Carbon deposit crystalline particles

The details of the structural characteristics of individual constituents in the various carbon deposits were obtained by examination of a number of specimens from each experiment in a JEOL 100 CX transmission electron microscope that was fitted with a high resolution pole piece, capable of 0.18 nm lattice resolution. Suitable transmission specimens were prepared by applying a drop of an ultrasonic dispersion of the deposit in iso-butanol to a carbon support film. In many cases the solid carbon product was found to consist entirely of filamentous structures. Variations in the width of the filaments as a function of both catalyst composition and growth conditions were determined from the measurements of over 300 such structures in each specimen. In certain samples evidence was found for the existence of another type of ca naceous solid, a shell-like deposit in which metal particles appeared to be encapsulated by graphitic platelet structures. Selected area electron diffraction studies were performed to ascertain the overall crystalline order of the carbon filaments and the shell-like materials produced from the various catalyst systems. 

Figure 13. Typical particulate deposits. Key a, larger crystalline particles, and agglomerations of smaller particles after 10,120 ton h methane b, development of stable crystal habit and c, particulate material breaking through laminar carbon...

In the combustion of methane, oxidation is accompanied by a thermal decomposition. Reactions of hydrocarbon radicals lead to unsaturated compounds such as gaseous olefins and acetylene which are then cyclized into condensed aromatic hydrocarbons. The aromatic compounds are subjected to further dehydrogenation in the reaction zone to produce carbon particles. This carbon black is a random aggregate of crystalline graphite embedded at a certain proportion in an amorphous matrix. Some hydrogen is always present in this carbon deposit. 

Fig. 13. The structure of Pt spheres changes dramatically as a function of the gas composition and temperature. Micrographs of Pt spheres in reaction mixtures, (a) After exposure to 10% NH3 in air at I350°C, the Pt sphere appears pitted, (b) Irregular crystalline structures build up on Pt sphere exposed to 10% CO in air at 1000°C. (c) Deep wavy channels form on Pt sphere used in 2% C,H8 oxidation, (d) Carbon particles deposited on platinum used in 14% C3Hg in air mixtures at 727°C (27).

The mineral matter in coal consists chiefly of silicate, sulphide, carbonate species, and chlorides and organo-metallic compounds associated with the fuel substance (1,2). The silicate mineral particles vitrify partially or completely, in the pulverized coal flame ( 3), and thus the silicate ash fraction of the initial deposit consists of particles of variable amounts of a glassy phase and crystalline species ( ). 

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