An On-line Automated Adiabatic Calorimeter in the 13–300 K. Heat Capacity of Cyclohexanol

Abstract

A computerized adiabatic calorimeter system operating in the temperature range 13–300 K is described. A digital voltmeter is used for energy measurement and the duration of energy input is determined by a program unit operated by 1 Hz pulse. Temperatures of the calorimeter are measured by a 25 Ω platinum resistance thermometer and an automated ac double bridge. The measured resistance is converted into temperature (IPTS-68) by a calibration table stored in a mini-computer. Criterion for the realization of thermal equilibration is that a temperature drift calculated from the latest six data becomes smaller than a preset value, usually 7×10−8 Ω s−1. The system is able to measure the heat capacity of solid and liquid in an intermittent heating mode and gives the computed results during measurement. Some examples of the test runs on cyclohexanol crystal are shown and the results are compared with those obtained by manual measurements by use of dc Müller bridge. A relaxational heat capacity anomaly observed in glassy crystalline state of cyclohexanol is discussed in correlation with a secondary relaxation observed by previous dielectric measurement.

The configurational entropy theory and the heat capacity decrease of orientationally disordered crystals on cooling to 0K

“…Hence, orientationally disordered crystals are said to supercool to a glass-like state, with the onset temperature T g;odcrys of the C p increase analogous to T g . A similar manner of C p increase has also been observed on heating TlNO 2 crystals (Moriya et al 1983), but here it was attributed to the increase in the anharmonicity of molecular librations when an increase in the population of point defects and in their di usion rate raised the probability of the vacancy or other defects reaching a lattice site next to the librating molecule (Johari et al 2000). In this case, the defect di usion rate seems to determine the temperature range of the sigmoid-shape C p increase.…”

“…Structural relaxation of the kinetically frozen crystal, as of all glasses, decreases its C p , H and S at a rate that increases with increasing T (Kishimoto et al 1980). Therefore it is expected that, for curve I, the dC p minimum would decrease.…”

Study of supercooled orientationally disordered binary solid solutions II: cyclohexyl derivatives, neopentanol and neopentylglycol

“…More experiments at ultralow frequencies with a better resolution is expected to resolve this issue. 41 and Kishimoto et al 77 Adachi et al 80 have attributed this process to the rotation of -OH bonds on the grounds that the activation energy is similar to the energy of hydrogen bond. Kuhns and Conradi 40 through their NMR measurements on CHXOL observe that the g motion modulates a substantial fraction of second moment and hence, must be a large motion involving all the molecules.…”

“…The pure materials used in this study, viz. CHXOL [molecular weight (MW) = 100.16 g mol À1 ], CHPOL (MW = 114.19 g mol À1 ), NPOL (MW = 88.15 g mol À1 ), NPGOL (MW = 104.15 g mol À1 ), CNCH (MW = 109.17 g mol À1 ) and CHC (MW = 118.61 g mol À1 ) were studied individually in detail by earlier workers using calorimetry [4][5][6]14,24,28,29,38,41,63,[66][67][68][69][76][77][78][79]81 and dielectric spectroscopy. 6,14,18,22,24,28,32,36,38,42,43,48,50,80,82 Cyclohexanol is one of the few substances that has been studied extensively using different techniques.…”

Crystalline thiophene - Calorimetric evidence for a glassy crystalline state in both phase sequences

“…This conjecture largely motivated the present study of thiophene that was performed between 14 and 300 K by means of an on-line automated adiabatic calorimeter [9,10]. A 0.3645 mole thiophene sample was used and its purity was determined to be 99.92 mole % by gas chromatography.…”