Technology Lab Diamonds

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What is a Lab Diamond?

A “lab diamond” is a man-made diamond that has been grown in a laboratory environment by one of the two currently available manufacturing processes:

HPHT (High Pressure High Temperature)
CVD (Chemical Vapor Deposition)

All real diamonds consist of pure crystallized carbon (pure carbon); this applies to both mine diamonds and lab diamonds. The growing process mimics/imitates natural growth in the deep interior of the Earth (HPHT) or in interstellar gas clouds (CVD).

Although the growth process is different from what occurs in nature, the chemical composition, physical properties, and optical characteristics of lab-grown diamonds are identical to those of diamonds mined/extracted from mines.

Lab-grown diamonds come in all sizes (currently up to over 10 carats), all shapes and all colors, and the light output is identical to that of mined diamonds.

HPHT (High Pressure, High Temperature)

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HPHT diamond, photo with permission of IGI “Courtesy of International Gemological Institute”.
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Illustration HPHT Press Machine

In HPHT synthesis, a press applies extremely high pressures and temperatures to a central growth chamber containing the necessary ingredients. This results in lab diamond crystals with combinations of cubic and octahedral faces. Similar to a honeycomb structure with squares.

HPHT

✓ Analogous conditions deep earth interior
✓ Approx. 1’500° Celsius (extremely high temperature)
✓ 400 tons per square inch (extremely high pressure)

Using the traditional diamond growth method “High Pressure High Temperature (HPHT) method”, Lab grown Diamonds are produced from carbon material in apparatus that mimics the high pressure high temperature conditions of natural diamond formation in the earth. This diamond growth process exposes carbon to extreme temperatures and pressures, replicating the extreme heat and pressure conditions deep within the Earth where mined diamonds form.

  • Diamond seed is placed in a specially developed press:
    This is a capsule in an apparatus capable of generating very high pressure.
  • Growth chamber is heated to 1’300-1’600 °C with pressures above 400 tons per square inch:
    Inside the capsule, a carbon feedstock such as graphite dissolves in a molten flux consisting of metals such as iron (Fe), nickel (Ni) or cobalt (Co), lowering the temperature and pressure required for diamond growth.
  • The molten metal dissolves the high purity carbon source
  • Carbon atoms are deposited on a small diamond seed crystal:
    → Lab diamond begins to grow
    The carbon material/atoms then migrate through the flux to the cooler diamond seed crystal and crystallize/grow on it to form a lab grown diamond crystal.
  • Crystallization takes place over a period of several weeks to months to grow one or more crystals
  • This grown rough diamond is then cut, polished and polishedby a diamond cutter

Growing colorless HPHT Lab diamonds was once a challenge. Nitrogen, which turns diamonds yellow, had to be kept away from the growing environment. In addition, growing high-purity colorless diamonds required longer growth times and better control of growth temperature and pressure conditions. However, recent technological advances have allowed laboratories to produce colorless crystals that are faceted as diamonds of 10 carats or more.

Making Fancy Color Diamonds

Addition of nitrogen → Yellow diamonds
Addition Boron → Blue Diamonds
Radiation & Heating → Pink & Red Diamonds (Rarer)

The addition of nitrogen during the growth process leads to yellow crystals, while the addition of boron leads to blue crystals. Other colors – such as pink and red – can be produced by radiation and heating, but are less common.

CVD (Chemical Vapor Deposition)

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CVD diamond, photo with permission of IGI “Courtesy of International Gemological Institute”.
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Illustration CVD synthesis

In CVD synthesis, microwaves split the hydrocarbon molecules fed into the reactor. These fragments migrate downward to the colder diamond nucleus and attach to the growing diamond surface. The Lab diamond grows in thin layers, and its final thickness depends on the time available for growth. The result is flat, tabular crystals (similar to a cube) whose outer surface is coated with black graphite.

CVD

✓ Analogous conditions of interstellar gas clouds (how cool is that?)
✓ Gas (methanes)
✓ Vacuum chamber
✓ Approx. 1’000° Celsius (high temperature, lower than HPHT)
✓ Microwave beam

Chemical vapor deposition (CVD) is a newer technique used to grow diamonds from a hydrocarbon gas mixture (e.g. methane). In the CVD process, a thin slice of a diamond seed (often an HPHT diamond) is placed in a sealed vacuum chamber and heated to about 900 degrees Celsius. A source of energy – such as a microwave beam – breaks down the gas molecules, and the carbon atoms diffuse toward the colder, flat diamond seed plates.

  • Diamond seed crystals → placed in diamond growth chamber
  • Chamber is filled with carbonaceous gas
  • Chamber is heated to about 900-1’200°C
  • A microwave beam causes carbon to precipitate from a plasma cloud and deposit on a seed crystal.
  • The diamonds are removed every few days to polish the surface to remove any non-diamond carbon before being put back in for waxing. Each batch of diamonds may require multiple stop/start cycles.
  • Crystallization takes place over a period of weeks, with several crystals growing simultaneously.
  • This grown rough diamond is then cut, polished and polished by a diamond cutter.