Agglomeration of Nanodiamond

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. 

Agglomerates of nanodiamond feature a hierarchical composition that is characterized by very tightly bound primary aggregates and by grape-like secondary 

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Two other crucial aspects must be considered for the production of nanodiamonds of reproducible quahty firstly, the impurities must be removed from the sample of course. Secondly, it is important for many further apphcations to release the primary particles from the agglomerates. Today there are various methods available that meet both requirements. 

Figure 5.9 Model demonstrating agglomerated nanodiamond (a) the HRTEM-image (b) shows the soot-like structures present on the surface of the diamond particles.

The sp -hybridized constituents of the nanodiamond sample (mostly the outer layers of the particles and, in parts, the material in the interstices of the agglomerates under examination) are characterized by two bands that have already been mentioned in the carbon nanotubes and onions the G- and the D-band. The exact position of the G-band (observed at about 1580 cm" ) depends on both the excitation wavelength (dispersion) and the particle size. With decreasing wavelength of... 

A suitably conducted thermal treatment, for instance, removes not only adsorbates, but also functional groups. At sufficient temperatures (usually >800 °C) in vacuo, the surface looses its functionalization, and a graphitization of the nanodiamond s outermost shell occurs. However, a thermal treatment still increases agglomeration, so a functionalization of single primary particles cannot be achieved in this manner so far. 

Nanodiamond consists of particles showing a size in the range of nanometers. A distinction has to be made between materials containing very small particles (d 4nm) on the one hand and larger nanodiamond particles on the other. Very small particles tend toward agglomerate formation, which is favored by the presence of graphitic carbon as well as by the functional groups situated on the particle surface. The preparation can be achieved in different ways (Box 5.1)... 

Y.L. Hsin, H.-Y. Chu, Y.-R. Jeng, Y.-H. Huang, M.H. Wang, and C.K. Chang, In situ de-agglomeration and surface functionahzation of detonation nanodiamond, with the polymer used as an additive in lubricant oil. Journal of Materials Chemistry, 21 (35), 13213-13222,2011. 

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