In 1941, General Electric formed an agreement with Norton and Carborundom to continue future development of diamond fusion. Heating carbon to 3000 degrees Celsius “under a pressure of 3.5 gigapascals was created for a few seconds”. World War II cut the project short. The project resumed at the General Electric Schenactady Laboratories and “a high-pressure diamond group was formed with F. P. Bundy and H. M. Strong”. Tracy Hall later joined the testing.
On December 16, 1954, Hall achieved the first commercially successful synthesis of a diamond. His achievement was announced on February 15, 1955. The diamond was very small (.15mm). It was not only small but it was an imperfect diamond as well.
It wasn’t until 1970 that synthetic gem quality diamonds were first produced by General Electric. Gem quality stones of 5mm (1.0ct) were produced. Those first diamonds were always yellow to brown in color. “Inclusions were common”. Colorless diamonds were produced by removing nitrogen and adding aluminum or titanium. If nitrogen was removed and boron was added, blue diamonds were produced. Irradiation was used to create pink or green diamonds. Memorial diamonds were also produced with cremated remains. The DeBeers Company grew diamonds up to 25 carats. Because of the cost of creating these large diamonds, synthetic diamond production was terminated when they reached a size of 1.0ct to 1.5ct.
Synthetic diamonds are produced using several methods. The first method used high pressure and high temperature (HPHT) and because of its low cost, is still used today. The second method uses chemical vapor deposition (CVD). “Other methods include explosive formation (forming detonation nanodiamonds) and sonication of graphic solutions”.
Detonation nanodiamonds are formed when a mixture absent of oxygen (TNT/RDX) is detonated in a closed chamber. Diamond particles are then produced.
Sonication uses ultrasound to perturb particles. It is known as an ultrasonic bath or an ultrasonic probe.
The hardest known materials are synthetic diamonds. Some synthetic single crystal diamonds are harder still than any known natural diamond.