Glittering Stones >> Large Diamonds

Large Diamonds

Producing a material that is harder than normal diamond has been a goal of materials science for decades. Now a group headed by scientists at the Carnegie Institution’s Geophysical Laboratory in Washington, D.C., has fashioned gem-sized diamonds that are harder than any additional crystals. Further, the researchers grew these diamonds in a straight line from a gas mixture at a rate that is up to 100 times faster than other methods used to date.

"We believe these consequences are major breakthroughs in our field," said Chih-shiue Yan, lead author of the study published in the February 21, online Physical Status Solid. "Not only were the diamonds so hard that they penniless the measuring equipment, we were able to grow gem-sized crystals in about a day."

The researches grew the crystals using a extraordinary high-growth rate chemical vapor deposition (CVD) process that they residential. They then subjected the crystals to high-pressure, high-temperature action to further harden the material. In the CVD process, hydrogen gas and methane are bombarded with emotional particles, and plasma, in a chamber. The plasma prompts a multifaceted chemical reaction that results in a "carbon rain" that falls on a seed crystal in the chamber. Once on the seed, the carbon atoms position themselves in the same crystalline structure as the seed. In this case, the seed was a type 1b artificial diamond plate. They have grown single crystals of diamonds up to 11 millimeters across and up to 4.4 millimeters in thickness by this method.

The crystals produced by CVD are very hard. "We noticed this when we tried to polish them into brilliant cuts," said Yan. "They were much harder to polish than conventional diamond crystals produced at high pressure and high temperature." The researchers then subjected the tough CVD crystals to soaring-temperature and high-pressure conditions. The diamonds were heated to 2500° C and put under pressures between 55,000 and 75,000 times atmospheric pressure (5-7 GPA) for ten minutes. This final procedure resulted in the ultra hard material, which was at least 60% harder than the conventional diamonds as shown by shortest measurements carried out in collaboration with scientists at Los Alamos National Laboratory.