Phase Behavior of Neohexanol up to Pressures of 300 MPa and Temperatures between 100 and 370 K

Abstract

The phase behavior of neohexanol has been studied at temperatures between 100 and 370 K and pressures up to 300 MPa with the aid of differential thermal analysis (DTA). The substance reveals three stable forms at atmospheric pressure (solid I, II, III) and a new high pressure modification (solid IV). Accordingly, two sets of triple point values have been established: (a) the (solid I + solid II + solid III) triple point at 70 MPa and 215 K; (b) the (liquid, solid I, solid IV) triple point at 88 MPa and 275 K. There is a further triple point (solid I, III, IV) expected immediately beyond the experimentally accessible pressure range (349 MPa, 251 K). Both phases solid I and IV are supposed to be orientationally disordered (“plastic”) phases. Furthermore at least two metastable solid phases occur, denoted as solid III″ and III″ which are readily obtained on cooling.

Key Words:

• phase transitions
• high pressure
• plastic crystals
• thermodynamics