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Cooking Up Superhard Diamonds

Popping diamonds into a high-pressure oven can make these hard minerals even harder.

Diamonds are more than just sparkling gems. They also happen to be one of the hardest materials on Earth.

Now, scientists have found a way to make diamonds even harder by cooking them under pressure with lots of heat. Using the new technique, Russell J. Hemley of the Carnegie Institution of Washington and his colleagues claim that they have made the hardest diamond crystal ever tested.

When exposed to high heat and pressure, diamonds become extremely hard.

When exposed to high heat and pressure, diamonds become extremely hard.

Carnegie Institution

All diamonds are made up of carbon atoms arranged in a regular pattern. Some diamonds come directly out of the ground. Some are made in the lab.

To make the gems even harder, Hemley and his group first used a process called chemical-vapor deposition to add more carbon atoms to previously created artificial diamonds. They then cooked these new diamonds with lots of heat and pressure.

Temperatures in the cooker reached 2,000 degrees Celsius. The pressure equaled that experienced 150 kilometers below Earth's surface. Under these conditions, the newly deposited diamonds became superhard.

The new diamonds were so hard, the researchers say, that they broke equipment worth about $10,000 while testing them. The testing machines couldn't even dent or scratch some of the diamonds.

The scientists say that they can adjust the cooking conditions to make their diamonds not only superhard but also supertough, so the gems won't crack or fracture easily.

Superhard diamond would be ideal as a coating for industrial tools and medical implants and as the stuff from which to make electronic devices that work under extreme conditions. Individual gems would also make gorgeous, durable jewelry.

The discovery of superhard and supertough diamonds could give new meaning to the old saying: Diamonds are forever.—E. Sohn

Going Deeper:

Weiss, Peter. 2004. Hard stuff: Cooked diamonds don't dent. Science News 165(Feb. 28):131. Available at http://www.sciencenews.org/articles/20040228/fob1.asp .

You can learn more about diamonds at www.amnh.org/exhibitions/diamonds/ (American Museum of Natural History).

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