Preparation process of low-agglomeration and high-fluidity SiC water-based granulation powder

Abstract

The application discloses a preparation process of low-agglomeration SiC water-based granulation powder suitable for pressureless sintering, and belongs to the technical field of silicon carbide powder granulation. In view of the defects of the existing water-based granulation process, such as hydrophilic agglomeration of SiC powder, poor stability of slurry, insufficient sintering activity of granulation powder and inability to meet the densification requirement of pressureless sintering, the micron-sized SiC powder is first subjected to surface modification by using argon-oxygen mixed plasma to control the polarity of the surface hydrophilic group; then, an environmentally-friendly water-based system slurry is prepared, and full-component uniform dispersion is realized by combining graded variable-particle-size SiC grinding balls and intermittent temperature control ball milling; the spray granulation temperature field parameters are optimized, and screening classification and low-temperature inert calcination are matched to remove organic residues. The granulation powder prepared by the process has high sphericity, excellent fluidity and extremely low agglomeration rate, the uniformity of the mixture of the powder and sintering additives is greatly improved, the initial temperature of pressureless sintering is significantly reduced, and the holding time is shortened, and finally, the density of the pressureless sintered SiC ceramic is greater than or equal to 96%, and the process is suitable for large-scale production of semiconductor structure ceramics.

Description

Technical Field

[0001] This invention relates to the field of SiC powder granulation technology, specifically to a preparation process for low-agglomeration, high-flowability SiC water-based granulated powder, which is applicable to powder pretreatment in the fields of high-performance SiC ceramics and semiconductor substrate materials. Background Technology

[0002] SiC materials possess high strength, high hardness, high temperature resistance, corrosion resistance, and excellent electrical properties, making them widely used in aerospace, electronics, and new energy fields. Water-based granulation powder has become the mainstream pretreatment method for SiC powder forming due to its advantages such as being environmentally friendly, free of organic solvent pollution, and low cost.

[0003] Currently, most existing SiC water-based granulation processes employ a single ball milling + spray granulation method, which has the following technical drawbacks: First, SiC powder has a strong surface polarity, making it prone to agglomeration in an aqueous medium. Uniform dispersion is difficult to achieve during ball milling, resulting in uneven particle size distribution and high agglomerate content in the granulated powder. Second, the slurry stability is poor during granulation, easily leading to stratification and sedimentation, affecting the molding performance of the granulated powder. Third, the powder's flowability and bulk density are insufficient after spray granulation, easily causing uneven green body density and increased defects during subsequent molding, thus affecting the performance of the final SiC product.

[0004] Furthermore, the poor mixing uniformity of sintering aids and SiC powder in existing processes leads to insufficient sintering activity of the granulated powder, requiring higher temperatures and longer sintering times in subsequent processes, thus increasing production costs. Therefore, developing a process to overcome these shortcomings and achieve low agglomeration, high fluidity, and high sintering activity SiC water-based granulated powder has significant practical implications and application value. Summary of the Invention

[0005] The purpose of this invention

[0006] To address the shortcomings of existing technologies, this invention provides a preparation process for low-agglomeration, high-flowability SiC water-based granulated powder. By optimizing the dispersion, mixing, granulation, and post-processing processes, the invention solves the problems of severe agglomeration, poor flowability, and insufficient sintering activity in existing processes, thereby obtaining SiC water-based granulated powder with stable performance and suitable for subsequent molding processes.

[0007] Technical solution

[0008] A process for preparing low-agglomeration, high-flowability SiC water-based granulated powder includes the following steps:

[0009] S1. Powder pretreatment: Select SiC raw powder with D50 of 0.5-1.2μm, place it in a vacuum drying oven, and dry it at 105-115℃ for 2-4 hours to remove the moisture and impurities adsorbed on the powder surface; place the dried SiC powder in a plasma treatment device and treat it with argon-oxygen mixed plasma for 30-60 minutes, with a plasma power of 150-250W and a volume ratio of argon to oxygen of 3-5:1. After treatment, surface-modified SiC powder is obtained.

[0010] S2. Slurry preparation: Add deionized water to a mixing tank, then add dispersant and binder in sequence. Turn on the stirring device and stir for 15-25 minutes at a speed of 300-500 r / min to completely dissolve the dispersant and binder, thus obtaining a base solution. Slowly add the surface-modified SiC powder and sintering aid obtained in step S1 to the base solution, adjust the stirring speed to 800-1200 r / min, and stir for 30-40 minutes to obtain a preliminary mixed slurry.

[0011] S3. Multi-stage ball milling dispersion: The initially mixed slurry is transferred to a planetary ball mill and milled in stages. First, SiC milling balls with a diameter of 8-10 mm are added at a ball-to-material ratio of 3-4:1, and the speed is 200-300 r / min for 1-2 hours. Then, SiC milling balls with a diameter of 3-5 mm are added to bring the ball-to-material ratio to 5-6:1, and the speed is adjusted to 400-500 r / min. Milling continues for 2-3 hours to obtain a uniformly dispersed water-based slurry. During the milling process, the slurry temperature is controlled to not exceed 50℃ to avoid binder decomposition.

[0012] S4. Spray granulation: The water-based slurry obtained in step S3 is filtered through a 200-300 mesh sieve to remove undispersed large particles; the filtered slurry is fed into a centrifugal spray granulator, with the feed rate controlled at 3-5 kg / h, the atomizer speed at 10000-15000 r / min, the hot air inlet temperature at 220-260℃, and the hot air outlet temperature at 90-110℃, to perform spray granulation and obtain primary granulated powder;

[0013] S5. Post-processing: The primary granulated powder is placed in a vibrating screen and graded using 40-mesh and 200-mesh standard sieves, collecting the particles that pass through the 40-mesh sieve and those that pass through the 200-mesh sieve. The sieved particles are then placed in a vacuum drying oven and dried at 80-90℃ for 1-2 hours to remove residual moisture. Finally, the dried particles are placed in a low-temperature calcination furnace and calcined at 300-350℃ for 30-60 minutes to remove organic residues from the granulated powder, yielding the SiC water-based granulated powder product.

[0014] Further, in step S2, the dispersant is a compound system of tetramethylammonium hydroxide (TMAH) and polyethylene glycol (PEG4000), wherein the amount of TMAH added is 0.2-0.5% of the SiC powder mass, and the amount of PEG4000 added is 0.3-0.6% of the SiC powder mass; the binder is polyvinyl alcohol (PVA) with a degree of polymerization of 1700-1800 and a degree of hydrolysis of 86-88%, and the amount added is 1.5-3.0% of the SiC powder mass; the sintering aid is a mixture of alumina (Al2O3) and yttrium oxide (Y2O3) with a mass ratio of Al2O3 to Y2O3 of 3:2, and the amount added is 7-13% of the SiC powder mass; the solid content of the water-based slurry is controlled at 45-55%.

[0015] Furthermore, in step S3, an intermittent ball milling method is adopted during the ball milling process, with a 10-minute stop after every 30 minutes of ball milling to avoid excessively high slurry temperature; after the ball milling is completed, a laser particle size analyzer is used to detect the D50 of the powder in the slurry to ensure that the D50 is controlled within 0.8-1.5μm and that the particle size distribution is uniform.

[0016] Furthermore, in step S4, the hot air of the spray granulator adopts a circulating hot air system, and the hot air velocity is controlled at 1.5-2.5m / s to ensure that the granulated powder particles have regular morphology and smooth surface.

[0017] Beneficial effects

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. This invention modifies the surface of SiC raw powder with plasma, which can reduce the surface polarity of the powder, reduce the agglomeration of the powder in the aqueous medium, and improve the compatibility of the powder with dispersants and binders, laying the foundation for the uniform dispersion of subsequent slurries.

[0020] 2. The graded ball milling dispersion process is adopted. By using an intermittent ball milling method with a combination of ball milling balls of different sizes, the powder can be fully dispersed while avoiding powder breakage caused by over-milling. This ensures that the slurry is evenly dispersed and has good stability, and effectively reduces the agglomerate content of the granulated powder.

[0021] 3. By optimizing spray granulation parameters and combining them with grading, sieving, and low-temperature calcination post-treatment, the resulting granulated powder particles are regularly spherical with smooth surfaces, narrow particle size distribution (median particle size 10-100 μm), and a bulk density of 0.85-0.92 g / cm³. 3 It has an angle of repose of 22-28°, excellent fluidity, and is suitable for subsequent molding processes such as dry pressing and isostatic pressing.

[0022] 4. When the sintering aid is mixed evenly with the SiC powder, the sintering activity of the granulated powder is significantly improved, the subsequent sintering temperature can be reduced by 50-100℃, and the sintering time can be shortened by 30-60min, effectively reducing production costs while improving the density and mechanical properties of the final SiC product.

[0023] 5. The entire process uses a water-based system, with no organic solvent pollution, making it environmentally friendly and pollution-free. The process steps are simple and highly controllable, making it suitable for large-scale industrial production. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the process for preparing high-density, pressureless sintering SiC granulated powder using plasma-assisted water-based graded ball milling according to the present invention. The flowchart illustrates the following steps: S1 – Powder pretreatment (vacuum drying + plasma surface modification); S2 – Water-based slurry preparation (mixing of dispersant, binder, SiC powder, and sintering aid); S3 – Multi-stage temperature-controlled graded ball milling (coarse grinding of large balls → fine grinding of small balls, intermittent temperature control); S4 – Spray granulation (filtration + centrifugal spray drying); S5 – Post-treatment (grading and sieving + vacuum drying + low-temperature calcination to remove organic matter); → Obtaining low-agglomeration, high-sintering-activity SiC water-based granulated powder.

[0025] Figure 2 This is a schematic diagram illustrating the plasma modification and graded ball milling dispersion mechanism of the present invention. Figure descriptions: 1 – Original SiC powder (agglomerated state); 2 – Plasma treatment device (Ar-O2 plasma); 3 – SiC particles after surface modification (improved dispersibility); 4 – Graded ball milling (large-size grinding balls + small-size grinding balls); 5 – Water-based slurry system; 6 – Spherical SiC granulated powder particles obtained by spray granulation; 7 – Uniformly distributed composite sintering aid. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0027] Example 1:

[0028] A process for preparing low-agglomeration, high-flowability SiC water-based granulated powder includes the following steps:

[0029] S1. Powder pretreatment: Select SiC raw powder with D50 of 0.8μm, put it into a vacuum drying oven and dry it at 110℃ for 3h; put the dried SiC powder into a plasma treatment device and treat it with argon-oxygen mixed plasma for 45min, with a plasma power of 200W and a volume ratio of argon to oxygen of 4:1 to obtain surface modified SiC powder.

[0030] S2. Slurry Preparation: Deionized water was added to a mixing tank, followed by TMAH, PEG4000, and PVA. The stirring device was turned on, and the mixture was stirred at 400 r / min for 20 min to ensure complete dissolution of all components. Surface-modified SiC powder and sintering aid (Al2O3 to Y2O3 mass ratio 3:2) were slowly added to the base solution. The stirring speed was adjusted to 1000 r / min, and the mixture was stirred for 35 min to obtain a preliminary mixed slurry with a solid content of 50%. The amounts of TMAH, PEG4000, PVA, and sintering aid were 0.3% and 10% of the SiC powder mass, respectively.

[0031] S3. Multi-stage ball milling dispersion: The initially mixed slurry is transferred to a planetary ball mill. First, 9mm diameter SiC milling balls are added at a ball-to-material ratio of 3.5:1, and the milling speed is 250 r / min for 1.5 h. Then, 4mm diameter SiC milling balls are added to replenish the ball-to-material ratio to 5.5:1. The milling speed is adjusted to 450 r / min, and the milling continues for 2.5 h. Intermittent ball milling is used (stopping for 10 min every 30 min). The slurry temperature is controlled to not exceed 50℃. After the ball milling is completed, the D50 of the powder in the slurry is measured to be 1.2μm.

[0032] S4. Spray granulation: The ball-milled slurry is filtered through a 250-mesh sieve and fed into a centrifugal spray granulator. The feed rate is controlled at 4 kg / h, the atomizer speed is 12000 r / min, the hot air inlet temperature is 240℃, the hot air outlet temperature is 100℃, and the hot air velocity is 2.0 m / s to perform spray granulation and obtain primary granulated powder.

[0033] S5. Post-processing: The primary granulated powder is sieved through 40-mesh and 200-mesh standard sieves to collect intermediate particles; it is placed in a vacuum drying oven and dried at 85℃ for 1.5h; then it is placed in a low-temperature calcination furnace and calcined at 320℃ for 45min to obtain the SiC water-based granulated powder product.

[0034] Testing showed that the SiC water-based granulated powder prepared in this embodiment had an agglomerate content of ≤3% and a bulk density of 0.88 g / cm³. 3 With a repose angle of 25°, a median particle size of 55 μm, and uniform particle size distribution, the SiC ceramic was sintered at 1750℃ for 2 h to obtain a density ≥96%.

[0035] Example 2:

[0036] A process for preparing low-agglomeration, high-flowability SiC water-based granulated powder includes the following steps:

[0037] S1. Powder pretreatment: Select SiC raw powder with D50 of 0.5μm, put it into a vacuum drying oven and dry it at 105℃ for 4h; put the dried SiC powder into a plasma treatment device and treat it with argon-oxygen mixed plasma for 30min, with a plasma power of 150W and a volume ratio of argon to oxygen of 3:1 to obtain surface modified SiC powder.

[0038] S2. Slurry Preparation: Deionized water was added to a mixing tank, followed by TMAH, PEG4000, and PVA. The stirring device was turned on, and the mixture was stirred at 300 r / min for 25 min to ensure complete dissolution of all components. Surface-modified SiC powder and sintering aid (Al2O3 to Y2O3 mass ratio 3:2) were slowly added to the base solution. The stirring speed was adjusted to 800 r / min, and the mixture was stirred for 40 min to obtain a preliminary mixed slurry with a solid content of 45%. The amounts of TMAH, PEG4000, PVA, and sintering aid were 0.2% and 7% of the SiC powder mass, respectively.

[0039] S3. Multi-stage ball milling dispersion: The initially mixed slurry is transferred to a planetary ball mill. First, SiC milling balls with a diameter of 8 mm are added, with a ball-to-material ratio of 3:1. The speed is 200 r / min, and the milling is carried out for 2 hours. Then, SiC milling balls with a diameter of 3 mm are added to replenish the ball-to-material ratio to 5:1. The speed is adjusted to 400 r / min, and the milling is continued for 3 hours. Intermittent ball milling is used (stopping for 10 minutes every 30 minutes). The slurry temperature is controlled to not exceed 50℃. After the ball milling is completed, the D50 of the powder in the slurry is measured to be 0.8 μm.

[0040] S4. Spray granulation: The ball-milled slurry is filtered through a 200-mesh sieve and fed into a centrifugal spray granulator. The feed rate is controlled at 3 kg / h, the atomizer speed is 10000 r / min, the hot air inlet temperature is 220℃, the hot air outlet temperature is 90℃, and the hot air velocity is 1.5 m / s to carry out spray granulation and obtain primary granulated powder.

[0041] S5. Post-processing: The primary granulated powder is sieved through 40-mesh and 200-mesh standard sieves to collect intermediate particles; it is placed in a vacuum drying oven and dried at 80℃ for 2 hours; then it is placed in a low-temperature calcination furnace and calcined at 300℃ for 60 minutes to obtain the SiC water-based granulated powder product.

[0042] Testing showed that the SiC water-based granulated powder prepared in this embodiment had an agglomerate content of ≤2.5% and a bulk density of 0.85 g / cm³. 3With a repose angle of 22°, a median particle size of 40 μm, and uniform particle size distribution, the SiC ceramic was sintered at 1700℃ for 2.5 h to obtain a density ≥95.5%.

Claims

1. A process for preparing low-agglomeration SiC water-based granulated powder adapted to pressureless sintering, characterized in that, Includes the following steps: S1. Powder pretreatment: Select α-SiC powder with D50 of 0.5~1.2μm and purity ≥99.5%, and vacuum dry at 105~115℃ for 2~4h; treat with mixed plasma of argon-oxygen volume ratio of 3~5:1 for 30~60min at power of 150~250W to obtain surface-modified SiC powder; S2. Preparation of water-based slurry: Dissolve the compound dispersant and PVA binder in deionized water in sequence, stir evenly, add modified SiC powder and Al2O3-Y2O3 composite sintering aid, and stir to prepare a premixed slurry with a solid content of 45~55%. S3, Multi-stage temperature-controlled ball milling: It adopts a two-step staged ball milling process, first using 8~10mm large-size SiC grinding balls for low-speed coarse grinding, and then using 3~5mm small-size grinding balls for high-speed fine grinding; the entire process is intermittent grinding with temperature control ≤50℃ to avoid decomposition of organic components; S4. Precision spray granulation: The slurry is filtered through a 200-300 mesh filter and then fed into a centrifugal spray granulator. The inlet hot air is 220-260℃, the outlet is 90-110℃, and the atomization speed is 10000-15000r / min to prepare spherical primary granulated powder. S5. Post-processing purification: Classify by 40~200 mesh sieve, vacuum dry at 80~90℃, and then calcine at 300~350℃ for 30~60min to remove organic residues, and obtain the finished granulated powder suitable for pressureless sintering.

2. The preparation process according to claim 1, characterized in that: In step S2, the compound dispersant is a mixture of tetramethylammonium hydroxide and PEG4000, with addition amounts of 0.2~0.5% and 0.3~0.6% of the SiC powder mass, respectively; and 1.5~3.0% of the PVA with a degree of polymerization of 1700~1800 and a degree of hydrolysis of 86~88%.

3. The preparation process according to claim 1, characterized in that: Step S3: Total ball-to-material ratio 5~6:1, stop the machine for 10 minutes to cool after every 30 minutes of ball milling, and control the slurry D50 at the end of ball milling to 0.8~1.5μm.

4. The preparation process according to claim 1, characterized in that: Step S5: The calcination atmosphere is inert air with slow cooling to prevent oxidation defects on the surface of the granulated powder.

Images