J. Chem. Eng. Data 1994,39,467-469
467
PVT Measurements on Fullerite from 30 to 330 OC and at Pressures to 200 MPa Weisheng Li,t Rex D. Sherwood, Donald M. Cox, and Maciej Radosz' Exxon Research & Engineering Company, Annandale, New Jersey 08801
Specific volumes of CdC70 (3:l) fulleritesare measured up to 330 "C and 200 MPa using a dilatometer-type PVT (pressurevolume-temperature) apparatus. The compressibility and thermal expansion of fullerites are found to be much higher than those of graphite. This is consistent with a lower degree of molecular and supermolecular (crystal) packing in fullerites compared to graphite.
Introduction 1
Fullerene molecules (bucky balls) are ball-like cage analogues of carbon. Their molecular packing and crystalpacking (e.g., face-centered cubic (fcc) for Cm) are less dense than those of graphite and diamond. This is consistent with the difference in density between fullerites and graphite or diamond. Here we use the term "fullerenes" for the molecules, and "fullerites" for the solids. For example, the densities of graphite and diamond are 2.267 and 3.515 gcm3 at 20 "C, respectively (I), while the density of Cm is only 1.65 gcm3 (2, 3). Larger fullerites are even less dense (2, 3). This is because there is more free volume between the cages and inside the cages. Therefore, the compressibilityand thermal expansion of such materials are expected to be much higher than those of graphite and diamond, which are known to be very low. This is consistentwith the isothermalbulk modulus of K/GPa = 18.1 + 5.7P/GPa determined by Duclos et al. (4) on the basis of the ambient-temperaturecompressibilitiesof C a fullerite up to 20 GPa. Also, Fischer and co-workers (5) report that the ambient-temperaturevolume compressibility of solid C a is 7.0 X 10-5 MPa-l, which is 3 and 40 times greater than those of graphite and diamond, respectively. However, there is a solid-solid phase transition (simple cubic to face-centered cubic) for C a at -13 "C a t ambient pressure (6, 7),which shifts to higher temperatures with increasing pressure at a rate of 0.117 KOMPa-l, as measured by Kriza and co-workers (8). This means that, above 350 MPa at ambient temperatures, the phase structure (crystal form) of C a fullerite is different from that at lower pressure. Therefore, the volume changes resulting from changes in pressurehave a contributionfrom the phase transition (similar to melting expansion), in addition to the compressibility contribution. This may indicate that there is a significant error in the results of Fischer and co-workers (5). High-pressure IR spectra (9,IO) show that intramolecular vibrations shift with increasingpressure, due to the reduction in intermoleculardistance. Furthermore,the frequencyshifts are found to be reversible up to 3200 MPa, which suggests that the fullerene cages do not collapse and rearrange themselves below 3200 MPa. Thus, further measurements on the compressibility, expansivity, and phase behavior of fullerites at both elevated temperature and pressure are necessary. It is the objective of this report to determine the fullerite compressibilityand phase behavior at higher temperatures from high-pressure, high-temperature PVT data, and to compare them to those of graphite.
* To whom correspondence should be a d d r d . t Preaent address:
Sun Chemical Corp., Carlstadt, NJ 07072.
0021-9568/94/ 1739-0467$04.50/0
Fullerite
Graphite
Figure 1. Photographs of fullerite and graphite cylinders. Experimental Section Fullerites used in this work are prepared by the carbon electricalarcingtechnique, and isolated by tolueneextraction. The samples contain about 75 mol 75 C a and 25 mol 94 C70 as determined by high-resolution 13C NMR. Graphite is a spectroscopy grade powder (SP-1)from Union Carbide. Sample powders are dried under vacuum at 100 "C for 24 h. Cylindrical samples (diameter 10.0 mm) are formed in a SPECAC die by slowly applying a total force of 2500 kg over a cross-section of 0.785 cm2 (P = 315 MPa) under vacuum. The densitiesof the cylindersare estimated from their lengths and diametersmeasured with a micrometer)and their masses (measured with an analytical balance). Pressure-volumetemperature (PVT) properties of fullerites and graphite are determined in a dilatometer-type PVT apparatus (11)manufactured by Gnomix,Inc. (Boulder, CO). A cylindricalsample with a totalvolume of about 1 cm3 is placed in a chamber with a flexible bellows. The volume in the chamber not taken by the sample is filled with mercury, after evacuation to 4-kPa vacuum. Isothermal compression experiments are conducted in the temperature range of 30350 "C and pressure range of 10-200 MPa, and extrapolated to 0 MPa. The temperature interval is 20 "C, and the residence time at each pressure is 60 s. The manufacturerquoted accuracy is 0.001-0.002 cm3*g1,but the resolution is about 10 times better.
Results and Discussion Pictures of the compressed fullerite and graphite samples are shown in Figure 1. The fullerite density, df, is found to be 1.58 gcm4, and the graphite density, d,, is found to be 2.15 gcm3, at ambient conditions. These values are close to the literature values of 1.65 and 2.267 gcm-3, respectively (I-3),which is our test for achieving good, void-free samples for subsequent PVT experiments. PVT results for fullerites given in Table 1and plotted in
0 1994 American Chemical Society
468 Journal of Chemical and Engineering Data,
Table 1. Isothermal PVT Results for C&,O GiventandPis V o + A v ) tl"C 30.0 30.0 30.0 29.8 29.9 30.0 30.0 30.0 29.9 29.9 29.8 29.9 29.9 30.0 30.0 30.0 29.9 29.9 29.9 29.9 29.9 51.1 51.1 51.1 50.9 50.8 50.7 50.7 50.7 50.7 50.7 50.7 50.7 50.7 50.7 50.7 50.7 50.7 50.7 50.6 50.7 50.8 71.4 71.3 71.5 71.5 71.5 71.4 71.4 71.4 71.5 71.5 71.5 71.5 71.4 71.5 71.5 71.5 71.5 71.5 71.5 71.5 71.4 91.1 91.2 91.5 91.6 91.7 91.6 91.6 91.8 91.8 91.8 91.8 91.8 91.9 91.8 91.8 91.8 91.8 91.8 91.8 91.8 91.9
PIMPa 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 0 10 20 30 40 50 60 70
80 90 100 110 120 130 140 150 160 170 180 190 200 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
AVI(cm3.g-1) 0.0017 0.0002 -0.0015 -0.0028 -0.0038 -0.0048 -0.0058 -0.0068 -0.0077 -0.0086 -0.0095 -0.0103 -0.0112 -0.0119 -0.0127 -0.0134 -0.0141 -0.0148 -0.0155 -0.0162 -0.0168 0.0008 -0.0003 -0.0014 -0.0026 -0.0037 -0.0048 -0.0058 -0.0067 -0.0076 -0.0084 -0,0093 -0.0102 -0.0110 -0.0117 -0.0125 -0.0132 -0.0140 -0.0146 -0.0153 -0.0160 -0.0167 0.0014 0.0003 -0.0009 -0.0021 -0.0032 -0.0042 -0.0053 -0.0062 -0.0071 -0.0080 -0.0089 -0.0097 -0.0106 -0.0113 -0.0121 -0.0128 -0.0135 -0.0142 -0.0149 -0.0155 -0.0162 0.0025 0.0013 0.0002 -0.O009 -0.0020 -0.0031 -0.0041 -0.0050 -0.0059 -0.0067 -0.0076 -0.0084 -0.0092 -0.0099 -0.0106 -0.0113 -0.0120 -0.0128 -0,0134 -0.0141 -0.0147
Vol.39,No. 3, 1994
( 3 1 ) Fullerites ( VO = 0.632 cma.glat 25 O C and 0.1 MPa, Specific Volume at
t/"C
PIMPa
110.9 110.9 111.2 111.4 111.5 111.6 111.7 111.8 112.0 112.1 112.2 112.3 112.3 112.2 112.3 112.3 112.3 112.3 112.3 112.4 112.3 130.9 130.9 131.2 131.3 131.5 131.7 131.8 132.0 132.2 132.3 132.4 132.6 132.7 132.8 132.9 133.0 132.9 132.9 132.9 132.9 132.9 150.8 150.8 151.3 151.4 151.4 151.5 151.6 151.9 152.0 152.2 152.5 152.7 152.9 153.0 153.1 153.3 153.5 153.7 153.7 153.7 153.7 170.9 170.9 171.4 171.5 171.5 171.5 171.8 171.9 172.0 172.2 172.4 172.6 172.9 173.0 173.2 173.4 173.5 173.6 173.8 174.0 174.1
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
AV/(cma.g*) 0.0042 0.0031 0.0020 0.0009 -0.0003 -0.0014 -0.0023 -0.0033 -0.0042 -0.0051
-0.o060 -0.0069 -0.0077 -0.0084 -0.0091 -0.0099 -0.0106 -0,0113 -0.0121 -0.0127 -0.0134 0.0079 0.0066 0.0054 0.0041 0.0028 0.0016 0.0005 -0,0005 -0.0015 -0.0025 -0,0034 -0.0043 -0.0052 -0.0061 -0.0069 -0.0077 -0.0084 -0,0092 -0.0100 -0,0107 -0.0114 0.0112 0.0098 0.0084 0.0071 0.0057 0.0044 0.0032 0.0021 0.0010 -0.0001 -0.0011 -0,0021 -0.0031 -0.0040 -0.0048 -0.0057 -0.0065 -0.0073 -0.0082 -0.0090 -0.0098 0.0153 0.0136 0.0120 0.0104 0.0090 0.0075 0.0062 0.0049 0.0037 0.0025 0.0014 0.0003 -0.O008 -0.0017 -0.0028 -0,0038 -0.0047 -0.0056 -0.0064 -0.0073 -0.0081
tl"C
PIMPa
191.0 191.1 191.6 191.7 191.7 191.7 191.7 191.9 192.1 192.2 192.5 192.6 192.9 193.1 193.4 193.6 193.8 194.0 194.1 194.3 194.3 210.9 210.9 211.5 211.8 211.7 211.9 212.1 212.2 212.4 212.6 212.8 212.7 212.7 212.9 213.0 213.2 213.5 213.8 214.0 214.3 214.4 230.7 230.6 231.4 231.8 231.9 232.0 232.3 232.4 232.6 232.9 232.9 232.9 232.9 233.1 233.1 233.3 233.5 233.7 234.0 234.3 234.6 250.4 250.3 251.2 251.9 252.1 252.4 252.5 252.5 252.6 252.7 253.0 253.1 253.4 253.6 253.5 253.5 253.7 253.8 254.0 254.1 254.4
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
AV/(cm*.gl) 0.0201 0.0182 0.0165 0.0147 0.0130 0.0115 0.0100 0.0086 0.0072 0.0059 0.0045 0.0034 0.0021 0.0009 -0.0002 -0.0013 -0.0025 -0.0035 -0.0045 -0.0055 -0.0064 0.0256 0.0233 0.0211 0.0190 0.0171 0.0153 0.0137 0.0122 0.0108 0.0094 0.0079 0.0064 0.0050 0.0036 0.0023 0.0010 -0.0002 -0.0014 -0.0025 -0.0036 -0.0046 0.0301 0.0273 0.0247 0.0223 0.0203 0.0182 0.0164 0.0148 0.0132 0.0118 0.0103 0.0089 0.0076 0.0063 0.0049 0.0036 0.0023 0.0010 -0.0001 -0.0013 -0.0025 0.0342 0.0309 0.0278 0.0251 0.0228 0.0206 0.0187 0.0168 0.0151 0.0135 0.0119 0.0106 0.0092 0.0079 0.0066 0.0053 0.0041 0.0030 0.0018 O.OOO6
-0.0006
t/"C
270.1 270.2 271.1 271.7 272.0 272.3 272.4 272.5 272.8 272.9 273.2 273.6 273.7 273.7 273.7 273.8 274.0 274.1 274.3 274.5 274.7 289.9 298.8 290.5 291.2 291.7 292.2 292.5 292.7 293.1 293.2 293.5 293.6 293.7 294.1 294.3 294.5 294.3 294.3 294.4 294.5 294.7 310.1 310.1 311.0 311.6 312.1 312.6 313.0 313.5 313.7 313.8 313.9 314.0 314.2 314.5 314.7 314.8 314.7 314.8 314.9 315.1 315.2 330.7 330.8 331.5 332.2 332.7 333.4 333.8 334.3 334.6 334.8 334.9 335.0 335.0 335.2 335.3 335.6 335.8 336.0 335.9 335.9 335.9
PIMPa 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 0 10 20 30 40 50 60 70 80
90 100 110 120 130 140 150 160 170 180 190 200 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
AV/(cma.gl) 0.0389 0.0349 0.0311 0.0279 0.0253 0.0228 0.0207 0.0187 0.0168 0.0152 0.0137 0.0121 0.0107 0.0093 0.0081 0.0068 0.0056 0.0044 0.0034 0.0023 0.0011 0.0443 0.0392 0.0345 0.0305 0.0276 0.0251 0.0227 0.0206 0.0186 0.0168 0.0150 0.0133 0.0119 0.0104 0.0090 0.0078 0.0064 0.0051 0.0040 0.0028 0.0016 0.0500 0.0437 0.0378 0.0335 0.0302 0.0273 0.0243 0.0221 0.0199 0.0180 0.0161 0.0143 0.0127 0.0111 0.0096 0.0081 0,0068 0.0055 0.0042 0.0029 0.0018 0.0570 0.0484 0.0403 0.0354 0.0315 0.0284 0.0255 0.0230 0.0207 0.0182 0.0162 0.0142 0.0125 0.0108 0.0093 0.0077 0.0063 0.0049 0.0036 0.0023 0.0010
Journal of Chemical and Engineering Data, Vol. 39, No. 3, 1994 469 0.055
I
I
0.045 0.035
0
O'Oi5 \ 0005 . ... v h
$
>I -0.005 v -0.015
p/
t
1
i
c -0.0254L'
fullerites graphite
P=O.lMPa
P=200MPa
t=50°C
t=250°C
2.7 X 10"' 0.9 X 10-4
1.3 X 10-4
1.4 X lo-' 1.2 X lo-'
2.6 X 10-4 1.9 X lo-'
0.2 X 10-4
thermal expansion (a)values are given in Table 2. They are calculated from the following formulas:
P d
1
Table 2. Compressibility and Thermal Expansion of Fullerites and Graphite a/K-l(5&250 "C) fl/MPa-1(&200 MPa)
-(-)
a = 1 AV V, ATP I
'
I
" I
70
'
100
'
I
" I
130
160
'
'
'
I
"
190 220
t/Oc
'
I
250
"
280
" I
'
310
"
340
Figure 2. Isobars for fullerites. From top to bottom, 10,50, 100,150, and 200 MPa. 1
I
0.015 0.005
A previous study suggests that fulleritesare extremely hard (4). We find that this can only be true to extremely high
pressures. At low and moderate pressures (up to several hundred megapascals), the free volumes between the carbon cages should contribute tremendous compressibility and thermal expansion, as shown in our data. Conclusions
-0.005
On the basis of specific volumes for CBO/C.IO (3:l) fullerites and graphite, measured up to 340 "C and 200 MPa, fullerite compressibilities and thermal expansions are found to be much higher than those of graphite. While graphite exhibits little isobaric thermal expansion at pressures above 10 MPa, fullerites exhibit significant and monotonic expansion. This is consistent with a lower degree of molecular and supermolecular packing in fullerites compared to graphite.
h
0.015
Acknowledgment
We thank B. Liang and J. Millar for conducting the 1sC NMR measurements. Literature Cited
t
I
do ' d o ' 120 ' 140 ' 160 ' 150 ' d o P/MPa Figure 3. Comparison of isothermal compressibility of fullerites (bottom two curves with open squares for 250 "C and filled squares for 50 "C) and graphite (top two curves with open circles for 250 "C and filled circles for 50 "C). -0.0Z5
d
'
do '
a0 ' 60
'
Figure 2 indicate considerable compressibility and thermal expansion. These results are measured isothermally starting at lowtemperatures. Compressibilityis found to be reversible; i.e., after reducing pressure at each temperature, the specific volume is restored to its initial low-pressurevalue. This means that the major contribution to the compressibility is from the material, not from possible porosity. Within the temperature range of 40-340 "C, there is no significant phase transition found at both ambient pressure and 200 MPa. Thermal expansion at each pressure shows an almost linear increase, as demonstrated in Figure 2. Figure 3 presents a comparison of two isotherms for fullerites and graphite with the same scales for the y axes. Fullerites are much more compressible than graphite (AV = -0.018 versus -0.011 cm3.g-1 at 50 "C and -0.035 versus -0.018 cm3.g-1 at 250 "C, respectively). Also,there is a large difference in thermal expansion. For example, for fullerites,the volume expansion is +0.031 cm3.g' in going from 50 to 200 OC at 10 MPa. By contrast, the corresponding expansion for graphite is only +0.007 cm3.g-*. A few average compressibility (8) and
(1) Dean, J. A. Lange's Handbook of Chemistry,13th ed.; McGrawH i k New Jersey, 1985; pp 2-3. (2) Kratschmer, W.; Lamb, L. D.; Fostiropoulos, K.; Huffman, D. R. Nature 1991, 347, 354-357. (3) Ruoff, R. S.;Thornton, T.;Smith, D. Chem. Phys. Lett. 1991,186, 456-458. (4) Duclos, S. J.; Brister, K.; Haddon, R. C.; Kortan, A. R.; Thiel, F. A. Nature 1991,351, 380-382. (5) Fischer, J. E.; Heiney, P. A.; McGhie, A. R.; Romanow, W. J.; Denenstein, A. M.; McCauley, J. P.; Smith, A. B., 111. Science 1991, 252, 1288-1290. (6) Dworkin, A,; Szwarc, H.; Leach, S.;Hare, J. P.; Dennis, T. J.; Kroto, H. W.; Taylor, R.; Walton, D. R. M. C.R. Acad. Sci. 111991, t.312, 979-982. (7) Tse, J. S.;Klug, D. D.; Wilkinson, D. A.; Handa, Y. P. Chem. Phys. Lett. 1991, 183,387-390. (8) Kriza, G.;Ameline, J.-C.;Jerome, D.;Dworkin,A,;Szwarc,H.; Fabre, C.; Schutz, D.; Rassat, A.; Bernier, P.; Zahab, A. J.Phys. I1991,1, 1361-1 364. (9) Aoki,K.;Yamawaki,H.;Kakudate,Y.;Yoshida,M.;Usuba,S.;Yokoi, H.; Fujiwara, S.; Bae, Y.; Malhotra, R.; Lorenta, D. J.Phys. Chem. 1991, 95, 9037-9039. (IO) Huang, Y.; Gilson, D. F. R.; Butler, 1. S. J. Phys. Chem. 1991,95, 5723-5725. (11) Zoller, P.; Bolli, P.; Pahud, V.; Ackermann, H. Reu. Sci. Instrum. 1976,47,948-952. Received for review August 17, 1993. Accepted February 3, 1994.0 a
Abstract published in Advance ACS Abstracts, March 1, 1994.
