九州大学学術情報リポジトリ
Kyushu University Institutional Repository
フラーレン類縁物質の炭化および構造解析
江頭, 港
九州大学総合理工学研究科分子工学専攻
https://doi.org/10.11501/3142487
出版情報：Kyushu University, 1998, 博士（工学）, 課程博士 バージョン：
THE CARBONIZATION AND STRUCTURAL ANALYSIS OF FULLERENE RELATED
MATERIALS
Minato EGASHIRA
March, 1998
i
. -· - ~ ---- .. ~ .. .. . . . . .. ~- --· ._ ... -., ... ·.-· ..
CONTENTS
Chapterl Introduction
1-1. The Overall Features of Fullerene
1-1-1. Fullerene ; Noble All sp2 Carbon Molecules 1-1-2. Preparation Methods of Fullerene
1-1-3. Structure and Physical Properties 1-1-4. Formation Mechanism
1-1-5. Application
1-2. The Chemical Reactivities of Fullerene 1-2-1. Additional Reactions
1-2-2. The Thermal and Oxidative Reactivities 1-3. The Structural Studies of Soot
1-4. The Conversions of Pentagonal Ring to Hexagon 1-5. Outline of the Present Thesis
References
Page 1 1 1 2 3 3 4 4 4 6 6 7 17
Chapter 2 Carbonization of C6o and C7o Fullerenes to Fullerene Soot
2-1. Introduction 23
2-2. Experimental 23
2-3. Results and Discussion 2-4. Conclusion
References
24 25 31
Chapter 3 Carbonization of Toluene Soluble Fraction of Fullerene Soot into Disk
3-1. Introduction 3-2. Experimental 3-3. Results
3-3-1. Sample Forms and Heating Procedures 3-3-2. Appearaances of Produced Carbon 3-4. Discussion
3-5. Conclusion References
32 32 33 33 33 34 35 45 Chapter 4 Structural Changes ofFullerene by Heat-treatment upto
Graphitized Temperature
4-3. Results
4-3-1. Weight and Compositional Changes 4-3-2. Changes in the Chemical Structure 4-3-3. Graphitic Change
4-4-4. Microscopic Observation 4-4. Discussion
4-5. Conclusion References
Chapter 5 Carbon Flameworks Produced in the Fullerene Related Materials
47 47 47 48 48 49 50
60
5-1. Introduction 61
5-2. Experimental 61
5-3. Results 62
5-3-1. Separation of Fullerene Soot 62
5-3-2. The Structural Analysis of Fs-TI before and
after Heat-treatment 63 5-3-3. The Structurral Analysis of Fs-TIQS 63 5-3-4. The Structural Analysis of Fs-QI 64
5-4. Discussion 64
5-4-1. The Separation of Fullerene Soot 64 5-4-2. Reactivity of Pentagonal Unit for the Oxidation 65 5-4-3. Conversion of Pentagon Unit into Hexagon 65
5-5. Conclusion 66
References 80
Chapter 6 Some Properties of Carbon Disk Prepared from Toluene Insoluble Fraction in Fullerene Soot
6-1. Introduction 81
6-2. Experimental 81
6-3. Results 82
6-3-1. The Yield of the Disk Derived from Fs-TI 82 6-3-2. The Structure of the Disks Derived from Fs-TI 82 6-3-3. The Properties of the Disk Derived from Fs-TI 83
6-4. Discussion 84
6-5. Conclusion 85
References 93
Synthetic Naphthelene Isotrovic Pitch
7-1. Introduction 94
7-2. Experimental 94
7-3. Results 95
7-3-1. The Effects of Fullerene on Carbonization of Pitch 9 5 7-3-2. The Chemical State of Fullerene in the Coke 96
7-3-3. The Intermediate Products 97
7-4. Discussion 97
7-5. Conclusion 99
References 112
Chapter 8 Conclusions
8-1. Summary of the Thesis 113
8-2. Summaries of Chapters 114
-,~- ; - .. ~ ... ···-- --~-·· ... -· ... , ,·-· ·
Chapter 1
INTRODUCTION
1-1. The Overall Features of Fullerene 1-1-1. Fullerene; noble all sp2 carbon 1nolecules
It has been believed for a long time that carbon has only two kinds of allotrope, sp3-combined diamond and sp2-con1bined graphite. In 1970s, a linear sp carbon tnolecule, so called carbine, was claimed to exist.
However, carbine is a rather unstable molecule and difficult to be synthesized[ 1]. The possibility of a spherical shape all-carbon molecule was described by Osawa in 1970[2]. In 1985, Kroto found a unique C6o molecule in the space radiospectroscopy. Kroto and Smalley vaporized graphite by laser ablation under lower pressure of He and detected the products of carbon clusters by in situ TOF-mass spectra. Among a number of short-lived carbon clusters, a molecule of 60 carbon atoms seemed most stable[3]. They speculated that the stability of C6o cluster came fro1n their spherical, closed shape consisting of 20 six-membered and 12 five-membered rings with no dangling bond as shown in Figure 1- 1. Because of analogical shape of the cluster with a dotne-building designed by Buckminster Fuller, Kroto named C6o buckminsterfullerene.
In 1990, Kratchmer et al. found a large amount of C6o formed in the soot produced by resistive heating of graphite electrode[ 4,5]. They succeeded to isolate C6o and C7o fullerenes from the soot, using Soxhlet extraction with nonpolar organic solvent such as benzene and toluene[5]. C6o and larger fullerenes were separated by liquid chromatograghy. Such a series of investigations stimulated a large number of research on fullerenes in their synthesis, reactivity, and application.
1-1-2. Preparation Methods of Fullerene
So far the five methods have been reported to synthesized fullerene : vaporization of high purity graphite by using resistive heating[6-8] ; AC or DC arc discharge of graphite[9-18] ; production of soot in flame through carefully controlled combustion of benzene[ 19-21] ; laser ablation of a rotating carbon disc under flowing argon[ 1 0] ; and a high frequency inductive heating[22]. All tnethods produce "soot", from which the fullerenes are extracted by appropriate solvents. Table 1-1
-,. .. - ~ -. -- . ~ . . . ·~ ... ~ .. .. . .. -' . . .. . .. ·~ . . ... ·:.
literatures for the synthesis of fullerene-containing soot by the arc discharge and resistive heating methods[23]. The arc discharge process appears to be more efficient than the resistive heating method[9 ,24].
Typically 10wto/o of toluene-soluble yield was reported by a wide range of experimental conditions as shown in Table 1-1.
Separation and purification of the fullerene is typically performed by extracting the soot first with benzene or toluene as shown in Table 1-1.
The extracted fullerenes of C6o to C96 are further purified by column chromatograph[6,7], HPLC[26-32] and GPC[33] by adjusting the packing materials and solvent. Other procedures such recrystalization[34], fractual crystallization[35], and sublimation[36,37] are also reported.
In spite of extensive research, yield of C6o is still low and its tedious purification is far from satisfaction for its application as a functional material.
1-1-3. Structure and Physical Properties
Sixty carbon atoms in C6o are located at the vertices of a regular truncated icosahedron where every site is all equivalent, being consistent with a single sharp line in NMR spectrum[6,38]. The average nearest neighbor carbon-carbon distance ac-e in C6o is 1.44A, almost identical to that in graphite (1.42A). Therefore, C6o molecule can be regarded as a
"rolled-up" graphene sheet. The diameter of the C6o molecule is 6.83A treating the atoms as points[39], while the outer diameter of the C6o molecule becomes 1 0.18A[ 40], including the n:-electron cloud.
Although all carbon atoms in C6o are equivalent, the three bonds emanating from each atom are not equivalent, two being electron-poor single bonds, and one being an electron-rich double bond. The single bonds that define the pentagon are longer than the average bond length of 1.44A, while the double bond are shortened to 1.40A[39,41-43].
Since valences of carbon atom in C6o are fully satisfied, the 1nolecules are expected to form a molecular crystal associated through van der Waals force being an insulator (or semiconductor). Reflecting the
l~z symmetry of C6o molecule, it has 46 molecular mode frequencies, including 4 of infrared-active (all with T1u symmetry) and 10 of Raman- active (2 with Ag symmetry and 8 with Hg symmetry). The Raman-active Ag breathing mode at 1469cm-I corresponds to tangential displacements of the 5 carbon atoms around each of the 12 pentagons[44,45] which is called
.. ,, - - -- ~ -. ~ ... -... , .... -.. ·-. . . . . . ... · .. --..
In the solid state, the C6o molecules crystallize into a cubic structure with a lattice constant of 14.17
A,
a nearest neighbor C6o-C6o distance of 10.02A, and a density of 1.72g/cm3[39]. The balls are rotating rapidly with three degrees of rotational freedom with their centers arranged on a face-centered cubic (fcc) lattice with one C6o ball per primitive fcc unit cell. The rotation of C6o ball is frozen in two of their three degrees of rotational freedom below 255K, and the anisotropic orientation among balls appears in the crystal[ 46,47 ,48].Fullerenes give molecular solids. Thus, their electronic structures are expected to be closely related to the electronic levels of the isolated molecules. If two single bonds along adjacent sides of a pentagon and one double bond between two adjoining hexagons were coplanar, they would be very similar to the sp2 trigonal bonding in graphite. Moreover, the curvature of the C6o surface causes the planar-derived trigonal orbitals to hybridize, thereby admixing some sp3 character to the sp2 bonding. The shortening of the double bonds and lengthening of the single bonds in the Kekule arrangement of the C6o molecule also strongly influence the electronic structure[ 49].
1-1-4. Fonnation Mechanism
Several basic and more detail grow1ng models of fullerene framework under the severe conditions such as arc discharge were proposed. Smalley et al. proposed pentagon road model on which only pentagon and hexagon are structural units and as many pentagons as possible are framed by avoiding the adjacent pentagon (isolated pentagon rule ; IPR) [50]. The importance of intermediate circular clusters during fullerene formation was proved[51]. The models based on the formation and rearrangement of circular clusters were also proposed[52,53].
1-1-5. Application
Fullerenes and fullerene-related compounds are known to show unique properties, and expected to their unique application.
As described in Section 1-1-3, C6o exhibits narrow HOMO-LUMO gap. This electronic structure provides some unique optical properties[54,55], for instance, photo-induced activation effect of oxygen rnolecule to singlet states[54]. Some A3C6o compounds (A ; alkali metals uch as K, Rb and Cs) have been known to show the high-temperature superconductivity[56]. RbxCsyC6o reached 33K of the critical
I
I
-.. -..- - ~-:--~- ... • .. • • r - • . • ·~ .- . . . .
a new concept of organic superconductor.
fullcrcncs doped with hctcro aton1s have been investigated, such as endohedral fulleroids Mx@ C g2[50,58,59], harogenated fullcrenes C60Fx[60,61], and tnany other organic derivatives being reported. These doping can functionalizc fullerenes for their applications.
Carbon nanotube, regarded as a tubler-shape higher fullerenc, is al o expected to carry potentials of their unique application especially ior the electronic usc. Since the discovery by Iijin1a[62], numerous investigations have n1ade it possible to synthesize and purify it in large an1ount[63,64,65]. Son1e interested properties of this material have been calculated[66,67 j and measured[68,69,70]. Nanotube scen1s to be useful as catalyst support[71] to provide its nanoscalc hole for chemical reactions in the restricted space[72].
1-2. The Chen1ical Reactivities of Fullerenes 1-2-1. Additional Reactions
Fullercncs have rnuch higher chemical reactivity than nonnal graphitic plane due to their bent sp2 orbitals and n-cloud orienting to exohedral. The natures of their double bonds are relatively closer to those of the conjugated poly-alkene. Besides, their narrow HOMO-LUMO gap provides them relatively high addition reactivities towards both electrophilic and nucleophilic agents[73]. Especially, C6o has a low reduction potential ( -0.36V vs SCE ; in benzene) and shows electron- accepting property[74].
Fluorine molecule easily reacts with C6o even at rootn ten1perature and provides adducts in broad distribution of the addition dcgrec[60
J.
Hydrogen can be also added to C6o by the Birch reduction and provides adducts upto C6oH36[75]. The additions of several agent, especially nucleophile, to C6o[73] and higher fullerenes[76] were reviewed by Hirsch and Diederich et al., respectively.
1-2-2. The Thennal and Oxidation Reactivities
C6o is known to sublitne at high te1nperatures. Kratchmer et al.
have reported that C6o sublimes in a vacuum at -400°C[5]. Milliken et al.
measured thermal gravimetric analysis (TGA) of C6o under N2 flow on ambient pressure and observed that C6o commenced to lose its weight at -600°C where a very small weight loss of graphite was compared as
and C70 fr 1n their polycrystalline tnixturc t be 40.1 and 43.0kcalln1ol at a erage ternpcraturcs of 707 and 739K, rcspectivelyl78]. The heat of sublin1ation f fcc C6o powder was also rncasured by Chen et a!. to be
~39kcal/n1oll79j. On the TGA of C6o n1casurcd by lstnail et a/.[801, the tnajor C6o sublin1ed, leaving behind a srnall arnount of non-volatile carbon residue, whose weight ranged 5-22o/o dependent on satnple preparation.
They proposed two possible origins of the residue : a by-product fanned during the sublin1ation of C60 by polyn1erization, or soot or particles that were occl udcd the aggregates.
Milliken eta!. also n1easured TGA of C6o in air as shown in Figure 1-2(B) [77]. C6o began to lose its weight at -480°C and con1pleted the weight loss by -650°C while graphite comtnenced losing weight at 700°C.
Weight uptake data under various conditions[77, 79,81] clearly indicate that C6o is reactive towards molecular oxygen. The reactivity of C6o at arnbient pressure and temperature with tnolecular oxygen to fonn an epoxide has been reported in a photoemission IR[82]. Werner et al.
analyzed the reactiivity of C6o solid towards 0 2 using several spectroscopies at the temperature range of 300-600K[83], and concluded that 02 molecule first intercalates at room temperature and reacts with C6o rnolccule to fonn C=O bond, deforn1ing the frarnework of Coo through the formation of peroxide and epoxide at 600K. Scanlon et al.
reported that the residual soot after the extraction of fullerene soot was more reactive than C6o so that 80wt o/o of this material burned out by the heat-treallnent at 400°C[84]. Chibante et al. reveal rather carbonaceous nature of oxidation product of toluene soluble fullerenes[85].
There arc some researches to use C6o as the catalysts for high temperature reactions. Malhotra et al. reported that C6o effectively catalyzed a hydrogen-transfer reaction of 1,2'-dinaphtylmethane at 400°C[86]. Hirschon et al. used fullerene soot and the residual soot after the extraction of fullerene as the catalyst of the dehydrogenative coupling of Inethane[87]. These fullerene-related materials can accelerate at lower temperature than other carbon materials. The rate-determining step was changed to the dehydrogenation of
c2
by the presence of fullerene soot, indicating catalytic effect of this material. Sakanishi et al. applied the soot for the cataly t support of the liquefaction of coal[88].Thus, the reactivity of fullerenes widely attracts researchers, thern1al reactivity of fullerene i not yet clarified under non-sublimation condition .
1-3. The Structural Studies of Soot
As described in Section 1-1-2, under the tnajor preparation processes of fullerene, arc discharge of graphite and con1bustion of hydrocarbon, the n1ain product is carbonaceous soot which is insoluble in solvents. It is impos ible to know its precise structure, and its similarity is postulated to much con1n1on atnorphous carbonaceous soot such as P AH and carbon blacks.
Kroto suggested the icospiral growth tnodel of soot which started frotn the corannulene-like c1ustcr[89] (described in Figure J -3).
According to this tnodel, fullerenes are the by-product in the growth process of soot. He conjectured that the presence of hydrogen atom stabilized opened clusters, accelerating the forn1ation of soot. This model indicates the structural relationship of soot and fullerene n1olecule, supported by Gerhardt et al., who found C6o+ as a don1inant ion in a flame[90].
Weber et al. produced toluene soluble fullerenes, especially significant percentage of Cs4 , by the heat-treattnent of the residual fullerene-soot after the extraction with toluene[91]. This re ult cannot be fully explained by Kroto's tnodel. More research is necessary to understand the probJen1.
Iijin1a first observed the closed-shell carbon bodies in an amorphous structure[92] (Figure 1-4). The observed carbon bodies were multi-shelled, so called "carbon onion". The carbon onion was reported by Ugarte et a/.[93], Stnalley et a/.[94], Endo and Kroto[95], and many other researchers[96,97].
Ugarte et a I. synthesized carbon onions and nanocapsu les by the heat-treatn1ent of residual fullerene soot after the extraction with toluene[98,99]. Under the observation of high-resolution TEM(Figure 1- 5), the amorphous soot is converted to the material resembling glass-like carbon after annealed at 1700°C for 18h. This rnaterial is further converted to onion-like particles of 2-3 shells at 2100°C, and then to those of 4-8 shells at 2250°C. Such a unique structure stimulates its unique application.
1-4. Convertions of Pentagonal Ring to Hexagon
Stone and Wales reported that photochemically-allowed transformations between two pyracy lene units can occur according to
I
-.-,.- -· • __ w,_~---· -. • • • .-•• ' •-. ·-•·••• "'"'' ... ·-•.•
rule (IPR). Although the energy level of 150-200 kcalllnol had been thought to be nece, sary for Stone-Wales traiL fonnation, Osawa eta/.
proved that less level of energy allow this transforn1ation[ 1011. Thus, the conversion of pentagon to hexagon is rather facile. Murry et al. applied this fact to the fragmentation of C6o through 7 -n1embered ring by laser annealing[ l 02].
Previou studies of conversion frorn pentagon in aron1atic hydrocarbons containing pentagon to hexagon were tnade by Mochida et a /.ll 03] and Otani et al. [ 104]. Figure l-6 shows the change of Ran1an spectra during the heat-treatn1ent of decacyclene[ 104]. The 1420cm-1 peak assigned for the "pentagonal pinch" of pentagonal ring disappeared by the heat-treatment at 7 50°C. The author concerns the deformation of pentagons in fullerenes and the structure of the product.
1-6. Outline of the Present Thesis
The application of fullerene is lin1ited because of its high cost due to the low yield. To find a way is to clarify the thern1al reactivity of fullerene. The thermal ·eactivity of C6o and its homologue fullerenes has been rarely discussed because of the sublimation of such fullerene n1olecules, although extensive researches have been performed in n1any organic reactions. The present author believes that the fullerenes C6o and C70 can be converted by the heat treattnent to amorphous carbon tnaterials which may have similar structure to that of the residual soot, to prove that the soot is produced consecutively by thermal polymerization of fullerenes. The carbonization in the solid pha e may be influenced very tnuch by the crystal structure of fullerenes.
Through the arc discharge of graphite electrode, the products from the anode are collected as soot, which are further fractionated into toluene-soluble C6o, C7o and some large fullerenes, toluene-insoluble but quinoline-soluble giant fullerenes, and insoluble an1orphous carbon particle. The author atternpted to reveal through the structural analy is and heat treatment of each fraction whether each fraction has similarity in their structure which will be thern1ally converted each other, as fullerenes to soot and giant fullerenes to toluene-soluble fullerenes, respectively, for example. Such a series of study will clarify the reactivity of f ullerene as an intermediate. The author expects to be able to propose ways to increase the yield of fullerenes in the arc discharge.
The author exan1ines a noble use of soot as well as fullerenes as the
carbonization of fullerenes is competitive with the sublimation, their carbonization yield will be enhanced by moulding into disk and inhibiting the sublimation. The residual soot is expected to provide similar carbon artifact by moulding into disk. After the graphitization, fullerenes and residual soot may provide unique carbon of spherical turbostratic layer and extremely low bulk density. The point is to clarify whether the fullerene or soot can give the artifact through the moulded carbonization.
The author also co-carbonizes fullerene with the synthesized isotropic pitch. Fullerenes is expected to react with hydrogen derived from components in the isotropic pitch at lower temperatures to modify the carbonization behavior of the isotropic pitch. Fullerene can affect effectively the carbonization of pitch through its dehydrogenating ability.
The content of the present thesis is summarized as follows.
Chapter 1. Introduction
The background/scopes of recent fullerene research and objectives of the present study are summarized.
Chapter 2. The carbonization of C6o and C7o fullerenes to fullerene soot The author examined the carbonization of C6o, C7o, and toluene- soluble component obtained from the fullerene soot by sol vent extraction.
Such a study may clarify the consecutive natures of a series of reactions to form first C6o and then soot.
Chapter 3. Carbonization of the toluene-soluble fraction of fullerene soot into a disk
Some attempts were made to increase the carbon yield from the fullerene, based on the observation that its sublimation took place around 1000°C, in competition with its carbonization.
Chapter 4. Structural changes offullerene by heat-treatlnent up to graphitization temperature
The structural changes of the fullerene were studied from the molecular crystal to the amorphous carbon and then to the spherical hollow structure through successive analysis with X-ray, Raman, Fe- SEM, TEM and STM/AFM techniques.
-
- - - - -
. ~ . . . . . ,~ ,-.. , ... , ... .-.,..--·--. - . .
Chapter 5. Carbon franzeworks produced in the fullerene related 1110 te ria Is
The products in the preparation of C6o fron1 graphite through arc discharge were separated and analyzed to clarify the correlation in their structure and their successive conversions
Chapter 6. So111e properties qf carbon disk prepared frrnn toluene insoluble fraction in fu/lerene soot
The carbonization of toluene insoluble fraction in the fullerene soot was studied by 1noulding to prepare the carbon artifact of unique properties and strength. Adhesion and fusion of the toluene-insoluble particles were particularly interested to develop the strength. Son1e properties of artifact due to the microhollow spheres were measured to suggest some application.
Chapter 7. Effects offullerene addition on the carbonization of synthetic naphthalene isotropic pitch
Fullerenes were co-carbonized with synthesized isotropic pitch derived fro1n naphthalene. This chapter describes the carbonization process of the mixture and how the chemical states of fullerene change during the carbonization with pitch.
Chapter 8. Conclusions
Conclusions of the thesis are sum1narized.
Figure 1-1. The Structure of C6o Molecule.[3]
Table 1-1. Sumtnary of Sotne Fullerene Synthesis Methods[23].
Discharge rnethod& Yield
He
unknown DC AC Current Voltage Pressure Contact Extraction
o/o % o/o (A) (V) (Torr) Method Method
8(3t) 8(3t) 100
so
37-75 resistive Soxhlet14 140-180 225 resistive boiling toluene
10±2 100-200 10-20 100 contact arc Soxhlet
10-15 150 27 100 contact arc boiling toluene
25-40 40-60 200 gravity
5-10 100-200 resistive
10 200 20 150 contact arc
7.7 55 100 gravity
3 130 100 gravity
16.2 9.3 105-110 24 250 contact arc Soxhlet
26 70 20 200 plas1na arc Soxhlet
12 200-250 20 contact arc reflux
8-12 110 high freq. toluene
t3% is the yield of pure C6o ; 8% is the yield of extractable material.
100 (b) graphite
~ 80 (o) Cso
;:
0'
"iii
~
60
1--1--~--.----1--r---t--•--1---t
100
(b) graphite
80
~ 60
;:
"iii 0' 40
~
20
0
0 200 400 600 800
Temperature (°C)
Figure 1-2. TGA Profiles of (a) C6o and (b) Graphite under N2 Flow(Top) and Air Flow(Bottom).[77]
Figure 1-3. Icospiral Model for the Growth of Soot[89]
Figure 1-4. TEM Image of Carbon Onion First Observed by Iijitna. [92]
Figure 1-5. HRTEM Images of heattreated carbon soot.[98]
(a) crude soot produced in the electric arc (b) soot annealed at 1700°C, 18h
(c) soot annealed at 1700°C, lh and 2100°C, lh (d) oot annealed at 1700°C, lh and 2250°C, lh
3000"C
2000'C
1800"C l600"C
1-tOO"C
1800 1-100 1000
RAMA~ SHifT (ca-l)
REFERENCES
1. Kudryavtsev, Y. P., Evsyukov, S., Guseva, M., Babaev, V. and Khvostov, V ., in Chen1istry and Physics of Carbon, Vol. 25, p. 1, Thrower, P. A. (ed.), Marcel Dekker, New York, 1997
2. Osawa, E., Kagaku(Japan), 1970, 25, 854
3. Kroto, H. W., Heath, J. R., O'Brien, S.C., Curl, R. F. and Smalley, R. E., Nature, 1985, 318, 162
4. Kratch1ner, W., Fostiropoulos, K. and Huffmann, D. R., Chen1.
Phys. Lett., 1990, 170, 167
5. Kratchmer, W., Lan1b, L. D., Fostiropoulos, K. and Huffmann, D. R., Nature, 1990, 347, 354
6. Taylor, R., Hare, J. P., Abdul-Sada, A. and Kroto, W., J. Chen1.
Soc. Chen1. Conunun., 1990, 1423
7. Ajie, H., Alvarez, M. M., Anz, S. J., Beck, R. D., Diederich, F., Fostiropoulos, K., Huffmann, D. R., Kratchmer, W., Rubin, Y., Schriber, K. E., Sensharma, D. and Whetten, R. L., J. Phys. Chen1.,
1990, 94, 8630
8. Cox, D. M., Behal, S., Creegan, K., Disko, M., Hsu, C. S., Kollin, E., Miller, J., Robbins, J., Robbins, W., Sherwood, R. D., Tindall, P., Fischer, D. and Meitzncr, G., in Mater. Res. Soc. S)n7p Proc.,
Averback, R. S., Bernholc, J. and Nelson, D. L.(eds.), p. 651, Materials Research Society, Boston, MA, 1991
9. Haufler, R. E., Conceicao, J., Chibante, L. P. F., Chai, Y., Byrne, N. E., Flanagan, S., Haley, M. M., O'Brien, S. C., Pan, C., Xiao, Z., Billups, W. E., Ciufolini, M. A., Hauge, R. H., Margrave, J. L., Wilson, L. 1., Curl, R. F. and Smalley, R. E., 1. Phys. Chen1., 1990, 94, 8634
10 Haufler, R. E., Chai, Y., Chibante, L. P. F., Conceicao, J., Jin, C., Wang, L.-S., Maruyama, S. and Smalley, R. E., in Materials
Research Society Sy1np. Proc., Averback, R. S.,
Bernholc, J. and Nelson, D. L.(eds.), p. 627, Materials Research Society, Boston, MA, 1991
11 Whetten, R. L., Alveraz, M. M., Anz, S. 1., Shriver, K. E., Beck, R. D., Diederich, F. N., Rubin, Y., Ettl, R., Foote, C. S.,
Dannanyan, A. P. and Arbogast, J. W., in Materials Research Society Synzposiu1n Proceedings, Averback, R. S., Bernholc, J. and Nelson, D. L.(eds.), p. 639, Materials Research Society, Boston,
12 Bac, Y. K., Lorentz, D. C., Malhotra, R., Becker, C. H., Tsc, D.
and Jusinski, L., in Materials Research Society Syn1posiunz
Proceedings, Averback, R. S., Bernholc, J. and Nelson, D. L.(eds.), p. 733, Materials Re earch Society, Boston, MA, 1991
13 Koch, A., Khe1nani, K. C. and Wudl, F., J. Org. Chenz., 1991, 56, 4543
14 Pang, L. S. K., Vassallo, A. N. and Wilson, M.A., Nature, 1991, 352, 480
15 Parker, D. H., Wurz, P., Chatterjee, K., Lykke, K. R., Hunt, J. E., Fellin, M. J., Hemtninger, J. C., Gruen, D. M. and Stock, L. M., 1.
An1. Chenz. Soc., 1991, 113, 7499
16. Shinohara, H., Sato, H., Saito, Y., Takayan1a, M., Izuoka, A. and Sugawara, T., 1. Phys. Chen1., 1991, 95, 8449
17. Saito, Y., Inagaki, M., Shinohara, H., Nagasbi1na, H., Ohkohchi, M.
and Ando, Y ., Clzenz. Phys. Lett., 1992, 200, 643 18. Weston, A. and Murphy, M., Carbon, 1996, 34, 1267
19. Howard, J. B., McKinnon, J. T., Marovsky, Y., Lafleur, A. and Johnson, M. E., Nature, 1991, 352, 139
20. Howard, J. B., McKinnon, J. Th., Johnson, M. E., Makarovsky, Y.
and Lafleur, A. L., 1. Phys. Chen1., 1992, 96, 6657
21. Richter, H., Fonseca, A., Gilles, J.-M., Nagy, J. B., Thiry, P. A., Rozenberg, R., de Hoffmann, E. and Pasch, H., Carbon, 1996, 3, 317
22. Peters, G. and Jansen, M., Angew. Chenz. Int. Ed. Engl., 1992, 31, 223
23. Parker, D. H., Chatterjee, K., Wurz, P., Lykke, K. R., Pellin, M.
J., Stock, L. M. and Hemtninger, J. C., Carbon, J 992, 30, 1167 24. Hare, J.P., Kroto, H. W. and Taylor, R., Che1n. Ph_>s. Lett., 1991,
177, 394
25. Walton, D. and Kroto, unpublished
26. Hawkins, J. M., Lewis, T. A., Loren, S.D., Meyer, A., Heath, J.
R., Shibata, Y. and Saykally, R., 1. Org. Chen1., 1990, 55, 6250 27. Cox, D. M., Behal, S., Disko, M., Gorum, S. M., Greany, M., Hsu,
C. S., Kollin, E. B., Miller, J., Robbins, J., Robbins, W.,
Sherwood, R. D. and Tindall, P., J. An1. Che1n. Soc., 1991, 113, 2940
28. Vas allo, A.M., Pahnisano, A. J., Pang, L. S. K. and Wilson, M.
Alvarez, M., Anz, S., Scnshanna, D., Wudl, F., Khernani, K. and Koch, A., Science, 1991, 252, 548
30. Pirkle, W. H. and Welch, C. J., J. Org. Clzenz., 1991, 56, 6973 31. Kikuchi, K., Nakahara, N., Wakabayashi, T., Honda, M.,
Matsun1iya, H., Moriwaki, T., Suzuko, S., Shirotnaru, H., Saito, K., Yan1auchi, K., Ikemoto, I. and Achiba, Y., Chen1. Phys. Lett., 1992, 188, 177
32. Jinno, K., Ohta, H., Saito, Y., Uetnura, T., Nagashin1a, H., Itoh., K., Chen, Y.-L., Luehr, G, Archer, J., Fetzer, J. C. and Biggs, W.
R., J. Chron1atogr. 1993, 648, 71
33. Meier, M. S. and Se1egue, J. P., J. Org. Che1n., 1992, 57, 1924 34. Coustel, N., Bernier, P., Azner, R., Zahab, A., Latnbert, J. M. and
Lyard, P., J. Che1n. Soc. Chen1. Convnun., 1992, 1402
35 Zhou, X., Gu, Z., Wu, Y., Sun, Y., Jin, Z., Xiong, Y., Sun, B., Wu, Y., Fu, H. and Wang, J., Carbon, 1994, 32, 935
36. Haluska, M., Kuzmany, H., Vybornov, M., Rogl, P. and Fejdi, P., Appl. Phys., 1993, A56, 161
37. Rietschel, H., Fullerene Sci. Tech., 1996, 4, 743
38. Johnson, R. D., Meijer, G. and Bethune, D. S., J. An1. Chen1. Soc., 1990, 112, 8983
39. Stephens, P. W., Mihaly, L., Lee, P. L., Whatten, R. L., Huang, S.
M., Kaner, R., Diederich, F. and Holczer, K., Nature, 1991, 351, 632
40. Kortan, A. R., Kopylov, N., Glarurn, S., Gyorgy, E. M., Ratnirez, A. P., Flen1ing, R. M., Thiel, F. A. and Haddon, R. C., Nature, 1992, 355, 529
41. David, W. I. F., Ibberson, R. M., Mattewman, J. C., Prassides, K., Dennis, T. J. S., Hare, J. P., Kroto, H. W., Taylor, R. and Walton, D. R. M., Nature, 1991, 353, 147
42. Fischer, J. E., Heiney, P. A., McGhie, A. R., Romanov, W. J., Denenstein, A. M., McCauley, Jr., J. P. and Smith III, A. B., Science, 1991, 252, 1288
43. Yannoni, C. S., Johnson, R. D., Meijer, G., Bethune, D. S. and Salem, J. R., J. Phys. Chen1., 1991, 95, 9
44. Eklund, P. C., Zhou, P., Wang, K.-A., Dresselhaus, G. and Dresselhaus, M. S., J. Phys. Chen1. Solids, 1992, 53, 1391
45. Zhou, P., Rao, A. M., Wang, K.-A., Robertson, J. D., Eloi, C. C., Meier, M. S., Ren, S. L., Bi, X. X., Eklund, P. C. and Dresselhaus,
46. Heiney, P. A., Vaughan, G. B. M., Fischer, J. E., Coustel, N., Cox, D. E., Copley, J. R. D., Neutnann, D. A., Kan1itakahara, W. A., Creegan, K. M., Cox, D. M., McCauley, Jr., J. P. and Sn1ith III, A.
B., Ph)s. Rev. B, 1992, 45, 4544
47. Heiney, P. A., Fischer, J. E., McGhie, A. R., Ron1anow, W. 1., Denenstein, A. M., McCauley, Jr., J. P., S1nith III, A. B. and Cox, D. E., Ph) s. Rev. Lett., 1991, 67, 1468
48. David, W. I. F., Ibberson, R. M., Dennis, T. J. S., Hare, J. P. and Prassides, K., Europhys. Lett., 1992, 18, 219
49. Dresselhaus, M. S., Dresselhaus, G. and Eklund, P. C., J. Mater.
Res., 1993, 8, 2054
50. S1nalley, R. E., Ace. Che1n. Res., 1992, 25, 98
51. Von Heiden, G., Gotts, N. G., and Bowers, M. T., Nature, 1993, 363, 60
52. Wakabayashi, T.and Achiba, Y., Che1n. Phys. Lett., 1992, 160, 465 53. Strout, D. L. and Scuseria, G. E., J. Phys. Chen1., 1996, 100, 6492 54. Arbogast, J. W., Darmanyan, A. P., Foote, C. S., Rubin, Y.,
Diederich, F. N., Alvarez, M. M., Anz S. J. and Whetten, R. L., J.
Phys. Chen1. 1991, 95, 11
55. Rao, A. M., Zhou, P., Wang, K. A., Hager, G. T., Holden, J. M., Wang, Y., Lee, W. T., Bi, X.-X., Eklund, P. C., Cornett, D. S., Duncan, M. A. and Atnstcr, I. J ., Science, 1993, 259, 955
56. Fleming, R. M., Ramirez, A. P., Rosseinsky, M. J., Murphy, D.
W., Haddon, R. C., Zahurak, S.M. and Makhija, A. V., Nature, 199 J' 352, 787
57. Tanigaki, K., Ebbesen, T. W., Saito, S., Mizuki, J., Tsai, J. S., Kubo, Y. and Kuroshitna, S., Nature, 1991, 352, 222
58. Takata, M., Utneda, B., Nishibori, E., Sakata, M., Saito, Y., Ohno M. and Shinohara, H., Nature, 1995, 377, 46
59. Nagase, S. and Kobayashi, K., J. Chen?. Soc. Chen1. Conunun., 1994, 1837
60. Kniaz, K., Pitcher, J. E., Selig, H., Vaughan, G. B. M., Romanov, W. J., Cox, D. M., Chowdhury, S. K., McCauley, J.P., Strongin, R. M. and Smith III, A. B., J. An1. Che1n. Soc., 1993, 115, 6060 61. Tohhara, H. et al., Synth. Met., 1995, 70, 1447
62. Iijima, S., Nature, 1991, 354, 56
63. Ebbesen, T. W., Ajayan, P. M., Hiura, H. and Tanigaki, K., Nature,
Nature, 1994, 370, 603
65. Kyotani, T., Tsai, L. and To1nita, A., Che1n. Mater., 1995, 7, 1427 66. Saito, R., Fujita, M., Dresselhaus, G. and Dresselhaus, M. S., Appl.
Phys. Lett., 1992, 60, 2204
67. White, C. T., Robertson, D. H. and Mint1nire, J. W., Phys. Rev. B, 1993, 47, 5485
68. Hiura, H., Ebbesen, T. W., Tanigaki, K. and Takahashi, H., Che111.
Phys. Lett., 1993, 202, 509
69. · Kosaka, M., Ebbesen, T. W., Hiura, H. and Tanigaki, L., Cheni.
Phys. Lett., 1995, 233, 47
70. Ebbesen, T. W., Proc. of the European Carbon CoT~ference, P. 725, Newcastle, UK, 1996
71. Planex, J. M., Coustel, N., Cox, B., Brotons, V., Kurnbhar, P. S., Geneste, R., Bernier, P. and Ajayan, P. M., J. Ani. Chen1. Soc.,
1994, 116, 7935
72. Kawashin1a, M., Kyotani, T. and Tomita, A., Proc. of 24th Carbon
Co1~{erence o.f1apan, 1997, 3A13, Ehin1e, Japan
73. Hirsch, A., The Cheniistry of Fullerenes, 1994, Georg Thieme Verlag.
74. Xie, Q., Cordero, E. P. and Echegoyan, L., 1. Ani. Cheni. Soc., 1992, 114, 3978
75. Hau_fler, R. E., Conceicao, 1., Chibante, L. P. F., Chai, Y., Byrne, N. E., Flanagan, S., Haley, M. M., O'Brien, S. C., Pan, C., Xiao, Z., Billups, W. E., Ciufolini, M. A., I-Iauge, R. H., Margrave, J. L., Wilson, L. 1., Curl, R. F. and Smalley, R. E., J. Phys. Chen1., 1990, 94, 8634
76. Thilgen, C., Hernnann, A. and Diederich, F., Angew. Chen1. Int.
Ed. Engl., 1997, 36, 2268
77. Milliken, J., Keller, T. M., Baronavski, A. P., McElvany, S. W., Callahan, J. H. and Nelson, H. H., Chem. Mater., 1991,3, 386 78. Pan, C., Sampson, M. P., Chai, Y., Hauge, R. H. and Margrave, J.
L., J. Phys. Chern., J. Phys. Che1n., 1991, 95, 2944
79. Chen, H. S., Kortan, A. R., Haddon, R. C. and Fleming, D. A., 1.
Ph)s. Che1n., 1992, 96, 1016
80. Ismail, I. M. K. and Rodgers, S. L., Carbon, 1992, 30, 229
81. Saxby, J.D., Chatfield, P., Palmisano, A. 1., Vassilo, M., Wilson, M. A. and Pang, I. S. K., J. Phys. Chent., 1992, 96, 17
82. Vijayakrishnan, V., Santra, A. K., Pradeep, T., Seshadr, R.,
1992, 198
83. Werner, H., Schedal-Niedrig, Th., Wohlers, M., Herein, D., Herzog, B. and Schlogl, R., J. Chen1. Soc. Parada) Trans., 1994, 90, 403
84. Scanlon, J. C., Brown, J. M. and Ebert, L. B., J. Phys. Chen1., 1994, 98, 3921
85. Chibante, L. P. F., Pan, C., Pierson, M. L., Haufler, R. E. and Heymenn, D., Carbon, 1993, 31, 185
86. Malhotra, R., McMillen, D. F., Tse, D. S., Lorents, D. C., Ruoff, R. S. and Keegan, D. M., Energy Fuels, 1993, 7, 685
87. Hirschon, A., Wu, H.-J., Wilson, R. B. and Malhotra, R., J. Phys.
Che1n., 1995, 99, 17483
88. Sakanishi, K., Hasuo, H., Kishino, M. and Mochida, 1., Energy&Fuels, 1996, 10, 216
89. Kroto, H., Science, 1988, 242, 1139
90. Gerhardt, P. H., Loffler, S. and Hoffmann, K. H., Chern. Phys.
Lett., 1987, 137, 306
91. Weber, J. V., Millon, E., Kubler, B., Theobald, J. and Muller, J.F., J. Anal. Appl. Pyrolysis, 1994, 29, 1
92. Iijima, S., J. Cryst. Growth, 1980, 50, 675 93. Ugarte, D., Nature, 1992, 359, 707
94. Guo, T., Nikolaev, P., Rinzler, A. G., Tomanek, D., Colbert, D. T.
and Smally, R. E., J. Phys. Che1n, 1995, 99, 10694
95. Endo, M. and Kroto, H. W., J. Phys. Chern., 1992, 96, 6941 96. Wang, Z. L. and Kang, Z. C., Carbon, 1997, 35, 419
97. Bourgeois, L. N. and Bursill, L. A., Chern. Phys. Lett., 1997, 277, 571
98. De Heer, W. A. and Ugarte, D., Che1n. Phys. Lett., 1993, 207, 480 99. Ugarte, D., Carbon, 1994, 32, 1245
100. Stone, A. J. and Wales, D. J., Che1n. Phys. Lett., 1986, 128, 501 101. Osawa, E., Honda, K., Slanina, Z., Ueno, H. and Matsu1noto, T.,
to be published.
102. Murry, R. L., Strout, D. L., Odom, G. K. and Scuseria, G. E., Nature, 1993, 366, 665
103. Mochida, 1., Miyasaka, H., Fujitsu, H. and Takeshita, K., Tanso(Japan), 1978, 92, 7
104. U, K., Otani,S., Kaneko, T. and Yoshimura, S., Proc. of 20th
Chapter 2
Carbonization of C6o and C7o Fullerenes to Ftdlerene Soot
2-1. Introduction
Since C60 in a bulk quantity has been produced from the graphite electrode through its electric arc discharge[ 1], its organic chemistry is now expanding to establish new aromatic concept[2].
The present procedure produces C6o at a yield of ca. 1 Owt%
regardless of the production facility. Although a higher yield of C6o is strongly desired, any preparation procedure gives a so-called "soot" as the major product which is basically insoluble in any solvent[ 1]. The soot appears to be sitnilar to a carbon black of large surface area[3-5]. It is an intriguing question whether C6o is an intern1ediate for the soot in the reaction initiated by the arc discharge or an independent product as described in Section 1-3.
In this chapter, the author examined the carbonization of C6o, C7o, and the toluene soluble component separated from the fullerene soot by solvent extraction. The reactivities of C6o, C7o fullerenes for carbonization, the structure of carbonized and graphitized product, and the relationship of the structure of these products to that of the residual soot after extraction from fullerene soot are discussed toward the problem described in Section 1-2-2. Such a study will clarify the consecutive natures of a series of reactions to form first C6o and then soot.
2-2. Experin1ental
The fullerene soot(Fs) was produced by arc discharge method using a graphite electrode and was separated into two fractions by Soxhlet extraction with toluene. About 10% of Fs is soluble in toluene. The toluene-soluble fraction(Fs- TS) was then isolated and re-crystallized by evaporating the solvent, and then heated in vacuum at 1 OOOC to remove the residual sol vent. The Fs- TS fraction was analyzed by high- performance liquid chromatography. The obtained Fs- TS powder thus obtained was used for the carbonization in the present study. Pure C60 (purity 99.9%) and C70 (purity 99.5%) were obtained from Shinku Yakin Co.
The heat-treatn1ent of Fs-TS powder was carried out by the following procedures; the sample was put in an alun1ina boat, placed in the electrical tube furnace and heated under flowing arg n (flow rate:
200ml/min) at a heating rate of 4 OC/min to the prescribed ten1perature, where it was held for 1 to 2 h. These temperatures were 200,400,500,800, and 1 000°C. The heating behavior was also probed by thermogravitnetric analysis(TGA) in flowing N2. Carbonaceous product at lOOOOC was further calcined and graphitized to 2500°C.
The heated materials(called TS-HT) of Fs-TS was extracted by toluene at room temperature. The toluene-soluble fraction in TS-HT(to be called TS-HT-TS)was also analyzed by HPLC. Both the total product and the toluene-insoluble fraction( to be called TS-HT-TI) were characterized by X-ray diffraction, and transmission electron microscopy(TEM).
2-3. Results and Discussion
Figure 2-1 illustrates the TGA profiles of C60 , C70 , and Fs-TS under N2 flow of 200 or 100 ml/min and heating rate of lOOC/min. Such substrates of C60 , C70 , and Fs-TS were found to exhibit sharp weight loss at 800~900°C, 800~900°C, 850~950°C, respectively (as reported by Milliken et al.[7]), leaving some carbonaceous soot-like product in the TG platinum pan. The yield of the soot-like product was trace from C60 , 6o/o from C70 , and 10% from Fs-TS under N2 flow of 200 ml/min. Larger fullerenes appear to give higher yield of soot-like product. C60 and C70 in Fs-TS appear to give more carbonaceous product than their isolated forms. C70 in Fs- TS appears to react together with C60 at a lower temperature of 800°C than that observed with pure C70 . The slower flow rate of 100 ml/min increased the yield of carbonaceous product from Fs- TS to 20%. Further slow rate of 50ml/min did not increase the yield.
Table 2-1 summarized the yields of remaining products from Fs-TS heated in an alumina boat. In an electric furnace, a trace amount of TI was formed by the heat treatment at 250°C. It should be noted that 10% of other TS, probably large fullerenes was produced by this temperature.
Higher ten1perature increased TI up to 24% by lOOOOC at the sacrifice of toluene soluble fullerenes while a large weight loss was found between 500 and 800°C where C60, C70 and TS might sublime.
Figure 2-2 illustrates the X-ray diffraction patterns of Fs-TS, and its heated products. The starting Fs-TS shows the typical pattern of C
background diffraction. The heat-treattnent destroyed the crystal completely by 1000°C. Graphitization at 2500°C provided a sharp diffraction at 26.0° with a small shoulder at 26.3 °. Such X-ray profiles of graphitized Fs-TS were very similar to that of the quinoline insoluble fraction(Fs-QI) in the soot graphitized at 2500°C[8].
Figure 2-3 illustrates the TEM bright field images of heated Fs-TS and QI. Both Fs-TS heat-treated at IOOOOC and as-extracted QI show grain-assemble forms as observed for soot by Werner et. al. [5] and by the present authors for QI[8]. The each grain carried very small planes randomly oriented. The graphitization at 2500°C developed very thin graphitic layers of about 1 ntn thick. The layers in the graphitized Fs-TS appeared spherical, fonning a hollow in the inside the grain, while those of graphitized Fs-QI were flake-like with some twists, as reported[9,10].
The present study revealed the successive carbonization of C60 and C70 through large fullerencs into soot-like substances which are very similar to the soot produced as the major by-product in the preparation of the fullerenes from the graphite electrode by electric-arc discharge. Very similar X-ray profile and TEM image after the graphitization indicate that the spherical surface of C60 due to CS rings is converted into hexagonal planes at elevated temperature above 800°C which will stack into the graphitic layers within limited range. The interlayer spacing is estimated around 0.3 nm to be called turbostratic. Spherical shape of turbostratic layers forming a hollow should be noted to inherit the grain of the molecular crystals of fullerenes. The yield of carbonaceous product from Fs-TS depends very much on the flow rate during the heat treatment. The competition of sublimation with carbonization is definitely suggested to govern the yield of the soot. Such conclusions indicate a way to increase the yield of C60 in its preparation by the rapid run-away of new born C60 from the hot zone in the electric arc discharge.
2-4. Conclusion
The toluene soluble fraction of fullerene soot(Fs-TS), containing 76wt% of C6o, 22wt% of C7o and 2wt% of higher fullerenes, was carbonized and graphitized. Although fullerenes sublimed around 800°C, ca. 20wt% of the sample remained after heattreated at 1000°C. The residue was more from higher fullerenes than pure C6o· C6o and C7o in F -TS were converted to toluene insoluble matter after heattreated up to 250°C, via higher fullerenes. The carbonized product of Fs-TS was a
soot-like amorphous carbon and appeared periherical turbostratic layers after graphitization. The similarity in the carbonization and graphitization behaviors of Fs-TS to that of quinoline insoluble soot(Fs-QI) indicates the consecutive formation of soot from C6o and fullerenes in arc discharge chamber, and a way to increase the yield of C6o in the preparation by the rapid run-away of new born C6o from the hot zone in arc.
0
~ ~
-50
~
-100
0 200 400 600 800
Temperature ( °C)
Figure 2-1. TG Profiles of Fullerenes in N2 flow 1) Fs-TS under a N 2 flow rate of 1 OOml/min 2) Fs-TS under a N 2 flow rate of 200ml/min 3) C6o under a N2 flow rate of 200ml/min 4) C7o under a N2 flow rate of 200ml/min
1)
2) 4)
3)
1000
Table 2-1. Compositions of Fs-TS and its Heated Products
1) Compositions(%)
Heat
Treatment C6o C7o Other TS Toluene-I nsoluble Loss 2)
non-treated
76 22 2
250°C, 2hrs
69 17 10 2 2
400°C, 2hrs
64 14 6 9 5
500°C, 2hrs
63 17 3 15 4
500°C, 5hrs
63 16 2 14 5
800°C, 2hrs
21 79
1000°C, lhr
24 76
1) Amount of Fs-TS : O.lOg heated in an alumina boat under Ar
flow rate 200ml/min, heating rate 4 OC/min 2) Sublimed
(a) ·-- --
(b)
(c)
10 15 20 25 30 35
(d)
24.0 25.0 26.0 27.0 28.0
2
fJ(degree)
Figure 2-2. X-ray Diffraction Patterns of Fs-TS and its Heated Products (a) Fs-TS
(b) Fs-TS heated at lOOOOC (c) Fs-TS heated at 2500°C
(d) detailed profile of (c) in the 28 range 24 ° to 28 °
SOnm
Figure 2-3. TEM Bright Field Images of Carbonized Fs-TS, Fs-QI, and their Graphitized Products
(a) Fs-TS heated at lOOOOC (b) graphitized Fs-TS (c) Fs-QI
(d) graphitized Fs-QI
REFERENCES
1. Kratschmer, W., Latnb, L, Foristopoulos, K. and Huffman, D., Nature, 1990, 347, 354.
2. Special issue of Ace. Che1n.Res., 25, 1992.
3. Bacsa, W. S., de Heer, W. A., Ugarte, D. and Chatelain, A., Chen1 .. Phys.Lett .. , 1993, 211,.346.
4. Kroto, H., Science, 1988, 242,.1139.
5. Werner, H., Merlin, D., Blocker, J., Menschke, B., Tegtmeyer, U., Schedel-Niedrig, T. H., Keil, M., Bradshaw, A.M. and Schlogl, R., Chenz.Phys.Lett., 1992, 194,.62.
6. Taylor, R., Parsons, J. P., Auent, A. G., Rannord, S. P., Dennis, J.
J., Hare, J.P., Kroto, H. W. and Watson, D. R. M Nature, 1991 351, 277 .
7. Milliken, J., Keller, T. M., Baronavski, A. P., McElvany, S. W., Callahan, J. H. and Nelson, H. M., Chem. Matter., 1991, 3,.386.
8. Egashira, M., Kaura, H., Korai, Y. and Mochida, I., to be subntitted to Carbon.
9. Ugarte, D., Carbon, 1994, 32,.1245.
10. de Heer, W. A., and Ugrate, D., Chem. Phys. Lett., 1993, 207,.480.
Chapter 3
Carbonization of Toluene Soluble Fraction of Fullerene Soot into Disk
3-1. Introduction
Since the discovery of a facile synthetic procedure[ 1], the fullerene(C6o and C7o) has attracted a great deal of research on its physical properties, che1nical reactivity and theoretical calculation as a unique highly-conjugated species[2]. The present author[3] has described its thermal reactivity to produce amorphous carbon particulate at 1 OOOOC which were converted at 2400°C into hollow spheres surrounded by turbostratic carbon layers in Chapter 2. Such graphitization behavior appears very similar to that of fullerene soot[3 .4] The carbon yield was rather limited as low as 24% by the carbonization of powdered fullerenes in a boat under the helium flow because they sublime around 800°C[5].
In this chapter, some attempts were made to increase the carbon yield from the fullerene based on the observation that its sublimation took place around 1 000°C, in competition with its carbonization. Hence the carbonization by placing the fullerene at the bottom of long quartz tube or by press moulding it into a disk was performed to suppress the sublimation before its thermal condensation and carbonization into non- sublimable substances. Some properties of the produced carbon disk were also investigated here for the noble application of fullerenes.
3-2. Experimental
Fullerene soot(Fs) was produced by the arc discharge 1nethod using a graphite electrode. The produced soot was separated into two fractions by Soxhlet extraction with toluene. About 10% of Fs was soluble in toluene. The toluene-soluble fraction(TS) was then recovered by evaporation, followed by vacuum drying to remove the residual solvent. The Fs-TS fraction consisted of C6o(76% ), C7o(22%) and 2% of the others (probably higher fullerenes) as determined by HPLC (Hitachi Co.; D-2500) analysis.
About 0.5 g( otherwise specified) of the Fs-TS powder obtained in this way was moulded in the disk of 20mm diameter and about 1.2mm
The heat-treatment of Fs-TS powders was carried out by the following two procedures as shown in Figure 3-1; (A), the sample was placed in the bottom of a test-tube (200mm high) which was purged with flowing Argas through aT-type tube attached at the top of the test-tube, and (B), the sample was placed in an alumina boat and heated in a horizontal tube furnace, being purged with Ar gas at 200ml/min.
Heating was programmed at 4 OC/min to the prescribed temperature, and held for 1h at that temperature. The temperatures investigated were 250, 500, 700, 800, 900, 1000, 1200 and 1300°C. The carbonaceous product at lOOOOC was further calcined and graphitized to 2400°C.
The heated products were observed by FE-SEM (JEOL Co.; JSM- 6320F). Bulk densities of the disks were calculated by measuring their volume and weight in the water.
3-3. Results
3-3-1. Sample Fonns and Heating Procedures
The yield of carbonaceous material from Fs-TS was markedly influenced by the sample form and heating procedure. Table 3-1 bows the yields obtained with Fs-TS of powder and disk at 900°C or 1 OOOOC in the tube A or boat B, respectively. The moulded disk (6MPa) yielded the largest amount of heated product, the yield reaching 94% when it was heated in the bottom of the tube A, and 54o/o heated even in a shallow boat B. The disk produced markedly higher yields than the powder by litniting sublimation of C6o molecules. Location in the bottom of a tube was more favorable for higher yields than in a shallow boat, again because of limited sublimation.
Figure 3-2 illustrates the relationship of the carbonization yield to the thickness of the disk( 6MPa, heattreated in the B Type furnace).
Thicker disks tended to provide higher yields, while the moulding pressure of 1.5 to 6 MPa appeared not to be as critical in obtaining high yield.
Figure 3-3 illustrates the influence of the heating rate. Rapid heating up to 4 OC/min increased the yield, but further increases in the heating rate provided no improvement. Competition of sublimation and carbonization is again suggested.
3-3-2. Appearances of Produced Carbon
Figure 3-4 shows the forms and appearances of the moulded
lOOOOC using procedure B at a heating rate of 4 OC!tnin, and final calcination at 2400°C. While there was a small shrinkage, the disk was basically 1naintained during the heat-treattnent. Sotne cracking and bending of the disks 1nay be observed in the photograph, but this can be avoided by lowering the heating rate and using procedure A which gives higher yield. Figure 3-4 also shows the forn1s and appearances of the graphitized disks produced at reduced moulding pressures (1.5MPa).
When the moulding pressure was 6MPa, the graphitized disk was mechanically strong like commercial hard carbons, while the lower pressure provided disks which were easily broken. The graphitized disk 1noulded at 1.5MPa appeared much less glossy, probably because of the porosity of the surface.
The apparent and bulk densities of Fs- TS disks and their heated products at the moulding pressures of 1.5and 6MPa are summarized in Table 3-2. While apparent densities of heated disks were influenced by the densities of the initial disk, their bulk densities appeared independent from the initial moulding pressure. The A type furnace provided a higher apparent density of the disk to almost the same to that of the initial disk reflecting very high carbon yield. Although the bulk densities of the disks heated to 1 OOOOC were similar to those of typical non-graphitizable carbon, those of the disk heated to 2400°C were markedly smaller.
Figure 3-5a and b show FE-SEM photographs of cross-sectioned surface of Fs- TS disk carbonized in A type and B type furnace, respectively. The areas near the surface of the disks showed granular assemble regardless the carbonization procedures of A and B, although the former procedure appeared to give more fused (Boarders of granulars becatne much less distinct). The inner areas of the two disks were very different. The procedure A gave no trace of granular, allowing a complete fused adhesion of grains to show continuous plate of no boundary, although some pores and cracks were observable under high magnification. In contrast, the procedure B showed again granular assetnbles in the inside of the disk. Their fusion was emphasized compared to the surface. Such results indicate the very different extent of ublimation according to the carbonization and moulding procedures as well as the location within the disk.
3-4. Discussion
Therefore the best way to increase the carbon yield is to limit the ublimation by increasing their partial pressure. A type method (placing satnple at the botto1n of the tube) is the preferable for this purpose. It is found through the present study that their subli1nation process was ahnost completely suppressed when the vapor of the fullerene was filled in the atmosphere at the upper part of the vertical test tube.
Moulding fullerene into the disk is also effective to increase the yield by lin1iting the sublimation. The smaller outer surface of the disk and diffusion inside the disk limit the sublimation in the competition with the carbonization. Hence a thicker disk gave a higher yield. It is also of value to point out that the bottom of the tube allowed a further higher yield of moulded disk, suggesting the the complete suppression of the sublimation pressure. The rapid heating increased the yield, the physical sublimation and chemical carbonization of different activation energies may response differently with the heating rate.
The dense packing of fullerene provided an amorphous carbon disk of high strength. The fullerene grains adhered each other, giving a high density when carbonized in the procedure A. Although the bulk of the disk stayed unchanged by the carbonization, the grains appeared to be fused to adhere at the chemical transformation of spherical structure of C6o into graphitic planer structure appears to be related to their fusion in the range of 700-800°C. Structural change of the fullerene is now under investigation.
It is also of value to mention that the density decreased by the graphitization. The small loss of weight and no shrinkage in a disk of very high carbon yield gave a hollow grain with graphitic skins, looking close to multi-walled tubular fullerene in Ref.[6], reducing the density as revealed by TEM in Chapter 2, while maintaining the form of the disk.
The high pressure of moulding and carbonization procedure of limiting sublimation can give textureless carbon plate of no boundary in the inside of the disk (60% volume) like the surface of glass-like carbon derived from thermosetting polymers. Complete fusion of the fullerene molecules as well as crystals is suggested during its carbonization. A unique preparation procedure of glass-like carbon artifact can be proposed.
3-5. Conclusion
Carbonization of toluene soluble fraction in the fullerene soot was
was found to increase the carbon yield to 94% by 900°C and 89o/o by 2400°C. The carbon yield was also found to be influenced by the thickness of the disk and the heating rate. All these results indicate that the carbonization competes the sublitnation. The carbon disk thus prepared showed appearance of glass-like carbon and had bulk density of 1.5g/cm3 at 900°C and 1.2g/cm3 at 2400°C. The reduction of the density by the graphitization reflects hollow spheres surrounded by their turbostratic layers in the graphitized disk.
-~ - - - - ~
Ar gas in Ar gas out
Sample
(A) Test-tube Type
lectric Furnace
Ar
..
Electric Furnace
Alumina Boat
Sample
(B) Boat in Flow
Figure 3-1. The Carbonization Methods of Fs-TS
Table 3-1. Yields of Heat-treatment
Forms (Heating System)
Powder (Type A)
Powder (Type B)
Disk (Type A)
Disk (Type B)
Carbon Yield (wt%)
39
24
94 54
Heating System : Type A - Bottom of Tube Type B - Boat on Flow Heating Temp. : Type A- 900°C,
Type B- lOOOOC Disk : 20mm<j>, thickness - ca.l.25mm
