How synthetic diamonds are made?

Diamond Synthesis was authenticated by General Electric in 1955. Today there are a number of laboratories which synthesizes diamonds, though largely of industrial quality. Since 1970, gem quality diamonds have been synthesized and with the growth of type la yellow diamonds for heat sinks and other industrial uses by Sumitomo Electric Co., it will not be too long before they are available easily.

The Reaction Cell (Flux)

• The reaction cell is made of pyrophyllite and is inside a carbon tube heater, which is heated by an electric current.
• Industrial grade synthetic diamond is used as the source of carbon.
• On each side of this carbon source is a catalyst, such as iron or nickel, which becomes molten on applying high heat and pressure.
• A temperature differential of about 10-15°C is maintained between the centre and the ends of the cell.
• The pressure applied to the reaction cell is 60,000 atmospheric pressure (approx. 900,000 psi).
• The carbon dissolves in the hotter part (1455°C) of the cell, moves through the metallic flux and recrystallises on the seed crystal where temperature is lower (1425°C).
• These conditions are maintained for several days at 60,000 atmospheric pressure.
• The pressure is applied in two different ways:
  1. Bert Apparatus Process
  2. Split Sphere Process

1. Belt Apparatus Process:
   • It consists of giant steel / bars or belts that apply pressure.
   • Reaction cell is placed m a die and swung into a space between two anvils.
   • The pressure is applied from top and bottom while heat is applied from sides.
   • The anvils and die are supported by multiple rings.
2. Split Sphere Process:
   • It consists of two sets of anvils, on which the pressure is applied.
   • The outer set consists of eight anvils forming a cavity in octahedron form.
   • Inside this set lies a set of six additional anvils.
   • These anvils form a cube shaped central cavity, in which the reaction cell is placed.
   • The pressure is applied by injecting liquid of unknown nature into the compression barrel which applies pressure onto the anvils.

Identification of synthetic diamond

• Magnification: The characteristic inclusions seen are:
  • Colour zoning in the form of a square or rectangle, the central area being surrounded by darker coloured areas.
  • Graining – Rectangular or octagonal shaped internal graining lines projecting outward from each corner.
  • Metallic Inclusions – Large rounded or elongated inclusions with a metallic lustre, numerous pinpoint inclusions.
• Ultra Violet Lamp: Green / Yellow Luminescence in both the waves.
• Spectroscopy – Moderate absorption band between 450 and 500nm, weak bands between 470 and 600nm.