I,\-DUSTRIdL
June, 1928
;1-VD E.VGINEERI.VG CHEAWISTRY
ascribes decrease in reactivity brought about thereby to shrinkage of cell space and (at temperatures above 850" C.) to graphitization through decomposition of methane. It may be observed further that in the preparation of active carbon by carbonization of bituminous coal the temperature is kept below 700" C. because if higher temperatures are used it is well known that the high-temperature product cannot be satisfactorily activated. Table V-Reactivities COKE
5
of Bright and Dull Portions of Cokes 4 a n d 5
TESTCONDITIONS
In air at llOOo C. for 60 minutes I n C 0 2 a t 1100°C.for60minutes
4
In air at 950' C.
In Cor at 950' C.
PORTIONREACTIVITY
Bright Dull Bright Dull Bright Dull Bright Dull
Per cent 73.4 82.4 16.9 24.9 63.6 69.9 9.6 32.4
Grams
1.0670 1.9940 1.7500 2.4860
.... .... .... ....
From this study of the phenomena of bIackening during the reactivity test it is evident that there is a separation of reactive and non-reactive particles by the action of the gas. The porous reactive particles are completely penetrated and the reaction progresses throughout the whole particle, whereas with the non-porous (bright) particles the reaction is confined mostly to the external surface. Reduction in size would be expected to have the greatest effect on reactivity of the latter. Whether the effect is due more largely to shrinkage, to stoppage of the pores by other forms of carbon, or to graphitization, it is difficult to tell. It seems certain that any of the gases used in the reactivity test would activate the porous particles and that the rate of reaction would be
621
increased as the test progressed. This was not noticed in any of the cokes tested in this investigation, but it was observed that the surface was gradually reduced by a coating of ash which would tend to counteract the activation tendency. Koppers,6 however, found that a number of samples showed increased reactivity while others showed decreased reactivity, as the test progressed. Conclusions
1-In general, reactivity varies inversely as bulk density and directly as volatile-matter content, but this relation does not always hold, particularly with cokes varying only slightly in reactivity. The effect of volatile-matter content h probably only incidental; it indicates the temperature conditions under which the coke was made, which are the governing factors. 2-Reactivity varies inversely with the size of test particles and will in general vary directly as the adsorptive power. Both properties affect the extent of reactive surface and hence are interrelated. Size of particles has perhaps the greatest influence on reactivity of high-temperature cokes, because their adsorptive capacity is very low. The reactions here appear to take place almost entirely at the external surface. 3-Different coke particles of the same sample show different reactivities, as is manifested by selective blackening of the more reactive particles during test. The duller portions of the same piece of coke, provided they come from the center of the coke charge, are much more reactive than the brighter portions-because they have not been subjected to severe heating conditions. Blackened particles found after making the reactivity test came originally from the dullest portions of the coke.
Carbon Blacks and Their Use in Rubber' I-Comparative Properties of Blacks and Tests in Uncured Rubber Norris Goodwin and C. R. Park DELANO LANI)CO.,2312 EAST52ND ST., LOS
XNGFLES, CALIF
UR howledge regardThe physical and chemical characteristics of several to explain experimental reing the physical and carbon blacks and of rubber stocks containing them sults where the information is chemical characterishave been investigated in order to determine their suitnot complete will be excused ability as Pigments in tire-tread stocks. Five blacks tics of pigments which make in consideration of the chief them more or less suitable as have been Studied-CharltOn lampblack, Micronex, aim of the work, which is only Super Spectra, Thermatomic, and Goodwin. Part I repre nforcing agents in cured to point out the facts, for the rubber goods is very incomresents a study of the Properties of the blacks themauthors realize that certain selves and their use in raw rubber. Part 11, to be pubplete. I n spite of s e v e r a l conclusions may have to be brilliant contributions in the lished in a subsequent issue, will describe tests on variqualified as new information field! we are still far from a ous cured rubber stocks containing the same blacks. becomes available. satisfactory understanding of F i v e b l a c k s h a v i n g as the principles involved in the preparation of compounds. widely different characteristics as possible have been chosen Lack of systematically arranged information is perhaps partly for study: responsible for this state of affairs. The object of this paper Charlton lampblack-an O i l black. was to assemble more detailed and well-organized informamade 'Or and tion in a small field. It is believed that a sufficient number w i & , gas of systematic efforts will place us in a position to understand for use (3) super spectra-^ channel-processgas black more completely the colloidal behavior of pigments in rubber in varnishes and enamels and perhaps in other media. (4) Therrnatomic-A gas black made by thermal decomposiThis study has been confined to the pigments most com- tion of natural gas. combustion monly used in tire treads-namely, carbon blacks-although ~ t w ( ~ by $ ~ ~ ~ ~ in rare cases other pigments have been introduced to illus- of ~ trate some particular point. It is hoped that a few attempts It was hoped that, by a large number of the 1 Received January 30, 1928 various physical and chemical properties of the blacks with
0
~~~~~~~~~$l;PardoecesS
~
~
the phyoical properties of vulcanizates prepared from them, some relationships between the two sets of properties might become apparent.. Characteristics of Blacks
As=-The ash was determined by igniting 2 to 10 grams of material to constant weight in a porcelain crucible over a Fisher burner. All values are on a moisture-free basis. Table IV-Ash BLACK
TRGESPECIFIC Gn.%vmu---The determination of specific gravity was carried out a t 15" C . in a pycnometer bottle upon a samplc dried at 105' C . Xylene was used as the liquid displaced. The ea?e of vetting and bhe higher temperature made available tlirough the use of this liquid f:u:ilitated the expulsion of entr:iined or absorbed gases. The blacks were always hsited in contact with xylene, allowed to stand overnight, a,nd heated again before the measurements were made. The d u e s thus determined are given in Table I. It appears h i m the wurk uf Lon@ tlial vaiues obtained by this method are satisfactory, and they are therefore used throughout all subsequent cslculai'ions. Tablo I-Specific Gravities of Blacks SIYPLB
ELICE
Cliarlion Chariton .~. e.xtiacted with acetone M,cro"rr Super spectra
1.65
1.72
Theirn?tomic Goodwin
The difierence in gravity among the various samples is not a new ohservation,3 nevertheless it is a rat.her curious result. It may be due to a variety of causes, such as incomplete wet.ting by the displaced liquid; inhomogeneity of the individual carbon particle, which is said tu cont,ain an appreciable amount of hydrocarbons either as admixed or adsorbed material; or to pore size within the individual particle. These probleuls have been discussed at some length by Lowry2 and others. Tho temperature of formation of the black3 does not in this case seem to be connected with thcir densities, as would be expected from the work of Roth, Naeser, and Dopke.4 APPARENTSPECIFIC Gravity----Thisquantity was obtained by tapping the black down in a 400-cc. Erlenmeyer flask and adding to keep to the mRrk until 10 minutes additioual tapping produced no further settling. The results a in Table 11 represent t,he condit,ion of the black as delivered
Chrilton
MicrOWS
Table 11-AP arent Densify of &)Lacks Grom De? -.
Charlfoii Micionrr
Super spcetm Thermafamc
0.15
0.2B
Table 111-Relative Densities a* Settled in Liquid De'ic. Charlfon 0.35 Micronex 0.40 Super Spectra 0.30 Tbumafornie 1.00 Goodwin 0.45
0.11 0.65 Goodwin 0.12 1 1. Am. Chcm. Soc., (16, 824 (1924). *Neal snd Perrolt, Bur. Minds. B d l . 19% (1922). B n . . 69, 1379 (1926).
'
P," rrnt . . . .. 0.08
0.01 0.08 0 04 0.04
Reddish, w i t e g r i t t ~ Reddish, trace of gnt, Reddish, free from p t Gray, S m d pellets fused io ciucible Reddish brown, slight grit
RNEINESS OF I)ivrsros---Figiae 1 shows phot.ographs of the blacks made with dark field illumination. The method of preparation and mounting was as follows: Tvo grams of black were milled into 100 grams of clean pale crepe. Two grams of this hatch were added to 25 ec. of xylene in a sample bottle and allowed to stand with occasional shaking until dispersion was complete. A small drop was then placed upon a slide, covered, and pressed under a 500gram weight for 3 hours, by which time flow had ceased. The available equipment prevented any more accurate method, but without doubt the fields represented in the figure contain approximately equal weight.s of black. The method therefore gives, if not the actual particle size, at least the order in which the blacks fall. The order of increasing particle size is Super Spectra, Micronex, Goodwin and Charlton about equal, Thermatomic. The particles of Super Spectra are so fine that they were photographed with difficulty and the foggy result here shown is the best of several attempts. I>IsPxnsIoN-These photographs do not represent the dispersion of the black in the original rubher black mix. I n the xylene solution the blacks all slowly Aoceulate and must be agitated before the mounts are made. The Thermatnmic sample shows a small floccule. This could ereily be broken by a.gitation. It is hoped that a careful study of this Bocculating tendency may give soiue interesting information. I n spite of excellent work by Green,s Spcar,a and others, no entirely satisfactory method has been developed for studying the dispersion of black in cured stocks. All methods proposed make use of smiling or some mechanical distortion and seem open to question on this account.
SUpcr svectia Thermatomic Figure I-Phofa&raphs of Blacks at 860 X
and might be oonsiderably altered by coinpression. The relative hulk volume settled from a liquid should give thc relation more satisfactorily than the apparent density in air. Samples which were well dispersed in mineral oil and allowed t,o settle for about 3 months gave the approximate relative densities shown in Table 111. NL*CH
Ch~lion xieroncri super s p e c t i a Thcrmiiornic OOOd~i"
REI*RBS
AS,
