Commercial and Experimental
Carbon Blacks AN X-RAY COMPARISON GEORGE L. CLARK, ALFRED C. ECKERT, J R . ~ ,AND ROBERT L. BURTON2 University of Illinois, Urbana, I l l . critical and quantitative x-raj diflraction study has been made of 66 carbon black samples for the primary purpose of characterizing and classifying many older commercial varieties and those developed during the war. The measurements involved are primarily two interplanar spacings, c for the flat hexagonal basal planes, and a which indirectly- measures the carbon-to-carbon distance within a plane; and also two crystallite dimensions, L, and La, in the corresponding directions, derived from the hreadths of diffraction interferenres. No two carbon
A
blacks give even approximately the same x-ray pattern. A direct relationship has been established between the ratio L,/L,, whioh measures flatness of shape, and ease of processing of channel carbons and structural characteristics. Interesting details are given for various carbon blacks and graphitic acids. One series of experimental carbon blacks is subjected to correlative physical, electron micro.: scope, and x-ray tests. The electron microscope particle is of the order of 25 primary crystallites measured from x-ray data.
T
interferences on a pattern give indications of the crystal development or distortion. Scattering of x-rays at sinal1 angles gives some information concerning the existence of clusters or particles or of voids between particles. As these data are collected from the various patterns, an attempt is made to correlate them with known properties and histories of the samples. Practical application of this study has been made in several directions. By the above-mentioned correlations i t is suggested that the x-ray pattern of a given carbon may be used to reveal the degree and direction of graphitization of the carbon and thus predict its adaptability to a given use. Patterns of synthetic mixtures of mesomorphic carbon (A-1) and graphite make possihle the suggestion of the use of such patterns for a determination of graphitic carbon in the presence of mesomorphic carbon blacks It is also suggested that a nomenclature for carbon blacks could well be based on their diffraction patterns. This study is an outgrowth of two recent contributions. In 1940, Clark and Rhodes (5) reported the first comprehensive preliminary study of mesomorphic carbon by the x-ray diffraction method. They limited their investigation t o a study of primary crystallite size. The present study supplements the work of Clark and Rhodes by making practical application of the facts revealed by their work and by applying the two-dimensional lattice concept and many other structural variables and measurements. I n 1942, Biscoe and Warren ( 1 ) published the results of x-ray studies on a very limited number of carbons as they graphitized. This study supplements their work in t h a t many more different carbons are used, and are found in many more different mesomorphic states than were reported by them. There have been a number of important contributions on methods and equations of evaluating size and shape of colloidal partirles from line broadening of diffraction interferences. Of these Warren’s equations are inost useful for carbon blacks:
HIS investigation wab undertaken, in one aspect, at the suggestion of the War Production Board for the purpose of organizing and coordinating the available information on carbon blacks. This information heretofore has been so scattered, contradictory, and controversial, in the opinion of many people, that the task of classifying carbon blacks has remained extremely difficult. S o serious attempt has been made previously t o correlate a classification based on crystalline states or structural stages, many of which have been observed, with practical co’nsiderations of method of production, use, rubber reinforcing properties, or easy, medium, or hard processing (EPC, MPC, HPC). As a tool for this classification and correlation, the xray diffraction method is the most promising and significant because by its use each black gives a characteristic pattern t h a t can be quantitatively examined. With such data may be correlated, as is done in this paper for typical series of samples, measurements with the electron microscope, which already has had wide usage for carbon blacks, and other types of chemical, physical, and mechanical data. X-RAY DIFFRACTION STUDIES
This study consists first in the examination of x-ray diffraction powder patterns made under identical conditions and measured with the greatest possible precision of about 66 samples of carbon and graphite, which are described in Table I. Typical chemical analyses for carbon, hydrogen, oxygen, and ash are listed in Table 11. These patterns are examined from six points of view, each revealing certain facts concerning the structural characteristics of the sample giving the pattern. The number and type of interferences on the pattern indicate the degree of crystallinity. The positions of the interferences give a means of calculating the interplanar spacings, c, for the basal planes; and a, which gives a measure of distances within the flat planes made up of hexagons of carbon atoms; and thus their variation from one sample to another. The shape or symmetry of the interferences reveals whether the interference was caused by structural elements which have a two-dimensional spatial arrangement or by elements which have a three-dimensional arrangement. The breadth of interferences gives a measure of crystallite (primary particle) size. The relative intensities of the
Lo = 0.89 A/B cos 0 (three-dimensional interference) La = 1.84 X/B cos 0 (two-dimensional interference)
(1)
(2)
A (sin 0) = 0.16 X/L, (correction of position of 2 for
using Bragg equation) (3) a indicates the a direction, the direction in planes of the hexagons, the [lo] direction. e indicates the c direction, the direction perpendicular t o the planes of t h e hexagons, the 10021 direction. I,, is the particle sihe in the a direction.
Present address, Battelle Memorial Institute, Columbus, Ohio. Present, address, E. I. du Pont de Nemours & Company, Cellophane niviaion. Buffalo, N. Y . 1
z
20 1
a
INDUSTRIAL AND ENGINEERING CHEMISTRY
291
TABLE I. DEsc!m?fIoN OF' SAMPLES .nrupir
Description
40.
-4.
Alssorted Couirrirci:ial Cnrbons
Cabot's S o . ti
L 1-%
lacquers Rubber channel black Rubber channel black Acetylene carbon Spectroscopic giagliitr
1-9 A-I 0 A.11 \
12
Cabot's No. 1 Cabot's No. $1
Treated for I 6 13. Samples -4-1,
c.
None (A-Y) 260 44 1 743 854 927 1077 927 (treati'd
H- 1 a-2
a-3
a-4
3-0
B-6 B-7 8-8
C,
i2.l
c-2
c-3
c-4 terns. Of all x-ray data the shape factor I;,/LC is most highly characteristic o f carbon type. The scattering of x-rays a t small angles increases with t'emperature of heat treatment a t low temperatures, thus indioating a growth of clusters of particles as previously observed. Patterns of carbons heat treated at, high temperatures show evidence of change in st,ructural dimensions in different direct,ions independently of each other. Patterns of a number of experiment a1 carbons show further the existence of carbon in many different mesomorphic states defined by the independent, variation of various st~ructuraldimensions of the element. Comparisons of patterns of various sta,rtirig materials and graphi tic acids derived t,herefrom shoiI- independent,ly vxriablc: dimensions in this class of substanres. Inspection of patterns of various natural and art.ificia,l graphiks reveals niarlted differences in the structural propert irs of these substjancw. Pat,terns of mixtures of graphite and an. amorphous carbon indicate t,he possibility of the development of practirnl met8hods
Vol. 41, No. 1
for quantitative deteririjiiation oi' gmyhi t,c i n thc presonoe ot amorphous carbon. D a t a collected here confirm t h e difference between partSiclc* diameters determined from electron microscope photograph,< and the crynt,allit,e dimensions derived from x-ray data. Thc, electroii microscope particle is of the order of 28 primary cryst'allites irieasuretl from x-ray rial a. has been subjected One series o f experimpntal carbon blac 1.0 correlative physical, elect,ron microscope, and x-ray Although there is considerable variation in order of 28 t y data, there are definite trends. One sample has maximum values particle size (100 inij teiisile, elonga,tions a t break, t,oa,r nce, and the x-ray value L,/L, which measures flatness o f ~
ACKNOWLEDGMENTS
6inc:erc thanks are extended to i'he carbon black manufacturers specifically mentioned in Table I , for their interest and cooperation in supplying the valuable group of specimens; to Mert o n Studebalrer, formerly of the General Atlas Carbon Company arid the JTar Production Hoard, now of the Phillips Petroleum Company; a,iid t o raendle of the Columbian Carbon Company for his eii , cooperation and the c1assific;ation according to carbon Table VI. This attempt t o assist. the great (barbon industry would have been obviously impossible wit,hoiit this generous a LITER 4TLIKh (X'FEU
(1) Biscua. .J., a i d IVarien, B. E J A p p l i e d Phys., 13, 364 (19421 (2) Brodie, B. C., Trans. Rou. Soc. (London), 149,249-59 (1859). (3) Clark, G . L.? and Rhodes, H D., INDEm;. CHEM.,ANAL.En., 12, 66-71 (1940). (4) Cranor, D. F., I n d i a n Rubber Wo~Lcf,107, 378 (1943). ( 5 ) Hoffman, U,, and Wilm, D., 2. Electroehem., 42, 504 (I93b). (6) Rudorff, W., Z . physzk. Chem., B45, 42-68 (1939). (7) Watson, J. H. L., J . A717djd Phuls., 18, 153 (1947) K X C ~ I V F IAiiguot I 2 , 1946
Ac CHARLES F. POE ANI) E. J1. VAN VLEET I:nii-ersity qf Colorado, Boulder, Cola. Strips o f stainless steel resist the rorrociing action of most dilute organic acids at 25" C. and at boiling temperatures, with the exception of lmiling oxalic acid in normal concentration. The most rapid rate of attack by the acids occurs during the first 24 hours. Boiling temperatures usualIy decrease the corroding action o f the acids on stainless steel, especially in the 0.01 N strength. The corrosive activit) of the organic acids on the stainless steel is not a dirert function o f their concentrations i n most instances.
I
N A previous investigation ( 6 ) the effect of acid foods on stainless steel cooking utensils was studied. Little iron or chromium was dissolved by any of the foods tested. The niaxi-
mum amount of iron dissolved, after boiling the food for 1 hour in a stainless steel utensil, was 6.9 parts pcr million (p.p.m.) when cherry juice was used as the test material. Under the same conditions, the maximum amount of chromium dissolved was 2.9 p.p.m. by tomato juice. Only small amounts of nickel were dissolved by the juices.
The object of the researrh reported here was to determine the quantitative corrosive effects of a few commoii organic acids on the chromium-nickel type of stainless steel used in the fabrication of cooking utensils. The acids weie chpsen from those commonly found in foods and those most important in general industry. Thc degree t o which stainless cooking ut ensils would contribute to thL presence of iron, chromium, and nickel in prepaied foods would depend largely on the kind and the amount of organic acid. pieqent in the foods. Stainless steel \$as first introduced to the general publlc 111 1914 in the form of table cutlery ( I ) , although such steels had been i n the process of development for inany- years. There are two great clasyes of stainless steel: firSt, those consi5ting of roughly 12 l o i4T0 chromium and 241, nickel; and secondly, those consisting oi more than 17y0chromium and 7% or more of nickel. T h e first alloy is hardened by quenching in water from high temperatures and the second is not. This seLond type of steel 1s more costly, but it is the more resistant to corrosion. It also lends itbelf to stamping into dishes and pans for kitchen uee. It is with thiy tvpe of s t a i n h s steel that this investigation \\as concerned.
