THERMAL-CONDUCTIVITY AND HEAT-CAPACITY OF CYCLOHEXANE UNDER PRESSURE

The transient hot-wire technique was used to determine the thermal conductivity, λ, and the specific heat capacity per unit volume, pcp, of cyclohexane up to 1.5 GPa in the range 120-340 K. The measurements were carried out in a piston-cylinder apparatus, 45 mm in internal diameter, cooled by liquid nitrogen. There is only a small (6%) increase in λ on freezing, while there is an increase by a factor of two corresponding to the plastic→ normal crystal transition. The variation of λ with temperature (T) at P = 0.03 GPa is d(lnλ) dT = -2.2×10-3K-1 for the liquid and d(ln λ) dT = -0.9× 10-3K-1 for the plastic crystalline phase. In the norm crystal phase an approximate T-1 dependence is observed. Within each of the phases λ increases linearly with pressure, and the slope of λ (P) is smallest in the plastic crystal phase. The existence of a recently reported new high pressure phase is evident from conductivity data. Qualitative ρCp -results are reported. © 1978.