Study on the HPHT synthetic diamond crystal from Fe-C（H） system and its significance

Investigations of crystal habit, micro-topographic imaging, micro-composition and micro-structural analysis of HPHT synthetic diamonds from the Fe-C（H） system indicate that most of them have an octahedral habit. The crystals grow mainly layer-to-layer from center to periphery. HPHT synthetic diamond is smaller in size than natural diamond because it only goes through nucleation and growth in the early stage. In the middle and late stages, due to the coalescence of diamond grains related to differences of surface energy, the growth of HPHT synthetic diamond is limited. The active energy （E） of transforming single nitrogen into a nitrogen-pair is lowered and the time of transforming single nitrogen into a nitrOgen-pair is shortened because of the existence of hydrogen. Therefore, aggregate nitrogen （A-centers） may exist in synthetic diamond from HPHT and explosive detonation processes. It needs further discussion on a worldwide view that the time of natural diamond formation extracted from nitrogen aggregation is some hundred million years. Consideration of the way in which surface energy influences the growth of diamond can help to understand some of the remaining issues （e.g. growth mechanism, etc.） in the HPHT synthetic process and effectively explain the formation of natural diamond in terms of HPHT thermodynamic theory. Especially, it is important to pay more attention to the influence of hydrogen on surface energy in that hydrogen may be a ＂bridge＂ for explaining the formation of HPHT synthetic and natural diamond.

Study on the HPHT synthetic diamond crystal from Fe-C(H) system and its significance

Investigations of crystal habit, micro-topographic imaging, micro-composition and micro-structural analysis of HPHT synthetic diamonds from the Fe-C(H) system indicate that most of them have an oc-tahedral habit. The crystals grow mainly layer-to-layer from center to periphery. HPHT synthetic dia-mond is smaller in size than natural diamond because it only goes through nucleation and growth in the early stage. In the middle and late stages, due to the coalescence of diamond grains related to dif-ferences of surface energy, the growth of HPHT synthetic diamond is limited. The active energy (E) of transforming single nitrogen into a nitrogen-pair is lowered and the time of transforming single nitro-gen into a nitrogen-pair is shortened because of the existence of hydrogen. Therefore, aggregate ni-trogen (A-centers) may exist in synthetic diamond from HPHT and explosive detonation processes. It needs further discussion on a worldwide view that the time of natural diamond formation extracted from nitrogen aggregation is some hundred million years. Consideration of the way in which surface energy influences the growth of diamond can help to understand some of the remaining issues (e.g. growth mechanism, etc.) in the HPHT synthetic process and effectively explain the formation of natural diamond in terms of HPHT thermodynamic theory. Especially, it is important to pay more attention to the influence of hydrogen on surface energy in that hydrogen may be a "bridge" for explaining the formation of HPHT synthetic and natural diamond.