Carbon black chemisorption

Physical adsorption—surface areas of any stable solids, e.g., oxides used as catalyst supports and carbon black Chemisorption—measurements of particle sizes of metal powders, and of supported metals in catalysts... 

In this article, we will discuss the use of physical adsorption to determine the total surface areas of finely divided powders or solids, e.g., clay, carbon black, silica, inorganic pigments, polymers, alumina, and so forth. The use of chemisorption is confined to the measurements of metal surface areas of finely divided metals, such as powders, evaporated metal films, and those found in supported metal catalysts. 

A second possibility is that the metal center remains intact, but the macrocycle ligands react with each other. In macrocycles treated in the absence of a support there is evidence that polymerization of the macrocycles occurs.76,111 Likewise, in the presence of a carbon black support, such polymerization could occur during pyrolysis and could possibly affect activity and stability for similar reasons to the ones mentioned in the previous paragraph.76,92 However, for a treatment above 400 °C (which produces a more active material) the macrocycle polymer is thought to decompose.92 Another possibility is that the heat treatment helps disperse the macrocycles on the support surface and leads to strong chemisorption rather than physisorption.110... 

The direct titration of the parent carbon black which also carries significant amounts of functional groups is not possible. From this, it can be seen that the two alternative chemisorption techniques both have their relevance in carbon chemistry. 

The inactivity of Graphon in the contacts with the white solids despite the near equivalence of its work function with that of BPL demonstrates an absence of coupling of the delocalized tr electron system of Graphon with the localized Bronsted and Lewis sites of the white solids. It is to be noted that electron transfer between the tt electron systems of different carbon blacks occurs quite readily. The oxide structures of carbon blacks are seen to play a fundamental role in this viewpoint at the microscopic level akin, for example, to the critical importance of the molecular structures of the adsorbates in chemisorption from the gas phase onto metals (41, 42) and metal oxides(43). 

The interactions between carbon blacks (other than graphitized carbons) and hydrocarbon elastomers are not purely physical. The increased interfacial adhesion resulting from chemisorptive mechanisms contributes significantly to the reinforcing action. 

Attempts to improve the reinforcing action of carbon black by providing additional chemisorptive attachments have been largely unsuccessful, except with rubbers of low chemical reactivity toward carbon black, e.g., butyl rubber. 

For the ensuing discussion of mechanical reinforcement effects it will for the most part be sufficient to regard the carbon black-rubber bond as predominantly physical, with a relatively minor, but significant portion of the surface involved in the formation of chemisorptive attachments or polymer grafts. 

The various assessments of the effects of carbon black on local segmental mobility by thermal and NMR measurements appear consistent with our understanding of carbon black-rubber bonding. As mentioned above, it has been estimated (91) that in a typical reinforcing furnace black only about 5 % of the surface is involved in chemisorptive attachments. Assuming 40 A2 for the area occupied by a monomer unit, one calculates 0.17 x 10 4 moles of chemisorptive attachments per gram of rubber for a loading of 100 phr of HAF black (80 m2/g). This is about... 

Blanchard and Parkinson6 postulated two types of attachments between a rubber matrix and its carbon black filler a strong type due to chemisorptive attachments and a weaker van der Waals type of bond. The former were considered to remain unbroken upon stressing the vulcanizate, but the latter suffered progressive rupture as the stress increased. 

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