Hans Darmstadt

Electrical conductivity of thermal carbon blacks : Influence of surface chemistry

Abstract The electrical conductivity of thermal and conductive carbon blacks with different chemistry was determined by impedance spectroscopy. Thermal blacks are suitable compounds for studying the influence of the chemistry on the conductivity since they have similar structures and surface areas, which strongly influence the conductivity. The conductivity was related to the carbon chemistry characterised by surface spectroscopic methods (ESCA and SIMS) and Raman spectroscopy, respectively. In general, the conductivity increases with decreasing concentration of surface oxygen and sulphur functional groups. However, different conductivities were observed for some samples with similar concentration of surface oxygen and sulphur functional groups. The conductivity correlated best with the polyaromatic character of the carbon black surface characterised by the C 2 H − /C 2 − peak ratio of the static SIMS spectra. The surface probed by SIMS is more important for the conductivity than the surface-near region probed by the asymmetry of the ESCA carbon peak. No correlation between the carbon black electrical conductivity and the carbon black bulk structure studied by Raman spectroscopy was found.

The vacuum pyrolysis of used tires: End-uses for oil and carbon black products

Abstract By vacuum pyrolysis, the rubber portion of used tires is transformed into oil and gas and the carbon black filler is recovered as pyrolytic carbon black (CBP). Several commercial applications for the different products have been investigated and are reported in this article. CBP surface chemistry and activity are similar to those of commercial carbon blacks. Therefore, CBP has the potential to replace commercial carbon black grades in certain rubber applications. CBP was successfully tested as a filler in road pavement. The total pyrolytic oil can be used as a liquid fuel. The oil can also be distilled into different fractions: a light, a middle distillate and a heavy fraction. The light fraction was positively tested as a gasoline additive. Furthermore, this fraction contains valuable chemicals such as d , l -limonene. The middle fraction was successfully tested as a plasticizer in rubbers. The heavy fraction represents a good-quality feedstock for the production of coke and can also be used in road pavements. The pyrolytic gas can be used as a make-up heat source for the pyrolysis process.

Electrical conductivity of conductive carbon blacks: influence of surface chemistry and topology

Conductive carbon blacks from different manufacturers were studied in order to obtain some insight into the relation between their electrical conductivity and their surface properties. The surface chemistry was studied by X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectroscopy (SIMS), whereas the topology of the carbon black surface was investigated using low-pressure nitrogen adsorption. All these techniques yield information on the graphitic character of the surface. In general, the electrical conductivity of the conductive blacks increases with the graphitic character of the surface. For low surface area conductive blacks, the electrical conductivity correlates well with the surface chemistry. In the case of the XPS and SIMS data, this correlation is also valid when other types of carbon blacks such as thermal and furnace blacks are included, confirming the determining influence of the carbon black surface chemistry on the electrical conductivity.

ESCA characterization of commercial carbon blacks and of carbon blacks from vacuum pyrolysis of used tires

Pyrolytic carbon blacks (CBp) were obtained by vacuum pyrolysis of used tires in a batch reactor at a total pressure ranging from 0.3 to 20.0 kPa, and temperatures ranging from 420 to 700°C. CBp differ from commercial carbon blacks used initially in the tire fabrication. A series of commercial carbon blacks with different surface areas and structures and CBp obtained under different pyrolysis conditions were characterized using ESCA and SEM techniques to investigate the effect of the pyrolysis conditions on the chemical nature of the surface of CBp.

Effects of surface treatment on the bulk chemistry and structure of vapor grown carbon fibers

Various surface treatments were performed previously to modify the surface condition of vapor grown carbon fibers (VGCF). However, by these surface treatments, in addition to the surface chemistry, the bulk chemistry and structure of the VGCF was influenced as well. Raman spectroscopy and nitrogen adsorption were used to study the changes in bulk chemistry and structure, and surface morphology, respectively, for surface treated VGCF. The bulk chemistry was compared with the surface chemistry obtained in an earlier study. In contrast to other types of carbon fibers, as-grown VGCF contain carbon atoms in an aliphatic environment in the bulk and have only a small pore volume. However, pores could be created in VGCF by surface oxidation. Furthermore, surface oxidation also decreased the order of the graphitic structures and the concentration of aliphatic structures in the bulk.

Characterization of pyrolytic carbon blacks from commercial tire pyrolysis plants

Abstract Pyrolysis of used tires yields oil and pyrolytic carbon black (CB P ). The tire pyrolysis process can be performed either in vacuo or at atmospheric pressure. The CB P recovered in both processes are different from the commercial carbon blacks used in the tire fabrication. Different spectroscopic methods such as ESCA, SIMS, Auger-spectroscopy and XRD were used to characterize CB P obtained in commercial tire pyrolysis plants operating in vacuo and at atmospheric pressure. The CB P characteristics were compared with those of rubber-grade carbon black. CB P from vacuum pyrolysis was found to be closer in their chemical nature to commercial carbon black than CB P from atmospheric pyrolysis.

Surface morphology and chemistry of commercial carbon black and carbon black from vacuum pyrolysis of used tyres

The surface chemistry and morphology of carbon blacks obtained by pyrolysis of used tyres (CBP) and of commercial carbon blacks was investigated by electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectrometry (SIMS) and fractal analysis using nitrogen adsorption data and small-angle X-ray scattering (SAXS). In contrast to commercial carbon blacks, carbonaceous deposits are formed on the CBP surface. The concentration of these carbonaceous deposits depends on the pyrolysis conditions, decreasing with decreasing pyrolysis pressure and increasing pyrolysis temperature. The carbon black surface is smoothed by the carbonaceous deposits. A relation exists between the fractal dimension, or roughness, of the CBP surface and the amount of carbonaceous deposits at constant pyrolysis temperature. The surface chemistry and morphology of CBP from pyrolysis at low pressures are similar to those of commercial rubber-grade carbon blacks.

Solid state 13C-NMR spectroscopy and XRD studies of commercial and pyrolytic carbon blacks

Abstract The bulk chemistry of commercial carbon blacks and carbon blacks obtained by vacuum pyrolysis (CBP) of used tires was investigated by 13C-NMR spectroscopy with and without magic angle spinning of the sample. Two different kinds of carbon atoms can be distinguished: Graphite like carbon atoms in poly-condensed aromatic rings and carbon atoms in a less ordered environment. Commercial carbon blacks and CBP obtained under different pyrolysis conditions have practically the same concentrations of the different types of carbon atoms in the bulk, whereas earlier ESCA and SIMS investigations have shown that the surface chemistry of CBP is different from commercial carbon blacks and depends strongly on the pyrolysis conditions. Thus, during the pyrolysis only the carbon black surface chemistry is changed. The carbon black bulk structure was also studied by X-ray diffraction. The XRD results, including the radial distribution function (RDF) indicated, in agreement with the NMR results, that the bulk structure of commercial carbon blacks and of CBP are similar.

Pore structure and graphitic surface nature of ordered mesoporous carbons probed by low-pressure nitrogen adsorption

Abstract Ordered mesoporous carbons (OMCs) were produced by pyrolysis of sucrose adsorbed in two different silica matrices (MCM-48 and SBA-15), followed by dissolution of the matrix in hydrofluoric acid. Subsequently, some of these OMCs were heat-treated at temperatures of up to 1600 °C. The OMC pore structure was studied by low-pressure nitrogen adsorption. Information on the graphitic order of the surface of the mesopore walls was also obtained from the nitrogen adsorption data. These results were correlated to the order of the graphene layers at the outer surface, which was studied by X-ray photoelectron spectroscopy (XPS). The OMCs were predominantly mesoporous, but they also contained micropores. For OMCs produced in an SBA-15 matrix, the micropore volume decreased upon heating. After heating to 1600 °C, nearly all micropores had disappeared. Furthermore, upon heating the width of the mesopores increased from 35 to 50 A. All these changes can be explained by a shrinking of the OMC framework upon heating. A different behavior was found for OMCs derived from MCM-48. Upon heating these materials at increasingly high temperatures, the width of the mesopores first decreased, and for temperatures above 1100 °C it increased again. For all OMCs studied the graphitic order of the mesopores and the order of the graphene layers at the outer surface increased upon heating. For a given temperature, the graphitic surface order of OMCs derived from SBA-15 and MCM-48 was similar.

Surface and bulk chemistry of charcoal obtained by vacuum pyrolysis of bark: influence of feedstock moisture content

Abstract Samples of maple bark and softwood bark with moisture contents ranging from 6 to 42 wt% were pyrolyzed under vacuum at a temperature of 775 K. Vacuum pyrolysis of maple bark yields approximately 30 wt% wood charcoal on an anhydrous basis. For softwood bark the charcoal yield is smaller (23–28 wt%). The charcoal yield of maple bark pyrolysis depended only slightly on the bark moisture. The surface and bulk chemistry development of the charcoals was studied by electron spectroscopy for chemical analysis (ESCA), secondary ion mass spectroscopy (SIMS) and Raman spectroscopy, respectively. With decreasing bark moisture the charcoal surface becomes more graphite-like, whereas the bark moisture had only a limited influence on the bulk structure. The high specific surface area of the charcoals at 200–300 m2/g makes these materials valuable feedstocks for the production of activated carbons.