Proceedings of the Fifth Conference on Carbon

634 Pages·1962·37.898 MB·English

PROCEEDINGS OF THE
Fifth
Conference on Carbon
VOLUME 1
Held at the
PENNSYLVANIA STATE UNIVERSITY
UNIVERSITY PARK, PENNSYLVANIA
A PERGAMON PRESS BOOK
THE MACMILLAN COMPANY
NEW YORK
1062
This book is distributed by
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Copyright © 1962
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FOREWORD
THE Fifth Carbon Conference was co-sponsored by the American Carbon Committee and
the Pennsylvania State University and was held at the Pennsylvania State University,
University Park, Pennsylvania, June 19-23, 1961.
Thanks are due to the Program Committee composed of Messrs. G. R. Hennig (Chairman),
L. E. Alexander, S. W. Bradstreet, R. J. Diefendorf, G. J. Dienes, S. Ergun, J. W. McClure,
R. E. Nightingale, M. L. Studebaker and E. C. Thomas, and the Foreign Correspondents:
Messrs. H. Akamatu, H. W. Davidson, X. Duval, V. A. Garten, K. Hedden and H. Tschamler
and to the Local Committee, as well as all the others whose cooperation has made this
Conference such a spectacular success.
This was the first Carbon Conference held outside of Buffalo and according to a decision
made in 1959, the first which set the Conferences in motion throughout the U.S.A. The next
Conference, already in preparation, will be held in Pittsburgh in June 1963.
The Fifth Conference surpassed previous ones so much that the Program Committee had
a very difficult time in scheduling all the papers in a way satisfactory to all people concerned.
Should this spectacular development of the carbon field continue and the popularity of these
Conferences grow still further, important decisions and changes in the mode of operation of
the Conferences, as well as in publication of the Proceedings, will have to be made.
All the papers presented at the Fifth Conference and submitted to the Proceedings could
not be placed in one volume. It was decided not to split the two volumes according to subject
matter, but in all fairness to those who submitted their paper early to go ahead with publica­
tion as fast as possible and include in this first volume all the papers which were submitted
first, which conformed to regulations, and did not require extensive edition, redrawing of figures,
etc. Of the 70 papers included in this volume, four were presented in the form of one paper
which was then divided in order to give appropriate credit to those whose work is discussed.
This is the fourth volume of the series and the third one published by Pergamon Press Inc.
The cooperation of all authors and of Pergamon Press Inc. in preparation of this volume
is greatly appreciated.
All remaining papers from the Conference which were either delayed in processing or were
late in being submitted will appear in the second volume.
S. MROZOWSKI
M. L. STUDEBAKER
P. L. WALKER, Jr.
Buffalo, New York
April 1962
THE AMERICAN CARBON COMMITTEE
EXECUTIVE COMMITTEE
S. Mrozowski, University of Buffalo, Dept. of Physics, Buffalo 14, New York (Chairman)
M. L. Studebaker, Phillips Chemical Company, 318 Water Street, Akron 8, Ohio
P. L. Walker, Jr., Pennsylvania State University, Division of Mineral Technology, Univer­
sity Park, Pennsylvania
TECHNICAL ADVISORY AND EDITORIAL COMMITTEE
Members of the Executive Committee and
R. C. Anderson, University of Texas, Dept. of Chemistry Austin 12, Texas (1963)
W. 0. Baker, Bell Telephone Laboratories, Murray Hill, New Jersey (1965)
J. C. Bowman, National Carbon Company, P.O. Box 6116, Cleveland 1, Ohio (1967)
V. R. Deitz, National Bureau of Standards, Washington 25, D.C. (1963)
G. R. Hennig, Argonne National Laboratory, Box 299, Lemont, Illinois (1965)
R. E. Nightingale, General Electric Co., Reactor and Fuels Research and Development,
Hanford Laboratories Operation, Richland, Washington (1967)
FINANCIAL COMMITTEE
C. W. Sweitzer, Columbian Carbon Company, P.O. Box 975, Princeton, New Jersey (1963)
(Chairman)
B. L. Bailey, Great Lakes Carbon Corp., Electrode Division, P.O. Box 637, Niagara Falls,
New York (1965)
G. I. Beyer, Pure Carbon Company, St. Marys, Pennsylvania (1967)
M. Cory, Graphite Specialties Corp., 64th and Pine Ave., Niagara Falls, New York (1963)
H. J. Dawe, Acheson Industries Inc., 321 Michigan National Bank Bldg., Port Huron,
Michigan (1965)
G. D. Graffin, Charles Pettinos, Inc., 1 E. 42nd Street, New York 17, New York (1967)
J. S. Mackay, Pittsburgh Chemical Company, Neville Island, Pittsburgh 25, Pennsylvania
(1967)
A. W. Wolff, National Carbon Company, 270 Park Avenue, New York 17, New York (1965)
R. L. Womer, Speer Carbon Company, St. Marys, Pennsylvania (1963)
PKOGRAM COMMITTEE FOR THE SIXTH CONFERENCE (Pittsburgh 1963)
S. Ergun, Bureau of Mines, 4800 Forbes Street, Pittsburgh 13, Pennsylvania (Chairman)
L. G. Austin, Pennsylvania State University, Division of Mineral Technology, University
Park, Pennsylvania
B. L. Bailey, Great Lakes Carbon Corp., Electrode Division, P.O. Box 637, Niagara Falls,
New York
J. C. Bowman, National Carbon Company, P.O. Box 6116, Cleveland 1, Ohio
R. J. Diefendorf, General Electric Research Laboratory, P.O. Box 1088, Schenectady,
New York
W. L. Hawkins, Bell Telephone Laboratories, Murray Hill, New Jersey
G. R. Hennig, Argonne National Laboratory, Box 299, Lemont, Illinois
C. A. Klein, Raytheon Company, Research Division, Waltham, Massachusetts
H. E. Martens, Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena 3, California
vi
THE AMERICAN CARBON COMMITTEE VÜ
D. S. Montgomery, Dept. of Mines and Technical Surveys, Ottawa, Ontario, Canada
M. L. Studebaker, Phillips Chemical Company, 318 Water Street, Akron 8, Ohio
J. R. Townsend, University of Pittsburgh, Dept. of Physics Pittsburgh, Pennsylvania
H. H. Yoshikawa, General Electric Co., Hanford Atomic Products Operation, Richland,
Washington
FOREIGN CORRESPONDENTS OF THE PROGRAM COMMITTEE
H. P. Boehm, University of Heidelberg, Institute of Inorganic Chemistry, Heidelberg,
Germany
X. Duval, University of Nancy, Laboratory of Mineral Chemistry, Nancy, France
A. Lahiri, Central Fuel Research Institute, Jeolgora, India
H. Tschamler, European Research Associates, Brussels, Belgium
T. Tsuzuku, Nihon University, Dept. of Physics, Tokyo, Japan
A. R. Ubbelohde, Imperial College, Dept. of Chemical Engineering and Chemical Technology,
London S.W.7, England
D. E. Weiss, Commonwealth Scientific and Industrial Research Organization, Div. of
Physical Chemistry, Melbourne, Australia
COMMITTEE FOR LOCAL ARRANGEMENTS FOR THE SIXTH CONFERENCE (Pittsburgh 1963)
R. A. Friedel, Bureau of Mines, 4800 Forbes Street, Pittsburgh 13, Pennsylvania (Chairman)
ELECTRONIC PROPERTIES OF GRAPHITE AND ITS
CRYSTAL COMPOUNDS IN THE DIRECTION OF THE c-AXIS
A. R. UBBELOHDE
Department of Chemical Engineering and Chemical Technology,
Imperial College of Science and Technology, London, England
(Manuscript received August 7, 1961)
Band theory can now be used to give a fairly satisfactory account of electronic properties of graphite
and of its crystal compounds in the direction of the α-axis but, as yet, yields a much less complete account
of corresponding properties in the direction of the c-axis. Important information includes the resistivity
and thermo-electric power of various graphites, and of crystal compounds derived from them.
For near-ideal graphites, the thermo-electric power shows a large anisotropy numerically, and also
has opposite signs in the direction of the c- and α-axes. Formation of crystal compounds either with elec­
tron donors or electron acceptors suppresses the difference in sign, and generally reduces the numerical
anisotropy. Changes in resistivity and in its temperature coefficient give additional information.
Traps and scattering effects may function anisotropically, for transport of charge in the direction of the
α-axis and c-axis.
I. INTRODUCTION It has likewise not been calculated how far
the repulsive forces between carbon hexagon
The crystal structure of ideal graphite points
networks depend on their stacking order. The
to marked anisotropy in many physical pro­
increase of c-spacing on passing from crystallo-
perties. Many of these, such as the mechanical
graphically well-stacked graphite, to turbo«
properties, can be correlated quite reasonably
stratic material, is probably to be explained
with the known difference in bonding parallel
on the basis that repulsive forces are higher
and perpendicular to the layers of carbon
between macromolecules when these are not
hexagon networks. However, electronic prop­
well aligned with respect to the relative posi­
erties show peculiarities and raise problems
tions of the carbon atoms in neighboring
that are by no means fully resolved, and which
layers.
it is useful to discuss.
Electrical resistivities of even the largest
One approach is to regard the carbon hexa­
aromatic hydrocarbons of known structure
gon networks in graphite as macromolecules
are extremely high, and do not yield precise
which constitute the limit to homologous
quantitative information by extrapolation to
series of aromatic hydrocarbons with fused
graphite. However, their mechanism of con­
benzene rings. In crystals of such hydro­
duction may be informative in relation to that
carbons, the packing distance between planar
of graphite in the direction of the c-axis.
neighboring molecules lies close to that in
Recent work on such hydrocarbons 1 suggests
graphite. For aromatic molecules of limited
that conduction involves the separation of
size mutual attractive forces can be attributed
positive and negative charges on the molecules,
to Van der Waals-London polarizations.
and that under the influence of an electric
Presumably infinite networks attract one
field these charges wander through the crystal
another by the same mechanism as smaller
by transfer to neighboring molecules. Con­
aromatic molecules, although no very satis­
ductivities are low and any electron bands
factory theoretical or even experimental
estimate seems to be available of the magni­
1 G. Martin and A. R. Ubbelohde, J. Chem. Soc,
tude of these attractive forces in graphite. 4948, (1961).
FIFTH CARBON CONFERENCE
can be regarded as extremely thin. When stacking defects or network defects of the
such aromatic hydrocarbons form crystal carbon hexagon macromolecules should affect
compounds with electron donors such as the the c-axis resistivity. On general grounds it
alkali metals or electron acceptors such as might be expected that stacking defects would
iodine the conductivity increases by many increase the scattering, and network defects
orders of magnitude. Recent work on thermo­ would increase the number of electron traps,
electric power shows that the carriers of charge and thus the relative proportion of positive
bear the appropriate sign. The temperature to negative carriers in the crystals. It appears
coefficient to be difficult to characterize various types of
1 dR crystal dislocations in the direction of the
RdT c-axis, for technical reasons. By way of illus­
tration, a possible contribution to large varia­
of resistivity falls to quite low values but still
tions of specific resistance in the direction of
remains negative in such compounds pointing
the c-axis of near-ideal graphite arises from
to an energy gap that has to be jumped in the
the presence of spiral dislocations with large
creation or migration of charge carriers.
Burgers vectors, such as those reported by
Theoretical and experimental work has Tsuzuku.2 Even if the anisotropy ratio of
yielded band models that give very useful undistorted graphite is 104 such spiral dislo­
representation of the electronic properties in
cations would certainly reduce the ratio in
the direction of the α-axis both for pure gra­
their immediate neighborhood, by providing
phite and for its crystal compounds. More
"α-axis" type of conduction up each spiral.
numerous unsolved problems arise in the
The fraction of the basal plane covered by
direction crossing the networks, along the
projections of such spirals can be used to give
c-axis. Analogies with electronic properties
a guide to the reduction in anisotropy ratio
of the hydrocarbons are likely to be most
due to their presence. A tentative working
useful in this direction.
hypothesis is that the composite resistivity
p * with ratio pc*jpa ~ 200 arises from a
c
fraction (1 — x) of the material with basal
II. ELECTRICAL RESISTIVITY IN THE
planes free from spirals, for which p\pa ~ 104
DIRECTION OF THE C-AXIS c
and a fraction x covered by projections of
One striking problem stems from a conflict spirals, which are assumed to have resistivities
of evidence about the electrical resistivity in approximately equal to p . Summation of
a
the c-axis direction.2 Work on small single resistances in a column of unit cross section
crystals of natural graphite has yielded fairly gives
consistent resistivities of about 3 X 10~5
1 (1 — x) x
ohm cm in the direction of the a-axis. Ac­
cording to some workers the anisotropy ratio lie J^c -H a
of electrical resistivity pc/pa is about 104. Multiplying up by Rc, and inserting appro­
According to other work, carefully substan­
priate numerical ratios for R /Ra and R/R*
c c c
tiated in its experimental details but which
mostly refers to crystals showing gross 50 = (1 - x) + 10% (lb)
twinning, the ratio is only about 200. This so that x ~ 5 X 10-2; this seems to be recon­
discrepancy is difficult to resolve, because it
cilable with observations. Even if p is some­
a
is not yet known theoretically to what extent
what larger for a spiral than p for the planar
a
crystals, spirals in low concentration can
2 Cf. references in A. R. Ubbelohde and F. A.
easily reduce the anisotropy to a marked
Lewis, Graphite and its Crystal Compounds, Oxford
University Press (1960). extent. Until ways of growing perfect single
ELECTRONIC PROPERTIES OF GRAPHITE 3
crystals of graphite become more manageable,
and ways of diagnosing stacking and network
defects more sensitive, particularly in the
direction of the c-axis, it seems difficult to
decide finally in favor of the high or the low
anisotropy ratio for ideal graphite. Two lines
of evidence are in favor of a high ratio, but
they are only indirect.
(1) If pyrolytic graphite is prepared by
cracking methane gas on to a flat substrate
heated to various temperatures by passing
very large electric currents through it, the
crystal defects show a progressive decrease of
disorder, which can be illustrated from plots
of the turbostratic p factor in the Franklin-
Bacon equation determined from X-ray
measurements of the c-axis spacing d,
1600 1800 2000 2200
d = 3.44 - 0.086(1 -p) ~ 0.064^(1 - p)
Temperature, °C
(2)
FIG. 2. Deposition temperature (°C) electrical
and from plots of the resistivities p c and pa resistivity as a function of deposition tem­
at room temperature. perature.
(Reproduced by courtesy of the Royal Society
Figures 1 and 2 show that as the crystal
from Blackman, Saunders and Ubbelohde, Proc.
order improves in these pyrolytic graphites Boy. Soc.)
the anisotropy ratio increases. The c-axis
curve in Fig. 2 could of course turn down
C _ 1
again for specimens of well oriented pyrolytic
graphite even more nearly free from defects
than those so far described. Suggestions have
C 2 U yö
indeed been obtained of such behavior but
not yet fully confirmed. It seems clear how­
ever that even if it does apply for ideal graphite
C4k
free from dislocations, the lower value of p\pa
c
o of about 200 must rise steeply to about 10 4
σ for a very small extent of disorder. If it is
Q- eventually confirmed, this steep rise could be
attributed to an anomalous increase in scat­
tering of charge carriers. Their mean free
0-8 k-
path in the direction of the c-axis could be
exceptionally large in ideal graphite and could
rapidly decrease as the disorder increases, but
:600 1800 2000 2200 such behavior would presumably require the
Temperature, °C
complete absence of traps. Until more
FIG. 1. Deposition temperature (°C) stacking
evidence is available, such a suggestion of an
disorder (p) as a function of deposition tem­
perature. anomalously steep effect of disorder on
(Reproduced by courtesy of the Royal Society scattering seems speculative. It is worthy
from Blackman, Saunders and Ubbelohde, Proc.
of consideration however, in view of other
Roy. Soc.)
4 FIFTH CARBON CONFERENCE
peculiarities of c-axis electronic properties,
which are at present more fully substantiated.
(2) In the direction of the α-axis the tem­
perature coefficient of near-ideal pyrolytic
graphite with resistivity ratio ~ 10 4 is slightly
negative, and the progressive elimination of
disorder from pyrolytic deposits leads to a
progressive change in accordance with expec­
tations from band theory.
Extrapolation from the behaviour of the
higher fused ring aromatic hydrocarbons
indicates a slight negative value of
1 dR
RdT
in the direction of the c-axis. Unfortunately,
for graphite with pcjpa ~ 200 the temperature
coefficients measured for four different single
crystals are not self-consistent. Our own data
3 4 5 6 7
in the direction of the c-axis do not lead to a n in CBrn xlO2
definite conclusion about the conduction
FIG. 3. Relative change in resistance R/Ro on
mechanism in this direction. intercalation of bromine.
(Reproduced by courtesy of the Royal Society
from Proc. Roy. Soc. 256A, 115, 1960.)
III. EFFECTS OF INTERCALATION WITH
CHARGE TRANSFER ON THE C-AXIS
RESISTANCE
Figures 3, 4, 5 illustrate the significant
finding that intercalations of different species
which have similar effects on p have very
a
different effects onp . A compact presentation
c
of the difference between donor and acceptor
types of intercalate is illustrated in Fig. 6.
Clearly, in the crystal compounds, c-axis con­
duction is more sensitive to the nature of the
intercalated species than a-axis conduction.
We have suggested that electrical conduction
in this crystal direction in the crystal com­
pounds resembles that postulated for the
Pauling model for metals.3 Such graphite
crystal compounds may be compared to salts
with tightly bound electrons, except that the
graphite compounds exhibit fractional charge
instead of unit charge transfer to the other
FIG. 4. Relative change in resistance R/Ro on
intercalation of bisulphate ion.
3 A. R. Ubbelohde, Proc. Third Carbon Conf. (Reproduced by courtesy of the Royal Society
Pergamon Press (1959) p. 329. from Proc. Roy. Soc. 258A, 329, 1960.)
ELECTRONIC PROPERTIES OF GRAPHITE
1000 species in the crystal when its concentration
A becomes appreciable. This fractional transfer
0500
confers a conductivity across the networks,
0-300 since excitation of electrons to a conducting
\\ state involves only very small energy changes.
*N^ This behavior may be contrasted with that
a-axis
in a conventional salt, in which charge transfer
0 050
o is practically unity and quite high activation
^ 0030
energy is required to switch an electron from
one atom to another. While such a model
- permits a quite reasonable extrapolation of
excitation energies for c-axis conductance
0005 C-axis N^
from those found with crystal compounds of
00Ü3
smaller hydrocarbons, it does not at present
permit quantitative calculations of the mobil­
. 1 1 1 11 1 1 1 1 1 1 ! 1 ity of the charge carriers. Nor can absolute
0 002 004 0 06 0 08 0 10 0 12
n in CKn estimates of conductance in the direction of
the c-axis theoretically yet be made for the
FIG. 5. Relative change in resistance RJRQ on
crystal compounds of graphite.
intercalation of potassium.
(Reproduced by courtesy of the Royal Society Obviously, formal application can be made
from Proc. Roy. Soc. 258A, 339, 1960.)
of mathematical techniques of electron band
theory; these require some very unusual band
conformations to explain the findings in the
direction of the c-axis. It is not clear, how­
ever, how far electron band theory which was
primarily developed to deal with the conse­
quences of regularities in crystal structure can
be usefully patched up to deal with properties
in the direction of the c-axis that appear to
be primarily determined by departures from
or lattice regularity, such as stacking disorder.
IV. THERMO-ELECTRIC POWER
Some additional insight into the electronic
properties of graphite and of its crystal com­
J I I L J I L_J 1 L pounds in the direction of the c-axis may be
012 008 004 0 004 008 C'?
obtained from studies of the thermo-electric
n in CKn
power.
FIG. 6. Comparison of relative resistance (c-axis) For graphite itself, a range of values is
for donor (right) and acceptor (left) crystal com­
found for the absolute thermo-electric power,
pounds of graphite. The abscissa scale, in units
of CX, refers to the curves A, B and C for which depending on the concentration and presum­
n
X = K, Br and £ HS04, respectively. The ably on the nature of the crystal defects
points representing the compounds of graphite
present. Figure 7 plots these values for con­
with iodine monochloride (#) and aluminium
chloride (C) are placed for convenience at the venience against specific resistance, regarded
position x = 0.125. as a rough measure of the crystal disorder.
(Reproduced by courtesy of the Royal Society
The most striking conclusion from these
from Proc. Roy. Soc. 258A, 339, 1960.)