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Synthetic diamond knowledge encyclopedia

October 30,2023


The crystal structure of synthetic diamond

Synthetic diamond  is obtained by the transformation of graphite and metal catalyst under ultra-high temperature and high pressure conditions, or by a certain method to activate the carbon-containing gas, so that the carbon atoms in it are supersaturated on the substrate (seed crystal) and grown into diamond. Its main constituent element is carbon atom. Diamond is a crystalline form of carbon, and when carbon atoms form diamond, carbon atoms bond with each other in 4 equivalent sp3 hybrid orbitals to form a regular tetrahedral structure. The regular tetrahedral structure formed by the sp3 hybrid orbital can exist in both the cubic crystal system and the densely arranged hexagonal crystal system, so diamond has two different crystal structures: cubic diamond and hexagonal diamond.


Morphological classification of diamond crystals

Under certain conditions, the crystal morphology of diamond is closely related to the growth conditions, and it can be said that different growth conditions have different crystal shapes. Among natural diamonds, the most common diamond crystal morphology is octahedral, while rhomboid dodecahedron is rare and cubic is even less common. In addition, there are convex octahedrons, convex dodecahedrons, convex hexahedrons and their polyforms, and due to the movement of the earth's crust and natural impact effects, there are more curved crystals than planar crystals. According to the different synthesis conditions, the crystal form of synthetic diamond can be divided into hexahedron, octahedron, hexahedral and octahedral poly, rhombic dodecahedron, octahedral and rhombic dodecahedral poly, and other intermediate polycrystals.




Definition of diamond crystal form

If the diamond crystal shape is divided into several crystal forms according to the shape: complete crystal shape, equal volume crystal form, non-equal crystal form, continuous crystal, polycrystalline and so on. The specific meanings are as follows:

1. Complete crystal shape:

(1) The crystal surface and crystal edge are clear, and the crystal growth is full;

(2) There are no more than two twin or symbiotic crystals;

(3) A quarter of the missing corners and a quarter of the pits on the crystal plane are allowed. This crystal has a good diamond crystal shape, high strength and impact resistance, making it an ideal cutting material.

2. Equal product crystal shape: the ratio of the long axis to the short axis of the crystal does not exceed 1.5:1 is an equal product crystal shape. The quality of such diamonds is not as good as that of complete crystalline diamonds, and although the shape is good, the strength is lower. At present, this type of diamond accounts for a large proportion of synthetic diamond production.

3. Non-isoproduct crystal shape: the ratio of the major axis to the short axis of the crystal exceeds 1.5:1 and is non-equal product. Such diamonds are of poor quality, not in good shape and have low strength.

4. Continuous crystals: Crystals with more than two common crystal faces or crystal edges and several incomplete crystals are linked crystals. When in use, the continuous crystal is usually broken into single crystals.

5. Polycrystalline: Many tiny crystals are irregularly aggregated and clustered called polycrystals. Such diamonds are of poor quality and have very low compressive strength.


The varieties and classification of synthetic diamond in China

China's new standard GB6405-86 is divided and named according to use. General products are divided according to the type of applicable binder, and special products are divided according to the type of product or processing object. For each diamond variety, the first capital letter in English for its main purpose is listed first, and D is used to represent diamond. For example: diamond for resin or ceramic bond abrasives,labeled RVD  (Diamond grains for Resinbinder and Vitrified bond); Diamond for metal bonds, labeled MBD (Diamond grans for Metal bond); Diamond for sawing, marked SMD (Diamond grains for Metals bond Saw); Diamond for grinding steel, marked SCD (Diamond for Carbide and Steel); Dressing tools are made of diamond, labeled DMD (Diamond grains for Metal bond Dressing tool), etc.


The scope of application of various varieties of synthetic diamond single crystal

Different varieties of diamond, the scope of application is also different, the following are the scope of application of several common varieties:

1. Diamond RVD of resin or ceramic bond abrasive: suitable for resin, ceramic bond mold or grinding;

2. Diamond MBD for metal bond: suitable for metal bond mold, electroplating crystal making, drilling tools or grinding, etc.;

3. Diamond SMD for sawing: suitable for sawing, drilling and correction tools;

4. Diamond SCD for steel grinding: suitable for steel or steel and cemented carbide combinations;

5. Dressing grade synthetic diamond DMD: suitable for dressing tools, single or multi-grain dressers, etc., optional particle size is 30/35 and coarse