Carbon deposit morphology

The Characterization of Carbon Deposit Morphologies Using In Situ Scanning Electron Microscopy... 

In this study, the solid carbon deposit morphology observed was different for different vegetable oil lubricants, depending on their chemical composition. The stressing... 

Deposits containing carbonate can be protective. The carbonate buffers acidity caused by the segregation of potentially acidic anions in and beneath deposits. However, deposits are rarely composed of only a single chemical mixed deposits are the rule. Deposit morphology also influences attack. Hence, although sometimes carbonate deposits are beneficial, they may also be deleterious. 

Herreyrc, S. and Gadelle, P., Effect of hydrogen on the morphology of carbon deposited from the catalytic disproportionation of CO, Carbon, 1995, 33(2), 234 237. 

The observations have shown that consideration must be given to several different processes of carbonate deposition and/or silica or iron oxide deposition in contact which such bacterial mats. Obviously some important lithification processes take place within the decay zone below the active photosynthetic zone. In most of the cases where lithification was observed there, it was carbonate lithification of a type not related to the photosynthetic depletion of C02. Different filamentous and coccoid cyanobacteria can become more or less lithified depending on slime production, mobilization, outer morphology and microenvironments. 

Changes in the morphological and structural characteristics of the carbon deposit resulting from pretreatment of the iron catalyst in H2S were determined from a combination of transmission electron microscopy techniques, X-ray diffraction, surface area measurements and controlled oxidation studies in CO2. Iron powder 200 mesh) was purchased from Johnson Matthey Inc. (99 99% purity) and had a BET surface area of 0.3 m2/g at -196°C, The gases used in this work CO (99 9%), hydrogen (99.999%), ethylene (99.999%), H2S/argon mixtures and helium (99,999%) were obtained from Alphagaz company and used without further purification. 

The results shown that the increase of the metal-to-acid ratio in the catalysts decreases the degree of coke polymerization it is richer in hydrogen and bums in a lower temperature range it influenced also on morphology of the carbon deposits on its surface. The TPO, TEM and activity results indicate the existence of a relation ship between the selectivity towards HBF and the nature of the coke. 

As shown in Fig. 2, the catalytic activity of the zeolite prepared by the direct heating method for methanol conversion was higher than that of the zeolite crystallization for 25 days by the standard preparation method. However, deactivation of the catalyst by carbon deposit occurred early in the reaction, just as with the catalyst prepared by the standard method. Differences in crystallite morphology between those prepared by the standard method and the direct heating method would be attributed to the stage of the precursor formation. Therefore, after the precursor formation the rapid heating was adopted as described below. 

---