Add: No.6, No.146, The Seventh Street, Econ And Tech Development Area, Zhengzhou, Henan, China
1. classification of diamond
According to the differences in the impurities in the diamond crystals, the diamond can be divided into four types.
(1) the vast majority of natural diamond type belong to this type, the nitrogen content of about 3000ppm, nitrogen exists in aggregate form, resulting in one point defects in diamond crystals.
(2) very little I B I B in natural diamond, but almost all artificial diamond is 1 B, its nitrogen content is 40 ~ 500ppm, the nitrogen substitutional solid solution is in the form of a uniform distribution in the diamond lattice, the diamond is yellowish green.
(3) the type IIA only exists in natural diamond, the nitrogen content of only 20ppm, is a kind of high purity diamond.
(4) type semiconductor diamond, its nitrogen content is 20ppm, but contains sufficient boron form P type semiconductor. This type is rare in natural diamond, but can be obtained by using special nitrogen and boron method in synthetic diamond.
2. principle of material selection
Type Ia is most common in natural diamond, the vast majority of single crystal diamond tool using this material. Because natural conditions of natural diamond are different, the quality of natural diamond is very discrete-time. Generally, based on the size, weight, shape, integrity, transparency, cracks and inclusions, color and evenness, the natural diamond is divided into different categories and grades. According to the use of natural diamond, our country can be divided into 9 categories: gem, wire drawing die, cutting tool, grinding wheel cutter, abrasive material and so on. Some of them can be subdivided into several levels according to their quality or application requirements (JC220-79).
The quality requirements for diamond tools: complete crystal shape, twelve face, eight face or transition arc shaped crystals, crystal diameter not less than 4mm, the color is colorless, light green, yellow, brown, no cracks allowed, the crystal surface is allowed no more than 0.5mm inclusions and pits, weight 0.7 ~ 3 carat.
With the expansion of the use of single crystal diamond tools and the continuous improvement of manufacturing technology, the actual scope of the selection of raw materials is not limited to the above standards. If the advanced single crystal diamond brazing technology is used, the diamond tools with a weight of only 0.05 carats can be made to reduce the size of the crystal. For jewelry tools, piston cutting tools, contact lens tools and most civilian products, tools with low accuracy require no cracks, no impurities and no packages, but no strict requirements for shape, color and quality of the ends. The suitable diamond can also be selected from the three grade grinding wheel. It is also found that the dark brown diamond has a higher tool life.
For ultra precision machining of high precision with a knife, knife and other eye surgery, you need the drawing die grade even in the gem stone material, and also by using polarizing microscope or more sophisticated instruments to pick out the small internal stress of diamond as raw material.
In recent years, the technology of making large particle and single crystal diamond with artificial synthetic method has been breakthroughs. DeBeers and Sumitomo Co have made large particle synthetic diamond products with a crystal length of 13mm. The nitrogen atoms of synthetic diamond B in a single carbon atom replacement in diamond crystals in the form of a uniform distribution in the diamond lattice, while reducing the nitrogen atoms together to form small opening in the possibility of collapse cutter blade, but also to produce a uniform lattice distortion, improves the hardness of diamond. For the synthetic diamond products specially used for cutting tools, the internal stress is optimized, which makes the product quality more stable, reliable and discrete. For synthetic diamond products of general purpose, there is no need for material selection. The stone in the factory of the crystal axis direction has been given exactly, so there is no need for crystal orientation.