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Professor Hanington's Speaking of Science: Creating diamonds
author:abrasivesunion   hits:1275times   pubdate :2015-02-05 11:07

The ability to create synthetic diamonds in the laboratory goes back a long time.

In 1893, Ferdinand Moissan mixed small pieces of graphite into a crucible of molten iron. When the assembly was rapidly cooled in a tank of water, the contraction generated by the thermal shrinkage of the iron produced enough pressure onto the hot carbon that tiny diamonds were removed when the iron was dissolved away by nitric acid. Many other scientists, including Sir William Crookes, inventor of the high voltage spectrum tube, claimed success with this technique in 1909.
This idea of squeezing graphite with tremendous pressure is actually found in nature when some nickel-iron meteorites are sliced open. Many times, the mineralogist uses many blades trying to cut through a diamond located inside the meteorite. Generally black and opaque, and not of gem quality, diamonds in iron meteorites are thought to have formed from the intense shock pressure and heating during the impact. Some Canyon Diablo meteorites, from the famous Meteor Crater in Winslow, Arizona, contain diamonds called Lonsdalerite.
You may be interested to know that Russian scientists have unearthed a large impact crater in eastern Siberia that contains “many trillions of carats” of what they are calling impact diamonds. Currently only good for industrial purposes, if this is true it far exceeds the known diamond deposits of the entire world.
In 1941, General Electric set a goal of manufacturing diamonds using a machine capable of subjecting small charcoal briquettes to high temperature and pressure simultaneously. In colossal machines designed by Percy Bridgman, carbon was heated to 3,000 degrees Celsius and squeezed with hydraulic rams to a pressure of over 510,000 psi for a few seconds. In the end, small diamonds were created that could be used for industrial purposes, such as imbedding into grinding wheels and cutting tools.
Bridgman won the 1946 Nobel Prize for this work and paved the way for others to develop the process. By building new rams out of tungsten carbide and elevating the pressure to over 1.6 million psi, the first commercially successful synthesis of diamond occurred in 1954. Although the GE stones and natural diamonds are chemically identical, their physical properties were not the same. The colorless synthetic stones produced strong fluorescence and phosphorescence under short-wavelength ultraviolet light, unlike natural diamonds.
Gem-quality diamonds can be manufactured nowadays by several new methods. One technique, called chemical vapor deposition, creates a carbon plasma over a suitable substrate onto which the carbon atoms deposit to form diamond. Unlike the older high pressure technique described earlier, CVD does not require high pressure. In fact, the carbon atoms are deposited under vacuum environments from hydrocarbon gases. By using microwave power to ionize the carbon gases, the atoms forming the diamond are deposited slowly, layer by layer, as they arrange themselves into perfectly formed crystal lattices.
Very small diamonds can be created by exploding carbon-containing mixtures within a metal chamber. During the explosion, the pressure and temperature in the chamber becomes high enough to convert the carbon of the explosives into diamond. Called “nanodiamond powder,” this material (made mostly in China) is used primarily in polishing applications.
Synthetic diamonds for use as gemstones, using both the high temperature and pressure process and grown CVD methods, currently represent approximately 2 percent of the gem-quality diamond market. They are available mostly in yellow and blue, and, to a lesser extent, colorless. The yellow color comes from nitrogen impurities in the manufacturing process, while the blue color comes from boron.
Gem-quality diamonds grown in a lab can be chemically, physically and optically identical to naturally occurring ones. Of course, the diamond mining industry has undertaken legal, marketing and distribution countermeasures to protect its market from the emerging presence of synthetic diamonds but inroads are being made.
One company, LifeGem, is producing diamonds from carbon found in hair or ashes of humans or animal remains. These synthetic diamonds are touted as “memorial diamonds” and range in price from $3,500 for small diamonds (about 0.3 carats) to $19,999 for stones weighing almost one carat. Although they use the high pressure, high temperature technique for their process, it’s reassuring to know, according to its brochure, LifeGem can synthesize up to 50 carats from a single cremated human body.
Several years ago, LifeGem announced they had synthesized three 0.56 carat blue round brilliant gems using 10 strands of hair from the remains of Ludwig van Beethoven (with added carbon). One of the three diamonds sold on Ebay for approximately $200,000, with the proceeds donated to charity.
Imagine the possibilities!