Structure of Carbon Blacks
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STRUCTURE OF CARBON BLACKS
T. W. Zerda, J. Qian, C. Pantea, and T. Ungar* TCU, Department of Physics, Fort Worth, TX 76129 * Eotvos University, Dept of General Physics, Budapest, Hungary
ABSTRACT X-ray diffraction, Raman spectroscopy, and neutron scattering were used to characterize structure of carbon blacks. Different grades, N990, N774, N299, N134, and N110, untreated, after heat treatment and compressed at 2.5 GPa have been investigated. The average sizes of the crystallites obtained by X-ray diffraction agree with those estimated from Raman spectra. The distribution functions of crystallite sizes were evaluated from X-ray diffraction using the recently developed method. Heat treatment results in increased vertical and lateral sizes of graphitic crystallites. Postproduction pressure treatment has little effect on the average sizes of the crystallites, however, it affects the crystallite size distribution function. The magnitude of strain within the crystallites is affected by applied pressure. The relative concentration of amorphous carbon blacks estimated from Raman spectra decreases with increasing temperature but not with increased pressure. It is suggested that the initial growth is associated with alignment of the existing graphitic planes and later by incorporating aromatic carbon into the crystallites.
INTRODUCTION Although the smallest indivisible unit of carbon black is the aggregate, in the TEM images aggregates appear to be formed by spherical particles, which are fused together. Aggregates connect through Van der Waals forces into networks called agglomerates1. Internal structure of aggregates is not well understood. Graphite-like, quasicrystalline domains, in which basal planes are parallel but angularly distorted and the spacing between the layers is different from that of pure graphite, have been detected in carbon black particles [1]. Biscoe and Warren [2] identified those structures as intermediate between crystalline and amorphous materials. Hereafter, the turbostratic quasi-crystalline domains are referred to as graphitic crystallites or nanocrystallites. Due to the lack of three-dimensional ordering, this nomenclature is not rigorously correct, but appears to be generally accepted in the scientific literature [1,2-5]. The structure of carbon black particles and their surface properties are important for many reasons. Different sites present on the surface determine reinforcing properties of carbon black in rubber [6]. The energy of interaction between the polymer and carbon black depends on nature and population of different sites. The most energetic sites, which very effectively adsorb polymers, are usually identified as crystallite edges. Crystallite flat surfaces and amorphous carbon present on the surface are considered less energetic sites. Thus to characterize reinforcing properties of carbon black it is necessary KK6.4.1
to determine the fraction of the surface occupied by amorphous carbon and estimate the size of the crystallites and their surface density. Relative concentration
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