Industrial diamonds, also known as synthetic diamonds, are produced by three main methods: High Pressure High Temperature (HPHT), Explosive Processing and CVD.
1.High Temperature and High Pressure
The composition of diamond is known to be only one kind of component, i.e. carbon (C), the composition of graphite is the same as that of carbon (C), only there is a difference in the structure, the SP2 structure of graphite is a two-dimensional molecular surface with three-way coordination (CN=3), and the SP3 structure of diamond is a three-dimensional molecule body with four-way coordination (CN=4), therefore, as long as graphite is added with enough pressure and temperature, that is, sufficient energy is given to it and appropriate catalyst is used, graphite can be converted into diamond. Catalyst, graphite can be converted into diamond. Generally speaking, the conversion of graphite into diamond requires a high temperature of 1200-1500 degree C, and at the same time, there should be a combined pressure of 50,000-70,000 atmospheres, and there are two types of mainstream production equipment, namely, the two-sided top and the six-sided top. More than 90% of the diamonds produced by high temperature and high pressure are produced by this method.
Explosive method is divided into two types, one is direct synthesis, is in the confined space ignited explosives, in the space due to the gas explosion of a large number of carbon atoms with each other together with the impact generated by high pressure, and in the absence of oxygen, the explosives itself carbon atoms instantly pressed into the dregs of the explosives, this way to get the diamond particles are extremely small than the surface of the positive, and therefore will be adsorbed by a large number of impurities, this direct synthesis is suitable for the production of mono-crystalline nano-diamonds.
Another explosive method is to use ultrasonic shockwaves to hit the graphite, so that the graphite is instantaneously converted into micron or nano diamonds, the manufacturing practice is to mix graphite and copper powder evenly and apply isostatic pressure to make a round rod, the round rod is sealed with a steel tube containing a vacuum layer, and then filled with several tons of explosives in the surrounding area, the ignition of the explosives will be squeezed from one end of the steel tube to the other, the graphite inside the tube will be in the instantaneous experience of several thousand degrees and 20~300,000 atmospheric pressure, in a few microseconds the graphite will be transformed into diamonds. The graphite inside the tube will instantly experience about several thousand degrees and about 200~300 thousand atmospheric pressure, and the graphite will be transformed into diamonds in a few microseconds. The diamonds produced by this method contain a large number of defective polycrystals, and have the appearance of popcorn or potato, so this method is mostly used to produce polycrystalline nano or micron diamonds.
CVD diamonds are produced by a relatively new method of cultivating diamonds, in which a vacuum chamber is filled with a carbon-containing gas (methane gas), and a carbon plasma is formed at the bottom of the chamber, which is continuously deposited on the carbon substrate at the bottom of the pressure chamber, and the whole crystallization process lasts for several weeks, resulting in flaky crystals that usually have a black rough edge, and crystals that are often brown in color, but can be removed by heat treatment. The resulting flakes usually have black rough edges and the crystals are often brown in color, but can be removed by heat treatment. Diamond crystals grown by CVD synthesis are mostly brown or light gray in color, but if small amounts of nitrogen or boron are added to the vacuum chamber, yellow, pink-orange, or blue crystals can be grown, and colorless crystals may be grown in this way, but the cultivation period is longer. Most of the diamonds cultivated by CVD synthesis are type IIa, while most of the colorless diamonds cultivated by CVD synthesis in the market are brown crystals that have been annealed and decolorized by HPHT. Diamonds produced by CVD synthesis and HPHT synthesis have different gemmological characteristics, with diamonds produced by CVD synthesis tending to have higher clarity and virtually no inclusions of minor dark colors.
