Carbon a streak on paper (hence its name, from the Greek verb "γράφειν" which means "to write"), while diamond is the hardest naturally occurring material known. Graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form at standard temperature and pressure. They are chemically resistant and require high temperature to react even with oxygen. The most common oxidation state of carbon in inorganic compounds is
Diamond-like carbon various ways at the nanoscale level of structure, DLC coatings can be made that at the same time are amorphous, flexible, and yet purely sp bonded "diamond". The hardest, strongest, and slickest is such a mixture, known as tetrahedral amorphous carbon (ta-C). For example a coating of only 2 μm thickness of "ta-C" increases the resistance of common (e.g., type 304) stainless steel against abrasive wear, changing its lifetime in such service from one week to 85 years. Such "ta-C" can be considered to be the "pure" form of DLC, since it consists only of sp bonded carbon atoms. Fillers