What is the difference between CVD artificial diamonds and HPHT cultivated diamonds-Part-3

HPHT diamond (high temperature and ultra high pressure synthesis method)

HPHT diamond is a more traditional diamond cultivation method, which uses molten metal alloys such as iron (Fe), nickel (Ni) or cobalt (Co) to form diamonds.

The HPHT diamond cultivation process takes place in a small capsule in a device with ultra-high pressure. In this capsule, the diamond powder is dissolved in the molten metal solvent, and then begins to crystallize to form diamond crystals. The entire crystallization process will take weeks or even months. At a time, one or more crystals are produced.

Except for the octahedron, the diamond crystals cultivated by HPHT technology are usually cubic crystals. Since natural diamonds and HPHT synthetic diamonds have different crystal shapes and their internal growth structures are also very different, we can distinguish between natural diamonds and HPHT synthetic diamonds through these two points.

In order to cultivate colorless HPHT diamonds, apart from the need to isolate nitrogen during the cultivation process, the cultivation of high-purity colorless diamonds (type IIa or weak type IIb) often requires a longer cultivation period and stricter temperature and pressure conditions. As a result, the cultivation cycle is longer than that of type Ib synthetic diamonds, so how to use HPHT synthesis to grow large-grain crystals has always been a problem. However, with the development of technology, it is now possible to use HPHT synthesis to grow more than 10 carats. Diamond crystals too.

During the cultivation of HPHT diamonds, it is also possible to add chemical elements or radiant heating to make the crystals appear blue or red, but this practice is not very common.

In addition, HTHP synthetic diamonds usually have certain visual characteristics, such as color distribution, fluorescence partition, grain structure, and metal inclusions. Most of the diamond crystals cultivated by HPHT are yellow, orange or brown, and almost all of them are type Ib diamonds.