10 Myths About Diamonds

Dec. 19, 2016
We debunk some of this most prevalent falsehoods associated with this unique engineering material.
Image courtesy of Thinkstock

You wouldn’t necessarily have assumed this to be the case, but myths associated with diamonds are actually quite prevalent. Here are 10 of the most common:

1. All diamonds are created by Mother Nature.

As far back as the 1950s, companies such as General Electric and Industrial Distributors Ltd. (later rebranded to Element Six) started producing diamonds in a high-pressure, high-temperature process (HPHT). Under these conditions, which mimic the environment 100 miles below the Earth’s surface, diamonds are grown using a source of carbon (typically graphite, such as that in a pencil), and a metal that acts as a solvent for the carbon.

Other methods have also been developed for synthesizing diamonds. The chemical vapor deposition (CVD) method creates a diamond crystal in a layer-by-layer process with pressure and temperature conditions that are wildly different from those used in HPHT. In CVD, growth conditions are created by the thermal disassociation of hydrogen combined with a gaseous source of carbon in plasma at a temperature above 2,000°C. The growth rates and control over purity in this method result in high-quality polycrystalline and single-crystal synthetic diamonds.

Today, the industrial world annually consumes about 800 tons of synthetic diamond. That’s about 150 times the weight of natural diamonds mined as gemstones.

2. Natural diamonds are the most flawless.

The most common form of natural diamonds contains impurities in their carbon crystal that that were are picked up from the environment they grew in. These diamonds, known as type Ia, make up 98% of all natural diamonds and contain up to 0.3% (or 3,000 parts per million) of nitrogen. This impurity often gives the diamonds a yellowish color due to the defects in the crystal that absorb light of a particular frequency. Colorless natural diamonds, type IIa, have low levels of nitrogen impurities and are extremely rare, accounting for only about 1% of mined diamonds.

But CVD gives engineers such control over the synthesis process they can manipulate the crystal structure down to the level of single-atom defects and impurity levels typically in the parts-per-billion range. This control makes for fewer flaws than natural diamonds and lets them be used in a range of new applications (e.g., radiation detectors and quantum technologies).

3. Diamonds are inherently expensive as an engineering material.

Natural diamonds are inherently variable due to their natural growth and different environments. This makes natural diamonds with precise characteristics difficult (if not impossible) to purchase in commercial quantities. Alternatively, synthetic diamonds for engineering and industrial applications are highly accessible and affordable. Through developments in HPHT, it is possible to buy diamonds suitable for many mechanical applications for as little as 15 cents/carat.

Different grades of synthetic diamond span a range of price, letting engineers leverage (and invest in) the material most suitable for their specific needs. Size and shape—as well as mechanical, thermal, and optical properties—can all be tailored to get the most suitable and cost-effective diamonds.

4. Diamonds are difficult to shape and integrate into devices.

Diamonds are characterized by exceptional hardness which, in the past, did make it difficult to process and shape them into engineered products. Diamonds are also chemically inert and are not readily coated and bonded using conventional techniques. However, developments in diamond processing, coating, mounting, and bonding now let engineers manipulate and customize diamonds into a range of shapes and bond them into various devices and applications.

For example, advances in diamond processing make it possible to fabricate complex, three-dimensional diamond tool geometries and optical components. Surface finishing can now give diamonds extreme levels of flatness and smoothness with low levels of surface damage for advanced optical applications. Diamond surfaces can be precisely patterned to mimic the structure of a moth’s eye and function as antireflective surfaces. Diamonds can also be given diffractive optical surfaces, thus increasing the damage threshold of diamond optics in high-power applications.

Further still, metallization and bonding schemes have been developed to install diamond components in electronic and optical devices with a high degree of mechanical stability and increased thermal performance. For advanced high-power semiconductor devices, techniques have even been developed to directly grow diamond materials onto semiconductor components—an accomplishment that achieves step-changes in thermal performance.

5. Diamonds are nicknamed “ice” due to their clear, sparkling properties when cut and polished.

The “ice” nickname for diamond predates cutting and polishing, and actually stems from diamond’s excellent thermal conduction properties. The crystal structure of diamond gives it thermal conductivities ranging from 1,000 to 2,000 W/mK (a thermal conductivity up to five times that of copper). Because of this characteristic, diamonds conduct heat away from the skin when touched, making it feel cold (i.e., like ice). This exceptional thermal property also makes diamonds ideal thermal management material in electronics.

6. Diamonds cannot have curved surfaces.

Diamonds are commonly thought to have flat edges or facets, but both HPHT and CVD synthesis can create diamonds with curved surfaces. HPHT, for example, can produce polycrystalline diamond in round, conical, ballistic, or other complex shapes without any post-manufacturing processing or shaping. These geometries have maximum cutting efficiencies in drilling and mining, and diamond tools maintain their shapes significantly longer than the next-best tungsten carbide alternative.

And although diamonds with curved surfaces won’t sparkle like an expertly cut faceted diamond, they can be used in loudspeakers for exceptional fidelity. Some companies use a tightly controlled CVD process to grow diamonds layer by layer on a substrate to precise shapes and dimensions. For example, this method can turn out hemispherical diamonds for use as loudspeaker tweeters in high-end audio equipment. The exceptional stiffness and low-density ratio of diamond makes it the top-performing material for this application. (Element Six continues to build on its diamond speaker dome technology design and fabrication method, for which it won a Queen’s Award for Innovation in 2012.)

7. Diamonds do not conduct electricity.

Many engineers once believed diamonds could not conduct electricity due to a tetrahedron structure made by covalent bonds between carbon atoms, which doesn’t allow for free electrons to carry current. Most natural diamonds are electrical insulators, but by manipulating the properties of diamond through CVD, it is possible to introduce controlled dopants that let the material conduct electricity quite effectively.

Adding boron to the lattice make diamonds blue at low concentrations and opaque at higher concentrations. At these high concentrations, diamonds behave like a metal and become a good conductor of electricity.

Boron doped diamonds (BDD) make excellent electrode materials with a larger electrochemical potential window in aqueous solutions than conventional electrode materials. BDD are also extremely chemical-stable and able to survive in extreme environments, such as highly contaminated waste water treatment applications.

8. Diamond is the hardest material, and therefore is the best for machining all materials.

Although it is true that diamonds are the hardest stable material, and that intrinsic resistance to deformation should make them ideal as cutting tools, there are other factors that have to be considered. For example, diamonds can have problems when cutting ferrous materials. At the high temperatures commonly reached in cutting tool operations, iron forms a carbide which quickly causes diamond to wear.

For machining ferrous alloys, it may be beneficial to adopt other superhard materials like cubic boron nitride (cBN), the second-hardest material after diamond. It is synthesized from hexagonal boron nitride under conditions similar to those used to turn graphite into synthetic diamonds. cBN’s high thermal stability and chemical resistance make it suitable for machining ferrous materials, an area where synthetic diamond abrasives are not normally employed.

9. The world’s biggest polished diamond is natural.

The largest natural diamond, the Cullinan, was approximately 3,100 carats (620 g) in rough form. The gemstone known as the Great Star of Africa was cut and polished from the Cullinan, and at 530 carats is the largest clear cut diamond in the world. However, polished CVD diamonds greatly outweigh this impressive stone. Optical windows that are made using CVD and then used in high-power lasers for cutting and welding can reach weight more than 1,000 carats.

10. Diamonds are forever.

Many believe that because of the hardness and durability of diamonds, they are practically indestructible. In fact, diamonds do not last forever. Diamonds and graphite are both made of carbon, only bonded differently. Diamonds degrade to graphite because graphite is a lower-energy configuration under typical conditions. However, before this degradation is possible, there is a significant energy barrier to overcome, which means this process is so slow that diamonds last billions of years. So although not exactly indestructible, diamonds can be considered as lasting “forever”—at least for us.

David Hardeman is a senior research scientist at Element Six.

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