Tribological applications

A wide variety of carbon materials is known for their applicability as a catalyst or support of it. Especially the activated carbons with their large specific surface can be employed. But also carbon nanotubes and, to some degree, the fullerenes may be used to the same end. Besides, carbon onions and onion-like carbons are promising for catalytic applications, too. They feature a considerable specific surface, bear little structural defects (at suitable preparation), and they are stable over a wide range of temperatures. 

when using porous carbons, the desorption of newly generated styrene from the catalyst surface was found to be hindered, and so the conversion was Hmited. The lack of any porosity in carbon onions should clearly be beneficial here, and indeed the conversion and the yields of styrene could be increased when using nano-onions or onion-Uke materiaL In samples of catalyst that had already been used, the onion stracture was found to be partly destroyed. Actually, the catalyst reaches full activity only in this state, which also accounts for the induction period observed. On the onions surface, presumably carbonyl groups and quinoid structures constituting the real active sites are formed. 

Carbon onions consist of carbon cages in a concentric arrangement, the sole interaction between them being of the van der Waals type. 

Carbon onions consist of a multilayered arrangement of individual, closed fullerene shells. Ideally, each contains N = N, / carbon atoms. 

In general, carbon onions are spherical, which implies a considerable number of defects in every shell as otherwise they would have to be Goldberg fullerenes with a faceted icosahedral symmetry. 

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GIAB studies of sputtered thin films of different composition for tribological applications have been reported [4.157-4.159]. The technique has been used to study the structure of very thin GdS layers (deposited by chemical bath deposition) for photovoltaic applications in combination with 6-26 diffraction it enabled identification of their polytype structure [4.160]. Glancing angle diffraction in the GIAB geometry... 

The most commonly used amphiphiles to build L-B hlms for tribological applications are the straight chain hydrocarbon compounds with simple functional groups such as the fatty acids, including stearic acids, arachidic acids, and behenic acids [32], but other amphiphilic molecules, e.g., 2,4-heneicosanedione and 2-docosylamina-5-nitropyridine, are also applied in some cases. There are two major systems of self-assembled monolayers, namely the alkylsilance derivatives (e.g., OTS, octadecyltrichlorosilane) on hydroxylated surfaces and the alkanethiols on metal substrates, which have been investigated extensively to examine their properties as solid lubricants and protective surface films [31 ]. 

Some grades are designed for tribological applications with low wear and low coefficient of friction. 

The abrasion resistance, generally fair, depends on the roughness, type and morphology of the opposing sliding surface. PTFE are often used for tribological applications. 

Neat and glass fibre reinforced grades can be used for tribological applications with rather high coefficients of friction in a range from 0.3 up to 0.5. 

General-purpose grades have a high coefficient of friction, 0.35-0.45 for example, but special grades are marketed for tribological applications with coefficients of friction ranging from 0.15 up to 0.2. 

Special grades with better wear resistance and coefficient of friction are marketed for tribological applications. 

The wear resistance and coefficient of friction are suitable for tribological applications. Tribological properties for a PV of 1.75MPa.m/s are, for example ... 

PTFE-Based Rubber Composites for Tribological Applications... 

NBR containing irradiated PTFE micropowder for high performance tribological applications [23]. 

Polymers were never intended to be bearing- or wear-resistant materials and in fact are usually unsuitable for tribological purposes. Hence, the number of polymers with valuable tribological properties is limited. Table 2 shows the most important polymers used for tribological applications along with their tribological characteristics [35]. 

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