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Scientific Approach to Grow Diamonds

Vishwas Purohit Sep 1, 2020
Diamonds are a girl's best friend, says the slogan by De Beers. It's Amitabh Bachchan who now states that diamonds are a man's best friend too, on an Indian Radio channel. Diamond business is big business and suppliers are now outsourcing their productions to laboratories. A look into how diamonds are grown in scientific labs.
Diamonds are carbon based structures formed naturally under high pressure and temperatures by a geological process. They have excellent physical properties useful for industrial applications and employed for their unparalleled optical properties in the jewelry business.
These natural allotropes of carbon are formed under a depth of 130 to 180 kilometers under the earth's crust, gaining their carbon atoms from carbon based minerals.
The growth of this particular allotrope of carbon takes a very long process under the earth lasting typically around 1 billion years. Diamonds come out onto the earth's surface sometimes by a volcanic eruption or are excavated by humans in coal mines.
The applications of diamond are ever-expanding leading to a huge demand which cannot be met by excavating natural diamond. Also, the prices for such diamonds are quite high for certain applications. The solution for this dilemma has been developed by scientists worldwide, i.e. the creation of the artificial diamond.
The first synthetic diamond was created in the 1940s with research being carried out in the United States, Russia and Sweden. These diamonds are grown by a process called Chemical Vapor Deposition (CVD) and High Pressure High Temperature (HPHT) synthesis.
The CVD method is comparatively more expensive as compared to the HPHT process due to the complicacy of machinery involved. Both the techniques have their own advantages and disadvantages. For e.g. the CVD method is more flexible in depositing diamond on a wide variety of substrates as compared to the HPHT which has the capacity to grow larger diamonds.

Chemical Vapor Deposition

The CVD method works using a 'bottoms-up' approach utilizing by using carbon atoms as a base to start from. Hydrocarbon groups are broken down inside a low pressure chamber to separate the hydrogen and carbon. The breakdown process typically ionizes these atoms giving the user, control over these atoms.
The ionizing process kicks the outer shell electron out of orbit and the whole atom gains a positive charge, which was earlier neutral. These ionized particles can then be accelerated, decelerated and focused dependent on deposition parameters. These ionized carbon atoms are the building blocks for forming diamonds.
The substrates where this deposition takes place are heated to around 700 to 800 degree centigrade. The ionized carbon atoms float around and settle on this substrate since they cannot settle down on a low temperature surface. These atoms collect an electron from the surface and become neutral once again.
Settled atoms then act as a 'seed', where other atoms can settle around and form the required diamond geometry which can then grow into larger sizes. This technique is highly dependent on process parameters like temperature, pressure, gas flow rates, rate of ionization and substrate material.

High Pressure High Temperature

The HPHT technique basically works by simulating the process of diamond formation under the earths crust. The major factors for diamond formation under the earth include carbon source, high pressure and high temperature.
In the case of a HPHT model, the high pressure source is provided by multi-sectioned anvils compacting a graphite source. Graphite, as is widely known, is another allotrope of carbon atoms wherein the atoms are arranged in a hexagonal array in a planar arrangement.
The high pressure and high temperature arrangement made possible by the anvil and temperature sources convert the planar arrangement into diamond-like formation of the atoms.
This approach is typically a top town approach wherein you change the property of a bulk material to tailor it into the form required by the user. This method is comparatively less expensive as compared to the CVD method.
Whatever the method of synthesis, the end result lies in aligning the carbon atoms in a diamond structure formation. Diamond prices, then vary depending upon the formation method of diamonds, whether it is geological, bottoms-up or the top-down approach.