Diamond is one kind of carbon. There are few types of diamond. See bellow:
1). Natural idamonds
Natural diamonds were reported in India about 700BC, but the technique of cutting and polishing to emphasize their beauty was not extablished until the late 14th century. The major source of natural diamond is the mineral kinberlite, which is found in igneous rocks and mined in Africa, Australia and Russia. Typically, only some 32carats of diamond are produced from 100tons of ore, the diamonds are identified by an X-ray beam, which causes the diamonds to luminesce, facilitating their separation and collection. A very small part of this output is selected for gemstones, which wil lose a further 50% of the weight when they are cut and the unselected material is then graded for industrial pruposes.
In the industrial sector, single crystals present an uninterrupted diamond cutting dege to give a surface finish to the workpiece better then 0.025um, but new developments with synthetically produced diamonds are rapidly displacing the natural product.
2). High pressure synthetic diamonds
Obviously, with the high cost of natural diamonds, there was always been a desire to manufacture diamonds synthetically. Examination of the phase diagram shows the very high temperatures and pressures are required to synthesize diamond from graphite and, fortunately, this can be avoided by using metal catalyst that ifself asts as a solvent for the diamond and the less soluble diamond phase crystallizes out. In this way, making larger diamonds is an expensive process, but synthetic diaminds are consistent and tool blanks can be sawn to give platelets up to 2mm thick and 8mm long.
3). Polycrystalline diamond (PCD)
Single crystal diamonds are bonded with Co or Ni under high pressure and high temperature to produce PCD, which has superior toughness to single crystal diamond, but due to the presence of cleavage planes, tends to be brittle and may fail under impact. PCD does, however, have a temperature limitation of 700C due to the presence of Co or Ni, with can promote reverse synthesis, I.e., conversion of diamond back to graphite. PCD diamond has become a high performance replacement for tungsten carbide tooling.
4). Chemical Vapor Deposition diamond
Coatings of diamond can be produced on a substrate by the reaction of carbon based gases with atomic hydrogen, in the presence of traces of oxygen, to give polycrystalline diamond, which grows in a columnar structure and is fully dense. CVD diamond has greater thermal stabilitythen PCD diamond, but is relatively brittle and the lack of electrical conductivity precludes the use of spark crosion.
Hollow diamond fibers have been produced by using the CVD process to coat diamond onto a wire, preferably with a relatively low thermal expension coefficient and having carbide-forming properties.
Diamond has also been deposited onto carbon fiber. Such as Pan and pitch carbon fibers with diameter as small as 5um by microwave H-palsma assisted chemical vapor depositon.
5). Diamond-like carbon (DLC)
DLC is a produce which is neither diamond nor graphite. It has properties similar to CVD diamond, but does not require a high remperature substrate. DLC is produced at low pressure by physical vapor deposition, such as ion beam sputtering using argon and a solid carbon barget as the cathode. It does have a maximum usage temperature of about 250C.
Diamond and graphite cannot be positively identified using electron diffraction techniques alone, but Raman spectroscopy will.