Preparation of Nanodiamond

Graphene has been prepared by different methods pyrolysis of camphor under reducing conditions (CG), exfoliation of graphitic oxide (EG), conversion of nanodiamond (DG) and arc evaporation of SiC (SG). The samples were examined by X-ray diffraction (XRD), transmission electron microscopy, atomic force microscopy, Raman spectroscopy and magnetic measurements. Raman spectroscopy shows EG and DG to exhibit smaller in-plane crystallite sizes, but in combination with XRD results EG comes out to be better. The CG, EG and DG samples prepared by us have BET surface areas of 46,... 

Graphene was prepared by four different methods, namely the reductive pyrolysis of camphor (CG), exfoliation of graphitic oxide (EG),4 conversion of nanodiamond (DG)5 and arc evaporation of SiC (SG).6 In the first method, to prepare CG, camphor was pyrolysed over nickel particles under a reducing atmosphere. The reaction was carried out in a two-stage furnace and camphor was slowly sublimed (170 °C) by heating from the first furnace to the second furnace held at 770 °C where the... 

Altogether the thermal transformation of nanodiamond turned out a suitable method to prepare macroscopic amounts of onion-like carbon. It is true that the products obtained are inhomogeneous to some extent and that the resulting onions show various deficiencies (defects, deviations from spherical shape), but still the heating of diamond in vacuo constitutes the best method to date to generate larger amounts of carbon onions and study in principle their physical and chemical properties. 

Appreciable amounts of perfectly spherical carbon onions are hard to obtain, and so only few experimental data on their electronic properties are available. For the irregular onion-hke carbon that may for instance be prepared from nanodiamond, on the other hand, the conductivity and other parameters have been studied much more extensively. 

Besides the direct generation of nanodiamond in a detonation, the required pressure can also be achieved by the achon of an external shock wave. Usually, the latter is induced by an explosion too and compresses the carbon material that is enclosed in a kind of capsule. A catalyst Hke, for example, copper, iron, aluminum, nickel, or cobalt is frequently employed in this process. It has already been mentioned in the introduction that nanoscale diamond particles had been prepared quite early by the conversion of other carbon materials in a shock wave. Soon after this discovery, researchers of the DuPont Corp. developed a method also based on shock action that yields very small diamond particles. These are processed by subsequent sintering to give utterly durable cutting and poHshing tools. 

Owing to its properties, nanodiamond like the classical diamond is an attractive material for many applications. For the time being, however, just a limited number of industrial scale processes has really been established due to its inhomogeneity and the variable quality available from different suppHers. Pioneers in this area are the countries of the former Soviet Union where by now access has been made to various fields of applicahon. The examples given herein comprise processes developed to an industrial scale already as weU as such stUl operahve on a laboratory scale. They include the preparation of composites and coatings, mechanical apphcations to reduce friction or to modify surfaces, uses in electro-deposition or biomedical apphcahons. 

The preparation of composite materials in general is a very important appHca-tion of the mechanical properties of nanodiamond. With many polymers like caoutchouc, polysiloxanes, fluoroelastomers polymethacrylates, epoxy resins, etc., composites with markedly improved mechanical characteristics have already been obtained from the noncovalent incorporation of nanodiamond by simple admixing during polymerization. The modulus of elasticity, the tensile strength, and the maximal elongation of the material all increase upon this modification. Depending on the basic polymer, just 0.1-0.5% (w/w) of nanodiamond are required to achieve this effect (Table 5.3). Polymer films can also be reinforced by the addition of nanodiamond. For a teflon film with ca. 2% of nanodiamond added, for example, friction is reduced at least 20%, and scratches inflicted by mechanical means are only half as deep as in neat teflon. 

A multitude of potential further applications opens up to nanodiamond materials in a variety of technological areas. Examples hitherto described include, among others, the preparation of field emitters for display uses. Current research focuses, for instance, on utilizing the lattice defects and the resulting fluorescence as weU as the unpaired spins. More applications are expected to emerge in the field of scratch-resistant transparent coatings. Moreover, it should be possible to realize... 

C-C. Li, and C-L. Huang, Preparation of clear colloidal solutions of detonation nanodiamond in organic solvents. Colloids and Surfaces Physicochemical Enginering Aspects, 353 (1), 52-56, 2010. 

Many methods have been reported for production of nanodiamonds (NDs) such as laser ablation, " plasma-assisted chemical vapor deposition," autoclave synthesis from supercritical fluids, ion irradiation of graphite, chlorination of carbides, electron irradiation of carbon onions, and ultrasound cavitation. Smaller NDs can be prepared by detonation processes that yield aggregates of NDs with sizes of 4-5 nm embedded in a detonation soot composed of other carbon allotropes and impurities. An explosive mixture having an overall negative oxygen balance provides a source of both carbon and energy for the conversion. Because of their small size (2-10 nm) detonation NDs have also been referred to as ultradispersed, nanocrystalline... 

Detonation nanodiamond has been coveted by Fe-, Co-, Ni-, Zn-, and Ce-containing nanoparticles prepared via themial destruction of metal-containing compounds. Composites comprised of the nanodiamonds covered by Fe- and Co-containing nanoparticles embedded within low density polyethylene matrix have been produced. 

C MAS-NMR spectroscopy was used to quantify the different carbon species in synthetically produced nanodiamonds.430 A 13C study has been reported to study the modification of the electronic properties of SWCNT by alkali intercalation.431,432 13C MAS-NMR data were used to study the structure of 13C-enriched SWCNT, prepared by catalytic decomposition of CH4.433 H, 13C and 15N MAS-NMR spectra of amorphous carbon nitride (a-CNx) films were consistent with sp2 hybridised nitrogen atoms in an aromatic carbon... 

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. 

The generation of high pressures by means of a detonahon in a confined container has been known for long. As early as in the 1960s it has been employed by soviet scientists to prepare nanodiamond, and by now the controlled detonation of explosives is performed even on a large scale. 

As discussed in Section 5.2.2, nanodiamond particles produced by detonation or shock wave synthesis exhibit a primary surface functionalization right from the preparation. It comprises a multitude of different groups, so it should be possible to make use of these functional groups. To ensure a reproducible quality of the secondary products obtained, however, a homogenization of the primary functionalities is required. There are several strategies to achieve this (Figure 5.29). 

The high thermal conductivity can be employed for nanodiamond applications as well. It is possible to prepare, for example, heat-conducting pastes. The material demand is only l-10gm here. Another positive effect of using the nontoxic nanodiamond powder is to avoid the customary, very poisonous paste of beryUium oxide in some of these applications. 

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)... 

As a resnlt of IBD and IBAD experiments [80], nanodiamonds immersed in the dominant sp amorphous carbon films were found. Patterns were formed via the dynamical process between the sputtering and the deposition effects [82]. Hexagonal nanosized diamonds were also prepared from the Ceo vapor with the simultaneons irradiation of 1.5-keV Ne" ions at a temperature of 700°C. Furthermore, although C and iridinm (Ir) are immiscible, defects introduced by C implantation conld favor the supersatnrated C atoms in the subsurface region. Fig. 26 shows an atomic force microscope (AFM) micrograph of... 

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