High-purity cubic boron nitride micropowder with narrow particle size distribution and preparation method thereof

Abstract

The present application relates to a kind of high-purity narrow particle size distribution cubic boron nitride micro powder, the cubic boron nitride micro powder purity ≥99.5%, particle size is concentrated distribution 0.5-10 μm, particle size distribution span ≤0.8, single particle crystal form is uniform, surface defect ratio ≤3%, impact toughness ≥130J, thermal stability ≥1450 DEG C.The present application realizes the overall performance improvement of CBN micro powder, simultaneously improves synthesis efficiency, reduces environmental protection cost, and is suitable for high-end precision machining application.

Description

[0001] This invention belongs to the field of superhard material preparation technology, specifically relating to a high-purity cubic boron nitride micro powder with narrow particle size distribution and its preparation method. Background Technology

[0002] Cubic boron nitride (CBN) is a superhard material second only to diamond. It has extremely high thermal stability and excellent chemical inertness. It does not react with ferrous metals at high temperatures and is widely used in precision grinding, tool coating, semiconductor wafer polishing, superhard composite materials and other fields. It is an irreplaceable core material for high-end precision machining.

[0003] The commonly used methods for preparing CBN micron powder currently suffer from three major drawbacks: First, the synthesis conversion rate is low, with conventional processes achieving only 70%-80% conversion. Unreacted hBN (hexagonal boron nitride, a common crystal form of boron nitride) and residual catalysts are difficult to remove, resulting in a micron powder purity of less than 95%. These impurities affect processing precision and service life. Second, the particle size distribution is wide, with conventional pulverization and grading processes having a particle size distribution range >1.2. Large particles can easily scratch workpieces, while fine powders suffer from severe agglomeration, failing to meet the high-end demands of semiconductor polishing and ultra-precision grinding. Third, there are numerous crystal defects. Uneven crystal growth during the synthesis process leads to a high proportion of surface defects, reducing impact resistance, toughness, and thermal stability, thus limiting its application in high-speed precision machining. Furthermore, existing purification processes use large amounts of strong acids, resulting in significant environmental pressure and high production costs, which are not conducive to large-scale production.

[0004] Therefore, developing a high-purity CBN micro powder with narrow particle size distribution and few crystal defects, along with an environmentally friendly and efficient preparation process, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies. Addressing the technical problems of low purity, wide particle size distribution, numerous crystal defects, low synthesis conversion rate, and poor environmental friendliness of purification processes in existing CBN micro powders, this invention provides a high-purity cubic boron nitride micro powder with narrow particle size distribution and its preparation method. This aims to comprehensively improve the performance of CBN micro powder, while simultaneously increasing synthesis efficiency, reducing environmental costs, and making it suitable for high-end precision machining applications.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A high-purity cubic boron nitride micro powder with narrow particle size distribution, wherein the cubic boron nitride micro powder has a purity ≥99.5%, a particle size concentrated in the range of 0.5-10 μm, a particle size distribution span ≤0.8, uniform crystal shape of single particles, a surface defect ratio ≤3%, an impact toughness ≥130 J, and a thermal stability ≥1450℃.

[0007] A method for preparing the above-mentioned high-purity, narrow-particle-size cubic boron nitride micro powder includes the following steps: S1 raw material pretreatment: Hexagonal boron nitride powder, composite lithium catalyst, nano CBN seed crystals and interface activator are mixed, ball-milled and sieved to obtain a uniform composite raw material. S2 High Temperature and High Pressure Synthesis: The composite raw materials are loaded into the synthesis column and placed in a six-sided top press. The synthesis pressure is set to 5.5-7.5 GPa and the synthesis temperature is set to 1550-1700℃. The temperature and pressure are maintained for 25-50 min to complete the phase transformation of HBN to CBN and obtain the synthesized green body. S3 Multi-stage Purification: After the synthetic green body is crushed, it is successively subjected to acid leaching, electrolytic purification and ultrasonic water washing to remove residual catalyst, unreacted HBN and impurities. After drying, purified CBN coarse powder is obtained. S4 Precision Grading: After the purified coarse CBN powder is pulverized by airflow, a multi-stage airflow grading process (the blower and grading wheel are adjusted to separate the powder into four stages) + ultrasonic sieving process is adopted to obtain narrow-distribution CBN micro powder with the target particle size. The finished product is obtained by vacuum packaging.

[0008] Specifically, in step S1, hexagonal boron nitride powder, composite lithium catalyst, nano CBN seed crystals, and interface activator are mixed in a mass ratio of 75-85:10-18:2-5:0.1-0.3, ball-milled and dispersed for 2-4 hours, and passed through a 200-300 mesh sieve to obtain a uniform composite raw material.

[0009] Furthermore, in step S1, the composite lithium catalyst is composed of Li3BN2, Li3N, and LiNH2 in a mass ratio of 4-6:2-4:1-3, with a preferred mass ratio of 5:3:2.

[0010] Furthermore, in step S1, the particle size of the nano-CBN seed crystals is 80-120 nm; the interface activator is boric acid.

[0011] Furthermore, in step S2, the synthesis column adopts a double-layer sealed structure, with the inner layer being a boron nitride crucible and the outer layer being a graphite heating jacket. The synthesis process adopts a linear pressure-temperature curve with a pressure increase rate of 0.2-0.3 GPa / min and a temperature increase rate of 80-100℃ / min.

[0012] Furthermore, in step S3, dilute hydrochloric acid is used for acid leaching, with a concentration of 1.5-2.5 mol / L, an acid leaching temperature of 60-80℃, and an acid leaching time of 3-5 hours.

[0013] Furthermore, in step S3, electrolytic purification uses a titanium electrode, with a current density of 15-25 mA / cm² and a purification time of 1.5-2.5 h.

[0014] Furthermore, in step S4, the airflow classification (pulverization) pressure is 0.4-0.6MPa, the induced draft parameters are 30-45Hz, the first-stage classifier parameters are 15-25Hz, the second-stage classifier parameters are 15-35Hz, the third-stage classifier parameters are 20-40Hz, the fourth-stage classifier parameters are 20-40Hz, and the classification accuracy is ±0.5μm; the ultrasonic sieving frequency is 20-40kHz, and the sieving time is 20-30min.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1) Excellent performance: The CBN micro powder of this invention has a purity of ≥99.5%, a particle size distribution range of ≤0.8, uniform crystal shape, few surface defects, and significantly improved impact toughness and thermal stability. It is suitable for high-end scenarios such as semiconductor polishing and ultra-precision grinding, and the processing accuracy and service life are improved by more than 30%. 2) High conversion rate: The composite lithium catalyst combined with nano CBN seeds precisely controls the phase transformation process, increasing the synthesis conversion rate to over 90%, significantly improving raw material utilization and reducing production costs; 3) Environmentally friendly process: The process adopts a combination of low-concentration dilute hydrochloric acid leaching and electrolytic purification, which greatly reduces the amount of strong acid used, has no harmful gas emissions, meets environmental protection production requirements, and is suitable for large-scale mass production. 4) Precise grading: The combination of multi-stage airflow grading and ultrasonic sieving process accurately controls particle size distribution, avoids fine powder agglomeration, has excellent micro powder dispersibility, and strong product consistency. Attached Figure Description

[0016] Figure 1 This is a flow chart of the CBN micro powder preparation process of the present invention; the chart clearly shows the complete preparation process of the present invention, with clear connections between each step, reflecting the core process design of environmentally friendly purification and precise classification. Figure 2 This is a particle size distribution diagram of the CBN micro powder prepared in Example 2 of the present invention; Figure 3 This is a SEM characterization image of the crystal form of the CBN micropowder prepared in Example 2 of the present invention. Detailed Implementation

[0017] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0018] In the following examples, all raw materials used are commercially available products in the field that can be directly purchased, or can be prepared using conventional techniques in the field. For example, hexagonal boron nitride (hBN) can be purchased online or offline from manufacturers in the field; in the examples, the product used is from Henan Nitrogen Boron New Materials Technology Co., Ltd.; 100nm and 90nm nano-CBN seed crystals are products sold by Zhengzhou Zhongnan Jiete and are prepared by high-pressure direct phase transition method. Example 1

[0019] A method for preparing high-purity cubic boron nitride micro powder with narrow particle size distribution (process flow diagram is shown) Figure 1 ), including the following steps: S1 Raw material pretreatment: 80 parts of hexagonal boron nitride powder, 15 parts of composite lithium catalyst (Li3BN2:Li3N:LiNH2=5:3:2, mass ratio), 4 parts of 100nm nano CBN seed crystals, and 0.2 parts of boric acid were mixed, ball-milled and dispersed for 3 hours, and passed through a 250-mesh sieve to obtain a uniform composite raw material. S2 High Temperature and High Pressure Synthesis: The composite raw materials are loaded into a double-layer sealed synthesis column and placed in a six-sided top press. The pressure is linearly increased to 6.2 GPa and the temperature is increased to 1620℃. The temperature and pressure are held for 35 min to obtain the synthesized green body. The synthesis column adopts a double-layer sealed structure, with a boron nitride crucible as the inner layer and a graphite heating jacket as the outer layer. The synthesis process adopts a linear pressure and temperature increase curve with a pressure increase rate of 0.2 GPa / min and a temperature increase rate of 85℃ / min. S3 Multi-stage purification: After the synthetic green body is crushed, it is acid-leached with 2 mol / L dilute hydrochloric acid at 70℃ for 4 hours, purified by titanium electrode electrolysis for 2 hours (current density 20mA / cm²), ultrasonically washed with water until neutral, and dried at 120℃ to obtain purified CBN coarse powder. S4 Precision Grading: Air pressure is adjusted to 0.5MPa, induced draft is adjusted to 40Hz, primary grading wheel parameters are 20Hz, secondary grading wheel parameters are 30Hz, tertiary grading wheel parameters are 35Hz, and quaternary grading wheel parameters are 40Hz. After the purified coarse CBN powder is pulverized by airflow at 0.5MPa, the powder is drawn out and passed through the primary, secondary, tertiary, and quaternary grading wheels to divide the powder into four particle size ranges. The corresponding powder (tertiary material) is selected for ultrasonic sieving, and finally the corresponding narrow distribution CBN micro powder is obtained with a grading accuracy of ±0.5μm. Ultrasonic sieving at 35kHz for 30min yields 1-3μm narrow distribution CBN micro powder, which is then vacuum packaged.

[0020] The CBN micro powder prepared in this embodiment has the following characteristics: purity 99.7%, particle size distribution range 0.65, surface defect ratio 2.1%, impact toughness 138J, thermal stability 1460℃, and synthesis conversion rate 93.2%. Example 2

[0021] A method for preparing high-purity cubic boron nitride micro powder with narrow particle size distribution includes the following steps: S1 Raw material pretreatment: 78 parts of hexagonal boron nitride powder, 17 parts of composite lithium catalyst (Li3BN2:Li3N:LiNH2=5:3:2, mass ratio), 4.5 parts of 90nm nano CBN seed crystals and 0.25 parts of boric acid were mixed, ball-milled and dispersed for 3.5h, and passed through a 300-mesh sieve to obtain a uniform composite raw material; S2 High Temperature and High Pressure Synthesis: The composite raw materials are loaded into a double-sealed synthesis column and placed in a six-sided top press. The pressure is linearly increased to 7.0 GPa and the temperature is increased to 1680℃. The temperature and pressure are held for 45 min to obtain the synthesized green body. The synthesis column adopts a double-sealed structure, with a boron nitride crucible as the inner layer and a graphite heating jacket as the outer layer. The synthesis process adopts a linear pressure and temperature increase curve with a pressure increase rate of 0.3 GPa / min and a temperature increase rate of 95℃ / min. S3 Multi-stage purification: After the synthetic green body is crushed, it is acid-leached with 2.2mol / L dilute hydrochloric acid at 75℃ for 4.5h, purified by titanium electrode electrolysis for 2.2h (current density 22mA / cm²), ultrasonically washed with water until neutral, and dried at 120℃ to obtain purified CBN coarse powder. S4 Precision Grading: Air pressure is adjusted to 0.55MPa, induced draft is adjusted to 40Hz, primary grading wheel parameters are 18Hz, secondary grading wheel parameters are 24Hz, tertiary grading wheel parameters are 32Hz, and quaternary grading wheel parameters are 36Hz. After the purified coarse CBN powder is pulverized by airflow at 0.55MPa, the powder is drawn out and passed through the primary, secondary, and tertiary grading wheels to separate the powder into four particle size ranges. The corresponding powder (secondary material) is selected for ultrasonic sieving, and finally the corresponding narrow distribution CBN micro powder is obtained with a grading accuracy of ±0.5μm. Ultrasonic sieving at 30kHz for 25min yields 4-8μm narrow distribution CBN micro powder, which is then vacuum packaged.

[0022] The CBN micro powder prepared in this embodiment has the following characteristics: purity 99.6%, particle size distribution range 0.63, surface defect ratio 2.5%, impact toughness 135J, thermal stability 1455℃, and synthesis conversion rate 92.8%.

[0023] Figure 2 The particle size distribution diagram of the CBN micro powder prepared in Example 2 of the present invention is given. Figure 2 The results show that the CBN micro powder prepared by this invention has a particle volume ratio of 80% with a particle size of 4.18 μm-7.73 μm and a particle volume ratio of 90% with a particle size of 3.86 μm-8.65 μm. The particle size is concentrated and uniformly distributed, which fully meets the requirements of semiconductor polishing and ultra-precision grinding for narrow particle size distribution.

[0024] Figure 3 The SEM characterization image of the crystal form of the CBN micropowder prepared in Example 2 of this invention is given. Figure 3 This invention demonstrates the advantages of CBN micropowder prepared by the present invention, which has a more complete crystal shape and fewer surface defects, thereby effectively improving the impact toughness and thermal stability of the micropowder.

[0025] Comparative example (existing conventional process)

[0026] Conventional process: Using hBN (hexagonal boron nitride) as raw material and Li3N as catalyst, a synthetic preform is obtained under pressure of 5.0 GPa, temperature of 1500℃, and holding time of 150 s. After crushing the synthetic preform, it is purified by sodium hydroxide at 300℃ and rinsed. It is then purified by heating with 99.8% concentrated acid at 200℃ and rinsed until neutral. CBN micropowder is prepared by wet method (dispersion in pure water) and fractionation. Taking the prepared 4-8 μm as an example, the following results were obtained: purity 95.2%, particle size distribution range 1.35, surface defect ratio 8.7%, impact toughness 102 J, thermal stability 1380℃, and synthesis conversion rate 78.5%.

[0027] The comparison shows that the CBN micro powder prepared by this invention has significantly better performance indicators than existing conventional processes, demonstrating outstanding advantages.

Claims

1. A high-purity, narrow-particle-size cubic boron nitride micro powder, characterized in that, The cubic boron nitride micro powder has a purity of ≥99.5%, a particle size distribution concentrated between 0.5-10μm, a particle size distribution span of ≤0.8, uniform crystal shape of single particles, a surface defect ratio of ≤3%, an impact toughness of ≥130J, and a thermal stability of ≥1450℃.

2. The method for preparing the high-purity, narrow-particle-size cubic boron nitride micropowder according to claim 1, characterized in that, Includes the following steps: S1 mixes hexagonal boron nitride powder, composite lithium catalyst, nano CBN seed crystals, and interface activator, then ball-mills and sieves to obtain a uniform composite raw material. S2 The composite raw materials are loaded into the synthesis column and placed in a six-sided top press. The synthesis pressure is set to 5.5-7.5 GPa and the synthesis temperature is set to 1550-1700℃. The temperature and pressure are maintained for 25-50 minutes to obtain the synthesized green body. After being crushed, the S3 synthetic preform is subjected to acid leaching, electrolytic purification, ultrasonic water washing, and drying to obtain purified CBN coarse powder. S4 Precision Grading: After the purified coarse CBN powder is pulverized by airflow, a multi-stage airflow classification + ultrasonic sieving process is used to grade it into narrow-distribution CBN micro powder with the target particle size, which is then vacuum-packaged to obtain the finished product.

3. The preparation method according to claim 1, characterized in that, In step S1, hexagonal boron nitride powder, composite lithium catalyst, nano CBN seed crystals, and interface activator are mixed in a mass ratio of 75-85:10-18:2-5:0.1-0.3, ball-milled and dispersed for 2-4 hours, and passed through a 200-300 mesh sieve to obtain a uniform composite raw material.

4. The preparation method according to claim 1, characterized in that, In step S1, the composite lithium catalyst is composed of Li3BN2, Li3N, and LiNH2 in a mass ratio of 4-6:2-4:1-3.

5. The preparation method according to claim 1, characterized in that, In step S1, the particle size of the nano-CBN seed crystals is 80-120 nm; the interface activator is boric acid.

6. The preparation method according to claim 1, characterized in that, In step S2, the synthesis column adopts a double-layer sealed structure, with a boron nitride crucible as the inner layer and a graphite heating jacket as the outer layer. The synthesis process adopts a linear pressure and temperature rise curve, with a pressure rise rate of 0.2-0.3 GPa / min and a temperature rise rate of 80-100℃ / min.

7. The preparation method according to claim 1, characterized in that, In step S3, dilute hydrochloric acid is used for acid leaching, with a concentration of 1.5-2.5 mol / L, an acid leaching temperature of 60-80℃, and an acid leaching time of 3-5 hours.

8. The preparation method according to claim 1, characterized in that, In step S3, electrolytic purification is performed using a titanium electrode with a current density of 15-25 mA / cm² and a purification time of 1.5-2.5 h.

9. The preparation method according to claim 1, characterized in that, In step S4, the airflow classification pressure is 0.4-0.6MPa, the classification accuracy is ±0.5μm, the ultrasonic sieving frequency is 20-40kHz, and the sieving time is 20-30min.

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