Synthetic diamond

Artificial way of non-diamond carbon structure into a diamond structure carbon, and by the formation of crystal nucleation and growth and polycrystalline diamond, or

the fine particles at high pressures and temperatures of diamond sintered polycrystalline diamond.
Artificial way of non-diamond carbon structure into a diamond structure carbon, and by the formation of crystal nucleation and growth and polycrystalline diamond, or

the fine particles at high pressures and temperatures of diamond sintered polycrystalline diamond. It is currently in production on a high-pressure research has been

applied

An important example.
From the thermodynamic point of view, the decision of graphite and other non-diamond structure carbonaceous material into a diamond can transition condition that the

latter must be less than the free energy of the former. This phase transition at high pressure, high temperature or other conditions involving components

The. Certain amount of pressure, temperature and component concentration of the internal energy of the system can be changed, so that the energy level of the valence

electrons at statistical weight change accordingly. This may be electron transfer and formation of a new state of the electronic structure of bonding, a phase

transition occurs

. If the energy change in favor of this occurs in the solid changes in the electronic structure, the high temperature phase transition occurs in the solid state, or

may occur in the molten state or vapor state. This change occurred in the melt condition that the bonding characteristics of the distribution of the valence electron

system

Total weight reduced accordingly, the role of the remote order tend to disappear coordination number is changed; the electronic excited state statistical weight tends

to increase, the role of short-range ordered increased accordingly. This change occurred in the gas condition that elemental interatomic or compound

Intermolecular bonding electron energy levels tend to disappear, all electronic transfers to a single atom or molecule level up, so that the electrons in the excited

state are more statistical weight increases. Accordingly, synthetic diamond can be solid, but also may be in the melt state and the vapor state conditions, which

Depends on the pressure, temperature and component concentration and other factors can cause changes in the system. From the kinetic point of view, but also requires a

carbonaceous material such as graphite into diamond with an appropriate transition rate. The diamond nucleation rate and the growth rate in both maxima

When the maximum rate of phase change.
The specific method of synthetic diamond currently up to a dozen. According to the characteristics of the technology used can be summarized as static, dynamic pressure

and low pressure three methods. Characterized by the formation of diamond can be summarized as directly, melting and other categories of media and outreach methods.
Direct method
The instantaneous static synthetic diamond or high pressure high temperature technology, ultra-high pressure or high temperature techniques, or a mixture of both

techniques, the carbonaceous material such as graphite or a molten state from a solid directly into the diamond, the diamond is obtained by this method micron size

polycrystalline powder

At the end.
Melting media law
Static high pressure synthetic diamond (50 ~ 100kb, namely 5 ~ 10GPa) and high temperature (1100 ~ 3000 ° C) technology through the carbonaceous materials such as

graphite and certain metals (alloys) reaction of diamond, cubic crystalline state of a typical ( hexahedron), octahedron and six - octahedral

Bodies and their transitional forms. Important applications in industry showing the value of the media law is mainly static melt. Obtained by this method abrasive

grade synthetic diamond production has more than natural diamond, to be further addressed is larger than coarse, increase conversion

Rate and improve the crystal quality. Currently under laboratory using static media studied melting quality single crystal diamond formation of large particles. Seeded

epitaxial growth method has been weighing 1 carat of large single crystals; using ordinary testing techniques slightly improved, he got about 2 to 4 mm

Crystals. This method also uses a large grain growth and sintering of polycrystalline diamond , which has been obtained in certain industrial applications, the key

problem is to further improve such a polycrystalline diamond compressive strength, impact strength, abrasion resistance and heat resistance, comprehensive performance

.
Epitaxy
Synthetic diamond is the use of certain pyrolytic carbonaceous substances and electrolytic precipitation of carbon or some of the diamond seed crystal substrate from

the effects of substances formed by epitaxial growth on.
The formation mechanism of diamond
At present, there are several theories as follows: Solvent doctrine that the metal (alloy) plays the role of carbon in a solvent; catalytic doctrine is considered to

be a catalyst; solid phase transition theory emphasizes the disintegration of the graphite crystal without bond breaking, after a simple deformation on formation of

diamond crystals.

But the doctrine of three typical models are often made with some of the main experimental phenomena and laws are contradictory. Thus, over the past decade, there has

been a solvent - catalyst, the catalyst - solvent, melting (melting) agent - catalyst (referred to as the melting media) and other theories to further explore the

metal used (together

Gold) role.