The hardest substance in nature, diamond, is an allotrope of carbon, which is the noble diamond we often say. It combines hardness, optical transparency, thermal conductivity, electrical insulation, high pressure resistance and weather resistance. Integrated, widely used in machining tools, optical materials, semiconductors and electronic devices and jewelry.
China began to synthesize diamonds in 1963. By the end of 2017, China's synthetic diamond production has accounted for more than 90% of the world's total output, and the quality has reached the international advanced level in recent years. The achievements in the production and quality of synthetic diamond in China are attributed to three major technological advances: the enlargement of the six-face press, the quality of the hard alloy top hammer, the industrialization of the powder catalyst and the indirect heating process (powder process).
I. Progress in key technologies for synthetic diamond in China
Industrial synthetic diamond, basically adopt high pressure and high temperature static method at home and abroad, the process flow is shown in the following figure.
â–²Synthetic diamond process
In the past 40 years since the birth of synthetic diamonds in China, diamonds have been basically synthesized using a sheet-like process (a combination of sheet-like catalyst and direct heating). In the early 1990s, the powder process was studied. After 10 years of hard work, industrial production began in 2001. Because of its superior output rate and quality, it was quickly applied in the whole industry in 2005. The application of the powder process, the large-scale synthesis of the press, and the strong support of the alloy top hammer have greatly promoted the development of China's diamonds to the world's advanced level.
2. Large-scale synthesis press
1. Chinese-style hinged six-sided press
China adopts a 90-degree three-axis press. This six-face press presses the three-axis pressure by a hinged structure. The figure below shows the physical and sectional views of the hinged six-face press.
â–²Hinged six-sided top press
The development of the six-face press is not only manifested in the increase of tonnage, but also has made significant progress in the structure of the cylinder, the accuracy of the machine, and control. From the structure of the cylinder, from the earliest flange support structure - the bottom structure, gradually to the bottom support - the bottom structure and the double support structure. From the perspective of accuracy, the centering accuracy of the press is controlled by the precision of the hinge beam and the assembly accuracy of the pinning pin, which is dominated by the distance between the axis of the ear beam of the hinge beam and the axis of the cylinder bore.
â–²The evolution of the cylinder structure
2. The rise of cylinderless presses
The so-called cylinderless press is a press that removes the high-pressure oil lining cylinder originally assembled in the hinge beam and makes the piston directly cooperate with the hinge beam. That is, the liner cylinder is a cylinder-cylinder combined structure with a cylinder press, and the linerless cylinder is a cylinder-cylinder integrated structure cylinderless press. The cylinderless press removes the liner cylinder, which removes the material, processing and heat treatment costs of the six high-strength alloy steel liner cylinders, greatly reducing the cost of the press, and increasing the size of the piston with the same size of the hinge beam. Increase the tonnage of the press, or reduce the oil pressure when the tonnage is constant. These advantages make cylinderless presses popular in recent years.
â–²Compared with cylinder press and cylinderless press
III. Quality improvement of cemented carbide top hammer
The development of China's cemented carbide top hammer from the earliest use of less than 3 kg to the current 50 kg is the promotion of large-scale presses and the result of advances in cemented carbide technology. As the diameter of the top hammer increases, the hammer consumption drops dramatically. The drop in hammer consumption means a decline in the cost of diamond production. This is due to the following: First, although the size of the top hammer is increased, the quality of the top hammer itself has been greatly improved; the second is the improvement of various performance parameters of the press, such as the improvement of neutrality, synchronism, and oil pressure stability. The application of program control has improved the service condition of the top hammer and contributed to the improvement of the service life of the top hammer. The third is the application of the powder process.
â–²Carbide top hammer
Process application of powder process
In the first 40 years of synthetic diamonds in China, the flake process was basically adopted. In 2005, the whole industry switched to the powder process. The difference is that the assembly structure of the composite block is different, as shown in the following figure.
â–² Assembly diagram of sheet process and powder process
The sheet-like process is that a graphite sheet and a catalyst sheet are alternately stacked in a synthesis cavity composed of pyrophyllite of a high-pressure pressure-transmitting medium, and a large current is introduced into the graphite sheet and the catalyst sheet by the conductive caps at both ends, and is heated by its own resistance. The so-called direct heating process. The powder process is a mixed powder of graphite powder and catalyst powder, which is cold pressed into a synthetic block, and then deoxidized, and the processed synthetic block is charged into the synthetic cavity of the pyrophyllite, and a large current is introduced into the winding by the conductive caps at both ends. On the thin piece heating element such as carbonaceous material around the synthesis block, a heating furnace is formed around the synthesis block to heat the intermediate synthesis block. This change is a major technological advancement in China's synthetic diamonds, which has greatly increased the price/performance ratio of diamonds.
summary
Under the background of reform and opening up, China's synthetic diamonds have been industrialized with the advancement of large-scale synthetic presses, high-quality carbide carbide top hammers, powdered catalysts and indirect heating processes. 1 person, its quality has caught up with the world's advanced level. This cannot but be said to be a great pride in China's manufacturing industry!
However, the industry is also clearly aware that this amazing achievement refers to the synthesis of single crystal diamonds, especially for sawing and drilling single crystal diamonds, the synthesis of polycrystalline diamond composite sheets, the synthesis of large particles and even gem-quality diamonds. Although China has made great progress in recent years, compared with the world's advanced level, the gap is still large, and polycrystalline diamond composite sheets are diamonds that are processed from hard and brittle non-metallic materials, such as stone, concrete, asphalt, etc. High-strength and toughness difficult to process metal materials and precious materials, such as titanium alloys, high-temperature alloys, semiconductor materials, etc., in some processing properties, superior to advanced processing materials of cemented carbide.
From the upgrading of industrial single crystal diamonds to polycrystalline and special single crystal diamonds, efforts still need to be made. It will take time to change from a diamond country to a diamond power.
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