Carbon 1967, Vol. 5, pp. 107-l 11. Pergamon Press Ltd. Printed in Great Eritain

AN X-RAY STUDY OF CARBON BLACKS

PRODUCED FROM COALS

JAMES BAYER and SABRI ERGUN

Solid State Physics, Pittsburgh Cod Research Center, Bureau of Mines, U.S. Department of the Interior, Pittsburgh, Pa.

(Received 30 November 1966)

Abstract-X-ray diffraction patterns of eight carbon blacks produced from coals have been studied. Layer diameters, La, obtained from the (100) and (110) reflections ranged from 6 to 178, and the stack heights, L,, derived from the (002) reflections, ranged from 12 to 148. The above values compare with 2Oh and 14A, respectively, obtained from the diffraction patterns of a commercial bfack, viz. Peiletex. It appears that coal blacks are structurally similar to well-known commercial blacks.

1. INTRODUCTION

CARBON blacks are produced by cracking gaseous hydrocarbons. Often the process takes the form of incomplete combustion to yield large amounts of solid residue. Recent investigations by JOHNSON

et al.(“) at the Bureau of Mines have shown that carbon blacks (in this study referred to as coal blacks) can be produced from coals. Since coals constitute a very large source of carbon, the above development has received wide attention. In this paper are reported the results of an X-ray study of the structure of eight coal blacks and of two com- mercial blacks, viz. P33 and Pelletex.

2. E~ERI~NTAL

Six of the samples studied were produced by passing pulverized high volatile coal in a con-

current stream of nitrogen or air through a vertical tube heated to 1250°C at various linear gas velocities. To determine the effect of lower temperatures, one run was conducted at 1000°C and another at 900°C. An electron micrograph of the black CB 22 is shown in Fig. 1. Chemical analyses of the blacks produced and the experi- mental conditions are listed in Tables 1 and 2, respectively.

X-ray scattering intensities were obtained using zirconium-filtered MoKu radiation with a 1” beam collimator having medium resolution Soller slits. The goniometer was moved through the angular range 28=2”-152” (at l/4” intervals in the 2”-50” range and l/2” intervals beyond SO’) by means of a step scanner. Scanning intervals {about 4.5 min)

TABLE 1. CHEMICAL ANALYSIS OF CARBON BLACKS DERIVED FROM COAL

Sample No. H C N 0 S Ash

CB 3,4 1.1 96.0 0.8 1,O 0.8 0.3

CB I,2 1.0 96.3 0.7 0.9 0.8 0.3

CB $6 0.7 96.5 0.8 0.8 0.8 0.4

CB 89 1.3 94.2 0.9 1.7 0.9 1.0

CB 22 0.9 96.3 0.9 0.8 0.8 0.3

CB lo,11 0.7 94.6 0.8 0.6 0.8 2.5

CB 19,20 2.7 90.0 0.9 4.7 1.0 0.7

CB 15,16 3.5 89.6 1.5 4.4 0.8 0.2

PelIetex 0.4 98.4 0.0 0.8 0.1 0.3 P33 0.5 98.7 0.1 0.6 0.1 -

107

wore d~t~~i~~d electronically by munitor~g the intensity of the primary beam, This was accomp- lished by measuring the intensities scattered from a mylar film (25 p thick} placed in front of the beam slit. An auxiliary detection system, composed of a scintillation counter, ~Fli~~atio~ system and sealef, controlled the step scanner, and a scaler- printer #m~mation recorded the intensity of the d&acted beam. The samples used in the stwiy were dab specimens 2.5 mm thick 40 mm long, pressed to a density of about 1.2 g/cm3. Data were obtained with samples placed both in trans- mission and reflection positions. The latter data were obtained to assure that the ~t~eren~e func- tion obtained was OR an absolute scale, A trans- mission spectrum from a powdered di~o~d (S- 20 & sample was also obtained for purposes of making corrections for instrumental bruadening. The correction was made by a direct method for unfolding the convolution products developed by ]ERGUN:2'

In Fig+ 2 are shown the scattered intensities of P33 befare and after correction for air sr;atter and ~~~~~~~~ broadened, Also ineluded in the f&xx is the (I 11) ~e~~~io~ of a powdered diamond sample used in correcting the observed intensities. The large breadth of the diamond peak is in part due to distortion of focusing in the trans- mission geometry when using thick samples. It is seen that the corrected pattern is much sharper than the observti

~o~~j~~on and absorption ~~e~tio~ were made by a method described by ERGBR, &YES and fl-hx RUREN.~~' Tn this method the equation for the

observed inteusi~es (corrected for air scatter au& instrumental broadening) i,s transformed into a linear form, ~(s,~T)=~[l-t_s(~,~~)] +E(s),wherci: i(s) ia the oscillatory part of the interference func- tion. If a proper value is assigned to ,O, a plot of (B vs. g yields a straight line having a slope and. intercept ,both equal to X; the ~~~~li~a~o~ constant, modified only by the ~~lat~on~ of i(s), determination of the proper value af &Y and K and, in fact, all of the computations im?oIved in treating the raw data were done using a computer. The interference functions obtained are shown in Figs, 3-5,

From Figs. 3-5 it is seen that the structme of coal blacks is very much the same as those of the two Eornrner~~l blacks included ia this study. According to the presently wepted concept postu- lated by W~N,(~*~) carbon blacks are composed of graphite-like layers, arranged roughly parallel and ~qu~dist~t in stacks of several layers, but otherwise random, and the layer separation is slightly larger than in graphite. Sizes of the layers and heights of the stacks can characterize the a~~~~ of a Ma& The ~~~d~ of the layer sizes and stack heights of carbon blacks, as reported in the literature, range from about 10 to SOA, whereas electron micrographs of the blacks show particle sizes of a much larger order of magni- tude. How these little stacks (crystallites) are held together to form larger spherical particles has been the concern af various ~v~tigato~ and remains so to&y. Presently* we are not concerned with this question, We are interested in deriving the struc-

FIG. 1. Electron micrograph of a coal black (CB 22).

AN X-RAY STURY OF CARBON BLACKS PRODUCED FROM COALS

s+!un ‘!‘=‘I0 ‘AlISN31Nl

110 JAMES BAYER and SABRI ERGUN

I- i_._

I.

Si!‘J” 3!WOW ‘AlISN31NI

AN X-RAY STUDY OF CARBON BLACKS PRODUCED FROM COALS 111

tural parameters of the coal blacks, using the accepted model, and comparing them with those of commercial blacks.

The layer sizes can be obtained in a simple manner from the (100) and (110) reflections using the formula

I K La=-

AS

where As is the width of the peak at half height, the height being measured above the straight line join- ing the two adjacent minima, and K is a constant. Originally the constant was calculated by Warren to be about 1.84. Recently, WARREN and BODEN-

STEIN@ considered the interaction between the different layers in a parallel layer group on the profile of the two dimensional reflections, and ob- served that the values of K depended upon the layer size (also probably to a lesser degree on the stack height), and that those for the (100) reflec- tions were different from those of the (110) reff ec- tions. We have calculated the values of L, using K’s extrapolated from the curves given by Warren and Bodenstein. The results are given in Table 2.

The stack height, L,, was calculated using the Scherrer equation

where As is, as before, the peak width at half peak intensity. The results are also included in Table 2. A third parameter that is often calculated from a profile analysis of the (002) reflections is the frac- tion of (so-called) amorphous or disorganized carbon. This parameter is one of convenience; we found that after correction for instrumental broadening its magnitude generally became neglig- ible.

From an inspection of Table 2 it is seen that the structural parameters of coal blacks prepared at 1250°C are about the same order of magnitude as those of Pelletex or P33 samples examined. L, values of the coal blacks range from 15 to 17A and those of the carbon blacks are ZOA. L, values of the coal blacks range from 13 to 14A, and those of Pelletex and P33 are 14 and 20& respectively. However, the coal blacks produced at 1000 and 900°C have lower layer diameters, i.e. 6 to 7A. These differences are consistent with the chemical analyses of the blacks shown in Table 1. The carbon contents of the coal blacks produced at 1250” are about 2 to 4 per cent lower than those of Pelletex or P33; they have slightly higher hydrogen, nitrogen and sulfur contents. The blacks produced at 1000°C or 900°C have about 9 per cent less carbon, 4 per cent more oxygen and about 2 to 3 per cent more hydrogen than Pelletex.

From a structural standpoint, coal blacks produced at 1250°C are very similar to these commercial carbon blacks. It appears that coals may be good raw materials for carbon blacks.

Acknowledgment-We wish to thank J. H. Field, Project Coordinator, Indirect Coal Conversion Processes, for making available the samples of coal blacks used in this study.

1.

2. 3.

4. 5.

6.

REFERENCES

JOHNSON G. E., DECKER I&‘. A., FORNEY A. J. and Field J. H., Carbon Blacks Produced from Coal, manuscript in preparation. ERCUN S., to be published. ERGUN S., BAYER J. and VAN BUREN W., J. Appl. Pkys., to be published. WARREN B. E., Pfzys. Reet. 59, 693 (1941). BISCOE J. and WARREN B. E., J. Appl. Phys. 13, 364 (1942). WARREN B. E. and BODENSTEIN P., Acta Cryst. 18, 282 (1965).