Carbon Black Surface Chemistry Research Articles

Assessment of the surface chemistry of carbon blacks by TGA-MS, XPS and inverse gas chromatography using statistical chemometric analysis

Abstract Four carbon blacks with different specific surface areas and surface chemistries (C32, C71, C159 and C178) were analyzed by transmission electron microscopy (TEM) and nitrogen adsorption isotherms at 77 K. Their surface chemistries were analyzed by X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis coupled with mass spectrometry (TGA-MS) and inverse gas chromatography (IGC). The carbon blacks contained 2.7–5.8 wt% volatiles corresponding to OH, C O, C O and COO groups. The surface chemistry parameters obtained with the different experimental techniques were inter-related by using chemometric statistical analysis tools. The application of this methodology showed that the carbon blacks with lower specific surface area (C32 and C71) had basic character (electron donor) mainly due to C O and C O groups, whereas the carbon black with the highest specific surface area (C178) showed acidic character (acceptor electron) due to its high content of OH groups. Moreover, the total surface energy and the dispersive component of the surface energy of the carbon blacks increased with the increase of their specific surface area. In general the specific interactions of the carbon blacks also increased with the increase of their specific surface area although C71 is exceptional due to higher oxygen content corresponding to C O groups.

PEMFC Catalysts Synthesis and Characterization: Relevance of Structural and Chemical Factors on Surface Diffusion Processes

Two series of proton exchange membrane fuel cell (PEMFC) catalysts have been synthesized by modifying two parameters, the reduction-step length and the carbon-black surface chemistry. The scope and applicability of conventional physical techniques for their structural characterization, such as X-ray diffraction or transmission electron microscopy, are compared with those of others involving chemical processes such as temperature-programmed oxidation, hydrogen chemisorption, or temperature-programmed desorption. The presented results show that these latter techniques provide valuable complementary information for the characterization of these catalysts. The influence of surface-diffusion processes on PEMFC catalyst properties is discussed in light of the presented characterization results.

Designing Pigments for Optimal Performance in Chemical Toners

Carbon black has historically been used in electrophotographic toners as a black pigment. Its properties influence some of the key performance attributes of the toner, including the printed image density and the toner's electrical characteristics. In the last decade demand for higher resolution and lower cost printing has driven significant improvements in toner performance. These changes have shifted the production of new toners from the conventional pulverization process to more complex chemical processes. In these new processes, carbon black and the other pigments are typically first dispersed into a liquid matrix (aqueous or organic solvent or monomer) and are then incorporated into the toner particle either by chemical assembly processes, such as emulsion aggregation, or direct polymerization. Throughout the various process steps the carbon black needs to remain dispersed in the matrix to optimize the performance.Cabot has developed surface modification technology that allows the design of the carbon black surface chemistry to match the properties of its surrounding matrix. In this presentation we will explore the sensitivity of the carbon black dispersion quality to changes in the polymer properties. We will also demonstrate how careful control of the surface chemistry can enhance the dispersion of the carbon black.

Influence of carbon black surface chemistry on the adsorption of model herbicides from aqueous solution

Influence of carbon black surface chemistry on the adsorption of model herbicides from aqueous solution

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.

Factors affecting the adsorption of stabilisers on to carbon black (flow micro-calorimetry studies): Part II : Hindered amine light stabilisers (HALS)

The interaction of hindered piperidine light stabilisers (HALS) with carbon black has been examined using flow micro-calorimetry (FMC) and Fourier transform infrared spectroscopy (FTIR). Significant differences in both the overall adsorption activity and molar heats of probe adsorption are observed. Differences in adsorption behaviour between different types of carbon black were clearly evident and, as with a previous paper (see reference 1, in the latter paper, surface chemistry of the carbon blacks investigated is extensively analysed by XPS, FTIR, N2 BET adsorption and Karl–Fischer analysis), were mainly to be due to differences in carbon black surface chemistry. The specific surface area merely physically affected the level and heat of adsorption (per unit mass of carbon black). Variation in the degree of substitution of the piperidine amine is an important factor that is found to influence the adsorption activity of HALS, as well as the number of adsorption active and sterically accessible functional groups per HALS molecule. In some cases the adsorbed HALS could be detected by FTIR; shifts in absorption frequencies associated with both the adsorbate and the substrate yielded significant insight into the mode of adsorption of several of the HALS investigated.

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.

Elastomer–carbon black interaction: Influence of elastomer chemical structure and carbon black surface chemistry on bound rubber formation

AbstractThe contribution of elastomer polarity and reactivity to bound rubber formation has been investigated. In this study, a number of elastomers of different chemical nature have been tested. The surface of the carbon black (N110) has also been modified by nitric acid oxidation in order to increase the concentration of surface functional groups. The experimental results have shown that the bound rubber formation is barely related to the polarity of the polymers. It is the reactive sites in both the elastomer and carbon black which are mainly responsible for bound rubber formation. It therefore appears that the elastomer/carbon black interaction leading to the formation of bound rubber is essentially a chemical process involving primary bond formation between elastomer and carbon black. The oxidized carbon black exhibits a higher surface activity which may be due to an increased concentration of oxygen‐containing reactive surface sites, namely, phenolic hydroxyl, carboxyl, lactone, and quinone groups. © 1995 John Wiley & Sons, Inc.

Relationship between carbon black surface chemistry and energy

Nitrogen adsorption data are interpreted in terms of surface area and porosity, for a range of carbon blacks and porous carbons, using the BET, αs and Dubinin–Radushkevich methods. The relative merits of these approaches for identifying and isolating adsorption in micropores, from adsorption on external surface, are considered. Heat of immersion (ΔimmH) data, for non-polar (n-heptane) and polar (water) liquids are related to surface structure and chemistry, respectively.An average value of ΔimmH≈ 107 mJ m–2 is obtained for the dispersion interaction of non-porous carbon blacks by immersion into n-heptane. Where nitrogen adsorption data indicate the presence of microporosity, higher values of ΔimmH are observed which are thought to contain a contribution due to enhanced adsorption forces within these pores. This indicates that the adsorption mechanism within the porosity is one of either primary or secondary micropore filling. Calculation of surface energy (γds) data from nitrogen spreading pressures also supports this conclusion.An approximately linear relationship is observed between the surface oxygen levels of several commercially available carbon blacks and their polar interaction with water. This linear relationship is confirmed by ΔimmH data for samples of one specific black which had been oxidised to varying levels, measured by X-ray photoelectron spectroscopy, (XPS), using an oxygen–ozone fluidised bed apparatus. This oxidation process is shown to lead to the development of carboxylic acid groups on the carbon surface; these have been identified using XPS chemical shift data, IR spectroscopy and pH measurement.

The Effect of Carbon Black Surface Properties and Structure on Rheometer Cure Behavior

Abstract The cure behavior of SBR and NR compounds was examined using the Monsanto Rheometer. The three cure parameters—induction period (td), rate of crosslinking reaction (k2) and maximum increase in torque (ΔL)—were derived from the Rheometer torque curves. The data so obtained were used to calculate Westlinning's αF-values. It was shown that (1) k2 decreases with increasing total acid concentration at the carbon black surface and (2) the value of αF is related to the filler structure and the crosslink density of the rubber matrix. It was also demonstrated that the crosslink density, as measured by ΔL, is influenced by the surface chemistry of carbon black. In SBR stocks the crosslink density increases with increasing total acid concentration, while in NR compounds the reverse is true. These findings were confirmed by examining the tensile properties of regular and oxidized HAF-LS black in SBR and NR compositions. Thus the effect of carbon black surface chemistry on crosslink density can be estimated, for a given recipe, from the value of k2. An empirical relationship between the cure parameters (αF and k2) and filler structure (as measured by extrusion shrinkage) was derived and tested on a wide range of carbon blacks. This relation gives a much better correlation coefficient than the simple relation between extrusion shrinkage and αF alone. Thus by full use of the Rheometer data, the extrusion shrinkage or other structure-related properties of carbon black filled stocks can be predicted.

Studies in surface chemistry of carbon blacks. Part I. High temperature evacuations

Surface complexes on 15 samples of carbon blacks of different varieties were studied by evacuating at 1200°. The total oxygen evolved as CO 2, CO and H 2O was fairly close to the value obtained by ultimate analysis. The total hydrogen evolved as water vapour and free hydrogen was significantly less, by 30–40 per cent, than the hydrogen content obtained by ultimate analysis, showing that hydrogen was held much more firmly. The evolution of CO 2 commenced at around 200–300° and finished at about 500–700° while that of CO commenced at approximately 500–700° and finished in the 1000–1200° temperature range. The liberation of free hydrogen commenced in the 500–700 range and continued even at 1200°. There was no correlation between total oxygen (or any part thereof) and total hydrogen (or any part thereof). The oxygen content was less than 1.5 per cent in furnace blacks, varied between 3 and 4 per cent in channel blacks and between 4 and 8 per cent in colour blacks. Broadly speaking, the furnace, channel and colour blacks contained 9, 25 and 30 mg oxygen/100 m 2 of the surface. The channel blacks ranked with furnace blacks in having a lower value of oxygen disposed off as CO 2-complex but with colour blacks in having a higher value of oxygen disposed as CO 2-complex but with colour blacks in having a higher value of oxygen disposed as CO-complex per unit surface. Suitable explanations based on the history of formation of the carbon blacks have been offered.

Use of Lithium Aluminum Hydride in the Study of Surface Chemistry of Carbon Black

Abstract Considerable interest has been focused in recent years on the effects of carbon black surface chemistry on its properties in rubber and other polymer systems. Methods have been developed in our laboratory for the quantitative characterization and description of the surface chemistry of carbon blacks. The total surface acidity as given by the active (acidic) hydrogen is determined by reaction with strongly basic lithium aluminum hydride in diethyl carbitol, or by equilibration with aqueous alkali under nitrogen. Exclusion of oxygen is essential since carbon blacks readily undergo base catalyzed oxidation. Selective neutralization techniques are employed to further differentiate between strong and weak surface acids. For example, using aqueous sodium bicarbonate solution, only those acids stronger than carbonic acid will be neutralized. Strong acids, as determined by bicarbonate neutralization, are shown to be aromatic carboxyl groups, while weak acids determined by difference between total acidity and strong acid content are phenols and hydroquinone derivatives. Neutral quinone and lactone surface groups are quantitatively determined by chemical reduction with lithium aluminum hydride, or alternatively by analysis of their thermal decomposition products (carbon monoxide and dioxide, hydrogen, and water) obtained on vacuum pyrolysis of carbon black. The distribution of neutral and acidic surface groups on representative channel, furnace, and thermal black is discussed in terms of the state of oxidation of the individual carbons.