Carbonized Silicas and Mixed Oxides

Kinetic studies of carbonization of a methane/carbon tetrachloride mixture at low pressure (2 kPa) at r 800°C allowed one to assume that pyrocarbon was formed from chlorinated intermediate species with apparent activation energy of 180 kJ/mol (Gun ko and Leboda 2002). At higher temperatures, the apparent activation energy was lower (140 kJ/mol) and unsaturated hydrocarbons were the most probable carbon precursors (Feron et al. 1999). Chemical vapor infiltration of pyrocarbon was studied at 1100°C and methane or methane/hydrogen mixture pressures ranging from 5 to 100 kPa on porous alumina ceramic as a substrate (pore diameters from 1 to 36 pm) 

FIGURE 4.2 TEM micrographs of pyrocarbon/silica samples obtained on the basis of silica gel by pyrolysis of acetylacetone—AC-3 (a) glucose—G1 (b) acenaphthene—AN2 (c) nickel acetylacetonate—CSfji (d) cobalt acetylacetonate—CS o (e) and on the basis of pyrogenic silica by pyrolysis of CHjClj, C/A-300 (Cc=20% w/w) (f). (Adapted with permission from Gun ko, V.M., Leboda, R., Skubiszewska-Zi ba, J., Turov, V.V., and Kowalczyk, R, Structure of silica gel Si-60 and pyrocarbon/silica gel adsorbents thermally and hydrothermally treated, Langmuir 17, 2001b, 3148. Copyright 2001 American Chemical Society.) 

Nuclear Magnetic Resonance Studies of Interfacial Phenomena 

The mentioned investigations showed a marked variety of pyrocarbon deposits. Now we will analyze pyrocarbon-silica (CS) using different methods to elucidate the relationships between the precursor composition and the parameters of the matrices, synthesis conditions, and the textural and adsorptive properties of final hybrid pyrocarbon-mineral materials affecting the interfacial phenomena with participation of water and organics adsorbed alone or co-adsorbed. 

Different silicas, such as porous silica gels (Tables 4.1 through 4.4), fumed silicas with nonporous primary particles and mixed nanooxides (Table 4.5), natural minerals, and metals deposited on 

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