Diamond type
Diamond type is a method of scientifically classifying diamonds by the level and type of their chemical impurities. Diamonds are separated into four types: Type Ia, Type Ib, Type IIa, and Type IIb. The impurities measured are at the atomic level within the crystal lattice of carbon atoms and so, unlike inclusions, require an infrared spectrometer to detect.
Diamond-like carbon
DLC exists in seven different forms. All seven contain significant amounts of sp hybridized carbon atoms. The reason that there are different types is that even diamond can be found in two crystalline polytypes. The more common one has its carbon atoms arranged in a cubic lattice, while the less common one, lonsdaleite, has a hexagonal lattice. By mixing these polytypes in 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 such as hydrogen, graphitic sp carbon, and metals are used in the other 6 forms to reduce production expenses or to impart other desirable properties.