Composite hard carbon

The first report on the electrical properties of composite hard carbon films was published by Jones and Stewart [154] who slightly doped their a-C H films with phosphorus, boron, or nitrogen and found increased conductivity with phosphorus and boron. For the conduction process they proposed a hopping of electrons in a region of high density of localized states for both doped and undoped samples. 

Ion Beam Deposition The most commonly used vacuum method for the rapid deposition of films (thin or thick) is sputtering (2M. This can be combined with ion beam techniques in a variety of ways (25) including (Figure 18) ion beam sputter deposition (IBSD) eg of oxide films or of hard carbon (26). In reactive systems the reactive gas is added to the argon ion beam. The properties of the deposited materials are modified substantially by varying the gas composition (Figure 19). 

Isotopic studies relating to nutrition and diet have originated from two diverse fields bio-medical research and archaeology Numerous studies have been reported by researchers in the areas of biochemistry and medicine using either isotopically enriched compounds or the natural variations in isotopic abundances Such studies usually involve a specific chemical as a tracer of biochemical pathways, and in these studies soft tissues or body fluids are analyzed Recent work in nutrition has begun to examine the isotopic composition of carbon in macronutrients in diets and their disposition in body tissues (1 2) The isotopic composition of hard tissue (i e bone) however has been largely ignored in biochemical studies ... 

Figure 23.5 Galvanostatic insertion-deinsertion of lithium in a composite constituted from hard carbon from viscose coated by a pyrocarbon film. Current load of 20mA/g. (Adapted from Ref. [22].)...

Fig. 13. ITie WET sequence modified for use with ID LC NMR The four SEDUCE RF pulses are 98.2°, 80.0°, 75.0° and 152.2° for B,-insensitive WET. Other angles are used in the case of B - and Tj-insensitive V T. The gradient pulses are each 2 ms long with amplitudes of 32, 16, 8 and 4Gcm , respectively, " ere is a delay of 2 ms between each gradient pulse and the next RF pulse. Carbon decoupling with a field strength of 100 Hz is applied during the H-selective pulses. Instead of a single (hard) irU excitation pulse, a volume selective composite hard ir/2 pulse scheme (i.e. 90°90 90°- 90°,) can be used which affords a flatter baseline.

Even simple polymers like polyethylene or polypropylene can form composites with carbon nanotubes. The embedding, however, is limited to noncovalent interaction due to the complete lack of functional groups. Yet on the other hand, the hydrophobic nanotube surface hardly poses any problems in a wetting by the nonpolar polymer chains or in the formation of noncovalently bound composites. 

On the other hand, sodium intercalates in the soft carbons with increasing facility as the maximal temperature of treatment of carbon (HTT) is lowered e.g., a petroleum coke at 1250°C leads to a third stage NaC24, and a coke heated at 800°C can lead to a first stage with a composition near NaCg. Hard carbons are also able to accept 20% of their weight or more of sodium, partly by intercalation, and more by adsorption and condensation in the porosity. ... 

The following methods have been described for the preparation of metal/organic composite films, i.e., metal/plasma polymer or hard carbon. 

It was established already in the first period of works on sodium ion batteries that contrary to the lithium ion, the sodium ion is not intercalated into the interlayer space of graphite. Sodium ions penetrate nongraphitized carbon materials, but the nature of this penetration is not intercalation. In the case of oil coke, the capacity values of 90 - 95 mAh/g were obtained, which approximately corresponds to the composition of NaC24. In the case of carbon black electrodes, capacity of about 200 mAh/g was obtained. Quite suitable materials for the negative electrode could be different varieties of nanoporous hard carbon (obtained, e.g., by pyrolysis of glucose). In this case, intercalation of sodium ions is provided not only by their intercalation into the interlayer space, but also by their adsorption on the inner nanopore surface. The capacity of electrodes of nanoporous hard carbon reaches 300 mAh/g. Most recently, negative electrodes of carbon nanotubes with nearly similar sodium intercalation capacity were described. 

The composites were typically prepared by means of milling the ingredients (silicon and graphite powders) for different time intervals. In addition, some samples were coated with a layer of hard carbon deposited from a gaseous phase by means of the thermal vapor deposition (TVD) technique. The volume resistance of the silicon powder was 1,500 Q cm, while that of the carbon-coated composite was only around 100 mQ cm. Composites containing comparatively large silicon particles (>1 pm) could cycle up to 50 cycles when the insertion capacity is limited (<800 mA h g ). These improved characteristics are ascribed mainly to the continuous electric networks around the silicon particles. In contrast, particulate silicon anodes, containing only silicon and PVDF, do not show considerable reversibility and deteriorate completely in just a few cycles. 

Pig. 1. Typical microhardness values of pol3maers compared with data for metals. LDPE, low density polyethylene HDPE, high density polyethylene iPP, isotactic polypropylene CEPE, chain-extended polyethylene POM, polyoxymethylene aPS, atactic polystyrene PET, poly(ethylene terephthalate) PEN, pol3Kethylene naphthalene-2,6-dicarboxylate) CF composite, carbon-fiber composite. Hardness data of metals and alloys markedly depend on composition, degree of work-hardening, processing conditions, etc. For this reason, the values in Figure 1 should be considered as typical values rather than as absolute values. Most of the data for metals are taken from Ref 1. 

Figure 3.2 SEM images of hard carbon coatings as a function of the composition of the feed gas. Each of the images shows the surface of the coating resulting from a feed gas composition consisting of (a) 0.1 %, (fa) 0.5%, (c) 1.0%, (d) 1.5%, and (e) 2.0% methane by volume in hydrogen. ...

The next generation of fibre-reinforced materials were the metal matrix composites (MMC) of ductile alloys reinforced with hard carbon or ceramic fibres and whiskers. The MMC offer serious advantages over other types of composites, mainly in the following aspects ... 

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