The most famous and desired gemstone in the world is a diamond. It’s combination of brilliance, fire (dispersion) and lustre make diamond unique amongst gemstones. It’s uniquely hard, transparent and, of course, shiny. It’s these characteristics that have earnt diamond the reputation as the perfect gemstone and consequently, an expensive price tag. Taking all of this into consideration, it is no surprise that scientists have tried to imitate diamonds for over 200 years. The first major breakthrough, however, did not come until the early 1950s when a Swedish engineering company, Allmanna Svenska Elektrisk Aktiebolaget, succeeded in growing 40 small diamond crystals in an apparatus called a sphere. Due to high cost of production and low quality output, early lab diamonds were predominately used for industrial use posing an insignificant threat to the diamond industry. During the past decade, however, technological developments has enabled quality to improve and production costs to fall.
The formation of natural diamonds is a complex process which requires precise pressure and temperature combinations. More specifically, diamonds form over millions, if not billions of years, at depths of approximately 150 km underneath earth’s surface, where temperatures are approximately 1100 ℃ and pressures of 50 kBar. The rough diamonds are then blasted to the Earth’s surface in rare volcanic eruptions in kimberlite rock. The challenge therefore for scientists wishing to simulate diamonds is to mimic these savage temperatures and vast pressures found deep under Earth’s cratons and not over millions of years but in days.
Currently, there are two main methods employed to produce synthetic diamonds:
High Pressure High Temperature (HPHT)
HPHT uses a reaction chamber with both diamond powder and a catalyst containing a mixture of nickel, iron and cobalt. When the diamond powder is exposed to high levels of heat and pressure it dissolves into the surrounding metallic solvent. Due to a temperature gradient within the reaction cell, the dissolved diamond re-crystallises at the base of the cell on a diamond seed crystal.
Chemical Vapour Deposition (CVD)
Similar to the HPHT method, the CVD process involves diamond growth at moderate-to-high temperatures (700–1300°C) but it differs from HPHT in that it uses very low pressures (less than 1 atmosphere) in a vacuum chamber. In the CVD process, an isolator and microwave generator is used to heat up a mixture of gases (oxygen, methane and hydrogen), with methane acting as the provider of necessary carbon. This reaction causes a plasma to form, which deposits carbon atoms onto a substrate allowing the crystallization process of a diamond to occur.