Thermal expansion of coronene C24H12 at 185–416 K

Konstantin D. Litasov • Pavel N. Gavryushkin •

Alexander S. Yunoshev • Sergey V. Rashchenko •

Talgat M. Inerbaev • Abdirash T. Akilbekov

Received: 12 April 2014 / Accepted: 15 October 2014

� Akademiai Kiado, Budapest, Hungary 2014

Abstract The coefficient of the thermal expansion of

P21/a coronene was measured using X-ray diffraction in

the temperature range from 185 to 416 K. It increases with

increasing temperature from 4.8 9 10-5 K-1 at 185 K to

4.9 9 10-4 K-1 at 416 K. At 298 K, a = 1.9 9 10-4 K-1.

In the temperature interval between 298 and 416 K, the

thermal expansion can be described by equation a =

-6.66 9 10-4 ? 2.72 9 10-6 T ? 4.62 T-2. Comparison

with previous data indicates that the thermal expansion of

PAHs decreases with an increasing amount of benzene rings

in their structure.

Keywords Coronene � Polycyclic aromatic

hydrocarbons � Thermal expansion � Thermodynamics

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are widespread

in natural environments and are extremely important for

physical chemistry and industrial applications. In nature,

they form by incomplete combustion and pyrolysis of

various organic materials. PAHs are present in coals, car-

bon black, crude oil, soot, soil, automobile exhaust, ciga-

rette smoke, and even in fried food [1]. Considerable

efforts have been made to monitor the concentrations of

PAHs because of their adverse effect on human health.

PAHs also occur as individual minerals accompanying ore

deposits; coronene (C24H12) comprises a major part of

carpathite (up to 100 %) and pendletonite (up to 99 %)

[2, 3]. In addition, PAHs are abundant in meteorites and

interstellar matter [4–8], where they probably form by

Fischer–Tropsch-type reactions in the solar nebulae at

about 1,300 K. The reactions involve CO, H2, CH4, and

possibly proceed at surfaces of dust grains using their

materials as catalysts. Along with other hydrocarbons,

PAHs may play a significant role in deep-seated fluids of

the Earth and planetary interiors. Evidence for the forma-

tion of PAHs at high pressures and temperatures comes

from their inclusions in deep-seated diamond and garnet

from kimberlites originated at depths of 150–250 km

below the Earth’s surface [9, 10].

The physical chemistry of PAHs and their derivatives

has been gaining an increased attention due to charge

transport and light-emitting capabilities in ordered films

and clusters, with a potential for application in optics and

organic electronics [11–13]. Exposure of organic crystals

to pressure and temperature can change the interatomic and

intermolecular distances resulting in phase transitions and

formation of new types of compounds such as conductive

phases formed in pentacene at 27 GPa [14] and those

predicted for benzene at extreme conditions of 190 GPa

[15]. In case of coronene, a very important feature can be

its application for estimating the resonance and bond

energy of fullerenes [16]. In addition, the relatively open-

K. D. Litasov (&) � P. N. Gavryushkin � S. V. Rashchenko

V.S. Sobolev Institute of Geology and Mineralogy, SB RAS,

3 Ac. Koptyuga Ave., Novosibirsk 630090, Russia

e-mail: klitasov@igm.nsc.ru

K. D. Litasov � P. N. Gavryushkin � A. S. Yunoshev �S. V. Rashchenko

Novosibirsk State University, 2 Pirogova St.,

Novosibirsk 630090, Russia

A. S. Yunoshev

M.A. Lavrentyev Institute of Hydrodynamics, SB RAS,

15 Lavrentieva Ave., Novosibirsk 630090, Russia

T. M. Inerbaev � A. T. Akilbekov

L.N. Gumilyov Eurasian National University, 2 Mirzoyana St.,

Astana 010008, Kazakhstan

123

J Therm Anal Calorim

DOI 10.1007/s10973-014-4253-x

shell molecular units of PAHs allow modification of con-

ductive properties by doping a pure phase with electron

donors and acceptors. The recent discovery of supercon-

ductivity in potassium-doped picene (C22H12) [17] revealed

an importance of studying the electronic structures of other

PAHs, especially at high pressures.

Coronene is a key PAH also referred to as superbenzene

due to the formation of a complete benzene ring circle

around a single ring. Its structure at an ambient pressure is

monoclinic with space group P21/a [3, 18]. The intermo-

lecular interactions of crystalline coronene are dominantly

non-local van der Waals forces [19]. A comprehensive

review of the thermochemical properties of coronene was

presented in [20], whereas its low-temperature heat

capacity was investigated by Wong et al. [21]. These

authors suggested a phase transition at 215–250 K resulting

in irreproducible heat capacity anomalies and another

phase transition at 140–180 K and near 50 K resulting in

significant changes of polarized luminescence spectra.

The pressure-induced transitions in coronene from

monoclinic to orthorhombic structure were suggested at

1 GPa [22], whereas Fourier transform infrared spectros-

copy experiments revealed a phase transition between 2.0

and 3.2 GPa [23]. In a recent work, Zhao et al. [24] argued

for a transition from P21/a to P2/m at 1.5 GPa and to Pmmm

at 12.2 GPa. However, no precise structural data for the high

pressure modifications were reported. At pressures above

30.5 GPa, coronene appeared to be amorphous [24]. On the

contrary, the Raman spectroscopy data presented in [24]

indicate phase transitions at 1.3 and 3.7 GPa. Thus, there is a

range of inconsistent phase transitions in coronene, which

can be caused by the use of different pressure media and

should be clarified in future studies at high pressures.

Although the thermal analysis has been applied for a

range of very complex compounds of technological appli-

cation [25, 26], simple organics, such as PAHs, have been

scarcely measured to characterize their solid and fluid

properties. In this paper, we present results of thermal

expansion measurements of P21/a coronene in comparison

with previously obtained measurements of PAHs and other

hydrocarbons.

Experimental

We used commercially available fluffy coronene aggre-

gates (Sigma-Aldrich, 99.9 %) consisting of needle-like

crystals as a starting material. The material was powdered

and mixed with CaF2 internal standard to monitor tem-

perature measurements by a thermocouple, since its posi-

tion was not exactly the same as that of the sample. This is

of special importance for high-temperature measurements

as at that we can expect a significant temperature gradient.

Low- and high-temperature X-ray diffraction experi-

ments were carried out using a Bruker D8 Advance dif-

fractometer, Cu Ka radiation, equipped with a vacuum

camera (Anton Paar TTK 450), a Temperature Control Unit

(Anton Paar TCU 100), and Nitrogen Suction Device

(Anton Paar LNC). During the experiment, the temperature

was monitored by a Pt thermometer placed close to sample.

Then, it was recalculated based on the unit cell parameter

of CaF2 standard, which was calibrated using the data from

[27]. The unit cell parameters were calculated using Win-

Plotr software [28].

Three diffraction patterns were collected at 2h intervals

of 8.5–13�, 17–19.5�, and 21.5–30� for each temperature.

This technique was used to increase the duration of accu-

mulation for measuring the last 2h interval angle, because

the three most critical peaks for the determination of cell

parameters of coronene fall within these intervals. These

peaks are (31�1), (21�2), and (41�1). Due to the strong pre-

ferred orientation of the sample, the intensities of these

peaks are very low. Therefore, relatively long diffraction

experiments are necessary for precise determination of

peak positions. In addition, before the X-ray diffraction

experiments, we performed the thermogravimetric (TG)

analysis of coronene using a Mettler TA300 system. A

3.3 mg specimen was heated in a Pt crucible from room

temperature to 723 K at a constant rate of 0.05 K s-1.

Results and discussion

Figure 1 shows results of TG measurements. The loss of

mass starts at 473 K, whereas intensive sublimation pro-

ceeds at temperatures higher than 573 K. The initial cor-

onene almost completely disappeared at 693 K. Thus, the

sublimation of coronene occurs at a significantly lower

2500

20

40

60

80

100

350 450

Temperature/K

Mas

s/m

ass%

550 650 750

Tm

= 7

11 K

Fig. 1 TG measurements of coronene. Tm—melting temperature

K. D. Litasov et al.

123

temperature than its melting point (709–711 K). The X-ray

diffraction measurements in a vacuum camera revealed a

significant sublimation of coronene at a lower temperature

of 450 K suggesting kinetic effect of sublimation, i.e.,

during the TG experiment, the heating of the sample was

much faster than during the X-ray diffraction experiment.

The X-ray diffraction patterns were obtained in the

temperature interval between 185 and 416 K (Table 1).

The lower limit of the temperature interval was chosen

according to the stability of P21/a coronene. The diffrac-

tion patterns of coronene contained 12–17 prominent peaks

of P21/a structure (Figs. 2, 3). The absence of significant

Table 1 Relationship between temperature and unit cell parameters, thermal expansion coefficient (a), and thermal Gruneisen parameter (cth) of

coronene

TCaF2/K aCaF2

/A a/A b/A c/A b/o V/A3 a/10-4 K-1 cth

185 5.4524 16.008(3) 4.681(1) 10.052(2) 110.72(2) 704.52(20) 0.48 1.72

205 5.4542 16.014(2) 4.682(1) 10.055(2) 110.73(2) 705.02(16) 0.60 1.90

235 5.4569 16.025(2) 4.684(1) 10.060(2) 110.74(2) 706.12(23) 0.87 2.34

254 5.4586 16.043(2) 4.685(1) 10.066(2) 110.78(2) 707.37(17) 1.15 2.82

268 5.4600 16.058(2) 4.688(1) 10.073(2) 110.82(2) 708.76(18) 1.35 3.13

274 5.4614 16.073(3) 4.690(1) 10.076(2) 110.86(2) 709.74(18) 1.48 3.34

279 5.4611 16.081(2) 4.692(1) 10.077(2) 110.89(2) 710.26(23) 1.60 3.55

289 5.4621 16.100(3) 4.693(1) 10.082(2) 110.92(2) 711.54(20) 1.76 3.75

298 5.4631 16.131(3) 4.695(1) 10.095(2) 110.99(2) 713.88(19) 1.93 3.99

303 5.4636 16.137(5) 4.695(2) 10.096(2) 111.00(2) 714.12(24) 2.10 4.28

316 5.4650 16.163(5) 4.698(2) 10.103(2) 111.07(2) 715.99(24) 2.43 4.74

344 5.4680 16.235(5) 4.704(2) 10.130(2) 111.27(3) 720.89(24) 3.07 5.53

377 5.4717 16.346(5) 4.712(2) 10.162(2) 111.53(2) 727.98(24) 3.90 6.53

404 5.4747 16.507(5) 4.717(3) 10.207(2) 111.80(2) 737.90(36) 4.62 7.41

416 5.4762 16.571(7) 4.721(2) 10.232(2) 111.85(3) 742.94(26) 4.92 7.77

TCaF2and aCaF2

, the temperature, and unit cell parameter estimated using CaF2 standard. One standard deviation is shown in parentheses

9

Inte

nsity

/arb

itrar

y un

its

10

001

200

201

201

202

002

401298 K

289 K

279 K

274 K

268 K

254 K

235 K

205 K

185 K

210

211

400

402

311

202

310

212

411

111

CaF

2

11 12 13 18 19

2θ/°

22 23 24 25 26 27 28 29

Fig. 2 X-ray diffraction patterns of coronene at temperatures below 298 K

Thermal expansion of coronene

123

changes in the diffraction patterns of coronene in the

studied temperature interval indicates the absence of phase

transitions.

The calculated unit cell parameters are shown in

Table 1. Figure 4 illustrates the relationship between the

volume of unit cell and the temperature or the coefficient of

thermal expansion. The coefficient of thermal expansion

(a) is calculated by equation:

a ¼ 1

V

oV

oTð1Þ

Coefficient a increases with the increasing temperature

from 4.8 9 10-5 K-1 at 185 K to 4.9 9 10-4 K-1 at 416 K.

At 298 K, a = 1.9 9 10-4 K-1. In the 298–416 K interval

the thermal expansion can be calculated by equation: a =

-6.66 9 10-4 ? 2.72 9 10-6 T ? 4.62 T-2 (Fig. 4).

Using the heat capacity (CP) data for coronene from [20, 21]

and the calculated isothermal bulk modulus KT = 7.6 GPa

(original data), we can estimate a thermal Gruneisen parameter

by equation:

cth V ; Tð Þ ¼ aKTV

CV

; ð2Þ

where CV = CP - a2KTV. In the 185–416 K temperature

range the parameter cth of coronene varies from 1.7 to 7.8

(Table 1).

Coronene is characterized by anomalous axial thermal

expansion. The variations of the unit cell parameters of

9

Inte

nsity

/arb

itrar

y un

its

10

001

200

201

201

202

002

400

212

111

411

CaF

2

311

202

310

11 12 13 18 19

2θ/°22

303 K

316 K

344 K

377 K

404 K

416 K

440 K

23 24 25 26 27 28 29

Fig. 3 X-ray diffraction patterns of coronene at temperatures above 298 K

100700 0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

710

720

730

740

750

200 300Temperature/K

V/Å

3

Temperature/K

α/1

0–4 K

–1

400 500 100

NaphthaleneAnthracene

0 200 300 400 500

(a) (b)

Fig. 4 Relationships between temperature and the volume of unit cell

(V) and the coefficient of volumetric thermal expansion (a) of

coronene. The quadratic equation fit of data is shown as a black line.

The coefficients of thermal expansion for naphthalene and anthracene

were calculated using the data from [29] and [30], respectively

K. D. Litasov et al.

123

coronene depending on temperature are plotted in Fig. 5.

The volumetric coefficient of thermal expansion calculated

using fictive unit-cell volumes, i.e., a3, b3, and c3 along the

longest axis aa is four times higher than ab and two times

higher than ac at 298 K (Fig. 6).

The available data on the thermal expansion of different

classes of solid hydrocarbon materials are very limited. The

thermal expansion was measured for naphthalene [29] and

anthracene [30] in a limited range of temperatures and an

insufficient amount of data points. In addition, the coeffi-

cients of thermal expansion were measured in deuterated

naphthalene and anthracene [31–33]. Deuterated naphtha-

lene and anthracene are characterized by slightly lower, but

very consistent thermal expansion compared to their

10010.02

10.06

10.10

10.14

10.18

10.22

10.26

15.9

16.0

16.1

16.2

16.3

16.4

16.5

16.6

16.7

200 300

Temperature/K

c/Å

a/Å

β/°

b/Å

400 500 100110.6

110.8

111.0

111.2

111.4

111.6

111.8

112.0

4.67

4.68

4.69

4.70

4.71

4.72

200 300

Temperature/K400 500

100 200 300 400 500 100 200 300 400 500

(a) (b)

(c) (d)

Fig. 5 Relationship between the temperature and the unit cell parameters of coronene

1000.995

1.005

1.015

1.025

1.035

200 300

Temperature/K

d/d 1

85

a/a185

b/b185

c/c185

400 500 1000

2

4

6

8

10

12

200 300

Temperature/K

α/1

0–4 K

–1

400 500

(a) (b)

αa

αb

αc

Fig. 6 Relationships between temperature, the relative axial expansion (T = 185 K was chosen as a zero value) (a), and the coefficient of

thermal expansion calculated from fictive volumes of unit cells along crystallographic directions (b)

Thermal expansion of coronene

123

hydrogen-bearing analogs. A comparison between coron-

ene and other PAHs shows that thermal expansion

decreases with an increasing number of carbon atoms

(molecular mass, benzene rings) (Fig. 4). This is consistent

with the data obtained from alkanes [34]. If the number of

carbon atoms in an alkane increases from 10 to 76, the

coefficient of thermal expansion at 298 K decreases from

1 9 10-3 to 3 9 10-4 K-1 [34]. These data indicate that

alkanes possess higher thermal expansion relative to the

studied PAHs at the same molecular mass or the same

number of carbon atoms.

The data on thermal expansion will be used as a proxy

for calculating the experimental and theoretical P–V–

T equations of state for coronene by analogy with a recent

study of naphthalene at high pressures and temperatures

[35]. The drastic decrease of the thermal expansion of

naphthalene takes place in a pressure range from 0 to

1–2 GPa [35]. We would like to apply these techniques and

data for other PAHs including coronene in future studies.

Conclusions

Parameters of thermal expansion of P21/a coronene were

measured using the X-ray diffraction method in the tem-

perature range from 185 to 416 K. The thermal expansion

in the temperature interval between 298 and 416 K can be

described by equation a = -6.66 9 10-4 ? 2.72 9

10-6T ? 4.62T-2. We compared the thermal expansion

data obtained for coronene with that for naphthalene and

anthracene and showed that the thermal expansion of PAHs

can decrease with an increasing amount of benzene rings in

their molecular structure.

Acknowledgements This work is supported by Ministry of Edu-

cation and Science of Russian Federation (No. 14.B25.31.0032) and

Russian foundation for basic research (No. 12-05-00841).

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Thermal expansion of coronene

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