Amorphous carbon materials properties

A term that refers to the various different forms of amorphous carbon materials that exhibit some of the properties of diamond. 

Diamond-like carbon (DLC) An amorphous carbon material with mostly sp bonding that exhibits many of the desirable properties of diamond but does not have diamond s crystal structure. 

Chapter 1 contains a review of carbon materials, and emphasizes the stmeture and chemical bonding in the various forms of carbon, including the foui" allotropes diamond, graphite, carbynes, and the fullerenes. In addition, amorphous carbon and diamond fihns, carbon nanoparticles, and engineered carbons are discussed. The most recently discovered allotrope of carbon, i.e., the fullerenes, along with carbon nanotubes, are more fully discussed in Chapter 2, where their structure-property relations are reviewed in the context of advanced technologies for carbon based materials. The synthesis, structure, and properties of the fullerenes and... 

Richter, F., et al., Preparation and Properties of Amorphous Carbon and Hydrocarbon Films, in Applications of Diamond Films and Related Materials (Y. Tzeng, et al., eds.), Elsevier Science Publishers, pp. 819-826 (1991)... 

Combined with appropriate amorphous carbon precursors graphite intercalation compounds could be used in one-stage process of production of carbon-carbon composites, which could possess attractive properties for such applications as supercapacitors elements, sorbents as well as catalyst supports and materials for energy- and gas-storage systems. 

Amorphous adsorbents, 1 587-589 for gas separation, 1 631 properties and applications, l 587t Amorphous aluminum hydroxide, 23 76 Amorphous carbohydrates, material science of, 11 530-536 Amorphous carbon, 4 735 Amorphous cellulose, 5 372-373 Amorphous films, in OLEDs, 22 215 Amorphous germanium (a-Ge), 22 128 Amorphous glassy polymers, localized deformation mechanisms in, 20 350-351... 

Carbon-based nanocomposite concepts have been successfully developed to limit or reduce these adverse effects and at the same time enhance the electron or ion transport [8]. CNT is an ideal building block in the carbon-inorganic composite/hybrid due to its mechanical, physical, chemical properties as mentioned above. CNTs are apparently superior to other carbonaceous materials such as graphite or amorphous carbon and are more adaptable to the homogeneous dispersion of nanoparticles than other carbonaceous materials [36],... 

For application in flow reactors the nanocarbons need to be immobilized to ensure ideal flow conditions and to prevent material discharge. Similar to activated carbon, the material can be pelletized or extruded into millimeter-sized mechanically stable and abrasion-resistant particles. Such a material based on CNTs or CNFs is already commercially available [17]. Adversely, besides a substantial loss of macroporosity, the use of an (organic) binder is often required. This material inevitably leaves an amorphous carbon overlayer on the outer nanocarbon surface after calcination, which can block the intended nanocarbon surface properties from being fully exploited. Here, the more elegant strategy is the growth of nanocarbon structures on a mechanically stable porous support such as carbon felt [15] or directly within the channels of a microreactor [14,18] (Fig. 15.3(a),(b)), which could find application in the continuous production of fine chemicals. Pre-shaped bodies and surfaces can be... 

In this article the infrared spectroscopic evidence for interstellar PAHs will be reviewed. The spectroscopic properties of PAHs studied in salt pellets rather than amorphous carbons will be primarily used since a wealth of very detailed information is available (thanks to the sustained, dedicated effort of Cyvin and his coleagues over many years) and molecule-sized emitters can account for many details of the interstellar spectra. Infrared spectra of amorphous carbon particles and carbonaceous films, synthesized to study the connections with interstellar carbonaceous material, are just now becoming available. The work of Bussoletti and coworkers ([33] and references therein) and Sakata and colleagues ([34] and references therein) is particularly noteworthy in this regard. 

At very high pressures, above 12 GPa, and temperatures above 1000 K, a transparent,yellowish, ultra-hard material, believed to consist of the remnants of collapsed molecules, is formed. In several cases ultrasonic, scratch, and indentation studies have shown this material to have a bulk modulus and hardness far exceeding that of diamond [123,131,147], although these reports are by no means uncontested [124,148,149]. The material is extremely disordered and probably has a high fraction of sp2 coordinated bonds, but the structure is unknown. There are some similarities with amorphous carbon (ta-C),but differences in Raman spectra and mechanical properties show that the structures differ. The question of bond types is interesting, since sp2 bonds are known to be stronger than sp3 ones. The materials are semiconducting and have Debye temperatures near 1450 K, somewhat lower than that of diamond [150]. 

Chlorinated aliphatic compounds were dechlorinated even in water by electrochemical reduction on a Zn-modified carbon cloth cathode consisting of partly amorphous and partly graphitized carbon material with 10 wt.% Zn [9]. This electrode has good adsorption properties, conductivity, and stability in different solvents, allowing the combination of both adsorption and... 

As shown in Section 3.2, polycrystalline diamond film is a heterogeneous system comprising diamond crystallites and intercrystallite boundaries, presumably consisting of amorphous carbon. This brings up the question To what extent do intercrystallite boundaries affect the electrochemical behavior of polycrystalline diamond electrodes To answer this question, the electrochemical properties of polycrystalline and single crystal diamond and amorphous carbon should be compared. In such a comparison, a model material of the intercrystallite boundaries should be chosen. 

In Section 2 we showed that the properties of amorphous carbon vary over a wide range. Graphite-like thin films are similar to thoroughly studied carbonaceous materials (glassy carbon and alike) in their electrode behavior. Redox reactions proceed in a quasi-reversible mode on these films [75], On the contrary, no oxidation or reduction current peaks were observed on diamondlike carbon electrodes in Ce3+/ 41, Fe(CN)63 4. and quinone/hydroquinone redox systems the measured current did not exceed the background current (see below, Section 6.5). We conventionally took the rather wide-gap DLC as a model material of the intercrystallite boundaries in the polycrystalline diamond. Note that the intercrystallite boundaries cannot consist of the conducting graphite-like carbon because undoped polycrystalline diamond films possess excellent dielectric characteristics. 

Many new phases of carbon have been discovered as an offshoot of attempts of artificial synthesis of diamond. Among these, a class of amorphous carbon and hydrocarbon phases exhibits properties close to those of diamond. These diamond-like phases are therefore considered to be promising technological materials. 

Unfortunately, current S3mthesis techniques, such as chemical vapor deposition, arc discharge, laser ablation, or detonation, typically lead to a mixture of various nanostructures, amorphous carbon, and catalyst particles rather than a particular nanostructure with defined properties, thus limiting the number of potential applications [1]. Even if pure materials were available, the size-dependence of most nanomaterial properties requires a high structural selectivity. In order to fully exploit the great potential of carbon nanostmctures, one needs to provide purification procedures that allow for a selective separation of carbon nanostructures, and methods which enable size control and surface functionalization. 

Current synthesis techniques are usually unable to provide large quantities of pure CNTs with well-defined physical and chemical properties [28]. The as-produced material is typically a mixture of different types of CNTs, amorphous carbon, catalyst particles, and defective or damaged tubes, all of which may impair potential applications. Another major challenge for a large number of applications rises from the strong tendency of CNTs to agglomerate and arrange in bundles. 

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