China's cubic boron nitride industry has developed for 50 years (1966~2016)

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Abstract Cubic boron nitride (CBN) is a typical III-V compound. It is a synthetic inorganic crystalline material. There is no primary ore in nature. In 1957, RHwentorf of General Electric Company of the United States used hexagonal boron nitride as raw material,...
Cubic boron nitride (CBN) is a typical III-V compound and is a synthetic inorganic crystalline material. There is no primary mineral in nature. In 1957, RHwentorf of General Electric Company of the United States synthesized the world's first CBN crystal under static ultra-high pressure and high temperature conditions using hexagonal boron nitride as raw material, alkali metal or alkaline earth metal and its nitride as catalyst. It has a zinc blende structure, hardness second only to diamond, good thermal stability and chemical stability, can withstand high temperatures above 1000 °C and is resistant to acid and alkali, and is chemically inert to iron elements at high temperatures, making up for the deficiency of diamond. Both form the perfect family of superhard materials that not only serve as abrasive materials for all materials in the world, but also have a wide range of functional uses.
At present, in terms of engineering materials, CBN is mainly used as super abrasive. It is the first choice for processing various steel, cast iron, nickel-based and cobalt-based alloys, especially in the field of modern precision machining, such as automotive, aerospace, precision machinery, microelectronics, etc. In the precision industry, it is an indispensable material for high efficiency, ultra-precision, energy saving and operation automation. Secondly, in terms of functional materials, CBN is an excellent semiconductor material, which can be made into high temperature resistant CBN-PN junction and light emitting diode. It can be used as an excellent anti-oxidation coating and optical window material. CBN crystals are also widely used in electro-optical crystals with a wide spectrum of applications, and have a very broad application prospect.
The methods for synthesizing CBN crystals include high temperature and high pressure catalyst method, high temperature and high pressure direct phase transformation method, high temperature and high pressure temperature gradient method, hydrothermal synthesis method and gas phase method. The catalyst method and the temperature gradient method are commonly used in the above methods, and the gas phase method is mainly used for film growth. At present, the high temperature and high pressure catalyst method is an industrial synthesis method that has an absolute advantage.

The first quarter is ready to take off
After the first CBN was successfully manufactured in the United States, by the 1960s, the former Soviet Union, Germany, Japan, and the United Kingdom successively synthesized the first CBN of each country. On the basis of synthesizing the first synthetic diamond in China, Lu Feixiong of Sanmao Institute carried out high-pressure synthesis research of CBN. In November 1966, the first cubic nitriding of China was synthesized on a 61-type two-face press. boron.
In the 1980s, the development of precision manufacturing and processing technology in Japan established a large number of consensuses on the use of CBN tools, and fully developed the application technology of CBN. This forward-looking work has brought the level of precision manufacturing industry in Japan to catch up with the United States. Since the 1980s, industrialized countries have developed CBN as an important material for high efficiency, energy conservation, ultra-precision and operational automation. CBN is developing very rapidly, with annual production growth of over 15%, and sales growth is almost in sync.
In the past 50 years of development, it has experienced several stages of development. China's cubic boron nitride has continued to grow and develop, its technical level has been continuously improved, its output has become higher and higher, and its market share has become larger and larger. It has become the world's cubic boron nitride production. The big country is becoming a strong country.

First, from scratch, slow development
About 20 years from 1966 to the mid-1980s was a period of slow development.
After the advent of cubic boron nitride in China in 1966, due to technical stability limitations at the time, coupled with weak basic industries, the mechanical industry was backward, and industrial demand was not as urgent as diamond. By 1970, it was only used in the machining of some tools. The cubic boron nitride catalyst composite material has only a single metal magnesium. The synthesis technology and production development are very slow. Only a type I product with grayish black and poor crystal form such as "cinder" can be produced; the synthesis chamber is small. The maximum cavity diameter is only Φ14mm; the yield is low and the synthesis stability is poor. There are only a few state-owned units engaged in CBN testing and production, such as Sanmao, Sixth Grinding Wheel, and Second Grinding Wheel. Until 1980, the total output of cubic boron nitride in the country was only over 600,000 carats in 10 years, and the gap between production and application level was significant. In 1983, the CBN-I type of cubic boron nitride of the sixth grinding wheel factory reached more than 2.4 carats, 150# was more than 64% in coarse proportion, and the compressive strength of 80# was above 2 kg/cm2. It produced CBN fine powder for China. CBN tools and CBN tools provide high-quality raw materials and contribute to the technological development of the industry.

Second, research and active results frequently
From the mid-1980s to the mid-1990s, about 10 years.
In the 1980s, with the reform and opening up, the development of automobiles, aerospace, mechatronics, microelectronics and other industries has injected new vitality into the development of cubic boron nitride in China. Foreign technical exchanges have become active, with frequent exchanges with Japan, the United States, and the former Soviet Union.
In 1983, the Japanese National Institute of Inorganic Materials, Fu Changxiu, visited the Sanmao Institute, and gave a technical lecture and exchange on cubic boron nitride synthesis. The topic of the new compound catalyst and how to synthesize the cubic boron nitride crystal was explained. .
In 1987, Yuan Tengzhong, a researcher at the Institute of Inorganic Materials, came to Sanmill's cubic boron nitride synthesis technology report, pointing out that high-quality composite boron nitride must be used in the synthesis of high-grade cubic boron nitride such as Mg3B2N4, Ca3B2N4, Sr3B2N4, Ba3B2N4, etc. The synthesis test was carried out on a hinged six-face press. The research on China is very inspiring.
Several key research institutes such as Sanmao Institute, Jilin University, and Changchun Institute of Applied Chemistry of the Chinese Academy of Sciences have begun to attach importance to and increase investment in the research of cubic boron nitride synthesis technology. Through the development and research of raw materials, catalysts and synthetic technologies, new catalysts have been used to make progress, and a series of scientific research results have been produced to synthesize high-grade cubic boron nitride of various colors, and gradually move from laboratory to small batches. Try the transition.
During this period, a strong representative research team emerged:
Research team of Professor Wang Guangzu from Sanmao. Professor Wang Guangzu directed the postgraduate Zhang Xiangfa to carry out systematic research on the influence of hexagonal boron nitride performance on cubic boron nitride synthesis, and to develop novel boron nitride catalysts, synthetic amber, black and other varieties of cubic boron nitride. In 1991 and 1993, Professor Wang Guangzu and Zhang Xiangfa graduate students reported at the 6th and 7th National High-Volume Academic Symposiums, including: "The Effect of Crystallinity of Hexagonal Boron Nitride on Cubic Boron Nitride Synthesis", "Mg- The effect of B2O3 on the growth of CBN crystals in BN series, the performance characteristics of several typical HBNs at home and abroad, the synthesis of water white CBN crystals under high temperature and high pressure, and the recrystallization of HBN under high pressure and high temperature. The production and research team of Xu Guotai senior engineer and Liu Xianghui engineer carried out research on magnesium-based multi-alloy catalyst. In December 1989, the high-quality CBN synthesis system process was identified by the scientific and technological achievements of the Ministry of Machinery, and the black type II CBN was put into production.
Research team of Professor Zhang Tiechen and lecturer of Ma Wenjun from Jilin University. At the 6th and 7th National High Voltage Academic Symposiums in 1991 and 1993, the report included: "Synthesis and Heat Resistance of Different Color Cubic Boron Nitride", "Large Granular Cubic Boron Nitride" Crystal Synthesis, "Effects of Oxidation Characteristics of Hexagonal Boron Nitride on Cubic Boron Nitride Synthesis", "Metal Film in Cubic Boron Nitride Synthesis", and CBN in Me-BN (Me=Mg, Ca) System Growth Mechanism, "The Effect of MgO on the Synthesis of CBN Using Mg Catalysts", "Synthesis of Millimeter Single Crystals in Mg-BN System", "Color of High Pressure Synthetic CBN", "A New Way to Improve the Production of Cubic Boron Nitride" The way of assembly and other research papers and research results.
Research team of Yan Xuewei, researcher and researcher of Cui Shuojing, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. In 1988, he published a paper entitled "New Catalytic Materials for High-Pressure Synthesis of Cubic Boron Nitride", which is the first paper on the synthesis of new catalytic materials Mg3B2N4 and Ca3B2N4 for cubic boron nitride. The follow-up research results and samples are in Lushan National Cubic boron nitride industry seminar and release at the 6th and 7th National High Voltage Symposium, including: "Study on HBN-CBN Conversion Behavior under High Pressure and High Temperature", "Vibration and Reflectance Spectra of Cubic Boron Nitride Research, "The distribution of pressure and temperature in cubic high-pressure cubic boron nitride synthesis chamber, dynamic process and its influence on products", "High-pressure synthesis of milky white cubic boron nitride" and other research results.
In addition, Li Xiangyao of Beijing Yanjiao Superhard Materials Research Institute is also engaged in the synthesis of amber CBN, and has done a lot of useful work in product development.
In the early 1990s, Professor Wang Guangzu and then General Manager of Zhengzhou Erqi Superhard Materials Co., Ltd. Wu Zhiying convened and organized three national cubic boron nitride industry seminars in Zhengzhou, Chongqing--Three Gorges and Lushan. The above research units and Shanghai Silicon Experts and representatives from the Salt Mine Institute, Changsha Mine, Second Grinding Wheel Factory, Sixth Grinding Wheel Factory, Suzhou Grinding Wheel Factory, Shanghai Grinding Wheel Factory attended the meeting. Amber samples were displayed at the meeting. The meeting minutes were called “Jilin University, Changchun”. The Institute of Applied Chemistry and the Sanma Institute first synthesized amber CBN single crystals, which ended the single, long-term stagnation of cubic boron nitride products, which made the research and production of cubic boron nitride a new step."
So far, China has mastered the advanced new boron nitride catalyst and multi-alloy catalyst technology, which can synthesize amber, light yellow, light white and brown CBN crystals except black type I and type II CBN products.
From 1991 to 1993, in order to help readers have a comprehensive and systematic understanding of the research content, level and development of foreign cubic boron nitride and its polycrystals, Wei Fengwu, editor of Abrasives and Grinding Magazine, should be invited. Wang Guangzu wrote "The Development Technology of Foreign Cubic Boron Nitride", which has 12 episodes, totaling about 60,000 words.
"Calcium Boron Nitride" written by Zhang Tiechen and Zou Guangtian (published by Jilin University Press), and "Synthesis and Application of Cubic Boron Nitride" by Wang Guangzu, Li Gang and Zhang Xiangfa (Henan Science and Technology Press published and obtained by Henan Science and Technology Publishing) The second prize) and the serialization of the publication, the positive role played by promoting the technological progress of China's cubic boron nitride research and production is self-evident!

Third, the market demand scale production
This stage has been a period of great development of China's CBN since the mid-1990s.
With good technical results, then the transformation to production is an inevitable choice. Due to high production costs and the market has not been fully developed, in 1994, Sanmao wanted to establish a CBN production base in Zhengzhou High-tech Zone, cooperation between Changchun Yinghua and FAW Transmission Shaft Factory, and Jilin University and Shenzhen Shenda Superhard Materials Co., Ltd. Co-production of CBN has not been implemented.
Although the annual production of CBN production has increased from 100,000 carats in 1985 to more than 500,000 carats in 1990 and more than 1.2 million carats in 1995, it has shown a clear growth trend, but the market and applications have not been pushed open. In terms of price, in 1990, the price of amber CBN was above 10 yuan/carat, and the price of ordinary type 1 black CBN was 3-4 yuan/carat. The high price also hindered the promotion and application of CBN.
At the end of the 1990s, the large-scale development of diamond presses was also reflected in the production technology of CBN. The large cavity reduces the manufacturing cost, and the price of the hexagonal boron nitride raw material decreases, and the price of the CBN decreases. Zhang Xiangfa and Zhang Kui have developed a synthetic technology for Φ25mm cavity high toughness CBN, and put it into production at Henan Huanghe Group Co., Ltd., with a yield of more than 12 carats, and the products are exported to the Japanese market with good cost performance.
In the 21st century, the large-scale and automation of the six-face press machine, the in-depth study of hexagonal boron nitride and catalyst, the gradual improvement of the synthetic process technology, and the rapid development of cubic boron nitride production. The rapid development of the automotive industry and the aerospace industry, the increasingly strong market demand has also played a strong role in the development of cubic boron nitride. The output of CBN has experienced rapid growth, with an annual growth rate of 100% for many years. In 2002, the annual output of CBN nationwide exceeded 100 million carats.
The professional companies producing CBN are mainly concentrated in Henan. Henan Fenike Superhard Material Co., Ltd. (formerly known as Wuyi County Superhard Material Factory established in 1988), started production of CBN by technology transfer of Sanmao, and moved to Zhengzhou High-tech Zone in 1995, which is a new round of CBN in China. An early CBN professional manufacturer that emerged in the tide of development. With its excellent operational capability, the company began to enter the international market with high cost performance. Its products were once in short supply, seeking to expand processing capacity on behalf of processing, and now the annual output exceeds 100 million carats. Zhengzhou Zhongnan Jiete Superhard Materials Co., Ltd. (established in 2000 by Zhang Kui and other cooperation with Zhongnan Diamond Co., Ltd.), the company's mature technology combined with the solid management style of the old military factory, began to enter the market in 2001. After more than 10 years of development, the annual production has exceeded 100 million carats. In addition, Henan Feimeng Diamond Industry Co., Ltd. and Zhengzhou Shenfa Superhard Materials Co., Ltd. each have a certain scale of CBN production capacity.

The second quarter is a strong development of the big country dream circle
First, the output leading edge is obvious
In the 21st century, China's CBN production has grown rapidly, from 100 million carats in 2002 to 200 million carats in 2005, and 300 million carats in 2010. China's CBN development has entered a benign track, according to the China Machine Tool Association Superhard Materials Branch. In 2012, China's CBN production was 380 million carats, accounting for 60% of the global total. More than 90% of the output is mainly concentrated in Henan Fenike Superhard Materials Co., Ltd., Zhengzhou Zhongnan Jiete Superhard Materials Co., Ltd. and Henan Feimeng.

Second, the technological progress is changing with each passing day (1) Touching the independent innovation of the media department
There are many kinds of catalysts for synthesizing CBN, and the catalysts mainly used for industrial synthesis of CBN are simple substances of alkali metals or alkaline earth metals, nitrides and boron nitrogen compounds. Such as lithium, lithium nitride (Li3N), lithium borohydride (Li3BN2); magnesium, magnesium nitride (Mg3N2), magnesium borohydride (Mg3B2N4); calcium, calcium (Ca3N2), calcium borohydride (Ca3B2N4) ) Wait. Because different catalysts have their own characteristics: such as different synthesis pressure and temperature; CBN crystal crystal form, defects and particle size are different; synthetic CBN color is different; the stability of the catalyst itself is different. They are usually mixed or re-formed into a composite for use as a catalyst in production.
From the 1970s to the end of the 1980s, Mg has been the mainstream catalyst for the synthesis of primary CBN in China.
In the mid-1990s, China paid more attention to the research and development of nitrogen-boride composite catalysts, and synthesized amber CBN with better crystal form and higher strength.
In the new century, in response to the needs of the international market, a touch media system suitable for the synthesis of black and brown CBN crystals has been developed. At present, each family has formed a color that can be synthesized - light yellow, yellow, orange red, brown and black; a series of touch media systems with toughness from brittle, medium toughness to high toughness CBN. Some enterprises have more than 60 varieties and grades, and they have begun to lead the world in this field.
(2) Structural optimization cavity expansion
Through the optimization of assembly structure, the temperature and pressure gradient in the cavity are reduced, and the growth density is uniform. The best level of CBN per unit volume growth can reach 5 ct/cc; the conversion rate of some high-yield CBN varieties reaches 70%.
Taking the Φ550 cylinder diameter press as an example, the maximum yield of the Φ40 cavity can reach 160 carats. The Φ650 cylinder diameter press can be used to synthesize CBN with a yield of more than 200 carats.
With the expansion of the CBN market, the diversified needs of users have led to the diversification of CBN synthesis processes. In terms of particle size, there are large particle CBN synthesis process, coarse particle synthesis process, fine particle synthesis process; high toughness synthesis process and brittle synthesis process in terms of toughness; in the form of crystal form, there is an isoform synthesis process and a sheet-like synthesis process. and many more.
(3) The raw materials are cheap and applicable
Due to the gradual increase in China's CBN production, the consumption of HBN for CBN synthesis has also increased year by year, and the current annual consumption is close to 200 tons. The domestic HBN product powder is mainly prepared by three methods: borax ammonia chloride method, borax urea method and borax melamine method. Its purity, impurity content, particle morphology, crystallinity and other properties are different from those of foreign products, but it is suitable for China's national conditions, and better meets the needs of CBN single crystal synthesis at present, and its high cost performance is to synthesize multiple varieties. The affordable CBN provides material assurance.
In recent years, some manufacturers have adopted a new process to produce high-purity and large-diameter HBN with a BN content of more than 99.5%. The crystals are relatively complete and regular, and the particle size is larger than 3 microns. The crystallinity GI value reached 1.6. After the secondary high temperature treatment, the maximum particle size can reach 20 microns, which is expected to be used in CBN synthesis.

Third, the variety is well-known worldwide
With the advancement of CBN synthesis technology in China, there are more than 60 kinds of product varieties and they are still increasing, and the available sizes of some varieties are 20/30.
In addition, in order to improve the combination of CBN abrasive and binder, and improve the thermal stability of the abrasive, the surface of the CBN abrasive is coated, nickel-plated and titanium-plated. As a derivative, China's CBN plating products are also developing very fast. Several large companies have their own nickel and titanium plating grades.
With the use of precision processing and PCBN synthesis, the rapid growth of the overall PCBN polycrystals has also grown simultaneously.
The series of CBNs enjoys a high reputation internationally.

Fourth, the application of a wide range of supply and demand
The largest application of CBN products is in the manufacture of CBN grinding wheels. Among the four binders (resin, ceramic, metal, electroplating) of CBN grinding wheels, CBN grinding tools with ceramic bonding agents are the fastest growing. Worldwide, the proportion of ceramic CBN abrasives has increased from 4% in the 1980s to more than 50% today, and the growth rate is rapid. Because ceramic CBN grinding tools have high grinding efficiency, good shape retention, high durability, easy dressing, high abrasive utilization rate (more than 75%, other types of bonding agent is 50-60%), long service life of grinding wheel, etc. Therefore, it is the first choice for efficient and high-precision grinding. Applications include automotive, aerospace, oil pump nozzles, compressors and more. In recent years, CBN application promotion has made great progress, and the use of manufacturers has increased rapidly. With incomplete statistics, there are more than 500 manufacturers of CBN in China, and the single manufacturer uses more than 4 million carats.
Secondly, domestic PCBN tools have experienced many years of development and have formed a certain scale. Especially in the past five years, the rapid development of the overall PCBN tools has led to a significant increase in the use of CBN micropowder. Several manufacturers of CBN single crystals have joined the synthesis to varying degrees. The ranks of PCBN, which also led to a steady increase in the production of CBN single crystals.
Foreign tool manufacturers have proved through a large number of application practices in recent years that China's CBN products are stable and reliable, and can fully meet the requirements of use. The export volume of CBN also increased rapidly, and some manufacturers' export and internal sales were basically equal. Therefore, the export volume of China's CBN can be seen.
In summary, China's CBN production is evaluated in terms of quantity, quality and market share: not only a large producing country, but also a strong country.

The third section looks forward to the future prospects.
(1) In order to realize the serialization of CBN product varieties and to adapt to different uses, we have carried out in-depth research on the preparation of two basic raw materials of CBN, namely hexagonal boron nitride and catalyst, especially catalyst. Because the study of catalysts plays a crucial role in the development of product varieties and their impact on performance.
(2) The development level of grinding wheel manufacturing technology and CBN grinding technology are important technical factors that restrict the application of CBN. The early development was slow to relate to it; it was also related to it when it developed faster. The single CBN product variety alone also affected its promotion. Through our efforts, CBN products have now been serialized and specialized. Therefore, CBN has a great development.
In addition to satisfying the fast-growing domestic market, CBN single crystal abrasives produced in China also occupy an important position in the international market with excellent cost performance. Exports are also developing very rapidly. International customers are widely recognized and have the right to speak in the world market.
(3) Although the growth of CBN is not as high as that of diamonds, its growth rate is as high as 24%, and its output has accounted for 60% of the world's total output. The main driving force is the continuous expansion of its application fields, the increase in the market caused by the transfer of manufacturing industries to China, and the increase in quality caused by the increase in quality.
China is not only a major producer of CBN, a major exporter, but also a strong producer. Currently ranked first in the world of CBN manufacturers.

Second, the development direction (a) to increase product added value
The 2009 Global Strategic Business Report: CBN Abrasives, published by Global Industry Analysis, estimates that the global market demand for CBN abrasives in 2012 will reach $194 million. The annual sales revenue of China's CBN abrasives is estimated at 40 million US dollars, accounting for less than 21%, and our production accounts for more than 60% of the world, indicating that the price of our products is low. In the future, we will increase the production ratio of high-grade CBN and increase the added value of products.
(II) Breaking through the production technology of microcrystalline CBN
Although several domestic companies have claimed to launch microcrystalline CBN products in recent years, they are actually similar in appearance. The performance gap with international famous brands is still large, and the application is very limited. In the future, we must increase development efforts and improve the production technology of microcrystalline CBN as soon as possible.
(3) Accelerate the pace of product standard setting
At present, there are only four national standard CBN varieties, which are far lower than the actual product variety. This has caused the inconvenience of the abrasive manufacturer and the grinding wheel manufacturer to communicate and accept, and it is urgent to establish a new series of product standards.

Third, a bright future (a) CBN development prospects are good
“Global Strategic Business Report: CBN Abrasives” published by Global Industry Analysis states that CBN is becoming the abrasive of choice for most grinding applications because it helps to achieve precise geometry and size, better surface finish and surface. Integrity, as well as reduced processing time. Because it is very suitable for use on CNC grinding machines, its use is increasing. In order to take full advantage of the advantages of CBN grinding and obtain better surface finish, structural integrity and longer service life, more and more car manufacturers have chosen CBN grinding wheels to replace traditional abrasive grinding wheels.
In some major industries, the amount of CBN will increase, showing good growth.
With the research and development of CBN large single crystals, the shape and size of CBN single crystals are severely limited, and the research and application of the basic properties of CBN crystals will be changed. On the one hand, large-size high-quality CBN single crystals are used to prepare single-crystal cutters with excellent performance; on the other hand, in the study of functional materials, large-sized CBN single crystals are necessary for studying the basic properties of heat, electricity, light, etc. It is necessary to prepare heat sinks, high temperature semiconductor devices and even special optical devices.

(II) Strengthening research and development and expanding varieties
1. The method for synthesizing CBN crystals in the past is based on the phase change, that is, changing the HBN phase into a CBN crystal under high temperature and high pressure. Studies have shown that CBN crystals can be prepared by chemically reacting compounds containing boron and nitrogen or compounds containing boron and nitrogen, completely away from the original mode of transformation.
In 2012, Professor Tian Yongjun of Yanshan University made breakthroughs in the research of polycrystalline superhard material synthesis technology and hardening mechanism of superhard materials. The high-temperature and high-hardness nano-twisted cubic boron nitride block was successfully synthesized by high temperature and high pressure technology. material.
They successfully synthesized a transparent nano-twisted cubic boron nitride using a special structure of onion boron nitride as a precursor. The average thickness of twins is only 3.8 nm, and its hardness reaches or exceeds the synthetic diamond single. Crystal, fracture toughness is higher than that of commercial cemented carbide, and the oxidation temperature is higher than that of cubic boron nitride single crystal itself. These excellent comprehensive properties indicate that the nano twin structure cubic boron nitride is a long-awaited tool material in the industry.
It has been shown that above the critical dimension (about 10-15 nm), the hardness and strength of metal and alloy materials increase with decreasing grain size (Hall-Page effect), but below the critical size, strength and hardness However, it decreases as the grain size decreases (anti-Hall-Page effect). Surprisingly, the nano-twined cubic boron nitride can continue to harden to 3.8 nm without softening as the thickness of the twin is reduced. Their theoretical analysis shows that at the nanoscale side, the hardening mechanism of polycrystalline polar covalent materials has the additional contribution of quantum confinement effect in addition to the well-known Hall-Page effect. The research results have broken through the traditional understanding of the material hardening mechanism, showing people a new way to synthesize high-performance superhard materials - to obtain ultra-fine nano twin crystal structure.
2. Cubic boron nitride film is an important development of thin film technology in the field of cubic boron nitride synthesis, and has become a new research hotspot, opening up a new application field for CBN.
3. The explosion method is a method for transforming HBN to produce WBN and CBN under the action of high pressure and high temperature of explosion shock wave. The pressure generated by this method is very high, but the equipment is simple and the cost is low, and the obtained product particle size is mostly on the order of submicron and nanometer. It has both high hardness and good toughness and is ideal for making abrasive pastes and polishing.
4. Compared with the traditional method for preparing CBN, the hydrothermal synthesis of CBN has the advantages of low cost, easy monitoring of the reaction process, less pollution, and good uniformity of the reaction system, especially for the growth of large crystals. The successful preparation of CBN crystallites by hydrothermal method has opened up a new technical route for the preparation of CBN. (This article is excerpted from the "Fifty Years of China's Superhard Materials Industry", please do not reprint.)

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