How HPHT works - the technology that makes flawless synthetic diamonds

It took billions of years for the Earth to form diamonds deep within its crust under conditions of phenomenally intense heat and pressure. But thanks to science, now it is also possible to recreate these conditions in the lab and produce synthetic diamonds that are not only much cheaper than natural diamonds but also of a higher quality. Remarkably, it all starts with some graphite -- the same material found in pencil lead.

The technology behind this remarkable ugly duckling-like transformation is called high pressure, high temperature, or HPHT for short. Here's all you need to know about it.

Same carbon, different arrangement

In the 18th century, European scientists were flabbergasted to learn that diamonds and graphite were essentially made out of the same thing: carbon. The difference between a material that is hard enough to cut through stone and its polar opposite that is so brittle it's used as pencil lead is owed to the crystal lattice -- the three-dimensional arrangement of atoms.

Diamonds (left) have a more complex crystal lattice structure compared to graphite (right) that is made of stacked hexagonal sheets. Credit: Wikimedia Commons.

In diamonds, carbon atoms are arranged tetrahedrally, which is a 3-D structure that is very resistant to compression, whereas graphite is made of layers of carbon atoms that are arranged in 6-membered, hexagonal rings.

Essentially diamond and graphite are allotropes of carbon -- different forms that an element can take.

In order to bond carbon atoms tetrahedrally, you need to subject them to intense heat and pressure. Typically, diamonds form at depths of around 150-200 kilometers below the surface of Earth, where temperatures average 900 to 1,300 degrees Celsius and the pressure is around 50,000 times greater than on the surface.

The diamonds that we see today were brought to the surface by a very deep-seated, violent volcanic eruption. These eruptions occurred a long time ago in the Earth's history during a time when the planet was much hotter. In the process, these ancient events carried the already-formed diamonds from the upper mantle to the surface of the Earth.

The science of synthetic diamonds

Diamonds are so fashionable because they are aesthetic, but also in limited supply, which makes them ideal for jewelry. However, their inherent low supply can be a headache for the other industries that depend on them.

Diamond is the hardest known natural substance. Diamonds are also chemically resistant and have the highest thermal conductivity of any natural material. These properties make them suitable for use as a cutting tool and for other uses where durability is required.

In the wake of World War 2, the U.S. government was made fully aware of the strategic importance of diamonds. Private companies were also economically incentivized to find solutions, which is why General Electric (GE) started “Project Superpressure”, which aimed to manufacture synthetic diamonds at the company's lab in New York.

After a number of false starts, on December 16, 1954, GE's Dr. Tracy Hall made history after he removed a glistering sample from the lab's high-pressure chamber. Later, Hall described this moment:

“My hands began to tremble; my heart beat rapidly; my knees weakened and no longer gave support. My eyes had caught the flashing light from dozens of tiny . . . crystals. I knew that diamonds had finally been made by man.”

For his efforts, Hall was awarded a $10 savings bond by General Electric. Enraged by the lack of credit and subsequent government intrusion in his patents, Hall left GE and founded MegaDiamond, which to this day remains one of the most important synthetic diamond providers in the world.

Dr. Tracy Hall, 1954. Credit: Wikimedia Commons.

Since the 1950s, scientists have improved upon Hall's methods greatly. Today's most effective presses are the cubic-type presses that can build up pressure of 70,000 bars per square inch, at a temperature of around 2,500°C.

Modern HPHT methods can create synthetic diamonds as large as 12 carats, which allows them to be sold as jewelry as well.

HPHT diamonds are virtually indistinguishable from natural diamonds

Despite what you might have heard from natural diamond dealers, synthetic diamonds aren't worse. That's just a myth. In fact, not even trained jewelers can spot the difference -- how could they if the two are, after all, chemically identical? Well not exactly. It is possible to tell a HPHT diamond apart from a natural one using advanced spectroscopic techniques to look for telltale features such as the lack of natural graining in the stone. In other words, you can tell if a diamond is synthetic if it's too perfect.

HPHT can be used to create synthetic diamonds from scratch or alter and improve natural diamonds through color enhancement.

To produce a synthetic diamond, carbon is first placed in a graphite capsule, along with a catalyst that enables the crystallization to form and a small seed diamond the size of a grain of sand, which functions as the starting point for diamond formation. It takes about two days under constant high temperature and pressure for the diamonds to form. The rough gem can then be cut and polished to fit the client's custom requirements -- even if that involves a loved one ashes.

Any carbon can be turned into diamond, why should carbon from cremated ashes be any different?

The cremated remains of a person can be turned into diamonds after an initial purification procedure that produces graphite out of 1%-4% of the total mass of the ashes. After another superheated purification process, the cremated remains are turned into 99.995% pure carbon that can be placed in the HPHT press.

Naturally grown diamonds are millions of years old and can be almost indestructible. Thanks to advances in technology that have shaped these forces of nature, it is now possible to condense this process in only a few days, enabling you to honor the memory of a loved one by immortalizing their ashes into diamond cremation jewelry.

Rather than keeping your loved one's cremated remains in an urn, why not treasure their memory inside a unique diamond that could outlive humanity itself.

This article was written by Tibi Puiu.

Tibi is a science journalist and co-founder of ZME Science. He writes mainly about emerging tech, physics, climate, and space. In his spare time, Tibi likes to make weird music on his computer and groom felines.

https://twitter.com/tibipuiu / https://www.linkedin.com/in/tibipuiu/