Man Made Diamonds
Creating Man Made Diamonds
There are two main ways that man made diamonds are fashioned.
The high pressure, high temperature process recreates conditions found deep inside the earth, where diamonds appear naturally. A belt press was the first successful design. This design has two anvils that press together which enable it to grow several diamonds in 1 cycle. These presses are usually used for industrial diamonds and powder. A cubic press uses six different anvils pressing onto a cube. These presses are usually used to produce industrial diamond powder. A BARS press was created by Russian scientists. It makes use of 6 inner anvils and 8 spherical outer anvils to apply hydraulic pressure to the growth cell. One cycle of a BARS machine makes one diamond crystal. These BARS presses are to-date, the best process to grow comparatively big gem-quality diamonds.
At the core of the HPHT machines is a growth cell. This cell contains all the elements and materials necessary to grow the diamond. This includes a small diamond seed, highly refined and purified graphite (carbon) as well as a catalyst of mixed metals and powders that facilitates the diamond growth. The growth cell is placed in the center of the machine and is heated to over 1,300 degrees Celsius and over 50,000 atmospheres of pressure is applied. When the temperature and pressure increases, the catalyst turns into a molten metal solution. Once the perfect conditions are reached, the graphite dissolves into this solution. Through a controlled cooling process over the course of several days, the carbon atoms gradually build upon the crystal structure of the diamond seed. The diamond usually grows in a truncated octahedron or a hexa-cubic shape, dependant upon parameters of the growth process. Once the machine runs its full cycle, the growth cell is removed. The new diamond is cleaned and able to be cut and polished, much like any other rough diamond. In the course of the growth, the temperature and pressure need to be maintained within a very strict set of parameters. If there’s any fluctuation, the diamond can either stop growing, or become so heavily included, the usable gem-quality size can be quite limited.
The different colored diamonds grow at different rates, which explains why the size availability varies based on the color.
Chemical vapor deposition is a really different process from high pressure, high temperature, though they both ultimately grow diamonds. The environment inside a CVD machine is a small percentage of 1 atmosphere of pressure. Carbon-based gasses, commonly methane, are introduced to the environment and are heated to many 100's of degrees Celsius which causes the gasses to break apart and release their carbon atoms. The carbon then "rains" down onto a diamond substrate, in which it slowly grows in layers (a few micrometers per hour) as a crystal. This technology is best suited to applications using thin layers of diamonds, like optics and semiconductors. CVD is capable of producing gem-quality diamonds, though the size of the polished diamond is limited by the thickness of the diamond wafer.
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