1646
LEROYE. ALEXANDER AND ELMER C. SOMMER
Vol. 60
SYSTEMATIC ANALYSIS OF CARBON BLACK STRUCTURES BY LEROYE. ALEXANDER AND ELMER C. SOMMER Department of Research in Chemical Physics, Mellon Institute, Pittsburgh IS,Pennsylvania Received July $0, 1066
Diffractometric intensities from carbon blacks were subjected to a precise, systematic analysis in order to disclose both major and minor differences in the structural parameters characterizing the seudo-crystals, or parallel-layer groups. The method yields the pseudo-crystal dimensions, L. and L,, the fraction of Jsorganized material, the proportion of sin le (unassociated) layers, and a rather precise choice of the distribution of numbers of layers constituting the pseudo-crystas. Results are given for three representative blacks: Acetylene, Furnex and Micronex.
Introduction I n a previous report2 a condensed account was given of an X-ray study of four reinforcing carbon blacks wherein a photographic procedure was employed, which, of course, placed a definite limitation on the accuracy of the intensity measurements. In addition, the use of Debye-Scherrer geometry unavoidably introduced some instrumental broadening into certain features of the diffraction pattern. These deficiencies precluded any attempt to evaluate minor differences in the structural parameters. When subsequently the need arose to measure systematically the structural features of a much larger number of blacks, improved experimental techniques were employed in order to disclose differences of both primary and secondary magnitude. However, time and cost factors required a compromise between the ultimate in accuracy on the one hand and routineness of the method on the other. It was decided that these requirements would be satisfied by employing a parafocusing Geigercounter diffractometer together with flat specimens of sufficient thickness to yield maximum diffracted energy over the entire range of Bragg angles involved.a Geometrical considerations, confirmed experimentally, showed that the use of such thick specimens did not appreciably alter the shapes and breadths of the diffraction lines studied, which are inherently very broad. As in the previous study, a curve-fitting interpretative method similar to that of Franklin4has been followed, but the (002) and (10)) rather than (002) and ( l l ) , line profiles have been analyzed. In addition to the parameters measured in the earlier investigation, it has been found possible to derive additional information : the fraction of single (unassociated) layers and the fractions of the layers that are associated in groups of 2, 3, 4 and so on. In the present paper attention is focused on the experimental technique and the interpretation of the data obtained, and the results for three carbon blacks are presented for purposes of illustration. No attempt has been made to assess the chemical significance of the structural data or to propose correlations with other physical characteristics. A full account of these properties for all the specimens included in the larger study is to be published later by the Research Laboratories of Columbian Carbon ( 1 ) This investigation was sponsored by the Research Laboratories of Colunibian Carbon Company. (2) L. E. Alexander and S. R. Darin. J . Chem. Phys., 23, 594 (1955); 24, I 1 18 (1960). (3) H. P. Khig and L. E. Alexander, ”X-Ray Diffraction Procedures,” John Wiley and Sons, New York, N . Y.,1954. pp. 252. 297. (4) R. E. Franklin, Acta Cryst., 3, 107 (1950).
Company. For the information of the general reader it must be emphasized that the present investigation embraces only carbons whose structures are based upon the random-layer lattice, that is, turbostratic
Experimental The carbon black samples were packed manually in a rectangular cavity of dimensions 1 X 2 X 0.4 cm. in a flat aluminum holder and analyzed with a Norelco wide-range diffractometer using CuKa radiation. An X-ray beam monitor with auxiliary synchronized counting and timing circuits was employed to compensate for variations in the intensity of the X-ray source.* Counts were recorded over the angular range 28 = 16-70’ and corrected for the dead time loss of the Geiger tube.’ Because of the small sensitivity of the Geiger counter to the shorter wave lengths the contribution of the general radiation could be determined with sufficient accuracy by remeasuring the intensity over the range 16-70’ with a 0.035-cm. aluminum filter in the path of the diffracted ray. This eliminated the Ka component but permitted about 70% of the general ra
