The Manufacture Methods of Diamonds

There are many methods to manufacture diamonds in the world, but the most common method is static high-pressure high-temperature synthesis with catalysts. According to the characteristics of the synthesis technology and the crystal growth mechanism, these methods can be categorized to the following types:

1) Static high-pressure high-temperature: This method also has two sub-types – with or without catalysts. The one without catalysts is to directly change graphite to diamonds under super high pressure and temperature. Its requirement for pressure is about 10 GPa, and requirement for temperature is above 3000 K. These requirements are higher than the requirements of the method with catalysts by about 1 time.

2) Dynamic high-pressure high-temperature: This method is also called explosive method, which changes graphite to diamond grains of micron sizes under instantaneous super high pressure and temperature which are generated and disappear very quickly. The pressure can reach 1000 GPa, and the time is only a few hundred microseconds.

3) Chemical Vapor Deposition (CVD): This method grows diamonds at low pressures (133 Pa – 106 kPa) and non-high temperatures (500 – 800°C). By this method, a hydrocarbon gas mixture is ionized into chemically active radicals to form diamonds. The advantages of CVD diamond growth include the ability to grow diamond over large areas and on various substrates, and the fine control over the chemical impurities and thus properties of the diamonds produced.