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Transmission electron microscopy of the carbon black primary particles

Carbon blacks are mostly used in car tyres, printing inks and plastics production. The properties of the rubber compound and vulcanized rubber (final product) are highly influenced by the primary particle size of carbon black. Beside this the shape of particle aggregation (structure) is also of great significance. In this work transmission electron microscopy (TEM) and Raman spectroscopy were used to investigate samples of carbon black in purpose of determining primary particle size. Five different samples of carbon black (CB1, CB2, CB3, CB4, CB5) produced by Petrokemija d.d., Kutina were investigated. TEM measurements were performed on “ JEOL” JEM-200CX, operated at 200 kV. For TEM measurements the samples were suspended in chloroform, treated in an ultrasonic bath, mounted onto the carbon-coated copper grids and finally dried in air. Raman spectroscopy measurements were performed using a computerized triple monochromator (DILOR Z24). The argon ion laser (Coherent, Innova 100) operating at 514.5 nm and 100 mW laser power was used for excitation. The laser beam was focused in the line shape to reduce the heating of the sample during the recording of the spectra. TEM results were fitted to log-normal distribution (Fig. 1.a, b and c) and mean average sizes of the particles were determined (Table 1). Results were compared to results of indirect method for estimation of primary particle sizes (Iodine absorption number). For samples CB1 and CB2 this two methods showed very good agreement in sizes, but for the samples CB4 and CB5 that was not the case. Two samples with the same estimated sizes CB4 and CB5 showed different average sizes observed by TEM (Fig. 2 b and c). From the shape of the distribution (Fig. 1 b and c) we observed smaller value than estimated. Moreover, CB5 had average particle sizes of about 17% smaller than C4 (Table 1). Raman analysis in all samples showed two peaks characteristic for carbon materials [1]. In Raman spectrum of sample CB5 one more peak at 973 cm-1 (↑ ) was observed. This band is not characteristic for carbon materials and its presence indicted possible contamination of the sample. According to the McCulloch et al [2] band width (FWHM) of D peak (1350 cm-1) can be taken as indication of disorder in the primary particles structure. The difference in the FWHM (fitted using Lorenzian band profile) observed in the investigated samples (Table 2) indicate different degree of disorder of primary particles in the carbon black samples. We showed that TEM is direct and powerful method for analysis of primary particle sizes. Raman spectroscopy is good complementary technique for indirect analysis of primary structure order of the carbon black particles. We observed decrease of order as sizes of particles increase.

carbon black; TEM; partcle sizes

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