Synthetic diamond

A synthetic diamond (also called diamond of synthesis or diamond of culture ) is produced by using various physical and chemical techniques, aiming at reproducing the structure of the natural Diamant S.

Synthetic diamonds (January 2006) are currently sold at prices from 10% to 50% lower than those of natural diamonds. Their annual production reached 3 billion carats (600 tons) and an amount of a billion dollar, to compare with the 130 million carats (26 tons) of the mining extraction.

History

The joaillers prefer to sell an luxury item, therefore rare, and far from wanting to increase the quantity available by it, they made large efforts to prevent that the stones of synthesis penetrates the market. On the other hand, industry appreciates the hard materials, as diamond (the Carbure of silicon, the Carbure of tungsten, etc). The diamond synthesis was one of the ways explored in this search for hard materials.

In 1892, Henri Moissan developed the electric furnace with arc making it possible to reach high temperatures (up to 3500 °C), and theoretically showed the possibility of synthesizing diamond. It heats coal with iron, and imposes a fast cooling, causing the contraction of iron, and thus the production of the enormous pressure necessary to the manufacture of diamond. The experiment of Moissan does not seem to have been conclusive, but it was succeeded by Ruff in 1917 (produced diamonds being very small, the maximum reached being only of 0,7 mm), then by Dr. Willard Hersey in 1926.

The history takes again only the February 16th 1953 with Stockholm in Sweden, at the time of project QUINTUS of the company of electricity ASEA. The technique, conceived by Baltzar von Platen and the young engineer Anders Kämpe, will be kept secret. One year later, General Electric repeats the operation and publishes its results in the magazine Nature . It is on this date that the creation of the first synthetic diamond is officially recognized.

At the end of the Years 1950, De Beers as well as the Russian and the Chinese began the synthetic manufacture of diamonds for industry. That have for consequence to make fall the value of the natural diamonds intended for industry.

The first true use of diamonds of synthesis in jewelry begins about the middle from the Années 1990. Today (January 2006), mainly two companies share the sector:

Gemesis (based with Sarasota in Florida)
Apollo Diamonds (based with Boston in the Massachusetts)

Gemesis was created by Carter Clarke, after its discovery of the Russian installations during the summer 1995. Since, Gemesis improves the technique High presses, high temperature (HPHT), which was developed in Russia. Apollo Diamonds for its part uses the technique Chemical vapor deposition (CVD), discovered by its founder, Robert Linares, in 1996.

Techniques

High presses, high temperature

Technique HPHT (in French High pressure, high temperature ) consists in making a mixture of carbon (in an abundant form) and metals of transition (which will act as solvents) and subjecting the whole to very an high pressure (approximately 58.000 atmospheres) and temperature (approximately 1.400°C). The formation of diamond is done then by germination and growth. In the method of the variation in temperature, a diamond germ is inserted in the engine before the reaction.

This technique produces for the moment only diamonds of colors (yellow, orange, pink and blue), which are not pure.

Several companies, like LifeGem or Algordanza, use this technique to carry out diamonds made up of carbon resulting from ashes from the Crémation.

Chemical vapor deposition

Technique CVD (in chemical French Plating in vapor phase ) created layers of diamond. The method is to place a layer of silica or diamond in a room where reign a pressure of a tenth of atmosphere. Hydrogen and Méthane are then injected and heated by Micro-onde S. the two gases are transformed into plasma and " tombent" on the substrate, forming a layer of diamond which grows with time (approximately 0,5 mm per day), in which small diamonds will be cut. The layers can also be useful such as they are for industry.

This technique produces diamonds much purer than those which are obtained with the HPHT.

Difference with natural diamonds

Currently (January 2006), it is rather difficult to make the difference between a synthetic and natural diamond. The giant of natural diamond De Beers, develops several techniques to detect these new diamonds.

One of these techniques is to detect the shape of growth of the diamond, which is not the same one as in nature. Thus, the diamonds obtained by method HPHT create sectors of growths in the shape of cubes. The certain shapes of impurities are also not present in nature.

Method CVD on the other hand, produced diamonds differentiable with more difficulty of natural diamonds, because being very pure, the impurities and the zones of cubic growth are less distinguishable. However, the nearly perfect purity of the diamonds produced by method CVD can be an index, thus inducing mistrust as for the origin of diamond.

Name in France

In France, the regular commercial practice for such diamonds obliges the salesmen to use the " term; synthétique" , so as not to mislead the customer.

Here an extract of the Decree 2002-65 of the January 14th 2002 relating to the trade of the gemmeous stones and pearls:

Article 4: The following qualifiers respectively supplement the denomination of the matters and products mentioned below:
(...)
- " synthétique" for the stones which are crystallized or recristallized products whose manufacture caused completely or partially by the man was obtained by various processes, whatever they are, and whose physical properties, chemical and of which the crystalline structure corresponds essentially to those of the natural stones that they copy;
(...)
Use of the terms: " élevé" , " cultivé" , " of culture" , " vrai" , " précieux" , " fin" , " véritable" , " naturel" is interdict to indicate the products enumerated with the present Article. (...)

Reference

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