Preparation method of silicon nitride combined silicon carbide brick ingot mould for industrial silicon casting

Abstract

The invention relates to the field of preparation of silicon carbide brick ingot molds, and discloses a preparation method of a silicon nitride combined silicon carbide brick ingot mold for industrial silicon casting, which comprises the following steps: S1, raw material preparation: proportioning silicon carbide aggregate, silicon powder and a sintering aid according to the mass percent of (80-90%): (8-15%): (1-5%); the silicon carbide aggregate is formed by grading coarse particles, medium particles and fine particles according to the mass ratio of (40-50): (30-40): (10-20); s2, mixing and modifying: ball-milling and mixing the raw materials in the step S1, and adding a surface modifier which accounts for 0.5-2% of the total mass of the raw materials; s3, molding: putting the mixed powder into a mold, and carrying out dry pressing molding or cold isostatic pressing molding at the molding pressure of 80-150MPa to obtain a green body; compared with the prior art, the method has the advantages that the silicon nitride combined silicon carbide brick ingot mold with high normal-temperature / high-temperature strength, excellent thermal shock resistance and erosion resistance is prepared by optimizing the raw material ratio, grain composition and sintering process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon carbide brick ingot mold preparation, in particular to a preparation method of a silicon nitride combined silicon carbide brick ingot mold for industrial silicon casting. BACKGROUND

[0002] In the production of industrial silicon and organosilicon, ingot molds are key equipment for carrying high-temperature molten silicon liquid and cooling and forming. Their performance directly determines the quality of the product, the operation efficiency and cost of the production line. Traditional ingot molds are mostly made of ordinary refractory bricks, high alumina bricks or single-component silicon carbide materials. These materials generally have insufficient high-temperature resistance, poor thermal shock resistance leading to cracking, and weak resistance to chemical corrosion by molten silicon and chlorine-containing atmosphere when they are subjected to molten silicon liquid at temperatures as high as 1400℃ or above for a long time. This results in short service life of the ingot mold, frequent replacement, increased production cost, and possible impact on the purity of the silicon ingot due to mold damage or contamination, and even production safety accidents.

[0003] Silicon nitride combined silicon carbide composite materials are considered to be one of the ideal materials for solving the above problems due to their excellent high-temperature strength, wear resistance and thermal shock resistance. However, the application of this material in the prior art still faces challenges. First, the microstructure of the material obtained by conventional preparation methods is not well controlled, and the interfacial bonding strength between the Si3N4 combined phase and the SiC particles needs to be improved, which affects the macroscopic mechanical properties of the material, especially the anti-cracking ability under rapid cooling and heating conditions. Second, if the material formula and sintering process are not optimized, it is difficult to simultaneously achieve high density, excellent high-temperature performance and high resistance to specific harsh environments (such as chlorine-containing atmosphere). In addition, there are technical bottlenecks in preparing such materials into large-size, complex-shaped ingot mold components that meet the requirements of industrial silicon casting, and precisely processing and assembling them while ensuring consistent performance. SUMMARY

[0004] (I) Technical problems to be solved

[0005] The technical problem to be solved by the present application is to provide a preparation method of a silicon nitride combined silicon carbide brick ingot mold for industrial silicon casting, which optimizes the raw material ratio, particle size distribution and sintering process to prepare a silicon nitride combined silicon carbide brick ingot mold with high room temperature / high temperature strength, excellent thermal shock resistance and corrosion resistance.

[0006] (II) Technical solutions

[0007] To solve the above technical problems, the technical solution provided by the present application is: a preparation method of a silicon nitride combined silicon carbide brick ingot mold for industrial silicon casting, comprising the following steps:

[0008] S1, raw material preparation: the silicon carbide aggregate, silicon powder and sintering aid are proportioned according to the mass percentage of 80%-90%:8%-15%:1%-5%; the silicon carbide aggregate is graded according to the mass ratio of (40-50):(30-40):(10-20) of coarse, medium and fine three particles;

[0009] S2, mixing and modification: the raw materials of step S1 are ball-mixed, and 0.5%-2% of surface modifier is added to the total mass of the raw materials; the mixed powder is obtained after uniform mixing;

[0010] S3, forming: the mixed powder is placed in a mold, and dry pressing or cold isostatic pressing is adopted, the forming pressure is 80-150 MPa, and the green body is obtained;

[0011] S4, sintering: the green body is placed in a nitrogen atmosphere sintering furnace, heated to 1400-1600℃ at a rate of 3-5℃ / min, and pre-nitrided for 1-3 hours, then further heated to 1750-1850℃ and kept for 2-6 hours for final sintering, and the silicon nitride bonded silicon carbide brick body is obtained after furnace cooling;

[0012] S5, processing and assembly: the sintered brick body is mechanically processed to the predetermined size, and is built into an ingot mold structure.

[0013] As an improvement, in step S1, the coarse particle size of the silicon carbide aggregate is 1-3mm, the medium particle size is 0.1-1mm, and the fine particle size is less than 0.1mm.

[0014] As an improvement, in step S1, the sintering aid is at least one of yttrium oxide, aluminum oxide and magnesium oxide.

[0015] As an improvement, in step S1, the purity of the silicon powder is not less than 99%, and the particle size D50 is 1-5μm.

[0016] As an improvement, in step S2, the surface modifier is a silane coupling agent or a titanate coupling agent.

[0017] As an improvement, in step S4, the pressure of the nitrogen atmosphere is 0.8-1.2MPa.

[0018] As an improvement, in step S4, microwave heating assisted sintering is adopted in the final sintering stage.

[0019] As an improvement, in step S1, the purity of the silicon carbide aggregate is not less than 98.5%.

[0020] As an improvement, in step S4, the rate of the furnace cooling is controlled at 2-5℃ / min, and after cooling to below 600℃, the furnace is naturally cooled to room temperature. A preparation method of a silicon nitride bonded silicon carbide brick ingot mold for industrial silicon casting

[0021] (III) Advantages

[0022] The present application has the advantages compared with the prior art: through the optimized silicon carbide particle grading, a close-packed skeleton structure is formed, combined with specific sintering aids and a segmented sintering process such as pre-nitriding + high-temperature final sintering, the generation, phase transition and micro-morphology of the Si3N4 bonding phase are effectively controlled, so that it forms a strong and tough interface bonding with the SiC particles. DETAILED DESCRIPTION

[0023] The summary of the application will be further described in detail below in combination with specific embodiments, but it should not be understood that the scope of the subject matter of the present application is limited to only the following examples.

[0024] Example One

[0025] A preparation method of a silicon nitride bonded silicon carbide brick ingot mold for industrial silicon casting, comprising the following steps:

[0026] S1, raw material preparation: the silicon carbide aggregate, silicon powder and sintering aid are matched in mass percentage of 80%:8%:1%; the silicon carbide aggregate is graded by coarse, medium and fine three particles in a mass ratio of 40:30:10, the coarse particle size of the silicon carbide aggregate is 1mm, the medium particle size is 0.1mm, and the fine particle size is less than 0.1mm, the sintering aid is yttrium oxide, and the purity of the silicon powder is not less than 99%, and the particle size D50 is 1μm;

[0027] S2, mixing and modification: the raw materials of step S1 are ball-mixed, and 0.5% of a surface modifier based on the total mass of the raw materials is added, and the mixed powder is obtained after uniform mixing, the surface modifier is a silane coupling agent or a titanate coupling agent;

[0028] S3, forming: the mixed powder is placed in a mold, dry pressing or cold isostatic pressing is adopted, the forming pressure is 80MPa, and a green body is obtained;

[0029] S4, sintering: placing the green body in a nitrogen atmosphere sintering furnace, heating to 1400℃ at a rate of 3℃ / min and holding for 1-3 hours for pre-nitriding, then continuing to heat to 1750℃ and holding for 2 hours for final sintering, and then furnace cooling to obtain a silicon nitride bonded silicon carbide brick body, the pressure of the nitrogen atmosphere is 0.8MPa, microwave heating assisted sintering is used in the final sintering stage, the rate of furnace cooling is controlled at 2℃ / min, and then furnace natural cooling to room temperature after cooling to below 600℃. A preparation method of a silicon nitride bonded silicon carbide brick ingot mold for industrial silicon casting

[0030] S5, processing and assembly: mechanically processing the sintered brick body to a predetermined size, and building into an ingot mold structure.

[0031] Example two

[0032] A preparation method of a silicon nitride bonded silicon carbide brick ingot mold for industrial silicon casting, comprising the following steps:

[0033] S1, raw material preparation: the silicon carbide aggregate, silicon powder and sintering aid are mixed in a mass ratio of 85:12:3; the silicon carbide aggregate is graded by coarse, medium and fine particles in a mass ratio of 45:35:15, the coarse particle size of the silicon carbide aggregate is 2mm, the medium particle size is 0.5mm, and the fine particle size is less than 0.1mm, the sintering aid is yttrium oxide and aluminum oxide, and the purity of the silicon powder is not less than 99% and the particle size D50 is 3μm;

[0034] S2, mixing and modification: the raw materials of step S1 are ball-mixed, and 1% of a surface modifier based on the total mass of the raw materials is added, and then uniformly mixed to obtain a mixed powder, the surface modifier is a silane coupling agent or a titanate coupling agent;

[0035] S3, forming: placing the mixed powder in a mold, and using dry pressing or cold isostatic pressing to form a green body at a forming pressure of 80-150MPa;

[0036] S4, sintering: placing the green body in a nitrogen atmosphere sintering furnace, heating to 1400℃ at a rate of 3℃ / min and holding for 1-3 hours for pre-nitriding, then continuing to heat to 1750℃ and holding for 2 hours for final sintering, and then furnace cooling to obtain a silicon nitride bonded silicon carbide brick body, the pressure of the nitrogen atmosphere is 0.8MPa, microwave heating assisted sintering is used in the final sintering stage, the rate of furnace cooling is controlled at 2℃ / min, and then furnace natural cooling to room temperature after cooling to below 600℃. S5, processing and assembly: mechanically processing the sintered brick body to a predetermined size, and building into an ingot mold structure.

[0037] Example three

[0038] A preparation method of a silicon nitride bonded silicon carbide brick ingot mold for industrial silicon casting, comprising the following steps:

[0039] S1, raw material preparation: the silicon carbide aggregate, silicon powder and sintering aid are matched in mass percentage 90:15:5; the silicon carbide aggregate is graded by mass ratio 50:40:20 of coarse, medium and fine particles, the coarse particle size of the silicon carbide aggregate is 3mm, the medium particle size is 1mm, and the fine particle size is less than 0.1mm, the sintering aid is selected from yttrium oxide, aluminum oxide and magnesium oxide, and the purity of the silicon powder is not less than 99%, and the particle size D50 is 5um;

[0040] S2, mixing and modification: the raw materials of step S1 are ball-mixed, and 2% of the total mass of the raw materials is added to the surface modifier, and the mixed powder is obtained after uniform mixing, and the surface modifier is a silane coupling agent or a titanate coupling agent;

[0041] S3, forming: the mixed powder is placed in a mold, dry pressing or cold isostatic pressing is adopted, the forming pressure is 150MPa, and the green body is obtained;

[0042] S4, sintering: the green body is placed in a nitrogen atmosphere sintering furnace, heated to 1600 DEG C at a rate of 5 DEG C / min, pre-nitrided for 3 hours, then continuously heated to 1850 DEG C and kept for 6 hours for final sintering, and the silicon nitride bonded silicon carbide brick body is obtained after furnace cooling, the pressure of the nitrogen atmosphere is 1.2MPa, microwave heating assisted sintering is adopted in the final sintering stage, the rate of furnace cooling is controlled at 5 DEG C / min, and the furnace is naturally cooled to room temperature after cooling to below 600 DEG C.

[0043] S5, processing and assembly: the sintered brick body is mechanically processed to a predetermined size, and is built into an ingot mold structure.

[0044] Although the embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of the present application is defined by the appended claims and their equivalents, in general, if a person skilled in the art is inspired by it, without departing from the purpose of the present application, without creative design, similar structure and embodiments of the technical scheme should belong to the protection scope of the present application.

Claims

1. A method for preparing a silicon nitride-bonded silicon carbide brick ingot mold for industrial silicon casting, characterized in that, Includes the following steps: S1. Raw material preparation: Silicon carbide aggregate, silicon powder and sintering aid are prepared in a mass percentage ratio of 80% to 90%: 8% to 15%: 1% to 5%; the silicon carbide aggregate is composed of coarse, medium and fine particles in a mass ratio of (40 to 50): (30 to 40): (10 to 20); S2. Mixing and Modification: The raw materials from step S1 are ball-milled and mixed, and a surface modifier accounting for 0.5% to 2% of the total mass of the raw materials is added. After mixing evenly, a mixed powder is obtained. S3. Molding: The mixed powder is placed in a mold and dry pressing or cold isostatic pressing is used to obtain a green body by a molding pressure of 80-150 MPa. S4. Sintering: The green body is placed in a nitrogen atmosphere sintering furnace and heated to 1400-1600°C at a rate of 3-5°C / min and held for 1-3 hours for pre-nitriding. Then, the temperature is further increased to 1750-1850°C and held for 2-6 hours for final sintering. After cooling in the furnace, silicon nitride bonded silicon carbide bricks are obtained. S5. Processing and Assembly: The sintered bricks are machined to the predetermined size and then assembled into a mold structure.

2. The method for preparing a silicon nitride-bonded silicon carbide brick ingot mold for industrial silicon casting according to claim 1, characterized in that, In step S1, the coarse particles of the silicon carbide aggregate have a particle size of 1-3 mm, the medium particles have a particle size of 0.1-1 mm, and the fine particles have a particle size of less than 0.1 mm.

3. The method for preparing a silicon nitride-bonded silicon carbide brick ingot mold for industrial silicon casting according to claim 1, characterized in that, In step S1, the sintering aid is at least one of yttrium oxide, aluminum oxide, and magnesium oxide.

4. The method for preparing a silicon nitride-bonded silicon carbide brick ingot mold for industrial silicon casting according to claim 1, characterized in that, In step S1, the purity of the silicon powder is not less than 99%, and the particle size D50 is 1-5 μm.

5. The method for preparing a silicon nitride-bonded silicon carbide brick ingot mold for industrial silicon casting according to claim 1, characterized in that, In step S2, the surface modifier is a silane coupling agent or a titanate coupling agent.

6. The method for preparing a silicon nitride-bonded silicon carbide brick ingot mold for industrial silicon casting according to claim 1, characterized in that, In step S4, the pressure of the nitrogen atmosphere is 0.8 to 1.2 MPa.

7. The method for preparing a silicon nitride-bonded silicon carbide brick ingot mold for industrial silicon casting according to claim 1, characterized in that, In step S4, microwave heating is used to assist sintering during the final sintering stage.

8. The method for preparing a silicon nitride-bonded silicon carbide brick ingot mold for industrial silicon casting according to claim 1, characterized in that, In step S1, the purity of the silicon carbide aggregate is not less than 98.5%.

9. The method for preparing a silicon nitride-bonded silicon carbide brick ingot mold for industrial silicon casting according to claim 1, characterized in that, In step S4, the furnace cooling rate is controlled at 2-5°C / minute, and after cooling to below 600°C, the furnace is allowed to cool naturally to room temperature.