Durable diamonds in a dash

Scientists in the US have produced gem-sized diamonds that are harder than any other crystals and at a rate of up to 100 times faster than other methods used.

A group headed by scientists at the Carnegie Institution’s Geophysical Laboratory in Washington, DC, has produced gem-sized diamonds that are harder than any other crystals and at a rate of up to 100 times faster than other methods used to date.

The process is said to open up an entirely new way of producing diamond crystals for electronics, cutting tools and other industrial applications.

‘This is a great example of fundamental research that will not only give us a better tool to duplicate conditions in the core of the Earth, but will stimulate many other scientific, technical and economic advances,’ said geologist James Whitcomb of the US National Science Foundation (NSF)’s division of earth sciences, which funded the research.

‘We believe these results are major breakthroughs in our field,’ said researcher Chih-shiue Yan. ‘Not only were the diamonds so hard they broke the measuring equipment, we were able to grow gem-sized crystals in about a day.’

The researchers developed a special high-growth rate chemical vapour deposition (CVD) process to grow crystals. They then subjected the crystals to high-pressure, high-temperature treatment to further harden the material.

In the CVD process, hydrogen gases and methane gases are bombarded with charged particles (plasma), in a chamber. The plasma prompts a complex chemical reaction that results in a ‘carbon rain’ that falls on a seed crystal in the chamber.

Once on the seed, the carbon atoms arrange themselves in the same crystalline structure as the seed. This method has been used to grow diamond crystals up to 10 millimetres across and up to 4.5 millimetres thick.

According to the researchers, CVD-produced crystals are very tough. ‘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 high-temperature and high-pressure conditions. The diamonds were heated to 2000 degrees C and put under pressures of 50,000 to 70,000 times atmospheric pressure for 10 minutes. This final process resulted in the ultra -hard material, which was at least 50 percent harder than conventional diamonds.