Structure of non-graphitising carbons

Abstract

Despite many years of research, the detailed atomic structure of many important carbon materials remains poorly understood. In particular, the structure of those carbons which can not be transformed into graphite by high temperature heat treatment has never been clearly established. These non-graphitising carbons are of considerable commercial importance in a variety of fields, and a better understanding of their structure is clearly needed. Recently, it has been suggested that non-graphitising carbons may have a microstructure which is related to that of fullerenes. In the present paper, the evidence for this will be considered in detail and the advantages of the new model over previous models of non-graphitising carbons will be discussed. As well as microporous nongraphitising carbons, other forms of carbon including glassy carbon and carbon fibres will be considered.IMRj304 IntroductionAlthough graphite is the most stable form of carbon at normal temperatures and pressures, it is a remarkable fact that many carbons can not be transformed into crystalline graphite even at temperatures of 3000°C and above. The so called 'non-graphitising' carbons tend to be hard, low density materials, with isotropic, microporous structures. 1 -6 In contrast, graphitising carbons are soft and non-porous, with densities much closer to that of crystalline graphite. Nongraphitising carbons can develop exceptionally high surface areas when 'activated' by treatment with a mild oxidising agent, and the resulting activated carbons are widely used as adsorbents and as catalyst supports. 4 -6 Despite their commercial importance, however, the detailed structure of these carbons at the atomic level is still poorly understood. The traditional view is that the microstructure consists of twisted networks of carbon layer planes crosslinked by bridging groups, explaining both their hardness and their resistance to graphitisation, 2 but the precise nature of such bridging groups has never been properly established. Earlier suggestions that Sp3bonding may be present in non-graphitising carbons do not appear to stand up to detailed analysis, as discussed in the 'Problems with early models' section later. The relatively recent discovery of the fullerenes,7-9 and subsequently of related structures such as carbon nanotubes 10 -12 and nanoparticles,13,14 has given us a new perspective on Sp2 bonded carbon structures. Most importantly, we now know that carbon structures containing non-six membered rings can be highly stable. It therefore seems worth considering the idea that microporous non-graphitising carbons may be fullerene-like in nature. Recent work has provided support for this view by showing that high temperature heat treatments can transform microporous carbons into fullerene like nanoparticles. 15 The purpose of the present paper is to consider further the evidence that non-graphitising carbons contain fullerene related elements. In addition to microporous carbons, a related class of non-graphitising carbon known as glassy carbon will also...

Evolution of glassy carbon under heat treatment: correlation structure–mechanical properties

“…Moreover, according to theoretic calculations of the STW defect in a flat graphene two characteristic Raman modes at 1122 and 1173 cm -1 are predicted [39]. We assume that the D4 and D5 peaks observable here for the glassy carbons can also come from the vibrations of carbon atoms in non-hexagonal rings such as STW defects which are considered as the reason of the fullerene-like structure of glassy carbons [6][7][8].…”

“…The most recent studies have suggested that glassy carbons have a fullerene-related structure. Such model of the structure, proposed by Harris [2,[6][7][8], consists of broken and imperfect fullerene fragments in the form of curved sp 2 -bonded graphene-like planes, which can be multilayered and which often surround closed pores. The presence of curvature has been attributed to the topological defects in the form of non-hexagonal carbon rings such as pentagons and heptagons that were directly observed by the high-resolution transmission electron microscope (HRTEM) [9].…”

“…Ordering within the layers is accompanied by increase in their sizes. However, even after heat treatment at temperatures of 3000°C and above the glassy carbons cannot be transformed into crystalline graphite [7,10] and preserve the general type of atomic disorder remaining features of the paracrystalline structure [12]. The structure is a key factor determining glassy carbon porosity, mechanical, and electronic properties.…”

Structural prediction of graphitization and porosity in carbide-derived carbons

“…They are highly sought after as they provide a visual representation of the structure and enable direct simulation of gas adsorption and other properties. [11,12] These models, which overlap with nanoporous carbons, can be divided into two groups: geometric models and simulation models. Geometric models are highly idealized and are often constructed by hand.…”

Carbon supported Ru clusters prepared by pyrolysis of Ru precursor-impregnated biopolymer fibers

“…The morphologies of the native and the pyrolized fibers were investigated by ESEM. [20] Fourier-transform infrared measurements of the untreated bacterial nanocellulose and samples pyrolized at 1000 °C and 1500 °C under N 2 are shown in Figure 2. The adsorption isotherms of Argon sorption measurements for two different BNC samples treated at 800 °C and 1500 °C under N 2 atmosphere and another sample treated at 1250 °C under Ar atmosphere were recorded (see Figure A in ESI).…”