 2021, with the application number 202111401328.0, and the title of the invention is "a method for preparing silicon nitride ceramic granulated powder", the entire content of which is incorporated by reference incorporated in this application.

technical field

The invention relates to the technical field of silicon nitride ceramics, in particular to a method for preparing silicon nitride ceramic granulated powder.

Background technique

Silicon nitride ceramic material has the properties of high strength, low density, strong wear resistance, good corrosion resistance, high thermal shock resistance, self-lubrication and good electrical insulation. It is the preferred material for the production of various structural ceramic parts. It has a wide range of applications in aerospace, machinery, chemical industry and other fields, and still has great development potential.

Increasing the green body density of silicon nitride can effectively increase its sintered density and reduce porosity, thereby improving the mechanical properties of the green body, and the improvement of the green body density is largely affected by the bulk density of the granulated powder. Generally, higher bulk density can obtain higher green body density under the same pressure.

The methods for preparing granulated powder include vacuum ball milling method, rotary vibrating screen and double cone mixer method, spray granulation method and so on. The traditional vacuum ball milling method for preparing powders with high bulk density has the disadvantages of complex equipment, high cost, and long time consumption; although the method of rotary vibrating screen and double cone mixer can pack powders of various densities, the remaining powder The waste and the complexity of the operation process also make this method difficult to apply on a large scale in production. Although the spray granulation method is simple to operate, the bulk density of the prepared ceramic powder is low.

Contents of the invention

The object of the present invention is to provide a preparation method of silicon nitride ceramic granulated powder, which can improve the bulk density of silicon nitride ceramic granulated powder.

In order to achieve the above-mentioned purpose of the invention, the present invention provides the following technical solutions:

The invention provides a kind of preparation method of silicon nitride ceramic granulated powder, comprises the following steps:

Grinding and mixing the sintering aid, water and silicon nitride raw powder to obtain the first slurry;

Polyvinyl alcohol and polyethylene glycol are dissolved in water to obtain a glue solution; the mass ratio of the polyvinyl alcohol and polyethylene glycol is (0.16-0.20): 1; the total mass of the polyvinyl alcohol and the alcohol polyethylene glycol It is 2-8% of the total mass of sintering aid and silicon nitride raw powder;

mixing the first slurry, glue solution and dispersant to obtain a second slurry;

The second slurry is subjected to spray granulation to obtain silicon nitride ceramic granulated powder; the inlet temperature of the spray granulation is 300-340°C.

Preferably, the mass of the sintering aid is 5-15% of the total mass of the sintering aid and silicon nitride raw powder.

Preferably, the sintering aid includes one or more of magnesium oxide, cerium oxide, aluminum oxide, samarium oxide, thorium oxide and lanthanum oxide.

Preferably, the solid contents of the first slurry and the second slurry are independently 40-50%.

Preferably, the dispersant includes sodium hexametaphosphate.

Preferably, the dispersant is added in an amount such that the viscosity of the second slurry is 2500-3500 mPa·s.

Preferably, grinding and mixing the sintering aid, water and silicon nitride raw powder includes: performing a first grinding and mixing of the sintering aid and part of the water, and then adding the silicon nitride raw powder and the remaining water for the second grinding and mixing .

Preferably, the particle size of the solid phase particles in the first slurry satisfies 0.8 μm<D50<1.5 μm.

Preferably, the pump pressure of the spray granulation is 840-920 MPa, the aperture of the nozzle is 0.8-1.0 mm, and the thickness of the rotary blade is 2-3 mm.

Preferably, said dissolving polyvinyl alcohol and polyethylene glycol into water includes: firstly adding polyethylene glycol into water, stirring at 50°C for 0.5h, then adding polyvinyl alcohol and continuing stirring at 50°C for 2h.

The invention provides a method for preparing silicon nitride ceramic granulated powder, comprising the following steps: grinding and mixing sintering aids, water and silicon nitride raw powder to obtain a first slurry; mixing polyvinyl alcohol and polyethylene glycol Alcohol is dissolved in water to obtain glue solution; the mass ratio of polyvinyl alcohol and polyethylene glycol is (0.16～0.20): 1; the total mass of polyvinyl alcohol and polyethylene glycol is sintering aid and silicon nitride 2% to 8% of the total mass of raw powder; mixing the first slurry, glue solution and dispersant to obtain a second slurry; spraying the second slurry to obtain silicon nitride ceramic granulation powder; the inlet temperature of the spray granulation is 300-340°C.

Polyvinyl alcohol (PVA) is an active binder, which has high viscosity when the temperature is higher than Tg (generally 75-85°C), while polyethylene glycol (PEG) can be worn as a plasticizer of PVA. Permeate PVA, separate the secondary bonds in its separation chain, thereby increasing the deformability of PVA; the present invention can make the liquid droplets produced during spray drying by controlling the mass ratio of PVA to PEG to be (0.16～0.20):1. The shrinkage is larger, and the accumulation between the powders is denser. Cooperating with the inlet temperature of the spray granulation, the water volatilization speed of the liquid in the spray granulation process can be controlled, and the granulation powder similar to red blood cells can be formed, so as to obtain higher looseness. packing density.

The method of the present invention can be used to obtain erythrocyte-like granulated powder with a dense internal structure. Although there are relatively large holes in the middle of the granulated powder, the powder in the granulated powder is packed relatively tightly, which can effectively increase the bulk density to 0.92g /cm ³ or more, and the hole in the middle of the granulated powder is conducive to the removal of gas during the pressing process and reduces the occurrence of cracks in the green body.

Detailed ways

The invention provides a kind of preparation method of silicon nitride ceramic granulated powder, comprises the following steps:

Grinding and mixing the sintering aid, water and silicon nitride raw powder to obtain the first slurry;

Polyvinyl alcohol and polyethylene glycol are dissolved in water to obtain a glue solution; the mass ratio of the polyvinyl alcohol and polyethylene glycol is (0.16-0.20): 1; the total mass of the polyvinyl alcohol and the alcohol polyethylene glycol It is 2-8% of the total mass of sintering aid and silicon nitride raw powder;

mixing the first slurry, glue solution and dispersant to obtain a second slurry;

The second slurry is subjected to spray granulation to obtain silicon nitride ceramic granulated powder; the inlet temperature of the spray granulation is 300-340°C.

In the present invention, unless otherwise specified, the raw materials used are commercially available products well known in the art.

In the invention, the sintering aid, water and silicon nitride raw powder are ground and mixed to obtain the first slurry.

In the present invention, the sintering aid preferably includes one or more of magnesium oxide, cerium oxide, aluminum oxide, samarium oxide, thorium oxide, and lanthanum oxide. When the sintering aid includes more than one, the present invention is There is no special requirement for the ratio of each sintering aid, and any ratio is acceptable. In the present invention, the D50 of the sintering aid is preferably <1 μm.

In the present invention, the D50 of the silicon nitride raw powder is preferably <2 μm, the mass content of the α phase is preferably greater than 90%, the specific surface area is preferably >10m ² /g, the mass content of oxygen is preferably <2.00%, and the mass content of iron is preferably <0.20%, the mass content of carbon is preferably <0.50%.

In the present invention, the mass of the sintering aid is preferably 5-15% of the total mass of the sintering aid and silicon nitride raw powder, more preferably 8-12%, and even more preferably 9-11%. In the present invention, the quality of the water is preferably such that the solid content of the first slurry is 40-50%.

In the present invention, the grinding and mixing of the sintering aid, water and silicon nitride raw powder preferably includes: performing the first grinding and mixing of the sintering aid and part of the water, and then adding the silicon nitride raw powder and the remaining water for the second grinding and mixing. 2 Grind to mix. The present invention has no special requirements on the proportion of the part of water and the remaining water, as long as the sintering aid and silicon nitride raw powder can be uniformly dispersed. In the present invention, the grinding mixing is preferably carried out in a drum mill. The present invention has no special requirements on the specific conditions of the first grinding and mixing and the second grinding and mixing, as long as the particle size of the solid phase particles in the first slurry satisfies 0.8 μm<D50<1.5 μm. The invention adopts step-by-step grinding to facilitate the uniform dispersion of the sintering aid in the silicon nitride slurry. The particle size of the sintering aid and the original silicon nitride powder is small, and it is easy to form false agglomeration. The present invention disperses the sintering aid and the original silicon nitride powder through grinding and mixing to obtain the first slurry with good dispersibility .

The invention dissolves polyvinyl alcohol and polyethylene glycol into water to obtain a glue solution.

In the present invention, the molecular weight of the polyvinyl alcohol is preferably 200,000; the molecular weight of the polyethylene glycol is preferably 20,000. In the present invention, the molecular weight refers to the average relative molecular weight, for example, when the molecular weight of polyethylene glycol is 20,000, it refers to PEG20,000.

In the present invention, the mass ratio of polyvinyl alcohol to polyethylene glycol is (0.16-0.20): 1, preferably (0.17-0.19): 1, most preferably 0.18: 1; the polyvinyl alcohol and polyethylene glycol The total mass of diol is 2-8%, preferably 3-7%, and more preferably 4-6% of the total mass of the sintering aid and silicon nitride raw powder.

In the present invention, the dissolving polyvinyl alcohol and polyethylene glycol in water preferably includes: first adding polyethylene glycol into water, stirring at 50°C for 0.5h, then adding polyethylene glycol and continuing to stir at 50°C for 2h . The present invention has no special requirements on the stirring rate, and the stirring rate well known in the art can be used. In the present invention, the amount of water added to the glue solution is preferably such that the solid content of the second slurry obtained after mixing the first slurry and the glue solution reaches 40-50%.

In the present invention, the polyvinyl alcohol, as an active binder, has higher viscosity when the temperature is higher than Tg, and polyethylene glycol (PEG), as a plasticizer of PVA, can penetrate PVA and separate its separation. The secondary bond in the chain increases the deformability of PVA; the present invention controls the mass ratio of PVA to PEG to be (0.16-0.20): 1, so that the shrinkage of the droplets during spray drying can be greater, and the powder The accumulation between them is more dense.

After obtaining the glue solution and the first slurry, the present invention mixes the first slurry, the glue solution and the dispersant to obtain the second slurry.

In the present invention, the mixing preferably includes: adding the first slurry to a stirring mill and stirring for 1 hour, then adding the glue solution and continuing stirring for 1 hour, and finally adding the dispersant. In the present invention, the added amount of the dispersant is preferably such that the viscosity of the second slurry is 2500-3500 mPa·s. In the present invention, the temperature of the second slurry is preferably 25-35°C.

After the second slurry is obtained, the present invention sprays and granulates the second slurry to obtain silicon nitride ceramic granulated powder.

In the present invention, the spray granulation is preferably carried out in a spray granulation tower, and the spray granulation tower preferably adopts a pressure spray gun. In the present invention, the inlet temperature of the spray granulation is 300-340°C, preferably 310-330°C, more preferably 320°C. The pump pressure of the spray granulation is preferably 840-920 MPa, more preferably 880 MPa; the aperture diameter of the nozzle is preferably 0.8-1.0 mm, more preferably 0.9 mm; the thickness of the rotary blade is preferably 2-3 mm, more preferably 2.5 mm.

In the spray granulation process of the present invention, the small droplets formed by the atomization of the second slurry through the nozzle of the spray gun fall after reaching a certain height, and the water in the droplets volatilizes during this process, and the spherical granulated powder is formed after drying . When the inlet temperature is higher than the inlet temperature of the present invention, the volatilization speed of the liquid at the highest point is faster, causing the water to be separated from the powder rapidly, and the granulated powder will burst due to rapid heating, forming a powder with poor sphericity. It is beneficial to improve the bulk density. When the inlet temperature is lower than the inlet temperature of the present invention, the granulated powder does not have enough heat to quickly shrink into a dense cell shape, but forms a loose spherical granulated powder, which will reduce the bulk density.

The method of the present invention can be used to obtain erythrocyte-like granulated powder with a dense internal structure. Although there are relatively large holes in the middle of the granulated powder, the powder in the granulated powder is packed relatively tightly, which can effectively increase the bulk density to 0.92g /cm ³ or more, and the hole in the middle of the granulated powder is conducive to the removal of gas during the pressing process and reduces the occurrence of cracks in the green body.

The preparation method of the silicon nitride ceramic granulated powder provided by the present invention will be described in detail below in conjunction with the examples, but they should not be construed as limiting the protection scope of the present invention.

The raw silicon nitride powder used in the following examples and comparative examples is high-purity silicon nitride raw powder, D50<2 μm, α phase mass content greater than 90%, specific surface area>10m ² /g, oxygen mass content<2.00%, iron The mass content of carbon is <0.20%, and the mass content of carbon is <0.50%.

Example 1

Add 15kg of sintering aids (thorium oxide and magnesium oxide, the mass ratio of thorium oxide and magnesium oxide is 1:4, D50<1μm) and 15kg of water into the drum mill for grinding and mixing for 6 hours, then add 85kg of high-purity silicon nitride Raw powder and 85kg of water are ground to 0.8<D50<1.5 μm to prepare the first slurry with better uniformity and a solid phase content of 50%. Add 2.54kg of polyethylene glycol (PEG, molecular weight 20000) into 20kg of water, heat and stir at 50°C for 0.5h to dissolve, then add 0.46kg of polyvinyl alcohol (PVB, molecular weight 200,000), stir and dissolve at 50°C for 2h to prepare a uniform glue solution. Add the prepared first slurry into the stirring mill and stir for 1 hour, then add the glue solution and continue stirring for 1 hour, add sodium hexametaphosphate to control the viscosity of the slurry at 3000mPa·s, and obtain the second slurry with good dispersibility and fluidity , the temperature of the second slurry is 30°C, a pressure spray gun is used, the pressure of the feed pump is 880MPa, the hole diameter of the spray sheet is 0.9mm, the thickness of the rotary sheet is 2.5mm, the inlet temperature is 320°C, and the granulated powder is obtained after spray granulation. The ratio of PVA to PEG mass was 0.18.

Example 2

Add 15kg of sintering aids (thorium oxide and magnesium oxide, the mass ratio of thorium oxide and magnesium oxide is 1:4, D50<1μm) and 15kg of water into the drum mill for grinding and mixing for 6 hours, then add 85kg of high-purity silicon nitride Raw powder and 85kg of water are ground to 0.8<D50<1.5 μm to prepare the first slurry with better uniformity and a solid phase content of 50%. Add 2.50kg of polyethylene glycol (PEG, molecular weight 6000) into 20kg of water, heat and stir at 50°C for 0.5h to dissolve, then add 0.50kg of polyvinyl alcohol (PVA, molecular weight 200,000) at 50°C, stir and dissolve for 2h to prepare a uniform glue solution. Add the prepared first slurry into the stirring mill and stir for 1 hour, then add the glue solution and continue stirring for 1 hour, add sodium hexametaphosphate to control the viscosity of the slurry at 3000mPa·s, and obtain the second slurry with good dispersibility and fluidity , the second slurry temperature is 30°C. A pressure spray gun is used, the pressure of the feed pump is 880MPa, the hole diameter of the spray sheet is 0.9mm, the thickness of the rotary sheet is 2.5mm, the inlet temperature is 320°C, and the granulated powder is obtained after spray granulation. The ratio of PVA to PEG mass was 0.2.

Example 3

Add 15kg of sintering aids (thorium oxide and magnesium oxide, the mass ratio of thorium oxide and magnesium oxide is 1:4, D50<1μm) and 15kg of water into the drum mill for grinding and mixing for 6 hours, then add 85kg of high-purity silicon nitride Raw powder and 85kg of water are ground to 0.8<D50<1.5 μm to prepare the first slurry with better uniformity and a solid phase content of 50%. Add 2.58kg of polyethylene glycol (PEG, molecular weight 20000) into 20kg of water, heat and stir at 50°C for 0.5h to dissolve, then add 0.42kg of polyvinyl alcohol (PVA, molecular weight 200,000) at 50°C, stir and dissolve for 2h to prepare a uniform glue solution. Add the prepared first slurry into the stirring mill and stir for 1 hour, then add the glue solution and continue stirring for 1 hour, add sodium hexametaphosphate to control the viscosity of the slurry at 3000mPa·s, and obtain the second slurry with good dispersibility and fluidity , the second slurry temperature is 30°C. A pressure spray gun is used, the pressure of the feed pump is 880MPa, the hole diameter of the spray sheet is 0.9mm, the thickness of the rotary sheet is 2.5mm, the inlet temperature is 320°C, and the granulated powder is obtained after spray granulation. The ratio of PVA to PEG mass was 0.16.

Comparative example 1

Add 15kg of sintering aids (thorium oxide and magnesium oxide, the mass ratio of thorium oxide and magnesium oxide is 1:4, D50<1μm) and 15kg of water into the drum mill for grinding and mixing for 6 hours, then add 85kg of high-purity silicon nitride Raw powder and 85kg of water are ground to 0.8<D50<1.5 μm to prepare the first slurry with better uniformity and a solid phase content of 50%. Add 2.60 kg of polyethylene glycol (PEG, molecular weight 20,000) into 20 kg of water at 50°C with stirring and dissolving for 0.5 h, then add 0.40 kg of polyvinyl butyral (PVA, molecular weight: 200,000) and dissolve at 50°C for 2 h to prepare Uniform and consistent glue solution. Add the prepared first slurry into the stirring mill and stir for 1 hour, then add the glue solution and continue stirring for 1 hour, add sodium hexametaphosphate to control the viscosity of the slurry at 3000mPa·s, and obtain the second slurry with good dispersibility and fluidity , the second slurry temperature is 30°C. A pressure spray gun is used, the pressure of the feed pump is 880MPa, the hole diameter of the spray sheet is 0.9mm, the thickness of the rotary sheet is 2.5mm, the inlet temperature is 320°C, and the granulated powder is obtained after spray granulation. The ratio of PVA to PEG mass was 0.15.

Comparative example 2

Add 15kg of sintering aids (thorium oxide and magnesium oxide, the mass ratio of thorium oxide and magnesium oxide is 1:4, D50<1μm) and 15kg of water into the drum mill for grinding and mixing for 6 hours, then add 85kg of high-purity silicon nitride Raw powder and 85kg of water are ground to 0.8<D50<1.5 μm to prepare the first slurry with better uniformity and a solid phase content of 50%. Add 2.45 kg of polyethylene glycol (PEG, molecular weight 20,000) into 20 kg of water and dissolve with stirring at 50°C for 0.5 h, then add 0.55 kg of polyvinyl butyral (PVA, molecular weight: 200,000) at 50°C, stirring and dissolving for 2 h to prepare a homogeneous Consistent gum solution. Add the prepared first slurry into the stirring mill and stir for 1 hour, then add the glue solution and continue stirring for 1 hour, add a dispersant to control the viscosity of the slurry at 3000mPa·s, and obtain the second slurry with better dispersibility and fluidity. The temperature of the second slurry is 30°C, the pressure spray gun is used, the pressure of the feed pump is 880MPa, the hole diameter of the spray sheet is 0.9mm, the thickness of the rotary sheet is 2.5mm, the inlet temperature is 320°C, and the granulated powder is obtained after spray granulation. The ratio of PVA to PEG mass was 0.22.

Comparative example 3

Add 15kg of sintering aids (thorium oxide and magnesium oxide, the mass ratio of thorium oxide and magnesium oxide is 1:4, D50<1μm) and 15kg of water into the drum mill for grinding and mixing for 6 hours, then add 85kg of high-purity silicon nitride Raw powder and 85kg of water are ground to 0.8<D50<1.5 μm to prepare the first slurry with better uniformity and a solid phase content of 50%. Add 2.54kg polyethylene glycol (PEG, molecular weight 20000) into 20kg water, heat and stir at 50°C for 0.5h, then add 0.46kg of polyvinyl alcohol (PVA, molecular weight 200,000) at 50°C, stir and dissolve for 2h to prepare a uniform glue solution. Add the prepared first slurry into the stirring mill and stir for 1 hour, then add the glue solution and continue stirring for 1 hour, add a dispersant to control the viscosity of the slurry at 3000mPa·s, and obtain the second slurry with better dispersibility and fluidity. The temperature of the second slurry is 30°C, the pressure spray gun is used, the pressure of the feed pump is 880MPa, the aperture of the spray sheet is 0.9mm, the thickness of the rotary sheet is 2.5mm, and the inlet temperature is 280°C. After spraying and granulating, the granulated powder is obtained. The ratio of PVA to PEG mass was 0.18.

Refer to GB 1479-84 to test the bulk density of the silicon nitride granulated powder of each embodiment and comparative example, and press each silicon nitride granulated powder into a green body. The bulk density and green body quality are shown in Table 1. Biscuit pressing conditions: use a mold with a certain shape to perform bisque pressing on the prepared granulated powder by cold isostatic pressing, the pressing pressure is 300MPa, the holding time is 60s, and the pressure relief rate is controlled at 1MPa/s.

Table 1 Bulk density and green body quality of silicon nitride granulated powder in Examples and Comparative Examples

Example	Bulk density g/cm 3	Bisque cracks
Example 1	0.936	none
Example 2	0.929	none
Example 3	0.922	none
Comparative example 1	0.925	have
Comparative example 2	0.912	none
Comparative example 3	0.885	none

As can be seen from Table 1, the silicon nitride ceramic granulated powder with low PVA/PEG ratio and high inlet temperature used in the present invention has a higher bulk density and no green body cracks than Comparative Examples 1 to 3; the reason is that in Comparative Example 1 Although there is a higher bulk density, too much addition of PEG will cause the rigidity of the binder to decrease at low temperature, and the cohesive force will decrease. In Comparative Example 2, the addition of PEG is less, and the fluidity of PVA molecules is relatively low. Poor, the granulated powder is difficult to shrink into a dense shell during the spray drying process, but forms a loose apple shape. In Comparative Example 3, the inlet temperature of the spray granulation tower is low, and the granulated powder does not have enough heat to shrink quickly Into a dense cell shape, but to form a loose spherical granulated powder.

In addition, when the inlet temperature is higher than 340°C, the granulated powder will burst due to rapid heating, forming a powder with poor sphericity, which is not conducive to the subsequent pressing of the green body.

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (16)

1. A preparation method of silicon nitride ceramic granulated powder, is characterized in that, comprises the following steps:

   Grinding and mixing the sintering aid, water and silicon nitride raw powder to obtain the first slurry;

   Polyvinyl alcohol and polyethylene glycol are dissolved in water to obtain glue solution; the mass ratio of polyvinyl alcohol and polyethylene glycol is (0.16～0.20): 1; the total mass of polyvinyl alcohol and polyethylene glycol is 2-8% of the total mass of sintering aid and silicon nitride raw powder;

   mixing the first slurry, glue solution and dispersant to obtain a second slurry;

   The second slurry is subjected to spray granulation to obtain silicon nitride ceramic granulated powder; the inlet temperature of the spray granulation is 300-340°C.
2. The preparation method according to claim 1, characterized in that the mass of the sintering aid is 5-15% of the total mass of the sintering aid and silicon nitride raw powder.
3. The preparation method according to claim 1 or 2, characterized in that the sintering aid comprises one or more of magnesium oxide, cerium oxide, aluminum oxide, samarium oxide, thorium oxide and lanthanum oxide.
4. The preparation method according to claim 1, characterized in that, the solid contents of the first slurry and the second slurry are independently 40-50%.
5. The preparation method according to claim 1, wherein the dispersant comprises sodium hexametaphosphate.
6. The preparation method according to claim 4 or 5, characterized in that the added amount of the dispersant is such that the viscosity of the second slurry is 2500-3500 mPa·s.
7. The preparation method according to claim 1, characterized in that, grinding and mixing the sintering aid, water and silicon nitride raw powder comprises: first grinding and mixing the sintering aid and part of the water, and then adding the nitriding The raw silicon powder and the remaining water are mixed for the second grinding.
8. The preparation method according to claim 1 or 7, characterized in that the particle size of the solid phase particles in the first slurry satisfies 0.8 μm<D50<1.5 μm.
9. The preparation method according to claim 1, characterized in that the pump pressure of the spray granulation is 840-920 MPa, the aperture of the spray plate is 0.8-1.0 mm, and the thickness of the rotary plate is 2-3 mm.
10. The preparation method according to claim 1 or 9, characterized in that the inlet temperature of the spray granulation is 320°C.
11. The preparation method according to claim 1, wherein said dissolving polyvinyl alcohol and polyethylene glycol into water comprises: first adding polyethylene glycol into water, stirring at 50°C for 0.5h, and then adding polyethylene glycol The alcohol was stirred at 50 °C for 2 h.
12. The preparation method according to claim 1, characterized in that the molecular weight of the polyvinyl alcohol is 200,000.
13. The preparation method according to claim 1, wherein the polyethylene glycol has a molecular weight of 20,000.
14. The preparation method according to claim 1, characterized in that, the D50 of the silicon nitride raw powder is <2 μm, the mass content of α phase is greater than 90%, the specific surface area is >10m ² /g, and the mass content of oxygen is <2.00%, The mass content of iron is <0.20%, and the mass content of carbon is <0.50%.
15. The preparation method according to claim 1, characterized in that D50 of the sintering aid is <1 μm.
16. The preparation method according to claim 1, wherein mixing the first slurry, the glue solution and the dispersant comprises: adding the first slurry to a stirring mill and stirring for 1 hour, then adding the glue solution and continuing to stir for 1 hour , and finally add the dispersant.