Tribological carbon onions

A. Hirata, M. Igarashi, T. Kaito, Study on solid lubricant properties of carbon onions produced by heat treatment of diamond clusters and particles. Tribology Int., 37(11-12) (2004) 899-905. 

Second, the use of CNTs embedded in a membrane matrix to provide nanochannels for precise separations (Fig. 30). The last example illustrates the influence of processing on the morphology of spherical silica particles produced by variation of the conditions particles can be produced as onion rings or with a hexagonal internal structure. Carbon onions can be produced and are found to have durable tribological properties (128) (Fig. 31). 

Figure 4.42 Operation principle of carbon onions in tribological applications. The lubricating effect is conserved even upon destruction of the onion structure.

Cabioc h et al. developed a method based on carbon ion implantation into a metal matrix (Ag, Cu), resulting in onions with typical diameters in the 3-15 nm range. Snfficient quantities could be produced for investigation of their optical, electronic, and tribological properties. Fourier transform infrared (FTIR) spectroscopy measurements on these carbon onions demonstrated that the most stable state for the onions consists of concentric spheres of fnllerenes. The electronic properties of the onions were characterized by spatially resolved electron energy loss spectroscopy (EELS) in transmission, and reflection mode. ... 

During the preparation of this chapter, such a new finding that carbon onion synthesized from diamond nanoparticle at 1600 °C shows a low friction coefficient of 0.005 in ultrahigh vacuum. Therefore, further application of nanolubricants to tribology is anticipated. 

Recently, a new synthesis method based on the decomposition of CH4 on NiO/Al composite powder led to a massive production of carbon onions of about Ig per hour [27, 28]. These carbon onions have a diameter from 5 to 50 nm but some carbon onions contain an Ni core. Wang et al. developed a synthesis method of carbon onions containing Fe core by CVD [29]. C2H2 is decomposed on ferrocene and leads to the formation of carbon onions 15 to 40 nm in diameter. The presence of a metallic core (Fe or Ni) can affect the tribological properties of carbon onions, as previously demonstrated in the case of carbon nanotubes. Carbon onions containing an Ni core would present interesting tribological properties similar to those of carbon nanotnbes (see Section 3.5.1.1). 

So far, very few stndies on the tribological properties of carbon onions are reported in the literature. Most of the smdies were carried out on carbon onions concern their synthesis and the determination of their structures. Cabioc h et al. smdied the tribological properties of silver films containing carbon onions [30]. The addition of onions does not have an effect on the friction coefficient, but an increase in lifetime of the coating by a factor of 15 was observed. Cabioc h et al. explained friction-reducing properties of carbon onions by the fact that they are embedded inside the metal, so they cannot roll. Hirata et al. smdied tribological... 

A study of the effect of the contact pressure on the Mction-reducing properties was performed with a concentration of 0.1 wt % (Figure 3.17). In a way similar to the other nanoparticles studied, the friction coefficient decreases with the contact pressure. A critical pressure of 1.42 GPa is highlighted, a pressure at which the friction coefficient becomes lower (0.06). A comparison of the tribological performances of carbon onions containing a diamond core and without a diamond core indicates a similar behaviour for the two samples (Figure 3.17). Quite similar friction coefficients are obtained with the two samples for each contact pressure studied. 

To understand tribological performances of carbon onions better, these results were compared with those obtained with pure PAO, PAO contaiiung 0.1 wt% graphite, PAO containing 0.1 wt % of nanodiamond used as precmsors for carbon onions synthesis and PAO containing 0.1 wt% of Ceo, which can be considered as a single-walled carbon onion. 

Other carbon nanoparticles may also present interesting tribological properties nanohorns [122], peapods (nanotubes filled with Ceo) [123] and C70. Furthermore, the study of their tribological properties may also lead to a better understanding of the lubrication mechanism of carbon nanotubes and carbon onions. 

Joly-Pottuz, L., Matsumoto, N., Kinoshita, H., Vacher, B., Belin, M., Montagnac, G., Martin, J. M. and Ohmae, N., Diamond-derived carbon onions as lubricant additives. Tribology International, 41 (2), 2008,69-78. 

Several types of nanoparticles can be envisaged as lubricant additives. The chapters of this book describe different possible nanolubricants nested nanoparticles (fuUerenes, onions and nanotubes) made on metal dichalcogenides or carbon, reverse overbased micelles, metallic nanoparticles and boron-based nanolubricants. In some cases, the authors chose to study these particles because their structure is close to well-known lamellar structures in tribology (for example inorganic fuUerenes of M0S2). However, dispersion of nanoparticles in oil is not always simple. Thus, in a first part, some rules will be shown about the dispersion of solid nanoparticles in a liquid. 

In Chapter 3, carbon nanotubes and onions are evaluated as potential anti wear and friction-reducing additives. Similarly to Chapter 2, analytical tools including surface analysis are found to be very useful for identifying the mechanism of action of nanotubes and onions as lubricants. Interestingly, the formation of lubricious iron oxides contributes to the tribological performance of these additives. 

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