Carbon is one of the most famous chemical elements to be found in our everyday lives. It can take many forms, which is why it's found in coal, steel tools, stainless steel cookware, plants and even the human body. A distinction is made between crystalline, amorphous and molecular carbon. Each of these varieties is based on a specific structure and therefore has different physical and chemical properties. Amorphous carbon has an excellent coefficient of friction and excellent resistance to abrasion.
What is amorphous carbon?
Chemically speaking, amorphous carbon is an allotropic form of carbon with no crystalline structure. This definition, which seems particularly technical, means that amorphous carbon actually represents a specific variety of carbon, with a structure different from that of crystalline carbon, as found in diamond and graphite. The term allotropic comes from the Greek and combines the notion of allos, other, and tropos, way. This qualifier indicates that carbon can exist in different forms, the three best known being crystalline carbon, amorphous carbon and molecular carbon. Each of these varieties of carbon has very specific properties.
In its natural state, carbon is ubiquitous, appearing as much in the tissues that make up the human body as in steel, plastic and minerals such as coal and diamond. Its many forms make it a unique chemical element, and as a result, two materials made of carbon can display diametrically opposed properties. To take the example of diamond, which is based on a crystalline structure, it is the hardest element on the planet, with a hardness of around 10,000 HV. Graphite, on the other hand, is the "softest element in the world". This great difference in value actually depends on the nature of the covalent bonds between these two chemical elements. Diamond forms SP3 bonds, while graphite creates SP2 bonds. This is a decisive parameter that can be influenced to transform material properties.
Why use this variety of carbon?
Because of its non-crystalline structure, amorphous carbon offers the possibility of forming different bonds and thus of revealing new physical and chemical properties. It can be used, for example, to produce adamantine carbon. By way of illustration, amorphous carbon is used in the manufacture of carbon fibers, famous for their lightness.
Controlling these different bonds is an excellent way of modifying the behavior of materials. Acting on the quantity of SP2 or SP3 bonds, for example, can produce DLC, Diamond Like Carbona solution developed by Thermi Lyon. It boasts very good wear resistance, close to that of diamond, which remains the ultimate abrasive, but also real flexibility, like graphite. Although graphite is not resistant to abrasive wear, it is a highly effective lubricant and is used in the composition of several oils. DLC technology has the advantage of being able to adapt to the environment of the parts it is used to manufacture, whether they require a good coefficient of friction or solid resistance to abrasion, for example.
DLC, a versatile solution based on amorphous carbon
Diamond Like Carbon can be manufactured by PVD or PACVD treatmenttreatment, i.e. by adding special layers to the surface of the parts. This process makes it possible to modify the SP2 and SP3 bonds of the materials, thus adapting the resistance of the parts to their working environment. Thus, if they require a high coefficient of friction, the treatment will emphasize SP2 bonds, whereas, if abrasion represents the greatest danger, DLC will have more SP3 bonds. The hydrogen content can also be adapted to give the DLC family different properties.
DLC can boast a particularly attractive hardness of up to 1,800 HV, greater than that of hard chromium or untreated steel, for example. In addition to its excellent coefficient of friction, it makes an interesting solid lubricant, highly resistant to corrosion and abrasion. Its anthracite-gray color is very appealing to certain professionals, such as those in the watchmaking industry, who see DLC as both a high-performance and aesthetically elegant solution. The technology is also a good electrical insulator and biocompatible. Its harmlessness to the human organism means it can be used in medical equipment and even prostheses.
Last but not least, DLC is produced in a vacuum, making it a carbon-neutral, eco-friendly technology. It is, in fact, a possible alternative to hard chrome, whose production method is still rather polluting.
