BINARY-SYSTEM NEOPENTYLGLYCOL PENTAGLYCERIN

The phase diagram of the plastic crystals Neopentylglycol (NPG) and Pentaglycerin (PG) has been established from 288 K until the liquid state. The NPG/PG system exhibits a demixing region in the solid state as a consequence of the difference between the ordered low-temperature forms of the pure compounds; the solid solution boundaries have been determined (0.07 and 0.53 molar fraction of PG) at 288 K. The equilibrium domains between the two solid phases and the plastic phase show an eutectoid invariant, with eutectoid composition of 0.29 +/- 0.02 molar fraction of PG and eutectoid temperature of 298.1 +/- 1.1 K. In the plastic phase, total miscibility is observed and, from a crystallographic point of view, an ideal behaviour can be assumed for the alloys. The plasticliquid equilibrium shows a Gibbs minimum corresponding to a concentration of 0.21 +/- 0.02 molar fraction of PG and a temperature of 379.6 +/- 2.0 K.