I was always taught the pure carbon could exist in one of three forms: carbon black, graphite, which is stacked sheets of carbon crystals making it quite soft and giving it a lubricating property, and diamond which is crystalline, hard, and abrasive.
Coal is and amorphous form of carbon which has been compressed. If you take that compression to the extreme, you can form a amorphous material that has a hardness similar to diamond. This conversion take place at a temperature of 1800 degrees Kelvin and 500,000 times atmospheric pressure. That is pretty extreme.
Amorphous diamond can be used as a coating for steel. Thus, it does have a myriad of potential applications, including razor blades. A patent application was filed for use of this type of coating on razor blades. It is US US5940975A filed in 1997.
Here is the abstract of that patent:
Reference:
https://patents.google.com/patent/US5940975A/en
Abstract:
Improved razors and razor blades and processes for producing razor blades or similar cutting tools with sharp and durable cutting edges, by hard-carbon coating of blades with amorphous diamond, preferably using a filtered cathodic arc plasma source. A coating of amorphous diamond having at least 40 percent sp3 carbon bonding, a hardness of at least 45 gigapascals and a modulus of at least 400 gigapascals is applied to the sharpened edge of a substrate. The substrate may be mechanically honed, and there is no interlayer between the substrate and the amorphous diamond coating. The coating imparts stiffness and rigidity to a thin blade while maintaining a high aspect ratio.
Although the concept has been around for 25 years, it seems that manufacturers waited for patent protection to expire before attempting to use the material as a blade coating. Only time will tell if amorphous diamond coating will revolutionize the razor blade industry in the same way that the Teflon coated stainless steel blades did in the 1960s.