J. Phys. Chem. 1992, 96, 17-18
17
Thermogravimetric Analysis of Buckminsterfullerene and Related Materials in Air John D. Saxby, S. Peter Chatfield, Andrew J. Palmisano, Anthony M. Vassallo, Michael A. Wilson, and Louis S. K. Pang* CSIRO Division of Coal and Energy Technology, PO Box 136, North Ryde. New South Wales, 2113 Australia (Received: September 30, 1991; In Final Form: November 8, 1991)
The oxidation of purified Cm was studied by thermogravimetricanalysis in air. Virtually no increase in weight due to added oxygen was observed before weight loss begins. It was shown that increasing the heating rate from 1 to 20 OC/min increases the temperature of maximum rate of weight loss from 444 to 600 OC. Upon heating at 1 OC/min in air, fullerene Cmshows the lowest temperature of maximum rate of weight loss (444 OC) compared to diamond (629 "C), graphite (644 "C), and soot (565 OC). This result can be attributed to conformational strain in Cm.
Introduction The newly discovered' and i ~ o l a t e d *third ~ ~ form of carbon known as buckminsterfullerene ( 0 ) has received considerable attention due to its unique structure and properties. The electronic: vibrati~nal,~,~ and magnetic ~roperties,~ superconductivity,S and redox behavior9have been reported. The molecule was shown to undergo addition with hydrogen3and fluorine'O and reaction with sulfur.'] Its unusual all-carbon structure consists of unsaturated five- and six-membered ringsI2 joined together in a spherical 60-atom structure with icosahedral symmetry. It has been demonstrated that metal atoms can associate with the molecule both insideI3and outside the cage.I4 All these studies aim at characterizing the properties which ultimately lead to identifying the many potential uses that this molecule can offerI5 and also its unusual chemistry. One poorly understood property that remains is its reactivity in air. Several reports on the thermal analysis of Cm in air by thermogravimetric analysis (TGA)l6I8 and emission infrared (IR)I9spectroscopy have appeared recently. The IR studies demonstrate structural changes with temperature while TGA gives a quantitative measure of the weight changes. It is known that the characteristics of thermal changes are dependent on heating rates. Many of the previously reported results disagree due to discrepancies in the heating rates used.1618 This report aims at providing a more comprehensive view of the TGA thermal behavior of Cm fullerene at a range of heating rates (1-20 OC/min) and an accurate comparison of the data to other forms of carbon, namely, diamond, graphite, and soot. Experimental Section Fullerene molecules were prepared by the carbon electrical arcing technique according to Haufler et al.3 The c 6 0 molecule was isolated and purifed using a newly developed chromatographic technique.20 Graphite was obtained from May & Baker (laboratory grade), diamond was De Beers synthetic diamond (1-2 pm particle size), and soot was obtained from Continental Carbon, N.S.W., Australia. Thermal analyses were carried out in a thermogravimetric analyzer controlled by a Rigaku TAS 100 data station. Approximately 5 mg of powdered sample was heated in an open platinum pan at variable heating rates in excess air. Results are shown in Figures 1 and 2 for purified c 6 0 and for typical samples of diamond, graphite, and soot under similar conditions. In order to remove traces of toluene from c60, the procedure of Milliken et a1.I6 was used in which the sample was evacuated, heated slowly to 210 OC, held at this temperature for 5 h, and then cooled to room temperature. The air flow was then started and the TGA run commenced. Results and Discussion (i) The curves in Figure 1 show the effect of heating rate on the combustion of Cm. Increasing the heating rate from 1 to 20 OClmin causes the temperature of maximum rate of weight loss To whom correspondence should be addressed.
0022-3654/92/2096-17$03.00/O
to increase from 444 to 600 "C. It is reasonable to ask, what is the lowest temperatureat which significant oxidation of Cm occurs in air? If 'significant" is defined as a 1% weight loss, then a loss of this magnitude has occurred at about 390 "C at 1 OC/min. Halving the heating rate at 20 OC/min lowers the temperature of maximum rate of rate of weight loss by 55 OC, while halving at 1 "C/min probably only lowers the temperature by 10 "C. Further extrapolation to infinitely slow heating (i.e., isothermal conditions over periods of hours) points to about 370 OC as a minimum temperature for "significant" oxidation in air. Overall, the present work highlights the need to define heating rates in any discussion of oxidation temperatures for c60. (ii) The curves in Figure 1 show minimal increase in weight due to added oxygen before the main combustion (gasification) weight loss begins. This result differs from that of Ismail,l* who reports chemisorption of up to 1.5 oxygen atoms per Cm molecule. We have also observed weight increases of this magnitude but only on crude Cm, which contains some C70and other forms of carbon and which has not been subjected to devolatilization by heating (1) Kroto, H. W.; Heath, J. R.; OBrien, S.C.; Curl, R. F.; Smalley, R. Nature 1985, 318, 162. (2) Kratschmer, W.; Lamb, L. D.; Fostiropoulos, K.; Huffman, D. R. Nature 1990, 347, 354. (3) Haufler, R. E.; Conceicao, J.; Chibante, L. P. F.; Chai, Y.; Byrne, N. E.; Flanagan, S.; Haley, M. M.; OBrien, S.C.; Pan, C.; Xiao, Z.; Billup, W. E.; Ciufolini, M. A.; Hauge, R. H.; Margrave, J. L.; Wilson, L. J.; Curl, R. F.: Smallev. R. E. J. Phvs. Chem. 1990. 94. 8634. (4) Lichte&rger, D. L.; Nebesny, K. W.; Ray, C. D.; Huffman, D. R.; Lamb, L. Chem. Phys. Letr. 1991, 176, 203. ( 5 ) Bethune, D. S.;Meijer, G.; Tang, W. C.; Rosen, H. J. Chem. Phys. Lerr. 1990, 174, 219. (6) Frum, C. I.; Engleman, Jr., R.; Hedderich, H. G.; Bernath, P. F.; Lamb, L. D.; Huffman, D. R. Chem. Phys. Lett. 1991, 176, 504. (7) Fowler, P. W.; Lazzeretti, P.; Zanasi, R. Chem. Phys. Lett. 1990,165, 19. (8) Hebard, A. F.; Rosseinsky, M. J.; Haddon, R. C.; Murphy, D. W.; Glarum, S. H.; Palstra, T. T. M.; Ramirez, A. D.; Kortan, A. R. Nature 1991, 350, 35 1. (9) Cox, D. M.; Behal, S.;Disko, M.; Gorun, S.;Greaney, M.; Hsu, C. S.;
Kollin, E.; Millar, J.; Robbins, J.; Robbins, W.; Sherwood, R.; Tindall, P. J . Am. Chem. SOC.1991, 113, 2940. (IO) Holloway, J. H.; Hope, E. G.; Taylor, R.; Langley, G. J.; Avent, A. G.; Dennis, T. J.; Hare, J. P.; Kroto, H. W.; Walton, D. R. M. J. Chem. Soc., Chem. Commun. 1991, 966. (1 1) Heyman, D. Carbon 1991, 29, 684. (12) Hawkins, J. M.; Meyer, A.; Lewis, T. A,; Loren, S.;Hollander, F. J. Science 1991, 252, 312. (13) Chai, Y.; Guo, T.; Jin, C.; Haufler, R. E.; Chibante, L. P. F.; Fure, J.; Wang, L.; Alford, J . M.; Smalley, R. E. J. Phys. Chem. 1991, 95, 7564. (14) Roth, L. M.; Huang, Y.; Schwedler, J. T.; Cassady, C. J.; Ben-Amotz, D ; Kahr, B.; Freiser, B. S . J. Am. Chem. SOC.1991, 113, 6298. (15) Stoddart, J. F. Angew Chem., Int. Ed. Engl. 1991, 30, 70. (16) Milliken, J.; Keller, T. M.; Raronavski, A. P.; McElvany, S. W.; Callahan, J. H.; Nelson, H. H. Chem. Mater. 1991, 3, 386. (17) McKee, D. W. Carbon 1991, 29, 1057. (18) Ismail, I. M. K. ACS Diu. Fuel Chem. 1991, 36, 1026. (19) Vassallo, A. M.; Pang, L. S . K.; Cole-Clarke, P. A.; Wilson, M. A. J . Am. Chem. SOC.1991, 113, 7820. (20) Vassallo, A. M.; Palmisano, A. J.; Pang, L. S . K.; Wilson, M. A. J. Chem. SOC.,Chem. Commun., in press.
0 1992 American Chemical Society
Letters
18 The Journal of Physical Chemistry, Vol. 96, No. 1 , 1992 1 2 0 1 , , , ( , , ,
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graphite, and soot showing weight loss and differential curves at a heating rate of 1 OC/min. Sample weight was about 5 mg;air flow rate was 100 mL/min. is compared with Figure 2. Sample-specific chemical and physical properties determine the weight loss and derivative curves for diamond, graphite, and soot. These curves for C60at 1 "C/min are more symmetrical than at higher heating rates. This results from a complex interaction of initiation and propagation reactions and the diffusion kinetics of oxygen into, and carbon oxides out of, the burning crystal. However, in gross terms the temperature of maximum rate of weight loss at 1 OC/min (444 "C) is much lower than that of diamond (629 "C), graphite (644 OC),and soot (565 "C). This result confirms the importance of conformational strain in enhancing the reactivity of C , toward oxygen. Diamond, graphite, and soot, unlike C,, all contain "dangling" bonds, yet despite this, appreciably higher temperatures are required to establish bulk oxidation in air compared with c 6 0 .
(21) Pan. c . ; SampSOn, M. P.; Chai, Y.; Hauge, J . Phys. Chem. 1991, 95, 2944,
R. H.;Margrave, J. L.
Acknowledgment. The authors thank Mr. Charlie Dawson and Mr. Tom McDonald for the construction of the fullerene generator. The National Energy Research Development and Demonstration Council of Australia is acknowledged for partial support of this work.
