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TOPIC: The Diamond Age


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Rhenium diboride
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Researchers have designed and made a material capable of scratching diamond and done it without resorting to harsh, high-pressure methods.
Diamond is the hardest material known and is used for drilling and cutting other hard materials. But diamond has its drawbacks it can't practically be used to cut anything containing iron because a chemical reaction during the high-speed drilling creates iron carbide, which ruins the diamond blade. Alternatives to diamond have been made, but creating them usually requires incredibly high pressures, which is expensive and inconvenient.
The second-hardest material known is boron nitride, with the boron and nitrogen atoms arranged in a cubic structure; it requires high pressures to make.

Rhenium diboride has a hardness of about 48 gigapascals (GPa); comparable to the strength of  boron nitride, which has a strength rating of about 45-50 Gpa. Diamond has a strength of  70-100 GPa.
The new material is made quite easily in the lab, under ambient pressure.

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New stiff material
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A material that is stiffer than diamond has been created by mixing particles of the mineral barium titanate and molten tin. Diamond was previously the stiffest material known.
The new material was made by a team from Washington State University and Wisconsin-Madison University, both in the US, and from Ruhr-University Bochum in Germany.
They mixed molten tin, heated to about 300ºC, with pieces of a ceramic material called barium titanium - often used as an insulator in electronic components. The particles were each about one-tenth of a millimetre in diameter and were dispersed evenly through the tin using an ultrasonic probe.

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Extreme pressures
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Much of what we know about how materials behave under extreme pressures and temperatures (millions of atmospheres and thousands of Kelvin) is learned using diamond anvil cells. In these tiny enclosures, material can be squeezed between the flat, hard, transparent faces of two gem quality diamonds. Because diamond is transparent over much of the electromagnetic spectrum, many types of radiation, such as laser beams or light emitted from or scattered by the sample (light containing valuable spectroscopic information) can enter and exit through the diamond windows.

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Scientists Melt Diamond
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So much for “diamonds are forever.” Scientists at Sandia National Laboratories have taken diamond, the hardest known natural material on Earth, and melted it into a puddle.
Diamond isn’t easy to melt, which is why the scientists used Sandia’s Z machine, the world’s largest X-ray generator, to subject tiny squares of diamond, only a few nanometers thick, to pressures more than 10 million times the atmosphere’s pressure at sea level.

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The Lesotho Promise
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The biggest diamond to be found in 13 years, the "Lesotho Promise," was sold on Monday at auction for more than $12 million and is expected to fetch in excess of $20 million once it is cut up.

The 603-carat (120 gram) diamond, named after the tiny African mountain kingdom where it was found, went under the hammer at the Antwerp Diamond Centre and was sold to the South African Diamond Corporation, owner of luxury jewellers Graff.

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The Diamond Age
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Researchers at the Carnegie Institution's Geophysical Laboratory have learned to produce 10-carat, 12-mm thick single-crystal diamonds at rapid growth rates (100 micrometers per hour) using a chemical vapour deposition (CVD) process.


 This size is approximately five times that of commercially available diamonds produced by the standard high-pressure/high-temperature (HPHT) method and other CVD techniques. In addition, the team has made colourless single-crystal diamonds, transparent from the ultraviolet to infrared wavelengths with their CVD process.
"High-quality crystals over 3 carats are very difficult to produce using the conventional approach" commented Dr. Russell Hemley who leads the diamond effort at Carnegie. "Several groups have begun to grow diamond single crystals by CVD, but large, colourless, and flawless ones remain a challenge. Our fabrication of 10-carat, half-inch, CVD diamonds is a major breakthrough."
The results were reported at the 10th International Conference on New Diamond Science and Technology, Tsukuba, Japan, on May 12, and will be reported at the Applied Diamond Congress in Argonne, Illinois, May 18.



Most HPHT synthetic diamond is yellow and most CVD diamond is brown, limiting their optical applications. Colourless diamonds are costly to produce and so far those reported are small. This situation limits general applications of these diamonds as gems, in optics, and in scientific research. Last year, the Carnegie researchers found that HPHT annealing enhances not only the optical properties of some CVD diamond, but also the hardness.
Using new techniques, the Carnegie scientists have now produced transparent diamond using a CVD method without HPHT annealing.
The diamond was laser cut (and inscribed) from a diamond block and only partially polished.
To further increase the size of the crystals, the Carnegie researchers grew gem-quality diamonds sequentially on the 6 faces of a substrate diamond plate with the CVD process. By this method, three-dimensional growth of colourless single-crystal diamond in the inch-range (~300 carat) is achievable.
Finally, new shapes have been fabricated with the blocks of the CVD single crystals.
The standard growth rate is 100 micrometers per hour for the Carnegie process, but growth rates in excess of 300 micrometers per hour have been reached, and 1 millimetre per hour may be possible. With the colourless diamond produced at ever higher growth rate and low cost, large blocks of diamond should be available for a variety of applications. "The diamond age is upon us," concluded Hemley.



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