Synthetic diamonds catch the public’s attention because they immediately think of the man-made diamonds replacing diamonds in the jewelry industry. However, the motivation behind researchers usually has more to do with industrial applications. Diamond’s hardness, high thermal conductivity, high electrical resistivity, optical transparency, resistance to chemicals, and other unique properties make it a valuable material for a variety of uses including surgical scalpel blades, equipment “windows” exposed to harsh environments, heat-spreaders for electronic devices, temperature and pressure sensors, and drill bits used in mining and oil exploration.
Scientists at the Carnegie Institution‘s Geophysical Laboratory recently announced an enhanced process for growing diamond crystals using the chemical vapor disposition (CVD). Most synthetic diamond methods require high temperature and extremely high pressure to mimic nature’s own diamond growing process. However, the CVD process uses high temperature but low pressure to produce single-crystal diamonds rapidly and with more controlled results.
The Carnegie researchers add a new twist to the synthetic diamond process by heating the diamonds at temperatures up to 2000 degrees Celsius but low (less than atmospheric) pressure to alter the color of the diamond. The raw synthetic diamond crystals are usually yellow-brown in color but this special annealing process transforms the color to a colorless or light pink hue. With the ability to use low pressure, researchers have been able to identify the specific crystal defects that cause color changes in diamonds.
This annealing process uses microwave plasma to produce the high heat at low pressure, yet keeping the diamond from changing to graphite. Producing colorless diamonds has been a challenge for synthetic diamond manufacturers and getting a faint pink color could end up being a bonus. This ability to produce colorless diamond crystals has value not only in the jewelry industry but also in many of the industrial applications where colorless transparency has increased value.