Diamond Gas?

By Avery Sisson

Valentin Margo New York, Diamond

I was recently browsing the local diamonds shelves at the jeweler, and I wondered why the jeweler was selling his synthetic lab grown diamonds for so much less than his natural diamonds because they look about the same to me.

We’ve all been told that diamonds are made under high pressure deep within the Earth, kind of like basketball superstars, but there have been years of research put into how to copy this natural process. This isn’t to say that your grandma’s diamond wasn’t under the ground being compressed in the Earth for 10 million years, but it is possible that it was created in another way.

Firstly, a little background on diamonds. Diamonds are very strong and very structured, almost pure carbon crystals; they are perhaps the most perfect structural compound on (or in) the Earth due to their purity. They are made from graphite in the Earth’s crust that has been under high temperature and high pressure for millions of years, and it’s even theorized that volcanic activity millions of years ago moved most of the diamonds we dig for today to the surface.

Gemological Institute of America, Diamonds of various colors

The structural purity (greater than 95%) is what is sold at the jeweler, these diamonds are usually completely transparent. Unpure diamonds can range in color from yellow to brown to blue to green and contain nitrogen or boron to impede on the carbon structure, color, luster, and transparency. These diamonds are usually used in other products like cutting blades or heat sinks.

Gemological Institute of America, Various diamonds from growth methods, CVD (left), HPHT (middle), natural (right)

So how are lab grown diamonds made? Well, most labs don’t have volcanoes in them to produce high pressure and high heat, however this is one of the ways labs mimic diamond growth. HPHT diamonds, aka high-pressure, high-temperature diamonds were first made with repeatability by a General Electric research group in 1955 led by Tracy Hall and Herbert Strong. Their process starts by placing graphite and high carbon materials (diamond seed) in a capsule of molten iron, nickel, or cobalt, surrounded by anvils and wrapped in a steel belt press to pressurize with. Their diamonds were small and not gem-quality, however the process could be easily reproduced and Hall later made many improvements to the process. This is still a widely used general procedure with variations to how pressure is applied to the capsule.

Another common way of crafting diamonds is by chemical vapor deposition, or CVD. CVD diamonds are made from a carbon containing gas, like methane, that is heated to 900-1200 °C and blasted with microwaves for multiple weeks. The carbon gas can deposit (change from the gas directly to the solid phase) on a diamond seed crystal, which sometimes is created with the HPHT process. Diamonds created this way must be removed from a graphite outer layer, like a shell, and annealed to the correct color. Diamonds made this way are indistinguishable from natural diamonds and are jeweler ready to be cut, polished, and sold. There are many improvements to this method over HPHT as the environment for the diamond growth is much cleaner than HPHT, less pressure is used, and crystal color can be more easily controlled.

Sustainable Nano, NSF Center for Sustainable Nanotechnology, nanodiamond powder (left), nanodiamond clump (right)

A more fun way of nanodiamond synthesis was started in the 1960s by the USSR utilizing explosive materials. Using explosions to create diamonds is called detonation nanodiamond. The high pressure, and high temperature caused by the shock wave of explosions is what causes a carbon rich environment to have enough pressure applied to create diamonds on a nanoscale. The explosive material contains a mixture of RDX and TNT put in a metal camber and filled with water, ice or gas. Diamonds made in this way have been up to 5nm in diameter. The soot of the explosion is anywhere from 25-85% of the weight of the yield and diamonds are usually made in a very small amount. Also, the purification process for this can be expensive, and obviously explosions are dangerous. Diamonds made in this manner are definitely not large enough for jeweler use.

Even though nanodiamonds can’t be used for jewelry, next time you see your mom, you might want to ask if her wedding ring was made from magma or from a plasma diamond gas.