Diamond nanodiamond particles

In comparison to bulk diamond, nanodiamond particles are distinctly more reactive. This may be explained by the larger number of defects and by a markedly enlarged surface. Both effects increase the number of potential sites for the attack of a reagent, thus facihtating chemical modifications of nanodiamond particles. These include not only a functionalization of the surface, but also a conversion into other forms of carbon as discussed in Section 5.5.3. Due to the defective structure and to the presence of small graphitic domains on the particle surface, these transformations as well proceed much easier here than with macroscopic diamond particles. 

The DND used in this work was represented by nanodiamond particles (4 nm in size, as determined from the pristine DND diffraction pattern peak width analysis. Fig. 1 b) partially aggregated into larger formations, including globules with the average diameter of -300 nm (Fig. la). Diamond nanoparticles within the aggregates are bound together with sp carbon [3] whose presence results in the broad peak at 20 = 22° in the diffraction pattern of the DND used. 

Depending on the method of their preparation, the individual nanodiamond particles do not exist as isolated crystallites, but they form tightly bound agglomerates. Apart from unordered sp - and sp -hybridized carbon, they may also include other impurities. The latter may originate either from synthesis or purification, for example, finely dispersed material from the reactor walls may contaminate the sample (Section 5.3). This is especially true for material produced by the detonation or shock wave method, whereas hydrogen-terminated diamond nanoparticles do not show this effect. 

From the hydrogenation or fluorination of a diamond material, a very hydro-phobic surface results that may then enter into an exchange with rather nonpolar compounds. A connection via Jt-stadting, however, plays just a minor role because graphitic fragments are only found in small domains on the particle surface. In the case of thermally graphitized nanodiamond particles, on the other hand, the conditions largely resemble those observed for multiwalled nanotubes. The interaction of the 7t-electrons with the polymer molecule causes a stable noncovalent incorporation into the composite. 

The generation of carbon onions in space has not yet been fuUy elucidated. However, it seems reasonable to assume that they originate from nanoscopic diamond particles. These may be converted into carbon onions upon heating, electron bombardment, or intensive irradiation (Section 4.3.5.4). The existence of nanodiamonds in extraterrestrial material could be confirmed by analyses on different meteorites. Especially the AUende meteorite contains significant amounts of tiny diamond particles (Section 5.1.2). 

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