Along the carbon way

ALONG

THE

CARBON

WAY*

A. PACAULT Centre de Recherches

Paul Pascal, 33405 Talence,

France

(Received 7 June 1973)

Abstract-The author reviews the main results on the electronic properties of carbons and on graphitization obtained in his laboratory during the past 20 years. Some new ways to attack the unsolved problems are suggested. INTRODUCTION

in 1895[8] and this behavior was confirmed with high accuracy[9]. Whatever the diameter of the polycyclic molecule is for scenes, coronene, violanthrene. . . , fulvene. . . their mean specific magnetic susceptibility is independent of temperature; it is about -0.7 X IO-” u.e.m. g-” as shown in Table 1, in which some values chosen from among those published at that time are given. On the other hand, the crystal susceptibilities vary with temperature. By use of the Krishnan method [ 1 l-131, we determined 1. TOWARDS THE “FIELD” OF CARBON for the first time the temperature variation My first scientific steps were guided by of the principal magnetic susceptibilities of benzene [ 14- 171 and naphtalene crystals the late and respected, Professor Paul Pascal (1880-1968) [l] the father of magneto[1X] and of many others[l9] (Table 2). We considered changes as being due to chemistry and author of the important rotation of the molecules in a crystal. By treatise of Inorganic Chemistry. At present, I am the head of the C.N.R.S. Research means of the magnetic anisotropv measureCenter which was given his name. ment, the orientation of the molecules in the I have shown in my thesis[2] that the crystal can be determined as a function of temperature if the temperature indepenexperimental values of diamagnetism 13-61 dence of the principal molecular suscepare closely linked to the resonance energy [2,7] and give information about the 7~ tibilities is assumed. delocalisation in the polycyclic The hypothesis was checked as soon as the electron first molecular structures were determined molecules. The mean magnetic susceptibility is inby X-rays at low temperature in particular, dependent of temperature as shown by Curie for naphtalene [20]. The principal molecular susceptibilities of naphtalene are calculated at 20°C and 195°C from the principal *George Skakel Memorial Award Lecture, crystal susceptibilities and the same values at 1 lth Biennial Conference on Carbon, Gatlinburg, Tennessee, June 7, 1973. these two temperatures are found. I The receipt of the George Skakel award from the American Carbon Committee make me reflect on my early scientific days. So I invite you today to journey with me along a scientific path which began far from the field of carbon and which led me unexpectedly to an approach to that subject Long exploration revealed many matter. secrets and enabled me to discover new, mysterious things in deverse ways.

CAR Vol

12 No

I-A

A. PACAULT

2

Table 1 [ 2,9, lo] -xh#

Benzene Naphtalene Anthracene Phenanthrene Perylene Coronene Ovalene

x 106 - xs x 106 54.8 93.6 134.2 132.0 171.4 268 353.8

0.705 0.733 0.753 0.741 0.680 0.809 0.889

-XMX 106 --x,$.x 106 dimethyl benzofulvene phenyl benzofulvene indene dibiphenylene ethylene acenaphtene acenaphtylene fluoranthene

105.1 130.5 83.4 38.5 110.8 111.6 138.0

0.674 0.640 0.718 0.769 0.720 0.733 0.683

xu = The mean molar magnetic susceptibility. xs = The mean specific magnetic susceptibility. A complete study of the temperature variation of the magnetic anisotropies of benzene[l6] led to the same results. Whatever the temperature is, the molecules retain a center of symmetry and the principal molecular susceptibilities are: Kn = Kzz = -34~9X10-6andK33=-94~6X10-6. Thus, although the 7r electrons are delocalised in these unsaturated molecules, their molecular diamagnetism is strictly independent of temperature. as early as 1934, Krishnan However, [21-231 and his co-workers showed that graphite has a mean susceptibility ten times greater than that of the organic molecules and a large magnetic anisotropy x1 - xll.

question arises: does a class of molecules exist between them which would have intermediate properties? I asked Marchand this question in 1952 and we decided on carbon blacks*, which led us both into the field of carbon. 2. A WALK THROUGH

THE

FIELD

OF

CARBON

For many years my co-workers and I have been studying the electronic and structural properties of carbon, but not involving ourselves in textural research, later we turned to graphitization.

2.1 Electronic properties of carbons Electronic poperties of carbon blacks. The Xl = - 0.5 x 10-6 u.e.m.g-’ carbon blacks proved to be a class of systems xi, = - 22 X lop6 u.e.m.g-’ I in which the quantized electronic levels of the polycyclic molecules come sufficiently xl1and x1 are the principal magnetic suscepclose to constitute an energy band and give tibilities respectively parallel to the graphitic a diamagnetism dependent on temperature. c axis and perpendicular to the graphitic When the mean diameter L, of the polycyclic planes reaches approximately 60 A, the c axis. mean diamagnetic susceptibility grows from In 1938[24,25], he showed that this about -085 X lo-” to -6.5 X 10-6u.e.m. g-’ magnetic anisotropy varies greatly between 90°K and 293°K. In 1941, using the theo(Fig. 1); it begins to vary with temperature retical results of Landau[26] and Stoner when the crystalite mean diameter L, is [27], he explained this by considering the 7~ over 36 A (Fig. 2) [112,29,32,179]. electrons as a free delocalised gas in the graphitic planes. *A conversation with Magat who suggested I Since the diamagnetic anisotropies of contact W. R. Smith from Cabot’s influenced my benzene and erauhite are so different, the choice.

ALONG THE CARBON

WAY

3

The temperature dependence of the magnetic anisotropy K is represented with fairly good accuracy by: Q-

x1 =-0.85

_K = ] _

x lo-“+

e-T11/7‘lyith

K.

=

NvpB”a2 3E@s

KO

Fig. 1. Mean magnetic susceptibility blacks as a function of the mean of cristallite.

1

0

Fig.

I

I

20

(0

I

60

I

80

Where UN = number of charge carriers pB = Bohr magneton mass of charge carrier ti=J.% m* effective mass of charge carrier lo = kTo = Fermi level S = surface occupied by rr electrons.

x of carbon diameter L,

I

I

1m

lo’/

K

T

2. Temperature variation of the mean magnetic susceptibility of carbon blacks.

This equation was established by applying Landau [26] and Stoner’s [27] calculations to a bi-dimensional gas of free charge carriers of effective mass m”‘[28-30,321. The obtained values of the parameters are reasonable. (Table 3). The original data obtained for carbon blacks as well as those relating to the benzene diamagnetic anisotropy were presented in 1957 at the Third Carbon Conference in Buffalo “From Benzene to Graphite”[33,34] where I was invited by Professor Mrozowski. Coming from spectroscopy, a field in which he was active in Poland before the Second World War, Professor Mrozowski became interested in carbon[35] and around 1950 proposed a qualitative model, well known ever since as Mrozowski’s Model. This model was to support the theories of many

Table 2 [ 181 Crystal susceptibilities

Molecular

susceptibilities

at 20°C

at - 195°C

at 20°C

at - 195°C

-XI1 x lO”= 54.4 -xn,x lo”= 76.4 -x33 x lo”= 150.0 e= 20”42’%25’

53.0 76.2 151.6 23” 30’ -c 40’

-K,, x IOfi= 54.7 -&,X lo”= 52.6 -I&x 10fi= 173.5

54.7 52.8 173.3

0=Angle between the crystal axis n and the principal ceptibility xzp in the plane of symmetry for naphtalene.

crystal

sus-

4

A. PACAULT

Table 3.

La (4 200-250 82 75 62

Carbons Graphite Thermax (3100°C) Spheron 6 (2700°C) Spheron 6 (2000°C) P33 (1500%)

To (“K) 350 375 460 490 660

researchers in the years to come. Around 1953, I realized while compiling my bibliography that our ways were similar though their origins were quite different. In 1952, Mrozowski mentioned in his paper [ 36]*, that he had started working on subjects which we, ourselves, were studying, and in 1954, one of his students, Pinnick[37], confirmed on other carbon types at room temperature, the results of Marchand?. We exchanged letters; he visited me in Bordeaux and from this time on we have been close friends. While the molecular dimagnetism was the root of our first work on carbon, the success in building a quantitative model[32] to explain their magnetism was responsible for keeping us ploughing through the “field” of carbon for a long time. Figure 3 shows the number of our papers vs time. Is it possible to use this model to explain all the electronic properties of all the kinds of carbons? That was the question which was underlying the whole of our research on electronic properties. The answer was closely linked to accurate measurements of various properties of the same samples. It became necessary therefore on the one *“It is felt that at this time it is more important to gather some additional data on susceptibilities of carbons under different conditions than to try to develop the theory further”. Mrozowski 1952 [36]. tWe would also mention the preliminary work of Wynne-Jones, Blayden and Iley[38] and the forerunning work of Miwa[39] measuring at ordinary temperature the magnetic susceptibility of sugar carbon and of lamp blacks.

& (Per 8) - 28.95 x -24.1 x - 18.45 x - 13.05 x -5.61 x

lo+ lO-‘j 1O-6 10-e lO-6

VN(per cm3’) 1.5 18 2.9 4.35 13.6

x x x x x

10’8 10IR 10’8 10’8 I0l8

ci= m/m* 296 246 188 133 57

hand, to find and develop measuring methods (Table 4), and on the other, to prepare well-defined samples of carbons. This variety of research concentrated in one laboratory was a consequence of the characteristics of the samples*, which practically excluded the utilization of the results obtained by other researchers on other samples. It is impossible to discuss here all the experimental work referred to in Tables 4 and 5, but I will recall here some of the more striking results that we published% Magnetic

anisotropy

of

a single

crystal of

Contrary to the other carbons, a single crystal of graphite is well defined, provided great care is taken in handling it to avoid edge disorientations. Since some graphite single-crystal properties were known, we have limited our studies to the temperature variation of the magnetic anisotropy from 20 to 2000°K. Krishnan’s measurements ranged only from 90 to 29’3°K. A new precision apparatus was developed in order to have a reliable reference. Instead of the dibenzyl monoclinic crystal used by Lonsdale, we took the orthorombic orthodiphenyl benzene, easier to obtain, and whose crystallographic axes are easily located its absolute ~52,531, and we measured magnetic anisotropy. graphite.

SThings improved in France after 1960 thanks to the French Carbon Research Group, one of

whose tasks was to prepare standard reference samples which were distributed on request. §We refer to Table 5 for bibliographic references which now will only be given ocassionally in the text.

ALONG THE CARBON WAY s .

number of Thesa

x

number

of Ph D X. x .

x . x

x x

.

x x

e

Fig. 3. Number of papers on carbon published by the Bordeaux

Table

The mined

susceptibility by Rabi’s

(xss - xII) was method between at 292°K: x1 1=-O-3

x lo-’

4. Bibliography of home made new apparatus electronic properties measurement

used for

Measurement of magnetic susce tibilities and of their temperature depen : ence.

40,41,42,43 44,45,46,47 48,49,50

Measurement of magnetic anisotropies and of their temperature dependence.

51,52,53,54

Measurement of galvanomagnetic properties and of their temperature dependence (Hall effect, resistivity and magnetoresistance).

55,56,57,58 59

Measurements of the photoconductivity high electrical resistivity substances.

60

of

Measurements by E. P.R. of paramagnetism and of its temperature dependence between 4°K and 298°K.

61

Development

62,63,64

of an X ray diffractometer.

x1 1of graphite method. The measured by 20 and

u.e.m.

2000°K.

was deteranisotropy Krishnan’s We found

g-’ independent

of T

xzr:,=-21.0

group.

X lo-” u.e.m.

g-’ a function

of Tzk

*These values are in agreement with those obtained by Krishnan between 90 and 293”K/ when corrections due to reference anisotropies (which are different) are taken into account.

_. . . ...

carbons

Low temperature

. ._ .. ..

Nttrogen Sodium Neutron irradiated carbons Lamellar bromine compounds

pitch coke Chlorine

Doped curbons (181) Boron-Graphite . .. . .. .... . . . . . pyrocarbon . . . . . . . . ...*

..

.. .. ._. . . __

I

non graphitizable

Carbon blacks. _.

Carbons

at 1600% . . . . . . . . . . . . . . . . . . . . . . . . pregraphitic . . . . . .

Pyrocarbon as deposited at21OtPC . . . . . .._.._......_...

Hexagonal graphite: single crystal Pyrographite . __._.. Rhombroedral graphite

Carbons

118,119

109

107

88,89

79,BO

Structure tx rays)

Table 5. Bibliography

128,129

126

116,117 118,119 121 122

114

109,28 29,112 33

54,133 134

119,120 121

69

88,89 69

107

69,BO 66

65,66 69,67

Diamagnetic anisotropy

properties

182

122 123,124 125 126 127, 128, 129

116,117 118,120 71

131,132

121

109 91,109 68.113 91

115

117 118

108,101 105.183

8687 93.94 100,101 102, 106 104.105,180

91,68

130

88.92 98,99

85

76

Graphitization (review 152, 174,85)

carbons

Specific heat

of various

110

58.68

91,88 89,57

89,90 96,97 99,103 108

83.84 72,68,71

71.72 68

70 75

82

68

67

Galvanomagnetic properties

Properties

and structural

Paramagnetism

work on electronic

81,82

73,X, 77 78.74

Diamagnetism

of our laboratory

111

95

Chemical properties

ALONG

THE

CARBON

WAY

7

The equation we had already proposed for carbon blacks is well suited for the anisotropy’s temperature dependence between 20 and 1000°K provided that an additional parameter is introduced. - 10” x (xS3 -x1,)

= 4.65 + 25.4(1 - e-2H”‘7)

Above 1000°K the equation is still valid but the values of the parameters have to be changed. These values however are doubtful because to the diamagnetism itself an effect connected with the lattice expansion is added which is hard to evaluate. The rhombohedral graphite cannot exist by itself like the hexagonal graphite, but 30% of the hexagonal can be transformed mechanically into rhombohedral form. Thus, its magnetic properties can be determined. The absolute value of its magnetic susceptibility was found to be greater than the one of hexagonal graphite and is about equal to that for a bidimensional graphitic system. As said before, polycrystalline carbons, are so difficult to characterize, that one has to measure all the properties for the same sample if one wants to get results which can be related to each other. This fact explains the way our systematic work was carried out from which only a few examples will be drawn here. The variation of most of the electronic and structural properties of a pitch coke and a pyrocarbon (whether boronated or not) are displayed on Figs. 4-7. The measured quantities are plotted vs the HTT temperature to which these materials were heat treated. In so doing, of course, we found some results previously published. Thus, we confirmed that the magnetic anisotropy of a 2100°C deposited pyrocarbon is greater than that of the graphite while the anisotropy of the same pyrocarbon, in heat-treatment passes through a minimum at 2600°C as was shown by Fischbach[135]. In the same way Klein’s results [136, 137, 1381 obtained for other pyrocarbon samples were found to be in agreement with our data.

I

19,

‘-1

1Lm

Y

1502

1

1

2500

2002

Fig. 4. Some electronic properties coke vs HTT.

.

151 2lal

2311)

2500

2700

2900

HTT

HTT

3000

of a pitch

d

x

0

(l/A)

L

a%

0

La (8)

d

h-x,)~~

I@ radm-’

‘C

Fig. 5. Some electronic properties of a pyrocarbon vs HTT.

In trying to interpret the magnetic results, we were hoping that a simple model would prove satisfactory for explaining all electronic properties. The equation formerly

A. PACAULT

A IO6 [m3Cb-I)

21w

2300

2500

2700

HTT ‘C

2900

2.x0

2400

2m

2800

HTT

C

Fig. 6. A, pII, Ap/p of a pyrocarbon (2100°C) (B = 1.1 Wb rnm2)vs HTT. A, pa, Ap/p of a pyrocarbon (2250°C) (B = 0.25 Wb m-*) vs HTT . Resistivity, pli lo6 (am): 0 at 80K; 0 at 296K. Hall coefficient A lo6 (m%b-I): A at 80K; LI at 296K. Magnetoresistance Ap/p%: 4 at 80K; 13 at 296K.

(b)

0

La

[I)

-. JO--3.40

01

2100

2300

2500

2700

HTT

15 2100

“C

Fig. 7. (x~~-xII)~~~, 4~12,TV,,,L, vs HTT (a) Boronated set up from the theory of the electron so well applicable to the diamagnetism

gas, of

carbon blacks, was found to apply to all kinds of carbons, but it required the introduction of a new parameter, which removes its former So

it

“elegance”. was

to

become

X=x0+

(K$3)

(1 -e-e17) parameters with

the

I

2300

I

I

25Lx)

2700

pyrocarbon. in which

(b) Pyrocarbon. x0 and K. are adjustable

and 8 becomes Fermi

I

HTT ‘c

level

loosely connected

TO. Table

6 gives

the

parameters for a number of carbons. Following a suggestion by Castle and Wobschall in 1957[139], a relation between the

diamagnetic

anisotropy

and

that

of the

ALONG

THE

CARBON

WAY

spectroscopic splitting factor g was sought. We pointed out that’ the anisotropy of the splitting factor for a pyrocarbon can be written as a function of temperature in form of the equation:

Since this is formally identical to that giving the temperature variation of the diamagnetic anisotropy, a linear relation between x33 - xl1 and gs3--gll of a pyrocarbon would follow. It was shown later[67] however that this does not apply to all carbons. Using simple models, one can determine from magnetic measurements the concentration of carriers, their effective masses, the position of the Fermi level and size of energy gap. Do these properties match with the transport properties? A theoretical study of a large number of our experimental resufts [SO, 31, 96, 97, 140-1481 led us unfortunately to a negative conclusion. The “bidimensional gas” model which explains the temperature variation of the diamagnetism of a carbon gives a rather poor representation of the paramagnetism and of the Hall effect. The disagreement between diamagnetism and paramagnetism as shown by Zanchetta[149] and Boy [148] is particularly obvious when HTT is over 2000°C. The disagreement between the Hall effect and diamagnetism is also found with the “simple two band model” (S.T.B.) used by Klein [150] and with the C.T. mode1 (“carbone turbostratique”). A large energy gap AE between the conduction and valance bands is necessary to explain the t.hermal variation of diamagnetism. On the contrary AE should be very small to explain the Hall effect. An “impurity band” added to the conduction and valence bands of the graphitic lattice could explain the paramagnetism: the low mobility of the impurity band charge carriers would yield a very small diamag-

*‘AE --F

’

I

STB N(E)

E

I

Fig. 8. Different band models of carbons. netism but would be sufficient to give a nearly zero Hall coefficient for the less graphitized carbons. Fig. 8 shows the number of models studied to find a single model able to explain all the electronic properties. Anyway, none of all these models enables one to foresee at 4°K a negative magnetoresistance which changes sign when the magnetic field increases, as it is found for some pitch cokes[?2,71]. None of these models can explain two properties at the same time and, therefore, none can be considered as a valid approximate representation of the electronic structure of carbons. We must conclude that the search for models simple enough to be used, that is to say, to account for the electronic properties and of course to predict them, seems destined to failure. We must look in other directions and give up models evolved from a theory which is valid for crystals, but, probably, unsuitable for unorganized substances. WouIdn’t it be better to choose the opposite approach by studying the amorphous sub-

A. PACAULT

Table 6 [69] Kind of substances studied and references

Parameters %

K.

0

Graphite single crystal Madagascar graphite purified G,[73] Go ground with steel grinder 2 mn with steel grinder 40 mn

1.85 2.5 0.86 1.9

25.4 25.4 40.80 34

237 216 220

Go ground during 8 mn with boron carbide [74] and heat-treated during 2 hr at HTT 1415°C 1620°C 2650°C

0.47 4.4 4.4

35 26.7 22.3

246 126 136

290

Rhombohedral graphite [78] Pyrocarbon Raytheon deposited at 21OO”C[9]

2.0

53.9

182

Pyrocarbons Carbone Lorraine [Sl] deposited at 2100°C and heattreated during 3h under argon atmosphere at HTT 2100°C 2580°C 2740°C 2800°C 2900°C

1.8 2.2 4.0 3.6 3.1

56.7 47.2 18.4 18.2 22.0

165 165 165 198 220

Pitch cokes heat-treated at HTT[89] 1700°c 1800°C 1900°C ?ooo”c 2650°C

1.50 2.60 2.30 O-46 2a70

7.85 8.80 13.81 25.2 20.6

468 330 325 350 238

stances and to consider the carbons as a case where these are in the process of organization? Briefly, all of our work on electronic properties can be summed up as follows: Obtaining reliable and accurate experimental data for numerous electronic and structural properties (X-ray structure, paramagnetism, electrical diamagnetism, magnetoresistance, Hall effect, resistance, specific heat) measured over a wide range of well defined carbons (Table 5). Impossibility to find a simple, single

0.85

159

74.5

model able to account for the electronic properties of each and all of these carbons. It seems useless to improve new modifications of Mrozowski’s model. One can try for a while to look for an explanation of the electronic properties of carbons in context of presently proposed theories of amorphous substances. This is the approach followed by Delhaes, who, had just discovered a MottAnderson transition in an anthracene coke. New experimental aspects leading to practical applications could spring from this new way tackling the problem. A recent paper by

ALONG THE CARBON WAY

Antonowicz and his co-workers[l51] on the “memory” of glassy carbons, seems to be encouraging in this respect. 2.2 Graphatzzation I have published two reviews* on graphitization[85, 1521. Let me sum up the main points: Except for a few papers, the heattreatment time of carbons did not receive attention until 1961 (Table 7). Previously, the researchers used to give only the heattreatment temperature and occasionally the treatment duration. From 1961 on, many publications focused attention on the heattreatment time (Table 7), hence results were obtained on the kinetics of graphitization. It can be followed by measuring, at a given temperature, a property vs time. Table 7 shows that many properties have been used to do this?. The kinetics of graphitization as followed by means of one of these properties is nearly the same whatever the carbon. Figures 9, 11,lS and 15 show the isothermal evolution of the magnetic susceptibitity and the Hall effect of pitch coke and those of the interlayer spacing and the magnetic anisotropy of a pyrocarbon, all vs treatment time. The graphitization isotherms of a carbon when plotted vs the logarithm of time can be superimposed by a translation (log k) along the abcissa axis. This property first mentioned by Fischbach [153] was checked by us in numerous cases. Figures 10, 12, 14 and 16 show how the isotherms of Figs. 9, 1I, 13 and 15 are translated, by this process, forming a single curve whose abcissa is D= kt (log k being the translation value allowing the superposition). Figure 12 obtained from Fig. 11 is certainly the most impressive one. It should be noted that such a property *Note a paper of Fischbach on the same subject[l53]. tWe can eliminate the specificity of the property by defining a degree of evolution [154-1561.

11

q.o-.-.-.-

1

HTT: I

2400

I

6.4 ‘_ C.-.-~-.-L---.-

g:

I

HTT

2Oc9Oy

5.6 4.8

6.8-

/

l_*- 4

Y.-e_

2040

4

H

TT; 2cWp:

P; .

.

3.6

. .

52

4.4

.

/

/.---

.e*

s:

I

I ’ ’ ’ ’ ’

6

flTT: -.-

__-#-

-2-0

HTT ;L900

Oc

HTT,~8@3O( HTT.

17OO=i

2.8 2.

1

apparit!on of the modulat~on(101.

Fig. 9. Variation of x vs heat-treatment time (pitch coke).

is generally incompatible with a representataion of the degree of evolution (Y of the graphitization by a sum of time exponential factors according to the formula a= Ae-“I’$_ Bepkzf+. . For example, it would be necessary that k, and kz obey Arrhenius Law with the same activation energy to account for the observed facts. The activation energies of the graphitization process are, for various carbons, around 180 to 250 kcal (see Table 4 [153]). Although the accuracy

of measurements

is somewhat

Fig.

11. Variation of the Hall coefficient heat-treatment time (pitch coke).

A,, vs

.

10'

I

0.

I

Owe&

105

I

107

I

Fig. 12. Pitch coke: singfe curve&

103

I

0+

Fig. 10. Pitch coke: single curve x =f(logD).

=f(D).

109

I

10”

I

.V 9.

a

bg 0 (min)

V “.

ALONG

THE

CARBON

Table

Year 1953

Author and reference

Studied properties

Honda and Ouchi [157

WAY

13

7.

Studied carbons

19571958

Kasatochkin and Kaverov [ 1581

P /d,,,,

Yubari Coking coal Petroleum coke Hongei anthracite Cellulose Petroleum coke

1960

Tarpinian[l59]

dw

Petroleum

1 X

HTT(“C)

1200 1400 1600 2000 to 2800

coke

2057 to 2727

L,

Maximum time of treatment

1 hr

1961

Fair and Collins [ 1601

p&l:!

Petroleum coke Pitch coke

2000 to 3000

20hr

19621973

Pacault Marchand and co-workers

& 9L y and magnetic anisotropy

Pitch coke Anthracene coke Pyrocarbon Carbon blacks

1400 to 2800

500 hr

Petroleum coke Pyzocarbon

2400 to 3000

200 hr

2500

120 min

RPala A, APIP 19631971

Fischbach[lGl,

1963

lshikawa Yoshizawa[l63]

Cokes

1963

Mizushtma[ 1641

Petroleum

coke

900 to 2500

160 min

1965

Pandic[l65]

Petroleum

coke

1400 to 2800

7 min

1965

Noda, Inagaki and Sekiya[l66]

??

Point out the positive action of oxygene during graphitization

1900 to 2380

4hr

1968

Noda[l67]

d,,,,

Polyvinyle chloride graphtitized under pressure

1450 1650 1750

1969

Bale[l68]

d 002

Cokes

1400 to 2400

17hr

1969

Murty[l04 1, Bierderman and Heintz [169]

Petroleum coke Gilsonite coke

2300 2700

54 hr

1971

Prost and Casparoux

Pyrocarbon deposited at 1600°C

1600 to 2400

15hr

1972

Flandrois and Tinga

Pitch coke Acetylene black

1400 to 2700

1Ohr

uo51

162, 1531

d,,,,L d 110, R, La, a

[86] j& d,,,

iz, A

90 min

A. PACAULT

14

r :9--%+

+ \

t 3

+

HTT’2550

.

HTT.

0

HTT.2650

‘c

26005: ‘c

.

8-

&s

I$

t 7P-

f %O.++A-~

--6-

3X0

I 6

4

2

8

10

l2

t(

hl )

5

Fig. 13. Pyrocarbon-variation of zO, vs heattreatment time.

I

102

+

HTT

255O’c

.

HTT

26w’c

0

HTT

265O’c

Fig. 14. Pyrocarbon-single

104 kg 0, (mm)

Fig.

2

4

6

103

‘0

‘

I bg 0; [mm)

Fig. 16. Pyrocarbon-single curve X =f(log

D).

Step processes were described as early as 1965 [loll*. What are these processes? The evolution of a property vs time, stops for a while, and then starts to change again [150,151,153,171]. The Figs. 17-19 and 20 show some experimental results. Are these an evidence of a new phenomenon: the step process? At the present time, it seems impossible to answer this question with certainty and one can argue for, as well as against it.

curve &, =f(log D).

x

HTT .25509:

.

HTT :.?6005: HTT

0

I

I

10'

10’

8

: 2650

10

Arguments against the existence of steps In spite of all the improvements brought in the control of furnaces, the temperature variation of at least by + 5°K cannot be avoided. Because of the high value of the this variation can be activation energy, equivalent to rather important error in time; the error on the abcissa of an experimental point is principally due to the temperature

VZ

12

t(hr)

15. Pyrocarbon-variation of X vs heattreatment time.

insufficient, it would seem that the transformation of a coke into graphite involves several activation energies[l05,170].

*This phenomenon is at present an exception outside of the biological world where for example, a crab grows by steps each time it mauls or sheds its shell. tDuring the graphitization of pyrocarbon 2100°C we can observe a discontinuity. Two distinct states can be clearly seen on Fig. 21 [153]. These stages which can be easily explained by the competition between the biperiodical and triperiodical structures support the existence of a step process.

ALONG

I

0’

2

I 6

4

I 8

I 12

10

I 16

1’4

t

THE

(

hr

CARBON

15

WAY

)

Fig. 17. Degree of graphitization g = (d& - dgi)/ (d’gZd’-- d’&) of a pitch coke vs treatment time at given HTT.

Fig. 20. Magnetic susceptibility of an anthracene coke vs treatment time at given HTT.

3w-

.

I

jn

1*

Fig.

1OH

6H

0

18. Magnetic susceptibility of an acetylene black vs treatment time at given HTT.

n

.

A-A, .

I

200-

I

.

n4

ISOCHRONAL

100 -

01

I

I

342

340

l

2550

‘I:

I

2600

‘C

V

2650

‘C

ISOTHERMAL

1

I

2 3 44

k.,

3 B :

$

s

+

‘X ,g

Irt

Series

0‘

2nd

,,

,,

I,

t

314

I

I,

I

3

variation

2

time. The

0

1

I

I

I

I

IO

20

30

40

50

d (1)

1

336

Fig. “1. Apparent crystallite layer diameter as a function of interlayer spacing for typical pyrocarbons.

+reo+men+

*

338

I t (Z)

Fig. 19. Magnetic susceptibility of a pitch coke vs treatment time at given HTT.

and not to error

in measuring

the

sample is not suddenly brought to and, in spite of the care taken, a temperature gradient occurs; the sample keeps

HTT

for approximately

a quarter

of an hour the

16

A. PACAULT

memory of the way it has been brought to HTT[172]. To reduce the influence of the observer, an apparatus was developed (Table 4) permitting to measure dOMof a carbon vs time “in situ” at the actual heattreatment temperature [63,64] (all the results published until there were obtained by quenching the sample to room temperature, at which the measurements were made). All the fluctuations recorded on the isotherms are on the verge of experimental error [A(&,,) = 0.01 A] The isotherms of graphitization do, =_f (time) obtained at HTT are smooth, within the measurement accuracy.

21 0

I 20

I 40

I w

80

loo

120

I 140

D, [min)

Fig. 22. Magnetic susceptibility of a pitch coke vs heat-treatment time. Single curve.

Arguments for the existence of steps

The temperature gradient does not introduce periodic fluctuations of magnetic susceptibility. This was proven by heating samples of composite carbonaceous material in the Odeillo solar furnace with a thermal gradient of about 1000°K cm-‘. The magnetic susceptibility decreases smoothly from the hottest face to the coldest (Appendix I). time of control of our The response furnaces is less than a minute and therefore cannot induce fluctuations of temperature with a larger period. The voltage has no periodic fluctuations likely to modify the temperature. Results can be reproduced. Figures I9 and 20, among others were obtained from three series of experimental points corresponding to three sets of independent measurements. The different isotherms superimpose very well (Figs. 22 and 23). The beginnings and the ends of steps of the same isotherm showing the property as a function of the logarithm of time, seem to form two straight converging lines [ 173,174l. It was checked by electron microscopy [ 1061 that samples treated to the same step were identical, morphologically and structurally. Thus, the accuracy on the ordinate is sufficient to.justify the presence of a step.

Fig. 23. Magnetic susceptibility of an anthracene coke vs heat-treatment time. Single curve.

functions[l76,177]. In this way, the steps disappear when the following errors are 2 0.8% on the ordinates and admitted: + 10% on the abcissas. This seems an overestimate of experimental errors. (Appendix II). Moreover, we have theoretical reasons to believe in the existence of the steps of graphitization [87]. As suggested by Mering and Oberlin[175], the graphitization process involves 4 kinds of to structures Fr, F2, F3, F4 corresponding various defects. If we assume such a mechanism we can show, from the thermodynamics of the irreversible processes[87], that the relaxation of a pyrocarbon (1600°C) towards graphite can be a periodic process. Figure 24 shows the agreement between the theo-

ALONG

THE

CARBON

M’AE

17

3. WHAT ELSE IN THE CARBON FIELD

~~63~-ZC16xex~(-OlZxT]-O775ex~[-0.0058xT)- 0.092

s,” (0.05.x

T + 2 57)~~

(- 0 007x

T)

Fig. 24. Magnetic susceptibility of a sample of pyrocarbon ( 1600°C) vs time (HTT = 2200°C) theoretical curve-experimental points. retical curve thus obtained and the experimental points. In conclusion, in spite of careful experimentation which seems hard to be improved, the experimental results do not allow us to state that the step process is a real phenomenon. However, we have good theoretical reasons to think that this is not impossible. Under these circumstances, it would be a pity not to point it out, since it can be an incentive for further research. Indeed, the studies of graphitization have taken us far from the carbon field and have led us to formulate an axiomatic of the evolution of systems which was confirmed in widely varied fields [ 15+156]. But the study of the conditions for the existence of dissipative structures [ 1761 will no doubt take us back to the graphitization process and then, we will be able to tell if graphitization is indeed a periodic dampened relaxation.

CAR

\‘<,I

12 No

I-B

As poppies and cornflowers bloom in a wheat field, so do other flowers grow in the carbon field in addition to the numerous varieties of carbon already found. There, lone wanderers were gathering many different species in the hope of composing a lovelier bouquet. From this desire, stemmed in 1960, the Groupe Francais d’Etudes des Carbones (GFEC) under the honorary presidency of Prof. Letort (who died in July 1972 and whose memory I would like to recall here). The group’s first steps were sponsored by the C.N.R.S. under the name, Programmed Cooperative Research (RCP 3). These men from different fields of interest, have been working in close cooperation to merge their knowledge into a publication: “Les Carbones” [ 1781 which many of you know and which we presented at the Cleveland Carbon Conference. Within the G.F.E.C., industrialists and University people work hand in hand; they meet once a year, far from the hustle and bustle of the city, to discuss their work programme, For some time now, welldefined carbon samples were being prepared and studied in many laboratories in order to obtain various comparable information. After ten years serving as head of the G.F.E.C., I requested in 1970, that I be replaced. Prof. Mering became president, but he died last March. The current president is Professor Donnet. Mysterious flowers are still to be found, such as the amorphous substances, whose properties must be studied, and which could suggest interesting applications unsuspected from those who believed in crystals. The Ovshinsky effect is already encouraging. New roads of exploration have been found and for a few years a phenomenology of evolution of systems is being developed as a result of new intellectual speculations. Friendships are made also through correspondence and travel. The various

18

A. PACAULT

opportunities we had to meet at the different carbon conferences were: 1957 1957 1959 1960 1961 1963 1964 1965

Buffalo London Buffalo Paris Penn&ate Pittsburgh Tokyo London

1965 1967 1968 1969 1970 1971 1972 1973

Cleveland Buffalo Paris Boston London Bethlehem Baden-Baden Gatlinburg

Prizes are also to be found in the carbon field. By awarding them to one person, it could be thought that it is easy to find them alone. In my case, it was certainly not true. Many researchers were needed, all of them gradually becoming responsible for their own research, plodding along with me. We had the stimulative atmosphere of the G.F.E.C. and I personally had the of my friend, cooperation marvelous Marchand, with whom I would like to share this distinction. I would like to thank the Committee most sincerely for the award, which is an honor not only for myself, but for my whole team.

REFERENCES sur Paul 1. Pacault A., Notice nCcrologique Pascal (1880-1968), Membre de la section de Chimie. C.r. hebd. Sbanc. Acad. Sci., Parzs %X,68-75.

magn~tochimiques 2. Pacault A., recherches (Thhses) Ann. Chim. 1,527 (1946). PrCcisions sur la 3. Pascal P. et Pacault A.-I. systtmatique magnCtochimique. C.r. hebd. Shanc. Acad. Scz., Paris 219,599(1944). Nouvelles pr&s4. Pascal P. et Pacault A.-II. ions sur la Systkmatique Magn~tochimique. C.r. hebd. St;anc. Acad. Sci., Paris 219,657(1944), C.r. hebd. Sianc. Acad. Sci., Paris 222,619 (1946). 5. Pacault A. Principes g&nCraux de la magnetochimie - Ses applications 2 l’&ude des compo& organiqies Rev. Scient. 32, 37, 38, 465 (1944).

~x~~~e~t~a X2,41

(1954).

6(a) Pacault A., Les systematiques magn&ochimiques. Rev. Gent. 3488, 38 (1948). (b) J. Hoarau, A. Pacault et P. Pascal. Les systbm-

7.

8. 9.

10.

11. 12. 13. 14.

15.

16.

17. 18.

atiques magn&ochimiques. Cahier Phys. 74, 30 (1956). Pacault A., Aromaticit~ et polarisabilit&Aromaticity, pseudo-aromaticity, anti-aromaticity. The Jerusalem Symposia or& Quantum Chemistry and Biochemistry, III-The Israel Academy of Sciences and Humanities, Jerusalem, pp. 39-47 (1970). Curie P., Ann. Phys et Chim. 5,289 (1895). Hoarau J., Th&se Paris 1954, Ann. Chim. (1954). Bergmann E. D., Hoarau J., Pacault A., Pulman A. et Pulman B., Recherches expkrimentales et theoriques sur l’anisotropie diamagnttique des compos&s aromatiques nonbenzenoides et des systhmes quil~oniques, I, Chim. Phys. 49,474 (1952). Krishnan K. S., Guha B. C. and Banerjee S. Trans. Roy. Sot. London A231,235 (1931). Krishnan D. S. and Banerjee S., Ibid. A 234, 265 (1935). Lonsdale K. and Krishnan D. S., P7oc. Roy. Sot. London A 156,597(1936). Pacault A., Lemanceau B. et Joussot-Dubien J. Le diamagnktisme du benzene. C.r. hebd. Sianc. Acad. Sci., Park 242,1305-1306 (1956). Hoarau J., Mme Lumbroso N. et Pacault A., Mesure des susceptibilit~s magnktiques principales des cristaux de benzkne entre - 180” et -2°C. C.r. hebd. Stfanc. Acad. Sci., Paris 242, 1702-4 (1956). Hoarau J., Joussot-Dubien J., Lemanceau B., Lumbroso N. et Pacault A. Anisotropie magn&ique du benzPne. Cahier Phys. 74, 34-37 (1956). Gay R. et Lemanceau B., Fabrication de monocristaux de benz$ne. Cahier Phys. 74, 39-40 (1956). Lumbroso N. et Pacault A., Susceptibilitks magn&iques de la motCcule de naphtalkne P - 195”. C.r. hebd. S&ant. Acad. Sci., Paris 245,686-g

(1957).

N., These Paris 1955, 19. Lumbroso-Bader Ann. de Chimie (1955). 20. Kitaigorodskii K., Z. Fzs Khzm. 1953; 27, 534; 1955 29,1897; 1955 29,2074. 21. Krishnan K. S., Nature 188, 174 (1934). 22. Krishnan K. S. Guha, Ind. J. Phys. 8, 345 (1934). 23. Krishnan K. S. et Ganguli N., Current Scz 8,472 (1935); PhiZMag21,355 (1936). 24. Krishnan K. S. et Ganguli N., 2. Kristal AlOO. 530 (1938). 25. Ganguli N. and Krishnan K. S., Proc. Roy. Sot. Al77.168 (1941). 26. Landau L., 2. Phys. 64,629 (1930).

ALONG

THE

27. Stoner E. C., Proc. Roy. Sot. A152,672 (1935). 28. Marchand A., Sur la susceptibilitC magn&ique de quelques noirs de carbone. C.r. hebd. Sianc. Acad. Sci., Paris 238, 460 (1954). 29. Marcharfd A., Variation thermique de la susceptibilitc? magnktique de quelques noirs de carbone. C.Y. hebd. Se’anc. Acad. Scz., Paris 238, 1645-7 30.

31.

32. 33.

34.

35. 36. 37. 38.

39. -10.

(1954).

Pacault A. et Marchand A., Etude du magnktisme d’un gaz d’klectrons i deux dimensions. C.r. hebd. Stfanc. Acad. Scz., Pam 241,489 (1955). Marchand A. et Pacault A., Etude du magnktisme d’un gaz d’klectrons a deux dimensions. Cahier Phys. 74, 37-38 (1956). hlarchand A., Th&se Paris 1956, Ann. Chimie 13,469 (1957). Pacault A. et Marchand A., A study of the magnetism and structure of carbon-blacks. Proc. 3rd Conf Carbon p. 37-41 (1957). Pacault A., Hoarau J.. Joussot-Dubien J., Lemanceau B. et Lumbroso N., Le diamagnetisme du benz&ne. Proc. -3rd Conj. Carbon. p. 43-9 (1957). Mrozowski S., Phys. Rev. 77, 838 (1950). i\lrozowski S., Phys. Rev. 85,609 (1952). Pinnick H. T., Phys. Rev. 91, 228 (1953); 84,319 (1954). Wynne-Jones H., Blayden E. et Iley M., Hrenw-toffChemie 33,268 (1952). Mica M.. Sci Rep. Tohoku Univ. 23.242 (1934). Pacault A., De la forme des pi&es polaires dans la mesure des susceptibilit& magnCtiques. C.r. hebd. Sdanc. Acad. Sri., Pans 224, 1500 (1947).

Pacault A., Hoarau J. et Joussot-Dubien J., De la forme des pi&es polaires pour la mesure de susceptibilite magnktique. C.r. hebd. SLanc. Acad. Sci., Parzs 232, 1930 (1951). 1”. Pacault A., l’ankerckhoven A., Hoarau J. et Joussot-Dubien J., Appareil pour la mesure des susceptibilit& Pendule de translation du type Weiss-Foex-Forrer. J. Chim.

41.

Phyc. 49.470

(1952).

Pacault A.. Lemanceau B. et Joussot-Dubien _I., Nouvelle mkthode de mesure des susceptibilit& magnktiques. C.r. hebd. S&znc. .4cad. Scz , PUG 237, 1156 (1953). -1-l. Joussot-Dubien J., Lemanceau B. et Pacault A.. Appareil klectronique de mesure des susceptibilit& magnktiques. J. Chim. Phys. 43.

198 (1956). -15. Pacault A., Lemanceau

B. et Joussot-Dubien .J., Pr&entation d’un appareil klectronique de mesures des susceptibilites ma@tiques-

CARBON

46. 47.

48.

49.

WAE

19

Applications - Actas do Congress0 - I volLisboa (1957). Hoarau J., Appareils de mesure des susceptibilitks magn&iques. Nature 3280 (1958). Joussot-Dubien J., Appareil Clectronique de mesure des susceptibilites magnktiques aux bases tempkratures. C.r. hebd. Sdanc. Acud. Sci., Paris 248,3165-6 (1959). Pacault A., Duchen J. et Baudet J., Description d’un nouvel appareil de mesure des variations de susceptibilitk magnktique. C.r. hebd. Se’anc. Acad. Scl., Paris 250, 3641 (1960). Regaya B. et Gasparoux H., Appareil adapt6 B l’&ude des t&s faibles variations de susceptibilitCs magnktiques. C.r. hebd. S4anc. Acad. Scz., Paris 272,724-726

(1971).

Gasparoux H. et Rouillon J. C., Appareil de mesure des susceptibilitCs magnktiques entre 77” et 3000°K. J. Chzm. Phys. 64, 1226 (1967). 51. Joussot-Dubien J. et Lemanceau B., Mesure de l’anisotropie diamagnktique en haute frCquence. C.r. hebd. Shanc. Atnd. Sci., Paw 242,1170-72 (1956). 52. Pointeau R. et Poquet E., Appareil de mesure des anisotropies magnktiques. C.r. hebd. Se’anc. Acad. SCI., Parzc. 249, 546-8 (1959). 53. Poquet E. Pacault A., Hoarau .J., Lumbroso N. et Zanchetta J. V., Mesure absolue d’une anisotropie magnbtique. C.r. hebd. Se’anc.

50.

Acad. Scz., Paris 250, 706 (1960).

Marchand A., Rouillon J. C. et Frdnc;ois d’Arcollieres F., Mesure simultanke ~1 citu’ du/et de l’anisotropie magnktique lors de l’insertion du brome dans un carbone. Carbon 9,349-353 (1971). 55. Bothorel P., Appareil de mesure de l’effet Hall pour solides pulv&ulents. C.r. hebd. S&nc. Acad. Sci., Paris 250,2892-4 (1960). 56. Bothorel P., Mesure de I’effet Hall de substances pulv&ulentes. C.r. hebd. SPanc. .4cad.

54.

Scl., Pam

250,4120-22

(1960).

Cherville J., Bothorel I’. et Pacault A., Etude de l’effet Hall et de la magn&&istance de carbones prCgraphitiques pulvPrulentsTechniques et r&hats-V” Curbon Conference-Penn State (1961). 58. Boisard F., Etude expkrimentale de la variation thermlque du coefficient de Hall de carbones pregraphitiques pulv&ulents. C.r. hebd. S&nc. Acad. Scz., Purls 258, 549-52 57.

(1964). 59.

Cherville J. et Bothorel P.. Contribution B I’ktude de I’effet Hall-Etude expkrimentale d’&hantillons pulvkrulents de forte r&istivitC Clectrique. Annul. chim (1964).

A. PACAULT

20

60. Barillot M. et Pointeau R., Realisation d’un appareillage destine a la mesure de la photoconductivite des composes de haute resistivite .J. Chim. Phys. 559 (1965). 61. Zanchetta J. V., Marchand A. et Pacault A., L’acu’-diphCnyl+picrylhydrazyl (DPPH), etalon de resonance paramagnetique electronique. Cr. hebd. Sk’anc. Acad. Sci., Paru 258,1496-99 (1964). 62. Fug G., Sanchez E., Gasparoux H. et Flandrois S., Amelioration de la sensibilite et de la vitesse de balayage d’un diffractiometre par couplage a un ordinateur. C.r. hebd. SLanc. Acad. Sci., Paris 271,784-787 (1970). 63. Fug G., Gasparoux H. et Piaud J. J., Description d’un dispositif de variation thermique permettant l’enregistrement d’un diagramme de diffraction X a des temperatures pouvant atteindre 3000°K. J. Phys. 5,1222 (1972). 64. Fug G., Gasparoux H. et Sanchez E., Couplage d’un diffractometre a un ordinateur et vue de l’etude de cinetiques rapides a des temperatures pouvant atteindre 2800°C. Colloqw interruztionaux C.N.R.S ., no 205. (Odeillo, 27-30 Septembre 1971) p. 133-138 (1973). 65. Poquet E., Lumbroso N., Hoarau J., Marchand A., Pacault A. et Soule D. E., Etude du diamagnetisme de monocristaux de graphite.]. Chim. Phys. 57,866 (1960). 66. Poquet Mme E., Variation a haute temperature de l’anisotropie magnetique du graphite monocristallin et du pyrocarbone. C.T. hebd. Skanc. Acad. Sci., Paris 257.1612-14 (1963). 67. Marchand A., Relationship between the gfactor and diamagnetic anisotropies of graphite and pyrocarbons. Carbon 7,329-334 (1969). 68. Delhaes P., Positive and negative magnetoresistances in carbons. Chemistry and Physics of Carbon. (Edited by P. L. Walker Jr.) Vol. 7, pp. 193-235 (1971). 69. Poquet Mme E. et Pacault A., Mise au point sur le magnetisme des carbones. Carbon 1, 71-74 (1963). 70. Delhaes P., Resonance paramagnetique des porteurs de charges libres: variation thermique de l’anisotropie de la largeur de raie dans un graphite monocristallin. C.r. hebd. Sianc.

Acad. Sci., Paris 265,575-578

(1967).

Zanchetta J. V., Belougne P. et Gasparoux H., Etude a 42°K de quelques proprietes galvanomagnetiques de pyrocarbones. Carbon 9, 139-158 (1971). 72. Delhaes P., Gasparoux H. et Uhlrich M., Anisotropic negative magnetoresistance in

71.

a pyrolytic-Carbon. Phys. Lett. 34A, 417-418 (1971). 73. Pacault A., Marchand A., Boy F. et Poquet Mme E., Accroissement du diamagnetisme d’un graphite nature1 par broyage. C.r. hebd.

Sianc.

Acad

Sk.,

Park

254,

1275-77

(1962). 74. Marchand A., Pacault A. et Forchioni A., Accroissement du diamagnetisme d’un graphite par broyage. C.r. hebd. Sianc. Acad. Sci., Paris 255 1257-9 (1962). 75. Delhaes P., Anisotropie du facteur-g d’echantillons pulverulents de graphite de Madagascar contenant une phase rhomboCdrique. Carbon 6,925-935 (1968). 76. Gasparoux H. et Lambert B., Etude de la cinetique de guerison des defauts trees dans un graphite par broyage. Carbon 8, 573-586 (1970). 77. Gasparoux H., Modification des proprietes magnetiques du graphite par creation de rhomboedriques. sequences Carbon 5, 441-451 (1967). 78. Gasparoux H. et Lambert B., PropriCtCs magnetiques d’un graphite de structure rhomboedrique entre 4,2 et 298°K. Corn@ Rend. 271,280-283 (1970). 79. Poquet E., Espagno L., Gay R. et Gasparoux des paramitres cristallins H., Evolution d’un pyrocarbone en fonction du traitement thermique. C.r. hebd. Uanc. Acad. Sci., Paris 255,2594-96 (1962). 80. Poquet E., Structure et proprietes diamagnetiques des pyrocarbones. J. Chim. Phys. 60,566-585 (1963). 81. Pacault A. et Poquet Mme E., Proprietes magnetiques des pyrocarbones. C.r. hebd. Sk’uanc.Acad. Sci., Paris 255,2106-2108

82.

(1962).

Pacault A., Uebersfeld J., Theobald J. G. et Cerutti M., Facteur de decomposition spectrale et susceptibilite diamagnetique des pyrocarbones. C.r. hebd. SLanc. Acad. Sci., Paris. 261,3589-3592

(1965).

Gromb S., Etude de proprietes electroniques de pyrocarbones et de leur variation thermique. C.r. hebd. SLanc. Acad. Sci., Paris 256, 4002-4 (1963). 84. Gromb S., Etude de proprietes electroniques de pyrocarbones. J. Chim. Phys. 864 (1964). 85. Pacault A., The kinetics of graphitization. In Chemistry and Physzcs of Carbon (Edited by P. L. Walker, J.), Vol. 7, pp. 107-154. Marcel Dekker, New York (1971). 86. Prost J. et Gasparoux H., Proprietes magnetiques et structurales d’un pyrocarbone depose a 1600°C. Rev. Chim. Minkral. 6, 275 (1969). 83.

ALONG

THE

87. Gasparoux H. et Prost J., Etude de la cinetique de graphitisation d’un carbone pyrolytique dCposC B 1600°C. J. Chim. Phys. 68,1267-1277 (1971). 88. Pacault A. et Marchand A., Propri&s klectroniques des carbones prkgraphitiques. J. Chim. Phys. 57,873 (1960). 89. Pacault A., Marchand A., Bothorel P., Zanchetta J. V., Boy F., Cherville J. et Oberlin M., Etude de la structure electronique de carbones prCgraphitiques. J. Chim. Phys. 57, 892 (1960). 90. Marchand A. et Delhaes P., Paramagn&isme thkorique et experimental de carbones des carbones prkgraphitiques. C.r. hebd. Sr’anc. Acad. Sci , Paris 256,3296 (1963). 91. Inagaki M., Komatsu Y. et Zanchetta J. V., Hall coefficient and magnetoresistance of carbons and polycristalline graphite in the temperature range 1.5”-300°K. Carbon 7. 163-175 (1969). 92. Delhaes P. et Hishiyama I’., Specific heat of soft carbons between 0.6” and 4.2”K. Carbon 8,31-38 (1970). 93. Mazza M., Marchand A. et Pacault A.. Contrigution g l’ktude cinktique de la graphitation. J. Chim. Phys. 59,657-58 (1962). 94. Mazza M., Contribution P 1’Ctude cinCtique de la graphitation. Etude magnktique. J. Chim. Phys. 721 (1964). 95. Gasparoux H.. Oxydation de graphite nature1 et des substances prkgraphitiques par le mklange sulfonitrique. C.r. hebd. Se’unc. Acad. Scz., Paris 264.376-379 (1967). 96. hlarchand A. et Delhaes P. Etude par R.P.E. de la d&localisation des klectrons dans les carbones prkgraphitiques. Proceedings of the XIIth

97.

98.

99.

100.

101.

Colloque

Ampire,

Bordeaux,

CARBOX

et Flandrois S., Sur un processus cinktique par &apes: la graphitation. C.1. hebd. Sbanc. Acad. Sci., Paris 260,4999-5002 102.

103.

104.

105.

106.

107.

108.

109.

110.

(1963),

pp. 135-40 (1964). Delhaes P. et Marchand A., Variation thermique du paramagnCtisme de Pauli: carbones prkgraphitiques. J. Phys. 28,67 (1967). Blondet-Gonte G., Delhaes P. et Daurel M., Specific heat of non-crystalline carbons between 1.3 and 4.3”K in presence of a strong magnetic field. Solid State Commun. 10.819-822 (1972). Delhaes P. et Blondet-Gonte G., Relationship between the linear term of the specific heat and a Curie law magnetic susceptibility in non-crystalline carbons. Phys. Lett. 40A, (3) (1972). Forchioni A., Boisard F. et Delhaes P.. Contribution ?I 1’Ctude cinktique de la graphitation (3eme mhmoire). J. Chim. Phys. 1289-1292 (1964). Pacault A., Marchand A., Gasparoux H.

21

WA\

111.

112.

113. 114.

115.

(1965).

Pacault A. et Gasparoux H.. Diamagn&me des carbones et processus de graphitation. C.r. hebd. Shanc. Acad. Sci., Paris 264, 1160-I 164 (1967). Delhaes P. et Marchand A., Analyse de la forme et de la position de signaux RPE graphitiques observCs sur des carbones pulv&ulents. Carbon 6,257-266 (1968). Pacault A.. Flandrois S. et Marchand A., Concerning the work of H. N. Murty, D. L. Bierderman and A. A. Heintz (letters to the editor). Carbon 9,87-88 (1971). Flandrois S. et Tinga A., Etude cinCtique de la graphitisation: dktermination du coefficient d’activation. Carbon 10, 1-12 (1972). Terriere G.. du Besset M., Oberlin A. et Pacault A., Etude en microscopic et diffraction klectronique de la cinktique de graphitation de diffkrents carbones. Carbon 7, 385391 (1969). Flandrois S., Etude magnktique de polyacktylenes. C.r. hebd. Skanc. Acnd. Scz., Paris 264, 1244-1247 (1967). Marchand A. et Amiell J., Etude cinCtique de la graphitisation du noir de carbone P33: R.P.E. et diamagnktisme. Carbon 8, 707-726 (1970). Pacault A. et Flandrois S.. Evolution des propriWs physiques d’un noir d’a&ylPne sous l’effet d’un traitement thermique. Rev. Chum. hlinbral6, 267 (1969). Delhaes P. et Carmona F., Etude par r&onante paramagnktique Clectronique, entre 4.2 et 300 K d’une famille de noirs de carbone. Carbon 10,667-690 (1972). Flandrois S., Etude du noir de carbone comme constituant du mClange des piles sPches du type LeclanchP. C.r hebd. Skanc Acad. Scl., Paris 264, 544-37 (1967). Marchand A., Variation thermique de la susceptibilitk cliamagnktique de quelques noirs de carbone entre -200°C et 1000°C. C.r. hebd. SLanc. Acad. Scl., Parts 239. 1609 (1954). of carbon Zanchetta .J. \:.. Conditioning blacks for the study of their electronic properties. Carbon 5,41 l-414 (1967). Marchand .4., Boy F. et Forchioni A., Susceptibilitk magnktique de charbons d’anthracene trait& entre 600 et 1200°C. J. Chum. Phys. 59. 1259 (1962). Marchand A., Delhaes P. et Zanchetta J. V., RPsonance paramagnktique Clectronique

22

116.

117.

118.

119.

120.

121.

122.

123.

A. PACAULT

de charbons d’anthracene et d’acridine. J. Chim. Phys. 60,688-90 (1963). Delhaes et Marchand A., Variations thermiques du diamagnetisme et de l’effet Hall d’un graphite polycristallin dope au bore. Cr. hebd. Skanc. Acad. Sci., Paris 259, 123126 (1964). Delhaes P. et Marchand A., PropriCtCs d’un graphite polycristallin electroniques dope au bore. Carbon 3,125-140 (1965). Delhaes P., PropriCtCs electroniques d’un pyrocarbone dope au bore. C.r. hebd. Shanc. Acad. Scz., Paris 261,1298-1300 (1965). Gasparoux H., Pacault A. et Poquet E., Variations thermiques du diamagnetisme et structure cristallographique d’un pyrocarbone dope au bore” Carbon 3, 65-72 (1965). Marchand A. et Dupart E., “Proprietes Clectroniques d’un pyrocarbone dope avec du bore: evolution en fonction du taux de bore” Carbon 15,453-469 (1967). Marchand A. et Castang-Coutou M. F., “Etude magnetique de la graphitisation de pyrocarbones dopes au bore” Carbon 9, 593-607 (1971). Delhaes P. et Marchand A., Proprietes Clectroniques d’un coke de brai dope au bore. Carbon3, 115-124(1965). Zanchetta J. V., Marchand A. et Pacault A., Etude par resonance paramagnttique Clectronique d’un complexe chlore-carbone. C.r. hebd. Uanc. 3287 (1964).

Acad.

Sci., Paris 258,

3285-

124. Zanchetta J. V., Marchand A. et Pacault A., Etude par resonance paramagnttique electronique d’un complexe chlore-carbone. C.r. hebd. Skanc. Acad. Sci., Paris 258, 40324035 (1964). 125. Pacault A., Marchand A. et Zanchetta J. V., Etude par resonance paramagnetique d’un complexe chlore-carbone.]. Chim. Phys. 1616-1620 (1964). 126. Marchand A. et Zanchetta J. V., Proprietes electroniques d’un carbone dope P l’azote. Carbon 3,483-491 (1965). 127. Zanchetta J. V. et Mrozowski S., Proprietes electroniques de carbones dopes au sodium. C.r. hebd. Sianc. Acad. Sci., Paris 264, 16211624 (1967). 128. Micaud G., Rappeneau J., Pacault A., Marchand A. et Amiell J., Processus de “degraphitation” sous l’effet des rayonnements neutroniques. J. Chim. Phys. no special, p. 129 (1969). 129. Rappeneau J., Micaud G., Pacault A.,

130.

131.

132.

133.

134.

Marchand A. et Amiell J., Evolution des proprietes electroniques de carbones irradies par les neutrons. Carbon 8,55-61 (1970). Delhaes P., Lemerle M. Y. et Blondet-Gonte G., Chaleur specifique entre 1,4 et 4,4”K en presence d’un champ magnetique variant de 0 a 40 kilogauss d’un graphite irradie par des neutrons. Cr. hebd. Skanc. Acad. Sci., Park 272,1285-1288 (1971). Pacault A., Marchand A., Amiell J., Dupart E., Rappeneau J., Micau G. et Wlodarsky R., Recuit thermique de carbones irradies par les neutrons; evolutions des proprietes Clectroniques. Carbon 10,449-454 (1972). Rappeneau J., Micaud G., Drouet A., Pacault A., Marchand A. et Dupart E., Proprietes Clectroniques et magnetiques de fibres de carbone; evolution sous irradiation neutronique. Carbon 10,455-462 (1972). Rouillon J. C. et Marchand A., Composes residuels de pyrocarbone et de brome: “hvsterese” du diamagnetisme et de la resistivite par rapport a la temperature. C.r. hebd. Se’anc. Acad. Sci., Parzs 274, 112-115 (1972). Marchand A. et Rouillon J. C., Migrations et changements de phase du brome dans ses composes residuels avec le carbone. C.r. hebd. SLanc. Acad. Sci., Paris 274, 225-228

(1972). 135. Fischbach D. B., Phys. Rev. 123, 1613 (1961). 136. Klein C. A., Proc. 5th Carbon Co@, Vol. 2, p. 11 (1962). Pergamon Press. 137. Klein C. A., Straub W. D. et Diefendorf R. J., Phys. Rev. 125,468 (1962). 138. Klein C. A. et Straub W. D., PhyA. Rev. 123, 1581 (1961). 139. Castle I. et Wobschall D. C., Proc. 3rd Carbon Conference, p. 129 (1959). Pergamon Press. 140. Marchand A., Stir I’activite magnetique des porteurs de charges libres dans les carbones graphitises. C.r. hebd. Skanc. Acad. Sci., Paris 245, 1534-1536 (1957). 141. Marchand A. et Lumbroso N., Magnetic susceptibility of a two-dimensional electron gas with an energy proportional to k”. Proc. 4th Conference on Carbon (1960). Pergamon Press. 142. Pacault A., Hoarau J. et Marchaad A., Aspects ¢s du diamagnetisme. Adv. Chem. Phys. III, 172-238 (1960). 143. Marchand A., Sur une modification du modele de Slonczewski et Weiss applicable aux carbones pregraphitiques. C.r. Sbanc. Acad. Sci., Paris 256,3070-3073 144.

Marchand

A.,

Anisotropie

(1963).

magnetique

ALONG

145.

146.

147.

148. 149. 150. 151. 152.

153.

154.

THE

theorique des pyrocarbones. Carbon 1, 75-84 (1963). Boy F. et Marchand A., V’alidite de quelques modeles Clectroniques simples de carbones. Carbon 5,227-241 (1967). Marchand A., Proprietes Clectroniques des carbones: modele bidimensionnel a trois bandes. C.r. hebd. Sianc. Acad. Sci., Paris 264, 1736-1739 (1967). Marchand A., Proprietes Clectroniques des carbones. Nouveau Trait; de Chimie Minerale, Tome VIII. fascicule 1, pp. 457-514. Masson & Cie (1968). Boy A., These, Bordeaux (1966). Zanchetta J. V., These, Bordeaux (1965). Klein C. A., J. Appt. Phys. 33,333s (1962). Antonowicz K., Cacha L. et Turlo J., Carbon 11, 1 (1973). Pacault A., Etude cinetique de la graphitation. Nouveau Traitb de Chimie Mi&rale, Tome VIII, fascicule 1, Masson & Cie (1968). Fischbach D. B., Chemistry and Physics of Carbon (Edited by P. Walker). Marcel Dekker, New York (1971). Vol. 7, p. 1. Pacault A., Contribution on the kinetics of complex systems. Nobel Symposium 5Fast Reactzons and Primary Processes in Chemical Kinetics, pp. 383-390, Interscience, Stockholm

(1967). 155. Pacault A., Contribution a l’etude de I’Cvolution des systemes. Cr. hebd. Seanc. Acad. Sci., Paris 268,383-386 (1969). 156. Pacault A., Introduction a une Etude phenomenologique de 1’Evolution des Systemes. pp. 39-66. Rheinisch-Westfalische Akademie der Wissenschaften, Dusseldorf (1971). 157. Honda H. and Ouchi K., Sci. Rep. Tohoku Univ. 37,55 (1953). 158. Kasatochkin V. I. and Kaverov A. T., Dokl. Akad. Nauk SSSR 117(5), 837 (1957); Sov. Phys. Dokl 3,655 (1958). 159. Tarpinian A., Degree of Master of Science, M .I .T. (1959); Tech. Rep. Watertown Lab Waterbury Mas Wal T 825 5-l (1960); Tarpinian A., et Tedmon C., ibid. 851, 5-l (1962). 160. Fair P. V. and Collins F. M., Proceedings of the 5th Conference on Carbon Vol. 1, p. 503. Pergamon Press, Oxford (1962). 161. Fischbach D. B., Applied Phys. Lett. 3 (1963); Fischbach D. B., Symposium on Carbon, Tokyo 111-22-111-23 (1964). Carbon Society of Japan. 162. Fischbach D. B., 18e’me Reunion annuelle de la Societb de Chimie Physique, no 24. J. Chim. Phys. 121 (1968). 163. Ishikawa J. et Yoshizawa S., Kogyo Kagaku

CARBON

WAY

“3

Zasshi (X,933-935 (1963). 164. Mizushima S., Proceedings of 5 th Conference on Carbon, Vol. 2, p. 439 Pergamon Press, Oxford (1963). 165. Pandic B., Second Conference on Industrial Carbon and Graphite, Society of Chemical Industry, London (1965). 166. Noda T., Inagaki M. et Sekiya T., Symposium on Carbon, Tokyo III, (1964); Carbon 3, 289 (1965). 167. Noda T., Carbon 6,125 (1968). 168. Bale E. S., Paper III, 3 conference on structural studies of partially ordered Materials, University of Sussex (1969). 169. Murty H. N., Biederman D. L. et Heintz E. A., Carbon 7,667-683 (1969). 170. Fischbach D. B., 11 th Carbon Conference. Gatlinburg (1973). 171. Fischbach D. B., Nature 200, 1281 (1963). 172. Gasparoux H., These, Bordeaux (1965). 173. Rouillon J. C., These de specialite. Bordeaux (1967). 174. Pacault A., Marchand A., Gasparoux H., Flandrois S. et Rouillon J. C.. Etude cinetique de la graphitation. J. Chim. Phys. no special, 104 (1969). 175. Oberlin A. et Mering J., Carbon 1,471 (1964). 176. Hanusse P., These de specialite, Bordeaux (1973). 177. Reinsch C. M., Num. Math. 10, 177-183 (1967). 178. Les Carbones. Ouvrage Ccrit en collaboration par les membres du groupe francais d’etude de carbones. Masson & Cie (1965). 179. Lumbroso-Bader N. et Marchand A., Susceptibilites magnetiques du graphite et des carbones graphitises. Influence du champ magnetique. C.r. hebd. Seanc. Acad. Sci., Parts 248,3433-5 (1959). 180. Mazza M., Gasparoux H. et Amiell J., Contribution a l’etude cinetique de la graphitation. 2eme memoire. J. Chin. Phys. 729 (1964).

Marchand A., Electronic properties of doped carbons. Chemistry and Phystcs of Carbon (Edited by P. L. Walker, Jr.), Vol. 7, pp. 155191. Marcel Dekker, New York (1971). 182. Carmona F. et Delhaes P., Interpretation des variations thermiques des grandeurs observables en resonance magnetique electronique d’une famille de noirs de carbone irradies aux neutrons. C.r. hebd. Shanc. Acad. Scz., Paris 272,649-652 (1971). 183. Ozanne N., Amiell J. et Bonnetain L., Carbonisation de &sines d’alcool furfurylique. Bull. Sot. Chim. 6, 1976-1982 (1971).

181.

24

A. PACAULT

APPENDIX by A. Pacault and P. Hanusse

I

Graphitizationin a temperaturegradient After firing a rocket engine it is possible to determine by magnetic studies, the highest temperature reached at various places in the nozzle when it is made of a polymer. As shown in our laboratory (D.R.M.E. report) the magnetic susceptibility of the resulting carbon yields information about the degree of graphitization and therefore the temperature reached by the material. The results obtained in this study seemed to indicate large magnetic susceptibility fluctuations across the thickness of the lining material. These findings suggested an analogy with the steps in the graphitization process and one could wonder if they might be due to presence of a temperature gradient in the nozzle lining. It was therefore desirable to experiment with a gradient under well defined conditions. The Odeillo solar furnace provided us with a large temperature gradient

=c

= z= 0;

1000°K

cm-1

aY where we heattreated samples of a carbon feltpolymer composite. The Fig. 25 shows, as a function of Z, the magnetic susceptibility obtained after three different exposure doses in the solar furnace. One sees that graphitization in a temperature gradient is, as expected, a monotonous function of thickness. So no particular phenomenon is observed. APPENDIX by P. Hanusse and A. Pacault

. L I

_ZlO"

50.

lrnl”50S

5

.. .

,

. 4

.

. .

3

.

2

1

l

0

. .

.

i0

DEPTH

Fig. 25. Magnetic susceptibility vs depth z in a sample of carbon composite submitted to various exposure time in a temperature gradient (dT/dz= 1000 K cm-‘). The magnetic measurement uncertainty may be estimated at 0.8%. The time uncertainty is negligible but one must consider the high activation energy (about 200 kcal): small temperature oscillations are equivalent to large time errors. We use spline functions to smooth curves with varying errors in X. Figures 26-29 show the curves obtained with this method from the experimental points presented on Figs. 18-20, and 24. (The first points on dashed curves are not considered).

II

A mathematical evaluation of the reality of the steps in graphitization Our first papers on graphitization kinetics were presented with smoothed out curves and it is only with some misgivings that we later suggested the existence of steps in the process. We were driven to it by a convergent set of experimental results confirmed by repeated measurements. However, the steps are small and only slightly larger than the experimental errors so that the drawing of a step curve is still largely a matter of subjective judgement. “Spline functions”[177] is a recent technique which allows an objective analysis of experimental curves. We used it to study several of the most characteristic susceptibility vs time curves previously obtained in our laboratory. This method consists in smoothing the curves by taking into account the position uncertainty of each point both in ordinate y and abscissa X.

Acetylene

black

ay-0.8

Y-

%

Fig. 26. Experimental results of Fig. 18 analyzed by Spline functions.

ALONG

THE

C4RBON

WA\

25

Anthracene

coke

Fig. 28. Experimental results of Fig. 20 analyzed by Spline functions.

Pitch

coke

(19)

Fig. 27. Experimental results of Fig. 19 analyzed by Spline functions. When an uncertainty of 0.8% in y and 5% in x are accepted, the steps are strongly attenuated but some “waves” remain. Although this procedure is objective, subjectivity reintroduces itself when one decides whether a 5% uncertainty is reasonable. For instance, a temperature fluctuation of 0.3% at 2000°C corresponds to a fluctuation of 15% in the reaction rate but its effects depend very much upon the frequency of the fluctuation. As far as can be estimated, the temperature fluctuations resulting from the furnace control are too fast to be effective. In the present state of the art, it seems impossible to obtain either a better accuracy in the measurements or a more precise mathematical analysis of the results so that the existence of steps remains subject to speculation. However, there is no doubt that graphitization is a complex process involving a very fast stage followed by a more or less fluctuating slow evolution.

~_QB%

Y

Pyrocorbon

16O@C

HTT

22OO’C

(h4)

Fig. 29. Experimental results of Fig. 21 analyzed by Spline functions.