Phase equilibria and eutectic growth in ternary organic system amino-methyl-propanediol–(D)camphor–neopentylglycol

Abstract

The temperature and enthalpy of transformations of organic alloys from the ternary system 2-amino-2-methyl-1,3-propanediol–(D)camphor–neopentylglycol (AMPD–DC–NPG) were measured by means of differential scanning calorimetry (DSC). The phase diagram of this ternary system was assessed via the CALPHAD approach using Thermo-Calc based on the thermodynamic descriptions of the constituent binaries published earlier and on the thermodynamic and phase equilibrium data measured in the present work for ternary alloys. Good agreement between the experimental and calculated data was achieved. Experiments and calculations show that the AMPD–DC–NPG exhibits a nonvariant quasiperitectic reaction at 336.1 K and composition AMPD-17.5 mol% DC-42.56 mol% NPG, with all solid phases being nonfaceted. Unidirectional solidification experiments were performed with three different alloys selected such that each exhibits a small amount of the primary BCC (AMPD solid solution), the FCC (NPG solid solution) and the hexagonal (DC solid solution) phase, respectively, in order to verify the nature of the phases involved in solid–liquid equilibria and the nature of coupled growth in this ternary system. We find that in all these cases once steady state growth is reached two solid phases grow at the solid–liquid interface with a rod-like coupled growth pattern: The hexagonal phase (DC solid solution) and the FCC phase (NPG solid solution).