Carbon 40 (2002) 929–937 Microstructure of carbon blacks determined by X-ray diffraction profile analysis a, a a b * ´ ´ U ´ ´ Tamas Ungar , Jeno Gubicza , Gabor Ribarik , Cristian Pantea , b T. Waldek Zerda a ¨ ¨ Eotvos University, Department of General Physics, P .O. Box 32, Budapest, H-1518 Hungary b TCU, Department of Physics, Fort Worth, TX 76129, USA Received 18 April 2001; accepted 21 August 2001 Abstract The microstructure of carbon blacks is investigated by X-ray diffraction peak profile analysis. Strain anisotropy is accounted for by the dislocation model of the mean square strain in terms of average dislocation contrast factors. Crystallite shape anisotropy is modeled by ellipsoids incorporated into the size profile function. Different grades of carbon blacks, N990, N774 and N134, untreated, heat-treated and compressed at 2.5 GPa have been investigated. The microstructure is characterized in terms of crystallite size-distribution, dislocation density and crystallite shape anisotropy. 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 average sizes of the crystallites obtained by X-ray diffraction agree with those estimated from Raman spectra. Applied pressure affects the magnitude of strain within the crystallites.  2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Carbon black; B. High pressure; C. X-ray diffraction; D. Crystallite size 1. Introduction [1–5]. The layer stacking disorder can be observed in principle by analysing HK bands in the diffractograms. Carbon black is generally used as a filler in rubber Rocking curves of the HK.0 type reflections would show production to modify the mechanical properties of the tire. extra broadening due to rotations around the hexagonal c Although the smallest indivisible unit of carbon black is axis whereas the 00.L type reflections would be broader in the aggregate, in the TEM images aggregates appear to be the u –2 u radial direction. This kind of layer stacking formed by spherical particles, which are fused together. disorder can be handled as effective boundaries of coher- Aggregates connect through Van der Waals forces into ently scattering domains where diffraction peak broadening networks called agglomerates [1]. The internal structure of is a measure of the size of these objects. aggregates is not well understood. Graphite-like, The structure of carbon black particles and their surface quasicrystalline domains, in which basal planes are parallel properties are important for many reasons. Different sites but angularly distorted and the spacing between the layers present on the surface determine reinforcing properties of is different from that of pure graphite, have been detected carbon black in rubber [6]. Energy of interaction between in carbon black particles [1]. Biscoe and Warren identified the polymer and carbon black depends on nature and those structures as intermediate between crystalline and population of different sites. The most energetic sites, amorphous materials [2]. Hereafter, the turbostratic quasi- which very effectively adsorb polymers, are usually iden- crystalline domains are referred to as graphitic crystallites tified as crystallite edges. Crystallite flat surfaces and or nanocrystallites. Due to the lack of three-dimensional amorphous carbon present on the surface are considered ordering, this nomenclature is not rigorously correct, but less energetic sites. Thus to characterize reinforcing prop- appears to be generally accepted in the scientific literature erties of carbon black it is necessary to determine the fraction of the surface occupied by amorphous carbon and estimate the size of the crystallites and their surface *Corresponding author. Fax: 136-1-372-2811. ´ E-mail address: ungar@ludens.elte.hu (T. Ungar). density. Relative concentration of amorphous carbon can 0008-6223 / 02 / $ – see front matter  2002 Elsevier Science Ltd. All rights reserved. PII: S0008-6223(01)00224-X