By Robert Hazen, Ph.D., George Mason University
More than 200 years ago, scientists began to explore ways to transform common graphite into synthetic diamonds. The change of a substance from one atomic arrangement to another using the exact same collection of atoms—particularly from one solid form to another solid form—is called a phase transformation. Early attempts focused on extremely high temperatures for the process.
Carbon Cousins
One of the most dramatic examples of phase transformations is provided by the element carbon, element 6, which occurs naturally in two forms. It occurs in the common black form called graphite and in the extremely hard form called a diamond. And these two compounds differ remarkably in their physical properties and their behavior.
Soft, black graphite is one of the softest materials known. It’s used as a lubricant. It’s the lead in your pencil, and as you write across a page, you strip off layers of the graphite structure, it’s so soft. But a diamond is colorless. It’s hard—indeed, the hardest known substance. And yet, it’s composed of the exact same element, carbon.
We now know that these differences are the result of the difference in the crystal structure of these two forms. Graphite, soft graphite, primarily has van der Waals bonds holding layers together. And you can see those flat layers of carbon atoms in which each carbon is linked to three others in a planar arrangement. That’s the low-pressure, soft form. And it’s the van der Waals bonds that make it soft.
Diamond, on the other hand, has a rigid, three-dimensional network in which every carbon is connected to four other carbons. This is an incredibly hard, incredibly strong structure because of this cross-linking, the three-dimensional arrangement of bonds. And so diamond is the hardest known material.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
Understanding How Nature Made Diamonds
It was not until the 1870s that geologists discovered the key to making diamonds. Two children were playing in a South African streambed, and they found a shiny pebble that weighed 20 carats. It came to be known as the “Eureka Diamond”. And that Eureka was the beginning of the South African diamond rush.
They found the first examples of diamonds in their native rock, a rock called kimberlite. And it turns out that that rock told an amazing story. Kimberlites are volcanic rocks, and they erupt from deep within the Earth. And in the final stages of these eruptions, the rocks come whooshing to the surface at the speed of sound, blasting out of the surface, showering diamonds over hundreds of square kilometers.
Geologists quickly realized that diamonds come from great depth in the Earth and that pressure is the key to its synthesis. Well, using theories that relate a material’s structure to its stability, scientists were able to calculate what those pressures were.
Not only does diamond require tens of thousands of atmospheric pressure, but it also requires temperatures over a thousand degrees to make the carbon atoms wiggle enough that they’ll break bonds and re-form from graphite to the diamond form.
Learn more about the discovery of radioactivity.
Failed Experiments to Synthesize Diamonds
For decades, many people tried, and many people failed spectacularly in their attempts to synthesize diamonds from graphite at high temperature and high pressure. One example is James Ballantyne Hannay, a Scottish chemist who tried an intriguing way of approaching the diamond synthesis problem. He had gun barrels, and he packed them full of carbon-rich materials.
He then welded the barrels shut and stuck them in a hot fire. Well, huge temperatures and pressures developed inside the gun barrels, but eventually, the barrels exploded. So, what Hannay did was went to larger and larger gun barrels, some of them up to several inches in diameter, which progressively exploded at higher and higher pressures with more and more violence. But Hannay did not make diamonds.
Another bizarre attempt was made by Baltzar von Platen, a Swedish inventor. In conjunction with the Swedish General Electric Company, von Platen had an idea for a machine in which he had a large sphere of metal split into pieces, the pieces forcing themselves down on a tiny carbon sample. Well, von Platen used a split-sphere device in which he divided up a sphere into six anvils, each of those anvils pressing down on the face of a cube. The cube was made of graphite.
Each of these experiments was then jacketed in copper, immersed in a huge water tank pressurized to thousands of atmospheres. And an inner core of thermite, a high-temperature explosive, was set off in order to generate the pressure and temperature needed to make diamonds. And the Swedish company failed time and time again at the cost of countless hundreds of thousands of dollars.
Learn more about what makes some types of atoms particularly unstable and reactive.
Synthetic Diamonds
It wasn’t until 1954 that a team of scientists at General Electric in Schenectady, New York, succeeded in making the very first synthetic diamonds. This was an amazing team effort. The way they went about it was to first assemble a team of scientists. They had materials engineers, chemists, physicists, people who approached different aspects of the diamond-making problem.
Well, it took several years, fits and starts, but eventually, in December of 1954, the first synthetic diamonds were manufactured by General Electric. And, in fact, in a matter of a few months, they were producing buckets of diamonds in a commercial process. Today, diamond synthesis is a worldwide enterprise of vast proportions.
Every year, more than a hundred tons of synthetic diamonds are manufactured in plants around the world. That’s more diamonds manufactured each year than all the gemstone diamonds that have been mined since biblical times combined. These synthetic diamonds are usually in the form of very fine-grain grit.
Common Questions about the Quest for Synthetic Diamonds
Compared to diamonds, natural or synthetic, graphite is much softer because of structural differences and bonds.
When the Eureka diamond was discovered in the 1870s, geologists started to understand what was going on in the depths of the Earth, helping them understand how to manufacture synthetic diamonds.
The company made the quest for a synthetic diamond a team effort. They hired specialists from various fields to help with the project.
