Detonation nanodiamond

Detonation nanodiamond (DND), also known as ultradispersed diamond (UDD), is diamond that originates from a detonation. When an oxygen-deficient explosive mixture of TNT/RDX is detonated in a closed chamber, diamond particles with a diameter of c. 5 nm are formed at the front of the detonation wave in the span of several microseconds.

The diamond yield after detonation crucially depends on the synthesis condition and especially on the heat capacity of the cooling medium in the detonation chamber (water, air, CO₂, etc.). The higher the cooling capacity, the larger the diamond yield, which can reach 90%. After the synthesis, diamond is extracted from the soot using high-temperature high-pressure () boiling in acid for a long period (ca. 1–2 days). The boiling removes most of the metal contamination, originating from the chamber materials, and non-diamond carbon.

Various measurements, including X-ray diffraction and high-resolution transmission electron microscopy revealed that the size of the diamond grains in the soot is distributed around 5 nm. The grains are unstable with respect to aggregation and spontaneously form micrometre-sized clusters (see figure above). The adhesion is strong and contacts between a few nano-grains can hold a micrometre-sized cluster attached to a substrate.

Nanosized diamond has extremely large relative surface area. As a result, its surface spontaneously attaches water and hydrocarbon molecules from the ambient atmosphere. However, clean nanodiamond surface can be obtained with appropriate handling.

The detonation nanodiamond grains mostly have diamond cubic lattice and are structurally imperfect. The major defects are multiple twins, as suggested by high-resolution transmission electron microscopy. Despite the carbon source for the diamond synthesis – TNT/RDX explosive mixture – being rich in nitrogen, concentration of paramagnetic nitrogen inside diamond grains is below 1 part per million (ppm). Paramagnetic nitrogen (neutral nitrogen atoms substituting carbon in the diamond lattice) is the major form of nitrogen in diamond, and thus the nitrogen content in DND is probably very low.

...
Wikipedia