Superhard materials refer to materials whose hardness can be compared with diamond
Superhard material is an important engineering material. It usually refers to a material with a hardness of 10 or close to the highest Mohs hardness value. It is mainly used in the processing of composite materials, inorganic non-metallic materials, and cemented carbide. Functional Materials. At present, common superhard materials include diamond (natural diamond and synthetic diamond), cubic boron nitride and so on.
At present, common superhard materials include diamond (natural diamond and synthetic diamond), cubic boron nitride (PCBN) and so on.
Among them, PCBN has high hardness, high wear resistance and stable performance at high temperatures, and is mainly used to manufacture various tools;
Diamond is divided into single crystal diamond, polycrystalline diamond (PCD) and CVD diamond. Single crystal diamond is used in grinding wheels, saw blades, etc., PCD is used in cutting tools, petroleum drill bits, CVD diamond is used in drawing dies, cutting tools, etc., high-end CVD diamond Used in electronic devices, aerospace and other fields.
Superhard materials can also be classified into single crystal superhard materials and polycrystalline superhard materials (also called "composite superhard materials"). Single crystal superhard materials include single crystal diamond, single crystal cubic boron nitride, etc., characterized by hardness High but small in size; polycrystalline diamond/cubic boron nitride is a composite material made of single crystal diamond/cubic boron nitride as the main raw material, adding metal and non-metal adhesives under high temperature and high pressure environment, composite superhard material Although the hardness and heat resistance are slightly worse, it has a larger cutting area and better wear resistance.
Composite superhard materials are mainly used in petroleum and natural gas, coal mines, automobiles, etc. Polycrystalline diamond for petroleum and natural gas is a cutting layer composed of a mixture of small diamond particles and a binder and a cemented carbide substrate layer sintered under high temperature and high pressure. The material has high strength, hardness and wear resistance. Inlaid on the oil and natural gas drill bit, it is the core component of the drill bit for cutting and tunneling. During the drill bit, the diamond composite sheet is gradually consumed. In the coal mining process, the diamond composite sheet plays the same role. The durability of PCD tools is dozens of times longer than that of carbide tools. The main processing objects are non-ferrous metals and non-metallic materials. Since the components of automobile engine pistons, pin holes, and carburetor generally contain more than 10% silicon and have high hardness, most of them are mass-produced in an assembly line, which makes alloy tools cost-effective and has good applicability for diamond tools.
Diamond Micro-powder plays an important role
The upgrading of the machinery manufacturing industry has driven the continuous increase in demand for diamond micropowder. Machinery, automobile manufacturing, home appliance manufacturing, etc. Industry upgrades in subdivided industries have driven the demand for high-end diamond tools. Artificial diamond tools have been widely used in precision machining in the automotive industry. High-end diamond tools can meet the high-precision requirements of cutting, grinding, polishing and other processes in the automotive manufacturing process.
Household appliances, especially refrigeration appliances, are one of the main application areas of synthetic diamond abrasive tools and cutting tools. The three major components of the compressor used in household air conditioners and refrigerators, pistons, cylinders, and upper and lower bearing seats, are mainly processed with diamond tools.
The rapid development of photovoltaic and LED fields has driven the high demand for diamond powder. The cutting process of monocrystalline silicon, polycrystalline silicon, sapphire and other photoelectric magnetic materials used in photovoltaic power generation and LED lighting is the area where the demand for diamond micropowder applications has increased the most.
The era of MINILED is coming, and the demand for sapphire cutting diamond micropowder has exploded
Artificially cultivated diamonds have become the absolute protagonist of superhard materials
Cultivated diamonds are a variety that was born based on the high-tech production technology of the superhard material industry. It was mainly developed for the purpose of cutting, grinding and processing of hard materials in modern industry. It has defeated it with higher hardness. The first-generation superhard material-cemented carbide, has replaced the second-generation superhard material-natural diamond at a lower price. Together with cubic boron nitride, it has become the absolute protagonist of superhard materials. The main application is PCD (Polymerized Diamond) composite blade cutters, which is to sinter extremely small particles (2-30m) of diamond powder and binder under high temperature and high pressure, and then cut, weld, and sharpen them. use.
High technical barriers to artificially cultivated diamonds
The technology of cultivating diamonds comes from the advancement of industrial science and technology. On the one hand, a powerful pressure generating device is required, and on the other hand, a container material that can withstand huge pressure is required, which is the principle of high temperature and high pressure method. Later, with the maturity of microwave technology, the high-purity methane gas is microwave-ionized at high temperature to produce uncharged plasma carbon and hydrogen atoms, and then the carbon atoms are allowed to adsorb and crystallize on the lower temperature substrate, which is later The principle of chemical vapor deposition method (CVD method). The technical barriers to cultivated diamonds are embodied in three aspects. First, because cultivated diamonds are different from industrial diamonds, their production cycle is very long. If there is no relative quantity, such as 1000-2000 sets or more, even if the manufacturer has some related technologies, it cannot be opened. The market, secondly, the industry is a heavy capital investment type. If there is not enough capital support in the short term, it is impossible to cause an impact on the existing leaders. Thirdly, in terms of technology diffusion, technical personnel with in-depth understanding of the integration of raw materials, production, and processes are scarce in the entire market, and the process of technology diffusion will be much slower than that of industrial diamonds.
Comparison of HPHT technology and CVD technology
High temperature and high pressure (HPHT) technology: The high temperature and high pressure technology completely simulates the growth process of natural diamonds, reproduces the reaction of the carbon element layer on the ground and converts graphite into diamonds. HPHT method (temperature at 1400°C-1700°C, pressure at 5.2GPa-5.6GPa) synthetic diamond refers to an environment that simulates the growth of natural diamonds. In a hexahedral high-pressure machine, graphite, diamond powder or graphite-diamond powder is used as carbon Source, equiaxed crystalline body formed in a growth environment such as high temperature and high pressure and metal catalyst. It only takes 2 weeks to produce 20 carats of cultivated diamonds using the high temperature and high pressure method. The growth process is to put high-purity graphite as a carbon source in the high-temperature zone of the growth chamber of the top press, and place diamond seeds in the low-temperature zone. Driven by a certain temperature gradient, the carbon source diffuses from the high concentration area at the high temperature to the low concentration area at the low temperature. The diamond seeds in the low temperature area are supersaturated and crystallized, then cooled and taken out, and concentrated nitric acid is used to remove the diamond surface的impurities.
Chemical vapor deposition (CVD) technology: usually under the action of high-temperature plasma, carbon-containing gas is dissociated, and carbon atoms are deposited on the substrate to form a diamond film. The substrate can be a non-diamond material, but single crystal diamonds are usually formed by the deposition of carbon atoms on the diamond substrate. Carbon-containing gas usually refers to a mixed gas containing nitrogen, methane and hydrogen. Methane is the source of carbon atoms in synthetic diamonds. Nitrogen can increase the growth rate, and hydrogen can inhibit the formation of graphite. Generally, CVD synthetic diamonds are carried out under low pressure and high temperature conditions, the pressure is generally less than one atmosphere, and the temperature is about 1000°C.
Both technologies have their own advantages. HTHP has higher efficiency and better color, and CVD purity is better. To produce 1 carat cultivated diamonds, because the high temperature and high pressure (HTHP) is formed by the connection of carbon atoms and carbon atoms, the growth cycle only takes a few days. Chemical vapor deposition (CVD) dissociates and grows carbon-containing gas on the cultivation of diamond seeds, and gradually accumulates and accumulates, which requires a growth cycle of several months. Because high temperature and high pressure (HTHP) requires a metal catalyst as a solvent to participate in the reaction, it will have some impact on the purity of the diamond, and the purity of chemical vapor deposition (CVD) is slightly better.
Large segment of artificially cultivated diamond production capacity in China
Limited by geographical conditions, the production capacity of natural diamonds is mainly concentrated in South Africa and Zaire, while the production capacity of artificially cultivated diamonds is mostly concentrated in China. In 2020, the global production capacity of cultivated diamonds will be about 6 to 7 million carats, of which China's production capacity will reach 3 million carats, far exceeding other countries, accounting for about 50%. Followed by India and the United States, with 1.5 million carats and 1 million carats respectively, accounting for more than 30% of the total. The remaining production capacity is distributed in Europe, the Middle East, Russia and other places.
After recent decades of development, the General Electric and Apollo, the British Sixth Element, Sumitomo, Russia`s New Diamond Technology, Singapore`s IIa Technology and other group companies have established a wide range of global diamond cultivation circles. Popularity, such as Diamond Foundry, Lightbox, Diama, GEMESIS and other cultivated diamond brand products, is gradually infiltrating from foreign markets to China's domestic market. Just like the natural diamond market, it will occupy and cultivate the high-end diamond consumer market before the market starts.
China's diamond production capacity is mainly concentrated in NBJZ Diamond Technology Corporation, SHZS CVD diamonds, HNHJ diamonds, ZNZS diamonds, HNHH and other companies. From the perspective of production technology, China mainly uses the HPHT and CVD method to produce diamonds, while the rest of the world basically uses the CVD method to produce diamonds. The HPHT method has almost formed a monopoly in the production of synthetic diamonds, and currently accounts for about 90% of the global HPHT method of producing and cultivating diamonds.
to be continued in next paper…