Thermodynamic description and unidirectional solidification of eutectic organic alloys: II. (CH3)2C(CH2OH)2–(NH2)(CH3)C(CH2OH)2 system Original Research Article

The temperature and enthalpy of melting of organic alloys from the binary system 2-amino-2-methyl-1,3-propanediol (AMPD) and neopentylglycol (NPG) were measured by means of differential scanning calorimetry (DSC) within the entire composition range. The analytical description of the Gibbs energies of pure AMPD and pure NPG was derived utilizing the data on temperature and enthalpy of transformations, and temperature dependencies of the heat capacity available in the literature. The phase diagram for the binary AMPD–NPG system was assessed via the CALPHAD approach using Thermo-Calc by simultaneously optimizing the thermodynamic and phase equilibrium data available in the literature and measured in the present work. An excellent agreement between the experimental and calculated data for the phase diagram as well as for the enthalpy of melting of the organic alloys was achieved. Experiments and calculations show that the binary AMPD–NPG system exhibits an eutectic reaction with the eutectic point at 378.3 K and 42.2 mol% NPG. The enthalpy of formation of the liquid, BCC and FCC phases derived from the optimisation proves an attractive interaction between dissimilar molecules in these phases. Unidirectional solidification of the eutectic alloy was performed in order to check the nature of the eutectic growth: We find that both solid phases grow with a non-facetted solid/liquid interface, but growth of a regular lamellar eutectic structure could not be observed.