Diamond nano-particles

The support for the metal nano-particles turns out to be as important as the nano-particles for providing their dispersion and stability. Studies on electron transfer are particularly important for carbon-based materials because those materials, such as glassy carbon, graphite, fullerene, and diamond with different electronic and structural properties, have been proved to possess distinctly different electrochemical properties from each other (Ramesh and Sampath, 2003). Carbon supports provide high electronic conductivity, uniform catalyst dispersion, corrosion resistance, and sufficient access of gas reactants to the catalyst (Ismagilov et al, 2005). In addition to electrical conductivity and surface area, hydrophobicity, morphology, porosity, and... 

The ultrafine diamond obtained by explosive detonation possesses two distinguishing features nano-scaled particle sizes and surface functional groups. 

Owing to their curved and defective structure, carbon onions are quite easily converted into other forms of carbon. The transformation of spherical particles into faceted nanoparticles by heating to at least 1900 °C has already been described in Section 4.3.5.3 on the thermal produchon of nano-onions from diamond particles. 

Little is known so far about the chemical properties, yet first results suggest a reactivity similar to that of multiwalled carbon nanotubes. Furthermore, a transformation of nano-onions into other forms of carbon can be achieved by heating (equihbration as faceted nanoparticles) or electron bombardment. In large carbon onions, a formation of small diamond clusters due to internal self-compression has been observed. These grow up to be nanoscale diamond particles under complete consumption of the onion structure. 

It is commonly recognized that a comprehensive understanding of the properties of a new material is an essential prerequisite to finding its new applications. In this respect, the study of ultrafine diamond is incomplete and its properties remain to be fully elucidated. For example, the nature of the surface functional groups and the method of their modification the nature of the agglomeration of ultrafine crystallites and effective methods of de-agglomeration to prepare mono-dispersed suspension the crystalline and surface structures of the nano-scaled diamond, etc., are appropriate subjects of research An efficient method for the determination of particle size distributions and structures of nano-sized particles in suspension is very important, and is worth developing in the near future. 

As mentioned above (see Sect. 2.3.4, Table 2.16), the experimental values of the band gaps ( g) in most substances increase as the grain sizes decrease. Diamond is an exception, its g decreasing together with the grain sizes. Here, an important role is played by the curvature of the surface layer, which results in the negative electron affinity of nano-diamond particles [30, 31]. 

Diamond and cBN powders produced by milling are essentially monocrystalline and dominate the market. However, polycrystalline diamond powder can also be produced by shock synthesis. Under suitable conditions, shock waves produced by explosively driven projectiles can produce HPHT conditions in confined volumes for a sufficient duration to achieve partial conversion of graphite into nanometer-sized diamond grains which can also sinter into micrometer-sized, polycrystalline partieles." This process was commercialized by DuPont to produce a polycrystalline DMP (trade name Mypolex ) that is more friable than monocrystalline DMP and is well suited to fine polishing applications. Hexagonal (graphite-hke) BN will also react under shock-synthesis conditions, but the dense, nanometersized particles that are produced are of the wurtzite phase (wBN) rather than the cubic phase. So far, nano-wBN has not achieved much commercial importance. 

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