Diamonds Are Weirder Than You Think

In Neal Stephenson’s science fiction masterpiece The Diamond Age: Or, A Young Lady's Illustrated Primer, microscopic nanobots build fantastic structures and extravagant objects out of diamond. They assemble mile-high buildings atom by atom, constructing colossal translucent towers stronger and more durable than anything we can imagine today. Of course those opulent towers are only accessible to a select few elites and the rest of humanity lives in nightmarish toxic squalor, but the theoretical technology is still fascinating. And its based on the very real and very strange properties of diamonds.   Diamonds are made of carbon, the fourth most abundant element in the universe, and the second most abundant element in your body. It is the key element of life, the backbone of organic chemistry. Carbon is special because it so easily bonds with other elements to create a huge variety of compounds and materials, everything from simple sugars to bones. Of course most recently it has gained fame as the core component of carbon fiber, a super-light and super-strong material made from carbon threads and resin. Carbon fiber’s strength is due in large part to its unique arrangements of carbon atoms. Carbon can bond to itself in many ways, creating complex structures with many different properties. In carbon fiber, the element bonds together to create extremely tough chains that resist stretching. Arrange those atoms differently, however, and you get bizarre and astonishing results.    Diamond is pure carbon arranged in a cubic crystal structure. Each atom is bonded to four other atoms to form a tetrahedron, or pyramid, shape. Carbon in this arrangement is incredibly hard, in fact it’s by far the hardest material we’ve discovered. Hardness is, simply put, how much a material resists denting or scratching. This is a well-known fact; we’ve all seen cat burglars using diamond glass cutters to steal priceless artifacts, or used diamond-coated drill bits or saw blades to cut through tough materials like steel. But diamonds have other amazing properties that are often overlooked.   Diamond has the highest thermal conductivity of any material. That means it can transfer heat better than anything else, which is why real diamonds can feel warm to the touch whereas cheap knockoffs feel cool. To understand just how amazing diamond is at transferring heat, we first need to understand thermal conductivity. Thermal conductivity is measured in Watts per meter-Kelvin, W/mK. A material with a conductivity value of 1 W/mK will transfer heat at a rate of 1 watt for every degree of temperature difference between opposite faces.    That’s all pretty meaningless without a solid example, though. Pure copper, the famously good electrical and thermal conductor, has a conductivity of around 400 W/mK. Gold measures in at 327 W/mK. Diamond, however, has a thermal conductivity between 1,500-2,200 W/mK.   Why can diamond conduct heat so well? Again, the secret lies in its structure. Heat can quickly and easily propagate through its cubic crystal structure in the form of atomic vibrations called phonons. In condensed-matter physics, a phonon is a unit of vibrational energy that arises from oscillating atoms within a crystal. Heat energy zips right through diamond’s crystal lattice.    Electrons, however, can’t travel through diamonds at all. This makes them electrically non conductive, in other words an insulator. Combine high thermal conductivity with zero electrical conductivity and you get a material that’s perfect for dissipating heat away from sensitive electronics. Electrical engineers use diamond to quickly and efficiently channel heat away from sensitive circuitry. These components, called diamond heat spreaders, are used in satellites, airplanes, and other equipment that must endure extreme conditions. They’re also used in high-performance computing, LED lighting systems, electric vehicles, radiofrequency (RF) transmitters, and high-power lasers.