Chemical

Diamond is chemically inert and (due to the high strength of the covalent bonds) is highly resistant to chemical attack by acids or other chemical reagents. The only exceptions are materials that at high temperatures act as oxidising agents - these provide the only effective way to attack diamond at normal pressures and temperatures (below about 1000°C). Salts, such as sodium nitrate, are known to attack diamond when in the molten state at temperatures as low as 450°C and, in oxygen itself, diamond starts to be oxidised at around 650°C.

The only other possible form of chemical attack is by two groups of metals. The members of the first group are strong carbide formers, and include tungsten, tantalum, titanium and zirconium. At very high temperatures, these will react chemically with diamond to form their respective carbides. The second group of metals includes iron, cobalt, manganese, nickel and chromium (and also the platinum group of metals). In the molten state these metals are true solvents for carbon.