Phase equilibria and eutectic growth in quaternary organic alloys amino-methyl-propanediol–(D)camphor–neopentylglycol–succinonitrile (AMPD–DC–NPG–SCN)

Abstract

Several key experiments were performed to determine the temperature of transformations of organic alloys from the ternary systems 2-amino-2-methyl-1,3-propanediol–(D)camphor–succinonitrile (AMPD-DC-SCN) and 2-amino-2-methyl-1,3-propanediol–neopentylglycol–succinonitrile (AMPD-NPG-SCN) by means of differential scanning calorimetry (DSC). The phase diagrams of these ternary systems were assessed via the CALPHAD approach using Thermo-Calc and the experimental data on phase equilibria were determined by the above key experiments. Good agreement between the experimental and the calculated data was achieved for both ternary systems. Combining the obtained thermodynamic descriptions with those obtained for two other ternary systems, AMPD–DC–NPG and DC–NPG–SCN, published earlier, the thermodynamic description for the entire quaternary system was created. In order to identify the phases involved in solid–liquid equilibria and the nature of coupled eutectic growth in quaternary alloys, several unidirectional solidification experiments were performed: two quaternary alloys with composition 37.5SCN–44.5DC–16.5NPG–1.5AMPD (wt%) and 34SCN–44DC–19NPG–3AMPD (wt%) were used for the experiments on monovariant eutectic growth. We find that in the last alloy the monoclinic NPG phase is fully suppressed by the addition of AMPD and three solid phases show coupled eutectic growth at the solid/liquid interface: the hexagonal phase (DC solid solution), the FCC phase (NPG–AMPD solid solution) and the BCC phase (SCN solid solution). The quasi-2D eutectic patterns obtained in a thin sample show the stacking sequence –BCC–Hex–FCC–Hex–. The volume ratio of Hex:BCC:FCC phases equals 4:3:2. In the quaternary alloy with 1.5 wt% AMPD the monoclinic NPG phase is present at the solid/liquid interface and the eutectic growth is rather irregular.