Pierre Figuiere

Pressure-volume-temperature relations for crystalline benzene

Abstract It is shown that a modified Bridgman sylphon method can be used to directly measure PVT data of reorientational solids. PVT properties of crystalline benzene are determined from −20 to 51°C to pressures up to 500 MPa (5 kbar). Isochoric paths of solid benzene are found to be linear and parallel in this range. Their mean slope value is in very good agreement with that we previously predicted from Raman spectroscopy experiments. From these results, it can be concluded that thermodynamic behaviour of reorientational crystalline benzene may be described in terms of a cubic crystal equation of state.

Calorimetric study of thiophene from 13 to 300 K. Emergence of two glassy crystalline states

Abstract Heat capacities of stable and metastable phases of thiophene crystal were measured in the 13 to 300 K temperature range with an on-line automated adiabatic calorimeter. The enthalpies and entropies of the transitions and fusion that occurred at the following temperatures were measured: The condition of existence and the precise temperature of the II 2 -to-II 1 phase transition were found. A glass-transitional behaviour was observed around 42 K for the stable V phase and around 37 K for the metastable II 2 phase. Thermodynamic properties in the crystal and liquid states were calculated from our calorimetric results. Comparison of the calorimetric entropy with the spectroscopic value shows that the stable V phase has a residual entropy of (1.25 ± 0.9) J·K −1 ·mol −1 and the metastable II 2 phase one of (1.48 ± 0.9) J·K −1 ·mol −1 . Thus, both stable and metastable phases of thiophene crystal provide new examples of glassy crystals.

High pressure calorimetry as applied to piezothermal analysis

This paper describes an apparatus which can be used to determine bulk thermal expansion coefficients of liquids as a function of temperature and pressure up to 10 kilobar in a temperature range from −20° to 100 °C. The principle of the method consists in measuring the heat of compression by a step by step procedure. The apparatus is a Joule twin calorimeter which is composed of a high pressure vessel and a reference cylinder. Temperature differences between these two components can be detected at better than 10−5 K by means of a gas thermometer, thus providing high sensitivity. Results are given for liquid n‐hexane and ethyl alcohol.

A magnetic-suspension apparatus to measure densities of liquids as a function of temperature at pressures up to 100 MPa Application to n-heptane

A densimeter designed for high-pressure work has been constructed. Densities of liquids have been measured with an accuracy of 0.2 per cent through the determination of the buoyancy of a magnetic float immersed in the samples. Thanks to a microbalance, a dynamic method is used to measure the total downward force of the magnetic-suspension system and of the floating buoy. The density of n-heptane has been determined from 298.15 to 373.15 K at pressures up to 100 MPa. Our results are compared with those previously published.

Heat capacities, enthalpies of transition, and thermodynamic properties of the three solid phases of p-dichlorobenzene from 20 to 330 K

Abstract The heat capacity of para -dichlorobenzene was measured by means of adiabatic calorimetry between 20 and 330 K. Two phase transitions were found at 271.77 and 304.35 K with transition enthalpies of (1256±4) and (214.5±0.9) J mol −1 respectively. Melting occurs at 326.155 K with ΔH = 18187 J mol −1 . Thermodynamic functions were calculated from these results. At 298.15 K, the heat capacity at saturation pressure C s , the entropy S o , and the function {G o (T)−H o (0)} T are 144.76, 174.49, and −88.25 J K −1 mol −1 , respectively. The third-law entropy of the gas under standard conditions is (336.54±1.5) J K −1 mol −1 .

First-order phase diagram of thiourea and raman spectroscopy

Abstract In this paper, the first-order phase diagram of thiourea has been determined by means of low-frequency Raman spectroscopy. This high-pressure phase (phase HP) previously discovere by Bridgman has been shown to be different from any of the five low-pressure modifications. But thermodynamical data derived from the phase diagram show that phase HP should be orthorhombic too. They also prove that a negative volume change accompanies the transition from the low-temperature ferroelectric phase to phase II. No conclusion concerning an eventual ferroelectric behaviour of phase HP could be drawn.

Raman Spectra in Molecular Solids: III.—Determination of the Phase Diagram of Solid P-Dichlorobenzene by High Pressure Raman Spectroscopy: Spoliation of the α-Phase

Abstract We have determined the phase diagram of solid p-dichlorobenzene by means of Raman spectroscopy up to five kilobars and we have shown that the triple point previously predicted between the three solid phases exists. The thermodynamical data for the different phase transitions are determined. We described a pressure treatment to get the equilibrium pressures at the transitions; this treatment shows that the “zone of indifference” can be diminished whereas the hysteresis range seems to be intrinsic to the solid sample. The explanation seems to lie in local stresses existing in the polycrystalline sample.

Thermodynamics of Molecular Reorientationally Disordered Phases at High Pressure

Abstract Thermodynamic properties of solid benzene and furan are investigated through Swensons equaiotn of state. It is found that those two solids, in their dynamic disordered state, behave like cubic crystals from the thermodynamic point of view. In particular, this means that the crystal lattice configuration remains constant at constant volume, which is supported by previous high pressure low frequency Raman measurements. This behaviour seems to be restricted to the reorientationally disordered phases. The relations between thermodynamics, local crystal configuration and dynamic disorder in molecular crystals is discussed in terms of atom-atom pair wise potentials, Frenkels model of molecular reorientations between discrete wells and the rotational diffusion model.