A CVD diamond (also called synthetic diamond, laboratory diamond or cultured diamond) is produced using different physical and chemical techniques, aimed at reproducing the structure of natural diamonds .
These synthetic diamonds are used in industry and can be of variable quality. According to several sources, the market for CVD diamonds (ecological or ethical diamonds) is expanding, particularly in the fields of jewelry, electronics and high technology, which demand high quality and purity.
The laboratory diamond market has grown from 1% of the rough diamond market from $ 14 billion in 2016 to around 2 to 3% in 2019.
Each diamond contains atoms other than carbon in concentrations detectable by analytical methods.
These atoms can regroup in macroscopic phases called inclusions . Impurities are generally avoided, but can be incorporated, as a means of controlling certain properties of the diamond.
For example, a pure diamond is an electrical insulator, but a diamond to which boron has been added is conductive, and in some cases superconductive , allowing it to be used for electronic applications.
Nitrogen impurities prevent movement of the structure and place the latter under compressive stress, thereby increasing its hardness and solidity.
The HPHT technique (in French High pressure, high temperature) consists of making a mixture of carbon (in abundant form) and transition metals (which will act as catalysts) and subjecting the whole to a very high pressure (about 58 000 atmospheres ) and temperature (around 1400 ° C).
Diamond formation then takes place by germination and growth.
In the temperature gradient method, a diamond seed is inserted into the reactor before the reaction.
This technique currently only produces colored diamonds (yellow, orange, pink and blue), due to inclusions of nitrogen and other impurities.
Several companies, such as LifeGem or Algordanza, use this technique to make diamonds composed of carbon from the cremation ashes.
Making the difference between a synthetic diamond and natural is difficult and may require specific hardware 17 .
Synthetic diamonds remain small and cannot yet compete with the world's largest rough diamond, the Cullinan , which weighs 3,106 carats, or 621 grams. The largest synthetic diamond ever produced weighs 155 carats and was obtained by researchers from the University of Augsburg 18 .
Natural diamond giant De Beers is developing several techniques to detect these new diamonds.
One of these techniques is to detect the growth form of the diamond, which is not the same as in nature.
Thus, the diamonds obtained by the HPHT method create growth sectors in the form of cubes. Certain forms of impurities are also not present in nature.
The CVD method, on the other hand, produces diamonds which are more difficult to differentiate from natural diamonds, because being very pure, impurities and zones of cubic growth are less distinguishable. However, the near perfect purity of the diamonds produced by the CVD method can be a clue, thus inducing mistrust as to the origin of the diamond.